A Study On The Genesis Of Lamasu-Saibo Cu Deposit In Western Tianshan,China

The Western Tianshan of China has superior metallogenic geological conditions for the form of porphyry Cu deposits,and the potential for searching for porphyry Cu deposits is huge.However,we have no substantial progress in this area until now.Chinese economic geologists are very interesting in how to find porphyry Cu deposits in Western Tianshan.It is a scientific,realistic and operable way to analysis the geological background,temporal and spatial distribution and identification signs of the porphyry Cu system in the Western Tianshan area from existing deposits and sites.Based on this,We took the Lamasu-Saibo Cu deposit of in the Western Tianshan as typical deposits.We have carried out field observation,indoor identification,rock geochemistry,mineral chemistry,stable isotope and isotope dating research.Through these works,we precisely define the age of its formation,analyze the geological background,and clarify the system of mineralization.So we can improve the level of ore deposit research,with a view to providing references of exploration and metallogenic regularization for regional porphyry copper deposits.There are a lot of plagiogranite porphyry veins,granodiorite porphyry veins and diabase veins in Lamasu-Saibo deposit,and the first two are closely related to the ore body.We got the weighted average age of plagiogranite porphyry is 385.7±3.2 Ma,the granodiorite porphyry is 379.3±2.6Ma,the diabase is 300.6±1.9 Ma through the zircon SHRIMP U-Pb dating.The plagiogranite porphyry veins and granodiorite porphyry formed in the continental margin arc background in Devonian.And they are formed by evolution of same mamga(magma temperature is about 700 ?).The initial magma may be formed by melting of the depleted mantle,but new crustal material was added during the ascent.The situ sulfur isotope analysis shows that the sulfur is mainly derived from the magmatic sulfur source.The sulfur isotopic equilibrium temperature calculation of the symbiotic pyrite,magnetite,and chalcopyrite mineral pairs indicates that the equilibrium temperature is between 200 and 350 °C,which is significantly lower than the porphyry crystallization temperature(about 600 °C).It is speculated that the ore-forming fluid may mainly come from deep rock bases.So we think the metallogenic mechanism should be that after porphyry veins are rapidly consolidated,the fluids differentiate from the lower rock strains and flow along deep contact zone to the shallow contact zone.Finally,due to the sudden changes in the physical and chemical environment,the deposits formed into ore deposits.According to the analysis of the Lamasu-Saibo Cu deposit,it is believed that the mediumacid porphyry body and its surrounding alteration zone,the intersection of the north-western and north-northwestward faults in the region,and the limestone(especially the interlayer fracture zone)can be used as an important basis for searching for the porphyry-skarn copper mineralization system in the region.