Wed 1st June @ 12 pm, Rm 312.222

Auriferous sulphides, most notably pyrite (FeS2) and arsenopyrite (FeAsS), are some of the most important strategic minerals on Earth because they host gold in many of the world’s major gold deposits. To increase our understanding of mineralisation processes, we combined atom probe microscopy, high-resolution secondary ion mass spectrometry (NanoSIMS), synchrotron X-ray fluorescence microscopy (XFM) mapping with the Maia detector and electron backscattered diffraction (EBSD) on arsenopyrite from the giant Obuasi gold deposit, Ghana.

The gold-rich arsenopyrites are shown to have undergone partial replacement by gold-poor, nickel-enrich arsenopyrite and indicate that large quantities of gold were remobilised via infiltration of only small volumes of fluid.

Atom probe tomography (APT) data revealed two types of gold distribution at the sub-micron scale in distinct sub-domains of the same arsenopyrite grain with, metallic gold nanoparticles (CAu = 724 ppm) and gold homogeneously distributed in the crystal lattice (CAu = 2,224 ppm). These results are not consistent with previous models that point to gold concentration as the key control on gold distribution, but instead we provide a new model for their formation.

These results provide fundamental information on gold distribution and remobilisation during ore deposit formation and deliver a framework for more efficient exploration strategies and metallurgical extraction of gold from sulfides.