The Petrology And Geochemistry Of Chen'er Gold Deposit Of Luonan County,Shanxi Province

Chen'er gold deposit is located in Luonan County,Shanxi Province in the southern margin of North China block.It is a typical quartz vein deposit and belong to the Xiaoqinling ore field.This deposit is related to Wenyu granitic intrusion,which mainly composed of biotite monzogranite.This paper reports the zircon U-Pb ages and geochemical characteristics of the Wenyu pluton.The results show that the crystallization age of the Wenyu pluton is 133±1.3 Ma.The Wenyu granites are enriched in silica ? aluminum ? alkali,and belong to high-K calc-alkaline and metaluminous I-type granite.Whole-rock trace element analysis of Wenyu granitic intrusion exhibit relatively depletion in Nb,Ta,and HREE,enrichment in Rb,Ba,Sr,and LREE,and free of negative Eu anomalies,suggesting that their source rocks may be garnet amphibolite without feldspar or eclogites.Wenyu pluton shares the same formation age with the other granite plutons in Eastrn Qinling region.It is thus followed that Late Mesozoic magmatic activity of the Eastern China was probably controlled by the subduction of the Pacific plate toward the Eurasian continent.This can explain the considerable transformation of tectonic structure in the Late Mesozoic Eastern China.This extension event developed large-scale detachment fault,caused crustal pressure reduction and temperature increase,and induced partial melting of thickened lower crust and finally formed the Wenyu pluton.Au-rich fluids were exsolved from the evolved magma,resulting in the formation of gold deposits.Systematic study of the ore minerals in the chen'er gold deposit indicating four mineralization stages: coarse-grained pyrite-quartz vein stage(?),quartz veinfine-grained pyrite stage(?),quartz-polymetallic sulfide stage(?),carbonate-quartz vein stage(?).Electron probe microanalysis(EPMA)reveals that Au-bearing minerals(native gold and electrum)commonly ranges between 0.03 mm to 0.3mm and occurs in the pyrite microfissures,envelop by pyrite and quartz,and attacthed by the pyrite.Au concentration decreases while that of Ag increases from core to rim in the native gold.The depletion of S in the pyrite and chalcopyrite,the ratio of Co/Ni>1,the enrichment of Ag in the galena,and the ratio of Ga/In < 1 in sphalerite,suggesting magmatic-hydrothermal ore-forming fluids for the Chen'er gold deposit.In addition,the presence of tellurium-and bismuth-bearing minerals reflects the contribution of mantle-derived materials to the ore-forming fluids.Gold fineness and the trace element compositons of pyrite and sphalerite indicating medium to low formation temperature for Chen'er gold deposit.