Investigating for dry stack tailings facility closure: multidisciplinary evaluation at the Pogo Mine, Alaska

Author(s): 
Dan Neuffer, Christopher Stevens, Russell Staines
Date: 
Sunday, June 8, 2014
First presented: 
PASTE 2014
Type: 
Published paper
Category: 
Geotechnical
Civil Engineering
Geochemistry
Environmental/Social
 
 
Sumitomo Metal Mining Pogo LLC (Pogo) is the operator of the Pogo underground gold mine, located near Delta Junction, Alaska. The mine has been in operation since 2006 and produces between 380,000 and 400,000 ounces of gold annually. Filtered tailings from the flotation circuit and waste rock from the mine are placed in the dry stack tailings facility (DSTF). Expansion of the DSTF from 7 M to 18 M t has prompted further evaluation of the facility for closure planning. This paper presents data from several components of a multidisciplinary DSTF closure study, including geotechnical and geochemical test results, in situ temperature and pore pressure measurements, and estimated freezing characteristics of tailings samples.
 
Results of this study indicate the DSTF is physically stable and is comprised of materials that are not potentially acid‐generating; these findings support operational material placement practices and elements of the DSTF closure plan. Geotechnical field and laboratory testing indicate that effective friction angles and dry densities of in situ DSTF materials are consistent with previous slope stability analyses. Geotechnical borehole drilling, thermal monitoring, and analysis indicate the presence of permafrost within the DSTF. Pore pressure measurements and drilling observations indicate a phreatic surface near the base of the DSTF. This study narrows the focus of data collection for future closure planning and provides an example of physical and chemical conditions within a dry stack tailings facility in a continental, subarctic climate. These findings are pertinent for planning, design, permitting, operation, and closure of dry stacks in similar climates.

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Feature Author

Dr. Christopher Stevens
Christopher Stevens, PhD., is a geocryologist who specializes in permafrost and cold regions work. He has 8 years of project and research experience in both terrestrial and subsea permafrost, for mining, highway infrastructure, utility corridors, and oil and gas projects in USA and Canada. His experience includes thermal analysis, terrain and climate analysis, permafrost and ground ice characterization, talik delineation, permafrost-groundwater interactions, design and implementation of permafrost monitoring programs, and numerical thermal modeling to assess thermal performance of infrastructure and potential impacts to the environment. His experience also extends to the design and evaluation of permafrost mitigation techniques used to achieve infrastructure and site stabilization in areas with ice-rich permafrost, including passive thermosyphons, active ground freezing, air convection, and thermal covers. Christopher has developed several novel satellite and ground-based geophysical applications for mapping degrading permafrost conditions and characterizing related environmental changes.
Geocryology and Cold Regions Specialist
PhD. Geology and Geophysics
SRK Alaska
SRK Turkey