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Two toxic-unit models that estimate the toxicity of trace-metal mixtures to benthic communities were compared. The chronic criterion accumulation ratio (CCAR), a modification of biotic ligand model (BLM) outputs for use as a toxic-unit model, accounts for the modifying and competitive influences of major cations (Ca²(+), Mg²(+), Na(+), K(+), H(+)), anions (HCO₃⁻, CO²⁻₃ ,SO²⁻₄, Cl⁻, S²⁻) and dissolved organic carbon (DOC) in determining the free metal ion available for accumulation on the biotic ligand. The cumulative criterion unit (CCU) model, an empirical statistical model of trace-metal toxicity, considers only the ameliorative properties of Ca²(+) and Mg²(+) (hardness) in determining the toxicity of total dissolved trace metals. Differences in the contribution of a metal (e.g., Cu, Cd, Zn) to toxic units as determined by CCAR or CCU were observed and attributed to how each model incorporates the influences of DOC, pH, and alkalinity. Akaike information criteria demonstrate that CCAR is an improved predictor of benthic macroinvertebrate community metrics as compared with CCU. Piecewise models depict great declines (thresholds) in benthic macroinvertebrate communities at CCAR of 1 or more, while negative changes in benthic communities were detected at a CCAR of less than 1. We observed a 7% reduction in total taxa richness and a 43% decrease in Heptageniid abundance between background (CCAR = 0.1) and the threshold of chronic toxicity on the basis of continuous chronic criteria (CCAR = 1). In this first application of the BLM as a toxic-unit model, we found it superior to CCU.

Sample of spheroidal sphalerite with dendritic sphalerite, galena, and iron sulfides (pyrite plus marcasite) from the Pomorzany mine. Note the "up direction" is indicated by "snow-on-the-roof" texture of galena and sphalerite alnong colloform layers of light-colored spahlerite. Hydrothermal sulfide clasts in the left center of the sample are encrusted by sphalerire and iron sulfides. Size of sample is 20x13 cm. Photo by David Leach. Chapter A of Mineral Deposit Models for Resource Assessment COVER:Sample of spheroidal sphalerite with dendritic sphalerite, galena, and iron sulfides (pyrite plus marcasite) from Pomorzany mine. Note the "up direction" is indicated by "snow-on-the-roof" texture of galena and sphalerite along colloform layers of light-colored sphalerite. Hydrothermal sulfide clasts in the left center of the sample are encrusted by sphalerite and iron sulfides. For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprodTo order this and other USGS information products, visit http://store.usgs.gov Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. AbstractThis report is a descriptive model of Mississippi ValleyType (MVT) lead-zinc deposits that presents their geological, mineralogical and geochemical attributes and is part of an effort by the U.S. Geological Survey Mineral Resources Program to update existing models and develop new models that will be used for an upcoming national mineral resource assessment. This deposit modeling effort by the USGS is intended to supplement previously published models for use in mineral-resource and mineral-environmental assessments. Included in this report are geological, geophysical and geochemical assessment guides to assist in mineral resource estimation. The deposit attributes, including grade and tonnage of the deposits described in this report are based on a new mineral deposits data set of all known MVT deposits in the world.Mississippi Valley-Type (MVT) lead-zinc deposits are found throughout the world but the largest, and more intensely researched deposits occur in North America. The ores consist mainly of sphalerite, galena, and generally lesser amounts of iron sulfides. Silver is commonly an important commodity, whereas Cu is generally low, but is economically important in some deposits. Gangue minerals may include carbonates (dolomite, siderite, ankerite, calcite), and typically minor barite. Silicification of the host rocks (or quartz gangue) is generally minor, but may be abundant in a few deposits. The deposits have a broad range of rel...

Geologic processes strongly influence water and sediment quality in aquatic ecosystems but rarely are geologic principles incorporated into routine biomonitoring studies. We test if elevated concentrations of metals in water and sediment are restricted to streams downstream of mines or areas that may discharge mine wastes. We surveyed 198 catchments classified as "historically mined" or "unmined," and based on mineral-deposit criteria, to determine whether water and sediment quality were influenced by naturally occurring mineralized rock, by historical mining, or by a combination of both. By accounting for different geologic sources of metals to the environment, we were able to distinguish aquatic ecosystems limited by metals derived from natural processes from those due to mining. Elevated concentrations of metals in water and sediment were not restricted to mined catchments; depauperate aquatic communities were found in unmined catchments. The type and intensity of hydrothermal alteration and the mineral deposit type were important determinants of water and sediment quality as well as the aquatic community in both mined and unmined catchments. This study distinguished the effects of different rock types and geologic sources of metals on ecosystems by incorporating basic geologic processes into reference and baseline site selection, resulting in a refined assessment. Our results indicate that biomonitoring studies should account for natural sources of metals in some geologic environments as contributors to the effect of mines on aquatic ecosystems, recognizing that in mining-impacted drainages there may have been high pre-mining background metal concentrations.

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