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The north-central US Midcontinent is underlain by a considerable thickness of sedimentary rocks, mostly Paleozoic, which lie upon a heterogeneous basement of Precambrian granitoid and metamorphic rocks. This article describes a representative sample of Midcontinent geology and explains why the authors believe this region is a 'new frontier' for mineral exploration and discovery. -Authors
A multielement extraction system is being used successfully to provide essentially interference-free geochemical analyses to aid in gold exploration. The Methyl isobutyl ketone-Amine synerGistic Iodide Complex (MAGIC) extraction system separates Ag, As, Au, Bi, Cd, Cu, Ga, Hg, In, Mo, Pb, Pd, Pt, Sb, Se, Sn, Te, Tl, and Zn from interfering geological matrices. Quantitative extraction of these elements is accomplished over a broad range of acid normality making it possible to economically determine all 19 elements from a single digestion or leach solution. The resulting organic extracts are amenable to analysis by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and flame atomic absorption spectroscopy (FAAS). For many years the principal shortcoming of ICP-AES was the complex spectral and stray-light interferences that were caused by the extreme variability of components such as Fe, Na, and Ca in common geological matrices. The MAGIC extraction allows determination of the extracted elements with enhanced sensitivity, from a virtually uniform matrix, by ICP-AES and FAAS. Because of its simultaneous multichannel capabilities, ICP-AES is the ideal instrumental technique for determining these 19 extracted elements. Ultratrace (sub-part-per-billion) determinations of Au and many of the other extracted elements can be made by graphite furnace atomic absorption spectroscopy (GFAAS), following back stripping of the extracts. The combination of the extraction followed by stripping of the organic phase eliminates 99.999% of potential interferences for Au. Gold determination by GFAAS from these extracts under the specified conditions yields a fourfold improvement in sensitivity over conventional GFAAS methods. This sensitivity enhancement and the interference-free matrix allow highly reliable determinations well into the parts-per-trillion range.
Results of drilling, logging, and testing of three exploration core holes, combined with results of geologic and hydrogeochemical investigations, have been used to present a reservoir model of the Platanares geothermal system, Honduras. Geothermal fluids circulate at depths ??? 1.5 km in a region of active tectonism devoid of Quaternary volcanism. Large, artesian water entries of 160 to 165??C geothermal fluid in two core holes at 625 to 644 m and 460 to 635 m depth have maximum flow rates of roughly 355 and 560 l/min, respectively, which are equivalent to power outputs of about 3.1 and 5.1 MW(thermal). Dilute, alkali-chloride reservoir fluids (TDS ??? 1200 mg/kg) are produced from fractured Miocene andesite and Cretaceous to Eocene redbeds that are hydrothermally altered. Fracture permeabillity in producing horizons is locally greater than 1500 and bulk porosity is ??? 6%. A simple, fracture-dominated, volume-impedance model assuming turbulent flow indicates that the calculated reservoir storage capacity of each flowing hole is approximately 9.7 ?? 106 l/(kg cm-2), Tritium data indicate a mean residence time of 450 yr for water in the reservoir. Multiplying the natural fluid discharge rate by the mean residence time gives an estimated water volume of the Platanares system of ??? 0.78 km3. Downward continuation of a 139??C/km "conductive" gradient at a depth of 400 m in a third core hole implies that the depth to a 225??C source reservoir (predicted from chemical geothermometers) is at least 1.5 km. Uranium-thorium disequilibrium ages on calcite veins at the surface and in the core holes indicate that the present Platanares hydrothermal system has been active for the last 0.25 m.y. ?? 1991.
Spatial analysis with a GIS was used to evaluate geothermal systems in Nevada using digital maps of geology, heat flow, young faults, young volcanism, depth to groundwater, groundwater geochemistry, earthquakes, and gravity. High-temperature (>160??C) extensional geothermal systems are preferentially associated with northeast-striking late Pleistocene and younger faults, caused by crustal extension, which in most of Nevada is currently oriented northwesterly (as measured by GPS). The distribution of sparse young (<1.5Ma) basaltic vents also correlate with geothermal systems, possibly because the vents help identify which young structures penetrate deeply into the crust. As expected, elevated concentrations of boron and lithium in groundwater were found to be favorable indicators of geothermal activity. Known high-temperature (>160??C) geothermal systems in Nevada are more likely to occur in areas where the groundwater table is shallow (<30m). Undiscovered geothermal systems may occur where groundwater levels are deeper and hot springs do not issue at the surface. A logistic regression exploration model was developed for geothermal systems, using young faults, young volcanics, positive gravity anomalies, and earthquakes to predict areas where deeper groundwater tables are most likely to conceal geothermal systems.
Exploration budgets fell for a fourth successive year in 2001. These decreases reflected low mineral commodity prices, mineral-market investment reluctance, company failures and a continued trend of company mergers and takeovers.
Modern remote sensing provides a means for locating and characterizing exposed mineralized systems in many parts of the world. These capabilities are non-invasive and help target specific areas for more detailed exploration. An example of how remote sensing technology can be used is evident from a study of the Questa Mining District, New Mexico. Analysis of low spectral resolution data from the Landsat Thematic Mapper satellite system clearly shows the regional distribution of two broad mineral groups often associated with mineralized systems: clay-carbonate-sulfate and iron oxides-iron hydroxides. Analysis of high spectral resolution data from the Airborne Visible and Infrared Imaging System (AVIRIS) shows the occurrence and distribution of many individual mineral species that characterize the pattern of hydrothermally altered rocks in the district.
Crude oil, natural gas and natural gas liquids/condensate resources are important for the redevelopment of Afghanistan's infrastructure. Improved living and economic conditions in Afghanistan require increasing the availability of energy particularly by exploitation of Afghanistan's petroleum resources. The four total petroleum systems are subdivided into units with homogeneous geologic traits and exploration efforts that include sufficiently homogeneous field-size populations for resource assessment. The greatest volume of undiscovered crude oil is estimated to be in the Afghanistan Eastern Suprasalt Thrusts and Folds Assessment Unit. The greatest volume of undiscovered natural gas is estimated to be in the Afghanistan Jurassic Evaporite Basin Subsalt Carbonates Assessment Unit.
Introduction: NASA has played an influential role in bringing the enthusiasm of space science to schools across the United States since the 1980s. The evolution of this public outreach has led to a variety of NASA funded education programs designed to promote student interest in science, technology, engineering, math, and geography (STEM-G) careers. Purpose: This paper investigates the educational outreach initiatives, structure, and impact of two of NASA's largest educational programs: the NASA Explorer School (NES) and NASA Spaceward Bound programs. Methods: The investigation further provides a detailed overview of the structure of these two NASA education outreach programs, while providing information regarding selection criteria and program developments over time. Results: Since its induction in 2003 the NES program has networked and provided resources to over 300 schools across the United States. Future directions include further development of mentor schools for each new NES school selected, while also developing a longitudinal student tracking system for NES students to monitor their future involvement in STEM-G careers. The Spaceward Bound program, now in its third year of teacher outreach, is looking to further expand its teacher network and scientific collaboration efforts, while building on its teacher mentorship framework.
The general effects of agriculture on in-stream fish communities in the Upper Midwestern United States have been well studied for nearly three decades (Karr et al. 1985; Nerbonne and Vondracek 1991; Zimmerman et al. 2001; Goldstein and Meador 2005). Specific impacts include: lowered water levels, sediment loading and nutrient enrichment, loss of riparian habitat, changes to channel morphometry and physical habitat, and changes to the forage base. As part of the National Fish Habitat Action Plan (NFHAP), an initiative to protect, restore, and enhance the nation's fish and aquatic communities, the Fishers and Farmers Partnership specifically focuses on working with agricultural producers to help protect and restore aquatic resources in the Upper Mississippi River Basin (UMRB) (Fig. 1). Successful protection and/or restoration will require the partnership and local conservation agencies to effectively communicate and work with local landowners. However, roughly 43% of the agricultural lands in the UMRB are not operated by those who own the land (National Agricultural Statistics Service 2009) and this is expected to increase as heirs of farm estates now reside greater distances from their home farms than ever before (Arbuckle 2010). It has long been presumed that changes in land ownership trends, toward more absentee landowners, would have important consequences for soil erosion and other conservation practices, as larger, more corporate agriculture, is thought to maximize farm income at the expense of environmental quality (Lee 1980). Absentee landowners may be less likely to take advantage of conservation programs. For example, land operated by renters lags enrollment in the Conservation Reserve (CRP) and Wetland Reserve (WRP) programs by 64% nation-wide (Petrzelka et al. 2009). Also, it has been found that the more detached an absentee landowner becomes from their land, both geographically and culturally, their commitment to land stewardship decreases (Arbuckle 2010). The Fishers and Farmers Partnership recognizes the challenge agricultural producers face in maintaining food and fiber production for a growing world population while also trying to improve environmental quality and fish habitat. This challenge is likely exacerbated when the landowners are absentee. Thus, reaching non-owner-operated farmers and convincing them to help protect and/or restore aquatic resources may be critical to the success of the Fishers and Farmers Partnership. In this study, we explored relationships among agricultural land use, land ownership, and native fish biodiversity in the UMRB as a first step toward helping the Fishers and Farmers Partnership identify specific locations in the UMRB that may pose conservation challenges. For example, places that have experienced a loss of native fish species richness relative to historical conditions and also have high proportions of absentee landowners may provide restoration challenges. We were also interested in identifying areas that have retained high levels of species richness and are owner-operated. These areas present good opportunities to work with local landowners to protect aquatic resources. To identify such areas, we addressed two primary questions: 1) Is there a relationship between the type of agricultural land use (i.e. cropland vs pastureland) and the % of land rented or leased within the UMRB? and 2) How does the type of agricultural production and whether land is rented or leased relate to the maintenance of historical levels of native fish species richness? We predicted that areas with large amounts of land devoted to crop production will have experienced the greatest losses of native fish species richness. However, our hypothesis is that watersheds with large amounts of land rented or leased will have experienced even greater declines in native fish species richness than would be predicted from the amount of cultivated cropland alone. By testing these hypotheses, we intended to identify watersheds that would be strong candidates for protection, restoration, and enhancement of fish species richness by accounting for land use and ownership characteristics.
The U.S. Geological Survey (USGS) has been systematically monitoring global nonfuel mineral exploration activities to anticipate the location and quantity of future nonfuel minerals supply for about 100 commodities, with an emphasis on precious and base metals. Since 1995, the USGS has developed an annual list of 100 noteworthy prospects that were considered to have a high level of potential for near-term development based on such criteria as intensity of drilling, level of capital investment, and size of resource. This study reviews the status of the U.S. sites included on these lists as of July 2011 and addresses domestic prospects not included on the lists that have come into production since 1995.
Exploration budgets fell for a fifth successive year during 2002. These decreases reflected unsettled mineral commodity prices and the continued reluctance to invest in mineral markets.
Sedimentary-type uranium deposits accumulate at favorable sites along a migration path which may be kilometers in length. Their source is a large volume of rock from which the uranium has been leached. The geochemical mobilities and half lives of uranium and its daughter products vary widely so that they are transported from the source rocks, at different rates, along the migration path to their ultimate site. The radioactive disequilibrium resulting from this process has been well documented in the immediate vicinity of ore deposits, and disequilibrium is commonly recorded on gamma-ray logs up the hydraulic gradient from uranium ore. Little is known about the state of secular equilibrium in the leached host rocks, which often represent the only part of the migration path that is at or near the surface and is thus most accessible to the exploration geophysicist. High-resolution gamma-ray spectrometry provides a means of investigating the disequilibrium associated with uranium leaching and migration. Direct measurement of uranium can be made by this method, and the equivalent weight percents can be determined for six of the seven daughter-product decay groups that characterize the state of radioactive equilibrium. The technique has been used quantitatively in laboratory studies, where the results compare favorably with radiochemical analyses; field experiments suggest that semi-quantitative data may be obtained at the outcrop.
Overcoming future difficulties in searching for ore deposits deeper in the earth's crust will require closer attention to the collection and analysis of more diverse types of data and to more efficient use of current computer technologies. Computer technologies of greatest interest include methods of storage and retrieval of resource information, methods for integrating geologic, geochemical, and geophysical data, and the introduction of advanced computer technologies such as expert systems, multivariate techniques, and neural networks. Much experience has been gained in the past few years in applying these technologies. More experience is needed if they are to be implemented for everyday use in future assessments and exploration.
Semi-quantitative spectrographic analyses of mineralized and unmineralized sandstone, siltstone, and claystone from the Catskill Formation of Devonian age in Bradford, Columbia, and Lycoming Counties, Pa., suggest that copper, silver, and uranium are the principal metallic elements concentrated in the mineralized rock. Lead, mercury, and molybdenum may be concentrated slightly in mineralized rock but values are too low to be of use in exploration. The deposits are too small to make large anomalies in stream sediments except in drainage basins of less than a few acres. However, if a large deposit were exposed to weathering, it would probably be detectable by stream sediment sampling. Analyses of oxalic acid leachates of the minus 80-mesh fraction of the stream-sediment samples gave more useful values than analyses of the minus 80-mesh samples in separating drainage basins that have copper deposits from those that have no known copper deposits.
Karangahake was the third largest gold producer in the Hauraki goldfield. In 2009, New Talisman Gold mines was granted a mining permit, and plans are underway to commence underground mine development of the Maria vein, which has a maiden Ore Reserve (consistent with the 2012 JORC Code) of 28 800 oz Au and 127 800 oz Ag. Exploration drilling at Rahu, located 2 km north of Karangahake has identified polymictic hydrothermal breccias and quartz veins that are strongly gold anomalous. Some quartz vein clasts within the breccia have up to 8.7 g/t Au, suggesting the presence of higher grade quartz vein(s) either below or directly adjacent to the breccias. A controlled source audio-frequency magnetotelluric (CSAMT) survey at Rahu revealed that strongly resistive zones extend below the Barbara and Eunice anomalies to at least 300 m depth and likely correspond to areas of increased silicification, breccias and/or veins. Future drilling will focus on these targets. Detailed geophysical, alteration and fluid inclusion studies have been undertaken at Karangahake, Rahu and Ascot (c 1 km NW of Rahu). Karangahake and Rahu both occur within a broad demagnetised zone, c 4.2 × 2.7 km, in which magnetite has been destroyed by strong hydrothermal alteration. At Karangahake, andesite and overlying minor rhyolite are replaced by adularia, chlorite, illite, pyrite, plus minor albite, epidote and calcite, which have formed from upwelling chloride waters that at depth were hotter than 280°C. At Rahu, localised adularia coupled with complex distributions of illite and interstratified illite-smectite, suggest cooler (c 180° to 240°C) and more focused fluid flow, as well as inferred cool groundwater influx. Fluid inclusion data suggest veins at Karangahake, Rahu and Ascot formed beneath palaeowater tables at 920 m, 440 m and 430 m relative to current sea level (asl), respectively. At Ascot, the presence of silica sinter at 135 m asl, which formed at the palaeosurface, is shallower compared to the fluid inclusion depth estimate and suggests that the palaeowater table here rose some 300 m during hydrothermal activity due to burial, resulting in overprinting. This overprint may also have occurred at Karangahake and Rahu, but the evidence is inconclusive; although burial during hydrothermal activity could explain the exceptional 700 m vertical range of mineralisation at Karangahake and raises the possibility of concealed mineralisation at depth elsewhere within the Karangahake alteration envelope.
The timing of spring phenology can be influenced by several drivers. Many studies have shown the effect of temperature on spring vegetation growth, but the role of moisture is complex and not as well researched. We explored drivers for aspen spring phenology in the mountains of the western U.S. While temperature exerted control over the timing of aspen green-up in the spring, snow moisture as measured by April 1 snow water equivalent (SWE), played a significant role especially in southern locations bordering the Colorado Plateau. Maximum spring temperatures (March-May) were significantly (p<0.01) correlated with the start of the growing season across the entire Wasatch and Uinta Mountains and most of the western and northern Southern Rocky Mountains. Spring SWE was significantly (p<0.01) correlated with the growing season start across all of the Wasatch and Uinta Mountains and more than half of the Southern Rockies. The locations that experienced a larger snow influence, given by linear regression and R2 values, were located adjacent to the drier Colorado Plateau and south of 40oN latitude. Historical spatial patterns of regional snow accumulations and anomalies in the western U.S. have been chiefly explained by decadal antiphasing patterns across a north-south dipole. Anomalously low SWE co-occurs with a Pacific/North American teleconnection winter circulation associated with strong high pressure over the Pacific Northwest. The pattern shown in aspen phenology in this study, where the timing of spring green-up in the southern half of the intermountain West (south of a zone from 40oN - 42oN and mainly west of the continental divide in Colorado) showed higher sensitivity to winter snow moisture, and this spatial pattern was supported by other studies. Although winter moisture was not as consistent a factor as temperature in driving the start of the season, this study shows evidence that possible future winter drought could shift the growing season earlier than temperature increases alone.
We present a series of debris-flow events and use combined sensor and video data to explore how sediment concentration and triggering rainfall intensity affect the velocity and discharge of debris-flow surges generated by surface-water runoff. We analyze an initial data set of 49 surges from four debris-flow events recorded by a monitoring system at Chalk Cliffs, Colorado and compare measurements of surge height, velocity, peak discharge, triggering rainfall intensity, and qualitative estimates of sediment concentration. Measurements of sediment concentration and velocity were obtained using an automated camera system with a high resolution and frame rate. We find that the triggering rainfall intensity of the debris flows, which affects the sediment-to-water ratio, is a strong control on surge velocity and peak discharge. While surges with high and low sediment concentrations both exceed the peak discharge of water-only flow, fluid-rich surges generated by high rainfall intensities have much greater velocities and peak discharges than sediment-rich surges generated by lower rainfall intensities. These observations suggest that rainfall intensity may be an important predictive variable in empirical relationships for estimating the velocity and peak discharge of runoff generated debris flows, which are common in alpine areas and burned steeplands.
(Re)insurance companies rely on earthquake risk models to estimate the frequency and severity of their potential financial losses. To protect themselves, they sometimes use parametric risk transfer solutions, which are derivative-form agreements that provide compensation as a function of routine measurable earthquake characteristics. These mechanisms typically remain in force for one to three years and assume seismic conditions—and our estimates of them—remain unchanged during this period. However, seismic risk estimates evolve continuously due to changes in nearby seismicity, sudden ruptures, slower redistributions of stress, or improvements in our own understanding of these phenomena. As a consequence, the likelihood of some loss-causing events might decrease and make the protection superfluous (wasted money), or, more problematically, it might increase and render the protection insufficient (increased risk). This paper explores the construction of parametric earthquake risk transfer mechanisms that adapt efficiently (i.e., near real-time) to changes in seismicity throughout the lifetime of the transaction. The mechanism proposes the periodic adjustment of the payment conditions of the parametric agreement in harmony with the evolving probabilities of event occurrence. This, we hypothesize, may result in a more efficient allocation of premiums that reflects the changing nature of seismic risk. To build the proposed dynamic risk transfer mechanism, we first employ one of the earthquake models commonly used in the (re)insurance industry to assess the risk of a portfolio of assets. The modeling exercise yields the expected frequency distribution of loss, which a standard (re)insurance transaction would typically consider constant for the entire coverage period. Here, we use these results simply as a baseline for the initial time step of reference. Next, we construct a retrospective update loop, which consists of two parts: (1) we obtain the earthquake occurrence rate conditions at a previous time step taking into account the changes in seismicity observed in the interim period; and (2) we use the modeled losses and adjusted frequencies at the new time step to build a parametric risk transfer solution. This parametric solution remains in force until it is updated at the next iteration. We also track the effects on the efficiency of the risk transfer solution and its premium if these continuous updates were not implemented. We apply the proposed mechanism to California and find that changes in seismicity can cause swings in the frequency of parametric payments (which is related to the premium paid for the cover) in average of 16% and up to 36% in any three-year period from 1986 to 2020. We also find that avoiding an update of the parametric solution on a yearly basis to match the new risk profile can decrease the efficiency of the cover (measured as the relative contribution to the average annual loss of the events covered) in the same time period by 13% on average and up to 35%.