The Weathering of a Sulfide Orebody: Speciation and Fate of Some Potential Contaminants

Abstract

Various potentially toxic trace elements such as As, Cu, Pb and Zn have been remobilized by the weathering of a sulfide orebody that was only partially mined at Leona Heights, California. As a result, this body has both natural and anthropogenically modified weathering profiles only 500 m apart. The orebody is located in a heavily urbanized area in suburban Oakland, and directly affects water quality in at least one stream by producing acidic conditions and relatively high concentrations of dissolved elements (e.g., ~500 mg/L Cu, ~3700 mg/L Zn). Micrometric-scale mineralogical investigations were performed on the authigenic metal-bearing phases (less than 10 mm in size) using electron-probe micro-analysis (EPMA), micro-Raman, micro X-ray absorption spectroscopy (mXAS), scanning X-ray diffraction (mSXRD) and scanning X-ray fluorescence (mSXRF) mapping techniques. Those measurements were coupled with classical mineralogical laboratory techniques, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Authigenic metal-bearing phases identified are mainly sulfates (jarosite, epsomite, schwertmannite), Fe (oxy-)hydroxides (goethite, hematite and poorly crystalline Fe products) and poorly crystalline Mn (hydr-)oxides. Sulfates and Fe (oxy-)hydroxides are the two main secondary products at both sites, whereas Mn (hydr-) oxides were only observed in the samples from the non-mining site. In these samples, the various trace elements show different affinities for Fe or Mn compounds. Lead is preferentially associated with Mn (hydr-)oxides and As with Fe (oxy-)hydroxides or sulfates. Copper association with Mn and Fe phases is questionable, and the results obtained rather indicate that Cu is present as individual Cu-rich grains (Cu hydroxides). Some ochreous precipitates were found at both sites and correspond to a mixture of schwertmannite, goethite and jarosite containing some potentially toxic trace elements such as Cu, Pb and Zn. According to the trace element distribution and relative abundance of the unweathered sulfides, this orebody still represents a significant reservoir of potential contaminants for the watershed, especially in the non-mining site, as a much greater proportion of sulfides is left to react and because of the lower porosity in this site.

Raman identification of Fe precipitates and evaluation of As fate during phase transformation in Tinto and Odiel River Basins

“…6A (5.10) than in 3C (5.95). Furthermore, Courtin-Nomade et al (2009) found the same trend between poorly or microcrystalline and well-crystallized goethite. The well-defined XRD diffractograms of goethite with less background noise in the ancient terrace samples in comparison to newly-formed goethite also corroborate the better crystallinity of goethite in the ancient samples ( Fig.…”

Mine Wastes

“…Weathering of sulfides may occur before, during or after mining. For example, if a sulfide orebody has been exposed by erosion and weathered by surface waters descending through the unsaturated zone, a near-surface oxidized layer of secondary minerals forms (Courtin-Nomade et al 2009;Gomes and Favas 2006;Williams 1990). Table 2.5 Examples of post-mining secondary minerals found in sulfidic mine wastes (after Alpers et al 1994;Bigham and Nordstrom 2000;Jambor et al 2000a, b;Nordstrom and Alpers 1999a) Sulfide oxidation prior to mining results in the formation of secondary minerals.…”

Hemimorphite as a natural sink for arsenic in zinc deposits and related mine tailings: Evidence from single-crystal EPR spectroscopy and hydrothermal synthesis

“…Numerous studies have demonstrated that the mobility and bioavailability of As are usually closely related to its host phases (i.e., minerals in many cases; Foster et al, 1998;Courtin-Nomade et al, 2009;Walker et al, 2009). Therefore, significant efforts have been devoted to the identification and development of minerals (or their synthetic equivalents) that are capable of fixing or minimizing the mobility and bioavailability of As in the environment (e.g., Bothe and Brown, 1999;Di Benedetto et al, 2006;Blanchard et al, 2007;Fernández-Martínez et al, 2008;Lee et al, 2009;Drahota and Filipi, 2009).…”

“…Arsenic has long been the subject of intense research, because it is one of the most common and highly toxic contaminants in surface environments, including those associated with mining activities and metallurgical processes (Nriagu, 1994;Foster et al, 1998;Courtin-Nomade et al, 2009;Walker et al, 2009). Numerous studies have demonstrated that the mobility and bioavailability of As are usually closely related to its host phases (i.e., minerals in many cases; Foster et al, 1998;Courtin-Nomade et al, 2009;Walker et al, 2009).…”