Abstract
New geological and litogeochemical data plus La-ICP-MS U-Pb isotopic study on the Jequie Complex, or Jequie “Block”, a granulite facies terrain of the Northeastern Sao Francisco Craton, allowed to propose that a new lithodemic unit, the Volta do Rio Plutonic Suite, should be created as a lower rank unit. The Jequie Complex is defined here as an intrusive complex metamorphosed in the granulite facies, containing an assemblage of plutonic calc-alkalic mafic to intermediate rocks, fractionated trondhjemites, tonalites and granodiorites, besides normal calc-alkaline tonalites/ granodiorites and rare metasedimentary remnants plus two different sets of leucogranites. The Volta do Rio Plutonic Suite is proposed as a lower range lithodemic unit belonging to the Jequie Complex. It is composed of granodiorites and monzogranites with porphyroclastic texture, even- -grained granitoids and fine-grained granitoids, besides an association of amphibole-bearing leucogranites and mafic to intermediate rocks. The metamorphosed mafic, intermediate and felsic rocks of the Jequie Complex compose a Cordilleran-type magnesian calc-alkalic association, which age is 2.7 Ga. In contrast, all the metagranitoids of the Volta do Rio Plutonic Suite show a distinctive ferroan (“A-type”) geochemical signature and the mafic and intermediate rocks associated to metaleucogranites show alkaline characteristics and host locally high-grade REE mineralizations contained in chevkinite group minerals. In the Volta do Rio Plutonic Suite, the porphyroclastic granites were dated at 2.6 Ga.The provisional age of alkaline mafic rocks with magmatic-hydrothermal REE mineralizations and of possibly coeval leucogranites is 2.5 Ga. These mineralizations are inedit in the world and the obtained time frame indicates the need to re-evaluate the geology and metallogenic potential of the Jequie Complex by considering its primordial igneous nature and by screening out its “granulitic” or “charnockitic” nature.
Highlights
The Jequié – Itagi area is located in the Jequié Complex, which is part of the São Francisco Craton (Almeida, 1977; Figure 1), the most extensive Archean – Paleoproterozoic crustal segment in South America
The maic rocks of the Jequié Complex may be described as three diferent groups: (i) “normal” calc-alkaline maic rocks; (ii) high-Mg cumulates and (iii) Fe-rich maic rocks
An association of “low-Ti” magnesian (Frost et al, 2001) tonalites, granodiorites and granites metamorphosed in the granulite facies was described by Barbosa et al (2002) (Figure 6)
Summary
The Jequié – Itagi area is located in the Jequié Complex, which is part of the São Francisco Craton (Almeida, 1977; Figure 1), the most extensive Archean – Paleoproterozoic crustal segment in South America. The Volta do Rio Suite was deined in the Jequié-Itagi region, there is evidence that it extends itself for more than 200 km northeastwards and to the South It hosts high-grade REE mineralizations in maic to intermediate rocks and magmatic-hydrothermal segregations and veins associated to leucogranites which are inedit in the world. The recognition of such a sequence of geological processes in the Jequié Complex and their dating may contribute to change the geological approaches to study the Jequié Complex and incentivate the exploration of its metallogenic potential for REE deposits
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