Geology Reports⌕ Search

Geology topics

Sharon F. Diehl

Publications and source records attributed to Sharon F. Diehl.

At least 19 recordsLinked to original sources
USGS2021

Geologic and hydrogeologic characteristics of the White River Formation, Lance Formation, and Fox Hills Sandstone, northern greater Denver Basin, southeastern Laramie County, Wyoming

In cooperation with the Wyoming State Engineer’s Office, the U.S. Geological Survey studied the geologic and hydrogeologic characteristics of Cenozoic and Upper Cretaceous strata at a location in southeastern Laramie County within the Wyoming part of the Cheyenne Basin, the northern subbasin of the greater Denver Basin. The study aimed to improve understanding of the aquifers/aquifer systems in these strata, motivated in part by declining groundwater levels and interest in exploring future groundwater supplies. Based on detailed geologic characterization using information obtained by drilling and coring a 960-foot-(ft) deep exploratory borehole, and comparisons with previously published descriptions, identified Cenozoic lithostratigraphic units included 40 ft of Quaternary older alluvial fan deposits consisting of an unconsolidated mixture of sand and gravel with lesser quantities of silt and clay in varying proportions and the underlying 407.3-ft-thick White River Formation of late Eocene-Oligocene age consisting largely of mudrocks with sparse thin beds of sandstone, muddy gravel, and conglomeratic mudrocks. Identified Upper Cretaceous lithostratigraphic units included the 351.6-ft-thick Lance Formation, consisting of terrestrial sedimentary rocks including mudrocks (muddy shale and silty and sandy shale, siltstone, claystone, and mudstone) interbedded with much smaller quantities of very fine- to medium-grained muddy and silty sandstone and coal; the 79.6-ft-thick Fox Hills Sandstone, consisting of a transitional marine sequence of muddy or silty sandstone present in five individual beds; and 86.7 ft of the upper transition member of the Pierre Shale, consisting largely of marine sedimentary rocks such as muddy shale. Beds of the upper and lower Fox Hills Sandstone were separated by tongues of the Lance Formation and upper transition member of the Pierre Shale, respectively. The White River hydrogeologic unit, consisting of the entire White River Formation or Group at the study site, did not contain any substantial secondary permeability features in the mudrocks that composed almost all the unit. A monitoring well (BR–1) was completed in the White River aquifer with the well screen open to the only coarse-grained unit (muddy sandstone) that had sufficient thickness and permeability to be considered as an aquifer. Sampling of the well for a broad suite of constituents indicated groundwater generally was of excellent quality except dissolved arsenic was detected at a concentration greater than the U.S. Environmental Protection Agency (EPA) Maximum Contaminant Level, and dissolved sodium was measured at a concentration greater than several EPA Drinking Water Advisory Levels (DWAs) for the constituent. Well development, well purging for groundwater sampling, and calculated aquifer properties indicated the sandstone aquifer screened by monitoring well BR–1 was not very productive. Analysis of the well water-level responses in BR–1 to atmospheric loading and Earth tides indicated the responses were consistent with a confined-aquifer response with wellbore-storage effects. Hydraulic properties estimated based on these responses yielded values of hydraulic conductivity ( K , 0.057 foot per day [ft/d]), specific storage ( Ss , 1.6×10 −6 per foot [ft −1 ]) and porosity ( n , 0.43). Water levels filtered to remove the effects of atmospheric loading and Earth tides indicated an upward trend (+1.13 foot per year [ft/yr]) during the period analyzed, September 5, 2014, to September 30, 2017. Lithologic characteristics of the Lance hydrogeologic unit, consisting of the entire Lance Formation at the study site, indicated a potential aquifer in a “sandy” interval in the upper part of the unit. Most of the Lance hydrogeologic unit below the “sandy” interval consisted of various low-permeability lithologies unlikely to yield substantial quantities of water. This lower part of the hydrogeologic unit likely functions as a confining unit separating the underlying Lance-Fox Hills aquifer. A geologic cross section constructed for this study indicated fine-grained sediments composed most of the Lance Formation/hydrogeologic unit not only at the study location, but also throughout southern Laramie County along the line of section and throughout the Wyoming and Colorado parts of the Cheyenne Basin. A monitoring well (LN–1) completed in a sandstone bed in the “sandy” interval of the Lance hydrogeologic unit produced a mean of about 23 gallons per minute (gal/min) during well development, indicating sandstone beds can form moderately productive confined subaquifers in this part of the hydrogeologic unit. Analysis of the well water-level responses in well LN–1 to atmospheric loading and Earth tides indicated the responses were consistent with a confined-aquifer response. Hydraulic properties estimated based on these responses yielded values for a lower bounding K of 0.60 ft/d, Ss of 1.6×10 −6 ft −1 , and n of 0.38. Water levels filtered to remove the effects of atmospheric loading and Earth tides indicated a downward trend (−0.86 ft/yr) during the period analyzed (November 8, 2014, to September 30, 2017). Analyses for a broad suite of constituents in samples from well LN–1 indicated groundwater quality generally was excellent, although dissolved sodium was measured at a concentration greater than two EPA DWA levels for the constituent. Because of the absence of any overlying or intertonguing sandstone beds belonging to the lower/basal part of the Lance Formation, the Lance-Fox Hills aquifer at the study site consisted only of the five sandstone beds of the Fox Hills Sandstone. The cross section constructed for this study illustrated how the Fox Hills Sandstone, and thus, most of the Lance-Fox Hills aquifer, consists of a series of sandstone bodies that overlap (shingle) upward to the east across southern Laramie County. These bodies collectively form a fairly continuous body of sandstone, thus potentially forming an areally extensive aquifer across southern Laramie County, and by extension, throughout most of the formation’s extent in the Wyoming part of the Cheyenne Basin, as is the case in the Colorado part of the basin. A monitoring well (FH–1) completed in part of the thickest sandstone bed of the Lance-Fox Hills aquifer was moderately to highly productive and easily produced 25 to 30 gal/min after development. Substantially larger water production rates likely could be obtained by penetrating the full thickness of this bed and by completing a well open to the other overlying and underlying sandstone beds of the aquifer. Analysis of the water-level responses in well FH–1 to atmospheric loading and Earth tides indicated the responses were consistent with a confined-aquifer response. Hydraulic properties computed based on these responses yielded values for a lower bounding estimate for K of 0.26 ft/d, for Ss of 1.0×10 −6 ft −1 , and for n of 0.41. Water levels filtered to remove the effects of atmospheric loading and Earth tides indicated a downward trend (−1.74 ft/yr) during the period analyzed, December 19, 2014, to September 30, 2017. Sampling of monitoring well FH–1 and two production wells completed in the Fox Hills Sandstone in other parts of Laramie County indicated groundwater quality generally is excellent, although pH exceeded a recommended EPA aesthetic drinking-water standard (Secondary Maximum Contaminant Level) in two of three sampled wells, total dissolved solids concentrations exceeded the Secondary Maximum Contaminant Level in one of the two sampled production wells, and dissolved sodium was measured in all three sampled wells at a concentration greater than two EPA DWA levels for the constituent. The Wyoming Class II agricultural (irrigation) sodium adsorption ratio standard of 8 was exceeded in all three sampled wells, indicating these waters are not suitable for irrigation use. Computed vertical hydraulic gradients indicated a strong potential for downward flow throughout the groundwater system at the study site, including from the low-yielding aquifer in the upper White River Formation/hydrogeologic unit (monitoring well BR–1) to the sandstone subaquifer in the Lance Formation/hydrogeologic unit (monitoring well LN–1), and from the Lance subaquifer (monitoring well LN–1) to the sandstone bed/aquifer that composes much of the Lance-Fox Hills aquifer thickness at the study site (monitoring well FH–1). However, large hydraulic-head differences between wells indicated high resistance to vertical flow attributable to the low vertical hydraulic conductivity of intervening strata, which consisted almost entirely of low-permeability mudrocks. The confined nature of the sandstone aquifers monitored by the various wells coupled with dissimilarities between groundwater-level fluctuations and trends in groundwater levels indicated downward flow through the intervening strata (primarily mudrocks in the various lithostratigraphic/hydrogeologic units) between the examined sets of wells likely was small.

Wyoming↗
USGS2016

Sedimentary exhalative (sedex) zinc-lead-silver deposit model

This report draws on previous syntheses and basic research studies of sedimentary exhalative (sedex) deposits to arrive at the defining criteria, both descriptive and genetic, for sedex-type deposits. Studies of the tectonic, sedimentary, and fluid evolution of modern and ancient sedimentary basins have also been used to select defining criteria. The focus here is on the geologic characteristics of sedex deposit-hosting basins that contain greater than 10 million metric tons of zinc and lead. The enormous size of sedex deposits strongly suggests that basin-scale geologic processes are involved in their formation. It follows that mass balance constraints of basinal processes can provide a conceptual underpinning for the evaluation of potential ore-forming mechanisms and the identification of geologic indicators for ore potential in specific sedimentary basins. Empirical data and a genetic understanding of the physicochemical, geologic, and mass balance conditions required for each of these elements are used to establish a hierarchy of quantifiable geologic criteria that can be used in U.S. Geological Survey national assessments. In addition, this report also provides a comprehensive evaluation of environmental considerations associated with the mining of sedex deposits.

Scientific Investigations Report↗
USGS2015

Evaluation of selected static methods used to estimate element mobility, acid-generating and acid-neutralizing potentials associated with geologically diverse mining wastes

A comparison study of selected static leaching and acid–base accounting (ABA) methods using a mineralogically diverse set of 12 modern-style, metal mine waste samples was undertaken to understand the relative performance of the various tests. To complement this study, in-depth mineralogical studies were conducted in order to elucidate the relationships between sample mineralogy, weathering features, and leachate and ABA characteristics. In part one of the study, splits of the samples were leached using six commonly used leaching tests including paste pH, the U.S. Geological Survey (USGS) Field Leach Test (FLT) (both 5-min and 18-h agitation), the U.S. Environmental Protection Agency (USEPA) Method 1312 SPLP (both leachate pH 4.2 and leachate pH 5.0), and the USEPA Method 1311 TCLP (leachate pH 4.9). Leachate geochemical trends were compared in order to assess differences, if any, produced by the various leaching procedures. Results showed that the FLT (5-min agitation) was just as effective as the 18-h leaching tests in revealing the leachate geochemical characteristics of the samples. Leaching results also showed that the TCLP leaching test produces inconsistent results when compared to results produced from the other leaching tests. In part two of the study, the ABA was determined on splits of the samples using both well-established traditional static testing methods and a relatively quick, simplified net acid–base accounting (NABA) procedure. Results showed that the traditional methods, while time consuming, provide the most in-depth data on both the acid generating, and acid neutralizing tendencies of the samples. However, the simplified NABA method provided a relatively fast, effective estimation of the net acid–base account of the samples. Overall, this study showed that while most of the well-established methods are useful and effective, the use of a simplified leaching test and the NABA acid–base accounting method provide investigators fast, quantitative tools that can be used to provide rapid, reliable information about the leachability of metals and other constituents of concern, and the acid-generating potential of metal mining waste.

Applied Geochemistry↗
USGS2015

Weathering and transport of chromium and nickel from serpentinite in the Coast Range ophiolite to the Sacramento Valley, California, USA

A soil geochemical study in northern California was done to investigate the role that weathering and transport play in the regional distribution and mobility of geogenic Cr and Ni, which are both potentially toxic and carcinogenic. These elements are enriched in ultramafic rocks (primarily serpentinite) and the soils derived from them (1700–10,000 mg Cr per kg soil and 1300–3900 mg Ni per kg soil) in the Coast Range ophiolite. Chromium and Ni have been transported eastward from the Coast Range into the western Sacramento Valley and as a result, valley soil is enriched in Cr (80–1420 mg kg −1 ) and Ni (65–224 mg kg −1 ) compared to median values of U.S. soils of 50 and 15 mg kg −1 , respectively. Nickel in ultramafic source rocks and soils is present in serpentine minerals (lizardite, antigorite, and chrysotile) and is more easily weathered compared to Cr, which primarily resides in highly refractory chromite ([Mg,Fe 2+ ][Cr 3+ ,Al,Fe 3+ ] 2 O 4 ). Although the majority of Cr and Ni in soils are in refractory chromite and serpentine minerals, the etching and dissolution of these minerals, presence of Cr- and Ni-enriched clay minerals and development of nanocrystalline Fe (hydr)oxides is evidence that a significant fractions of these elements have been transferred to potentially more labile phases.

California↗
USGS2014

Assessment of the geoavailability of trace elements from selected zinc minerals

This assessment focused on five zinc-bearing minerals. The minerals were subjected to a number of analyses including quantitative X-ray diffraction, optical microscopy, leaching tests, and bioaccessibility and toxicity studies. Like a previous comprehensive assessment of five copper-bearing minerals, the purpose of this assessment was to obtain structural and chemical information and to characterize the reactivity of each mineral to various simulated environmental and biological conditions. As in the copper minerals study, analyses were conducted consistent with widely accepted methods. Unless otherwise noted, analytical methods used for this study were identical to those described in the investigation of copper-bearing minerals. Two sphalerite specimens were included in the zinc-minerals set. One sphalerite was recovered from a mine in Balmat, New York; the second came from a mine in Creede, Colorado. The location and conditions of origin are significant because, as analyses confirmed, the two sphalerite specimens are quite different. For example, data acquired from a simulated gastric fluid (SGF) study indicate that the hydrothermally formed Creede sphalerite contains orders of magnitude higher arsenic, cadmium, manganese, and lead than the much older metamorphic Balmat sphalerite. The SGF and other experimental results contained in this report suggest that crystallizing conditions such as temperature, pressure, fluidization, or alteration processes significantly affect mineral properties—properties that, in turn, influence reactivity, solubility, and toxicity. The three remaining minerals analyzed for this report—smithsonite, hemimorphite, and hydrozincite—are all secondary minerals or alteration products of zinc-ore deposits. In addition, all share physical characteristics such as tenacity, density, streak, and cleavage. Similarities end there. The chemical composition, unit-cell parameters, acid-neutralizing potential, and other observable and quantifiable properties indicate very different minerals. Only one of each of these minerals was studied. Had this assessment included multiples of these minerals, geochemical and mineralogical distinctions would have emerged, similar to the results for the two sphalerite specimens.

Arizona;Chihuahua;Colorado;New York↗
USGS2014

Geologic and hydrogeologic characteristics of the Ogallala Formation and White River Group, Belvoir Ranch near Cheyenne, Laramie County, Wyoming

The geologic and hydrogeologic characteristics of Tertiary lithostratigraphic units (Ogallala Formation and White River Group) that typically compose or underlie the High Plains aquifer system in southeastern Wyoming were described physically and chemically, and evaluated at a location on the Belvoir Ranch in Laramie County, Wyoming. On the basis of this characterization and evaluation, three Tertiary lithostratigraphic units were identified using physical and chemical characteristics determined during this study and previous studies, and these three units were determined to be correlative with three identified hydrogeologic units composing the groundwater system at the study site—a high-yielding aquifer composed of the entire saturated thickness of the heterogeneous and coarse-grained fluvial sediments assigned to the Ogallala Formation (Ogallala aquifer); an underlying confining unit composed primarily of very fine-grained volcaniclastic sediments and mudrocks assigned to the Brule Formation of the White River Group and some additional underlying sediments that belong to either the Brule or Chadron Formation, or both (Brule confining unit); and an underlying low-yielding aquifer composed primarily of poorly sorted fluvial sediments assigned to the Chadron Formation of the White River Group (Chadron aquifer). Despite widely varying sediment heterogeneity and consolidation, some limited hydraulic connection throughout the full vertical extent of the Ogallala aquifer was indicated but not conclusively proven by interpretation of similar chemical and isotopic characteristics, modern apparent groundwater ages, and similar hydraulic-head responses measured continuously in two Ogallala aquifer monitoring wells installed for this study at two different widely separated (83 feet) depth intervals. Additional work beyond the scope of this study, such as aquifer tests, would be required to conclusively determine hydraulic connection within the Ogallala aquifer. Groundwater levels (hydraulic heads) measured continuously using water-level recorders in both monitoring wells completed in the Ogallala aquifer showed a consistent strong upward vertical gradient in the Ogallala aquifer, indicating the potential for water to move from deeper to shallower parts of the aquifer, regardless of the time of year and the presumed effects of pumping of public-supply and industrial wells in the area. Continuous measurement of groundwater levels in the shallowest monitoring well, installed near the water table, and examination of subsequently constructed water-level hydrographs indicated substantial groundwater recharge is likely during the spring of 2009 and 2010 from the ephemeral stream (Lone Tree Creek) located adjacent to the study site that flows primarily in response to spring snowmelt from the adjacent Laramie Mountains and surface runoff from precipitation events. Using the water-table fluctuation method, groundwater recharge was estimated to be about 13 inches for the period beginning in early October 2009 and ending in late June 2010, and about 4 inches for the period beginning in March 2011 and ending in early July 2011. Comparison of previously measured groundwater levels (hydraulic heads) and groundwater-quality characteristics in nearby monitoring wells completed in the Chadron aquifer with those measured in the two monitoring wells installed for this study in the Ogallala aquifer, combined with detailed lithologic characterization, strongly indicated the Brule confining unit hydraulically confines and isolates the Chadron aquifer from the overlying Ogallala aquifer, thus likely limiting hydraulic connection between the two units. Consequently, because of the impermeable nature of the Brule confining unit and resulting hydraulic separation of the Ogallala and Chadron aquifers, and compared with local and regional hydrostratigraphic definitions of the High Plains aquifer system, the groundwater system in Tertiary lithostratigraphic units overlying the Upper Cretaceous Lance Formation at the location studied on the Belvoir Ranch was defined as being composed of, from shallowest to deepest, the High Plains aquifer system (high-yielding Ogallala aquifer only, composed of the saturated Ogallala Formation); the Brule confining unit composed of the Brule Formation of the White River Group and an underlying fine-grained depth interval with sediments that belong to either the Brule or Chadron Formation, or both; and the low-yielding Chadron aquifer (composed of poorly sorted coarse-grained sediments with substantial fine-grained matrix material assigned to the Chadron Formation of the White River Group).

Wyoming↗
USGS2013

Solid-phase data from cores at the proposed Dewey Burdock uranium in-situ recovery mine, near Edgemont, South Dakota

This report releases solid-phase data from cores at the proposed Dewey Burdock uranium in-situ recovery site near Edgemont, South Dakota. These cores were collected by Powertech Uranium Corporation, and material not used for their analyses were given to the U.S. Geological Survey for additional sampling and analyses. These additional analyses included total carbon and sulfur, whole rock acid digestion for major and trace elements, 234 U/ 238 U activity ratios, X-ray diffraction, thin sections, scanning electron microscopy analyses, and cathodoluminescence. This report provides the methods and data results from these analyses along with a short summary of observations.

South Dakota↗
USGS2012

Assessment of the geoavailability of trace elements from minerals in mine wastes: analytical techniques and assessment of selected copper minerals

In this study, four randomly selected copper-bearing minerals were examined—azurite, malachite, bornite, and chalcopyrite. The objectives were to examine and enumerate the crystalline and chemical properties of each of the minerals, to determine which, if any, of the Cu-bearing minerals might adversely affect systems biota, and to provide a multi-procedure reference. Laboratory work included use of computational software for quantifying crystalline and amorphous material and optical and electron imaging instruments to model and project crystalline structures. Chemical weathering, human fluid, and enzyme simulation studies were also conducted. The analyses were conducted systematically: X-ray diffraction and microanalytical studies followed by a series of chemical, bio-leaching, and toxicity experiments.

Scientific Investigations Report↗
USGS2010

Mineralogical and chemical characteristics of some natural jarosites

This paper presents a detailed study of the mineralogical, microscopic, thermal, and spectral characteristics of jarosite and natrojarosite minerals. Systematic mineralogic and chemical examination of a suite of 32 natural stoichiometric jarosite and natrojarosite samples from diverse supergene and hydrothermal environments indicates that there is only limited solid solution between Na and K at low temperatures, which suggests the presence of a solvus in the jarosite-natrojarosite system at temperatures below about 140 C. The samples examined in this study consist of either end members or coexisting end-member pairs of jarosite and natrojarosite. Quantitative electron-probe microanalysis data for several natural hydrothermal samples show only end-member compositions for individual grains or zones, and no detectable alkali-site deficiencies, which indicates that there is no hydronium substitution within the analytical uncertainty of the method. In addition, there is no evidence of Fe deficiencies in the natural hydrothermal samples. Hydronium-bearing jarosite was detected in only one relatively young supergene sample suggesting that terrestrial hydronium-bearing jarosites generally are unstable over geologic timescales. Unit-cell parameters of the 20 natural stoichiometric jarosites and 12 natural stoichiometric natrojarosites examined in this study have distinct and narrow ranges in the a- and c-cell dimensions. There is no overlap of these parameters at the 1r level for the two end-member compositions. Several hydrothermal samples consist of fine-scale (2–10 lm) intimate intergrowths of jarosite and natrojarosite, which could have resulted from solid-state diffusion segregation or growth zoning due to variations in the Na/K activity ratio of hydrothermal solutions.

Geochimica et Cosmochimica Acta↗
USGS2010

Integration of tectonic, sedimentary, and geohydrologic processes leading to a small-scale extension model for the Mormon Mountains area north of Lake Mead, Lincoln County, Nevada

Scattered remnants of highly diverse stratigraphic sections of Tertiary lacustrine limestone, andesite flows, and 23.8–18.2 Ma regional ash-flow tuffs on the north flank of the Mormon Mountains record previously unrecognized deformation, which we interpret as pre–17 Ma uplift and possibly weak extension on the north flank of a growing dome. Directly to the north of the Mormon dome, 17–14 Ma ash-flow tuffs and rhyolite are interstratified with landslides, debris avalanches, debris flows, and alluvial-fan deposits that accumulated to a thickness of more than 2 km in an extension-parallel basin. The source for the landslides and debris avalanche deposits is unknown, but it was probably an adjacent scarp along a transverse fault bounding an early part of the Mormon dome. An average 45° of easterly tilt of the entire Tertiary basin-fill succession represents the major post–14 Ma deformation event in the region. We question the basis for the published estimate of 22 km of westerly displacement on the Mormon Peak detachment fault and, on the basis of landslides in the upper plate having a probable source in the adjacent Mormon dome, constrain the heave to ~4 km. We interpret the dome and basin as coupled strains similar to others in the region and suggest that these strains reflect a waveform pattern of extension-normal lateral midcrustal ductile flow. Previously, doming was interpreted as an isostatic response to tectonic unloading by large-displacement detachment faults or as pseudo-structural highs stranded by removal of middle crust from adjacent areas. Moreover, we argue that the strong thinning of upper-plate rock successions throughout the Mormon Mountains and Tule Springs Hills resulted from a loss of rock volume by protracted fluid flow, dissolution, and collapse, seriously limiting the usefulness of upper-plate strain in evaluating extension magnitude. We present a geohydrologic model that couples uplift driven by ductile inflow with dissolution driven by fluid infiltration, possibly augmented by mantle-derived CO 2 -rich fluids. Karsting in the uplands led to carbonate sedimentation in adjacent lowlands. Whether or not our downward revision of extension in the Mormon Mountains is valid, extension at that latitude is isolated from extension in the Lake Mead area by a low-strain corridor between the two areas. Recognition of the isolated and potentially diminished strain impacts estimates of maximum finite elongation of the Basin and Range Province because one of three vector paths used in those estimates passes through the Mormon Mountains.

Nevada↗
USGS2010

Fluid flow, solution collapse, and massive dissolution at detachment faults, Mormon Mountains, Nevada

Dissolution has removed large volumes of rock at low-angle normal faults, i.e., detachment faults, in the Mormon Mountains and the Tule Springs Hills in the eastern Basin and Range Province, southeastern Nevada. Evidence for major dissolution includes widespread solution-collapse breccias, meter-scale stylolite structures, and high-angle accommodation faults that terminate at or merge with dissolution seams. Chemically reactive fluids moving along the fault zones led to a strong depletion of 18 O in the detachment fault breccias (e.g., a δ 18 O decrease of 8‰ relative to the unaltered rocks). These strong chemical shifts, demonstrated by (1) negative oxygen isotope values and (2) steep compositional gradients marked by metal enrichment in elements such as Au, Ag, Ti, Pb, Zn, and Cu, are generally restricted to the narrow (<1 m to 8 m) microbreccia zones. Extensional faulting and fracturing, accompanying regional uplift, opened conduits for the influx of meteoric waters from above and hydrothermal fluids from below. As the largest, most permeable structures that formed during uplift, detachment faults focused the fluid flow. In this deformation and hydrogeologic model, dissolution-caused stratal thinning is a major complement to detachment faulting and is an important process that resolves void space issues in the reconstruction of cross section.

Nevada↗
USGS2010

A deposit model for Mississippi Valley-Type lead-zinc ores

This report is a descriptive model of Mississippi Valley-Type (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 relationships with their host rocks that includes stratabound, and discordant ores; in some deposits, stratiform and vein ore are important. The most important characteristics of MVT ore deposits are that they are hosted mainly by dolostone and limestone in platform carbonate sequences and usually located at flanks of basins, orogenic forelands, or foreland thrust belts inboard of the clastic rock-dominated passive margin sequences. They have no spatial or temporal relation to igneous rocks, which distinguishes them from skarn or other intrusive rock-related Pb-Zn ores. Abundant evidence has shown that the ore fluids were derived mainly from evaporated seawater and were driven within platform carbonates by large-scale tectonic events. MVT deposits formed mainly during the Phanerozoic with more than 80 percent of the deposits hosted in Phanerozoic rocks and less than 20 percent in Precambrian rocks. Phanerozoic-hosted MVT deposits also account for 94 percent of total MVT ore, and 93 percent of total MVT lead and zinc metal. Many MVT deposits formed during Devonian to Permian time, corresponding to a series of intense tectonic events during assimilation of Pangea. The second most important period for MVT deposit genesis was Cretaceous to Tertiary time when microplate assimilation affected the western margin of North America and Africa-Eurasia. Many subtypes or alternative classifications have been applied to MVT deposits. These alternative classifications reflect geographic and or specific geological features that some workers believe set them apart as unique (for example, Appalachian-, Alpine-, Reocin-, Irish-, Viburnum trend-types). However, we do not consider these alternative classifications or sub-types to be sufficiently different to warrant using them. This report also describes the geoenvironmental characteristic of MVT deposits. The response of MVT ores in the supergene environment is buffered by their placement in carbonate host rocks which commonly results in near-neutral associated drainage water. The geoenvironmental features and anthropogenic mining effects presented in this report illustrates this important environmental aspect of MVT deposits which separates them from other deposit types (especially coal, VHMS, Cu-porphyry, SEDEX, acid-sulfate polymetallic vein).

Scientific Investigations Report↗
USGS2008

Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System Underlying Northern Preble County, Ohio

The U.S. Geological Survey (USGS), in cooperation with the Miami Conservancy District, collected and analyzed samples of the aquifer materials and ground water from multiple depths at two sites in northern Preble County, Ohio. The aquifer materials included glacial deposits and Silurian carbonate bedrock. In the study area, elevated arsenic concentrations have been detected in ground water from both types of aquifers. The aquifer materials were described in terms of the stratigraphy and the bulk elemental composition of 70 samples. In addition, six water-producing horizons were selected for more detailed study; ground-water quality was analyzed, microanalytical techniques were used to examine thin sections of the aquifer materials, and simplified geochemical modeling was done to identify plausible reactions between the ground water and aquifer materials. At both study sites, the highest solid-phase arsenic concentrations were from a roughly similar stratigraphic position - a transition zone that extends from just above the Wisconsinan/Illinoian contact to just below the Pleistocene/Silurian contact. For carbonate bedrock, the solid-phase arsenic concentrations were generally low (<1 to 4 mg/kg (milligrams per kilogram)). The one notable exception was a thin horizon about 10 feet below the top of bedrock, which had an arsenic concentration of 42 mg/kg. This horizon showed some textural and compositional evidence of alteration by geothermal fluids. Additional study might be warranted to investigate whether arsenic concentrations in ground water from carbonate bedrock could be decreased by excluding discrete horizons from the open intervals of wells. For glacial deposits, solid-phase arsenic concentrations were slightly higher in fine-grained deposits (2 to 20 mg/kg) than in coarse-grained deposits (2 to 9 mg/kg). In ground water, arsenic concentrations ranged from <1 to 51 ug/L (micrograms per liter); samples from two horizons had concentrations greater than the U.S. Environmental Protection Agency Maximum Contaminant Level (MCL) of 10 ug/L. Dissolved arsenic concentrations appear to be more closely related to redox conditions of the ground water than to the arsenic content of the aquifer materials. Geochemical modeling and thin-section analysis were generally consistent with the idea that arsenic was released to water from iron oxides under iron-reducing conditions. In addition, there was some evidence in support of the idea that arsenic can be removed from ground water by precipitation of sulfide minerals, which occurs under sulfate-reducing conditions. At one site, the dissolved arsenic concentrations in two water-bearing horizons increased from <1 to 51 ug/L over a depth of 15 feet. The large increase might be due to a shift from sulfate-reducing to methanogenic conditions; in the absence of sulfate reduction, arsenic is not sequestered in sulfide minerals and may accumulate in the ground water.

Scientific Investigations Report↗
USGS2006

The use of synthetic jarosite as an analog for natural jarosite

The presence of jarosite in soil or mining waste is an indicator of acidic sulfate-rich conditions. Physical and chemical properties of synthetic jarosites are commonly used as analogs in laboratory studies to determine solubility and acid-generation of naturally occurring jarosites. In our work we have mineralogically and chemically characterized both natural and synthetic jarosites. Analysis of 32 natural hydrothermal and supergene K- and Na-jarosites indicates no (< 5 mole %) solid solution between K and Na end members. Instead, our detailed study of cell dimensions and composition reveals discrete mixtures of K and Na end members. Hydronium-bearing jarosite was detected in only one natural sample, and it appears that hydronium-bearing jarosites are metastable. Although the presence of hydronium in jarosite cannot be directly measured, we found that when synthetic hydronium-bearing jarosites are heated at 120°C for 78 days or 240°C for 24 hours, Fe(OH)SO4 is formed. The Fe(OH)SO4 is easily detected by X-ray diffraction and, hence, can be used as a post-mortem indicator of the presence of hydronium jarosite. Results from our synthetic jarosite studies indicate that natural metastable hydronium-bearing jarosite or iron-deficient forms of natural jarosite likely play an important role in acid generation in some mining wastes, but are not accurately represented by synthetic jarosite prepared by commonly used methods. The widespread practice of heating to at least 110°C after jarosite synthesis appears to drive off structural waters from protonated hydroxyl sites, which changes the properties of the jarosite. Therefore, synthetic jarosite should not be heated above 95 oC if it is to be used as an analog for low-temperature natural jarosite in mining wastes.

Conference Paper↗
USGS2006

Magnetic properties, acid neutralization capacity, and net acid production of rocks in the Animas River Watershed Silverton, Colorado

Federal land managers along with local stakeholders in the Upper Animas River watershed near Silverton, Colorado are actively designing and implementing mine waste remediation projects to mitigate the effects of acid mine drainage from several abandoned hard rock metal mines and mills. Local source rocks with high acid neutralization capacity (ANC) within the watershed are of interest to land managers for use in these remediation projects. A suite of representative samples was collected from propylitic to weakly sericitic-altered volcanic and plutonic rocks exposed in outcrops throughout the watershed. Acid-base accounting laboratory methods coupled with mineralogic and geochemical characterization provide insight into lithologies that have a range of ANC and net acid production (NAP). Petrophysical lab determinations of magnetic susceptibility converted to estimates for percent magnetite show correlation with the environmental properties of ANC and NAP for many of the lithologies. A goal of our study is to interpret watershed-scale airborne magnetic data for regional mapping of rocks that have varying degrees of ANC and NAP. Results of our preliminary work are presented here.

Conference Paper↗
USGS2004

Surficial geologic map of the southeast Memphis Quadrangle, Shelby County, Tennessee

The depiction of geology on this map is designed to aid in urban planning and analysis of potential damage in the event of strong earthquake motion. The geologic map by itself does not analyze potential earthquake damage, but is designed to be used by seismologists who perform such analyses. Wind-deposited silt and clayey silt (loess) is the predominant surficial deposit. Loess entirely covers the upland (everyplace in the map area that is not a valley occupied by a stream) to depths of 4.5-16 m. The second most abundant deposit is silty alluvium, which is confined to the narrow floodplains and is 1-10 m thick. Sparse, unconsolidated, pebbly sand alluvium is 0.5-3 m thick and is confined to point bars and channel deposits in the narrow, incised channel of Nonconnah Creek. The nature of geologic materials to a degree determines the severity of damage to infrastructure sustained during a strong earthquake.

Scientific Investigations Map↗