Scott, Peter W.; Jackson, Trevor A.; Dunham, Ansel C.
Author Affiliation, Ana.
Ore mineral associations and industrial minerals in the ultramafic rocks of Jamaica and Tobago
Caribbean Journal of Earth Science
Date of Publication
The ultramafic rocks in Jamaica are dunites with minor lherzolite, most of which are at least partly serpentinised. They are part of a dismembered ophiolite complex. In Tobago, dunes, wehrlites, pyroxenites and hornblendites constitute the lower part of a Cretaceous plutonic complex of island arc affinity. The chromite in Jamaica is high Al and Mg, whereas that in Tobago is rick in Fe, as in Alaskan-type intrusives. Ni-Cu-PGE assemblages in Jamaica consist of pentlandite, with paragenetically later low temperature heazlewoodite, awaruite and native copper, the latter comtimes Pt and Pd enriched. The low temperature assemblage is probably associated with the serpentinisation event. In Tobago there is a sulphide assemblage of pentlandite, pyrrhotite, pyrite, chalcopyrite, much less affected by later alteration, and Pt, and RhPtIr phases. The dunites in Jamaica have sufficient MgO to be considered a potential source of industrial olivine. The higher Fe in the olivine from Tobago indicates that olivine cumulates in plutonics from island arc settings are less suitable source of the mineral. Although oxide minerals develop during tropical weathering in the Blue Mountains of Jamaica, the formation of Nilaterites is unlikely because of the high topographic relief. In Tobago the prospect for Ni-laterites is low as there is much less Ni in the olivines. Chrysotile asbestos, talc and magnesite are absent in both ultramafic complexes. This is likely to be a consequence of the lack of secondary serpentine recrustallisation to form fibrous chrysotile veins, the deep tectonic level and lack of hydrothermal circulation for magnesite formation, and the absence of metamorphic/metasomatic events and/or late stage extension tectonics which might have yielded talc.....