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TitleSpeciation of arsenic in mine tailings and pore water, Lower Seal Harbour Gold District, Nova Scotia
AuthorDaniels, C M; Parsons, M B; Jamieson, H E; Hall, G E M; Vaive, J E
SourceGAC-MAC-CSPG-CSSS Halifax 2005, building bridges - across science, through time, around the world: abstracts/AGC-AMC-SCGP-SCSS Halifax 2005, Jeter des ponts entre les disciplines scientifiques, les époques, et unifier le monde : recueil des résumés; GAC-MAC-CSPG-CSSS Joint Meeting, Abstracts vol. 30, 2005 p. 39-40
Alt SeriesEarth Sciences Sector, Contribution Series 2004430
MeetingHalifax 2005: GAC-MAC-CSPG-CSSS - AGC-AMC-SCGP-SCSS; Halifax, NS; CA; May 15-18, 2005
File formathtm; pdf
ProvinceNova Scotia
AreaSeal Harbour
Lat/Long WENS -62.0000 -61.5000 45.2500 45.0000
Subjectsgeochemistry; hydrogeology; mine waste products; tailings; tailings geochemistry; arsenopyrite; arsenic; sulphides; gold; x-ray diffraction; x-ray diffraction analyses; pore fluids
ProgramMetals in the Environment (MITE)
AbstractArsenopyrite and other As-bearing sulphides occur naturally in most lode gold deposits of the Cambro-Ordovician Meguma Group in Nova Scotia, and are present at high concentrations in the tailings at past producing mines. Chemical analyses of 520 tailings samples collected from 15 gold districts in 2003 and 2004 show a wide range in As concentrations, from 9 mg/kg to 31 wt.%. In addition to As-bearing sulphides, X-ray diffraction data indicate that As is also hosted by a variety of more soluble, weathering-related phases, such as scorodite (FeAsO4·2H2O). The main objective of the present study is to examine the speciation of As in tailings and pore waters in different environmental settings to better understand the processes that control the mobility of As from these mine wastes. Field studies in 2004 focused on tailings at the Lower Seal Harbour (LSH) Gold District in eastern Nova Scotia, which was active intermittently from 1894 to
1942. Early gold recovery efforts employed stamp mills and mercury amalgamation, whereas later operations used cyanidation as the
primary extraction method. Tailings from the LSH mine are voluminous, and have been transported more than 1 km to the ocean
where they form a tailings flat in the intertidal zone. Occasionally, local residents harvest clams from this area. Tailings and pore water
samples were collected from three sites around LSH with contrasting environmental conditions: (1) subaerially exposed tailings ('oxidized' site); (2) submerged tailings in a shallow, marshy area ('reduced' site); and (3) tailings from the intertidal zone ('marine' site). In-situ pore water samples were obtained using peepers (dialysis membrane samplers), and duplicate tailings cores were collected adjacent to the peepers at each site. Analyses of As(III)/As(V) in the pore waters reveal a transition from oxidized to reduced conditions at depths of approximately 30 cm, 2 cm and 10 cm at the oxidized, reduced, and marine sites, respectively. In general, the total dissolved concentrations of As, Fe, and Mn increase as the pore waters become more reducing, whereas the concentrations of total dissolved S decrease. The average concentration of As in the solid phase is approximately 4 to 8 times greater at the onland sites as compared to the marine site, which may reflect dilution of the tailings by natural marine sediments. Sequential extractions will be used to characterize the partitioning of As in the tailings, and should help to clarify the geochemical controls on the observed pore water concentrations.