东沟含钼斑岩由太山庙岩基派生?

Was Donggou porphyry Mo deposit derived from Taishanmiao batholith?

河南汝阳东沟斑岩型钼矿是近年来发现的超大型钼矿床,含钼斑岩被认为是太山庙岩基的岩枝或晚期分异产物。据此,东沟钼矿的形成似乎与太山庙岩基的岩浆分异作用有关。文章依据地质学、岩石学、岩石地球化学和温度场分析,认为东沟花岗斑岩是独立于太山庙岩基的另一次岩浆活动的产物。其依据为:①根据前人发表的测年结果,太山庙岩基和东沟斑岩体的形成时间相差约3Ma,不应当认为形成时间一致;②太山庙岩基厚约3.5km,其出露高度大于东沟斑岩体,且东沟斑岩体距太山庙岩基约7km,其间不存在大断裂,两者的空间分布关系不符合深部岩浆房分异模型;③东沟斑岩体含有高温石英斑晶,是高温岩浆固结的产物,而太山庙岩基是相对低温岩浆的深成侵入体;④以东沟斑岩体为中心分布有相对完整的同心环状Pb-Zn矿点,表明成矿时期存在由内向外逐渐降低的温度场。因此,东沟斑岩不应当是太山庙岩基的岩枝或晚期分异产物。此外,根据花岗质岩石钼平均丰度和含矿流体中钼溶解度的最新实验资料进行质量平衡计算,结果表明东沟斑岩不能提供足够的成矿物质,东沟钼矿的形成必须有额外的成矿物质来源。因此,东沟钼矿的成因与透岩浆流体成矿作用有关,岩浆体系和成矿体系是两个独立的地质体系。综合分析表明,岩浆来自大于30km的下地壳,而成矿物质及流体具有多来源的特点。

The Donggou porphyry Mo deposit, located in Ruyang County of Henan Province, is a giant ore deposit discovered in recent years. The Donggou molybdenum-bearing porphyry is considered to be an apophysis or a fractionated product from the adjacent Tai- shanmiao batholith. Accordingly, the ore-forming process of this deposit seems to be relevant to the differentiation of Taishanmiao batholitic magma. Based on an analysis of geology, petrology, geochemistry and temperature field, the authors hold that the Donggou granite porphyry is a product of another magmatic activity independent of Taishanmiao batholitic magma, as shown by the following evidence： ① According to the age data available, the Taishanmiao batholith was generated earlier than the Donggou porphyry by 3 Ma, suggesting that the two intrusions were not contemporaneous. ② The thickness of the Taishanmiao batholith is about 3.5 km and the exposed elevation is higher than Donggou porphyry by 600 m, and there are no larger faults within the distance of about 7 km between the intrusions. Such a spatial relationship is not consistent with the differentiation model of a deep magma chamber. ③ The Donggou porphyry, containing high-temperature quartz phenocrysts, is a product consolidated from the high temperature magma. On the contrary, the Taishanmiao batholith is a pluton with relatively low initial temperature. ④ There are Pb-Zn ore deposits or spots composing a relatively complete ring with the Donggou porphyry as the center, showing that there existed a temperature field around the Donggou porphyry and that the temperature field was not destroyed by the heat from the Taishanmiao intrusion during mineralization. Therefore, the Donggou porphyry should not be considered as an apophysis or a product fractionated from the adjacent Taishanmiao batholith. In addition, based on the average Mo concentration of granotoid and the latest experimental data of molybdenum solubility in the ore-bearing fluid, the mass balance calculation shows that the Donggou porphyry was unable to provide adequate ore-forming matter to form a giant deposit. Therefore, the formation of the Donggou porphyry Mo deposit is attributed to the contribution from additional sources of ore-forming matter. Accordingly, the Donggou porphyry Mo deposit can be thought to be genetically related to the trans-magmatic fluid. That is to say, the magmatic system and the ore-forming system can be regarded as two independent geo- logical systems. A comprehensive analysis indicates that Donggou porphyry magma was derived from the lower crust deeper than 30 km, and the ore-forming matters and fluids had different sources.