A Study On The Intermediate-Acidic Magmatic Activity And Au Metallogenesis In Zhongchuan Area,West Qinling

The Western Qinling,located in the west part of the Qinling orogen,has experienced multiple structural movement and complex processes of crustal evolution.This area hosts numerous ore deposits(e.g.,gold,lead,zinc,mercury,antimony and other multi-metal deposits),and a large amount of Indosinian intermediate-acid intrusions.The Western Qinling has been the subject of intense geologic study,as well as mineral exploration.However,the controversies on the intrusive sequence,the source characteristics,and structural setting of the Indosinian intermediate-acid plutons,lead to an ambiguous relationship between magmatism and gold mineralization,and thus bring difficulty in mineral prospecting.Based on a systematic study of lithological characteristics,whole rock major and trace elements,as well as the U-Pb,Lu-Hf isotopic systems and trace elements in zircons,this paper discusses the intrusive sequence,source features,structural setting,and genetic mechanism of intermediate-acid plutons in Zhongchuan district.On the other hand,on the basis of a sound work from our project team and other previous researchers,an investigation has been carried out on the temporal and spatial distribution of the gold deposits in Western Qinling.Case studies on three gold deposits(i.e.,Zhaishang,Mawu,and Liba gold deposits)featuring the migration behaviour of mineralization-related fluid and characteristics of corresponding source materials,reveal the relationship between the Indosinian magmatic activity and gold mineralization,and provide insights into the gold ore-forming regulations.The main results are as follows:(1)the five intermediate-acid plutons are the products of two stages of magmatic activities(i.e.,the Middle Triassic and Late Triassic,respectively),with the features of continuity and pulsation.(2)Based on different origins,the five plutons could be divided into three different source groups: ?.Mantle + sedimentary source group(e.g.,Zhongchuan,Jiaochangba,and Lvjing plutons),which is mainly derived from the partial melting of the continental lithospheric mantle and metagreywacke with poor clay in the old crust,and show chemical signatures of both I-type and S-type granites;?.Mantle + igneous rock source group(e.g,the Luchuba pluton),which is mainly derived from the partial melting of the continental lithospheric mantle and metatonalite in the old crust,and consists of I-type granites;?.Sedimentary source group(e.g.,the Baijiazhuang pluton),which is derived from single source,such as the clay-rich metapelitic part of the old crust,different from the other four plutons.(3)The intermediate-acid plutons are the products of the collision of the Yangtze and Qinling Blocks,following the end of northward subduction of the Yangtze Block.(4)The Indosinian magmatic activities in Western Qinling is not only closely related to the gold deposits both spatially and temporally,but it also supplied necessary metallogenetic materials.(5)In Western Qinling,the plutons showing close relation with gold metallization are mainly derived from the partial melting of the continental lithospheric mantle and metagreywacke with poor clay in the old crust.They interacted with the fluid generated from altered oceanic crust and molten sedimentary,which produced the granites that bear chemical signature of both I-type and S-type granites.