滇东南铝土矿床地球化学特征及成矿物质来源研究

Geochemical characteristics and ore-forming materials of bauxite deposits in southeast Yunnan Province

滇东南地区铝土矿资源丰富。本文以滇东南沉积型铝土矿为对象,研究了铝土矿的地球化学特征,进而对其成矿物质来源进行了讨论。含铝岩系之中富含稀土元素、分散元素镓、黑色金属元素钛和稀土金属元素铌,均已达到工业开采要求。含铝岩系的稀土总量总体较高,但样品之间稀土总量差别较大;具中等程度的铕负异常;铈异常较为复杂,具铈正异常和铈负异常;稀土配分曲线均为向右倾斜的弱＂V＂字型曲线,斜率不等,反映稀土元素分馏程度不等;稀土配分曲线特征与下伏咸宁组灰岩的稀土曲线特征一致,说明含铝岩系与下伏威宁组灰岩关系密切。含铝岩系明显富集大离子亲石元素Li、U、高场强元素Nb、Ta、Zr、Hf、Th、过渡元素V、Cr、Ti和分散元素Ga,其余元素则明显亏损。野外观察发现含铝岩系直接在风化壳上沉积,含铝岩系具复杂的铈异常和中等的Th/U比值（3-7）、高的Sr/Ba比值（〉1）以及高钛率值（3.41-44.02）。这些特征说明滇东南铝土矿的成矿物质主要来源于下伏威宁组灰岩风化形成的风化壳,沉积作用起到了对风化壳上成矿物质的改造作用。

There exist abundant bauxite resources in southeastern Yunnan Province. Taking sedimentary bauxite deposits insoutheastern Yunnan Province as the research objects, the authors studied their geochemical characteristics and discussed their ore- forming material sources. These deposits are enriched in rare earth elements, dispersed elements gallium, ferrous metal element Ti and rare metal element Nb in aluminum-containing rocks, with the reserves attaining the requirements of industrial exploitation. In aluminum-containing rocks, there are generally high REE values and big differences between samples, with the characteristics of moderate Eu negative anomaly, complex Ce anomalies composed of poaitive and negative anomalies. REE distribution patterns for normalized aluminum-containing rocks exhibit rightly-oblique curve with weak ＂V＂ shape and different slopes, reflecting varying degrees of REE fractionation. REE characteristics are similar to features of underlying limestone of Weining Formation, which shows that there exists a close relationship between aluminum-containing rocks and limestones of Weining Formation. Aluminum- containing rocks are enriched in LILE elements Li, U, high field strength elements Nb, Ta, Zr, Hf, Th, transition elements V, Cr, Ti, and dispersed elements Ga, with the obvious depletion of the remaining elements. The authors found that aluminum-containing rocks deposited directly in the weathering crust. Aluminum-containing rocks have complex Ce anomalies and moderate Th/U （3- 7）, high Sr/Ba （〉 1） and high A12O/TiO2 （3.41-44.02）, suggesting that main ore-forming materials of sedimentary bauxite deposits were derived form the weathering crust of limestones of Weining Formation, and sedimentation played the role of the reformation of the ore-forming materials of the weathering crust.