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At least 91 records · Page 5Linked to original sources
USGS1997

Mineral-resource data bases

Data bases are essential for modern scientific research. The new and exciting work being done in the Mineral Resource Program in the U.S. Geological Survey (USGS) usually begins with the question, "Where are the known deposits?" A mineral-resource data base containing this type of information and more can be useful not just to USGS scientists, but to anyone who needs such data. Users of the data bases from outside the USGS include mining and exploration companies, environmental groups, academia, other Federal Agencies, and the general public. At present, the USGS has two large mineral-resource data bases, MRDS (Mineral Resource Data System) and MAS (Minerals Availability System). MRDS was built and is mamtained by the USGS, and MAS was built and maintained by the Bureau of Mines. In 1996, after the Bureau was abolished, MAS was transferred to the USGS. The two data bases were compiled for different purposes and contain very different mformation. For instance, MAS contains information on costs, details of mining methods, and feasibility studies. MRDS has mineralogical and geologic data that are not contained in MAS. Because they are both mineral-resource data bases, however, they contain some information in common, such as location, name(s) of sites, and commodities present. Both data bases are international in scope, and both are quite large. MRDS contains over 110,000 records, while MAS has over 220,000. One reason that MAS has more records is that it contains information on smelters, mill sites, and fossil fuel sites, as well as mineral- resource sites. The USGS is working to combine the information in both data bases. This is a large undertaking that will require some years to complete. In the interim, information from both data bases will still be available

Fact Sheet↗
USGS2015

Hydrothermal alteration and diagenesis of terrestrial lacustrine pillow basalts: Coordination of hyperspectral imaging with laboratory measurements

We investigate an outcrop of ∼187 Ma lacustrine pillow basalts of the Talcott Formation exposed in Meriden, Connecticut, USA, focusing on coordinated analyses of one pillow lava to characterize the aqueous history of these basalts in the Hartford Basin. This work uses a suite of multidisciplinary measurements, including hyperspectral imaging, other spectroscopic techniques, and chemical and mineralogical analyses, from the microscopic scale up to the scale of an outcrop. The phases identified in the sample are albite, large iron oxides, and titanite throughout; calcite in vesicles; calcic clinopyroxene, aegirine, and Fe/Mg-bearing clay in the rind; and fine-grained hematite and pyroxenes in the interior. Using imaging spectroscopy, the chemistry and mineralogy results extend to the hand sample and larger outcrop. From all of the analyses, we suggest that the pillow basalts were altered initially after emplacement, either by heated lake water or magmatic fluids, at temperatures of at least 400-600°C, and the calcic clinopyroxenes and aegirine identified in the rind are a preserved record of that alteration. As the hydrothermal system cooled to slightly lower temperatures, clays formed in the rind, and, during this alteration, the sample oxidized to form hematite in the matrix of the interior and Fe 3+ in the pyroxenes in the rind. During the waning stages of the hydrothermal system, calcite precipitated in vesicles within the rind. Later, diagenetic processes albitized the sample, with albite replacing plagioclase, lining vesicles, and accreting onto the exterior of the sample. This albitization or Na-metasomatism occurred when the lake within the Hartford Basin evaporated during a drier past climatic era, resulting in Na-rich brines. As Ca-rich plagioclase altered to albite, Ca was released into solution, eventually precipitating as calcite in previously-unfilled vesicles, dominantly in the interior of the pillow. Coordinated analyses of this sample permit identification of the alteration phases and help synthesize the aqueous history of pillow lavas of the Talcott formation. These results are also relevant to Mars, where volcanically-resurfaced open basin lakes have been found, and this Hartford Basin outcrop may be a valuable analog for any potential volcano-lacustrine interactions. The results can also help to inform the utility and optimization of potentially complementary, synergistic, and uniquely-suited techniques for characterization of hydrothermally-altered terrains.

Connecticut↗
USGS2019

SUSTAIN drilling at Surtsey volcano, Iceland, tracks hydrothermal and microbiological interactions in basalt 50 years after eruption

The 2017 Surtsey Underwater volcanic System for Thermophiles, Alteration processes and INnovative concretes (SUSTAIN) drilling project at Surtsey volcano, sponsored in part by the International Continental Scientific Drilling Program (ICDP), provides precise observations of the hydrothermal, geochemical, geomagnetic, and microbiological changes that have occurred in basaltic tephra and minor intrusions since explosive and effusive eruptions produced the oceanic island in 1963–1967. Two vertically cored boreholes, to 152 and 192 m below the surface, were drilled using filtered, UV-sterilized seawater circulating fluid to minimize microbial contamination. These cores parallel a 181 m core drilled in 1979. Introductory investigations indicate changes in material properties and whole-rock compositions over the past 38 years. A Surtsey subsurface observatory installed to 181 m in one vertical borehole holds incubation experiments that monitor in situ mineralogical and microbial alteration processes at 25–124 ∘C. A third cored borehole, inclined 55∘ in a 264∘ azimuthal direction to 354 m measured depth, provides further insights into eruption processes, including the presence of a diatreme that extends at least 100 m into the seafloor beneath the Surtur crater. The SUSTAIN project provides the first time-lapse drilling record into a very young oceanic basaltic volcano over a range of temperatures, 25–141 ∘C from 1979 to 2017, and subaerial and submarine hydrothermal fluid compositions. Rigorous procedures undertaken during the drilling operation protected the sensitive environment of the Surtsey Natural Preserve.

Scientific Drilling↗
USGS2009

III.-The Work of Prof. Henry Carvill Lewis in Glacial Geology

The recent notice of the life and work of Prof. Henry Carvill Lewis, whose lamented death occurred in Manchester, July 21st, 1888, in his thirty-fifth year, well indicates the wide range of his scientific labours. He published valuable results of investigations in astronomy, mineralogy and petrology, and especially in glacial geology, the last being based on his exploration of the drift and its terminal moraines in the United States, and later in Ireland, Wales and England. The present article reviews his contributions to our knowledge of these drift formations and of the history of the Ice Age, bringing into comparison and correlation the glacial records of America and Europe. Comprehensive as were Professor Lewis' observations and studies in this field, he was planning yet more thorough and extensive exploration of the drift in Britain, Germany and Scandinavia, when he was taken from us.

Geological Magazine↗
USGS2025

Geochemical evidence for the origin of late Quaternary loess, Seward Peninsula, Alaska

Loess is the most widespread surficial deposit in the state of Alaska. Although loess of last glacial age is common in mid-continental North America, records of last glacial loess in Alaska have been elusive. Here we report a record of last glacial loess on the Seward Peninsula, along with studies of a transect of loess localities also thought to date to the last glacial period. Highly diverse hypotheses on the origin of loess on the Seward Peninsula include local volcanic rocks and mountain ranges to the north and south, as well as offshore deposits. We present particle size and mineralogical and geochemical data that indicate that the most likely sources for loess in this part of eastern Beringia are glaciogenic silt particles of the Kobuk River and Noatak River, both of which drain the Brooks Range to the northeast. Northeasterly paleowinds were therefore responsible for loess on the Seward Peninsula. Such winds probably occurred during late summer or early autumn, when river discharge was at a minimum but temperatures were still above freezing. Northeasterly winds during the last glacial period are in good agreement with a recent paleoclimate model.

Alaska↗
USGS2020

Cyclic shear zone cataclasis and sintering during lava dome extrusion: Insights from Chaos Crags, Lassen Volcanic Center (USA)

The ascent and extrusion of crystal-rich magma is commonly facilitated by deformation partitioned within annular, conduit-parallel shear zones. The physical properties and textures of the shear zone materials, where exposed at surface, provide a record of ascent and eruption dynamics. We describe the shear zone developed in Dome C, part of Chaos Crags in the Lassen Volcanic Center (California, USA). The extruded shear zone comprises volcanic fault gouge and variably densified cataclasites. The competent cataclasites evidence deep-seated gouge production followed by gouge densification within the conduit on the timescale of lava dome ascent. Textural, geochemical and mineralogical data identify solid-state sintering as the densification mechanism. At the temperatures and pressures in the volcanic conduit, solid-state sintering causes rapid porosity and permeability loss within the gouge and concomitant material strengthening. Longer dwell times (i.e., slower ascent) allow for more sintering, producing stronger, denser and less permeable cataclasites. At Chaos Crags, we use the extent of sintering, quantified by residual porosity, to recover minimum in-conduit dwell times necessary to produce the observed cataclasites. Our analysis of the Dome C cataclasites suggests a maximum linear ascent rate of 10 m/day and a minimum ascent time of 100 days. We evaluate the consequences of shear zone lithification by solid-state sintering for the eruption of other crystal-rich, glass-poor magmas. Chaos Crags cataclasites preserve evidence of multiple cycles of fracturing, cataclasis and (re-)sintering suggesting a mechanism for transitions between effusive and explosive phases of dome-building eruptions.

California↗
USGS1997

Core OL-92 from Owens Lake: Project rationale, geologic setting, drilling procedures, and summary

Several lines of evidence indicated that Owens Lake, a now-dry lake in southeast California, would probably yield a continuous and climatically informative sedimentary record. Also, the details of modern climate and runoff in the area are exceptionally well known, providing a firm basis for interpreting various types of evidence from a core in terms of past climates. Drilling was carried out in early 1992 to retrieve this record. The resulting core, OL-92, was taken from the south-central part of the lake (lat 36°22.85′ N, long 117°57.95′ W). Lake surface elevation at the drill site is 1,085 m. The core’s length is 322.86 m, recovery was ~80%, and the age of its basal sediments is ~800 ka. Study of the core has revealed lithologic, chemical, mineralogic, geophysical, and paleontologic evidence that reflects alternating periods of high- and low-volume runoff into Owens Lake. This volume presents these studies and summarizes their paleoclimatic significance.

California↗
USGS1988

Ferromanganese deposits from the Gulf of Alaska Seamount Province: Mineralogy, chemistry, and origin

Ferromanganese-oxide deposits dredged from four seamounts (Welker, Miller, Murray, and Patton) in the Gulf of Alaska Seamount Province include poorly crystallized microlaminated crusts on basalt substrate, well-crystallized Mn-oxide veins in epiclastic sedimentary rocks, and crystalline Mn-oxide layers and micronodules in phosphorite. The principal rock types dredged are alkali-basalt pillow fragments and tuffaceous conglomerate and sandstone. The glassy rims of pillow fragments, the glassy goundmass of large volcanic clasts, and the tuffaceous component of the sediment are altered to palagonite. Other low-temperature alteration products include phillipsite, smectite, and carbonate-apatite.Thick (10–50 mm) Fe–Mn crusts consist mainly of δ-MnO 2 ; straight and cuspate growth laminae indicate variable growth rates and periods of nondeposition. A larger number of detrital particles toward the top of thick crusts record the increasing influence of active volcanoes of the Aleutian arc during northwestward movement of the Pacific plate. Thick crusts on basalt substrate have higher Mn/Fe ratios and lower Co content than Fe–Mn crusts from low-latitude seamounts of the central Pacific region. Thin (< 10 mm) crusts on volcaniclastic substrate contain todorokite and birnessite and have higher Mn/Fe ratios, Ni, and Cu and lower Fe and Co than thick Gulf of Alaska crusts.Veins of todorokite and cryptomelane with complex internal structure occur in altered tuffaceous sandstone and conglomerate from Miller Seamount. Fibrous todorokite has a composition similar to those of other marine examples but may contain up to 7% Mn 2+ in M2 sites. Microprobe analysis of the marine cryptomelane indicates a composition that is approximately (K,Ba) 1–2 (Mn 4+ ,Co) 7–8 O 16 ∙ x (H 2 O).A third type of Fe–Mn deposit in phosphorite is an intimate mixture of todorokite (and minor δ-MnO 2 )-bearing layers and micronodules, carbonate-apatite, and phillipsite that encloses grains of altered volcanic glass and lithic fragments.The microlaminated structure, mineralogy (predominantly δ-MnO 2 ), and composition (Mn/Fe ratio and transition metal, rare earth element, U, and Th contents) of the thick crusts are characteristic of hydrogenetic Fe–Mn crusts elsewhere in the Pacific. Conversely, the crystallinity and chemical composition of the Mn-oxide veins and thin crusts indicate formation during diagenesis of the volcanogenic sediment substrate. Mn and other transition metals are mobilized during low-temperature oxidative alteration (palagonitization) of basaltic volcanic glass; the oxidation of Fe 2+ to Fe 3+ during palagonitization and the dissolution of the dilute biogenic fraction of the sediment combine to lower the Eh of ambient pore fluid and enhance the mobility of Mn 2+ . Diagenesis in the phosphatic sandstone from Patton Seamount involves organic-rich sediment and pore waters elevated in phosphorus owing to upwelling above a large volcanic edifice.

Alaska↗
USGS1994

Physical, chemical, and biological data for detailed study of irrigation drainage in the Uncompahgre Project area and in the Grand Valley, west-central Colorado, 1991-92

Because of concerns about potential effects of irrigation drainage on fish and wildlife resources and on human health, the U.S. Department of the Interior initiated a program in 1985 to assess water-quality problems associated with Federal irrigation projects in the Western United States. Physical, chemical, and biological data were collected for a detailed study of irrigation drainage in the Uncompahgre Project area and in the Grand Valley, west-central Colorado, during 1991-92. This report lists onsite measurements and concen- trations of major constituents, trace elements, and stable isotopes for surface-water- and ground-water-sampling sites. Insecticide data collected in the Grand Valley are presented. Ranges of specific-conductance measurements and dissolved- oxygen concentrations for selected wells and a daily record of water-level altitude and specific conduc- tance for a well in the Grand Valley are presented. The report presents historical water-level and dissolved-solids data for two wells in the Grand Valley. Concentrations of trace elements, major constituents, total carbon, and organic carbon in bottom-sediment, bedrock, and in aquifer-sediment samples and semiquantitative data on clay and bulk mineralogy of samples of the Mancos Shale are presented. The report contains selenium-speciation data for selected water and bottom-sediment samples and selected aquifer-test results. Biological samples collected in the Uncompahgre Project area and in the Grand Valley included aquatic plants, aquatic invertebrates, fish, birds, and bird eggs. The report lists concentrations of trace elements in biological samples collected in 1991-92. A limited number of biological samples were analyzed for pesticides, PCB's, and polycyclic aromatic hydrocarbons.

Open-File Report↗
USGS2006

Shocked plagioclase signatures in Thermal Emission Spectrometer data of Mars

The extensive impact cratering record on Mars combined with evidence from SNC meteorites suggests that a significant fraction of the surface is composed of materials subjected to variable shock pressures. Pressure-induced structural changes in minerals during high-pressure shock events alter their thermal infrared spectral emission features, particularly for feldspars, in a predictable fashion. To understand the degree to which the distribution and magnitude of shock effects influence martian surface mineralogy, we used standard spectral mineral libraries supplemented by laboratory spectra of experimentally shocked bytownite feldspar to deconvolve Thermal Emission Spectrometer (TES) data from six relatively large (>50 km) impact craters on Mars. We used both TES orbital data and TES mosaics (emission phase function sequences) to study local and regional areas near the craters, and compared the differences between models using single TES detector data and 3 &#xD7; 2 "> 3×2 detector-averaged data. Inclusion of shocked feldspar spectra in the deconvolution models consistently improved the rms errors compared to models in which the spectra were not used, and resulted in modeled shocked feldspar abundances of >15% in some regions. However, the magnitudes of model rms error improvements were within the noise equivalent rms errors for the TES instrument [Hamilton V., personal communication]. This suggests that while shocked feldspars may be a component of the regions studied, their presence cannot be conclusively demonstrated in the TES data analyzed here. If the distributions of shocked feldspars suggested by the models are real, the lack of spatial correlation to crater materials may reflect extensive aeolian mixing of martian regolith materials composed of variably shocked impact ejecta from both local and distant sources.

Icarus↗
USGS1998

Ordovician K-bentonites in the Argentine Precordillera: Relations to Gondwana margin evolution

Ordovician K-bentonites have now been recorded from >20 localities in the vicinity of the Argentine Precordillera. Most occur in the eastern thrust belts, in the San Juan Limestone and the overlying the Gualcamayo Formation, but a few ash beds are known also from the central thrust belts. The oldest occur in the middle Arenig I. victoriae lunatus graptolite ( Oe. evae conodont) Zone, and the youngest in the middle Llanvirn P. elegans ( P. suecicus ) Zone. Mineralogical characteristics, typical of other Ordovician K-bentonites, include a matrix of illite/smectite mixed-layer clay and a typical felsic volcanic phenocryst assemblage: biotite, beta-form quartz, alkali and plagioclase feldspar, apatite, and zircon, with lesser amounts of hornblende, clinopyroxene, titanite and Fe-Ti oxides. The proportions of the mineral phases and variations in their crystal chemistry are commonly unique to individual (or small groups of) K-bentonite beds. Glass melt inclusions preserved in quartz are rhyolitic in composition. The sequence is unique in its abundance of K-bentonite beds, but a close association between the Precordillera and other Ordovician sedimentary basins cannot be established. The ash distribution is most consistent with palaeogeographical reconstructions in which early Ordovician drifting of the Precordillera occurred in proximity to one or more volcanic arcs, and with eventual collision along the Andean margin of Gondwana during the mid-Ordovician Ocloyic event of the Famatinian orogeny. The Puna-Famatina terrane northeast of the Precordillera might have served as the source of the K-bentonite ashes, possibly in concert with active arc magmatism on the Gondwana plate itself.

Geological Society Special Publication↗
USGS2021

Brine-driven destruction of clay minerals in Gale crater, Mars

Mars’ sedimentary rock record preserves information on geological (and potential astrobiological) processes that occurred on the planet billions of years ago. The Curiosity rover is exploring the lower reaches of Mount Sharp, in Gale crater on Mars. A traverse from Vera Rubin ridge to Glen Torridon has allowed Curiosity to examine a lateral transect of rock strata laid down in a martian lake ~3.5 billion years ago. We report spatial differences in the mineralogy of time-equivalent sedimentary rocks <400 meters apart. These differences indicate localized infiltration of silica-poor brines, generated during deposition of overlying magnesium sulfate–bearing strata. We propose that destabilization of silicate minerals driven by silica-poor brines (rarely observed on Earth) was widespread on ancient Mars, because sulfate deposits are globally distributed.

Science↗
USGS2008

Mineralogic Causes of Variations in Magnetic Susceptibility of Late Pleistocene and Holocene Sediment from Great Salt Lake, Utah

We describe here results of magnetic susceptibility (MS) measurements and magnetic mineralogy of sediments sampled in three cores from the south basin of Great Salt Lake. The cores were obtained in 1996 with a Kullenburg-type piston corer at sites in close proximity: core 96-4 at 41 deg 01.00' N, 112 deg 28.00' W and cores 96-5 and 96-6 at 41 deg 00.09' N, 112 deg 23.05' W. Cores 96-5 (2.16 m long) and -6 combine to make a composite 11.31-m sediment record. Sediments in core 96-4 (5.54 m long) correspond to the approximate depth interval of 3.9-9.6 m in the composite core of 96-5 and -6 based on similarities in the MS records as described below. The central goal of the research was to provide a sediment record of paleoenvironmental change in the northeastern Basin and Range Province over the past 40,000 years. Specific targets included a sedimentologic record of lake-level change combined with a pollen record of climatic change.

Open-File Report↗
USGS2005

Role of ground water in geomorphology, geology, and paleoclimate of the southern High Plains, USA

Study of ground water in the Southern High Plains is central to an understanding of the geomorphology, deposition of economic minerals, and climate change record in the area. Ground water has controlled the course of the Canadian and Pecos rivers that isolated the Southern High Plains from the Great Plains and has contributed significantly to the continuing retreat of the westward escarpment. Evaporative and dissolution processes are responsible for current plateau topography and the development of the signature 20,000 small playa basins and 40 to 50 large saline lake basins in the area. In conjunction with eolian processes, ground water transport controls the mineralogy of commercially valuable mineral deposits and sets up the distribution of fine efflorescent salts that adversely affect water quality. As the water table rises and retreats, lunette and tufa formation provides valuable paleoclimate data for the Southern High Plains. In all these cases, an understanding of ground water processes contributes valuable information to a broad range of geological topics, well beyond traditional interest in water supply and environmental issues.

Colorado, Kansas, New Mexico, Texas↗
USGS2016

Geochemistry, Nd-Pb Isotopes, and Pb-Pb Ages of the Mesoproterozoic Pea Ridge Iron Oxide-Apatite–Rare Earth Element Deposit, Southeast Missouri

Iron oxide-apatite and iron oxide-copper-gold deposits occur within ~1.48 to 1.47 Ga volcanic rocks of the St. Francois Mountains terrane near a regional boundary separating crustal blocks having contrasting depleted-mantle Sm-Nd model ages (T DM ). Major and trace element analyses and Nd and Pb isotope data were obtained to characterize the Pea Ridge deposit, improve identification of exploration targets, and better understand the regional distribution of mineralization with respect to crustal blocks. The Pea Ridge deposit is spatially associated with felsic volcanic rocks and plutons. Mafic to intermediate-composition rocks are volumetrically minor. Data for major element variations are commonly scattered and strongly suggest element mobility. Ratios of relatively immobile elements indicate that the felsic rocks are evolved subalkaline dacite and rhyolite; the mafic rocks are basalt to basaltic andesite. Granites and rhyolites display geochemical features typical of rocks produced by subduction. Rare earth element (REE) variations for the rhyolites are diagnostic of rocks affected by hydrothermal alteration and associated REE mineralization. The magnetite-rich rocks and REE-rich breccias show similar REE and mantle-normalized trace element patterns. Nd isotope compositions (age corrected) show that: (1) host rhyolites have ɛ Nd from 3.44 to 4.25 and T DM from 1.51 to 1.59 Ga; (2) magnetite ore and specular hematite rocks display ɛ Nd from 3.04 to 4.21 and T DM from 1.6 to 1.51 Ga, and ɛ Nd from 2.23 to 2.81, respectively; (3) REE-rich breccias have ɛ Nd from 3.04 to 4.11 and T DM from 1.6 to 1.51 Ga; and (4) mafic to intermediate-composition rocks range in ɛ Nd from 2.35 to 3.66 and in T DM from 1.66 to 1.56. The ɛ Nd values of the magnetite and specular hematite samples show that the REE mineralization is magmatic; no evidence exists for major overprinting by younger, crustal meteoric fluids, or by externally derived Nd. Host rocks, breccias, and magnetite ore shared a common origin from a similar source. Lead isotope ratios are diverse: (1) host rhyolite has 206 Pb/ 204 Pb from 24.261 to 50.091; (2) Pea Ridge and regional galenas have 206 Pb/ 204 Pb from 16.030 to 33.548; (3) REE-rich breccia, magnetite ore, and specular hematite rock are more radiogenic than galena; (4) REE-rich breccias have high 206 Pb/ 204 Pb (38.122–1277.61) compared to host rhyolites; and (5) REE-rich breccias are more radiogenic than magnetite ore and specular-hematite rock, having 206 Pb/ 204 Pb up to 230.65. Radiogenic 207 Pb/ 206 Pb age estimates suggest the following: (1) rhyolitic host rocks have ages of ~1.50 Ga, (2) magnetite ore is ~1.44 Ga, and (3) REE-rich breccias are ~1.48 Ga. These estimates are broadly consistent and genetically link the host rhyolite, REE-rich breccia, and magnetite ore as being contemporaneous. Alteration style and mineralogical or textural distinctions among the magnetite-rich rocks and REE-rich breccias do not correlate with different isotopic sources. In our model, magmatic fluids leached metals from the coeval felsic rocks (rhyolites), which provided the metal source reflected in the compositions of the REE-rich breccias and mineralized rocks. This model allows for the likelihood of contributions from other genetically related felsic and intermediate to more mafic rocks stored deeper in the crust. The deposit thus records an origin as a magmatic-hydrothermal system that was not affected by Nd and Pb remobilization processes, particularly if these processes also triggered mixing with externally sourced metal-bearing fluids. The Pea Ridge deposit was part of a single, widespread, homogeneous mixing system that produced a uniform isotopic composition, thus representing an excellent example of an igneous-dominated system that generated coeval magmatism and REE mineralization. Geochemical features suggest that components in the Pea Ridge deposit originated from sources in an orogenic margin. Basaltic magmatism produced by mantle decompression melting provided heat for extracting melts from the middle or lower crust. Continual addition of mafic magmas to the base of the subcontinental lithosphere, in a back-arc setting, remelted calc-alkaline rocks enriched in metals that were stored in the crust. The St. Francois Mountains terrane is adjacent to the regional T DM line (defined at a value of 1.55 Ga) that separates ~1600 Ma basement to the west, from younger basements to the east. Data for Pea Ridge straddle the T DM values proposed for the line. The Sm-Nd isotope system has been closed since formation of the deposit and the original igneous signatures have not been affected by cycles of alteration or superimposed mineralizing events. No evidence exists for externally derived Nd or Sm. The source region for metals within the Pea Ridge deposit had a moderate compositional variation and the REE-rich breccias and mineralized rocks are generally isotopically homogeneous. The Pea Ridge deposit thus constitutes a distinctive isotopic target for use as a model in identifying other mineralized systems that may share the same metal source in the St. Francois Mountains terrane and elsewhere in the eastern Granite-Rhyolite province.

Missouri↗
USGS2013

Holocene dynamics of the Florida Everglades with respect to climate, dustfall, and tropical storms

Aeolian dust is rarely considered an important source for nutrients in large peatlands, which generally develop in moist regions far from the major centers of dust production. As a result, past studies assumed that the Everglades provides a classic example of an originally oligotrophic, P-limited wetland that was subsequently degraded by anthropogenic activities. However, a multiproxy sedimentary record indicates that changes in atmospheric circulation patterns produced an abrupt shift in the hydrology and dust deposition in the Everglades over the past 4,600 y. A wet climatic period with high loadings of aeolian dust prevailed before 2800 cal BP (calibrated years before present) when vegetation typical of a deep slough dominated the principal drainage outlet of the Everglades. This dust was apparently transported from distant source areas, such as the Sahara Desert, by tropical storms according to its elemental chemistry and mineralogy. A drier climatic regime with a steep decline in dustfall persisted after 2800 cal BP maintaining sawgrass vegetation at the coring site as tree islands developed nearby (and pine forests covered adjacent uplands). The marked decline in dustfall was related to corresponding declines in sedimentary phosphorus, organic nitrogen, and organic carbon, suggesting that a close relationship existed between dustfall, primary production, and possibly, vegetation patterning before the 20th century. The climatic change after 2800 cal BP was probably produced by a shift in the Bermuda High to the southeast, shunting tropical storms to the south of Florida into the Gulf of Mexico.

Florida↗
USGS2004

Secondary Mineral Deposits and Evidence of Past Seismicity and Heating of the Proposed Repository Horizon at Yucca Mountain, Nevada

The Drift Degradation Analysis (DDA) (BSC, 2003) for the proposed high-level radioactive waste repository at Yucca Mountain, Nevada, describes model simulations of the effects of pre- and post-closure seismicity and waste-induced heating on emplacement drifts. Based on probabilistic seismic hazard analyses of the intensity and frequency of future seismic events in the region (CRWMS M&O, 1998), the DDA concludes that future seismicity will lead to substantial damage to emplacement drifts, particularly those in the lithophysal tuffs, where some simulations predict complete collapse of the drift walls. Secondary mineral studies conducted by the U.S. Geological Survey since 1995 indicate that secondary calcite and silica have been deposited in some fractures and lithophysal cavities in the unsaturated zone (UZ) at Yucca Mountain during at least the past 10 million years (m.y.), and probably since the tuffs cooled to less than 100?C. Tuff fragments, likely generated by past seismic activity, have commonly been incorporated into the secondary mineral depositional sequences. Preliminary observations indicate that seismic activity has generated few, if any, tuff fragments during the last 2 to 4 m.y., which may be inconsistent with the predictions of drift-wall collapse described in the DDA. Whether or not seismicity-induced tuff fragmentation occurring at centimeter to decimeter scales in the fracture and cavity openings relates directly to failure of tuff walls in the 5.5-m-diameter waste emplacement drifts, the deposits do provide a potential record of the spatial and temporal distribution of tuff fragments in the UZ. In addition, the preservation of weakly attached coatings and (or) delicate, upright blades of calcite in the secondary mineral deposits provides an upper limit for ground motion during the late stage of deposition that might be used as input to future DDA simulations. Finally, bleaching and alteration at a few of the secondary mineral sites indicate that they were subjected to heated gases at approximately the temperatures expected from waste emplacement. These deposits provide at least limited textural and mineralogic analogs for waste-induced, high-humidity thermal alteration of emplacement drift wall rocks.

Water-Resources Investigations Report↗
USGS2006

Sulfate deposition in subsurface regolith in Gusev crater, Mars

Excavating into the shallow Martian subsurface has the potential to expose stratigraphic layers and mature regolith, which may hold a record of more ancient aqueous interactions than those expected under current Martian surface conditions. During the Spirit rover's exploration of Gusev crater, rover wheels were used to dig three trenches into the subsurface regolith down to 6-11 cm depth: Road Cut, the Big Hole, and The Boroughs. A high oxidation state of Fe and high concentrations of Mg, S, Cl, and Br were found in the subsurface regolith within the two trenches on the plains, between the Bonneville crater and the foot of Columbia Hills. Data analyses on the basis of geochemistry and mineralogy observations suggest the deposition of sulfate minerals within the subsurface regolith, mainly Mg-sulfates accompanied by minor Ca-sulfates and perhaps Fe-sulfates. An increase of Fe2O3, an excess of SiO2, and a minor decrease in the olivine proportion relative to surface materials are also inferred. Three hypotheses are proposed to explain the geochemical trends observed in trenches: (1) multiple episodes of acidic fluid infiltration, accompanied by in situ interaction with igneous minerals and salt deposition; (2) an open hydrologic system characterized by ion transportation in the fluid, subsequent evaporation of the fluid, and salt deposition; and (3) emplacement and mixing of impact ejecta of variable composition. While all three may have plausibly contributed to the current state of the subsurface regolith, the geochemical data are most consistent with ion transportation by fluids and salt deposition as a result of open-system hydrologic behavior. Although sulfates make up >20 wt.% of the regolith in the wall of The Boroughs trench, a higher hydrated sulfate than kieserite within The Boroughs or a greater abundance of sulfates elsewhere than is seen in The Boroughs wall regolith would be needed to hold the structural water indicated by the water-equivalent hydrogen concentration observed by the Gamma-Ray Spectrometer on Odyssey in the Gusev region.

Journal of Geophysical Research E: Planets↗