Alkaline Rocks and Carbonatites of the World

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Ipanema

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Occurrence number: 
025-00-098
Country: 
Brazil
Region: 
Sao Paulo
Location: 
Longitude: -47.6, Latitude: -23.43

An approximately circular complex of nearly 13 km2, Ipanema intrudes Precambrian schists and Permian Tubarao sandstones which are fenitized (Davino, 1975). Rock types described include glimmerite, sovite dykes and veins, aegirinite, mainly as veins, lusitanite, pulaskite and shonkinite, but the distribution is poorly known because of deep weathering. Enrichments of apatite and magnetite occur in the laterite cover, and blocks of silexite are widespread. Leinz (1940) gives petrographic descriptions of many rock types and a range of chemical analyses. Aegirine-rich rocks average more than 80% aegirine, together with orthoclase and a little amphibole. These grade with decrease in pyroxene through lusitanites to umptekites. There are also syenitic rocks with a little quartz and small dykes of shonkinite consisting of phenocrysts of aegirine-augite, biotite, nepheline and apatite in a groundmass of aegirine and orthoclase.

Economic: 
Both primary and secondary apatite deposits are found and reserves in excess of 100 million tons have been proved with a planned production capacity of 330 000 tons grading 38% P2O5 (Aps and Born, 1975). Five million tons of vermiculite are also present. An open pit operation is now being worked.
Age: 
K-Ar on biotite from shonkinite gave 138.2 and 121.8 Ma and on fenite (whole rock) 123.2 Ma (Amaral et al. 1967, Table 2).
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. APS, V. and BORN, G.H. 1975. Pesquisa do minerio fosfatico de Ipanema. Geologia e Metalurgia, Sao Paulo, 37: 24-34. DAVINO, A. 1975. Geologia da Serra de Aracoiaba, Estado de Sao Paulo. Boletim Instituto de Geociencias Universidade de Sao Paulo, 6: 129-44. LEINZ, V. 1940. Petrologia das jazidas de apatita de Ipanema. Boletim, Departamento Nacional da Producao Mineral, Divisao de Fomento da Producao Mineral, 40: 1-52
Fig. 216 Ipanema (after Davino, 1975).
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