Exhalación hidrotermal asociada al protolito de mármoles baritínicos de alto grado en las Sierras Pampeanas de San Luis.

GONZÁLEZ, PABLO D.; SATO, ANA MARÍA; LLAMBÍAS EDUARDO; CAVAROZZI, CLAUDIA; MAGGI, JORGE

La Plata

Congreso; 16° Congreso Geológico Argentino; 2005

Asociación Geológica Argentina

Structural analyses, metamorphic assemblages and whole rock geochemical data carried out on barite bearing marbles and calcsilicate rocks of the Nogolí Metamorphic Complex (Sierras Pampeanas de San Luis) indicate that these rocks are high grade metamorphic equivalents of hydrothermal bedded carbonate-sulfate deposits. Alternating beds of granoblastic marbles composed of calcite, siderite, barite, apatite and barite-tourmaline-fluorite bearing calcsilicate rocks are interlayered with micaschists of felsic volcanic-piroclastic protoliths and meta-cherts. They are affected by Famatinian (Ordovician) NNE- to NE trending penetrative foliation and medium P (Barrovian type) / amphibolite facies regional metamorphism. In marbles, high Ba, Sr and P contents are coupled with strong LREE enrichment relative to HREE, slight negative Eu- and absence of Ce anomalies. Such REE pattern are similar to that of present day low temperature (<250° C) hydrothermal venting associated to white smokers in oceanic environments. The association of hydrothermal bedded meta-calcareous/sulfate horizons, felsic meta-volcanic flows and meta-cherts within the same sequence is interpreted as part of a subaqueous volcanic edifice. Despite massive sulfide ore bodies were not reported up to now in Sierra de San Luis, we cannot rule out the beds of marbles and calcsilicate rocks of Nogolí Metamorphic Complex as metamorphosed equivalents of non-mineralized higher levels of Volcanic Hosted Massive Sulfide deposits.