Ppb Pd Research Articles

Using the High Mobility of Palladium in Surface Media inExploration for Platinum Group Element Deposits: Evidence from the Lac desIles Region, Northwestern Ontario

Platinium group element (PGE) mineralization is commonly accompanied by large amounts of Ni-Fe sulfides, which are explored for using a variety of geophysical and geochemical methods. Appreciation of a new type of PGE mineralization is emerging, hosted by gabbroic rocks with low concentrations (<5 vol %) of disseminated sulfides. The host rocks commonly display textural complexity, such as brecciation, pods and veins of pegmatite, and magma mingling of different lithological units. Examples include the Lac des Iles deposit in northwestern Ontario, the East Bull Lake suite in eastern Ontario, and several intrusions in the Kola Peninsula, and northern Finland. Such mineralization does not result in prominent geophysical and geochemical anomalies, thus posing a challenge for exploration. We initiated a project to develop new geochemical exploration approaches for such PGE deposits with low sulfides and selected the Lac des Iles district, northern Ontario, Canada, which contains one producing mine and many Pd showings. Mineralization is hosted by gabbroic rocks with low concentrations (<5 vol %) of sulfides. Enriched elements include Pd, Pt, Au, Ni, Cu, and Co. In separate sulfide-rich mineralization, base metals can be abundant, up to 1 wt percent, but Pd is insignificant (<200 ppb). This reduces the relevance of Ni, Cu, and Co as possible pathfinders for sulfide-poor PGE mineralization, leaving Pd, Pt, and Au. A detailed study in the Baker zone at the Lac des Iles mine and the Legris Lake property indicates the essentially immobile nature of Pt in these surface environments. By contrast, Pd is depleted in B horizon soil, suggesting its removal during the conversion of C to B horizon soils. The loss of Pd in B horizon soil reflects the transport of Pd as neutral and anionic complexes, probably with OH ‐ and possibly with organic ligands, which are not adsorbed by Fe oxyhydroxides in the soils. Instead, Pd migrates in solution to accumulate in humus in swamps and organic-rich lake sediments downslope from mineralization. The distribution of Pd in humus, therefore, provides a distal indicator of nearby mineralization. Total digestion of humus using fire assay or aqua regia yielded up to 160 ppb Pd, whereas a variety of commercially available leaching methods extracted few ppb Pd. The results indicate that Pd is tightly held in organic matter. This behavior of Pd contrasts with many metallic elements, such as Cu and Ni, that are enriched in B horizon soil and may be extracted by a variety of leaching techniques. Palladium arsenides, tellurides, antimonides, and sulfides are unstable in weathering environments and their dissolution releases Pd to surface waters. Therefore, Pd can be used to indicate other PGE mineralization as it is always abundant among PGE. Where PGE mineralization is associated with high concentrations of Fe sulfides, their oxidation produces acidic waters, which further promotes Pd dispersion. Thus, the findings of this study are applicable to exploration for both sulfide-rich and -poor PGE mineralization.

The Concentration of the Platinum-Group Elements in South African Komatiites: Implications for Mantle Sources, Melting Regime and PGE Fractionation during Crystallization

We have analysed 18 samples of komatiite from five consecutive lava flows of the Komati Formation at Spinifex Creek, Barberton Mountain Land. Our samples include massive komatiite, various types of spinifex-textured komatiite, and flow-top breccias. The rocks have low platinum-group element (PGE) contents and Pd/Ir ratios relative to komatiites from elsewhere, at 0·45–2 ppb Os, 1–1·4 ppb Ir, <1–5 ppb Ru, 0·33–0·79 ppb Rh, 1·7–6 ppb Pt, 1·6–6·1 ppb Pd, and Pd/Ir 3·3. Pt/Pd ratios are c. 1·1. Platinum-group elements are depleted relative to Cu (Cu/Pd = 15 300). They display a tendency to increase in the less magnesian samples, suggesting that the magmas were S-undersaturated upon eruption and that all PGE were incompatible with respect to crystallizing olivine. Komatiites from the Westonaria Formation of the Ventersdorp Supergroup and the Roodekrans Complex near Johannesburg have broadly similar PGE patterns and concentrations to the Komati rocks, suggesting that the PGE contents of South African ultrabasic magmas are controlled by similar processes during partial mantle melting and low-P magmatic crystallization. Most workers believe that the Barberton komatiites formed by relatively moderate-degree batch melting of the mantle at high pressure. Based on the concentration of Zr in the Komati samples, we estimate that the degree of partial melting was between 26 and 33%. We suggest that the low PGE contents and Pd/Ir ratios of all analysed South African komatiites are the result of sulphides having been retained in the mantle source during partial melting. The difference in Pd/Ir between our samples and Al-undepleted komatiites from elsewhere further suggests that the PGE are fractionated during progressive partial melting of the mantle. Thus, our data are in agreement with other recent studies showing that the PGE are hosted by different phases in the mantle, with Pd being concentrated by interstitial Cu-rich sulphide, and the IPGE (Os, Ir, Ru) and Rh resting in monosulphide solid solution included within silicates. Pt is possibly controlled by a discrete refractory phase, as Pt/Pd ratios of most komatiites worldwide are sub-chondritic.

Geochemistry and mineralogy of Platinum-group elements in the Ransko gabbro–peridotite massif, Bohemian Massif (Czech Republic)

The Ransko gabbro–peridotite massif in Eastern Bohemia is a strongly differentiated intrusive complex of Lower Cambrian age. The complex hosts low grade Ni–Cu ores mainly developed close to the contact of olivine-rich rocks with gabbros, in troctolites and, to a much lesser extent, in both pyroxene and olivine gabbros and plagioclase-rich peridotites. The ore zone is characterized by strong serpentinization and uralitization. The total Ni + Cu locally reaches up to 4 wt%. Anomalous concentrations of platinum-group elements (PGE's) (maximum 532 ppb Pd, 182 ppb Pt, 53 ppb Rh, 15 ppb Ru, 41 ppb Ir) were detected in samples of Cu–Ni and Ni–Cu ores (maximum 2.63 wt% Ni and 2.31 wt% Cu) from the Jezirka orebody. The main ore paragenesis includes pyrrhotite, pentlandite, chalcopyrite, cubanite, pyrite, magnetite, mackinawite, valleriite, ilmenite and sphalerite. During this work, michenerite, froodite, sperrylite, gold, native bismuth, altaite, tsumoite, hessite, an unnamed Bi–Ni telluride, cobaltite–gersdorffite and galena were newly identified. The host rocks originated through partial melting of a slightly depleted mantle source with noble metals scavenged from this primitive magma prior to the development of these rocks.

Contamination-free preparation of geological samples for ultra-trace gold and platinum-group element analysis

In order to determine the most contaminant-free sample processing procedures for ultra-trace platinum-group element (PGE) and gold analysis, we have crushed and milled pure quartz in a variety of media and then performed analysis by inductively coupled plasma mass spectrometry (ICP-MS) using isotope dilution (Pt, Pd, Ru and Ir) and external calibration (Au and Rh). Initial sample desegregation was best achieved in a Mn steel jaw crusher which contributed <0.1 ppb Pt and Au, <0.05 ppb Pd and Ru, <0.01 ppb Rh and <0.006 ppb Ir. Final milling must be performed in a ceramic mill (or presumably agate, although this mill composition was not investigated). Up to 0.008 ppb Ir and 0.08 ppb Au can be contributed from the ceramic mill (α-alumina in our case), but other elements were at or below the limits of detection. Tungsten carbide appears to be a problem, both in terms of Au contribution (up to 0.19 ppb from the tungsten carbide press) and an isobaric interference of tungsten oxide on 198Pt. The latter problem can be avoided by choosing alternate Pt isotopes for spike and reference (e.g., 194Pt and 195Pt, respectively). Based on these results, we have determined that the optimum low-contaminant processing for whole rock analysis is initial crushing in the Mn steel jaw crusher followed by milling in α-alumina ceramic. This results in below detection limit blanks for Pt, Pd and Ru and a total contribution of up to 0.008 ppb Ir, 0.01 ppb Rh and up to 0.18 ppb Au. For mineral separates such as magnetite, sulphide or chromite, a combination of steel crushers and mills can be used, provided suitable acid washing is performed prior to sample dissolution and analysis.

Platinum-group elements in the Icelandic rift system: melting processes and mantle sources beneath Iceland

Thirty new platinum-group element (PGE) analyses of various basalt types from Iceland are presented in this study. The analysed samples are divided into three groups based on their Mg-contents, high-Mg tholeiites (10–14 wt.% MgO), composed of primitive olivine tholeiites and picrites, evolved olivine tholeiites (7–10 wt.% MgO) and evolved basalts (4–7 wt.% MgO) consisting of FeTi basalts, quartz tholeiites and alkaline basalts. The high-Mg tholeiites have a range of compositions between a relatively Cu-rich and Pd-poor (120 ppm Cu and 6 ppb Pd) end-member and a relatively Cu-poor and Pd-rich (74 ppm Cu and 17 ppb Pd) end-member. There is a positive correlation between the highly siderophile elements, whereas Cu and Pd correlate negatively between the Cu-rich primitive olivine tholeiite and the Cu-poor picrite end-member. Negative correlation between Cu and the PGEs cannot be reconciled in a model where the two end-members form by varying degrees of partial melting of a common source. The sub-primitive mantle Cu/Pd ratio of the picrite end-member (∼4300) could indicate a strongly depleted mantle source, where Pd was efficiently retained in mantle sulphide, relative to Cu, during previous melt extraction episodes. In mantle melting models presented here, the picrite composition can be approximated by 25% melting of a mantle source that previously lost a normal MORB component ( F∼15%). The olivine tholeiite end-member (Cu/Pd∼19000) can be approximated in mantle melting models by assuming derivation from a separate source, one slightly Cu-enriched source undergoing melting beneath a rift. Based on Cu and Pd variations, the majority of high-Mg tholeiites are interpreted to be mixtures between melts derived from highly depleted to slightly enriched sources, which is consistent with previous studies of Sr–Nd isotopic variations. The similar range in Cu/Pd ratios of the high-Mg tholeiites and the evolved olivine tholeiites could infer that the latter evolved from parental liquids similar to the high-Mg tholeiites under S-undersaturated conditions. Relatively high Pd and low Ir concentrations in the evolved olivine tholeiite samples (∼7 wt.% MgO) indicate, too, that these magmas underwent S-undersaturated fractionation during which Pd accumulated in the melt whereas Ir was incorporated into the fractionating assemblage. This is in contrast to the group of evolved basalts with less than 7 wt.% MgO with low PGE contents and high Cu/Pd ratios that strongly suggest that these samples have experienced S-saturation. We propose a scenario for melt generation beneath the Icelandic rift zone, where picritic magma is generated from a highly depleted mantle, whereas primitive olivine tholeiite magma forms from the depleted as well as a Cu-enriched source. It is proposed that Cu-enriched mantle domains were exhausted at depth since their melting products are absent in the most depleted picrite derived from the uppermost part of the central melting region. The olivine tholeiites can be approximated by around 11–12% partial melting in a triangular melting regime beneath the Icelandic rift zone. The olivine tholeiites are interpreted to reflect efficient melt collection from the deepest and most distal parts of the melting triangle. In contrast, the picrite represent a high degree of melting ( F∼25%) without incorporation of melt batches from the Cu-enriched mantle source.

Palladium soil geochemistry, Baronskoye Pd–Au prospect, Sverdlovsk oblast, Russia

A programme of B-horizon soil sampling coupled with low detection-limit, fire-assay/ICP-MS analysis for Pd, Au and Pt was carried out on the Baronskoye prospect in the Central Urals of Russia in 1999 and 2000. Of the three precious metals, Pd proved to be particularly effective in locating occurrences of very low-sulphide Pd-Au mineralization of inferred hydrothermal, shearzone type within pyroxenites and gabbros in fairly flat, thickly forested terrain. In contrast, potential pathfinder elements, such as Cu, Ni, Ag, As and Te, as determined by a separate aqua regia digestion/ ICP-MS analytical package, were found to be of little use.At a threshold of 55 ppb Pd the soil-sampling results clearly defined a northwest-trending linear anomaly over the pyroxenite. Although usually only about 20 m wide, this Main Anomaly, with a maximum value of 447 ppb Pd, can be traced along strike for 900 m and is well supported by Au at the 20-130 ppb level and by Pt in the range 10-45 ppb. An intermittently developed Eastern Split Anomaly was identified about 20 m east of the Main Anomaly, and a potentially more important Northeastern Anomaly, about 320 m × 150 m, was found 200 m to the east of the northern end of the Main Anomaly and just inside the gabbro surrounding the pyroxenite. Testing of the three soil anomalies by diamond drilling in 2000 confirmed the presence of sporadic Pd-Au mineralization in the bedrock below all of them.

THE PLATINUM-GROUP MINERALS IN THE UPPER SECTION OF THE KEIVITSANSARVI Ni Cu PGE DEPOSIT, NORTHERN FINLAND

The Keivitsansarvi deposit, in northern Finland, is a low-grade dissemination of Ni–Cu sulfides containing 1.3–26.6 g/t PGE. It occurs in the northeastern part of the 2.05 Ga Keivitsa intrusion and is hosted by olivine wehrlite and olivine websterite, metamorphosed at greenschist-facies conditions. The sulfide-mineralized area shows variable bulk S, Ni, Co, Cu, PGE, Au, As, Sb, Se, Te and Bi contents. S and Au tend to decrease irregularly from bottom to top of the deposit, whereas Ni, Ni/Co, PGE, As , Sb, Se, Te and Bi tend to increase. Thus, the upper section of the deposit has low S (<1.5 wt.%) and Au (160 ppb on average), b ut elevated levels of the PGE (2120 ppb Pt, 1855 ppb Pd on average). Sulfides consist of intergranular, highly disseminated aggregates mainly made up of pentlandite, pyrite, and chalcopyrite (all showing fine intergrowths), as well as nickeline, mauch erite and gersdorffite in some samples. Most platinum-group minerals occur as single, minute grains included in silicates (57%) or attached to the grain boundaries of sulfides (36%). Only a few PGM grains (6%) are included in sulfides. Pt minerals (mainly moncheite and sperrylite) are the most abundant PGM, whereas Pd minerals (mainly merenskyite, Pd-rich melonite, kotulskite and sobolevskite) are relatively scarce, and most contain significant amounts of Pt. Whole-rock PGE analyses show a general Pd enrichment with respect to Pt. This discrepancy results from the fact that a major part of Pd is hidden in solid solution in th e structure of gersdorffite, nickeline, maucherite and pentlandite. The mineral assemblages and textures of the upper section of the Keivitsansarvi deposit result from the combined effect of serpentinization, hydrothermal alteration and metamorphism of preexisting, low-grade disseminated Ni–Cu ore formed by the intercumulus crystallization of a small fraction of immiscible sulfide melt. Serpentinization caused Ni enrichment of sulfides and preserved the original PGE concentrations of the magmatic mineralization. Later, coeval with greenschist-facies metamorphism, PGE and some As (together with other semimetals) were leached out from other mineralized zones by hydrothermal fluids, probably transported in the form of chloride complexes, and precipitated in discrete Ni–Cu–PGE-rich horizons, as observed in the upper part of the deposit. Metamorphism also caused partia l dissolution and redistribution of the sulfide (and arsenide) aggregates, contributing to a further Ni enrichment in the sulfide ores.

A Platinum Group Element and Re–Os Isotope Investigation of Siderophile Element Recycling in Subduction Zones: Comparison of Grenada, Lesser Antilles Arc, and the Izu–Bonin Arc

Os/Os signatures (0·134–0·164), which are even more The picritic (MgO >13·5%) lavas of Grenada provide a unique radiogenic than peridotite xenoliths previously measured from mantle opportunity to evaluate the platinum group elements (PGE) and wedges modified by addition of subducted material. Crustal conOs isotope compositions of primitive subduction-generated melts. tamination appears unable to explain all of the Os isotope enrichment Compared with other arc lavas they have undergone very limited and thus elevated Os/Os may reflect the modification of the crustal contamination (> 2%) of sediment and/or slab-derived fluids enriched in range of parental melts can explain all major element variations). radiogenic Os. Despite their primitive nature, the picritic lavas contain very low concentrations of PGE (<0·2 ppb Ir, 1–4 ppb Pd) compared with other high-MgO lavas such as kimberlites, komatiites and plumerelated picrites. This is probably due to a combination of lower

Palladium, platinum and gold distribution in porphyry Cu±Mo deposits of Russia and Mongolia

The porphyry Cu–Mo deposits in the southern Siberian craton and Northern Mongolia including subduction-, collision-, and rift-related igneous series of early Paleozoic to Mesozoic age, are all characterized by varying crustal contribution to their parent magmas and the presence of explosive breccias. Precious metal and associated element contents are reported for mineralized samples, sulphide concentrates, and chalcopyrite–molybdenite flotation concentrates from porphyry Cu±Mo intrusions of Russia (Sora, Aksug and Zhireken) and Mongolia (Erdenetiun-Obo). Average PGE contents in rocks are 17 ppb Pd and 22 ppb Pt in the Aksug deposit, 13 ppb Pd and <10 ppb (detection limit) Pt in the Sora, 14 ppb Pd and 21 ppb Pt in the Erdenetuin-Obo and 18 ppb Pd and 28 ppb Pt in the Zhireken deposit. Average gold content in rocks is 61 ppb in the Aksug deposit, 17 ppb in the Sora, 21 ppb in the Erdenetuin-Obo, and 30 ppb in the Zhireken deposit. The highest average 2.3 ppm Ag was recorded in the rocks of the Sora deposit. In general, the precious metal distribution in the studied deposits has no apparent relationship with the alteration types. The molybdenum content in rocks ranges between <1 and 128 ppm Mo in the Aksug deposit, from <1 to 5400 ppm Mo in the Sora deposit, from 2 to 755 ppm Mo in the Erdenetuin-Obo deposit, and from 3 to 1530 ppm Mo in the Zhireken deposit. The average copper content in rocks is 1540 ppm in the Aksug deposit, 460 ppm in the Sora deposit, 1460 ppm in the Erdenetuin-Obo deposit, and 220 ppm in the Zhireken deposit. The Cu–Mo ratios are highest in the Aksug and Erdenetuin-Obo deposits and lowest in the Sora and Zhireken deposits. The correlation matrix for selected major and trace element data on mineralized samples and sulphide concentrates (34 samples) indicates that precious metals are associated with either chalcopyrite or molybdenite. Copper shows a strong positive correlation with Au and Pd ( r≥+0.91) while Mo shows a strong positive correlation with Pt ( r=+0.98). In addition, Mo exhibits a strong positive correlation with W ( r=+0.94). An interelement positive correlation between precious metals is 0.57 (Ag–Au). The Pd and Pt contents of both chalcopyrite and molybdenite in flotation concentrates are low, varying from 9 to 83 ppb Pd and from <10 to 110 ppb Pt. The highest values recorded are 924 ppb Pd in sulphide concentrates from the Aksug deposit, and 684 ppb Pd and 299 ppb Pt in sulphide concentrate from breccia of the Zhireken deposit. The highest gold content, 5450 ppb Au, is in chalcopyrite flotation concentrate from the Aksug deposit, whereas in the majority of concentrates the gold content is in the order of a few hundreds parts per billion. The relatively low contents and limited variation of the precious metal contents in the individual deposits of Russia and Mongolia point to the essential role of the composition of the source and composition of parent magmas.

PLATINUM-GROUP MINERAL ASSEMBLAGES AND CHROMITE COMPOSITION IN THE ALTERED AND DEFORMED BACURI COMPLEX, AMAPA, NORTHEASTERN BRAZIL

In the Bacuri complex, Amapa, Brazil, there is good evidence for Pd mobility both during serpentinization and lateritization. In non-lateritized, serpentinized samples, Pd bismuthide occurs with chalcopyrite in chlorite-filled veins that cross-cut serpentine and chromite probably only a few tens of micrometers from the source of the platinum-group elements (PGE). Low Pt/Pd values of less than one are characteristic of magmatic values, and sporadic higher values of up to 4 indicate partial removal of Pd. The highest Pt/Pd values (up to 26) occur in laterites, where Pt remains but Pd has been extensively removed. The PGE are concentrated in non-lateritized rock-types including chromitite, serpentinite containing disseminated chromite, and sulfide-bearing serpentinite. The highest whole-rock PGE concentrations are 166 ppb Pt and 609 ppb Pd. Osmium, Ir and Ru concentrations in the chromitite can be attributed to the presence of laurite and irarsite, whereas sulfide-bearing serpentinite contains sperrylite. Pd–Bi tellurides, including sobolevskite and michenerite, are the most common platinum-group minerals. They commonly occur with pentlandite and (less common) pyrrhotite, typically partially altered to millerite, magnetite, pyrite, nickeloan pyrrhotite, maucherite and gersdorffite, all of which form less than 1% of these rocks. Chromitite in folded layers 3–4 m thick has Cr/(Cr + Al) values of 69.0–84.1, Mg/(Mg + Fe2+) values of 27.6–51.4, and TiO2 values of up to 1.69%, compositions most typical of chromite from a stratiform complex of continental origin.

A Gold- and Platinum-Mineralized Layer in Gabbros of The Kap Edvard Holm Complex: Field, Petrologic, and Geochemical Relations

The Lower Layered Series a cumulates of the Kap Edvard Holm Complex contain a stratiform layer, 1 to 20 m thick and > 6 km long, that is mineralized with gold and platinum-group elements (PGEs). The Lower Layered Series a cumulates (>650 m thick) are dominated by modally layered gabbro with lesser volumes of granular anorthosite and troctolite that together form 2- to 30-m-thick layers that are most abundant above the mineralized layer. Minor volumes of poikilitic wehrlite form a few 1- to 2-m-thick layers throughout the section. Field and petrographic relations as well as cryptic variations in cumulus mineral compositions indicate that the Lower Layered Series a formed in an open system magma chamber from repeated magma injections. Within the mineralized layer, average concentrations over 3 m thickness are 250 ppb Pt, 40 ppb Pd, and 50 ppb Au, with individual samples containing up to 5 ppm Pt and 6 ppm Au. The concentrations of Ir, Os, Ru, and Rh are uniformly low (<20 ppb). Stratigraphic zoning of Pt, Pd, and Au is consistent along strike with peak Au concentrations overlying Pt and Pd peaks. Platinum minerals are primary Pt-Fe alloy, sperrylite, and moncheite, with secondary Pt sulfide overgrowths. Gold occurs as alloys with Ag and Cu. These minerals are found in contact with primary and secondary silicates and oxides and with intercumulus base metal sulfides that consist of the assemblage bornite + chalcopyrite + digenite. Deposition of the mineralized layer is associated in space and time with injections of plagioclase-saturated, primitive magma that mixed with more evolved, resident magma. These events caused efficient partitioning of Au and PGE into sulfides derived from a large volume of magma, deposition of these sulfides to form the mineralized layer, and subsequent deposition of the overlying anorthosite layers. The wehrlite layers, however, were formed by postcumulus reactions between gabbro cumulates and hydrous, intercumulus melts, probably derived from the compacting cumulus pile. Subsolidus reactions between primary minerals and meteoric hydrothermal solutions caused extensive alteration of the mineralized gabbro, oxidation and desulfurization of Cu-Fe sulfides and local recrystallization of PGE minerals.

Platinum-group elements and Os isotopic characteristics of the lower oceanic crust

We present osmium isotopic compositions and Os, Re and platinum-group element (PGE) contents in the lower oceanic crust gabbros from ODP Site 735B on the Southwest Indian Ridge. The average gabbros are very depleted in PGEs, e.g. the Os concentrations are very low and range from 0.5 to 38 ppt. One troctolite sample is an exception, containing, e.g. 376 ppt Os, 396 ppt Ir and 8 ppb Pd. Re contents are extremely heterogeneous, ranging from 128 ppt to 28 ppb. The present day 187Os/ 188Os varies from 0.140 to 0.467, and correlates with Rb/Cs, suggesting that seawater alteration affected the Os isotopic system. The average Os content in the lower oceanic crust is about 9 ppt while median value for Re is about 487 ppt. Such very high Re/Os is relatively similar to the upper MORB-type oceanic crust, indicating that recycled ocean crust basalts and gabbros will rapidly develop very radiogenic Os isotopic signatures.

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.

Palladium, platinum and gold concentration in porphyry copper systems of Greece and their genetic significance

Compilation of new and published data on precious metal and associated trace-element contents in mineralized porphyry copper intrusions of Greece indicates that the Pd content in the potassic–propylitic zone of the Skouries deposit is relatively high, ranging between 60 and 200 ppb (average 110 ppb), whereas in the porphyry copper intrusions of Gerakario and Pontokerasia, it is very low (3 ppb Pd). The oxidized zone of Fissoka (OP-65) exhibits low Pd and Cu contents, but higher Au, Te, As, Pb and Zn contents. The Pt content is much lower than Pd in the porphyry copper intrusions studied. The Pd/Pt ratio in the Skouries deposit ranges from 9 to 60, while it is much lower (<2) in the mineralized samples from Fissoka, Gerakario and Pontokerasia. A decrease of the Pd content and Pd/Pt ratio with increasing Te, As, Pb and Zn content may indicate that the Pd distribution in porphyry copper systems is effected by the evolution of the magma-hydrothermal system. Also, mineralogical and geochemical data on the Skouries deposit, coupled with textural relations between base metal sulphides, PGM and Au–Ag tellurides, indicate that the main Pd-bearing mineral, merenskyite, is associated with the vein-type chalcopyrite or bornite, and was deposited during the main stage of mineralization. The high magmatic oxidation state and the magmatic features of the hydrothermal system (limited participation of meteoric portion) in the Skouries intrusion may be a strong control of its Pd potential. Assuming that Pd is mainly associated with chalcopyrite in the porphyry copper deposits, the calculated Pd (from measured Pd) contents in chalcopyrite (average 3300 ppb Pd) are relatively high, and comparable to that in the chalcopyrite concentrate made after the processing of large composite drill-hole samples (2400 ppb Pd to 21 wt.% Cu). It is considered to be an encouraging economic factor for Pd as a by-product, probably along with Au, although the main product is Cu.

Specific Spectrophotometric Determination of Palladium with N, N'-Diphenylbenzimidoylthiourea

ABSTRACT A specific method for the spectrophotometric determination of palladium with N.N'-diphenylbenzimidoylthiourea (DPB1TU) is described. The method in new, simple, rapid and applicable over 0.3-1.0 M HC1 and free from interferences of the precious metals i.e. Ag, Au, Pt, Ir, Rh, Ru, Os. The value of molar absorptivity of the complex in the term of Pd is (2.50)x104 L mole−1 cm−1at λmax 365 nm in chloroform. The detection limit of the method at 3 σ a is 80 ppb Pd. The composition of the complex and effect of diverse ions in the determination of Pd are discussed. The application of the method has been tested for the analysis of the metal in catalytic material.

SULPHIDE MINERALOGY AND CHALCOPHILE/SIDEROPHILE ELEMENT GEOCHEMISTRY OF ABYSSAL PERIDOTITES FROM THE MARK AREA (20-24°N MID-ATLANTIC RIDGE, SOUTH OF THE KANE TRANSFORM)

SULPHIDE MINERALOGY AND CHALCOPHILE/SIDEROPHILE ELEMENT GEOCHEMISTRY OF ABYSSAL PERIDOTITES FROM THE MARK AREA (20-24°N MID-ATLANTIC RIDGE, SOUTH OF THE KANE TRANSFORM)

Geology, genesis, and metamorphic history of the Namew Lake Ni-Cu deposit, Manitoba

The Namew Lake Fe-Ni-Cu sulfide deposit, 60 km south of Flin Flon, Manitoba, is hosted by an undifferentiated metapyroxenite sill enclosed within Early Proterozoic orthogneisses and covered by Paleozoic sedimentary rocks. The Namew Lake pyroxenite contains a relict igneous mineral assemblage of olivine + orthopyroxene + clinopyroxene + or - spinel + or - sulfides, suggesting derivation from a low Mg komatiitic or high Mg basaltic magma.Sulfide ore in the Namew Lake pyroxenite occurs as 3- to 10-mm blebs of disseminated Fe-Ni-Cu sulfides that accumulated during crystallization of olivine and pyroxene. A 0.5- to 5-m-thick layer of massive sulfide at the hanging-wall contact may represent a gravitationally segregated basal layer of a sill and suggests that the mine stratigraphy is inverted. Although the massive sulfides were compositionally modified during metamorphism and supergene alteration, the disseminated sulfides exhibit coherent geochemical trends and may preserve the average composition of the sulfide melt (recalculated to 100% sulfide: ca. 36% S, 42% Fe, 16% Ni, 6.1% Cu, 0.23% Zn, 148 ppm Pb, 5,300 ppb Pd, and 88 ppb Ir). Assuming a silicate/sulfide mass ratio of ca. 560 calculated from the platinum-group element (PGE) contents, the Ni content of a parental magma that would be in equilibrium with sulfides of that composition is similar to that of typical komatiites, but the Cu, Zn, and Pb concentrations are much higher. Thus, a komatiitic magma with ordinary Ni and PGE contents may have partially assimilated volcanogenic Cu-Zn-Pb sulfides, resulting in a high Mg basaltic magma from which the silicates and sulfides subsequently crystallized and equilibrated.The Namew Lake pyroxenite and associated sulfides were affected by five phases of deformation and three phases of metamorphism. The first deformational event in the area, D 1 , involved migmatization and isoclinal folding at upper amphibolite facies conditions. In addition, sheeted tonalites and diorites intruded prior to or during D 1 . D 2 folded the gneisses into domes, synforms, and antiforms. D 3 involved minor boudinage of the pyroxenite, intrusion of dikes, and displacement of the sulfides updip. D 4 shearing locally increased the thickness of the pyroxenite. D 5 and subsequent deformations produced brittle faulting with minor displacement, open folds of the ore horizon, and large-scale domain-bounding faults.The Namew Lake pyroxenite was metamorphosed at upper amphibolite facies (M 1 ), at lower amphibolite facies (M 3 ), and at greenschist facies (M 5 ). M 1 metamorphism of the pyroxenite produced partial replacement of the host pyroxenite by pargasitic amphibole. M 3 produced successive partial replacement by talc + dolomite, tremolite, and biotite, with greatest alteration at the edges of the pyroxenite and near crosscutting dikes. M 5 produced minor serpentine and cummingtonite. Most or all elements, including rare earth elements (REE), were mobile to varying degrees during M 1 , M 3 , and M 5 , resulting in the observed compositional variability of the Namew Lake pyroxenite.

Sulfur isotope systematics and platinum group element behavior in REE-enriched metasomatic fluids: A study of mantle xenoliths from Dish Hill, California, USA

The sulfur isotopic compositions, trace and rare earth element (REE), and platinum group element (PGE) contents were determined for a suite of anhydrous spinel lherzolite xenoliths and their metasomatized equivalents from Dish Hill, California, USA, to evaluate the mobility of these elements in metasomatic fluids. Anhydrous xenoliths have REE patterns that vary from being slightly LREE-depleted to flat, as well as variable enrichments of LILE (Ba and Sr) and HFSE (Th and Nb) that indicate they were affected by cryptic metasomatism. The formation of amphibole in xenoliths (modal metasomatism) is accompanied by pronounced enrichments in HFSEs and REES, particularly LREEs. With the exception of a single xenolith with slightly elevated PGE contents, the metasomatic fluids did not produce any appreciable changes in the platinum group element (PGE) contents, suggesting these elements are relatively immobile under these mantle conditions. Typical concentrations of PGEs in xenoliths from Dish Hill are 0.8 ppb Os, 1 ppb Ir, 0.6 ppb Rh, 2.5 ppb Pt, 1.8 ppb Pd, and 1.7 ppb Au. Modal metasomatism has resulted in a variable increase in sulfur content of the xenoliths, from a value of <10 ppm for anhydrous xenoliths, to between 25 and 120 ppm for amphibole-rich xenoliths. The δ 34S values of sulfides in anhydrous xenoliths from Dish Hill are near +7, which are unusually high for the mantle and indicate that the lithospheric mantle under California was most likely affected by subduction of crustal sulfur. Sulfides in amphibole-bearing xenoliths have variable but generally lower δ 34S values of 3 to 8.7, suggesting that some portion of the metasomatic sulfur was derived from an asthenospheric mantle source with a more primordial sulfur isotopic composition.

Origin of Proterozoic metal-rich black shales from the Bohemian Massif, Czech Republic

Proterozoic metal-rich black shales (metasiltstones) in the Bohemian Massif are always closely associated with submarine mafic volcanic rocks and occur in (semi)isolated basins that formed most likely in connection with the evolution of an Upper Proterozoic intracontinental rift. The black shales are characterized by an average of 3.5 wt percent C organic , and 5.2 wt percent S and carry up to 0.42 wt percent Zn, 0.21 wt percent V, 0.12 wt percent Ni, 0.12 wt percent Cr, 0.12 wt percent Cu, 0.06 wt percent As, 0.03 wt percent Mo, 132 ppb Au, 102 ppb Pd, 25 ppb Pt, 1.7 ppb Rh, and 1.3 ppb Ru. Their thickness varies from about 1 to 45 m. Sulfide minerals often include abundant framboidal pyrite, which occurs widely in C organic -rich layers. Grainy pyrite, Zn, Ni, Cu, and Mo sulfides appear to be restricted to late quartz and carbonate veinlets. Mo selenide, Mo telluride, galena, berthierite, and gold are very rare. Sulfur isotope results suggest the dominant source of sulfur to have been seawater sulfate, reduced by bacteria under different conditions. The delta 13 C values of the organic matter (-24.2 to -37.5ppm) reflect the combination of the carbon isotope composition of dissolved HCO 3 , its high concentration, and the type of organisms. The results of Rock-Eval pyrolysis as well as laser Raman spectroscopy show a high maturity, close to that of well-crystallized graphite. Fluid inclusion and stable isotope data from quartz and carbonate veinlets of very low grade regionally metamorphosed metalrich black shales at Kamenec and highly metamorphosed facies at Hromnice indicate that they resulted from the interaction between 18 O-rich fluids, volcanics, and metasediments. The interaction could have occurred during subsea-floor or later regional metamorphism.

Platinum-group minerals in the Santo Tomas II (Philex) porphyry copper-gold deposit, Luzon Island, Philippines

Mineralized quartz diorites of the Santo Tomas II porphyry copper-gold deposit, carry high Au contents (average: 1.8 ppm) as well as 160 ppb Pd and 38 ppb Pt. Values of other platinum-group elements (PGE) and rhenium are below the analytical detection limits. There is a significant positive correlation between Au and Cu. The highest Pd values were detected in the most Au- and Cu-rich rocks. Platinum-group minerals (PGM) occur exclusively as inclusions in chalcopyrite and bornite. Potential Pd and Pt contents in sulphide concentrates are estimated at 1.5 g/t and 0.4 g/t, respectively. The precious metal assemblages consist of merenskyite (main PGM), kotulskite, moncheite, native gold, electrum, hessite and petzite. Polyphase fluid inclusions in quartz veinlets, associated with a PGM-bearing bornite-chalcopyrite-magnetite assemblage, are characterized by high salinity (35 to > 60 eq. wt% NaCl) and high trapping temperatures (between 380 and 520 °C). They may represent primary magmatic-hydrothermal fluids, which have been responsible for the transport of Pd, Pt and Au as chloride complexes.