The Wells 6.0 magnitude earthquake of February 21, 2008, occurred on a previously unrecognized northeast-striking southeast-dipping fault situated beneath Town Creek Flat, a few miles north of Wells, Nevada. Focal depth of the earthquake was 5 miles (8 km). Bedrock geology in the surrounding ranges did not indicate the existence of the fault prior to the earthquake, and no surface rupture has been observed related to the earthquake. Faults with a similar trend and attitude had not been observed in the southern Snake Mountains. Correlation of the earthquake fault to structures south of Wells that bound the East Humboldt Range and Clover Hill is plausible. High-angle northwest-trending faults in the southern Snake Mountains and Windermere Hills, adjacent to the earthquake foci, may have been responsible for partitioning aftershocks. This fault, referred to as the Wells earthquake fault (WEF), is an approximately 55° southeast-dipping normal fault (Smith and others, this volume). Its dip direction is opposite to that of most recognized Cenozoic (Neogene) high-angle faults in the immediate vicinity that are related to uplift of the Snake Mountains and Windermere Hills northwest and northeast of Wells, respectively. The geometry of the WEF was resolved by Smith and others (this volume) based on 3-D resolution of the main earthquake and subsequent aftershocks. The bedrock geology of the southern Snake Mountains, Windermere Hills, Clover Hill and northern East Humboldt, and Wood Hills, which bound the earthquake area, provided no suggestions that a fault, especially one capable of producing a large earthquake, was present at the surface location of the WEF. Attitudes of bedding-parallel faults and of stratigraphic units in the southern Snake Mountains are roughly parallel to the WEF, and thus, following the earthquake, it was initially postulated that there might be a relationship between the two. However, this does not appear to be the case. Rather, the earthquake fault may be related to a system of east-dipping normal faults south of Wells that bound the eastern flanks of the Ruby Mountains, East Humboldt Range, and Clover Hill (figure 1). Aftershocks from the main earthquake were distributed in a belt extending north from Wells and occurred in two major clusters/groups with an intervening area of lower occurrence (figure 2). Based on bedrock geology in the southern Snake Mountains and Windermere Hills, we interpret the frequency distribution of the aftershocks to be influenced/controlled by two or more high-angle west-northwest-striking faults, rather than a single northeast-striking fault. This interpretation suggests that the west-northwest-striking faults are deep-penetrating structures and of regional significance, as proposed by Thorman and Ketner (1979). It follows that future earthquakes may occur where oblique high-angle faults intersect rangebounding faults in the Basin and Range Province. This paper focuses on the nature of the west-northwest-trending faults, their ages, recurrent movements, and lateral and vertical continuity. In deciphering the geology of these ranges, comprehending the regional and local stratigraphy and structures is critical. As in much of the Basin and Range Province, it is impossible to do one without understanding the other.

In 2004, a specific need for data on mercury use in South America was indicated by the United Nations Environmental Programme-Chemicals (UNEP-Chemicals) at a workshop on regional mercury pollution that took place in Buenos Aires, Argentina. Mercury has long been mined and used in South America for artisanal gold mining and imported for chlor-alkali production, dental amalgam, and other uses. The U.S. Geological Survey (USGS) provides information on domestic and international mercury production, trade, prices, sources, and recycling in its annual Minerals Yearbook mercury chapter. Therefore, in response to UNEP-Chemicals, the USGS, in collaboration with the Economic Section of the U.S. Embassy, Lima, has herein compiled data on Peru's exports, imports, and byproduct production of mercury. Peru was selected for this inventory because it has a 2000-year history of mercury production and use, and continues today as an important source of mercury for the global market, as a byproduct from its gold mines. Peru is a regional distributor of imported mercury and user of mercury for artisanal gold mining and chlor-alkali production. Peruvian customs data showed that 22 metric tons (t) of byproduct mercury was exported to the United States in 2006. Transshipped mercury was exported to Brazil (1 t), Colombia (1 t), and Guyana (1 t). Mercury was imported from the United States (54 t), Spain (19 t), and Kyrgyzstan (8 t) in 2006 and was used for artisanal gold mining, chlor-alkali production, dental amalgam, or transshipment to other countries in the region. Site visits and interviews provided information on the use and disposition of mercury for artisanal gold mining and other uses. Peru also imports mercury-containing batteries, electronics and computers, fluorescent lamps, and thermometers. In 2006, Peru imported approximately 1,900 t of a wide variety of fluorescent lamps; however, the mercury contained in these lamps, a minimum of approximately 76 kilograms (kg), and in other products such as batteries and computer electronics is not recycled and may ultimately be released to the environment.

Reclamation and recycling of mercury from used mercury- containing products and treatment of byproduct mercury from gold mining is vital to the continued, though declining, use of this metal. Mercury is reclaimed from mercury-containing waste by treatment in multistep high-temperature retorts-the mercury is volatized and then condensed for purification and sale. Some mercury-containing waste, however, may be landfilled, and landfilled material represents loss of a recyclable resource and a threat to the environment. Related issues include mercury disposal and waste management, toxicity and human health, and regulation of mercury releases in the environment. End-users of mercury-containing products may face fines and prosecution if these products are improperly recycled or not recycled. Local and State environmental regulations require adherence to the Resource Conservation and Recovery Act and the Comprehensive Environmental Response, Compensation, and Liability Act to regulate generation, treatment, and disposal of mercury-containing products. In the United States, several large companies and a number of smaller companies collect these products from a variety of sources and then reclaim and recycle the mercury. Because mercury has not been mined as a principal product in the United States since 1992, mercury reclamation from fabricated products has become the main source of mercury. Principal product mercury and byproduct mercury from mining operations are considered to be primary materials. Mercury may also be obtained as a byproduct from domestic or foreign gold-processing operations. In the early 1990s, U.S. manufacturers used an annual average that ranged from 500 to 600 metric tons of recycled and imported mercury for fabrication of automobile convenience switches, dental amalgam, fluorescent lamps, medical uses and thermometers, and thermostats. The amount now used for fabrication is estimated to be 200 metric tons per year or less. Much of the data on mercury is estimated because it is a low-volume commodity and its production, use, and disposal is difficult to track. The prices and volumes of each category of mercury-containing material may change dramatically from year to year. For example, the average price of mercury was approximately $150 per flask from 2000 until 2003 and then rose sharply to $650 per flask in fall 2004 and approximately $850 per flask in spring 2005. Since 1927, the common unit for measuring and pricing mercury has been the flask in order to conform to the system used at Almaden, Spain (Meyers, 1951). One flask weighs 34.5 kilograms, and 29 flasks of mercury are contained in a metric ton. In the United States, the chlorine-caustic soda industry, which is the leading end-user of elemental mercury, recycles most of its mercury in-plant as home scrap. Annual purchases of replacement mercury by the chlorine-caustic soda industry indicate that some mercury may be lost through evaporation to the environment, put into a landfill as industrial waste, or trapped within pipes in the plant. Impending closure of domestic and foreign mercury-cell chlorine-caustic soda plants and the shift to nonmercury technology for chlorine-caustic soda production could ultimately result in a significant volume of elemental mercury for recycling, sale, or storage. Globally, mercury is widely used in artisanal, or small-scale, gold mining. Most of that mercury is lost to the environment and is not recycled. The recycling rate for mercury was not available owing to insufficient data in 2000, and the efficiency of mercury recycling was estimated to be 62 percent.

Debris flows caused by El Niño events, earthquakes, and glacial releases have affected northern Perú for centuries. The Muralla Pircada, a northeast-trending, 2.5 km long stone wall east of the Santa Rita B archaeological site (Moche-Chimú) in the Chao Valley, is field evidence that ancient Andeans recognized and, more importantly, attempted to mitigate the effects of debris flows. The Muralla is upstream from the site and is perpendicular to local drainages. It is 1–2 m high, up to 5 m wide, and is comprised of intentionally-placed, well-sorted, well-rounded, 20–30 cm cobbles and boulders from nearby streams. Long axes of the stones are gently inclined and parallel local drainage. Case-and-fill construction was used with smaller cobbles and pebbles used as fill. Pre-Muralla debris flows are indicated by meter-sized, angular boulders that were incorporated in-place into construction of the dam and are now exposed in breeches in the dam. Post-Muralla debris flows in the Chao Valley are indicated by meter-sized, angular boulders that now abut the retention dam.

The Santa Rita B archaeological site is in the Chao Valley, approximately 65 km southeast of Trujillo, northern Peru. Location of Santa Rita B at the emergence of several drainages from the Andean cordillera is an important factor in the almost continuous occupation of the site over the past 3,000 years. Mineral resources are abundant throughout the Andes; however, the north coast of Peru was an important center for pre-Columbian mining, metallurgy, and craftsmanship. Success of the Chavin, Moche, Chimu, and other north coast cultures is directly related to the availability and exploitation of mineral and energy resources that include: gold (?silver), as electrum, mainly from placers, and copper from local oxide and carbonate occurrences and from sulfides related to copper porphyry occurrences in the cordillera. An alloy of these three metals is referred to as tumbaga, which is the primary material for Andean metalcraft. Anthracite was used for mirrors by north coast cultures and is available near Rio Chicama, Rio Santa, and east of Santa Rita B. These outcrops are a part of the Alto Chicama, Peru's largest coalfield, which extends from Rio Chicama, in the north, for 200 km southward to Rio Santa. Charcoal from the algorrobo tree and llama dung are considered to be the common pre-Columbian energy sources for cooking and metalwork; however, availability and the higher heat content of anthracite indicate that it was used in metallurgical applications. Bitumen is available from petroleum seeps near Talara, north of the study area, and may have been used as glue or as cement. Hematite, goethite, limonite, and manganese oxides from clay-altered volcanic rock may have provided color and material for ceramics. Guano from the Islas Gua?apes, Chinchas, and Ballestas was used as fertilizer for cotton and other crops.

Interpretation of K-Ar and 40 Ar/ 39 Ar dates from highly altered, potassium-metasomatized rocks at detachment faults in the Southwestern United States is difficult.The effects of added potassium, indicated by rock analyses with excessive K20, and elevated temperature.indicated by reset K-Ar and fission-track dates from upper-and lower-plate rocks at detachment faults, are implicit thermal and chemical problems in the interpretation of potassium-dependent dates.In order to resolve these problems, comparative study of volcanic rocks that ( 1) are well-defined regionally and structurally, (2) have well-constrained regional chemistry and geochronology, and (3) have correlative metasomatized and unaltered sections must be made.The Windous Butte ash-flow tuff is one of several potassium-metasomatized volcanic units at Ragged Ridge, in the upper plate of a complicated detachment fault zone in the northern Grant Range.It is a calc-alkalic, rhyolitic to dacitic ash-flow tuff, and its Oligocene age is well constrained at 31.4-31.2Ma.At Ragged Ridge, which is 3-4 km from the detachment zone, the Windous Butte is potassium metasomatized (>9.0 weight percent K20 and <1.0 weight percent Na 2 0).At Stone Cabin Ridge, 7 km southeast of Ragged Ridge, the Windous Butte is unaltered (4-5 weight percent K 2 0 and 2-3 weight percent Na20).In order to constrain timing of the alteration and determine the effect of K-metasomatism on potassium-dependent mineral dates, feldspar and biotite separates from two sites at Ragged Ridge and two sites at Stone Cabin Ridge were dated by the 40 Arf3 9 Ar thermal release method.X-ray diffraction (XRD) analyses indicate that adularized sanidine is present in Ragged Ridge separates and only sanidine is present in Stone Cabin Ridge separates.Sanidine spectra from Stone Cabin Ridge are not disturbed and have plateau dates of 31.3±0.1 Ma and 31.2±0.1 Ma.Spectra for adularized sanidine from Ragged Ridge show apparent argon loss with stairstep patterns that indicate growth of adularia as late as ~20 Ma.Biotite dates from Ragged Ridge (two dates of 31.5±0.1 Ma) and Stone Cabin Ridge (31.7±0.1 Ma and 31.5±0.1 Ma) are slightly disturbed, but plateau dates are concordant.This indicates that temperatures associated with the alteration did not exceed 280°C.Disturbed spectra from adularized sanidine from potassium-metasomatized rocks at Ragged Ridge are interpreted to indicate that alteration occurred at ~ 20 Main response to detachment and associated hydrothermal circulation of potassium-rich brines.Results of this study are applicable to the interpretation of 40 Ar/3 9 Ar dates from incipiently to pervasively potassium metasomatized upper-plate volcanic rocks at three detachment faults in Arizona.

Journal of Geophysical Research: Solid EarthVolume 100, Issue B8 p. 15545-15548 CorrectionsFree Access Correction to “The 40Ar/39Ar ages and tectonic setting of the middle Eocene northeast Nevada volcanic field” by William E. Brooks, Charles H. Thorman, and Lawrence W. Snee William E. Brooks, William E. BrooksSearch for more papers by this authorCharles H. Thorman, Charles H. ThormanSearch for more papers by this authorLawrence W. Snee, Lawrence W. SneeSearch for more papers by this author William E. Brooks, William E. BrooksSearch for more papers by this authorCharles H. Thorman, Charles H. ThormanSearch for more papers by this authorLawrence W. Snee, Lawrence W. SneeSearch for more papers by this author First published: 10 August 1995 https://doi.org/10.1029/95JB02130Citations: 4AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume100, IssueB810 August 1995Pages 15545-15548 RelatedInformation

Widespread rhyolitic to andesitic calc-alkaline volcanic rocks in northeast Nevada and northwest Utah are part of a distinct Eocene eruptive sequence that is older than previously believed.Parts of this volcanic terrane, the central part of the Northeast Nevada volcanic field, are exposed over a large area that extends in an east-west direction from the Silver Island Mountains, Utah, to Elko, Nevada, and in a north-south direction from an area a few miles north of Wells, Nevada, to the Deep Creek Range, Utah.The type area for the Northeast Nevada volcanic field is at Nanny Creek, in the northern Pequop Mountains, where the base of the volcanic sequence, unconformable on Eocene lacustrine deposits, includes rhyolitic ash-flow tuffs that are overlain by a monotonous series of dacitic to andesitic flows and flow breccias that were locally erupted.The similarities in age, chemistry, and mode of occurrence of these volcanic rocks throughout the field indicate that they are part of the same widespread Eocene volcanic sequence.

Eighteen new [sup 40]Ar/[sup 39]Ar dates indicate that widespread rhyolitic to andesitic calc-alkaline volcanic rocks in NE Nevada and NW Utah are part of a distinct eruptive sequence that is late Middle Eocene in age, considerably older than previously believed. Most of the rocks were erupted at 41--39 Ma. The presently recognized extent of the field spans 11 ranges from near Elko on the west to the Silver Island Mts on the east and from 20 miles north of Wells to the southern Deep Creek Range. The authors informally designate this the Nanny Creek volcanic field, the type area being Nanny Creek, in the northern Pequop Mts, where compositional and stratigraphic features of the field are clearly displayed. Typically, the base of the sequence includes one or more rhyolite ash-flow tuffs and (or) dacite flows; sources for the tuffs probably were outside the study area as they all appear to be outflow-facies rocks. The similarities in age, chemistry, and mode of occurrence of these rocks throughout their extent indicate that they are all part of the same eruptive sequence. The widespread occurrence of ash-flows in the lower part of the eruptive cycle suggests that the region initially was one ofmore » moderate to low relief. The central part of the field rests with angular discordance on Devonian to Triassic rocks, whereas the western and eastern parts rest with angular discordance on lower Eocene rocks (Elko and White Sage basinal rocks, respectively). Ostracode-bearing limestones at several localities in the central part of the field are parallel to the overlying volcanics rocks; the authors interpret the limestones to be correlative with the Elko and White Sage and the limestone/volcanic contact to be a disconformity that is correlative with the angular unconformities to the east and west. These relationships identify a widespread pre-late Middle Eocene deformational event during which the Elko and White Sage basins, but not the intervening area, were deformed.« less

Analyses in this compilation are for samples of volcanic rocks collected during geologic mapping in the Pedregosa Mountains quadrangle, Cochise County, Arizona, during 1982 and 1983.Volcanic rocks in the field area are Cretaceous to Quaternary in age and include basalt, andesite, intrusive and extrusive rhyolite, pyroclastic rocks, and ash-flow tuff.Detailed descriptions and isotopic ages of the Pedregosa volcanic rocks, discussion of the structural geology, and descriptions of the Paleozoic rocks in the field area are given in Drewes and Brooks (1988).Major and trace element analyses for selected rocks are compiled in table 1. Ash-flow tuffs in the Pedregosa Mountains, especially the tuff of Bruno Peak (Tbn), are outflow of the Turkey Creek caldera based on these analyses and rock descriptions (du Bray and Pallister, 1991).No prospects, mines, or altered rock indicative of mineralization were found during our study.However, Packsaddle Mountain, in the west-central part of the quadrangle (plate 1), is a garnet-bearing, high-silica (74 wt.percent) rhyolite.Age of this rhyolite (23 Ma); F, U, and Th content; presence of garnet; high silica content; thick, 5 m apron of vitrophyre (83E119B) and pyroclastic debris invite comparison with topaz rhyolites described by Burt and others (1982).Topaz rhyolites, though not mineralized themselves, may indicate a F-rich magma with possible Mo, W, and other elements.Therefore, Mo and W analyses for the rhyolite of Packsaddle Mountain (Tpi, 83E119A, B) are listed on table 2, and F, U, and Th analyses are compiled on table 3.Latitudes and longitudes for analyzed samples of volcanic rocks are included on table 2 and a sample locality map, plate 1, is in the pocket.

A U.S. Geological Survey report is presented giving a preliminary geologic map of the Oxley Peak Quadrangle, Elko County, Nevada.

\u by HBr-BfT digestion -AAS method * Hg by KMO