ISOTOPIC ANALYSIS OF Cu IN SOLID GEOLOGICAL MATERIAL AT THE PARÁ-ISO LABORATORY (UFPA), BRAZIL

The non-traditional stable isotopes like Cu, Fe or Zn are useful tracers of geological, biological and environmental processes. However, in Brazil, studies of Cu isotopes are still limited. This work presents the two-step chromatographic separation protocol and isotopic analysis of Cu implemented in the Laboratory of Isotope Geology at UFPA for solid samples with different matrices. The implemented protocol allows the separation of Cu, Fe and Zn from each other and from the matrix elements, using Teflon® chromatographic columns filled with AG-MP resin. The separation and purification protocol were tested on chalcopyrite (CPY), Cu ore tailings (RMC), bottom sediment (SED) and Cu reference solution in concentration (Mixed Titrisol® Solution). The copper fractions were separated from the main interfering elements (Ti, Fe, Zn, Ni, Pb, Ca, Mg and Na) with 6N HCl without the presence of H2O2. Recovery rates greater than 97% and a blank of 2 ng were achieved after the chromatographic procedure. Cu concentrations were determined on a quadrupole-ICP-MS (Thermo Scientific model iCAP-Q). The Cu isotopic compositions of isotopic reference Cu solutions (NIST SRM 976, ERM-AE633 and ERM-AE647), geological reference material (BCR-1), CPY samples from different Cu deposits in the Carajás Mineral Province, Eastern Amazonia  (Sossego, Igarapé Bahia, Pojuca and Gameleira deposits) and solid samples from the Sossego deposit (chalcopyrites, ore tailings, concentrate, crushed ore and sediment) were measured using a induced plasma mass spectrometer MC-ICP-MS with magnetic field and multi-collectors (Thermo Finnigan model Neptune). Instrumental mass discrimination was corrected by the Sample-Bracketing-Standard (SSB) method with high precision and reproducibility (2σ < 0.06‰, n = 18). The Cu ERM-AE633 and ERM-AE647 reference solutions were calibrated against the NIST SRM 976 reference solution providing δ65Cu values [-0.03 ± 0.03‰ (n = 10) and 0.18 ± 0.03‰ (n = 3); respectively] reproducible and consistent with previous work. δ65Cu values of Cu isotopic reference solutions NIST SRM 976 and ERM-AE633, before (0.03 ± 0.04‰ and -0.02 ± 0.03‰) and after (0.02 ± 0.03‰ and -0.01 ± 0.03‰) chromatographic separation procedure, demonstrated that the AG-MP1 resin did not cause the isotopic fractionation of copper. A value of δ65Cu equal to 0.09 ± 0.06 ‰ was obtained for the geological reference material BCR-1. CPYs from Cu deposits of the Carajás Mineral Province, eastern Amazonian Craton showed isotopic signatures from -0.25 ± 0.008‰ to 0.58 ± 0.01‰ characteristic of primary chalcopyrites from mineral deposits of hydrothermal origin. In the Sossego Copper deposit, products from the various processing stages of copper ore have a homogeneous isotopic signature (δ65Cu = -0,36 ± 0,09‰ a -0,21 ± 0,05‰), distinct from tailings basin sediments and river bottom sediments (δ65Cu = 0,32 ± 0,06‰ a 0,59 ± 0,02‰). Therefore, the Cu isotopic composition showed potential as an additional parameter to control process quality to produce Cu concentrate and detect possible contamination in the tailing basin.