FIELD, LABORATORY, AND REMOTE SENSING SPECTRAL ANALYSIS OF MINERAL DEPOSITS RELATED TO DEEP WEATHERING IN THE GREATER ANTILLES AND VIRGIN ISLANDS

Minerals and mineral products have been important to commerce in the Caribbean Basin since pre-Columbian times. The Greater Antilles produce >10% of the world’s nickel (Cuba) and bauxite (Jamaica) and contain at least seven porphyry copper-gold deposits. Recently, this region has been affected by major hurricanes such as Irma, Maria, and Fiona. In Puerto Rico as a result, emphasis has also been placed on assessing the quality, quantity and distribution of the island's industrial mineral resources needed for infrastructure reconstruction.

Laboratory spectral studies were conducted on a suite of samples collected from Puerto Rico and the U.S. Virgin Islands during fieldwork in 2018. These samples were analyzed using laboratory spectral reflectance methods covering the < 1-µm wavelengths in the visible and near infrared (VNIR), > 2-µm wavelengths in the shortwave infrared (SWIR), and the 8- through 14-µm wavelength range also known as the thermal infrared (TIR). The TIR data were converted to emissivity to facilitate comparison with data collected by remote sensing instruments such ASTER on the Terra satellite and ECOSTRESS on the International Space Station. In addition, cloud-free ASTER imagery covering parts of Cuba and Jamaica was calibrated to both VNIR-SWIR reflectance and TIR emissivity. The imagery for the chosen areas shows well-exposed landscape features due to active or recent mining of Ni-Co laterite and Al-bearing bauxite deposits, respectively.

The distribution and abundance of gibbsite, kaolinite and serpentine minerals in exposed lateritic deposits and mine waste in Jamaica and Cuba are shown as ASTER mineral maps. Laboratory spectral analysis of samples from porphyry, skarn and epithermal vein occurrences from Puerto Rico indicate a variety of minerals related to weathering and/or hydrothermal alteration. Limestone displays a variety of carbonate mineral features that include impurities such as quartz, clay, and mica. Finally, samples from the Water Island Formation in the Virgin Islands display spectral features indicative of rare earth elements (REEs) in deeply weathered volcanic rocks mapped as Cretaceous “Quartz keratophyre” dikes and plugs. This work demonstrates the utility of spectral studies at various scales for on-going and future mineral exploration and assessment work.