Abstract. Precambrian emerald deposits of Brazil are
found in a typical geologic setting with Archean base-
ment and supracrustal, ultramafic, granitoid and rocks.
Volcano-sedimentary series occur as imbricated struc-
tures or as bodies affected by complex folding and defor-
mation. Emerald mineralization belongs to the classic
biotite-schist deposit, which formed by the reaction of
pegmatitic veins within ultrabasic rocks. At the same
time, pegmatite-free emerald deposits linked to ductile
shear zones are also known. Emerald formation is attrib-
uted to infiltrational metasomatic processes provoking a
K-metasomatism of the ultrabasic rocks and also a desil-
ication of the Pegmatites. A new classification based on
the geological setting, structural features, and ore parage-
nesis fs proposed. .