Textural, trace element, and sulfur isotope analyses of pyrite from the Yindongpo deposit, East Qinling Orogen: Implications for gold mineralization

The Yindongpo deposit is a large-scale gold deposit with complicate mineralization types in East Qinling Orogen, triggering the debate on its ore genesis. Here we conduct textural, in situ trace elements and sulfur isotope analyses of pyrite to elucidate the genesis of gold mineralization in the Yindongpo deposit. Three types of pyrite were identified according to their occurrences in different hydrothermal veins. Py-I mainly formed in the host rock, parallel to the foliation of the schist, occurring as crystal nodules with blurred boundary. Py-II principally occur in the quartz-pyrite veins crosscutting the stratum. It is characterized by the pervasive occurrence of sulfide and silicate inclusions, which suggest phase separation (fluid boiling) took place during its formation. Py-III commonly precipitate within quartz-dolomite-pyrite veins crosscutting or overprinting former quartz-pyrite veins, commonly associated with coarse-grained sulfides and native gold/electrum. All pyrite types exhibit a superimposed history. The Co, Ni, As characteristics and delta 34S data show that from Py-I, through Py-II, to Py-III, the portion of magmatic-hydrothermal fluid is increasing. Gold is tightly associated with base metal sulfides (galena, sphalerite, chalcopyrite), filling the voids, cracks, or margins of Py-I, Py-II, and Py-III. The trace element bounded in the lattice of base metal sulfides include: (1) Cd for sphalerite, (2) Ag, Sb for galena, (3) Ag for tetrahedrite. Combined with previous studies, we conclude that the magmatic-hydrothermal activities at Early Cretaceous formed the major gold mineralization in the Yindongpo deposit.