GEOLOGY
The emerald deposit is situated in the Seridó Mobile Belt
(figure 3), which is dominated by continental-scale strikeslip
shear zones trending northeast to north-northeast.
The rocks consist of basement gneiss, a metasedimentary
sequence called the Seridó Group, and the Brasiliano
igneous suite (Souza Neto et al., 2008). The basement
gneiss comprises metamorphosed (mig matitic) igneous
rocks of tonalitic to granitic composition and minor
metabasic lenses. The Seridó Group consists of marble,
gneiss, quartzite, metaconglomerate, and mica schist.
The Brasiliano igneous suite includes porphyritic and
fine-grained granites with minor aplites and pegmatites
that are widely distributed. The granitoid rocks have UPb
zircon ages of 610–555 Ma and were intruded during
the Brasiliano orogeny (610–530 Ma), while the peg -
matite bodies are con strained by ages between 510–480
Ma (U-Pb dating of uraninite and columbite) and 523
Ma (average Ar/Ar date of biotite from the pegmatites;
Souza Neto et al., 2008).