新疆白杨河Be-U矿床中铍、铀成生关系--来自萤石LA-ICP-MS稀土元素的约束

Relationship Between the Beryllium and Uranium Mineralization in Baiyanghe Be-U Deposit,Xinjiang:Constrain From Fluorite REE by LA-ICP-MS

与高硅富氟火成岩有关的铍矿床中常伴有铀矿化,但铍、铀的成生关系仍不清楚。新疆西北部的白杨河矿床与高硅富氟花岗斑岩密切相关,铍、铀矿化相伴而生,为解决上述问题提供了理想对象。前人开展的矿床地质特征及成矿年代学研究,初步揭示了铍、铀矿化形成于不同成矿期。文章以白杨河矿床为研究对象,对与成矿作用密切相关的脉石矿物--萤石,开展了岩矿相学研究和LA-ICP-MS稀土元素分析。结果显示,萤石的形成贯穿了整个成矿过程,包括岩浆阶段萤石、Be矿化期钠长石阶段萤石、Be矿化期电气石阶段萤石、Be矿化期方解石阶段萤石和U矿化期伊利石阶段萤石;Be矿化期3阶段萤石为同一期流体演化的产物,产出于不同Ca/F比值的环境中,它们应由花岗斑岩所分异的岩浆热液(经历了>250℃的高温演化),在低温(<250℃)、氧化条件下沉淀而成;U矿化期萤石应是后期流体(未经历>250℃的高温演化)作用下,由早期萤石重结晶而成,其沉淀于还原环境中。

The Be deposits related to high-silica,high-fluorine igneous rocks are commonly accompanied by U mineralization,but the relationship between Be and U mineralization remains unclear.Be and U mineralization are closely related to the high-silica,high-fluorine granitic porphyry in Baiyanghe deposit which is located in northwestern Xinjiang and provides an ideal case for the study of the above-mentioned problem.The previous geology and geochronology research have revealed that the Be and U mineralization was formed in different periods.Therefore,further identifying the characteristics of Be and U mineralization,can not only deepen the metallogenic theory,but also support the neexploration of Be and U in the region.The studies of petrography,mineralogy and REE geochemistry on fluorites were carried out in this paper.The results showed that the fluorites in Baiyanghe deposit can be divided into five stages:the magmatic stage fluorite,the Be-mineralization period albite-bearing stage fluorite,the Be-mineralization period tourmaline-bearing stage fluorite,the Be-mineralization period calcite-bearing stage fluorite and the U-mineralization period illite-bearing stage fluorite;the Be-mineralization period fluorites were the product of fluid in the same period time,occured in different Ca/F ratio environment,and deposited in low temperature(<250℃),oxidation condition by magmatic fluid which underwent the evolution of high temperature(>250℃);the U-mineralization period fluorite may be remobilization of early fluorite by later fluids which did not undergo the evolution of high temperature(>250℃),and deposited in a reduction environment.