青海治多县当江铜多金属矿床成因、成矿时代及大地构造背景

Study on genesis,mineralization age and tectonic setting of Dangjiang copper polymetallic deposit in Zhiduo County,Qinghai Province

当江铜多金属矿床新发现于2014年,地处西南三江成矿带北段、青海省南部治多县多彩铜多金属矿整装勘查区,成矿时代尚未精确限定,矿床成因也未形成统一认识。通过高精度LA-ICP-MS锆石微区原位U-Pb同位素测年,获得与铜矿化、铅锌矿化密切相关的流纹岩锆石^(206)Pb/^(238)U年龄加权平均值为227.5±1.7 Ma,确定矿化发生在晚三叠世。通过与尕龙格玛铜多金属矿的对比研究,以及含矿围岩、蚀变特征、矿石矿物、矿石类型等分析,认为其成矿于巴塘群第二岩组火山岩韵律层中,形成过程与火山喷发作用密切相关,后期构造作用为成矿元素富集起着叠加构造的作用,矿床成因为火山喷流沉积-叠加改造型。综合判断认为,当江铜多金属矿形成于北羌塘地块北部的陆缘裂谷环境,为进一步深入研究西南三江成矿带北段铜多金属矿形成构造环境和扩大找矿提供了新思路。

The Dangjiang copper polymetallic deposit,located in the northern section of the"Sanjiang metallogenic belt",is newly discovered in 2014 in Duocai copper polymetallic deposit integrated exploration area in Zhidoi County,southern Qinghai Province.The mineralization age has not been precisely defined,and unified understanding of the genesis of Dangjiang copper polymetallic deposit has not been formed.LA-ICP-MS zircon U-Pb dating shows that the weighted mean age of rhyolite,which is closely related with copper,lead and zinc mineralization,is 227.5±1.7 Ma,in the Late Triassic.Through the comparative study with Galonggema copper polymetallic ore deposit and the analysis of its ore-bearing wall rock,alteration characteristics,ore minerals and ore types,It is believed that the ore-forming process is closely related with volcanic eruption,and the mineralization is formed in the volcanic rhythmical layer of the second rock formation in Batang Group.It is considered that the deposit is formed as volcanic exhalation sedimentation-superimposition reworking type,and the tectonism plays the role of superposition structure for enrichment of ore-forming elements.Comprehensively,we consider that Dangjiang copper polymetallic deposit is formed in the continental margin rift tectonic setting in the northern part of the north Qiangtang block,which provides a new perspective for further studying the tectonic setting of copper polymetallic deposits in the northern"Sanjiang metallogenic belt"and expanding prospecting.