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Economic Geology News

For Rare Metal Exploration, go to Supercontinents? (16 July 2014)

Peak amalgamation of supercontinents appears to control the timing of numerous important Ta deposits (as shown for Africa by U/Pb dating of CGM: Melcher et al. in press), and globally, of many provinces of the “granitophile” rare element deposits (tin, tungsten, Ta, Be, Li etc.).

Yet, I am not convinced that there is a difference in metallogeny between amalgamation of all continents into one (forming a true supercontinent such as Pangaea), or of only a few continents (no true supercontinent, e.g. Gondwana; or a simple continental collision such as the Caledonian one between Laurentia and Baltica). If, to continue with the example of the granitophile elements, significant deposits occur likewise in Rodinia, Gondwana and Pangaea, the common factor is wide-spread flooding of the crust by granites. And that may be caused by a variety of plate tectonic processes (to be specified), and not the 5th or 6th continent being amalgamated. I tend to doubt that there is a magic “metallogenic supercontinent process” and I suggest that the tool box of plate tectonics or better, of the Earth’s dynamics, is the rational approach to scientific analysis and to building exploration models. To answer the question stated in the title – by all means, go to the supercontinents for rare metal exploration. But do not trust the label alone!

Correlation is no positive proof of causation ... or is it?

If you wish to read more on this subject – look at my blogs dated 16 June, and 20 February, 2014.

Melcher F., Graupner T., Gäbler H.-E. et al. (in press) Tantalum–(niobium–tin) mineralisation in African pegmatites and rare metal granites: Constraints from Ta–Nb oxide mineralogy, geochemistry and U–Pb geochronology. Ore Geology Reviews

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Metallogenesis Related to Supercontinents – Still a Hot Topic! (16 June 2014)

In my earlier News blog “Are Supercontinents an Exploration Guide? (20 February 2014)” I doubted that the sole existence of a supercontinent would provide valuable hints for exploration. Meanwhile, I continued to follow this topic closely. Many current papers mention some relation between supercontinents and ore deposit formation, but omit to provide details. There seem to be authors who attribute any mineralisation, if dated before, during and after the actual assembly of a supercontinent as relevant in this respect. Others maintain that a supencontinent is only in existance when it is fully amalgamated. Before assembly, during welding and breakup, supercontinents display a variety of plate tectonic processes that we have learnt to understand and to use for exploration and scientific studies. And what about the peak of welding and the following period of supercontinent stasis before new-born plates start to drift away? Are all deposits that originate during this period causally related to the supercontinent?

If you are interested in this topic, do come to Leoben/Austria on 24 June 2014 (16,00 h). I’ll talk on the subject at Mining University, Chair of Economic Geology, Peter Tunnerstrasse 5, Seminarraum B.

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Are we Running out of Gold? If you Believe this Statement, look at the Australian Success Story (23 May 2014)

There is a deluge of warnings in public and scientific media that we are running out of mineral resources of substances such as oil, phosphate and, yes, gold too. While I do recognize the need for forecasts I am skeptical of many predictions of doom.

Concerning gold, I would like to support my views by reporting on a short paper by Neil Phillips (2013) who is a leader in the Australian gold exploration industry. Look at some facts:

Australia's gold production has been 265 +/- 50 tonnes per year for the past 23 years. For 2012, the figure of 248 t is only 20 per cent below the historical peak for Australia of 314 t in 1997 and second only to China (403 t, USGS 2014). From 1980 onward, annual production rose steeply from <50 t to present levels.

Australia's national gold resources are expressed as economic demonstrated resources (EDR) annually published by Geoscience Australia (2013). EDR is essentially a sum of reserves and most of the measured and indicated resources (these are JORC terms; see my News blog dated (8 April 2013).

At the end of 2013, Australia's gold resources (EDR) were approximately 9900 t Au. You do recognize that obviously, when resources increase, more ounces must have been found than were produced. This is true for most years since Australian gold production started to rise in 1980. Today, Australia owns the largest gold resources on the Earth.

Explorations costs in Australia are reported on a national scale. During the past nine years, EDR has risen by 4518 t and Australia has produced 2241 t Au, implying added resources of 6759 t in that period. The total expenditure on gold exploration over the same period was $4950 million (2012 AUD) that equates to $22.8 per ounce.

Neil concludes that adding 6000 t gold to Australia’s EDR in ten years is an extraordinary achievement. The EDR resource/production ratio is currently >30 years. The outlook for gold mining in Australia is bright. “Risks are complacency, hubris and high costs of extraction, rather than running out of resources.”

Would you agree with me that three hearty cheers are due to our Australian mates in gold exploration?

There is one point that I would like to add to this story:

Australia is not unique in its gold endowment. In my opinion, this success is due to a number of factors, of which outstanding people in geological research and its application, and general support of mining by society and government may be the most important. Other countries might emulate this path to prosperity.

A few weeks ago I spoke to students at Vienna University on “Geological energy resources – How much longer will they last?” I presented the current global reserve/resource and production figures and explained that forecasts based on these figures necessarily reflect present and past technologies. Revolutionary jumps in technology (remember shale gas and oil) cannot be predicted. Humans are extremely inventive and ours is a time of precipitate advance. So we should not stare at statistical predictions of “the end of gold, oil etc.” but get to work inventing new methods.

Phillips, G. N. (2013) Australian gold exploration – a quick audit (or how do we measure success?). AusIMM Bulletin no. 4 August 2013, 22-25.

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Metals can be Recycled, but Coal and Hydrocarbons are Burnt. Is Uranium Dissolved in the Global Oceans the Long Term Solution to Humanity’s Energy Thirst? The Novel Technology of Molecular Recognition may be the Key (14 April 2014)

Large potential U resources assure future supplies, but new mines and technologies will be needed, especially for eventual exploitation of the giant uranium mass dissolved in seawater (estimated at 4.5 x 10 9 tonnes U). This is one of the goals persued by applying molecular recognition principles to the design of new separation agents selective for individual metal ions (Izatt et al. 2014). In nuclear waste cleanup, hydrometallurgical applications of the technology are already now well established. This is only one highlight in an excellent review paper that provides many insights, apart from explaining and illustrating the principle of molecular recognition. Current commercial applications in the mining industry include the large-scale purification of metals such as cobalt (deleterious Cd), gold (Cu) and copper (Bi).

Izatt, R.M., Izatt, St.R., Bruening, R.L. et al. (2014) Challenges to achievement of metal sustainability in our high-tech society – a tutorial review. Chem. Soc. Rev. 43, 2451-2475.

Abstract: Achievement of sustainability in metal life cycles from mining of virgin ore to consumer and industrial devices to end-of-life products requires greatly increased recycling rates and improved processing of metals using conventional and green chemistry technologies. Electronic and other high-tech products containing precious, toxic, and specialty metals usually have short lifetimes and low recycling rates. Products containing these metals generally are incinerated, discarded as waste in landfills, or dismantled in informal recycling using crude and environmentally irresponsible procedures. Low recycling rates of metals coupled with increasing demand for high-tech products containing them necessitate increased mining with attendant environmental, health, energy, water, and carbon-footprint consequences. In this tutorial review, challenges to achieving metal sustainability, including projected use of urban mining, in present high-tech society are presented; health, environmental, and economic incentives for various government, industry, and public stakeholders to improve metal sustainability are discussed; a case for technical improvements, including use of molecular recognition, in selective metal separation technology, especially for metal recovery from dilute feed stocks is given; and global consequences of continuing on the present path are examined.

Key learning points (Izat et al. 2014)

(1) Since Earth’s metal supply is finite, burgeoning consumption of metals by consumers and industry is unsustainable without efficient recycling.

(2) Due to the unique chemical and physical properties of metals, scientific discoveries have enabled the creation of a myriad of high-tech products that have transformed 21st century society.

(3) Vastly improved value recovery from end-of-life metal products is needed both by increasing the rate of metal recycling and by improving the performance of collection and recycling technologies, some of which rely on informal methods that are disastrous from environmental and health standpoints but essential to the economies of many nations.

(4) Improved selective, environmentally friendly, and commercial processes for separation and recovery of metals (precious, specialty including rare earth, toxic, and radioactive) in pure form with minimum carbon footprint are essential to sustainability of metal life cycles from mining to end-of-life to recycling.

(5) Along with improvements in technology, increased awareness of the urgency of global metal sustainability and resolve-to-action on the part of public, government, press, scientific, and industry stakeholders is needed to ensure a workable solution to sustainability of metal life cycles for future generations.

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First Industrial-Scale Application of Gold Thiosulfate Leaching (19 March 2014)

In an article “Taking cyanide out of the gold equation” CSIRO (Australia) reports that later this year, Barrick Gold’s thiosulfate leaching process will attain full-scale production at the company’s Nevada Goldstrike mine.

Goldstrike is one of the largest Carlin-type gold deposits. Exploitation started in 1986 with oxidized ore. Later, gold was extracted by autoclaving or roasting and cyanide leaching. Starting in Q4/2014 in the autoclave circuit designed to process refractory sulfide ore, thiosulfate (S2O32-) lixiviant is to replace cyanide. CSIRO supported Barrick Gold by developing and applying an improved resin elution process at a demonstration plant at Goldstrike.

You are probably aware, that Carlin-type ore is different from typical gold ore; therefore, the thiosulfate leaching process is not applicable and economic for all gold deposits. Main features and genetic interpretations of Carlin gold are summarised in my “Economic Geology” (page 212); alternatively start a search with Muntean et al. (2011).

Muntean, J.L., Cline, J.S., Simon, A.C. & Longo, A.A. (2011) Magmatic–hydrothermal origin of Nevada's Carlin-type gold deposits. Nature Geoscience 4, 122 – 127.

Barrick’s summary description of Goldstrike mine

Taking cyanide out of the gold equation

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Are Supercontinents an Exploration Guide? (20 February 2014)

To state the question in a less shortened way – do geological data about the amalgamation, stasis and disaggregation of supercontinents (SC) serve strategic exploration? We might ask also (1) are there mineralisation types that occur in all or in most supercontinents and (2) which deposits may be prospective exploration targets? (3) is there any type of mineralisation that is restricted to SC and therefore, can be a pathfinder to supercontinents? And finally, (4) is there any practical advantage for exploration in the study of supercontinents?

Xin-Fu Zhao et al. (2013), for example, write that “continental blocks that once were part of Columbia, notably where rift basins developed in such blocks, may have potential to host sedimentary rock-hosted stratiform Cu deposits (SSC)". Should explorationists pack their gear and search all fragments of former Nuna/Columbia supercontinent for SSC?

Supercontinents are amalgamations of several or all continental plates of the Earth, formed by long-lived plate convergence punctuated by distensive events before peak assembly. After a geologically short period of stasis (the SC stage), tensional tectonics initiate fragmentation and the growth of new oceans, thus terminating one “supercontinent cycle”. Of course, ore formation is potentially associated with all contributing individual process systems, including subduction and delamination, arc and anorogenic magmatism, oceanic and continental rifting, basin formation, orogenesis, diagenesis, metamorphism and post-collisional collapse.

Let us first list the major supercontinents that are reasonably well known and widely accepted:

Comprehensive studies on the metallogenetic characteristics and evolution of the individual supercontinents are not available. Generally, continental deposit types such as sedimentary rock-hosted stratiform Cu deposits or sedimentary Fe ore deposits are cited as examples of the link between supercontinents and ore formation.

Always being short of time, for this blog I can only scan easily available information. One useful source is Chapter 6 “Ore deposits in a global tectonic context” (p 311-343) in Robb (2005). Laurence Robb does not, however, describe metallogeny in the respective supercontinent cycle but in time periods.

Nuna in the Paleoproterozoic, seems to lack remarkable mineralisation apart from the giant Pb-Zn-Ag deposits of eastern Australia (Mt. Isa etc.) and the unique IOCG deposit at Olympic Dam in Southern Australia, all of which seem to be related to the postpeak-assembly fragmentation of Nuna.

Rodinia in the Neoproterozoic, amalgamated by pan-Rodinian (or “Grenvillean”) orogenic events in the Late Mesoproterozoic. In North America, prepeak-assembly anorogenic magmatism and rifting are related to deposits of Fe-Ti, Pb-Zn and Cu-Ag. In central Africa, a flare-up of Sn-W-Au fertile granites marks the time of peak assembly, possibly caused by collisional indentation followed by delamination (Pohl et al. 2013).

Gondwana was assembled by long-lived plate convergence in the Late Neoproterozoic; it includes the spectacular Cu-Co resources of the Copper Belt in South-Central Africa that are most likely of peak-assembly diagenetic-hydrothermal origin.

Pangea welded by Late Paleozoic Variscan (or Hercynian or Appalachian) orogenic convergence, displays a multitude of economically significant deposits types, including prepeak-assembly VMS and sedex deposits such as the giant massive sulphide ore province of the Iberian Pyrite Belt with pyrite, copper, tin, lead, zinc and gold, and in the US, MVT Pb-Zn. Peak-assembly granite-related deposits comprise Sn, Cu, W, Bi, U, Au-As-Sb, Li and F. One of the most metal-endowed sutures worldwide is the 3000 km-long Palaeozoic accretionary orogenic collage of the Altaids in Central Asia, which marks the collision zone between Gondwana and Eurasia (Xiao et al. 2009). Postpeak-assembly giants include the Noril’sk Ni-Cu-PGE ore bodies, coking coal across much of the northern hemisphere, the diagenetic-hydrothermal European Copper Shale, and evaporites that include K-salt deposits, in Canada and Germany.

Conclusions? I feel that within parts of one supercontinent, for example Nuna/Columbia, consideration of metallogenic characteristics of one fragment may assist exploration in another fragment of similar geology (e.g. Xin-Fu Zhao et al. 2013). This principle was already recognized by Petrascheck (1965). The introductory questions might best be answered by (1) there are no mineralisation types that occur in all or in most supercontinents; (2) therefore, there are no specific supercontinent-related exploration targets; (3) there is no mineralisation that is restricted to SC; (4) there appears to be little practical advantage for exploration in the study of supercontinents. Overall, the toolbox of plate tectonics (Wilson cycles etc.) at the present level of refinement seems to suffice for building exploration models.

Would you like to contribute your experiences and opinion to this discussion?


Abu-Alam, T.S., Santosh, M., Brown, M. & Stüwe, K. (2013) Gondwana collision. Miner. Petrol. 107, 631-634.

Evans, D.A.D. & Mitchell, R.N. (2011) Assembly and breakup of the core of the Palaeoproterozoic-Mesoproterozoic supercontinent Nuna. Geology 39, 443-446.

Petrascheck, W.E. (1965) Typical features of metallogenic provinces. Economic Geol. 60, 1620-1634.

Pohl, W.L., Biryabarema, M. & Lehmann, B. (2013) Early Neoproterozoic rare metal (Sn, Ta, W) and gold metallogeny of the Central Africa Region: a review. Applied Earth Science 122, 66-82.

Robb, L.J. (2005) Introduction to Ore-Forming Processes. 373 pp. Blackwell.

Wegener, A. (transl. J.G.A. Skerl) (1924) Origin of continents and oceans. Methuen, London.

Xiao Wenjiao, Kröner, A. & Windley, B. (2009) Geodynamic evolution of Central Asia in the Paleozoic and Mesozoic. Int. J. Earth Sci. 98, 1185-1188.

Xin-Fu Zhao, Mei-Fu Zhou, Jian-Wei Li & Liang Qi (2013) Late Proterozoic sedimentary rock-hosted stratiform copper deposits in South China: their possible link to the supercontinent cycle. Miner Deposita 48, 129-136.

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Sustainable mining - sodium carbonate extraction from Lake Magadi, Kenya (25 January 2014)

You may remember, that the term “sustainable” was first coined about 300 years ago for the management of forests, demanding “that the amount of wood cut should not exceed the growth rate” (Carlowitz 1713). According to this narrow definition, very few mineral deposits are renewable, but the Magadi soda mine may be one of the class:

In the recent past, I had the occasion to visit the Lake Magadi area in the East African Rift (EAR) Valley, Kenya, near the border to Tanzania in the South. Lake Magadi in Kenya and Lake Natron in Tanzania are parts of a large saline lake system that may have originated in the early Pleistocene. This part of the rift is marked by the giant active carbonatite volcano Oldoinyo Lengai, the peak of which towers about 2600 metres above the lakes. Both lakes are saline, with a chemical composition of waters characterised by high concentrations of sodium and carbonate. They are typical “soda lakes” of the EAR.

Holocene trona beds are 7 to 40 m thick, sourced from surface runoff, groundwater, geothermal springs and precipitated by evaporation (Eugster 1970). Fluorine contents in this trona ore are significant, occurring in the form of 22 wt. % villiaumite (NaF) and ~6% fluorite. This seems to imply a genetic relation to the unique fluorine-rich natrocarbonatite lavas of Oldoinyo Lengai, probably by supergene leaching.

At Magadi, trona is extracted by dredging and lake brines are also used as a source of soda and halite. During my studies, heavy rains had raised the lake level and diluted the brines. Evaporation will, however, soon re-establish saturation levels. The rate of replenishement of the deposit is reported to exceed production making Magadi one of the rare examples of literally sustainable mining. In neighbouring Tanzania, a project to exploit soda from a bay of Lake Natron is disputed because of possible negative consequences for the lake’s famous flamingo population. At Magadi, flamingos seem to be perfectly oblivious of the industrial activity.

Use of soda ash (Na2CO3) is mainly in glass manufacturing, followed by chemicals, soap and detergents, pulp and paper production, water treatment, bentonite activation, animal feed and flue gas desulfurization, dechlorination and defluorination. The annual production of soda ash (natural and synthetic) is ~52 Mt/a but only 13 Mt are primary mining products, almost wholly from the Green River Basin, USA. This region dominates world mine output, whereas Turkey, Kenya and Botswana are minor producers. In Turkey, two newly discovered and very large trona deposits are presently prepared for production: Kazan with resources of 600 Mt at 31% trona and nearby Beypazari with 230 Mt at 70% trona. China leads in the production of synthetic soda.

Papers for further reading:

Eugster, H.P. (1970) Chemistry and origin of the brines of Lake Magadi, Kenya. SEPC Publ. Geol. Soc. 3, 215-235.

Jones, B.F., Eugster, H.P. & Rettig, S.L. (1977) Hydrochemistry of the Lake Magadi basin, Kenya. Geochimica et Cosmochimica Acta 41, 53-72.

Moor, J.M. de, Fischer, T.P., King, P.L. et al. (2013) Volatile-rich silicate melts from Oldoinyo Lengai volcano (Tanzania): Implications for carbonatite genesis and eruptive behavior. Earth and Planetary Science Letters 361, 379-390.

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The Origin of Banded Iron Ores (BIFs) Illuminated by Geomicrobiology (29 November 2013)

Yesterday I attended an inspiring lecture by Andreas Kappler (University of Tübingen) who reported on recent results of his group’s research on the role of microbes in the precipitation and diagenesis of Archaean-Proterozoic BIFs. Considering that BIFs are the largest metal concentrations on Earth I assume you will be interested to have the gist of his talk.

We all know, of course, that most scientists relate the precipitation of the giant mass of iron contained in Superior type BIF to the stepwise transition of oceans and atmosphere from a reduced to an oxidized state (the “Great Oxidation Event” GOE between 2.45 and 2.2 Ga).The basic agreement is that the ores are abiotic chemical or biogenic precipitates from seawater. The most common hypothesis is that “The atmosphere may have been nearly free of oxygen when the oxygen in the oceans first started to increase. Blooms of the earliest photosynthetic microorganisms (cyanobacteria) increased oxygen concentration in seawater and caused oxidation of dissolved Fe(II) and precipitation of insoluble Fe3+(OH)3.”

Andreas approached the work by looking at various elements of this hypothesis and using different methods including isotopes, ecophysiological and phylogeny studies, molecular and mineral marker analysis, and sedimentological reconstructions. to investigate the possible role of microbes.

The paper cited below (Posth et al. 2013) provides an overview and references to other papers dealing with details. It can be downloaded using the link provided.

To summarize the results in a few words: The role of cyanobacteria is diminished whereas a number of other iron-oxidising (producing the iron oxide sediments) and iron-reducing bacteria (essential in diagenesis) is recognized and described. Many of them are still around and can be observed doing their work. The difference is that today, little dissolved Fe(II) is available.

Posth, N.R., Konhauser, K.O. & Kappler, A. (2013) Microbiological processes in BIF deposition. Sedimentology 60, 1733-1754.


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Kibaran (Meso- to Early Neoproterozoic) Metallogeny in the Central Africa Region Updated (10 January 2014)

Early Neoproterozoic rare metal (Sn, Ta, W) and gold metallogeny of the Central Africa Region: a review. Pohl, Walter L., Biryabarema, Michael & Lehmann, Bernd (2013) Applied Earth Science (Transactions of the Institute of Mining and Metallurgy London, and the Australasian Institute of Mining and Metallurgy Melbourne) 122, 66-82.

Abstract The four metals of economic significance in the Central Africa or Great Lakes region, i.e. gold, tin, tantalum and tungsten, are part of one composite metallogenic system that operated at about 980 ± 20 Ma. The main driving agent was peraluminous ilmenite-series granite magmatism, synchronous with intracratonic compression and associated with the final amalgamation of the supercontinent Rodinia. The granitic melts were emplaced at intrusive levels of ≥2 kbar (≥8 km); the intrusions display a variable and often advanced degree of fractionation, including abundant Sn-Ta-Li-Be-Rb-Cs pegmatites, and are associated with hydrothermal systems enriched in tin, tungsten and/or gold. Based on cumulative past production and present metal prices, gold in hydrothermal quartz veins is the major commodity, followed by tin either in rare metal pegmatites or in sheeted, hydrothermal quartz veins. Many deposits in the province occur in siliciclastic metasedimentary, or metabasaltic roof rocks above parental granites; mainly in its western part, the zone of mineralisation retracts into the granite roof. Typically in the first case, antiformal sites acted as fluid escape zones, with carbonaceous or metabasaltic rocks as chemical traps for tungsten and gold. Examples of pegmatitic and magmatic-hydrothermal deposits are presented in some detail in order to illustrate characteristics and genetic controls, and to support the metallogenic hypothesis here advanced.

Impeding strategic exploration, published elements of understanding the evolution and mineralisation of the Kibara belt are contradictory and essential links are missing, foremost an understanding of the 1 Ga “flare up” of fertile granites. Towards solving this conundrum we suggest that the key is delamination of the mantle lithosphere and dense mafic lower crust, residual after extraction of voluminous 1.38 Ga granitic melts. During pan-Rodinian orogenic events, the Tanganyika spur of the Tanzania craton acted as an indentor whose impact caused foundering of the early Kibaran lithosphere. Consequent influx of asthenospheric heat triggered large-area crustal melting that resulted in the tin granites. The stress state was largely compressive but possibly punctuated by short or local extensional events. The correlation of geological evolution and mineralisation substantiates the formal recognition of a Kibara Metallogenic Domain, that is composed of two units: (1) The Mesozoic (1.4 Ga) Kabanga-Musongati nickel (±copper, cobalt, platinum) province; and (2) the early Neoproterozoic (1Ga) Kibara rare metal and gold province that is the main subject of this paper. The present understanding of the operating metallogenic systems remains limited. Regarding the application of modern concepts and technologies, this province is drastically underexplored.

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A New Review of my Economic Geology book (10 September 2013)

Long expectations bring good results: The latest issue of Economic Geology (journal published by the Society of Economic Geologists, Denver, USA) contains a review of my book, written by Eric Anderson from the US Geological Survey, Denver.

Eric gives a very good overview of the contents and concludes with positive verdicts such as

“well organized”

“particularly enlightening”

“helpful reference material when starting new mineral exploration projects”

“suitable textbook for upper-level undergraduate or first-year graduate courses”

“introductory to the economic geology professional”

“nice addition to the libraries of professional geoscientists”

You will, I hope, sympathize with me that I am very pleased and grateful. Praise from the world’s leader in the advancement and promotion of economic geology is a wonderful distinction.

If you wish to read the full text, here is the reference:

Economic Geology (former Bulletin of the Society of Economic Geologists), September-October 2013, v. 108, p. 1517-1518, doi:10.2113/econgeo.108.6.1517

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The Bushveld PGE, Cr, Fe and V Ores – an Integrated Metallogenetic Model (12 August 2013)

Like probably most economic geologists not closely following the discussions regarding layered mafic intrusions and platinum metallogeny, I did notice the contradictory genetic hypotheses being published over the years but felt unable to extract the most likely variants. Now, we have access to what I believe is an excellent paper on the origin of the Bushveld and its mineral treasures: Maier et al. (2013) present an integrated model, from magma derivation in a combined plume and metasomatized subcontinental lithospheric mantle (SCLM) setting through magma emplacement to the formation of layered cumulates and the PGE reefs. All along this narrative, observations and newest hard data (such as the chemical stratigraphy or the composition of parental magmas B1 to B3) are employed in order to deduce the likeliness (or not) of previous major genetic arguments such as in-situ contamination of melt by felsic country rocks, or Boudreau’s magmatic fluid origin for PGE mineralisation. By the way, both hypotheses are considered not applicable by Maier et al. (2013).

It is not possible to mention here all highlights of this rich paper. I’ll only try to trace the main path that leads to PGE enrichment and mineralisation. The story starts with Mid-Archaean extraction of komatiites and formation of the Kapvaal SCLM that was depleted in Pd but retained 4 ppb Pt. In the Neoarchaean and early Proterozoic, subduction metasomatized the refractory residue, introduced sulphur and volatiles, fertilised and oxidised the SCLM. At 2.05 Ga, a mantle plume induced heat and added primitive melts, and caused partial melting of the Kapvaal SCLM resulting in formation of the Bushveld B1 siliceous high-Mg basaltic liquid, which extracted most of the Pt and Pd of the affected mantle and consequently displays concentrations of 33 ppb Pt+Pd at Pt/Pd 1.5. Along its path into the shallow crust, it acquired a strong crustal chemical component. Its progressive fractional crystallisation formed cumulates of olivine, chromite, orthopyroxene, clinopyroxene, plagioclase and sulphide droplets. Reversals of the expected sequence are explained by major replenishments. Lopolithic subsidence caused increasingly inward-dipping layering. This resulted in liquefaction and slumping of relatively liquid-rich, semi-consolidated cumulate layers towards the center, causing features such as potholes, gaps, pipes (including the iron-rich ultramafic “hortonolites”) and numerous smaller deformational patterns. Slurries unmixed under gravity and flow forces into bands of plagioclase, pyroxene, PGE-rich sulphides and oxides (cumulate sorting). This is at the origin of the PGE reefs and the chromite and magnetite seams of the Bushveld.

Maier et al. (2013) terminate the paper with a concise chapter on “Implications for PGE Prospectivity” in layered mafic-ultramafic intrusions that should be useful for explorationists. Scientists will be delighted to study the text in detail and scan the closely printed 10 pages of references. The article is not marked as a review paper but for most of us will be exactly that – a systematic study and an up-to-date interpretation of all genetic elements.

I strongly recommend that whoever needs a profound insight into the Bushveld or the general economic geology of layered mafic-ultramafic intrusions should start with this paper.

Maier, W.D., Barnes, S.-J. & Groves, D.I. (2013) The Bushveld Complex, South Africa: formation of platinum–palladium, chrome- and vanadium-rich layers via hydrodynamic sorting of a mobilized cumulate slurry in a large, relatively slowly cooling, subsiding magma chamber. Miner. Deposita 48, 1-56.

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Geometallurgical Application of Portable X-Ray Fluorescence (pXRF) Analysers (18 July 2013)

In exploration and in mining geology, portable X-ray fluorescence (pXRF) analysers are widely used for on-site data acquisition but there are few refereed published papers that provide information on best practice.

Allow me to remind here the occasional users of geochemistry, citing from my Economic Geology book (page 427), that in some applications such as exploration geochemistry, analytical data need not in all cases be equal to the absolute element content in a sample, or in other words, accuracy may not be essential. Deviations of ±30% from the absolute tenor (e.g. an international or self-produced inhouse laboratory standard) are tolerated, if the relative error remains within narrow limits. In contrast, excellent reproducibility of results, that is high precision, is absolutely required. This is the base for any data evaluation, especially if the contrast between background and anomalies is small. In contrast to exploration, data for reserve estimation must have high accuracy and precision.

In a paper that appeared in print this spring, Gazley et al. (2012) describe a geometallurgy application of pXRF: Amphibolite-facies metabasalts at Plutonic Gold Mine, Western Australia, contain an estimated resource of 10.5 Moz of Au. Based on the observation that high As in the mill feed resulted in poor metallurgical performance, a dense network of more than 70,000 core and underground channel samples was extended throughout the ore body. Apart from arsenic, 31 other elements were determined using pXRF. Gold was measured routinely by fire assay in the mine laboratory where all sample preparation and pXRF analysis took place. The visualization software used was Leapfrog 3-D. Different geometallurgical types of Au mineralisation based on Au/As ratios were mapped in three dimensions. Optimising the mill feed by blending ore is expected to essentially improve metallurgical performance. The authors explain that their motive for choosing pXRF analysis was the low cost of ca. 1 US $ per sample analysed.

In one of the last issues of the AusIMM Bulletin, Michael Gazley (2013) provided valuable advice how to use pXRF units for reliable and valid results. To allow you checking if your routine stands up to Michael’s standards, I mention some of the points he discusses:

Gazley, M.F. (2013) Is there reliability and validity in portable X-ray fluorescence spectrometry? The AusIMM Bulletin no. 2 April 2013, 68-72.

Gazley, M F; Duclaux, G; Fisher, L A; de Beer, S; Smith, P; Taylor, M; Swanson, R; Hough, R M; Cleverley, J S (2012) 3D visualisation of portable X-ray fluorescence data to improve geological understanding and predict metallurgical performance at Plutonic Gold Mine, Western Australia. Applied Earth Science 120, 88-96.

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Geoengineering – Salvation or Doom? (21 June 2013)

What is geoengineering? – Mining professionals may be excused if they believe that the term signifies large-scale change of land by mining or by civil works but this activity is correctly called geotechnical landscape engineering. “Geoengineering” designates a large number of conceptual methods that may be useful for reducing global warming. Note that few of these concepts have been practically evaluated. Examples include the reduction of incoming sun light by spreading reflective aerosols such as sulfate in the stratosphere (imitating volcanic eruptions) or spraying condensation nuclei to increase clouds. Remember that spraying clouds with silver iodide is much used already now for rain-making and hail prevention. Where I live now, valuable wine plantations are guarded against hail by small spraying planes circling through the storm clouds.

Another path of geoengineering is fertilizing the oceans with iron. Iron is the main limiting factor of phytoplankton growth in the high oceans. Phytoplankton blooms are followed by an increase in higher life and a rain of dead organic matter to the deep-sea floor and burial in marine sediments. The result is sequestration of carbon from the atmosphere (Boyd 2007). By the way, natural input of iron and other micronutrients is provided by dust; its increase since 1.25 Ma accounted for up to 50% of CO2 reduction and the consequent ice ages (Martínez-Garcia et al. 2011). This is a reminder that we should not overdo things – a new ice age would exterminate our civilization.

In 2012, the largest iron fertilizing project yet was carried out in the Pacific Ocean, financed by the Haida (a North American native people). Two hundred tonnes of iron-rich dust were dumped over an area of one square kilometre in order to acquire carbon credits, boost phytoplankton growth and salmon stocks. For the Haida, salmon is an important food and has great cultural significance. The induced algal bloom spread across about 10,000 km2. If the salmon run improves as hoped will only be known in 2014.

The figures illustrate that the mining industry should not hope for geoengineering to become a major new customer. Consider that the global iron ore production in 2012 was 3000 million tonnes (USGS 2013). Mined sulfur has been displaced by desulfurization sources such as natural gas and petroleum. And silver? Silver is mainly a co- or by-product in lead-zinc, copper and gold deposits. Global mine production in 2012 was 24,000 t of silver and recycling satisfies a considerable part of consumption. The rather low price of the metal does not indicate an impending shortage. More frequent cloud seeding will make little difference.

The tiny intervention by the Haida attracted ethical critics and furious hate attacks. Scientific investigations such as small field trials are not possible. Governments have launched deliberations by commissions and academies but prefer to stay out of trouble. Yet a regulated social bargain on small-scale research leading to international norms of cooperation and transparency is urgently needed (Parson & Keith 2013). The alternative is secret jostling for an advantage in knowledge and capability.

Boyd, P.W. (2007) Biochemistry - iron findings. Nature 446, 989-991.

Martínez-Garcia, A., Rosell-Melé, A., Jaccard, S.L. et al. (2011) Southern Ocean dust–climate coupling over the past four million years. Nature 476, 312–315.

Parson, E.A. & Keith, D.W. (2013) End the deadlock on governance of geoengineering research. Science 340, 1278-1279.

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Engineering for Perpetuity – Tailings Storage Facilities (3 June 2013)

Engineering structures in mining (such as pit slopes etc.) are commonly dimensioned for temporary use with a low safety margin. There are few exceptions from this rule. Typically, these concern permanent structures left behind by a mine, e.g. roads or dams, that must be durable in the ordinary way of civil engineering with projected life times of ca. 50 years. Life time is controlled by many factors, of which the quality of materials employed stands out. In wide parts of public construction, low costs are imperative and therefore, lower quality (and shorter life time) is accepted. Early damages and constant repairs are the consequence.

In contrast to the common practice sketched above, the Western Australian Department of Mines and Petroleum (below) proposes that the design life of a a tailings storage facility (TSF) in the mining industry should normally be considered to be perpetuity.

For a geologist this raises the question ‘What is perpetuity’? The Chambers Dictionary defines the word as “something lasting forever”. Being involved in the discussions concerning storage of radioactive waste, I am somewhat doubtful of the German demand that safe storage should be guaranteed for 1 Million years (see my post in News Archive August 25, 1999). My doubts increase when facing the word perpetuity.

There is no question, of course, that as a hazard for humans, nature and water, waste should be safely stored. It is truly insupportable when global tailings dams failure incidence is still about one case annually. And I welcome the challenge to the geological profession to investigate and predict the probable long-term evolution of a site. Yet I hesitate to agree with a term that asks for an unlimited look into the future of the Earth.

What is your opinion? Join the discussion in LinkedIn group “Mining Professionals” or respond by email.

Department of Mines and Petroleum (2013) Tailings Storage Facilities in Western Australia – Code of Practice. 15 pp. Resources Safety, Department of Mines and Petroleum, Western Australia (Draft for public comments).

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Gold in the Witwatersrand – New Genetic Evidence (10 May 2013)

The Witwatersrand District in South Africa is the most remarkable concentration of gold on Earth. Although mining seems to be in decline, understanding the processes leading to formation of the gold-bearing reefs is one of the most important ambitions of economic geology. Recent publications contribute illuminating data.

Read the following extract from my “Economic Geology” (page 220) where you also find microphotographs of uraniferous gold ore (Figure 2.26a and b); text updated:

The scientific consensus on the origin of the Witwatersrand gold reefs is the “modified placer model”. Alternative genetic interpretations persist, however, foremost the hydrothermal-epigenetic, metamorphogenic model described in detail by Phillips & Powell (2012). Yet, geological observations, rhenium-osmium dating and recently published trace elements signatures of uraninite in the reefs (Depiné et al. 2013) support a placer origin of the gold. The latter is based on REE contents of uraninite revealing its origin (Mercadier et al. 2011).

The ultimate source of the giant mass of gold is not exposed and not known. Most probably, the Witwatersrand palaeorivers eroded giant primary gold sources in older granite-greenstone belts. Hydrothermally altered granites and felsic volcanics were present in the catchment area and may have been a source of gold. Predominant pebbles in the reefs (quartz, quartzite, black schists and chert) provide no clear hint at a specific source. Trace element signatures, however, such as elevated Au (up to 67 ppm), Th, W, Bi, Mo, Ta, Y and REE of uraninite occurring with placer gold in the Witwatersrand reefs clearly point to a highly differentiated granitic source (Depiné et al. 2013).

Finally, the extraordinary size of the Witwatersrand gold province (holding resources of about 100,000 tonnes gold) must be sought in processes preparing the fertile parental mantle, and in the major crust-building event, which caused metal extraction and formation of the primary crustal gold concentrations at about 3030 Ma.


Depiné, M., Frimmel, H. E., Emsbo, P., Koenig, A. E. & Kern, M. (2013) Trace element distribution in uraninite from Mesoarchaean Witwatersrand conglomerates (South Africa) supports placer model and magmatogenic source. Mineralium Deposita 48, 423-435.

Mercadier, J., Cuney, M., Lach, P. et al. (2011) Origin of uranium deposits revealed by their rare earth element signature. Terra Nova 23, 264-269.

Phillips, N.G. & Powell, R. (2012) Origin of Witwatersrand gold: a metamorphic devolatilisation‐hydrothermal replacement model. Applied Earth Science: IMM Transactions B120, 112-129.

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Rules for Reserve and Resource Estimation Updated: JORC 2012 (8 April 2013)

Financing the establishment of a new mine or the enlargement of an existing operation are commonly based on selling shares in a company on stock markets. This allows investors to have a part in the fortunes (or the ruin) of an enterprise. Even people with little money to spare can participate because of the generally low price of single shares (mostly from cents to a few hundred dollars). Stock markets are essentially organisations that facilitate the exchange between buyers and sellers of securities (shares). All large and many small mining companies are registered on one ore more of the great exchanges (for example, Rio Tinto on the LSE – the London Stock Exchange).

Early stock markets (say those in the Australian gold fields around 1850) were practically unregulated. Information on underlying assets of shares offered was mostly hearsay. Most investors lost their money.

Since then, the need of buyers for reliable information has increasingly been answered and today, professional societies such as the Australasian Institute of Mining and Metallurgy (AusIMM) take a center role in further development and continuing improvement of the rules of reporting. Reporting signifies first of all the publication of reserves and resources of deposits, but also other company communications that influence the share price. The past excesses of wild promises such as having found masses of pure gold somewhere in a small mine in the outback are not possible any more. Stock markets have their own set of rules (the “listing rules”, for example, concerning transparency) that complement the more technical rules promulgated by professional societies.

If you are curious, have a look at the new Australian Securities Exchange (ASX) Listing Rules.

The most important asset of a mine is the ore in place. In countries with an important mining sector, its qualification and quantification is the subject of codes similar to the one, the update of which is reported here: Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves (The JORC Code). The 2012 edition can be downloaded for free (link below). It may be used already now and must be applied after the end of 2013.

The JORC Code provides minimum standards, recommendations and guidelines for Public Reporting in Australasia of Exploration Results, Mineral Resources and Ore Reserves. It defines terms and provides guidelines. It stipulates that a Competent Person bound by a professional code of ethics signs off the document. The Public Report must contain all relevant information that investors and their professional advisers require. If you ever find the time I suggest that you search for an example of a Public Report in a company’s website directed to shareholders and investors. For professionals such as geologists, metallurgists and miners it makes interesting reading. I assume that many of you will be curious to read the precise definition of Resources versus Reserves. Here it is (extract from JORC 2012):

“A ‘Mineral Resource’ is a concentration or occurrence of solid material of economic interest in or on the Earth’s crust in such form, grade (or quality), and quantity that there are reasonable prospects for eventual economic extraction. The location, quantity, grade (or quality), continuity and other geological characteristics of a Mineral Resource are known, estimated or interpreted from specific geological evidence and knowledge, including sampling. Mineral Resources are sub-divided, in order of increasing geological confidence, into Inferred, Indicated and Measured categories.”

“An ‘Ore Reserve’ is the economically mineable part of a Measured and/or Indicated Mineral Resource. It includes diluting materials and allowances for losses, which may occur when the material is mined or extracted and is defined by studies at Pre-Feasibility or Feasibility level as appropriate that include application of Modifying Factors. Such studies demonstrate that, at the time of reporting, extraction could reasonably be justified. “

The Australian code is an exemplary standard. Companies that try to tap the North American financial markets, even if they operate in say, Africa, often prefer to use the rules set by the Canadian Institute of Mining, Metallurgy and Petroleum (CIM 2013) where links to codes in other countries are also available.


CIM (2013) Standards on mineral resources and mineral reserves. Canadian Institute of Mining, Metallurgy and Petroleum.

JORC (2012) Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves (The JORC Code). The Joint Ore Reserves Committee of The Australasian Institute of Mining and Metallurgy, Australian Institute of Geoscientists and Minerals Council of Australia.

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Impressions from Kivu Province, DR Congo (28 February 2013)

Back from the Congo, I am writing up the scientific and Coltan Project related results of our field studies (cf. previous News dated 30 January 2013). These may be published elsewhere in due time. Here, allow me to share with you some of the vivid impressions, scenes and sights.

Americans – a fleet of heavy SUVs taking elderly donors to visits of humanitarian projects.

Artisanal miners – cassiterite, columbite (coltan) and gold are worked by thousands of men with very simple tools (we saw no women or children labour on the sites that we visited). Eluvial placers in open pits in weathered rock and regolith, alluvial placers along streams, and underground hard rock ore are extracted. Although we have met very knowledgeable and experienced mining professionals managing such operations, lack of capital limits improvement of technology and of working conditions.

Bisie near Walikale in North Kivu – possibly the greatest new tin deposit in the Kibara metal province. About ten years ago, it was found and developed by artisans and quickly became the country’s largest producer of cassiterite. In 2010, the DRC government closed the operation in the fight against conflict minerals. Since then, a junior explorer revealed potential resources of 500,000 tonnes tin metal contained.

Force majeure – in trade and insurance often used to exclude liability; in the Congo, it also designates “closed” areas.

Gold See Photo Gallery. The artisanal gold mine at Mkungwe in South Kivu is a paragon of a well organised non-industrial enterprise. Thousands find work there, and this illustrates the tragic conflict between the interests of the many as opposed to the efficiency, development and progress that only industrial mining can bring about.

Helicopter – the main overland transport vehicle, because of poor roads, force majeure and road blocks.

Industrial mining – the hope for modern exploration know-how and technologies, provision of funds for mine development, efficient and responsible best practices, and contributions to public and private wealth of the country; but feared by artisans because often, they lose informally held ground to the companies taking up licenses. As far as possible, peaceful co-existence should be agreed.

Pakistanis – the UN peace-keeping force in this region is manned by fierce-looking (but undoubtedly kind and helpful) soldiers from Pakistan.

Ruzizi River bridge - the passage from Rwanda into Congo. Ruzizi is the overflow from Lake Kivu down south to Lake Tanganyika. It was the setting that C.S. Forrester had in mind when writing the novel “The African Queen” that refers to the year 1914 and was filmed with Humphrey Bogart and Katharine Hepburn in 1951. Have you seen it?

Metal tracking – mines in the region struggle to establish a system tracking their ore from the mine to licensed buyers, in order to avoid the ban on conflict minerals (eg. the US Dodd-Frank Act 2010; see my News item dated 21 November 2011) and to regain access to world markets.

Twangiza gold mine – a beacon for an increasing contribution of industrial mining to the development of Kivu Province and a paragon of community engagement. Mining started in 2011 based on oxide reserves of 15 Mt at 2.26 g/t gold. At full capacity projected to produce some 120,000 ounces of gold each year.

Women – a stream of women carring heavy loads, apparently mainly food, from Rwanda into Bukavu town, which when we passed through was reportedly cut off from its agricultural hinterland by one of the militias that are the bane of the region.

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Africa calling - notice of absence (30 January 2013)

In February, I’ll be participating as a Senior Consultant in the Annual Workshop of the Coltan Environmental Management Project (CEMP) at Kigali, Rwanda. This year, field studies will take us to tantalum, tin and gold mines in the DR Congo, west of Bukavu town in Kivu Province. For most of this time, I may not be available for contact by internet nor telephone.

The Coltan Environmental Management Project (full name: Sustainable Restitution/Recultivation of Artisanal Tantalum Mining Wasteland in Central Africa) is a research initiative by academics from four countries in the Central Africa Region (Burundi, DR Congo, Rwanda and Uganda, all sharing part of the Kibaran tantalum-tin-tungsten-gold metallogenetic province) and Germany, and is supported by VW-Foundation (Hannover). Recognizing that the prosperity of the region is advanced by exploitation of the rare metals, we aim to reconcile mining with nature and people, and with the environment, by searching best methods of rehabilitating abandoned mines and of environmental and socio-economic management of current mining. Geology, geomorphology, biology, agriculture, and economic, soil and social sciences are involved. A science-based toolbox of mitigation technologies, and guidelines for socially and environmentally responsible tantalum mining and mine closure are being developed.

The Tantalum-Niobium International Study Center (TIC) estimates that “most likely” global resources of tantalum comprise 260,000 t (contained metal). World mine production in 2011 was about 1,000 t Ta, 25 % of which originated from artisanal mines in Central Africa (essentially North and South Kivu in DRC, Rwanda and Burundi). The Kibara metallogenetic province is a large region affected by an intracontinental orogenic phase due to the final welding of Supercontinent Rodinia (~ 1000-900 Ma; “pan-Rodinian orogenic events”: Li et al. 2008). Tin-tantalum (Be-Li) pegmatites are related to granites of S-type character. Eluvial and proximal alluvial placers often host rich ore, whereas to my knowledge, industrial-scale hard rock mining has not yet been tried in the region. In the past, the province was systematically investigated by classical propecting methods but is drastically underexplored by modern technologies.

If you should be interested in more details concerning the metallogeny of tantalum and its companions niobium and scandium, look up the sample chapter “Niobium and Tantalum” under the heading “Economic Geology Book” on this website.

More information on the Coltan Project such as participating scientists and institutions, and the results of a pilot phase in 2007 can be found at: Coltan Environmental Management Project ("Sustainable Restitution/Recultivation of Artisanal Tantalum Mining Wasteland in Central Africa")

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There is nothing so ruinous as the search for gold ... (10 January 2013)

Yesterday I attended a lecture on Earth resources, given by the leader of one of the largest geoscience research institutions in Europe. The speaker somewhat hurried through his excellent presentation from satellite geophysics through conventional and unconventional hydrocarbons to global warming, but one fact caught my eye: Gold reserves will last only 18 years. In principle, this is wonderful news for explorers, miners and investors: Gold is scarce and prices must continue to rise.

Wishing you a properous New Year, allow me to entertain you with some thoughts on gold exploration:

Together with platinum and rhenium, gold is one of the rarest elements. Surprisingly, gold deposits are quite common, in numbers, geographic spread and genetic diversity. Clearly, relatively common melts and crustal fluids are able to mobilize, transport and concentrate gold. Metamorphic and magmatic fluid systems are prolific producers of primary gold deposits. This is illustrated by thousands of gold deposits that formed in orogenic belts from large volumes of crustal rocks with a near-ordinary geochemical background. The group is called “orogenic gold deposits”, which are understood as products of crustal-scale massive flow of aqueous-carbonic metamorphic fluids and of more local magmatic-hydrothermal fluids during orogeny. The majority of primary gold deposits originated in subduction, accretion and collision settings. The “unified” metallogenetic model by Hronsky et al. (2012) proposes that fertile lithospheric mantle provides a source of gold, which can be extracted by transient events of melting or fluid generation; lithospheric-scale structures allow the focused transport of fertile magmas or fluids to the upper crust.

Exploration for gold is exceptional because even today, prospectors and small companies may, with luck, find a new viable deposit. The relatively high probability of success, low stakes and big rewards contribute to gold being the most explored-for metal. Projects are based on geological concepts (e.g. the “unified genetic model” of Hronsky et al. 2012 for large areas, scaling down to structural and lithological controls, metamorphic gradient, etc.) and involve mineralogical, geochemical and geophysical methods. Note that “data by itself does not make a discovery”; it is the intellectual input (Phillips 2012).

Are you interested? Before investing all your money in the shares of a promising junior exploration team, read what the Scottish founder of modern economic science, Adam Smith, thought about gold exploration:

“Of all those expensive and uncertain projects, however, which bring bankruptcy upon the greater part of the people who engage in them, there is none perhaps more perfectly ruinous than the search for new silver and gold mines” (Adam Smith 1776)

Be not discouraged, however. My opinion is still what I wrote in my Economic Geology book (the third and forth paragraphs above).


Hronsky, J.M.A., Groves, D.I., Loucks, R.R. & Begg, G.C. (2012) A unified model for gold mineralisation in accretionary orogens and implications for regional-scale exploration targeting methods. Miner. Deposita 47, 339-358.

Phillips, N.G. (2012) Gold exploration success. Applied Earth Sci. (Trans. Inst. Min. Metall. B) 120, 7-20.

Adam Smith (1776) The Wealth of Nations. Book IV/VII. Of Colonies.

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Tell the miners from me... Abraham Lincoln on the Economic Relevance of Mining (10 December 2012)

In a speech on April 14, 1865, Lincoln said “Tell the miners from me, that I shall promote their interests to the utmost of ability; because their prosperity is the prosperity of the Nation”

Grand words, but today, how many politicians, economists and ordinary people would support the statement that “the miners’ prosperity is the prosperity of the Nation?”

Arguments supporting this include increasing wealth from local to national level, and near the new mine improved or new infrastructure, often new churches, schools, clubs, hospitals and housing. All over the world, thousands of towns owe their existence to earlier or present mining. Locals profit by jobs, better education and contact with migrant labour and professionals. Mines were at the origin of the first unions and of the earliest mutual life, accident and sickness insurances. In many cases, when mines have a long live, the people form strong emotional bonds and are proud of “their mine”.

In spite of the pros I fear that the image of mining in the broad public is rather that mines have a negative environmental and social impact, and intensify the “resource curse”. After all, media consumers throughout the world are perpetually bombarded with news how bad mining is. I think all readers will easily recall one or more examples.

The resource curse, or the “paradox of plenty”, describes a correlation between a high national income from mineral resources and a loss of economic growth, government mismanagement, weak, ineffectual, unstable and corrupt institutions, and in some cases, internal or international armed conflict. Wikipedia provides a detailed description of the origin and various threads of the discourse, but let us leave the details to economists and sociologists. The last section of the Wiki article is the one to read: Criticisms. Remember that correlation is not necessarily causation. If governments are weak and corrupt, is it a wonder that a sudden flood of money intensifies the misuse of power? To find the reverse proven, look at Norway that is a shining example how a high income from oil and gas may be a blessing if wisely managed.

My conclusions are: We, the Mining Professionals, should work inside our industry towards ever better E&S management at all scales. And towards outsiders, we should do our best to hold up the banner of our industry. In the Epilogue to my Economic Geology book I have written words that both set the standard and are a call for action:

"well-managed extraction of minerals has every potential to contribute to communal wealth, a sustainable and vital social and natural environment, and peace."

Do you approve, or oppose?

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Romance, Nuclear Reactors and Meteorites (23 November 2012)

Have you ever looked up at a brilliant night sky, admiring the stars, and told your partner “My dear, look at all these beautiful nuclear reactors”?

If you ever did, you have my full admiration.

As probably most geologists, I rather have my eyes on the ground, both in the field and in my scientific reading. Claude Allégre writes of “geological myopia” (but means the lower resolution of age dating as the geological age increases).

Not long ago, the Natural History Museum of Vienna re-opened its meteorite collection, one of the most remarkable in the World. Fittingly, the meteorite chamber is next to the dinosaurs (you do remember that the unpronouncable Chicxulub asteroid is responsible for their demise). Admiring the beautiful specimen and the skilled arrangements (assisted by a virtual impact simulator), we found the lack of the barest chemical information on meteorites strange.

So I sat down with my copy of Allégre’s “Isotope Geology” (2008). Let me sum up some of the information found, supplemented by tielines to economic geology:

Meteorites are rocks that fall from the sky. Essentially, they consist of metallic iron, some FeS (troilite) and mafic silicates in different mixtures. Most are as old as the Sun, the Earth and the other planets (4.5 Ga). The common “chondrites” display a chemical composition that is considered to be roughly similar to the whole Earth. Chondrites are often used for normalising data in order to reveal the geochemical variation of certain elements such as the Rare Earths in rock and ore-forming processes. Iron meteorites have elevated trace concentrations of highly siderophile elements (HSE) such as Re, Os, Ir, Ru, Rh, Pt and Au, and of “common” siderophile elements Ni, Co, Mo, C, P, Ge and Sn. The observation that Palaeoarchaean (3.45 Ga) Barberton komatiites are depleted in platinum group elements (PGE) is explained by effective abstraction of siderophile elements of primordial Earth from the “magma ocean” into the core. Only the Late Archaean (2.5-2.8 Ga) komatiites display HSE enrichment, e.g. in the nickel sulfide deposits of Western Australia. At that time, cosmic matter that bombarded the Earth in the intervening time had been mixed into the mantle, which thereby became a fertile source.

Although some meteor iron may have been used by man, the Sudbury nickel-copper mining district is, to my knowledge, the only example of profuse ore formation directly related to an impact of extra-terrestrial matter.

The Universe started with the Big Bang, some 13 billion years ago. All the chemical elements we now find in our galaxy formed after the Big Bang but pre-date the formation of the Solar System (4.5 Ga ), apart from nuclides that originated by later radioactive decay. By nuclear fusion, the Sun burns hydrogen to helium (the nuclear reactor warming our home planet...). Also by fusion, heavy elements are produced in Red Giants (such as Betelgeuse in Orion’s belt). When these explode as Supernovae the material is scattered into interstellar space. From rubble of former stars, our Solar System condensed and arranged its central star with orbiting planets. -- This is the shortest possible version of the story how matter originates by nucleosynthesis.

And the beautiful reactors on the sky? Well, all stars are fusion reactors, of variable mass, composition, brightness and surface temperature. Their colours are a function of surface temperature; red is lowest, rising through yellow (the Sun), white and blue to violet. For more detail, look up the Hertzsprung-Russell diagram in Wikipedia.

Is this tale of the coherence between the Universe and our existence not a good reason to have romantic feelings when you are out with your friend looking at the Milky Way?


Allégre, Claude J. (2008) Isotope Geology. 512 pp. Cambridge University Press.

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Orogenic Gold to Volcanogenic Massive Sulfides – an Extension to D.I. Groves’ Crustal Continuum Model (10 November 2012)

All exploration professionals are familiar with David Groves’ (1993) insight that gold deposits in accretionary orogenic belts occur from deep (hypozonal) to shallow (epizonal) depths, ranging from granulite facies to very low grade metamorphic rocks. Hydrothermal alteration coincides with the metamorphic grade of the host rocks. The deep Au-As association changes to mesozonal Au-As-Te and epizonal Au-Sb. Towards the surface, Hg-Sb anomalies may betray the systems and can be used for regional exploration.

In the latest issue of Mineralium Deposita, a novel extension of the model is presented by Jaguin et al. (2012), based on precise age dating of rocks and mineralization along the Antimony Line in the Murchison Greenstone Belt, South Africa. Allow me to cite the short description of the situation from page 245 of my Economic Geology (Pohl 2011):

Significant metamorphogenic antimony deposits occur in the Archaean (~3 Ga) Murchison Greenstone Belt, South Africa, along a shear zone that extends over 50 km (termed the “Antimony Line”, AL) and is marked by strong hydrothermal alteration. Komatiites, for example, were transformed into conspicuous massive talc-carbonate rocks. Host rocks of orebodies include quartz-chlorite and quartz-muscovite schist, quartzite, metabasalt and banded iron formations. All these rocks display alteration in greenschist facies and addition of CO2.

Orebodies are structurally controlled and consist of quartz-carbonate-pyrite-arsenopyrite veins and impregnation zones with traces of scheelite, magnesite and talc, which were originally worked for gold (total past output ~32 t Au from 89 sites). Present mining targets antimony with by-product gold. Ore minerals include antimonite, berthierite, tetrahedrite and complex sulphosalts. 34S data imply a magmatic source of sulphur, probably leached from komatiites. Carbonate 13C (-4.7‰) is too heavy for biogenic carbon and suggests a deep origin of CO2. The crustal-scale shear zone of the AL may have allowed upward flow of mantle fluids. One genetic model emphasizes deep metamorphic fluids that distilled antimony and gold from metapelites (Pearton & Viljoen 1986). Orebody characteristics and metamorphogenic hypotheses applied to the orogenic antimony-gold deposit Wiluna in Western Australia are very similar (Hagemann & Lüders 2003). Several of the AL deposits are genetically related to felsic intrusions (Jaguin et al. 2012) as proposed in the general model of orogenic gold metallogeny (Figure 2.22).

Jaguin et al. (2012) find that gold and antimony ore displays the same age (within error margins, measured by Pb-Pb of pyrite) as the granodiorites (zircon U-Pb) and, significantly, felsic metavolcanic schists that host volcanogenic massive sulfide (VMS) ore bodies along a linear structure that parallels the Antimony Line. In their Figure 4, they propose that at 2.97 Ga, the two lines were superposed and that the VMS Cu-Zn deposits formed in a shallow sea above the hydrothermal orogenic Au-Sb metallogenetic system from the same fluid and liquid conduit.

What is the use of this model for exploration? Well, if you have an Archaean or Palaeoproterozoic orogenic Au system with felsic intrusives, you should locate apical parts and study these and their roof, and you might search for nearby cosanguineous volcanics and base metal VMS deposits. In the inverse case, find cosanguineous intrusions and related orogenic Au-Sb. It would help if you can dertermine the vector of increasing metamorphic grade and its relation (dip direction) to the present land surface.


Groves, D.I. (1993) The crustal continuum model for late Archean lode gold deposits of the Yilgarn Block, Western Australia. Miner. Deposita 28, 366-374.

Hagemann, S.G. & Lüders, V. (2003) P-T-X conditions of hydrothermal fluids and precipitation mechanism of stibnite-gold mineralization at the Wiluna lode-gold deposits, Western Australia: conventional and infrared microthermometric constraints. Miner. Deposita 38, 936-952.

Jaguin, J., Poujol, M., Boulvais, P. et al. (2012) Metallogeny of precious and base metal mineralization in the Murchison Greenstone Belt, South Africa: indications from U-Pb and Pb-Pb geochronology. Miner. Deposita 47, 739-747.

Pohl, W.L. (2011) Economic Geology, Principles and Practice: Metals, Minerals, Coal and Hydrocarbons – an Introduction to Formation and Sustainable Exploitation of Mineral Deposits. 663 Pages, 294 Figures, 28 Tables and 65 Colour Photographs. Wiley-Blackwell, Oxford.

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The Domination of the World Iron Ore Markets by Australia and Brazil – Based on Questionable Geological Models? (22 October 2012)

In the April 2012 issue of the AusIMM Bulletin, Desmond Lascelles published an impatient short article on the continuing acceptance of established views about the origin of iron ore deposits derived from Precambrian banded iron formations (BIF) and asked if generally accepted models were “science or religion”. In the same issue, Erick Ramanaidou & Martin Wells pointedly report new and established models side by side. Recently, in the June 2012 issue of the AusIMM Bulletin, the main target of Lascelles’ attack, Richard Morris, published a brief response (Letter to the Editor). In the journal’s website, a more detailed version of the response with a list of relevant papers is available.

Indeed, an increasing trickle of papers in influential professional media inspires radical novel interpretations that are profoundly changing the genetic debate. But how certain is it that the new models apply to all deposits, or are the established and the new models valid for different sites? Considering that iron and steel have an enormous importance in our economies and that a huge annual mine production must continuously be replaced by new reserves, the answer to this question is highly relevant. Exploration has to be based on the best science and certainly not on beliefs.

Let me try to subsume the building blocks of genetic models and main points of contention: Essentially, banded iron formations (BIF) consist of thin quartz and magnetite layers forming sedimentary units that reach lateral extensions of thousands of kilometres and a thickness of hundreds of metres. Geological setting and associated rocks allow a subdivision of BIF into two types: 1) Algoma type in submarine island arc volcanic settings; and 2) Superior type in ancient marine shelf sediments. A third type, Rapitan, is closely related to glaciogenic marine sediments of “Snowball Earth” but is economically insignificant.

Iron formations of the Superior type are the Earth’s main concentration of iron and the largest source of iron ore. They are ancient marine sediments of global extension, preserved in remnants of basins that reach tens of thousands of square kilometres. Layering, banding and lamination characterize these iron-rich rocks, which were formed in the Early Palaeoproterozoic (2500-1800 million years ago, or 2.5-1.8 Ga).

Most scientists relate the precipitation of the giant mass of iron contained in Superior type BIF to the stepwise transition of oceans and atmosphere from a reduced to an oxidized state (the “Great Oxidation Event” GOE between 2.45 and 2.2 Ga). Before the GOE, high concentrations of reduced iron (Fe+2) in ocean water were derived from both submarine-exhalative systems and continental weathering. Supposedly, GOE was caused by blooms of the earliest photosynthetic microorganisms (cyanobacteria), increasing oxygen concentration in seawater. Dissolved Fe+2 was oxidized and precipitated as insoluble Fe3+(OH)3.

Parallel to BIF formation, multiple environmental changes of earth systems took place. Recently in Nature (2012), Keller & Schoene suggested that the temporal coincidence of GOE, BIF and remarkable changes of igneous rock compositions at about 2.5 Ga indicates a common cause that must be sought in mantle processes, not in photosynthetic life.

Primary BIF rocks have an Fe2O3 / SiO2 ratio of 0.98-1.26, typically 25-45 wt. % Fe, less than 3 % each of Al2O3, MgO and CaO, and small tenors of Mn, Ti, P and S. At sufficiently high magnetite grade and suitability for low-cost magnetic processing, the rocks are exploited as “taconite ore”.

Many BIF-based iron ore mines, however, extract parts of primary iron formations that were locally enriched to iron tenors reaching 68%. These deposits make Australia and Brazil world powers in iron ore export markets, similar to Saudi Arabia in crude oil. For this enrichment, two different and mutually incompatible process systems are proposed:


the “new creed”: hypogene hydrothermal replacement of chert bands by magnetite and Ca-Fe-Mg carbonates, and progressive hematitisation by basinal brines; hydrothermal alteration assemblages and high grade iron ore crosscut the dominant magnetite-quartz banding of BIF and depletion of heavy oxygen confirms a metasomatic origin; later, in the supergene (weathering) domain, leaching and purification to “high-grade hematite ore” of 60-68 wt. % Fe;


the “accepted model”: atmospheric oxygen drives a supergene electrochemical transfer process. This involves the reduction of O2 to (OH)- in ground water of exposed BIF, consuming electrons conducted by the magnetite-kenomagnetite horizons from the deep, tectonically-related, reacting zones, during the conversion of Fe2+ to Fe3+ (Morris 2012). Iron from the surface is mobilised as Fe2+, possibly by bacteria, and transferred to the reaction zone in ground water. Later leaching at the surface resulted in “mimetic martite-goethite ore”; martite is a term that denotes hematite replacing magnetite.

In conclusion, there is hardly an aspect of BIF-hosted iron ore formation that is not disputed, from the peculiar conditions that caused deposition of these conspicuous strata to the precise pathways for the local formation of huge, nearly monomineralic, high-grade iron oxide ore bodies. Consensus seems limited to the supergene nature of the last step of upgrading. The next generation of iron ore deposits, however, will be buried and accordingly, similar to copper porphyries, ore bodies must be found underneath cover. For that purpose, reliable genetic and exploration models are clearly needed. Comprehensive research of iron ore formation systems is in progress in order to fully understand the “plays”. This work should not neglect another class of giant iron ore deposits: the metasomatic siderites, which have a hydrothermal origin similar to (i); read more in my “Economic Geology” on page 59ff: 1.1.9 Hydrothermal metasomatic ore deposits.

Improved understanding of high-grade iron ore formation will be rewarded by improved predictive capabilities, successful exploration and with it, continuing supply of iron and steel for the world.

Read more in:

Dalstra, H. & Guedes, S. (2004) Giant hydrothermal hematite deposits with Mg-Fe metasomatism: a comparison of the Carajas, Hamersley, and other iron ores. Economic Geol. 99, 1793-1800.

Keller, C.B. & Schoene, B. (2012) Statistical geochemistry reveals disruption in secular lithospheric evolution about 2.5 Gyr ago. Nature 485, 490-493.

Morris, R.C. (2012) A brief response to ‘Iron ore genesis models – science or religion?’ D. Lascelles. The AusIMM Bulletin 3, Letters to the Editor

Pohl, W.L. (2011) Economic Geology, Principles and Practice: Metals, Minerals, Coal and Hydrocarbons – an Introduction to Formation and Sustainable Exploitation of Mineral Deposits. 663 Pages, 294 Figures, 28 Tables and 65 Colour Photographs. Wiley-Blackwell, Oxford.

Thorne, W., Hagemann, S., Vennemann, T. & Oliver, N. (2009) Oxygen isotope compositions of iron oxides from high-grade BIF-hosted iron ore deposits of the central Hamersley Province, Western Australia: Constraints on the evolution of hydrothermal fluids. Economic Geol. 104, 1019-1035.

Thorne, W.S., Hagemann, S.G. & Barley, M. (2004) Petrographic and geochemical evidence for hydrothermal evolution of the North Deposit, Mt. Tom Price, Western Australia. Miner. Deposita 39, 766-783.

Zerkle, A.L., Claire, M.W., Domagal-Goldman, S.D., Farquhar J. & Poulton, S.W. (2012) A bistable organic-rich atmosphere on the Neoarchaean Earth. Nature Geoscience 5, 359-363.

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The Golden Age of Gas? Or a Penguin in Your Garden? (22 September 2012)

The International Energy Agency (IEA, Paris) paints an optimistic future for the world economy and the environment, but only if the social license for the exploitation of abundant shale gas resources can be won. Beginning in the 1990ies and until now, shale gas is only produced in the United States, where in various ways, its impact is highly beneficial:

(1) Greens should laud the heavy reduction of carbon dioxide emissions by 450 Mt caused by shale gas replacing coal in electricity production (from 50 to 42% and still falling) and heating. In contrast, the EU’s CO2 emissions are still increasing as ever more coal is burnt, because after nuclear fission coal is the cheapest way to produce electricity, and average gas prices are five times the level in the USA; therefore in Germany, nuclear power is mainly replaced by coal. (2) Once again, the USA are pioneers in a new technology, which boosts the economy, creates jobs for all levels of society, saves costs for importing expensive energy and provides an income by exporting knowledge. (3) Wealth is created for a broad sector of society, from the long-time unemployed and rural land owners to professionals, industry and the whole nation.

In a special report on unconventional gas (“Golden Rules for a Golden Age of Gas”, May 2012) the IEA investigates benefits and disadvantages of this development. Overall, the Agency concludes that the world’s economy would see significant growth if other nations should embrace the technology. This is, of course, no question in China, which is thought to host the largest resources of unconventional gas and is already a big producer of coal bed methane. Other countries hesitate, including most of the European Union. Many people are scared by media reports that predict various hazards ranging from earthquakes to poisoned air, soil and water. A sudden gusher of water, mud, gas and petroleum in your front lawn – truly a nightmare!

By the way, fracking fluid is not a horrendous brew but water with high-purity quartz sand (“fracking sand”) conditioned by a small dose of about 1% of gels as a thickener, chelants for breaking down the gels in the opening fractures, friction reducers such as talc, and a biocide (similar to common detergents) to inhibit formation of bacterial slimes.

In order to help the hesitant nations and the concerned people to question, and when enlightened, hopefully to accept shale gas development, IEA proposes the Seven Golden Rules, which adress the industry in demanding best practice but assist state authorities and stakeholders in critical enquiries. Here is a short summary:

1 Measure and disclose environmental and operational data, engage the people at all stages

2 Watch where you drill, from siting a well to (seismic) monitoring the propagation of hydraulic fractures

3 Isolate wells, especially from freshwater aquifers, and prevent leaks of fluids

4 Treat water responsibly, regarding the amount used and safe disposal of waste water

5 Eliminate venting, minimize flaring and other emissions (e.g. vehicles, pumps and compressors)

6 Think big related to local development, infrastructure, land use, air quality, traffic and noise

7 Ensure a consistently high level of environmental performance and assist independent monitoring.

The big international companies now entering the field should have no problem with these rules; they reflect established best practice in the oil and gas industry. The small pioneer companies may have made initial mistakes but by now, the tight gas production technology is safe. So, instead of that gusher, it appears more likely that one morning, you find a penguin rearing her young in your garden.

In my Economic Geology, you can find the principles of hydraulic fracturing explained on page 567, and its mechanics in Figure 1.39 (page 65). Induced seismic activity (man-made earthquakes) is introduced on page 577. The Barnett Shale, where the new drilling and fracturing technology first took off, is presented on page 565.

The International Energy Agency’s Seven Golden Rules (2012)

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Tailings and Other Dams – Always a Risky Part of Mining (22 August 2012)

Every year, among many thousands of mines on the world, which safely operate tailings or slimes dams, a small number experience dam failure. Resulting mud flows may kill people and destroy property, and only these reports reach the media.

An exception concerning attention in the media was the artificial river bank dam break in the Yallourn East Field of the giant lignite mining district in the Latrobe Valley, Victoria, Australia. In order to allow an expansion of the mine and provide access to coal reserves lasting until 2032, a diversion of Morwell river along the pit was built only a few years ago, costing A$120 million. Although the work won an award for engineering excellence and prompted claims that it would survive a one-in-10,000 years flood, the dam collapsed in early June 2012, due to profuse rains. The river rushed into the open cut. Mine production fell away sharply and the operator TruEnergy/EnergyAustralia is in great financial troubles. The precise cause may never be found out because a long sector of the dam was simply washed away.

Common causes of dam collapse include overtopping and erosion, or failure by hydraulic phenomena within the dam, which are commonly subsumed as “piping”. Richards & Reddy (2007) provide a comprehensive review of the published literature on piping and differentiate between backward-erosion, internal erosion, tunneling, suffosion and heave. Allow me to refer here mainly to the first, which is nearest to the literal meaning of the word piping.

In geotechnical terms, piping sensu stricto affects non-cohesive materials (e.g. sand, the coarse fraction of processing waste), which is typically used to construct so-called permeable tailings dams ( Economic Geology page 452). Flow of seepage water sweeps out particles especially where the flow concentrates at an exit point on the outward slope of a dam. Loss of reciprocal support of remaining grains increases erosion and flow, causing the pipe to grow inwards (backward-erosion) until collapse intervenes. The main control on piping is the velocity of intergranular flow, which is a function of the hydraulic gradient. Already, Henry Darcy (1856) had recognized the relationship between head, length of flow path and the fluid velocity, the latter being the key in our context.

Poor construction of the dam, insufficient compaction adjacent to outlet pipes or other structures such as the drainage below the dam, insufficient basal drainage, settlement of the dam, cracks formed by an earthquake and foremost, poor maintenance of the embankment are common causes of piping. Typical triggers of final failure are heavy rains or snow melt. This is no excuse before the law – precipitation data including extremes are available for nearly every location on this world. Damages would be force majeure in commercial matters, but not in criminal courts. Depending on the situation of your dam (e.g. endangering people and valuable property or not) the drainage must be dimensioned to deviate the mass of water recurring every 25-100 years or more.

Note that piping is different from failure modes that are considered by common geotechnical stability calculation software. Because the construction of a flow net (or even a simple sketch) allows estimating the flow velocity of water within the dam, this is one response to finding a new spring or patch of seepage on the dam slope. A high flow velocity deduced from the flow net would, of course, be a call for urgent measures such as immediately moving people to safety, out of the way of a possible mass flow.

Let me sum up: Earth dams are always a hazard. To reduce the risk, responsible management should establish a regular control roster of dams, involving engineers, surveyors and geologists. During and after heavy rains, have your dams closely patrolled. The discovery of overtopping or an incipient concentrated leakage from the embankment, heave near the toe or the formation of sinkholes demands immediate action. For this case, a plan of emergency and disaster management should be in place. Once endangered people are cared for, you may consider to take preventative actions, in order to reduce the probability of collapse. Immediate removal of any standing water from the upstream-side would be an obvious example. Your geotechnical crew should prepare worst case scenarios and a variety of responsive actions. Let them be inspired by the classic book of Terzaghi (1996).

Richards, K.S. & Reddy, K.R. (2007) Critical appraisal of piping phenomena in earth dams. Bull. Eng. Geol. Environ. 66, 381-402.

Terzaghi, K., Peck, R.B. & Mesri, G. (1996) Soil mechanics in engineering practice. 3rd ed. 729 pp. Wiley.

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Gold Exploration – Contrasting Most Recent Strategies (1 August 2012)

Imagine that you are responsible for the exploration strategy of one of the major players. Your task is, of course, to locate the next generation of profitable deposits. In the spectrum of possible strategies, two recent papers propose widely different approaches. The first is all about geological modelling (Hronsky et al. 2012), whereas the second works with advanced statistical analysis of the large and still expanding public domain data base (Barnett & Williams 2012). The example used is a region in Western Australia, where the state invests heavily in precompetitive data collection (including a mines data bank, geological mapping, geochemical, magnetic, gravity and radiometric surveys).

The first paper by Hronsky et al. (2012) proposes a “unified model” of gold metallogeny in accretionary orogens. Accretionary settings are very common long-lived sites of plate convergence, and consist of diverse geological domains, including accretionary wedges, island arcs, continental fragments, clastic sedimentary basins and overprinting magmatic belts. Examples are the Cordilleras of both Americas, the Palaeozoic orogens in Eastern Australia, and the 3000 km-long Palaeozoic accretionary orogenic collage of the Altaids in Central Asia.

The model invokes a process system that starts with fertilization of the upper mantle, and continues with mobilisation of the gold, and its transfer to the shallow crust where deposits may be formed. Regional-scale exploration should investigate the lithospheric architecture, map the degree of upper mantle fertilisation, and assess major magmatic and metallogenetic events. Recognition of lithosphere-scale structures and pipe-like channels that enable the rise of melts and fluids leads to the identification of promising target areas.

Do note, that this approach emulates the “petroleum systems” method in the oil and gas industry that so successfully keeps us supplied with plenty of oil and gas. Because of its insights and holistic nature, the paper by Hronsky et al. (2012) deserves the distinstion “best metallogeny paper for many years”.

In my opinion, the second paper by Barnett & Williams (2012) is equally remarkable. The authors demonstrate a targeting method that disregards genetic models and is founded in digital data mining of a large set of public domain data, which are processed by artificial neural network statistics and probabilistic modeling. A sample area in Western Australia yields precisely defined new targets for detailed gold exploration. More than 250 primary and derived data layers were assembled. In this Archaean region, many orogenic gold deposits are already known and the multivariate statistics of their setting is the input for calculating the output, that is the probability of gold mineralisation at any grid element. This is an area of thick regolith, yet geochemical analysis of mulga leaves (the mulga tree, Acacia aneura, characterises the Australian outback) turns out to be one guide to buried ore, and K-U-Th derived radiation allows mapping of in-situ rocks. Proximity to shear zones and faults is another relevant metallotect. Gravity and lithology are useful, magnetics seem to be least indicative.

Now, which method would you choose for your team and your dollars?

Barnett, C.T. & Williams, P.M. (2012) A radical approach to exploration: Let the data speak for themselves! Soc. Economic Geol. (SEG) Newsletter 90, pages 1, 12-17.

Hronsky, J.M.A., Groves, D.I., Loucks, R.R. & Begg, G.C. (2012) A unified model for gold mineralisation in accretionary orogens and implications for regional-scale exploration targeting methods. Miner. Deposita 47, 339-358.

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BP’s Statistical Review of World Energy 2012: Updating my Economic Geology, Pages 465-468, Introducing Fossil Fuels (18 July 2012)

In 2011, the WORLD’s PRIMARY ENERGY SUPPLY (ca. 12,300 Mt oil equivalent) was provided by 33.1% from petroleum, 23.7% natural gas, 30.3% coal, 6.5 % hydroelectricity, 4.9% nuclear power and 1.5% renewables (BP Statistical Review of World Energy 2012). Detailed data and projections about renewables can be found in the annual World Energy Outlook by The International Energy Agency (IEA). The base load, that is continuous reliable large scale supply of the rapidly growing world electricity demand, is guaranteed by coal and nuclear power. This is contrasted by the widely fluctuating output of wind and solar power. Electrical energy storage technologies of the scale needed, however, are as yet unavailable; at present, pumped hydroelectric systems account for 99% of world storage capacity (Dunn et al. 2011).

World energy CONSUMPTION habitually grows by ~2-3% per year (2.5% in 2011). For many years now, growth was restricted to emerging industrial nations (Brazil, China, India, Southeast Asia), mainly based on coal.

Today’s COAL deposits that can be exploited under existing economic and operating conditions (“PROVEN RESERVES”) contain ~ 860,000 Mt. Of this total, one half comprises black coal and anthracite, the remainder brown coal and lignite (BP Statistical Review of World Energy 2012). World PRODUCTION of coal and lignite in 2011 was ~7695 Mt (equal to 3955 Mt of oil equivalent), an increase of 6.1% over 2010. The largest producers of coal in decreasing order are China (49.5%), USA (14.1%), Australia (5.8%), India (5.6%), Indonesia (5.1%), Russia (4.0%) and South Africa (3.6%).

Dividing reserves by annual production (R/P) renders the so-called “static period of availability” of coal reserves at ~112 years. Of course, the ratio does not define the end of coal, because additional giant resources are available. It illustrates only the difference between coal and other raw materials, concerning the rules for defining coal reserves and the long-term nature of planning. At face value, coal reserves are assured for a much longer time than petroleum (at the end of 2011 ~54 years, the Canadian oil sands not included) and natural gas reserves (~64 years, not including shale gas and other unconventional sources).

NOTES. The figures, as always, ask for interpretation. (1) China by far dominates coal production and consumption. Annual production in 2011 was 9% above 2010, although it strives hard to develop all other available energy sources, including nuclear, hydro, wind, photovoltaics, coal bed methane (CBM) and shale gas. (2) The US consumption of coal is falling because of abundant CBM and cheap shale gas (current prices are about 1/5 compared with the average in Europe). (3) Based on the above figures, and the fact that burning one tonne of black coal containing 80% carbon (C) generates nearly 3 t CO2, you will probably like to draw your own conclusions. But who wants to throw the first stone? The rapid increase of prosperity and living standards in today’s industrial nations also started with coal, during the Industrial Revolution in the 18th Century.

BP Statistical Review of World Energy 2012

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Copper Porphyry Origin: Fundamental New Thoughts (11 June 2012)

In my Economic Geology (2011), I wrote on page 132 ‘Metallogeny is the science of origin and distribution of ore deposits in geological space and time (Louis de Launay 1897)’. Another statement, equally true, might have been ‘Metallogeny is not a consolidated body of knowledge but an assemblage of structured and unstructured information in perpetual flux.’ In order to better understand the second, just read the following:

Sources of the metals concentrated in porphyry copper ore deposits of volcanic arcs at convergent plate margins are deep magmas that evolve while rising, but ultimately a fertile mantle. Melts and supercritical fluids that originate in the subducting slab of oceanic crust and the mantle wedge were thought to be oxidized and only for this reason, able to dissolve and transport chalcophile metals (Mungall 2002). Last November, Richards (2011) demonstrated that fertile arc suites are marked by amphibole and biotite phenocrysts, which indicate hydrous magmas with 4-8% H2O, and that these melts are not adakites (the product of slab-melting) but form in the mantle wedge. He writes ‘just add water’ (derived from the dehydrating slab). Now, new models of the redox state of arc magmas from the mantle source to volcanic arcs imply a reduced source (Lee et al. 2012):

The authors present evidence that mantle source regions of arc magmas are not anomalously enriched in Cu and that sub-arc fertile mantle with 30 ppm Cu and 200 ppm S is not highly oxidized nor are the partial melts derived from it. Average uppermost mantle displays low fO2 (oxygen fugacity) values of ΔFMQ = –1 to 0 (log10 unit deviations from the fayalite-magnetite-quartz buffer), at which the prevailing oxidation state of sulphur is S 2– stabilizing sulphides. Consequently, mantle melting induces formation of sulphide melts, which sequester Cu and other chalcophile elements into pyroxene-sulphide cumulates (containing up to 400 ppm Cu) in sub-arc lithospheric mantle or the deep crust. The segregated silicate melts rise towards the surface and consequently, the continental crust is depleted in copper. The key to the formation of copper porphyries may be localized high-degree remelting of the pyroxenite-sulphide cumulates in thickened and heated arc roots that may be triggered by bursts of fluid release from the subducting slab. The hydrous (Richards 2011) and Cu-rich magmas feed Cu-porphyries. Cu-enrichment of melt requires suppression of sulphide crystallization and high solubility of sulphur in the melt, which are achieved through rapid rise (decompression) and fO2 increase. At fO2 increasing through FMQ+1 and +2, sulphur S 6+ is stable as sulphate (SO4 2-) resulting in a 10-fold increase in total S solubility.

For our friends working in exploraton and extraction of copper, this revolutionary concept will not have immediate consequences, although geochemists might search for new subtle keys indicating fertile igneous suites. Richards (2011), by the way, points out that hydrous phenocrysts such as amphibole and biotite are visible keys for high water contents of the melt. Of course, the hunt is on to find hitherto unknown fertile mantle regions. Some can be located by scanning mantle xenoliths in volcanic rocks (e.g. Cu and S-rich pyroxenites in Late Miocene basalts of eastern California: Lee et al. 2012). Similarly, gold-fertile mantle may be revealed by anomalous Au traces in xenoliths, basalts and lamprophyres (Hronsky et al. 2012).

If the reduced-mantle hypothesis is confirmed to be generally applicable to volcanic arcs, it is a sobering thought that, because of the high density of these rocks, most copper sequestered from mantle melts into pyroxenite cumulates eventually founders into the convecting mantle (Lee et al. 2012).

Hronsky, J.M.A., Groves, D.I., Loucks, R.R. & Begg, G.C. (2012) A unified model for gold mineralisation in accretionary orogens and implications for regional-scale exploration targeting methods. Miner. Deposita 47, 339-358.

Lee, C.-T.A., Luffi, P., Chin, E.J. et al. (2012) Copper systematics in arc magmas and implications for crust-mantle differentiation. Science 336, 64-68.

Mungall, J.E. (2002) Roasting the mantle: slab melting and the genesis of major Au and Au-rich Cu deposits. Geology 30, 915-918.

Pohl, W. (2011) Economic Geology, Principles and Practice: Metals, Minerals, Coal and Hydrocarbons – an Introduction to Formation and Sustainable Exploitation of Mineral Deposits. 663 Pages, 294 Figures, 28 Tables and 65 Colour Photographs. Wiley-Blackwell, Oxford.

Richards, J.P. (2011) High Sr/Y arc magmas and porphyry Cu ± Mo ± Au deposits: just add water. Economic Geol. 106, 1075-1081.

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Core Logging in Coal Exploration: A New Australia-Wide Standard (18 May 2012)

Good digital logs of drill core are a valuable asset. But if there is a Babel of 30 different languages as existed until recently in Australia, such an asset may turn into a big headache, for example, when projects are bought and sold. Translation is always costly and error prone.

This is why recently, The Australasian Institution of Mining and Metallurgy (AusIMM) published a new standard for logging coal core (CoalLog – The Australian Coal Logging Standard). If you are at all working with core, have a look into the website of AusIMM (below). Under Codes & Accreditation, you will find the new CoalLog Standard as well as the JORC and VALMIN Codes, and the Code of Ethics. All are highly recommendable and can be freely downloaded.

Allow me to quote from the description: “During the period 2010-2012, three sub-committees (geological, geotechnical, and data transfer) with representatives from most major Australian coal mining, consulting, and software companies developed 'CoalLog' which includes data entry sheets and standard code lookup tables for header, drilling, lithology and geotechnical data as well as a format for the transferal of this data.”

The whole package consists of a manual (pdf), logging sheets and dictionaries (pdf and xls), and test data (csv). The manual explains logging procedures and comprises 123 pages (ca. 5 MB); it was assembled by B. Larkin (GeoCheck Pty Ltd) & D.R. Green (Green Exploration & Mining Services Pty Ltd).

Readers working with other minerals and building their own logging codes may profit from the description of transferrable features, such as the recording of point load data or of parting planes.

In my Economic Geology book, specifics of drilling and logging in coal exploration are described in Chapter 6.5 Applications of Coal Geology (page 507-518). Admittedly, although core logging principles are explained, protocols are not discussed. You will understand that I am pleased to provide instead a link to this authoritative and detailed source.

AusIMM webpages

W. Pohl (2011) Economic Geology, Principles and Practice: Metals, Minerals, Coal and Hydrocarbons – an Introduction to Formation and Sustainable Exploitation of Mineral Deposits. 663 Pages, 294 Figures, 28 Tables and 65 Colour Photographs. Wiley-Blackwell, Oxford.

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The June 2012 Rio Conference: Earth Systems Governance and Planetary Stewardship by the United Nations? (24 April 2012)

An article in Science reports on the main conclusions of a 10-year social science-based research program (the Earth System Governance Project) under the auspices of the International Human Dimensions Programme (IHDP). Preparing for the 2012 United Nations (UN) Conference on Sustainable Development at Rio de Janeiro in June, Biermann et al. (2012) call for seven measures:

1 Upgrade the UN Environment Programme (UNEP) to the formal, more weighty role of an Agency.

2 Create a UN Sustainable Development Council.

3 Establish global framework conventions for emerging technologies such as nanotechnology and geo-engineering.

4 Global trade, investment and financial regimes must be submitted to and ruled by sustainability policies.

5 International norm-setting should be voted for by qualified majorities; any veto powers are to be abandoned.

6 Empower stakeholders, citizens and consumers by transparency, access to decision-making and consultative rights.

7 Provide strong support for poorer countries.

As an economic geologist I am not able to fully foresee all consequences if the proposals should be realized. But I am in no doubt that the impact on the raw materials industry would be great indeed.

Looking at best practices in the extractive industry, principles and tools for socially and environmentally sustainable exploitation and site restitution are highly developed. Already, they have been embraced by most large companies working in voluntary submission to the Equator Principles (EPs), a set of rules for determining, assessing and managing social and environmental risk. Yet, the transition to “green” mining has only started. For the near future, we may expect an avalanche of innovation and penetration of best practice throughout the world. Wise national and international governance should aim to support this change. Can we expect this from the United Nations?

Biermann, F., Abbot, K., Andresen, S. et al. (2012) Navigating the Anthropocene: Improving Earth System Governance. Science 335, 1306-1307 (16 March 2012).

Earth System Governance Project

International Human Dimensions Programme

Equator Principles

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Geological Mapping Self-Taught – Useful Books (2 April 2012)

When I studied geology at Vienna University, all teachers and students of all levels (some 50-70 at this time) decamped in summer to spend 14 days in the Alps, mapping in groups of 2-3 a share of some particular tectonic or lithologic unit. Every winter, a smaller but highly motivated group did one week of underground mine mapping. This way, most of us collected 8-10 mapping courses through the years and really learnt mapping and a lot of geology besides.

Today, even the best schools provide but an introduction to geological mapping. Learning on the job, self-teaching or booking one of the field courses offered by institutions such as SEG and AusIMM are possible solutions for nearly all those in industry who are for the first time asked to produce a geological map.

For on-the-job self-teaching, I recommend to buy Basic Geological Mapping and this is also the choice for students in geological mapping courses. It is a small handy format booklet which you can at all times take to the field for quick reference and useful advice. Figures and photographs lack colour but assist understanding. Chapters on safety, equipment and topographic base maps (needed to plot geology) are followed by the core content: methods of geological mapping, using tools such as air photographs, digital terrain models (DTMs), GPS, geophysical data and surveying, measuring bedding and structures, and map symbols.

Useful hints concerning the geological setting of the mapping project (e.g. sediments, igneous rocks, etc.) follow; I love the little chapter “Economic Geology” pressed into 3 pages but have only praise for it, even if my own book needs nearly 700 pages to “introduce” the subject. For mine maps, the reader is referred to Marjoribanks (2010) where the subject is presented within 10 pages. How to produce field maps and good field notes is very lucidly described; myself, I always had a problem with “neatness” but I do fill my notebook with detailed sketches, diagrams and cross sections, often drawn to scale, apart from text as the authors suggest. Once the field work is done it is time to produce fair copy maps and sections; here, drawing by hand or with software (e.g. CorelDraw) is equally explained. Of course, every map needs explanations or a proper report and how to make this is very well described. Similar to “proper” books, this little manual contains References and an Index.

Geological Field Techniques is the book for professionals and advanced students with similar contents as the first but more details and lavishly illustrated in colour. I would not think that you should take it in your rucksack for a rainy week in the mountains but it might do well for reading in the tent during long, dark evenings. All themes are more broadly presented and very well explained. Sedimentology including sequence stratigraphy, structural analysis and metamorphic rocks attracted my attention. Economic geology and mine mapping are not touched nor have I found a reference to DEMs and LIDAR. References are disseminated in single chapters. There is a good Index at the end (although the term “mineral deposits” leads to sampling igneous rocks for zircon). Actually, there is a short chapter on sampling although without any references nor touching those aspects that are essential in economic geology. Compared with the first, this book packs much more information, is more pleasing and costs little more. Yet I am glad that I acquired both books.

Basic Geological Mapping. 5th Edition. Richard J. Lisle (Cardiff University), Peter Brabham (Cardiff University), John W. Barnes (University College of Swansea, UK). ISBN: 978-0-470-68634-8. Paperback, 230 pages ca. £ 22.50. ©2011 Wiley-Blackwell.

Geological Field Techniques. Angela L. Coe (Editor) (The Open University) ISBN: 978-1-4443-3062-5. Paperback, 336 pages ca. £ 25. ©2010 Wiley-Blackwell.

Marjoribanks, R. (2010) Geological methods in mineral exploration and mining. 2nd ed. 238 pp. Springer. Hardcover 109.95 Euro.

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A Case Study for Top Explorationists: Buried Ore Deposit Geochemical Discovery Methods Revealed (8 March 2012)

Certainly, you do remember that the top business schools teach by analyzing and working through case studies. Here is one for top people in exploration:

In Chapter 5.2.4 of my Economic Geology, you will find 6 pages of dense theoretical and practical advice how to use geochemistry for finding ore, including the case where the ore body is buried beneath younger cover rocks, which theoretically block all geochemical signals. If this case is an important part of your work, you may like to read a lucid paper in the SEG Bulletin of Economic Geology (Muntean & Taufen 2011).

The physical background of the paper is the Carlin gold mining district in Nevada. Let me illustrate the geological setting of Carlin gold if you should not remember details ( Economic Geology page 212):

The precise origin of “sedimentary rock hosted, disseminated” gold deposits, which are clearly epigenetic is still disputed. The economically most prominent examples occur in Palaeozoic carbonate rocks near Carlin/Nevada/USA, as replacement and breccia orebodies that were probably formed in the Eocene (Hofstra & Cline 2000, Hofstra et al. 2003). Gold production, reserves and resources of the Carlin trend are thought to exceed 3800 tonnes. Hydrothermal “jasperoid” (silicified decarbonated limestone), dissolution collapse breccia and anomalous arsenic (+Hg, Tl and Sb) characterize alteration. Gold precipitation was induced by sulphidation when H2S-rich auriferous fluids reacted with reduced iron in the host rocks. One genetic hypothesis implicates an Eocene mantle diapir (Oppliger et al. 1997). New dating suggests that the ores formed while a large plutonic complex was emplaced at depth (40-36 Ma: Ressel & Henry 2006). Most of the fluids seem to be meteoric (Henry & Boden 1998) but water and sulphur (Kesler et al. 2005) in ore-related minerals have a magmatic (or metamorphic) component. Also, Johnston et al. (2008) provide links between Carlin deposits and magmatic activity. Pulsed incursion of magmatic Au-As-Hg-Cu-Te fluids of high-sulphidation epithermal character is suggested by Barker et al. (2009). Large et al. (2011) suggest that carbon-rich shales in the host rock suite may have sourced both Au and As. Overall, derivation of the Carlin deposits from deep calc-alkaline magmatism triggered by delamination and asthenospheric upwelling and magmatic-hydrothermal fluids seems to be the accepted interpretation (Muntean et al. 2011, Sillitoe 2010).

In the 1990s Placer Dome did a thorough search in the area adjacent to the very first Carlin gold deposit discovered (Gold Acres, in 1922) and in 2002 charged Muntean & Taufen (2011) with a series of orientation surveys how to discover gold ore under alluvial valley fill. Several new deposits were found and are in operation. Barrick Gold inherited the project and generously allowed publication of the work. Although restricted to a specific environment (e.g. alkaline soil and groundwater, calcareous host rocks, very arid climate), the study can be read as a detailed and systematic description of the most important unconventional geochemical exploration methods including groundwater, soil gas and vegetation.

The authors report that gold ore covered by nearly 100 m of transported soil and alluvium is readily detected by anomalous Au, As, Zn and Bi at the surface. The upward transport of metals from buried ore and primary dispersion halos may be due to several mechanisms such as evaporative suction (visible in caliche/calcrete formation), capillary action, and plant roots. In the Carlin district, gas flow, barometric and seismic pumping may be invoked. An elevated CO2 flux (and O2 minima) was found above oxidizing pyritic gold ore at depth, probably due to reaction of acidity with the host carbonate (Muntean & Taufen 2011). The gas flow may lift trace metals in submicron particulate or volatile compound form (Klusman 2009).

Groundwater chemistry surveyed for permitting and environmental monitoring of the Pipeline gold mine, Nevada, is illustrated by Muntean & Taufen (2011). Originally, before mining, the flow was across the deposit; a plume of sulphate, As, Sb, K, F and Zn downflow from the ore clearly pointed to the ore body. The pre-mining groundwater table in this area, however, was at a depth of ~100 m; the costs of drilling to this depth for water samples would hardly have been considered rational.

The foregoing provide a few samples of the treasures to be found in this paper. Using it, I hope you will succeed in your own search for hidden ore. A recent paper by Neil Phillips (2012) is the ideal companion by presenting the strategic background of successful gold exploration. His remark “data by itself does not make a discovery, it is the intellectual input”, might be the motto of all exploration teams.

Muntean, J. & Taufen, P. (2011) Geochemical exploration for gold through transported alluvial cover in Nevada: examples from the Cortez Mine. Economic Geol. 106, 809-833.

Muntean, J.L., Cline, J.S., Simon, A.C. & Longo, A.A. (2011) Magmatic–hydrothermal origin of Nevada's Carlin-type gold deposits. Nature Geoscience 4, 122 – 127.

Phillips, N.G. (2012) Gold exploration success. Applied Earth Sci. (Trans. Inst. Min. Metall. B) 120, 7-20.

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Shale Gas, Hydraulic Fracturing and Social Reconciliation (5 February 2012)

Shale gas is natural gas (mainly methane) hosted in pores and fractures of fine-grained sediments which commonly are mature hydrocarbon source rocks. In contrast to conventional gas reservoirs, “tight” rocks like shale, coal or some sandstones have such a low permeability that free flow of the gas to a production drill hole is insufficient. In the recent past, ingenious engineering developments suddenly allowed economic extraction, opening up immense gas resources that were hitherto not recoverable. The key is precise directional drilling of curved holes including kilometre-long horizontal lengths. A bed of gas shale is developed by parallel holes at a distance that is determined by artificially enhanced permeability. The enhancement is induced by hydraulic fracturing which is a time-tested method in the hydrocarbon industry to improve the flow of gas and oil from reservoir rocks of poor permeability.

Allow me to insert three passages from my Economic Geology as a foundation of understanding the issues.

First – the beginnings (Page 565):

The pioneering discovery and conceptual innovation took place in the Fort Worth region in Texas where production started in 1999. Mississippian (Early Carboniferous) Barnett Shale near Fort Worth is a thick organic-rich shale (TOC 3-5 wt. % of kerogen type II) which hosts giant recoverable gas resources (~850 x 109: Pollastro et al. 2007) and currently provides an important share of US gas production. Although extraction is more expensive compared to conventional deposits, the impact of a large newly available energy source triggered a highly rewarding world-wide search for tight shale gas deposits.

The giant gas play in the Barnett Shale underlays a wide area of northwestern Texas where for >100 years conventional hydrocarbon deposits had been exploited, many of which were sourced from Barnett Shale. For some time already, the province was considered to be mature (approaching the end of production). Innovative thinking led to the recognition that source and reservoir may be one within this 300 m thick unit. Seals are provided by dense footwall and hanging wall limestones. The newly found gas resources are in shale with a maturity Ro > 1.1%. Wet gas occurs in the maturity zone Ro 1.1-1.4%; near the Ouachita Structural Front at Ro >1.4% only dry gas is found (Pollastro et al. 2007). The strong horizontal heat gradient may have been caused by fluids driven from the Ouachita orogen. In-situ gas was generated by cracking of oil and bitumen and is unassociated (no oil).

Second - hydraulic fracturing (also called fracking, Page 567):

For flow stimulation, a fluid (usually water, exceptionally CO2 or nitrogen) is injected under very high pressure. Induced fractures reach a length of 1000 m and a surface in the order of km2. Their orientation is a function of the attitude of the rock mass stress vectors (page 562). As they open, these fractures partly follow pre-existing structures such as joints but also break through “bridges” of intact rock. This causes seismic signals that are actually used to monitor the propagation of fractures by geophysical methods. In rare cases, e.g. in proximity of active faults, injection of fluids may assist stress release in the form of earthquakes (page 577). To inhibit reclosure of induced fractures, silica sand or corundum pellets are co-injected. By this method, the flow of gas and oil from “tight” formations to the well is dramatically improved.

So why the fuss in the media and the anxieties of the people when fracking is not new at all? The reported incidences of frac fluid or methane spilling into groundwater or breaking through the surface point to the problem no.1 which is that many of the most economic gas shale plays are very near the land surface, in contrast to the commonly deep conventional reservoirs that are covered by impermeable seal rock. Nobody ever heard that frac fluid injected at a depth of thousands of metres ever reached the surface. And problem no.2 with shale gas, number and scale of fracking operations have damatically increased, raising the probability of unforeseen events caused, for example, by unknown structural connectivity between the rock unit being fracked and the surface.

What can be done to reconcile people with shale gas extraction? The main task for a company is, of course, to apply best practice in all operations, from exploration to monitoring during drilling, fracking and extraction, and when restoring the sites. Transparency and efforts to engage the people are at least as important. Minimize any impact on their quality of life. Of course, everywhere you will meet a hard-core NIMBY troup (Not In My Back Yard). As an answer, double your social activities. Explain things patiently and repeatedly to the media and the concerned public. Regulating, licensing and controlling authorities are often caught between their task to act in the interest of the state or nation (in order to provide energy, work, economic growth) and their responsibility for concerned local people. Obviously, the role of the civil services in mediation is to contribute independent professional advice.

Concerned communities should insist on clear answers to two main questions: i) the planned pressure management; and ii) the fate of the injected fluid.

If you wish for more information I suggest you visit the very informative “Natural Gas from Shale” website of the Government of New Brunswick (Canada). By the way, this is also available in French, if you prefer this language. The site includes lots of detail, e.g. on chemicals used in frac fluids and an extensive bibliography of scientific papers, reports and regulations concerning the environmental impact of shale gas operations, most of which is directed to professionals.

Shale Gas Science, Technology, Legislation and Environmental Considerations

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