磷锰钠矿是一种罕见的磷酸盐矿物,国内目前尚无报道,特别是原生矿物,国内外均未发现。已有少量资料认为磷锰钠矿为磷锰锂矿经钠交代形成,为次生矿物。磷锰锂矿为伟晶岩中的常见矿物,普遍认为其为富磷伟晶岩中岩浆阶段的产物,为原生矿物。本文在茶卡北山稀有金属伟晶岩中发现有磷锰钠矿和发育在其上的磷锰锂矿,磷锰钠矿均表现为完整的矿物颗粒,不具交代残余的痕迹,并具有原生矿物特征的磷灰石蚀变;而磷锰锂矿为不规则状,发育在磷锰钠矿上,表现为典型的交代特征。同时电子探针数据显示磷锰钠矿的Mn/Fe值为1.692~1.875,磷锰锂矿的Mn/Fe值为2.519~2.548,这也指示了磷锰钠矿早于其上磷锰锂矿的形成,磷锰钠矿应为原生矿物,其上的磷锰锂矿为次生成因。而伟晶岩区成矿熔体成分更高的锰含量可能是磷锰钠矿出现的原因。磷锰钠矿上发育的磷锰锂矿和氟磷灰石蚀变特征反映了后期氧化作用和富Li、Mn、Ca、F流体的交代作用;同时结合区内锂辉石的蚀变,说明茶卡北山伟晶矿床内存在着锂的地球化学循环。

Natrophilite is a rare phosphate mineral that has not been reported in China, especially its primary mineral, which has not been discovered both domestically and internationally. The literature with a few data suggests that natrophilite is formed by sodium replacement of lithiophilite as a secondary mineral. Lithiophilite is a common mineral in pegmatite, which is generally believed to be a product of the magmatic stage in phosphate rich pegmatites as a primary mineral. In this article, natrophilite and lithiophilite developed on natrophilite were found in the Chakabeishan rare-metal pegmatite. Natrophilite is characterized by euhedral mineral particles without any metasomatism, and has primary mineral features of apatite alteration. And the lithiophilite is irregular and develops on the natrophilite, showing typical metasomatic characteristics. Moreover, electron probe data showed that the Mn/Fe values of natrophilite were 1.692-1.875, and the Mn/Fe values of lithiophilite were 2.519-2.548. This also indicates that the formation of natrophilite occurred earlier than that of lithiophilite. Natrophilite should be the primary mineral, and the lithiophilite should be the secondary mineral. The higher manganese content of the parent magma in the pegmatite area may be a possible reason for the occurrence of natrophilite. The alteration of lithiophilite and fluoroapatite developed on the natrophilite reflect the later oxidation and metasomatism of Li, Mn, Ca, and F rich fluids. Meanwhile, combined with the alteration of spodumene in this area, it is indicated that there is a geochemical cycle of lithium in the Chakabeishan deposit.