Raw materials for ceramic tiles in the Santa Gertrudes pole, Brazil

The Santa Gertrudes ceramic manufacturing pole, located in the state of Sao Paulo, south-eastern Brazil, produces around 20 million m 2 of tiles per month (∼240 million m 2 /year) at 42 manufacturing units. The main characteristics of the tiles produced here are the body's reddish colour, glazed surface, water absorption between 6 and 10 % (Bllb type), and their floor and wall applications, particularly indoor applications. The manufacturing route consists of dry powder preparation, dry pressing, and rapid and single firing. In addition, one particular characteristic of the ceramics produced in the Santa Gertrudes pole is the unique and single raw material (clay) used in the body's composition. This material comes from clayey rocks in the Parana basin, a huge Phanerozoic intracratonic sedimentary basin covering 1,100,000 km 2 in southern Brazil, and 100,000 km 2 each in Uruguay, Paraguay and Argentina. In the region of the Santa Gertrudes pole, clayey rocks used as raw material in the manufacture of ceramic tile bodies are grouped in the Permian Corumbatai Formation (Pc). This is a 130-m-thick layer of shallow reddish marine sediment containing claystone, shale, siltstone and fine sandstone embedded in dark bituminous shale, with carbonate rocks at the bottom (Irati Formation) and topped by fluvial-Aeolian sandstone units (Piramboia and Botucatu Formation(, which forms a coarsening upward sequence characterising a regressive sedimentary cycle. The main minerals in these clayey rocks are illite, with minor amounts of smectite and kaolinite, and quartz, feldspar, hematite and iron hydroxides. The sandy facies are rich in feldspar, whose granulometric size is less than 120 μm. Biogenic fragments (bone beds and coquina) are present in centimetre layers. The main oxides present here and their approximate chemical composition are: SiO 2 (67 %), Al 2 O 3 (15 %), Fe 2 O 3 (5 %), K 2 O (3-4 %), Na 2 O (0.5 %) and CaO (0.5 %). Despite a preference for the bottom and intermediary stratigraphic portions of the Corumbatai Formation, mining activities take place throughout the unit, from top to bottom, except where clayey rocks display severe weathering, silica and/or carbonate veins, biogenic concentrations, basaltic intrusions and intercalations of sandy facies. Mining is conducted by traditional open pit methods, involving the usual stages of clearing the vegetation and stripping, followed by blasting or hydraulic scraping (depending on rock strength) using single or multi benches. The ore, in the form of rocks and pebbles, is then loaded onto trucks and transported as run-off-mine to outdoor aging stockpiles or to a primary crushing plant, where it is spread onto outdoor terraces and subjected to blending, grain size reduction, homogenisation and drying. Two or three layers from different extraction points are usually mixed in a final blend. Upon completion of the outdoor operations, the output goes to indoor stockpiles and finally to dry powder preparation. The average monthly production of clay exceeds 400,000 t. Most of the 20 existing mining sites are run by ceramics-owned enterprises, while the remaining manufacturers (about 40%) are supplied by independent producers.