河北阳原—矾山环状杂岩体的岩浆不混溶成因及矾山式铁磷矿床成因探讨

SILICATE LIQUID IMMISCIBILITY OF THE YANGYUAN-FANSHAN COMPLEX IN HEBEI PROVINCE AND THE ORIGIN OF THE FANSHAN TYPE PHOSPHORUS DEPOSITS

河北阳原—矾山杂岩体是由两个类似的辉石岩系、正长岩系组成的环状富磷杂岩体。其中,辉石岩系赋存有岩浆型磷灰石矿床。阳原富磷岩浆液态不混溶,产生富铁的辉石质岩浆和富硅的正长质岩浆。在岩浆不混溶过程中,其性质受岩浆熔体结构控制的主要元素和微量元素,依其离子性质和场强,不同程度地富集于不混溶的富铁相或富硅相中。磷做为高场强元素,亦发生重新分配,高度集聚,并强烈地富集于不混溶的辉石质岩浆中,形成阳原低品位磷矿。矾山岩浆液态不混溶,产生互不混溶的三液相,即辉石质岩浆、正长质岩浆和磷酸盐液相(矿浆)。在不混溶过程中,P_2O_5进入辉石质岩浆,直至P_2O_5达到饱和,残余的P_2O_5构成磷酸盐液相。矾山岩浆的三相不混溶作用导致了矾山三个矿带的形成。

The Fanshan-Yangyuan complex includes two similar ring-shaped phosphorus-rich complexes consisting mainly of pyroxenite and syenite,and the magma type phosphorus deposits occur in pyroxenite series. This paper presents systematically geological,petrologicaf and geochemical evidence for silicate liquid immiscibility of the Fanshan-Yangyuan complex and points out that the immiscibility of the Yangyuan phosphorus-rich magma produced pyroxenitic (FeO-rich)-syenitic (SiO2-rioh) magma units. In the process of unmixing, the major and trace elements were controlled by melt structure and concentrated in Fe-rich or Si-rich melt according to theia/ ion characters and the strength of ionic field. The high field strength element——phosphorus was redistributed, intensely accumulated and concentrated in Fe-rich pyroxenitic magma, forming the Yaugyuan low-grade phosphorus deposit. The Fanshan phosphorus-rich magma experienced unmixing and hence produced three sorts of immiscible liquids:pyroxenitic magma, syenitic magma and phosphate melt. During the unmixing of Fanshan magma, P_2O_5 which had been concentrated in immiscible pyroxenitic magma reached saturation and the remaining P_2O_5 became free and formed phosphate liquid. The three phase immiscibility of Fanshan magma resulted in the formation of three phosphorus ore zones.