Platinum-group Element Occurrences Research Articles

The effect of platinum-group minerals on differentiation of platinum-group elements in magmatic sulfide deposits: Evidence from the Cu-Ni-PGE deposits in the Yangliuping area of the Emeishan large igneous province, SW China

Platinum-group minerals (PGM) are important host phases for platinum-group elements (PGE) in magmatic sulfide deposits. Recent studies have demonstrated that some PGM, such as sperrylite, can crystallize early from sulfide liquids. It is important to determine whether and how these PGM particles affect the enrichment and differentiation of PGE in Cu-Ni-PGE deposits. The magmatic sulfide deposits in the Yangliuping area (mainly consisting of the Yangliuping deposit and Zhengziyanwo deposit) are the largest Cu-Ni-PGE deposits in the Emeishan large igneous province, SW China. Primitive-mantle normalized PGE patterns and fractional crystallization modelling show that massive ores in the Yangliuping deposit are enriched in Pd and Pt. In contrast, massive ores, breccia ores and Cu-rich ores in the Zhengziyanwo deposit are depleted in Pt. Scanning electron microscopy (SEM), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), focused ion beam (FIB) and transmission electron microscopy (TEM) were used to constrain the occurrence of PGE in the massive ores from the two deposits. Mass balance calculation shows that <7% of Ir, Rh and Pt occur in base metal sulfides (BMS, mainly pyrrhotite, pentlandite and chalcopyrite) as solid solution in both the Yangliuping and Zhengziyanwo massive ores. 17% and 91% Pd are present in solid solution within BMS in the Yangliuping and Zhengziyanwo massive ores, respectively. In the Yangliuping massive ores, PtAs2 and Pd-PGM particles were commonly found within BMS crystals, and Ir-Rh-(Pt) sulfarsenides enclosed in cobaltite-gersdorffite solid solution (CGSS) are enriched in Pt. In contrast, in the Zhengziyanwo massive ores, no PtAs2 particles and fewer Pd-PGM particles were found, and Ir-Rh-(Pt)AsS particles enclosed in CGSS are poor in Pt. The distribution, mineralogy and microstructures of Ir-Rh-(Pt)AsS, PtAs2 and Pd-PGM particles in both the Yangliuping and Zhengziyanwo deposits suggest that they mainly crystallized from sulfide liquids or formed from Pd-Pt-semimetal-rich droplets. We suggest that the incorporation of Pd-PGM and PtAs2 particles into MSS cumulates led to the enrichment of Pd and Pt in the Yangliuping massive ores. In the Zhengziyanwo deposit, early fractional crystallization of PtAs2 reduced the Pt content in sulfide liquids and resulted in the formation of Pt-depleted sulfide ores and low-Pt Ir-Rh-(Pt)AsS particles, but no Pt-rich sulfide ores have been found to date. As a result, the role of PGM particles should be considered when using PGE to trace the formation process of Cu-Ni-PGE deposits. This study also provides additional evidence that the behavior of Pt in sulfide liquids is influenced by thermodynamic conditions and As, and suggests a potential for Pt-rich sulfide ores exploration in the Zhengziyanwo deposit.

Geophysical mapping of the occurrence of platinum group elements in the main sulphide zone of the Great Dyke in Zimbabwe

This work sought to establish the geophysical signature of platinum group elements in a mineralized sulphide host rock. It has been established that complex resistivity of rocks depends on frequency. The variation of resistivity magnitude and phase for the samples were taken for frequencies in the range 10−2 to 102 Hz. In the first part, the mathematical relationship between resistivity amplitude and phase with frequency was obtained based on the Cole-Cole model equation. A MATLAB Code based on the direct inversion of the apparent resistivity spectrum was used to extract the “Cole-Cole” parameters. In the second part an experimental procedure to obtain the data was designed and a discussion of the results obtained was made. Overally, the results confirm the model to be a good candidate for use in mapping the occurrence of platinum group elements in sulphide zones. Its frequency dependency parameter c is the critical anomaly detection parameter. Several efforts to solve this problem by other geophysical methods failed to yield the desired or useable results. The reason was the complex and inverse nature of the problem. The practical method chosen from a host of geophysical methods was complex resistivity measurements based on the “Cole-Cole model”. The knowledge gap being bridged in this study involves the use of this method to detect the base of the main sulphide zone.

The Ferguson Lake deposit: an example of Ni–Cu–Co–PGE mineralization emplaced in a back-arc basin setting?

The world’s largest Ni–Cu–Platinum group element (PGE) deposits are dominantly hosted by ultramafic rocks within continental extensional settings (e.g., Raglan, Voisey’s Bay), resulting in a focus on exploration in similar geodynamic settings. Consequently, the economic potential of other extensional tectonic environments, such as ocean ridges and back-arc basins, may be underestimated. In the northeastern portion of the ca. 2.7 Ga Yathkyed greenstone belt of the Chesterfield block (western Churchill Province, Canada), the Ni–Cu–Co–PGE Ferguson Lake deposit is hosted by &gt;2.6 Ga hornblenditic to gabbroic rocks of the Ferguson Lake Igneous Complex (FLIC), which is metamorphosed up to amphibolitic facies. The FLIC has a basaltic composition (Mg# = 31–72), flat to slightly negatively sloped normalized trace element patterns (La/YbPM= 0.7–3.5), and negative Zr, Ti, and Nb anomalies. The FLIC rocks are geochemically similar to the 2.7 Ga back-arc basin tholeiitic basalts from the adjacent Yathkyed and MacQuoid greenstone belts (Mg# = 30–67; La/YbPM= 0.3–3.0), but the Ferguson Lake intrusions appear to be more crustally contaminated. We interpret the FLIC to have formed in an equivalent back-arc basin setting. This geodynamic setting is rare for the formation of Ni–Cu–PGE occurrences, and only few examples of this tectonic environment (or variations of it, e.g., rifted back-arc) are found in other Proterozoic and Archean sequences (e.g., Lorraine deposit, Quebec). We suggest that back-arc basin-derived mafic rocks within the Yathkyed and other Neoarchean greenstone belts of the Chesterfield block (MacQuoid and Angikuni) could represent important targets for future mineral exploration.

Advances in trace platinum group elements speciation and preconcentration of chelate resins in seawater.

The content and occurrence of platinum group elements have a close relation with their biogeochemical behavior and ecological risk in seawater. However, the determination of the PGE content and morphology in seawater is difficult. The characterization of chelating resins for specific elements and specific ligand structures provides a potential for breakthrough in this problem. This review reported the major speciation of PGEs in seawater, discussed the adsorbing mechanism of resin, and compared the adsorption capacity of different types of chelate resin. Finally, some conclusions were drawn. First, the inorganic complexes of PGEs in seawater were mainly composed of [MCl3OH2-]/[MCl42-](M=Pt,Pd) and M(OH)33-n(n=3-6) (M=Rh); Second, chelate resins had certain recognition for different complex morphology of PGEs; Third, nitrogen-sulfur chelate resin was the ideal resin for studying PGEs in seawater under practical conditions.

New mineralogical and isotopic constraints on Main Zone-hosted PGE mineralisation at Moorddrift, northern Bushveld Complex

The northern limb of the Bushveld Complex, South Africa contains a number of occurrences of platinum-group element (PGE) mineralisation within Main Zone rocks, whereas the rest of the complex has PGE-depleted Main Zone units. On the farm Moorddrift, Cu–Ni–PGE sulphide mineralisation is hosted within the Upper Main Zone in a layered package of gabbronorites, mottled anorthosites and thin pyroxenites. Our observations indicate that a 10-m-thick, ‘reef-style’ package of mineralisation has been extensively ‘disturbed’, forming a mega breccia which in some localities may distribute mineralised rocks over intersections of over 300 m. The sulphides are made up of pyrrhotite, pentlandite and chalcopyrite, heavily altered around their margins and overprinted by secondary pyrite. Platinum-group mineral assemblages typical of primary magmatic deposits, with Pt and Pd tellurides and sperrylite, are present in the ‘reef-style’ package, whereas there is a decrease in tellurides and an increase in antimonides in the ‘disturbed’ package, interpreted to be related to hydrothermal recrystallization during veining and brecciation. Sulphur isotopes show that all sulphides within the mineralised package on Moorddrift have a crustal signature consistent with local country rock sediments of the Transvaal Supergroup. We interpret the mineralisation at Moorddrift as a primary sulphide reef, likely produced as a result of the mixing of crustally contaminated magmas in the Upper Main Zone, which has been locally disrupted post-crystallisation. At present, there are no firm links between Moorddrift and the other known PGE occurrences in the Main Zone at the Aurora and Waterberg projects, although the stratigraphic position of all may be similar and thus intriguing. Nonetheless, they do demonstrate that the Main Zone of the northern limb of the Bushveld Complex, unlike the eastern and western limbs, can be considered a fertile unit for potential PGE mineralisation.

PGE-Rich Ni-Cu Sulfide Mineralization in the Flin Flon Greenstone Belt, Manitoba, Canada: Implications for Hydrothermal Remobilization of Platinum Group Elements in Basic-Ultrabasic Sequences

The Flin Flon greenstone belt is best known for its world-class volcanogenic massive sulfide deposits. However, the recent discovery of the McBratney platinum group element (PGE)-Au occurrence and other PGE occurrences has drawn attention to the potential for Ni-Cu-PGE (Au) deposits in this belt. The McBratney occurrence contains some of the highest PGE and Au grades found in this type of deposit in North America (up to 207 g/t Pd, 34 g/t Pt, 2.6 g/t Rh, and 75 g/t Au). It is hosted in chlorite-actinolite and chlorite schists of the Bear Lake magmatic unit in the Bear Lake block of the Flin Flon greenstone belt. The metamorphosed host rocks are komatiitic and tholeiitic in composition. The mineralization is hydrothermal and postdates the regional, retrograde metamorphic event. It occurs as sulfide-rich veins and surrounding disseminated zones controlled by faults, as well as isolated disseminated zones within chlorite-actinolite and chlorite schists. Platinum group minerals (PGM) and gold are spatially and temporally associated with pyrrhotite, chalcopyrite, carbonate, second generation chlorite, chamosite and, locally, stilpnomelane. In the disseminated zones, these phases replace the metamorphic actinolite-chlorite assemblage in both types of host rocks. Locally the veins are layered with pyrrhotite-rich zones and chalcopyrite-rich zones. The PGM include, in order of abundance, Te-rich sudburyite, borovskite, sperrylite, sudburyite, an unknown Pd-Te-Sb mineral, temagamite, and merenskyite, which occur mainly as inclusions in the sulfides. Minor amounts of PGE also occur within chlorite, carbonate, and stilpnomelane, and Au-Ag alloy is observed locally included in Fe sulfides in association with sphalerite. The mantle-normalized metal distribution shows that the McBratney mineralization is enriched in Bi, As, Au, Pd, Cu, Pt, Rh, Os, Ru, Zn, Re, and Ag; the mineralization is both enriched and depleted in Ir and Cr, and it is depleted in Ni in all analyzed samples when compared with typical komatiitic magmatic ore. The mineral assemblage suggests that the hydrothermal fluids were reduced (pyrrhotite-pyrite stable), neutral to alkaline, and CO 2 bearing (carbonate-chlorite stable). Chlorite geothemometry indicates that the hydrothermal assemblage formed at temperatures ranging from 250° to 350°C. Under these conditions, PGE may have been transported mainly as bisulfide complexes and their precipitation likely occurred due to reactions of the hydrothermal fluids with the Fe-rich host rocks, which led to the formation of Fe sulfides, reduction of the activity of the bisulfide, and formation of PGM. Palladium precipitated mainly as tellurides and antimonides; however, Pt formed an arsenide. The abundant As, Te, and Sb may have been crucial in forming high-grade PGE ore. Sulfur isotope data indicate that magmatic rocks or fluids were likely the sources of sulfur, which may include the metamorphosed basic-ultrabasic sequence, hidden magmatic Ni-Cu sulfide mineralization, or fluids derived directly from postmetamorphic magmatic rocks.

Concentrations and modes of occurrence of platinum group elements in the Shengli River oil shale, northern Tibet, China

The Shengli River–Changshe Mountain oil shale zone, located in the North Qiangtang depression, northern Tibet plateau, represents a potentially large marine oil shale resource in China. Twenty-one samples including oil shale, micritic limestone and marl were collected from the Shengli River area to determine the contents, distribution patterns and modes of occurrence of platinum group elements (PGEs) in marine oil shale. Oil shale samples from the Shengli River area have high ash yield (61.86–67.48%) and total organic carbon content (8.02–13.67%) with low total sulfur content (0.76–1.39%) and intermediate shale oil content (3.60–16.30%). The total PGE content in oil shale samples is very low (average 1.749 ng/g), approximately half the mean value of Chinese coals, but higher than that of USA coals. PGEs in oil shale samples from the Shengli River area are characterized by high Pd (average 0.82 ng/g), Os (average 0.15 ng/g) and Pt (average 0.66 ng/g) contents compared with Ru (average 0.05 ng/g), Rh (average 0.05 ng/g) and Ir (average 0.02 ng/g). Distribution patterns of individual PGEs are not uniform in the Shengli River oil shale section. The lower marl layer is characterized by the highest Ru and Rh concentrations, whereas the upper marl layer is characterized by the highest Os and Ir concentrations. The highest Pt and Pd concentrations are found in the lower and upper parts of oil shale seams, respectively. The individual PGEs in the oil shale samples from the Shengli River area exhibit various modes of occurrence. Ru is mainly present in P-bearing minerals and partly associated with the clay and Ca-bearing minerals. Rh is mainly controlled by clay minerals and partly present in the form of apatite. Os occurs mainly in clay minerals and, to a lesser extent, in pyrite and apatite. Pd and Ir are mainly associated with Ca-bearing minerals and apatite. Pt is mainly present in Ca-bearing minerals and partly related to organic matter and apatite.

Base metal (BM) and platinum-group elements (PGE) mineralogy and geochemistry of the elmaslar chromite deposit (Denizli, sw turkey): implications for a local BM and PGE enrichment

The Elmaslar Chromite Deposit (ECD) in Denizli (SW Turkey) consists of chromitite enveloped by highly refractory replacive dunite within a depleted harzburgite. The composition of chromian spinel is Cr-rich suggesting derivation from boninitic melt-peridotite interaction beneath a supra-subduction zone. The chondrite normalized PGE patterns show predominance of Ir-group (IPGE) over Pd-group PGE (PPGE) that is consistent with ophiolitic podiform chromitites in general. The primary PGM paragenesis of ECD mainly consists of laurite-erlichmanite series with minor Pd bearing phases. Dominance of Osrich laurite over the Os-poor ones suggests initially high fS2 during crystallization of chromitite. It also indicates a slow cooling rate of the chromitite parent melt. Coexistence of irarsite with erlichmanite suggests increase in As activity during late stages of chromitite crystallization. One peculiar contact zone sample with disseminated-massive chromitite enveloped by dunite shows unusually high PPGE content and positive-sloped chondrite normalized PGE pattern. This enrichment is attributed to a two stage process: (i) primary and local sulfur saturation, (ii) followed by secondary hydrothermal alteration causing smallscale remobilization and precipitation of PGE. No mode of occurrence is suggested for the primary and local sulfur saturation stage, because there is no direct field evidence on the geological setting of the sample. However, it is clear that the effects of this event were limited and not deposit wide. The secondary enrichment of PGE is mainly attributed to introduction of fluids during serpentinization. The amphibole-pyroxene-spinel-silica-carbonate rocks found in the stockpiles of ECD are remarkable. The role of these rocks, in the secondary PGE enrichment in ECD stays to be questioned. They mark further low-temperature CO2-metasomatism in ECD and provide promising indicators for investigating secondary PGE occurrences in chromitites.

Platinum-group elements in alpine-type ultramafic rocks and related chromite ores of the main ophiolite belt of the Urals

On the basis of a representative collection of ultramafic rocks and chromite ores and a series of technological samples from the largest (Central and Western) deposits in the Rai-Iz massif of the Polar Urals and the Almaz-Zhemchuzhina and Poiskovy deposits in the Kempirsai massif of the southern Urals, the distribution and speciation of platinum-group elements (PGE) in various type sections of mafic-ultramafic massifs of the Main ophiolite belt of the Urals have been studied. Spectral-chemical and spectrophotometric analyses were carried out to estimate PGE in 700 samples of ultramafic rocks and chromite ores; 400 analyses of minerals from rocks, ores, and concentrates and 100 analyses of PGE minerals (PGM) in chromite ores and concentrates were performed using an electron microprobe. Near-chondritic and nonchondritic PGE patterns in chromitebearing sections have been identified. PGE mineralization has been established to occur in chromite ore from all parts of the mafic-ultramafic massifs in the Main ophiolite belt of the Urals. The PGE deposits and occurrences discovered therein are attributed to four types (Kraka, Kempirsai, Nurali-Upper Neiva, and Shandasha), which are different in mode of geological occurrence, geochemical specialization, and placer-forming capability. Fluid-bearing minerals of the pargasite-edenite series have been identified for the first time in the matrix of chromite ore of the Kempirsai massif (the Almaz-Zhemchuzhina deposit) and Voikar-Syn’ya massif (the Kershor deposit). The PGE grade in various types of chromite ore ranges from 0.1–0.2 to 1–2 g/t or higher. According to technological sampling, the average PGE grade in the largest deposits of the southeastern ore field of the Kempirsai massif is 0.5–0.7 g/t. Due to the occurrence of most PGE as PGM 10–100 mm in size and the proved feasibility of their recovery into nickel alloys, chromites of the Kempirsai massif can be considered a complex ore with elevated and locally high Os, Ir, and Ru contents. The Nurali-Upper Neiva type of ore is characterized by small-sized primary deposits, which nevertheless are the main source of large Os-Ir placers in the Miass and Nev’yansk districts of the southern and central Urals, respectively.

Probabilistic neural networks applied to mineral potential mapping for platinum group elements in the Serra Leste region, Carajás Mineral Province, Brazil

This work presents an application of probabilistic neural networks to map the potential for platinum group elements (PGE) mineralization sites in the northeast portion of the Carajás Mineral Province (CMP), Brazilian Amazon. Geological and geophysical gamma-spectrometric and magnetic data were used to generate evidential maps to derive input feature vectors. Feature vectors representing known mineralized locations were used as training data. The networks were created based on the training dataset and the evidential maps were classified in terms of probabilities using these networks. We have produced mineral potential models that depict classes with high, moderate and low favorability for Au-PGE mineralization sites and a model with high and low favorability classes for Cr-PGE mineralization sites. The cut-off values for each class were selected as the inflexion points of the curves of favorability against cumulative percentage of the study area. These curves were also used to check for the efficiency of the models by plotting the favorability values at the training sites. Leave-one-out tests were applied to validate the models and the overall accuracy is 87.5%. For Au-PGE mineralization sites, the high favorability areas accounts for 0.57% of the study area and are comprised mainly within meta-pelites and meta-siltites. For Cr-PGE mineralization sites, the high favorability areas are much more restrict and accounts for only 0.17% of the study area, being associated chiefly with mafic and ultramafic rocks. These mineral potential maps can be used as reconnaissance guides for future detailed ground surveys of possible new PGE occurrences, which is of critical importance to shorten exploration time and costs in such densely forested Amazonian terrains.

Cartografia do potencial de Au-Pd-Pt e EGP-Cr-Ni na região de Serra Leste (Carajás) utilizando-se a técnica ACP e classificadores hiperespectrais

This work comprises a study about the favorability for occurrence of Platinum Group Elements (PGE) deposits in the Serra Leste region, Carajas Mineral Province (CMP). This region is characterized by adverse atmospheric conditions and difficulties of access due to presently dense equatorial forest cover. Considering these natural characteristics, high density and resolution airborne geophysical data were utilized in case studies associated to two types of PGE mineralizations: (i) the Serra Leste deposit – a particular case of Au-Pd-Pt hosted by metasediments; and (ii) the Luanga deposit - a classical occurrence of PGE-Cr-Ni hosted by mafic-ultramafic rocks. Maps of the amplitude of the analytic signal, individual K, eTh, eU, channels, total count and radioelement ratios (eU/eTh, eK/eTh), were generated. These interpretative products enabled the discrimination of the Serra Leste and Luanga deposits by means of the analysis of its magnetic and radiometric signatures. On the basis of the geophysical signatures and descriptive models of these two deposits, Principal Component Analysis (PCA), Spectral Angle Mapper and Mixture Tuned Matched Filtering techniques were applied to the geophysical database, seeking the mapping of areas with similar characteristics to these two deposits. The results showed the utility of these classification techniques (first developed for processing of multispectral and hyperspectral data) for extended use on airborne geophysical data, permitting the mapping of targets more favorable to host PGE deposits, which are of geological, metalogenetic and economic interests in the study area. Although the present testing proved quite promising and advantageous against other techniques, care must be taken to apply such approcahes to geophysical data, an issue also discussed as a topic of this study.

Cartografia do potencial de Au-Pd-Pt e EGP-Cr-Ni na região de Serra Leste (Carajás) utilizando-se a técnica ACP e classificadores hiperespectrais

This work comprises a study about the favorability for occurrence of Platinum Group Elements (PGE) deposits in the Serra Leste region, Carajás Mineral Province (CMP). This region is characterized by adverse atmospheric conditions and difficulties of access due to presently dense equatorial forest cover. Considering these natural characteristics, high density and resolution airborne geophysical data were utilized in case studies associated to two types of PGE mineralizations: (i) the Serra Leste deposit - a particular case of Au-Pd-Pt hosted by metasediments; and (ii) the Luanga deposit - a classical occurrence of PGE-Cr-Ni hosted by maficultramafic rocks. Maps of the amplitude of the analytic signal, individual K, eTh, eU, channels, total count and radioelement ratios (eU/eTh, eK/eTh), were generated. These interpretative products enabled the discrimination of the Serra Leste and Luanga deposits by means of the analysis of its magnetic and radiometric signatures. On the basis of the geophysical signatures and descriptive models of these two deposits, Principal Component Analysis (PCA), Spectral Angle Mapper and Mixture Tuned Matched Filtering techniques were applied to the geophysical database, seeking the mapping of areas with similar characteristics to these two deposits. The results showed the utility of these classification techniques (first developed for processing of multispectral and hyperspectral data) for extended use on airborne geophysical data, permitting the mapping of targets more favorable to host PGE deposits, which are of geological, metalogenetic and economic interests in the study area. Although the present testing proved quite promising and advantageous against other techniques, care must be taken to apply such approcahes to geophysical data, an issue also discussed as a topic of this study

LOW-DENSITY REGIONAL GEOCHEMICAL MAPPING OF GOLD AND PALLADIUM HIGHLIGHTING THE EXPLORATION POTENTIAL OF NORTHERNMOST EUROPE

The <2-mm fraction of 605 samples of the C-horizon of podzols collected from an area of 188,000 km2 in the European Arctic was analyzed for Au and Pd by a method using reductive coprecipitation to enrich Au and platinum group elements (PGE) prior to analysis. Due to the low detection limits (0.1 ppb Au, 0.2 ppb Pd) only 2 percent of all samples returned values below the detection limit for Au, and 10 percent were below the detection limit for Pd. The resulting geochemical maps show clear regional distribution patterns, notwithstanding the very low sample density of 1 site per 300 km2. All known Au and PGE occurrences are associated with geochemical anomalies and several new targets for exploration were identified. Low-density geochemical mapping of Au and Pd with low detection limits in C-horizon soils can thus be used as a relatively inexpensive tool to define prospective areas within large regions.

Platinum-Group Element and Re-Os Isotope Variations of the High-Grade Kilvenjarvi Platinum-Group Element Deposit, Portimo Layered Igneous Complex, Finland

The Kilvenjarvi deposit is a high-grade platinum-group element (PGE) deposit located in the basement below the Portimo Layered Igneous Complex, Finnish Lapland. It consists of a stockwork of massive Cu-Fe-Ni sulfide veins, up to a meter wide, which cut metamorphic banded gneiss, amphibolite, and granite. The veins are surrounded by intense sulfide disseminations that are accompanied by an alteration of the basement mineral assemblage to chlorite, calcite, orthoamphibole, monazite, and an unidentified hydrous ferroaluminous silicate. The veins locally carry in excess of 110 ppm PGE, and neighboring rocks in the basement that contain disseminated sulfides locally carry 25 ppm PGE. The PGE are hosted primarily by michenerite (PdBiTe) and sobolevskite (Pd[Bi,Te]), with only very few grains of merenskyite, sperrylite, vysotskite-braggite, paolovite, cooperite, and isomertieite. The massive sulfide veins host two distinct mineral assemblages that reflect an event of sulfur addition. The primary assemblage of chalcopyrite, pentlandite, and pyrrhotite is similar to that of common orthomagmatic sulfides and appears to represent the crystallization product from a sulfide melt. However, the primary minerals have been replaced extensively by a low-temperature secondary assemblage of chalcopyrite, pyrite, marcasite, Ni-bearing pyrite, violarite, and millerite. The disseminated sulfides in the basement lithologic units comprise only the secondary assemblage and are notably richer in chalcopyrite than the massive sulfide veins. The sulfides are associated with chlorite and calcite, indicating that they were likely introduced by carbon-rich (CO 2 or CH 4 ) hydrothermal fluids. The Kilvenjarvi deposit is extremely fractionated in PGE compared to unmineralized rocks and PGE occurrences within the Portimo Complex. Os and Ir concentrations are very low, and Pd/Ir ratios reach 2.5 × 10 5 . The massive and disseminated sulfides can be distinguished by their slightly different PGE patterns. Most notably, the massive sulfides are richest in Pd, and the disseminated sulfides are richest in Pt and Au. This fractionation appears to be consistent with an initial concentration in a magmatic sulfide melt followed by hydrothermal redistribution. The Re-Os isotopes have been significantly affected by Re mobility and cannot be used for dating. However, platinum-group mineral separates from the Kilvenjarvi deposit have nearly uniform isotopic compositions ( 187 Os/ 188 Os = 0.18–0.20) that are invariably higher than rocks from the Portimo Complex. Thus, it is evident that the Kilvenjarvi deposit had a significantly higher crustal contribution (possibly accounting for up to 18% of the Os) than parental magmas for the Layered series of the Portimo Complex. Contamination and fractional sulfide crystallization within the Portimo Marginal series may have been responsible for this isotopic signature. The deposit has some similarities to the various offsets associated with the Sudbury structure, Canada. A primary magmatic origin of the sulfides and PGE is evident from the mineralogy, geochemistry, and isotope geochemistry. However, the deposit has been subjected to extensive hydrothermal alteration involving carbon-rich fluids and resulting in a partial redistribution of the sulfides, PGE, and Re, extensive recrystallization, and a partial resetting of the Re-Os isotope system.

Platinum-group element occurrences in Britain: magmatic, hydrothermal and supergene

In-situ platinum-group element-bearing mineralization of magmatic, hydrothermal and near-surface origin occurs widely in Britain. In addition, grains of platinum-group minerals and other phases that contain platinum-group elements (PGE) have been found in overburden and stream sediments without any identified bedrock source.The Caledonian mafic-ultramafic intrusions of northeast Scotland have been a major target of investigations by the British Geological Survey. Magmatic copper-nickel sulphide deposits, with up to 500 ppb Pt + Pd, have been identified in the Knock intrusion and at Arthrath, near Ellon, in contaminated and xenolithic gabbroic rocks. A magmatic origin, subsequently modified by hydrothermal reworking at high temperatures in shear zones, is proposed for the mineralization in these areas. PGE enrichments, up to 280 ppb Pt + Pd, also occur in clinopyroxene-bearing ultramafic rocks in deformed mafic-ultramafic intrusions along a major shear zone in the upper Deveron valley near Huntly.At Loch Borralan, on the northwestern margin of the Scottish Caledonides, PGE mineralization, up to 878 ppb Pt + Pd, occurs over a 2-km strike length. Two phases of mineralization are evident: a late magmatic phase comprising base-metal sulphides and rare PGE sulphides; and a later, low-temperature phase with PGE tellurides and antimonides associated with shearing, brittle fracturing and veining. A hydrothermal origin that involved the introduction of As and Sb and the redistribution of early formed sulphides is proposed for this mineralization.High PGE concentrations occur at several stratigraphic levels in the Unst ophiolite, Shetland. Pt and Pd both exceed 100 ppm close to the basal thrust of the ophiolite in a zone of talc-carbonate alteration. Lowergrade Pt-Pd-dominant mineralization has also been reported in the cumulate sequence of the complex. Elsewhere on Unst PGE mineralization more typical of ophiolites, dominated by Os, Ir and Ru, occurs in association with chromitites.Recent studies have identified platinum-group minerals (PGM) in layered ultramafic rocks in the Tertiary igneous centres on Rum, Mull and Skye in northwest Scotland. In each case abundant and diverse PGM assemblages have been recorded and a combined orthomagmatic-hydromagmatic origin has been proposed.In several parts of Britain a gold-PGE association has been identified at the boundary between Permian red-bed basins and underlying reduced strata. Complex Au-Pt-Pd grains and discrete PGM are widespread in drainage sediments and overburden derived from the Lower Devonian and Permo-Triassic rocks in the South Hams area and the Crediton Trough in Devon, and the Mauchline and Thornhill basins in southern Scotland. The genesis of the precious-metal grains is attributed to metal transportation in saline, oxidizing fluids with deposition along faults and in favourable host rocks due to mixing with reduced rocks or fluids.

Unconventional PGE occurrences and PGE mineralization in the Great Dyke: metallogenic and economic aspects

Platinum group elements (PGE) are strategic materials because 96–99% of the world production is derived from just five mining districts and because they cannot be replaced as catalysts in many chemical processes. In order to lessen the strategic character of PGE, both conventional deposits and unconventional PGE mineralizations were investigated in an attempt to locate viable deposits which would diversify the supplier base. In the Great Dyke, conventional PGE mineralization occurs in the form of pristine sulfide ores mined underground and oxidic surface ores. New observations such as bimodal distributions of the PGE in the Main Sulfide Zone (MSZ), elevated Pt/Pd ratios in the oxidized MSZ compared to the sulfidic part and distinct differences between the platinum group mineral (PGM) assemblages of the MSZ and stream sediments of adjacent rivers emphasize the fact that even though the Great Dyke seems to be the second or third largest PGE occurrence in the world, the complicated PGE distributions and supergene redistributions should be kept in mind during planning and mine operation. Investigations of unconventional PGE occurrences in ophiolites, Alaskan-type intrusions, porphyry copper deposits and in the Kupferschiefer show that economically exploitable PGE concentrations can be expected in a broader variety of host rocks than considered favourable in the past. In the Albanian Mirdita ophiolite average contents of 860 ppb Pt and 60 ppb Pd were detected. Flotation concentrates of porphyry copper deposits, for example from Mamut, Malaysia, Santo Tomas, Philippines, Elacite, Bulgaria, and Ok Tedi, Papua New Guinea, contain between 827 and 1860 ppb Pd + Pt. In selected profiles of the Polish Kupferschiefer average contents of 255 ppb Pt, 94 ppb Pd, 2.4 ppm Au and 13.0 ppm Ag were analysed. The distribution of the PGE resources in the world and the annual production rates, however, underline the fact that the chances for a significant change in the supplier base are relatively low. The Bushveld Complex will remain the largest producer, followed by Noril'sk-Talnakh, Sudbury and Stillwater. If the operations in the Great Dyke reach their planned capacities, the Great Dyke will rank in third place among the PGE-producing deposits in the world.

Occurrence of noble metals in aluminum‐ and chromium‐ rich objects in ordinary chondrites and of baddeleyite (ZrO2) in a chromite inclusion

Abstract— Platinum group elements (PGE) enrichments are found in Fe‐Ni blebs (&lt;1 μm) in Al‐ and Cr‐rich objects in the ordinary chondrites Ste. Marguerite, Forest Vale, Montferré. In Ste. Marguerite, high ZrO2 concentrations (baddeleyite) are also present in a chromite inclusion. Iridium enrichment in this material compared to its metal content is confirmed by INAA. The widespread occurrence of PGE in Al‐ and Cr‐rich objects, mostly present in H‐group chondrites of nearly equilibrated types, must be taken into account to understand their conditions of formation.

An overview of the PGE concentrations in the Shetland ophiolite complex

Abstract Extremely anomalous platinum-group element (PGE) concentrations are known at one site, Cliff, in the Shetland ophiolite complex. Systematic PGE analysis of all the mafic and ultramafic igneous and alteration lithologies in the ophiolite has revealed many lower grade anomalous PGE occurrences throughout the cumulate ultramafic sequence and their distribution is described here. More sites with PGE enrichments as anomalous as those at Cliff have not been found. At Cliff the anomalous values of over 60 ppm Pt + Pd are restricted to a chromite-rich sulphide-bearing dunite forming a small part of a 200 m dunite lens in mantle harzburgite close to the basal thrust of the ophiolite. Lower values of up to 6.4 ppm Pt + Pd occur in chromite-poor, sulphide-rich dunites also within this dunite lens. The only other chromite-rich dunite lens in the Cliff area also has detected Pt and Pd but with low Pt + Pd values of 200 ppb. In contrast, harzburgites, metasediments underlying the basal thrust, serpentinites from the basal thrust and internal faults are all barren of Pt and Pd (detection limit = 20 ppb). In the Cliff area, therefore, detected PGE values are restricted to magmatic chromite-rich dunite lenses. PGE analyses of drill core from beneath the disused chromite quarries at Cliff are low (227 ppb Pt + Pd) indicating that the extremely anomalous PGE values are very restricted. This supports the idea that PGE, concentrated magmatically within the dunite lens at Cliff, may have been remobilized locally to produce extremely anomalous PGE values in an alteration zone only a few metres in diameter. Elsewhere in the ophiolite, anomalous Pt + Pd values of up to 4 ppm occur in chromite-rich, sulphide-bearing dunite within the dunite unit, which stratigraphically overlies the harzburgite. Pt + Pd concentrations of up to 1 ppm are present in the pyroxenites and wehrlites of the upper part of the ultramafic sequences. High-level wehrlites and pyroxenites within the gabbro unit, representing late ultramafic differentiates, contain lower levels of PGE of up to 310 ppb Pt + Pd. The gabbros all have less than 20 ppb Pt and Pd. This distribution indicates that the PGE concentrations occur in specific primary magmatic lithologies and pathfinder analysis shows that they are associated with Ni, Cu, Au and Cr. PGE have not been found above detection limits in fault zones away from primary PGE mineralization sites and it is concluded that PGE are not significantly hydrothermally reconcentrated. At Cliff, remobilization may have occurred over short distances of only a few metres at most.

The Lac des Iles Complex, Ontario: petrology and platinum-group-elements mineralization in an Archean mafic intrusion

The Lac des Iles Complex is a late Archean, mafic to ultramafic complex that is host to 20.4 × 106 t Pt, Pd, and Au mineralization with an average grade of 6.34 g/t platinum-group elements (PGE). The 30 km2 complex, located in the Wabigoon Subprovince, consists of several coalescing mafic to ultramafic intrusive centers. The complex is emplaced into early gneissic tonalite and is contemporaneous with late granitoids.The magmatic evolution of the complex reflects the emplacement of multiple pulses of previously fractionated magma, some of which underwent subsequent in situ fractionation. Distinct magma sequences are recognized on the basis of intrusive relationships, differences in the cumulus minerals, crystallization order, and trace-element chemistry. These sequences are (1) hornblende gabbro, (2) gabbro and gabbronorite, and (3) ultramafic. Where there is evidence of intrusive relations, the most primitive sequences are emplaced late and occur toward the north end of the complex. Microprobe analyses indicate the following compositional ranges of mineral phases within the complex: olivine–Fo84–76, orthopyroxene—En82–67Fs15–30Wo2–3, and clinopyroxene—En53–46Fs3–12Wo41–51. Cyclic layering is developed only in the northern ultramafic part of the complex where several cycles of mesocumulate- to adcumulate-textured wehrlite, clinopyroxenite, and websterite are identified.Although the parental magma compositions are not well constrained, model calculations using major-element and rare-earth-element (REE) contents of cumulus phases and adcumulate rocks indicate that the parental magmas had mol MgO/(MgO + FeO) ranging from at least 0.61 to 0.54 and had fractionated REE abundances with CeN/YbN of approximately 5.0. Mineral chemistry and crystallization sequences indicate that the ultramafic and gabbroic parts of the complex had tholeiitic basalt parental magmas of picritic and high-alumina affinities, respectively.The major PGE mineralization at Lac des Iles occurs in the Roby Zone along the interface between the gabbro and gabbronorite in the southern part of the complex. This interface has been intruded by a sheet of pyroxene cumulate, which is probably part of the ultramafic sequence. The PGE sulphide mineralization in the Roby Zone is associated with disseminated chalcopyrite, pyrrhotite, pentlandite, pyrite, and altered silicates in (1) the pyroxene cumulate sheet, (2) the mixed gabbro–gabbronorite, and (3) the gabbroic pegmatite dikes and breccia zones. Cl-rich apatite and monazite are accessory phases associated with PGE mineralization PGE occurrences are also present within sulphide-bearing orthopyroxene–clinopyroxene cumulates in the northern ultramafic part of the complex. The Roby Zone mineralization is localized by mixing the PGE and sulphide-rich gabbronorite and pyroxene cumulates with the volatile-rich gabbro. The PGE are redistributed by late magmatic volatile activity, which generated mineralized gabbroic pegmatites and breccia zones.