A preliminary study of modes of occurrence of gold in the Miaolong Au-Sb deposit of Sandu area, Guizhou Province

Abstract: In this paper electron microprobe analyzer (EMPA) and scanning electron microscopy were used (SEM) to investigate the content, distribution and concentrations of Au, As, S, Fe and Sb in the gold-bearing minerals of different ore-forming stages in the Miaolong Carlin-type gold-antimony deposit. Arsenian pyrite and arsenopyrite are recognized as the most important gold-bearing minerals in this deposit. The values of sulfur and iron in pyrite formed at the sedimentary rock-forming stage are close to their theoretical values, whereas the sulfur values of the pyrite formed at the early metallogenic stage and the core of annulus pyrite at the S1 sub-stage of the main metallogenic stage are close to the theoretical value where the iron content of core of annulus pyrite is characterized by weak losses. The values of sulfur and iron in the outer rings of annulus pyrite are characterized by weak depletion. The pyrite of the sedimentary rock-forming stage is framboidal and contains no arsenic or antimony. The content of gold is low, with an average of 59×10-6. The coarse-grained pyrite (≥100 μm) formed at the early hydrothermal rock-forming stage is low in As and Au, with their values being 0.205% and 0.00275% on average. The outer ring of the zonal fine-grained pyrite (<50 μm, mainly about 10-20 μm) formed at the S1 sub-stage of the main hydrothermal ore-forming period is rich in As and Au. The values of As are 0.1961% - 7.897% with an average of 1.4668% and the values of Au are 40×10-6-905×10-6 with an average of 429×10-6. The arsenopyrite formed at the S2 sub-stage is characterized by enrichment of sulfur and depletion of arsenic. The values of Au are 230×10-6 -1400×10-6 with an average of 643×10-6, and the values of Sb are 0.019%-0.50% with an average of 0.087%. The values of Au in stibnite formed at the late stage is low, with an average of 237×10-6. The values of Au from sedimentary rock-forming stage→early ore-forming stage→main ore-forming stage→late ore-forming vary in order of low or none→low→high→low. Au exists as isomorph (solid solution) in arsenopyrite and pyrite.