Geology, mineralogy, origin and possible applications of some Argentinian kaolins in the Neuquen basin

The geology and genesis of three kaolin deposits (Las Mellizas, Chita and Misud), located in the Neuquén basin were studied. Kaolin mineralogy and oxygen isotopic data indicate that kaolinite comes from a weathered area developed during the lower to middle Jurassic times; the kaolinite was then transported and deposited in a fluvial environment. I/Sm comes from in situ illite degradation. Kaolin properties are related to mineralogical and chemical composition and to compactation and cementation. Low plasticity of these kaolins is due to high degrees of compactation undergone, and plasticity increases as I/Sm content increases. Viscosity is related to pH: in low pH clay suspensions the edge faces are positively charged, so on stirring, they collide with the negative charged faces forming card-house structures, thus enhancing the viscosity. Cementation effects makes it difficult to get dispersed suspensions. As a ceramic raw material, these kaolins are considered stoneware clays. When kaolins with lower iron oxide content are mixed with quartz and feldspar, an optimum white stoneware is obtained at 1150°C. On this basis, the three deposits can be exploited to make stoneware products, but selected beds should be mined in order to obtain the best quality.