INVESTIGATIONS OF SANDS FROM A SMALL DELTA AT GUANAJIBO, PUERTO RICO

Sands are a natural resource used in basic and advanced geotechnical applications. Coastal sands from various locations in Puerto Rico are the subject of current investigations for their suitability in geotechnical, environmental, and mineral resource uses. The suitability of these sands is expected to vary. As part of this broader investigation, we collected and analyzed sands from an accessible small delta at Guanajibo, Puerto Rico, located near occurrences of serpentinite. These sands displayed a uniquely dark gray to black overall appearance, setting them apart from numerous other sites. The sands were analyzed using Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS). Mineral phases present include olivine, pyroxene, oxides, and other phases indicative of ultramafic provenance of the bulk of the sand. Grains of finely crystalline aragonite were also present, displaying detectable amounts of Ba. Elements present included Mg, Fe, Ca, Ti, Cr, Ni, P, Mn, Zn, and others. Mineral textures observed include a grain with textures indicative of olivine undergoing serpentinization, displaying fibrous veins within a coherent non-fibrous grain. This particular grain shows chemical compositions that strongly support this interpretation. Larger grains with a uniformly fibrous texture were also observed. Initial work indicates that such sands are likely unsuitable for environmental purposes but are of interest for further geochemical exploration study for resources. More detailed analyses of these sands may provide justification for systematic exploration of critical mineral resources in the area. Caution should be taken, however, as there is potential for asbestos-related minerals (chiefly chrysotile) to occur as indicated by altered olivines, and thus future exploration should consider potential asbestos risks.