贵州新民铝土矿矿床Li的地球化学特征与富集机制探究

新民铝土矿床位于黔北务川-正安-道真地区(简称务正道地区)大塘向斜东翼,铝土矿(岩)型Li资源丰富.含矿岩系大竹园组(P1d)不同岩性的w(Li)有差别:土状-半土状铝土矿平均w(Li)为16.34×10-6,致密块状铝土矿平均w(Li)是803.84×10-6,铝土岩平均w(Li)是1436.22×10-6,黏土岩的平均w(Li)是786.62×10-6,梁山组泥岩的平均w(Li)是51.82×10-,韩家店群泥岩(页岩)的平均w(Li)是48.52×10-6,黄龙组灰岩的平均w(Li)是 11.99×10-6.由此可知,研究区铝土矿(岩)型Li资源主要富集在含矿岩系中上部的致密块状铝土矿、铝土岩和黏土岩中,顶板、底板以及土状-半土状铝土矿w(Li)较低.Li主要赋存于高岭石中,伊利石(水云母)和残存的三水铝石、勃姆石也可富集少量Li,当样品中赋锂矿物(高岭石、伊利石(水云母)、三水铝石和勃姆石)都存在时,高w(Li),主量元素w(Al3O2)、w(SiO2)、w(MgO)、w(K2O)、w(TiO2)和w(TFe2O3)与w(Li)的相关性也证实了上述结果.研究区的地球化学比值 CIA、w(Sr)/w(Cu)、u(CaO)/w(MgO)、w(Sr)/w(Ba)、w(V)/w(V+Ni)和 w(La)/w(Y)综合显示,炎热潮湿的古气候下,有机质腐烂形成酸性环境,半封闭海湾环境下,黏土化阶段中等强烈的化学风化程度和适宜的风化暴露剥蚀时间利于铝硅酸盐矿物和硅酸盐矿物化学键断裂,富集Al3+形成高岭石;风化程度过于强烈和长时间的风化剥蚀,继续脱Si富Al形成以硬水铝石为主的铝土矿;弱酸性-弱碱性以及氧化-还原过渡条件下,使得高岭石能最大程度的吸附Li元素.

Geochemical characteristics and enrichment mechanism of Li in Xinmin bauxite deposit, Guizhou

Xinmin bauxite deposit is located in the eastern wing of the Datang syncline in Wuchuan-Zheng'' an-Daozhen area (also called Wuzhengdao for abbreviation) in northern Guizhou, and there are abundant bauxite (stone) type Li resources. The w(Li) of different lithologies of ore-bearing strata Dazhuyuan Formation (P₁d) are slightly different:the average w(Li) of earth-semi-earthy bauxite is 16.34×10^-6, the average w(Li) of compact massive bauxite is 803.84×10^-6, the average w(Li) of bauxite stone is 1436.22×10^-6and that of clay stone is 786.62×10^-6, the average w(Li) of mudstone in Liangshan Formation is 51.82×10^-6, the average w(Li) of mudstone (shale) in Hanjiadian Group is 48.52×10^-6, the average w(Li) of Huanglong Formation limestone is 11.99×10^-6. It can be concluded that the bauxite (stone) type Li resources in the study area are mainly enriched in compact massive bauxite, bauxite stone and clay stone in the middle and upper part of the ore-bearing strata, and the Li content of foot wall, hanging wall and earth-semi-earthy bauxite is low. In mineral assemblages, Li mainly enriched in kaolinite, illite (hydromica), residual gibbsite and boehmite also host small amounts of Li. Li content is high when those Li-bearing minerals (kaolinite, illite/hydromica, gibbsite and boehmite) are all in the sample, and the correlation between the major elements w(Al₃O₂), w(SiO₂), w(MgO), w(K₂O), w(TiO₂) and w(TFe₂O₃) and w(Li) also confirms this result. The geochemical ratios of CIA, w(Sr)/w(Cu), w(CaO)/w(MgO), w(Sr)/w(Ba), w(V)/w(V+Ni) and w(La)/w(Y) in the study area show that in the hot and humid paleoclimate, the organic matter decays to form an acidic environment. In the semi-closed bay environment, the moderate strong chemical weathering degree and suitable weathering exposure and erosion time in the clayification stage are beneficial to the chemical bond breaking of aluminosi-licate minerals and silicate minerals, and the enrichment of Al³⁺ to form kaolinite; after strong and long time weathering & erosion, Si was continually removed but Al enriched to form bauxite dominated by diaspore. In a weak acid-weak alkaline and oxidation-reduction transition conditions, kaolinite can adsorb Li to the maximum extent. Key Words:geology, bauxite (stone) type Li resources, kaolinite, influencing factors, enrichment mechanism, Xinmin