Alkaline Rocks and Carbonatites of the World

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Chiriguelo (Cerro Cora; Juan Caballero I)


Occurrence number: 
Longitude: -55.08, Latitude: -22.05

Chiriguelo is an approximately circular complex about 6 km in diameter. Precambrian schists and quartzites, overlain by Palaeozoic sedimentary rocks, are domed around the complex, and on the southern and eastern margins these rocks are overlain unconformably by basalts of the Alto Parana Formation. The complex contains a central sovitic core which is intersected by rodbergite and late carbonatite stringers. There is an annular intrusion of apatite-melanite syenite the whole being surrounded, and partly capped, by potassic fenites. Fenitization extends unevenly into schists and gneisses in which concentrations of thorite and REE-bearing minerals occur.

Laterite has been developed only on a small scale but monazite, cerianite and plumbo-pyrochlore have been identified within it (Mariano and Druecker, personal communication, 1985). Premoli and Velazquez (1981) report a strong radiometric expression and high U values; separated uranopyrochlore gave Nb2O5 47.8%, UO2 13.3%, and ThO2, 0.1% (Premoli and Velazquez, 1981).
K-Ar on biotite from sovite gave 128±5 Ma (Mariano and Druecker, personal communication, 1985)
MARIANO, A.N. and DRUECKER, M.D. 1985. Alkaline igneous rocks and carbonatites of Paraguay. Abstracts with Programs, Geological Society of America, 17: 166. MARIANO, A.N., personal communication, 1985. PREMOLI, C. and VELAZQUEZ, J.C. 1981. Preliminary reconnaissance for uranium in Paraguay. In Uranium deposits in Latin America: geology and exploration. International Energy Agency, Vienna: 373-94.
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith