January 2003 – Emmons Lecture
“DROUGHT AND GLOBAL CLIMATE CHANGE: IS 2002 A GLIMPSE OF THE FUTURE?”
Dr. Kevin Trenberth
National Center for Atmospheric Research
The atmosphere is global and Colorado’s weather and climate are largely determined by influences from elsewhere. In fact the atmosphere is a “Global Commons” and serves as a dumping ground for pollution from all nations. Air over one nation is half way around the world a week later, as shown by manned balloon flights. While rain is a remarkable cleanser of the atmosphere, some gases are not affected, long-lived and changing our climate. Global warming is happening. In Colorado, as in other mountain areas, this means more precipitation falls as rain instead of snow, snow melts sooner, and there is less snow pack as we go into the summer. Risk of summer drought increases. With it comes increased heat waves and wildfires. The summer of 2002 is perhaps a taste of what we can expect more of in the future?
In this talk we will review broad aspects of the 2002 drought and wildfires, and discuss factors that cause drought and climate change. El Niño and La Niña are factors in interannual variability and in setting up the current conditions, while global warming is a slow but relentless influence that will emerge more strongly as time goes on. Water will become a valuable resource.
February 2003
“VERMICULITE DEPOSITS AND ASBESTOS—EXAMPLES FROM COLORADO AND ELSEWHERE.”
Bradley S. Van Gosen and Heather A. Lowers
U.S. Geological Survey, Lakewood, CO
Vermiculite, used in many commercial applications, is a water-rich, platy mineral formed by the weathering of mica minerals. When heated to 800°C or higher, the water contained within the vermiculite is converted to steam, which pushes apart the mineral’s plates; this expands the mineral accordion-like by six times or more its original thickness. Heat-expanded vermiculite is very light weight, has fire- and sound-proofing properties, and is thus well suited for many uses, such as in low weight insulating building materials. Unfortunately, health hazards are now known to be associated with some vermiculite materials.
Vermiculite was mined and milled from 1923 to 1990 near the small town of Libby in northwestern Montana. The Libby (“Zonolite”) mine was the world’s largest producer of vermiculite during its operation. Unusually high rates of respiratory ailments and mortality due to asbestosis within Libby mine and mill workers and residents have been recognized in recent years; these respiratory diseases have been linked directly to occupational and environmental exposure to amphibole asbestos particles intergrown within the Libby vermiculite deposit. As a result, the U.S.Geological Survey began a study to determine if amphibole asbestos minerals are common as accessories in other vermiculite deposits.
The study of U.S. vermiculite has involved the mineralogical analyses of vermiculite-rich samples collected previously from 62 vermiculite mines and deposits in 10 States. These samples were collected during the 1940s, 1960s, and 1970s as part of a reconnaissance survey of the Nation’s vermiculite resources. The mineralogy of these samples was compared with those of a representative suite of 30 samples collected recently from the former mining operations at Libby. In our study, the Libby and U.S. reconnaissance samples were analyzed by X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, and electron probe microscopy.
Despite the reconnaissance nature of the sampling, the mineralogic characterization of the vermiculite samples revealed consistent results. Our analyses indicate that (1) fibrous (asbestiform) amphiboles are not common in all types of vermiculite deposits, but they also showed that (2) the geology and asbestos mineralogy of the Libby deposit is not unique. “Type 1” vermiculite deposits are those that formed in geologic environments similar to the Libby deposit—that is, relatively quartz-deficient, potassium-sodium- calcium–rich igneous intrusions that are usually zoned. We found that all the type 1 deposits sampled consistently contain fibrous amphiboles (asbestos). “Type 2” vermiculite deposits are those that formed where masses of ultramafic rock were intruded by granite and (or) felsic pegmatite; these types of deposits also often contain fibrous amphibole. Both type 1 and type 2 vermiculite deposits occur in Colorado. Two “type 1” deposits are known in southern Colorado; one abandoned vermiculite mine site is being considered for asbestos abatement and reclamation, whereas another site is being sampled and evaluated. Asbestos-rich deposits of “type 2” have been recently identified in a remote area of north-central Colorado.
“SHAKING UP THE GREAT WHITE NORTH: GEOLOGIC EFFECTS OF THE 3 NOVEMBER 2002 M7.9 DENALI EARTHQUAKE, CENTRAL ALASKA.”
Stephen F. Personius
U.S. Geological Survey, Lakewood, CO
On November 3, 2002, a M7.9 earthquake generated about 330 km of surface rupture on parts of three faults in central Alaska. These surface ruptures rank among the largest strike-slip ruptures in the past two centuries, and their length and amount of offset are comparable to those of the great California earthquakes of 1857 and 1906. The earthquake epicenter was located in the central Alaska Range about 150 km south of Fairbanks, Alaska. Seismological data indicate that the earthquake initially began as a reverse-slip rupture that, 15 seconds later, became a right-lateral strike-slip rupture. The reverse-slip motion produced thrust faulting along 45 km of the newly discovered Susitna Glacier fault. Some scarps on the Susitna Glacier fault are more than 6 m high, but average dip-slip displacements are about 3 m. The northeastern end of ruptures on the Susitna Glacier fault intersect the Denali fault, where right-lateral strike-slip ruptures extend eastward for more than 210 km along the Denali fault. Lateral offsets average about 5 m on the Denali fault, and we measured a maximum offset of 8.8 m about 170 km east of the epicenter. Much of the rupture on the Denali fault occurred in glacier-filled valleys, which produced spectacular surface expressions of lateral-slip faulting in glacial ice. Eastward, the slip transferred from the Denali fault onto the southeast-trending Totschunda fault, where lateral offsets averaged about 1.5 m and the ruptures continued an additional 75 km to the southeast.
Strong ground motion from the earthquake generated major landslides and avalanches throughout the Alaska Range, but it did little damage to manmade structures in the sparsely populated region. Surface manifestations of earthquake-induced liquefaction included lateral-spread failures and sand blows in saturated sediments along many streams and lakes in the region. The mapped trace of the Denali fault crossed the Trans-Alaska Pipeline and thus poses a serious environmental and economic threat to central Alaska. The 2002 fault rupture underwent 3.9 m of dextral slip beneath the pipeline, and we measured as much as 6 m of lateral slip at nearby sites. Fortunately, the pipeline had been designed to accommodate 6.1 meters of dextral slip and 1.5 m of vertical slip at the fault crossing and withstood the earthquake without failure. The “design” rupture was based on preconstruction geologic studies that clearly demonstrate the value of earthquake science in engineering design and risk mitigation.
March 2003
“EVALUATION OF TECTONIC AND CLIMATIC CONTROLS ON LATE CENOZOIC INCISION OF THE ROCKY MOUNTAINS”
Paul Heller and Margaret McMillan
Department of Geology, University of Wyoming
The Rocky Mountain orogenic plateau is characterized by high elevations (>2 km) and deep post-Laramide incision (up to 1.2 km). While it is not clear when modern elevations were first attained, most studies indicate that incision began during the past 10 m.y. and may coincide with elevation gain. The ultimate cause of downcutting reflects the interplay between regional tectonic uplift and climate change. We evaluate the relative roles of these driving mechanisms by mapping the distribution of, and incision into, a variety of paleodatums. These datums include high-level subsummit erosion surfaces, the maximum elevation of once-continuous remnants of post-Laramide basin deposits, young volcanic flows, and pedimented terraces. These surfaces are not contemporaneous, but they are all post-Laramide in age and so provide an envelope for the magnitude of incision.
Results indicate that (1) the incision pattern is broadly domal, paralleling the trend of the Rio Grande Rift in Colorado and the Bighorn Mountains in Wyoming, and decaying to the north and east over distances of several hundred kilometers; (2) the pattern of incision matches regional topography of the Rockies, except in areas of most active recent tectonics; (3) in several places, most notably the western Great Plains, incision is associated with surfaces that have been tilted after deposition, and (4) the turnaround from net aggradation to incision took place ~6 ± 1 Ma.
The distribution of incision suggests that tectonic uplift exerts major control. The broad wavelength of downcutting, which parallels regional isostatic anomaly trends, suggests upper mantle involvement in the origin of uplift. Climate clearly influences second-order features such as knick-zone migration and details of the erosion pattern. Our results appear to differ with those derived from published paleobotanical estimates of elevation change since the end of the Laramide orogeny. However, the uncertainties in those estimates (up to ±1.5 km) are not inconsistent with our results.
“EVEN IN BOULDER: THE BOULDER OIL FIELD, 1901 – TODAY”
Matthew R. Silverman
Consulting Petroleum Geologist
An oil field in Boulder? Tofu and granola, yes. Sandals and love beads, sure. Even Mork and Mindy. But an oil field?
Over one hundred years ago, in 1901, the Boulder Oil Field was discovered just northeast of the eponymous Colorado town. It is the second oldest field in the state and one of the oldest producing anticlines in the Rockies. The field was discovered the same year as Spindletop, and its early development shares some of that boomtown atmosphere and scandal. An effort is now underway to get landmark designation at the Boulder discovery, now ironically the site of the only well still producing in the field.
Wells had been drilled in the area to follow up on oily odors and seeps as early as 1892. Dowsing by a group associated with Isaac Canfield, one of the pioneers of Colorado’s oil industry at Florence, led to the Boulder discovery, the McKenzie Well. Early wells were drilled with cable tools, and production generally came from depths of 800 to 3,000 feet. Most wells were shot with nitroglycerin to improve production. About 100 wells were drilled in the first few years; nearly 200 have been drilled in all.
Boulder was the focus of a forgotten boom. Over a hundred oil companies sprouted up, and promoters promised “Oil or money refunded.” One University of Colorado professor (later to become the State Geologist) raised $500,000, equivalent to several million dollars today. A now-venerated pioneer photographer used doctored pictures to promote investment. Wells were drilled with “other people’s money” and with little or no financial reward for most investors. The wily Canfield got out early, in 1902.
Located at the western margin of the Denver Basin, the field is associated with one of the en echelon anticlines near the foothills of the Front Range. A nose and small closure, whose axes are roughly parallel to the mountains, control the field structurally. Production is from sand lenses and fold-related fracture porosity in the Late Cretaceous Pierre Shale, which is also the source rock. Fractures have contributed most of the production.
Boulder Field opened the oil industry of the northern Denver Basin. It has produced about 800,000 barrels of oil, but the lone remaining well—one of the longest continuously producing wells in the country—may be slated for the salvage yard of history. Efforts are underway to preserve the McKenzie Well as an historic landmark, safeguarding a rich chapter in the development of oil and gas in the Rockies.
April 2003 – Annual Family Night
“TROPICAL RAINFORESTS, DINOSAURS, AND DRINKING WATER: THE ODD URBAN GEOLOGY OF THE DENVER BASIN”
Dr. Kirk Johnson
Curator of Paleontology and Head of the Department of Earth Sciences at the Denver Museum of Nature & Science
The city of Denver lies above nearly 12,000 feet of horizontal sedimentary rocks. Many of these layers are exposed around the margins of the Denver Basin, a geologic depression that formed around 68 million years ago in response to the uplift of the Colorado Front Range. Sediments shed from the uplifting Rockies during the Late Cretaceous and early Paleogene form the top 2,000 to 3,000 feet of the Denver Basin sequence, and these rocks lie immediately beneath the cities of Denver and Colorado Springs.
Rapid urban growth in the 1990s caused thousands of excavations that yielded hundreds of new, but ephemeral, fossil sites. Several of these discoveries received extensive media coverage because they occurred in public sites like the Denver International Airport, Coors Field, and the margins of local interstate highways. Most of the discoveries were mundane but a few have been spectacular. The most notable include a partial Tyrannosaurus rex skeleton at a suburban house site in Littleton and a 64 million-year-old tropical rainforest along the side of Interstate 25 in Castle Rock. This T. rex skeleton is the only one from Colorado, and the rainforest is arguably the oldest one known to date, on Earth.
Research on these sites is shedding light on the nature of the landscapes that formed during the Laramide orogeny and their relationship to the Cretaceous-Tertiary boundary extinctions and the origin of modern biomes. Groundwater is an important and limited resource for the growing population of the semiarid region and the Denver Basin bedrock aquifers are found in the same synorogenic strata that contain fossils of dinosaurs and rainforests. Using data from a network of two cored wells and hundreds of logged wells and surface observations, we are able to place both the fossil sites and the aquifers in a temporally calibrated stratigraphic framework that is based on an understanding that the basin was filling as the mountains were uplifting. The Denver Basin Project to links primary research on geology and paleontology with assessments of the groundwater resource and delivers the results to not only the scientific community but also to the 3.5 million residents of the Front Range Urban Corridor.
September 2003
“CENOZOIC ALTITUDES AND PALEOBOTANY OF WESTERN-INTERIOR UNITED STATES”
Warren Hamilton
Department of Geophysics, Colorado School of Mines
A century of geologic research constrains Cenozoic evolution of regional topography. The high Late Cretaceous-early Paleogene continental divide passed near tracts now in central Nevada (Basin-Range province has since doubled in width, and lowered), and lithostatic head drove thin-skinned Sevier foreland thrusting. The east foot of the thrust belt was near sea level almost to the end of Cretaceous time and likely was little above it when thrusting ceased. The continental divide lay south of since-raised Colorado Plateau in Arizona, which lacked a thrustable stratal wedge. Structural relief of the central and southern Rocky Mountains mostly dates from latest Cretaceous and early Paleogene Laramide crustal shortening, but basins remained low, accumulating sediment, until late Cenozoic regional uplift resulted in sluicing of basins and incision of Plateau, mountains. Great Plains floristic determinations of paleoclimates (Axelrod, MacGinnitie, Leopold) accord with this scenario.
This voluminous evidence is dismissed by theorists (e.g., Chase, Molnar, England) who assume that present high western-interior regional altitudes could only result from Laramide deformation. They seek support in simplistic analysis of fossil-leaf physiognomy by Wolfe and Gregory. Wolfe rejected floristics and assumed that leaf shapes alone can define mean annual temperatures (MAT), independent of annual distributions of temperature and precipitation. He applied fuzzy multivariate analysis of rank and polynomial (nonlinear and non-normal) variables of size and shape of woody-dicot leaves in small samples—statistical mumbo-jumbo. Fit of this defective model to modern floras is very weak where it works at all—many common assemblages wholly misfit—but Wolfe applied it rigidly to paleofloras. The Paleogene MATs thus deduced for western-interior US frequently are too cold (thus increasing deduced altitudes) for the palms, crocodilians, and large tortoises present but ignored. The large climate signal in conifers, monocots, ferns, etc. is also ignored. Global variation of temperature with continental surface altitude is typically 5-6 degrees C per km, and this was used by Axelrod for conversion to paleoaltitude of early Tertiary equable-climate floras using sophisticated climatic variables; but present variation of MAT for extremely continental (and extended) western US is about 3 degrees per km, which Wolfe used inappropriately for Paleogene floras, thus doubling paleoaltitude conversions. Further, Wolfe’s method deduces large, sudden altitude jumps where floral changes signal changes in equability.
“EVALUATION OF TECTONIC AND CLIMATIC CONTROLS ON LATE CENOZOIC INCISION OF THE ROCKY MOUNTAINS”
Paul L. Heller
Department of Geology and Geophysics, University of Wyoming
The Rocky Mountain orogenic plateau is characterized by high elevations (>2 km) and deep post-Laramide incision (up to 1.2 km). While it is not clear when modern elevations were first attained, most studies indicate that incision began during the past 10 m.y. and may coincide with elevation gain. The ultimate cause of downcutting reflects the interplay between regional tectonic uplift and climate change. We evaluate the relative roles of these driving mechanisms by mapping the distribution of, and incision into, a variety of paleodatums. These datums include high-level subsummit erosion surfaces, the maximum elevation of once continuous remnants of post-Laramide basin deposits, young volcanic flows and pedimented terraces. These surfaces are not contemporaneous, however they are all post-Laramide in age and so provide an envelope for the magnitude of incision.
Results indicate that: 1) the incision pattern is broadly domal, paralleling the trend of the Rio Grande Rift in Colorado and the Bighorn Mountains in Wyoming, and decaying to the north and east over distances of several hundred kilometers; 2) the pattern of incision matches regional topography of the Rockies, except in areas of most active recent tectonics; 3) in several places, most notably the western Great Plains, incision is associated with surfaces that have been post-depositionally tilted, and 4) the turnaround from net aggradation to incision took place ~6+1 Ma.
The distribution of incision suggests that tectonic uplift exerts major control. The broad wavelength of downcutting which parallels regional isostatic anomaly trends suggests upper mantle involvement in the origin of uplift. Climate clearly influences second-order features such as knick-zone migration and details of the erosion pattern. Our results appear to differ with those derived from published paleobotanical estimates of elevation change since the end of the Laramide orogeny. However the uncertainties in those estimates (up to +1.5 km) are not inconsistent with our results.
October 2003
“HISTORIC COAL MINING IN JEFFERSON, BOULDER AND WELD COUNTIES, COLORADO”
Chris Carroll
Colorado Geological Survey
Colorado’s coal mining history began in the early 1860s near Marshall, Colorado. Originally produced as home heating fuel, coal and coke quickly became important commodities for Front Range industries and transportation. From 500 short tons produced in 1864 for home heating fuel, the annual coal production grew to over 13 million short tons by 1918. By the end of the nineteenth century more than 50 million short tons of coal were produced statewide.
The early supply of coal was mined from the Cretaceous Laramie Formation coal that crops out between Golden and Erie along the northwestern rim of the Denver Basin. Coal was produced from the Foothills coal field to supply the nearby gold mining industry and a growing metropolis in Golden. Mining vertical coal seams brought many challenges for the early miners, such as poor ventilation, vertical haulages, fires, and groundwater flooding. By 1900 local coal mining moved on to more conventional methods of room and pillar mining on flatter strata. The Leyden Mine produced more than 5 million short tons of coal to 1950; part of the production supplied the Denver trolley service.
The Northern coal fields, or the Boulder-Weld coal field, produced 112 million short tons of coal between 1864 and 1988. This subbituminous A and B coal supplied Denver with home heating fuel, fuel for coal-fired power plants, and transportation purposes. Mined mostly in the winter owing to increased demand and lack of an ability to maintain high-slacking coal stockpiles, this coal was produced from up to seven coal seams in the Laramie Formation. Most of the mining was underground at depths ranging from 20 to more than 500 feet deep. Typical coal quality from one large mine, the Rocky Mountain Fuel Company’s Columbine Mine near Erie, was 9,800 Btu/lb heat value, 5.6% ash, 0.4% sulfur. The last underground mines to close were the Lincoln and Eagle Mines, which Longwall mined until the late 1970s.
“EVEN IN BOULDER: THE BOULDER OIL FIELD, 1901 – TODAY”
Matthew R. Silverman
Consulting petroleum geologist
An oil field in Boulder? Tofu and granola, yes. Sandals and love beads, sure. Even Mork and Mindy. But an oil field?
Over one hundred years ago, in 1901, the Boulder Oil Field was discovered just northeast of the eponymous Colorado town. It is the second oldest field in the state and one of the oldest producing anticlines in the Rockies. The field was discovered the same year as Spindletop, and its early development shares some of that boomtown atmosphere and scandal. An effort is now underway to get landmark designation at the Boulder discovery, now the site of the only well still producing in the field.
Wells had been drilled in the area to follow up oily odors and seeps as early as 1892. Dowsing by a group associated with Isaac Canfield, one of the pioneers of Colorado’s oil industry at Florence, led to the Boulder discovery, the McKenzie Well. Early wells were drilled with cable tools, and production generally came from depths of 800 to 3,000 feet. Most wells were shot with nitroglycerin to improve production. About 100 wells were drilled in the first few years; nearly 200 have been drilled in all.
Boulder was the focus of a forgotten boom. Over a hundred oil companies sprouted up, and promoters promised “Oil or money refunded.” One University of Colorado professor (later to become the State Geologist) raised $500,000, equivalent to several million dollars today. A now-venerated pioneer photographer used doctored pictures to promote investment. Wells were drilled with “other people’s money” and with little or no financial reward for most investors. The wily Canfield got out early, in 1902.
Located at the western margin of the Denver Basin, the field is associated with one of the en echelon anticlines near the foothills of the Front Range. A nose and small closure, whose axes are roughly parallel to the mountains, control the field structurally. Production is from sand lenses and fold-related fracture porosity in the Late Cretaceous Pierre Shale, which is also the source rock. Fractures have contributed most of the production.
Boulder Field opened the oil industry of the northern Denver Basin. It has produced about 800,000 barrels of oil, but the lone remaining well—one of the longest continuously producing wells in the country—may be slated for the salvage yard of history. Efforts are underway to preserve the McKenzie Well as an historic landmark, safeguarding a rich chapter in the development of oil and gas in the Rockies.
November 2003
“GEOCHEMICAL AND GEOPHYSICAL DETERMINATION OF THE FATE OF SEPTIC TANK EFFLUENT IN TURKEY CREEK BASIN, COLORADO”
Kathleen E. Dano (speaker), Eileen Poeter, and Geoffrey Thyne
Colorado School of Mines
With rapid population growth in the Turkey Creek basin of Jefferson County, Colorado, water quality has become an important issue. A comparison of recent chemical data and historical data showed that surface water quality had declined at a rate three times as fast as that of the ground water. All of the 5000 homes in the basin use septic tanks for wastewater disposal. It is our hypothesis that after leaving a septic system, some of the effluent filters through the high-permeability regolith until it reaches the regolith-bedrock interface. This “perched” effluent then flows laterally down gradient and discharges into surface water with only limited treatment.
Various geophysical methods were used to locate this effluent at the regolith-bedrock interface. Where areas of saturation were detected, shallow piezometers were installed to sample the effluent plume. The samples were chemically analyzed for major and trace ions. Surface and ground water samples from the basin were then analyzed for the chemical fingerprint determined for the field site. Some surface and ground water samples do appear to be chemically altered by septic effluent. A water budget was completed for the system, allowing the velocity and other parameters of the septic effluent flowing along the regolith-bedrock interface to be calculated.
“LATE QUATERNARY PALEOSEISMIC HISTORY OF THE UEMACHI BLIND THRUST SYSTEM IN METROPOLITAN OSAKA, JAPAN, BASED ON HIGH-RESOLUTION STRATIGRAPHIC ANALYSIS OF FAULT-PROPAGATION FOLDS”
Eric Cannon (speaker), K.J. Mueller, Y. Sugiyama, N. Kitada, and S. Sundermann
University of Colorado, Boulder
We analyze the growth of the Uemachi fault system in metropolitan Osaka, Japan, by using shallow continuously cored borings and a high-resolution seismic reflection profile to determine the record of large magnitude Late Quaternary earthquakes on blind thrust faults. The 45-km-long, north-trending, multi-segment Uemachi fault system manifests itself as a series of he shallow subsurface flexures that are largely buried. The flexures are forelimbs of active fault-propagation folds formed by west- to northwest-vergent, coseismic slip on blind thrust faults.
Late Quaternary stratigraphy in the Osaka Basin is characterized by sequences of alternating marine clays deposited during marine transgressions that are interbedded with coarse fluvial sediment deposited in a floodplain during lowstands. The bases of the two youngest highstand deposits, termed the Ma12 and Ma13 marine clays, are 127 ky and 9 ky in age, respectively. We use a dataset containing several thousand boreholes that penetrate the Ma12 and Ma13 clays across the central Osaka Basin to determine the fault segment geometry and vertical uplift rates across the flexures. The uplift rate for the main Uemachi fault is approximately 0.5 m/ky using the vertical relief and age of the Ma12 clay layer across the flexure, in agreement with 0.4 m/ky for the long-term uplift rate based on vertical offset of the 1.12 Ma Ma0 clay layer found in the OD-1 and OD-2 deep boreholes.
An S-wave seismic profile with sub-meter reflector resolution, located along the Yodogawa River in central Osaka, is tied to five continuously cored boreholes (lengths range from 37 to 50 m) for 250 m across the forelimb of folded late Pleistocene to Holocene sediments. Deformation recorded in growth strata suggests that the most recent earthquake on the Uemachi fault occurred between approximately 9,500 yr B.P. and 2,500 yr B.P. and resulted in 3 m of uplift. The seismic moment for this event may have been between 6.9 and 7.5 on the basis of our estimates. Assuming that 3 m of uplift occurs in a characteristic earthquake and that the fault maintains a long-term uniform slip rate of 0.4-0.5 m/ky, we estimate that in the last 1.12 Ma, the Uemachi fault may have generated approximately 140 to 190 earthquakes with a recurrence interval of 6 to 8 ky.
December 2003 – Presidental Address
“WHAT’S HAPPENING IN THE MINERAL AND MINERAL FUEL INDUSTRIES IN COLORADO?”
James A. Cappa
Colorado Geological Survey
INTRODUCTION
The Colorado Geological Survey (CGS) Mineral Resources Section estimates the total value of 2002 mineral and mineral fuel production in Colorado to be $3,723 million, a 20 percent decrease from the 2001 total value of $4,645 million.
Mineral fuel and CO2 production values for 2002 are estimated at:
- oil $417.6 million
- natural gas $1,943 million
- CO2 $117.7 million
- coal $616 million
The total estimated value of oil, natural gas, and CO2 production in 2002 was $2,478 million, which is down 31 percent from the 2001 value of $3,610 million. Colorado natural gas production increased and oil production declined; however, both prices for gas and oil declined during most of 2002. The value of CO2 production decreased from $122 million to $118 million, primarily owing to decreased production. Estimated production volumes for 2002 total 821 billion cubic feet of gas, 19.2 million barrels of oil, and 294 billion cubic feet of CO2.
The CGS forecasts total natural gas production to increase to 840 BCF in 2003, a 2.3 percent increase. Oil production is forecast to remain flat at 19.2 million barrels. Total production value is forecast to be $2.30 billion, a 15 percent increase over 2002 value.
Coal production increased from the 2001 level of 33.4 million tons to a record 35.2 million tons in 2002. Coal prices, which vary from mine to mine, are estimated at an average $17.50 per ton for 2002. The value of Colorado coal production is estimated at $616 million, up 23 percent from the 2001 value of $502 million. The CGS estimates that coal production will set a new record of 36 million tons for 2003.
Gold prices increased significantly in 2003 compared to the depressed prices during the previous four years. As of early October 2003, the spot gold price was around $380 per ounce, whereas the average gold price in 2002 was $310 per ounce. This is good news for Colorado’s only operating gold mine, the Cripple Creek & Victor Mine (CC&V) in Teller County. This world-class mine employs about 300 people and produced 224,000 ounces of gold in 2002. In late 2002, CC&V completed its two-year, $168.5 million expansion and capital improvement program. With the expanded production capacity, the mine is expected to produce 300,000 to 400,000 ounces of gold per year in 2003 and beyond. The current reserve base is sufficient to support gold production until 2012 at the expanded production rate.
The Henderson Mine in Clear Creek County continues to be North America’s largest primary producer of molybdenum. The underground mine is owned by Climax Molybdenum Company, a subsidiary of Phelps Dodge Corp., and employs approximately 300 people. In 2002, the mine produced 20.5 million pounds of molybdenum metal, an increase of 9 percent over the 18.8 million pounds produced in 2001. Molybdenum prices have risen significantly in the past two years. As of October 2003, the price for molybdic oxide was more than $6.00 per pound compared to an average price of $3.75 per pound in 2002 and $2.36 per pound in 2001. The Henderson Mine hopes to increase production by 5 percent over the next year and an additional 5 percent the following year.
COALBED METHANE
Included in the production numbers for natural gas is the production of naturally occurring methane gas from subsurface coal beds. Known as coalbed methane (CBM), this subset of natural gas is becoming increasingly important in Colorado. Only seven years after CBM production reporting commenced in Colorado, CBM production surpassed that of conventional natural gas. However, 2001 saw a resurgence in the production of conventional natural gas, which once again surpassed CBM production.
CBM is natural gas (methane) that is produced specifically from subsurface coal beds that contain significant quantities of methane gas, chemically identified as CH4. Long considered an undesirable and dangerous by-product of many Colorado coals, this colorless and odorless gas, often capable of spontaneous combustion, was responsible for many coal fires and mine explosions. The petroleum industry, in conjunction with State and Federal agencies, developed techniques to extract methane from coal beds using drill rigs and subsurface completion technologies similar to those used to produce natural gas from conventional reservoirs, predominantly sandstones and limestones. Coal beds were identified as unconventional gas reservoirs, subject to tax credits in the late 1980s and early 1990s. Though the tax credits provided the initial economic impetus to explore for these unconventional reservoirs, successful drilling and completion technologies allowed the extraction of CBM to become fully profitable even after the tax credits expired in the early 1990s.
Coal-bearing units underlie approximately 28 percent or 29,600 square miles of Colorado. As such, it is no surprise that CBM exploration and development is so prolific in the state. A number of reservoir components related to subsurface coal beds control how methane is trapped in the coal and whether it can be recovered economically. Factors such as the preserved gas content in the coals, the amount of water in the coals, the ability of both water and gas to flow to a well bore, the reservoir pressure exerted on the coal, and the thickness and depth of the coal are all significant. As the number of successful CBM operations continues to increase in Colorado, it becomes apparent that these critical factors exist, in some unique combination, for all coals.
Given the fact that more than 1,700 historic coal mines have been in operation in the state during the past 120 years, ample data can be derived from those operations. The presence in coal mines of methane gas and dust, capable of spontaneous combustion, caused numerous explosions and fires in the mines. Other observable indications have been documented as well.
GOLD
The Cripple Creek district is located within a small (approximately 6 square miles), 32–28 million year old alkalic intrusive-diatreme complex emplaced at the junction of four Precambrian igneous and metamorphic units. Diatremes are neck-like volcanic features composed of breccia formed by the explosive activity that results when molten rock interacts with abundant groundwater near the surface. The complex consists primarily of a large mass of phonolite, an alkalic igneous rock, and phonolite breccia. There are also lake sediments, tree trunks, and coal layers within parts of the complex, which indicate that these igneous rocks formed a small volcanic center at the surface.
Because of their unique composition, ore deposits associated with alkalic igneous rocks have a distinctive set of gangue and ore minerals. The principal ore minerals in the Cripple Creek district are gold telluride minerals: calaverite and rarely sylvanite and petzite. Calaverite from district mines contains 39 percent to 43 percent gold and minor amounts of silver.
The Cripple Creek district is in Teller County, well south of the Colorado Mineral Belt. The district is the most important gold-producing camp in the state; it has produced more than 23 million ounces of gold since its discovery in 1891. In comparison, the entire state of Colorado has produced about 44 million ounces. Four main types of ore deposits are found within the Cripple Creek district: vein deposits, diatreme-hosted deposits, hydrothermal breccia-hosted deposits, and bedded rock-hosted deposits.
MOLYBDENUM
The Henderson ore body was discovered by exploration drilling by Climax geologists beneath the Urad molybdenite deposit, which was exposed on Red Mountain near Berthoud Falls in Clear Creek County. The Urad deposit was so named because early prospectors thought the yellow minerals at the prospect were uranium oxide minerals. AMAX completed mining of the Urad deposit in 1974; that deposit yielded 13.7 million tons of ore grading 0.35 percent MoS2-about 96 million pounds of molybdenite.
