贵州北部铝土矿床成矿地质条件、机制问题

MINERALIZATION GEOLOGICAL CONDITIONS AND MECHANISM PROBLEMS OF BAUXITE DEPOSITS OF THE NOTH PART OF GUIZHOU PROVINCE

本文讨论了黔中古陆北部及黔北古陆下石炭统铝土矿床,即所谓的息熄式铝土矿床.本类型铝土矿床系古陆经过长期红土化风化作用而形成的古风化壳原地残积和原地堆积的.下伏基岩为碳酸盐岩的为原地堆积侣土矿床;下伏基岩为页岩、粉砂岩及细碎屑岩有连续过渡的现象的为原地残积铝土矿床,均属古风化壳型铝土矿床.其共同特点是:矿体中均含红土化风化壳物质;无水体中沉积结构、构造;无动物化石及其碎屑.碎屑、豆鲕红土化形成时的特征明显,如豆鲕外壳有较多的氧化铁包壳薄膜.

In the north of Guizhou the geological time of bauxites are early Permian, The some of them .(in the south of Zwenyi, Xifen and Kayang) are the type of accumulation in situ of crust of weathering their basements are clolomilite of Loshang 9 an group (∈2-3) -Others (in the Zwenyi, Ongan and Zhenan, Daoahen) are the type of head of crust of weathering, their bed rocks are shale, silt with limestone of Tongxiu formatis (O3) and Hanjiadion formation (S2) There are phenonmena of transition between ore deposits and bed rocks.The mettenls of the bauxites origin the weathering of rocks under it. The thickness of disintegration reduce gradutly from south to north.Its 700-1000m in the south of Zwenyi, Xifen and Kayanf, 400-500m in the Zwenyi and Ongan, more than 200m in the Zhenan and Daozhen. In the study area, the weathering and disintegrats were from Caledonian to thfe middle of Idercynian.During this time, the crust elerats slomly, up to the early of Permian, the sea mater inter intrusted the study area.In Interral time of weatherding and disintegration is about 1-1.22 hundred M.Y., the time of formed laterite is about 0.48 hundred M.Y. In this area, the characteristic of the bauxites are follows: 1. There are no parallel beding, structures, textures formed in the water, no Zooliths and its fragments.These imply the bauxites formed-under the atmosphere conditions.2.If bed rocks are shale, silt and other clastic rocks, so have phenomena of transition, i.e., the strate which have beding gradualy change to the strata which have no beding from lower to upper. The phenomena of head in situ is quite'clear. If the bed rocks is carbonate, the change of the thinkness of ore body is obvious, generaly it's from less than one meter to several tens meters, the ore body formed in the dolines.In this condition, the ore body is little, its length is only seversl hundred meters and the wide is about 100-300m.3. Sometimes, the swamp developed during the time of bauxite formed, hence, there are the bands of a carbonolite and poor coal in the bauxites.