Semi-quantitative mineralogical valuation of the non-nickeliferous weathering crusts in the northeast of Cuba

Abstract

This study presents a semi-quantitative mineralogical evaluation of the non-nickeliferous weathering crusts in the areas of Baconal, El Culebro, Caimanes and Farallones in the northeast of Cuba. The main objective of this study is to determine the main mineral phases, their vertical distribution and concentration, as well as the degree of mineral transformation in the weathering profiles. Sixteen samples were analyzed by X-Ray Diffraction and the diffractograms were used in qualitative and semi-quantitative phase analyses using ANALYZE and AUTOQUAN programs. The degree of mineral transformation in relation to phase distribution and concentration as weathering progressed was evaluated using the Mineralogical Index of Alteration. The main mineral phases present in Baconal and El Culebro are Kaolinite (50-75%), Kaolinite-Montmorillonite (50-75%), Quartz (25-50%), Plagioclase, mainly Albite (25-50%) and Hematite (<10%). In Caimanes and Farallones the principal mineral phases present are Kaolinite, Hematite, Quartz, Potassic feldspars, mainly as Orthoclase, all with more than 75%, Halloysite (<10%), and Montmorillonite (<10%). Extreme primary mineral transformation is evidenced in the intermediate and upper layers in Baconal, El Culebro and Caimanes (Mineralogical Index of alteration values between 29 and 98 %). This transformation is also evidenced in the whole Farallones profile (98-99 %). In conclusion, the non-nickeliferous weathering crusts in Baconal, El Culebro, Caimanes and Farallones are mainly kaolinitic clays.