Abstract

Deposits in the Postmasburg field, South Africa, confined to rocks of the Transvaal Supergroup, occupy a significant place in world resources of the manganese and iron ores. The ore deposits represent karst residual accumulations. Several elements (B, Cr, Ni, Zn, Ge, As, Se, Mo, Ag, Cd, Sb, Te, W, Pb, REE) in them make up an assemblage providing insight into the geochemistry of the processes of ore formation. Among these elements, Mo, As, Ag, and REE are most representative. Molybdenum is marked by the chemosorptional incorporative nature of accumulation in these ores, sometimes with the formation of epictic overgrowths of the ferrimolybdate-type minerals. Arsenic, which is leached from the substrate rocks and accumulated in karst ferromanganese and iron ores, reflects total impact of the dominating iron oxide minerals upon its mobility. The behavior of Ag is controlled by the processes of supergene alteration of Archean–Early Proterozoic carbonate rocks and ores of the banded iron formation (BIF). Comparison of the distribution of rare earth elements (REE) in the karst iron, ferromanganese, and manganese ores, as well as banded iron ores, demonstrates that these elements display similar values of the cerium (C/Ce*) and europium (Eu/Eu*) anomalies, but differ in terms of the HREE and LREE fractionation (typical values: Ce/Ce* = 0.7‒1.0; Eu/Eu* = 0.8‒1.1). Banded iron and associated manganese ores were accumulated in the marginal anoxic-dysoxic marine basin, which was constrained by the continental land. Anoxic and dysoxic conditions were created by an intense hydrothermal activity.

中文翻译：

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稀有元素-卡拉哈里和马萨诸塞州锰矿田中锰和铁矿的形成环境标志（南非）：交流2。马萨诸塞州铁矿和锰田

摘要

南非的Postmasburg油田的矿床仅限于Transvaal Supergroup的岩石，在世界锰和铁矿石资源中占有重要地位。矿床代表岩溶残余堆积物。其中的几种元素（B，Cr，Ni，Zn，Ge，As，Se，Mo，Ag，Cd，Sb，Te，W，Pb，REE）组成一个组合，可提供对矿石形成过程的地球化学的深入了解。在这些元素中，Mo，As，Ag和REE最有代表性。钼的特征是这些矿石中积累的化学吸附结合性，有时会形成铁钼酸盐型矿物的过度生长。砷从基底岩石中浸出并积累在喀斯特铁锰和铁矿石中，反映出主要的氧化铁矿物对其迁移率的总体影响。Ag的行为受太古宙—早元古代碳酸盐岩和带状铁矿（BIF）矿石的超基因改变过程控制。比较岩溶铁矿，锰铁矿和锰矿以及带状铁矿中稀土元素（REE）的分布情况，结果表明这些元素显示出相似的铈（C / Ce *）和euro（Eu / Eu *）异常，但在HREE和LREE分级方面有所不同（典型值：Ce / Ce * = 0.7‒1.0； Eu / Eu * = 0.8‒1.1）。带状铁和伴生的锰矿聚集在边缘缺氧-缺氧的海洋盆地中，而该大陆盆地受其约束。缺氧和缺氧条件是由强烈的水热活动造成的。