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At least 1,513 records · Page 84Linked to original sources
USGS2007

Bald Mountain gold mining district, Nevada: A Jurassic reduced intrusion-related gold system

The Bald Mountain mining district has produced about 2 million ounces (Moz) of An. Geologic mapping, field relationships, geochemical data, petrographic observations, fluid inclusion characteristics, and Pb, S, O, and H isotope data indicate that An mineralization was associated with a reduced Jurassic intrusion. Gold deposits are localized within and surrounding a Jurassic (159 Ma) quartz monzonite porphyry pluton and dike complex that intrudes Cambrian to Mississippian carbonate and clastic rocks. The pluton, associated dikes, and An mineralization were controlled by a crustal-scale northwest-trending structure named the Bida trend. Gold deposits are localized by fracture networks in the pluton and the contact metamorphic aureole, dike margins, high-angle faults, and certain strata or shale-limestone contacts in sedimentary rocks. Gold mineralization was accompanied by silicification and phyllic alteration, ??argillic alteration at shallow levels. Although An is typically present throughout, the system exhibits a classic concentric geochemical zonation pattern with Mo, W, Bi, and Cu near the center, Ag, Pb, and Zn at intermediate distances, and As and Sb peripheral to the intrusion. Near the center of the system, micron-sized native An occurs with base metal sulfides and sulfosalts. In peripheral deposits and in later stages of mineralization, Au is typically submicron in size and resides in pyrite or arsenopyrite. Electron microprobe and laser ablation ICP-MS analyses show that arsenopyrite, pyrite, and Bi sulfide minerals contain 10s to 1,000s of ppm Au. Ore-forming fluids were aqueous and carbonic at deep levels and episodically hypersaline at shallow levels due to boiling. The isotopic compositions of H and O in quartz and sericite and S and Pb in sulfides are indicative of magmatic ore fluids with sedimentary sulfur. Together, the evidence suggests that Au was introduced by reduced S-bearing magmatic fluids derived from a reduced intrusion. The reduced character of the intrusion was caused by assimilation of carbonaceous sedimentary rocks. Tertiary faults dismember the area and drop down the upper part of the mineralizing system to the west. The abundant and widespread kaolinite in oxide ores is relatively disordered (1A polytype) and has ??D and ??18O values suggestive of a supergene origin. The deep weathering and oxidation of the ores associated with exhumation made them amenable to open-pit mining and processing using cyanide heap leach methods. ?? 2007 Society of Economic Geologists, Inc.

Economic Geology↗
USGS2008

Tertiary tilting and dismemberment of the laramide arc and related hydrothermal systems, Sierrita Mountain, Arizona

Multiple lines of evidence, including new and published geologic mapping and paleomagnetic and geobarometric determinations, demonstrate that the rocks and large porphyry copper systems of the Sierrita Mountains in southern Arizona were dismembered and tilted 50?? to 60?? to the south by Tertiary normal faulting. Repetition of geologic features and geobarometry indicate that the area is segmented into at least three major structural blocks, and the present surface corresponds to oblique sections through the Laramide plutonic-hydrothermal complex, ranging in paleodepth from ???1 to ???12 km. These results add to an evolving view of a north-south extensional domain at high angles to much extension in the southern Basin and Range, contrast with earlier interpretations that the Laramide systems are largely upright and dismembered by thrust faults, highlight the necessity of restoring Tertiary rotations before interpreting Laramide structural and hydrothermal features, and add to the broader understanding of pluton emplacement and evolution of porphyry copper systems. ?? 2008 Society of Economic Geologists, Inc.

Economic Geology↗
USGS1938

Outlook for further ore discoveries in the Little Hatchet Mountains, New Mexico

The Little Hatchet Mountains contain two mining districts, the Eureka silver-lead-zinc district and the Sylvanite gold district, the deposits of each being associated with a mass of monzonite that intrudes Lower Cretaceous sediments. The same formations crop out in both districts, having been duplicated by a large post-ore fault, and the two monzonite masses and their accompanying mineralized zones lie at essentially the same stratigraphic position in the two fault blocks. The deposits of the Eureka district are mesothermal whereas those of the Sylvanite district are hypothermal, but the two groups are mineralogically similar in many respects.As the two monzonite exposures are several miles apart, the natural inference is that there are two separate intrusions. Contrary to this inference, the evidence of structure, mineralogy, and petrology indicates that the two monzonite masses are faulted parts of the same body and that the mineralized areas of the Eureka and Sylvanite districts were originally continuous and zonally related, the original igneous mass having been a flat-lying sill-like streamer, 7 miles or more long, that was bordered by a contact-metamorphic halo and that formed the core of a zone of mineralization.The economic implications of this interpretation are three-fold: (1) the mineralized zone is limited in thickness and is restricted, like a bedded deposit, to a particular sedimentary horizon; (2) the area between the Eureka and Sylvanite districts, hitherto considered barren, should contain mineralized ground at variable depths below the surface; and (3) the deposits change along the trend of the zone from the gold deposits of the one district to the silver-bearing base-metal deposits of the other. In structure and size the deposits in the hidden parts of the mineralized zone probably are similar to those already known. Under the alternative interpretation that the two districts are separate centers of activity, the outlook for future successful prospecting depends upon the depths at which the underlying Paleozoic limestones lie and the possibility of large deposits having been formed in them.

New Mexico↗
USGS1938

Manganese deposits of the Drum Mountains, Utah

More than 15,000 tons of manganese ore has been produced from small deposits in the Drum Mountains in west-central Utah. Lenses of rhodochrosite, now largely weathered near the surface to manganese oxides, lie parallel to the bedding of Cambrian dolomites and shales near faults that are nearly normal to bedding. Two varieties of rhodochrosite, one fine-grained, dark-gray or black, and massive, the other coarser-grained, pink, and generally occurring in veinlets in the gray variety, are present. The gray contains less MnCO 3 and FeCO 3 , but more CaCO 3 and MgCO 3 than the pink variety. The deposits are interpreted as bodies that replaced favorable dolomite or limestone beds. The gray rhodochrosite first replaced the dolomite or limestone; the pink variety later formed veinlets in the gray rhodochrosite and replaced it to a small extent.

Utah↗
USGS1946

Stages and epochs of mineralization in the San Juan Mountains, Colorado, as shown at the Dunmore Mine, Ouray County, Colorado

The Dunmore lode is localized along a persistent fissure zone over two miles long and averaging nearly 100 feet in width along the length of the Dunmore claim. The fault in which the lode is located offset the pre-Cambrian quartzite and slate walls about 4,500 feet prior to deposition of the overlying thick San Juan tuff. Late Tertiary faulting extended the fissure into the San Juan tuff, dropping the south side about 80 feet. Although most of the lode crops out in the pre-Cambrian rocks, it extends upward across the profound unconformity into the tuff. The lode is complex, containing sharply marked fissure veins, sheared slate dragged into the fault zone, a sheared dike, breccia chimneys, and pebble dikes. An assemblage consisting of quartz, sericite, kaolin, and pyrite appears to be of early Tertiary age. The more productive part of the lode, however, is late Tertiary and consists of a hematite chimney inclosing a copper shoot, a tungsten chimney, and compound base-metal fissure veins. These chimneys and veins are mostly localized along early Tertiary structures, but their mineral sequences correlate them with the second stage of late Tertiary deposition recognized by Burbank in the adjoining Red Mountain and other districts. The Dunmore lode, however, is believed to have been deposited at greater depth and higher temperature and nearer to a source of supply than the lodes of these districts. In structure as well as mineral assemblages the Dunmore lode shows a connection between the chimneys and veins of the region.

Colorado↗
USGS1948

The bedding-replacement fluorspar deposits of Spar Valley, Eagle Mountains, Hudspeth County, Texas

The Spar Valley fluorspar district in the Eagle Mountains, Hudspeth County, Texas, is one of the few in the western United States containing bedding-replacement fluorspar deposits. The deposits at Spar Valley resemble the bedding-replacement deposits of the Cave in Rock fluorspar district of southern Illinois. Two distinct deposits, the North and the South ore bodies, are present. The North ore body is larger and has been developed by diamond drilling and mining; the following statements apply chiefly to it.The fluorspar partly replaces a sequence of three sandy limestones interbedded with four calcareous shales in the lower part of the Edwards limestone of Lower Cretaceous age. The fluoritized beds, which dip 40 degrees SW in conformity with underlying limestone, are overlain by thick impermeable gouge along a bedding-plane fault dipping slightly more than 40 degrees SW. The high-grade beds were derived from the sandy limestones, and the low-grade beds, which contain as much as 28 percent of CaF 2 , were formed from the calcareous shales. The selectiveness of replacement by the fluorine-bearing solutions, due to differences in the chemical composition, texture, and degree of brecciation of the original rock, resulted in bedding-replacement deposits of variable fluorite content.A reduction in volume, which accompanied the replacement, led to the development of many cavities. During the later stages of fluoritization these cavities were lined with fluorite crystals, early fluorite grains were coated and interstices between them were filled, and fluorite veins were formed in the ore beds and the underlying dense limestone.

Texas↗
USGS1979

Environment of ore deposition in the Creede mining district, San Juan Mountains, Colorado; Part IV, source of fluids, from oxygen, hydrogen, and carbon isotope studies

The hydrogen isotopic composition of fluids responsible for formation of the near-surface silver-base metal vein deposits at Creede was measured by direct analysis of inclusion fluids in sphalerite, quartz, and rhodochrosite and was estimated from analyses of illite and chlorite. The oxygen isotopic composition was determined directly on inclusion fluids in sphalerite and was estimated from analyses of quartz, illite, rhodochrosite, siderite, and adularia. The carbon isotopic composition was estimated from analyses of rhodochrosite and siderite. The ranges in isotopic composition for water and CO 2 in the fluids associated with the formation of each of the minerals is given below (number of determinations given in parentheses):Mineral delta D (sub H 2 ) O ppm delta 18 O (sub H 2 ) O ppm delta 13 C (sub CO 2 ) ppmSphalerite -81 to -54 (4) -10.1 to -4.5 (4)Quartz -97 to -86 (4) -5.9 to 1.8 (18)Illite -62 to -50 (8) -1.6 to 1.2(7)Chlorite -64 to -55 (10) -2.2 to 0.8 (10)Adularia 4.2 (1)Rhodochrosite -82 to -78 (2) 4.2 to 9.4 (9) -5.7 to -4.2 (9)Siderite 4.9 to 9.9 (6) -6.9 to -2.7 (6)The delta D (sub H 2 ) O and delta 18 O (sub H 2 ) O values of fluids associated with the formation of sphalerite, quartz, illite/chlorite, and carbonate minerals differ substantially from one another, and these differences appear to have been maintained throughout the depositional history, regardless of the positions of the minerals in the paragenetic sequence.The data suggest that waters from three coexisting reservoirs fed the vein system alternately and episodically during vein formation, and apparently there was little mixing of the fluids from the different reservoirs. The hydrogen, oxygen, and carbon isotope data suggest that the carbonate waters were deep seated, probably dominantly magmatic, in origin. The sphalerite and illite/chlorite waters must have been dominantly meteoric in origin and substantially oxygen shifted by exchange with the volcanic country rocks. The quartz waters were also oxygen shifted meteoric waters but were some 40 per mil lower in deuterium content than the sphalerite and illite/chlorite waters.We propose that the quartz fluids entered the vein system from reservoirs beneath the mountainous areas to the north in the vicinity of the present Continental Divide, but that the sphalerite and illite/chlorite fluids entered the vein system from a topographically low area to the south along the structural moat of the Creede caldera. The difference in delta D between the two meteoric waters may reflect differences in altitude of the recharge areas for the two reservoirs or may be clue to isotopic evolution of the closed-basin lake and interstitial waters in the moat surrounding the Creede caldera.

Colorado↗
USGS1985

Geology of the Brick Flat massive sulfide body, Iron Mountain cluster, West Shasta district, California

The Brick Flat massive sulfide body is one of a group of 8 individual bodies that constitute the Iron Mountain cluster in the S part of the West Shasta district. Before they were separated by postmineral faulting, 5 of the 8 sulfide bodies formed a single large deposit about 1375 m long with a mass of some 23 million metric tons. The pyritic Brick Flat sulfide body is one of the 5 faulted segements of this deposit. The Brick Flat massive sulfide lies within medium phenocryst rhyolite that is characteristic of the ore-bearing middle unit of the Balaklala Rhyolite. It is interpreted to be downfaulted a vertical distance of 75 to 85 m from the Old Mine sulfide-gossan orebody along the N-dipping Camden South fault. It is bounded in turn on its N side by another parallel fault, the Camden North, which drops the orebody down another 75 m to the level of the Richmond orebody. -from Author

Economic Geology↗
USGS1985

The plumbotectonics of the West Shasta mining district, eastern Klamath Mountains, California

The tectonic setting comprising the West Shasta mining district has often been compared with that of primitive island arcs. Concentrations of uranium, thorium, and lead and lead isotope compositions were determined for Devonian ores and rocks of the West Shasta district, eastern Klamath Mountains, California, to help evaluate the tectonic classification. The lead isotope pattern is found to be complex. From comparison of the data with those on younger ores and rocks in the region and with those isotopic patterns found in modern tectonic terranes, however, a number of conclusions are possible. A lead isotope point for the Devonian oceanic mantle is now well established from this study on the West Shasta district. This isotopic composition is in agreement with that suggested by Slawson in 1983--i.e., from a sample of massive sulfide ore from the Golinsky deposit--with a 206 Pb/ 204 Pb of 17.830, a 207 Pb/ 204 Pb of 15.450, and a 208 Pb/ 204 Pb of 37.313. If the Devonian mantle is analogous to the modern mantle, the determined value is probably at the more radiogenic end of the Devonian oceanic mantle array.Some samples of volcanic rocks and ores that have elevated values of 207 Pb/ 204 Pb and 208 Pb/ 204 Pb indicate that subducted pelagic sediments or interaction of the magmas with other sediments downsection have been involved to varying degrees in the generation of magmas. The high ratios were not attained by addition of lead to the volcanic rocks or ores during subsequent magmatic events, such as intrusion of the Permian Pit River stock to the east or of the Cretaceous Shasta Bally batholith that crops out to the south and west and may underlie part of the district. Some values of 207 Pb/ 204 Pb are sufficiently high as to suggest that West Shasta may have developed nearer a continent than was previously supposed. Lead isotope data for Quaternary volcanic rocks are somewhat more radiogenic than for Cretaceous ores and plutonic rocks. Permo-Triassic ores are again a bit less radiogenic. The isotopic differences between the Permo-Triassic and Quaternary data could be accounted for by a value for 238 U/ 204 Pb of 10.42 in common source material. Using this value of 238 U/ 204 Pb to calculate even further back to 400 m.y., the resulting ratios are found to fall very close to the "best value" for the lead isotope mixing line between the Devonian mantle and pelagic sediments. We interpret this intersection to be the "mean value" for the assimilated Devonian sediment lead--18.250 for 206 Pb/ 204 Pb and 15.582 for 207 Pb/ 204 Pb. As deduced for the lead isotope composition for the Devonian mantle at this location, the pelagic sediment, lead isotope composition also is toward the more radiogenic end of the values expected for pelagic sediments in the Devonian. Lack of sediments in the observed volcanic section of the West Shasta district suggests a submerged volcanic-arc setting (as interpreted by others for the Troodos and Samail ophiolites) rather than an island-arc situation (such as the Green Tuff area of Japan) or an incipient spreading ridge setting (that might have grown to be a subaerial Iceland). The elevated values of 207 Pb/ 204 Pb for some samples suggest a submerged volcanic are whereas the exceedingly low values of thorium--which is not easily mobilized during alteration events--for both basaltic andesites and plagiorhyolites is suggestive of depleted source material such as is found for most oceanic spreading centers. Elevated values of 207 Pb/ 204 Pb are exceedingly rare in midocean ridge basalts and low contents of thorium are known in island arcs, so a submerged volcanic arc is the preferred interpretation. Some similarity exists between the 206 Pb/ 204 Pb values of Devonian ores having elevated values of 207 Pb/ 204 Pb and those of the Permo-Triassic ores of the East Shasta district, as mentioned by Slawson in 1983. This similarity is now confirmed to be a coincidence. We find it due first of all to some incorporation of sediment lead in the magmas, followed later by some migration of radiogenic lead--probably locally derived--into the ores during subsequent events. Because there was some postdepositional lead migration into the ores, some migration of copper also into the ores cannot be excluded. Lead, especially radiogenic lead, however, is more mobile than copper. As the migrating lead is deduced to have been locally derived from the observed section rather than exotically derived, any copper added was probably locally derived also.

Economic Geology↗
USGS2014

Paleoseismology of the Southern Section of the Black Mountains and Southern Death Valley Fault Zones, Death Valley, United States

The Death Valley Fault System (DVFS) is part of the southern Walker Lane–eastern California shear zone. The normal Black Mountains Fault Zone (BMFZ) and the right-lateral Southern Death Valley Fault Zone (SDVFZ) are two components of the DVFS. Estimates of late Pleistocene-Holocene slip rates and recurrence intervals for these two fault zones are uncertain owing to poor relative age control. The BMFZ southernmost section (Section 1W) steps basinward and preserves multiple scarps in the Quaternary alluvial fans. We present optically stimulated luminescence (OSL) dates ranging from 27 to 4 ka of fluvial and eolian sand lenses interbedded with alluvial-fan deposits offset by the BMFZ. By cross-cutting relations, we infer that there were three separate ground-rupturing earthquakes on BMFZ Section 1W with vertical displacement between 5.5 m and 2.75 m. The slip-rate estimate is ∼0.2 to 1.8 mm/yr, with an earthquake recurrence interval of 4,500 to 2,000 years. Slip-per-event measurements indicate Mw 7.0 to 7.2 earthquakes. The 27–4-ka OSL-dated alluvial fans also overlie the putative Cinder Hill tephra layer. Cinder Hill is offset ∼213 m by SDVFZ, which yields a tentative slip rate of 1 to 8 mm/yr for the SDVFZ.

California;Nevada↗
USGS1992

Aluminum in soil solutions from a subalpine spruce-fir forest at Whiteface Mountain, New York

Direct or indirect Al toxicity has been suggested as a principal factor in forest tree declines. We monitored ambient soil solutions in undisturbed and experimentally manipulated soils from a fir [ Abies balsamea (L.) Mill.]-spruce forest on Whiteface Mountain, NY, in order to characterize soil solution Al concentrations over a range of acid anion loadings. Under both natural and experimental conditions total Al and labile Al concentrations rarely exceeded values (180–250 µmol L −1 ) associated with reduced root growth in red spruce ( Picea rubens Sarg.). Over a 2-yr period ambient soil solutions averaged 76 and 46 µmol L −1 total Al in the organic and mineral horizons, respectively. The highest monthly mean concentrations occurred in winter. Disturbance-induced NO 3 accumulation and simulated acid rain applications produced higher peak Al values in experimental plots than were observed in undisturbed and untreated plots. Although soils of the fir-spruce zone exhibited the potential to yield solutions with phytotoxic Al concentrations, it appears that such concentrations are both spatially and temporally limited and infrequently present a direct stress to root growth in red spruce.

New York↗
USGS1985

Geophysical techniques for reconnaissance investigations of soils and surficial deposits in mountainous terrain

Two techniques were assessed for their capabilities in reconnaissance studies of soil characteristics: depth to the water table and depth to bedrock beneath surficial deposits in mountainous terrain. Ground-penetrating radar had the best near-surface resolution in the upper 2 m of the profile and provided continuous interpretable imagery of soil profiles and bedrock surfaces. Where thick colluvium blankets side slopes, the GPR could not consistently define the bedrock interface. In areas with clayey or shaley sediments, the GPR is also more limited in defining depth and is less reliable. Seismic refraction proved useful in determining the elevation of the water table and depth to bedrock, regardless of thickness of overlying material, but could not distinguish soil-profile characteristics.

Soil Science Society of America Journal↗
USGS2001

Strontium isotope evolution of pore water and calcite in the Topopah Spring Tuff, Yucca Mountain, Nevada

Yucca Mountain, a ridge of Miocene volcanic rocks in southwest Nevada, is being characterized as a site for a potential high-level radioactive waste repository. One issue of concern for the future performance of the potential repository is the movement of water in and around the potential repository horizon. Past water movement in this unsaturated zone is indicated by fluid inclusions trapped in calcite coatings on fracture footwall surfaces and in some lithophysal cavities. Some of the fluid inclusions have homogenization temperatures above the present-day geotherm (J.F. Whelan, written communication), so determining the ages of the calcite associated with those fluid inclusions is important in understanding the thermal history of the potential repository site. Calcite ages have been constrained by uranium-lead dating of silica polymorphs (opal and chalcedony) that are present in most coatings. The opal and chalcedony ages indicate that deposition of the calcite and opal coatings in the welded part of the Topopah Spring Tuff (TSw hydrogeologic unit) spanned nearly the entire history of the 12.8-million-year-old rock mass at fairly uniform overall long-term rates of deposition (within a factor of five). Constraining the age of a layer of calcite associated with specific fluid inclusions is complicated. Calcite is commonly bladed with complex textural relations, and datable opal or chalcedony may be millions of years older or younger than the calcite layer or may be absent from the coating entirely. Therefore, a more direct method of dating the calcite is presented in this paper by developing a model for strontium evolution in pore water in the TSw as recorded by the strontium coprecipitated with calcium in the calcite. Although the water that precipitated the calcite in fractures and cavities may not have been in local isotopic equilibrium with the pore water, the strontium isotope composition of all water in the TSw is primarily controlled by water-rock interaction in the overlying nonwelded and essentially unfractured Paintbrush Group tuffs (PTn). The method of dating secondary minerals from known strontium evolution rates in rocks cannot be used in this study because it assumes the water that deposited the minerals was in isotopic equilibrium with the rock, which is not the case for the pore water in the TSw. Therefore, the evolution of the strontium isotope composition of the water that deposited the calcite, as recorded by the strontium coprecipitated with calcium in the calcite, was used to develop a model for determining the age of the calcite.

Nevada↗
USGS2006

Lithostratigraphy and shear-wave velocity in the crystallized Topopah Spring Tuff, Yucca Mountain, Nevada

Evaluation of the potential future response to seismic events of the proposed spent nuclear fuel and high-level radioactive waste repository at Yucca Mountain, Nevada, is in part based on the seismic properties of the host rock, the 12.8-million-year-old Topopah Spring Tuff. Because of the processes that formed the tuff, the densely welded and crystallized part has three lithophysal and three nonlithophysal zones, and each zone has characteristic variations in lithostratigraphic features and structures of the rocks. Lithostratigraphic features include lithophysal cavities; rims on lithophysae and some fractures; spots (which are similar to rims but without an associated cavity or aperture); amounts of porosity resulting from welding, crystallization, and vapor-phase corrosion and mineralization; and fractures. Seismic properties, including shear-wave velocity (Vs), have been measured on 38 pieces of core, and there is a good "first order" correlation with the lithostratigraphic zones; for example, samples from nonlithophysal zones have larger Vs values compared to samples from lithophysal zones. Some samples have Vs values that are outside the typical range for the lithostratigraphic zone; however, these samples typically have one or more fractures, "large" lithophysal cavities, or "missing pieces" relative to the sample size. Shear-wave velocity data measured in the tunnels have similar relations to lithophysal and nonlithophysal rocks; however, tunnel-based values are typically smaller than those measured in core resulting from increased lithophysae and fracturing effects. Variations in seismic properties such as Vs data from small-scale samples (typical and "flawed" core) to larger scale transects in the tunnels provide a basis for merging our understanding of the distributions of lithostratigraphic features (and zones) with a method to scale seismic properties.

Conference Paper↗
USGS2005

Bait stations, hard mast, and black bear population growth in Great Smoky Mountains National Park

Bait-station surveys are used by wildlife managers as an index to American black bear ( Ursus americanus ) population abundance, but the relationship is not well established. Hard mast surveys are similarly used to assess annual black bear food availability which may affect mortality and natality rates. We used data collected in Great Smoky Mountains National Park (GSMNP) from 1989 to 2003 to determine whether changes in the bait-station index (ΔBSI) were associated with estimated rates of bear population growth (λ) and whether hard mast production was related to bear visitation to baits. We also evaluated whether hard mast production from previous years was related to λ. Estimates of λ were based on analysis of capture-recapture data with the Pradel temporal symmetry estimator. Using the Akaike's Information Criterion (AIC), our analysis revealed no direct relationship between ΔBSI and λ. A simulation analysis indicated that our data were adequate to detect a relationship had one existed. Model fit was marginally improved when we added total oak mast production of the previous year as an interaction term suggesting that the BSI was confounded with environmental variables. Consequently the utility of the bait-station survey as a population monitoring technique is questionable at the spatial and temporal scales we studied. Mast survey data, however, were valuable covariates of λ. Population growth for a given year was negatively related to oak mast production 4 and 5 years prior. That finding supported our hypothesis that mast failures can trigger reproductive synchrony, which may not be evident from the trapped sample until years later.

North Carolina, Tennessee↗
USGS2010

Testing a Mahalanobis distance model of black bear habitat use in the Ouachita Mountains of Oklahoma

Regional wildlife–habitat models are commonly developed but rarely tested with truly independent data. We tested a published habitat model for black bears ( Ursus americanus ) with new data collected in a different site in the same ecological region (i.e., Ouachita Mountains of Arkansas and Oklahoma, USA). We used a Mahalanobis distance model developed from relocations of black bears in Arkansas to produce a map layer of Mahalanobis distances on a study area in neighboring Oklahoma. We tested this modeled map layer with relocations of black bears on the Oklahoma area. The distributions of relocations of female black bears were consistent with model predictions. We conclude that this modeling approach can be used to predict regional suitability for a species of interest.

Oklahoma↗
USGS2010

Habitat selection of Rocky Mountain elk in a nonforested environment

Recent expansions by Rocky Mountain elk (Cervus elaphus) into nonforested habitats across the Intermountain West have required managers to reconsider the traditional paradigms of forage and cover as they relate to managing elk and their habitats. We examined seasonal habitat selection patterns of a hunted elk population in a nonforested high-desert region of southwestern Wyoming, USA. We used 35,246 global positioning system locations collected from 33 adult female elk to model probability of use as a function of 6 habitat variables: slope, aspect, elevation, habitat diversity, distance to shrub cover, and distance to road. We developed resource selection probability functions for individual elk, and then we averaged the coefficients to estimate population-level models for summer and winter periods. We used the population-level models to generate predictive maps by assigning pixels across the study area to 1 of 4 use categories (i.e., high, medium-high, medium-low, or low), based on quartiles of the predictions. Model coefficients and predictive maps indicated that elk selected for summer habitats characterized by higher elevations in areas of high vegetative diversity, close to shrub cover, northerly aspects, moderate slopes, and away from roads. Winter habitat selection patterns were similar, except elk shifted to areas with lower elevations and southerly aspects. We validated predictive maps by using 528 locations collected from an independent sample of radiomarked elk (n = 55) and calculating the proportion of locations that occurred in each of the 4 use categories. Together, the high- and medium-high use categories of the summer and winter predictive maps contained 92% and 74% of summer and winter elk locations, respectively. Our population-level models and associated predictive maps were successful in predicting winter and summer habitat use by elk in a nonforested environment. In the absence of forest cover, elk seemed to rely on a combination of shrubs, topography, and low human disturbance to meet their thermal and hiding cover requirements.

Journal of Wildlife Management↗
USGS2010

Bighorn sheep response to road-related disturbances in Rocky Mountain National Park, Colorado

Bighorn sheep (Ovis canadensis) use of Sheep Lakes mineral site, Rocky Mountain National Park, Colorado, USA, has decreased since 1996. Officials were concerned that human disturbance may have been contributing to this decline in use. We evaluated effects of vehicular traffic and other road-related disturbance on bighorn use of Sheep Lakes in the summers of 2002 and 2003. We found that the time and number of attempts required by bighorn to reach Sheep Lakes was positively related to the number of vehicles and people present at Sheep Lakes. Further, the number of bighorn individuals and groups attempting to visit Sheep Lakes were negatively affected by disturbance associated with the site. The number of vehicles recorded the hour before bighorn tried to access Sheep Lakes best predicted an animal's failure to cross Fall River Road and reach Sheep Lakes. We conclude that human and road-related disturbance at Sheep Lakes negatively affected bighorn use of the mineral site. Because Sheep Lakes may be important for bighorn sheep, especially for lamb production and survival, the negative influence of disturbance may compromise health and productivity of the Mummy Range bighorn sheep.

Journal of Wildlife Management↗