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At least 451 records · Page 25Linked to original sources
USGS1976

Halogen contents of igneous minerals as indicators of magmatic evolution of rocks associated with the Ray porphyry copper deposit, Arizona

The contents of Cl, F, and H 2 O+ (calculated) in some hydrous igneous minerals in intrusive rocks of Laramide age (70-60 m.y.) near Ray, Ariz., appear to be related to the age and the chemistry of the whole-rock samples. Apatite and biotite in younger, more silicic rocks contain more F but less Cl and H 2 O+ than apatite and biotite in older, more mafic rock; the same relations hold for F and H 2 O+ in sphene. Correlations of the abundance of Cl, F, and H 2 O+ in hornblende with rock chemistry and age are not as strong as for apatite, biotite, and sphene; igneous (?) epidote does not contain Cl and F in amounts detectable by electron microprobe analysis. The contents of Cl, F, and H 2 O+ in whole-rock samples decrease with increasing differentiation index and decreasing age. Data for a single pluton of variable composition mirror the results for a suite of different plutons and dikes. The data are satisfactorily although not exclusively explained by postulating that the melts each contained progressively less Cl, F, and H 2 O and that the hydrons minerals consumed most of the Cl, F, and H 2 O in the magmas. The data may also be explained by postulating that (1) the stocks evolved Cl-bearing water during their ascent and crystallization, or that (2) Cl and H 2 O were concentrated during differentiation of the stocks but the minerals failed to record their buildup. Both alternative explanations find problems with and require special conditions to satisfy field, chemical, and experimental data. If many of the special conditions are not met, a nearby batholithic parent to the stocks is not a favorable source of the mineralized fluids at Ray. Propylitic alteration of biotite results in Cl-poor chlorites and may have provided some Cl to hydrothermal fluids; biotite may have also supplied some F to propylitizing fluids through alteration.

Arizona↗
USGS1997

Continents as lithological icebergs: The importance of buoyant lithospheric roots

An understanding of the formation of new continental crust provides an important guide to locating the oldest terrestrial rocks and minerals. We evaluated the crustal thicknesses of the thinnest stable continental crust and of an unsubductable oceanic plateau and used the resulting data to estimate the amount of mantle melting which produces permanent continental crust. The lithospheric mantle is sufficiently depleted to produce permanent buoyancy (i.e., the crust is unsubductable) at crustal thicknesses greater than 25–27 km. These unsubductable oceanic plateaus and hotspot island chains are important sources of new continental crust. The newest continental crust (e.g., the Ontong Java plateau) has a basaltic composition, not a granitic one. The observed structure and geochemistry of continents are the result of convergent margin magmatism and metamorphism which modify the nascent basaltic crust into a lowermost basaltic layer overlain by a more silicic upper crust. The definition of a continent should imply only that the lithosphere is unsubductable over ≥ 0.25 Ga time periods. Therefore, the search for the oldest crustal rocks should include rocks from lower to mid-crustal levels.

Earth and Planetary Science Letters↗
USGS1978

Intrusive rocks northeast of Steamboat Springs, Park Range, Colorado

Major Precambrian and minor Tertiary intrusive rocks northeast of Steamboat Springs in the Park Range between 40°30' and 40°45' N. lat. are described and compared with related rocks elsewhere in Colorado and Wyoming. The Precambrian intrusives were emplaced in a sequence of high-grade interlayered felsic gneisses, amphibolites, and pelitic schists of sedimentary and volcanic origin. These rocks are cut by a major northeast-trending Precambrian shear zone where mainly left lateral movement of 1/ 2 to 1 mile is certain. Cumulative movement of many miles is possible. The Precambrian intrusives consist of a batholith, the Mount Ethel pluton, a smaller Buffalo Pass pluton, and small dikes or lenses of fine-grained porphyry, pegmatites, and ultramafics. The Mount Ethel pluton is an oval shaped body 7 miles wide by about 40 miles long (shown by geophysical data to extend beneath younger sediments in North Park). Outer batholithic contacts are sharp and dip steeply outward at about 85°. Five mappable internal variants consist, in order of decreasing age, of granodiorite, quartz monzonite porphyry of Rocky Peak, quartz monzonite of Roxy Ann Lake, granite and quartz monzonite, and. leucogranite. Internal contacts between these plutonic variants are sharp, and evidence of liquid-solid relationships abounds; despite this, all rocks except the granodiorite contribute to an Rb-Sr whole-rock isochron indicating emplacement about 1.4 b.y. (billion years) ago. The most important variants volumetrically are: the quartz monzonite porphyry of Rocky Peak, which forms an irregular 2-mile-thick carapace or mapped band around the west edge of the pluton and is lithologically similar to nearby Sherman Granite, and the quartz monzonite of Roxy Ann Lake, which forms most of the rest of the pluton and is lithologically similar to Silver Plume Granite. An apparent Sherman -Silver Plume dichotomy with similar rock types and similar relative ages is noted throughout Colorado plutons of that age. The Buffalo Pass pluton consists of the quartz monzonite and gra- nodiorite augen gneiss of Buffalo Mountain and equigranular quartz monzonite gneiss. Internal contacts are not exposed. These rocks contribute to an Rb-Sr whole-rock isochron indicating syntectonic emplacement 1.7-1.8 b.y. ago, essentially the same as the metamorphism of the felsic gneiss wallrocks in the area of this report, and of rocks of Boulder Creek age elsewhere in Colorado. The fine-grained porphyry dikes cut the Buffalo Pass pluton, the ultramafics, and some pegmatites. The dikes are within the age range of the Mount Ethel pluton and are older than the mylonite and shear zones. They occur in both an older northwest-trending and a somewhat younger northeast-trending set but do not appear to change compositionally from one set to the other. Regional considerations indicate that they were emplaced between about 1.1 and 1.5 b.y. ago, a time when intermediate to mafic dikes were commonly emplaced throughout Colorado, Wyoming, and southwestern Montana. The pegmatite and ultramafic bodies are not dated directly, but clustering of many pegmatites outside the contacts of the Mount Ethel pluton may indicate a genetic relation of the pegmatites to the Mount Ethel rocks. Fluorite is a common accessory mineral in the rocks of the Mount Ethel pluton; it has not been observed in this area in the petrographically similar rocks of the Buffalo Pass pluton. Fluorite was precipitated most abundantly from the Precambrian magma that formed the quartz monzonite of Roxy Ann Lake. In 70 percent of these rocks fluorite is observed in amounts as great as 2 percent and is successively less abundant in both older and younger plutonic phases. Textural evidence indicates that, although most fluorite is intergrown with and contemporaneous with other magmatic minerals, some fluorite is associated with alteration minerals in a manner demonstrating its mobility since its initial deposition.

Colorado↗
USGS1953

Geochemical studies of clay minerals III. The determination of free silica and free alumina in montmorillonites

Determination of free silica by the method proposed made possible the derivation of logical formulas for several specimens of montmorillonites for which the formulas could not be derived from the analyses alone. Other montmorillonites, for which logical formulas could be derived from their analyses, were found to contain small amounts of free silica or free alumina. Others were found to contain neither free silica nor free alumina. The method consists of the following steps: (1) digestion of 1 g of the specimen with 0.5 N NaOH solution in a covered platinum crucible or dish on a steam bath for 4 hrs, stirring the mixture at 30-min intervals, (2) filtration of the undissolved material, followed by washing several times with 1% NaOH solution, (3) neutralization of the filtrate with HCl, addition of 5 ml HCl in excess and determination of SiO and Al 2 O 3 in the usual way and (4) calculation of the amount of free SiO 2 or free Al 2 O 3 if any and the amount of attack of the clay structure by the treatment from the ratio of SiO 2 to Al 2 O 3 dissolved and the ratio of SiO 2 to Al 2 O 3 obtained on analysis. Tests with 5% Na 2 CO 3 solution, the reagent formerly used for the solution of free SiO 2 in rocks and minerals, showed that solution of opal by this reagent is always fractional, never complete, no matter how small the amount present or how long the period of treatment. Re-treatment of the sample results in 90–95% solution if 10 mg or less of opal is present, but for larger amounts of opal the percentage dissolved decreases as the amount present increases. On the other hand, 75 ml of 0.5 N NaOH completely dissolves as much as 400 mg of opal in 4 hrs digestion in a covered platinum crucible or dish, on a steam bath. However, a weaker solution or a shorter period of digestion does not effect complete solution. The same amount (75 ml) of 0.5 N NaOH also dissolves 90 mg of cristobalite and 57 mg of quartz having a grain size of less than 2 microns. Use of NaOH also permits determination of the amount of alumina dissolved, and estimation of the extent to which the clay structure was attacked by the treatment.

Geochimica et Cosmochimica Acta↗
USGS2009

Methods for Estimating Water Withdrawals for Mining in the United States, 2005

The mining water-use category includes groundwater and surface water that is withdrawn and used for nonfuels and fuels mining. Nonfuels mining includes the extraction of ores, stone, sand, and gravel. Fuels mining includes the extraction of coal, petroleum, and natural gas. Water is used for mineral extraction, quarrying, milling, and other operations directly associated with mining activities. For petroleum and natural gas extraction, water often is injected for secondary oil or gas recovery. Estimates of water withdrawals for mining are needed for water planning and management. This report documents methods used to estimate withdrawals of fresh and saline groundwater and surface water for mining during 2005 for each county and county equivalent in the United States, Puerto Rico, and the U.S. Virgin Islands. Fresh and saline groundwater and surface-water withdrawals during 2005 for nonfuels- and coal-mining operations in each county or county equivalent in the United States, Puerto Rico, and the U.S. Virgin Islands were estimated. Fresh and saline groundwater withdrawals for oil and gas operations in counties of six states also were estimated. Water withdrawals for nonfuels and coal mining were estimated by using mine-production data and water-use coefficients. Production data for nonfuels mining included the mine location and weight (in metric tons) of crude ore, rock, or mineral produced at each mine in the United States, Puerto Rico, and the U.S. Virgin Islands during 2004. Production data for coal mining included the weight, in metric tons, of coal produced in each county or county equivalent during 2004. Water-use coefficients for mined commodities were compiled from various sources including published reports and written communications from U.S. Geological Survey National Water-use Information Program (NWUIP) personnel in several states. Water withdrawals for oil and gas extraction were estimated for six States including California, Colorado, Louisiana, New Mexico, Texas, and Wyoming, by using data from State agencies that regulate oil and gas extraction. Total water withdrawals for mining in a county were estimated by summing estimated water withdrawals for nonfuels mining, coal mining, and oil and gas extraction. The results of this study were distributed to NWUIP personnel in each State during 2007. NWUIP personnel were required to submit estimated withdrawals for numerous categories of use in their States to a national compilation team for inclusion in a national report describing water use in the United States during 2005. NWUIP personnel had the option of submitting the estimates determined by using the methods described in this report, a modified version of these estimates, or their own set of estimates or reported data. Estimated withdrawals resulting from the methods described in this report may not be included in the national report; therefore the estimates are not presented herein in order to avoid potential inconsistencies with the national report. Water-use coefficients for specific minerals also are not presented to avoid potential disclosure of confidential production data provided by mining operations to the U.S. Geological Survey.

Scientific Investigations Report↗
USGS2016

Concentrations of mineral aerosol from desert to plains across the central Rocky Mountains, western United States

Mineral dusts can have profound effects on climate, clouds, ecosystem processes, and human health. Because regional dust emission and deposition in western North America are not well understood, measurements of total suspended particulate (TSP) from 2011 to 2013 were made along a 500-km transect of five remote sites in Utah and Colorado, USA. The TSP concentrations in μg m −3 adjusted to a 24-h period were relatively high at the two westernmost, dryland sites at Canyonlands National Park (mean = 135) and at Mesa Verde National Park (mean = 99), as well as at the easternmost site on the Great Plains (mean = 143). The TSP concentrations at the two intervening montane sites were less, with more loading on the western slope of the Rocky Mountains (Telluride, mean = 68) closest to the desert sites compared with the site on the eastern slope (Niwot Ridge, mean = 58). Dust concentrations were commonly highest during late winter-late spring, when Pacific frontal storms are the dominant causes of regional wind. Low concentrations (<7 wt%) of organic matter indicated that rock-derived mineral particles composed most TSP. Most TSP mass was carried by particle sizes larger than 10 μm (PM >10 ), as revealed by relatively low average daily concentrations of fine (<5 μg m −3 ; PM 2.5 ) and coarse (<10 μg m −3 ; PM 2.5–10 ) fractions monitored at or near four sites. Standard air-quality measurements for PM 2.5 and PM 10 apparently do not capture the large majority of mineral-particulate pollution in the remote western interior U.S.

Aeolian Research↗
USGS1983

Mineral resource assessment of the Iron River 1° x 2° quadrangle, Michigan and Wisconsin

The Iron River 1? x 2? quadrangle contains identified resources of copper and iron. Copper-rich shale beds in the north part of the quadrangle contain 12.2 billion pounds (5.5 billion kilograms) of copper in well-studied deposits including 9.2 billion pounds (4.2 billion kilograms) that are economically minable by 1980 standards. At least several billion pounds of copper probably exist in other parts of the same shale beds, but not enough data are available to measure the amount. A small amount, about 250 million pounds (113 million kilograms), of native copper is known to remain in one abandoned mine, and additional but unknown amounts remain in other abandoned mines. About 13.25 billion tons (12.02 billion metric tons) of banded iron-formation averaging roughly 30 percent iron are known within 500 feet (152.4 meters) of the surface in the Gogebic, Marquette, and Iron River-Crystal Falls districts. A small percentage of that might someday be minable as taconite, but none is now believed to be economic. Some higher grade iron concentrations exist in the same iron-formations. Such material was the basis of former mining of iron in the region, but a poor market for such ore and depletion of many deposits have led to the decline of iron mining in the quadrangle. Iron mines of the quadrangle were not being worked in 1980. Many parts of the quadrangle contain belts of favorable host rocks for mineral deposits. Although deposits are not known in these belts, undiscovered deposits of copper, zinc, lead, silver, uranium, phosphate, nickel, chromium, platinum, gold, and diamonds could exist.

Michigan, Wisconsin↗
USGS1982

Mineral-resource assessment of the Iron River 1° x 2° quadrangle, Michigan and Wisconsin

The Iron River 1° x 2° quadrangle contains identified resources of copper and iron. Copper-rich shale beds in t1n north part of the quadrangle contain 12.2 billion pounds (5.5 billion kg) of copper in well-studied deposits including 9.2 billion pounds (4.2 billion kg) that are economically mineable by 1980 standards. At least several billion pounds of copper probably exist in other parts of the same shale beds but not enough data are available to measure the amount. A small amount, about 250 million pounds (113 million kg), of native copper is known to remain in one abandoned mine, and additional but unknown amounts remain in other abandoned mines. About 13.25 billion tons (12.02 billion t) of handed iron-formation averaging roughly 30 percent iron are known within 500 feet (152.4 m) of the surface in the Gogebic, Marquette, and Iron River-Crystal Falls districts. Some, probably small, percentage of that might someday be mineable as taconite, but none is now believed to be economic. Some higher grade iron concentrations exist in tin same iron-formations. Such material was the basis of former mining of iron in the region, but a poor market for such ore and depletion of many deposits has lead to the decline of iron mining in the quadrangle. No iron mines of the quadrangle were being worked in 1981. Many parts of the quadrangle contain belts of favorable host rocks for mineral deposits. Although no deposits are known in these belts, undiscovered deposits of copper, zinc, lead, silver, uranium, phosphate, nickel, chromium, platinum, gold, and diamonds could exist.

Michigan, Wisconsin↗
USGS2010

Hydrogen and oxygen isotope constraints on hydrothermal alteration of the Trinity peridotite, Klamath Mountains, California

The Trinity peridotite represents a rare opportunity to examine a relatively fertile plagioclase peridotite that was exhumed and later subjected to intrusive events in a seafloor environment, followed by its emplacement and incorporation into a continent. Over 250 stable isotopic determinations on whole rocks and minerals elucidate the hydrothermal evolution of the Trinity complex. All three serpentine polymorphs are present in the Trinity peridotite; these separate on the basis of their δD values: antigorite, -46 < δD < -82‰ and lizardite and chrysotile, -90 < δD < -106 and -110 < δD < -136‰, respectively. Antigorite coexists with chlorite, talc, and tremolite in contact aureole assemblages associated with Silurian/Devonian gabbroic plutons. Lizardite and chrysotile alteration carries a meteoric signature, which suggests association with post-emplacement serpentinization, or overprinting of earlier low-temperature seafloor serpentinization. Regionally, contours of δD values exhibit bull's-eye patterns associated with the gabbroic plutons, with δD maxima coinciding with the blackwall alteration at the margins on the plutons. In contrast to the hydrogen isotope behavior, oxygen isotope values of the three polymorphs are indistinguishable, spanning the range 5.3 < δ 18 O< 7.5, and suggesting low integrated fluid fluxes and strongly 18 O-shifted fluids. Inferred primary δ 18 O values for peridotite, gabbro, and late Mesozoic granodiorite indicate a progressive 18 O enrichment with time for the source regions of the rocks. These isotopic signatures are consistent with the geology, petrochemistry, and geochronology of the Trinity massif, which indicate the following history: (1) lithospheric emplacement and cooling of the peridotite in an oceanic environment ~472 Ma; (2) intrusion of gabbroic plutons into cold peridotite in an arc environment between 435 and 404 Ma; and finally (3) intrusion of felsic plutons between 171 and 127 Ma, long after the peridotite was incorporated into the continental crust.

California↗
USGS2015

Geochronology of Cenozoic rocks in the Bodie Hills, California and Nevada

The purpose of this report is to present geochronologic data for unaltered volcanic rocks, hydrothermally altered volcanic rocks, and mineral deposits of the Miocene Bodie Hills and Pliocene to Pleistocene Aurora volcanic fields of east-central California and west-central Nevada. Most of the data presented here were derived from samples collected between 2000&ndash;13, but some of the geochronologic data, compiled from a variety of sources, pertain to samples collected during prior investigations. New data presented here (tables 1 and 2; Appendixes 1&ndash;3) were acquired in three U.S. Geological Survey (USGS) 40 Ar/ 39 Ar labs by three different geochronologists: Robert J. Fleck (Menlo Park, CA), Lawrence W. Snee (Denver, CO), and Michael A. Cosca (Denver, CO). Analytical methods and data derived from each of these labs are presented separately. The middle to late Miocene Bodie Hills volcanic field (BHVF) is a large (>700 km 2 ), long-lived (~9 million years [m.y.]), episodic eruptive complex (John and others, 2012) in the southern segment of the ancestral Cascades arc (du Bray and others, written commun., 2015) north of Mono Lake and east of Bridgeport, California (fig. 1). The field is near the west edge of the Walker Lane and the northwest edge of the Mina deflection where structures related to these shear zones may have localized magmatism. The Walker Lane (fig. 1) is a broad, northwest-striking zone of right-lateral shear that accommodates right-lateral motion between the Pacific and North America plates; the Mina deflection constitutes a 60-km-long right step in the Walker Lane (Faulds and Henry, 2008; Oldow, 1992, 2003; Stewart, 1988). The Bodie Hills volcanic field includes at least 31 volcanic rock units erupted from 21 significant volcanic eruptive centers. Four trachyandesite stratovolcanoes developed along the margins of the volcanic field and numerous silicic trachyandesite to rhyolite flow dome complexes erupted more centrally. Volcanism in the Bodie Hills volcanic field peaked at two periods, ~15.0 to 12.6 million years before present (Ma) and ~9.9 to 8.0 Ma, which were dominated by emplacement of large stratovolcanoes and large silicic trachyandesite-dacite lava domes, respectively. A final period of small-volume silicic dome emplacement began in the western part of the volcanic field at ~6 Ma and culminated at ~5.5 Ma (John and others, 2012).

California, Nevada↗
USGS1999

Dating methods

One of the greatest contributions of geochemistry to man's knowledge of the Earth and solar system has been the development and application of chemical and isotopic techniques used to measure the passage of time. Rates of geologic processes, rates of biological evolution, and contemporaneity of past events all depend on accurate ages of geologic materials. Many geochemical methods have been used to determine ages of rocks and minerals; the ages determined may record the time of mineral crystallization or recrystallization, the time of last heating beyond a given temperature (see Geothermometers ), or the time elapsed since exposure on the surface. The basic requirement for a chemical or isotopic geochronometer is some measurable parameter that changes as a function of time. Furthermore, for accurate ages to be determined, the parameter must have a known (and invariant) relationship with age or must be able to be calibrated.

Book chapter↗
USGS1973

Stages in the P-T path of ascending basalt magma: an example from San Quintin, Baja California

Late Pleistocene or Recent lavas from San Quintin, Baja California are basanitoids and alkali basalts. The surface quench temperatures of the lavas average 1 005° C with log f O 2 "> f O 2 fO2 =−11.4, as deduced from the groundmass Fe-Ti oxides. Spinel lherzolite xenoliths and megacrysts of augite and andesine have been found in lava flows and cinder deposits. Using analytical data on the rocks and minerals and simple thermodynamic expressions, the pressures and temperatures of equilibration of lavas and xenoliths, megacrysts and phenocrysts have been calculated. The lavas could have been in equilibrium with lherzolite at 1 330–1 410° C and 27.5–31.6 kb, the more silica-poor liquid having the higher values. The basanitoid could have equilibrated with the megacrysts at about 10.5 kb and with phenocrysts at about 1.4 kb and 1130° C. The variation in composition of the lavas may be explained by a rising zone of melting within the mantle, the most silica-poor liquid having the deepest source. The source of the San Quintin basalts is probably related to spreading of the ocean floor in the Gulf of California.

Baja California, San Quintin↗
USGS1977

State of stress in the lithosphere: Inferences from the flow laws of olivine

The experimental flow data for rocks and minerals are reviewed and found to fit a law of the form {Mathematical expression} where {Mathematical expression} This law reduces to the familiar power-law stress dependency at low stress and to an exponential stress dependency at high stress. Using the material flow law parameters for olivine, stress profiles with depth and strain rate are computed for a representative range of temperature distributions in the lithosphere. The results show that the upper 15 to 25 km of the oceanic lithosphere must behave elastically or fail by fracture and that the remainder deforms by exponential law flow at intermediate depths and by power-law flow in the rest. A model computation of the gravitational sliding of a lithospheric plate using olivine rheology exhibits a very sharp decoupling zone which is a consequence of the combined effects of increasing stress and temperature on the flow law, which is a very sensitive function of both. ?? 1977 Birkha??user Verlag.

Pure and Applied Geophysics PAGEOPH↗
USGS2008

Plant response to nutrient availability across variable bedrock geologies

We investigated the role of rock-derived mineral nutrient availability on the nutrient dynamics of overlying forest communities (Populus tremuloides and Picea engelmanni-Abies lasiocarpa v. arizonica) across three parent materials (andesite, limestone, and sandstone) in the southern Rocky Mountains of Colorado. Broad geochemical differences were observed between bedrock materials; however, bulk soil chemistries were remarkably similar between the three different sites. In contrast, soil nutrient pools were considerably different, particularly for P, Ca, and Mg concentrations. Despite variations in nutrient stocks and nutrient availability in soils, we observed relatively inflexible foliar concentrations and foliar stoichiometries for both deciduous and coniferous species. Foliar nutrient resorption (P and K) in the deciduous species followed patterns of nutrient content across substrate types, with higher resorption corresponding to lower bedrock concentrations. Work presented here indicates a complex plant response to available soil nutrients, wherein plant nutrient use compensates for variations in supply gradients and results in the maintenance of a narrow range in foliar stoichiometry. ?? 2008 Springer Science+Business Media, LLC.

Ecosystems↗
USGS1985

Experimental chemical weathering of various bedrock types at different pH-values. 1. Sandstone and granite

Experimental chemical weathering of the so-called Old Rag Granite and Massanutten Sandstone, Virginia, U.S.A., has produced a comparison with the natural environment, and prediction of the effect of acid precipitation. The experimental results of the release of elements, dissolution of minerals, total rock weathered and the degree of weathering as function of volume of leachate were plotted. These data were compared with the natural environment. The use of the plots to predict the effect of high levels of rain acidity on weathering of these rocks is demonstrated. A nonexpandable 14-Å clay was developed from the alteration of biotite during the experimental chemical weathering of the granite at pH 4. This interstratified Al(OH)—mica clay resembles those of the soil developed on the granite and sandstone. Hydroxy-Al may be precipitating between the mica interlayers and producing a 14-Å spacing. Development of this clay by chemical alteration of biotite may change the current hypotheses about its origin in the soils of northeastern U.S.A. While Al-hydroxide seems to regulate Al concentrations in stream waters at the present level of rain acidity, it was found that at lower pH and in the presence of high sulfate concentrations, Al solubility may be controlled by Al-sulfate phase(s).

Virginia↗
USGS1991

Leaching of 226Ra from components of uranium mill tailings

A sequential extraction procedure was used to characterize the geochemical forms of 226 Ra retained by mixtures of quartz sand and a variety of fine-grained rock and mineral species. These mixtures had previously been exposed to the sulfuric acid milling liquor of a simulated acid-leach uranium milling circuit. For most test cases, the major fraction of the 226 Ra was extracted with 1 mol/1 NH 4 Cl and was deemed to be exchangeable. However, 226 Ra retained by the barite-containing mixture was resistant to both 1 mol/1 NH 4 Cl and 1 mol/HCHCl extraction.

Hydrometallurgy↗
USGS2009

Weathering of the New Albany Shale, Kentucky, USA: I. Weathering zones defined by mineralogy and major-element composition

Comprehensive understanding of chemical and mineralogical changes induced by weathering is valuable information when considering the supply of nutrients and toxic elements from rocks. Here minerals that release and fix major elements during progressive weathering of a bed of Devonian New Albany Shale in eastern Kentucky are documented. Samples were collected from unweathered core (parent shale) and across an outcrop excavated into a hillside 40 year prior to sampling. Quantitative X-ray diffraction mineralogical data record progressive shale alteration across the outcrop. Mineral compositional changes reflect subtle alteration processes such as incongruent dissolution and cation exchange. Altered primary minerals include K-feldspars, plagioclase, calcite, pyrite, and chlorite. Secondary minerals include jarosite, gypsum, goethite, amorphous Fe(III) oxides and Fe(II)-Al sulfate salt (efflorescence). The mineralogy in weathered shale defines four weathered intervals on the outcrop-Zones A-C and soil. Alteration of the weakly weathered shale (Zone A) is attributed to the 40-a exposure of the shale. In this zone, pyrite oxidization produces acid that dissolves calcite and attacks chlorite, forming gypsum, jarosite, and minor efflorescent salt. The pre-excavation, active weathering front (Zone B) is where complete pyrite oxidation and alteration of feldspar and organic matter result in increased permeability. Acidic weathering solutions seep through the permeable shale and evaporate on the surface forming abundant efflorescent salt, jarosite and minor goethite. Intensely weathered shale (Zone C) is depleted in feldspars, chlorite, gypsum, jarosite and efflorescent salts, but has retained much of its primary quartz, illite and illite-smectite. Goethite and amorphous FE(III) oxides increase due to hydrolysis of jarosite. Enhanced permeability in this zone is due to a 14% loss of the original mass in parent shale. Denudation rates suggest that characteristics of Zone C were acquired over 1 Ma. Compositional differences between soil and Zone C are largely attributed to illuvial processes, formation of additional Fe(III) oxides and incorporation of modern organic matter.

Applied Geochemistry↗