A white bentonite from San Juan Province, Argentina — geology and potential industrial applications

A comprehensive study was undertaken to evaluate the development potential of an unusually white bentonite deposit of Quaternary age in San Juan Province, Argentina. The deposit consists of partially or fully altered pumices and breccias intruded by andesitic dikes. The main alteration products are montmorillonite and zeolites and the intensity of the alteration is variable. The higher-grade regions of the deposit are structurally controlled. Eighty-nine samples were collected in the field and evaluated in the laboratory for mineralogy, brightness, swelling, and viscosity. Minerals present in all the samples are montmorillonite, opal C-T, and albite. Zeolites are common in the majority of samples; mordenite and clinoptilolite are the most prevalent species. Quartz, sanidine, calcite, biotite, halite, and gypsum are present as minor components in some samples. Brightness was the only property tested that consistently showed high values in all of the higher-grade material. Swelling and viscosity values were dependent on the amount of montmorillonite present. The mineral assemblage indicates a cool hydrothermal process, although meteoric influence is also possible. Shear zones and dikes appear to have been the channels for fluid migration. Field and laboratory evidences combine to show that, although there is abundant white material present in the deposit area, much of this material is low in clay content and of poor quality. The higher-grade materials are randomly distributed in small pockets throughout the deposit. A wet process will be necessary to produce a high-quality product.