K_2O－Al_2O_3－SiO_2－H_2O－F_2O_（－1）体系中某些矿物的平衡关系及其对斑岩Mo、Sn矿床蚀变分带的应用

SOME MINERAL EQUILIBRIA IN THE SYSTEM K_2O-Al_2O_3-SiO_2-H_2O-F_2O_(-1) AND THEIR APPLICATION TO ALTERATION ZONING IN PORPHYRY Mo,Sn DEPOSITS

本文利用有关物相的热力学性质，计算了１×１０２ＭＰａ、５００℃和６００℃条件下Ｋ２Ｏ－Ａｌ２Ｏ３－ＳｉＯ２－Ｈ２Ｏ－Ｆ２Ｏ－１体系中钾长石、白云母、黄玉和红柱石平衡关系的ｌｏｇａＨＦ－ｌｏｇａＫＦ图，结果表明，（１）该体系中较高的ａＫＦ利于钾长石的形成，较高的ａＨＦ利于黄玉的形成，而较低的ａＫＦ和ａＨＦ则只能稳定白云母和红柱石。（２）温度的降低导致黄玉相对钾长石、白云母和红柱石的稳定域增大，而白云母则相对钾长石和红柱石稳定域增大，表明温度下降有利于黄玉和白云母的形成。许多斑岩Ｍｏ、Ｓｎ矿床都包含有钾长石→黄玉→绢云母的蚀变分带序列，可近似地用Ｋ２Ｏ－Ａｌ２Ｏ３－ＳｉＯ２－Ｈ２Ｏ－Ｆ２Ｏ－１体系中钾长石、白云母和黄玉２间平衡关系的ｌｏｇａＨＦ—ｌｏｇａＫＦ图进行解释，蚀变过程中流体相ａＨＦ和ａＫＦ演化及体系温度的下降是导致斑岩Ｍｏ、Ｓｎ矿床钾石→黄玉→绢云母分带规律的两个决定因素。

The thermodynamic properties of related phases are used to calculate the equilibrium relationships of Kfeldspar,muscovite,topaz and andalusite in the system K2O-Al2O3-SiO2-H2O-F2O-1 at 1×102MPa,600℃ and 500℃ conditions,which are expressed in logaHF-logaKF diagrams.The major results are:1.The higher aKF and lower aHF in this system is favourable for formation of K-feldspar,and in opposite to this,topaz is stable.In lower aHF and aKF condition,muscovite and andalusite can be stabilized.2.With the falling down of temperature in this system,the stability field of topaz is expanded relative to those of Kfeldspar,muscovite and andalusite,and the stability field of muscovite is expanded relative to thise of K-feldspar and andalusite, which show the decreasing of temperature is favourable for formation of topaz and muscovite.The above calculated results can be used to explain the formation mechanism of K-feldspar-topaz-muscovite alteration zoning in porphyry Mo, Sn deposits.