The Ni-Bi-Au association at Kamariza and ‘km-3’, Lavrion ore district, Greece

Abstract

The Lavrion ore district, located about 50 km southeast of Athens (Greece), contains a variety of ore types including porphyry Mo-W, skarn Fe-Cu-Bi-Te, carbonate-replacement Pb-Zn-Cu-Ag±Au-Bi and vein-type Pb-As-Sb-Ag and Pb-Ni-Bi-Au (Solomos et al. 2004; Voudouris et al. 2008; Bonsall et al. 2011; Kolitsch et al. 2015). Mineralization was synchronous to the intrusion of a Miocene granodiorite body in the footwall of the Western Cycladic Detachment System and related felsic dikes and sills within marbles and schists, which locally cross-cut the detachment. Carbonate-sericite altered microgranodioritic dikes and sills at Kamariza are crosscut by porphyry-style quartz-sericite-calcite stockworks hosting pyrrhotite, pyrite, arsenopyrite, chalcopyrite and sphalerite (e.g. the same metallic minerals present in the carbonate-replacement and vein ores). The dikes and sill display enrichment in Ni (up to 220 ppm), Cu (up to 175 ppm), As (up to 510 ppm), Mo (up to 6 ppm) and Pb (up to 830 ppm), as measured by ICP-MS. The Ni-Bi-Au association at the Clemence mine in Kamariza is a vein-type mineralization developed at the contact between marbles and schists. The mineralization also expands in the marbles unit, forming carbonate-replacement bodies. It consists of native gold and bismuthinite intergrown with gersdorffite, enclosed in galena. Bulk ore analyses reveal Au and Ag grades exceeding 100 ppm, Pb and Zn > 1 wt. %, Ni up to 9700 ppm, Co up to 118 ppm, Sn > 100 ppm and Bi > 2000 ppm. New mineralogical and mineral-chemical data from the Ni-Bi-Au association suggest gold deposition with oscillatory zoned gersdorffite following initial deposition of pyrite and arsenopyrite. Oscillatory zoning in gersdorffite is related to variable As, Ni and Fe contents, indicating fluctuation of arsenic fugacity in the hydrothermal fluid. Chalcopyrite, tennantite and enargite rimming gersdorffite suggest an evolution towards higher sulfur fugacity in the mineralization with time. Stannite enclosed in pyrite and native antimony enclosed in galena are decribed here for the first time in the Clemence ore assemblage. At the ‘km-3’ locality, the Ni sulfides and sulfarsenides, vaesite, millerite, ullmannite and polydymite, are enclosed in gersdorffite and/or galena. At this location mineralization occurs in the form of calcite and galena veins crosscutting and cementing brecciated marbles, within the detachment fault. Mineralization is enriched in Mo (up to 36 ppm), As and Ni (both >1 wt. %), Co (up to 1290 ppm), whereas other elements occur in lesser amounts: Te (up to 2 ppm), Sn (up to 8.5 ppm), Bi (up to 1.3 ppm). Gersdorffite at ‘km-3’ is homogenous and contain less Fe (up to 2 wt. %) than that from the Clemence mine (up to 9 wt. %), probably related to lower temperatures of their formation. The geochemical and mineralogical data from this study support previous models for a magmatic contribution of metals to the ore system, although a remobilization from previous mineralization and/or country rocks cannot be ruled out.