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B. R. Berger

Publications and source records attributed to B. R. Berger.

At least 19 recordsLinked to original sources
USGS2007

The 3D fault and vein architecture of strike-slip releasing- and restraining bends: Evidence from volcanic-centre-relatedmineral deposits

High-temperature, volcanic-centre-related hydrothermal systems involve large fluid-flow volumes and are observed to have high discharge rates in the order of 100-400 kg/s. The flows and discharge occur predominantly on networks of critically stressed fractures. The coupling of hydrothermal fluid flow with deformation produces the volumes of veins found in epithermal mineral deposits. Owing to this coupling, veins provide information on the fault-fracture architecture in existence at the time of mineralization. They therefore provide information on the nature of deformation within fault zones, and the relations between different fault sets. The Virginia City and Goldfield mining districts, Nevada, were localized in zones of strike-slip transtension in an Early to Mid-Miocene volcanic belt along the western margin of North America. The Camp Douglas mining area occurs within the same belt, but is localized in a zone of strike-slip transpression. The vein systems in these districts record the spatial evolution of strike-slip extensional and contractional stepovers, as well as geometry of faulting in and adjacent to points along strike-slip faults where displacement has been interrupted and transferred into releasing and restraining stepovers. ?? The Geological Society of London 2007.

Conference Paper↗
USGS2007

Crustal controls on magmatic-hydrothermal systems: A geophysical comparison of White River, Washington, with Goldfield, Nevada

The White River altered area, Washington, and the Goldfield mining district, Nevada, are nearly contemporaneous Tertiary (ca. 20 Ma) calc-alkaline igneous centers with large exposures of shallow (<1 km depth) magmatic-hydrothermal, acid-sulfate alteration. Goldfield is the largest known high-sulfidation gold deposit in North America. At White River, silica is the only commodity exploited to date, but, based on its similarities with Goldfield, White River may have potential for concealed precious and/or base metal deposits at shallow depth. Both areas are products of the ancestral Cascade arc. Goldfield lies within the Great Basin physiographic province in an area of middle Miocene and younger Basin and Range and Walker Lane faulting, whereas White River is largely unaffected by young faults. However, west-northwest–striking magnetic anomalies at White River do correspond with mapped faults synchronous with magmatism, and other linear anomalies may reflect contemporaneous concealed faults. The White River altered area lies immediately south of the west-northwest–striking White River fault zone and north of a postulated fault with similar orientation. Structural data from the White River altered area indicate that alteration developed synchronously with an anomalous stress field conducive to left-lateral, strike-slip displacement on west-northwest–striking faults. Thus, the White River alteration may have developed in a transient transtensional region between the two strike-slip faults, analogous to models proposed for Goldfield and other mineral deposits in transverse deformational zones. Gravity and magnetic anomalies provide evidence for a pluton beneath the White River altered area that may have provided heat and fluids to overlying volcanic rocks. East– to east-northeast–striking extensional faults and/or fracture zones in the step-over region, also expressed in magnetic anomalies, may have tapped this intrusion and provided vertical and lateral transport of fluids to now silicified areas. By analogy to Goldfield, geophysical anomalies at the White River altered area may serve as proxies for geologic mapping in identifying faults, fractures, and intrusions relevant to hydrothermal alteration and ore formation in areas of poor exposure.

Nevada, Washington↗
USGS2006

Geologic, hydrologic, and geochemical interpretations of mineral deposits as analogs for understanding transport of environmental contaminants

Base- and precious-metal mineral deposits comprise anomalous concentrations of metals and associated elements, which may be useful subjects for study as analogs for migration of environmental contaminants. In the geologic past, hydrothermal mineral deposits formed at the intersection of favorable geologic, hydrologic and geochemical gradients. In the present, weathering of these sulfide-rich deposits occurs as a result of the interplay between rates of oxygen supply versus rates of ground or surface-water flow. Transport and spatial dispersion of elements from a mineral deposit occurs as a function of competing rates of water flow versus rates of attenuation mechanisms such as adsorption, dilution, or (co)precipitation. In this paper we present several case studies from mineralized and altered sedimentary and crystalline aquifers in the western United States to illustrate the geologic control of ground-water flow and solute transport, and to demonstrate how this combined approach leads to a more complete understanding of the systems under study as well as facilitating some capability to predict major flow directions in aquifers.

Journal of Geochemical Exploration↗
USGS2004

Environmental behavior of two molybdenum porphyry systems

Our study focuses on the geology, hydrology, and geochemistry of a variety of molybdenum (Mo) porphyry systems. The systems are either high fluorine, granite, Climax-type, systems (e.g. Mount Emmons/ Redwell Mo deposit, Colorado and Questa Mo deposit, New Mexico) or low fluorine granodiorite systems (e.g. Buckingham Stockwork Mo deposit, Battle Mountain, Nevada and Cannivan Gulch Mo deposit, Montana). The water quality of streams, natural springs, mine discharge, and ground water from drill holes were assessed in the region of these deposits. The ultimate goal of our study is to understand the environmental behavior of these Mo porphyry systems in the context of geologic setting, hydrologic regime, and climate.

Conference Paper↗
USGS2003

Utility of high-altitude infrared spectral data in mineral exploration: Application to Northern Patagonia Mountains, Arizona

Synoptic views of hydrothermal alteration assemblages are of considerable utility in regional-scale minerals exploration . Recent advances in data acquisition and analysis technologies have greatly enhanced the usefulness of remotely sensed imaging spectroscopy for reliable alteration mineral assemblages mapping. Using NASA's Airborne Visible Infrared Imaging Spectrometer (AVIRIS) sensor, this study mapped large areas of advanced argillic and phyllic-argillic alteration assemblages in the southeastern Santa Rita and northern Patagonia mountains , Arizona . Two concealed porphyry copper deposits have been identified during past exploration , the Red Mountain and Sunnyside deposits, and related published hydrothermal alteration zoning studies allow the comparison of the results obtained from AVIRIS data to the more traditional field mapping approaches. The AVIRIS mapping compares favorably with field-based studies. An analysis of iron-bearing oxide minerals above a concealed supergene chalcocite deposit at Red Mountain also indicates that remotely sensed data can be of value in the interpretation of leached caps above porphyry copper deposits. In conjunction with other types of geophysical data , AVIRIS mineral maps can be used to discriminate different exploration targets within a region.

Economic Geology↗
USGS2003

Structural localization and origin of compartmentalized fluid flow, Comstock lode, Virginia City, Nevada

Bonanza-grade orebodies in epithermal-style mineral deposits characteristically occur as discrete zones within spatially more extensive fault and/or fracture systems. Empirically, the segregation of such systems into compartments of higher and lower permeability appears to be a key process necessary for high-grade ore formation and, most commonly, it is such concentrations of metals that make an epithermal vein district world class. In the world-class silver- and gold-producing Comstock mining district, Nevada, several lines of evidence lead to the conclusion that the Comstock lode is localized in an extensional stepover between right-lateral fault zones. This evidence includes fault geometries, kinematic indicators of slip, the hydraulic connectivity of faults as demonstrated by veins and dikes along faults, and the opening of a normal-fault-bounded, asymmetric basin between two parallel and overlapping northwest-striking, lateral- to lateral-oblique-slip fault zones. During basin opening, thick, generally subeconomic, banded quartz-adularia veins were deposited in the normal fault zone, the Comstock fault, and along one of the bounding lateral fault zones, the Silver City fault. As deformation continued, the intrusion of dikes and small plugs into the hanging wall of the Comstock fault zone may have impeded the ability of the stepover to accommodate displacement on the bounding strike-slip faults through extension within the stepover. A transient period of transpressional deformation of the Comstock fault zone ensued, and the early-stage veins were deformed through boudinaging and hydraulic fragmentation, fault-motion inversion, and high- and low-angle axial rotations of segments of the fault planes and some fault-bounded wedges. This deformation led to the formation of spatially restricted compartments of high vertical permeability and hydraulic connectivity and low lateral hydraulic connectivity. Bonanza orebodies were formed in the compartmentalized zones of high permeability and hydraulic connectivity. As heat flow and related hydrothermal activitv waned along the Comstock fault zone, extension was reactivated in the stepover along the Occidental zone of normal faults east of the Comstock fault zone. Volcanic and related intrusive activity in this part of the stepover led to a new episode of hydrothermal activity and formation of the Occidental lodes.

Economic Geology↗
USGS1996

Geology and structural evolution of the Muruntau gold deposit, Kyzylkum desert, Uzbekistan

The Muruntau gold deposit in the Kyzylkum desert of Uzbekistan is the largest single deposit (??? 1100 tonnes of gold) of the class of low-sulfide syndeformation/synigenous gold deposits formed in the brittle/ductile transition zone of the crust within transpressional shear zones. Hosted by the Cambrian to Ordovician Besopan Suite, the ores were deposited in pre-existing thrust-fault- and metamorphism-related permeabilities and in synmineralization dilational zones created in a large fault-related fold. The Besopan Suite is a 5,000-m-thick sequence of turbiditic siltstones, shales and sandstones. The ore is primarily localized at the base of the Besopan-3 unit, which is a 2,000-m-thick series of carbonaceous shales, siltstones, sandstones and cherts. Initial gold deposition took place within the Sangruntau-Tamdytau shear zone, which was developed along the stratigraphic contact between the Besopan-3 and Besopan-4 units. During the mineralization process, folding of the Besopan Suite and a left-step adjustment in the Sangruntau-Tamdytau shear zone were caused by two concurrent events: (1) the activation of the left-lateral Muruntau-Daugyztau shear zone that developed at nearly a 90?? angle to the preceding shear zone and (2) the intrusion of granitoid plutons. These structural events also resulted in the refocusing of hydrothermal fluid flow into new zones of permeability.

Ore Geology Reviews↗
USGS1993

Integrated mineral-resource and mineral-environmental assessments of public lands: Applications for land management and resource planning

Mineral-deposit geology is an important control on natural contamination from unmined mineral deposits, and on the environmental effects of mining and mineral processing. The U. S. Geological Survey, Office of Mineral Resources (USGS/OMR) is now integrating geology-based environmental assessments into its mineral resource assessments of public and other lands. This report presents prototype mineralenvironmental assessments of the State of Colorado and the San Juan National Forest. The following pages will show examples of how geologic information can be used to help predict and prevent adverse environmental effects of mineralresource development.

Colorado↗
USGS1992

Mineral resource assessment of the Dillon 1° x 2° quadrangle, Idaho and Montana

The Dillon 1 ° x2° quadrangle in southwestern Montana and east-central Idaho was investigated as part of the U.S. Geological Survey's Conterminous United States Mineral Assessment Program (CUSMAP) to determine its mineral resource potential. An interdisciplinary study was made of geology, geochemistry, geophysics (gravity and aeromagnetics), remote sensing, and mineral deposits. The results of those studies, as well as mineral resource assessment of numerous mineraldeposit types, are published separately as a folio of maps. This report summarizes the studies, provides background information on them, and presents a selected bibliography relevant to the geology and mineral resources of the quadrangle. The quadrangle contains large resources of gold and substantial resources of talc and chlorite, all of which were being mined in the 1980's and early 1990's. Submarginal resources of molybdenum, copper, tungsten, and iron range from moderately large to large. Other commodities that may be present in significant amounts are chromite, lead, zinc, silver, barite, zeolite minerals, and various nonmetallic metamorphic minerals.

Idaho, Montana↗
USGS1992

Maps showing mineral resource assessment for vein and replacement deposits of base and precious metals, barite, and fluorspar, Dillon 1° x 2° quadrangle, Idaho and Montana

This report is one of several that assess the mineral resources in the Dillon quadrangle. For the purpose of the assessment, the deposits that are known in the quadrangle, or suspected to be present from a knowledge of the geologic setting, have been grouped into 30 deposit types on the basis of the mineralogy or commodity in the ore and the structural or depositional setting of the deposit. The emphasis in these assessment reports is on metallic minerals, but some important nonmetallic minerals are also considered. Fossil fuels are beyond the scope of this investigation, phosphate and uranium have been investigated previously (Swanson, 1970; Wodzicki and Krason, 1981 ), and certain nonmetallic minerals, including bulk commodities such as sand and gravel, are in large supply and thus are not considered. The mineral resource assessment discussed in this report concentrates on a single deposit type (of the total of 30 types) that we call "vein and replacement deposits of base and precious metals." Base and precious metals produced from such deposits are copper, lead, zinc, gold, and silver. Vein deposits of barite and fluorspar are also discussed, but because they seem to be of minor importance, they are treated briefly. Vein and replacement deposits of base and precious metals are classified as a single deposit type rather than as numerous possible subordinate types that might be distinguished on the basis of mineralogy, metal content, or other factors, because the characteristics of the ore, the ore bodies, and the structural setting are not sufficiently well known to yield a consistent detailed classification for the entire quadrangle. Furthermore, the criteria used here to explain the localization of deposits are too general to allow discrimination among subordinate types at a scale of 1 :250,000 or smaller. In assessing mineral resources, we have adopted a general philosophy similar to that of Harrison and others ( 1986). We attempt to identify parts of the quadrangle that are favorable for the occurrence of mineral resources, and we make an assignment of the relative resource potential of all parts of the quadrangle. We do not attempt to locate specific exploration targets nor to determine the quantity of reserves or resources present.

Idaho, Montana↗
USGS1992

Maps showing mineral resource assessment for copper and molybdenum in porphyry and stockwork deposits and for tungsten, iron, gold, copper, and silver in skarn deposits, Dillon 1° x 2° quadrangle, Idaho and Montana

This report is one of several in the series that assess the mineral resources of the Dillon quadrangle. For the purpose of the assessment, mineral deposits· in the quadrangle that are either known or suspected from a knowledge of the geologic setting have been grou~d into 30 deposit types on the basis of mineralogy, commodity, or structural or depositional setting. The emphasis in these assessment reports is on metallic minerals, but some important nonmetallic minerals will also be assessed. Fossil fuels are beyond the scope of this investigation; phosphate and uranium have been investigated previously (Swanson, 1970; Wodzicki andKrason, 1981); and certain nonmetallic. minerals, including bulk commodities such as sand and gravel, are in large supply and thus not considered. The ·mineral resource assessment discussed in this report considers two deposit types: (1) porphyry or stockwork deposits of copper. and molybdenum (referred to generally in this report as porphyry deposits) and (2) skarn deposits of tungsten, iron, gold, copper, and silver. Combining copper and molybenum porphyry deposits into a single deposit type is believed necessary for this purpose· mainly because the two metals are found together in most .deposits in the quadrangle, a geochemical signature unique to each has not been determined, and the significant petrologic characteristics of many associated plutons are not well known, especially characterist~cs of subsurface plutons whose presence is .inferred from geophysical data. In assessing mineral resources,· we have adopted a general philosophy similar to that of Harrison and others (19S6). We attempt to identify those parts of the quadrangle that are favorable for the occurrence of mineral resources. We do not attempt to locate specific exploration targets nor to determine the quantity of reserves or resources present.

Idaho, Montana↗
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↗