Geochemical studies of the bauxite deposits of the Mackenzie Region, Guyana.

Guyana is one of the major bauxite-producing countries in the world and the majority of the ore is at present mined in the MacKenzie- Ituni region near the Demerara River by the Demerara Bauxite Company. The bauxite deposits underlie considerable thicknesses of Tertiary sands, clays and lignites of the Berbice (White Sand) Formation and appear to be associated with the sub-topographic basement highs. Many geologists consider the bauxites to have been formed by in situ residual weathering of the basement rocks, while others consider they are derived by weathering of sedimentary clays and sandy clays. Guyana appears to have both types of deposit. The primary object of the study was to investigate the nature of the genetic relationship between the bauxite deposits of the MacKenzie-Ituni area and the basement rocks beneath them. The approach was essentially geochemical, although some mineralogical studies were also made. The distributions of selected elements within six complete bauxite to bedrock profiles were investigated. Elemental distribution on an areal scale in two orebodies was also studied to ascertain whether elemental trends in the bauxites could be related to bedrock variations. The majority of the analyses were carried out on an ARL29000 direct-reading optical emission spectrometer and the methods developed for this and other projects are contained in the Appendix. It is concluded that the deposits are derived from superjacent bedrock although the relationship between bauxite and bedrock is obscure. The controlling factor in the location of bauxite deposits in this area is considered to be the intensity of weathering that has taken place, and this in turn depends on a variety of factors