Abstract

CUBAS VILLALBA, Narciso; SALINAS FRANCO, Néstor Damián  and  LOPEZ, Diego Adán. Geology of the alkaline-carbonatitic complexes, northeast of Eastern Paraguay. Rep. cient. FACEN [online]. 2021, vol.12, n.2, pp.104-109. ISSN 2222-145X.  https://doi.org/10.18004/rcfacen.2021.12.2.104.

The alkaline-carbonatite complexes of the Chiriguelo and Sarambí hills form well-defined circular structures, with a diameter between 5 and 7 km, about 25 and 68 km respectively, to the west of Pedro Juan Caballero, Northeast of Eastern Paraguay. These alkaline-carbonatite igneous complexes belong to the Alkaline Province of the Amambay of Mesozoic age, which intruded the oldest units that range from the crystalline ba- sement of Precambrian age to the Upper Carboniferous; these units at the same time were raised and exposed in the peripheries of the intrusion forming their outer ring, where the metamorphic rocks of the crystalline basement and the Paleozoic sediments emerge.

Lithologically, the igneous silicates rocks are micaceous pyroxenite that is occupying the central portion of the circular structure, surrounded by alkaline syenite, nepheline syenite, trachytes, phonolites and lamprophires dikes, which in turn were intruded by transgressive carbonatite classified as sovite, silicocarbonatite , ferrocarbonatite and rodbergite; the intrusion of magma of carbonatic nature, in turn has produced intense fenitization of su- rrounding of the Precambrian and Paleozoic rocks. In the central portion of the annular structure, the carbonatite bodies that are currently heavily weathered are located, with significant development of decalcified clay soil that normally contains anomalous concentrations of associated minerals such as the Rare Earths Elements (REE), strontium, pyrochlore, apatite, magnetite and barite.

Keywords : Chiriguelo; Saramabí; alkaline-carbonatitic magmatism; fenite; graben; Alkaline Province.

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