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Transport and fixation of Au, Pt and Pd around the Lac Sheen Cu-Ni-PGE occurrence in Quebec, Canada

1992; Elsevier BV; Volume: 46; Issue: 2 Linguagem: Inglês

10.1016/0375-6742(92)90079-n

1879-1689

Nigel J. Cook, Scott A. Wood, Yingsu Zhang,

Groundwater and Isotope Geochemistry

Analysis of lake waters, groundwaters, soils and lake sediments from the vicinity of the Lac Sheen Cu-Ni-PGE prospect (Temiscaminque region, Quebec) for Pt, Pd and Au indicates that weathering processes have mobilized Pt and Pd from their source in exposed lenses of sulphide-bearing amphibolite. Detection limits as low as 2.5 ng/L Au and Pd and 10 ng/L Pt for waters and 0.5 ppb Au and Pd and 2 ppb Pt for soils and sediments have been attained using Te co-precipitation combined with graphite furnace atomic absorption spectrophotometry. Gold contents of natural waters from the immediate vicinity of Lac Sheen showed a distinct anomaly (<2.5–1000ng/L) relative to regional background (<2.5–100 ng/L). Based on sampling in August and November 1989 and June 1990, no significant seasonal or water depth variations were detected, and groundwaters were not distinct from lake waters. Much of the Au appears to be present in true solution. Significant concentrations of Pt (<10–150 ng/L) and Pd (<2.5–400 ng/L) were also detected, predominantly in dissolved form, in Lac Sheen waters and associated groundwaters. Platinum and Pd, unlike Au, exhibited mild and extreme seasonal variations, respectively. Concentrations in the soil samples were: Au (<0.5–57 ppb); Pd (<0.5–29 ppb); and Pt (<2–306 ppb). Anomalous concentrations of Pt, Pd, Cu and Ni in B-horizon soil clearly identify known mineralization. In addition to a weak Au anomaly near known mineralization, several other Au anomalies are irregularly scattered throughout the study area, perhaps reflecting the dispersion of this metal rom several sources. Anomalous concentrations of Pd, and to a lesser extent Cu, exhibit a more systematic pattern and are found both down- and up-ice, whereas additional Pt anomalies are found only several hundred meters to the north of the known mineralization. The Au, Pt and Pd contents of Lac Sheen sediment samples ranged from below the detection limit up to 65, 122 and 38 ppb, respectively. The average metal contents of Lac Sheen are not statistically different from the background measured in lake sediments from surrounding lakes with no known associated mineralization. However, the average concentrations of all three metals in all the lake sediments are well above crustal averages. These findings may be a result of a generally elevated regional background for Au, Pt and Pd, owing to the widespread occurrence of mafic/ultramafic rocks and sub-economic to economic occurrences of these metals in the Abitibi-Temiscamingue region. The results of this study clearly indicate that Pd is more mobile than Pt in surficial environments. It is probable that organic complexes play a role in the aqueous transport of these elements at Lac Sheen.