Abstract:
This paper is the result of mineral exploration engineering.
Objective To determine the occurrence of Au and elements feature of the sulfide.
Methods The Sawayaerdun orogenic gold deposit (explored Au: 127 t, prospective Au: 350 t) in the western Tianshan is chosen and the microscopic petrography study, EMPA, LA-ICP-MS and FESEM analysis have been applied.
Results Except for "visible gold", the result indicate that "invisible gold" is likely present as solid soluation (Au+) in the pyrite and arsenopyrite in the Sawayaerdun deposit. Three generations of auriferous pyrite have been recognized. The pyrite with framboidal texture (Py0) are disseminated in the host rock, and are locally enriched in gold. They have relatively high values of Ag、As、Bi、Ni、Cu、Pb、Sb. The anhedral pyrite (Py1), associated with silicified rocks and quartz veins that experienced strong deformation, have an average Au content of 0.050%. They have high contents of Co、Mn、Zn. The euhedral-subhedral pyrite (Py2) are best developed in the main orebodies, and have an average Au content of 0.052%. Comparing to Py1, Py2, they have lower contents of trace elements.
Conclusions The Py0 are interpreted to have formed contemporaneously with the ore-bearing rocks. Py1 are interpreted to have formed in the syn-tectonic stage, during the collision between the Tarim craton and the Central Tianshan terrane in the Late Carboniferous, whereas Py2 were formed in a later mineralization event, during the late- to post-tectonic stage in the Early Permian. Ore-bearing strata could be the initial source bed of gold, meantime provides the trace elements when forming gold-bearing sulfides. The ore-forming fluids were probably metamorphic fluids deriving from dehydration of the sedimentary strata. The study results suggest that multi-stage of gold mineralization have developed in the Sawayaerdun deposit, similar metallogenic process may exist in other homogeneous deposits in the Western Tianshan Orogen.
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