Abstract

Black rock-coatings have formed during the interaction of smelter-emitted sulfuric acid and metal(loid)-rich particulate matter with aerially exposed rocks in Trail, BC, Canada. The chemical and mineralogical composition of the coatings indicate the past emission of Pb, Zn, Sb, As, Te, Sn, Se, Ag, and In-bearing contaminants. Black rock-coatings were collected along the Columbia River Valley and characterized with a combination of laser-ablation inductively coupled plasma-mass spectroscopy, scanning electron microscopy with energy dispersive spectroscopy, and transmission electron microscopy. The coatings contain elevated concentrations of Pb (3.8–10 wt.%), As (0.07–5.2 wt.%), Zn (0.09–2.0 wt.%), Sb (0.1–1.5 wt.%), Sn (500–1400 mg/kg), Bi (40–600 mg/kg), Se (5–40 mg/kg), and Ag (20–120 mg/kg). The matrix of the coatings is composed of amorphous silica formed by the non-stoichiometric dissolution of silicate minerals on aerially exposed rocks. Particulate matter and aerosols trapped by the initial silica-gel type material are preserved in the silica matrix and include various aggregation stages of emitted and/or in situ-formed anglesite (individual nanoparticles, aggregates of nanoparticles, and single crystals); euhedral cubic crystals of franklinite, ZnFe2O4; and particulate matter composed of valentinite and senarmontite (orthorhombic and cubic Sb2O3, respectively), oxyplumboroméite (Pb2Sb2O7), and an unidentified indium-oxide or oxy-salt phase. The latter Sb- and In-bearing phases are the major hosts of As, Te, Sn, Se, and Ag in these coatings. Similar to the black rock-coatings in Sudbury and Rouyn Noranda, the coatings in Trail can be considered chemical and mineralogical records of the type of local ore and particulate matter emitted in the past from the smelter and ore or waste-rock piles associated with the smelting operations. The chemical and mineralogical composition of the coating suggests that residents in Trail may have been exposed to particulate matter containing Pb, As, Te, Sn, Se, Ag, Bi, and In.

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