Bauxite formation on Tertiary sediments and Proterozoic bedrock in Suriname

Abstract

The lateritic bauxite deposits in Suriname are traditionally distinguished into Coastal plain bauxites and Plateau bauxites, a subdivision that is primarily based on their topographic and geographic position. The first group is located in the lowlands of the coastal plain, while the second group is located on relatively high plateaus in the country’s interior. The Coastal plain deposits are mostly buried under younger sediments. Bauxite formation in Suriname peaked in Late Cretaceous – Early Tertiary times, when favourable conditions for bauxitisation prevailed worldwide. The parent rock composition is the most influential difference between these two deposit groups as the Coastal plain bauxites originated on Cenozoic sediments, and the Plateau bauxites on a diverse collection of Proterozoic rocks, which range from (ultra)high-temperature metamorphic gneissic and amphibolitic rocks in the Bakhuis Mountains (Granulite Belt in west Suriname) to greenschist-facies metabasalts and other meta-igneous rocks in the Greenstone Belt in east Suriname (Nassau Mountains, Lely Mountains and Brownsberg). The more ferruginous character of the Plateau bauxites is directly correlated to the higher iron contents of their crystalline parent rocks. The major element concentrations are linked to the principal minerals in specific zones of the lateritic profile as gibbsite is the prominent aluminum-bearing phase in the bauxite zone, while kaolinite prevails in the saprolite, and hematite and goethite are dominant in the duricrust that is covering the lateritic profiles. Bauxites are products of several weathering processes such as leaching of soluble elements ( e.g. Si, K, Na, Mg and Ca) from unstable minerals in the precursor rock, relative accumulation of poorly soluble or immobile components ( e.g. Al, Ti, Zr, Nb), and iron enrichment controlled by fluctuating groundwater levels and redox conditions. The enrichment of high field-strength elements (HFSE) and heavy rare earth elements (HREE) can be directly correlated to the resistance of zircon and other mineral hosts against weathering, especially in the Coastal plain bauxites where placer-like accumulations of these particular minerals are present in the terrigenous precursor sediments. Trace element signatures and petrologic observations of the Coastal plain deposits revealed that there is no direct genetic relationship between bauxite and the underlying saprolitic clay. The geochemical signatures, grade and volumes of the Surinamese bauxites are influenced by certain weathering processes (leaching, enrichment, fractionation), the primary compositional differences of parent rocks, nature and content of the accessory minerals, landscape morphology, local hydrological conditions, drainage efficiency, and unequal responses to multiple bauxitization cycles.