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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.

SOURCES

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.

Links

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).

References

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?

Reference

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.

References:

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:

(i)

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;

(ii)

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.

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 et.al. (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.

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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 S⁶⁺ 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).

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.

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

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.

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

Adam Smith (1723-1790) and Expectations for the New Year (1 January 2012)

At this time of the year, media like to report on the financial and economic expectations for the New Year. Students and practitioners of economic geology, even those not holding shares in the industry, must be equally concerned about the near future. And we are not only passive recipients as after all, our work concerning raw materials always impacts on the world of economy, even if some its output is at the moment purely scientific.

With the light touch due for an optimistic start into the New Year, I wish to add my voice. Realizing my own limitations in soothsaying, I have searched Adam Smith’s classic, “The Wealth of Nations” (1776) for his views on minerals. Let me cite a few gems which I have found:

"The most abundant mines either of the precious metals or of the precious stones could add little to the wealth of the world. A produce of which the value is principally derived from its scarcity, is necessarily degraded by its abundance."

"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."

"Neither are the profits of the undertakers of silver mines commonly very great in Peru. (...) When any person undertakes to work a new mine in Peru, he is universally looked upon as a man destined to bankruptcy and ruin..."

I do hope that the last will not dishearten our friends working in Peru. Even a great man can err. Adam Smith’s negative opinions are influenced by effects of the flood of silver from America which was released by the Spanish conquest (beginning in 1492 with the arrival of Christopher Columbus). All over Europe, the consequent devaluation and financial crisis broke mining and caused havoc in the economy. The “Little Ice Age” with some of the worst cold spells of the last 2500 years and persisting from about 1600 to 1815 CE added food shortages and general misery. But this is another story.

Disproving Adam Smith we have learnt in recent times that gold and silver do have a stabilising role in private and public economy, but alone cannot guarantee wealth. Generally, I still maintain that “well-managed extraction of minerals has every potential to contribute to communal wealth, a sustainable and vital social and natural environment, and peace” (the very last phrase in my Economic Geology book).

In case that Adam Smith is unknown to you, allow me to add a few words. He was one of the stars of the Scottish Enlightenment, together with men such as David Hume and a founding father of geology – James Hutton. Equal to Paris, the Scottish Enlightenment was leading the evolution of new thinking concerning liberty, reason, free speech, and the role of science, religion and the state. This was one of the drivers starting the Industrial Revolution. Adam Smith tought moral and social philosophy. His interest in economy was aroused by contacts with the great French philosophers of his time. His book “The Wealth of Nations” became the base of modern economic thinking, with ideas such as that the self-interest of individuals and the division of labour lead to increasing wealth of society (the “invisible hand”).

If you search for more detail, Wikipedia offers an elaborate biography of Adam Smith

Adam Smith (1776) An Inquiry into the Nature and Causes of the Wealth of Nations (Wikipedia article on the book)

Coltan Project Meeting at Kigali, Rwanda (21 November 2011)

Reconciling People and Nature with Tantalum Mining

At the beginning of November 2011, 40 participants, 2 representatives of Volkswagen Foundation and 1 senior consultant (myself) followed the call by Bernd Lehmann (the Project Coordinator) to exchange news about work in progress. If you are interested in the project’s evolution, please refer to my “News Archive” (February 24, 2009) and to the entry in “News” (2nd May, 2011).

The papers presented at the meeting will, in due course, be available for download from the Coltan project’s website . In this website, you can also find a short introduction into the structure, methods and aims of the project.

We have found that in many respects, Rwanda is a beacon of well-managed mining in central Africa. The country is in the middle of a mining and exploration boom, concerning tin, tungsten, tantalum/niobium and gold. Yet, modern exploration methods are hardly applied; presently important deposits such as Cyuri in Rwanda, Kabarore in Burundi and the giant Bisie deposits near Walikale in Congo were discovered by traditional methods. Note that the LME price of tantalite is at nearly 300 US $ per kilogram. The reconciliation of mining and the people (from the diggers to small-scale farmers and the women) is rapidly gaining ground. The larger mines have already submitted an Environmental Impact Declaration (EID) under Rwandan law and have submitted to an independent CTC (Certified Trading Chains) audit. The latter describes the operation in detail, including the established certification scheme, and allows a close estimate of the production capacity. This is a response to widespread concern that sales revenues for minerals from the DR Congo feed armed conflict and abuse of its population.

CTC audits and certified trading are obligations resolved by the International Conference on the Great Lakes Region (ICGLR) aiming to enable bona fide legal mines to export minerals whereas conflict minerals originating from sources dominated by illegal armed groups remain excluded from trade. CTC systems buildup is supported by the German Federal Ministry for Economic Cooperation and Development (BMZ) through a mission at Kigali from “BGR (Federal Institute of Geosciences and Natural Resources, Hannover)” . One of the components for control is the Analytical Fingerprint (AFP) method developed by Frank Melcher and his team at BGR, which is able to identify the source of minerals. Of course, some time will pass till the hundreds of mines producing Au, Sn, Ta and W in the Great Lakes Region will have established CTC and been audited.

In Rwanda, the traceability of tin, tungsten and tantalum ore concentrate and gold is largely guaranteed, because the country’s administration is very efficient. The high costs of the controls, however, turn out to be an economic disadvantage as buyers will not pay above international stock exchange prices. In the countries surrounding Rwanda, the introduction of controls is slower but The International Tin Research Institute (ITRI) with its ”Tin Supply Initiative (iTSCi)“ based on due diligence guidelines published by the Organisation for Economic Co-operation and Development (OECD) and the United Nations (UN) offers to assist producers wishing to join the CTC process.

The Congo (DRC) reportedly suffers from a buyers’ strike – export of Sn, Ta and W concentrate has come to a halt. No company trading with the Unites States dares to infringe upon the Dodd-Frank Financial Act (July 2010) which imposes full traceability on imports from conflict regions. The US Securities and Exchange Commission is presently preparing the looming "conflict metals" law. Although another German project tries to introduce CTC in the eastern Congo, nobody knows at present, how and when an effectual CTC system might be working in the forest mountains of the DRC. Meanwhile, the population continues to suffer, but this time from losing their income and going hungry.

Contrary to pilot phase data collected in the Gatumba area, more detailed geochemical work demonstrated that in this mining district, arsenic is not a risk for drinking water. However, arsenic is a common companion of tin, tungsten and tantalum ore in the whole Western Rift Region, and drinking water wells in all mining camps and nearby river valleys must be monitored. Note that eventual pollution need not be related to mining, as demonstrated by the example of Bangladesh (refer to my “Economic Geology”, page 247). The blog posted by Steve Drury in the Earth Pages on November 16, 2011, “South Asian arsenic update” summarises an illuminating new paper which includes exemplary Bengal Basin-wide hydraulic and geochemical modelling.

As demonstrated by results presented at Kigali, the Coltan-Project progresses in great strides. One field of positive results is the research dedicated to identify the best approach to convert pegmatite waste remaining after ore extraction to agricultural use. Greenhouse experiments at Butare and field trials at Gatumba (see Photo Gallery) clearly show that fertility keys are addition of organic substance and adjusting the pH to near-neutral values (all soils at Gatumba are acidic, caused by natural leaching, not by mining).

If you are interested in an authentic source on the human, military and political background of the recent Congo wars and the role of minerals, I recommend the following book:

Dancing in the Glory of Monsters – The collapse of the Congo and the great war of Africa, by J.K. Stearns, 2011, Public Affairs, New York.

Field Geologists’ Manual – Essential not only for Practitioners (11 October 2011)

In September, the Australasian Institution of Mining and Metallurgy (AusIMM) released the latest (5th) edition of this time-tested source. Since I first joined this society as a young man, previous editions accompanied my professional activities.

First compiled by Don A. Berkman in 1976, the book provides a “comprehensive reference for field geoscience work”. It evolved into one of the best-selling publications of AusIMM. The foreword to the most recent edition presents the work as “bridging the gap between theory and practice and equipping explorers with the resources to undertake field work in Australia and throughout the world”. I can only add my voice to that of the numerous supporters of these statements.

What kind of information can you expect from this book? Before I point out some details, you might look at the Contents pages of the Field Geologists’ Manual (Monograph 9) which are freely accessible in the AusIMM website. And now to selected examples which may characterise the book.

In my opinion, the Index is an important characteristic of a good book. In this Manual, it has grown from 5 pages in the 4th to 10 in the 5th edition. Generally, much of the book reproduces information from the 4th edn. (2001) but there are moderate updates in all chapters. Pages have grown from 395 (2001) to 479 in 2011.

Examples of data which you will not find in Wikipedia, are (1) 21 pages of minerals (listing composition, crystal system, density, hardness, and remarks such as metal content in ore minerals); (2) a brief presentation of diamond indicator minerals and their characteristic geochemical properties; (3) a lucid short description of hydrothermal alteration, veins and breccia related to ore; (4) regolith terminology (Australian, but exemplary for us all wherever we work); and (5) in Chapter 9 – Geophysics (pages 283-303), comprehensive tables of relevant physical properties of ore, minerals and rocks.

Almost wholly new is Chapter 11 - Sampling, Analysis and Quality Control (page 311-333). Text and colour graphs provide a concise but very rich overview of the subject, supported by up-to-date references. Based on the Periodic Table, the most suitable analytical methods are shown for each element (e.g. for lithium ICP-MS, ICP-OES and AAS). Specifics of analysing gold, base metals, iron ores, nickel laterite ore, uranium, REE and PGE are explained.

Updated is Chapter 12 - Reporting (pages 335-362). Here, the reporting requirements for companies listed on the Australian Securities Exchange (ASX), the National Stock Exchange (NSX) or the New Zealand Stock Exchange (NZX) are covered. The chapter includes the JORC Code (2004). Many countries have similar rules, but for practitioners working in those that do not it is very useful to know the obligations.

Chapter 13 - Geometric and Surveying Data (pages 363-397) is thouroughly revised and enlarged compared to the last edition. It starts by explaining projections and coordinate systems, including transformations. This is followed by essentials of using GPS, differential GPS, classical surveying and its instruments, classical tachymetry, and compass and tape traverses.

A whiff of adventure comes with Chapter 15 – Resources, Templates and Further Reading (427-467), which among many others displays tables explaining petroleum industry abbreviations, or should I write slang? What about C&K meaning “choke and kill”? Or JS, “junk sub”, whatever that is. But seriously, I am very much of the opinion that oil and gas are part of economic geology, and we can learn much from our friends working in that industry

Practitioners should find this book an absolutely essential tool. Having the suspicion that many geologists working in research positions have little knowledge of critical procedures such as representative sampling and quality control of analyical data, I strongly suggest that this book should be at hand for all geoscientists.

Rutter, H., Clements, A. & Cooper, C. (Compilers) (2011) Field Geologists’ Manual, 5th edn., 479 pp, Monograph 9, AusIMM, Parkville (available in print or CD format).

Ancient Life, and Iron Ore at the Redox Interface (6 September 2011)

Life at the cathode is the title of an interesting and highly readable communication by Steve Drury on the Earth-Pages website. He refers to a recent paper in Nature that describes hydrogen as the energy source of life at deep-sea hydrothermal vents. Steve goes on to a more general look at the importance of redox processes in geology. His choice of the title refers to the generalization of the Earth’s largely reduced subsurface as an anode and its surface as the cathode (the “earth battery”). This is, as you know, due to the gradual transition of oceans and atmosphere from a reduced to an oxidized state which is called the “Great Oxidation Event”. The word “event” is somewhat misleading, because even in geological notion the passage took a long time indeed.

During the passage and ever since then, the interface between the two domains was the stage of ore-forming processes such as produced, for example, the unconformity, IOCG and sandstone-hosted uranium deposits. The largest metal concentrations are iron ores related to Precambrian banded iron formations (BIF). Scientific opinions converge on the hypothesis that in the Late Archaean and Early Palaeoproterozoic (2.6-1.8 Ga) “the atmosphere may have been nearly free of oxygen while the oxygen in the oceans started to increase. Seasonal blooms of the earliest photosynthetic microorganisms (cyanobacteria) increased oxygen concentration in seawater that oxidized and precipitated dissolved Fe2+ in the form of oxy-hydroxides” (my Economic Geology page 102). Worldwide, a huge mass of iron oxide mud assembled in the oceans. Little trace, however, remains of the tiny workers that achieved all this; surprisingly, the BIF display extremely small organic carbon contents.

Illumination comes from a recent paper by Yi-Liand-Li et al. (2011) who trace the continuity of phosphorus (apatite) from (iron-oxidizing) phytoplankton to bacterial Fe(III) reduction on the seafloor. Apatite nano-crystals in the 2.48 Ga Dales Gorge Member of the Brockman Iron Formation in Western Australia ( Economic Geology , Plate 1.67, p. 156-157) resemble modern biogenic apatite and Fe(III) acetate salt implies the presence of microbes in the iron mud. This is an indirect confirmation that loss of carbon in BIF is the result of early diagenetic anaerobic microbial activity that partially reduced Fe(III) and oxidized the carbon to CO2. And it is a strong pointer that the ordinary paragenesis of BIF, comprising magnetite, siderite and many Fe(II)-rich silicates is probably diagenetic, not low-grade metamorphic as often thought.

Although many new questions arise, this paper is a significant and remarkable step forward in our understanding of BIF origin.

Yi-Liang Li, Konhauser, K.O., Cole, D.R. & Phelps, T.J. (2011) Mineral ecophysiological data provide growing evidence for microbial activity in banded-iron formations. Geology 39, 707-710.