Genetic environment of germanium-bearing gold-silver vein ores from the Wolyu mine,Republic of Korea

The Wolyu mine is one of the largest vein-type gold-silver-bearing epithermal systems in the Youngdong district and is the first gold-silver deposit in Korea found to contain significant germanium, in the form of argyrodite (Ag₈GeS₆). Mineralized veins (78.9 ± 1.2 Ma) crosscutting Late Cretaceous hostrock tuff and quartz porphyry (81.5 ± 1.8 Ma) consist of three stages of quartz and carbonates, the first of which contains pyrite, basemetal sulfides and Au-Ag-minerals. Stage I Au-Ag-Ge-mineralized veins show a systematic variation of mineral assemblage with time: (1) quartz + pyrite; (2) quartz + pyrite + sphalerite + electrum + argentite; (3) carbonate + quartz + sphalerite + electrum + argentite; (4) carbonate + native silver + argentite + Ag-sulfosalts + argyrodite + sphalerite. Calculated values of temperature and sulfur activity are: assemblage (1), 360-280°C and 10^–7-10^–10; (2), 280-210°C and 10^–10-10^–14; (3), 210-180°C and 10^–14-10^–16; (4), 180-155°C and 10^–17-10^–18. These data, the frequent association of gold with sulfides, and the abundance of pyrite in alteration zones indicate that decreasing sulfur activity and cooling were important in triggering gold deposition. Hydrogen and oxygen isotope compositions of ore fluids display a systematic variation with increasing time. Within the main Ag-Au-Ge mineralization, D and ¹⁸O values decrease with the transition from quartz to carbonate deposition (from -78 and –2.8% to –90 and –8.7%., respectively), indicating increasing involvement (mixing) of less evolved meteoric water which resulted in progressive cooling and dilution of ore fluids in the shallow ( 370–600 m) Wolyu epithermal system.     

Surficial geology of the Chicxulub impact crater,Yucatan, Mexico

The Chicxulub impact crater in northwestern Yucatan, Mexico is the primary candidate for the proposed impact that caused mass extinctions at the end of the Cretaceous Period. The crater is buried by up to a kilometer of Tertiary sediment and the most prominent surface expression is a ring of sink holes, known locally as cenotes, mapped with Landsat imagery. This 165 ± 5 km diameter Cenote Ring demarcates a boundary between unfractured limestones inside the ring, and fractured limestones outside. The boundary forms a barrier to lateral ground water migration, resulting in increased flows, dissolution, and collapse thus forming the cenotes. The subsurface geology indicates that the fracturing that created the Cenote Ring is related to slumping in the rim of the buried crater, differential thicknesses in the rocks overlying the crater, or solution collapse within porous impact deposits. The Cenote Ring provides the most accurate position of the Chicxulub crater's center, and the associated faults, fractures, and stratigraphy indicate that the crater may be 240 km in diameter.     

Rock thermal data at the grain scale: applicability to granular disintegration in cold environments

Consideration of the mechanisms associated with the granular disintegration of rock has been limited by available data. In most instances, both the size of the transducer and the nature of the study have negated any applicability of the resulting data to the understanding of grain‐to‐grain separation within rock. The application of microthermocouples (≤0·15 mm diameter) and high‐frequency logging (20 s intervals) at a taffoni site on southern Alexander Island and from a rock outcrop on Adelaide Island (Antarctica) provide new data pertaining to the thermal conditions, at the grain scale, of the rock surface. The results show that thermal changes (ΔT/t) can be very high, with values of 22 °C min^?1 being recorded. Although available data indicate that there can be differences in frequency and magnitude of ?uctuations as a function of aspect, all aspects experienced some large magnitude (≥2 °C min^?1) ?uctuations. Further, in many instances, large thermal changes in more than one direction could occur within 1 min or in subsequent minutes. These data suggest that the surface grains experience rapidly changing stress ?elds that may, with time, effect fatigue at the grain boundaries; albedo differences between grains and the resulting thermal variations are thought to exacerbate this. The available data failed to show any indication of water freezing (an exotherm) and thus it is suggested that microgelivation may not play as large a role in granular breakdown as is often postulated for cold regions, and that in this dry, Antarctic region thermal stress may play a signi?cant role. Copyright © 2003 John Wiley & Sons, Ltd.     

Great expectations: can international emissions trading deliver an equitable climate regime?

Climate change equity debates tend to focus on achieving a fair and global ‘allocation’ of emission rights among countries. Allocation proposals typically envision, if implicitly, two purposes for international emissions trading. First, trading is expected to serve as a cost-effective means of promoting compliance with emissions targets. Second, trading is posited as a means to generate financial transfers, typically from industrialized to transitioning and developing countries.This article investigates the common assumption that international emissions trading will effectively serve both of these purposes. We conclude that the two purposes might not be mutually supportive, and that efforts to use international emissions trading as a financial transfer mechanism may potentially undermine cost-effectiveness goals. International emissions trading on a global scale would create new risks in terms of both cost-effectiveness and environmental performance, some of which will be challenging to manage. In particular, uncertainties over market prices and trading eligibility, coupled with the costs of participation, may together be the Achilles heel of some allocation proposals that entail large financial transfers from industrialized to developing countries. Any proposal for an ‘equitable’ allocation of emission allowances, we conclude, must be cognizant of the risks and costs implied by a reliance on international emissions trading. We offer some suggestions to this end.     

Cathodoluminescence petrography and isotope geochemistry of KT impact ejecta deposited 360 km from the Chicxulub crater, at Albion Island, Belize

The depositional and diagenetic history of Cretaceous–Tertiary (KT) impact ejecta deposited 360 km from the Chicxulub crater, at Albion Island, Belize, has been investigated using integrated cathodoluminescence and isotopic analyses. A quarry exposes 26 m of Upper Cretaceous Barton Creek Formation dolomitized marine limestone overlain by 16 m of dolomitized Albion Formation impact ejecta. The Albion Formation consists of a lower fine‐grained ≈1‐m‐thick spheroid bed and an upper 15‐m‐thick coarse conglomeratic diamictite bed. A 14‐event paragenetic sequence has been documented and used as a temporal framework to interpret chemostratigraphic trends in bulk rock δ¹⁸O, δ¹³C and ⁸⁷Sr/⁸⁶Sr. The uppermost surface of the Barton Creek Formation was subaerially exposed before the KT impact, as indicated by a brecciated palaeosol that caps upsection decreases in δ¹³C and δ¹⁸O. Small 1‐cm‐diameter spheroids in the spheroid bed exhibit vermicular crystalline textures but lack the concentric zonations common to accretionary lapilli. These spheroids are hypothesized originally to have been impact glass or reactive Ca and Mg oxide dusts that adhered to water vapour particles condensing from the cooling impact vapour cloud. The spheroids were dolomitized soon after deposition. The earliest dolomitization in the matrix sediments of the Albion Formation was also post‐depositional, replacing clays formed by devitrification of impact glass. Dolomite and clay ⁸⁷Sr/⁸⁶Sr exhibit a distinct symmetrical distribution in the spheroid bed ranging from 0·707745 to 0·707872. Although unproven, this may represent primary changes in the chemical composition of the impact glass. The limestone clasts in the diamictite bed were dolomitized before the KT impact and exhibit upsection decreases in bulk rock ⁸⁷Sr/⁸⁶Sr. This suggests that the clasts were excavated from strata equivalent in age or older than the Barton Creek Formation at locations closer to, or in, the Chicxulub crater.     

Field-scale Variations in Plant and Grasshopper Communities: A GIS-based Assessment

GIS technology allowed us to examine species-specific occurrence and abundance patterns of important grassland herbivore species through the use of appropriate statistical methods and the superior spatial representation commonly available in existing GIS packages. The study was conducted on a 254 ha grassland area located 10 km south of Three Forks, Gallatin County, Montana, in the Agropyron spicatum province of the western steppe region of the U.S.A. From an ecological perspective, grasshopper species distribution and abundance patterns observed on a local, non-uniform landscape (2.6 km 2) were consistent with results found in other studies at the valley (≈1,400 km 2) and state-level (≈237,000 km 2) scales. Our observations at the local scale further demonstrate the importance of vegetation type and specific local stand physiognomies in structuring grasshopper populations. The application of results from studies conducted at various scales to the development of decision support tools for resource managers is also discussed.     

Combining dissolved, suspended and bed load stream geochemistry to explore for volcanic massive sulfide deposits: Big Salmon Complex, northern British Columbia

Exploration successes for volcanogenic massive sulfide (VMS) deposits, such as Kudz Ze Kayah, Wolverine and Fyre Lake in the Yukon–Tanana Terrane and Slide Mountain Terrane (southern Yukon Territory) have spurred interest in the correlative rocks in the Big Salmon Complex in northern British Columbia. In an effort to further the utility of multi-media stream geochemistry in exploration frontiers that are forested, heavily drift covered, or buried, the primary streams of 19 watersheds from the East Teslin Lake (National Topographic System (NTS): 104N/9, 16) and Teh Creek areas (NTS: 104O/11, 12, 13, 14) of the Big Salmon Complex were analyzed for Cu, Pb, and Zn and other parameters in the dissolved load, suspended load and bed load. Traditionally, exploration based on stream geochemistry has employed the bed load and more recently the dissolved load chemistry, but almost never the suspended load despite strong differences in the geochemical signatures of the three media. Here, we document that copper, lead, and zinc partition into the dissolved, suspended, and bed loads differently and that the magnitude of anomalies is different for each media. The adsorbing capacity of the suspended load may make it a more sensitive indicator of mineral deposits on a regional basis than either the trace-element-poor dissolved load or the bulk-rock-diluted bed load which are likely better indicators of local mineralization. It is clear that each phase contributes unique information about the distribution of elements in the watershed that could be considered in exploration models.We also show that summing standardized element concentrations and summing the sums across media appears to be an effective method to reduce the data without loss of important information. We likewise investigated the utility of calculating major element normalized enrichments for exploration and find that it is a promising approach.     

Evaluation of the SNOWPACK model’s metamorphism and microstructure in Canada: a case study

The snow thermodynamic multi-layer model SNOWPACK was developed to address the risk of avalanches by simulating the vertical properties of snow. Risk and stability assessments are based on the simulation of the vertical variability of snow microstructure, as well as on snow cohesion parameters. Previous research has shown systematic error in grain size simulations (equivalent optical grain size) over several areas in northern Canada. To quantify the simulated errors in snow grain size and uncertainties in stability, the snow specific surface area (SSA) was measured with a laser-based instrument. Optical grain size was retrieved to validate the optical equivalent grain radius from SNOWPACK. The two study plots are located in Glacier National Park, BC, and Jasper National Park, AB, Canada. Profiles for density and stratigraphic analysis were obtained as well as grain size profiles, combined with snow micropenetrometer (SMP) measurements. Density analysis showed good agreement with the simulated values (R² = 0.76). Optical grain size analysis showed systematic overestimation of the modeled values, in agreement with the current literature. The error in SSA evolution for a rounding environment was mostly constant, whereas error for conditions driven by a temperature gradient was linked to the size of the facetted grains.     

Dating prehistoric bog-fires in northern England to calendar years by long-distance cross-matching of pine chronologies

The ages of prehistoric fires can be approximated by radiocarbon dating of charcoal or associated material, but such dating is often inaccurate and at best imprecise. Pine trunks preserved in British and Irish peats occasionally show firescars, which might be dated through dendrochronology to yield calendar-year dates. However, unlike oak, there is no master pine chronology to provide absolute dates, so dating is dependent on interspecies cross-matching; for sites in the British Isles with no dated oaks, calendar-year dating of prehistoric pines has hitherto proved impossible. We present a first success in dating, accurately and precisely, prehistoric fire events recorded in subfossil bog-pine trunks, using long-distance cross-matching of pine chronologies between White Moss, Cheshire, and the Humberhead Levels, England. Results demonstrate a bog-fire in Cheshire in spring 2800 BC, and again in 2710 BC, between spring and summer. Further successful long-distance cross-matching of pine would permit international climatological comparisons. © 1997 John Wiley & Sons, Ltd.