蒸发岩盆地杂卤石成因及找钾意义

THE GENESES OF POLYHALITE IN EVAPORITE BASIN AND THEIRSIGNIFICANCE IN POTASH FORMATION

全球大型杂卤石矿床主要分布在二叠纪、三叠纪以及古近纪-新近纪这三个时期的地层中，并集中在北纬20～50＆#176;之间，我国正处于这一富集区内。由于杂卤石较其他含钾矿物溶解度低，因此常常被保留下来，为寻找可溶性钾盐或富钾卤水提供了有利线索。通过分析杂卤石成因类型并结合海水演化特点认为蒸发岩盆地杂卤石成因主要有两种：①原生沉积，但需要一定附加条件，即盐湖浓缩到硫酸钾镁盐沉积阶段时有外来钙离子的补给，或在硫酸钙盐沉积阶段有外来钾镁离子的补给，主要以前者为主；②后生交代，富钾镁的卤水通过构造裂隙运移并与石膏（或硬石膏）接触发生交代作用形成杂卤石。

Polyhalite is a double salt of magnesium and potassium mineral, They abundantly distributed in rock salt formations, but has obvious regularity, the world＆#39;s large Polyhalite ore deposits are mainly distributed in the Permian, Triassic and Paleogene-Neogene in strata in the three period, and focus between 20＆#176;to 50 ＆#176; north latitude, our country is in this enrichment stripe. Due to polyhalite than other potassium mineral solubility is low, so often be preserved for soluble potassium or rich brine potassium provide clues. At present,there are three kinds of polyhalite causes： primary sedimentary, penecontemporaneous metasomatism, epigenetic metasomatism. through the analysis of polyhalite genetic types and combining with the characteristics of evolution of seawater,I think its cause mainly has two kinds：first, primary sedimentation, but need some additional conditions , the salt concentration to potassium and magnesium salt phase have external calcium ion to supply （or the calcium sulfate salt deposition phase has a foreign supply of Mg and K rich brines）;Second, epigenetic metasomatism.the percolation of Mg and K rich brines through the gypsum layer occurs metasomatism.