Comparative study on metallogeny of the mesozonal Mingsai and epizonal Mazhala gold deposits,southern Tibet:Constraints from geology,in-situ trace element,and sulfur isotope analysis of sulfides
Tethyan Himalaya is a famous Cenozoic gold metallogenic province formed by continental collision in southern Tibet.However,gold deposits are distributed sporadically,and systematic comparison of alteration,fluid composition,and mineralization process between those deposits at different tectonic levels(like mesozonal and epizonal ones)are absent.In this study,detailed comparisons between the hydrothermal alteration,sulfide textures,in-situ trace elements,and sulfur isotope compositions of the Mingsai Au deposit with the Mazhala Au-Sb deposit in the eastern part of Tethyan Himalaya to probe the mineralization process,ore-forming fluid composition,and controls on the genesis.Both deposits occur in Jurassic slate and tuff interlayer.Among them,the weakly altered slates comprise disseminated pyrite-ankerite-sericite-quartz along the bedding,while the tuff interlays are characterized by intense alterations of replacing feldspar,biotite,and other minerals with ankerite-chlorite-sericite and developing a large amount of euhedral to subhedral pyrite and arsenopyrite.Slate-host pyrites(Pysa in Mingsai and Pysb in Mazhala)with a homogeneous texture have low contents of Au(averaged at 0.33 × 10-6)and other trace elements,and a broad range of δ34S value(Pysa:8.12‰～15.6‰;Pysb:-24.3‰～3.36‰),which is consistent with the δ34 S value of regional Jurassic strata.Meanwhile,pyrites within the tuff interlayer of the Mingsai deposit(Pyva)have a concentric ring texture with highest Au(averaged at 14.3 × 10-6)and As,while pyrites within the tuff interlayer of the Mazhala deposit(Pyvb)have an irregular core-rim texture and high contents of Au(averaged at 3.8 × 10-6),Cu,Pb,and Sb.The tuff-host pyrites have similar δ34S values with the arsenopyrites(averaged at 2.7‰of Pyva and 2.4‰ of arsenopyrite in Mingsai;3.2‰ both for Pyvb and arsenopyrite in Mazhala),which is comparable with the δ34S value of pyrite in other orogenic gold deposits in southern Tibet.The significant variance of sulfur isotope composition in the slate-host barren pyrites,in the two deposits mentioned above,may be the result of ore-fluids reacting with the wall-rock that contains different sedimentary pyrite.However,the tuff-host auriferous pyrites have similar δ34S values with arsenopyrites can be attributed to the homogeneous fluid-rock interaction of congenetic fluids and the same surrounding rocks.As a preliminary conclusion,this research proposed that widespread tuff interlayers could be the preferential lithology for orogenic gold mineralization in southern Tibet.Orogenic gold deposits at different tectonic levels have an analogous source.The diversity of the mineralization system is controlled by different fluid-rock interaction processes.
万方数据
维普
