论我国铝土矿床类型及其红土化风化壳形成机制问题

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;δ18O‰及δD‰值证为风化物;除Ⅰ_c外均无动物化石及其碎屑.

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

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: I_a, 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. I_c 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.