湖北狮子立山锶(铅锌)矿区石英闪长玢岩锆石SHRIMP U-Pb定年及其意义

SHRIMP zircon U-Pb dating of quartz diorite porphyry from the Shizilishan Sr(Pb-Zn) deposit in Hubei Province and its geological significance

湖北狮子立山锶(铅锌)矿床是我国重要的超大型锶矿床之一,产出于鄂东矿集区北部铁山岩体东缘的狮子立山岩体(主要为石英闪长玢岩)与三叠纪蒸发岩地层(嘉陵江组)的接触带或附近。本文对矿区内的石英闪长玢岩与成矿作用之间的关系和该岩体的年代学开展了详细的研究工作。结果表明,狮子立山岩体与锶矿成矿作用可能存在密切的联系,矿床中的部分Sr可能来自于石英闪长玢岩的强烈蚀变。锆石SHRIMP U-Pb的定年工作得到2个石英闪长玢岩样品的形成时代分别为138.6±0.8Ma和138.9±1.2Ma,二者在误差范围内基本一致,这些数据与前人获得的铁山岩体的成岩时代基本一致,暗示本次测得的石英闪长玢岩的样品年龄可靠性较高,且很可能与铁山岩体是同一地质背景下的产物,即形成于区域晚侏罗-早白垩世岩石圈由挤压到伸展的转换环境。狮子立山岩体的侵位地层及矿床中硫同位素组成的特征与程潮和金山店矽卡岩型铁矿具有明显的相似性,暗示在狮子立山矿床附近具有寻找矽卡岩型铁矿床的潜力。

Shizilishan Sr （Pb-Zn） deposit is one of the important super-large strontium deposits in China, and is developed along the contact zone between Triassic evaporite strata （Jialingjiang Formation） and the Shizilishan stock （mainly as quartz diorite porphyry）, which is located at the eastern margin of the Tieshan pluton, Edong district. In this paper, the relationship between the quartz diorite porphyry and the ore-forming process, as well as the chronology of quartz diorite porphyry are studied. The results show that Shizilishan stock probably had a close relationship with the strontium mineralization and some of the strontium in the deposit may come from the strong alteration of the quartz diorite porphyry. Zircon SHRIMP U-Pb dating shows that two quartz diorite porphyry samples reveal 138.6±0.8Ma and 138.9±1.2Ma, respectively, which were basically the same within error. Additionally, these ages are almost the same with Tieshan pluton, suggesting that they are highly reliable and the Shizilishan stock probably has same background with Tieshan pluton and both produced under the lithosphere tectonic switched from the Late Jurassic transpressive to earliest Cretaceous extensional regimes. Emplacement strata of the Shizilishan stock and distribution of sulfur isotopic composition of the deposit are similar to that of Chengchao and Jinshandian Fe skarn deposit, suggesting that there is potential to find Fe skarn deposit around the Shizilishan Sr （Pb-Zn） deposit.