Lateritization as a Major Process of Ore Deposit Formation in the Amazon Region

The Amazon region is characterized by the development of deep chemical weathering represented by widespread lateritic covers and soils. Two distinct periods of laterite formation can be distinguished: mature laterites from the Eocene-Oligocene (and locally from the end of the Cretaceous), and immature laterites from the Pleistocene. The older laterites occur on plateau landscapes, and the younger ones on widespread hilly to flat lowlands. Both types show complete or truncated profiles, generally covered by deep yellow to brown topsoils. The mature laterite profiles contain high concentrations of gibbsite and/or aluminum phosphate, whereas the immature ones are poor in these minerals. The Amazon region is rich in mineral deposits related to lateritic profiles. Some mineral deposits are of primary origin but were concentrated to economic grades by lateritic processes. The most important ore deposits are of iron, aluminum (bauxite), kaolin, manganese, gold, nickel, copper and phosphate. These are mainly related to mature profiles. The wide spectrum of ore deposits and mineralogical and geochemical complexity of the Amazon laterites has been promoted by: (1) the prevalence of ideal conditions for laterite formation throughout much of the Tertiary; (2) the presence of varied basement lithologies due to contrasting geological environments; and (3) a variety of epigenetic alteration types. The lateritic profiles show a well-developed ore zonation which is related to specific lateritic horizons. Iron and gold deposits occur in the ferruginous horizon, which is nearest the surface; the central aluminous horizon hosts bauxites, aluminum phosphate, strontium and gold; and the lower clayey horizon contains deposits of manganese, nickel, copper and kaolin. Resistate phases which residually accumulate throughout entire profiles include titanium (as ilmenite and anatase), chromium (as chromite), tin (as cassiterite), yttrium (as xenotime), and niobium (mainly as ilmenorutile). Epigenetic alteration, caused by swamp environments developed above truncated lateritic profiles, has led to the formation of high grade kaolin and refractory bauxites. The laterites in the Amazon region contain most of all known kinds of ore mineralization related to laterite processes.
Keywords: Amazon Region, Laterite formation, Mineral deposits.
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Summary: A consistency-driven pairwise comparisons method for mineral potential assessment is presented, using a simplified case of volcanic-associated massive sulfide type deposits as an example. Geological, geochemical, and geophysical criteria are considered on two levels: local and regional. The local geological criteria are subdivided into stratigraphy, lithology, alteration and/or mineralization, and structure. The concept of geomerit index and a procedure for computing this index are introduced...
Publication: Exploration & Mining Geology
Author(s): WALDEMAR W. KOCZKODAJ: Centre in Mining and Mineral Exploration Research Laurentian University, Sudbury, Ontario, Canada P3E 2C6; WILLIAM O. MACKASEY: WOM Associates, 140 Crater Crescent, Sudbury, Ontario, P3E 5Y8
Keywords: Mineralogy, Geological criteria, Geochemical criteria, Geophysical criteria
Issue: 1
Volume: 6
Year: 1997
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Summary: The Sudbury Structure consists of three major components: 1) the Sudbury Basin; 2) the Sudbury Igneous Complex which surrounds the basin as an elliptical collar; and 3) an outer zone of shatter-coned and intensely brecciated footwall rocks. Although the Sudbury Event which formed the structure may be unique, the area has, in fact, been shaped by a series of tectonic, magmatic and mineralization events which can be considered in terms of two Wilson cycles of continental extension and closure....
Publication: Exploration & Mining Geology
Author(s): DON H. ROUSELL, HAROLD L. GIBSON: Mineral Exploration Research Centre Department of Earth Sciences, Laurentian University, Sudbury, Ontario, Canada P3E 2C6, and
IAN R. JONASSON: Mineral Deposit Division, Geological Survey of Canada 601 Booth Street, Ottawa, Ontario, Canada K1A 0E8
Keywords: Mineralization, Sudbury structure, Tectonic events, Magmatic events
Issue: 1
Volume: 6
Year: 1997
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Summary: Measurement of natural radioactivity has been used in both a qualitative and a quantitative way in mineral exploration, particularly in the search for uranium. In the last five years, the Kernfysisch Versneller Instituut (KVI) and British Geological Survey (BGS) have designed, built and tested a new detector system that greatly improves quantitative applications in mineral exploration, especially on the seafloor and in the nearshore zone. The new system is an enhancement of an earlier BGS...
Publication: Exploration & Mining Geology
Author(s): D.G. JONES, P.D. ROBERTS: British Geological Survey, Keyworth, Nottingham NG12 5GG, United Kingdom; A. ROZENDAAL, W.G. MACDONALD: Department of Geology, University of Stellenbosch, P.O. Box X01, Matieland 7602, Stellenbosch, South Africa
Keywords: Radioactivity, KVI, BSG, Mineral exploration, Mineral Processing, Heavy-mineral concentration, On-line quality control
Issue: 1
Volume: 6
Year: 1997
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Summary: The Navan zinc-lead ore deposit (70 million tonnes) is hosted principally (97%) by the Meath Formation (Lower Carboniferous, Courceyan, Navan Group), comprising a lower, mainly carbonate mudstone unit, the Stackallan Member, and an upper grainstone-dominated unit. The Stackallan Member, about 60 m thick, comprises about 35 peritidal cycles including an oolitic grainstone interval. Grainstones forming the upper part of the formation, about 150 m thick, comprise at least six shallowing-upward...
Publication: Exploration & Mining Geology
Author(s): GIANCARLO RIZZI and C.J.R. BRAITHWAITE Department of Geology and Applied Geology
University of Glasgow, G12 8QQ, Scotland
Keywords: Navan zinc-lead ore deposit, Meath Formation, Mudstone, Upper grainstone-dominated unit
Issue: 1
Volume: 6
Year: 1997
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