Discussion On The Genetic Mechanism Of Cenozoic Polymetallic Deposits In Western Yunnan Province

The research area locates at west margin of Yangtze plate and also is one activeCenozoic deformation zone. The tectonic movement in the western Yunnanexperienced Techys evolutionary stages and intracontinental tectonic evolutionarystages，the deep faults are active for a long geologic time and cut through the cruststrongly. It is the deep faults controlled the sedimentary construction，metamorphism，magmatic activity and the related mineralization. This article reveals the typicalgeological features of Machangqing deposit，is that from rock to contact zone to wallrock which corresponds to porphyry Mo deposit，skarn-type Cu(Mo) deposit andtectonoclastic altered rock-type Au deposit. And the Laowangzhai Au deposit iscontrolled by different magmatic rocks，especially lamprophyre. The magmatismeffects on the mineralization is that the ore bearing mantle fluid which accompanywith mantle magma to replace the different rocks，so the metallogenetic overlappingin crustal-mantle interaction was triggered and soon promoted.Petrologic researches show that a kind of black opaque solid materials developsalong or in the cracks or cleavages of hornblende following the silicification，carbonatization and sulfidation. The electron microprobe， scanning electronmicroscopy and spectroscopy results confirm that opaque solid materials arecomposed of silicate，carbonate and sulfide ultramicroscopic cryptocrystalline solid. Itis believed that the black opaque solid materials can promote and causemetallogenesis. They are the ore-forming mantle fluid which is independent frommagma and accompany with mantle magma. What should be paid more attention isprecipitation-crystal texture and Liquation intergrowth texture which imply that the transition of melt and hydrothermal fluid. The black opaque solid materials are theproducts of rapid cooling of ore bearing mantle fluid which moved with alkalinemagma and the relics of mantle fluid and participation in crustal-mantle interaction.They are microscopic trace of mantle fluid metasomatism and power producer andmaterial source of deep geochemistry which can promote metallogenesis andcrustal-mantle interaction.The element geochemistry proved that the ore-forming fluid and magmatic fluidboth origin from enriched mantle and the ore-forming fluid is one kind of mantle fluidwhich was wrapped in and unmixed with the magma. During the evolution of magmaand mantle fluid，the rock were synchronically self-replaced and altered by the mantlefluid going with the process of magma crystallizing to form deposit in magma bodyor its deep-seat； The mantle fluid also will separate from magma，enter into thecontact zone between magma body and wall rock or strata next to the contact zonereplacing and altering，and promoting crustal-mantle interaction and superpositionmetallogenesis. As a result，from the magatite body to the wall rocks，the metallogenictemperature changed from high to low forming different commodities and types ofmetallogenetic influence in different localizations as a kind of series mineralization.