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Cerro Siete Cabezas is a syenitic alkaline complex located on the Paraguay River of north-western Paraguay, belonging to the Alto Paraguay Igneous Province. It consists of a circular main body of ~4 km2 and two minor stocks to the south-east: the 1.0 x 0.2 km elongated, E-W trending Stock I, and the ~0.4 km2 circular Stock II. Rocks are predominantly nepheline syenites and syenites in the main body and Stock II, with quartz syenite and alkali granites restricted to Stock I. The main intrusive body is peralkaline and silica-undersaturated, with the presence of both miaskitic (titanite and zircon) and agpaitic (eudialyte) HFSE bearing phases classifying them as transitional agpaitic. The two stocks are dominated by quartz-bearing lithologies, being silica-oversaturated with lower alkalinity indices, with Stock 1 playing host to most of these rocks. Notable minerals include aegirine-augite, apatite, cancrinite, and fluorite. Geochemical data, including whole rock major and trace element, mineral chemical, and Sr-Nd isotopic, can be found in Comin-Chiaramonti and Gomes (2005).
COMIN-CHIARAMONTI, P., GOMES, C.B., CENSI, P., GASPARON, M. & VELÁZQUEZ. 2005. Alkaline complexes from the Alto Paraguay Province at the border of Brazil (Mato Grosso do Sul state) and Paraguay. In: Comin-Chiaramonti, P. & Gomes, C.B. (eds) Mesozoic to Cenozoic alkaline magmatism in the Brazilian Platform. Editora Universidade de São Paulo, São Paulo, 71-89. VELÁZQUEZ, V.F., GOMES, C.B., LAURENZI, M., TEXEIRA, W. & COMIN-CHIARAMONTI, P., 1996. Contribution to the geochronology of the Permo-Triassic alkaline magmatism from the Alto Paraguay Province. Revista Brasileira de Geociências 26, pp 73-89