Platinum Mineralization Research Articles

Palladium and platinum minerals in Au-Pd ores of the Chudnoe deposit (Subpolar Urals, Russia)

Research subject. Minerals of palladium, platinum, and native gold, localized mainly in the veins of chromium-containing mica (fuchsite) in rhyolites. Aim. Clarification of the localization features of platinum group minerals, their species diversity, determination of the composition of minerals, relationships between precious metal minerals, establishment of the sequence of formation. Methods. Polished sections from ore samples and concentrates of heavy minerals mounted in epoxy resin were studied using optical and electron microscopes. The composition of minerals was determined using a scanning electron microscope with an energy dispersive spectrometer. Results. The main Pd minerals of the deposit are isomertieite/pseudomertieite and mertieite, the minor ones are ateneite and the unnamed Pd6BiSe mineral, and the platinum mineral is sperrylite. Isomertieite/pseudomertieite forms intergrowths with gold of any composition and structure, while mertieite occurs only with relatively low-copper gold of a homogeneous structure; therefore, significant areas of ore zones are characterized by the presence of one of the palladium arsenoantimonides. In some areas of ores, the replacement of isomertieite/pseudomertieite by mertieite wass established. Conclusions. The formation of fuchsite veinlets and the native gold, palladium minerals, and sperrylite contained therein is associated with one stage of mineral formation. Cr, Au, Pd, and Pt in ores form a single geochemical association, which indicates a common source of these elements. This source is most likely to be derivatives of basite-hyperbasite magmatism.

PLATINUM GROUP MINERALS OF THE BAIMKA GOLD PLACER CLUSTER, WESTERN CHUKOTKA: THE NEW DATA

The results of the study of the platinum group minerals of the Baimka gold placer cluster, Western Chukotka, Russia, are presented. Platinum group minerals belong to the iridium-platinum and platinum miner- alogical-geochemical types with the Late Jurassic cumulative pyroxenite-gabbro complexes as a probable source. Platinum group minerals came to alluvial gold placers primarily from intermediate reservoirs, which is the Volgian volcanic-sedimentary sequence. Rounded silicate glass inclusions are a specific feature of platinum minerals from the Baimka placer cluster.

Morphology and structural evolution of fine beach gold in comparison to detrital platinum, southern New Zealand

AbstractBeach placer gold has been mined around the world historically, but extraction of fine (~ 100 µm) gold particles is notoriously difficult. This study illustrates morphological and mineralogical changes that transform fine gold during aeolian processes on windy beaches and contribute to mine concentration inefficiencies. Sandblasting on exposed beaches in southern New Zealand has caused extreme attenuation of edges of gold flakes that were previously transported in rivers for > 200 km. Flakes have been transformed into complex but compact toroids and spheroids with thin (~ 20 µm) internal and external strands of attenuated gold. Most of the gold within the attenuated strands has recrystallised to fine (micron-scale) undeformed grains with little or no Ag (< 1 wt%). Some coarse (> 40 µm) gold grains remain from the precursor fluvial particles, and these retain original Ag contents (1–10 wt%). These coarse grains show substantial internal crystallographic deformation and sub-grain formation, although some of these strain effects may have been inherited from fluvial transport. Co-existing detrital platinum minerals are much less malleable than gold during sandblasting and have only minor (10-µm scale) toroidal deformation on edges of fluvial flakes. The complex frameworks of the fine toroidal and spheroidal gold particles can include air, water, and clay, which lowers their average density and so they commonly float on water and are readily entrained with other heavy minerals. The fine particle size, compact shapes, and clay coatings also resist mercury amalgamation.

Paragenetic Association of Platinum and Gold Minerals in Placers of the Anabar River in the Northeast of the Siberian Platform

Areal placers of diamond and precious metals (platinum and gold) of unknown origin are widespread in the Anabar River basin on the northeastern part of the Siberian Platform. This article discusses the typomorphic features of palladium gold (porpezite) and ferroan platinum, which, in addition to fragmented individual grains, sometimes form close growths, which indicates their obvious genetic relationship. This can be used to delimit the primary sources of commercial components of complex placers by their genetic types. The composition of minerals was determined on a Camebax-Micro (Cameca, France) microprobe analyzer, and their microstructural relationships were studied using the scanning microscope JSM-6480LV JEOL. Determination of the structure and parameters of elementary lattices of minerals was carried out on the D8 Discover diffractometer. According to microprobe analysis, the Pd content in porpezite ranges from 0.73% to 12.83%, Ag does not exceed 2.75% and Cu reaches 3–4%. Considering the composition, such a gold–platinum mineral association from placers of the Anabar river is close to precious metals from placers of the Gulinsky massif, as well as Au–PGE ore occurrences related to ultramafic–mafic intrusions of other regions of the world. Complex gold–platinum-metal mineralizations are usually closely related to parent rocks and are often observed in sulfide and chromite ores of layered ultramafic–mafic intrusions with complex metasomatic and hydrothermal transformations. It is shown that in such cases gold and platinum form a magmatogenic paragenesis of minerals that coexist until the separation of hydrothermal solutions from magma, which, as a rule, transports Au and Ag with a small fraction of PGE from the fluid-ore-magmatic system in accordance with the model of the formation of gold–porphyry deposits. Within the Anabar diamond-bearing region, according to modern geophysical data, a significant number of local gravimagnetic anomalies associated with the presence of intrusive massifs of basic and alkaline-ultrabasic rocks in the cover and within the basement have been identified. This allows us to assume that the buried parent rocks of the Anabar Au–Pt placers may be located in both the Precambrian and Phanerozoic strata.

Identification of mineral associations in skarn-rare-metallic deposits in Western Uzbekistan

This article solves the applied scientific problem of identifying mineral carriers and mineral associations of platinum mineralization in the skarn-gold-rare metal Koytash and Lyangar deposits. One of the applied research tasks was to identify the forms of mineral carriers and mineral associations of platinum-metal mineralization for these deposits. We carried out geological fieldwork of the Koytash and Lyangar deposits, which included a sampling of sulphide-rare metal and silver-polymetallic ores, and conducted laboratory studies by using mass spectrometry, atomic absorption, electron microprobe, and other modern methods. This article addresses the complex formation of sulphide-rare-metal and silver-polymetallic ores of the above-mentioned deposits. The formation of mineral associations bearing rare-metal (W-Mo) mineralization that formed in the early alkaline stage, in almost all sites, is completed by sulphide-rare metal and silver-polymetallic mineralization that often carry industrial-grade concentrations of noble and other metals. We have identified a recommended location for the concomitant extraction of useful components, the mineral composition, and the impure elements in them. These data show the prospects of sulphide-rare metals and sulphidepoly-metallic ores in the Koytash deposit for precious metals, bismuth, etc.

Platinum-metal mineralization of the Norilsk district: history and prospects of research

Relevance. Since the 19th century, the Norilsk Ore district has been one of the world leaders in the production of platinum metals. Long-term research focused on the detection of sulfide platinum-copper-nickel ores contributed to the accumulation of a large volume of scientific material on the geology and ore content of the Norilsk region. Due to the emergence of new methods for ores studying, it seems necessary to analyze previously published data and assess the prospects for the joint application of traditional and modern methods in solving the problem of understanding the ore formation process. The purpose of the work – to summarize information about the geology of the Norilsk ore region and the platinum-metal mineralization associated with it, to note the main scientific achievements and identify promising areas for further research. Results. Thanks to comprehensive production and research geological works, differentiated basite-ultrabasite intrusions and ore-containing Paleozoic-Mesozoic sedimentary volcanic rocks of the Norilsk region have been studied at the highest level. The geological structures of the region and its metallogeny are also studied in detail. However, there is still no unambiguous understanding of the geodynamics of the magmatic process and, accordingly, the mechanism of formation of ore-bearing intrusions. Conclusions. In the conditions of depletion of known deposits, the decoding of the genesis of ores of the Norilsk region becomes particularly relevant. The use of modern computer X-ray microtomography in addition to geochemical and petrological studies makes it possible to analyze the three-dimensional distribution of platinum and sulfide minerals, to identify textural and structural evidence of processes that were previously questioned. The results of these studies may lead to a reassessment of established models of ore genesis, as well as an increase in the efficiency of ore processing.

190Pt–4He Age of Native Platinum Minerals of the Baimka Gold Placer Cluster, Western Chukotka

190Pt–4He Age of Native Platinum Minerals of the Baimka Gold Placer Cluster, Western Chukotka

190Pt-4He dating of platinum mineralization in Ural-Alaskan-type complexes in the Kamchatka region: evidence for remobilization of platinum-group elements

190Pt-4He dating of platinum mineralization in Ural-Alaskan-type complexes in the Kamchatka region: evidence for remobilization of platinum-group elements

Platinum-Group Minerals in the Placer of the Kitoy River, East Sayan, Russia

The platinum-group minerals (PGM) in placer deposits provide important information on the types of their primary source rocks and ores and formation and alteration conditions. The article shows for the first time the results of a study of placer platinum mineralization found in the upper reaches of the Kitoy River (the southeastern part of the Eastern Sayan (SEPES)). Using modern methods of analysis (scanning electron microscopy), the authors studied the microtextural features of platinum-group minerals (PGM), their composition, texture, morphology and composition of microinclusions, rims, and other types of changes. The PGM are Os-Ir-Ru alloys with a pronounced ruthenium trend. Many of the Os-Ir-Ru grains have porous, fractured, or altered rims that contain secondary PGE sulfides, arsenides, sulfarsenides, Ir-Ni-Fe alloys, and rarer selenides, arsenoselenides, and tellurides of the PGE. The data obtained made it possible to identify the root sources of PGM in the placer and to make assumptions about the stages of transformation of primary igneous Os-Ir-Ru alloys from bedrock to placer. We assume that there are several stages of alteration of high-temperature Os-Ir-Ru alloys. The late magmatic stage is associated with the effect of fluid-saturated residual melt enriched with S, As. The post-magmatic hydrothermal stage (under conditions of changing reducing conditions to oxidative ones) is associated with the formation of telluro-selenides and oxide phases of PGE. The preservation of poorly rounded and unrounded PGM grains in the placer suggests a short transport from their primary source. The source of the platinum-group minerals from the Kitoy River placer is the rocks of the Southern ophiolite branch of SEPES and, in particular, the southern plate of the Ospa-Kitoy ophiolite complex, and primarily chromitites.

Occupational Hearing Loss for Platinum Miners in South Africa: A Case Study of Data Sharing Practices and Ethical Challenges in the Mining Industry.

Background: The relevant legislation ensures confidentiality and has paved the way for data handling and sharing. However, the industry remains uncertain regarding big data handling and sharing practices for improved healthcare delivery and medical research. Methods: A semi-qualitative cross-sectional study was used which entailed analysing miners’ personal health records from 2014 to 2018. Data were accessed from the audiometry medical surveillance database (n = 480), the hearing screening database (n = 24,321), and the occupational hygiene database (n = 15,769). Ethical principles were applied to demonstrate big data protection and sharing. Results: Some audiometry screening and occupational hygiene records were incomplete and/or inaccurate (N = 4675). The database containing medical disease and treatment records could not be accessed. Ethical challenges included a lack of clarity regarding permission rights when sharing big data, and no policy governing the divulgence of miners’ personal and medical records for research. Conclusion: This case study illustrates how research can be effectively, although not maliciously, obstructed by the strict protection of employee medical data. Clearly communicated company policies should be developed for the sharing of workers’ records in the mining industry to improve HCPs.

Magmatic volatiles and platinum-group element mineralization in the Stillwater layered intrusion, U.S.A.

Abstract The activity of volatile-rich fluids may be important in the evolution of basaltic magmatic systems and associated precious metal ore formation. There is evidence for Cl-rich fluids within the Stillwater Complex (Montana, U.S.A.), which have been linked to platinum and palladium mineralization in the economically important Johns-Manville (J-M) Reef ore body. We present the first data set for heavy halogens (Cl, Br, and I) and natural noble gas isotopes in bulk rock and mineral separates from the Peridotite Zone and the Olivine-Bearing Zone I of the Stillwater Complex, including samples from the J-M Reef and G Chromitite bodies. Our data reveal concentrations of 4 to 13 500 ppm for Cl, 26 ppb to 360 ppm for Br, and <1 ppb to 9 ppm I over the whole sample set. Cl, Br, and I correlate well with each other implying a shared process and/or distribution in mineral species. Br/Cl and I/Cl ratios span a range from 0.3 to 35 × 10−3 and 5 to 900 × 10−6 by weight, respectively, encompassing MORB-like to more enriched compositions, particularly for Br/Cl. High-Br/Cl ratios compared to MORB in some Stillwater samples suggest fractionation of halogens during the exsolution of a volatile-rich fluid to explain the most Br-enriched samples. More generally, the presence of minerals such as scapolite, hornblende, and apatite in the most halogen-enriched samples suggests that the halogen-bearing fluids were derived from the cooling of the intrusion rather than late-stage (low-temperature) metamorphism. The combined halogen abundance and noble gas isotope data set imply that crustal contamination may have played a limited role in the crystallization of pegmatoids and the G Chromitite but is not required to account for the halogen budget of the J-M Reef. High-halogen contents in the sulfide-bearing J-M Reef and associated lithologies are consistent with the influence of fluid-related activity during platinum-group element (PGE)-Reef formation, lending weight to the hydromagmatic model for mineralization in the Stillwater intrusion. Our new data also imply chalcophile tendencies of Br and I over Cl in sulfides in natural systems, hinting at the importance of sulfide liquid interaction with halogen-rich fluids in the formation of sulfide-hosted precious metal ore deposits.

Platinum and gold placer from Tugidak Island, Alaska: Platinum-group minerals and their inclusions, gold, and chromite mineralogy

ABSTRACT Black sand beach placers from Kodiak, Sitkinak, and Tugidak Islands, Alaska, have been mined intermittently for gold and minor platinum-group alloys for more than 100 years. High-grade platinum-rich magnetic separate and accompanying black sand from the southern beach placer of Tugidak Island were studied using electron microprobe WDS and scanning electron microscope EDS; mineral classification and identification were based on these techniques. The major platinum mineral is isoferroplatinum, followed by minor tetraferroplatinum and tulameenite, and rare ferronickelplatinum. Two types of alteration were identified in about 3–4% of the alloy grains: rim formation involving Pt loss and increased Fe, Ni, and/or Cu, and fracturing and vein filling by Cu-rich alloy. Ruthenium-Ir-Os-Pt alloys occur as inclusions and veins as well as form part of composite grains. Ten percent of the alloy grains contain a large variety of platinum-group minerals (PGM). Inclusions of cuprorhodsite, malanite, cuproiridsite, laurite, erlichmanite, cooperite, braggite, bowieite, kashinite, miassite, hollingworthite, irarsite, sperrylite, stillwaterite, genkinite, stibiopalladinite, keithconnite, zvyagintsevite, and probable palladodymite and vincentite were identified. Two unidentified inclusion phases also occur. Most of the PGM inclusions are primary and were trapped by a growing crystal from a melt; some inclusions exhibit textures that suggest trapping of an As,Te,S-rich immiscible melt. Secondary inclusions and evidence of deformation were observed in a few alloy grains. Associated with PGM inclusions or as separate inclusions are various base-metal sulfides. Two silicate-melt inclusions in one isoferroplatinum grain have an andesite–shoshonite composition. Minor gold and Ag-rich gold in the high-grade magnetic separate contain magnetite, pyrrhotite, and chromite inclusions. The gold composition suggests that their sources are the numerous quartz veins and apophyses related to granitoids on Kodiak Island. The composition of the placer chromite is similar to chromite from the Border Ranges mélange fault system and suggests that the Uyak Complex ultramafic and mafic rocks are part of a supra-subduction-zone ophiolite and are the source of the platinum-group minerals.

PLATINUM METAL MINERALIZATION OF THE SOUTH URALS MAGMATIC COMPLEXES: GEOLOGICAL AND GEODYNAMIC CHARACTERISTICS OF FORMATIONS, PROBLEMS OF THEIR GENESIS, AND PROSPECTS

In the South Urals, we have identified and investigated two platinum-bearing formations – ophiolite chromitebearing complexes, and the Khudolaz differentiated mafic-ultramafic complex with sulfide Cu-Ni mineralization. The ophiolite chromite-bearing complexes include fragments of the upper mantle and lower crust of the Paleouralian Ocean, which were induced by collision onto the edge of the East European platform. The origin of the Khudolaz complex is related a mantle plume activity. Here, we review and compare the main features of platinum-metal mineralization (PMM) in these two formations.The article presents the results of mineralogical and geochemical studies of PMM associated with chromite and sulfide Cu-Ni ores. In association with chromitites, two types of PMM are distinguished: (1) predominating refractory platinoids in chromitites of the mantle unit of the section, and (2) predominating platinum and palladium in chromitites of the transitional wehrlite-clinopyroxenite complex. Compositions of platinum group minerals (PGM) and relations between their elements and host minerals suggest that the minerals of the ophiolite chromite-bearing complexes are of a restite origin, while the Khudolaz complex results from a combination of magmatic processes and solid-phase redistribution of material. Palladium (michenerite, froodite, merenskyite, borovskite, sudburyite) and platinum (sperrylite, moncheite) minerals are found in magmatic sulfide ores of the Khudolaz complex, which were subjected to hydrothermal metasomatization. Texture observations using electron microscope and optical (reflected light) images, as well as LA ICP MS analyses of sulfides suggest late- and post-magmatic crystallization of PMM in three phases: (1) immiscible metalloid or highly fractionated residual sulfide melts trapped in sulfides; (2) segregation of isomorphic impurities of platinum group elements (PGE) and chalcogenide elements from sulfide solid solutions; and (3) interaction of hydrothermal fluids with soluble sulfides.Prospective for PMM are extended bodies of disseminated chromitites in marginal dunites of the Kraka and Nurali massifs, and wehrlite-clinopyroxenite complexes of the same massifs containing PGE (above 500 ppb). In the Khudolaz complex, promising PMM bodies are low-metasomatized parts of sulfide ore bodies (1 ppm of ΣPGE and above) located in the largest massifs, Severny Buskun and Zapadny Karasaz. Exocontact zones of these intrusions are also promising for PMM.

Spatial association between platinum minerals and magmatic sulfides imaged with the Maia Mapper and implications for the origin of the chromite-sulfide-PGE association

ABSTRACT The spatial association between Pt minerals, magmatic sulfides, and chromite has been investigated using microbeam X-ray fluorescence (XRF) element mapping and the Maia Mapper. This lab-based instrument combines the Maia parallel energy dispersive (ESD) detector array technology with a focused X-ray beam generated from a liquid metal source. It proves to be a powerful technique for imaging Pt distribution at low-ppm levels on minimally prepared cut rock surfaces over areas of tens to hundreds of square centimeters, an ideal scale for investigating these relationships. Images of a selection of samples from the Bushveld Complex and from the Norilsk-Talnakh ore deposits (Siberia) show strikingly close association of Pt hotspots, equated with the presence of Pt-rich mineral grains, with magmatic sulfide blebs in all cases, except for a taxitic low-S ore sample from Norilsk. In all of the Bushveld samples, at least 75% of Pt hotspots (by number) occur at or within a few hundred microns of the outer edges of sulfide blebs. In samples from the leader seams of the UG2 chromitite, sulfides and platinum hotspots are also very closely associated with the chromite seams and are almost completely absent from the intervening pyroxenite. In the Merensky Reef, the area ratio of Pt hotspots to sulfides is markedly higher in the chromite stringers than in the silicate-dominated lithologies over a few centimeters either side. We take these observations as confirmation that sulfide liquid is indeed the prime collector for Pt and, by inference, for the other platinum group elements (PGEs) in all these settings. We further propose a mechanism for the sulfide-PGE-chromite association in terms of in situ heterogeneous nucleation of all these phases coupled with transient sulfide saturation during chromite growth and subsequent sulfide loss by partial re-dissolution. In the case of the amygdular Norilsk taxite, the textural relationship and high PGE/S ratio is explained by extensive loss of S to an escaping aqueous vapor phase.

Platinum mineralization and geochemistry of the Matysken zoned Ural-Alaskan type complex and related placer (Far East Russia)

Ural-Alaskan type complexes are the sources for unique placer platinum deposits and contain platinum-group minerals (PGM) within lodes. Such complexes occur along modern and ancient convergent tectonic margins and are comprised of dunite, wehrlite, clinopyroxenite and gabbro, which gradually interchange towards the marginal parts of the complex. In-situ PGM are largely restricted to chromitites, which are comprised of small veinlets and schlieren of chromian spinel in the dunite unit. PGM mineralization in chromitites can be extremely rich; however, their distribution is very sporadic, without any apparent regularity. Moreover, the role of accessory chromian spinel and post-magmatic overprinting of platinum group element (PGE) concentrations is poorly defined. Detailed studies of PGM assemblages, including those in chromitites, serpentine veinlets in dunites, and wehrlites, combined with PGE geochemistry could provide insights into the distribution and processes responsible for PGE accumulation.The Matysken complex in the Koryak Highlands (Far East Russia) is comprised of dunite, wehrlite, clinopyroxenite and gabbro units, and has a classic zoned structure, rendering it an excellent example of an Ural-Alaskan type complex, ideal for this case study. This locality contains mm-scale isoferroplatinum (Pt3Fe) nuggets that cement chromitites and occur as µm-scale euhedral inclusions in chromian spinel. Placer PGM assemblages in the nearby Matysken River consist of exactly the same assemblages of minerals that are found in dunites and chromitites but with larger compositional scatter, reflecting a complex history of alluvium accumulation, which was sourced from different eroded parts of the complex. Detailed textural investigations discovered a diverse array of hydrous silicate–related mineralization, including euhedral isoferroplatinum grains in chlorite matrix, isoferroplatinum–amphibole intergrowths, and a wide range of PGE, Fe and Cu alloys, sulfarsenides and antimonides, which formed in serpentine veinlets together with awaruite (Ni3Fe) and base metal sulfides. This provides further evidence that isoferroplatinum, which is widely accepted to be a magmatic mineral, may form under a wide range of conditions, including during serpentinization.Dunites have fractioned primitive mantle-normalized PGE patterns, typical of Ural-Alaskan type complexes, with strong enrichments in Pt and depletions in Ir, Ru and Pd. PGE, with an exception of Pd, are quite uniformly distributed in dunite containing accessory chromian spinel, with good correlations between PGE and Cr. This correlation, together with data from previous studies, allowed us to calculate the concentration of Pt in accessory chromian spinel (probably hosted as minute PGM inclusions), which is of the same grade as for chromitites (ppm levels). This suggests that the formation of chromitites does not concentrate PGE over Cr, but only assembles them into larger aggregates, causing the observed unevenness in the PGM distribution.

Platinum mineralisation in the Owendale Uralian-Alaskan-type complex, New South Wales, Australia: The effects of serpentinization on Cu-PGE-Ni sulphides

Significant, albeit highly erractic, PGE mineralization is hosted in the ultramafic rocks of the Owendale Complex, a Uralian-Alaskan type intrusion in the Fifield region of central New South Wales, Australia. Three types of PGE mineralization have been identified in drill core samples of these rocks. The first to be recognized was PGE mineralization associated with “P-units” which are narrow (a few millimetre to 2 m wide) lenses of pegmatoidal clinopyroxenites within olivine clinopyroxenites; the best intersection of this type of mineralization averaged 13.19 g/t Pt and 0.90 g/t Pd over 1.57 m, has very low S contents and contains a primary magmatic PGM assemblage. Two types of PGE mineralization occur within dunites and wehrlites, a low-Cu Pt type and a high-Cu Pt type of mineralization. The low-Cu Pt type of mineralization consists mainly of disseminated Cu-Pt-(Fe) alloys that lie along the mesh lines of partially serpentinized olivine; this type of mineralization can have grades of up to 25 g/t Pt but very low amounts of Cu, S, Au and Pd. The high-Cu Pt type of mineralization consists of disseminated, partially oxidised PGE-rich Cu sulphides with Pd-bearing PGM; this type of mineralization has up to 25 g/t Pt and elevated levels of Cu, S, Se, Au and Pd. The Pt:Ir:Rh ratios of the low-Cu Pt and the high-Cu Pt types of mineralization are virtually identical attesting to a common source, but with variable removal of the more mobile Pd, Au, Cu and Se. Some of the high-Cu Pt type sulphides are associated with an unusual Cr-Al-Ti-Mg-rich magnetite that occurs in veins and pods that are up to 15 cm thick. Phlogopite is a common accessory mineral in the dunites and wehrlites, occurring as disseminated grains and pods of mica that are up to 4 cm wide, and as selvedges along the Cr-Al-Ti-Mg-rich magnetite veins. Owendale represents a staging chamber in which olivine cumulates, followed by clinopyroxenite cumulates, were formed and later infiltrated from above by immiscible Fe-rich and Cu-sulphide melts. It is suggested that the phlogopite was produced by K2O-rich fluids released from the monzonites and diorites that intruded the ultramafics and which also drove serpentinisation. Serpentinisation altered the dunite/wehrlites with small amounts of sulphides to remove all the S and most of the Cu, Au, and Pd to leave only Cu-Pt-(Ni-Fe) alloys, forming the low-Cu Pt type of mineralization, whereas the magmatic sulphides in dunites/wehrlites with larger amounts of sulphides were only partially altered, forming the high-CuPt type of mineralization. The Pt alloys produced during serpentinization of the PGE-rich Cu sulphides at Owendale are predominantly Cu-rich, unlike the Pt-Fe alloys found in the placer deposits associated with most Uralian-Alaskan complexes. However, the Owendale Complex was lateritized, as were the Uralian-Alaskan Complexes in the Urals. It is possible that during lateritization, the Cu-Pt-Fe alloys were converted into Pt-Fe alloys similar to those found in the Pt placers.

ANALYSIS OF THE DEPENDENCE STRUCTURE BETWEEN MINERALS PRICES AND THE RAND/USD EXCHANGE RATE USING COPULAS

Copula functions are flexible tools for modelling the dependence structure between variables. In this research, we extend the literature on currency-commodity relationship using copulas. We examine the dependence structure between gold, platinum mineral prices and RAND/USD exchange rate. ARMA (1, 1)-EGARCH (1, 1) and ARMA(1, 1)-APARCH (1, 1) models under different error terms including normal, student-t and skewed student-t were fitted to the returns of commodity prices and the exchange rate. Constants and time varying copulas were then employed to examine the commodity-currency dependence structure. The results show evidence of a positive, strong dependence between gold, platinum prices and the RAND/USD exchange rate. The analysis relies on Clayton, rotated Clayton, Student-t, Gumbel, rotated Gumbel, Plackett and Joe Clayton copulas and provide an indication of leverage effects. The results of the time varying Normal copula indicate that fluctuations in gold and platinum prices generate Rand/USD volatility.

Ultramafic Zoned Complexes of the Urals and Siberia: New Geochemical Evidence of Magmatic Origin

AbstractUltramafic (dunite‐clinopyroxenite) complexes with platinum mineralization are common in different tectonic settings. Among them are zoned complexes of the Ural‐Alaskan type, zoned complexes of platforms (Konder massif, Siberia), as well as layered intrusion complexes (Gulin massif, Siberia). In determining the genesis of these formations, an important role belongs to the study of melt inclusions and rock‐forming minerals, including clinopyroxene.Clinopyroxenes of the ultramafic complexes exhibit a general trend of evolution, expressed as a decrease in magnesium content (Mg# = 0.95 to 0.7) and an increase in the contents of titanium and aluminum oxide (0–4.5% and 0.5–7.0%, respectively) in the dunite ‐ clinopyroxenite series. In the coordinates of Ti ‐ AL (IV) the clinopyroxenes of the Ural‐Alaskan complexes of the Platinum belt form a linear trend of compositions with a slight increase (0–0.03 f.u.) in the titanium contents. In comparison with them the clinopyroxenes of the zoned platform complexes (Konder massif) demonstrate a shift in the trend of compositions, due to an increase in the titanium content to the moderate (0.05 f.u.) values. For the layered intrusions (Gulin pluton), it is typical another trend of clinopyroxene compositions with significantly higher titanium contents (0.04–0.12 f.u.) at the similar level of aluminum. Clinopyroxene compositions of zoned complexes of the Platinum belt are “controlled” by the area of boninites and tholeites of island arcs, and the zoned complexes of platforms by the areas of island arc tholeites and sub‐alkaline intraplate basalts. Clinopyroxenes of the layered intrusions are located in the field of compositions of alkaline intraplate or MORB basalts.The geochemical study of clinopyroxenes, performed by laser ablation method (LA‐ICP‐MS) at the University of Kanazawa (Japan) and the Institute of Geology and Geochemistry of the UB RAS (Zaitseva et al., 2018), established the following features: (1) In ultrabasites of zoned complexes of the Urals and Siberia (Konder massif), clinopyroxene is characterized by an arc‐shaped distribution of rare earth elements with increasing contents from dunites to pyroxenites at a relative deficit of heavy REE (LaN/YbN = 1.2–5.4). In magnetite clinopyroxenites (enriched REE), its composition is close or identical to that in orthoclase‐bearing pyroxenites (tylaites). Negative anomalies of lead, zirconium, hafnium, and titanium, as well as positive anomalies of strontium, are typical for clinopyroxene zoned complexes. (2) In ultrabasites of layered intrusions (Gulin massif) clinopyroxene is characterized by higher level of light lanthanides with a steeper slope of the REE distribution spectra (LaN/YbN = 8–13). Lead, zirconium and hafnium anomalies are also inherent in the compositions; unlike the zoned complexes a weak negative anomaly of strontium and a positive anomaly of titanium are observed.Using the partition coefficients between clinopyroxene and the melt, the compositions of parental melts for ultramafic complexes were calculated. In general, these model melts are characterized by oblique spectra of compositions typical of island arc and intraplate environments (Fig. 1). Model melts corresponding to the Ural‐Alaskan‐type zoned complexes (Platinum belt) show low levels of REE with a noticeable deficiency of heavy lanthanides (LaN/YbN = 8–25). By their high (≥ 2) CaO/Al2O3 ratio, they are close to ankaramite type island arc melts, differing by a steeper slope of the REE distribution spectra. Model melts corresponding to the zoned platform complexes (Konder massif) demonstrate a higher level of REE content and a deficit of heavy REE (LaN/YbN = 38), with a similar distribution pattern. At a lower Ca/Al ratio (0.4–1.9), they are close to melts of the picritic type. In comparison with them, model melts corresponding to the layered intrusions (Gulin massif) demonstrate a significantly higher level of REE and a steeper slope of the distribution spectra (LaN/YbN = 67–103), typical of alkaline mechmitic melts. In general, the results of the mineralogical and geochemical study of clinopyroxenes of ultramafic complexes correlate well with the data on melt inclusions in spinels from dunites (Simonov et al., 2017).

Platinum mineralization of the Epilchik Ural-Alaskan type zoned complex (Far East Russia)

The Epilchik Ural-Alaskan type mafic-ultramafic zoned complex, located in the northernmost part of the Koryak-Kamchatka Platinum Belt (Russian Far East), contains lode platinum mineralization. The outcrops of the complex are crossed by the Snegovaya River, which hosts placer platinum-group minerals (PGM) occurrences. The primary PGM assemblage of the Epilchik lode chromitites is typical for Ural-Alaskan type complexes, dominated by Ir-rich isoferroplatinum which occurs as small euhedral inclusions within chromite. Secondary alloys include tetraferroplatinum (PtFe), tulameenite (Pt2FeCu), an unnamed Fe3Pt compound, and Pt-bearing native iron, which form alteration rims around isoferroplatinum or occupy fractures in chromite. Other secondary minerals from lode chromitites are hollingworthite (RhAsS) and Os-Fe alloy (“hexaferrum”). The PGM assemblages of the Snegovaya River placer occurrences are comparable with those of the lode chromitites with a predominance of Ir-rich isoferroplatinum and secondary alloys, including tetraferroplatinum, tulameenite, and an unnamed Fe3Pt compound. However, placer occurrences are much richer in regard to mineral diversity, comprising native osmium (Os,Ir), native iridium (Ir,Os), laurite (RuS2), erlichmanite (OsS2), cuprorhodsite (CuRh2S4), cuproiridsite (CuIr2S4), Co-malanite (Cu(Pt,Co)2S4), unnamed sulfides Rh3S4, (Rh,Pt)S, sperrylite (PtAs2), platarsite (PtAsS), irarsite (IrAsS), hollingworthite (RhAsS), osarsite (OsAsS), cooperite (PtS), native gold, unnamed telluride (Pt2Te), and an unnamed Fe-Ir-Rh alloy. Similarities between lode and placer mineralization indicate that the Epilchik complex was the dominant source for the placers. The larger diversity of PGM in placers may be attributed to the heterogeneity of samples which could be derived from unsampled or unexposed outcrops of the complex. Alteration of isoferroplatinum to secondary intermetallic compounds occurred via progressive development of reduced conditions as a result of serpentinization. Subsequent pervasive As-mineralization redistributed platinum-group elements, including Os and Ir. A final mineralizing pulse deposited sporadic native gold and Pt telluride minerals. A comparison of key mineralogical and physical features between the Epilchik complex and other Ural-Alaskan type complexes is used to determine the economic potential for placers along the Snegovaya River. Key criteria include (1) the size and degree of erosion of the outcrop area of the complex; (2) the predominance of isoferroplatinum over native platinum; (3) high Ir content in Pt-Fe alloys; and (4) the predominance of secondary intermetallic compounds over sulfides. Based on these criteria, the occurrences associated with the Epilchik complex are considered prospective for high volume and economic grade accumulations of PGE. This method is useful for assessing the economic potential of placer occurrences during indirect early-stage prospecting with a limited sample suite.

Processing of platinum group metal ores in Russia and South Africa: current state and prospects

The presented study is devoted to a comparative review of the mineral raw material base of platinum group metals (PGMs) and technologies of their processing in South Africa and Russia, the largest PGM producers. Mineralogical and geochemical classification and industrial value of iron-platinum and platinum-bearing deposits are presented in this work. The paper also reviews types of PGM ore body occurrences, ore processing methods (with a special focus on flotation processes), as well as difficulties encountered by enterprises at the processing stage, as they increase recovery of the valuable components. Data on mineralogical features of PGM deposits, including the distribution of elements in the ores, are provided. The main lines of research on mineralogical features and processing of raw materials of various genesis are identified and validated. 
 Sulfide deposits are found to be of the highest industrial value in both countries. Such unconventional PGM sources, as black shale, dunites, chromite, low-sulfide, chromium and titanomagnetite ores, anthropogenic raw materials, etc. are considered. The main lines of research that would bring into processing non-conventional metal sources are substantiated.
 Analysis of new processing and metallurgical methods of PGM recovery from non-conventional and industrial raw materials is conducted; the review of existing processing technologies for platinum-bearing raw materials is carried out. Technologies that utilize modern equipment for ultrafine grinding are considered, as well as existing reagents for flotation recovery; evaluation of their selectivity in relation to platinum minerals is presented.
 Basing on the analysis of main technological processes of PGM ore treatment, the most efficient schemes are identified, i.e.,gravity and flotation treatment with subsequent metallurgical processing.