河北丰宁撒岱沟门钼矿床成岩成矿年代学及成矿岩体地球化学特征

撒岱沟门钼矿床是位于华北克拉通北缘的一个大型斑岩型钼矿床。前人获得的成矿岩体的年龄与成矿年龄差别较大, 为此本研究对矿区内不同特征的花岗岩开展了锆石U-Pb测年和与辉钼矿伴生的白云母40Ar/39Ar测年, 并对这些岩石开展了岩石地球化学和Sr-Nd-Hf同位素地球化学测试, 以及成矿岩体磷灰石EPMA主量元素成分测试, 旨在进一步厘定成矿岩体, 以便加深对成岩成矿演化过程的认识。结果表明: 撒岱沟门钼矿白云母40Ar/39Ar坪年龄为(237±2) Ma, 与赋矿白色黑云母二长花岗岩锆石U-Pb年龄(240±1) Ma和前人获得的辉钼矿Re-Os年龄在误差范围内一致, 成岩成矿作用发生在中三叠世, 而赋矿的另外一种岩体, 即红色黑云母二长花岗岩的年龄为(248±1) Ma, 说明其是成矿前的侵入体。赋矿红色和白色黑云母二长花岗岩均为高硅、富碱、富钾的I型花岗岩, 属于准铝质到弱过铝质、高钾钙碱性至钾玄岩系列, 并在Sr-Nd-Hf同位素组成上显示同源特征, 表明其主要来源于古元古代壳源物质的部分熔融, 与华北克拉通2.3~1.9 Ga的构造演化密切相关。成矿岩体中的岩浆磷灰石具高F、低Cl特征, 反映F在撒岱沟门钼矿的形成过程中扮演了重要角色。

Metallogenic and Petrogenic Geochronology and Geochemical Features of the Ore-related Granite in the Sadaigoumen Mo Deposit,Fengning, Hebei Province

The large-sized Sadaigoumen porphyry Mo deposit is located on the north margin of the North China Craton. Previous studies show that there is a big gap between the age of ore-related granite and ore-forming ages, which is inconsistent with the current consensus that a porphyry deposit is formed in a short duration. In order to solve this problem, the authors carried out U-Pb dating of the zircons from different granites in the ore district and 40Ar/39Ar dating of the muscovite from the molybdenite-bearing quartz vein. In addition, the study of the whole rock geochemistry and Sr-Nd-Hf isotopes of the granites and analysis of the major elements for the apatite from the ore-related granite were conducted in this paper. The results show that the muscovite yielded an 40Ar/39Ar plateau age of (237±2) Ma, which is consistent with the zircon U-Pb weighted mean age of (240±1) Ma for the white biotite monzogranite. These data are also coeval, within error, with the molybdenite Re-Os age (ca. 237 Ma) in this deposit obtained by previous research. This shows that the white biotite monzogranite is an ore-related granite, while the red biotite monzogranite with the zircon U-Pb age of (248±1) Ma is a pre-mineralisation intrusion. Geochemically, both the white and red biotite monzogranites belong to the metaluminous to slightly peraluminous high-K calc-alkaline to shoshonite I-type granitoids with high SiO2, alkline and K2O content. Sr-Nd-Hf isotope data demonstrate that these granites were formed by partial melting of the pre-existing Paleoproterozoic crust, which was intimately related to the evolution of the North China Craton during ca. 2.5~1.9 Ga. Apatite from the ore-related white monzogranite is characterized by high F and low Cl content, which is indicative of a high F parental magma of the deposit, and this feature possibly played a significant role in the Mo mineralisation at Sadaigoumen.