桂北宝坛锡多金属成矿区平英岩体晚期侵入岩的年代学、地球化学特征及其地质意义

桂北宝坛锡多金属成矿区内岩浆活动频繁，其中与锡多金属成矿作用有关的平英岩体由早晚两期侵入岩组成，且晚期侵入岩中常含有较多的电英岩包体。岩石学、锆石U-Pb年代学和地球化学研究表明：平英岩体晚期侵入岩主要岩性是（中）细粒斑状黑云母（二长-）碱长花岗岩；晚期侵入岩的形成年龄为（769.2±2.5）Ma，而电英岩包体的形成年龄为（795.1±3.1）Ma；平英岩体总体以富含大离子亲石元素（LILE，包括Rb、Th和U等）、贫高场强元素（HFSE，包括Nb和Ti等）为特征，其早期侵入岩属于高钾钙碱性强过铝质S型花岗岩，具有明显的Th-U元素"U"型峰值以及Ti元素"V"型谷值，晚期侵入岩属于钾玄岩系列岩石，具有U元素"V"型尖峰值以及La-Nd和Eu-Ti元素"U"型谷值，二者在地球化学特征上存在较大的差异。结合岩浆源区性质的研究结果，早期侵入岩属于造山后花岗岩类，可能是源自泥质岩类部分熔融形成的岩浆，再经历高程度分离结晶作用形成的产物；而晚期侵入岩属于非造山花岗岩类，可能是源自泥质岩和砂屑岩类部分熔融形成的岩浆与幔源岩浆发生了不同程度的混合形成的产物。结合电英岩包体和寨滚锡多金属矿床中岩浆热液成矿阶段形成的电英岩脉在成因上存在亲缘关系，且其形成年龄与田棚岩体的形成年龄基本一致的特征，推测电英岩包体应为晚期侵入岩侵位过程中捕获早期侵入岩（田棚岩体）侵位过程中形成的岩浆热液型电英岩脉而形成的包体，其形成年龄可能代表了本区电英岩成矿阶段的成矿年龄。

Geochronology,Geochemistry and Geological Significance of the Latest Intrusive Rocks in Pingying Granite Pluton from Baotan Tin Polymetallic Metallogenic Area,Northern Guangxi

The polymetallic mineralization system of the Baotan Sn deposit frequent magmatic activities in northern Guangxi, the Pingying plutons are composed of early intrusions and late intrusions which is related to the polymetallic mineralization system of Sn deposit. The latter often contains more tourmalite-quartz enclaves. A study on petrology, zircon U-Pb geochronology and geochemistry, shows that the latest intrusive rocks in the Pingying granite pluton is composed of(medium) fine-grained porphyritic biotite(monzonite-) alkali feldspar granite. The U-Pb zircon dating results show that the formation age of the late intrusions was in(769.2±2.5) Ma, and that of the tourmaline-quartz spherulitic bodies was in(795.1±3.1) Ma. The Pingying plutons are generally characterized by rich large ion lithophile elements(LILE, including Rb, Th, U, etc.) and depleted high field strength elements(HFSE, including Nb, Ti, etc.). However, the early and late intrusions are quite different from each other in terms of geochemical characteristics: The early intrusions is belonging to high-K calc-alkaline strongly peraluminous S-type granite, with obvious "U"-shaped peaks for Th-U and "V"-shaped troughs for Ti on the trace elements spider diagram;While the late intrusions is belonging to the shoshonite series, which show "V"-shaped peaks for uranium(U) and "U"-shaped troughs for La-Nd and Eu-Ti on the trace elements spider diagram. According to the results of the study on the properties of the magma source region, the early intrusions belongs to the post-orogenic granite, and may be derived from magma generated by the partial melting of argillaceous rocks and then fractional crystallization of high degree;The late intrusions falls into the non-orogenic granite, and may be the product of the mixing of various degrees of magma and mantle-derived magma generated by the partial melting of argillaceous rocks and psammitolite. There was a genetic relationship between the tourmalite-quartz veins formed in magmatic water at the metallogenic stage of tourmalite-quartz enclaves combined with Zhaigun tin-polymetallic deposit. Moreover, the formation age was basically the same as that of Tianpeng rock mass. Therefore, it is speculated that the tourmalite-quartz enclaves were formed by late intrusive rock capturing the magmatic hydrothermal tourmalite-quartz vein formed during the emplacement of early intrusive rock(Tianpeng rock mass), and the formation age may represent the metallogenic age of tourmalite-quartz mineralization in this area.