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Economic Geology News

Brownfield Mines – Remediate or Extract Remaining Resources? (25 May 2016)

The Iberian Pyrite Belt (IPB) in Southwestern Europe with the giant abandoned Rio Tinto mines is an outstanding example for this antagonism. Let us first look at the geological and environmental situation:

The IPB is an arcuate volcanic-sedimentary belt of Lower Carboniferous age that contains one of the greatest concentrations of sulphide (mainly pyrite) mineralisation on Earth, with resources in excess of 1700 Mt of sulphide totalling 15 Mt Cu, 13 Mt Pb, 35 Mt Zn, 46 kt Ag and 880 t Au (Adamides 2013). It originated in a supra-subduction setting during the final stages of the collisional assembly of Africa with Iberia, which ended with the formation of Supercontinent Pangaea. About 100 deposits form this metallogenetic province and during >4500 years, hundreds of mines have exploited metals and sulfur. The largest cluster of ore bodies is the Rio Tinto mining district that prior to erosion and mining, contained an estimated 500 Mt of massive sulphide and a considerable volume of auriferous gossan.

“Perhaps the most infamous historical mine wastes are those in the Río Tinto Mining District in Andalusia, Spain” (Hudson-Edwards 2016)

Situated at the sources of the Tinto river, the Rio Tinto mine is the subject of hot debates in science and environmental communities concerning causation and mitigation of acid drainage and metal contamination affecting the river. Mining at Río Tinto had a first flush in 2500 BCE marked by a metal spike in the river’s estuary (Leblanc et al. 2000) and finally closed in 2001. Remediation at closure was limited; Rio Tinto mine was more or less abandoned. Presently, parts of the mine are exhibited as part of a mining museum. In recent years, work is in progress towards opening a new mine (Adamides 2013), though not without opposition.

The Tinto river is 90 km long. Its mean discharge is relatively small—about 15 m3/s; flow ranges from 1 to 100 m3/s depending on seasonal variations, that include dry spells and rainy periods with floods. The Tinto river sediments are gray sands, including quartz, rock particles and abundant detrital pyrite grains that are weakly weathered and slightly rounded (Leblanc et al. 2000). Pebble beds above the water line are coated by ochreous rinds of earthy minerals such as goethite, jarosite and schwertmannite (see Photograph). Ochre formation is one of several processes that induce an attenuation of the solute load along the course of Rio Tinto towards the coast (Cánovas et al. 2014).

Rio Tinto
Rio Tinto some kilometers downstream of the brownfield mining area. Vegetation is healthy but the banks are marked by conspicuous ochre.

There is little doubt that the heritage of large-scale industrial mining that started at about 1850 is the main cause of acid mine drainage (AMD) and its effect on the river. Yet, as a scientist, I wish there were more data concerning the state of the river in the geological past. Today, Tinto river is marked by high acidity (pH 1.5–2.5), a high solute load and brown-red colour in dry seasons, and a unique, rich fluvial biodiversity of extremophiles (plants, eucaryotes, photosynthetic algae, microorganisms, fungi) that even caught the attention of space research. Before mining, large supergene copper-silver enrichment ore bodies and auriferous gossans existed at the later Rio Tinto mine. It appears likely, that the supergene history of the district began in the Eocene (early Tertiary), when the global climate was hot and humid (the last “hothouse Earth” in geological history). Afterwards and until today, weathering must have progressed in a stop-and-go fashion, as climate varied. Undoubtedly, a large mass of acidity must have passed into the river and through the Huelva estuary into the Atlantic Ocean. But when did the river and its biota acquire their present characteristics? When and how fast developed the singular acidophilic ecosystem?

What would be your advice to the authorities in Andalusia? Ban all future mining and remediate at all costs, or encourage the exploitation of remaining ore? The first would have to be paid by the taxpayer, Spanish or European, whereas the second might contribute to restoration costs and develop into a showcase of modern green mining. – I vote for the latter decision!


References:


Adamides, N.G. (2013) Rio Tinto (Iberian Pyrite Belt): a world-class mineral field reopens. Applied Earth Science 122, 2-15.

Cánovas, C.R., Olías, M. & Nieto, J.M. (2014) Metal(loid) attenuation processes in an extremely acidic river: The Río Tinto (SW Spain). Water Air Soil Pollut 225: Article 1795

Hudson-Edwards, K. (2016) Tackling mine wastes. Science 352, 288-290. DOI: 10.1126/science.aaf3354

Leblanc, M., Morales, J.A., Borrego, J. & Elbaz-Poulichet, F. (2000) 4500-year-old mining pollution in southwestern Spain: long-term implications for modern mining pollution. Economic Geol. 95, 655-662.


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Bliss – Geological Underground Mapping (11 April 2016)

Recently, I spent one week dedicated to geological underground mapping. Already as a student, I loved this work and I still do. Assembling data step by step and constructing a 3D image of the geological situation in a confined space from limited exposures is intellectually (and physically) most rewarding.

Walter
Walter explaining geology © Wolf Pohl

Allow me to cite updated text concerning mine mapping from section 5.3.1 of my Economic Geology (2011) book:

Geological mapping of natural outcrops and of man-made exposures is the most important task of the mine geologist. A complete and up-to-date documentation of all geological data is the precondition for both day-to-day management (first of all ore production: Daniels & Mascini 2012) and for serious decisions concerning, for example, a large drilling program, or for the mine and district-scale water management. Field mapping should be carried out at suitable detail (e.g. at 1:1000; note that data in modern software being scalable, such figures rather indicate the needed resolution), whereas display scales of geological mine maps and sections should be equal to the geodetic mine plans. The area surrounding the mine is typically mapped at a scale such as 1:10,000. Airborne or satellite-based synthetic aperture radar interferometry (InSAR) and LIDAR (light detection and ranging) processed into digital elevation models (DEM’s) may provide precise topographical base maps. LIDAR is able to penetrate vegetation cover. Quarry slopes are often surveyed with ground-based LIDAR scanners. Orthophoto-like images are made by surveying pits and the mine near-field with unmanned aerial vehicles (UAVs or “drones”). Acquisition of geological and other field data is increasingly executed through personal digital assistants (PDAs) and tablet PCs (Thum & de Paoli 2015).

Never neglect preparing geological overview sections through the mine. One mine I got to know as a forensic expert suffered a catastrophic mud inrush because a stope was driven upward into water-logged hangingwall sediments. Nobody had ever asked where exactly the hard rock/overburden boundary was. This mine had to be abandoned.

Modern mine management software packages includes components for geological work but GIS software, Leapfrog®, Maptec’s Vulcan® and Micromine®, or powerful 3D modelling tools such as Paradigm GOCAD® may be employed for handling multiple data sources (geological maps and sections, geophysics, drillhole logs; Saalmann & Laine 2014). Integrated digital processing of geological data and of mine planning is standard in most mines. The practical arts of geological mine mapping have been admirably described by McKinstry (1948), but consult also Marjoribanks (2010) and Lisle et al. (2011).


References:


Daniels, A. & Mascini, J. (2012) The benefits of mine-scale three-dimensional structural modelling at Macraes gold mine, central Otago, New Zealand: a case study. Applied Earth Science (Trans. Inst. Min. Metall. B) 12, 3-11.

Lisle, R.J., Brabham, P., Barnes, J.W. (2011) Basic geological mapping. 5th ed., 230 pp., Wiley-Blackwell.

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

Thum, L. & de Paoli, R. (2015) 2D and 3D GIS-based geological and geomechanical survey during tunnel excavation. Engineering Geol. 192, 19–25.


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Exploring in Europe? Investigate the Minerals4EU Website! (9 March 2016)

If you should be the Exploration Vice President of an overseas enterprise considering to look for potential targets in EU-Europe, you might profitably consult the Minerals4EU facility, as described in their homepage.

The Minerals4EU facility aspires to bring Europe’s minerals related geodata into one, virtual, place through a web portal so that users can more easily get the information they need, directly onto their computer, and free-of-charge. The Minerals4EU facility is based on an EU mineral intelligence network delivering the web portal including a GIS based facility, a European Minerals Yearbook and a Foresight Study. The EU minerals intelligence network comprises foremost EU-European national geological surveys. It publishes data, information and knowledge on mineral resources around Europe. In mid-2015, the website went online. Users may find, view and acquire standardized and harmonized georesource and related data, such as geological and mine maps, information on geophysical data, and papers that locate and describe mineral deposits, districts and provinces.

If you are acquainted with the standard of Australian support for mineral explorers, Mr. VP, you may be somewhat disappointed. This has several causes:

Yet, the Minerals4EU initiative must be lauded. In time, it may grow into a wonderful resource such as the services provided by Geoscience Australia . If you, Mr.VP, have the funds to assign staff or a consultant to a thorough search concerning your favoured mineral or metal and deposit type, this will be worth it. Minerals4EU will serve as a spring board to more detailed information.

Europe may not be the first choice for globally operating exploration, but it offers strategic advantages and a great diversity of mineral deposits, from Archaean Ni-komatiites to Proterozoic and Palaeozoic iron, gold, rare and base metals, Mesozoic copper porphyries, and Cenozoic epithermal gold. Along the Mediterranean, subduction-related and volcanogenic deposit formation extends into the Holocene. You are aware that giant Rio Tinto has entered the scene (in former Yugoslavia)?


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What is metallogeny? Is it of any Use? (10 February 2016)

The term METALLOGENY was coined by Louis de Launay (1860-1936), who is described as the greatest French geologist ever (see link below). He is still remembered for his lucid descriptions of the giant gold and diamond deposits in South Africa. Let us commemorate the 80th anniversary of his death.

De Launay (1913) created single handedly the science of metallogeny and discovered most of the principles that we still connect with it, although not necessarily with the same words. Here I refer to concepts such as metallogenetic* districts, epochs, maps, metallotects and provinces. He also established a rational genetic classification of mineral deposits.

Today, the “Glossary of Geology” (Neuendorf et al. 2005) defines the term as follows: Metallogeny - the study of the genesis of mineral deposits, with emphasis on their relationship in space and time to regional petrographic and tectonic features of the Earth’s crust.

The scale of metallogenic studies is always regional in extent; I believe that the term should not be applied for the genetic study of one specific deposit. Often these studies include the whole crustal section and may involve parts of the mantle. Fundamental questions typically asked are the source of metals and the circumstances of their mobilisation, migration and eventual enrichment resulting in ore deposit formation.

Ore deposit formation is a function of the Earth’s process systems. Like our understanding of these systems, metallogeny is not a consolidated body of knowledge but an assemblage of structured and unstructured information in perpetual flux.

Most tangible is metallogeny in the printed metallogenetic maps that were produced in the second half of the 20th Century, in order to allow a synopsis of metallogenetic, geological (metallotects) and basic economic data (e.g. the size of deposits). This work improved understanding, but the promised boost of exploration successes was meager. New finds were rather due to application of novel technologies such as remote sensing. The almost global availability of mineral deposit data, however, must have guided numerous investment decisions and exploration programmes.

Currently, digital media and supporting mineral deposit data banks are replacing the printed maps; stacked data (including geology, geophysics, geochemistry etc.) are analysed in GIS or comparable software, often draped over satellite images or digital elevation models (DEMs). Spatial metallogenetic information still serves scientific interests, but its main use is practical, for estimates of undiscovered resources and mineral deposits, and for mapping mineral prospectivity that facilitates strategic planning of exploration (e.g. Carranza & Sadeghi 2010). Modern mineral prospectivity modelling relies on a process-based, or “mineral systems” approach; although the processes cannot be directly observed or mapped, they can be translated into proxies such as wide alteration halos or syngenetic faults that may be recognizable.

Would you support my conclusion that although printed metallogenetic maps are a thing of the past, research of ore deposit formation and its mappable proxies ("metallotects") remains an essential component of high-tech resource estimates, prospectivity modelling and exploration?


*A linguistic note: In British English, the word “metallogenic” refers to an element that occurs as an ore or a naturally occurring metal (e.g. gold). Metallogenetic, in contrast, is something relating to metallogeny (The Chambers Dictionary, 10th ed. 2006).



References:


Carranza, E.J.M. & Sadeghi, M. (2010) Predictive mapping of prospectivity and quantitative estimation of undiscovered VMS deposits in Skellefte district (Sweden). Ore Geology Reviews 38, 219–241.

Launay, Louis de (1913) Traité de métallogénie : gîtes minéraux et métallifères : gisements, recherche, production et commerce des minéraux utiles et minerais, description des principales mines (3 volumes), Paris, C. Béranger.

http://www.annales.org/archives/x/launay.html (Louis de Launay’s life and work; in French language; accessed 10 February 2016)


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Anthropocene Revisited – Is Formalisation Useful for Geology? (16 January 2016)

Recently, a paper in Science (Waters et al. 2016) described the profound influence of humans on Earth surface processes. In conclusion, the two dozen authors support formalisation of the Anthropocene as a new Epoch (equal to Holocene or Pleistocene) in the Geological Time Scale. Recognizing that human impact started with ice age hunters and accelerated to our days, the authors do not settle on a specific event or year but propose more research. Yet they state, that the start of the Anthropocene may be defined by a Global Standard Stratigraphic Age (GSSA) coinciding with detonation of the Trinity atomic device at Alamogordo, New Mexico, on 16 July 1945 CE, or with global fall-out signatures from nuclear tests that peak in about 1963.

The impact of humanity on the Earth is excellently summarized and the paper* is a very useful source of hard data on man-made global change. Yet I feel that there is one big misunderstanding on the part of the authors – they do not describe rocks but mainly processes and their signatures, such as nuclear fall-out, accelerated extinction of species, increase of CO2 in the atmosphere, and climate change. And, strangely, they describe the onset of a geological epoch; rather a point in geological time, or an initial event, than its evolution.

In arguing for the formalisation of the Anthropocene as a new geological Epoch the authors neglect to ask if this will be of any use for geological practice and research. – I would not deny, however, that it will make catchy headlines in grant applications and in the media, but what about the geologist in the field?

Waters et al. refer to waste dumps (of mines or cities) as examples of Anthropocene deposits. But already now it is common practice to depict such features on geomaps. Is it of geological interest to separate pre- and post-1945 waste? Shall we measure traces of fall-out nuclides in dumps or soil in order to determine an Anthropocene age? Or, because practically the whole Earth is already impacted by humans, certainly by nuclear fall-out, shall we simply call all surfaces Anthropocene in age?

In my opinion, formalisation of the term “Anthropocene” as a new geological Epoch is useless for geologists and is therefore redundant.

You may also look at an earlier News Weblog on my website (News Archive 2015): The Anthropocene – a Voice of Reason (24 March 2015)


*Waters, C.N., Zalasiewicz, J., Summerhayes, C. et al. (2016) The Anthropocene is functionally and stratigraphically distinct from the Holocene. Science 351, pp. DOI: 10.1126/science.aad2622



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