Abstract
Auriferous tourmalinites of the Anticlinal de Mariana region, southeastern Quadrilatero Ferrifero, have long raised debates regarding their origin. Genetic models have considered the tourmalinites as syngenetic, invoking the importance of exhalative focus, as well as epigenetic formation as a result of hydrothermal alteration and/or granitic magmatism. This study was centred on the Passagem, Mata Cavalo, Scliar and Chico Rei gold deposits, where three distinct modes of tourmaline occurrences were identified: (T1) tourmaline as the essential component of stratiform tourmalinites; (T2) tourmalines concentrated as hydrothermal alteration envelopes around gold –bearing quartz-carbonate-sulphide veins; (T3) aggregates of tourmalines as part of gold –bearing quartz-carbonate-sulphide veins. In spite of their compositional differences, all belong to the group of alkaline tourmalines and are classified as dravite. Combining field relationships, together with petrography, mineral chemistry and Nd isotope data, the following conclusions regarding the origin of the gold-related tourmalinites may be pointed out: i) boron-rich submarine exhalative fluids caused the syngenetic precipitation of the stratiform bodies of tourmalinites; ii) remobilization of boron, possibly by metamorphic fluids sensu stricto derived from the metamorphic devolatilization of the enclosing rocks and deep-seated synmetamorphic fluids, may have caused the precipitation of vein-related tourmaline, as part of an epigenetic gold-bearing hydrothermal system.
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