长英质岩浆中液态不混溶与成矿作用关系的实验研究

The Experimental Study About The Liquid Immiscibility and Ore-Forming process In Felsic Magma

本文的实验研究表明：１２５０℃（１０５Ｐａ）条件下呈均一状态的花岗岩－ＫＢＦ４－Ｎａ２ＭｏＯ４体系，在１０００℃条件下发生液态不混溶形成三种熔体：相对偏酸性的液滴、相对偏基性的熔体和成矿熔体。成矿熔体中富含ＣａＯ、ＭｇＯ和ＭｏＯ２组分。红外光谱研究表明：硅酸盐熔体结构以［ＳｉＯ４］基团为主，而成矿熔体结构中存在Ｃａ—Ｆ、Ｃａ—Ｏ—Ｍｏ、Ｈ—Ｏ—Ｈ以及Ｘ─ＯＨ（Ｘ＝阳离子）基团，说明Ｈ２Ｏ和Ｆ富集在成矿熔体中。液态不混溶作用产生的三种不混溶熔体的结构差异明显，主要表现在结构单元中桥氧数目的变化，相对偏酸性的Ａ类小球体的结构单元中桥氧数最高，基底玻璃熔体中桥氧数则相对较少，而成矿熔体中不存在桥氧。本实验研究结果表明长英质岩浆中的液态不混溶可直接导致成矿熔体的形成。这意味着长英质岩浆中的液态不混溶可直接导致斑岩矿床的形成。

This experimental study demonstrated that the granite-KBF4-Na2MoO4 system is homogeneous at 1250℃ (105 Pa), which through liquid immiscibility at 1000℃ decomposed in three melts: relative acid globe, relative basic melt and ore-forming melt. In ore-forming melt CaO, MgO and MoO2, are concentrated. Micro-IR spectra shows that the structures of the silicate melts (relative acid globe and basic melt) mainly consist of [SiO4] group; but in the structure of the ore-forming melt exist Ca-F, Ca-OMo, H-O-H, and X-OH (X=cations) groups demonstrating that H2O and F concentrated in the oreforming melt. The melt structures of the above three immiscible melts mainly differ in the number of bridge oxygen: the highest in the relative acid globe and lower in the relative basic melt, but in the melt structure of the ore-forming melt all oxygen is non-bridge oxygen. The results of our experimental study demonstrated that the process of the liquid immiscibility in felsic magma can directly form ore-forming melt. This implies that the liquid immiscibility in felsic magma can directly induce the formation of porphery deposit.