表生风化淋滤作用的演化和为沉积矿床提供矿质能力的研究

THE EVOLUTION OF SUPERGENE WEATHERING AND ITS ABILITY OF SUPPLYING ORE-FORMING ELEMENTS

作者提出在火山脱气阶段形成强酸性和还原性雨水的风化淋滤条件,在火山间歇期形成饱含CO_2气雨水和氧化能力较强的风化淋滤条件下,地史晚期的火山间歇期则形成近似于现代空气雨水的风化淋滤条件。作者用自己设计的模拟实验仪器对多种岩石类型进行了三种大气雨水的风化淋滤模拟实验,计算了元素的带出强度和伴生关系,结合地质情况讨论了雨水pH值的历史演化,风化淋滤作用为沉积矿床提供金属元素的条件,以及风化壳矿床类型的历史演化等问题。

Based on research on the association of sedimentary minerals in the early geological his-tory, experimental studies of some deposits and equilibrium between the atmosphere and sea-water, the authors consider that supergene weathering has a history of evolution in a definite direction: in the early geological history there was strongly acidic and reducing rainwater, the rainfall was abundant and the superficial temperature was relatively high. So supergene we-athering in the early geological period had supplied large quantities of ore-forming elements into the sea, creating favourable conditions for the formation of sedimentary deposits, but no crustsedentary Fe, Al and Mn ores were formed. In the late geological history the rainwater became weakly acidic and strongly oxidizing and terrestrial water became neutral-alkaline and strongly oxidizing. The rainfall and the superficial temperature became moderate. Just then, there were formed a lot of ores on the contiets as crustsedentary Fe, Al and Mn ore de-posits. Meanwhile, the sedimentary deposits decceased in numbers. The sequence of forma-tion of these crustsedentary ore deposits in the geological history is: Fe ores→A1 ores and caly minerals→Mn ores→Co and Ni ores. The evolution of supergene weathering is the inevitable outcome of volcanodegassing in the earth, which changed from strong to weak.