PROSPECÇÃO MAGNETOMETRICA DE DEPOSITOS OXIDO-SILlCATICOS'-DE MANGANES COM JACOBSITA, NO CEARA

BoI. IG, Instituto de Geociências, USP, V. 14:13-20, 1983

PROSPECÇÃO MAGNETOMETRICA DE DEPOSITOS OXIDO-SILlCATICOS '-DE
MANGANES COM JACOBSITA, NO CEARA

por

EVARISTO RIBEIRO FILHO
Departamento de Geologia Econômica e Geofísica Aplicada - IG-USP

e

JOSÉ MA RCIO LINS MARINHO
Universidade Federal do Ceará

ABSTRACT
Jacobsita occurs in metamorphic oxide-silicatic manganese protore in Itacirna, in the manganese district of Pacatuba, Ceará, Brazil. Precambriam gneisses and schists are the host rocks of the lenses of the manganese protore which was weathered at the surface, forming small ore deposits. All the Precambrian roeles in this area belong to the Maranguabe Metamorphic Complex and are located in the
J aguaribeana folding belt. The assemblage of primary manganese minerals in the protore consists of rhodonite, spessartite, tephroite, jacobsite and hausmannite. Manganese silicates and hausmannite were altered to aMn0 2 , but the jacobsite shows only incipient alteration.
In spite of the presence of two micas in the gneissic country rock, the metamorphism is believed to be of high grade, as evidenced by the assemblage of manganese metamorphic minerals. Probably the regional metamorphic rocks underwent two different phases of metamorphism.
The manganese content of the manganiferous rocks varies from 10.0 to 38.0%.
The magnetometric anomalles were very useful in establishing the form and dimensions of both the manganese ore and protore. The Mn-deposits of Itacirna have very small reserves, consequent1y their resources have no economic interest.

da aos depósitos de manganês não foge a esta norma, uma vez que depósitos de manganês portadores do mineral magnético jacobsita são raros. Apesar de pouco usada a prospecção magnetométrica já se mostrou útil na região do distrito manganífero de Urandi, na Bahia
(Ribeiro Filho e Ellert, 1969), bem como na região de Itacima, no Ceará, onde ocorrem os depósitos de que trata o presente