2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 296-6
Presentation Time: 10:15 AM

A CONCEPTUAL MODEL FOR THE FLUSHING OF COAL WASTE ROCK PILES IN THE ELK VALLEY, BRITISH COLUMBIA, CANADA


KUZYK, Terryn, Civil and Geological Engineering, University of Saskatchewan, Saskatoon, SK S7N 5A9, Canada, BARBOUR, Lee, Department of Civil, Geological and Environmental Engineering, University of Saskatchewan, Saskatoon, SK S7N 5A9, Canada and HENDRY, Jim, Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2, Canada

Accessing coal resources is often achieved using surface mining methods, which remove overlying (overburden) rock. This waste rock is then placed in adjacent areas, creating unsaturated waste rock piles, many of which are underlain by rock drains formed during the natural segregation of the rock during end dumping. These rock drains act as conduits for water moving through the overlying unsaturated waste rock. Data collected from rock drains can provide a bulk measurement of the rates of production of constituents of interest (CIs) from the overlying unsaturated waste rock and their leaching rates. This study included development of a conceptual model for the long-term release of nitrate (NO3), selenium (Se) and sulfate (SO4) from waste rock piles by interpreting water discharge and chemistry data measured at the outflows of several rock drains at five mine sites in the Elk Valley. These rock drains represent a range of waste rock pile ages (0 to 30+ years since placement) and methods of construction. CIs were used to develop trends for evaluation of weathering and flushing of the CIs following pile construction. The rock drain data was augmented by high-resolution, concentration-depth profiles of pore waters squeezed from core samples collected from waste rock piles overlying the rock drains. Analyses of the data sets suggest that the initial effluent water chemistry observed in the rock drains is dominated by the first flushing of pore water from the waste rock. This initial pore water is assumed to contain CIs derived primarily from blasting and pile construction and consequently is characterized by constant SO4/NO3 and elevated Se/SO4 ratios. If NO3 acts as a conservative tracer in the piles, then any post-depositional oxidation which would generate additional Se and SO4 from sulfide minerals in the waste rock will be reflected in increased SO4/NO3 ratios (decreasing NO3 associated with flushing) while maintaining a constant Se/SO4 ratio. Based on this interpretation, it is anticipated that the generation of Se and SO4 beyond the first pore volume of water can be estimated.

Session No. 296

T103. Mining and the Environment: Addressing Common Challenges Faced across the Mining Industry (Posters)
Wednesday, 22 October 2014: 9:00 AM-6:30 PM
Exhibition Hall C (Vancouver Convention Centre-West)
Geological Society of America Abstracts with Programs. Vol. 46, No. 6, p.718
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