1978 Volume 28 Issue 152 Pages 385-396
The Campo Formoso area is well known in Brazil as a locality of chromite occurrences since the end of the 19th century and the chrome ore has been produced in a comparatively large scale since the early 1960s by FERBASA mainly from the Pedrinhas mine. The prospected area during three years from 1972 by the Companha Mineracao Serra da Jacobina (SERJANA) is located east to the Pedrinhas mine and is about 110km2 in area which corresponds to the expected narrow serpentinite zone occupying a part of the west margin of the Serra da Jacobina.
The geology of the peripheral district of the Serra da Jacobina is composed of Caraiba group, sepentinite, Jacobina group, gneissose granite and later granite of Precambrian in age. The Caraiba group, composed of gneiss, migmatite, schist as well as ultramafic complex or single ultramafic body, together with gneissose granite and later granite forms a gently undulating peneplane. The Jacobina group, mainly composed of psamitic, pelitic and conglomeratic sediments and metamorphosed to the amphibolite facies, forms the Serra da Jacobina of about 200km in N-S length and under 10km in width elevating under 300m above the peneplane and thrusts up the Caraiba group on the west side of the Serra da Jacobina. The chromitite bearing serpentinite composed mainly of serpentinite accompanying partly pyroxinite, hornblendite and talc schist occurs below the above-mentioned thrust and forms a colluvial slope below the escarpment of the Jacobina group. Though it is continuous from the Cascabulhos area to near Campo Formoso about 20km in entire length and under several hundred meters in width, it becomes thinner and lenticular northward. The age of this serpentinite is thought to be prior to the Jacobina group because of the presence of burried chromite placer deposits in the latter.
In the Limoeiro area, almost southwesternmost part of the prospected area, two layers of chromitite occur in the serpentinite-saprolite and are characterized by predominant friable low grade ore and scarce high grade lump ore, which are common to the already known other deposits in the area. Also, some detrital chrome deposits occur on the colluvial slope.
The Limoeiro mine was placed in operation in 1977 and 82, 000 tons of chromite lump and concentrate were produced.
