Ophiolite-related associations of platinum-group minerals at Rudnaya, western Sayans and Miass, southern Urals, Russia

2018 ◽  
Vol 82 (3) ◽  
pp. 515-530 ◽  
Author(s):  
Andrei Y. Barkov ◽  
Nadezhda D. Tolstykh ◽  
Gennadiy I. Shvedov ◽  
Robert F. Martin
Keyword(s):  
Southern Urals ◽  
Chromian Spinel ◽  
Type Alloy ◽  
Chelyabinsk Oblast ◽  
The Southern Urals ◽  
Platinum Group Minerals ◽  
Pge Mineralization ◽  
Fe Alloys ◽  
Platinum Group ◽  
Western Sayan

ABSTRACTWe describe similar assemblages of minerals found in two placers in Russia, both probably derived from an ophiolitic source. The first is located along the River Rudnaya in the western Sayan province, Krasnoyarskiy kray, and the second pertains to the Miass placer zone, Chelyabinsk oblast, in the southern Urals. The platinum-group element (PGE) mineralization in both cases is mostly (at least 80%) represented by alloy minerals in the system Ru–Os–Ir, in the order of occurrence osmium, ruthenium and iridium. The remainder consists of Pt–Fe alloys and species of PGE sulfides, arsenides, sulfarsenides, etc. The associated olivine and amphiboles are supermagnesian, and the chromian spinel has a high Cr# value. The observed enrichment in Ru, typical of an ophiolitic source, may be due to high-temperature hydrothermal equilibration and mobilization in the ophiolite, as is the enrichment in Mg and Cr. Low-temperature replacement of the alloys led to the development of laurite, sulfoarsenides and arsenides. Some placer grains in both suites reveal unusual phases of sulfo-arsenoantimonides of Ir–Rh, e.g. the unnamed species (Rh,Ir)SbS and (Cu,Ni)1+x(Ir,Rh)1–xSb, wherex= 0.2, and rhodian tolovkite, (Ir,Rh)SbS. Two series of natural solid-solutions appear to occur in the tolovkite-type phases. Among the oddities in the Rudnaya suite are globules of micrometric PGE sulfides, crystallites of platinum-group minerals, amphibole, and chalcopyrite bearing skeletal micrometric monosulfide-like compounds (Cu,Pt,Rh)S and (Pd,Cu)S1–x. Pockets of fluxed evolved melt seem to have persisted well below the solidus of the host Pt3Fe-type alloy.

The evolution of the ore-forming system in the low sulfide horizon of the Noril'sk 1 intrusion, Russia

2019 ◽  
Vol 83 (5) ◽  
pp. 673-694 ◽  
Author(s):  
Nadezhda D. Tolstykh ◽  
Liudmila M. Zhitova ◽  
Maria O. Shapovalova ◽  
Ivan F. Chayka
Keyword(s):  
Mafic Magma ◽  
Chromian Spinel ◽  
Reducing Conditions ◽  
Platinum Group Minerals ◽  
Sulfide Melt ◽  
Formation And Evolution ◽  
Fe Alloys ◽  
Platinum Group ◽  
Monoclinic Pyrrhotite ◽  
Increased Activity

AbstractWe present here new data on the low-sulfide mineralisation in the upper endocontact of the Noril'sk 1 intrusion. Twenty four mineral species of platinum-group elements and their solid solutions, as well as numerous unnamed phases, including an Sb analogue of vincentite, As and Sn analogues of mertieite-I and a Sn analogue of mertieite-II have been found. It is shown that the features of the mineral association: (1) the atypical trend of TiO2 and Fe2+ in chromian spinel; (2) the composition of the Pt–Fe alloys with a Fe/Fe + Pt range of 0.26–0.37 (logfO2 ≈ – (9–10); and (3) crystallisation of high-temperature sperrylite from silicate melt (at >800°C and logfS2 < –10.5), which is possible under fO2 of FMQ to FMQ-2 in mafic magma, are due to the reducing conditions of their formation and evolution. Droplet-like inclusions of silicate-oxide minerals in сhromian spinels and sulfides in platinum-group minerals are interpreted to be trapped droplets of co-existing sulfide melt. The captured sulfide melt has evolved in the direction of increasing the fugacity of sulfur: troilite + pentlandite (Fe>Ni) – in sperrylite (paragenesis I) to monoclinic pyrrhotite + pentlandite (Ni≈Fe) + chalcopyrite – in Pt–Fe alloys (paragenesis II). Paragenesis from the sulfide aggregates in the silicate matrix are more fractionated: pyrrhotite + pyrrhotite (Ni>Fe) + chalcopyrite (III) and pyrite + pentlandite (Ni>>Fe) + millerite (IV). Pd arsenides and antimonides crystallised later than sperrylite and isoferroplatinum, as a result of the evolution of a sulfide melt with an increased activity of the element ligands (Te, Sn, Sb and As).

Platinum-group minerals of the F and T zones, Waterberg Project, far northern Bushveld Complex: implication for the formation of the PGE mineralization

2018 ◽  
Vol 82 (3) ◽  
pp. 539-575 ◽  
Author(s):  
Matthew J. G. McCreesh ◽  
Marina A. Yudovskaya ◽  
Judith A. Kinnaird ◽  
Christian Reinke
Keyword(s):  
Bushveld Complex ◽  
Magmatic Sulfides ◽  
Platinum Group Minerals ◽  
Pge Mineralization ◽  
Base Metal Sulfides ◽  
Fe Alloys ◽  
Platinum Group ◽  
Current Stage ◽  
Southern Marginal Zone ◽  
Sulfide Assemblage

ABSTRACTThis study provides the first detailed mineralogical data on platinum-group element (PGE) mineralization of the Waterberg Project, in a previously unknown segment of the Bushveld Complex located in the Southern Marginal Zone of the Limpopo Belt. The lower ultramafic F zone is dominated by sperrylite (up to 82 area%) with minor Pt–Pd bismuthotellurides, Pd–Ni arsenides, Au–Ag alloy, Rh–Pt sulfoarsenides and rare Pt–Fe alloys. The upper more felsic-rich gabbroic T zone is dominated by Pt–Pd bismuthotellurides (up to 90 area%), Pd tellurides and Au–Ag alloy with rare sperrylite, braggite, Pd stannides and antimonides. The platinum-group minerals (PGM) of the F zone are associated mainly with magmatic base-metal sulfides (pyrrhotite, troilite, chalcopyrite and pentlandite), that have undergone alteration during significant serpentinization, accompanied by the formation of the secondary sulfide assemblage. The T zone in a leucogabbroic sequence contains relics of magmatic sulfides and is characterized by the development of the indicative chalcopyrite-millerite-pyrite assemblage, which is associated with widespread hydrothermal quartz and hydrous silicates (amphiboles, phlogopite, epidote and chlorite). The fluid-induced style of PGM remobilization, the high Au/PGE and the high proportion of native gold in the high-grade T zone ores in the magnetite-bearing leucogabbroic rocks are unique to the Bushveld Complex. The genesis of the T ores is interpreted as a result of primary PGE enrichment in the zone of interaction between the first influxes of the Upper Zone fertile melt and a resident gabbroic melt at the top of the Troctolite-Gabbronorite-Anorthosite (TGA) fractionated sequence with subsequent fluid remobilization. Whether the hydrothermal overprint facilitated the PGE sequestration in a favourable setting or dispersed the pre-existing magmatic concentrations along fluid pathways remains essentially unresolved at the current stage.

scholarly journals The Fate of Platinum-Group Minerals in the Exogenic Environment—From Sulfide Ores via Oxidized Ores into Placers: Case Studies Bushveld Complex, South Africa, and Great Dyke, Zimbabwe

Minerals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 581 ◽  
Author(s):  
Thomas Oberthür
Keyword(s):  
South Africa ◽  
Bushveld Complex ◽  
Relative Proportion ◽  
Stable Phase ◽  
Sulfide Ores ◽  
Great Dyke ◽  
Platinum Group Minerals ◽  
Fe Alloys ◽  
Platinum Group ◽  
Liberation Analysis

Diverse studies were performed in order to investigate the behavior of the platinum-group minerals (PGM) in the weathering cycle in the Bushveld Complex of South Africa and the Great Dyke of Zimbabwe. Samples were obtained underground, from core, in surface outcrops, and from alluvial sediments in rivers draining the intrusions. The investigations applied conventional mineralogical methods (reflected light microscopy) complemented by modern techniques (scanning electron microscopy (SEM), mineral liberation analysis (MLA), electron-probe microanalysis (EPMA), and LA-ICPMS analysis). This review aims at combining the findings to a coherent model also with respect to the debate regarding allogenic versus authigenic origin of placer PGM. In the pristine sulfide ores, the PGE are present as discrete PGM, dominantly PGE-bismuthotellurides, -sulfides, -arsenides, -sulfarsenides, and -alloys, and substantial though variable proportions of Pd and Rh are hosted in pentlandite. Pt–Fe alloys, sperrylite, and most PGE-sulfides survive the weathering of the ores, whereas the base metal sulfides and the (Pt,Pd)-bismuthotellurides are destroyed, and ill-defined (Pt,Pd)-oxides or -hydroxides develop. In addition, elevated contents of Pt and Pd are located in Fe/Mn/Co-oxides/hydroxides and smectites. In the placers, the PGE-sulfides experience further modification, whereas sperrylite largely remains a stable phase, and grains of Pt–Fe alloys and native Pt increase in relative proportion. In the Bushveld/Great Dyke case, the main impact of weathering on the PGM assemblages is destruction of the unstable PGM and PGE-carriers of the pristine ores and of the intermediate products of the oxidized ores. Dissolution and redistribution of PGE is taking place, however, the newly-formed products are thin films, nano-sized particles, small crystallites, or rarely µm-sized grains primarily on substrates of precursor detrital/allogenic PGM grains, and they are of subordinate significance. In the Bushveld/Great Dyke scenario, and in all probability universally, authigenic growth and formation of discrete, larger PGM crystals or nuggets in the supergene environment plays no substantial role, and any proof of PGM “neoformation” in a grand style is missing. The final PGM suite which survived the weathering process en route from sulfide ores via oxidized ores into placers results from the continuous elimination of unstable PGM and the dispersion of soluble PGE. Therefore, the alluvial PGM assemblage represents a PGM rest spectrum of residual, detrital grains.

Magnetic signature of magnetite‐enriched rocks hosting platinum‐group element mineralization within the Archean Boston Creek Flow, Ontario

Geophysics ◽  
1998 ◽  
Vol 63 (2) ◽  
pp. 440-445 ◽  
Author(s):  
Michelle S. Larson ◽  
William E. Stone ◽  
William A. Morris ◽  
James H. Crocket
Keyword(s):  
Platinum Group Element ◽  
Magnetic Anomalies ◽  
Ore Deposits ◽  
Group Element ◽  
Rock Types ◽  
Platinum Group Minerals ◽  
Pge Mineralization ◽  
Geophysical Surveys ◽  
Close Proximity ◽  
Platinum Group

Ground‐based magnetometer surveys detect high‐positive magnetic anomalies (up to 72 000 nT) which coincide with the location of subeconomic, magnetite‐associated platinum‐group element (PGE) mineralization within the Boston Creek Flow iron‐rich basalt, Archean Abitibi Greenstone Belt, Ontario. The magnetic anomalies confirm the presence of magnetite‐enriched zones (up to 20 modal%), and reveal that they are ovoid in shape, up to 10 m in size, and along strike from each other in the central gabbro‐diorite layer. Geological and geochemical surveys and mineralogical studies indicate that these zones host smaller zones of disseminated chalcopyrite + pyrite, some of which, in turn, host platinum‐group minerals (PGM) and are enriched in PGE and related metals (whole‐rock [Formula: see text], Ag = 1300 ppb, Cu = 0.3%, V = 0.1%, Ni = 0.05%, Ti = 2.5%, and Fe = 25%). The coincidence of the high‐positive magnetic anomalies with the location of PGE mineralization, points to ground‐based magnetometer surveys as a valuable exploration tool for magnetite‐associated PGE ore deposits. The distribution of the residual magnetic field anomalies indicate that such surveys are especially useful in: (1) identifying rock types and mapping their distribution in areas of limited outcrop exposure; (2) locating magnetite‐enriched gabbroic rock bodies, even in close proximity to serpentinized olivine cumulate rocks; and (3) delineating the detailed geometry of magnetite‐enriched rocks that may carry significant amounts of PGE and PGMs. Exploration strategies should be designed to use ground‐based geophysical surveys, in conjunction with geological and geochemical surveys, to locate and delineate the geometry of magnetite‐enriched zones within thick, differentiated mafic‐ultramafic volcanic flows and plutonic bodies.

New data on platinum group elements in sulfide deposits of the Southern Urals

2015 ◽  
Vol 464 (1) ◽  
pp. 898-902 ◽  
Author(s):  
S. G. Kovalev ◽  
V. N. Puchkov ◽  
D. N. Salikhov
Keyword(s):  
Southern Urals ◽  
Platinum Group Elements ◽  
The Southern Urals ◽  
Sulfide Deposits ◽  
Platinum Group

Redox-controlled chalcophile element geochemistry of the Polaris Alaskan-type mafic-ultramafic complex, British Columbia, Canada

2021 ◽  
Vol 59 (6) ◽  
pp. 1627-1660
Author(s):  
Dejan Milidragovic ◽  
Graham T. Nixon ◽  
James S. Scoates ◽  
James A. Nott ◽  
Dylan W. Spence
Keyword(s):  
Parental Magma ◽  
Primitive Mantle ◽  
Sulfide Saturation ◽  
Element Geochemistry ◽  
Positive Dependence ◽  
The North ◽  
Economic Significance ◽  
Pge Mineralization ◽  
Fe Alloys ◽  
Platinum Group

ABSTRACT The Early Jurassic Polaris Alaskan-type intrusion in the Quesnel accreted arc terrane of the North American Cordillera is a zoned, mafic-ultramafic intrusive body that contains two main styles of magmatic mineralization of petrologic and potential economic significance: (1) chromitite-associated platinum group element (PGE) mineralization hosted by dunite (±wehrlite); and (2) sulfide-associated Cu-PGE-Au mineralization hosted by olivine (±magnetite) clinopyroxenite, hornblendite, and gabbro-diorite. Dunite-hosted PGE mineralization is spatially associated with thin discontinuous layers and schlieren of chromitite and chromitiferous dunite and is characterized by marked enrichments in iridium-subgroup PGE (IPGE) relative to palladium-subgroup PGE (PPGE). Discrete grains of platinum group minerals (PGM) are exceedingly rare, and the bulk of the PGE are inferred to reside in solid solution within chromite±olivine. The absence of Pt-Fe alloys in dunite of the Polaris intrusion is atypical, as Pt-enrichment of dunite-hosted chromitite is widely regarded as a characteristic feature of Alaskan-type intrusions. This discrepancy appears to be consistent with the strong positive dependence of Pt solubility on the oxidation state of sulfide-undersaturated magmas. Through comparison with experimentally determined PGE solubilities, we infer that the earliest (highest temperature) olivine-chromite cumulates of the Polaris intrusion crystallized from a strongly oxidized ultramafic parental magma with an estimated log f(O2) &gt; FMQ+2. Parental magmas with oxygen fugacities more typical of volcanic arc settings [log f(O2) ∼ FMQ to ∼ FMQ+2] are, in turn, considered more favorable for co-precipitation of Pt-Fe alloys with olivine and chromite. More evolved clinopyroxene- and hornblende-rich cumulates of the Polaris intrusion contain low abundances of disseminated magmatic sulfides, consisting of pyrrhotite and chalcopyrite with minor pentlandite, pyrite, and rare bornite (≤12 wt.% total sulfides), which occur interstitially or as polyphase inclusions in silicates and oxides. The sulfide-bearing rocks are characterized by strong primitive mantle-normalized depletions in IPGE and enrichments in Cu-PPGE-Au, patterns that resemble those of other Alaskan-type intrusions and primitive arc lavas. The absolute abundances and sulfur-normalized whole-rock concentrations (Ci/S, serving as proxy for sulfide metal tenor) of chalcophile elements, including Cu/S, in sulfide-bearing rocks are highest in olivine clinopyroxenite. Sulfide saturation in the relatively evolved magmas of the Polaris intrusion, and Alaskan-type intrusions in general, appears to be intimately tied to the appearance of magnetite. Fractional crystallization of magnetite during the formation of olivine clinopyroxenite at Polaris resulted in reduction of the residual magma to log f(O2) ≤ FMQ+2, leading to segregation of an immiscible sulfide melt with high Cu/Fe and Cu/S, and high PGE and Au tenors. Continued fractionation resulted in sulfide melts that were progressively more depleted in precious and base chalcophile metals. The two styles of PGE mineralization in the Polaris Alaskan-type intrusion are interpreted to reflect the evolution of strongly oxidized, hydrous ultramafic parental magma(s) through intrinsic magmatic fractionation processes that potentially promote sulfide saturation in the absence of wallrock assimilation.

scholarly journals Placer platinum-group minerals in the Shetland ophiolite complex derived from anomalously enriched podiform chromitites

2018 ◽  
Vol 82 (3) ◽  
pp. 491-514
Author(s):  
Hazel M. Prichard ◽  
Saioa Suárez ◽  
Peter C. Fisher ◽  
Robert D. Knight ◽  
John S. Watson
Keyword(s):  
Cold Climate ◽  
Source Rocks ◽  
Ophiolite Complex ◽  
Cu Alloy ◽  
Platinum Group Minerals ◽  
Small Streams ◽  
Podiform Chromitites ◽  
Fe Alloys ◽  
Platinum Group

ABSTRACTHighly anomalous platinum-group element (PGE) concentrations in the podiform chromitites at the Cliff and Harold's Grave localities in the Shetland ophiolite complex have been well documented previously. The focus of this study is alluvial platinum-group minerals (PGM) located in small streams that drain from the PGE-rich chromitites. The placer PGM assemblage at Cliff is dominated by Pt-arsenides (64%) and Pd-antimonides (17%), with less irarsite–hollingworthite (11%) and minor Pd-sulfides, Pt–Pd–Cu and Pt–Fe alloys and laurite. Gold also occurs with the PGM. Alluvial PGM have average sizes of 20 µm × 60 µm, with sperrylite the largest grain identified at 110 µm in diameter, matching the range reported for the primary PGM in the source rocks. The placer assemblage contains more Pt-bearing and less Pd-bearing PGM compared with the rocks. The more resistant sperrylite and irarsite–hollingworthite grains which are often euhedral become more rounded further downstream whereas the less resistant Pd-antimonides which are commonly subhedral may become striated and etched. Less stable phases such as Pt- and Pd-oxides and other Ni-Cu-bearing phases located in the rocks (i.e. Ru-pentlandite, PtCu, Pd–Cu alloy) are absent in the placer assemblage. Also the scarce PGM (PdHg, Rh- and Ir-Sb) and Os in the rocks are absent. At Harold's Grave only three alluvial PGM (laurite, Ir, Os) and Au were recovered reflecting the limited release of IPGM from chromite grains in the rocks. In this cold climate with high rainfall, where erosion dominates over weathering, the PGM appear to have been derived directly from the erosion of the adjacent PGE-rich source rocks and there is little evidence of in situ growth of any newly formed PGM. Only the presence of dendritic pure Au and Pd-, Cu-bearing Au covers on the surface of primary minerals may indicate some local reprecipitation of these metals in the surficial conditions.

scholarly journals Platinum-Group Minerals of Pt-Placer Deposits Associated with the Svetloborsky Ural-Alaskan Type Massif, Middle Urals, Russia

Minerals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 77 ◽  
Author(s):  
Sergey Stepanov ◽  
Roman Palamarchuk ◽  
Aleksandr Kozlov ◽  
Dmitry Khanin ◽  
Dmitry Varlamov ◽  
...  
Keyword(s):  
Morphological Features ◽  
Middle Urals ◽  
Transport Distance ◽  
Mechanical Attrition ◽  
Platinum Group Minerals ◽  
Placer Deposits ◽  
Fe Alloys ◽  
Platinum Group ◽  
Ore Zones

The alteration of platinum group minerals (PGM) of eluval, proximal, and distal placers associated with the Ural-Alaskan type clinopyroxenite-dunite massifs were studied. The Isovsko-Turinskaya placer system is unique regarding its size, and was chosen as research object as it is PGM-bearing for more than 70 km from its lode source, the Ural-Alaskan type Svetloborsky massif, Middle Urals. Lode chromite-platinum ore zones located in the Southern part of the dunite “core” of the Svetloborsky massif are considered as the PGM lode source. For the studies, PGM concentrates were prepared from the heavy concentrates which were sampled at different distances from the lode source. Eluvial placers are situated directly above the ore zones, and the PGM transport distance does not exceed 10 m. Travyanistyi proximal placer is considered as an example of alluvial ravine placer with the PGM transport distance from 0.5 to 2.5 km. The Glubokinskoe distal placer located in the vicinity of the Is settlement are chosen as the object with the longest PGM transport distance (30–35 km from the lode source). Pt-Fe alloys, and in particular, isoferroplatinum prevail in the lode ores and placers with different PGM transport distance. In some cases, isoferroplatinum is substituted by tetraferroplatinum and tulameenite in the grain marginal parts. Os-Ir-(Ru) alloys, erlichmanite, laurite, kashinite, bowieite, and Ir-Rh thiospinels are found as inclusions in Pt-Fe minerals. As a result of the study, it was found that the greatest contribution to the formation of the placer objects is made by the erosion of chromite-platinum mineralized zones in dunites. At a distance of more than 10 km, the degree of PGM mechanical attrition becomes significant, and the morphological features, characteristic of lode platinum, are practically not preserved. One of the signs of the significant PGM transport distance in the placers is the absence of rims composed of the tetraferroplatinum group minerals around primary Pt-Fez alloys. The sie of the nuggets decreases with the increasing transport distance. The composition of isoferroplatinum from the placers and lode chromite-platinum ore zones are geochemically similar.

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