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R R Large - One of the best experts on this subject based on the ideXlab platform.
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Pyrite compositions from vhms and orogenic au deposits in the yilgarn craton western australia implications for gold and copper exploration
Ore Geology Reviews, 2016Co-Authors: I A Belousov, R R Large, L V Danyushevsky, S Meffre, J A Steadman, T BeardsmoreAbstract:Abstract The Archaean Yilgarn Craton (Western Australia) is a world-class metallogenic province, hosting considerable resources of Au, Ag, Ni, Cu, Zn and Fe. Here we present trace element compositions of Pyrite from > 30 orogenic Au and 5 volcanic hosted massive sulphide (VHMS) deposits across the Yilgarn. Pyrites from VHMS deposits tend to have higher Sn, Se, Cu, Pb, Bi and lower Ni relative to orogenic deposits. VHMS deposit Pyrites commonly have Co > Ni, As > 100Au, Te > Au, Se > Te. Orogenic gold deposits could be subdivided based on association of Au with As or Te. Pyrites from Au As ores generally have Pb/Bi > 5, Se/Te > 5, Pb/Sb 100 and the majority of Au is refractory (in Pyrite structure). At the same time Au Te association Pyrites are characterised by lower values of Pb/Bi, Se/Te and Tl/Te, higher values of Ag/Au, Pb/Sb and Au generally resides in inclusions of different compositions. Our data can be used at the exploration stage to distinguish between VHMS vs Orogenic Au signatures. For all studied deposits inclusion populations are summarised with implications for Au and Ag deportment. Orogenic Au deposits from the Yilgarn mostly have multistage formation histories reflected in the presence of multiple generations of Pyrites. However, only some deposits record multiple high Au mineralisation events.
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trace element content of sedimentary Pyrite in black shales
Economic Geology, 2015Co-Authors: Daniel D Gregory, R R Large, L V Danyushevsky, J A Halpin, Elena Lounejeva Baturina, Timothy W Lyons, Selina Wu, Patrick J Sack, Anthony Chappaz, Valeriy V MaslennikovAbstract:Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of 1,407 sedimentary (diagenetic and syngenetic) Pyrites from 45 carbonaceous shale and unconsolidated sulfidic sediment samples, ranging in age from Paleoarchean to present day, show a considerable range of trace element compositions. Arsenic, Ni, Pb, Cu, and Co are among the most abundant trace elements, with medians ranging from 100 to 1,000 ppm. Less abundant elements Mo, Sb, Zn, and Se have median ranges of 10 to 100 ppm, and Ag, Bi, Te, Cd, and Au have median ranges of 0.01 to 10 ppm. Our dataset reveals three main groups of trace elements that are incorporated into Pyrite in different ways. Group 1 elements (As, Ni, Co, Sb, Se, and Mo) are contained uniformly throughout the Pyrite and may be held within the Pyrite crystal structure or as nanoinclusions evenly distributed within Pyrite. Group 2 elements (Bi, Pb, Ag, Au, Te, and Cu) generally occur uniformly at low concentrations and may be incorporated into the Pyrite structure but are highly variable at high concentrations, where they may also occur as microinclusions. Group 3 elements (Zn and Cd) tend to have highly variable abundances and generally occur in Pyrite as microinclusions of sphalerite. Factor analyses of the dataset identified five factors that account for 65.4% of the variance in Pyrite trace element concentrations. Factor 1 includes Pb, Bi, Au, and Te, and explains 18.1% of the variance, possibly due to As(II) ( Qian et al., 2013 ) or As(III) substituting for Fe in Pyrite, which induces the uptake of these elements. Factor 2 includes Co, Ni, and As and accounts for 13.6% of the variance, possibly due to the presence of As(蜂) substituting for S(蜂I) in Pyrite, which, in turn, promotes the uptake of Ni and Co. Factor 3 includes Zn and Cd and explains 12.3% of the variance and is due to the presence of sphalerite inclusions. Factor 4 includes Se, Ag, and Sb and explains 11.0% of the variance, which is believed to reflect coeval input of these elements into the oceans during periods of increased oxygenation. Factor 5 includes Mn, Cu, and Mo and explains 10.4% of the variance. It is likely that this behavior is due to these elements being delivered together to the sediments by adsorbing to Mn (hydro)oxides, which are released when the Mn (hydro)oxides dissolve in reducing bottom waters or pore waters. Variations in Pyrite texture do not show consistent compositional patterns between different samples, though within the same sample later formed Pyrite tends to have lower trace element abundance. Many trace elements associated with mafic extrusions/circulation of fluids through mafic rocks (Ni, Co) are more enriched in Archean sedimentary Pyrite at times when mafic volcanism/circulation of fluids through mafic rocks was more active. Similarly, some trace elements tend to be more enriched in Phanerozoic Pyrite due to increasing levels of atmospheric oxidation.
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gold and trace element zonation in Pyrite using a laser imaging technique implications for the timing of gold in orogenic and carlin style sediment hosted deposits
Economic Geology, 2009Co-Authors: R R Large, L V Danyushevsky, Chris Hollit, Valeriy V Maslennikov, S Meffre, S E Gilbert, S W Bull, R J Scott, Poul Emsbo, Helen ThomasAbstract:Laser ablation ICP-MS imaging of gold and other trace elements in Pyrite from four different sedimenthosted gold-arsenic deposits has revealed two distinct episodes of gold enrichment in each deposit: an early synsedimentary stage where invisible gold is concentrated in arsenian diagenetic Pyrite along with other trace elements, in particular, As, Ni, Pb, Zn, Ag, Mo, Te, V, and Se; and a later hydrothermal stage where gold forms as either free gold grains in cracks in overgrowth metamorphic and/or hydrothermal Pyrite or as narrow goldarsenic rims on the outermost parts of the overgrowth hydrothermal Pyrite. Compared to the diagenetic Pyrites, the hydrothermal Pyrites are commonly depleted in Ni, V, Zn, Pb, and Ag with cyclic zones of Co, Ni, and As concentration. The outermost hydrothermal Pyrite rims are either As-Au rich, as in moderate- to highgrade deposits such as Carlin and Bendigo, or Co-Ni rich and As-Au poor as in moderate- to low-grade deposits such as Sukhoi Log and Spanish Mountain. The early enrichment of gold in arsenic-bearing syngenetic to diagenetic Pyrite, within black shale facies of sedimentary basins, is proposed as a critical requirement for the later development of Carlin-style and orogenic gold deposits in sedimentary environments. The best grade sediment- hosted deposits appear to have the gold climax event, toward the final stages of deformation-related hydrothermal Pyrite growth and fluid flow.
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multistage sedimentary and metamorphic origin of Pyrite and gold in the giant sukhoi log deposit lena gold province russia
Economic Geology, 2007Co-Authors: R R Large, L V Danyushevsky, Valeriy V Maslennikov, Francois Robert, Zhaoshan ChangAbstract:Gold mineralization at Sukhoi Log in eastern Siberia is hosted in a deformed Neoproterozoic organic-bearing and pyritic black shale and siltstone sequence that is folded into a tight overturned anticline. The deposit contains about 30 million ounces of gold at an average grade of 2.0 g/t Au and is one of the largest known undeveloped gold resources. The high-grade gold zone forms a gently dipping tabular body in the core of the anticline. The best gold grades occur in narrow, bedding-parallel Pyrite-quartz veinlets that have been folded during the main deformation event. Lower grade gold is associated with disseminated Pyrite developed in and around the high-grade core of the deposit. Detailed paragenetic studies of the mineralization and host rocks have defined six stages of Pyrite development in the carbonaceous sediments. The two earliest forms of Pyrite, termed py1 and py2, are commonly developed in stratiform layers of micron-sized crystals, framboids and fine euhedra, which are interpreted as synsedimentary to early diagenetic in origin. Coarser grained, bedding-parallel aggregates of inclusion-rich Pyrite, termed py3, contain inclusions of arsenoPyrite, native gold and gold tellurides and are interpreted to form during late diagenesis and earliest deformation. Coarse euhedral Pyrite, py4, overgrows the earlier Pyrite (py1, py2, and py3), and the slaty cleavage developed in the host rocks, indicating a syndeformation timing. Late- stage, inclusion-free Pyrite, py5, overgrows and replaces earlier sulfides and is considered to be syn- to late deformation. Laser-ablation inductively coupled plasma mass spectrometry (LA-ICPMS) analyses of the various Pyrite types indicate that the synsedimentary py1 contains the highest levels of invisible gold, varying from 0.4 to 12.1 ppm, with a mean of 3.22 ppm Au, and 1,900 ppm As. Py1 is also enriched in a suite of trace elements (Mo, Sb, Ni, Co, Se, Te, Ag, Cu, Pb, Zn, Mn, Ba, Cr, U, V), which are similar to those concentrated by organic processes in euxinic sedimentary environments. Later generations of Pyrite, from py2 to py5, including Pyrite in bedding- parallel Pyrite-quartz veinlets, contain progressively lower contents of invisible gold and most other trace elements. However, this metamorphic and postmetamorphic Pyrite contains microinclusions of free gold, arsenoPyrite, pyrrhotite, sphalerite, and chalcoPyrite. The paragenetic, textural, and chemical relationships at Sukhoi Log suggest that gold was clearly initially introduced prior to cleavage development, accompanying sedimentation of the organic-rich shales and fixed during diagenesis within the structure of diagenetic arsenian Pyrite. Subsequently, accompanying deformation, gold was liberated from recrystallized diagenetic Pyrite to become concentrated as free gold and gold tellurides within metamorphic Pyrite and folded bedding-parallel Pyrite-quartz veinlets. Two key processes are considered vital to the formation of the Sukhoi Log deposit: original synsedimentary and early diagenetic concentration of gold, dissolved within arsenian Pyrite in organic-rich black shales, and metamorphic processes that liberated gold from the early forms of arsenian Pyrite, to be concentrated as free gold, and gold tellurides within late diagenetic and metamorphic Pyrite and associated Pyrite-quartz veinlets in the core of an overturned anticline. These ore-forming processes are unlikely to be unique to Sukhoi Log; other black-shale and turbidite-hosted deposits that occur in rifted continental margin environments, which have undergone collision and basin inversion, may form by similar processes.
L V Danyushevsky - One of the best experts on this subject based on the ideXlab platform.
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Pyrite compositions from vhms and orogenic au deposits in the yilgarn craton western australia implications for gold and copper exploration
Ore Geology Reviews, 2016Co-Authors: I A Belousov, R R Large, L V Danyushevsky, S Meffre, J A Steadman, T BeardsmoreAbstract:Abstract The Archaean Yilgarn Craton (Western Australia) is a world-class metallogenic province, hosting considerable resources of Au, Ag, Ni, Cu, Zn and Fe. Here we present trace element compositions of Pyrite from > 30 orogenic Au and 5 volcanic hosted massive sulphide (VHMS) deposits across the Yilgarn. Pyrites from VHMS deposits tend to have higher Sn, Se, Cu, Pb, Bi and lower Ni relative to orogenic deposits. VHMS deposit Pyrites commonly have Co > Ni, As > 100Au, Te > Au, Se > Te. Orogenic gold deposits could be subdivided based on association of Au with As or Te. Pyrites from Au As ores generally have Pb/Bi > 5, Se/Te > 5, Pb/Sb 100 and the majority of Au is refractory (in Pyrite structure). At the same time Au Te association Pyrites are characterised by lower values of Pb/Bi, Se/Te and Tl/Te, higher values of Ag/Au, Pb/Sb and Au generally resides in inclusions of different compositions. Our data can be used at the exploration stage to distinguish between VHMS vs Orogenic Au signatures. For all studied deposits inclusion populations are summarised with implications for Au and Ag deportment. Orogenic Au deposits from the Yilgarn mostly have multistage formation histories reflected in the presence of multiple generations of Pyrites. However, only some deposits record multiple high Au mineralisation events.
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trace element content of sedimentary Pyrite in black shales
Economic Geology, 2015Co-Authors: Daniel D Gregory, R R Large, L V Danyushevsky, J A Halpin, Elena Lounejeva Baturina, Timothy W Lyons, Selina Wu, Patrick J Sack, Anthony Chappaz, Valeriy V MaslennikovAbstract:Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of 1,407 sedimentary (diagenetic and syngenetic) Pyrites from 45 carbonaceous shale and unconsolidated sulfidic sediment samples, ranging in age from Paleoarchean to present day, show a considerable range of trace element compositions. Arsenic, Ni, Pb, Cu, and Co are among the most abundant trace elements, with medians ranging from 100 to 1,000 ppm. Less abundant elements Mo, Sb, Zn, and Se have median ranges of 10 to 100 ppm, and Ag, Bi, Te, Cd, and Au have median ranges of 0.01 to 10 ppm. Our dataset reveals three main groups of trace elements that are incorporated into Pyrite in different ways. Group 1 elements (As, Ni, Co, Sb, Se, and Mo) are contained uniformly throughout the Pyrite and may be held within the Pyrite crystal structure or as nanoinclusions evenly distributed within Pyrite. Group 2 elements (Bi, Pb, Ag, Au, Te, and Cu) generally occur uniformly at low concentrations and may be incorporated into the Pyrite structure but are highly variable at high concentrations, where they may also occur as microinclusions. Group 3 elements (Zn and Cd) tend to have highly variable abundances and generally occur in Pyrite as microinclusions of sphalerite. Factor analyses of the dataset identified five factors that account for 65.4% of the variance in Pyrite trace element concentrations. Factor 1 includes Pb, Bi, Au, and Te, and explains 18.1% of the variance, possibly due to As(II) ( Qian et al., 2013 ) or As(III) substituting for Fe in Pyrite, which induces the uptake of these elements. Factor 2 includes Co, Ni, and As and accounts for 13.6% of the variance, possibly due to the presence of As(蜂) substituting for S(蜂I) in Pyrite, which, in turn, promotes the uptake of Ni and Co. Factor 3 includes Zn and Cd and explains 12.3% of the variance and is due to the presence of sphalerite inclusions. Factor 4 includes Se, Ag, and Sb and explains 11.0% of the variance, which is believed to reflect coeval input of these elements into the oceans during periods of increased oxygenation. Factor 5 includes Mn, Cu, and Mo and explains 10.4% of the variance. It is likely that this behavior is due to these elements being delivered together to the sediments by adsorbing to Mn (hydro)oxides, which are released when the Mn (hydro)oxides dissolve in reducing bottom waters or pore waters. Variations in Pyrite texture do not show consistent compositional patterns between different samples, though within the same sample later formed Pyrite tends to have lower trace element abundance. Many trace elements associated with mafic extrusions/circulation of fluids through mafic rocks (Ni, Co) are more enriched in Archean sedimentary Pyrite at times when mafic volcanism/circulation of fluids through mafic rocks was more active. Similarly, some trace elements tend to be more enriched in Phanerozoic Pyrite due to increasing levels of atmospheric oxidation.
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gold and trace element zonation in Pyrite using a laser imaging technique implications for the timing of gold in orogenic and carlin style sediment hosted deposits
Economic Geology, 2009Co-Authors: R R Large, L V Danyushevsky, Chris Hollit, Valeriy V Maslennikov, S Meffre, S E Gilbert, S W Bull, R J Scott, Poul Emsbo, Helen ThomasAbstract:Laser ablation ICP-MS imaging of gold and other trace elements in Pyrite from four different sedimenthosted gold-arsenic deposits has revealed two distinct episodes of gold enrichment in each deposit: an early synsedimentary stage where invisible gold is concentrated in arsenian diagenetic Pyrite along with other trace elements, in particular, As, Ni, Pb, Zn, Ag, Mo, Te, V, and Se; and a later hydrothermal stage where gold forms as either free gold grains in cracks in overgrowth metamorphic and/or hydrothermal Pyrite or as narrow goldarsenic rims on the outermost parts of the overgrowth hydrothermal Pyrite. Compared to the diagenetic Pyrites, the hydrothermal Pyrites are commonly depleted in Ni, V, Zn, Pb, and Ag with cyclic zones of Co, Ni, and As concentration. The outermost hydrothermal Pyrite rims are either As-Au rich, as in moderate- to highgrade deposits such as Carlin and Bendigo, or Co-Ni rich and As-Au poor as in moderate- to low-grade deposits such as Sukhoi Log and Spanish Mountain. The early enrichment of gold in arsenic-bearing syngenetic to diagenetic Pyrite, within black shale facies of sedimentary basins, is proposed as a critical requirement for the later development of Carlin-style and orogenic gold deposits in sedimentary environments. The best grade sediment- hosted deposits appear to have the gold climax event, toward the final stages of deformation-related hydrothermal Pyrite growth and fluid flow.
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multistage sedimentary and metamorphic origin of Pyrite and gold in the giant sukhoi log deposit lena gold province russia
Economic Geology, 2007Co-Authors: R R Large, L V Danyushevsky, Valeriy V Maslennikov, Francois Robert, Zhaoshan ChangAbstract:Gold mineralization at Sukhoi Log in eastern Siberia is hosted in a deformed Neoproterozoic organic-bearing and pyritic black shale and siltstone sequence that is folded into a tight overturned anticline. The deposit contains about 30 million ounces of gold at an average grade of 2.0 g/t Au and is one of the largest known undeveloped gold resources. The high-grade gold zone forms a gently dipping tabular body in the core of the anticline. The best gold grades occur in narrow, bedding-parallel Pyrite-quartz veinlets that have been folded during the main deformation event. Lower grade gold is associated with disseminated Pyrite developed in and around the high-grade core of the deposit. Detailed paragenetic studies of the mineralization and host rocks have defined six stages of Pyrite development in the carbonaceous sediments. The two earliest forms of Pyrite, termed py1 and py2, are commonly developed in stratiform layers of micron-sized crystals, framboids and fine euhedra, which are interpreted as synsedimentary to early diagenetic in origin. Coarser grained, bedding-parallel aggregates of inclusion-rich Pyrite, termed py3, contain inclusions of arsenoPyrite, native gold and gold tellurides and are interpreted to form during late diagenesis and earliest deformation. Coarse euhedral Pyrite, py4, overgrows the earlier Pyrite (py1, py2, and py3), and the slaty cleavage developed in the host rocks, indicating a syndeformation timing. Late- stage, inclusion-free Pyrite, py5, overgrows and replaces earlier sulfides and is considered to be syn- to late deformation. Laser-ablation inductively coupled plasma mass spectrometry (LA-ICPMS) analyses of the various Pyrite types indicate that the synsedimentary py1 contains the highest levels of invisible gold, varying from 0.4 to 12.1 ppm, with a mean of 3.22 ppm Au, and 1,900 ppm As. Py1 is also enriched in a suite of trace elements (Mo, Sb, Ni, Co, Se, Te, Ag, Cu, Pb, Zn, Mn, Ba, Cr, U, V), which are similar to those concentrated by organic processes in euxinic sedimentary environments. Later generations of Pyrite, from py2 to py5, including Pyrite in bedding- parallel Pyrite-quartz veinlets, contain progressively lower contents of invisible gold and most other trace elements. However, this metamorphic and postmetamorphic Pyrite contains microinclusions of free gold, arsenoPyrite, pyrrhotite, sphalerite, and chalcoPyrite. The paragenetic, textural, and chemical relationships at Sukhoi Log suggest that gold was clearly initially introduced prior to cleavage development, accompanying sedimentation of the organic-rich shales and fixed during diagenesis within the structure of diagenetic arsenian Pyrite. Subsequently, accompanying deformation, gold was liberated from recrystallized diagenetic Pyrite to become concentrated as free gold and gold tellurides within metamorphic Pyrite and folded bedding-parallel Pyrite-quartz veinlets. Two key processes are considered vital to the formation of the Sukhoi Log deposit: original synsedimentary and early diagenetic concentration of gold, dissolved within arsenian Pyrite in organic-rich black shales, and metamorphic processes that liberated gold from the early forms of arsenian Pyrite, to be concentrated as free gold, and gold tellurides within late diagenetic and metamorphic Pyrite and associated Pyrite-quartz veinlets in the core of an overturned anticline. These ore-forming processes are unlikely to be unique to Sukhoi Log; other black-shale and turbidite-hosted deposits that occur in rifted continental margin environments, which have undergone collision and basin inversion, may form by similar processes.
T Beardsmore - One of the best experts on this subject based on the ideXlab platform.
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Pyrite compositions from vhms and orogenic au deposits in the yilgarn craton western australia implications for gold and copper exploration
Ore Geology Reviews, 2016Co-Authors: I A Belousov, R R Large, L V Danyushevsky, S Meffre, J A Steadman, T BeardsmoreAbstract:Abstract The Archaean Yilgarn Craton (Western Australia) is a world-class metallogenic province, hosting considerable resources of Au, Ag, Ni, Cu, Zn and Fe. Here we present trace element compositions of Pyrite from > 30 orogenic Au and 5 volcanic hosted massive sulphide (VHMS) deposits across the Yilgarn. Pyrites from VHMS deposits tend to have higher Sn, Se, Cu, Pb, Bi and lower Ni relative to orogenic deposits. VHMS deposit Pyrites commonly have Co > Ni, As > 100Au, Te > Au, Se > Te. Orogenic gold deposits could be subdivided based on association of Au with As or Te. Pyrites from Au As ores generally have Pb/Bi > 5, Se/Te > 5, Pb/Sb 100 and the majority of Au is refractory (in Pyrite structure). At the same time Au Te association Pyrites are characterised by lower values of Pb/Bi, Se/Te and Tl/Te, higher values of Ag/Au, Pb/Sb and Au generally resides in inclusions of different compositions. Our data can be used at the exploration stage to distinguish between VHMS vs Orogenic Au signatures. For all studied deposits inclusion populations are summarised with implications for Au and Ag deportment. Orogenic Au deposits from the Yilgarn mostly have multistage formation histories reflected in the presence of multiple generations of Pyrites. However, only some deposits record multiple high Au mineralisation events.
K M Frost - One of the best experts on this subject based on the ideXlab platform.
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postmagmatic variability in ore composition and mineralogy in the t4 and t5 ore shoots at the high grade flying fox ni cu pge deposit yilgarn craton western australia
Economic Geology, 2012Co-Authors: Jane E Collins, Steffen Hagemann, Campbell T Mccuaig, Stephen Barnes, K M FrostAbstract:The high-grade Flying Fox komatiite-hosted Ni sulfide deposit, located in the Forrestania greenstone belt of the Archean Yilgarn Craton, Western Australia, is hosted in a deformed and metamorphosed volcano-metasedimentary succession. Postmineralization events have sheared and modified the texture and composition of the original massive sulfide ore, creating up to 11 distinct ore shoots including massive, stringer/vein, and breccia sulfides composed of pyrrhotite, pentlandite, chalcoPyrite, and variable abundances of Pyrite ranging up to 40 vol %. Nickel and platinum group elements (PGE) tenor variations were investigated in two ore shoots, T4 and T5. All mineralization styles show considerable variability in Ni tenor. PGEs show strong linear correlations between Ir, Os, Ru, and Rh, but poor correlation between Pt, Pd, and Cu. The normalized molar proportions of Fe, Ni, and S, projected into the Fe-Ni-S ternary system, show a distinct linear trend of Pyrite addition to a typical primary magmatic composition and no correlation with mineralization style. The high Pyrite content present throughout the Flying Fox ore is also associated with elevated Cu and As contents and is interpreted to be primarily due to the addition of Pyrite from circulating Fe-, S-, Cu-, and As-enriched fluids creating Pyrite-pentlandite intergrowths. Localized mechanical segregation of Pyrite, sulfidation of pyrrhotite to Pyrite, and oxidation of pyrrhotite to Pyrite + magnetite has also contributed to these increased Pyrite contents, although to a lesser extent. The addition and segregation of Pyrite has diluted the Ni tenor, with no evidence to suggest chemical mobilization of Ni.
Rodney C Ewing - One of the best experts on this subject based on the ideXlab platform.
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the coupled geochemistry of au and as in Pyrite from hydrothermal ore deposits
Geochimica et Cosmochimica Acta, 2014Co-Authors: Artur P Deditius, Martin Reich, Stephen E Kesler, Satoshi Utsunomiya, Stephen L Chryssoulis, John L Walshe, Rodney C EwingAbstract:The ubiquity of Au-bearing arsenian Pyrite in hydrothermal ore deposits suggests that the coupled geochemical behaviour of Au and As in this sulfide occurs under a wide range of physico-chemical conditions. Despite significant advances in the last 20years, fundamental factors controlling Au and As ratios in Pyrite from ore deposits remain poorly known. Here we explore these constraints using new and previously published EMPA, LA-ICP-MS, SIMS, and μ-PIXE analyses of As and Au in Pyrite from Carlin-type Au, epithermal Au, porphyry Cu, Cu-Au, and orogenic Au deposits, volcanogenic massive sulfide (VHMS), Witwatersrand Au, iron oxide copper gold (IOCG), and coal deposits. Pyrite included in the data compilation formed under temperatures from ~30 to ~600°C and in a wide variety of geological environments. The Pyrite Au-As data form a wedge-shaped zone in compositional space, and the fact that most data points plot below the solid solubility limit defined by Reich et al. (2005) indicate that Au1+ is the dominant form of Au in arsenian Pyrite and that Au-bearing ore fluids that deposit this sulfide are mostly undersaturated with respect to native Au. The analytical data also show that the solid solubility limit of Au in arsenian Pyrite defined by an Au/As ratio of 0.02 is independent of the geochemical environment of Pyrite formation and rather depends on the crystal-chemical properties of Pyrite and post-depositional alteration. Compilation of Au-As concentrations and formation temperatures for Pyrite indicates that Au and As solubility in Pyrite is retrograde; Au and As contents decrease as a function of increasing temperature from ~200 to ~500°C. Based on these results, two major Au-As trends for Au-bearing arsenian Pyrite from ore deposits are defined. One trend is formed by Pyrites from Carlin-type and orogenic Au deposits where compositions are largely controlled by fluid-rock interactions and/or can be highly perturbed by changes in temperature and alteration by hydrothermal fluids. The second trend consists of Pyrites from porphyry Cu and epithermal Au deposits, which are characterised by compositions that preserve the Au/As signature of mineralizing magmatic-hydrothermal fluids, confirming the role of this sulfide in controlling metal ratios in ore systems.
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a proposed new type of arsenian Pyrite composition nanostructure and geological significance
Geochimica et Cosmochimica Acta, 2008Co-Authors: Artur P Deditius, Satoshi Utsunomiya, Rodney C Ewing, Devon Renock, C V Ramana, Udo Becker, Stephen E KeslerAbstract:This report describes a new form of arsenian Pyrite, called As3+-Pyrite, in which As substitutes for Fe [(Fe,As)S2], in contrast to the more common form of arsenian Pyrite, As1--Pyrite, in which As1- substitutes for S [Fe(As,S)2]. As3+-Pyrite has been observed as colloformic overgrowths on As-free Pyrite in a hydrothermal gold deposit at Yanacocha, Peru. XPS analyses of the As3+-Pyrite confirm that As is present largely as As3+. EMPA analyses show that As3+-Pyrite incorporates up to 3.05 at % of As and 0.53 at. %, 0.1 at. %, 0.27 at. %, 0.22 at. %, 0.08 at. % and 0.04 at. % of Pb, Au, Cu, Zn, Ni, and Co, respectively. Incorporation of As3+ in the Pyrite could be written like: As3 + + y Au+ + 1 - y (□) ⇔ 2 Fe2 +; where Au+ and vacancy (□) help to maintain the excess charge. HRTEM observations reveal a sharp boundary between As-free Pyrite and the first overgrowth of As3+-Pyrite (20-40 nm thick) and co-linear lattice fringes indicating epitaxial growth of As3+-Pyrite on As-free Pyrite. Overgrowths of As3+-Pyrite onto As-free Pyrite can be divided into three groups on the basis of crystal size, 8-20 nm, 100-300 nm and 400-900 nm, and the smaller the crystal size the higher the concentration of toxic arsenic and trace metals. The Yanacocha deposit, in which As3+-Pyrite was found, formed under relatively oxidizing conditions in which the dominant form of dissolved As in the stability field of Pyrite is As3+; in contrast, reducing conditions are typical of most environments that host As1--Pyrite. As3+-Pyrite will likely be found in other oxidizing hydrothermal and diagenetic environments, including high-sulfidation epithermal deposits and shallow groundwater systems, where probably kinetically controlled formation of nanoscale crystals such as observed here would be a major control on incorporation and release of As3+ and toxic heavy metals in oxidizing natural systems.
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solubility of gold in arsenian Pyrite
Geochimica et Cosmochimica Acta, 2005Co-Authors: Martin Reich, Stephen E Kesler, Satoshi Utsunomiya, Christopher S Palenik, Stephen L Chryssoulis, Rodney C EwingAbstract:Although Au and As can be enriched up to the weight percent level in arsenian Pyrite, there is little knowledge of their limiting concentrations and nature of incorporation. This study reports SIMS and EMPA analyses showing that As and Au contents of arsenian Pyrites plot in a wedge-shaped zone with an upper compositional limit defined by the line CAu=0.02⋅CAs+4×10−5CAu=0.02⋅CAs+4×10−5 indicating a maximum Au/As molar ratio of ∼0.02. Arsenian Pyrites with Au/As ratios plotting above this limit contain nanoparticles of native Au, as observed by HRTEM imaging/EDS analysis and SIMS depth profiling. In this case, a significant amount of the total Au is present in its elemental form. In arsenian Pyrites with Au/As < 0.02, native Au nanoparticles were not observed by HRTEM, and all of the Au measured is inferred to be structurally bound in solid solution. The microanalytical results, coupled with previously published XANES-EXAFS spectroscopic measurements confirm that arsenian Pyrite compositions plotting above this limit contains Au0, whereas arsenian Pyrite compositions plotting below the limit contain Au+1. On the basis of these observations, the upper bound is interpreted to represent a solubility limit for solid solution of Au as a function of As in arsenian Pyrite between ∼150°C and ∼250°C, the approximate conditions under which samples used in the study were deposited. The Au-As composition of arsenian Pyrite relative to this limit can be used to predict the chemical state of Au as well as the saturation state of Au in the hydrothermal solution that deposited it. These observations confirm that the parent hydrothermal solutions for the giant Carlin-type deposits, where solid solution of Au is dominant in arsenian Pyrite, were largely unsaturated with respect to Au0.
