冈底斯东段山南地区第三纪矽卡岩-斑岩Cu-Mo-W(Au)多金属矿床勘查模型及深部找矿意义

The Metallogenic Model of Eocene Skarn Cu-Mo-W(Au) Deposits in the Eastern section of Gangdese,Southern Tibet and Its Implication for Ore-Search Towards the Deep Subsurface

冈底斯东段南缘的山南地区分布有努日、明则、克鲁、冲木达和陈坝等中到大型Cu-Mo-W(±Au)矿床,与含矿矽卡岩有关的侵入岩形成于20～30Ma之间,为高钾钙碱性中酸性岩,形成于碰撞晚期构造背景。矿化赋存于下白垩统比马组的碳酸盐岩和其它钙质岩石与岩体的外接触带内及斑岩体内,主要矿化类型为矽卡岩型、斑岩型和热液脉型,构成完整的斑岩-矽卡岩、脉状铜-钼-钨±金多金属成矿体系,矿化组合主要为Cu-W-Mo、Mo、Cu-Au和Cu矿化。外接触带的蚀变以矽卡岩化、角岩化为主,而内接触带上主要为岩体的绢云母化、硅化、绿泥石化等,内矽卡岩不发育。山南地区的矽卡岩型铜-钼-钨(金)矿床均赋存于浅部矽卡岩中,在明则矿区矽卡岩型矿化之下发现了斑岩型钼矿化的存在,暗示该区的矽卡岩型矿化可能与冈底斯中带相似,具有统一的斑岩型-矽卡岩型成矿系统,由此建立了该地区的成矿模式,指出了找矿方向。

Medium-sized and large-scale skarn Cu-Mo-W（Au）deposits,e.g.Nuri,Mingze,Kelu,Chongmuda and Chenba,are distributed in the Shannan area of the eastern section of the Gangdese belt.Intrusion-related skarn copper mineralization belongs to high K and calc-alkaline rock series,located in the late collision magmatic arc and formed between 20 to 30Ma.Copper mineralization occurs at the exocontact zone of the lower Cretaceous Bima Formation carbonate and other calcareous-bearing sedimentary rocks with intrusions.At present,three main mineralization types are identified,including skarn type,hydrothermal vein type and porphyry type.Mineralizing associations are Cu-W-Mo,Mo,Cu-Au and Cu.In ore districts,those mineralization types form an entire porphyry-skarn Cu-Mo-W（Au）ore-forming system.Alterations of the exocontanct are mainly skarnization and hornfelsization,while the alterations of the endocontact are sericitization,silicification,and chloritization of intrusions.The Cu-Mo-W（Au）deposits in the Shannan area are interpreted as the shallow level.Appearance of porphyry molybdenum mineralization in the Mingze deposit implies that skarn mineralization of the study area resemble to those in the central sub-metallogenic belt,having a uniform porphyry-skarn ore-forming system.Based on data above,a metallogenic model is built to indicate further ore-search direction towards the deep subsurface.