Gold-Molybdenum Mineral System In The Ore-Forming Concentration District Of The Xiong'ershan And Waifangshan

Xiong'ershan-Waifangshan ore concentration field is a significant economic ore field yielding gold,molybdenum and so on.Previous researchers have done much research on gold and molybdenum deposits of different periods in this region,but seldom work on superimposed mineralization.Hence,based on analysis of petrogeochemistry,stable isotope,fluid inclusion,Fe and Re-Os isotope,we analyse the process of superimposed orogeny and mineralization,and try to build mineral system.The main achievements are summarized below:The LA-ICP-MS U-Pb dating of zircons yields ages of 1828~1780 Ma,by which we constrain the time of eruption of the Xiong'er Group.Analysis of petrogeochemistry data indicate that volcanic rocks of Xiong'er Group formed in rift environment.The transition from syn-collision to post-collision in Eastern Qinling Orogen likely occurred during the Triassic,possibly around 227 Ma.We put forward that there were two syenite forming periods in Triassic,intruding in the partial extension environment during the main collision process of the Qinling Orogen,and extension background during the post-collision stage,respectively.The Wuzhangshan,Baituyuan Granite intruded in 160 Ma,166 Ma,respectively,and formed in continental arc setting.Taishanmiao Batholith consists of three phases,intruding in 125,121,115 Ma,respectively,and formed in large scaled thinned the North China Craton.We divide the mineralization process into six epoches as follows: 1875~1855 Ma,porphyry molybdenum formed in subduction environment;1831~1680 Ma,porphyry molybdenum formed in rift environment;250~227 Ma,orogenic molybdenum deposits formed in syn-collision environmen;227~194 Ma,orogenic and carbonatite molybdenum deposits formed in post-collision environment;164~135 Ma,porphyry molybdenum formed in subduction environment;135~116 Ma,orogenic gold deposits,magmatic hydrothermal gold and molybdenum deposits formed in thinning lithosphere environment.orogenic gold deposits,magmatic hydrothermal gold deposits and so on,as well as superimposed mineralization,showing as Triassic orogenic molybdenum deposit being superimposed by Cretaceous orogenic gold deposit in Huaishuping mineral deposit,and early Lower Cretaceous porphyry molybdenum being superimposed by late Lower Cretaceous magmatic hydrothermal gold deposit in Qiyugou mineral deposit.We establish gold-molybdenum mineral system in the Ore-Forming Concentration District of the Xiong'ershan and Waifangshan,and the forming mechanism of main deopists are shown as follows: Orogenic molybdenum deposits formed in syn-collision and post-collision environment between North China Craton and Yangtze Plate,metamorphic fluids in former setting originated from subducting plate with magmatic fluids,carried crust-mantle mixed sourced molybdenum and deposited in interlayer gliding fault,while metamorphic fluids in latter one extracted molybdenum from crust and deposited in the same kind of fault;Carbonatite molybdenum deposits formed in post-collision environment,and magmatic fluids carring mantle sourced molybdenum contributed to mineralization;Orogenic gold deposits and magmatic hydrothermal gold deposits formed in thinning lithosphere environment,owing to metamorphic fluids mixed with some magmatic fluids extracting crust sourced gold and magmatic fluids bringing mantle sourced gold,respectively;Porphyry molybdenum formed in subduction,rift and thinning lithosphere environment,result from magmatic fluids carring crust-mantle mixed sourced molybdenum.