David M. Sutphin

Statistical variability of the geochemistry and mineralogy of soils in the Maritime Provinces of Canada and part of the Northeast United States

A soil geochemical survey in the Maritime Provinces of Canada and part of the Northeast United States was completed for the North American Soil Geochemistry Landscapes Project. Soil samples, derived largely from unsorted glacial till, were collected over 349 sites, from 0 to 5 cm depth (regardless of horizon), A-, and C-horizons. The 0 to 5 cm depth interval represents the soil of interest in health risk assessments and is termed the Public Health (PH-) layer. The <2 mm fraction of each sample was analysed for a broad suite of major and trace elements using a near-total four-acid digestion, and major mineralogical components were determined by quantitative X-ray diffraction. Multivariate statistical analyses of the logcentred soil geochemistry from the PH-layer and the two soil horizons, and of the soil mineralogy from the A- and C-horizons, reveal distinctive inter-element relationships from deeper soil (represented by the C-horizon) upwards into topsoil (represented by the A-horizon and PH-layer). Statistical dispersion of several elements increases upwards in the soil profile. Maximum data dispersion occurs in the PH-layer and A-horizon soils. Elements including S, P, Pb, Hg, Cd, Se, Mo, Sb, Bi and Sn are relatively enriched in the PH-layer and A-horizon, and are positively correlated with increasing organic carbon contents. The relative enrichment of groups of elements in the C-horizon, in contrast to those elements in the A-horizon and PH-layer, suggests a composition that reflects the geochemistry of the glacial till that is derived from the local bedrock. Elements such as Ni, Mg, Cr, V, Co, Fe and Sc, represent a mafic component of the parent material, and relative enrichments of K, Rb, Zr, rare-earth elements, Li and Al indicate a more felsic component. The patterns revealed by the application of multivariate methods to the soil chemistry and mineralogy are attributed to underlying geology, soil-forming processes, and anthropogenic activity, or combinations of all three factors. Both the soil geochemistry and mineralogy were tested in their ability to predict soil horizon and underlying bedrock lithology or time-stratigraphic assemblages. The geochemistry and mineralogy of the soils are both good for predicting soil horizon; however, the soil geochemistry is better for predicting the underlying lithologies/assemblages than the soil mineralogy.

Characteristics of water-well yields in part of the blue ridge geologic Province in Loudoun County, Virginia

Loudoun County, Virginia, which is located about 50 km to the west of Washington, DC, was the site of intensive suburban development during the 1980s and 1990s. In the western half of the county, the source of water for domestic use has been from wells drilled into the fractured crystalline bedrock of the Blue Ridge Geologic Province. A comprehensive digital database that contains information on initial yield, location, depth, elevation, and other data for 3651 wells drilled in this 825.5-km2 area was combined with a digital geologic map to form the basis for a study of geologic and temporal controls on water-well yields. Statistical modeling procedures were used to determine that mean yields for the wells were significantly different as a function of structural setting, genetic rock type, and geologic map unit. The Bonferroni procedure then was used to determine which paired comparisons contributed to these significant differences. The data were divided into 15 temporal drilling increments to determine if the time-dependent trends that exist for the Loudoun County data are similar to those discovered in a previous study of water-well yields in the Pinardville 7.5-min quadrangle, New Hampshire. In both regions, trends, which include increasing proportions of very low yield wells and increasing well depths through time, and the counterintuitive result of increasing mean well yields through time, were similar. In addition, a yield-to-depth curve similar tothat discovered in the Pinardville quadrangle was recognized in this study. Thus, the temporal model with a feed-forward-loop mechanism to explain the temporal trends in well characteristics proposed for the New Hampshire study appears to apply to western Loudoun County.

Summary of the mineral- and energy-resource endowment, BLM roswell resource area, east-central New Mexico

In this summary of two comprehensive resource reports produced by the U.S. Bureau of Mines and the U.S. Geological Survey for the U.S. Bureau of Land Management, we discuss the mineral- and energyresource endowment of the 14-millon-acre Roswell Resource Area, New Mexico, managed by the Bureau of Land Management. The Bureau and Survey reports result from separate studies that are compilations of published and unpublished data and integrate new findings on the geology, geochemistry, geophysics, mineral, industrial, and energy commodities, and resources for the seven-county area. The reports have been used by the Bureau of Land Management in preparation of the Roswell Resource Area Resource Management Plan, and will have future use in nationwide mineral- and energy-resource inventories and assessments, as reference and training documents, and as public-information tools.In the Roswell Resource Area, many metals, industrial mineral commodities, and energy resources are being, or have been, produced or prospected. These include metals and high-technology materials, such as copper, gold, silver, thorium, uranium and/or vanadium, rare-earth element minerals, iron, manganese, tungsten, lead, zinc, and molybdenum; industrial mineral resources, including barite, limestone/dolomite, caliche, clay, fluorspar, gypsum, scoria, aggregate, and sand and gravel; and fuels and associated resources, such as oil, gas, tar sand and heavy oil, coal, and gases associated with hydrocarbons. Other commodities that have yet to be identified in economic concentrations include potash, halite, polyhalite, anhydrite, sulfur, feldspar, building stone and decorative rock, brines, various gases associated with oil and gas exploration, and carbon dioxide.