江苏徐州西村金伯利岩管地质特征及其找矿意义

Geological characteristics and prospecting significance of kimberlite pipe in Xicun area of Xuzhou, Jiangsu Province

西村岩管是在苏北地区发现的第一个金伯利岩管,颠覆了苏北地区无金伯利岩的历史。从岩石学、地球化学和伴生矿物等方面分析了西村岩管的地质特征,并进一步探讨其金刚石找矿意义。从区域背景和金刚石形成条件看,西村地区具备了金伯利岩侵位和金刚石矿形成的基本地质条件,而西村岩管为金刚石矿就位提供了母岩条件;西村金伯利岩与山东、辽宁金伯利岩具有相似的地球化学特征,是幔源岩浆低程度部分熔融的产物,且在岩浆上升过程中普遍遭受了壳源物质的混染,后期碳酸盐化现象普遍发育;其相容元素含量与山东金伯利角砾岩相似,均为典型的金伯利岩型配分模式,稀土元素表现为轻、重稀土元素强烈分馏的特征;伴生指示矿物主要为榴辉岩型含铬镁铝榴石、富铬透辉石和富镁铬尖晶石,其特征均表现出含矿金伯利岩的特点。

The Xicun kimberlite pipe was discovered for the first time which has ended the kimberlite-nonexistent history in northern Jiangsu Province. The geological characteristics of Xicun pipe were analyzed by petrology, geochemistry and associated minerals, and the prospecting significance was discussed. According to the regional background and the conditions of the diamond formation, it is considered that there existed basic geological conditions for kimberlite emplacement and diamond ore formation in Xicun area. The Xicun kimberlite pipe provided mother rock conditions for diamond ore. The Xicun kimberlites have similar geochemical characteristics to Shandong and Liaoning kimberlites. They were all formed by low degree partial liquation of the mantle-derived magma. Besides, they suffered hybridism of the earth crust in the process of magma rising and widespread carbonatization in the late period. The values of compatible elements are similar to those of Shandong kimberite breccia, which constitute the typical patterns of kimberlite. The heavy and light rare earth elements are characterized by strong fractionation. Associated indicator minerals include eclogite-type pyrope, chrome-rich diopside, and magnesium-rich chrome spinels, which show the characteristics of ore-bearing kimberlite.