河北省木吉村铜(钼)矿床蚀变分带过程中元素迁移定量分析

为了研究木吉村斑岩型铜(钼)矿床蚀变过程中元素的迁移规律,拟推流体演化规律,笔者通过对赋矿闪长玢岩体的强硅化带、钾长石化带、石英绢云母化带、青磐岩化带中分别取样测试分析,利用Grant方程定量探讨了各蚀变带围岩中主量元素、稀土元素和微量元素的带入、带出特征,结果表明:岩浆初始热液流体富K而贫Na。相对原岩(蚀变弱的青磐岩化带),在各蚀变带中Fe_2O_3、MgO、P_2O_5和TiO_2从深部强硅化带到浅部石英绢云母化带总体上由带出变为带入,SiO_2、MnO则与上述大体相反,FeO在各蚀变带主体为带出元素。各稀土元素从深部向浅部石英绢云母化带带入特征明显,同时各蚀变带在稀土元素球粒陨石标准化曲线上表现出斜率一致的右倾型特征,说明轻重稀土分馏较明显,轻稀土富集,重稀土亏损。Cu和Mo在石英绢云母化带中富集尤为明显,其次在钾长石化带也明显富集,即海拔400~500 m为主要的Cu、Mo富集区。

A quantitative discussion on element mass migration during alteration processes in the Mujicun Cu (Mo) deposit, Hebei Province

In order to deeply study the migration regularity of element and preliminarily infer the fluid evolution during alteration processes in the Mujicun Cu (Mo) deposit, the authors tested and analyzed the samples which were respectively collected from the strongly silicified zone, the potassic zone, the quartz-sericitic zone and the propylitic zone in the ore-bearing diorite porphyrite body. Through calculation based on the formula by Grant, the authors made a tentative quantitative discussion on characteristics of the gains and losses of elements during their migration. The results demonstrate that mass migration of different elements show certain regularities within the range of mineralized alteration:(1) the initial hydrothermal fluid is rich in K and is poor in Na. Compared with least-altered rocks (the propylitic zones), the losses of Fe₂O₃, MgO, P₂O₅ and TiO₂ turn into the gains in altered rocks from deep strongly silicified zone to shallow quartz-sericitic zone, with the generally opposite migration regularity of SiO₂ and MnO, and FeO is depleted in the three alteration zones. (2) The migration regularity of rare earth elements is similar to that of Fe₂O₃ and some other components. The REE curves assume a rightly dipping REE pattern, indicating obvious fractionation between LREE and HREE, with the enrichment of LREE and the losses of HREE. (3) Cu and Mo are especially enriched in the quartzsericitic zone and also relatively enriched in the potassic zone. These data suggest that the altitude of 400-500 m in the diorite porphyrite body is the main Cu and Mo enrichment area.