西天山乔霍特铜矿成矿背景与矿床成因探讨

本文对西天山乔霍特铜矿的围岩火山岩、矿化火山岩和矿石的主、微量元素、Sr-Nd同位素地球化学特征进行了详细研究,并对呈小岩株状侵入到火山岩地层中的辉绿岩进行了单颗粒锆石LA-ICP-MS U-Pb精确定年.研究表明,围岩火山岩为形成于岛弧区弧后拉张环境中的钙碱性火山岩,系受俯冲带中流体交代的地幔源区通过岩浆结晶分异而来,乔霍特铜矿成矿物质与围岩火山岩具有相同的物质来源.辉绿岩单颗粒锆石LA-ICP-MS U-Pb定年获得281.0±1.9Ma年龄,结合前人研究成果,我们认为:奥陶纪或更早时期,南天山洋向北侧中天山地体下俯冲,在乔霍特地区形成岛弧带,奥陶纪晚期(约450Ma)具Ⅰ型花岗岩性质的岩浆侵位,形成了出露于矿区南侧的花岗闪长岩体;中-晚志留世(约430Ma),在浅海相岛弧区弧后盆地中火山喷发形成了巴音布鲁克组火山岩,与火山岩同期的火山喷流-沉积作用形成了乔霍特铜矿初始矿源层;志留纪后,南天山洋持续向北俯冲,于石炭纪末最终闭合,大洋岛弧火山与中天山古老陆块碰撞拼接,281Ma的辉绿岩呈小岩株状侵入到围岩火山岩地层中,初始矿体伴随南天山洋的持续俯冲及西天山增生造山作用受到了强烈的构造叠加改造,最终形成了空间上呈近东西向成群、成带与主控矿断裂近平行展布的矿体.乔霍特铜矿系发育于造山带中的VMS型矿床,应属火山喷流沉积+后期构造热液叠加改造型铜矿,是南天山洋俯冲、闭合及西天山增生造山综合作用的结果.

Metallogenic background and metallogenesis of Qiaohuote copper deposit,Western Tianshan Mountains

In this study,we research the major,trace element and Sr-Nd isotopic characteristics of volcanic host rocks,mineralized rocks,and ores of Qiaohuote copper deposit located in the Southeast of Yili block,Western Tianshan Mountains.We also conducted in situ zircon U-Pb LA-ICP-MS dating of the diabase,which intruded into the volcanic host rocks of Qiaohuote copper deposit.It is inferred that the volcanic rocks which are mostly composed of calc-alkaline andesitic volcanic rocks are interpreted as the derivatives of a mantle source modified by subduction zone fluids derived from the northward subducted Southern Tianshan oceanic slab in an island back-arc extensional environment.Laser ablation-ICPMS(LA-ICPMS)U-Pb zircon ages of 281.0±1.9Ma were obtained for diabase.The data presented here in conjunction with previously published data suggest that it was an island arc environment as the northward subduction of Southern Tianshan Ocean during Ordovician or even earlier in Qiaohuote region,and I-type granodiorite formed during Late Ordovician(ca. 450Ma).The host rocks of Qiaohuote deposit formed by the persistent subduction of Southern Tianshan Ocean during Middle-Late Silurian(ca. 430Ma),and meanwhile the volcanic exhalation-sedimentation,which was contemporaneous with the submarine volcanic rocks,produced the primary mineralization of the Qiaohuote copper deposit.Afterward,the ore bodies and host rocks were reworked and overprinted intensively by structures corresponding with the overall collisional orogenic process of the Western Tianshan during Late Carboniferous and Early Permian,the island arc crashed and fitted with the Central Tianshan block as then the diabase intruded into the host volcanic rocks(281Ma).The Qiaohuote copper deposit is a volcanic exhalation and sedimentation-structural reworking and overprinting type deposit,which formed by complicated processes involving the subduction and closing of Southern Tianshan Ocean and the accretionary orogenic process of Western Tianshan.