Characteristics Of Gold-bearing Minerals And Its Significance In Gold-antimony Polymetallic Metallogenic Belt, Southern Tibet

Gold-antimony polymetallic metallogenic belt in southern Tibet is a hot area which attract the attention of many scholars in recent years. This paper will take the typical deposits Chalapu gold deposit, Mazhala Gold-antimony deposit and Bangbu gold deposit as the research object.Based on the field geological survey, observation on the hand specimen and The electron microscope.combined with EMPA Analysis, the paper will study the Characteristics of gold-bearing minerals and gold occurrence in the three deposits, discussing the mineralization evolution and ore deposit types.The gold occurrence in Chalapu gold deposit is domined by invisible gold which exists in pyrite and arsenopyrite. pyrites can be devided into Py1,Py2 and Py3. Py1 formed in sedimentary environment display as framboidal,colloidal.They have the highest contents of Au,showing the Au enrichment in sedimentary diagenetic stage.Py2 formed in the early stage of hydrothermal display show similar elementary composition with Py1, showing an inheritance relationship. The main hydrothermal stage Py3 accompanying with arsenopyrite are the most important gold-bearing minerals. In Pyrites formed in Py1 and Py2 Au mainly presents as nanometer-sized particles of native Au(Au0),whereas in Py3 mostly occars as Au+. The characteristic above are similar to most Carlin-type gold deposit.Visible gold and invisible gold are both adequate in Mazhala gold-antimony deposit.Visible gold often exists in stibnite and quartz vein as fracture, intergranular or package gold. The invisible gold mainly exists in pyrites. Pyrites can be devided into Py1,Py2 and Py3. Py1 formed in sedimentary environment have the adequate contents of Au, showing the Au enrichment in sedimentary diagenetic stage.Py2 accompanying with arsenopyrite have the highest contents of Au、As,showing the Au、As enrichment in early hydrothermal fluid.Part of Py2 present ruptured to Py3 due to orogeny extrusion, this process released part of the Au, As into the metamorphic fluid.Invisible Au mainly presents as nanometer-sized particles of native Au(Au0) in Py1.Both Au+ and Au0 are found in Py2. The characteristic above are similar to most orogenic gold deposit.The gold occurrence in Bangbu gold deposit is domined by visible gold which exists in Quartz vein, pyrite as fracture, intergranular or package gold. The content of invisible gold which exists in pyrite and arsenopyrite is low. pyrites can be devided into euhedral Coarse grain Py1,subhedral fine grain Py2 and euhedral fine grain aggregate Py3. Three types of pyrite did not show any obvious successively relationship. The invisible gold mainly occur in fracture core of Py1 and Py2, which mainly presents as nanometer-sized particles of native Au(Au0). The characteristic above are similar to most orogenic gold deposit.