Demetrios G. Eliopoulos

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.

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 minerals and tetraauricupride in ophiolitic rocks of Skyros island, Greece

SummaryIn the serpentinizedophiolitic rocks from Skyros island, two distinct assemblages of base metal sulphides (BMS) and platinum-group minerals (PGM) occur. The first (early) generation is associated with chromitites which are enriched in platinum-group elements (PGE). The highest values were recorded in samples from Achladones (Ru 1210, Ir 780, Os 630, Rh 228, Pt 208, Pd 22; all values in ppb). Mineral inclusions in chromite consist of Ni-Fe sulphides and Os-rich laurite, and crystallized at high sulphur fugacity (fS2) during chromite formation. The second (late) generation is closely associated with Au-rich, PGE-poor magnetite ores which host a complex assemblage of inclusions consisting mainly of graphite, Cu-Fe- and pure Cu sulphides, sperrylite and tetraauricupride. Their accompanying hydrous silicates are Cl-bearing. It is assumed that this mineral assemblage was deposited by hydrothermal processes during serpentinization.ZusammenfassungIn den serpentinisierten Ophiolithen der Insel Skyros wurden zwei unterschiedliche Bildungsgenerationen von Sulfiden (BMS) und Platinmineralen (PGM) festgestellt. Die erste (frühere) Generation ist an Chromitite gebunden, die hohe Gehalte an Elementen der Platingruppe (PGE) aufweisen. Die höchsten PGE-Kontzentrationen wurden in den Proben der Lokalität Achladones gefunden (Ru 1210, Ir 780, Os 630, Rh 228, Pt 208, Pd 22; alle Gehalte in ppb). Die Einschlüsse in Chromit bestehen aus Ni-Fe Sulfiden und Os-reichem Laurit. Diese Minerale kristallisierten bei hoher Schwefelfugazität (fS2) während der Bildung der Chromite. Die zweite (spätere) Generation ist eng assoziiert mit Au-reichen und PGE-armen Magnetiten. Sie führen eine komplexe Einschluß-Paragenese bestehend aus Graphit, Cu-Fe- und reinen Cu Sulfiden sowie Sperrylith und Tetraauricuprid. Die begleitenden Hydrosilikate sind Cl-haltig. Die Bildung dieser Mineralparagenese wird durch hydrothermale Prozesse während der Serpentinisierung erklärt.

Mineralogical and geochemical characteristics of the Skouries porphyry-Cu-Au-Pd-Pt deposit (Greece): Evidence for the precious metal

SEM/EDS studies on drill core samples from the deeper parts of the Skouries deposit showed frequent association of magnetite and Cu-minerals (bornite and chalcopyrite) with inclusions of thorite, U-bearing thorite, hydroxyl-apatite and rare earth element (REE)-enriched silicates of the epidote-group (allanite), zircon and rutile, linked to pervasive potassic and propylitic alteration type, in the central parts of the deposit. Isotopic and fluid inclusion trends in the Skouries porphyry Cu deposit seem to be systematic, beginning with high δ18O and low δD values for fluids in equilibrium with vein quartz representative of the main stage of Cu, Au, Pd, Pt mineralization, to low δ18O and high δD values for fluids linked with the pyrite-chalcopyrite mineralization.

Factors controlling palladium and gold contents in the Aksug porphyry Cu-Mo deposit (Russia)

Two stages of economic copper mineralization can be distinguished in the Aksug porphyry Cu-Mo deposit. The first stage, consisting mainly of pyrite and chalcopyrite is accompanied by abundant rutile and monazite. The second stage, consisting mainly of chalcopyrite, is associated with the telluride PdTe2 (merenskyite), electrum (18 wt% Ag) and monazite. Mineralogical, geochemical and textural data indicate that precious metals are closely associated with zones of propylitic alteration, vein-type chalcopyrite and a strongly evolved mineralized system.