Greg Druschel

University of Vermont

This activity was used for an introductory Geochemistry class, which contained students from sophomore level to master's students. We took the trip in mid-October, about as late as possible in Vermont, after they had gained some previous field experience and lab work in addition to an in introduction to these principles in class.

Concepts

• thermodynamic controls on mineral precipitation/ dissolution
• acid-base and redox chemistry basics

Skills

• basic sampling
• field measurements
• (both skills could be taught there, but we had the students out doing this in Lake Champlain the month before, so they could jump into the meat of the project more quickly)

The activity was used to cement some concepts of our previous discussion on thermodynamics, acid-base, and redox chemistry. In addition the students measured the samples with an IC for anions in lab the following week, and combined with other data, generated a database with which to do some calculations using PHREEQCI in a lab the week after that. Several students chose an aspect of this work to expand into the research paper they wrote in this class as well.

• recognize and describe chemical changes resulting in mineral oxidation and precipitation
• be able to reconstruct those changes in a thermodynamic framework (speciation modeling, use of Eh-pH diagrams)
• identify significant changes in redox state and how that impacts metal transport, microbial ecology
• importance of keeping a detailed field book and appreciation for proper field sampling techniques (in situ measuremnts, filtration, etc.)

• assessment of changing geochemical conditions and attempts to trace sources
• adapting their sampling strategy in response to observations/ field results
• testing hypothesis-driven sampling to understand a complex system
• bringing together water(chemical and hydraulic)-rock-atmosphere-microbe interactions

• discussion/ problem solving as a group
• evaluating sampling strategies
• computational component to understanding a field observation

In this field-based exercise, students were given a tour of an abandoned mine site and asked to utilize a set of field measurements to describe the spatial details of metal transport. This drew on previous experience with field measurements and prompted them to work together to solve an observed chemical evolution of a contaminated brook. The exercise is an excellent example for students to bring together acid-base chemistry, redox chemistry, and thermodynamic concepts together to describe a reasonably complex system. The field component was completed in a full day, but we will be expanding this next fall for a 2 day exercise (weekend). The exercise was coupled with subsequent labs to complete analysis of the water samples and accomplish speciation calculations using PHREEQCI.

I was quite impressed with the student's performance in these activities, and if anything the first trip showed me that even more could be done. Next Fall we will additionally include an exercise specifically on filtration and possibly more sediment characterization and mineral surface chemistry.

SEG Guidebook Series Volume 35 includes quite a lot about the mine waste materials and water chemistry (Bob Seal, Jane Hammerstrom, and Nadine Piatek have done a large volume of great work there) as well as a chapter on the mine deposit (Slack et al.) and history (Kierstad) for this mine and the Elizabeth mine (which is now a Superfund site).