CoGeochemData: Colorado geochemical data

In USGS-R/GcClust: Clustering geochemical data with HMC sampling

Colorado geochemical data

Description

In 2006, soil samples were collected at 960 sites (1 site per 280 square kilometers) throughout the state of Colorado. These samples were collected from a depth of 0-15 centimeters and, following a near-total multi-acid digestion, were analyzed for a suite of 44 major and trace elements.

Usage

CoGeochemData

Format

The organization of the data is described in the package documentation.

Details

The data are from Smith and others (2010); selected summary statistics of these data are presented in Ellefsen and others (2014).

These data have been edited to make them suitable for analysis. First, field sample "06co437" has been deleted because it has an anomalously high copper concentration. Second, elements silver (Ag), cesium (Cs), mercury (Hg), tellurium (Te), and selenium (Se) have been deleted because 98%, 77%, 69%, 94%, and 45%, respectively, of the measured concentrations are below the lower limit of determination. (The lower limit of determination is the threshold for left-censoring.) The lower limits of determination are listed in Table 1 of Smith et al., 2010.

Third, elements antimony (Sb), arsenic (As), bismuth (Bi), cadmium (Cd), indium (In), phosphorous (P), and sulfur (S) have 0.208%, 0.417%, 1.15%, 5.62%, 14.1%, 0.521%, and 3.02%, respectively, of the measured concentrations below the lower limit of determination. These left-censored concentrations were assigned concentrations equal to 0.65 times their respective lower limit of determination (Palarea-Albaladejo and others, 2014). Finally, element concentrations were scaled, as necessary, so that the units for all concentrations are "mg/kg" or equivalently "ppm".

After this editing, there are 959 field samples for which 39 element concentrations are reported. The locations of the field samples are specified by lattitude and longitude using the WGS84 datum.

Source

http://pubs.usgs.gov/ds/520/

References

Ellefsen, K.J., Smith, D.B., Horton, J.D., 2014, A modified procedure for mixture-model clustering of regional geochemical data: Applied Geochemistry, vol. 51, p. 315-326, doi: https://doi.org/10.1016/j.apgeochem.2014.10.011.

Palarea-Albaladejo, J., Martin-Fernandez, J.A., Buccianti, A., 2014, Compositional methods for estimating elemental concentrations below the limit of detection in practice using R: Journal of Geochemical Exploration, vol. 141, p. 71-77, doi: https://doi.org/10.1016/j.gexplo.2013.09.003.

Smith, D.B., Ellefsen, K.J., and Kilburn, J.E., 2010, Geochemical data for Colorado soils-Results from the 2006 state-scale geochemical survey: U.S. Geological Survey, Data Series 520, 9 p.

USGS-R/GcClust documentation built on April 17, 2023, 8:08 p.m.