CO2‐rich fluid from metamorphic devolatilization of the Triassic Orogeny: an example from the Qiaxia copper deposit in Altay, NW China
CO2‐rich fluid from metamorphic devolatilization of the Triassic Orogeny: an example from the Qiaxia copper deposit in Altay, NW China
复制标题
DOI：
10.1002/gj.2536
复制
发表时间：
2014-11
影响因子：
1.8
通讯作者：
Yi Zheng;Li Zhang;Huayong Chen;Dengfeng Li;Chengming Wang;Jing Fang
中科院分区：
文献类型：
--
作者：
Yi Zheng;Li Zhang;Huayong Chen;Dengfeng Li;Chengming Wang;Jing Fang
恰夏铜存款矿床产于阿尔泰造山带的火山-沉积型克兰盆地中，呈脉状产出，受北西向构造控制。矿区暴露的火成岩和沉积岩层经历了绿片岩相变质作用，表现为绿泥石-绿帘石-黑云母±石榴石±角闪石组合。热液成矿作用可分为早、中、晚三个阶段，分别以条带状磁铁矿石英脉、铜多金属石英脉和碳酸盐石英±黄铁矿细脉为代表。主要矿石矿物包括黄铜矿和其他多金属硫化物，主要形成于中期阶段。栖霞铜存款中的流体包裹体有4种类型：水相包裹体（W型）、碳水相包裹体（C型）、纯碳相包裹体（PC型）和含子矿物包裹体（S型）。早期石英捕获在335-388 °C的温度下完全均质化的C-和W-型原生FI，具有5.51-8.66重量%的低盐度。NaCl当量;而晚期石英或方解石仅包含W型FI，均质温度为122-239 °C，盐度为0.18-7.86 wt.% NaCl当量这表明成矿系统是从富CO2变质演化到贫CO2变质，并加入了晚期大气降水，在演化过程中可能发生了显著的CO2逃逸。所有四种类型的FI的共存只能在中间阶段的矿物中观察到，即使在晶体的微观区域中，代表了从沸腾流体系统中捕获的缔合物。这些FI主要在288至329 °C的温度范围内均质化，具有3.39-11.75重量%的两个盐度簇。NaCl当量和38.93-46.37重量% NaCl当量，分别在中期阶段，独特的富CO2 FI包括C-和PC-类型，这意味着金属沉淀是由流体沸腾、CO2逃逸和主要来自变质脱挥发分作用的瞬时过饱和引起的。因此，可将恰夏铜存款作为三叠纪陆-陆或陆间碰撞变质挥发作用形成的造山矿脉铜系统的一个实例，并提出了一个存款-规模的成矿模式来解释恰夏铜存款的形成机制。版权所有© 2013约翰威利父子有限公司.
The Qiaxia Cu deposit occurs as veins controlled by NW‐extending structures in the Devonian volcano‐sedimentary Kelan Basin of the Altay orogenic belt, Xinjiang, China. Igneous and sedimentary strata exposed in the mining area have been subjected to greenschist‐facies metamorphism represented by an assemblage of chlorite–epidote–biotite ± garnet ± amphibole. The hydrothermal ore‐forming process can be divided into the early, middle and late stages, represented by banded magnetite‐quartz, Cu‐polymetallic‐quartz veins and carbonate‐quartz ± pyrite veinlets, respectively. The main ore minerals including chalcopyrite and other polymetallic sulphides are revealed to have mainly formed in the middle stage. Four types of fluid inclusions (FIs), including aqueous (W‐type), carbonic‐aqueous (C‐type), purely carbonic (PC‐type) and daughter mineral‐bearing (S‐type), have been identified at the Qiaxia copper deposit. The early‐stage quartz captures the C‐ and W‐type primary FIs completely homogenized at temperatures of 335–388 °C with low salinities of 5.51–8.66 wt.% NaCl equiv.; whilst the late‐stage quartz or calcite contains only the W‐type FIs with homogenization temperatures of 122–239 °C, and salinities of 0.18–7.86 wt.% NaCl equiv. This indicates that the metallogenic system evolved from CO2‐rich, metamorphic to CO2‐poor, with the addition of late meteoric fluid, and that a significant CO2‐escape may have occurred during the evolution. The coexistence of all four types of FIs can only be observed in the middle‐stage minerals, even in the microscopic domain of a crystal, representing an association trapped from a boiling fluid system. These FIs are homogenized at temperatures ranging mainly from 288 to 329 °C, with two salinity clusters of 3.39–11.75 wt.% NaCl equiv. and 38.93–46.37 wt.% NaCl equiv., respectively. The unique CO2‐rich FIs including C‐ and PC‐types in the middle stage implies the metal precipitation results from fluid boiling, CO2‐escape and transient oversaturation primarily from metamorphic devolatilization. Hence, the Qiaxia Cu deposit can be taken as an example of an orogenic lode Cu system resulting from metamorphic devolatilization in Triassic continent‐continental or intercontinental collision; and a deposit‐scale metallogenic model has been proposed to interpret the mechanism of formation of the Qiaxia Cu deposit. Copyright © 2013 John Wiley & Sons, Ltd.