Complexo máfico-ultramáfico estratiforme de tucunduba (CMUET)

Abstract

In the city of Caucaia, metropolitan region of Fortaleza, there is a set of metamafic and metaultramafic rocks, cutted off by tertiary subvokanic and volcanic dykes, which intruded granitic-migmatitic rocks of Ceará Complex, Caninde Unit, near the western edge of the Serra de Maranguape. This intrusion is part of the layered Mafic-Ultramafic Complex of Tucunduba (CMUET), which is a medium-sized layered body that has 5 km long by 1 km wide in average on surface. It geometry is roughly ellipsoidal, tending to a boomerang forni, with the main axis oriented N25E and its layers dipping NW. Its deformation and metamorphism occurred in the transition from high amphibolite to low-pressure granulite facies during the Brazilian orogeny. The CMUET has been divided into three zones: 1) Ultramafic Zone composed by metahornblende pyroxenite, actinolite pyroxenite, actinolite clinopyroxenite, metahornblende clinopyroxenite, actinolitite, and talc-serpentine-peridotite. 2) Transition zone between the ultramafic and mafic zones, characterized by mixing of magmas with texture of rocks and varied structure, consisting of magnetite pyroxenite, magnetitites, and an undivided cycle of metahornblende gabbros, metahornblende gabbronorites and metapyroxenitos; 3) Mafic zone is divided into two subzones: the Lower Mafic Zone located in the eastern and southern portion of CMUET composed by magnetitite, metahorblende gabbro, metahornblende gabronorito, and leucogabronorito; the Upper Mafic zone located along the western and northern edge of the complex formed by magnetitite, metahornblende gabronorite, and metagabronorite; furthermore, the surrounding rocks are metahornblende gabronorite and metahornblende pyroxenite, mostly fme-grained rocks. Thus, the development of CMUET occurred in an open magmatic system containing two magma pulses at least, followed by fractionated crystallization and magmas hybridization processes that generated the different units of CMUET. Data of soil geochemistry show the existence of potential targets for sulphides with anomalous values in S, Cu, Co and Ni, and oxides with high Ti and V leveis. However, in surface mineralization only in V-Fe-Ti oxides are found. The ore occurs in two lithotypes: a) the massive magnetitites; b) disseminated mineralization in magnetite pyroxenites. In both the dominant ore are magnetite and ilmenite, also, Cusulphide spots. The gangue minerais are represented by amphibole, spinels clinopyroxene, and plagioclase.