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Precious Metals vs. Base Metals: Nature and Experiment

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A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Deposits".

Deadline for manuscript submissions: closed (17 February 2023) | Viewed by 10117

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Dr. Nadezhda Tolstykh

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Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Siberia, Russia
Interests: platinum mineralization in placers associated with various types of mafic-ultramafic complexes; ore content of mafic-ultramafic intrusions; typomorphic features of various types of sulfide ores of Cu-Ni deposits; PGE-minerals; Au-Ag mineralization and conditions of its formation in the epithermal gold deposits
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Dr. Elena F. Sinyakova

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Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Siberia, Russia
Interests: phase relations in the ore-forming systems; experimental modeling of fractional crystallization sulfide melts; the role of chalcophile elements in the formation of precious metal minerals

Special Issue Information

Dear Colleagues,

Base metals including iron, lead, copper, nickel, aluminum, and zinc are widely used in industry. They are invaluable to the global economy due to their utility and ubiquity. Precious metals include gold and silver, as well as platinum group metals (PGM) Os, Ir, Ru, Rh, Pt, and Pd. Precious metals are rare and have a high economic value, used both in industry and in jewelry production.

However, the metallogenic associations of precious metals with base metals are well known. They appear both in Cu–Ni deposits with PGM and Au, and in gold deposits of various types.

PGE and Au(Ag) differentiation in silicate magma is mainly governed by variations in oxygen and sulfur fugacity, whereas in the sulfide melt it is controlled by the distribution coefficients of elements between MSS, ISS, and sulfide liquid, causing the mineralogical and geochemical zoning observed in igneous sulfide ore bodies. The ore-geochemical zoning of gold deposits is usually formed under the influence of one- or multi-stage processes with a change in the physicochemical parameters of ore-forming systems.

The development of new research methods and the improvement of the experimental base make it possible to reveal new aspects of the conditions for the crystallization of precious and base metals. Experimental studies, both in the field of the behavior of precious and base metals during the crystallization of PGE-containing sulfide ores, and in the field of crystallization of Au–Ag compounds, are important topics of our Special Issue.

Original research papers and reviews are welcome in this Special Issue. Research areas may include (but are not limited to) the following topics:

Behavior of PGE and Au(Ag) in magmatic and hydrothermal environments;
Geochemistry of natural sulfide ores containing PGM;
Fractionation of noble and base metals in the process of evolution of ore-forming systems;
Mineral associations in various types of rocks of mafic-ultramafic intrusions;
Conditions of crystallization of gold deposits, forms of concentration, transfer and precipitation of Au and Ag;
Minerals—indicators of conditions of crystallization of precious metal ores;
Experimental substantiation of the behavior of base and noble metals (PGM) in the course of fractional crystallization of sulfide melts;
Experimental studies to identify the crystallization conditions for unique Au and Ag compounds;
Experimental synthesis of noble metal minerals and substantiation of new minerals.

We look forward to the remarkable results of your research in this Special Issue.

Dr. Nadezhda Tolstykh
Dr. Elena F. Sinyakova
Guest Editors

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Keywords

sulfide ores
Cu–Ni deposits
minerals of platinum metals
gold deposits
Au–Ag mineralization
Cu–Fe–-Ni–-S--PGE system
experimental modelling
phase equilibria
fractionation

Published Papers (6 papers)

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Research

23 pages, 26591 KiB

Open AccessArticle

The Role of Te, As, Bi, and Sb in the Noble Metals (Pt, Pd, Au, Ag) and Microphases during Crystallization of a Cu-Fe-S Melt

by Elena Fedorovna Sinyakova, Nikolay Anatolievich Goryachev, Konstantin Aleksandrovich Kokh, Nikolay Semenovich Karmanov and Viktor Aleksandrovich Gusev

Minerals 2023, 13(9), 1150; https://doi.org/10.3390/min13091150 - 30 Aug 2023

Viewed by 716

Abstract

Quasi-equilibrium directional crystallization was performed on a melt composition (at. %): 18.50 Cu, 32.50 Fe, 48.73 S, 0.03 Pt, Pd, Ag, Au, Te, As, Bi, Sb, and Sn, which closely resembles the Cu-rich massive ores found in the platinum-copper-nickel deposits of Norilsk. Base metal sulfides (BMS) such as pyrrhotite solid solution (Fe,Cu)S_1±δ (Poss), non-stoichiometric cubanite Cu_1.1Fe_1.9S₃ (Cbn*), and intermediate solid solution Cu_1.0Fe_1.2S_2.0 (Iss) are progressively precipitated from the melt during the crystallization process. The content of noble metals and semimetals in the structure of BMS is below the detection limit of SEM-EDS analysis. Only tin exhibits significant solubility in Cbn* and Iss, meanwhile Pt, Pd, Au, Ag, As, Bi, Sb, and Te are present as discrete composite inclusions, comprising up to 11 individual phases, within their matrices. These microphases correspond to native Au, native Bi, hessite Ag₂Te, sperrylite Pt(As,S)₂, hedleyite Bi₂Te, michenerite PdTeBi, froodite PdBi₂, a solid solution of sudburite-sobolevskite-kotulskite Pd(Sb, Bi)_xTe_1−x, geversite PtSb₂, and a multicomponent solid solution based on geversite Me(TABS)₂, where Me = Σ(Pt, Pd, Fe, Cu) and TABS = Σ(Te, As, Bi, Sb, Sn). Most of the inclusions occur as thin layers between BMS grain boundaries or appear drop-shaped and subhedral to isometric grains within the sulfide matrix. Only a small fraction of the trace elements form mineral inclusions of sizes ≤ 0.5 μm in Poss, most likely including PtAs₂ and (Pt,Pd)S. It is likely that the simultaneous presence of noble metals (Pt, Pd, Au, Ag) and semimetals (As, Te, Bi, Sb) in the sulfide melt leads to the appearance of liquid droplets in the parent sulfide melt after pyrrhotite crystallization. The solidification of droplets during the early stages of Cbn* crystallization may occur simultaneously with the cooling of later fractions of the sulfide melt, resulting in the formation of Iss. In addition, abundant gas voids containing micro-inclusions were observed in Cbn* and Iss. These inclusions showed similar chemical and mineral compositions to those in BMS matrices, i.e., the presence of gas bubbles did not affect the main features of noble metal fractionation and evolution. Therefore, it is reasonable to assume that ore particles suspended in the melt are either trapped by defects at the crystallization front or transported towards gas bubbles via the Marangoni effect. Full article

(This article belongs to the Special Issue Precious Metals vs. Base Metals: Nature and Experiment)

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14 pages, 4647 KiB

Open AccessArticle

Comparative Experiments on the Role of CO₂ in the Gold Distribution between Pyrite and a High-Salinity Fluid

by Yuri Laptev, Anna Doroshkevich and Ilya Prokopyev

Minerals 2023, 13(4), 464; https://doi.org/10.3390/min13040464 - 25 Mar 2023

Viewed by 908

Abstract

Experimental studies were conducted to identify the physical and chemical features of gold’s behaviour in hydrothermal processes linked to ore formation and involving CO₂ in oxidized deposits. With the aid of the autoclave method, in a temperature range of between 200 and 400 °C, the isochoric dependences of the PVT parameters of concentrated sulphate chloride fluids were plotted, both in the presence and absence of CO₂. Our experiments established that concentrated sulphate–chloride fluids (22 wt % Na₂SO₄ + 2.2 wt % NaCl) that lack CO₂ are characterized by a wide supercritical temperature range, with homogenization temperatures of between 250 and 325 °C. In the presence of CO₂, the same type of fluids showed heterogenization at a molar fraction of X_CO₂ = 0.18 (t = 192 °C, P = 176 bar). The process of homogenization for these low-density and high-salinity fluids was impossible at temperatures between 375 and 400 °C and at pressures between 600 and 700 bar. The behaviour of gold was studied during its interaction with a basic composition fluid of sulphate–chloride. We applied the autoclave method under the conditions of a simultaneous synthesis of pyrite and gold dissolution (metallic Au), at a temperature of 340 °C and at a pressure of 440 bar. High Au concentrations (up to 4410 ppm of Au in CO₂-bearing fluids) were attained at high gold solubilities (up to 13.5 ppm in the presence of CO₂), owing to the process of Au reprecipitation within the pyrite phase. We did not detect Au in the pyrite when we used the XRD or SEM methods, which suggested that it might be present as invisible gold. High values of the distribution coefficient (K_D = C_Au(solid)/C_Au(solution)) in the fluids lacking (K_D = 62) and bearing CO₂ (K_D = 327) empirically confirmed the possibility that gold concentrates in pyrite in structurally non-binding forms. Full article

(This article belongs to the Special Issue Precious Metals vs. Base Metals: Nature and Experiment)

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20 pages, 18699 KiB

Open AccessArticle

Au-Ag-Se-Te-S Mineralization in the Maletoyvayam High-Sulfidation Epithermal Deposit, Kamchatka Peninsula

by Nadezhda Tolstykh, Maria Shapovalova and Maksim Podlipsky

Minerals 2023, 13(3), 420; https://doi.org/10.3390/min13030420 - 16 Mar 2023

Cited by 2 | Viewed by 1273

Abstract

The Maletoyvayam high-sulfidation (HS) epithermal Au-Ag deposit is one of the numerous hydrothermal deposits of the Kamchatka volcanogenic belt, consisting of two main associations: Au-rich (Ag-free) and Ag-bearing. The first one derived from acidic solutions, whereas the second assemblage crystallized from moderately dilute solutions, with both occurring at high oxygen fugacity. The Au-rich association contains the most atypical gold chalcogenides of the Au-Se-Te-S system, which are characterized by Se-S and Te-Se substitutions, e.g., a complete series from maletoyvayamite to tolstykhite Au₃(Se,S)₄Te₆; a series of auroselenide Au(Se_1.00–0.64S_0.36–0.00); a combined series of gachingite Au(Te,Se) and unnamed Au(Se,Te): Au(Te_0.80–0.40Se_0.20–0.60). Meanwhile, in the second Ag-bearing assemblage, sulfides of the Au-Ag type prevails, e.g., petrovskaite AuAgS, miargyrite (Ag,Au)(Sb,As)S₂, uytenbogaardtite Ag₃AuS₂, fischesserite Ag₃AuSe₂ with Au-Ag substitution, and tolstykhite. The Se/S ratio, of the second association, decreases while increasing the Ag concentration in the ore-forming system, including Au-Ag substitutions. The Au content in miargyrite (Au,Ag)SbS₃ reaches up to 0.48 apfu, suggesting the existence of a new mineral phase of composition AgAuSb₂S₆. Au oxide complexes, in both associations, are represented by either a mixture of redeposited gold and Fe-Sb oxide or a homogeneous (Au,Sb,Fe)₂O₃ composition. These oxides are formed by replacement of calaverite. The ore mineralization of this HS deposit is considered unique due to the special conditions of the ore-forming environment, such as acidic solutions, high oxygen fugacity, and log fSe₂ above −5.7; all contributed to the formation of AuSe phases. Full article

(This article belongs to the Special Issue Precious Metals vs. Base Metals: Nature and Experiment)

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30 pages, 15637 KiB

Open AccessArticle

Volcano–Plutonic Complex of the Tumrok Range (Eastern Kamchatka): An Example of the Ural-Alaskan Type Intrusion and Related Volcanic Series

by Ivan F. Chayka, Nikolay I. Baykov, Vadim S. Kamenetsky, Anton V. Kutyrev, Evgenii V. Pushkarev, Adam Abersteiner and Vasily D. Shcherbakov

Minerals 2023, 13(1), 126; https://doi.org/10.3390/min13010126 - 15 Jan 2023

Cited by 3 | Viewed by 2184

Abstract

Zoned plutons, composed of dunites, pyroxenites, and gabbroic rocks, have been referred to as the Ural-Alaskan type complexes (UA-complexes) and occur in numerous paleo-arc settings worldwide. Many of these complexes are source rocks for economic placers of platinum-group metals. Thus, it is important to understand how UA-complexes form and the origin and behavior of platinum-group elements (PGEs). It is widely assumed that the UA-complexes result from differentiation of supra-subduction high-Ca high-Mg sub-alkaline magmas. However, there is a lack of direct evidence for the existence and differentiation of such magmas, mainly because cases of UA-complexes being spatially and temporally linked to co-genetic volcanics are unknown. We studied an UA-complex from the Tumrok range (Eastern Kamchatka) where a dunite-clinopyroxenite-gabbro assemblage is spatially and temporary related to high-Ca volcanics (i.e., picrites and basalts). Based on the mineral and chemical composition of the rocks, mineral chemistry, and composition of melt inclusions hosted within rock-forming minerals, we conclude that the intrusive assemblage and the volcanics are co-genetic and share the same parental magma of ankaramitic composition. Furthermore, the compositions of the plutonic rocks are typical of UA-complexes worldwide. Finally, the rocks studied exhibit a full differentiation sequence from olivine-only liquidus in picrites and dunites to eutectic crystallization of diopside or hornblende, plagioclase, and K-Na feldspar in plagio-wehrlites and gabbroic rocks. All these results make the considered volcano–plutonic complex a promising case for petrological studies and modelling of UA-complex formation. Full article

(This article belongs to the Special Issue Precious Metals vs. Base Metals: Nature and Experiment)

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16 pages, 4173 KiB

Open AccessArticle

The Role of Selenium and Hydrocarbons in Au-Ag Ore Formation in the Rodnikovoe Low-Sulfidation (LS) Epithermal Deposit, Kamchatka Peninsula, Russia

by Nadezhda Tolstykh, Maria Shapovalova, Elena Shaparenko and Daria Bukhanova

Minerals 2022, 12(11), 1418; https://doi.org/10.3390/min12111418 - 09 Nov 2022

Cited by 3 | Viewed by 1541

Abstract

Gold-silver mineralization in the Rodnikovoe LS epithermal deposit is characterized by selenium speciation. Two main alternating ore assemblages have been identified: silver-aguilarite-acanthite and gold-uytenbogaardtite-acanthite. The former mineral association is intergrown with secondary silver (Ag_0.77–0.91), whereas the latter assemblage is closely associated with high-grade gold (Au_0.63–0.67). However, both are dominated by Ag_0.49–0.56Au_0.44–0.51 alloys. The geochemical evolution of the ore-forming system developed in the direction: Fe → Cu; Ag → Au; S → Se; As → Sb. Organic compounds (1 relative %) of both biogenic and thermogenic origin were found in fluid inclusions. These molecules participated in the formation of Ag,Au-complexes and transported noble metals along with selenium. Hydrothermal fluids are characterized by fSe₂/fS₂ ratios < 1, conditions such that the deposition of selenide minerals is inhibited, except for the naumannite and acanthite series. These conditions allow active entry of selenium into sulfosalts (the selenium substitutes for sulfur). Full article

(This article belongs to the Special Issue Precious Metals vs. Base Metals: Nature and Experiment)

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19 pages, 4563 KiB

Open AccessArticle

Formation of Noble Metal Phases (Pt, Pd, Rh, Ru, Ir, Au, Ag) in the Process of Fractional Crystallization of the CuFeS₂ Melt

by Elena Fedorovna Sinyakova, Inga Grigorievna Vasilyeva, Aleksandr Sergeevich Oreshonkov, Sergey Vladimirovich Goryainov and Nikolay Semenovich Karmanov

Minerals 2022, 12(9), 1136; https://doi.org/10.3390/min12091136 - 07 Sep 2022

Cited by 6 | Viewed by 1809

Abstract

The quasi-equilibrium directional crystallization of the melt composition (at. %): Cu 24.998, Fe 25.001, S 49.983, with Ag 0.002, Pd 0.003, Ru 0.004, Rh 0.006, and Au, Pt, Ir (each as 0.001) was carried out. The crystallized cylindrical ingot consisted of two primary zones and three secondary zones with different chemical and phase compositions. The compositions of the primary zones corresponded to high-temperature intermediate solid solution (zone I) and liquid enriched in sulfur (zone II). The compositions of the secondary zones corresponded to low-temperature intermediate solid solution and chalcopyrite (zone Ia), the same intermediate solid solution with chalcopyrite and bornite (zone Ib), and again with bornite, chalcocite, and idaite (zone II). We plotted the distribution curves of Fe, Cu, and S along the ingot, calculated the distribution coefficients of the components during directional crystallization, and clearly showed that, from the initial stoichiometric composition CuFeS₂, the intermediate solid solution enriched in Fe and depleted in S is crystallized. Based on the data of directional crystallization and thermal analysis, a cross section was constructed in the intermediate solid solution-sulfide melt region of the Cu-Fe-S system. With solubility in the solid Cu-Fe sulfides lying below detection limit of scanning electron microscopy/energy-dispersive X-ray spectrometry (SEM/EDS), noble elements occurred as individual phases of a size more often <10 µm. They were identified as Ag, RuS₂, PdS, Au* (an Au based alloy), (Rh, Ir, Ru)₃S₈, (Rh, Ir)₃S₈, Rh₃S₈, and (Cu, Fe)_~2(Pt, Rh)₁S_~5 phases by electron microprobe. Based on ab initio calculations of crystal structure, electronic band structure, and lattice dynamics of idealized laurite RuS₂ phase and the idealized Ir₃S₈, Rh₃S₈, and Ru₃S₈ phases, the interpretation of Raman spectrum of the cation-mixed (Ru, Rh, Ir)S₂ sulfide was presented for the first time. Full article

(This article belongs to the Special Issue Precious Metals vs. Base Metals: Nature and Experiment)

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