Arsenic and Antimony Geochemistry of Neutral Mill Tailings at the Giant Mine, NT

Hilger, David; Ptacek, Carol; Blowes, David; Bain, Jeff; Thomas, Tauhid-Brian

Poster Hall

Arsenic and Antimony Geochemistry of Neutral Mill Tailings at the Giant Mine, NT

David Hilger University of Waterloo

Carol Ptacek University of Waterloo

David Blowes University of Waterloo

Jeff Bain Department of Earth and Environmental Sciences, University of Wateloo

Tauhid-Brian Thomas Crown-Indigenous Relations and Northern Affairs Canada

Résumé - Abstract

Arsenic and Antimony Geochemistry of Neutral Mill Tailings at the Giant Mine, NT

David M. Hilger¹, Carol J. Ptacek¹, David W. Blowes¹, Jeff G. Bain¹, Tauhid-Brian Thomas²

¹Dept. of Earth and Environmental Sciences, University of Waterloo, Waterloo, ON

²Crown-Indigenous Relations and Northern Affairs Canada, Gatineau, QC

Arsenic (As) and antimony (Sb) contamination of groundwater is a global issue, associated with extraction of base and precious metals including Au. Arsenic is highly toxic and a known carcinogen. Antimony is an emerging element of concern with known toxicity to biota and has an EPA maximum contaminant level of 6 µg L^-1. Arsenic is often associated with gold bearing mineral deposits with As abundant within Au-bearing pyrite (FeS₂) and arsenopyrite (FeAsS). The association of Sb with Au deposits in the form of sulfidic minerals such as stibnite (Sb₂O₃), tetrahedrite ((Cu,Fe)₁₂Sb₄S₁₃) and berthierite (FeSb₂S₄) is less well documented. The Giant Mine is a legacy Au mine located 5 km from the city center of Yellowknife, NT, Canada which operated between 1948 and 1999. As a by-product, 16 Mt of As (3000 mg kg^-1)- and Sb (220 mg kg^-1)-bearing mill tailings, composed of roaster residue and flotation tailings, were produced. Tailings within storage impoundments were subjected to weathering processes over the last 20 years. The mobility of As and Sb within the neutral-pH mill tailings was examined versus depth using mineralogical and geochemical characterization techniques. Core samples were collected and analyzed for total C-S and the mineralogical composition was determined using X-ray fluorescence, optical microscopy, scanning electron microscopy-electron dispersion spectroscopy, and synchrotron-based bulk and microprobe measurements. Porewater was collected from the vadose and saturated zone and analyzed for pH, Eh, alkalinity, and major and minor dissolved ions, and interpreted using geochemical modelling. The tailings are of low risk for acidic mine drainage, active oxidation of sulfide minerals is present to a depth of 3 m, and arsenopyrite persists with low alteration in weathered samples. Dissolved concentrations of As and Sb are elevated in the groundwater and vadose zone respectively. Arsenic mobility is associated with reducing conditions with no apparent tie to solid phase speciation. Antimony liberation is associated with sulfide mineral oxidation. The management of As and Sb in neutral mine drainage tailings requires consideration of the respective conditions in which these elements are mobile.

Biographie du présentateur - Biography of the presenter

Name: David Hilger Education: BSc Environmental Earth Science, MSc Soil Chemistry Current Position: PhD Student in Hydrogeochemistry at the University of Waterloo, supervised by Carol Ptacek and David Blowes Research Project: TERRE-NET 1B Evaluation of Remediation Options at the Giant Mine, NT.