贵州北部铝土矿床成矿地质条件、机制问题

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.

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;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.

黔西碳酸盐地层中菱铁矿床风化铁帽的地球化学特征

Zonal distributien can be noticed in gossan resulted from siderite in carbonate strata, and this can be accounted for by zoning Of ground water. Because siderite is more insoluble than its wall rocks, gossan generally develops at the same place of siderite outcrop. Systimatic variation in chemistry is recognizable from ore body upwards to the surface. The gosasn is high in Fe, Mn but impoverished in S, P, Pb,Zn, Ge, Ga, Cd, Ag. This characteristic may serve as an indicator to distinguish siderite gossan from sulphide gossan in this region.