福建马坑矽卡岩型铁(钼)矿床地质特征及辉钼矿Re-Os同位素年龄

福建马坑矿床为赋存于莒舟—大洋花岗岩外接触带黄龙组(C2h)灰岩和林地组(C1l)碎屑岩层间构造破碎带中的大型层控矽卡岩型铁(钼)矿床。笔者利用Re-Os同位素方法对矿体中7件辉钼矿样品进行了成矿时代研究,获得的模式年龄为(131.9±1.9)～(133.3±2.3)Ma,加权平均年龄为(133.0±0.8)Ma,表明马坑铁(钼)矿床的成矿作用发生于早白垩世;其与莒舟花岗岩体的岩浆活动和侵位年龄一致,表明为同一构造-岩浆-流体活动的产物。7件辉钼矿样品中,5件样品Re质量分数为(0.47～5.14)×10-6,另外2个分别为51.87×10-6和186.2×10-6,再考虑到莒舟—大洋岩体为弱过铝壳源型花岗岩,推断成矿物质主要为地壳来源,可能混有少量地幔物质。白垩纪马坑铁(钼)矿的成矿可能为华南岩石圈减薄的响应。

Geology and Molybdenite Re-Os Ages of Makeng Skarn-Type Fe-Mo Deposit in Fujian Province

Makeng Fe-Mo deposit is a large strata-bound skarn-type deposit occurred in the exo-contact zone of the Juzhou-Dayang granite and hosted by interbedfaults between Huanglong Formation(C2h) carbonates and Lindi Formation(C1l) clastic rocks.Seven molybdenite samples separated from the Makeng skarn ore bodies were used for Re-Os dating.The obtained the model ages range from(131.9±1.9) Ma to(133.3±2.3) Ma,averaging at(133.0±0.8) Ma,indicating that the major metallogenic stage occurred at the Early Cretaceous,which is consistent with the emplacing age of the host rock Juzhou granitic pluton.Our results suggest that they are products of the same epoch magma,structure,and fluid activities.Five out of seven molybdenite samples show Re contents at 0.47×10-6~5.14 ×10-6,and the other two at 51.87×10-6 and 186.2×10-6,respectively.Combined with fact that the Juzhou-Dayang pluton are the crust-derived granite,we infer that the ore-forming material mainly derived from upper crust with minor addition from the mantle.The metallogenic epoch of Makeng Fe-Mo deposit may consider as the response to the Late Mesozoic regional lithospheric thinning in the South China block.