Geology, mineralogy, and sulfur isotopes of the Mowana copper deposit, Matsitama Schist Belt, NE Botswana
Geology, mineralogy, and sulfur isotopes of the Mowana copper deposit, Matsitama Schist Belt, NE Botswana
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DOI：
10.1111/rge.12263
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发表时间：
2021-06
期刊：
影响因子：
1.4
通讯作者：
Amogelang Kooganne;A. Imai;A. Agangi;R. Takahashi
中科院分区：
文献类型：
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作者：
Amogelang Kooganne;A. Imai;A. Agangi;R. Takahashi
Mowana热液铜矿床位于博茨瓦纳东北部津巴布韦克拉通西南部的Matsitama-Motloutse杂岩内。本研究旨在根据地质学、石英结构、矿石矿物学、绿泥石地温测量和硫同位素分析来记录矿化特征。该矿床位于新太古代至古元古代 Matsitama 沉积群的碳质和泥质变沉积岩的石墨片岩透镜体内，呈北北东走向且几乎垂直倾斜（70-80°）的布须曼线。围岩热液蚀变以硅化、绿泥石化、绿帘石化、绢云母化、赤铁矿、方解石化等为特征。根据蚀变矿物组合，主要矿化阶段归因于温度在 ~200 至 ~340°C 之间的接近中性 pH 的流体。莫瓦纳矿床的贱金属矿化至少演化为两种矿脉类型。第一类矿化类型以石英+方解石±钾长石脉和角砾岩为代表，其特征是沉积主要黄铜矿、黄铁矿、少量斑铜矿和微量方铅矿。以石英+方解石±萤石矿脉为代表的2型矿脉含有大量方铅矿。矿床浅层广泛分布的表生矿化表现为大量存在辉铜矿、斑铜矿、蓝铜矿、角铁矿、孔雀石和赤铁矿。从 1 型矿脉中绿泥石地温测量获得的温度表明，与绿泥石蚀变相关的矿化是在 340 至 400°C 的温度范围内形成的。矿石矿物组合为：黄铁矿、斑铜矿和黄铜矿，与绿泥石地温测量数据相结合表明 1 型矿脉形成于中至高硫化状态。硫化物测定的硫同位素比表明，岩浆硫和/或主变沉积岩的淋滤以及海水硫酸盐的封闭系统还原是硫的来源。
The Mowana hydrothermal Cu deposit is located within the Matsitama–Motloutse Complex in the southwestern part of the Zimbabwe Craton in the northeastern part of Botswana. This study aims to document the characteristics of the mineralization based on geology, quartz textures, ore mineralogy, chlorite geothermometry, and sulfur isotope analyses. The deposit is hosted by the NNE‐striking and nearly vertically dipping (70–80°) Bushman Lineament, within the graphitic schist lenses in the carbonaceous and argillaceous metasedimentary rocks of the Neoarchean to Paleoproterozoic Matsitama Sedimentary Group. The hydrothermal alteration of the host rocks is characterized by silicification, chloritization, epidotization, sericitization, hematite, and calcite alteration. Based on the alteration mineral assemblage, the main mineralization stage is attributed to near neutral pH fluids at temperatures between ~200 and ~340°C. The base metal mineralization of the Mowana deposit was evolved in at least two vein types. The first mineralization type, represented by the quartz+calcite±K‐feldspar veins and breccias is characterized by the precipitation of principal chalcopyrite with pyrite, minor bornite, and trace amounts of galena. The Type 2 veins represented by the quartz+calcite±fluorite veins, host appreciable amounts of galena. The supergene mineralization widely distributed in the shallow levels of the deposit is manifested by the significant presence of chalcocite, bornite, covellite, anglesite, malachite, and hematite. The temperature obtained from the chlorite geothermometry in the Type 1 veins indicate that the mineralization associated with chlorite alteration formed at a temperature ranging from 340 to 400°C. The ore mineral assemblage: pyrite, bornite, and chalcopyrite, paired with the chlorite geothermometry data indicate that the Type 1 veins formed at an intemediate to high sulfidation state. Sulfur isotopic ratios determined on the sulfides indicate the magmatic S and/or leaching of the host metasedimentary rocks and closed system reduction of seawater sulfate as the sources of S.