Itapirapua

stripes

Occurrence number:

025-00-103

Country:

Brazil

Region:

Sao Paulo

Location:

Longitude: -49.2, Latitude: -24.5

Carbonatite:

Yes

This is a body of about 4.5 km2 elongated northwest-southeast and intruded into Precambrian granites of the Tres Corregos complex. Itapirapua comprises mainly nepheline syenites with lesser amounts of melteigite, malignite, pulaskite, mariupolite and carbonatite; dykes of tinguaite are present within and around the intrusion and some marginal fenitization occurs. The nepheline syenites contain aegirine-augite/aegirine, studied by Gomes et al. (1970), and much cancrinite, some sodalite and melanite, zoned examples of which were investigated by Gomes (1969); biotite, wollastonite, pectolite, fluorite, eucolite, pyrite, pyrrhotine, calcite and zeolites also occur. Analyses of a range of rocks are given by Gomes and Dutra (1970). The carbonatites, which form small dykes and veins, are orthoclase sovites and apatite-orthoclase sovites. They are confined to the central part of the intrusion where they cut nepheline syenite; analyses are available in Gomes and Dutra (1969). The fenites include aegirine-augite and alkali-amphibole-bearing varieties.

Economic:

A funnel-shaped orebody on the southern side of the complex is being worked for granular magnetite.

Age:

104.8 Ma on alkali feldspar from nepheline syenite and 101.4 Ma on biotite from melteigite, both by K-Ar (Amaral et al. 1967; Gomes and Cordani, 1965).

References:

AMARAL, G., BUSHEE, J., CORDANI, U.G., KAWASHITA, K. and REYNOLDS, J.H. 1967. Potassium-argon ages of alkaline rocks from southern Brazil. Geochimica et Cosmochimica Acta, 31: 117-42. FERREIRA, F.J.F. and ALGARTE, J.P. 1979. O comportamento aeromagnetometrico-cintilometrico das principais rochas alcalinas dos estados de Sao Paulo e Parana. Atas do 29 Simposio Regional de Geologia, Rio Claro, 2: 195-208. GOMES, C.B. 1969. Electron microprobe analysis of zoned melanites. American Mineralogist, 54: 1654-61. GOMES, C.B. 1970. Petrologia do macico alcalino de Itapirapua. Boletim IGA, Instituto de Geociencias e Astronomica, Universidade de Sao Paulo, 1: 77-197. GOMES, C.B. and CORDANI, U.G. 1965. Geocronologia do macico alcalino de Itapirapua, SP. Anais da Academia Brasileira de Ciencias, 37: 497-501. GOMES, C.B. and DUTRA, C.V. 1969. A short note about the carbonatites from Itapirapua, Sao Paulo, Brazil. Anais da Academia Brasileira de Ciencias, 41: 195-8. GOMES, C.B. and DUTRA, C.V. 1970. Some geological features of the alkaline rocks of Itapirapua, Sao Paulo, Brazil. Anais da Academia Brasileira de Ciencias, 42: 521-34. GOMES, C.B., MORO, S.L. and DUTRA, C.V. 1970. Pyroxenes from the alkaline rocks of Itapirapua, Sao Paulo, Brazil. American Mineralogist, 55: 224-30

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