Chemical analyses of rock samples collected in east-central Idaho during a study of mineralization in the northern Lemhi Range, Lemhi County, Idaho

Abstract

An improved method for the determination of trace levels of arsenic and antimony in geologic materials by automated hydride generation-atomic absorption spectroscopy:

Solute sources and water mixing in a flashy mountainous stream (Pahsimeroi River, U.S. Rocky Mountains): Implications on chemical weathering rate and groundwater–surface water interaction

“…1). The basement rocks cover large proportions of the Lemhi Range and comprise the Mid-Proterozoic Swauger Formation containing mainly fluvio-lacustrine feldspathic arenites (N 80% quartz, b12% K-feldspar; b1% lithic fragments) (Connor et al, 1991). Carbonate rocks occur mainly in the southwestern parts of the watershed in the Lost River Range as thick limestone and dolomite banks (Fisher et al, 1992; Link and Janecke, 1999).…”

“…It is therefore important to apply Ca/Na sil and Mg/Na sil ratios of watershedrepresentative and relatively unaltered silicate bedrock samples. To account for uncertainty in the calculated chemical weathering rates, we utilize two sets of Ca/Na sil and Mg/Na sil ratios: (1) values of 0.63 (Ca/Na sil ) and 0.92 (Mg/Na sil ) corresponding to the geometric mean ionic ratios of silicate bedrock samples (equal proportions of volcanic and metamorphic rocks) collected in Central Idaho (data from McIntyre et al, 1982;Connor et al, 1991), and (2) values of 1.50 (Ca/Na sil ) and 2.06 (Mg/Na sil ) which correspond to the geometric mean Ca/Na and Mg/Na values of the volcanic and metamorphic source waters in the study area. These are assumed to be influenced only by silicate weathering without major contribution from secondary calcite dissolution or atmospheric precipitation (mean precipitation Ca/Na and Mg/Na = 0.17 and 0.30, respectively).…”