Carnaíba mining district, Pindobaçu, Bahia, Brazili

Regional Level Types
Carnaíba mining district	Mining District
Pindobaçu	Municipality
Bahia	State
Brazil	Country

The emerald discoveries, concentrated in the Pindobaçu municipality, 30 kilometres south of Campo Formoso, are considered to be the most important deposits to have been found to date in Brazil. The deposits are globally known as Carnaíba.

The geological context is a mid-pre-Cambrian north-south trend, composed mainly of quartzitic rock, surrounded everywhere by more ancient gneiss. Ultrabasic rock intruded on the west side of the range, where chromite mines are worked. The emerald deposits occupy the same structural position as the chromite, around a large granite batholith. The latter forms a series of pegmatite veins of one to two meters width, made up of oligoclase - often kaolinized – muscovite and beryl. Quartz veins sprout from them with beryl, schorl and biotite, in the ultrabasic rock as well as in the quartzite encasing them. In contact with the pegmatites, a micaceous rock with a thickness varying from one to two meters, known as sludite, can be observed.
This rock is essentially composed of mica, intermediate between biotite and phlogopite, arranged in parallel scales. Hence the frequently-used name of biotiteschist. Emerald is scattered in the sludite or lies in aggregates associated with quartz, molybdenite, apatite, schorl, black mica and scheelite specks. The occurrence is classified as a migmatite pegmatite of hybrid origin. It is intrusive in the ultrabasic rock of the penultimate Tectonic phase which marked the emergence of the Jacobina range.

The emerald crystals reach a few centimetres in diametre, with an intense, greasy, vitreous lustre, rarely transparent, but always of a lovely green, much desired by cutters and collectors.

Mining in Carnaíba is presently undergoing difficulties and production is declining. Almost all the vertical shafts have reached a depth of 150 metres; water is continuously infiltrating the work front, forcing the garimpeiros into an endless pumping ordeal.

Work is less complicated in the Marota occurrence, six kilometres from the Jacobina mountains. Here, open-pit mining is often possible. Emerald crystals from this mine are mostly large, sometimes attaining 500 carats. The colour, however, is less intense than those produced uphill, and is restricted in many cases to the crystal's surface.