Ore-forming Fluids Characteristics Of The Daping Gold Deposit, Western Yunnan, China

Daping gold deposit is a huge gold deposit in Jinshajiang-Ailaoshan Cenozoic metallogenic belt. The latest study implied that an epithermal mineralization process overprinted the main orogenic mineralization process. It is unique in the belt. In this study, the geological features are summarized to enhance the evidence of an epithermal gold mineralization. Bsaed on the geological features, ore-forming fluid characteristics and resource of ore-forming material studies are carried out to discuss the forming process of orogenic Au mineralization and epithermal Au-multi-metal mineralization in Daping gold deposit. Many achievement are obtained:1. In Daping gold deposit,the main ore body in the deposit shows many similarities to orogenic mineralization: the deposit was controlled by The regional fault and its secondary fault; the ore bodies are left arranged in high angle faults; vein mineralization is largely development;Au-mineralization is main type.2. The sorth part of Daping gold deposit shows many similarities to epithermal mineralization process: mineral veins are horizontally located in structural fracture zone; the net-like structure, comb-like structure and breccia structure of ore are widely existed; the high enrichment of Ag, Pb, Cu; adularia-calcite mineral assemblage was observed; alteration zoning shows silicification、sericitization、carbonation、propylization from inner to exterior.3. Three types of fluid inclusion are obverve: H2 O type, CO2 and CO2-H2 O type. CO2-H2 O type is the dominant in both of orogenic and epithermal mineralization process. Microthermometic data indicate trapping temperature of 250℃~290℃ in orogenic mineralization process, and 250℃~330℃ in epithermal mineralization processt. The two process share some same fluid component features: Na+、K+ dominated positive ions, and Cl-、SO42- dominated negative ions. H2 O and CO2 are the main gas component in both of the two process. Meanwhile, the epithermal minenal process have a higher content in K+、SO42-. Above all, the fluid characateristics share many commons between the epithermal mineralization precess and the orogenic mineralization process,this means ore forming fluid activity lasts a long time.4. Both mineralization share many similarities in isotope study. δ18OV-SMOW is 10.9‰ ~ 14.3‰, δD is-113‰ ~-40‰, δ34S is 2‰ ~ 10‰; δ13CV-PDB is-7.6~-2.3‰. Isotopic tracing study imply that H2 O 、 CO2、S are derived from crust-mantle interaction, and affected by matermorphism. Pb isotope study shows a relationship with lamprophyre and diorite. Besides, the enrichment factor of lamprophyre is 181.44 and diorite is 1.57, indicating that the mass of Pb is related to lamprophyre.5. Summerize all the imformation of geological feature, ore-forming fluids characteristics, derive of ore-forming material and tectonic setting evolution, and an epithermal mineralization overprint the former orogenic mineralization. The former orogenic mineralization was formed in the process of collisional orogeny, the later epithermal mineralization may formed during process of post-collision.