Hydrothermal Alteration and Element Migration Patterns in the Zhangjiawu Uranium Deposit, Northern Zhejiang Province, China

Abstract

The Zhangjiawu uranium deposit is the largest volcanic rock-type uranium deposit in the northern Zhejiang Province, China. The deposit has developed hydrothermal alteration, with obvious alternating zoning phenomena from the mineralized center to the fresh surrounding rocks. Based on detailed field and petrographic observations of typical ore bodies, the uranium mineralized section of the Zhangjiawu uranium deposit was divided into mineralized central, ore-side alteration, near-ore alteration and far-ore alteration zones, whose hydrothermal alteration intensity decreases sequentially. Using the standardized Isocon diagram method, the results show that CaO, MgO, Na2O, P2O5, LOI, Zn, Co, Cu, Pb and heavy rare earth elements (HREE) show gain during uranium mineralization, while K2O, Cs, Rb and Tl show loss, which is consistent with the development of hematite mineralization, sodic feldsparization and carbonation in the mine area. A negative correlation of MnO and MgO in the alteration zone indicates a possible elemental convective equilibrium migration mode in the ore zone. The migration mechanism of the elements indicates that the migration of P2O5 and HREE indicates the deep source nature of the mineralizing fluids, and that alteration can lead to a reduction in the activity of uranyl complexes, the formation of a reducing environment and a neutral to weak alkaline environment favorable for uranium precipitation, which can lead to uranium precipitation and enrichment of mineralization. The study of hydrothermal alteration and elemental migration patterns of the deposit provides supporting evidence for a better understanding of the process of uranium mineralization in Zhangjiawu, and also provides a basis for the next step of mineral search and exploration.