Magnetic and radiometric signatures of alkaline rocks and gabbros from the Ponta Grossa Arch, southeastern Paraná Basin, Brazil

Vinicius Antunes Ferreira Da Silva,Francisco José Fonseca Ferreira

doi:10.1590/2317-4889202120200051

Vinicius Antunes Ferreira Da Silva, Francisco José Fonseca Ferreira

Open Access

https://doi.org/10.1590/2317-4889202120200051

Copy DOI

Abstract

We present airborne magnetic and radiometric characteristics of some igneous suites from the Ponta Grossa Arch Alkaline Province (southern Brazil), namely the Bairro da Cruz, Banhadão, Barra do Itapirapuã, Mato Preto and Tunas complexes, Barra do Teixeira Phonolite, Itapirapuã Nepheline syenite, and José Fernandes Gabbro. We applied magnetic susceptibility 3D inversions using the total magnetic anomaly data together with its analytic signal of the vertical integral and the vertical integral of the analytic signal for the Bairro da Cruz, José Fernandes, and Tunas intrusions. Gamma-ray spectrometric methods involved analyses of basic, ternary, and ratio maps, thorium-normalized parameters, and radioelement concentrations at sampled data points. Stacked profiles from geophysical data were generated for each rock. The Bairro da Cruz, José Fernandes, and Tunas intrusions are associated with dipolar anomalies with normal polarity whereas their inversions show low magnetic susceptibility values. Gamma-ray spectrometric results allowed us to verify that all complexes are enriched mainly in eTh. Carbonatite bodies showed the highest contents of eTh and eU. Our findings are consistent with geophysical responses of alkaline bodies and impact the understanding of geophysical signatures, especially radiometric ones, of alkaline provinces in Brazil.

Highlights

The Ponta Grossa Arch (PGA) is an uplifted domain located in the southeastern Paraná Basin and its Precambrian basement (Fig. 1)
This arch hosts both alkaline and carbonatitic-alkalic intrusions. These complexes were studied by Almeida (1983), who labeled them as the Ponta Grossa Arch Alkaline Province (PGAAP)
No significant representation of classical dipolar anomalies was observed for IT, Barra do Itapirapuã (BIT), BN, Barra do Teixeira (BT), and Mato Preto (MP) igneous rocks even when total magnetic anomaly (TMA) data were interpolated in a rectangular area around the location of the intrusions

Summary

Introduction

The Ponta Grossa Arch (PGA) is an uplifted domain located in the southeastern Paraná Basin and its Precambrian basement (Fig. 1) This arch hosts both alkaline and carbonatitic-alkalic intrusions. These complexes were studied by Almeida (1983), who labeled them as the Ponta Grossa Arch Alkaline Province (PGAAP). Alkaline intrusions have been recognized and detailed in different scales by airborne magnetic and gamma-ray spectrometric surveys These surveys contribute to a variety of geological and geophysical interpretations and modeling applications, such as mapping of bedrocks and mineral exploration (Airo et al 2014), as well as the discovery of uranium deposits in alkaline igneous complexes (e.g. Cercado Mine in Poços de Caldas, Forman and Angeiras 1981). Carbonatitic-alkalic complexes may show potential for rare earth elements (REE), niobium, and vermiculite mineralizations which are resources with economic importance for Brazil (Gomes and Comin-Chiaramonti 2005)

Objectives

Methods

Results

Conclusion