Kaolin deposits in the lower cretaceous Baqueró formation (Santa Cruz Province, Patagonia, Argentina) |
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| Authors: | MF Cravero EA Dominguez |
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| Abstract: | Sedimentary kaolin deposits in the Lote 18 area (Santa Cruz Province, Patagonia, Argentina) have been mined since 1951. They constitute 30% of the country's production and are mainly used in the ceramic whiteware industry. The deposits belong to the Baqueró Formation (Lower Cretaceous) and unconfomably overlie either the ash-flow tuffs of the Chon-Aike Formation (Middle Jurassic), which are altered to kaolinite and minor illite, or the ash-fall tuffs of Bajo Grande Formation (Upper Jurassic-Lower Cretaceous), which are altered mainly to smectites. The presence of illite or smectite, as well as the kaolinite crystallinity, depends on the stratigraphic position of the kaolin horizons within the Lower Member of the Baqueró Formation and on the lithology of the underlying rocks. Kaolin beds composed of well-crystallized kaolinite at the base of the sequence overlaying Chon-Aike rocks are the purest. Kaolinite becomes less well cystallized with transport. Edge-to-face and swirl SEM textural patterns indicate the compaction of flocculated clays and clay movement during drainage and compaction. Mineralogical, petrological, and physico-structural evidence (i.e., form, extent, thickness) indicates that the kaolin deposits are sedimentary, formed by the transportation and deposition of previously formed kaolinite. Kaolin beds are ovoidal in plan and lenticular in profile, with thickness ranging from centimeters to 11 meters, and the culmination of fining-upward clastic sequences. Sedimentary facies analysis indicates that the kaolin deposits were formed in a fluvial environment from currents with a high suspended-load/bed-load ratio, as would result from deposition in ox-bow lakes. |
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