The Porangatu deposit is controlled by the same regional fault that controls Santa Terezinha deposit
. Beryl, including emerald
, is in metasomatic zones of metamorphosed ultramafic rocks in pegmatite, quartz, and quartz-oligoclase veins.
The dark green emeralds are hosted in glimmerites as small crystals 0.5 to 1 cm long. Pegmatites are characterized by colourless beryls, and the quartz-oligoclase and quartz veins contain pale green and bluish beryls.
Ref: E.Ya. Kievlenko (2003) Geology of gems, p. 92