Paramagnetic centers in kaolinite and the history of weathering crusts

Abstract

Although the Ity deposit is the oldest operating mine in Ivory Coast, very few studies exist on this deposit. It is situated in Western Ivory Coast, some 700 km northwest of Abidjan. The mine is presently operated and mined by SMI (Société des mines d'Ity — Society of Ity Mines), and has produced one million ounces of gold since its opening in 1991. All mined ore bodies are hosted in laterite and clay formations. The gold deposits in the Ity area form a cluster of mining operations of various sizes (Flotouo, Zia, Mont Ity), hosted in a Birimian volcano-sedimentary belt. The mineralization is mostly located at the contact between a granodiorite–tonalite intrusive body and sediments. Primary gold mineralization occurs in the form of veinlets and, mostly, skarn at the contact between the granitic intrusion and limestone. Calc-silicate minerals such as diopside and andradite dominate the skarn. However, the economic gold mineralization at Ity is associated with the saprolitic zone (50–120 m thick), and consists of several mineralized lenses of clayey and ferruginous material (“Terres noires”), and of sedimentary breccia layers. A thick laterite horizon (a minimum of 10 m) overlies the saprolite and covers the land throughout the region; it is mineralized in the deposit area. This contribution provides a summary of the geological and mineralogical relationships at the Ity deposit, presents new data on skarn-type gold mineralization, and summarizes its history, from the first findings, through exploration and mining assessment.