长江中下游层控铜矿床的成矿作用

STRATA-BOUND COPPER ORE DEPOSITS IN THE LOWER REACHES OF THE CHANGJIANG(YANGZI) RIVER

对长江中下游铜铁矿床的成因和成矿作用的认识至今众说纷纭.作者据多年在该区找矿勘探实践和成因研究,提出矿床属沉积或火山沉积-热液叠加型成因.矿床沉积于固定层位,表现明显的层控持点;凹陷沉积盆地或占海盆地边缘、近乐西向和近南北向隐伏基底断裂交汇结点控制矿床分布;后期岩浆侵入和区域变质作用使矿床受热液作用叠加和改造.据此,摆脱了局限于小侵入体与灰岩接触带或矿区周边找矿的认识,从而扩大了找矿远景.

In the fault depression troughs along the lower reaches of Changjiang River, occur a numher of important stratiform sulfide ore deposits, such as Chenmenshan, Wushan in Jiangxi Provice, Mashan, Dongguanshan, Xinqiao, Magushan, and Tongguanshan, Anhui Provice, Qixiashan, Jiangsu Provice, which were formerly considered as typical post-magmatic hydrothermal products. Detailed field and laboratory investigation reveals that they are stratiform sulfide ore deposits related to submarine volcanism. These deposits are strictly stratabound in the Middle Carboniferous series, and frequently in the upper Permian series and lower Triassic series. Dacitic and rhyolitic lavas and volcanoclastics have been found in the ore bearing sequences. Therefore the metals and sulphur in these deposits came from different source-beds. The high concentration of As in the ores, and the Co/Ni ratios being greater than 1 in the pyrites indicate their affilition with submarine volicanism, thermal springs and exhalations. The values of S/Se ratios and δ^(34)S show that, in addition to deep sources, the reduction of sea-water sulphate also contributed a part to the sulphur in the ores, and biogenic processes may locally be postulated in some of the deposits.