论我国铝土矿床类型及其红土化风化壳形成机制问题

DISSCUSSION ON THE PROBLEMS OF BAUXITE DEPOSITS AND THEIR LATERITIC RESIDUUM AS MECHANISM FOR THE MINEROGENETE OF BAUXITE IN CHINA

中国铝土矿床98％以上为古风化壳型,少量属红土型.前者分六个亚型,即铝硅酸盐岩古风化壳原地残积(Ⅰ_a);碳酸盐岩古风化壳准原地堆积(Ⅰ_b)、异地堆积(Ⅰ_c)以及异地沉积(湖水)(Ⅰ_d);I_(ca)古风化壳异地沉积(海相);Ⅰ_f碳酸盐岩古风化壳准原地堆积(或沉积)—现代喀斯特堆积等六个亚型.ⅠⅠ_b、Ⅰ_c三亚型矿床在大气条件下就位,就位以后继续红土化,为此矿层很少层理;矿石中常有渗流管、渗流凝胶.Ⅰ_d、Ⅰ_e亚型在水体中沉积,有层理,无渗流管、渗流凝胶.所有铝土矿床的矿物组成及矿石结构、构造都是含铝岩石红土化风化作用易溶物淋失,难溶的钛、铝、铁质残留的风化壳铝土物质;无水体中结构、构造特征;δ^(18)O‰及δD‰值证为风化物;除Ⅰ_c外均无动物化石及其碎屑.

1. The bauxite deposits in China can be divided into palaeoresidiuum bauxite deposits type (type Ⅰ) and laterite deposits type (type Ⅱ ) . The former can be diviede into six subtypes: Ia, alumina silicates rock palaeoresidiuum autochthonous residure bauxite deposit subtype; I b, carbonates rock palaeoresidiuum autochthonous accumulated bauxite deposit subtype; I c, the one of carbonate rock palacordsidiuum allogenically accumulate; I d, the one of carbonate rock palaeoresidiuum allogcnically sedimentary (lacustrine; I e, the one of palaeoresidiuum allogenically sedimentary (marine); I e, the one ofcarbonatcs rock palaeoresidiuum autochthonous accumulate (or sedimented) -the one or modern karst accumulate. 2. The minerals association of palaeoresidiuum bauxite deposit and laterite bauxite deposit of China are all the same, they are: alumina mincral+clay mincral+iron mineral+a small quantity titanic mineral and heavy mineral. The alumina mineral in type II is gibbsite, and in type I is diaspore, because the type I was prod-ucted in paloeozoic. and was dehydrated easy. The texture and structure of bauxite ores in type I . and type II such as clastic, pisolitic, oolitie, nodules (concretions) are the very same, therefore the type I and type n are all the product of latcritization in the palaeoresidiuum. According to the oxygen and hydrogen isotope constitute of the mineral composition in type I and type II and the mineral composition in the textures such as clastic, oolitic, pisolitic of the type I and type II , the δ18O‰ (SMOW) range from +5 to +20, δD‰ from -50 to -100.The data indicate that the clastic, oolitic, pisolitic bauxite ores are the product of weathering as well. 3. The laterite bauxite deposit (type II) and 60% of palaeoresidiuum bauxite deposit such as subtype I a, I b. I c are the lateritization weathering alumina material autochthonous residue. accumulated or allogencally accumulated occured under the atmosphere condition. 40% of palaeoresidiuum bauxite deposit such as subtype I d. Ic is the aluminal materials allogenically sedimented in lacustrine or marine which are the product of lateritization. Subtype I e is the karst accumulated under modern atmosphere condition which is from the subtype I bor I d.