『Abstract
　At the Ashanti concession, Ghana, gold-bearing quartz veins and disseminated sulphide loads occur in narrow (1-3 m) shear zones with altered argillites and metatholeiite host rocks. The mineralisation is concealed by up to 10 m of kaolinite-mica forest ochrosol soils, beneath which is a saprolitic zone of leached rock extending down 60-70 m to the hypogene ore zone. In the unweathered hypogene orebody, gold occurs as free grains in quartz, as sub-microscopic inclusions in the disseminated arsenopyrite, as gold tellurides and as aurostibite. The gold is released from the hypogene orebody by physical dissaggregation and chemical dissolution, the latter involving hydroxyl, thiosulphate, cyanide, and fulvate complexing. Dissolution and reprecipitation of the gold appears to have taken place largely in situ with little evidence of supergene enrichment. Consequently, the gold mineralogy of the soils is complex with residual and secondary gold grains exhibiting widely different textural and compositional characteristics. Residually enriched grains display pitted, rounded surfaces and have silver-depleted rims, while supergene gold grains are compositionally homogenous and have unpitted surfaces. The supergene grains display platelet, dendritic, irregular and octahedral habit. A fine grained spongy form of gold has also been observed from weathered telluride-bearing quartz veins. Much of the secondary gold is intergrown with iron oxides and hydroxides. The gold mineralogy of the Ashanti soils appears to be controlled by physico-chemical processes active during the lateritic pedogenesis producing residual and supergene enrichment of gold.

Keywords: gold; supergene mineralisation; Ashanti; Ghana』

Introduction
Gold mineralogy of the saprolite
　Native gold in the lower saprolite
　Gold grains in the upper saprolite
　The oxidation of arsenopyrite
　The oxidation of gold tellurides and aurostibite
Gold mineralogy of the soil profiles
　Residual gold grains
　Supergene gold grains
Supergene mobilisation of gold in tropical weathering profiles
　(i) Preferential dissolution of silver
　(ii) Electrorefining
　(iii) Chemical transportation of gold in supergene fluids
Conclusions
Acknowledgements
References

熱帯風化断面における金の浅成移動
　粒子の縁辺部が金に富むメカニズム
�@自然金-銀合金（エレクトラム）から、銀が優先的に溶解する。
�A粒子と溶液の界面で金-銀合金が溶解し、金が粒子表面に直ちに沈殿するような、自己電気精製過程による。
�B酸化された金を含む浅成流体が還元環境に出会って、エレクトラム粒子に沈殿する。