Morphological characterization of lode gold in the auriferous quartz veins at M’Popo mine, Angola, by computed tomography and optical microscopy

ABSTRACT

Auriferous vein samples of the Angolan M’Popo deposit were characterized by a combination of 2D microscopy and 3D computed tomography (CT) in order to visualize and assess the gold distribution and gold morphology in in situ high-grade gold ore. The 0.1–2.4 m wide hydrothermal quartz veins in the Mesoproterozoic M’Popo granitic complex are composed mainly of quartz and pyrite, minor other sulfides and (visible) gold. The favourable X-ray attenuation/density contrast within this mineral assemblage allows delineation of the gold particle fraction so that gold particles of <0.01–19.95 mm³ in volume have been identified. Statistical analysis reveals that the bulk (∼99.98%) of all gold particles belong to the smallest volume classes (≤0.02 mm²) while large particles (>0.5 mm³) are few. The contrast between rounded, compact smaller particles and branched larger ones is clearly expressed in the CT reconstructions while transitions between these reflect a likely continuum in gold mineralization.

KEYWORDS:

• M’Popo mine
• computed tomography
• lode gold mineralization
• Angola

Acknowledgements

We are grateful to W. Ließmann and K. Strauß (both of Clausthal University of Technology (TUC), Mineral Resources) for free access to the wonderful ore sample collection at TUC, their support in choosing the right samples for this study, and for their patience during many hours in front of ore microscopes in challenging corona virus times. Special thanks are directed to F. Pauly (Forschungszentrum Jülich GmbH (FZJ)) for the possibility to lead R. Gainov carry out first test analyses at FZJ and to B. Lottermoser for the possibility to develop a new CT laboratory from ‘zero’ at the Institute of Mineral Resources Engineering (RWTH Aachen University) and to perform this CT investigation as well as other CT projects.

Disclosure statement

No potential conflict of interest was reported by the author(s).