In situ characterization of gold in arsenopyrite combining large area SEM imaging and nano-scale HRTEM studies: an example from the Dome Mine, Timmins, Ontario

Dirk Schumann1,2, Jessica Maarit Stromberg3, Alexandre Laquerre2, Dave Mayer2, Mike W Phaneuf2, Hojatollah Vali4 and Neil Banerjee3, (1)Fibics Incorporated, Ottawa, ON, Canada, (2)Fibics Inc, Ottawa, ON, Canada, (3)Western University, Department of Earth Sciences, London (Ontario), ON, Canada, (4)McGill University, Anatomy and Cell Biology, Montreal, QC, Canada

Contact First Author: Dirk Schumann; dirkschumann11@gmail.com

Abstract ID#: 35190

 

English Abstract:
The in situ characterization of minerals associated with ore zones and geochemical anomalies is a novel tool that can increase exploration and extraction efficiency. The knowledge of how gold occurs within sulphide minerals (e.g., in the lattice or as nano-particles) is of great importance to mining companies in order to define effective extraction methods. Bulk rock and microprobe analyses alone lack the spatial resolution and sensitivity necessary to accomplish the required level of characterization. We present a suite of advanced SEM, FIB and TEM techniques that can be applied sequentially and quickly.

A sample from the Dome Mine in Timmins, Ontario was analyzed using large area SEM imaging, TEM specimen preparation, and high-resolution TEM (HRTEM) characterization. The primary gold hosting mineral at the Dome Mine is pyrite that contains free gold as inclusions, fracture filling, and along grain boundaries as well as "invisible" gold in arsenopyrite. Of special focus for this study was the gold associated with the arsenopyrite.

The samples were imaged in a Zeiss Sigma HDVP SEM using the large area imaging module Atlas 5. Overview mosaics with the BSE signals were acquired at a resolution of 100 nm/pixel. Areas of interest for TEM specimen preparation were additionally imaged at 15 nm/pixel. The image mosaics were combined with µXRF elemental maps and FIB foils were extracted. HRTEM analyses of the extracted FIB sections reveal areas with complex zonation patterns in the arsenian-pyrite. Zones with irregular copper-rich inclusions alternate with zones of As-rich bands (50 to 400 nm in width). EDX line scans across arsenopyrite inclusions revealed the presence of Au bound to the crystal lattice of the arsenopyrite crystals.

The applied sequence of techniques enabled a quick and systematic characterization of gold mineralizations from a micro to the nanometer scale in a reasonable time.

Back to: Mineral Structure, Electron Microscopy, Element Partitioning, and Mobility I