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Evolution of the Munali Intrusive Complex: Host to a carbonate-rich Ni-(Cu-PGE) sulfide deposit
Ore Geology Reviews ( IF 3.3 ) Pub Date : 2022-09-19 , DOI: 10.1016/j.oregeorev.2022.105109
Daryl E. Blanks, David A. Holwell, Stephen J. Barnes, Louise E. Schoneveld, Adrian J. Boyce, Laston Mbiri

The Munali Intrusive Complex is hosted within supracrustal metasedimentary rocks located along a major structural lineament within the Zambezi Belt in southern Zambia. The complex comprises unmineralised gabbro surrounded by a marginal heterogeneous mafic–ultramafic breccia unit that is host to Ni-Fe sulfide. This marginal unit comprises a range of variably evolved brecciated mafic–ultramafic rocks that include gabbro, olivine-gabbro and dolerite, alongside younger, pegmatitic, apatite-magnetite-bearing clinopyroxenite, wehrlite and dunite. The magmatic evolution is most consistent with a model whereby early mafic rocks interact with hot, MgO- and volatile-rich melts along gabbro contacts, causing localised metasomatism of gabbro and pyroxenites, and progressively replacing pyroxene-rich rocks with olivine, forming pegmatitic ‘replacive dunites’. Sulfide mineralisation is characterised by a carbonate-rich apatite-magnetite-bearing assemblage predominately present as lenses of semi-massive to massive sulfide ore. The complex is enveloped almost entirely within a unit of marble, yet C and O isotope signatures of carbonate at Munali have revealed a clear mantle signature for some of the carbonate associated with sulfide, alongside a more dominant, crustally derived component. The carbonate occurring alongside sulfide displays micro to macro textures signifying the presence of carbonate melts formed from anatectic melting of the country rocks. The presence of fracture sets that define coarse breccia clasts (>1 m) indicate that the host rock was significantly crystallised and brittly deformed prior to carbonate and sulfide melt infiltration. Both carbonate and sulfide melts appear to have independently utilised these pre-existing weaknesses producing a pseudobreccia, and accounting for the seemingly chaotic nature of the orebody. The indication of sulfide being a significantly later phase suggests that the sulfide did not form in situ and was mobilised from elsewhere to be subsequently emplaced late within the Munali system.



中文翻译:

Munali 侵入杂岩的演化:富含碳酸盐的 Ni-(Cu-PGE) 硫化物矿床的宿主

Munali 侵入杂岩位于赞比亚南部赞比西带内的主要构造线沿线的地壳变沉积岩中。该复合体包括未矿化的辉长岩,​​周围是边缘异质镁铁质-超镁铁质角砾岩单元,该单元以 Ni-Fe 硫化物为主。这个边缘单元包括一系列变化不定的角砾镁铁质-超镁铁质岩石,包括辉长岩、橄榄辉辉石和辉长岩,以及较年轻的伟晶岩、含磷灰石-磁铁矿的单斜辉石、wehrlite 和纯纯岩。岩浆演化最符合早期镁铁质岩石与辉长岩接触处富含MgO和挥发分的热熔体相互作用,导致辉长岩和辉石岩的局部交代作用,并逐渐用橄榄石取代富含辉石的岩石,形成伟晶质“替代品”的模型。沙丘”。硫化物矿化的特征是富含碳酸盐的磷灰石-磁铁矿组合,主要以半块状到块状硫化矿的透镜体形式存在。该复合体几乎完全包裹在一个大理石单元内,但 Munali 碳酸盐的 C 和 O 同位素特征揭示了一些与硫化物相关的碳酸盐的明显地幔特征,以及更占主导地位的地壳衍生成分。与硫化物一起出现的碳酸盐显示出微观到宏观的纹理,表明存在由乡村岩石的深熔熔融形成的碳酸盐熔体。定义粗角砾岩碎屑(> 1 m)的裂缝组的存在表明,在碳酸盐和硫化物熔体渗透之前,主岩显着结晶和脆性变形。碳酸盐和硫化物熔体似乎都独立利用了这些预先存在的弱点,产生了假角砾岩,并解释了矿体看似混乱的性质。硫化物明显较晚的迹象表明,硫化物不是在原位形成的,而是从其他地方调动起来的,随后在 Munali 系统的后期就位。

更新日期:2022-09-19
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