新疆伽师砂岩型铜矿床地质及S、Pb同位素地球化学

Geology and S-,Pb-isotopic Geochemistry of the Jiashi Sandstone-type Copper Deposit,Xinjiang,China

西南天山新生代山前盆地中的伽师铜矿是新疆近年发现和开发的一个重要的砂岩型铜矿,矿体产于古近系灰白色含岩屑钙质细砂岩中,呈与地层整合的板状、层状。矿石中硫化物主要为辉铜矿,矿体深部出现斑铜矿,极少量黄铁矿、闪锌矿等,硫化物多交代砂岩中胶结物或碎屑颗粒形成胶结结构,矿石发育稀疏浸染状、团块状、结核状等多种构造。矿石的硫同位素3δ4SV-CDT在-33.4‰^-24.6‰之间。矿石的铅同位素组成206Pb/204Pb=18.376~18.607、207Pb/204Pb=15.612~15.655、208Pb/204Pb=38.475~38.747。铜的硫化物矿化表现为含铜盆地流体(地下水)交代砂岩而沉淀,铜矿体形成于古近系细砂岩成岩晚期,矿石硫来源于细菌还原硫酸盐,矿石铅同位素组成指示成矿金属元素来自沉积盆地周围的蚀源区。

The Jiashi copper deposit,located in Cenozoic piedmont basin system of southwestern Tianshan in Xinjiang,is an important sandstone type copper deposit which has been discovered and mined recently.The ore bodies are tabular or stratiform in shape and occur in Neogene light grey detritus bearing calc sandstone.The sulfide minerals in the ores are mainly chalcocite,fewer pyrite and sphalerite.Bornites occur at the deep part of the ore bodies.The ore shows disseminated,lumpish and nodular structures,and the sulfide minerals replaced the cemented calcites in the sandstone and formed a cemented texture.The ore δ34SV-CDT varies from-33.4‰ to-24.6‰.The 206Pb/204Pb,207Pb/204Pb and 208Pb/204Pb of ore sulfide vary from 18.376 to 18.607,15.612 to 15.655 and 38.475 to 38.747,respectively.It is suggested that the Jiashi copper mineralization was a replacement of the sandstone by copper-bearing basin fluid（underground water）.The ore bodies formed during late diagenetic stage of the sandstone in Paleogene.The ore sulfur was derived from sulfate reduced by bacteria and the composition of the Pb isotope indicates that the metal were originated from the erosion source area around the sedimentary basin.