Provenance of beach gray sands from western México

Twenty-nine surficial beach dark colored sand samples from about 6500 km of the western littoral of Mexico were chemically and petrologically analyzed to search for the relationship between their heavy mineral content and metal and rare earth element variations. Sand samples were dried and grouped according to color in three classes of gray. In order to search for a possible influence on petrological and chemical variations, the sands were also grouped according to grain size, sorting, composition, main sources, wave energy, and climate. It was observed that quartz, feldspars, and rock fragments averaged low values and, as the sand darkened, the heavy mineral content increased. Also, the higher content of heavy minerals in dark gray and very dark gray sands correlated with a humid rather than arid climate. Rare earth element and other trace element contents seemed to be related more to the composition of the source area than to heavy mineral content. However, some elements, such as Zn, Hf, Th, Ni, and Cr, did relate more to heavy mineral content. Geochemical and petrological analyses of these sands suggest that most are derived from juvenile sources. Sedimentary processes such as wave energy appear to play a significant role locally in heavy mineral content, making the energy conditions of the beach environment an important local factor. Concentrations of rare earth and other elements are not of economic interest.