Arkansas Geochemistry


As defined by Goldschmidt (1954), geochemistry is the study of the distribution and amounts of the chemical elements in minerals, rocks, soils, water, and the atmosphere, and the study of the circulation of the elements in nature, on the basis of the properties of their atoms and ions. (AGI Glossary of Geology, 1987) More generally, Clarke (1924) defined geochemistry as all geological study involving chemical change. A major concern of geochemistry is the general overall evaluation of the abundances of the elements in the earth's crust and in major classes of rocks and minerals.

The application of geochemistry to geological, economic, and environmental problems is a very powerful tool, when properly applied by those trained in the interpretation of analytical results. However, misinterpretation of data and/or lack of understanding of potential problems can lead to incorrect conclusions from raw or baseline chemical data. Books are published detailing the interpretation and practical application of chemical data to the above mentioned fields. Instruction in the interpretation of analytical data is beyond the scope of this short article.

In Arkansas, selected sets of geochemical data are available for portions of Arkansas, some of which are published as topical studies. Most analyses, however, are published within other bodies of work as tables, charts, and so forth, and not as stand alone studies.

Examples of topical studies include AGS information-circulars 28-A, 30, 32, 33, 35, and 37. These publications examine various aspects of the inorganic geochemistry of lignite and rock units in central and north Arkansas, and organic geochemistry of the Fayetteville Shale. Examples of chemical analyses being published as part of geological studies include AGS information-circulars 20-K, 22, 23, 27, and 34 where tables of analytical data are presented and interpreted as part of the study of coal, black shale, and cinnabar, manganese, and ilmenite deposits in Arkansas. Check the AGS Publications section to find all published AGS geochemical data.

Topics involving geochemistry may vary depending upon the subject of study from very site specific to regional. A statewide geochemical study by the AGS was only recently completed and its data is related to soils and stream sediments, not to rocks.

Trace Metals Found in the Bedrock of the Ouachita Mountain Region of Arkansas

This Microsoft Excel® spreadsheet contains the trace concentrations (expressed in ppm) of arsenic, chromium, copper, lead, mercury, nickel, and zinc in over 700 samples collected from the Ouachita Mountain drainage basins of the Little Missouri, Caddo, Ouachita, and Saline rivers. Each sample is located by latitude and longitude and includes a stratigraphic and lithic description. This is the sample set that formed the basis of AGC information-circulars 32 & 35.

Excel Trace Metals found in the bedrock of the Ouachita Mt. Region of Arkansas

Whole-Rock Geochemical Analyses

The Earth Mapping Resources Program provides support to the State Surveys for geochemical analyses for various critical minerals. Whole-rock analytical geochemical analyses was done by the USGS Geology, Geophysics, and Geochemistry Science Center in Denver, Colorado. Analyses were accomplished for major elements by wavelength dispersive x-ray fluorescence spectrometry (WDXRF) and a 61 element ICP-OES-MS sodium peroxide fusion (ICP-61) package to support minor and trace element analyses, including the rare earth elements.

Geochemical analyses for Batesville Manganese District. Samples in this spreadsheet were collected during field work focusing on the Cason Formation since it contains phosphate and rare earth elements.
Excel Geochemical analyses for Batesville Manganese District

Geochemical analyses for three Devonian sandstone samples. Samples in this spreadsheet were collected to examine Devonian units in Arkansas that may contain phosphate or rare earth elements.
Excel Geochemical analyses for three Devonian sandstone samples