| 桂西地区沉积型铝土矿矿石构造特征及地质意义 |
| 投稿时间：2024-07-05 修订日期：2024-11-07 点此下载全文 |
| 引用本文：罗靖伟.桂西地区沉积型铝土矿矿石构造特征及地质意义[J].地质与勘探,2025,61(1):24-39 |
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| 基金项目:国家自然科学基金项目（编号：41362006）资助 |
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| 中文摘要:桂西地区沉积型铝土矿矿石构造类型主要有致密块状、碎屑状、豆（鲕） 状及土状铝土矿等四种，不同矿石构造类型在空间上存在一定差异，其与成矿作用之间的关系尚不清楚。本研究在野 外调查的基础上，通过分析桂西地区沉积型铝土矿矿石岩相学和地球化学特征，查明沉积型铝土矿含矿岩系层序组合差异性及原因，探讨其指示意义。野外调查发现桂西不同地区沉积型铝土矿含矿岩系的铝土矿层中矿石组合顺序存在一定差异：东兰-巴马-凤山成矿区铝土矿层由底部至顶部矿石构造类型表现为“致密块状-豆（鲕） 状-碎屑状+土状”；靖西成矿区、平果成矿区铝土矿层由底部至顶部矿石构造类型表现为“豆（鲕） 状-致密块状/碎屑状-碎屑状/土状”；乐业成矿区铝土矿层由底部至顶部矿石构造类 型表现为“土状-致密块状/碎屑状-豆（鲕）状”。矿石化学风化指数（CIA=87.69~99.90）、成分变异指数（ICV=0.07~1.17）、硅铝率（SiO2/Al2O3=0.03~1.09）、Th/U值（2.36~37.95）、δCe值（0.57~39.02） 指 示所有构造类型的铝土矿均经历了淋滤作用。土状、豆（鲕）状、碎屑状铝土矿较致密块状铝土矿具有更高的铝硅比（Al2O3/SiO2，A/S），说明前三者较后者脱硅更为彻底，其中土状铝土矿A/S值（0.91~34.12）和Al2O3含量（29.62%~74.73%）最高，致密块状铝土矿最低（A/S值0.93~2.80，Al2O3含量31.54%~59.75%），指示土状铝土矿所经历淋滤作用最强，致密块状铝土矿所经历淋滤作用最弱。不同成矿区铝土矿层中铝 土矿类型横向产出存在较大差异，差异原因主要与淋滤作用有关，淋滤作用强度控制矿石构造类型差异，而淋滤作用强度又受地势控制，地势越高，淋滤作用越强。从铝土矿层底部矿石构造类型在横向上的变化特征发现，铝土矿层形成早期乐业成矿区地势最高，靖西、平果成矿区地势相对较高，东兰-巴马-凤山成矿区地势最低，不同成矿区铝土矿在横向上产出存在差异主要受古地形控制。 |
| 中文关键词:沉积型铝土矿 矿石特征 淋滤作用 古地形 桂西 |
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| Structural characteristics and geological significance of sedimentary bauxite ore in western Guangxi |
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| Abstract:The sedimentary bauxite ore structures in western Guangxi mainly include four types: dense block, detrital, bean (oolitic), and soil like bauxite. There are certain spatial differences among different ore structure types, and their relationship with mineralization is still unclear. Based on field investigations, this study identified the differences and reasons for the sequence combination of sedimentary bauxite ore-bearing rock series through ore lithology and geochemical characteristics, and explored their indicative significance. Field investigations suggest that there are certain differences in the sequence of ore combinations in the bauxite layers of sedimentary bauxite bearing rock series in different regions of western Guangxi. The bauxite layers in the Donglan-Bama- Fengshan mineralization area exhibit a "dense block (ooid) - detrital+soil" ore structure type from bottom to top. The structural types of bauxite deposits in the Jingxi and Pingguo mineralization areas from bottom to top are characterized by "bean (oolitic) - dense block/detrital-detrital/earthy". The structure type of bauxite deposits in the Leye mineralization area from bottom to top is characterized by "soil like-dense block/detrital-bean (ooid) like". The chemical weathering index (CIA; 87.69~99.90), compositional variation index (ICV; 0.07~1.17), silicon aluminum ratio (SiO2/Al2O3; 0.03~1.09), Th/U value (2.36~ 37.95), and δCe value (0.57~39.02) indicate that all types of bauxite structures have undergone leaching. Soil shaped, bean shaped, and detrital bauxite have higher aluminum to silicon ratios (Al2O3/SiO2, A/S) than dense block shaped bauxite, indicating that the first types three have more thorough desilication than the latter. Among them, soil shaped bauxite has the highest A/S value (0.91~34.12) and Al2O3 content (29.62%~74.73%), while dense block shaped bauxite has the lowest (A/S value 0.93~2.80, Al2O3 content 31.54%~59.75%), indicating that soil shaped bauxite has the strongest leaching effect and dense block shaped bauxite has the weakest leaching effect. There are significant differences in the horizontal output of bauxite types in bauxite deposits in different mineralization areas, mainly due to leaching. The intensity of leaching controls the differences in ore structure types, while the intensity of leaching is controlled by terrain. The higher the terrain, the stronger the leaching effect. The lateral variation characteristics of the ore structure types at the bottom of the bauxite layer indicate that the terrain of the Leye mineralization area was the highest in the early formation of the bauxite layer, while the terrain of the Jingxi and Pingguo mineralization areas was relatively high, and the terrain of the Dongba Fengcheng mining area was the lowest. The differences in the lateral production of bauxite in different mineralization areas are mainly controlled by ancient topography. |
| keywords:sedimentary bauxite, ore characteristic, leaching, ancient landform, western Guangxi |
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