贵州晴隆锑矿床中萤石的Sr同位素地球化学

Strontium Isotope Geochemistry of Fluorites from Qinglong Antimony Deposit in Guizhou Province

对黔西南晴隆锑矿床中的萤石进行了Sr同位素分析 ,得到其Sr同位素比值为 0 .70 76 6～0 .70 932。这个比值明显高于赋矿的二叠系茅口组灰岩和峨眉山玄武岩 ,表明成矿流体相对富集放射成因87Sr。由于该矿成矿流体的Sr同位素比值明显高于峨眉山玄武岩 ,因此将其成矿作用仅仅简单归结于与玄武岩火山活动有关的岩浆热液是不妥的。同时 ,成矿流体Sr同位素比值也高于二叠纪灰岩的Sr同位素比值 ,指示成矿流体不可能为单纯的二叠纪海水 ,而应该有更为富集放射成因Sr的岩石的贡献 ,可能是这些二叠系岩石下伏的地壳基底。先前对矿床稀土元素地球化学研究得到 ,成矿物质有外部地壳岩石参与 ;氢氧同位素地球化学研究发现 ,成矿流体为大气降水演化产物而不是海水 ;成矿物质 (F和Sb)具有赋矿围岩以外的来源。结合萤石的Sr同位素分析 ,可以认为晴隆锑矿不是简单的“海相火山喷流沉积成因”或“原地改造产物” ,成矿流体和成矿物质均具有外部来源参与而不单单是来自赋矿围岩 。

The Qinglong antimony deposit in southwestern Guizhou is an important Sb producer in South China. Despite previous detailed investigations, no agreement has been reached on the source of ore forming materials. Sr isotope ratios of fluorites from the Qinglong antimony deposit are in the range of 0.70776 to 0.70932. These are significantly higher than Sr isotope ratios for host sedimentary and igneous rocks of 0.70672 to 0.70821 for the Permian Maokou limestone and of 0.70441～0.70638 for the Emeishan basalt, respectively. It appears that the ore forming fluid is relatively enriched in radiogenic 87 Sr, suggesting an exterior origin (probably deeper sedimentary or basement rocks) rather than the country rocks, and an open system of Sb F mineralization. Because the Sr isotope ratios of the ore forming fluid are significaly higher than those of the Emeishan basalt, it is not appropriate to ascribe the Sb F mineralization in Qinglong deposit to magmatic hydrothermal process associated with the basaltic eruption. The Sr isotope ratios of the fluorites are also higher than those of the Permian limestone and coeval seawater, so it is impossible that the ore forming fluid could be derived only from the Permian seawater. Consequently a genetic model of submarine volcanic sedex is also not suitable for this antimony deposit. This conclusion coincides with our previous result deduced from REE geochemistry. Existing hydrogen and oxygen isotope studies of ore forming fluid indicate an origin of highly evolved meteroric water (by reaction with host rocks) rather than seawater. Considering that the ore forming fluid and the metallogenic materials such as F and Sb were not simply derived from the host rocks, the Sb F mineralization at Qinglong district was not resulted from in situ remobilization as expected.