9. Integrated Approaches for Predicting Potential Environmental Effects Associated with Mineral Mining

The USGS is developing methodologies to assess potential environmental effects associated with future mining of undiscovered mineral resources.  The geology of specific ore deposit types can be used as the key to identifying the potential amount and nature of waste material, including compounds of environmental concern. These waste products will serve as “source terms” for modeling potential transport and fate processes through various pathways to surrounding ecosystems. 

To date, attempts to predict the behavior of mine wastes by the regulatory and scientific communities typically have relied upon series of standardized testing protocols, computer modeling, or both.  These protocols are commonly developed and approved using a specific type of waste.  However, they typically are applied to a broader range of materials and conditions than originally specified, which may lead to erroneous interpretation of results.  Likewise, computer modeling is limited by the availability of solubility, thermodynamic, and kinetic data of appropriate phases.  Similarly, regulatory insights into the toxicity of metals are on a metal-by-metal basis, but natural systems commonly contain multiple metals for which the additive toxicity is inadequately understood.

The goal of this research under this Opportunity is to gain quantitative insights into the cycling of acid, sulfur, metals, and related compounds in mine settings.  This can be achieved by conducting laboratory experiments designed to collect fundamental data needed to interpret processes acting at mine sites, and then applying these new results to interpret environmental signatures at field sites.  For example, the acid-generating potential of mine wastes is commonly evaluated using acid-base accounting (White et al., 1999), which looks at the difference between acid-generating potential and acid-neutralizing potential.  However, this approach relies on equilibrium and kinetic data, which are limited or lacking for many important waste phases, such as jarosite.  Because of uncertainties in the reaction kinetics it is unclear how important of a contributor to acid generation jarosite is.  Carefully constructed laboratory experiments on synthetic jarosites, jarosite-rich mine wastes, or both may shed light on this problem. 

A related problem concerns the weathering of primary ore and waste minerals.  These phases weather to a variety of secondary products, which ultimately control the mobility of the elements from the primary phase.  Accurate modeling and prediction therefore depends upon reliable solubility and kinetic data for these important secondary phases.  Those data are largely not available.  For example, when estimating the toxicity of metals in sediments, it is generally assumed that reactions with acid-volatile sulfur sequester metals making them unavailable.  However, many of these concepts are based on laboratory experiments investigating interactions of aqueous cadmium with iron monosulfide (DiToro et al., 1990).  Similar studies with a comparable level of rigor have yet been conducted to understand the interactions of other metals from more complex sulfide systems.  Successful applicants will have a multitude of opportunities to advance our knowledge of elemental cycling in mine settings through integrated studies combining laboratory experiments with field studies.

References

Di Toro, D. M., Mahony, J. D., Hansen, D. J., Scott, K. J., Hicks, M. B., Mayr, S. M., and Redmond, M. S., 1990, Toxicity of cadmium in sediments: The role of acid volatile sulfide: Environmental Toxicology and Chemistry, v. 9, p. 1487–1502.

White, W.W., III, Lapakko, K.A., and Cox, R.L., 1999, Static-test methods most commonly used to predict acid-mine drainage: practical guidelines for use and interpretation, in Plumlee, G.S., and Logsdon, M.L., eds., The environmental geochemistry of mineral deposits, part A: Processes, techniques, and health issues:  Reviews of Economic Geology, v. 6A, p. 325–338.

Proposed Duty Station: Reston, VA

Areas of Ph.D.:Geology, mineralogy, geochemistry, hydrology, environmental science

Qualifications: Applicants must meet one of the following qualifications: Research Geologist, Research Chemist, Research Hydrologist

(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Research Advisor(s): Robert Seal, (703) 648-6290, rseal@usgs.gov; I-Ming Chou, (703) 648-6169, imchou@usgs.gov; John Besser, (573) 876-1818, jbesser@usgs.gov

Human Resources Office contact: Brian Arnold-Renicker, (703) 648-7468, brenicke@usgs.gov

Summary of Opportunities