Many accomplishments are made in the mechanistic study of iron source material migration for the formation of large-scale iron ore deposits during the Precambrian period.However, a few factors have yet to be fully resolved.In particular, still in debate are multiple theories on the genesis of cast iron deposits (non-Algoma type) of continental source.We have investigated the continental migration of iron source materials for the Ryongyon iron ore deposits in the Korean Peninsula as an example.From our geochemical study and the work of previous researchers, we showed that the iron ore was not Algoma type but formed from migration and sedimentation of weathered continental source materials under strong acidic conditions.As we know, during the Precambrian time, oxygen was depleted in the atmosphere and water with no ozone layers formed therefore no plants grew on land.Then, how did such a strong acidic environment occur?To clarify, we performed thermodynamic calculations on prevailing materials (at the time) that could convert water into acid in the environment.The results revealed that, when sulphide (such as pyrite) weathering occurred, it developed an iron source capable of medium degree weathering and transport.This result is consistent with the fact that the pH value was less than 3.5 for waters from the sulphide-rich stratum where iron content was much higher than in non-sulphide containing strata.Thus we conclude that sulphide weathering played a non-negligible role in the formation of continental source iron deposits.%前寒武纪时期铁矿形成过程中铁物质如何迁移的研究, 已取得了众多科研成果, 但仍有些问题未得到很好的解决.尤其是对陆壳来源性铁矿床 (非Algoma类型) 的成因, 仍然具有诸多争议, 焦点主要集中在铁迁移问题.笔者以朝鲜半岛龙渊铁矿床为例研究了铁介质形成和运输的问题.首先通过铁矿石的地球化学研究和前人研究结果的考察, 发现此铁矿床不属于Algoma类型, 而是在强酸性介质条件下陆壳物质风化、移动和沉积而形成的.那么为什么会出现如此强大的酸性环境条件呢?为了揭示这一点, 对在当时环境下把水的性质能够变成酸性的物质进行了热力学计算.研究结果表明, 当硫化物如黄铁矿风化时, 形成了能够使铁源物质风化和迁移的介质.这些结果也符合这样一个事实, 即目前从富含硫化物地层淋沥的水的pH值小于3.5, 并且铁含量远高于非硫化物类型的地层.本次研究结果表明, 陆壳来源的铁矿床形成过程中, 不能忽视硫化物的风化作用.
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