西藏首例独立钼矿--冈底斯沙让大型斑岩钼矿的发现及其意义

Discovery of sharang large-scale porphyry molybdenum deposit,the first Single Mo deposit in Tibet and its significance

近年来西藏冈底斯斑岩成矿带找矿取得了一系列重大突破,迄今冈底斯带上的斑岩—矽卡岩铜钼矿床蚀变及矿化年龄主要集中在30～12Ma,形成于印度与亚洲大陆晚碰撞伸展环境或陆内后碰撞造山挤压向伸展走滑转换的过渡环境,但是与碰撞背景有关的独立斑岩钼矿还未见报道。笔者通过对沙让钼矿的多次考察和钻孔岩心的系统观察编录,主成矿岩体为花岗斑岩,强烈蚀变地段可达9km2。根据矿床的含矿斑岩(花岗斑岩)、热液蚀变类型及分带、脉系与矿化特征,认为沙让钼矿应归为独立的斑岩钼矿,产于碰撞环境的主碰撞阶段(55Ma)。并基于与同类矿床蚀变矿化范围、强度的对比和TEM、激电探测,矿化延伸可达800m深度,成矿条件优越,具有很大的找矿潜力。沙让独立斑岩型钼矿类型的确立将进一步丰富冈底斯这一巨型斑岩成矿带的成矿谱系,具有重要的区域找矿意义和研究价值。

Recently, series of major breakthroughs for porphyry copper exploration have been made in the Gangdese Metallogenic belt in Tibet. Alteration and mineralization ages of the Gangdese porphyry-skarn Cu（Mo） deposits concentrate in the range of 30-12 Mr, formed in the extension environment of late stage of collision between India and the Asian continents or the transitional environment from the post-collisional compression setting to strike-slip extension. However, the independent porphyry molybdenum deposit associated with the collisional setting has not been reported so far. This paper studies the ore-bearing porphyries, the types and horizational and vertical zonation of hydrothermal alteration, the characteristics of hydrothermal vein system and mineralization, according to the systmatic fieldwork and the mapping work of the drilling holes. The granitic porphyry is the ore-forming intrusion with intensive alteration of 9 km^2 in area. It concludes that, Sharang porphyry molybdenum is single porphyry molybdenum without any other important accompanying metal resources and it has been formed in the main collisional setting around 55 Ma. This study compares the scale of alteration and the intensity of mineralization with the same type of molybdenum deposits. Based on the comparisons and the results of TEM and induced electrical survey, the Sharang porphyry molybdenum deposit has rather large vertical extension to 800 m in the depth and showes excellent metallogenic conditions and great potential for further exploration. The establishment of the Sharang single porphyry molybdenum deposit will enrich the metallogenic pedigree of the giant Gangdese porphyry metallogenic belt. This discovery has a great significance for regional research and prospecting.