新太古界Campbellrand亚群白云岩岩溶系统对南非Postmasburg锰矿田的影响
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本文为河北地质大学青年科技基金资助项目(编号:QN202130)的成果


Impact of Neoarchean Campbellrand Subgroup dolostone karst system on Postmasburg manganese field, South Africa
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    摘要:

    为分析新太古界Campbellrand亚群白云岩基底形成的岩溶系统对南非Postmasburg锰矿田发育和分布的影响,利用XRF和偏光显微镜鉴定技术,结合野外地质调查和岩芯钻探,对矿石的矿物成分、矿体中的Mn、Fe空间分布、Doornfontein砾岩的结构特征、白云岩容矿构造的形态进行了研究。结果表明:Maremane穹隆上的Campbellrand亚群白云岩遭受了两次大规模的溶蚀。溶蚀构造引起沉积物分异,沉积建造底部Mn质最为富集,向外、向上逐渐由Fe质主导,形成褐锰矿—方铁锰矿—赤铁矿的序列,顶部则演变为铝土质岩。沉积序列中Mn+Fe质和Al质含量呈现出较强的负相关性。溶坑的特殊形态导致矿体受层控,但并不呈现规则的层状形态。东矿带的Wolhaarkop硅质角砾岩与白云岩中的燧石和硅质白云岩密切相关,而混合带和西矿带普遍发育的Doornfontein砾岩则是岩溶作用影响下锰质的成岩作用被推迟所形成,它们都是成矿期岩溶系统发育的间接产物。溶坑底部的锰土混合物揭示了成矿后期溶蚀作用的发生和沉积序列的坍塌破碎,小型的断层也造成了矿体的严重破碎和顶板地层的褶曲。Gamagara低山脊两侧分布的小型堆积型矿体也与后期地表岩溶系统长期的发育有关。

    Abstract:

    Postmasburg manganese field of South Africa was formed on dolostone platform of Neoarchean Campbellrand Subgroup. dolostone karst system played an important role in shaping the orebodies and orebelts. The impact of karstfication on development and distribution of ore is studied to reveal the genesis of Postmasburg manganese field. Methods: Based on field geological survey and diamond drilling, XRF and polarization microscope observationare applied to study mineral component of ores, spatial distribution of Mn and Fe, structure of Doornfontein conglomerate and host structure of dolostone .Results: Two large karstification occurred on Maremane Dome. The paleokarst cave led to differentiation of the sediments. Mn accumulated at the bottom of sedimentary formation while Fe was dominant upwards and outwards, thus a mineral series of braunite—bixbyite—hematite has been formed till replaced by aluminous shale at the top. In the sedimentary sequence, the content of Mn+Fe assemblage shows highly negative correlation with Al.Conclusions: The special geometry of karst sinkholes create stratabound ore bodies with irregularly shaped layers. The Wolhaarkop breccias in Eastern Belt are intimately associated with chert and siliceous dolostone , while Doornfontein conglomerates widespread in Mixed Type and Eastern Belt are formed in postdating lithification resulted by karstification, both of which are indirect products of karst system in mineralization period. The mixture of wad at the bottom of sinkholes indicates reactivitation of palaeokarst after mineralization and collapse of sedimentary sequence. Small faults destroyed ore bodies and folded the roof. Alluvial canga deposits with small size along Gamagara ridge also correlate with subsequent longterm development of surficial karst system.

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常洪伦,杜俊,杨大勇,时毓,王青春,张聚全,李甘雨.2022.新太古界Campbellrand亚群白云岩岩溶系统对南非Postmasburg锰矿田的影响[J].地质论评,68(5):2022092001,[DOI].
CHANG Honglun, DU Jun, YANG Dayong, SHI Yu, WANG Qingchun, ZHANG Juquan, LI Ganyu.2022. Impact of Neoarchean Campbellrand Subgroup dolostone karst system on Postmasburg manganese field, South Africa[J]. Geological Review,68(5):2022092001.

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  • 收稿日期:2022-04-08
  • 最后修改日期:2022-09-13
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  • 在线发布日期: 2022-09-19
  • 出版日期: 2022-09-15