Mineral Indicators For Petrogenesis And Mineralization Of Late Paleozoic Intrusive Rocks In The Boluokenu, West Tianshan

The formation of skarn-porphyry Fe-Cu polymetallic deposits in the Boluokenu metallogenic belt in the West Tianshan,Xinjiang is closely related to the Late Paleozoic intermediate-acid intrusive rocks widely distributed in this region.In this paper,four typical granite bodies,Husite,Dawabulake,Lailisigaoer and Nailenggele,are studied.Their lithofacies composition,rock type,and chemical composition of rock-forming minerals are compared and analyzed.On this basis,the relationship between mineral composition and diagenesis and mineralization is discussed,and the mineralization intensity and type of rock bodies are analyzed and discriminated.Plagioclases in Husite and Dawabulake intrusions are all andesine;Potassium feldspar belongs to K-sanidine;biotites are Mg-biotite;amphiboles are mainly magnesiohornblende with a small amount of edenite.Plagioclases in the Lailisigaoer intrusion are mainly andesine with a small amount of oligoclase;Potassium feldspar is K-sanidine;biotites are mainly Mg-biotites and magnesium-rich Fe-biotites;amphiboles are mainly magnesiohornblende.Plagioclases in Nailenggele granite are mainly albites(Na-rich feldspar)and andesine;Potassium feldspar is K-sanidine;biotites are mainly Fe-biotites with some siderophyllite;amphiboles are mainly Ferro-actinolite and Ferro-edenite with a small amount of magnesiohornblende.All these granites belong to I-type granites.The Husite,Dawabulake and Lailisigaoer granites were formed in the continental arc margin environment raleted to subduction southward from the North Tianshan Ocean under the Yili Plate.The Nailenggele granites may have formed in the background of the transition from collision to intracontinental extension.The diagenetic material of the granites mainly came from the lower crust,mixed with a small amount of mantle-derived material.Petrographic and mineralogical characteristics indicate that the dark inclusions in the Husite monzonitic granite are the products of magma mixing.Mineral chemical composition and mineral thermobarometer show that Husite granites have high diagenetic temperature and various but generally low diagenetic pressure.Dawabulake granites have high diagenetic temperature and low diagenetic pressure.Lailisigaoer granite has various but generally low diagenetic temperature and pressure.Nailenggele granites have low diagenetic temperature and high diagenetic pressure.Based on field investigation and systematic mineralogical study,the granite bodies studied are divided into Husite and Dawabulake intrusions,which are genetically related to skarn Fe-Cu deposits,Lailisigaoer intrusion related to porphyry Cu-Mo deposits and Nailenggele intrusions,Husite syenite granite and granite aplite,which are not related to mineralization.The differences in mineralogical composition between ore-forming and non-mineralized rocks and between different types of mineralized rocks essentially reflect the differences in magmatic composition,differentiation degree and oxygen fugacity.The granites related to skarn Fe-Cu deposit have low differentiation degree,high oxygen fugacity and crystallization temperature of magma.The granite related to porphyry Cu-Mo deposit has high differentiation degree,high oxygen fugacity of magma,various but generally low crystallization temperature of magma.The granite not obviously related to mineralization has high differentiation degree,and the oxygen fugacity and crystallization temperature of magma are low.