Characteristics and genetic indication significance of fluid inclusions in the Zhujiawa molybdenum deposit

The Zhujiawa molybdenum deposit is one of the large-size deposits recently discovered in the middle part of northern margin of North China Platform. The research on this deposit is relatively insufficient. The deposit is similar to the Caosiyao molybdenum deposit in metallogenetic mechanism in that they are both controlled by hypabyssal super-hypabyssal acidic rock from deep source. The characteristics of ore-forming fluid constitute the key problem in revealing the genesis of ore deposits. In this paper, eleven core samples of molybdenum mineralization were collected from No.ZK2-1 and No.ZK2-2 drill hole. The results show that the fluid inclusions can be divided into four types. They are liquid-rich phase inclusions, daughter-minerals three phase inclusions, gas-rich phase inclusions and CO₂-bearing three phase inclusions. Among them, CO₂-bearing three phase inclusions are less distributed, whereas the other three types of inclusions are common. Homogenization temperatures and salinities of daughter mineral-bearing three phase inclusions are the highest, at about 400℃ and 45% Na Cleqv respectively. Homogenization temperatures and salinities of liquid-rich phase inclusions are 277.43℃ and 20% Na Cleqv respectively. Homogenization temperatures and salinities of gas-rich phase inclusions and CO₂-bearing three phase inclusions are 380℃ and 30℃, 6%NaCleqv and 2.04% NaCleqv respectively. The initial fluid has the characteristics of high temperature, high salinity and rich CO₂, and the fluid inclusion has the characteristics of the porphyry mineralization system within the continent. The fluid inclusion composition of gas and liquid phase shows that ore-forming fluid mostly contains H₂O, Cl^-, F^-, Na⁺, K⁺, and minor Ca²⁺ and SO₄^2-. Diagnostic ion ratios indicate that ore-forming fluid was derived from magmatic fluid. The ore-forming fluid in general belongs to the H₂O-NaCl system. Hydrogen and oxygen isotopic composition of the fluid inclusion in quartz indicates that the water in ore-forming fluid was derived from magmatic. Boiling of the ore-forming stage led to the precipitation of molybdenite.