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Sample Design and Analysis for Regional Geochemical Studies¹

ABSTRACT

The compilation of baseline geochemical data prior to the development of large-scale energy projects is necessary in order to assess possible impacts the development may have on the local environment. Most studies are site specific and difficult to integrate where several independent studies are being carried out on adjacent projects. Methods are presented, hierarchial analysis of variance complemented with kriging, to carry out preliminary geochemical baseline determinations over relatively large regions. These efficient, low-cost methods provide data on natural compositional trends with a known degree of reliability. Soil molybdenum from the Piceance Basin of Colorado and Uinta Basin of Utah are used to illustrate the methods. Sample densities ranging from one per 62 km² to one per 0.5 km² are evaluated with respect to effectiveness in presenting the distribution of soil molybdenum of these areas. A sample density of one per 47 km² was determined to be adequate by analysis of variance, for low resolution mapping of a portion of the eastern Uinta basin. Maps generated by geostatitical analysis followed by kriging provide a visual representation of soil molybdenum and the associated estimation variance. A density of one sample per 62 km² was demonstrated not to be adequate for low resolution mapping of soil molybdenum in the Piceance basin. A higher sampling density of one per 0.66 km² was utilized in mapping soil molybdeuum of oil shale Tract C-a and vicinity. Analysis of variance demonstrates this is an adequate density for mapping at higher resolution. Geostatistical analysis and kriging were used to generate an estimate map and variance estimate for Tract C-a and vicinity.

Key Words: oil shale • trace elements • geochemical baseline • kriging • variograms • geostatistics

¹ Supported in part by the U.S. Dep. of Energy, Contract no. EV-10298-2.

² Professor of Geochemistry, Dep. of Chemistry & Geochemistry, Colorado School of Mines, Golden, CO 80401.

Received for publication February 27, 1984.