东天山白石头泉天河石花岗岩岩浆-热液过渡阶段的副矿物

Accessory minerals formed during magmatic-hydrothermal transition of Baishitouquan amazonite granite,Eastern Tianshan

新疆哈密星星峡白石头泉天河石花岗岩从下往上分为5个岩相带,即淡色花岗岩、含天河石花岗岩、天河石花岗岩、含黄玉天河石花岗岩和黄玉钠长花岗岩。各相带中都有一些岩浆晚期形成的不规则状孔洞。孔洞多小于2 mm,其充填物以萤石为主,并有石榴石、锡石、钠长石和白色云母等。这些充填物是岩浆-热液过渡阶段晚期的产物。充填物的成分表明,贫钙镁铁而富氟的过铝花岗岩,其岩浆-热液过渡阶段的晚期产物以含大量萤石为特征,并表明氟化物或氟络合物是该阶段流体中锡的重要搬运形式。该阶段初步富集锡的孔洞流体如因构造裂隙贯通而发生运移,就可能在有利地段聚集,形成脉状锡矿床。

The Baishitouquan amazonite granite pluton near Xinxinxia of Hami County,Xinjiang,China,includes five lithological zones.They are,up the pluton,the leucogranite zone,amazonite-bearing granite zone,amazonite granite zone,topaz-bearing amazonite granite zone and topaz albite granite zone.Irregular-shaped cavities formed during the late magmatic stage are found in all the five zones.These cavities,mostly less than 2 mm in size,were filled dominantly with fluorite accompanied by garnet,cassiterite,albite and white mica.These infilling minerals were crystallized late at the magmatic-hydrothermal transition stage.The composition of the infillings indicates that the product at this stage is an evolving calcium-,magnesium-,and iron-poor and fluorine-rich peraluminous granite,which is characterized by abundant fluorite,and that the fluorides or fluorine complexes are the important forms that transport tin in fluids at this stage.In case the cavities are connected by tectonic fractures,the tin initially enriched in the infilling fluids will migrate and then precipitate the metallic minerals at favorable sites with formation of a vein-type tin deposit.