Cu-Fe Bearing Zinc Sulfide from Laloki Stratabound Massive Sulfide Deposit, Papua New Guinea: Chemical Characterization

摘要

A strange, unidentified, Cu-Fe bearing zinc sulfide occurs in the Laloki massive sulfide deposit, Papua New Guinea. The mineral is optically uniform in texture but is chemically variable and zoned even within a single grain. Copper contents very from 0.1 up to 8.85 wt percent. Iron reaches 18.31 wt percent at maximum and decreases as Cu increases. It is remarkable, however, that the total Fe+Cu remains essentially unchanged between roughly 18 and 20 wt percent. Zn and S are least variable, giving 45.85-47.84 wt percent and 33.48-34.58 wt percent, respectively. Other trace elements such as Cd and Mn are in general less than 0.2 wt percent. It is strongly suggested that the mineral in question constitutes a unique Fe-Cu substitutional solid solution series belonging essentially to the Zn-Fe-Cu-S system.The ideal chemical formula of the solid solution series can well be presented as Zn_10(Fe, Cu)_5S_15 or Zn_2(Fe, Cu)S_3, where Fe is always greater than Cu. It is intriguing that chalcopyrite blebs are recognizable restrictively only in nearby portions of the Cu-rich end member with the ideal composition close to Zn_10Fe_3Cu_2S_15. It has been confirmed by vacuumsealed heating experiments that this mineral is decomposed to produce chalcopyrite and Fe-bearing normal sphalerite at temperatures below 200 deg C. This would provide another evidence for the existence of such distinct phase as suggested here.