通过对金鸡窝铜矿区花岗闪长斑岩进行详细的岩相学研究和黑云母成分的电子探针原位分析,厘定了黑云母形成的物理化学条件,并探讨了其成岩成矿意义.电子探针研究显示:花岗闪长斑岩中黑云母的Ti为0.44～0.47 apfu,Mg/(Mg+ Fe)比值范围为0.58～0.62,结合其化学成分在10 TiO2 FeO*-MgO图解和Mg-(Fe2++Mn)-(AlⅥ+ Fe3++ Ti)图解中的投影,认为该岩体中黑云母具有富镁贫铁特征,属于原生黑云母.黑云母氧化系数(fO)范围为0.31～0.67,MF值范围为0.38～0.41,MgO含量为13.27％ ～14.28％,K2O为3.59％ ～8.93％,Na2O为0.26％ ～3.28％,FeO为15.74％ ～17.30％,TiO2为3.93％ ～4.19％,Al2O3为13.52％ ～14.19％,单位分子中阳离子数AlⅣ为2.00～2.24 apfu,AlⅥ为0.15～0.41 apfu,指示其岩体属于高钾质钙碱性系列的同熔型(或Ⅰ型)花岗岩,具有壳幔混源成因的特征.黑云母结晶温度为734～748℃,结晶压力为71～89 MPa,相当于深度2.7～3.3km,平均深度为3.0 km.黑云母化学成分投点主要落在Fe2O3-Fe3O4缓冲线之上,表明其形成于高氧逸度环境,且有利于铜矿的形成.%Based on detailed petrographical and mineralogical compositional features of biotite from the granodiorite porphyry around the Jinjiwo deposit in the Jiurui ore district,the authors not only established the physicochemical conditions of the mineral formation but also explored its significance for rock and ore formation.Major element composition of the biotite phenocrysts of the samples was measured by the electron probe micro-analyzer (EPMA).The Ti content and the Mg/(Mg + Fe) ratios of the biotite from the Jinjiwo granodiorite porphyry are 0.44～0.47 apfu (atoms per formula unit) and 0.58～0.62,respectively,and the compositions of these biotite are plotted in both the domain of the primary magmatic biotite and that of the Mg-rich biotite.These features suggest that the biotite phenocrysts of the samples are all eastonite,and that these analyzed biotites display the Mg-rich and Fe-poor characteristics.The oxidation coefficient and the MF values of biotites are 0.31～0.67 and 0.38～0.41,respectively.Biotite has 13.27％～14.28％ MgO,3.59％～8.93％ K2O,0.26％～3.28％Na2O,15.74％～17.30％ FeO,3.93％～4.19％ TiO2,and 13.52％～14.19％ Al2O3,respectively.It contains about 2.00～2.24 apfu of tetrahedral AlⅣ and 0.15～0.41 apfu of octahedral AlⅥ.The TAl content of biotite can be used to figure out the solidification pressure of the granitoid.Considering the composition of biotites together with experimental results of the former research,which falls on or above Fe2O3-Fe3O4 buffer in the Fe3 +-Fe2 +-Mg diagram,the authors consider that the biotites from granodiorite porphyry in the study region were crystallized under the condition of temperatures 734～748℃ and pressures 71～89 MPa,corresponding to solidification depth 2.7～3.3 km.The above characteristics suggest that the Jinjiwo granodiorite porphyry belongs to high potassium Ca-alkaline series,showing the typical syntexis type (or Ⅰ-type) granitoid derived from a crust-mantle mixing source,and that the pluton was formed in a relatively high oxygen fugacity environment,which was beneficial to copper mineralization.
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