THE EPITHERMAL DEPOSITS IN THE NORTHERN MARGIN OF NORTH CHINA CRATON: SPATIOTEMPORAL DISTRIBUTION AND TECTONIC SETTING
QI Jin-ping~1, CHEN Yan-jing~(1,2), Li Qiang-zhi~1 1.Department of Geology, Peking University,Beijing 100871,China; 2.Institute of Geochemistry, Chinese Academy of Sciences,Guiyang 550002,China
This paper summarizes the geological-geochemical characteristics of the E-W trending epithermal Au/Ag deposits in the northern margin of North China craton.The epithermal Au/Ag deposits distribute in the Liao-Ji block,Yanshan orogen and the northern end of the Taihang Mountains,in the Mesozoic volcanic basin which was superimposed onto the cratonic basement. Occurrences of the deposits are controlled by faults and/or volcanic craters. Most of the isotope ages for ores and related igneous rocks fall in a span of 170 Ma~100 Ma. The ore-forming fluid-systems were dominated by meteoric water, with input of magmatic fluid, as traced by D-O isotope systematics. Ore metals, indicated by S-Pb isotopes, were mainly sourced from Precambrian basement and contaminated by cover-strata of the craton. Consequently, it is argued that the metallogenic belt along the northern margin of the North China craton was resulted from the Siberia-North China continental collision, instead of from the subduction of the Paleo-Asian, Pacific and Mongol-Okhotsk oceanic plates. The metallogenic magma-fluid systems were originated from intracontinental (A-type) subduction during continental collision. The large-scale granitic magmatism and metallogenesis occurred at transition regime from collisional compression to extension.