Alkaline Rocks and Carbonatites of the World

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Tapira

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Occurrence number: 
025-00-067
Country: 
Brazil
Region: 
Minas Gerais
Location: 
Longitude: -46.83, Latitude: -19.88

Tapira is an almost circular intrusion about 6 km in diameter emplaced in Precambrian quartzites of the Canastra Group, which strike parallel to and dip away from the contact. The complex is deeply weathered for between 30 and 200 m. The distribution of rock types is not fully known, but part of the claims of the company V.A.L.E.P. have been explored in detail by drilling, trenching etc. which indicated that fresh rock consisted of 80% ultrabasics, mostly diopsidic pyroxenites, 5% potassic felsic rocks, principally trachytes and syenites, 3% sovite and 12% secondary quartz-rich rocks (silexite). The pyroxenite is micaceous and rich in apatite and perovskite, with minor magnetite, ilmenite, melanite, olivine and sphene. Locally olivine predominates to give dunites and phoscorites. A melilite-rich rock (uncompahgrite) has also been described (Guimaraes et al. 1980) containing 63% melilite, together with phlogopite, apatite, opaques, diopsidic augite and perovskite. A further rock type is composed dominantly of apatite with abundant perovskite and subordinate sphene and magnetite. Dyke rocks include bostonites: an analysis of one gave 14.4% K2O (Alves, 1960, p. 17). Herz (1976, p. 6) describes perovskite occurring in veins and disseminations in the country rock. An irregular fenite aureole extends for up to 2.5 km.

Economic: 
The residual deposits include: (1) A principal area of residual apatite ores which has total reserves of 740 million tons at an average grade of 8.3% P2O5 with a cut off at 5% P2O5 (Cruz et al. 1976). Large scale production began in 1979. The plant has a capacity of 900 000 tons of apatite concentrates (36% P2O5) annually. (2) Reserves of titanium ore (anatase) overlying the phosphate ore are reported as 190 million tons at an average grade of 21.9% TiO2 at a cut off at 15% TiO2 (Cruz et al. 1976). These are not utilized as yet. (3) Niobium deposits (bariopyrochlore and pyrochlore) are present, but not worked (one company reports reserves of 60 million tons, averaging 1.5% Nb2O5). Residual rare earth ores and vermiculite deposits are also known (Cruz et al. 1976).
Age: 
K-Ar on biotite from bebedourite (biotite pyroxenite) gave 69.5±3.5 Ma (Hasui and Cordani, 1968).
References: 
ALVES, B.P. 1960. Distrito niobio-titanifero de Tapira. Boletim Departamento Nacional da Producao Mineral, 108: 1-49. CRUZ, F.F., CHABAN, N., MACHADO, P.T., TOWNEND, R. and MACHADO, J.E. 1976. Aspects of the superficial phosphorus and titanium deposits of the Tapira carbonatite complex, Minas Gerais, Brazil. 25th International Geological Congress, Australia, Abstracts, 1: 209-10. GUIMARAES, I.G., AMARAL, M.A.M. and GARCIA, L.R.A. 1980. Uncompahgrito de Tapira, MG. Anais Congresso Brasileira de Geologia, 31(4): 2050-8. HASUI, Y. and CORDANI, U.G. 1968. Idades potassio-argonio de rochas eruptivas Mesozoica do oeste mineiro e sul de Goias. Anais Congresso Brasileiro de Geologia, 22: 139-43. HERZ, N. 1976. Titanium deposits in alkalic igneous rocks. Professional Paper, United States Geological Survey, 959-E: 1-6
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith