黔北务正道地区铝土矿基础地质与成矿作用研究进展

Advances in Basic Geology and Metallogenic Regularity Study of Bauxite in Wuchuan-Zheng′an-Daozhen Area, Northern Guizhou Province

务正道地区铝土矿底板地层黄龙组类化石及铝土矿层大竹园组、梁山组的孢粉化石限定,大竹园组的时代为早二叠世。大竹园组铝土矿的沉积环境为向北半封闭的海湾或海泛湖。铝土矿形成于低纬度热带气候条件下,气候具旱季、雨季之分,盆地水体为弱酸性还原条件,陆地植物生态系统和盆地微生物生态系统对铝土矿的形成起了重要作用。铝土矿的主要物源为志留系韩家店组和石炭系黄龙组双重物源。陆源区风化的铝质通过胶体作用搬运到盆地中形成铝土质岩。铝土矿层形成之后,又经历了多期次暴露地表的风化淋滤。淋滤作用分别在渗流带和潜流带形成土状、半土状铝土矿和致密状铝土矿,盆地内部铝土岩破碎和胶体凝聚分别形成碎屑状、豆鲕状铝土矿。风化过程中多数元素发生了不同程度的丢失,而SiO2的流失程度明显大于Al2O3,从而形成铝土矿矿层。因此,盆地的沉积体系和古地理控制了铝土矿矿系的分布范围和厚度,多期次的淋滤作用控制了铝土矿的品质和矿层的厚度。

The formation age of Dazhuyuan Formation bauxite deposit layers in Wu-Zheng-Dao Area, is re- stricted by fusuline and foraminifer fossils in underlaid Huanglong Formation and sporopollen fossils in Dazhuyuan Formation and superjacent Liangshan Formation, and is early Permian. The sedimentary envi- ronment of Dazhuyuan Formation bauxite deposit is a bay or a transgression lake which is half closed to- wards North. The bauxite is formed under the conditions of hot climate in low-latitude, and it can be sub- divided into dry and wet seasons. The water body in the sedimentary basin is of weak acid reducing condi- tion. Both of the landplant ecosystem and the basin microbe ecosystem have crucial impacts on the mineral- ization of bauxite. Hanjiadian Formation and Huanglong Formation provide double provenances for baux- ite. Weathered aluminous materials are transported into the basin through the colloidal effect to form alu- minous rock. Bauxite layers undergo several times of exposing and leaching processes after their forma- tions. The leaching process leads to formation of earthy and half-earthy bauxite in the vadose zone and compact bauxite in the hyporheic zone. Crushed mudcracks form clastic bauxite and colloid coacervation forms ooidal bauxite. During the weathering process, instead of preservation, aluminum and ore-forming elements all experience element loss of varying degrees, and the SiO2 loss degree is obviously higher than that of Al2 O3 to form bauxite layers. Therefore, the sedimentary system of the basin and paleogeography control the distribution and thickness of bauxite layers, and multiperiod leaching processes control the quality and thickness of bauxite.