Located at southeastern margin of the Kazakhstan plate, Huaniushan was one of the most important Mo, Pb-Zn-Ag and Au metallogenic district, and was considered as one of the key parts of the Beishan orogenic belt. The Precambrian and Phanerozoic granitoid intrusives and the related Mo, Pb-Zn-Ag and Au deposits(prospects)were widely distributed. Geochronological study of these granitoids attracted geologists’ attention both at home and abroad. The 40Ar/39Ar isotope data for K-feldspar separates from the potassium granite of the eastern Huaniushan granitoid intrusive, northwestern Gansu province, were presented in this paper. Eleven stepwise heating Ar data of the K-feldspar separates gave an 40Ar/39Ar isochron age of 194.25±1.96 Ma(2σ)and 40Ar/36Ar initial value of 288.87±2.17(2σ), which was obviously close to Nier’s value. This age might represent the crystallization time of the K-feldspar of the potassium granite from the eastern Huaniushan granitoid intrusive, and was considered as the youngest age of tectono magmatic events occurring within the Huaniushan district. Although no clear correlation existed in between the 40Ar/39Ar age of the K-feldspar from the potassium granite and lead isotopic model age of the sulfide separates from the Mo, Pb Zn Ag and Au ore veins, some of these galena separates had modal age of 126～180 Ma, which was lower than that of the 40Ar/39Ar isochron age of the K-feldspar. The molybdenum, lead zinc silver and gold deposits(prospects)showed a clear temporal relation to the Yanshanian high K granite. The isotopic age data and field petrological observation indicated that the latest emplacement event of the granitoid magma occurred during the Mesozoic Yanshanian orogeny, and was genetically associated with Mo, Pb Zn Ag and Au mineralization.
Nie Fengjun,Jiang Sihong,Liu Yan et al. 40Ar/39Ar ISOTOPIC AGE DATING ON K-FELDSPAR SEPARATES FROM EASTERN HUANIUSHAN GRANITE, GANSU PROVINCE, AND ITS GEOLOGICAL SIGNIFICANCE[J]. Chinese Journal of Geology, 2002, (4): 415-422.