广西平果沉积型铝土矿Ga的分布特征与沉积环境关联性探讨

广西平果上二叠统合山组沉积型铝土矿储量大，并以伴生稀散元素Ga为特色。从主量成分和微量元素角度研究平果铝土矿的地球化学特征、形成环境及其与Ga的相互关联性，对综合回收利用和提升矿床经济价值有重要帮助。通过对整个研究区内均匀采集的18件不同类型的矿石及铝土岩样品进行金属Ga和常量、微量元素测试，经统计学方法计算和相关性图解分析，发现样品中Ga平均含量已达到工业品位（0.002×10-2）。但在不同类型矿石中的富集程度不同:豆鲕粒状铝土矿>致密块状铝土矿>铝土岩。而且Ga含量与Al₂O₃含量呈显著正低相关性；与SiO₂含量呈显著负相关关系；与V含量呈显著正低相关关系；与稀土元素相关性不强，无明显规律性。通过对那豆沉积型铝土矿床古地理环境和不同类型样品Sr/Ba比值、Ga的富集、LREE/HREE比值分析发现:区内沉积型铝土矿主成矿期为较稳定、酸性、潮湿的滨海至浅海相环境；而且从二叠纪合山组早期的滨海相氧化环境逐步过渡到二叠纪合山组后期的浅海相还原环境。矿石类型则由早期的紫红色致密块状矿化变化为青灰色至灰黑色鲕粒状矿化。 

Correlation between the distribution characteristics of gallium and sedimentary environment of sedimentary bauxite in Pingguo County, Guangxi, China

The Pingguo area in Guangxi Province has considerable reserves of sedimentary bauxite of the Upper Permian Heshan Formation which are characterized by the occurrence of associated dispersed element Ga (gallium). It is of great significance to study the geochemical characteristics and depositional environment of the sedimentary bauxite and their correlation with Ga in the deposit on the basis of major and trace element analyses. This research helps to improve the comprehensive recovery and utilization of bauxite, and also to increase the economic values of the deposit. The contents of major and trace elements, including the Ga concentrations, were measured in 18 different types of ores and bauxite samples which were collected in the study area. The results calculated by statistical method and analyzed by correlation diagram show that the average content of Ga in the samples reaches the industrial grade (0.002×10^-2), but the enrichment degree of Ga in different ore types accords with the regular rule of oolitic bauxite>dense massive bauxite>aluminous rock. Ga shows a significantly positive lower correlation with Al₂O₃, but a significantly negative correlation with SiO₂, In addition, the Ga concentrations show a slightly positive lower correlation with V and Zr, and no significant correlation with rare earth elements. Based on the analyses of the paleo-geographic environment, Sr/Ba ratios, Ga enrichment and LREE/HREE ratios of different types of samples, this study suggests a costal to shallow marine facies with a relatively stable, acidic and humid climatic condition during the main metallogenic period of the sedimentary bauxite in the Pingguo area. Moreover, an oxidation environment of the coastal facies during the early deposition of the Upper Permian Heshan Formation was gradually transformed into a reducing, shallow marine facies during the late deposition of the Upper Permian Heshan Formation. Correspondingly, the ore type changed from the purplish red, dense massive mineralization to lime gray to grayish dark, oolitic mineralization.