Re–Os and Ar–Ar dating of the Dahu Au (Mo) deposit in the Xiaoqinling area, West Henan: Constraint on its metallogenetic stages

This paper is the result of mineral exploration engineering.

Objective The East Qinling molybdenum belt which located in the North China craton is the second largest Mo belt in the world, among which occur the most famous orogenic gold deposits of the Xiaoqinling. In recent years, through the implementation of geological survey engineering, molybdenum mineralization with industrial significance has been found in the deep of Dahu Au (Mo) deposit from Xiaoqinling area, and molybdenum ore mining has begun. Through the constraint on its metallogenetic stages, it is helpful to study the Au−Mo metallogenic regularity.

Methods In this paper, based on the Crisis Mine deep−seated deposits prospecting in Xiaoqinling area, we studied the metallogenic model of deep Au (Mo) deposit, and analyzed the role of molybdenite Re–Os and K–feldspar ⁴⁰Ar/³⁹Ar isotope dating in the classification of metallogenic stages.

Results Six molybdenite samples from the S35 ore vein yield Re–Os isotopic isochron age of (214.9±5.2) Ma (MSWD=0.77), with model ages ranging from (192.3±2.9) Ma to (223.4±3.2) Ma. K–feldspar samples from F5 ore vein yield Ar–Ar weighted plateau age of (95.22±1.16) Ma and the isochron age of (95.10±4.57) Ma.

Conclusions Molybdenite age suggests that the Mo mineralization in S35 vein occurred in Indosinian period, and K–feldspar age indicates a new tectono–magmatic–thermal event during the Middle Yanshanian, and this hydrothermal event may contribute to metallogenic activity of Au (Mo) deposit, which superimposed the molybdenum mineralization events of Indosinian. Combined with the results of hand samples and BSE images analysis, it is concluded that there are at least two episodes of hydrothermal event related to Au (Mo) mineralization in Dahu Au (Mo) ore district.