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.