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首页> 外文期刊>South African journal of geology >Gabbro-norite-hosted Ni-Cu-(Co)-sulphide mineralization in southern Namaqualand and its relationship to the cupriferous Koperberg Suite of the Okiep Copper District, South Africa
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Gabbro-norite-hosted Ni-Cu-(Co)-sulphide mineralization in southern Namaqualand and its relationship to the cupriferous Koperberg Suite of the Okiep Copper District, South Africa

机译：纳马夸兰郡南部由Gabbro-norite承载的Ni-Cu-（Co）-硫化物矿化及其与南非Okiep铜区的铜质Koperberg套间的关系

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Small Ni-Cu-(Co) massive sulphide deposits are located 140 km south of the well-known Okiep Copper District within a polyphase deformed, granulite facies metamorphic section of the mid-Proterozoic Namaqua-Natal belt in western Namaqualand. Massive sulphides, consisting of magnetic pyrrhotite with minor exsolved cobaltian pentlandite and chal-copyrite as well as pyrite, are concentrated towards the structural (possibly original) base of an orthomagmatic gabbro-norite host rock. The bodies are small, irregularly shaped and structurally attenuated parallel to the regional foliation. The gabbro-norite host displays in situ segregations of anorthosite, diorite, and glimmerite. It is juxtaposed with small bodies of non-mineralized norite and quartz-norite, collectively known as the Nuwefontein Suite, and extensively developed younger charno-enderbite. The largest two of the massive sulphide lenses have a combined in situ ore resource of 2 million metric tons at a grade of 0.88 % Ni, 0.20 % Cu, 410 ppm Co, and negligible platinum group elements. A comparative petrochemical study with the cupriferous mafic rocks of the time-equivalent Koperberg Suite of the Okiep Copper District shows the pre- to syntectonic two-pyroxene granulites to be the closest analogy to the mineralized gabbro-norites. The similar geo-chemical characteristics of both the Nuwefontein and Koperberg suites indicate a common upper-mantle-lower-crust derived, calc-alkaline, high-alumina, basaltic parent magma generated in a subduction-related tectonic environment. A two-stage evolutionary genetic model is proposed. The early intrusive phases consisted of gabbro-norite sills and dykes with minor associated Ni-Cu-Co massive sulphide mineralization (Hondekloof type). This was followed by later, diapir-shaped, composite mafic intrusions dominated by anorthosite (Koperberg type). Mineralization consists of disseminated chalcopy-rite and bornite, hosted mainly by the last hypermelanic low-sulphur magnetite-rich phases. This interpretation is consistent with the Fram and Longhi model proposed for the generation of anorthosite complexes from basaltic magmas. It is apparent that orthomagmatic base metal mineralization associated with calc-alkaline magmatism extends beyond the perimeters of the Okiep Copper District in western and southern Namaqualand.
机译：小的镍-铜-（钴）块状硫化物矿床位于著名的奥基普铜矿区以南140公里处，位于纳马夸兰西部中元古代纳马夸-纳塔尔带中的多相变形粒状相变质带中。块状硫化物，由磁性黄铁矿与少量溶解的钴铁蒙脱石，黄铜矿-黄铁矿以及黄铁矿组成，集中于正磁辉长辉石-黑铁矿基质岩石的结构（可能是原始的）基础上。主体很小，形状不规则，并在平行于区域叶的结构上衰减。辉长岩-黑铁矿主体显示原位铁矿，闪长岩和闪锌矿的原位偏析。它与未矿化的Norite和石英Norite的小物体并置在一起，统称为Nuwefontein Suite，并广泛开发了较年轻的黑炭黑咬合剂。块状硫化物透镜中最大的两个具有200万吨的综合原矿资源，品位为0.88％的镍，0.20％的铜，410 ppm的钴和可忽略不计的铂族元素。用俄亥俄铜矿区等效的Koperberg Suite的铜质镁铁质岩石进行的比较石化研究表明，前至同构造的二-花岗岩是最接近矿化辉长岩的类比。 Nuwefontein和Koperberg套件的相似地球化学特征表明，在俯冲相关的构造环境中产生了常见的上地幔-下地壳，钙碱性，高氧化铝，玄武岩母岩浆。提出了两阶段进化遗传模型。早期侵入相包括辉长岩-norite门槛和堤坝，伴有少量相关的Ni-Cu-Co大块硫化物矿化（Hondekloof型）。随后是后来的斜岩状复合镁铁质侵入体，其主要成分是无钙铝石（Koperberg型）。矿化作用由弥散的黄铜矿和斑铁矿组成，主要由最后的高黑色素低硫磁铁矿富集相组成。这种解释与从玄武岩浆中生成钙铁矿复合体的Fram和Longhi模型是一致的。显然，与钙碱性岩浆作用有关的正岩系贱金属矿化作用超出了纳马夸兰西部和南部的奥基普铜矿区的范围。

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