内蒙古包头—白云鄂博地区金矿的同位素研究

AN INVESTIGATION ON ISOTOPE COMPOSITIONS IN THE GOLD DEPOSITS OF BAOTOU-BAIYUNEBE DISTRICTS, INNER MONGOLIA

从内蒙古包头至白云鄂博地区,横跨高、中、低级变质岩区,都发现有金矿及金矿化点。对三个主要金矿床的Pb、S、Rb—Sr、K—Ar等同位素的研究表明,成矿物质来自变质岩和花岗岩,成矿时代与古生代晚期华北陆台活化的岩浆作用有关。铅的混合模型说明在不同变质岩区变质岩和花岗岩对矿源的贡献不同。

An isotopic study was carried out on three gold deposits located in the northern edge of North China Plate, which cut through high, middle and low-grade metamorphic rock areas. All the deposits have an anomalous lead composition,and define a line with different slope on a plot of 207Pb/204Pb vs. 206Pb/204Pb diagram,and the rock or k-feldspar leads plot near or on these lines.The ores lead composition can be interpreted by a mixing model. A K-Ar age of 281.5 Ma and a median Rb-Sr age of 295.6 Ma was given by the hydrothermal minerals from Shibaqinhao deposits, and the age of granite occurred in other two deposits give a similar age.If we suppose the mineralization happened during Late Paleozoic, the ore Pb-Pb mixing line suggests an age similar to zircon U-Pb age of the metamorphic parentage rocks in different deposits.The isotope compositions indicate that the metallic components in hydrothermal fluids were derived from both metamorphic and granitic rocks. Acc ording to lead mixing model, the authors calculated the Pb mixing proportion in gold deposits in metamorphic rock and granite.