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

分布于海南省东方县东部抱板～二甲和大蟹岭一带的抱板群与奥陶～志留系的南碧沟群之间为断裂相接.在此断裂带中分布有著名的抱板～二甲金矿床及其北部的土外山金矿点.抱板群为含矿层位,其形成时代为中～晚元古代.金矿的形成时代为228±5Ma.据此,对在海南省,甚至两广寻找同一时代和同一地质条件的金矿,提供了很有价值的线索.

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 ^(48)Ar-^(39)Ar 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.