| Chang'an Chong deposit is located in Jinping County,Honghe Hani and Yi Autonomous Prefecture,Yunnan Province,Southwest China.The mining area is located in the south section of Ailaoshan structural belt,at the junction of Yangtze plate and Indosinian plate,with Ailao Mountain body in the northeast and tengtiaohe fault in the southwest.The strata in the mining area are mainly Ordovician and Silurian dolomite and limestone,while the magmatic rocks are mainly Cenozoic syenite and syenite porphyry,and the structure in the area is mainly NW trending.There are six typical rock bodies exposed in the mining area,of which the No.2 rock body is the most closely related to the copper molybdenum mineralization.The contact alteration zone on the southeast side of II rock body is characterized by typical alteration zoning of skarn type deposits,where metasomatism is strong,skarnization,potassification,silicification,sericitization and other alterations are widely developed,copper mineralization mainly occurs in the skarnization zone,molybdenum mineralization mainly occurs in the internal alteration zone,and a large number of metal sulfides(such as chalcopyrite,molybdenite,pyrite,etc.)are developed.The ore-forming fluid of the deposit is characterized by middle temperature,low density and low salinity.The study of fluid inclusions in quartz vein in each mineralization stage shows that the ore-forming fluid of the deposit is generally characterized by medium high temperature,medium low density and low salinity,and the fluid temperature of Molybdenite pyrrhotite stage,which is closest to molybdenum mineralization,is generally higher than that of brass pyrite stage,which is closest to coppermineralization.H-O isotopic study shows that the ore-forming hydrothermal solution is mainly derived from magmatic water,and some atmospheric water may be mixed in later stage.The study of sulfur isotopes shows that the sulfur in the deposit comes from magma,which provides rich ore-forming materials for the formation of the deposit,while Pb is characterized by orogenic lead,which comes from the deep and undergoes some degree of crustal contamination.The EPMA mineralogical analysis of plagioclase,biotite and amphibole in quartz syenite of ore-forming body shows that the ore-forming magma has more than medium oxygen fugacity(both biotite and amphibole indicate that oxygen fugacity is greater than NNO),and the water content of magma calculated by amphibole is about 4%,which belongs to water rich magma,and it isconducive to the full differentiation of metals into fluids in the late crystallization period.The formation age of quartz syenite is 34.5 ± 0.3Ma,which is closely related to mineralization.In addition,the deposit shows typical syngenetic characteristics,so the mineralization age and diagenesis age are basically the same,and the deposit was formed in early Oligocene.The study of petrochemistry shows that the ore bodies of Chang'an Chong and Tongchang have the characteristics of high silicon,high alkali,rich potassium and rich calcium,which are similar to the potassic/ ultrapotassic magmas widely exposed in the area.Hark diagram reveals that the ore bodies of Chang'an Chong and Tongchang are the products of the same magma evolution,both of which are derived from the partial melting of the regional potassic / ultrapotassic lower crust,and then it has experienced a certain degree of separation and crystallization.During the formation of the deposit,the regional tectonic dynamic system has changed from collision to shear,which provides a good channel for magma upwelling.In a word,the Chang'an deposit is a skarn copper molybdenum composite deposit formed in the continental collision orogenic environment. |
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