大兴安岭南段敖仑花斑岩钼(铜)矿床成矿流体来源与成矿作用:稳定同位素C、H、O、S和放射性Pb同位素约束

The Source of Hydrothermal Fluids and Mineralization in the Aolunhua Porphyry Mo-Cu Deposit,Southern Da Hinggan Mountains:Constraints from Stable(C,H,O and S) and Radiogenic(Pb) Isotopes

基于稳定同位素C、H、O、S和放射性Pb同位素的测试和分析,对大兴安岭南段敖仑花斑岩钼(铜)矿床成矿流体的来源进行了示踪,探讨了流体演化与成矿作用过程。新的稳定同位素数据显示:敖仑花矿床成矿热液具有混合来源性质;脉石矿物石英中流体的C、H、O同位素和矿石硫化物的S同位素组成指示成矿络合剂主要来自地幔,同时在热液期经历了地壳流体参与的过程;辉钼矿中放射性成因的Pb同位素组成表明,成矿物质(Mo)主要来自造山带物质,部分来自深部幔源。根据H、O同位素组成变化和已有流体包裹体资料,认为敖仑花矿床早、中阶段两次矿化的成矿机制不同:早阶段金属矿化主要与岩浆水和大气降水的流体混合有关,而中阶段大规模成矿作用主要是由流体沸腾所致。综合区域地质演化认为:敖仑花矿床是大兴安岭南段在晚侏罗世—早白垩世时期演化为弧后伸展背景、陆内造山带物质重新活化、壳幔岩浆-热液相互作用的产物,同时暗示壳幔作用强烈的地区利于内生金属矿床成矿。

Stable（C,H,O and S） and radiogenic（Pb） isotopes of hydrothermal solutions from the Aolunhua Mo-Cu deposit in southern Da Hinggan Mountains were analyzed with the purpose of determining the source of the ore-forming fluids and tracing the ore-forming process.New isotopic data indicate that the hydrothermal solutions were not from a single source.C,H,O and S isotopic compositions of the ore-forming fluids show that the metallogenic complexing agent had a hybrid origin,derived mainly from the mantle and subordinately from the crust.The Pb isotopic compositions of the molybdenite suggest that molybdenum came mainly from the juvenile orogenic belt,with a small amount derived from the mantle.Distinct metallogenic mechanism was identified based on stable isotope compositions and previous fluid inclusion studies.The mineralization at the early stage was caused by a mixing between magmatic fluid and meteoric water.However,mineralization at the prevailing metallogenic stage resulted from the fluid boiling.Distinct from the porphyry deposits formed in arc settings and collisional orogenic settings,the Aolunhua porphyry Mo-Cu deposit was formed in a unique geological setting related to reactivation of a juvenile orogen under an extensional back-arc regime during the Late Jurassic and Early Cretaceous period.Interaction between magmas and hydrothermal fluids from the mantle and the crust formed a hybrid system,which created essential conditions for subsequent mineralization.It is thus held that more importance should be attached to this ore-forming process so as to recognize potential fertile intrusions.