海南东方二甲抱板群和金矿的时代

THE TIME OF THE BAOBAN GROUP AND GOLD ORE AT ERJIA, DONGFANG, HAINAN PROVENCE, CHINA

The Baoban Group is a suit of the metamorphics series consisted of the quartz-mica schist, hounblende schist, plagioclase hornblendite and different type of the migmatites. An age of the automorphic zircons from the migmatite at Erjia has been determined by U-Pb method. The concordia diagram gives an upper intercept age of 1145_-25⁺⁴⁰ Ma. This data can be looked on the forming age of the migmatite. Obviously, primary diagenetic time of the Baoban Group must be more than 1145 Ma, may be middle Proterozoic or even more older. It may also be theoldest metamorphosed basement of the Jiangnan Palaeocontinent in Hainan.Both ⁴⁸Ar-³⁹Ar ages of 228 ± 5Ma and 226 ± 2Ma(1)are the the plateau and all melt ages of a sericite sample from the Au-bearing phyllonite at Erjia respectively. We regard 228 Ma as the sericite froming age, i. e. Au-mineralization time, because we consider the Au ore and the sericites to be formed simultaneously.