Abstract The paper presents the results obtained from petrographic and lithogeochemical studies of Tertiary alluvial deposits in the Buchansvale 61 IQ farm around the Ventersdorp region. These are unconsolidated manganese-bearing sediments of alluvial origin, currently making up the West-wits alluvium which overlies the manganiferous dolostones of the Transvaal Basin in a weathering crust. Mineralogically, the alluvial deposits are composed mainly of detrital quartz, feldspars, and grains of zircon and traces of ilmenite. Authigenic mineral phases are predominantly composed of clays and iron oxides, cryptomelane (KMn8O16), hollandite/romanechite (BaMn8O16/10), spinel-galaxite (Mn2+Al2O4) and other manganese oxides/oxyhydroxides. Quartz modal content makes up an average of 70% of all detrital framework grains. The content of feldspar, cement minerals and clays seldom exceeds 20%. An extensive diagenetic replacement of detrital grains and early formed authigenic mineral and cements by Mn oxides is evident. The study applied the method of modal composition analytical study to count the percent ratios of framework grains (grains of quartz, feldspar, pyroxene, amphibole, mica, etc.) in the samples in order to reconstruct their source regions. According to the observations made from the data interpretation, the probable sources of the sediments were inferred from old recycled orogens and cratonic interiors. It was further noticed that the sediments are characterized by arkoses to subarkoses and subordinate quartz arenite. These observations indicate the near source regions, most probably a combination of Pretoria Group sediments and Black Reef Quartzite. Sedimentation occurred in a low-lying plain characterized by tropical-moderately humid and subhumid climates. Here, in combination with increased pH of the basinal waters which is attributable to surficial weathering of the Malmani Dolostones and intensive oxidation, a replacement of detrital grains with manganese dioxide precipitates became prominent.

中文翻译：

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南非文特斯多普地区含锰冲积矿床的矿物组成及源区重建

摘要 本文介绍了对文特斯多普地区周围 Buchansvale 61 IQ 农场第三纪冲积矿床的岩石学和岩石地球化学研究结果。这些是冲积成因的松散含锰沉积物，目前构成 West-wits 冲积层，覆盖在风化壳中的德兰士瓦盆地含锰白云岩上。在矿物学上，冲积矿床主要由碎屑石英、长石、锆石颗粒和微量钛铁矿组成。自生矿物相主要由粘土和氧化铁、钾锰矿 (KMn8O16)、荷兰石/罗纹石 (BaMn8O16/10)、尖晶石-galaxite (Mn2+Al2O4) 和其他锰氧化物/羟基氧化物组成。石英模态含量平均占所有碎屑骨架晶粒的 70%。长石的含量，水泥矿物和粘土很少超过 20%。Mn 氧化物对碎屑颗粒和早期形成的自生矿物和胶结物进行了广泛的成岩作用是明显的。本研究采用模态成分分析研究的方法，对样品中骨架颗粒（石英、长石、辉石、角闪石、云母等颗粒）的百分比进行计数，以重建其源区。根据资料解释的观察结果，沉积物的可能来源是从古老的再生造山带和克拉通内部推断出来的。进一步注意到沉积物的特征是长石到亚长石和次要石英砂岩。这些观察表明近源区，很可能是比勒陀利亚群沉积物和黑礁石英岩的组合。沉积发生在低洼平原，其特征是热带中等湿润和半湿润气候。在这里，与由于 Malmani 白云岩的表面风化和强烈氧化导致的流域水 pH 值升高相结合，用二氧化锰沉淀物替代碎屑颗粒变得突出。