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Results for “California Journal of Mines and Geology”

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

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7 recordsLinked to original sources
USGS1946

Geology and nickel mineralization of the Julian-Cuyamaca area, San Diego County, California

The Julian-Cuyamaca area is in the San Diego Mountains, one of the Peninsular Ranges of southern California. It lies in San Diego County, about 3 miles south of Julian, and approximately 60 miles northeast of San Diego. The area was mapped, and its nickel mineralization studied, from March to June, 1944; the work was part of the U. S. Geological Survey's program of strategic mineral investigations.

California↗
USGS1989

Soil geochemistry of Mother Lode-type gold deposits in the Hodson mining district, central California, U.S.A.

The Hodson mining district is in the westernmost foothills of the Sierra Nevada in California, about 17 km west of the town of Angels Camp. This district is part of the West Gold Belt, which lies about 12-16 km west of, and generally parallel to, the better known Mother Lode Gold Belt in central California. The district produced several million dollars worth of Au between about 1890 and 1940. The geologic setting and mineral deposits in the West Gold Belt are generally similar to those in the Mother Lode Gold Belt. Rocks in the study area are of Jurassic age and consist of a mixture of (1) fine-grained, generally thin-bedded, clastic sedimentary rocks that have been metamorphosed to slates, schists, and phyllites, and (2) massive volcanic flows and welded tuffs that have been metamorphosed to metabasalts and metatuffs. All rocks were intensely faulted and folded during the Late Cretaceous Nevadan orogeny; northnorthwest- and northwest-trending faults dominate. Mining in the area was of low-grade gold-pyrite ores occurring principally in the carbonatized wall rocks adjacent to the major northwest-trending Hodson fault and its splays. Minor amounts of other sulfide minerals (principally chalcopyrite, arsenopyrite, sphalerite, and galena) are locally associated with the Au deposits.

California↗
USGS2004

Interseismic strain and rotation rates in the northeast Mojave domain, eastern California

The northeast Mojave domain, a type locality for bookshelf faulting, is a region of east striking, left-lateral faults in the northeast corner of the Mojave block, a block otherwise dominated by ∼N40°W striking, right-lateral faults. Paleomagnetic evidence suggests that blocks within the domain have rotated clockwise about a vertical axis as much as 60° since 12.8 Ma [Schermer et al., 1996] . In 1994, and again in 2002, the U.S. Geological Survey surveyed an array of 14 geodetic monuments distributed across the northeast Mojave domain. The 2002 survey results were adjusted to remove the coseismic offsets imposed by the nearby Hector Mine earthquake (16 October 1999, M w = 7.1). The adjusted deformation across the array appears to be uniform and can be approximated by the principal strain rates ε 1 = 28.9 ± 9.1 N77.2°W ± 4.8° and ε 2 = −48.2 ± 8.9 N12.8°E ± 4.8° nstrain yr −1 ; extension reckoned positive, and quoted uncertainties are standard deviations. That strain accumulation could be released by slip on faults striking N32°W but not by bookshelf faulting on the east striking faults alone. The vertical axis rotation rate of the northeast Mojave domain as a whole relative to fixed North America is 71.0 ± 6.4 nrad yr −1 (4.07° ± 0.37° Myr −1 ) clockwise, about twice the maximum tensor shear strain rate. The observed rotation rate acting over 12.8 Myr would produce a clockwise rotation of 52.1° ± 4.7°, exclusive of possible coseismic rotations. That rotation is in rough agreement with the paleomagnetic rotation accumulated in the individual fault blocks within the northeast Mojave domain since 12.8 Ma.

California↗
USGS2025

Gas emissions from the Sulphur Bank Mercury Mine hydrothermal system, Clear Lake volcanic field, California

The Sulphur Bank Mercury Mine (SBMM) hydrothermal system offers insights into active degassing processes in the Clear Lake volcanic field (CLVF), a high-threat region based on its record of Holocene eruptions and proximity to populated areas. Here we present chemical and isotopic analyses of gas samples collected between 2015 and 2023, along with the first comprehensive CO 2 flux survey of the SBMM area conducted in 2023. Sampled gases are CO 2 - and CH 4 -rich (≥84 and 6 mol% in dry gas, respectively) with high mantle-derived helium contributions ( 3 He/ 4 He = 6.54–7.86 R C /R A ). Carbon isotopic compositions of CO 2 (δ 13 C = −10.0 to −9.5 ‰) and CH 4 (δ 13 C = −35.8 ‰) indicate mixed sources, with significant contributions from metamorphism of organic-rich Franciscan Complex rocks hosting the hydrothermal system. Modeling of gas compositions shows that scrubbing by interaction with air-saturated groundwater strongly influences observed compositional variability. From our CO₂ flux measurements, we estimate the deeply derived CO 2 emission rate from the SBMM hydrothermal area (0.2 km 2 ) at 240 t d −1 , comparable to many quiescently degassing volcanoes worldwide. We also provide a first-order estimate of CH 4 emissions at approximately 0.5 t d −1 . Our findings establish crucial baseline data for future volcanic monitoring efforts, enhancing detection capabilities for potential changes in this active hydrothermal system. This work contributes to the broader understanding of volatile contributions from volcanic and metamorphic sources to the global carbon budget, while highlighting the strong influence of bedrock geology on gas compositions in the CLVF.

California↗
USGS1987

Geochemical studies in the Indian Pass and Picacho Peak Bureau of Land Management Wilderness study areas, imperial county, Southern California

The U.S. Geological Survey has conducted geochemical studies in the Indian Pass (CDCA-355), 124 km 2 , and Picacho Peak (CDCA-355A), 23 km 2 , Wilderness Study Areas (WSA's) as part of a program to evaluate the mineral resource potential of designated areas in the California Desert Conservation Area. These two WSA's are of particular interest because they lie within a region which has intermittently produced significant quantities of Au since the mid-1800's, and is currently the site of much exploration activity for additional Au resources. Within a 15-km radius of the WSA's, there is one actively producing gold mine, a major deposit which began production in 1986, and one recently announced discovery. In the reconnaissance geochemical surveys of the two WSA's - 177 μm (-80 mesh) stream sediments, heavy-mineral concentrates from stream sediments, and rocks were prepared and analyzed. Four areas of possible exploration interest were identified within the WSA's. The first area is characterized by anomalous W and Bi in nonmagnetic heavy-mineral concentrates, and is underlain primarily by the Mesozoic Orocopia Schist which has been intruded by monzogranite of Oligocene age. Alteration and mineralization appear to be localized near the intrusive contact. The mineralized rock at the surface contains secondary Cu and Fe minerals where the monzogranite intrudes the metabasite horizons of the Orocopia Schist and scheelite where the monzogranite intrudes marble within the Orocopia Schist.

Journal of Geochemical Exploration↗
USGS2008

Mineralogical and compositional characteristics of Late Permian coals from an area of high lung cancer rate in Xuan Wei, Yunnan, China: Occurrence and origin of quartz and chamosite

Some townships in Xuan Wei County, Yunnan Province, have one of the highest lung cancer mortality rates in China and the epidemic disease in the area has generally been attributed to the polycyclic aromatic hydrocarbons (PAHs) released from domestic coal burning. However, the cancer-causing culprit is not settled as Tian [Tian, L., 2005. Coal Combustion Emissions and Lung Cancer in Xuan Wei, China. Ph.D. thesis, University of California, Berkeley.] found nanometer quartz in these coals, soot emissions, and lung cancer tissues. We have conducted mineralogical and geochemical studies of the coals from Xuan Wei for the purpose of shedding light on the minerals which may be related to the epidemic lung cancer. In this paper, abundances, modes of occurrence, and origins of minerals and elements in the coals from two mines in Xuan Wei have been studied using optical microscope, low-temperature ashing, X-ray diffraction analysis, scanning electron microscope equipped with energy-dispersive X-ray spectrometer, and inductively-coupled plasma mass spectrometry. The minerals in the coals are mainly composed of quartz, chamosite, kaolinite, and calcite. The particle size of quartz is rather small, mostly less than 20????m and it is of authigenic origin. Chamosite occurs mainly as cell-fillings. The occurrence of quartz and chamosite indicates that they were derived from the hydrothermal fluids. Epigenetic calcite is derived from calcic fluids. Kaolinite is derived mainly from sediment source region of Kangdian Oldland to the west of coal basin. The composition of Xuan Wei coal is high in SiO2, Fe2O3, TiO2, CaO, MnO, V, Co, Ni, Cu, and Zn. The high SiO2 content is attributed to quartz, and the Fe2O3 content to chamosite. The high Mn and low Mg contents in the coal indicate the inputs of hydrothermal fluids. CaO occurs mainly in epigenetic calcite. Elements Ti, Co, Ni, Cu, Zn, and rare earth elements were derived from the basaltic rocks at sediment source region. ?? 2008 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗
USGS2012

Seismicity and shear strain in the southern Great Basin of Nevada and California

This study examines the relationship between the distribution of small earthquakes (M L ≤4.3) and mechanisms of strain accumulation and relaxation in an area with long repeat times between large events, the Southern Great Basin Seismic Network (SGBSN) region. The Great Basin is a unique continental extensional province characterized by normal and strike-slip faulting, high heat flow, crust of thin to normal thickness, and high elevations. The SGBSN is operated to provide data to address suitability issues pertaining to Yucca Mountain, Nevada which is being evaluated as a potential site for a national mined geologic nuclear waste repository. Suitability issues include estimation of the probability of occurrence of future damaging earthquakes, the characterization of the mechanisms that drive hydrologic flow, and the identification of fractures (faults) that might act as flow conduits or barriers. This study attempts to explain the distribution of small earthquakes in terms of spatial variations in the shear strain field; where strain concentrates there should be a greater number of small earthquakes. Strain field models are constructed under the assumption that long term fault behavior perturbs an otherwise uniform strain field. These strain field models are then interpreted with regard to the regional tectonics and site suitability issues. Modeling results provide one possible explanation of why earthquake clusters cover regions much larger than the surface projections of any of mapped major faults; clusters in a wide band along and extending northeast of the northern half of the Furnace Creek fault may correspond to elevated shear strains along the fault and a broad cluster in the Pahranagat Shear Zone may be associated with shear strain arising from a distribution of smaller localized faults. The relatively large number of small earthquakes in the southern and eastern portions of the Nevada Test Site is consistent with the strain field models. A minimum in shear strain at Yucca Mountain is predicted by all models consistent with an almost total lack of earthquakes observed there. The region to the west of the Death Valley/Furnace Creek fault system, the portion of the study area with the most active deformation but few small earthquakes, is an area of low shear strain. A possible reason for this is that the fault configuration in the area is optimal for accommodating regional deformation via large earthquakes or creep. While there is also a relative lack of earthquakes at Yucca Mountain, this may be indicative of a lack of accumulating strain energy and thus, a lower potential for a large earthquake.

Journal of Geophysical Research↗