陆相砂岩型铜矿床矿物组合分带的logf_(O_2)-logf_(S_2)相图——以楚雄盆地大姚铜矿床为例

Application of Thermodynamics logf_(O_2)-logf_(S_2) to Mineral Assemblade Model of Sandstone-Hosted Type Copper Deposits in the Chuxiong Basin,Central Yunnan

楚雄盆地是扬子地块西南缘著名的砂岩型铜矿集区,其中,大姚六苴铜矿床是其典型代表。从紫色砂岩向浅色砂岩,金属矿物组合依次呈现赤铁矿→辉铜矿→辉铜矿+斑铜矿→斑铜矿+黄铜矿→黄铁矿的水平分带。以矿物分带中的金属矿物组合为主要研究对象,结合流体包裹体测试成果,构建和绘制了大姚铜矿床主要成矿温度下的logf_o_2-logf_S_2,相图,理论计算结果与宏观、微观地质特征吻合。依据logf_o_2-logf_s_2相图,而且进一步阐述了主要金属矿物组合沉淀的logf_o_2-logf_s_2条件与分带机理,认为楚雄盆地砂岩铜矿床金属矿物组合及其分带受logf_o_2-logf_s_2控制;温度下降,矿物沉淀所需的logf_o_2,logf_s_2值也随之下降;辉铜矿(Cu_2S)形成所需的logf_o_2-logf_s_2范围较宽,即流体运移过程中易沉淀出辉铜矿。研究为该类矿床成矿机制的研究提供了重要依据。

Sandstone-hosted copper deposits of Chuxiong basin in the southwest of Yangzi Block,is China's famous sandstone type copper ore concentration area.Among them,Liuju copper deposits in Dayao is a typical representative.From purple sandstone to light-colored sandstone,the metallic minerals assemablde present a horizontal zoning in turn from hematite,chalcocite,chalcocite +bornite,bornite +chalcopyrite to pyrite.Metallic minerals assemablde in the mineral zoning are the main object of the study,and together with the test results of fluid inclusion,the logf_O_2-logf_S_2 phase diagram of Dayao copper deposit under ore-forming temperature has been built and drawn.The results of theoretic calculation are consistent with the macro-geological and micro-geological characteristics.Based on the logf_O_2-logf_S_2 diagram,the precipitation conditions and zoning mechanism of major metallic minerals assemablde are elaborated.It is believed that metallic mineral zonage of the sandstone copper deposit in Chuxiong Basin is under the dual control of logf_O_2 and logf_S_2.The decline of the logf_O_2 and logf_S_2 is according with the temperature reduction,chalcocite(Cu_2S) can stay stable in a wider range.In other words,this condition makes it easier to formate the chalcocite(Cu_2S)in the process of the fluid migration.The study has provided an important basis for the ore forming mechanism of such mineral deposits.