The stricto sensu granitic magmatism, denominated Boa Sorte Granite, that
occur in the southeast region of Pará, at the limit between the counties of Água
Azul do Norte and Canaã dos Carajás, in the south portion of the Carajás
Domain. It is formed predominantly by monzogranites that have biotite as major
ferromagnesian mineral, and have been initially correlated to Plaquê Suite. The
Magnetic Susceptibility (MS) studies on 60 representative samples of the two
different facies of this pluton gave values of SM variables. The behavior of
these values allow distinguish two distinct populations, designated of A and B.
The values of MS obtained range from 0,0027 x10-3 to 27,8000 x10-3 SIv, with
an average 3,9045 x10-3 SIv, increasing from the population A towards to
population B. The opaque mineral phases present in the rocks of the Boa Sorte
granite are magnetite, ilmenite (trellis, external and internal composite and
sandwich) and hematite. Textural features and semiquantitative compositions of
the Fe-Ti oxides suggest the existence and formation of titanomagnetite during
the early stage of crystallization. Destabilization processes allow the
replacement of the magnetite by titanite. During the subsolidus stage, the
titanomagnetite originated poor titanium magnetite and ilmenite from oxyexsolution
processes. Under more oxidizing conditions the magnetite is affected
by the martitization process giving rise to hematite. The highest values of
magnetic susceptibility are related to samples with higher modal content of
magnetite, while the samples with the lowest magnetic values have magnetite
with intense martitization process. Some features allow classify the Boa Sorte
granite as magnetite-series granite, which including the relatively high values of
SM and the modal content of opaque minerals (> 0.1%) with a strong presence
of magnetite in this pluton. Through the nature of Fe-Ti oxide minerals, it was
possible to define that the Boa Sorte granite was formed under conditions of
high oxygen fugacity, between HM and FMQ buffer, above NNO, reaching in
subsolidus condition, fugacity above HM buffer.
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