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Jamaican Bauxite - Moneague/Ewerton, Kendal/Kirkvine, Nain/Alpart, Discovery Bay, Manchester |
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Jamaica |
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Al
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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Two thirds of the island of Jamaica was covered by thick lateritic soil, 30% of which was high grade bauxite. These bauxites have been exploited in operations such as those at and around Moneague/Ewarton, Tobolski/Browns Town, Claremont, Discovery Bay, Port Kaiser, Kendal/Kirkvine, Nain/Alpart, Manchester and South Manchester (#Location: Ewarton - 18° 16' 15"N, 77° 4' 12"W; Discovery Bay - 18° 27' 43"N, 77° 25' 27"W; Alpart - 17° 57' 3"N, 77° 37' 12"W; Manchester - 17° 58' 15"N, 77° 24' 54"W).
The longitudinal core of the 250 x 70 km, east-west elongated, island of Jamaica is occupied by a series of disrupted basement highs of Lower Tertiary and Cretaceous igneous (including andesite, pyroclastics, lesser dacite and basalt and 85 Ma granodiorite), metamorphic rocks (at 47 Ma) and clastic sedimentary rocks. These are overlain to the north, west and south by up to 610 m of Middle Eocene to Lower Miocene pure limestones (the White Limestone) that underlie the bulk of the bauxite deposits. The suceeding sequence comprises Pliocene to Holocene chalky limestones, plantonic micrites containing chert nodules and marl, and clastic sedimentary rocks to the north and west, followed by Pleistocene to Holocene alluvium mainly along the southern coast.
The main zone of bauxite forms a hoseshoe shaped arc that is approximately 180 km long and 10 to 30 km in width wrapping around the basement core to the island, the "Central Island Inlier". Two broad styles of bauxite are recognised in Jamaica, namely blanket and pocket deposits. They are irregular in shape and sizes and rest on the karst topography. In some of the irregular sink-holes, narrow pipes of bauxite extend downwards into the limestone to depths of 7 to 8 m, and narrow pinnacles extend upwards into the bauxite. At the other extreme, bauxite extends over the limestone ridges to form sheets. The deposits range from "deep" sinkholes that are 15 m in diameter, to broad shaped bowls >10 km in across, with the largest 30 km wide.
The blanket type of deposits are mainly restricted to depressions formed by tilted fault blocks of the Lower Miocene limestone on the southern side of Jamaica. Most of the deposits on the north side of the island and to the west of the Central Island Inlier of basement are of the pocket style up to 30 m thick preserved in sink holes within the Eocene and Oligocene limestones.
While bauxite has been formed from lateritic weathering of a wide range of lithologies of differing age, the bulk of the economic bauxite appears to have been derived by Terra Rosa modification of Miocene volcanic ash deposited between 25 and 8.5 Ma. Some of the bauxite is derived from younger alluvium. The process of bauxite formation commenced soon after the underlying limestones emerged from the ocean at 25 Ma in the east.
Most bauxite deposits are overlain by by soil that is rarely as much as one metre thick, although in the Manchester and Alpart deposit areas, detrital material, mainly limestone gravel overlies the bauxite and is from <1 to ~30 m thick. In a few places, calcite from the overburden has mixed with the bauxite, resulting in CaO contents of up to 7%.
The bauxite in Jamaica is a mixed trihydrate and monohydrate type containing considerable iron minerals (hematite and goethite) and a few other impurities. In many deposits the goethite contains aluminium as an isomorphous substitution of iron. Gibbsite is the principal aluminium mineral and is chiefly present as <1 µm grains. Nordstrandite a polymorph of gibbsite has also been found locally. Boehmite is found in most deposits, and in some locations may be up to 20% of the ore, but is commonly 7 to 10% of the bauxite. Kaolinite and halloysite are the principal clay minerals, but only occur in minor amounts in the mined ore, but are abundant in the low grade high-silica bauxite. Other impurities include quartz, chlorite, montmorillonite, muscovite, garnet, anatase, rutile, calcite, collophane, apatite, ilmenite, magnetite, chromite, zircon, tourmaline, titanite, feldspars, sulphides and several hydrous manganese bearing minerals.
The key to the development of the bauxites is believed to be the strong vertical drainage through the pure, Middle Eocene to Lower Miocene karstic weathered limestones allowing for extreme leaching of the parental tuffs.
High grade bauxite is defined locally as having an average of >50% Al2O3 and <5% SiO2. Low grade bauxite has a similar Al2O3 content, but 5 to 10% SiO2. Terra Rosa red soil contains >10% SiO2, but lesser Al2O3. Both bauxite and Terra Rosa soil contain 6 to 26% Fe2O3.
In 1984, the Jamaica Bauxite Institute listed reserves as >2 Gt @ >40% Al2O3, <10% SiO2. This excludes bauxite below inhabited areas, and distal to the main producing areas which may exceed 500 Mt (Patterson et al., 1986).
Much of this summary is drawn from Patterson, S.H., Kurtz H.F., Olson, J.C. and Neeley, DC.L., 1986 - World Bauxite Resources; U.S. Geological Survey Professional Paper 1076-8."
The most recent source geological information used to prepare this decription was dated: 1986.
Record last updated: 4/2/2016
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Ewarton Discovery Bay Alpart Manchester
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Comer J B, 1974 - Genesis of Jamaican bauxite: in Econ. Geol. v69 pp 1251-1264
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Comer J B, Naeser C W and McDowell F W, 1980 - Fission-track ages of zircon from Jamaican bauxite and Terra Rosa: in Econ. Geol. v75 pp 117-121
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