Geochronology of Baogutu porphyry copper deposit in Western Junggar area, Xinjiang of China

摘要

Baogutu copper deposit in Western Junggar area is a mesoscopic porphyry deposit found in recent years. Study on its geochronology will help further understand ore genesis and regional ore-forming pattern. A series of small quartz-diorite and granodiorite stocks outcrop at Baogutu area, numbered I―X according to their size. A detailed exploration on Number V stock confirmed it as a mesoscopic scale copper deposit, and various exploration work has been carried out on other stocks with ore-forming evidence. This paper studies geochronology of Number V stock using zircon SHRIMP U-Pb and single mineral K-Ar method. Twenty-five SHRIMP ages yield two 206Pb/238U weighed mean ages of 335.6 ± 7.8 Ma and 311.4 ± 3.3 Ma respectively. The older date is considered to be inherited zircon from either surrounding rock tuff or deep granitoid batholith, whereas the younger date is the formation age of ore-bearing intrusion. K-Ar ages of ore-forming biotites, 296.0 ± 3.7 Ma and 297.3 ± 3.8 Ma, in combination with Re-Os age of molybdenite, 310 Ma, confirm the ore-forming age of 310-296 Ma. Granophyre and dioritic porphyrite dikes cut Number V stock and their K-Ar ages range from 278 to 240 Ma, which confine the lower boundary of the mineralization. The framework of Baogutu ore-forming geochrono-logy can be established based on these data.