Study On The Dark Minerals' Chemical Composition And Its Origin In Intermediate-acid Rock At Guyang Area,Inner Mongolia

The compositions of black colored minerals such as biotite,amphibole in the intermediate-acid rock has close correlation with geochemical and geophsicalconditions when they formed,which can be used as an important indicator and discrimination in the disgenesis and ore forming process.This thesis gained data from ICPMS,EPMA and Raman spectrometer,and interpreted the disgenesis and ore forming process by analysing the compositions of biotite,amphibole in the intermediate-acid rock in Guyang area.TTG rock suite are developed in late Archean at Guyang area,the Paleoproterozoic intermediate-acid rock mass are widely exposed in this rock suit.Petrogeochemistry in the study area shows that the rock are mainly dioritic,which belongs to intermediate-acid rock,Sample TX07? TX09 ?TX10 have lower U/Th values and higher Rb/Sr values,which indicates the mixed crust-mantle affinity,Sample TX08 has lower U/Th values and lower Rb/Sr values,which indicates the mantle compositon affininty.Ca-Mg amphiboles were identified by EMPA analysis,biotite and phlogopite are dominant in micas,and the biotite is classified to magnisium based type.Biotite and phlogopite are of high magnisum,low manganese and low titianium characteristics,showing that ferrous ion is of high proportion in the total iron,and it is probable in reducing environment.Raman spectrum data show that calcic amphibole is of typical absorpotion peak in the1100 1080cm-1 area,especially acute in the 667cm-1 area,which indicates there existed Si-Al-Ti isomorphism substitute.Mica shows Si?Al??-O stretching vibration 1000cm-1 area,absorpotion band existed in 1000 960cm-1 area,which is negative correlation with Al?numbers.With increasing the Mg/?Mg+Fe2+?values,it shifts to high frequency direction,positive correlating with Al?numbers,and Si-Al-Ti isomorphism substitute becomes weak,which aggrees with low oxygen fagacity indicating by the low titanium and low AlVI value in biotite.The log(f_H2O)/(f_HF)^fluid,log(f_H2O)/?fHCI?)^fluid and log(f_HF)/?fHCI?^fluidvalue of hydrothermal fluid coexsiting with the intermediate-acid rock are 1.25¹.86,3.22³.54 and 1.25¹.86,respectively.Plot of lgfO2-T for biotite indicates that biotite crystallization temperature is from 968? to 1024?,logf O2 is form-9.2 to-12.7,which is of low oxygen and higher crystalization temperature.Triangular diagram MgO-TFeO-Al2O3 and TFeO/?TFeO+MgO?-MgO for biotites of Sample TX07?TX09?TX10 show that the rock source is of crust-mantle origin and that of TX08 shows it is manlte origin.