Alkaline Rocks and Carbonatites of the World

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Los Alisos


Occurrence number: 
Longitude: -64.73, Latitude: -23

A near vertical, sheet-like intrusion extends intermittently over 10 km and has an outcrop width of 20-80 m. The rock, formerly described as kimberlite, is now considered an alnoite. It consists of phlogopite plates up to 5 mm across, serpentinized olivine, diopside, perovskite, apatite, Ti-magnetite and areas of a secondary material, possibly after melilite, containing andradite, although Ti-andradite is also an accessory constituent. Small veins contain phlogopite, katophorite, serpentinized olivine, leucite, calcite, acmitic pyroxene and andradite. Analyses of the mineral phases are available in Meyer and Villar (1984) and of rocks in Villar et al. (1981).

A K-Ar age determination gave 305±10 Ma (Meyer and Villar, 1984, p. 743).
MEYER, H. O. A. & VILLAR, L. M. 1984. An alnoite in the Sierras Subandinas, northern Argentina. Journal of Geology, 92, 741-51. VILLAR, L. M., PEZZUTTI, N. E. & SVETLIZA, S. S. de 1981. Las kimberlitas micaceas de Los Alisos, Sierras Subandinas de Salta. Significado geologico-economico. VIII Congreso Geologico Argentino, 4‚ 903-19
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