El skarn Cañada del Puerto (31°25? LS; 64°54?LO), provincia de Córdoba: otro ejemplo de metasomatismo caracterizado por fluidos ricos en agua, hidrógeno y flúor.

FRANCHINI, MARTA; RAÚL LIRA; JORGE SFRAGULLA

Revista de la Asociación Geológica Argentina

Asociación Geológica Argentina

Lugar: Buenos Aires; Año: 1998 vol. 53 p. 247 - 260

0004-4822

Cañada del Puerto Skarn, province of Córdoba, Argentina: other example of water, hidrogen and fluor-rich metasomatism. Cañada del Puerto skarn is located in the western contact zone of the granitic Achala intrusive complex, in the Oriental Pampean ranges of Argentina. The skarn is formed in the Precambrian metamorphic basement spatially associated with a granitic pegmatite. Skarn is zoned in terms of relative proportions of silicates content: pyroxene zone, garnet zone, vesuvianite zone, and wollastonite zone. Wollastonite zone constitutes more than 50 percent of the skarn. These zones broadly correspond with varying degrees of replacement of schists, amphibolites and calcic-magnesium marbles. Late, quartz-vesuvianite and quartz-pyroxene veins crosscut early zones. Pyroxene is Mg rich (Hd26-51; Jo0.13-5) and in most analysis Mg/Fe ratio is greater than 1. Garnet is iron-poor (Ad12-27; Py0.13-18), contains between 0.22 to 0.27 wt % fluorine, nF/(nF+n0H) is lower than 0.55 and Al/Fe ratio is always greater than 1. Vesuvianite is iron poor and contains between 0.87 and 2.07 wt % fluorine. Measured homogeneization temperatures from silicates range between 180 and 455°C; the lowest temperatures correspond to vesuvianite and quartz. Fluid salinities range from 1 to 12 wt percent NaCl equivalent for most silicates. Pressure estimates from clusters of fluid inclusions with evidence for boiling are lower than 700 bars. The skarn mineralogy, composition and fluid inclusion characteristics have been incorporated into a general model of skarn which can be applied to the hierarchy of barren skarns in Córdoba basement: low to moderate saline concentrations in hydrothermal fluids, weakly compositional zoned minerals, iron-poor silicates, the absence of metals as well as prominent retrograde phases such as biotite or amphibole, and higher values of both aH20 and aH+aF- in the fluids relative to large and mineralized skarn systems.