|
|
|
| DUCTILE SHEAR ZONE AND GOLD METALLIZATION IN THE SAHENTUOHAI-DASHANKOU METALLOGENIC BELT,SOUTHERN TIANSHAN,CHINA |
| MENG Xiang-jin1, YE Jin-hua1, WANG Li-ben2 |
1. Yichang Institute of Geology and Mineral Resources, Yichang 443003, China;
2. Institute of Mineral Deposits, Chinese Academy of Geological Science, Beijing 100037, China |
|
|
|
|
Abstract The Dashankou and Sahentuohai ductile shear zones,in which gold deposits occur,present the characteristic of ductile and brittle deformation The ductile shear zones are strongly schistosed belts with several kinds of foliation well developed The grain size of rocks and minerals reduces,and the fabrics change in the ductile shear zones There are many kinds of mesoscopic structures in the shear zones such as rotated boudinage,kink band,asymmetic fold,fractures,tectonic lens and shear-crack,which provide space for auriferous fluid precipitation The geometric characters of the structure in the shear zone decide the shape and orientation of orebodies within it Auriferous mylonite with disseminated ore is formed at high temperatures in the stage of plastic deformation Gold-bearing quartz network is formed during the transformation from ductile to brittle deformation In the brittle deformation stage,gold orebodies are mainly in quartz veins The homogenization temperatures of quartz fluid inclusions in all kinds of ores in the shear zones show that the temperatures at which auriferous mylonite and quartz vein formed are continous and that the gold metellogenis is a continuum from the stage of mylonite to that of quartz vein The mineralization is infiltration-metasomatism in the earlier stage and infilling in latter There are obvious changes in compositions of the rocks from the wallrock to the strongly deformed rock in the shear zones The contents of FeO,MgO,SiO2,Fe2O3,SO3,Au,As,Cu,Sb,Bi and Ag increase but that of CaO decreases form the margin to the core of the shear zones The components that increase strongly in auriferous mylonite are MgO,SO3,SiO2,FeO and Fe2O3 The changes of compositions in the rocks within the shear zones indicate that the shear deformation results in a deal of moving fluid The mineral assemblage becomes simple in strong deformation belt as quartz-sericite-ferrodolomite(calcite) The main mineral alteration in the rocks are silicification,sericitation and ferrodolomitization(calcitization) The occurance of quartz-pyrite-bearing mylonite is due to the moving in of FeO,SiO2,Fe2O3 and SO3 to strong deformation belt The silicon-rich solution containing amount of metallogenic elements such as Cu,As,Au,Sb,Bi and Ag becomes mineralization fluid The SiO2 precipitation is accompanied by the separating out of gold from the fluid during the shear zone developing The shear-crack,fracture and other brittle structures become ore-controlling structure Mylonite and shear deformation in splitting,pressolution and plastic deforming play an important role in the activation,movement and enrichment of gold The ductile shear deformation and demetamorphism is an important mechanism for the formation of auriferous fluid The gold deposits in Dashankou-Sahentuohai metellogenic province have a close relation to the ductile-brittle shear zones spatially,temporally and genetically.
|
|
Received: 12 July 1999
|
|
|
|
|
|
|
|
|
2000, Vol. 9 
