Tectonic Evolution And Typical Deposits In The Southern Segment Of The Ganzi-Litang Orogenic Belt

The Ganzi-Litang orogenic belt is an important tectonic unit in the“Sanjiang”orogen,the belt is also a very important Au-Cu polymetallic metallogenic belt.In this paper,a detailed study on the ophiolite,the Suoluogou orogenic gold deposit and the Degongniuchang porphyry copper deposit in the Southern Ganzi-Litang orogenic belt,and then summarize the model of the tectonic evolution and metallogenic about the Ganzi-Litang orogenic belt.From this study,following achievements about the genesis of ophiolite;the source of ore-forming materials,the metallogenic age and the characteristics of ore-forming fluids in the Suoluogou large gold deposits;the genesis of the ore-bearing porphyry rocks,the source of ore-forming materials and the characteristics of ore-forming fluids of Degongniuchang copper deposit have been obtained.1.The wall rock of the Suoluogou large gold mine is ophiolites,its lithologies are peridotite,MORB basalt,OIB basalt,siliceous rock,limestone.The peridotite is a harzburgite,which has a low degree of partial melting during the formation process,and it is also affected the subduction of the Ganzi-Litang ocean.2.It is determined that the Suoluogou large gold deposit is an orogenic gold deposit with a mineralization age of 238±52 Ma.The source of ore-forming materials is mainly from mantle,it is closely related to the ophiolite in the wall rock.From the early stage to the late stage,the ore-forming fluid evolves from a medium-high temperature,CO₂-rich metamorphic hydrothermal fluid to a low-temperature,CO₂-lean atmospheric precipitation hydrothermal fluid.The main factor of mineral precipitation is decreasing temperature of the ore-forming fluid,CO₂ escaping and the sulfide precipitation.3.The age of Degongniuchang ore-bearing porphyry is around 214 Ma.The petrogenesis is crustal melting because of heat that the mantle source magma above the subduction zone providing,and mixed with this mantle source magma,suggest that the Ganzi-Litang ocean basin is not closed at this time.The source of ore-forming material of the porphyry copper deposit is magma in depth due to the?³⁴S value of chalcopyrite and pyrite are similar to the S isotope composition of meteorite.The Pb isotope characteristics indicate that the source of ore-forming material is mainly crust-mantle mixed.Fluid inclusion studies show that the early-middle of the porphyry copper deposit is a medium-high temperature,medium-low salinity V-L and L-V system hydrothermal system,it is related to the magmatism which is formed by the subduction of the Ganzi-Litang paleo-Tethys ocean.In the late stage,only the low-temperature,medium-low salinity L-system hydrothermal system was developed,and there was no mineralization in this period.