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<p>The Robertson mine, NV is projected to generate 482 Mt of waste rock, of which ≈ 14% will have an acid base accounting (ABA) neutralization potential ratio (NPR) &lt; 1.2. One pit, Gold Pan, will excavate materials previously mined at the Little Gem mine, that were placed in an uncovered waste rock dump 80–115&#xa0;years ago, and have since remained undisturbed. The objective of this study was to determine if the Little Gem dump geochemistry could provide clues to future waste rock reactivity and the potential for groundwater impacts from the new Robertson waste rock disposal facility (WRDF). In 2020, the Little Gem dump was drilled to evaluate potential acid generation impacts to the subsurface. A mineralogical analysis demonstrated As, Cu, and Sb attenuation by precipitating Mn- and Fe-oxides within 3&#xa0;m of the dump base; this finding was confirmed and quantified by alluvial attenuation batch tests. In conjunction with the lack of subsurface impact, recharge in this arid area is negligible. Drain-down through an adjacent closed heap leach pad declined exponentially within one year of emplacement in 2003 of a 0.3&#xa0;m vegetative cover to 0.15 LPM (0.04&#xa0;gpm), with no flow two years later. Post-closure groundwater impact from the future WRDF is not anticipated due to the low draindown rates, alluvial attenuation of percolating dump solutes, the depth to groundwater (≈ 90&#xa0;m below ground surface) and an ABA ratio that is substantially more alkaline than the Little Gem dump.</p>

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A Novel Approach to Estimate Natural Attenuation of Solutes Beneath a Century-Old Waste Rock Dump: Implications for Future Waste Rock Disposal Facility Groundwater Quality Impacts

  • 期刊论文

  • 发表日期：

    2025年4月30日

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  • Andy Davis,
  • N. Sims,
  • J. Collord,
  • A. Chouinard

摘要

The Robertson mine, NV is projected to generate 482 Mt of waste rock, of which ≈ 14% will have an acid base accounting (ABA) neutralization potential ratio (NPR) < 1.2. One pit, Gold Pan, will excavate materials previously mined at the Little Gem mine, that were placed in an uncovered waste rock dump 80–115 years ago, and have since remained undisturbed. The objective of this study was to determine if the Little Gem dump geochemistry could provide clues to future waste rock reactivity and the potential for groundwater impacts from the new Robertson waste rock disposal facility (WRDF). In 2020, the Little Gem dump was drilled to evaluate potential acid generation impacts to the subsurface. A mineralogical analysis demonstrated As, Cu, and Sb attenuation by precipitating Mn- and Fe-oxides within 3 m of the dump base; this finding was confirmed and quantified by alluvial attenuation batch tests. In conjunction with the lack of subsurface impact, recharge in this arid area is negligible. Drain-down through an adjacent closed heap leach pad declined exponentially within one year of emplacement in 2003 of a 0.3 m vegetative cover to 0.15 LPM (0.04 gpm), with no flow two years later. Post-closure groundwater impact from the future WRDF is not anticipated due to the low draindown rates, alluvial attenuation of percolating dump solutes, the depth to groundwater (≈ 90 m below ground surface) and an ABA ratio that is substantially more alkaline than the Little Gem dump.