Hydrothermal alteration and Cu-Co mineralization at the peripheral zone (Target H) of the Kitumba iron-oxide copper-gold system, Mumbwa District, Zambia
Hydrothermal alteration and Cu-Co mineralization at the peripheral zone (Target H) of the Kitumba iron-oxide copper-gold system, Mumbwa District, Zambia
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赞比亚蒙布瓦区 Kitumba 氧化铁铜金系统外围带（目标 H）的热液蚀变和铜钴矿化
DOI：
10.1111/rge.12274
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发表时间：
2021
期刊：
影响因子：
1.4
通讯作者：
Echigo Takuya
中科院分区：
文献类型：
--
作者：
Simusokwe Mukuka;Watanabe Yasushi;Echigo Takuya
目标H是在赞比亚中部蒙姆瓦区发现的一个新的铜矿远景。蒙布瓦地区的铜矿化与胡克岩基的花岗岩-石英正长岩侵入有关的热液系统有关。热液系统的范围尚未被记录在案，但在花岗岩-石英正长岩体的边缘发现了各种铜矿远景，包括目标H。本研究的目的是利用岩相学、地球化学和硫同位素资料研究H靶区的地质特征，以了解热液系统边缘的成矿特征。富铜、富钴矿体赋存于与新元古代加丹加超群昆德伦古群相关的粉砂岩和角砾岩中。粉砂岩由砂岩和泥岩交替组成，砂岩和泥岩由成岩石英、钠长石、白云石、方解石和白云母组成。角砾岩与层理平行，产于褶皱破碎的粉砂岩单元中。岩石地层学的特征是三个域：角砾岩、过渡岩和主岩，根据粉砂岩和角砾岩的比例进行定义。热液蚀变使成岩矿物发生了变质作用，形成了受主岩原生矿物学控制的蚀变产物：钾长石和白云母取代了粉砂岩中的钠长石和白云母，菱铁矿和赤铁矿取代了角砾岩中的白云石和方解石。含或不含菱铁矿和赤铁矿的细脉中均可观察到热液方解石。铜矿化与热液蚀变有关，以黄铜矿、斑铜矿和辉铜矿的形式赋存于角砾岩和网纹矿脉中。地球化学与岩性相关图解表明，大部分铜矿化赋存于角砾岩中。角砾岩中Co的异常丰度与角砾岩中的铜有关，但两种金属并未表现出相似的富集和亏损行为。富铜矿体赋存于赤铁矿为主的角砾岩域中，富钴矿体赋存于过渡域菱铁矿为主的角砾岩单元中。除铜和钴外，地球化学数据还显示，角砾岩中Fe、P、Ba、Mo、Pb、W、U、V和轻稀土元素显著富集。硫化物矿物的硫同位素显示角砾岩中较轻的δ34S值在5~9‰之间，而粉砂岩中的重δ34S值约为17~28‰。角砾岩中硫化物测得的δ34S值与位于热液系统中心的基通巴矿床测得的值相当。我们提出了目标H角砾岩中富铜钴矿体的岩浆热液成因。角砾岩是来自基通巴矿床的富铁氧化物金属流体的输导通道。流体与富含白云石的粉砂岩的冷却和反应引发了氧化还原反应，沉积了铜硫化物矿物和异常浓集的钴。
Target H is a new Cu prospect discovered in the Mumbwa district of central Zambia. Copper mineralization in the Mumbwa district is linked to the hydrothermal system associated with the granite‐quartz syenite intrusions of the Hook batholith. The extent of the hydrothermal system has not been documented, but various Cu prospects, including Target H, have been discovered at the margins of the granite‐quartz syenite bodies. The objective of this study is to investigate the geological characteristics of the Target H prospect using petrographic, geochemical, and sulfur isotope data in order to understand the features of mineralization at the margin of the hydrothermal system. The Cu‐ and Co‐rich orebodies are hosted in siltstone and breccia correlated to the Kundelungu Group of the Neoproterozoic Katanga Supergroup rocks. The siltstone consists of alternating beds of sandstone and mudstone that are composed of diagenetic quartz, albite, dolomite, calcite, and muscovite. Breccia occurs parallel to the bedding planes and in the folded and fractured siltstone units. Lithostratigraphy is characterized by three domains: breccia, transition, and host rock, which are defined depending on the proportion of siltstone and breccia. The diagenetic minerals have been modified by hydrothermal alteration, resulting in alteration products controlled by the primary mineralogy of the host rocks: K‐feldspar and muscovite replace albite and muscovite in siltstone, while siderite and hematite replace dolomite and calcite in breccia. Hydrothermal calcite is observed in the veinlets with or without siderite and hematite. Copper mineralization is associated with hydrothermal alteration and occurs as chalcopyrite, bornite, and chalcocite in breccia and stockwork veins. Diagrams correlating geochemistry to lithology show that the bulk of Cu mineralization is hosted in the breccia. An anomalous concentration of Co occurs with Cu in breccia, but the two metals do not show similar enrichment and depletion behaviors. The Cu‐rich orebody forms in hematite‐dominated breccia domain, whereas Co‐rich orebody forms in siderite‐dominated breccia units in the transition domain. In addition to Cu and Co, geochemical data show significant enrichment of Fe, P, Ba, Mo, Pb, W, U, V, and light rare earth elements in the breccia. Sulfur isotopic values of sulfide minerals show lighter δ34S values between 5 and 9‰ in the breccia and heavy δ34S signatures of approximately 17–28‰ in the siltstone. The δ34S values measured from sulfides in the breccia were comparable to the values obtained from the Kitumba deposit, which is located at the center of the hydrothermal system. We propose a magmatic‐hydrothermal origin for the Cu‐ and Co‐rich orebodies in the breccia at Target H. Breccia was the conduit for iron‐oxide‐rich metal‐bearing fluids that originated from the Kitumba deposit. Cooling and reaction of the fluids with dolomite‐rich siltstone triggered a redox reaction that deposited Cu sulfide minerals and an anomalous concentration of Co.