Mapping New IOCG Mineral Systems in Brazil: The Vale do Curaçá and Riacho do Pontal Copper Districts

Sérgio Hühn,Carla Braitenberg,Adalene Silva,Francisco Ferreira

doi:10.3390/min10121074

Abstract

The Vale do Curaçá and Riacho do Pontal copper districts are located within the northern part of the Archaean São Francisco Craton and represent two pulses of mineralization. The copper districts have been identified as Iron-Oxide-Copper-Gold (IOCG) classes of deposits. An older metallogenic event associated with the Caraíba copper deposit, which is located in the Vale do Curaçá district, is related to Palaeoproterozoic (ca. 2 to 2.2 Ga) hydrothermal processes. A younger Neoproterozoic (ca. 750 to 570 Ma) episode of volcanism and associated plutonism is represented by the Riacho do Pontal mineral district. Seismic tomography data from across east-central Brazil show that the multiage Carajás province and Vale do Curaçá and Riacho do Pontal copper districts sit along either side of a prominent NW-trending upper lithospheric high-velocity zone. The edges of the high-velocity zone point to long-lived subparallel transcrustal structures that have been the focus of multiple reactivations and copper mineralization events. Regional gravity and magnetic maps show that the Vale do Curaçá copper district extends over an area greater than 110 km by 22 km. The magnetic and gravity values show significant variations correlated with this area. The district includes high gravity values associated with the Caraíba copper mine (>−35 mGal), which has a greater density (3.13 g/cm3) than the nonmineralized host rock density (2.98 g/cm3). The gravity anomaly signature over the Riacho do Pontal copper district is characterized by a 40-km long NW–SE trending Bouguer gravity low. The Ria4 occurrences of the Riacho do Pontal copper district are situated in these regional low-gravity domains. Data from regional airborne magnetic and ground gravity surveys were inverted to obtain a 3D magnetic susceptibility and density model, respectively, for the known districts. The results show that the Caraíba deposit is characterized by a both dense and magnetic source showing structural control by thrust shear zones. The 2D and 3D geological models show two main NNW prospective trends. Trends I and II have a sigmoidal shear shape and are positioned in the contact zone between domains with high magnetic susceptibility (SI > 0.005) and density > 0 g/cm3). Trend I is 40 km × 10 km in size and hosts the Caraíba, Surubim, and Vermelho copper mines and other minor deposits. The results obtained from the 3D magnetic inversion model for the region of the Riacho do Pontal district show weak magnetic anomaly highs extending along a NW–SE magnetic gradient trend. The gradient is related to mapped shear zones that overprint older and deeper NE–SW features of the São Francisco cratonic root. The area includes high gravity values associated with the Caraíba copper deposit, which has a greater density (3.13 g/cm3) than the nonmineralized host rock density (2.4 g/cm3).

Highlights

World-class IOCG (Iron Oxide Copper-Gold) deposits express their metallogenic footprint in different tectonic settings through variable volumes of associated alteration and metal endowments, which can be geophysically sensed [1,2,3,4]
An overarching goal of our study is to develop a better understanding of the deep crustal and lithospheric structural controls for Palaeoproterozoic and Neoproterozoic mineralization events
Modelling is an Oasis Montaj cloud and clustered computing package that allows the inversion of geophysical data in 3D [66,67]. It uses a Cartesian Cut Cell (CCC) and the algorithm has been simplified by Ellis and MacLeod [67] in order to represent geological surfaces with better accuracy

Summary

Introduction

World-class IOCG (Iron Oxide Copper-Gold) deposits express their metallogenic footprint in different tectonic settings through variable volumes of associated alteration and metal endowments, which can be geophysically sensed [1,2,3,4]. IOCG mineralization is often controlled by shear system zones and involves high concentrations of magnetite and/or hematite. Magnetic and gravity signatures related to magnetite- and hematite-rich copper ore zones have led the mining community and other researchers to use these data as an effective exploration tool to find new IOCG deposits [5,6,7,8]. The orebodies are structurally controlled by stretching lineations associated with the shear zone. These important geologic features of IOCG mineralization are often expressed in physical property changes related to density, magnetization, and seismic velocities at a wide range of scales [1,5,10]

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