The use of geochemical data to model soil mineralogy represents a new application of widely available information with significant potential for environmental risk management. To model soil mineralogy, elements must be apportioned among their mineral hosts. Models require knowledge of which minerals are digested by different acids and estimates of mineral compositions, and they are limited in their degrees of freedom by the number of elements available. Normative mineralogical approaches have been used for rock analyses but are generally not suitable for soils, which are more complex media. Two modeling approaches have been used. One, represented by SEDNORM (Cohen and Ward, 1991), LPNORM (De Caritat et al., 1994), and MODAN (Paktunc, 1998), uses a best-fit solution to a series of linear equations. A second, NORMA (Räisänen et al., 1995), is based on two geochemical digestions, one total (fusion-based) and the other partial (aqua regia-based) and applied to two mineral groups: minerals soluble and minerals insoluble in aqua regia. In Finland, that approach has been successfully applied to soils derived from acidic parent materials.

For MITE II, existing geochemical and mineralogical data collected from soil profiles (Klassen, 2003) will be used to estimate mineralogy. The methodology incorporates the best features of the two modeling approaches represented by NORMA and by MODAN. For the soil profiles, geochemical data are based on parallel analyses of sample splits using weak acid (hydroxylamine hydrochloride), strong acid (aqua regia), very strong acid (HF-HNO3-HCLO4), and total (fusion) digestions, and instrumental neutron activation analyses (INA). Using MODAN, mineral group reconstructions will be carried out in sequence from most labile to most resistate. The use of multiple digestions increases the number of minerals that can be modeled using a constant number of elements. The modeling approach will be verified with reference to mineral analyses of the clay-sized (<0.002mm) and the silt and clay-sized fractions using XRD and SEM-EDS analyses.

Outputs

Protocols that use geochemical data to model soil mineralogy. The work increases the value of geochemical datasets, representing a new basis for characterizing soil properties and interpretation of geochemical background.

Participants

• Dr. R.A. Klassen, Terrain Science Division, GSC.
• Dr. G. Bonham-Carter, Mineral Resources Division, GSC.
• Dr. D. Paktunc, Canadian Metals and Energy Technology Center (CANMET)
• R.D. Knight, Terrain Science Division, GSC.

References

Cohen, D., and Ward, C.R., 1991, SEDNORM-A program to calculate a normative mineralogy for sedimentary rocks based on chemical analyses: Computers and Geoscience, v. 17, p. 1235-1253.

De Caritat, P., Bloch, J., and Hutcheon, I., 1994, LPNORM: A linear programming normative analysis code: Computers and Geoscience, v. 20, p. 313-347.

Klassen, R.A., 2003. Soil profiles in naturally metal-rich terrains of eastern Canada: physical and geochemical data. Open File 1745. Geological Survey of Canada, CD.

Paktunc, A.D., 1998, MODAN: An interactive computer program for estimating mineral quantities based on bulk composition: Computers and Geoscience, v. 24, p. 425-431.

Räisänen, M.L., Tarvainen, T., and Aatos, S., 1995, NORMA - A program to calculate a normative mineralogy for glacial tills and rocks from chemical analysis: Geologiska Foreningan Forhandlingar, v. 117, p. 215-224.