象牙海岸Issia地区铌钽砂矿的研究(英文)

在西非的象牙海岸Issia地区分布着许多铌钽矿床,包括原生矿和砂矿。原生矿产在分带很好的伟晶岩中。这个地区发育着许多花岗岩和花岗伟晶岩。伟晶岩可分为:(1)分异不好的伟晶岩,无矿化;(2)含Be伟晶岩,分带较好,见绿柱石;(3)含Be-Nb-Ta的伟晶岩,分带很好,是矿体;(4)Be-Nb-Ta-Li伟晶岩,分带很好,是矿体。除了10多个原生矿外,还有许多砂矿。砂矿有两种类型:一种近原生矿的坡积砂矿,另一种是经河流冲刷搬运后的冲积砂矿。我们选择了Etienne-Meguhe砂矿作为近原生矿的坡积砂矿的代表,Bemadi矿作为河流冲积型的砂矿的代表,对这两种类型的砂矿的风化、搬运、沉积机理进行了比较研究。研究发现不同的搬运距离和搬运模式对铌钽砂矿的主要矿物——铌钽铁矿的化学性质没有什么影响,而其物理形态则发生了变化。坡积型砂矿的铌钽铁矿常与石英、长石等矿物连生,其颗粒大小与原生的Nb-Ta伟晶岩中的铌钽铁矿一致;经河流冲积而形成的砂矿中,铌钽铁矿颗粒变小、轮廓变得圆滑,几乎无连生矿物,但矿体集中,常在河流的冲积扇中分布,易开采。

OLUMBITE-TANTALITE DISTRIBUTION AND PLACER FORMATION IN HUMID TROPICAL AREAS:AN EXAMPLE FROM THE ISSIA COLUMBITE-TANTALITE DISTRICT,CENTRAL WESTERN IVORY COAST

The Etienne-Meguhe and Bemadi mines are the major columbite-tantalite deposits of the Issia district, Central Western Ivory Coast. They are different in geomorphology, style of mineralization and geological evolution. The Etienne-Meguhe deposit, located on a large interfluve, is an eluvial deposit resulting from kaolinization which produced a significant volume reduction and the subsequent concentration of chemically stable minerals, such as quartz, and niobium-tantalum and beryllium bearing minerals. The Bemadi deposit is an ideal placer resulting from river transport which caused fragmentation, rounding, and finally accumulation of dense minerals along natural traps. Concerning the formation and distribution of the supergene mineralization, it is shown that the surficial natural processes within humid tropical environments generate neither mineral growth nor chemical changes in columbite-tantalite minerals. Under these conditions, the columbite-tantalite grains do however become more and more rounded and their size decreases gradually without any chemical changes. Thus, under atmospheric conditions in the humid tropical areas, even if the chemical properties of this mineral are preserved, the physical properties change gradually from the eluvial zones to the alluvial zones.