红土型金矿床综述(英文)

近二十年来 ,热带地区普遍存在的红土型风化作用及其对矿床与矿化带的影响引起了普遍的关注。红土型风化壳的主要矿物成分是以铁铝的氧化物及氢氧化物和粘土矿物为主 ,如针铁矿、赤铁矿、铝土矿、高岭石及石英等 ,与其未风化的母岩相比 ,含有相当高的铁和铝。红土型风化过程中 ,易溶元素均不同程度地被淋滤 ,而难溶元素则相对富集。红土型金矿床就是在这样强烈的风化作用中由原生的金矿化带进一步富集而成 ,并可形成极富的矿体。金矿体常常赋存于风化壳的上部 ,易于露天开采。目前 ,在澳大利亚、巴西、巴布亚新几内亚、印度以及非洲的一些国家均发现了红土型金矿床。红土型风化剖面一般可分为 5个特征带 ,由上而下为 :表土带、铁质带、斑点带、浅色带、腐岩带 ,下面即为未风化的母岩 ,金矿体主要赋存于铁质带和斑点带中。红土型风化壳厚度变化很大 ,薄则几米 ,厚可达数百米。金在风化过程中往往向矿化带两侧运移 ,矿体常呈上宽下窄状。次生金常呈自形晶、树枝晶、浑圆状及不规则状产出 ,并常常与铁质结核共生。一般地说 ,次生金的成色很高 ,因为红土型风化作用常常是在氧化并且酸性的地球化学环境中进行 ,金和银主要以氯化物的形式运移 ,局部地球化学环境的变化可导致金的沉淀 ,而银的氯化物则较稳定 ,?

LATERITIC GOLD DEPOSITS:AN OVERVIEW

One of the most fascinating problems in economic geology is to understand the behaviour of surface ore deposits under conditions of intense tropical weathering. Since the 80's, studies have shown that gold is mobile in supergene lateritic weathering conditions. Laterite profiles are usually composed of five main zones in variable combinations above the unweathered rocks. They are topsoil zone, ferruginous zone, mottled zone, pallid zone, and saprolite zone. Laterite profiles vary enormously in scale, which may be a few meters to hundreds of meters thick. Lateritic gold deposits are developed on primary gold mineralization zones, such as quartz veins, quartz lodes, stockworks or auriferous mylonitic breccia zones, which may be either econo mic or subeconomic before the lateritization. Secondary gold grains may occur in a variety of forms including euhedral crystals, rounded grains, dendritic growths or irregular masses. The secondary gold is characterized by a great fineness. This phenomenon can be explained by leaching of Ag and crystallization of secondary gold during lateritization. Both inorganic and organic ligands can stabilize gold in solution. The major inorganic ligands include Cl - in very acidic, oxidizing conditions, S 2O 2- 3 under alkaline oxidizing conditions, OH - under neutral and alkaline conditions, and possibly CN - locally, in environments where there is biogenic production of cyanide.Colloids are the other possible forms of surficial gold migration. The Precipitation of gold could take place as a result of dilution and change of pH or oxygen fugacity.