Tertiary and Cretaceous western US coal provides the nation with its most prolific coal mining regions. Wyoming leads the nation in producing low-sulfur Tertiary coal from its 17 world-class surface mines in the Powder River Basin. Wyoming produces 400 MT of coal annually, which is more than the next six coal-mining states combined. Colorado is ranked ninth, and has increased its production of Cretaceous coal by 10% in the past year. The economic value of coal production in the two states is about $6 billion annually.
Wyoming produces coal mostly from the Paleocene Tongue River member of the Ft. Union Formation. Colorado coal is from the Cretaceous Mesaverde Group (Upper Williams Fork and Bowie members) and the coal-bearing part of the Dakota Sandstone on the western slope, and the Paleocene/Cretaceous Raton Formation near Trinidad. Paleocene coals of the Rocky Mountains and Northern Great Plains contain low sulfur and ash content, while the Cretaceous coals have low to moderately low sulfur and ash, marking these coals as the most important compliant coal resources in the US.
Bio for Chris Carroll:
Chris was with the Colorado Geological Survey (CGS) from 1989 to 2012. He has authored or co-authored nine geologic quadrangles maps in Colorado Springs, Durango, South Park, and Glenwood Springs, and mapped over 100 miles of the Fruitland Formation coal outcrop in the Colorado part of the San Juan Basin. He recently began work with the Wyoming State Geological Survey as their coal geologist. His main coal research interests include coal resource assessments and coal availability studies in the Somerset, Yampa, White River, Danforth Hills, and Trinidad coal fields. He has completed several publications on coal resources in Colorado, and is the author of the Historic Coal Mines of Colorado, the Colorado Coal Directory, and the Coal Resource Maps of Colorado. He is currently working with the USGS on a cooperative National Coal Resource Data System (NCRDS) coal program in the Greater Green River area of south-central Wyoming.
Mr. Carroll is a graduate of the University of California at Santa Barbara in geology with an emphasis in geophysics. Chris is the past-president of the Friends of Dinosaur Ridge, and past chair of the Geological Society of America’s Coal Geology Division. Most importantly he is an expert whitewater rafter with over 10,000 miles of rivers in the western and southwestern US.
The northern Rio Grande rift – new geological studies in the upper Arkansas River valley region, Colorado
A talk by Karl S. Kellogg, U.S. Geological Survey
(with major contributions from Cal Ruleman, Ralph Shroba, Bob Bohannon, Wayne Premo, Mike Cosca, and Keenan Lee)
It has been 125 years since Samuel Emmons published his USGS monograph on the Leadville mining district. Since then, dozens of
geologists have published papers and maps on the geology and ore deposits of the upper Arkansas River valley, between Leadville and Salida. The USGS is currently undertaking a fresh geological look at this major extensional feature, a northern expression of the Rio Grande rift, employing detailed mapping of more poorly understood areas and reinterpretation of many previously studied regions.
Recently acquired LiDAR data and new isotopic dating has greatly facilitated this research. A 1:50,000-scale geologic map of the region, based, in part, on the new mapping, nears completion and extends into the Proterozoic metamorphic and intrusive rocks in the adjacent Sawatch and Mosquito Ranges. This talk will first present an overview of the geology of the upper Arkansas River Valley region,
followed by a presentation of some of the new features and ideas we have developed.
The grabens that control the upper Arkansas River valley are filled with thick basin-fill deposits (mostly Dry Union Formation), which occupy two major sub-basins. Along the Arkansas River locally there are at least 5 major alluvial terraces, and an equivalent number of pediment surfaces that slope from the Sawatch Range on the west side of the valley, all documenting deep erosion since the end of the Tertiary. Numerous new U/Pb and Ar40/Ar39 isotopic ages better constrain the timing of both Proterozoic and Late Cretaceous to early Tertiary intrusive events. New detailed mapping, coupled with 10Be cosmogenic surface-exposure ages, have revealed the timing and rates of late Pleistocene deglaciation. Many previously unrecognized Neogene and Quaternary faults, some with possible Holocene dis-placement, have been identified. As participant on a CSS fieldtrip observed this fall, glacial dams that impounded the Arkansas River at Clear Creek and Pine Creek failed at least 3 times during the middle and late Pleistocene, resulting in catastrophic floods and deposition of enormous boulders (some > 10 m long) downstream; at least two failures occurred during the late Pleistocene Pinedale glaciation.
Biography of Karl Kellogg
Karl received his B.A. degree from UC Berkeley in 1966, and Ph.D. in geology from CU Boulder in 1972. He feels like he almost lived his retirement early for several years, teaching for Outward Bound School, travelling, and working part time for the USGS on 3 expeditions to Antarctica (and once more with the New Zealand
Antarctic Research Program), before settling down to teach geology for two years at Cal State University, Sono-ma. He joined the USGS full time in 1980, first working on the Saudi Arabian program for 3 years. His USGS career has also involved working on the Volcanic Hazards Program and mapping in (1) the Idaho and Montana thrust and foreland provinces, (2) the Transverse Ranges of California, and (3) central Colorado. He is author or co-author on over 100 scientific publications (excluding abstracts), including 37 geological maps. He was presi-dent of the Colorado Scientific Society in 1997. His hobbies involve bicycling, river running, forest management on his family’s tree farm, skiing, and photography.
What Can I Do to Help the Colorado Geological Survey?
A talk by Vince Matthews, Colorado Geological Survey
Transfer of the Colorado Geological Survey from the Department of Natural Resources to the Colorado School of Mines is now formalized by Legislative Action. However, the conditions of that transfer were developed largely behind closed doors outside the legislative process, with minimal outside input. The DNR proposal has eliminated all state funding for groundwater, oil, gas, coal, minerals, geothermal, CO2 sequestration, and ground water quality programs. There are substantial ramifications for the people of Colorado. However, there is some support in the Legislature for restoration of some programs, but strong constituent support will be necessary to accomplish this.
Biography of Vince Matthews
Vince Matthews is a former State Geologist and Director of the Colorado Geological Survey. Vince re-ceived Bachelors and Masters degrees in Geology from the University of Georgia and a Ph.D. from the University of California, Santa Cruz. He held tenured positions at two universities and has taught geology at the University of California, University of Northern Colorado, Arizona State University, the Frank Lloyd Wright School of Architecture, and the University of Texas of the Permian Basin.
As an executive in the natural resources industry for Amoco, Lear, Union Pacific, and Penn Virginia, Matthews explored for oil & gas in virtually every basin in the U.S., including Alaska and the Gulf of Mexico. Vince is the author of more than 70 technical articles and abstracts and was senior editor of the multiple, award-winning publication, Messages in Stone: Colorado’s Colorful Geology and the map, A Tourist Guide to Colorado Geology.
NOAA scientists have been increasing the sophistication of earth system models, with atmospheric, ocean, land surface, chemistry components and even volcanic eruptions. One such relatively new global model is called FIM (Flow-following finite-volume Icosahedral Model (FIM) – http://fim.noaa.gov) which uses a soccer-ball-like grid to cover the earth’s surface. The FIM model has a 60-level atmospheric model run down to 10km horizontal resolution. It is coupled with a 20-level ocean model, atmospheric chemistry with 20-60 independent species variables, and a multi-level land-vegetation-snow-surface parameterization at each horizontal land grid point. The FIM coupled earth system model has been enhanced with volcanic plume rise and volcanic ash transport in the atmosphere.
The components of the earth system model will be briefly explained and how they interact. Various forecasts will be shown, including a case from the Eyjafjallajokull (Iceland) eruption in April 2010 and hurricane forecasts for Hurricanes Sandy and Isaac, the two US land-falling hurricanes in 2012.
Stan Benjamin leads the development of weather forecast and earth
system forecast models at the NOAA (National Oceanic and Atmospheric Administration) Earth System Research Laboratory (ESRL) in Boulder, CO. Stan holds a B.A. in math (Albion College, Michigan), and M.S. and Ph.D. in meteorology from Penn. State University.
Simulation and Observations of the Denver Basin Aquifer System
By Suzanne Paschke
The Denver Basin aquifer system is a critical water resource for growing municipal, industrial, and domestic uses along the semiarid Front Range urban corridor of Colorado. The confined bedrock aquifer system is located along the eastern edge of the Rocky Mountain Front Range where the mountains meet the Great Plains physiographic province. Continued population growth and the resulting need for additional water supplies in the Denver Basin and throughout the western United States emphasize the need to continually monitor and reassess the availability of groundwater resources.
In 2004, the U.S. Geological Survey initiated large-scale regional studies to provide updated groundwater-availability assessments of important principal aquifers across the United States, including the Denver Basin. This study of the Denver Basin aquifer system evaluates the hydrologic effects of continued pumping and documents an updated groundwater-flow model useful for appraisal of hydrologic conditions. The updated model includes a fully three-dimensional geologic framework, explicit representation of streams and the alluvial aquifer, time-varying recharge and evapotranspiration boundary conditions, spatial variation of hydraulic conductivity and specific yield, and used recently-available modeling tools for improved model calibration and sensitivity analysis. The presentation will provide an overview of the updated model construction, calibration, and results.
Sinkhole Hazards of Colorado
By Jon White
Sinkholes form from the collapse of the ground surface as the roof of an underground void or cavern fails and the void space propagates to the surface. The width of the underground roof failure that has “chimneyed” its way upwards to the surface is called the throat of the sinkhole. Sinkholes can be small or very large depending on the size of the cavern and width of the throat. Small sinkholes and mild ground depressions often result from the pip-ing of fine-grained sediments into a bedrock fissure or pipe. Large sinkholes result when bridged sediments or rock catastrophically collapse into near-surface, deep voids so that vertical or bell-shaped holes spontaneously open at the surface with little or no warning.
In broad terms, sinkholes are grouped into two types, man-made and natural. Man- made sinkholes result from the intentional, or unintentional removal of underground material. The most common are mine subsidence fea-tures. Others are related to failures of underground culverts, broken water mains, or sewers where the surround-ing soil or sediments have washed away. Naturally-forming sinkholes form from the dissolution of bedrock or the piping and dispersion of erodible, clay-rich, sediments with high sodium ion concentrations. It is the presence of slightly acidic or fresh water that causes dissolution.
The typical rock types that can dissolve are limestone, including other rocks composed of calcium carbonate and evaporite rocks composed of evaporite minerals such as halite, anhydrite, and gypsum. It is the dissolution of the rock that creates caverns, open fissures, subterranean and emergent streams, breccia pipes, subsidence sags, closed depressions, and sinkholes; landforms known collectively as karst morphology. The sinkholes and large piping voids that can form in clay-rich soils, generally in arid to semi-arid climates adjacent to deep arroyos, are referred to as psuedo-karst landforms. Most cataloged sinkholes in Colorado are from the dissolution of evapo-rite minerals. Evaporite rock is easily eroded and forms mountain valleys in Colorado. These valleys, with their proximity to surface water, were originally homesteaded so are now private lands and available for development.
Colorado has a history of both natural and man-made sinkhole occurrences. This presentation will identify areas in Colorado conducive to sinkhole formation and give examples of various types throughout the state. This presentation is based, in large part, on a recently completed Colorado Geological Survey publication, Colorado Map of Potential Evaporite Dissolution and Evaporite Karst Subsidence Hazards, which is available free on-line at http://geosurvey.state.co.us/pubs/online/Pages/default.aspx
Suzanne Paschke is presently the Associate Director for Hydrologic Studies at the U.S. Geological Survey Colorado Water Science Center. With 25 years of experience in hydrogeologic evaluation and water-quality assessments, recent projects include publication of the Denver Basin groundwater-flow model and evaluation of groundwater quality in the South Platte River basin as part of the USGS National Water-Quality Assessment Program. Previous experience includes software development and teaching at the International Ground-Water Modeling Center as well as hydrogeologic site investigations and modeling projects for private and government clients. Dr. Paschke holds a B.S. in Geology from the University of Wyoming and M.E. and Ph.D. degrees in Geological Engineering from the Colorado School of Mines.
Jon White is a senior engineering geologist at the Colorado Geological Survey with almost 30 years of professional experience. Jon’s current focus is geologic and geologic hazard mapping. He has authored or coauthored numerous papers and publications, technical presentations, web-site content, geologic maps, and field trip guidebooks. Jon has worked in the areas of evaporite karst, swelling soils, collapsible soils, dispersive soils, rockfall, land-slides, and debris flows. In 2009, he garnered the John C. Frye Award in Environmental
Geology as lead author of the CGS publication, Collapsible Soils in Colorado.
The USGS Circular “Ground water and surface water – A single resource” has greatly changed the thinking of water-resource scientists and managers since it was published in 1998. The concept that groundwater and surface water are actually one resource, linked at the sediment-water interface of lakes, wetlands, streams, and estuaries, is now widely accepted. Study of the physical, geochemical, and biological processes that control and are affected by the linkages between groundwater and surface wa-ter is not just the esoteric pursuit of scientists, however. These processes and linkages are directly rele-vant to the public. Examples from across the country will illustrate how the public is affected, some-times greatly, by the linkage between groundwater and surface water, and how improved understanding of processes and exchanges at this interface has influenced water-management decisions.
Donald Rosenberry is a research hydrologist with the USGS National Research Program in Denver, Colorado, specializing in processes that affect exchange between groundwater and surface water, and in develop-ing new tools for quantifying fluxes at the sediment-water interface. Don received his training in geography, geology, hydrogeology, and fluvial geomorphology at Bemidji State University, University of Minnesota, and University of Colorado. Concepts and methods related to exchange between groundwater and surface water are tested at three long-term research sites where things are relatively well known. New ideas and un-derstanding usually come from taking the show on the road, however, where results seldom turn out as expected.
Geologically, the end of the Pleistocene marks a period of mass extinction. Five theories have been proposed to explain this extinction event: human overkill, a hyper-disease, an extraterrestri-al impact event, climate change, or some combination of climate change and overhunting. In order to evaluate these theories, we need to first determine if the extinctions were synchronous and provide the chronometric resolution needed to demonstrate or negate synchronous extinction as well as explore how species respond to climate change and what role climate plays in species extinction.
Kenneth Barnett Tankersley, Ph.D.
Dr. Tankersley is an archaeological geologist and Quaternary scientist. He earned his baccalaureate and masters’ degrees at the University of Cincinnati, his doctorate at Indiana Univer-sity, and conducted post-doctorate research at the Quaternary Research Program, Illinois State Museum. With funding from the National Science Foundation, the National Academy of Sciences, the L.S.B. Leakey Foun-dation, Earthwatch, the International Research and Exchange Program, the Court Family Foun-dation, the Charles Phelps Taft Foundation, and the University of Cincinnati Research Council, he has conducted investigations across the western Hemisphere and Eastern Siberia. This re-search has resulted in a consistent and sustained record of performance with more than 120 pro-fessional publications. Additionally, his research has been featured on the National Geographic Channel, the Discovery Channel, the History Channel, the Animal Planet, BBC Nature, NOVA, PBS, in Science, National Geographic News, Geo, the Wall Street Journal, the New Yorker magazine, Scientific American, Archaeology magazine, and on All Things Considered as well as local, national, and international newspapers, magazines, radio and television programs. He has been a Foreign Delegate for the National Academy of Science, a Delegate of the International Geology Congress, a Carnegie Mellon Scholar Lecturer, guest editor of Scientific American magazine, and a Gubernatorial appointed member of the Native American Heritage Commis-sion. Dr. Tankersley’s current research is innovative and interdisciplinary, focusing on archaeo-logical geology problems associated with periods of climatic, environmental and catastrophic change. From an evolutionary perspective, these are significant periods of change, which force species to economically adapt, downsize, or migrate.
Tectonics and Gold Metallogeny
Dr. Richard Goldfarb, USGS
The temporal pattern for different types of gold deposits will vary with evolving global tectonic geodynamics, such that a particular deposit type will tend to have a characteristic time-bound nature. Factors bearing on the age distribution of a particular type of gold deposit include uneven preservation, data gaps, and long-term secular changes in the Earth System.
The distribution of gold-rich porphyry and epithermal deposits is skewed towards the late Cenozoic. The ores are associated with subvolcanic plutonic complexes and shallower parts of oceanic and continental arcs in the convergent margins of the circum-Pacific and Tethyan of southern Europe. Most deposits that formed in the upper few km of crust before ca. 20–30 Ma, were uplifted and eroded, and thus lost from the geologic record, although significant exceptions date back through all Phanerozoic orogens, and even to the Archean. Carlin-type deposits are only widely recognized in Nevada (Tertiary) and perhaps along the SW edge of the Yangtze craton (Jurassic), so knowledge about these remains are too limited to confidently relate the ores to major global tectonic patterns.
Orogenic gold deposit formed in medium-grade metamorphic belts tens of millions of years subsequent to host rock deposition. The deposits in both eastern China and Sonora are hosted in high-grade rocks and provide global anomalies where deposits post-date host rock metamorphism by billions of years, leading to revisions in the
ore genesis model. Preserved orogenic gold deposits correlate in time with addition of new oceanic lithosphere to craton margins during supercontinent growth at ca. 2.8–2.55 Ga, 2.1–1.75 Ga, and 650–35 Ma. Major lithospheric instabilities controlling ore formation include thickening by terrane accretion, subduction of a spreading ridge,
rollback or delamination of subducted oceanic lithosphere, or Precambrian plume events. The ca. 3.0 Ga timing of stabilization of subcontinental lithospheric mantle (SCLM) below the Kaapvaal craton indicates that the Witwatersrand gold ores cannot be Late Archean orogenic deposits.
The IOCG deposits represent the one group of gold ores in intracratonic settings, typically 100–200 km inland from the craton margins, where extension and anorogenic magmatism occur between areas of Archean and Proterozoic SCLM. The partial melting of metasomatized SCML, either by mantle underplating or plume episodes, leads to IOCG development in buoyant and refractory Precambrian cratons, such that even shallowly formed deposits
have been preserved.
Richard J. Goldfarb is a senior research geologist with the Minerals Program of the U.S. Geological Survey, where he has been employed for more than 33 years. Rich’s major expertise has been on the geochemistry and geology of ore deposits with emphasis on Phanerozoic lode gold. Much of his earlier career work concentrated on the Tertiary gold deposits of southern Alaska. Results from this work were used to develop ore genesis models for giant gold deposits
elsewhere in Alaska and in other parts of the North American Cordilleran.
In recent years, Rich has conducted detailed studies on the understanding of the distribution of gold deposits through space and time, compiling the most comprehensive global description of their distribution and evaluating the controlling tectonic/geologic features. He has senior-authored and co-authored more than 200 refereed publications in economic geology. Rich has served as
President of the Society of Economic Geologists, is a past Silver Medalist and Thayer Lindsley lecturer of the society, has served as chief editor of Mineralium Deposita, is presently on the editorial boards of Economic Geology and Gondwana Research, and was one of the co-editors of the Economic Geology One Hundredth Anniversary Volume.
He received his BS in geology from Bucknell University, MS in hydrology from MacKay School of Mines, and Ph.D in geology from the University of Colorado in 1988.
#1. Melissa A. Foster1,2, Miriam Duhnforth3, and Robert S. Anderson1,2
1INSTAAR, University of Colorado, 2Dept. of Geological Sciences, University of Colorado, 3 Dept. of Earth and Environmental Sciences, Ludwig- Maximilians-University, Munich, Germany.
“Young Strath Terraces on Western High Plains Record Climate-Paced Variations in Sediment Supply from Colorado Front Range Rivers.”
The formation of strath terraces along the Colorado Front Range records recent exhumation, as rivers incise vertically and laterally leaving thinly mantled gravel-capped surfac-es behind. Approximately 6 alluvial units have been mapped along 300 km of the western High Plains based on soil development and elevation; each unit was thought to repre-sent a fairly consistent elevation of the Denver basin during various stages of exhumation, driven by base-level fall of the South Platte River. Absolute dates, however, that can be compared to the existing relative age chronology exist at only a few locations so far.
Recent cosmogenic radionuclide (CRN) dates on terraces north of Boulder, CO, indicate that these surfaces are up to an order of magnitude younger than the correlative alluvial units to the south of Boulder. We present new CRN data from middle Pleistocene surface that yield a date of ~ 91 ka, far younger than expected based on correlation, but in accord with the 10Be-based age (95 ka) of the Rocky Flats surface just above it.
The new dates on strath surfaces in the western High Plains are consistent with a fluvial history marked by long periods of aggradation and lateral planation, punctuated by brief episodes of rapid incision through soft shale underlying the Boulder area. This model supports a “top-down” approach in which fluvial incision and aggradation are driven by variable sediment production from source basins in the adjacent crystalline Front Range: glacial and periglacial climates produce high sediment yields leading to aggradation and lateral planation; extreme interglacial climates correspond with low sediment supply, leading to vertical bedrock incision. Under this model: (1) strath terraces cannot be correlated based on elevation alone, (2) exhumation of the Denver basin is likely spatially and temporally variable due to climatically-driven variations in sediment supply, and (3) Front Range rivers likely experienced a complex and basin-specific history of aggradation and incision over the Quaternary.
#2. A.L. Hantsche, “Rare Earth Analysis of Anhydrite Veins and Source Magmas from the Ertsberg Mining District, Papua, Indonesia.”
The Ertsberg Mining District in Papua, Indonesia is home to the supergiant Grasberg porphyry copper deposit, the Kucing Liar skarn deposit, and several other major Cu+Au ore bodies. These deposits formed when magmatic fluids moved towards the surface along a fluid pressure gradient, mineralizing the surrounding country rock. This project concerns the chemistry of veins – extension fractures mineralized by the passage of hydrothermal fluids. The Rare Earth Element (REE) content of ninety-six anhydrite vein samples were analyzed by ICP-MS and compared to REE patterns of thirty-five district intrusive bodies.
The igneous rocks have La/Yb ratios that range from 5 to 13. The anhydrite REE patterns were divided into categories based on La/Yb ratio: 1) high [>13], 2)“igneous” [5 to 13], 3) low [<5], and 4) very low when REE abundances were below detection. The igneous rocks lack Eu anomalies, but the anhydrite has both positive and negative anomalies.
Anhydrite samples from the Ertsberg District have La/Yb values ranging from 2 to more than 150. Experiments and theory indicate ligand complexation stabilizes LREE in aque-ous solutions at high temperatures. This causes the La/Yb ratio of a fluid precipitating anhydrite to increase from below parental magmatic values (La/Yb < 5) to higher values (La/Yb >13) as anhydrite precipitates during fracture flow.
Studies conclude that Eu in high temperature fluids exists solely as Eu2+. Eu2+ fractionates preferentially into anhydrite compared to the other REE, resulting in a positive Eu anomaly. Over time, this Eu depletion causes a negative Eu anomaly in late stage anhydrite.
The REE patterns of anhydrite record the chemical evolution of magmatic fluids during flow along open fractures causing anhydrite veining. REE pattern variations in anhydrite appear to be an indicator of relative distance from the fluid source, with positive Eu anomalies and low La/Yb ratios nearer the source and negative Eu anomalies and higher La/Yb in distal occurrences.
Mapping efforts by the Colorado Geological Survey along the southeastern flank of the Sand Wash Basin in northwestern Colorado shed new light on the structural evolution of the basin. Well known Laramide structural features are being documented in greater detail while previously undocumented features come to light with care-ful mapping of subtle structural fabrics. Northwest-trending faulted folds dominate the structural grain and are cross-cut by a series of northeast-trending flexures. The flexures likely represent surface expressions of deeper faults. Although individual offsets on the northeast flexures tend to be small, less than 30m, the features do ap-pear to compartmentalize the main northwest structural components delineating distinct structural domains. Rela-tionships of the features demonstrate a history of Laramide compression with a clear Neogene overprint. Neo-gene features include scarps developed on a Quaternary landscape and a network of 24 Ma and 8 Ma igneous centers. The igneous centers fall close to intersections of the dominating northwest grain with northeast flexures.
Peter Barkmann, Colorado Geological Survey
A native of arid Northern New Mexico, Peter Barkmann obtained a Bachelor of Science Degree in Geology from Western Washington University in 1976 and a Master of Science Degree in Geology from the University of Montana in 1984. His geological background spans minerals exploration; petroleum develop-ment and exploration, geothermal exploration; and water resources. For the past 27 years he has focused mainly on groundwater resources and environmental geology. Peter joined the Colorado Geological Survey in 2002 where he conducts regional water resource investigations, environmental assessments, and manages the Ground Water resources program. In addition, he has been contributing to geologic mapping efforts in the STATEMAP 1:24,000 Geologic mapping program. He is author of the recent Cross-sections of the fresh-water strata of the Denver Basin publication and co-author for the Bedrock Geologic Map of the Denver Basin, Artificial Recharge of Ground Water in Colorado-A Statewide Assessment, as well as the award winning Ground Water Atlas of Colorado.
Jeffrey Hrncir, Department of Physical and Environmental Sciences, Colorado Mesa University- “The Green River Basin Kimberlitic Indicator Mineral Anomaly Revisited.”
The Green River Basin of southwestern Wyoming is host to one of the largest kimberlitic indicator mineral (KIM) anomalies in North America. The classic KIM’s pyrope garnet and Cr-diopside, along with other mantle mineral grains and deep lithospheric xenoliths, are found in stream sediments, harvester ant mounds, pediment gravels, and the Bishop Conglomerate over a 2,000-km2 region. Limited source rocks for KIM grains are known in lamprophyric diatreme breccias found in the extreme southern portion of the anomaly almost 90 kilometers to the south of the northernmost KIM grain occurrences. Geologic and sedimentologic characteristics unique to this basinal setting govern maximum transport distances and dispersal of KIM grains from host rock sources. For the first time, transport distances for KIM grains are reported for the Green River Basin through stream sediment sampling downstream of the Cedar Mountain lamprophyric diatremes and are compared to data compiled for other kimberlite fields in the Rocky Mountains. Although absolute maximum transport distances for KIM grains were not determined, the recov-ery of thousands of KIM grains over a distance of 1.4 km downstream of the DK diatreme suggests significantly greater maximum transport dis-tances for grains in this sedimentologic setting than in regions of crystalline basement elsewhere in the Rockies. Furthermore, the retention of surficial features such as relict igneous matrix, partial kelyphite rims on pyrope garnet, and delicate euhedral projections on clinopyroxene grains demonstrates the buffering effects of the suspended sediment load on KIM grain abrasion during fluvial transport in periodic flash flooding events. For the first time, an estimated age assignment of ~34 Ma for the Cedar Mountain lamprophyric breccia pipes is proposed utilizing newly recog-nized age criteria provided by the abundance of Uinta Mountain Group quartzites within the breccia (incorporated from Bishop Conglomerate) and the appearance of deep lithospheric xenoliths and megacrystic KIM grains within intact basal Bishop Conglomerate exposures. The spatial coinci-dence of the KIM anomaly with the approximate trace of the Moxa Arch suggests deep-seated structural control over the emplacement of lampro-phyric magmas, similar to what is seen in the Leucite Hills lamproite field to the northeast. The results of this study have important implications for future exploration in the basin and separate KIM anomalies found in sedimentary-dominated bedrock elsewhere on the Wyoming Craton.
Leif Anderson, Institute of Arctic and Alpine Research, University of Colorado, Boulder – “The Effect of Interannual Variability Forced Glacial Advances on the Moraine Record: A Case Study from the Colorado Front Range During the Last Glacial Maximum.”
Valley glacier moraines are commonly used to infer mean climate conditions (annual precipitation and mean melt-season temperature) at the time of formation. However, recent research has demonstrated that even in steady climates, substantial decadal-scale fluctuations in glaci-er length also occur in response to stochastic, year-to-year variability in mass balance. All climates, steady or transient, include interannual varia-bility. When interpreting moraine sequences it is therefore important to include the effect of interannual variability on glacier length because mo-raines can be 1) formed by interannual variability forced advances or 2) formed by advances forced by a combination of a climate change compo-nent and an interannual variability component. We address this issue for eleven LGM glaciers from the Colorado Front Range, USA. Using a linear glacier model that allows for a thorough exploration of parameter uncertainties, supplemented by a shallow-ice flowline model, our analyses suggest that i) individual LGM terminal moraines were formed by a combination of climate change and interannual variability forced advances; ii) estimates of mean climate using maximum LGM glacier geometries are ~10–15% too extreme; and iii) classic ‘recessional’ moraines may be formed by re-advances during the LGM as opposed to re-advances or standstills during deglaciation.
It is often assumed that century scale glacial standstills were required to form large (>10 m in relief) LGM terminal moraines. Our numerical model suggests that the longest standstills for the modeled glaciers lasted ~50 years. Historical records of interannual variability forced glacier advances, which formed >10 m terminal moraines provide modern validation to our conclusions. We expect interannual variability to play an important role in kilometer-scale glacier fluctuations and moraine emplacement in the past and present as well as in maritime, Alpine, and continental settings (e.g. Oerlemans, 2001).
Richard Zaggle, Colorado State University- “Petrogenetic Analysis of the Wenatchee Ridge Orthogneiss in the North Cascade Mountains, Washington State.”
Petrogenetic analysis of the Wenatchee Ridge Orthogneiss (WRO) (Magloughlin & Evans, 1987) in the Nason Terrane of the North Cascade Mountains has been undertaken in order to gain insight into epidote-bearing TTG plutonism associated with mid-Cretaceous orogenesis in the North American Cordillera. Discriminant analysis indicates the WRO is very similar to Archean TTGs based upon characteristic geochemi-cal values (Yb <1, Sr/Y >150, La/Yb >15, Y<6) and thus may provide insight into Archean crustal generation processes.
Samples were taken from within the pluton and from within the surrounding banded gneiss (Tabor et al., 1987). The pluton is chemi-cally heterogeneous and samples all show some degree of foliation which is concordant with the foliation in country rocks. Samples range from leucotrondhjemite to granodiorite and contain oligoclase, quartz, muscovite, biotite, and epidote. SiO2 is 56.3-76.8% and REE data show that the samples are highly depleted in HREEs, variably depleted in LREEs, and have an average Eu/Eu* of 1.36±0.5. Though positive Eu anomalies are typically associated with plagioclase accumulation, the WRO appears to lack any correlation between plagioclase and Eu/Eu*.
Geochemical results and the tectonic setting of the WRO indicate the initial magma may have formed as a partial melt of overthick-ened eclogitic crust. The subsequent LREE depletion and high positive Eu anomalies in the most evolved samples may be controlled by amphi-bole, epidote, and/or titanite fractionation. LA-ICP-MS analyses will indicate whether these phases had significant control on the REE signature of the WRO.
Deformation-driven differentiation would have controlled any fractionation of amphibole, epidote, and/or titanite in the WRO magma which has viscosities ≥106.8 Pa·s at 1000°C calculated using the method of Giordano et al. (2008). Differentiation likely occurred simultaneously with intrusion into a lower crustal zone of plastic strain, resulting in the WRO’s heterogeneity, sheeted nature, and syn-tectonic fabric.
Exploring Areas of Natural Acid Rock Drainage in Colorado
Matthew A. Sares1, Jeffrey P. Kurtz2, Dana J. Bove3, and John T. Neubert4
with P.L. Hauff, D.A. Bird, D.C. Peters, F.B. Henderson III, D.W. Coulter
Colorado has a world-class mining heritage that is known for historic development of precious and base metal deposits throughout the mountainous portion of the state. Unfortunately, the environmental legacy of some historic mines has led to acid mine drainage that pol-lutes streams with acidic, metal- laden water.
In Colorado, water quality degradation caused by acid mine drainage from historic mines became a major focus of federal and state envi-ronmental regulation, resulting in numerous cleanup initiatives. Identifying and remediating major mining sources of acid- and metal-loading to streams ensued. This focus was appropriate and necessary, but the natural geologic setting of the mines was often not recog-nized in early cleanup efforts.
In the late 1980s and -90s, geologists involved in programs to identify mining point sources of environmental degradation observed areas of acidic and metal-laden water not associated with mining, but occurring upstream of any significant mining or anthropogenic impacts. Anecdotal and a few documented accounts of these natural occurrences led the Colorado Geological Survey to embark on a statewide in-ventory of natural acid rock drainage (NARD).
In the study, “Natural Acid Rock Drainage Associated with Hydrothermally Altered Terrane in Colorado,” eleven different headwater areas were documented as exhibiting NARD upstream of mining impacts. These areas include the Silverton and Lake City calderas, Plato-ro-Summitville caldera complex, Kite Lake (San Juan Mountains), East Trout Creek (San Juan Mountains), La Plata Mountains, Rico Mountains, Grizzly Peak Caldera, Ruby Range, Montezuma Stock, Red Amphitheatre (Mosquito Range), and Rabbit Ears Range.
The study collected extensive water quality data at 101 sites; 86 of these were determined to have no anthropogenic influence. In addition, hydrothermal alteration was mapped in several areas through field mapping and remote sensing data compilation. The severity of NARD in an area was directly related to the intensity of alteration and sulfide mineral content. In all of the areas studied, changes in water chem-istry, from essentially untainted (near neutral pH/low metal) to NARD (acidic/high metal) water are readily related to changes in alteration type and intensity.
In NARD areas, stream water quality standards were exceeded most often for pH (77%), Mn (67%), Al (76%), Cu (58%), Zn (58%), Fe (44%), and Cd (44%). Less common exceedances included Ni, SO4, Pb, Tl, As, F, Ag, Cl, Cr.
Many of Colorado’s NARD areas are in watersheds where both natural and historic mine-induced acid rock drainage affect water quality. Detailed characterization of the natural and anthropogenic sources is especially important in drainage basins slated for mine-reclamation projects so that realistic remediation goals can be defined.
1 Colorado Div. of Water Resources, 2EnviroGroup Ltd, 3U.S. Geological Survey, 4U.S. Forest Service (retired)
Matt Sares is the Manager of Hydrogeologic Services at the Colorado Division of Water Resources (DWR). In this capacity he addresses the geological and hydrogeological in-formation needs of DWR to ensure wise regulatory decisions pertaining to groundwater.
Previously, Matt spent 20 years with the Colorado Geological Survey (CGS), ultimately serving as its Deputy Director. While there he directed efforts to compile statewide infor-mation on geothermal resources, hydrogeology, aquifer storage and recharge, abandoned mines, and natural acid rock drainage. Matt has a graduate degree in hydrogeology from the Colorado School of Mines.
Matt and his co-authors received the Geological Society of America’s “John C. Frye Award” for the work being presented.