西藏甲玛铜多金属矿床深部斑岩矿体找矿突破及其意义

Prospecting Breakthrough of the Deep Porphyry Ore Body and Its Significance in Jiama Copper Polymetallic Deposit,Tibet,China

甲玛铜多金属矿是西藏冈底斯成矿带中东段勘查程度最高、成矿元素与矿体类型复杂的超大型斑岩-矽卡岩型矿床。通过4年多、近350个钻孔的验证,不仅实现了矽卡岩矿体的找矿突破,同时在0—40线深部发现了产于二长花岗斑岩与石英闪长玢岩中的斑岩钼(铜)矿体,建立了"四位一体"的找矿勘查模式。斑岩矿体赋存标高一般处于4 600m以下,矿体走向NW—SE,倾向NE,近直立,矿体垂向延伸大于350m;斑岩矿石以发育细脉-浸染状、网脉状构造为特征;矿石中的矿石矿物主要为黄铜矿与辉钼矿,少见斑铜矿;脉石矿物主要为石英。初步查明:与铜矿化有关的含矿岩体主要为偏中性的石英闪长玢岩,蚀变以典型的细粒热液黑云母交代角闪石斑晶和基质而成的黑云母化蚀变为主;与钼矿化有关的含矿岩体主要为二长花岗斑岩,蚀变以硅化为主,次为绿帘石化、泥化和钾化。斑岩体与碳酸盐岩接触带常产出厚度超过200m的巨厚矽卡岩矿体,且在岩体一侧有内矽卡岩产出。甲玛深部斑岩矿体的发现不仅证实了"斑岩-矽卡岩型"的矿床成因观点,而且完善了甲玛矿床成矿模式与勘查模型。

Jiama copper polymetallic deposit is a superlarge porphyry-skarn one in the middle-eastern Gangdese metallogenic belt.It has the highest level of prospecting,a variety of ore-forming elements and ore body types,and brings huge economic benefit for Tibetan.Based on the ＂quaternity＂ prospecting model and nearly 350 drillholes in more than four years,not only has the skarn mineralization prospecting been achieved,but also the porphyry copper-molybdenum ore bodies have been proved from the 0 line to 40 line.In depth,porphyry molybdenum（copper） ore bodies are located in the monzonite granite porphyry and quartz diorite porphyrite.Porphyry ore bodies are generally below 4 600 m,with the strike NW—SE,dipping in NE direction,nearly vertical,and with vertical extension over 350 m.The porphyry ore is characterized by veinlet-disseminated structure,ore minerals mainly include chalcopyrite and molybdenite,with rare bornite,and the gangue mineral is mainly quartz.It is preliminary ascertained that the ore-bearing rock of the copper mineralization is mainly quartz diorite porphyry,with potassic alteration typically formed by the phenocrysts and matrix of hornblende replaced by the fine-grained hydrothermal biotite.The ore-bearing rock of molybdenum mineralization is acidic monzogranite porphyry,with the major alteration of silicification,secondary epidotization,argillization and potassic alteration.The huge skarn ore body,over 200 m wide,usually occurs around the contacts between the carbonate and porphyry.There develops endoskarn on the side of the porphyry.The deep porphyry ore body in Jiama deposit not only confirms the view that the deposit belongs to the porphyry-skarn deposit,but also perfects the metallogenic model and exploration model of Jiama deposit.