9 research outputs found

    The Distribution of Precious and Energy-Critical Elements at the Scale of a Porphyry Copper Deposit

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    Magmatic-hydrothermal porphyry copper deposits are the world\u27s primary sources of Cu. Moreover, these may contain extractable concentrations of rare metal(loid)s e.g., Se, Te, In, Co, Ge, Ga, Ag, Au and Re. Some of these elements are classified as energy critical elements, whose shortage is considered a limiting factor for emerging energy technologies; diversifying their supply is critical. Porphyry copper deposits (PCDs) are mined at low grades, but vast tonnages. Hence, even low concentrations of by-product elements can represent a significant resource. However, the deportment of ECEs and precious metals in Cu ores, their distribution at the mineral- and orebody-scale is poorly understood in most PCDs. This lack of information limits the effective recovery of rare metal(loid)s and causes an unnecessary waste of resources. This situation can be remedied with element deportment studies; by informing geometallurgy, economic and ecologic benefits can be promoted in the form of improving recovery, adding value to ore resources and helping to reduce the dispersion of deleterious metal(loid)s into the environment. This is the motivation for the current research project. A fundamental aim of this study is to determine and compare the ECE and precious metal inventory of copper ores from four different porphyry Cu systems to identify deposits of high rare metal(loid) potentials; these are Quebrada Blanca, La Fortuna and Relincho in Chile, and Bingham Canyon (USA). Additionally, internal zonation within the orebodies and processes leading to enrichment and secondary redistribution of ECEs and precious metals are investigated. These objectives are addressed with: characterising ore mineral species (SEM-EDS); analysing their trace element contents (LA-ICP-MS); determining the nature of trace element residence in their host minerals; quantification of major and minor ore minerals; visualising the trace element partitioning between complex mineral textures, and advancing the relevant micro-analytical techniques (LA-ICP-MS mapping). Element deportment results show that bornite (Cu5FeS4), chalcopyrite (CuFeS2) and pyrite (FeS2) are the most common primary hydrothermal sulphide minerals in Cu ores from the four PCDs. The highest by-product potentials were found for Se, Ag, In, Te, Au and Bi; contents of other ECEs (Co, Ge and Ga) are negligible. Bornite is the main host for Se, Ag, Te and Bi, and chalcopyrite for In. Discrete native gold and electrum grains, as well as Ag-telluride minerals contribute to the overall deportment of Au, Ag and Te. Primary Cu-(Fe) sulphides from La Fortuna deviate most prominently from the other three deposits, with distinctly lower Ag and Bi, but the highest Au and In contents. Copper sulphides from the three remaining PCDs show similar contents in potential by-product elements; but respectively highest concentrations were recorded for the following deposits: Bingham (Se); Quebrada Blanca (Ag, Bi); and Relincho (Te). Two-dimensional trace element maps (by LA-ICP-MS) of complex textures revealed that secondary processes can promote the redistribution of rare metal(loids) at various scales. Firstly, digenite (Cu9S8) exsolution within bornite during the late cooling stages of the hydrothermal system at Bingham led to characteristic partitioning of precious metals and Te into digenite. Secondly, at Quebrada Blanca downward-propagating supergene weathering fluids induced the replacement of chalcopyrite by chalcocite (Cu2S) and thereby introduced elevated precious metal contents. The resulting complex deportment has potential implications for geometallurgy. Lastly, the La Fortuna and Relincho deposits are only 40 km apart but show very different metal(loid) endowments; copper ore from La Fortuna bears high Au contents, and from Relincho high Mo, Ag and Te contents. Findings suggest that this divergence in credit element enrichment is likely related to the exsolution of mineralising fluids at relatively shallow depth at La Fortuna (3 km)

    Quantitative data extraction from orthopyroxene trace element maps and its potential to examine the formation of the UG2 unit, Bushveld complex

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    We present a mineral chemical stratigraphy across the UG2 Unit, situated in the Upper Critical Zone of the Bushveld Complex. The magmatic evolution of the rocks hosting this world-class ore deposit for chromium and platinum group elements (PGEs) is still under debate. Orthopyroxene is a common phase across the magmatic stratigraphy of the unit. It hosts trace metals, whose relative contents can record information about magmatic processes. This study determined laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) trace element data for orthopyroxene and spot LA multi-collector ICP-MS Sr-isotope data for plagioclase. Mapping of trace element distributions revealed internal zoning in Cr, V, Y, and Th. Unlike in conventional spot analysis, quantitative trace element concentrations were extracted post-analysis from two-dimensional LA-ICP-MS maps. This approach offered advantages over spot analysis. The maps revealed internal complexities (e.g., inclusions, exsolved phases, zonations and diffusion halos) that could be avoided with suitable thresholds for chemical filter elements (i.e., 100 ppm < Cr < 4000 ppm, Y < 6 ppm), permitting fast, automated extraction of pure orthopyroxene data pixels from elemental maps covering noritic, troctolitic, anorthositic and chromititic mineral assemblages. Diffusive equilibration in orthopyroxene was evaluated by comparing zonations in elements with different known diffusivities. Magnesium and Ni are homogenously distributed, indicative of rapid diffusive processes, while Cr and V show zonations, interpreted to largely reflect primary distribution. Thorium and Y apparently diffused along discrete pathways, indicated by concentration anomalies following orthopyroxene lamellae. A systematic study of the trace element inventory of orthopyroxene across the succession of the UG2 Unit, complemented with Sr isotope signatures of plagioclase, revealed clear evidence for open-system processes: compatible elements (Cr, Ni) are decoupled from Mg# variations in orthopyroxene from specific UG2 subunits; distinct Mg# peaks coincide with negative V excursions in orthopyroxene from chromite-bearing subunits; towards the top of the unit, plagioclase shows a distinct Sr/ Sr peak and orthopyroxene shows Cr-depleted and Th-enriched rims. These chemical features cannot be explained by crystal mixing alone and argue for the involvement of at least two chemically distinct melts in the formation of the studied UG2 section

    Vectors to ore in replacive volcanogenic massive sulphide deposits of the northern Iberian Pyrite Belt: Major and trace element mineral chemistry

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    As part of a broader characterization and study of vectors to ore in VMS systems of the Iberian Pyrite Belt (IPB, Spain), we have investigated in detail mineral chemistry vectors in a representative replacive deposit hosted in felsic volcanic rocks. At the Aguas Te ̃nidas deposit (northern IPB) the hydrothermal system affected rocks of an originally homogeneous composition extending hundreds of metres beyond its footprint. The major and trace element chemistry of white micas, chlorite and carbonates have been analysed by electron microprobe (EMP) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to characterize geochemical vectors across the extent of the hydrothermal system at Aguas Teñidas. White micas are dominated by muscovite in both regionally altered lithologies and within the hydrothermal system, with coexisting paragonite occurring in a halo beyond the first disseminated pyrite surrounding the stockwork and in the proximal hanging wall. Systematic variations have been observed in FeO/(FeO + MgO) and Na2O/(Na2O + K2O) across the alteration zone. Chlorite is predominantly clinochlore in composition, with chamosite restricted to the centre of the hydro-thermal system. In regionally altered lithologied it is characterized by a constantly low Al and AlIV at variable Fe/(Fe + Mg); in rocks influenced by the hydrothermal system it presents higher AlIV and total Al, and a progressive increase in Al, AlIV and Fe/(Fe + Mg) towards its core. Regional carbonates consist of calcite, with additional dolomite forming in proximal rocks. Iron content in dolomite increases towards the centre of the hydrothermal system, with ankeritic compositions becoming dominant. Systematic variations in Ba, Cs, Li, Pb, Rb, Sn, Sr, Tl and Zn have been observed in white micas consistent with a proximal-distal transition (vector). Trends in chlorite have been less well characterized due to analytical limitations, although variations have been observed in the contents of As, Co, Li and Zn. A schematic model has been proposed which accounts for the observed mineralogical and mineral chemistry trends across the hydrothermal footprint of the Aguas Te ̃nidas VMS deposit. Major element signatures in white micas and chlorite are interpreted as having been controlled by the upwards and outwards flow of hot reducing Fe-rich hydrothermal fluids producing a coupled increase in temperature and fluid Fe/(Fe + Mg), and a decrease in fO2, with increasing fluid/rock ratios towards the centre of the stockwork. The data presented herein are not only applicable to VMS exploration in the IPB, but on a broader scale improve our general understanding of vectors to ore in VMS deposits in general

    Community recommendations for geochemical data, services and analytical capabilities in the 21st century

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    The majority of geochemical and cosmochemical research is based upon observations and, in particular, upon the acquisition, processing and interpretation of analytical data from physical samples. The exponential increase in volumes and rates of data acquisition over the last century, combined with advances in instruments, analytical methods and an increasing variety of data types analysed, has necessitated the development of new ways of data curation, access and sharing. Together with novel data processing methods, these changes have enabled new scientific insights and are driving innovation in Earth and Planetary Science research. Yet, as approaches to data-intensive research develop and evolve, new challenges emerge. As large and often global data compilations increasingly form the basis for new research studies, institutional and methodological differences in data reporting are proving to be significant hurdles in synthesising data from multiple sources. Consistent data formats and data acquisition descriptions are becoming crucial to enable quality assessment, reusability and integration of results fostering confidence in available data for reuse. Here, we explore the key challenges faced by the geo- and cosmochemistry community and, by drawing comparisons from other communities, recommend possible approaches to overcome them. The first challenge is bringing together the numerous sub-disciplines within our community under a common international initiative. One key factor for this convergence is gaining endorsement from the international geochemical, cosmochemical and analytical societies and associations, journals and institutions. Increased education and outreach, spearheaded by ambassadors recruited from leading scientists across disciplines, will further contribute to raising awareness, and to uniting and mobilising the community. Appropriate incentives, recognition and credit for good data management as well as an improved, user-oriented technical infrastructure will be essential for achieving a cultural change towards an environment in which the effective use and real-time interchange of large datasets is common-place. Finally, the development of best practices for standardised data reporting and exchange, driven by expert committees, will be a crucial step towards making geo- and cosmochemical data more Findable, Accessible, Interoperable and Reusable by both humans and machines (FAIR).ISSN:0016-7037ISSN:1872-953


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