Geochemistry and chronology of large-superlarge nonmetal deposits in eastern Zhejiang Province: A case study

From geology and geochemistry studies on four typical large-superlarge nonmetal deposits in eastern Zhejiang Province, it is concluded that nonmetal mineralization is an in situ reduction process in which SiO₂ and Fe₂O₃ are lost, and Al₂O₃ and K₂O are enriched. Moreover, incompatible elements are depleted in zeolite but enriched in alunite. Rb-Sr isotopic age of zeolite and K-Ar isotopic age or micro-area⁴⁰Ar-³⁹Ar isochron age of alunite are coincident with their geological data. respectively. Comparison studies of various chronology methods indicate that K-Ar and Rb-Sr methods are effective for zeolite and alunite, but should be carefully used for pyrophyllite, dekite and illite. From isotopic ages of ore and wall rocks of zeolite and alunite, it could be deduced that the age difference of metallogenism and volcanism is about 10–20 Ma.