南秦岭老君庙金矿床载金含砷黄铁矿矿物学研究及其地质意义OA

The Laojunmiao gold deposit,located between the Gongguan and Qingtongou super-large Hg-Sb de-posits,is a medium-size gold deposit recently discovered in the South Qinling Orogenic Belt.The gold mineral-ization mainly hosted in the clastic-carbonate rocks of the Upper Devonian Xichahe Formation.Controlled by stratigraphy and structure,the orebodies are distributed along the EW-trending structural fracture zone,and the mineralization is relatively concentrated at the intersection of faults.However,there is still a lack of systematic research on the distribution pattern of gold in minerals and the types of deposits.Based on field investigations,mineralogy observations,backscattered electron(BSE)imaging,and electron probe micro probe analysis(EP-MA),the compositions of the gold-bearing minerals and the occurrence state of Au in the Laojunmiao gold de-posit are determined,and the deposit's genesis was discussed.The results show that the mineralization process of the Laojunmiao gold deposit can be divided into three stages:sedimentary-diagenetic stage,hydrothermal miner-alization stage,and supergene oxidation stage.The gold mineralization during the hydrothermal stage is predom-inantly fine-grained disseminated type,which can be subdivided into three substages:Quartz+Arsenic-bearing pyrite stage(Ⅰ),Quartz+Arsenic-bearing pyrite+Arsenopyrite+Sphalerite stage(Ⅱ),and Quartz+Calcite stage(Ⅲ).Arsenic-bearing pyrite and arsenopyrite are both gold-bearing minerals,but pyrite is the primary gold-bearing mineral.Both sedimentary-stage pyrites(Py1 and Py2)and hydrothermal-stage pyrites(Py3 and Py4)contain gold.The gold content of hydrothermal-stage pyrites is significantly higher than that of sedimentary-stage pyrites,and there is a positive correlation between Au and As.Gold primarily exists as invisible gold.Au in sedimentary-stage pyrites(Py1 and Py2)occurs primarily as gold nanoparticles(Au0);while gold in hy-drothermal-stage pyrites(Py3 and Py4)and arsenopyrite(Apy)occurs as lattice gold(Au+).The results indicate that the Laojunmiao gold deposit show similargeological characteristics,metallogenic conditions,and gold oc-currence modes with typical Carlin-type gold deposits.Compared with the δFe-δS,δFe/δS-As,and(Fe+S)-As systems of various genetic types of gold deposits in China,the pyrite mineralization during the mineralization period all falls within the Carlin-type gold deposit region.Therefore,the Laojunmiao gold deposit could be clas-sified as a Carlin-type gold deposit.