Session 5 | Track B | Site Characterization & Monitoring
Abstract
This paper describes the mineralogical and structural characterization of the tailings matrix at BHP’s legacy San Manuel copper mine in Arizona, USA. The methods and results are described, including key learnings related to the approach. The work included a variety of imaging techniques to characterize intact tailings solids including computerized tomography scans (CT) and quantitative scanning electron microscopy (QEMSCAN) at micron scale applied to samples subjected to undrained triaxial shear tests as well as unstrained samples, and bulk X-ray diffraction (XRD) tests on the clay-sized minerals. In addition, characterization of the tailings porewater, meteoric water mobility procedure (MWMP) tests and equilibrium modelling on the resulting solutions were used to infer whether certain mineral phases were in equilibrium with secondary mineral phases to further support interpretation of the mineralogical findings. This work is intended to supplement an advanced geotechnical characterization program described in the Part 1 companion paper (Casey et al, 2022).
The results showed clear evidence that carbonate, iron oxide, and sulfate minerals are not functioning as mineral cements and that pervasive loose or unstable structures such as stacked mica grains or bridging structures are not present. Very fine-grained (<2 um clay size) sheet silicate minerals are a more significant component of the tailings samples than previously understood. These occur as a matrix surrounding and often supporting larger (30 to 60 µm) quartz and feldspar particles.
BHP’s aspiration is to have zero harm from tailings. Working with others and sharing progress with industry is a key aspect of making this aspiration a reality and is a key driver for this paper.
Authors
- Kelly Sexsmith | SRK Vancouver
- Tom Kotzer | SRK Vancouver
- Ryan Chambers | BHP
- Jim Casey | Klohn Crippen Berger
- Rick Friedel | Klohn Crippen Berger
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