西藏甲玛矿区角岩特征及其对深部找矿的意义

Hornfels feature in the Jiama ore deposit, Tibet and its significance on deep prospecting

角岩是西藏甲玛铜多金属矿床近年来钻探工作大量揭露的赋矿围岩之一,其中蕴藏的钼铜资源量已达大型以上规模,不但为甲玛增加资源量提供了新的保障,而且在矽卡岩型和斑岩型之外增加了一种新的矿石类型。但角岩的研究相对薄弱,对其在深部找矿方面的研究更是空白。本文通过对甲玛角岩基本特征的研究,归纳了角岩的空间分布,分析了角岩的物质组成,结合角岩中裂隙的统计结果,推测了深部岩体的中心位置,为深部找矿提出了建议。认为甲玛矿区角岩分布广但厚度不均匀,以ZK3218钻孔最厚(达1027m),向周围逐渐减薄,到矿区西南角和西端多个钻孔中尖灭。角岩型矿体以辉钼矿和黄铜矿为主,ZK3217钻孔中矿体厚达900m,紧邻ZK3218钻孔,矿化普遍,但品位较矽卡岩低。角岩中裂隙统计表明,在ZK1616至ZK3216一带,裂隙密度达40条/米以上,向周围减少。综合角岩的岩石学、矿物学和地球化学等特征,认为甲玛矿区为角岩提供热源的深部岩浆分布在ZK3216-ZK3217-ZK3218一带,建议布置深钻,深部可能存在矽卡岩型矿体和斑岩型矿体。

Hornfels has become one of the most important host rocks in the Jiama copper polymetallic deposit since the drilling exploration exposed it more in recent years. The molybdenum and copper resources hosted in hornfels have assessed to reach the large scale, so it will provide more resources for the mine as a new ore type besides skarn type and porphyry type ore in Jiama. However, study on hornfels in Jiama is at the very low level, especially on its significance on deep prospecting. Hornfels feature in Jiama has been studied including analysis on its space distribution, mineral assemblage, chemical component and statistic on fracture in hornfels. Based on the above feature, the speculation on the center location of deep rock body and suggestion on deep prospecting have been discussed. Hornfels in Jiama spreads widely with uneven thickness. In drillhole ZK3218, it reaches 1027m thick, and hornfels trends to less thick in the surrounding and thins out in some drillholes in the southwest end and west end. Molybdenite and chalcopyrite are the main ore mineral in hornfels with wide scope but lower grade than skarn. The hornfels type orebody in drillhole ZK3217 reaches 900m thick locating closely to ZK3218. The statistic on fractures in hornfels has showed the concentrated area circled the drillhole ZK1616-ZK3216 with more than 40 fractures in each meter and gets less in around. Combined with the above feature of hornfels, it’s suggested to arrange the deep drilling in the area of ZK3216-ZK3217-ZK3218 which is supposed to be the heat center for hornfels, and the deep drilling may hit the skarn type orebody and porphyry type orebody.