Comparison of Duluth Complex Rock Dissolution in the Laboratory and Field

Abstract

The quality of drainage and the release of sulfate, calcium, and magnesium from five field test piles of Duluth Complex rock with sulfur contents of 0.63% (three piles), 0.79%, and 1.41 % were determined for periods of 12 to 14 yr. The pH of drainage from the piles decreased over time and with increasing solid-phase sulfur content. The ultimate drainage pH values for the 0.63% S piles ranged from 4.8 to 5, similar to values observed in the laboratory. Ultimate drainage pH values for sulfur contents of0.79% (pH 4) and 1.41 % (pH 3.5) were about one unit lower than the corresponding laboratory values for these sulfur contents. Over the entire period of record, average rates of sulfate release (2.1 to 10.5 mmol/mt/d) and magnesium release (0.55 to 3.7 mmol/mt/d) increased as the solid-phase sulfur content of the pile increased, while those of calcium release (1.2 to 2.4 mmol/mt/d) were relatively constant with respect to solid-phase sulfur content. Annual release rates for sulfate and calcium were relatively constant over time, while those for magnesium tended to increase over time. Annual release rates for all three parameters increased with increased annual drainage volume, a variable not examined in the laboratory. Release rates in the field were typically 10% to 30% (and in one case, nearly 40%) of those observed in the laboratory. Empirical neutralization potentials in the field decreased as solid-phase sulfur content decreased and were typically 10% to 50% of the corresponding average laboratory values. The empirical neutralization potentials to maintain drainage pH above 6.0 were approximately 0.5% to 8% of ABA NP values for Duluth Complex rock.

Novel Microbial Assemblages Dominate Weathered Sulfide-Bearing Rock from Copper-Nickel Deposits in the Duluth Complex, Minnesota, USA

“…Our (Fig. 2), consistent with numerous Duluth Complex weathering experiments that have shown similar correlations with sulfide mineral content of the rock (34,43,44). From the available data, we were not able to discern whether the observed trends in microbial community structure and diversity were related to pH itself, to sulfide mineral content, or to a combination of these and other factors.…”

Preoperational assessment of solute release from waste rock at proposed mining operations

“…That is, higher concentrations may be reached under operational conditions. Field testing has been conducted at various scales, ranging from barrels (Costin et al 2011, Shaw and Samuels 2012, Aranda et al 2009) to test bins (Soto et al 2012, Salzsauler et al 2012, Bertrand et al 2012 to test piles of various sizes (Lapakko 1993, Lapakko 1994, Bailey et al 2012, and full-size operational monitoring ( Figure 6). Testing of this nature has been typically conducted at operational mine sites where larger masses of material are readily available and mining personnel and equipment are available to assist in construction and monitoring.…”

Equilbrium Modeling of Trace Metal Transport From Duluth Complex Rockpile

“…Sulfate concentrations have increased almost two-fold, a result highly dependent on fluctuations in transport flow. However, according to Lapakko (1994), the annual sulfate release rate has remained fairly steady, increasing only slightly from 1978-1991, indicating the oxidation of sulfide minerals within the pile. Concentrations of trace metals Co, Cu, Ni and Zn have also increased with time, a result of the decreasing effiuent pH over time.…”

“…In the early 1970's AMAX Exploration Inc. began evaluating the potential of an area in the vicinity of the town of Babbitt, MN for the mining and extraction of copper and nickel (Lapakko, 1994). In 1977, a joint effort between the State of Minnesota and AMAX produced six stockpiles containing lean ore material from a shaft dug in 197 5.…”