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

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

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。

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.