| The Jiagantan gold deposit which is located in Western Qinling Orogenic Belt,is a recently found large-size gold deposit in Xiahe County of Gannan Tibetan Autonomous Prefecture in Gansu Province.The rocks in the Jiagantan area contain feldspar quartz sandstone,silty slate,lithic sandstone of the Lower Triassic Longwuhe Formation.Gold ore bodies are produced in the NWW-striking fault fracture zone,distributed in the shape of geese and feather.The ore-bearing rocks are feldspar quartz sandstone interbedded with silty slate.178 gold ore bodies have been delineated in mineralized area.The ore type is sulfide-sandstone type.There is no obvious difference in lithology with the test sample in this article.Ore minerals are mainly composed of pyrite,arsenopyrite and limonite,with a small amount of chalcopyrite and sphalerite.The main types of the wall rock alteration are silicidation,sericification and carbonate.Wrapped gold is the primary occurrence of gold in nature.Limonite is most closely related to the occurrence of gold.The mineralization process is mainly gold-bearing hydrothermal filling and replacement,which has the characteristics of multi-phase metallogenesis.The genesis type is tectonic alteration rock type gold deposit.In this paper,we report on the whole-rock major and trace element compositions of ore-bearing sandstone sample,The results show that the index of compositional variability and the chemical index of alteration for different samples are similar,revealing a relatively fresh,weakly matured origin with medium chemical weathering.The rocks have the similar trace and REE patterns with the post-Archean shales from Australia and upper continental crust,characterized by enrichment in LREE and stabilization of HREE.The protoliths of the ore-hosting sandstone are composed of sedimentary rock,belongs to proximal sedimentary and transportation deposit.The provenances are jointly contributed by felsic igneous rock and quartzose sediments,the sedimentary environment is likely related to the active continent margin.Through the Longwuhe Formation of detrital zircon LA-ICP-MS U-Pb dating and Lu-Hf isotope studies,reveal the age spectrum of 309-255 Ma,484-352 Ma,1941-1761 Ma and 2562-2262 Ma,responding to Kenorland,Columbia,Gondwana and Pangaea supercontinent events.In combination with regional geological data and igneous event,south margin of North China Block,North Qilian,East Kunlun and North Margin of West Qinling provides source of Longwuhe Formation together.The provenances are more complex.According to the 240 Ma upper limit of the sedimentary age of the Longwuhe Formation in this paper,and previous studies about the age of the magmatic rocks that intrusive in Longwuhe Formation,it can be obtained the sedimentary age is 240 Ma-238 Ma,which is part of Early Triassic.Detrital zircon age spectrum display characteristics of backarc basin,reveal that the Paleotethys Ocean is subducting northward along the Mianlue suture zone,forming the tectonic background of active continental margin on the north side of the Mianlue Ocean basin. |
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