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At least 703 records · Page 39Linked to original sources
USGS2003

The west-central Florida inner shelf and coastal system: A geologic conceptual overview and introduction to the special issue

This paper provides an overview for this special publication on the geologic framework of the inner shelf and coastal zone of west-central Florida. This is a significant geologic setting in that it lies at the center of an ancient carbonate platform facing an enormous ramp that has exerted large-scale control on coastal geomorphology, the availability of sediments, and the level of wave energy. In order to understand the Holocene geologic history of this depositional system, a regional study defined by natural boundaries (north end of a barrier island to the apex of a headland) was undertaken by a group of government and university coastal geologists using a wide variety of laboratory and field techniques. It is the purpose of this introductory paper to define the character of this coastal/inner shelf system, provide a historical geologic perspective and background of environmental information, define the overall database, present the collective objectives of this regional study, and very briefly present the main aspects of each contribution. Specific conclusions are presented at the end of each paper composing this volume. ?? 2003 Elsevier B.V. All rights reserved.

Marine Geology↗
USGS1994

Guidelines for collecting and processing samples of stream bed sediment for analysis of trace elements and organic contaminants for the National Water-Quality Assessment Program

A major component of the U.S. Geological Survey's National Water-Quality Assessment program is to assess the occurrence and distribution of trace elements and organic contaminants in streams. The first phase of the strategy for the assessment is to analyze samples of bed sediments from depositional zones. Fine-grained particles deposited in these zones are natural accumulators of trace elements and hydrophobic organic compounds. For the information to be comparable among studies in many different parts of the Nation, strategies for selecting stream sites and depositional zones are critical. Fine-grained surficial sediments are obtained from several depositional zones within a stream reach and composited to yield a sample representing average conditions. Sample collection and processing must be done consistently and by procedures specifically designed to separate the fine material into fractions that yield uncontaminated samples for trace-level analytes in the laboratory. Special coring samplers and other instruments made of Teflon are used for collection. Samples are processed through a 2.0-millimeter stainless-steel mesh sieve for organic contaminate analysis and a 63-micrometer nylon-cloth sieve for trace-element analysis. Quality assurance is maintained by strict collection and processing procedures, duplicate samplings, and a rigid cleaning procedure.

Open-File Report↗
USGS2022

Baseline gene expression levels in Falkland-Malvinas Island penguins: Towards a new monitoring paradigm

Health diagnostics of wildlife have historically relied on the evaluation of select serum biomarkers and the identification of a contaminant or pathogen burden within specific tissues as an indicator of a level of insult. However, these approaches fail to measure the physiological reaction of the individual to stressors, thus limiting the scope of interpretation. Gene-based health diagnostics provide an opportunity for an alternate, whole-system, or holistic assessment of health, not only in individuals or populations but potentially in ecosystems. Seabirds are among the most threatened marine taxonomic groups in the world, with ~25% of this species currently listed as threatened or considered of special concern; among seabirds, the penguins (Family Spheniscidae) are the most threatened seabird Family. We used gene expression to develop baseline physiological indices for wild penguins in the Falkland-Malvinas Islands, and captive zoo penguins. We identified the almost complete statistical separation of penguin groups (gentoo Detroit Zoo, gentoo Falkland-Malvinas Islands, rockhopper Detroit Zoo, and rockhopper Falkland-Malvinas Islands) based on gene expression profiles. Implementation of long-term longitudinal studies would allow for the assessment of temporal increases or decreases of select transcripts and would facilitate interpretation of the drivers of change.

Life↗
USGS1991

Techniques and strategies for data integration in mineral resource assessment

The Geologic and the National Mapping divisions of the U.S. Geological Survey have been involved formally in cooperative research and development of computer-based geographic information systems (GISs) applied to mineral-resource assessment objectives since 1982. Experience in the Conterminous United States Mineral Assessment Program (CUSMAP) projects including the Rolla, Missouri; Dillon, Montana; Butte, Montana; and Tonopah, Nevada 1?? ?? 2?? quadrangles, has resulted in the definition of processing requirements for geographically and mineral-resource data that are common to these studies. The diverse formats of data sets collected and compiled for regional mineral-resource assessments necessitate capabilities for digitally encoding and entering data into appropriate tabular, vector, and raster subsystems of the GIS. Although many of the required data sets are either available or can be provided in a digital format suitable for direct entry, their utility is largely dependent on the original intent and consequent preprocessing of the data. In this respect, special care must be taken to ensure the digital data type, encoding, and format will meet assessment objectives. Data processing within the GIS is directed primarily toward the development and application of models that can be used to describe spatially geological, geophysical, and geochemical environments either known or inferred to be associated with specific types of mineral deposits. Consequently, capabilities to analyze spatially, aggregate, and display relations between data sets are principal processing requirements. To facilitate the development of these models within the GIS, interfaces must be developed among vector-, raster-, and tabular-based processing subsystems to reformat resident data sets for comparative analyses and multivariate display of relations.

Conference Paper↗
USGS1973

A study of the distribution of the polychlorinated biphenyls in the aquatic environment

Data gathered from monitoring activities and project studies indicate the ubiquitous occurrence and distribution of polychlorinated biphenyls in the aquatic environment. Residues have been detected in samples from 19 States, representing nearly every region of the country. Concentrations ranged from 0.1 to 4.0 ug/l in unfiltered water samples and 5.0 to 3,200 ug/kg in bottom sediments. PCB residues were also found in fish and aquatic plants. Samples were prepared by the same techniques used for general chlorinated insecticide detection, with special attention to cleanup and separation of PCB's from other compounds. Basic identification and quantification were made by dual-column electron-capture gas chromatography and confirmed by gas chromatography mass spectrometry whenever possible. The sampling program is expected to be broadened geographically in 1973 and increased in successive years in order to more adequately define the distribution of PCB residues in the major drainage basins of the United States.

Journal of Research of the U.S. Geological Survey↗
USGS1953

A life history study of the yellow throat

Investigations concerning the life history of the Yellow-throat were made in southern Michigan during the spring and summer of 1938. Supplementary information was also obtained at Arlington, Virginia, in 1940 and at the Patuxent Research Refuge, Maryland, in 1947.....Resident males established territories almost immediately upon arrival in spring. In southern Michigan some resident males arrived at least as soon as, if not before, transient males. Most females appeared on their nesting ground about a week later. Adults were engaged in nesting activities from the time of their arrival in spring until the advent of the post-nuptial molt in late summer.....Typical Yellow-throat habitat consists of a mixture of a dense herbaceous vegetation and small woody plants in damp or wet situations. At Ann Arbor, the Yellow-throat was a common breeding species in its restricted suitable habitat. The population density in one area of suitable habitat was about 69 territorial males per 100 acres. Of 11 territorial males that were intensively studied, one was polygamous (with two mates), nine were monogamous, and one was probably monogamous (with at least one mate).....The song of the individual Yellow-throat was heard throughout the breeding season except for the courtship period. Two major types of song were the common song given while perched, and an occasional, more elaborate, flight song. Most males sing in spurts, singing at fairly regular intervals for a considerable period and then abruptly ceasing for another period. The vocabulary of both sexes included several types of call notes that appeared either to have special functions or to represent outward expressions of distinct emotional states of the bird.....Resident males were antagonistic toward each other throughout the breeding season. Most remained on well-established territories during this period. Territories of 10 monogamous males ranged in size from .8 to 1.8 acres but the territory of one polygamous male occupied. 3.4 acres. The behavior of males during inter-territorial encounters was similar in some respects to their behavior when courting females.....While courting females, the males are very attentive and seldom sing for about one week. During the courtship period the female locates the nesting site and builds the nest without assistance from the male.....Nests, constructed of dried plant materials, were situated on or near the ground and were supported on all sides by stems of herbaceous plants or limbs of shrubs. Many nests were composed of three layers with the coarser materials being used in the outer layer.....The full clutch of eggs in 12 nests ranged from 4 to 6 (average, 4.6). Early clutches seem to be larger than later ones. After the first egg is laid, one is laid on each succeeding day until the clutch is complete. Incubation period is about 12 days. Incubation is only by the female. Records of daytime incubation schedules of three females about half way through incubation indicate that the periods spent on and off the nests average about 61 and 16 minutes, respectively.....Young Yellow-throats usually remain in the nest for eight or nine days. During this period they grow and develop rapidly. Their weight quintuples in six days. Both sexes are active in feeding the young and in removing excreta from the nest. Records of feeding at three nests showed a range of one feeding per 5 1/2 minutes to one feeding per 22 minutes, the rate increasing with age of young. Adults care for the young for at least two weeks after the young leave the nest.....Ten of 12 females that were intensively studied were successful in raising young beyond the nestling stage. Only one of these raised two broods, although three females built at least three nests each. In 19 nests, 11 (58 per cent) produced nestlings and 7 (37 per cent) produced fledglings. In total, the 19 nests produced an average of one fledgling Yellow-throat per nest. Of 22 nests that were found near Ann Arbor, 10 (45

The Wilson Bulletin↗
USGS1955

A study of radioactivity in modern stream gravels and its possible application as a prospecting method

Traverses along some streams of the Colorado Plateau in areas known to contain minable uranium deposits show that anomalous radiation in the stream gravels can be detected with a suitable counter downstream from the deposits. The amount of radiation is influenced by the size of the uranium deposit, the size of the drainage area of the stream, the grain size of the sediments, and the lithology of the rocks over which the stream flows. The spacing of the stations where readings are taken is controlled by the size of the stream, and special readings are also taken directly downstream from important tributaries. An anomaly is empirically defined as a 10 percent rise over background. Radioactive material from large uranium deposits has been detected as much as 1 mile downstream. Radioactive material from smaller deposits is detachable over shorter distances. The method is slow but appears to be a useful prospecting tool under restricted conditions.

Colorado;Utah↗
USGS2009

One size does not fit all: Adapting mark-recapture and occupancy models for state uncertainty

Multistate capture?recapture models continue to be employed with greater frequency to test hypotheses about metapopulation dynamics and life history, and more recently disease dynamics. In recent years efforts have begun to adjust these models for cases where there is uncertainty about an animal?s state upon capture. These efforts can be categorized into models that permit misclassification between two states to occur in either direction or one direction, where state is certain for a subset of individuals or is always uncertain, and where estimation is based on one sampling occasion per period of interest or multiple sampling occasions per period. State uncertainty also arises in modeling patch occupancy dynamics. I consider several case studies involving bird and marine mammal studies that illustrate how misclassified states can arise, and outline model structures for properly utilizing the data that are produced. In each case misclassification occurs in only one direction (thus there is a subset of individuals or patches where state is known with certainty), and there are multiple sampling occasions per period of interest. For the cases involving capture?recapture data I allude to a general model structure that could include each example as a special case. However, this collection of cases also illustrates how difficult it is to develop a model structure that can be directly useful for answering every ecological question of interest and account for every type of data from the field.

Book chapter↗
USGS1992

Regional evaluations of acid deposition effects on forests: Eastern spruce-fir

Having reviewed the results of the Integrated Forest Study (IFS) project, we now try to place the results in a larger perspective by very briefly summarizing acid deposition effects and their potential role in forest health in the several forest types represented in the IFS project. This chapter gives brief overviews of the situation in eastern spruce-fir, eastern hardwood, and southern pine forests in North America; and a very brief overview of air pollution in arid forest ecosystems in Europe (with special emphasis on the situation in Norway where the single European IFS site was located). What follows in this chapter is by no means intended to be a comprehensive review of forest health and atmospheric deposition; such an analysis would require a volume of this size for each forest type and is well beyond the scope of this chapter. A comprehensive analysis of forest health and the role of atmospheric deposition has been published for Norway spruce in Europe (Schulze et al. 1989), and one is in preparation for red spruce (Eagar and Adams, in press); the reader is referred to those volumes for a far more detailed discussion than is possible here. The intent of this chapter is merely to highlight those aspects of forest health and atmospheric deposition that have bearing on, or that can be illuminated by, the IFS results.

Book chapter↗
USGS2014

Understanding thermodynamic relationships and geochemical mass balances from catchment to coast: A tribute to the life and career of Owen P. Bricker III

This special volume of aquatic geochemistry is dedicated to the memory of Owen Peterson Bricker III (1936–2011) and serves as a tribute to his life and career. Owen had a distinguished and productive research career in both academics at Johns Hopkins University (Fig. 1) and as a public servant with the Maryland Geological Survey, the US Environmental Protection Agency, and the US Geological Survey. He was a pioneer and leader in aqueous geochemistry, who applied a study approach that quantified mineral weathering reactions and equilibrium thermodynamic relations to better understand the chemical evolution of stream water in small watersheds. He will be especially remembered for his efforts to establish rigorous field studies in small catchments around the United States as a means of quantifying the sources of acid-neutralizing capacity that affect the chemical status and biological health of natural waters.

Aquatic Geochemistry↗
USGS2016

Establishing links between streamflow and ecological integrity in the Sudbury River (Northeastern U.S.)

With increased pressure from a growing human population, managers are challenged to understand how novel disturbances (e.g., climate change, increased water withdrawals, urbanization) may affect natural resources. The Sudbury River is a National Wild and Scenic River located in suburban Boston, Massachusetts (Northeastern US) with myriad impairments (e.g., mainstem impoundments, withdrawals, and urbanization) that is under increasing pressure from hydrologic alteration. We sampled fish, mussel, and macroinvertebrate assemblages in the Sudbury River and used species traits to investigate potential effects of past and future flow alteration on biota. Analysis of 33 years of stream gage data indicates continued hydrologic alteration of the Sudbury River, likely related to increased urbanization and water withdrawals over that time. These changes include a roughly 200% increase in rise rates of flows, an approximate 65% decrease in 1-day minimum flows, and a trend towards increasing high flow pulse counts. Biotic sampling in summer of 2014 demonstrated that the Sudbury River is now dominated by generalist species. Of five mussel species sampled, all are generalists in their habitat requirements. Though one mussel species of special concern was sampled, the most abundant species collected were the widespread Eastern elliptio (58%) and Eastern lampmussel (40%). We used the target fish community (TFC) model to assess the degree to which the fish assemblage deviated from that expected for a river with similar zoogeographic and physical features. Overall, the current community has a 22.7% similarity to the TFC. Of the four fluvial specialist species present in the TFC, only fallfish was sampled in our study. While the TFC showed that the historical assemblage was likely dominated by fluvial specialist and fluvial dependent species, the current assemblage is overwhelmingly dominated by macrohabitat generalists (90.6% of fishes sampled). These results are consistent with other studies that show shifts in assemblages from fluvial specialists to habitat generalists with hydrologic alteration. If the current trends continue, it is likely that biotic assemblages will experience increasing pressure from hydrologic alteration. While hydrologic alteration is likely impacting biotic assemblages in the Sudbury River, other factors such as high temperatures, low dissolved oxygen, high nutrients, low availability of high-quality habitat, and poor habitat connectivity may also be negatively impacting biotic assemblages. Comparisons to other rivers and a complete longitudinal habitat survey could help to identify availability of unique habitats and representativeness of this study. While this study suggests impacts of flow on biota, future studies with quantitative, habitat-specific sampling during different flow levels could help to directly identify links between hydrologic alteration and biotic impairment in the Sudbury River.

Massachussetts↗
USGS2002

Geographic information systems compilation of geophysical, geologic, and tectonic data for the Bering Shelf, Chukchi Sea, Arctic margin, and adjacent landmasses

The accompanying CD-ROM contains a compilation of geophysical, geologic, and tectonic data for the Bering Shelf, the Chukchi Sea, the Arctic margin, and adjacent landmasses. These data sets focus on Alaska, the Russian Far East, and the continental shelves that link these two landmasses. For compatibility with other available geographic information system (GIS) products, our GIS compilation extends from 120°E to 115°W, and from 40°N to 80°N. This area encompasses the region from the modern Paciµc plate boundary of the Japan, Kurile, and Aleutian subduction zones, the Queen Charlotte transform fault, and the Cascadia subduction zone (in the south) to the continent-ocean transition from the Eurasian and North American continents to the Arctic Ocean (in the north); and from the diffuse Eurasian–North American plate boundary, including the probable Okhotsk plate (in the west) to the Alaskan-Canadian Cordilleran fold belt (in the east). The CD-ROM comprises thematic layers of spatial data sets for topography, gravity µeld, magnetic µeld, earthquakes, volcanoes, geology, tectonostratigraphic terranes, and cultural reference features, and also includes metadata (data about the data) for all these data sets. The spatial data sets can be viewed, analyzed, and plotted with commercial GIS software (ArcView and ARC/Info) or through a freeware program (ArcExplorer) that is included on this CD-ROM. This GIS compilation provides data for studies of the Mesozoic and Cenozoic collisional and accretionary tectonics that assembled this continental crust and of the neotectonics of active and passive plate margins in this region, and for constructing and interpreting geophysical, geologic, and tectonic models of the region.

Alaska↗
USGS2003

Land use and land cover change in the Greater Yellowstone Ecosystem: 1975-1995

Shifts in the demographic and economic character of the Greater Yellowstone Ecosystem (GYE) are driving patterns of land cover and land use change in the region. Such changes may have important consequences for ecosystem functioning. The objective of this paper is to quantify the trajectories and rates of change in land cover and use across the GYE for the period 1975-1995 using satellite imagery. Spectral and geographic variables were used as inputs to classification tree regression analysis (CART) to find "rules" which defined land use and land cover classes on the landscape. The resulting CART functions were used to map land cover and land use across seven Landsat TM scenes for 1995. We then used a thresholding technique to identify locations that differed in spectral properties between the 1995 and 1985 time periods. These "changed" locations were classified using CART functions derived from spectral and geographic data from 1985. This was similarly done for the year 1975 based on Landsat MSS data. Differences between the 1975, 1985, and 1995 maps were considered change in land cover and use. We calibrated and tested the accuracy of our models using data acquired through manual interpretation of aerial photos. Elevation and vegetative indices derived from the remotely sensed satellite imagery explained the most variance in the land use and land cover classes (-i.e., defined the "rules" most often). Overall accuracies from our study were good, ranging from 94% at the coarsest level of detail to 74% at the finest. The largest changes over the study period were the increases in burned, urban, and mixed conifer-herbaceous classes and decreases in woody deciduous, mixed woody deciduous-herbaceous, and conifer habitats. These changes have important implications for ecological function and biodiversity. The expansion of mixed conifer classes may increase fuel loads and enhance risk to the growing number of rural homes. The reduction of woody deciduous cover types is likely reducing population sizes for the numerous plant and animal species that specialize on this habitat type. Some of these species are also negatively influenced by the increase of rural homes in and near woody deciduous habitats.

Idaho, Montana, Wyoming↗
USGS2019

Primarily resident grizzly bears respond to late-season elk harvest

Autumn ungulate hunting in the Greater Yellowstone Ecosystem carries the risk of hunter–grizzly bear ( Ursus arctos ) conflict and creates a substantial challenge for managers. For Grand Teton National Park, Wyoming, USA, a key information need is whether increased availability of elk ( Cervus canadensis ) carcasses during a late autumn (Nov–Dec) harvest within the national park attracts grizzly bears and increases the potential for conflict with hunters. Using a robust design analysis with 6 primary sampling periods during 2014–2015, we tested the hypothesis that the elk harvest resulted in temporary movements of grizzly bears into the hunt areas, thus increasing bear numbers. We detected 31 unique individuals (6 F, 25 M) through genetic sampling and retained 26 encounter histories for analysis. Markovian movement models had more support than a null model of no temporary movement. Contrary to our research hypothesis, temporary movements into the study area occurred between the July–August (no hunt; N̄ 2014–2015 = 5) and September–October (no hunt; N̄ 2014–2015 = 24) primary periods each year, rather than during the transition from September–October (no hunt) to November–December (hunt; N̄ 2014–2015 = 15). A post hoc analysis indicated that September–October population estimates were biased high by detections of transient bears. Grizzly bear presence during the elk hunt was limited to approximately 15 resident bears that specialized in accessing elk carcasses. The late timing of the elk hunt likely moderated the effect of carcasses as a food attractant because it coincides with the onset of hibernation. From a population response perspective, the current timing of the elk harvest likely represents a scenario of low relative risk of hunter–bear conflicts. The risk of hunter–grizzly bear encounters remains, but may be more a function of factors that operate at the level of individual bears and hunters, such as hunter movements and bear responses to olfactory cues.

Wyoming↗
USGS1981

Post-fire succession of the herbaceous flora in southern California chaparral

Postfire succesion of the temporary herbaceous and suffrutescent cover was studied after chaparral fires in San Diego County, California, USA. Four categories of species make up the temporary cover. (1) "Generalized herbaceous perennials" are present before and after fire. Populations of these herbs are sparse under the shrub canopy. They resprout after fire from bulbs or other underground parts and postfire populations are sparse. (2) "Generalized annuals" are present in openings before fire but produce their peak population size in the first few years after fire. (3) Specialized "fire—annuals" are more or less restricted to the 1st postfire yr. (4) Specialized "fire—perennials" (subshrubs) are uncommon before fire, establish from seed in the 1st postfire yr and reach maximum cover in the 3rd and 4th yr. Community—level changes in cover and diversity are interpreted in light of differences in population dynamics of the four groups. Specis richness was highest in the 1st yr after fire because this was the only time all four groups were present together. Throughout succession herbaceous species richness was positively related to herb cover, negatively related to elevation and unrelated to slope aspect. The number of annual species fluctuated greatly through succession at all sites, but the number of herbaceous perennials did not. Herb cover fluctuated markedly from year to year and was positively related to amount of annual precipitation and negatively related to subshrub or "fire—perennial" cover. Artificial seeding with annual rye grass Lolium multiflorum had not apparent effect on total herb cover since sites with poor Lolium establishment had as high or higher herb cover as sites with high Lolium establishment. Lolium success was at the expense of the native cover and this negative effect was greatest on the "fire annuals."

Ecology↗
USGS2005

Remote sensing for environmental site screening and watershed evaluation in Utah Mine lands: East Tintic mountains, Oquirrh mountains, and Tushar mountains

Imaging spectroscopy-a powerful remote-sensing tool for mapping subtle variations in the composition of minerals, vegetation, and man-made materials on the Earth's surface-was applied in support of environmental assessments and watershed evaluations in several mining districts in the State of Utah. Three areas were studied through the use of Landsat 7 ETM+ and Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data: (1) the Tintic mining district in the East Tintic Mountains southwest of Provo, (2) the Camp Floyd mining district (including the Mercur mine) and the Stockton (or Rush Valley) mining district in the Oquirrh Mountains south of the Great Salt Lake, and (3) the Tushar Mountains and Antelope Range near Marysvale. The Landsat 7 ETM+ data were used for initial site screening and the planning of AVIRIS surveys. The AVIRIS data were analyzed to create spectrally defined maps of surface minerals with special emphasis on locating and characterizing rocks and soils with acid-producing potential (APP) and acid-neutralizing potential (ANP). These maps were used by the United States Environmental Protection Agency (USEPA) for three primary purposes: (1) to identify unmined and anthropogenic sources of acid generation in the form of iron sulfide and (or) ferric iron sulfate-bearing minerals such as jarosite and copiapite; (2) to seek evidence for downstream or downwind movement of minerals associated with acid generation, mine waste, and (or) tailings from mines, mill sites, and zones of unmined hydrothermally altered rocks; and (3) to identify carbonate and other acid-buffering minerals that neutralize acidic, potentially metal bearing, solutions and thus mitigate potential environmental effects of acid generation. Calibrated AVIRIS surface-reflectance data were spectrally analyzed to identify and map selected surface materials. Two maps were produced from each flightline of AVIRIS data: a map of iron-bearing minerals and water having absorption features in the spectral region from 0.35 µ m to 1.35 µ m and a map of minerals (including clays, sulfates, micas, and carbonates) having absorptions in the spectral region from 1.45 µ m to 2.51 µ m. Several methods were used to verify the AVIRIS mapping results, including field checking of selected locations with a portable spectrometer, visual inspection of the AVIRIS reflectance spectra, and X-ray diffraction (XRD) analysis of field samples. The maps of iron-bearing minerals derived from analysis of the visible (VIS) and near-infrared (NIR) regions of the electromagnetic spectrum were shown to be more consistently reliable in indicating the presence of jarosite than were the maps generated from analysis of the short-wave infrared (SWIR) region. When present in abundance, phyllosilicate minerals tend to dominate the SWIR and mask the spectral features of jarosite in that wavelength region. The crystal field absorptions of jarosite in the VIS and NIR spectral regions will commonly be present regardless of whether the Fe-OH absorption feature near 2.27 µ m can be detected. For this reason, the VIS and NIR were preferable to the SWIR for the remote spectroscopic identification of jarosite (and other iron-bearing minerals). Large exposures of unmined hydrothermally altered rocks occur throughout the three study areas. These rocks commonly contain sulfide or sulfate minerals that produce sulfuric acid upon subaerial oxidation. The acid may be introduced into local surface and ground water and thus lower the baseline (that is, the premining) pH for a watershed.

Utah↗
USGS1980

A generalized garnet-forming reaction for metaigneous rocks in the Adirondacks

A generalized reaction is presented to account for garnet formation in a variety of Adirondack metaigneous rocks. This reaction, which is the sum of five partial reactions written in aluminum-fixed frames of reference, is given by: 4(y+1+w)Anorthite+4 k(y+1+2 w)Olivine +4(1-k)(y+1+2 w)Fe-oxide+(8(y+1) -4 k(y+1+2 w))Orthopyroxene = 2(y+1)Garnet +2(y+1+2 w)Clinopyroxene+4 wSpinel where y is a function of plagioclase composition, k refers to the relative amounts of olivine and Fe-oxide participating in the reaction, and w is a measure of silicon mobility. When mass balanced for Mg and Fe, this reaction is found to be consistent with analyzed mineral compositions in a wide range of Adirondack metaigneous rocks. The reaction applies equally well whether the garnets were formed directly from the rectants given above or went through an intermadiate stage involving the formation of spinel, orthopyroxene, and clinopyroxene. The actual reactions which have produced garnet in both undersaturated and quartz-bearing rocks are special cases of the above general reaction. The most important special cases appear to be those in which the reactants include either olivine alone (k=1) or Fe-oxide alone (k=0). Silicon is relatively immobile (w =2) in olivine bearing, magnesium-rich rocks (k???1), and this correlates with the increased intensity in spinel clouding of plagioclase in these rocks. Silicon mobility apparently increases in the more iron-rich rocks, which also tend to contain clear or lightly clouded plagioclase. In all the rocks studied the most common composition of metamorphic plagioclase is close to An33 (i.e., y=1). Plagioclase of lower anorthite content may be too sodic to participate in garnet formation at the P-T conditions involved. ?? 1980 Springer-Verlag.

Contributions to Mineralogy and Petrology↗
USGS1984

Characteristics of some silver-, and base metal-bearing, epithermal deposits of Mexico and Peru

Introduction Lithotectonic, mineralogical, and geochemical data on two silver- and base metal-bearing deposits from Peru and two from Mexico are compiled to facilitate comparisons with other epithermal deposits. Silver and base metal-bearing deposits of Mexico and Peru constitute an important portion of the world silver production derived from shallow, vein-type deposits hosted in volcanic rocks. Although these deposits are generally similar to epithermal deposits of Nevada and Colorado in the western United States, they have some important differences. Because of this, data on the geological attributes of these deposits are very useful for developing models of ore formation that can be used in mineral exploration. The data collected for this compilation are presented in the following pages in summaries of the important characteristics of each deposit. This compilation, which shows the complexities in the geology of epithermal ore deposits in Mexico and Peru, serves as a basis for further comparisons among epithermal deposits throughout the world. The case studies provide data useful to geologists and exploration!'sts interested in developing models of ore formation to be used in exploration for mineral deposits of this type. The deposits described in this report are the Guanajuato district of Guanajuato, Mexico, the Pachuca-Real del Monte district of Hidalgo, Mexico, the Colqui district of Lima, Peru, and the Julcani district of Huancavelica, Peru. Although many characteristics of the geology and geochemistry of this type of deposit were considered, the most important criterion for choosing these deposits was that they have substantial quantities of precious- and base-metal mineralization. Additional criteria for selecting the deposits were that they be hosted primarily by calc-alkaline volcanic rocks of intermediate to silicic composition and that they be younger than Tertiary in age. Many deposits in Mexico and Peru and other parts of Central and South America were excluded because the literature describing the districts is not readily available. Furthermore, many districts have not been examined in detail or the information available is of limited geological scope. The four districts that are compiled in this report were chosen because they are described in abundant literature dating from early mining reports on the general geology and mineralogy to very recent data on detailed geochemical and mineralogical studies. They were chosen as being fairly typical, classic examples of near-surface, low-temperature vein deposits as described by Lindgren (1928) in his treatise on ore deposits (Mineral deposits, McGraw-Hill, 1049 p.). These deposits are similar in aspects of their geology and geochemistry to many of the famous, epithermal silver mining districts in Colorado and Nevada including Creede, Colorado, Tonapah, Nevada, and the Sunnyside Mine of the Eureka district, Colorado, and, in the special case of Julcani, to Summitville, Colorado, and Goldfield, Nevada. The characteristics that distinguish them include overall size, production and alteration assemblage. The information documented in each summary will be used in a forthcoming series of papers on the comparative anatomy of precious and base metal deposits in North and South America.

Guanajuato, Hidalgo. Huancavelica, Lima↗