Mineralogía magnética de la Formación Alcaparrosa (Ordovícico) y del pórfiro pérmico que la intruye, Calingasta, provincia de San Juan

GEUNA, S. E.; ESCOSTEGUY, L.D.

Buenos Aires

Congreso; 8vo. Congreso de Mineralogía y Metalogenia; 2006

ABSTRACT: The Alcaparrosa Formation near Calingasta, San Juan Province, is mainly represented by metabasalts and dolerites as part of an Ordovician metasedimentary sequence. It is intruded by a moderately ferromagnetic Permian rhyodacite porphyry which generated a 3-km-long alteration halo on the Ordovician rocks. The study of magnetic properties has shown that the intrusion of the porphyry is responsible for a widespread remagnetization of Alcaparrosa Formation, carried either by pyrrhotite or magnetite. The abundance of magnetic minerals is usually low, although locally high amounts of monoclinic pyrrhotite (and hence high values of susceptibility and remanence) have been found. Positive, induction-dominated magnetic anomalies are expected over the porphyry, whereas negative, remanence-dominated anomalies should be produced by local concentrations of pyrrhotite.The Alcaparrosa Formation near Calingasta, San Juan Province, is mainly represented by metabasalts and dolerites as part of an Ordovician metasedimentary sequence. It is intruded by a moderately ferromagnetic Permian rhyodacite porphyry which generated a 3-km-long alteration halo on the Ordovician rocks. The study of magnetic properties has shown that the intrusion of the porphyry is responsible for a widespread remagnetization of Alcaparrosa Formation, carried either by pyrrhotite or magnetite. The abundance of magnetic minerals is usually low, although locally high amounts of monoclinic pyrrhotite (and hence high values of susceptibility and remanence) have been found. Positive, induction-dominated magnetic anomalies are expected over the porphyry, whereas negative, remanence-dominated anomalies should be produced by local concentrations of pyrrhotite. Palabras clave: pirrotina - magnetita - magnetismo de rocas - remagnetización - pórfiro Keywords: pyrrhotite - magnetite - rock magnetism - remagnetization - porphyry: pyrrhotite - magnetite - rock magnetism - remagnetization - porphyry