Title
Characterization of Wetland Soils Receiving Drainage from an Abandoned Mine in Southwestern Montana
Document Type
Grant
Publication Date
9-1-2015
Department
Geoscience
Abstract
The Bismark Mine in Montana was mined for copper, lead, and small amounts of silver and gold between 1913 and 1963. The geology of the area consists mainly of Precambrian Pony Series (quartzofeldspathic gneiss) and the Tobacco Root Batholith (quartz-monzonite granite), which intrudes the Pony Series. Mineralization occurs within fissures near the contact between the granite and gneiss. Pyrite, chalcopyrite, and molybdenite are found in addition to the primary ore minerals (Ag, Au, Cu, and Pb) in these veins. Bismark Mine is situated near several of these fissures. During mining, pyrite (an iron sulfide mineral) is also extracted and discarded with the waste rock (tailings). The tailings were deposited downslope from the main (lowermost) adit, and once the mine closed, a wetland developed over the tailings due to water flowing from the main adit and springs on the surrounding slope. Pyrite oxidation typically leads to the formation of acidic waters. However, water tested from the adits and seeps have a pH value between 6.78 and 8.05. One possible explanation is that the flow bypasses the mined area and any remaining zones of pyrite through fractures in the rock. The chemistry of the main adit includes: 15 µg/L of zinc, 14.8 µg/L of lead, 43 µg/L copper, 11.7 µg/L of chromium. The purpose of this research was to evaluate the concentration of trace metals in the soils formed in the wetland area receiving drainage from the abandoned Bismark Mine and to evaluate potential mobility of these metals. Twelve grab samples of the soils were collected from two separate soil pits in the wetland area by students enrolled in Indiana University’s field camp in the summer of 2015. Samples were placed in labeled, Ziploc® bags and were transported to Winona State University (WSU) for analysis. In the laboratory, pH, loss on ignition (LOI; used as a proxy for soil organic matter), moisture content and easily mobilized elements were determined. Splits of the samples were sent to Activation Laboratories in Ancaster, Ontario, Canada, for total metal analysis using acid digestion followed by analysis on ICP-OES. The pH of the samples varied from 2.91 to 6.44. Soil organic matter ranged from 0.0014 g/g to 0.6382 g/g, with most of the values falling between 0.0192 g/g to 0.3193 g/g. Results from total metal analysis and extracted metal from both pits will be presented.
Content Notes
Poster, Final Report Form
First Advisor
Candace Kairies-Beatty
