富氟钡型碳酸岩岩浆的演化机制及其成矿效应

Evolvement and Ore-Forming Process of Carbonatite Magma

碳酸岩可分为原始地幔原生碳酸岩和广义"碳酸岩"——富氟钡型碳酸岩。相对于原生碳酸岩,富氟钡型碳酸岩含有大量挥发分和碱土元素,产出了众多稀土矿床,具有较高的成矿潜力。理论和实验研究表明,在碳酸岩岩浆演化过程中,挥发分和碱土元素是岩浆发生不混溶作用的关键因素,而且不混溶作用相对结晶分异作用更利于成矿元素的富集。因此,可以推断挥发分和碱土元素是富氟钡型碳酸岩的成矿的关键因素,不混溶模式是富氟钡型碳酸岩岩浆演化和成矿的主要机制。但是,这仅为理论推断的结果,而且许多实验的研究对象是未发生稀土矿化的碳酸岩,数据的说服力较弱。在我国富氟钡型碳酸岩矿床中,山东微山稀土矿床具有成矿元素高度富集,代表了富氟钡型碳酸岩成矿强度大的特点;而白云鄂博铁—稀土矿床则代表了富氟钡型碳酸岩成矿规模大的特点,二者相辅相成,是研究富氟钡型碳酸岩成矿效应的理想对象。

Carbonatite can be divided into primary carbonatite and F--Ba rich type carbonatite. The later characterized by richment of volatile and alkaline earth element in magma, procuded many REE deposit, and has strong potential for ore-forming, research of theory and experiment showed that F, Ba, and other alkaline earth, volatile are the key factor to induce the immiscibility among silicate, carbonate, or salt melts; and the immiscibility is better for richment of ore-forming elements than fractional crystallization. Therefore, whether volatiles and alkaline earth elements are the key factor for F--Ba rich type carbonatite to mineralize？ and is immiscibility the main mechanism for F--Ba rich type carbonatite to mineralize？ This viewpoint only deduced from theory and experiment. It is necessary to test this point by studying typical deposit. The Weishan REE deposit in Shandong province with high enrichment of REE presents the character of high intensity of ore-forming for F--Ba rich type carbonatite, and the Bayan Obo Fe--REE deposit presents the character of producing giant REE deposit for F--Ba rich type carbonatite. The two deposits are the ideal objects to understand the ore-forming of F--Ba rich carbonatite magma.