桂西铝土矿中火山灰特征及其地质意义  

Characteristics and geological significance of volcanic ash in bauxite in western Guangxi

作　　者：张启连 陈有斌 刘希军[4] 黄文芳 韦访 黄光琼 黎家龙 徐海棚 梁国科 叶宝月 ZHANG Qilian;CHEN Youbin;LIU Xijun;HUANG Wenfang;WEI Fang;HUANG Guangqiong;LI Jialong;XU Haipeng;LIANG Guoke;YE Baoyue(Guangxi Institute of Geological Survey,Nanning,530023;Guangxi Institute of Survey of Geological Environment,Nanning,530023;3274 Team of Guangxi Bureau of Geology,Guangxi,536005;Guilin University of Technology,Guangxi,541004)

机构地区：[1]广西地质调查院,南宁530023 [2]广西环境地质调查院,南宁530023 [3]广西274地质队,广西北海536005 [4]桂林理工大学,广西桂林541004

出　　处：《地质论评》2022年第2期531-550,共20页Geological Review

基　　金：“广西关键矿产资源深部勘查人才小高地(编号:桂组通字[2019]85号,2019-2023年)”;“桂西地区沉积型铝土矿控矿因素、成矿规律与找矿预测研究(编号:广西壮族自治区地质矿产局桂地矿综研[2021]85号)”;“桂西锂矿资源调查评价(编号:广西壮族自治区地质矿产局桂地矿地[2021]14号)”的成果。

摘　　要：岩溶型铝土矿中火山物质参与成矿的直接证据需要进一步明确。通过线路调查和剖面研究,在桂西大范围内的铝土矿及其早期的铝土质岩中观察到大量的火山灰,含量大于30%;火山灰种类有岩屑、晶屑、玻屑和火山尘,塑性—半塑性变形及刚性爆裂显著,自由降落为主,属原地—准原地沉积;火山灰易于分解为水铝石、高岭石、赤铁矿等微细矿物,屑状火山灰相对尘状火山灰更易于矿化,大量火山灰主要以直接铝土矿化作用成矿。元素地球化学特征显示铝土矿和铝土质岩具有亲岩浆性,不活动元素图解判别及铝土矿测年数据显示火山灰原岩浆以碱性玄武岩为主,与岛弧火山岩一致,主要来自于哀牢山—松马造山带的二叠纪岛弧,铝土矿层具有穿时性,部分火山灰可来源于峨眉山火成岩。铝土矿层中的火山灰丰富,跨度长,可能是瓜德鲁普世末生物灭绝的肇凶。Objectives:So far the volcanic material has rarely been found in karst bauxite, and the direct evidence of volcanic material participating in mineralization of karst bauxite needs to be further clarified.Methods:Based on line survey and section study,such as microscopic observation and elemental analysis of rocks and ores Results: A mass of of volcanic ash is observed in bauxite and early aluminite rocks within western Guangxi, with at least 30% content;and the types of volcanic ash include detritus, crystal fragment, hyaloclastic fragment, volcanic dust, with significantly Plastic or semi-plastic deformation and obviously rigid burst, and showing freelyfalling. and deposited in situ or half in situ;and the volcanic ash is easy to decompose into boehmite, kaolinite, hematite and other fine minerals, and the clastic volcanic ash is easier to mineralize than the dusty one, and a lot of volcanic ash had made directly bauxite mineralization. Element geochemical characteristics of bauxite and bauxitic rock show that the volcanic ash had originated in magma, and the discrimination diagram of immobile elements of bauxite and bauxitic rock and dating data indicate that the ash had been mainly made of alkaline basalt magma from Ailaoshan—Songma volcanic arc, which is consistent with the modern island arc volcanic rocks,. the Emeishan igneous rock had taken park in mineralization too duing the diachronism of bauxite formation. Owing abundance and long duration, the volcanic ash may be the cause of the mass extinction at the end of Guadalupian. Conclusions: Bauxite mineralization had been developed directly by volcanic ash, and the volcanic ash had mainly come from the Ailaoshan—Songma orogenic belt, partly from Emeishan igneous rock;and the volcanic ash may be the cause of the mass extinction at the end of Guadalupian.

关 键 词：铝土矿 火山灰 岛弧火山岩 地质意义 桂西 

分 类 号：P618.45[天文地球—矿床学]