Studies On Geological And Geochemical Characteristics And Genesis Of The Lianzigou Gold Deposit In Xiaoqinling District

The Lianzigou gold deposit is an important gold deposit in the Jialu gold field that is located in the Xiaoqinling region.The deposit is hosted by the highly metamorphic gneiss which is the main rock type of the Q incanggou Formation of the Archean Taihua Group.The orebody are controlled by the structural fracture altered zone.In the deposit area,few granitoid bodies and only some intermediate-mafic dykes could be found.Ores mainly occur as quartz-veinand and altered rock types.Through systematic geochemical investigation of the Lianzigou gold deposit,conclusions about the mineral composition,the occurence of gold,the genesis and mineralization mechanism of this deposit have thus been drawn as follows:?1?Based on the detailed field geological survey and systematic laboratory study,including microscope observation and electron microprobe analyses,the mineral composition has been identified.The results show that Lianzigou gold deposit yields various types of metal minerals,the metal minerals are mainly composed of pyrite and galena,generated following native gold,electrum,chalcopyrite,sphalerite,tetrahedrite,krennerite,calaverite,altaite,melonite,petzite,hessite,native tellurium,magnetite,bornite and so on.Nonmetallic minerals are mainly consist of quartz,K-feldspar,calcite,sericite,chlorite.The gold minerals are native gold and Au-Te-Ag series minerals.Gold is enclosed as fissure-filling,such as intergranular,interlocking and inclusion form.?2?Geochemical analyses of rock and ore shows that the wall rock of ore are mainly of intermediate-basic volcanic types.The trace element analyses reflect the main ore-forming elements have been carried into and out during the metallogenic process.The rare earth elements contents show the inheritance between the ore and surrounding rock,reflecting the exchange between ore-forming fluid and surrounding rock has been occurred.?3?The study of fluid inclusion shows that the ore-forming fluid is middle-to-low in temperature,low in salinity,middle-to-low in pressure,low in density and medium-low depth.The ore-forming fluid belongs to NaCl-H₂O-CO₂ system.Laser Raman spectroscopic analysis shows that the gas composition of fluid inclusions are mainly CO₂ and a few H₂O and N₂.The hydrogen and oxygen isotopic composition shows that ore-forming fluid has the characteristic of magmatic water and atmospheric precipitation.He-Ar isotopes demonstrate clear mixing trends between crustal and mantle-derived components.The source of sulfur may come from deep source,due to sulfur isotope fractionation effect in the process of mineralization,the sulfur isotopic compositions in sulfides are close to light sulfur.The lead isotopic compositions are stable,and the origin of lead in the deposit was mainly from mantle source assimilated with crustal source.?4?In extensional regime,the fracture zone in Taihua group of Xiaoqinling area are therefore widening,and provide enough transferring passage for the deeply derived ore-forming fluid.The magmatic fluid mixed with the shallow fluid and then fully reacted with the wall rock to exchange the mass a nd transfer through water-rock reaction,generating potassic alteration zone in the wall rock.The physic-chemical conditions of the ore-forming fluid change gradually and made the ore-forming material enrichment,precipitated the ore metal eventually.