滇东地区下寒武统磷块岩的次生变化及其形成机制

SECONDARY ENRICHMENT OF PHOSPHORITE IN EASTERN YUNNAN AND ITS FORMATION MECHANISM

滇东地区磷块岩在表生条件下所发生的一系列变化,是受其表生地球化学制约的,本文讨论了次生磷块岩的形成问题。

Secondary changes of phosphorite in eastern Yunnan are all restricted by the surface eochemical condition. Carbonate minerals are chemically more active than phosphate minerals. ased on 'the principle of restraint of chemical reaction', the author considers that the rosion of the former should take place prior to that of the latter, that is, the activity of arbonate minerals will prevent phosphate minerals from erosion. Porous structures speed up the rosion of the deposits. This results in the decrease in CaO/P_2O_5 ratio and the relative nrichment of phosphate minerals. It is only when carbonate minerals are all leached out and he H of the natural water decreases to a certain value that phosphate minerals can be resolved. s esult, secondary phosphorite is formed, PO_4^(3-) is dissociated from the solution, REE are elatively enriched, grade of phosphorite is lowered, and ores are impoverished.Illite, formed y hydrolysis of volcanic ash, is the main clay mineral in weathering phosphorite. Aluminium in econdary phosphor-aluminate minerals such as brazilianite comes from illite whereas PO_4^(3-) rom phosphorite.