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最近的研究表明,在厚冰川覆盖层上方,存在着空间上与地下矿体有联系的地球化学异常。现存的模型只能解释薄覆盖层中的地球化学异常,对这类异常何以会在厚层且年轻的覆盖层中出现,则无法作出解释。此前还没有提出过能够解释厚覆盖层中地球化学异常的新模型。本文讨论了现存模型的一些问题,并提出了一种新的解释模型,认为电化学引发的物质搬运是厚冰川沉积层上方地化异常形成的原因。大多数地表介质的氧化还原梯度较其下部地层更大,因此,基岩中石墨或金属硫化物等近垂向的电子导体,可在深部富还原剂和浅部富氧化剂地层之间的氧化还原场中形成“回路”。电子沿这一导体向上移动,消耗了上覆地层中的氧化剂。因此,与周围地层相比,导体上方地层出现负的氧化还原异常。由于导体上方地层氧化还原梯度较高,被还原的负离子会从导体顶部快速向外迁移,在还原区和氧化区之间形成氧化还原前缘。该氧化还原前缘以远远大于化学扩散的可量化的速率向外并向上推进,直到进入氧化剂不断补充的氧化环境中。这样,基岩处的氧化还原非均质性便传播到了地表,并在基岩矿体和地表之间形成永久性的“还原性岩石柱体”。在横向上,“还原柱”边缘区的氧化还原梯度比其顶部高,导致离子流在还原柱边缘区富集。地表沉积物中出现的“免耳”状异常,可能是由被还原负离子向上往还原柱两侧迁移与被氧化正离子向还原柱内部迁移共同作用的结果。在还原柱顶部,土壤介质中铁、锰和共沉淀元素含量贫乏,因为这类元素在还原环境中活动性较高。
Recent studies have shown that above the thick glacial overburden there are geochemical anomalies that are spatially associated with underground ore bodies. Existing models can only explain geochemical anomalies in thin overburden and no explanation can be given as to why such anomalies occur in thick, young overburden. No new model capable of accounting for the geochemical anomalies in thick overburden has been proposed before. This article discusses some of the problems with existing models and proposes a new model of interpretation that suggests that the electrochemical-induced material handling is responsible for the formation of anomalies over the thick glacial sediments. Most surface media have a redox gradient that is larger than the underlying formation, so near vertical electron conductors, such as graphite or metal sulfides, in the bedrock can be redox between the deep rich reductant and the shallow, oxidant-rich formations The field formed “loop ”. Electrons move up this conductor, depleting the oxidizer in the overburden. Therefore, negative redox anomalies appear in the formation above the conductor compared to the surrounding strata. Due to the high redox gradient of the formation above the conductor, the reduced anions migrate rapidly outward from the top of the conductor, forming a redox front between the reduction and oxidation zones. The redox front advances outwardly and upwardly at a quantifiable rate much greater than chemical diffusion until it enters an oxidizing environment where the oxidant is continually replenished. In this way, the redox heterogeneity at bedrock propagates to the surface and forms a permanent “reducing rock pillar ” between bedrock and surface. In the horizontal direction, the redox gradient in the “reduced column” edge region is higher than its top, resulting in an enrichment of the ion flux at the edge of the reduction column. The appearance of “Avoid ” anomaly in the surface sediments may be the result of the migration of the reduced anions up to both sides of the reduction column and the migration of the oxidized positive ions to the interior of the reduction column. At the top of the reduction column, the contents of iron, manganese and coprecipitates in the soil medium are poor due to the high mobility of these elements in the reducing environment.