胶东玲珑金矿田煌斑岩蚀变过程元素迁移行为及其意义

Element Transfer Behaviors and Its Application During Lamprophyre Alteration in the Linglong Gold Deposit,Jiaodong Peninsula,China

胶东矿集区内普遍发育煌斑岩脉,对煌斑岩的热液蚀变现象进行研究可以揭示蚀变流体的地球化学特性。对玲珑金矿田两处新鲜与蚀变煌斑岩进行了56项氧化物和微量元素分析,结果发现玲珑金矿田的煌斑岩为富钾煌斑岩,稀土元素在煌斑岩蚀变过程中未发生明显分异现象。确定煌斑岩蚀变过程中的不活动元素可以采用坪台法,其优点在于克服了等浓度图解法中拟合过原点直线的技术缺陷。质量平衡计算法与元素含量比值法的本质区别在于二者相差一比例系数,即蚀变岩与原岩的质量比率,元素含量比值法可视为质量平衡计算法在岩石轻微蚀变时的一个特例。玲珑金矿田的煌斑岩与金矿成矿流体具有相同的构造通道,引起煌斑岩蚀变的这期金矿成矿流体富K2O、Rb、Be、Ba、W、Pb、Zn、Sb、B、Mn、Ta,贫Na2O、CaO、MgO、Sr等元素,可选取W、Pb、Zn、Sb、B、Be、Rb、Ba为该区金矿的成矿指示元素。

Lamprophyre dikes occur commonly in the Jiaodong ore cluster area.The altered lamprophyre rock is a good object to trace the geochemical characteristics of the alteration fluid.Two pairs of fresh and altered lamprophyre rocks were collected in the Linglong gold deposit on which 56 items of major oxides and trace elements were analyzed.The results indicate that the lamprophyre is rich in K2O and the REE didn＇t fractionate during the lamprophyre alteration in the Linglong gold deposit.Immobile plateau is a good method to determine the immobile elements during the lamprophyre alteration which overcomes the technical default of the Isocon method for fitting a line through the zero.Two methods of mass balance calculation and element content ratio were used here to discover the rich elements resulted from the alteration.The essential difference between these two methods is that the method of mass balance calculation includes a coefficient called the mass ratio of altered rocks to parent rocks relative to the method of element content ratio.The method of element content ratio can be viewed as a special example of the mass balance calculation method when the mass ratio of altered rocks to parent rocks is near to one.The transfer path of gold ore-forming fluid could be the same as that of the lamprophyre dikes in the Linglong gold deposit.The fluid which altered the lamprophyre rock was rich in K2O,Rb,Be,Ba,W,Pb,Zn,Sb,B,Mn,Ta,and poor in Na2O,CaO,MgO,and Sr.These elements of W,Pb,Zn,Sb,B,Be,Rb,and Ba can be selected as ore-forming indicator elements in the Linglong gold deposit area.