The Study Of Tectonic-Magmatic-Hydrothermal Metallogenic Model Of Carlin-type Gold Deposit In Southwestern Guizhou Province,China

The Southwestern Guizhou Province is one of the most significant region of Carlin-type gold deposits in China,and has enormous metallogenic potential.Because of scattered researches and scarce regional study,numbers of aspects are still unsolved which impede the understanding of metallogenic model in the study area as well as the initiation of prospecting works.Based on detailed field works,this thesis selected three representative deposits?Shuiyindong,Nibao,Yata?,aiming to have a better understanding of ore deposit geology,geochemistry,sources and characteristics of ore-forming fluid,source of fluid and metal and ore-forming processes,and build up a regional metallegenic model.According to detailed observation during the field work,three types of ore-controlling structure have been identified,which are unconformity type,composite type and fault type.Mineral assemblages and mineralization stages are similar between these three structures.The results of fluid inclusion study suggest similar characteristics of ore fluid,which is that is medium-low temperature,low salinity with different gas contents,in a same H₂O�CO₂�NaCl�CH_4,N₂ system.The H-O,C-O and He-Ar isotopic data indicate that the initial source of ore fluid in three structures is the mixture of magmatic water,sedimentary water and metamorphic water and subsequent mixing with magmatic water,organic water and convecting meteoric water from deep to shallow during mineralization.Ore-rock reaction,fluid mixing and boiling are major factors for metal deposition,and gold,arsenic,tungsten,mercury are introduced with the ongoing of mineralization.The firstly found dolerite in the Nibao gold deposit emplaced in Late Triassic.Obvious Nb,Ta and Th?HFSE?depletion and low Tb/Yb ratio?1.9-2.1?indicate the magma was derived from low-degree?5¹0%?partial melting of enriched mantle at90km underground which consist of 75%garnet peridotite and 25%spinel peridotite.The relationship between immobile element and major elements suggests the fractional crystallization of olivine and clinopyroxene prior to emplacement.Medium-degree crustal contamination was evidenced by Sr-Nd and Lu-Hf isotopic results.Based on in-situ analyses of four types of pyrite,gold was transported as Au?HS?⁰or Au?HS?² complex and was absorbed into pyrites as solid solution during the substitution of S by As.Rapid decompression and phase separation are both key triggers for the formation of Au-As-Cu rims which are identified in ore stage pyrite.The Youjiang Basin experienced relative completed Wilson cycle from Early Devonian to Late Triassic,we considered the partial melting of enriched mantle,upwelling asthenosphere and strong crust-mantle interaction were all triggered by the break-off of the subduction plate and considered as a key factor for the tectonic-magmatic-hydrothermal metallogenic event in the study area.We finally built up a tectonic-magmatic-hydrothermal metallogenic model on the basis of all researches in the thesis.