New occurrences of watanabeite, colusite, “arsenosulvanite” and “Cu-excess” tetrahedrite-tennantite at the Pefka high-sulfidation epithermal deposit, northeastern Greece
Repstock, Alexander; Voudouris, Panagiotis; Kolitsch, Uwe
published: Apr 1, 2015
ArtNo. ESP154019202009, Price: 29.00 €
The high- to intermediate-sulfidation epithermal Cu-Au-Ag-Te deposit at Pefka in northeastern Greece reveals an extraordinary and rare polymetallic ore-mineralogy including several Cu-, Bi-, Sn-, Ge-, V-, As-, Hg-, Au- and Ag-bearing sulfides, sulfosalts, tellurides, native elements and the rare Cu-sulfosalts and chalcogeno-salts watanabeite, colusite, “arsenosuvanite” and “Cu-excess” tetrahedrite-tennantite. Paragenetic sequences suggest deposition of an earlier high-sulfidation metallic ore assemblage (e.g. enargite/luzonite, goldfieldite and native gold), followed by an intermediate-sulfidation ore assemblage (composed of tetrahedrite-tennantite and various tellurides). Watanabeite, colusite and “arsenosulvanite” are intergrown with enargite/luzonite and native copper, thus clearly belonging to the high-sulfidation stage of ore deposition at Pefka. “Cu-excess” tetrahedrite-tennantite postdates enargite/luzonite, thus suggesting deposition at the transition from high- towards intermediate-sulfidation fluid states. Of all known occurrences worldwide, the As:Sb ratio of the Pefka watanabeite is the closest to the type material from the Teine mine, Hokkaido. An extremely Sb-rich analog to watanabeite (with up to 1.4 apfu Sb) detected during this study at Pefka mine, seems to fill the gap within the solid solution between the As-rich member and an unnamed Sb-dominant phase. Colusite at Pefka ranges in composition from colusite sensu stricto to stibiocolusite. In comparison to colusite, “arsenosulvanite” is Sn-free or relatively Sn-poor and moderately anisotropic. The fahlore-group minerals at Pefka reveal an excess in Cu-contents of up to 11.73 and 11.03 apfu for tennantite and tetrahedrite, respectively. Thus, our results suggest that the term “Cu-excess” can be applied for the whole tetrahedrite-tennantite solid solution series. We also detected “Cu-excess” compositions for Zn-bearing, Fe-free tennantite that has not been previously reported. We suggest a continuous evolution of the Pefka hydrothermal system from initial high-temperature (> 280 °C) high-sulfidation, oxidizing conditions, towards lower-temperature and lower-sulfidation, more reduced conditions with time. This evolution is also reflected in the paragenetic sequence of the fahlore group minerals (e.g. early extreme “Cu-excess” tennantite and tetrahedrite with > 11 apfu Cu was followed by moderate to weak “Cu-excess”-, and finally by fully substituted tennantite and tetrahedrite), being the result of decreasing copper content in the hydrothermal system. The abundance of tellurides and native tellurium in the mineralization is compatible with direct deposition of metals from the vapor phase of a buried porphyry body.