Abstract:

The Sifangdianzi Mo deposit in Jilin Province is a recently discovered quartz-vein type molybdenum deposit. The orebodies are mainly hosted in monzogranite. Its ore-forming processes can be divided into three stages: barren quartz-vein stage, quartz-molybdenite-pyrite stage and quartz-carbonatate stage. By the LA-ICP-MS U-Pb dating of zircons, we obtained the age of 170.0±1.0 Ma for granodiorite, and the age of 179.0±1.0 Ma for monzogranite. Based on the Re-Os dating of molybdenite from quartz vein type ore, the model ages obtained are from 175.0±2.6 to 176.5±2.6 Ma averaged at 176.1±1.1 Ma, and having an isochronic age of 176.6±4.2 Ma. It is indicated that the Sifangdianzi Mo deposit was formed in the early Jurassic Period. SiO₂ values of the granitic rocks change from 66.17% to 76.60%, Na₂O and K₂O are in the range of 3.15% to 5.40% and 2.42% to 5.42% respectively, their Rittmann indexes vary from 2.17 to 2.93; Their REE patterns demonstrate right-oblique linear REE patterns, the trace elements show relative enrichment of the large ion lithophile elements, and depletion of the high field strength elements. The geochemical characteristics of the granitic rocks imply they belong to I-type granite. The geotectonic mechanisms responsible for the diagenesis and mineralization were probably related to subduction of the paleo-Pacific Plate to the Eurasian continent.

Key words: zircon LA-ICP-MS age, molybdenite Re-Os age, rock geochemistry, the Sifangdianzi molybdenite Mo deposit, Huadian County of Jilin Province