Re- Os Isotopic Dating of Molybdenites from the Shazigou W- Mo polymetallic Deposit,Inner Mongolia and its Geological Implications
The Shazigou W- Mo polymetallic deposit of Inner Mongolia is located in the southwest of the Xilamulun molybdenum metallogenic belt in the northern margin of the North China Craton. The molybdenites occurring as quartz-molybdenite-pyrite assemblages are usually vein-like,existing in the wallrock fractures. In order to determine the metallogenic age of this W- Mo deposit,we have made measurements to Re- Os isotope on 5 molybdnite samples collected from the deposit,yielding the model ages between( 241. 2 ± 3. 4) Ma and( 245. 2 ± 4. 3) Ma,with an average value of 243. 8 ± 1. 6Ma. It indicates that the mineralization in the Shazigou W- Mo multi-metal deposit occurred in the early Triassic. The Re contents of molybdenites in Shazigou vary from 1. 231μg / g to 1. 704μg / g,which can be used as an important indicator on the source of ore-forming material. It is likely that the Mo ore-forming material in the deposit was derived from the upper crust. Comparing with other Mo or Mo-bearing deposits in the regional molybdenum metallogenic belt,it is inferred that the formation of the Shazigou W- Mo deposit is associated with the collision of the North China and Siberria Plates after the closure of the Paleo-Asian Ocean. The ore-forming age of this deposit provides new evidence for the tectonic magmatic mineralization in the northern margin of the North China Plate in the of early Triassic,which will help expand the scope of regional prospecting.