云南东川群碎屑锆石年代学和元素地球化学及其地质意义

东川式铜矿主要分布在云南省中北部的康滇地区,属于典型的沉积岩型容矿铜矿床,以东川地区的东川铜矿床铜储量最大。东川群是东川式铜矿的主要赋矿围岩,查明东川群物源对于识别沉积作用的源区、沉积构造环境和Cu成矿作用以及对于研究沉积岩型容矿铜矿床的成矿模式具有重要意义。本文对东川地区东川群的因民组、黑山组、青龙山组样品的碎屑锆石进行了LA-ICP-MS U-Pb定年和原位微量元素分析。结果表明,东川群绝大多数碎屑锆石属岩浆锆石,且来自S型花岗岩源区。所有锆石显示了～2.7Ga、～2.5Ga、～2.2Ga、～1.8Ga和～1.5Ga等5个年龄峰值,首次确定青龙山组最大沉积年龄为～1220Ma。东川群含矿地层成岩和成矿物质具有二元特征:地层主体成分来自于毗邻的哥伦比亚造山带的S型花岗岩,而金属Cu应为同一造山带内先期存在的Cu矿床或者富Cu岩石经过剥蚀、搬运和沉积成矿作用富集的。

Detrital zircon chronology and element geochemistry of the Dongchuan Group in Yunnan Province and its geological significance

Dongchuan-type copper deposit, a typical sediment-hosted stratiform copper deposit, is distributed in the Kangdian area in the central and northern part of Yunnan Province. This deposit is the most important Dongchuan-type copper deposit which is hosted in Dongchuan Group, in the Kangdian area in Yunnan Province. As a result, discrimination of the provenance of Dongchuan Group is very important for tracing the sediment source regions, tectonic environment and the copper mineralization of the deposit. In this study, zircons from the strata of Yinmin, Heishan and Qinglongshan formations of the Dongchuan Group were applied for LA-ICP-MS U-Pb dating and in-situ trace elements analysis. The results demonstrate that most of the detrital zircons in Dongchuan Group were of magmatic-origin, i.e., mainly from S-type granites. The detrital zircons ages from Dongchuan Group show five age peaks, which are ~2.7Ga, ~2.5Ga, ~2.2Ga, ~1.8Ga, and ~1.5Ga, respectively. The maximum zircon age is 1220Ma, which provided constrains on the sedimentary age of the Qinglongshan Formation for the first time. Our studies suggest that the materials of the Dongchuan Group deposit-host strata, including sediments and Cu metals, were from two endmembers: the sediments come from the S-type granitoids of the adjacent Columbia orogen, while the copper come from the erosion and transportation processes of a pre-exist Cu deposit or Cu-rich magmatic rocks in the same orogen.