Oscillatory Zoned Gersdorffite and the Ni-Bi-Au Association at Clemence Mine and Km 3 Locality, Lavrion District, Greece

Vein-type Pb-Ni-Bi-Au-Ag mineralization at Clemence mine in Kamariza and the Km 3 locality in the Lavrion area was synchronous with the intrusion of a Miocene granodiorite body and related felsic and mafic dykes and sills within marbles and schists that constitute the footwall of the Western Cycladic Detachment System. The Ni-Bi-Au association at Clemence mine consists of initial deposition of pyrite and arsenopyrite followed by an intergrowth of native gold-bismuthinite and oscillatory zoned gersdorffite. Oscillatory zoning in gersdorffite is related to variable As, Ni and Fe contents, indicating fluctuation of arsenic and sulfur fugacity in the hydrothermal fluid. A late evolution towards higher sulfur fugacity in the mineralization is evident by the deposition of chalcopyrite, tennantite, enargite and galena rimming gersdorffite. At the Km 3 locality, the observed Ni sulfides and sulfarsenides, vaesite, millerite, ullmannite and polydymite, are enclosed in gersdorffite and/or galena. The gersdorffite is homogenous and contain less Fe (up to 2 wt %) than that from the Clemence mine (up to 9 wt %). Bulk analyses for Clemence ore reveal Au and Ag grades exceeding both 100 g/t, Pb and Zn > 1 wt %, Ni up to 9700 ppm, Co up to 118 ppm, Sn > 100 ppm and Bi > 2000 ppm. The Km 3 mineralization is enriched in Mo (up to 36 ppm), Ni (>1 wt %) and Co (up to 1290 ppm). Despite local variations, both districts are characterized by a common fluid evolution similar to the broad Lavrion area.