El placer lateral de playa Mejías (noreste de Cuba Oriental): un ejemplo de interacción de procesos aluviales y marinos en la concentración de minerales de elementos preciosos

R. DÍAZ-MARTÍNEZ, J.A. PROENZA, J. COMAS, O. FERNÁNDEZ-BELLÓN, J.M. FABRA, O. GUINART, Joan-Carles MELGAREJO

Abstract


The playa Mejías lateral placer is the most important placer in Cuba. Its mineralogical composition (magnetite, chromite, rutile, ilmenite, orthopyroxene) reveals that the ophiolites of the Mayarí-Baracoa Belt are the main source area. However, other sources are demonstrated for by the presence of 4 different morphological types of zircon crystals, and minerals related to listvaenitic mineralizations (calcosilicates, carbonates). Also, precious metals have been recognized . Previous to their fluvial transport, electrum grains were depleted in gold in the lateritic environment, producing silve r-rich rims to the electrum grains. The gold particles were transported by rivers as fine-sized particles of electrum with various compositions, and as Au-amalgam. During their fluvial transport, the smaller gold grains coalesced to form larger grains, and a final generation of highly pure gold cemented the subgrains. Then, the particles were deposited in a beach lateral placer, where the grains were leached by sea water, giving rise to corrosion textures. The particles of EGP minerals found are grains of osmium-rich laurite replaced by laurite veins associated with symplectitic intergrowths of a third laurite generation (having intermediate compositions between the above laurite generation) and iridioarsenite, as a consequence of serpentinization at the source. Leaching by sea water produces a depletion in osmium in the particles.

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