摘要
黄玉的形成条件是阐明含黄玉岩石成因的关键。为定量解释黄玉的岩石学成因意义，本文利用黄玉和与其共存的矿物及流体组分的热力学性质，计算了花岗岩－Ｈ＿２Ｏ－ＨＦ体系中有关反应的ｌｏｇａＨＦ－ＩｏｇａＫＦ，ＩｏｇａＨＦ－ｌｏｇＡＡｎ，ｌｏｇａＨＦ－Ｔ图及Ｔ－Ｐ图。利用上述计算结果，本文解释了含黄玉花岗质岩石及其极端分异产物的形成条件和斑岩Ｍｏ、Ｓｎ矿床蚀变分带的形成机制。
The formation conditions of topaz seem to be the key for the understan-ding of the topaz-bearing rock genesis,In order to quantitatively explain the petrologic role of topaz,the authors used the thermodynamic properties of topaz and coexisting minerals(andalusite,muscovite,K-feldspars, albite,fluorite and quartz)as well as fluid components(H_2O,HF, KF and NaF)to calculate the mineral equilibria of related reactions in the granite-H_2O-HF system,which are expressed in loga_(HF)-loga_(KF),loga_(HF)-loga_(An),loga_(HF)-T and T-P diagrams.The major results are:1.An increase in HF activity of the granite-H_2O-HF system is favorable to the formation of topaz,Within a specific range of HF activity,topaz maycoexist with alkali-feldspars and muscovite,However, the condition of higherHF activity can only stablize the topaz+quartz assemblage.2.With the falling of temperature,the stability field of topaz is expa-nded relative to the stability fields of andalusite.muscovite,K-feldspar andalbite,and the stability field of muscovite is expanded relative to the fieldsof andalusite and K-feldspar。3.Fluorination reactions between plagioclase and HF produce the fluo-rite±topaz+quartz assemblage. They buffer the anorthite component activityin plagioclase.The system of higher a_F or a_(HF) can only stablize albite alongwith topaz. 4.Relative to the F-free granite system,the pressure lower limit of muscovite4 stability descends and its temperature upper limit ascends in theF-bearing granite system. In the presence of topaz,muscovite as a magmaticmineral can be stable above the solidus of F-bearing granite under thepressures as low as(1-2)×10￣8Pa. The above calculated results can be used to explain the formation condi-tions of topaz-bearing granitic rocks and their extreme differentiates and theformation mechanism of alteration zones in porphyry Mo,Sn deposits.
出处
《岩石矿物学杂志》
CAS
CSCD
1995年第2期97-108,共12页
Acta Petrologica et Mineralogica
关键词
黄玉
红柱石
白云母
碱性长石
矿物平衡
岩石学
topaz,mineral equilibria of topaz-bearing assemblages,genesis of topaz-bearing rocks
