USGS Science⌕ Search

SEARCH · USGS Science

Results for “Geosciences”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

752 records · Page 42Linked to original sources
USGS1996

Porphyry deposits of the Canadian Cordillera

Porphyry deposits are intrusion-related, large tonnage low grade mineral deposits with metal assemblages that may include all or some of copper, molybdenum, gold and silver. The genesis of these deposits is related to the emplacement of intermediate to felsic, hypabyssal, generally porphyritic intrusions that are commonly formed at convergent plate margins. Porphyry deposits of the Canadian Cordillera occur in association with two distinctive intrusive suites: calc-alkalic and alkalic. In the Canadian Cordillera, these deposits formed during two separate time periods: Late Triassic to Middle Jurassic (early Mesozoic), and Late Cretaceous to Eocene (Mesozoic-Cenozoic). Deposits of the early Mesozoic period occur in at least three different arc terranes (Wrangellia, Stikinia and Quesnellia) with a single deposit occurring in the oceanic assemblage of the Cache Creek terrane. These terranes were located outboard from continental North America during formation of most of their contained early Mesozoic porphyry deposits. Some of the deposits of this early period may have been emplaced during terrane collisions. Metal assemblages in deposits of the calc-alkalic suite include Mo-Cu (Brenda), Cu-Mo (Highland Valley, Gibraltar), Cu-Mo-Au-Ag (Island Copper, Schaft Creek) and Cu-Au (Kemess, Kerr).The alkalic suite deposits are characterized by a Cu-Au assemblage (Copper Mountain, Afton-Ajax, Mt. Milligan, Mount Polley, Galore Creek). Although silver is recovered from calc-alkalic and alkalic porphyry copper mining operations, silver data are seldom included in the published reserve figures. Those available are in the range of 1-2 grams per tonne (g??t-1). Alkalic suite deposits are restricted to the early Mesozoic and display distinctive petrology, alteration and mineralization that suggest a similar tectonic setting for both Quesnellia and Stikinia in Early Jurassic time. The younger deposits, late Mesozoic to Cenozoic in age, formed in an intracontinental setting, after the outboard host arc and related terranes accreted to the western margin of North America. These deposits are interpreted to occur in continental arc settings, and individual deposits are hosted by a variety of older country rocks. These younger deposits also show a spectrum of metal associations: Cu-Mo (Huckleberry, Berg), Cu-Au (-Mo) (Bell, Granisle, Fish Lake, Casino), Mo (Endako, Boss Mountain, Kit-sault, Quartz Hill), Mo-W (Logtung), Au-W (Dublin Gulch) and Au (Ft. Knox). There may be a continuum between Mo, Mo-W, Au-Mo-W and Au deposits. The distribution and timing of these post-accretion deposits likely reflect major crustal structures and subduction geometry. Cordilleran porphyry metallic deposits show the full range of morphological and depth relationships found in porphyry deposits worldwide. In addition, the Cordillera contains numerous alkalic suite deposits, which are rare worldwide: the unusual, possibly syntectonic Gibraltar deposit; and end-member gold-rich granite-hosted deposits, such as Ft. Knox (Alaska).

Geoscience Canada↗
USGS1997

Ice-sheet sourced juxtaposed turbidite systems in Labrador Sea

Ice-sheet sourced Pleistocene turbidite systems of the Labrador Sea are different from non-glacially influenced systems in their facies distribution and depositional processes. Two large-scale sediment dispersal systems are juxtaposed, one mud-dominated and associated with the Northwest Atlantic Mid-Ocean Channel (NAMOC), the other sand-dominated and forming a huge submarine braided sandplain. Co-existence of the two systems reflects grain-size separation of the coarse and fine fractions on an enormous scale, caused by sediment winnowing at the entrance points of meltwater from the Laurentide Ice Sheet (LIS) to the sea (Hudson Strait, fiords) and involves a complex interplay of depositional and redepositional processes. The mud-rich NAMOC system is multisourced and represents a basinwide converging system of tributary canyons and channels. It focusses its sand load to the central trunk channel in basin centre, in the fashion of a "reverse" deep-sea fan. The sand plain received its sediment from the Hudson Strait by turbidity currents that were generated either by failure of glacial prodelta slopes at the ice margin, or by direct meltwater discharges with high bedload concentration. We speculate that the latter might have been related to subglacial-lake outburst flooding through the Hudson Strait, possibly associated with ice-rafting (Heinrich) events.

Geoscience Canada↗
USGS1999

Tectonics of Atlantic Canada

The tectonic history of Atlantic Canada is summarized according to a model of multiple ocean opening-closing cycles. The modern North Atlantic Ocean is in the opening phase of its cycle. It was preceded by an early Paleozoic lapetus Ocean whose cycle led to formation of the Appalachian Orogen. lapetus was preceded by the Neoproterozoic Uranus Ocean whose cycle led to formation of the Grenville Orogen. The phenomenon of coincident, or almost coincident orogens and modern continental margins that relate to repeated ocean opening-closing cycles is called the Accordion Effect. An understanding of the North Atlantic Ocean and its continental margins provides insights into the nature of lapetus and the evolution of the Appalachian Orogen. Likewise, an understanding of lapetus and the Appalachian Orogen raises questions about Uranus and the development of the Grenville Orogen. Modern tectonic patterns in the North Atlantic may have been determined by events that began before 1000 m.y.

Geoscience Canada↗
USGS2006

Helping Students make the transition from novice learner of ground-water concepts to expert using the Plume Busters software

Environmental and earth science students are novice learners and lack the experience needed to rise to the level of expert. To address this problem we have developed the prototype Plume Busters?? software as a capstone educational experience, in which students take on the role of an environmental consultant. Following a pipeline spill, the environmental consultant is hired by the pipeline owner to locate the resulting plume created by spill and remediate the contaminated aquifer at minimum monetary and time cost. The contamination must be removed from the aquifer before it reaches the river and eventually a downstream public water supply. The software consists of an interactive Java application and accompanying HTML linked pages. The application simulates movement of a plume from a pipeline break throug h a shallow alluvial aquifer towards the river. The accompanying web pages establish the simulated contamination scenario and provide students with background material on ground-water flow and transport principles. To make the role-play more realistic, the student must consider cost and time when making decisions about siting observation wells and wells for the pump-and-treat remediation system.

Journal of Geoscience Education↗
USGS2006

Teachers doing science: An authentic geology research experience for teachers

Fairmont State University (FSU) and the West Virginia Geological and Economic Survey (WVGES) provided a small pilot group of West Virginia science teachers with a professional development session designed to mimic experiences obtained by geology majors during a typical summer field camp. Called GEOTECH, the program served as a research capstone event complimenting the participants' multi-year association with the RockCamp professional development program. GEOTECH was funded through a Improving Teacher Quality Grant administered by West Virginia Higher Education Policy Commission. Over the course of three weeks, eight GEOTEACH participants learned field measurement and field data collection techniques which they then applied to the construction of a surficial geologic map. The program exposed participants to authentic scientific processes by emphasizing the authentic scientific application of content knowledge. As a secondary product, it also enhanced their appreciation of the true nature of science in general and geology particular. After the session, a new appreciation of the effort involved in making a geologic map emerged as tacit knowledge ready to be transferred to their students. The program was assessed using pre/post instruments, cup interviews, journals, artifacts (including geologic maps, field books, and described sections), performance assessments, and constructed response items. Evaluation of the accumulated data revealed an increase in participants demonstrated use of science content knowledge, an enhanced awareness and understanding of the processes and nature of geologic mapping, positive dispositions toward geologic research and a high satisfaction rating for the program. These findings support the efficacy of the experience and document future programmatic enhancements.

Journal of Geoscience Education↗
USGS2009

International year of planet earth 7. Oceans, submarine land-slides and consequent tsunamis in Canada

Canada has the longest coastline and largest continental margin of any nation in the World. As a result, it is more likely than other nations to experience marine geohazards such as submarine landslides and consequent tsunamis. Coastal landslides represent a specific threat because of their possible proximity to societal infrastructure and high tsunami potential; they occur without warning and with little time lag between failure and tsunami impact. Continental margin landslides are common in the geologic record but rare on human timescales. Some ancient submarine landslides are massive but more recent events indicate that even relatively small slides on continental margins can generate devastating tsunamis. Tsunami impact can occur hundreds of km away from the source event, and with less than 2 hours warning. Identification of high-potential submarine landslide regions, combined with an understanding of landslide and tsunami processes and sophisticated tsunami propagation models, are required to identify areas at high risk of impact.

Geoscience Canada↗
USGS2011

A lognormal distribution of metal resources

For national or global resource estimation of frequencies of metals, a lognormal distribution has commonly been recommended but not adequately tested. Tests of frequencies of Cu, Zn, Pb, Ag, and Au contents of 1 984 well-explored mineral deposits display a poor fit to the lognormal distribution. When the same metals plus Mo, Co, Nb2O3, and REE2O3 are grouped into 19 geologically defined deposit types, only eight of the 73 tests fail to be fit by lognormal distribution, and most of those failures are in two deposit types suggesting a problem with those types. Estimates of the mean and standard deviation of each of the metals in each of the deposit types are provided for modeling.

Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Sc↗
USGS2011

Quality of our groundwater resources: Arsenic and fluoride

Groundwater often contains arsenic or fluoride concentrations too high for drinking or cooking. These constituents, often naturally occurring, are not easy to remove. The right combination of natural or manmade conditions can lead to elevated arsenic or fluoride which includes continental source rocks, high alkalinity and pH, reducing conditions for arsenic, high phosphate, high temperature and high silica. Agencies responsible for safe drinking water should be aware of these conditions, be prepared to monitor, and treat if necessary.

Geosciences↗
USGS1999

Coal-fired power generaion, new air quality regulations, and future U.S. coal production

Tighter new regulation of stack gas emissions and competition in power generation are driving electrical utilities to demand cleaner, lower sulfur coal. Historical data on sulfur content of produced coals shows little variability in coal quality for individual mines and individual coal-producing counties over relatively long periods of time. If coal-using power generators follow the compliance patterns established in Phase I of the 1990 Clean Air Act Amendments, then the industry's response to the tighter Phase II emissions standards will result in large amounts of coal production shifting from higher sulfur areas to areas with lower cost low sulfur coal. One reason this shift will likely occur is that currently only 30% of U.S. coal-fired electrical generating capacity is equipped with flue-gas scrubbers. In 1995, coal mines in the higher sulfur areas of the Illinois Basin and Northern and Central Appalachia employed 78% of all coal miners (>70,000 miners). A substantial geographical redistribution of the nation's coal supplies will likely lead to economic dislocations that will reach beyond local coal-producing areas.

Environmental Geosciences↗
USGS2000

A new look at natural disasters

We are paying a high price for the way we live on our beautiful but dangerous planet. Last year the world experienced deadly earthquakes in Turkey, Taiwan, Colombia and Greece; floods and devastating landslides in Venezuela; hurricanes along the Atlantic Coast that forced evacuation of millions; and numerous smaller disasters. As bad as these events were, they were not extraordinary viewed in the context of previous 20th century occurrences.

News and Trends in the Geosciences↗
USGS2014

Major and trace element geochemistry and background concentrations for soils in Connecticut

Soil samples were collected throughout Connecticut (CT) to determine the relationship of soil chemistry with the underlying geology and to better understand background concentrations of major and trace elements in soils. Soil samples were collected (1) from the upper 5 cm of surficial soil at 100 sites, (2) from the A horizon at 86 of these sites, and (3) from the deeper horizon, typically the C horizon, at 79 of these sites. The <2-millimeter fraction of each sample was analyzed for 44 elements by methods that yield the total or near-total elemental content. Sample sites were characterized by glacial setting, underlying bedrock geology, and soil type. These spatial data were used with element concentrations in the C-horizon to relate geologic factors to soil chemistry. Concentrations of elements in C-horizon soils varied with grain size in surficial glacial materials and with underlying rock types, as determined using nonparametric statistical procedures. Concentrations of most elements in C-horizon soils showed a positive correlation with silt and (or) clay content and were higher in surficial materials mapped as till, thick till, and (or) fines. Element concentrations in C-horizon soils showed significant differences among the underlying geologic provinces and were highest overlying the Grenville Belt and (or) the Grenville Shelf Sequence Provinces in western CT. These rocks consist mainly of carbonates and the relatively high element concentrations in overlying soils likely result from less influence of dilution by quartz compared to other provinces. Element concentrations in C-horizon soils in CT were compared with those in samples from other New England states overlying similar lithologic bedrock types. The upper range of As concentrations in C-horizon soils overlying the New Hampshire-Maine (NH-ME) Sequence in CT was 15 mg/kg, lower than the upper range of 24 mg/kg in C-horizon soils overlying the same sequence in ME. In CT, U concentration means were significantly higher in C-horizon soils overlying Avalonian granites, and U concentrations ranged as high as 14 mg/kg, compared to those in C-horizon soil samples collected from other New England states, which ranged as high as 6.1 mg/kg in a sample in NH overlying the NH-ME Sequence. Element concentrations in C-horizon soils in CT were compared with those in samples collected from shallower depths. Concentrations of most major elements were highest in C-horizon soil samples, including Al, Ca, Fe, K, Na, and Ti, but element concentrations showed a relatively similar pattern in A-horizon and surficial soil samples among the underlying geologic provinces. Trace element concentrations, including Ba, W, Ga, Ni, Cs, Rb, Sr, Th, Sc, and U, also were higher in C-horizon soil samples than in overlying soil samples. Concentrations of Mg, and several trace elements, including Mn, P, As, Nb, Sn, Be, Bi, Hg, Se, Sb, La, Co, Cr, Pb, V, Y, Cu, Pb, and Zn were highest in some A-horizon or surficial soils, and indicate possible contributions from anthropogenic sources. Because element concentrations in soils above the C horizon are more likely to be affected by anthropogenic factors, concentration ranges in C-horizon soils and their spatially varying geologic associations should be considered when estimating background concentrations of elements in CT soils.

Connecticut↗
USGS1990

Overview of the effects and influence of the activity of Mount St. Helens in the 1980s

The cataclysmic eruption of Mount St. Helens on May 18, 1980, made an enormous impact on the science of volcanology. The eruption was in daylight in clear weather, which provided an unprecedented opportunity to investigate relations among observations, products, and effects of a large explosive eruption. The May 18 events and subsequent activity stimulated perhaps the most intensive studies ever made at an active composite volcano, leading to greatly enhanced insights into both geologic and hydrologic processes operative in explosive volcanism. The eruption also disrupted much of the social and economic fabric of the Pacific Northwest. Volcanologists were called upon to explain the activity, in layman's terms, to government and corporate officials, the news media, schools, and the public at large. People eventually learned to live with the volcano and its uncertainties, and volcanologists better learned their role in helping society deal with a major natural disaster. Difficulties encountered at volcanic crises elsewhere in the world in the 1980s demonstrate that these are hard lessons. In future years, a paramount challenge for scientists will be to help society apply what has been learned at Mount St. Helens to crises both nearby and far away.

Washington↗