Magmatism In The Bastielieke Tungsten-copper Deposit In The Southern Margin Of Altay

The medium-sized Bastielieke tungsten-copper deposit is a newly discovered deposit in the Kelan Basin at the southern margin of Altay Orogenic Belt.The skarn hosted the orebody which is at the outer contact zone between the granitoids and volcanic-sedimentary rocks of the Upper Silurian to Lower Devonian Kangbutiebao Formation.Two-mica granite,biotite granite and monzogranite outcrop in the Bastielieke ore district showing obvious spacial relation to the hosted ore deposits.The petrogenesis of these rocks associated with the tungsten mineralization is indefinitve.LA-ICP-MS zircon U-Pb geochronology and geochemical analysis of major and trace elements and zircon Hf isotope are performed to discuss their petrogenesis.The main conclusions are as follows:(1)These granites show consistent weighted mean ²⁰⁶Pb/²³⁸U ages of 282.3±3.2 Ma,284.3±2.2 Ma and 284.8±2.3 Ma,respectively,which indicate that the Permian magmatic events at the southern margin of Altay is consistent to the ages of mineralization.(2)These granitoids exhibit high Si O₂concentration(73.6%to 78.3%),and low Fe O(0.42%to 2.50%)and Mg O(0.02%to 0.30%)and Ti O₂(0.04%to 0.24%)and Ca O(0.19%to 0.75%)concentrations.The petrologic and geochemical data indicate that these rocks are high-K calc-alkaline and weak peraluminious to strongly peraluminous granitoids(A/CNK>1.0).The total REE contents of these granites vary from 20.3×10^-6 to 328×10^-6with different chondrite-normalized REE patterns.All samples display noticeable negative anomalies of Nb,Ti,P,Sr,Ba and strong positive anomalies of Rb,Th,U and Pb.(3)zircon?_Hf(t)values range from+3.8 to+11,two stage model ages(t _DM2)ranging from 1.0 Ga to 0.60 Ga.(4)These granitoids which is similar to the geochemical behavior of the fractionated I-A type granitoids of the Permian magmatic events.Two-mica granite is quite different with granite and monzogranite in petrologic and geochemical features.Combined with regional geology,we suggest that they are in a post-collision environment by two independent magmatic events.(5)Two-mica granite,biotite granite and monzogranite are derived from melting of the juvenile crust and mantle,and followed by subsequent crystallization fractionation in deeper magma chamber.These granites provide key ore components for the formation of Bastielieke tungsten-copper deposit and preconcentrate tungsten by crystallization fractionation and melts-fluid metamatism.