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At least 1,639 records · Page 91Linked to original sources

USGS2026

Severity and certainty metric for kelp stressors: A tool for research, management, and conservation

Foundation species face multiple threats, and many are in decline worldwide. Kelps are no exception, with declines documented throughout their range. Stressors such as warming, eutrophication, and reduced water quality—often linked to human activities—are well recognized, yet their relative severity and certainty have not been systematically evaluated. Such a framework may aid scientific, regulatory, and conservation organizations in prioritizing actions and decision making. Here we build on a conceptual model of stressors to kelp in the Salish Sea by rating stressor severity and scientific certainty. We convened a panel of regional kelp experts to perform the rating exercise for two canopy taxa, Nereocystis luetkeana and Macrocystis tenuifolia , as well as a grouping for understory species, including both the sporophyte (adult) and gametophyte (juvenile) life stages for these algae. Our process produced a rich dataset which can be separated by stressor, taxa, and life stage allowing for broad applications. The panel identified temperature, low nutrients, and substrate change/benthic sedimentation as the most severe stressors to kelp, with relatively high certainty for most taxa. Certainty scores were relatively high for Nereocystis and Macrocystis sporophytes but were considerably lower for understory species and the gametophyte life stage, for most stressors, highlighting research gaps. Our data set could be applied for management prioritization, setting ecological baselines, and spatial modeling exercises. We encourage scientific, regulatory, and conservation organizations to consider both our data and our process when evaluating their needs. As foundation species continue to face threats, exercises such as this can provide scientists and managers with actionable indices that support strategies to stem degradation.

Ecological Indicators↗

USGS2021

Metal accumulation varies with life history, size, and development of larval amphibians

Amphibian larvae are commonly used as indicators of aquatic ecosystem health because they are susceptible to contaminants. However, there is limited information on how species characteristics and trophic position influence contaminant loads in larval amphibians. Importantly, there remains a need to understand whether grazers (frogs and toads [anurans]) and predators (salamanders) provide comparable information on contaminant accumulation or if they are each indicative of unique environmental processes and risks. To better understand the role of trophic position in contaminant accumulation, we analyzed composite tissues for 10 metals from larvae of multiple co-occurring anuran and salamander species from 20 wetlands across the United States. We examined how metal concentrations varied with body size (anurans and salamanders) and developmental stage (anurans) and how the digestive tract (gut) influenced observed metal concentrations. Across all wetlands, metal concentrations were greater in anurans than salamanders for all metals tested except mercury (Hg), selenium (Se), and zinc (Zn). Concentrations of individual metals in anurans decreased with increasing weight and developmental stage. In salamanders, metal concentrations were less correlated with weight, indicating diet played a role in contaminant accumulation. Based on batches of similarly sized whole-body larvae compared to larvae with their digestive tracts removed, our results indicated that tissue type strongly affected perceived concentrations, especially for anurans (gut represented an estimated 46–97% of all metals except Se and Zn). This suggests the reliability of results based on whole-body sampling could be biased by metal, larval size, and development. Overall, our data shows that metal concentrations differs between anurans and salamanders, which suggests that metal accumulation is unique to feeding behavior and potentially trophic position. To truly characterize exposure risk in wetlands, species of different life histories, sizes and developmental stages should be included in biomonitoring efforts.

Environmental Pollution↗

USGS2020

Increased prespawning mortality threatens an integrated natural- and hatchery-origin sockeye salmon population in the Lake Washington Basin

The life cycle of diadromous fishes such as salmonids involves natural mortality in a series of distinct life history stages, occurring sequentially in different habitats. Decades of research have emphasized mortality at the embryo, juvenile, and sub-adult stages but it is increasingly clear that some adults that survive and return to freshwater habitats die during the final homeward migration or after they reach the spawning grounds, prior to breeding. These are termed “en route” and “prespawning” mortality, respectively, and can threaten populations depleted by mortality at previous stages. In this study, we present evidence that the sockeye salmon, Oncorhynchus nerka, population that returns to the Lake Washington Basin, in Washington State, USA, is experiencing both forms of adult mortality. Counts of the salmon entering the basin on their return migration in June and July were compared to counts in the major spawning grounds in September through November for 1995–2018. The disparity has increased markedly in recent years. The counts on the spawning grounds have decreased as a proportion of the number entering the system with an average 49 % of sockeye unaccounted for, consistent with increased en route mortality. In addition, prespawning mortality rates have increased in salmon that reach the Cedar River, the main spawning tributary, both at a hatchery holding adult fish in 1995–2018, and in the naturally spawning populations when monitored in the last five years. Hatchery records indicated <10 % prespawning mortality for 1995–2010, increasing to an average 43 % for 2014 – 2018. Recent carcass surveys in the Cedar River documented that 33.6% (2014), 22.3% (2015), 30.3% (2016) and 50.0% (2018) of female sockeye died before completing spawning. These recent increases in prespawning mortality have been associated with warm water during entry to freshwater, but comparably warm water in past decades had no such effect. Steady warming of river temperatures around the median run completion date from < 8.0 °C to > 13.0 °C was correlated with increased prespawning mortality rates at the hatchery from 1995–2018. We conclude that warming conditions during migration and spawning, in concert with other factors such as infections with pathogens, are responsible for the increased prespawning mortality of adult sockeye salmon that are high enough to threaten the population’s viability.

Washington↗

USGS2025

Fisheries dependent and independent data inform a capture technique for an emerging invasive fish species in the mainstem Mississippi River; Black Carp Mylopharyngodon piceus

Black Carp Mylopharyngodon piceus were imported into the United States in the 1970s and 1980s for use in aquaculture; escape occurred and reported wild captures increased. Lacking species-specific capture methods, we assessed fisheries dependent incidental Black Carp catches for a common method, hoop nets, by kernel density analysis to identify an area of increased reporting and compare frequency of reports for water temperature, river stage, and capture date to identify seasonality. We then used fisheries independent effort to identify co-occurrence of species via non-metric multi-dimensional scaling and fit Black Carp catch and environmental covariates by generalized linear models to assess site-specific environmental covariates facilitating capture. The best approximating distribution was refitted for predictions and inference. The greatest density of fisheries dependent hoop net captures (39 %) was near the confluence of the Missouri and Mississippi rivers, primarily from July-September. Captures were characterized by median water temperature 26.7°C, river stage 5.02 m, and 223 day-of-year (DOY; mid-August). Ordination of fisheries independent catch identified similarity in environmental covariates of Smallmouth Buffalo Ictiobus bubalus and Black Carp. The probability of capturing ≥ 1 Black Carp increased with DOY, decreased with increasing current velocity, and increased with depth. Most captures occurred in outside bends (87 %) or side channels (12 %). Probability of Black Carp capture was low but increased in summer and early fall when stage is lower, facilitating reduced current velocity and access to deeper areas. Results may be validated beyond this river segment to test if site-specific hydrology or habitat characteristics facilitated increased commercial and biologist capture and for replication.

Illinois, Missouri↗

USGS2016

Study of thermochemical sulfate reduction mechanism using compound specific sulfur isotope analysis

The sulfur isotopic fractionation associated with the formation of organic sulfur compounds (OSCs) during thermochemical sulfate reduction (TSR) was studied using gold-tube pyrolysis experiments to simulate TSR. The reactants used included n -hexadecane ( n -C 16 ) as a model organic compound with sulfate, sulfite, or elemental sulfur as the sulfur source. At the end of each experiment, the S-isotopic composition and concentration of remaining sulfate, H 2 S, benzothiophene, dibenzothiophene, and 2-phenylthiophene (PT) were measured. The observed S-isotopic fractionations between sulfate and BT, DBT, and H 2 S in experimental simulations of TSR correlate well with a multi-stage model of the overall TSR process. Large kinetic isotope fractionations occur during the first, uncatalyzed stage of TSR, 12.4&permil; for H 2 S and as much as 22.2&permil; for BT. The fractionations decrease as the H 2 S concentration increases and the reaction enters the second, catalyzed stage. Once all of the oxidizable hydrocarbons have been consumed, sulfate reduction ceases and equilibrium partitioning then dictates the fractionation between H 2 S and sulfate (&sim;17&permil;). Experiments involving sparingly soluble CaSO 4 show that during the second catalytic phase of TSR the rate of sulfate reduction exceeds that of sulfate dissolution. In this case, there is no apparent isotopic fractionation between source sulfate and generated H 2 S, as all of the available sulfate is effectively reduced at all reaction times. When CaSO 4 is replaced with fully soluble Na 2 SO 4 , sulfate dissolution is no longer rate limiting and significant S-isotopic fractionation is observed. This supports the notion that CaSO 4 dissolution can lead to the apparent lack of fractionation between H 2 S and sulfate produced by TSR in nature. The S-isotopic composition of individual OSCs record information related to geochemical reactions that cannot be discerned from the δ 34 S values obtained from bulk phases such as H 2 S, oil, and sulfate minerals, and provide important mechanistic details about the overall TSR process.

Geochimica et Cosmochimica Acta↗

USGS2019

Tourmaline boron and strontium isotope systematics reveal magmatic fluid pulses and external fluid influx in a giant iron oxide-apatite (IOA) deposit

Tourmaline is a common boron-bearing mineral in hydrothermal system and has been widely used as a mineral probe to reconstruct geological processes because of its broad range in composition and resistance to metasomatic alteration. The origin of Kiruna-type iron oxide-apatite (IOA) deposits, commonly linked to andesitic subvolcanic or volcanic rocks, is highly controversial. Constraints on the evolution of these mineralizing systems are needed to advance understanding of the ore-forming process. In this study, we apply in situ elemental and combined B-Sr isotopic analyses of tourmaline to elucidate the nature and evolution of the subsurface hydrothermal system associated with IOA mineralization in the giant Taocun deposit, eastern China. Taocun is hosted at the top of a diorite intrusion and exhibits three stages of hydrothermal alteration that contain tourmaline: pre-ore Na alteration (Tur I), syn-ore magnetite formation and associated Ca-Fe alteration (Tur II), and post-ore Ca-Mg alteration with sulfide veins (Tur III). Compositional data for each stage of tourmaline plot along the “oxy-dravite”–povondraite join, which is indicative of precipitation from relatively oxidizing fluids. Ranges of Sr-isotopic compositions in Tur I (0.7065–0.7078) and Tur II (0.7068–0.7076) are identical to those of the igneous host rocks, indicating precipitation from magmatic-hydrothermal fluids. The range of B-isotopic compositions in Tur I (δ 11 B values of −6.3‰ to −1.2‰) is also consistent with a magmatic source. Higher δ 11 B values (−2.4‰ to 5.4‰) obtained from Tur II are mainly ascribed to Rayleigh fractionation in the magmatic-hydrothermal system as tourmaline precipitated. Post-ore Tur III has a wide range of mostly lower B-isotopic compositions (−8.5‰ to 0.8‰) that record another pulse of magmatic fluid input. This interpretation is supported by the enrichment of Na, Li, Be, W, Sn, V, and Ti in Tur III, relative to Tur I and II. However, the higher Sr-isotope composition (0.7076–0.7086) of Tur III and available O-isotope composition (−7‰ to 3.5‰) of fluids of this stage record the infiltration of meteoric ground water from adjacent sedimentary country rocks. The results suggest that the Taocun IOA deposit formed in a magmatic-hydrothermal system characterized by two (or more) pulses of magmatic fluid discharge from subvolcanic diorite intrusions, followed by the influx of external ground water as the system waned. This study highlights the utility of tourmaline as a robust geochemical and isotopic monitor of ore-forming processes in such systems.

Ningwu IOA district↗

USGS2018

A sequential selective dissolution method to quantify storage and stability of organic carbon associated with Al and Fe hydroxide phases

Stabilization of SOM (soil organic matter) is regulated in part by sorption and desorption reactions happening at mineral surfaces, as well as precipitation and dissolution of organo-metal complexes. Fe and Al hydroxides play a particularly significant role in SOM stabilization in soils due to their ubiquitous distribution and their highly reactive surface properties. Iron and Al hydroxides exist in soils across a wide spectrum of crystallinity, ranging from dissolved Fe and Al cations which combine with organics to form organo-metal precipitates to the more crystalline end members, goethite and gibbsite, which sorb SOM through a variety of molecular interactions. Though the importance of these sorption and precipitation reactions has long been recognized, the distribution of SOM among Fe and Al hydroxides of differing crystallinity has not been well quantified, nor has the timescale over which these stabilization mechanisms operate. In an attempt to measure the distribution of organic C among (i) Al- and Fe-humus complexes (ii) short-range-order (SRO) Al and Fe hydroxide surfaces and (iii) crystalline Fe oxyhydroxide surfaces, a single method combining several selective mineral dissolutions was applied to soils of four different geneses (a tropical forest Andisol, a temperate forest basaltic Mollisol, a Mediterranean coastal prairie Mollisol, and a northern mixed hardwood forest Spodosol). The traditional reactants used in selective dissolutions were replaced with carbon-free analogues so that the carbon released along with the Fe and Al at each stage of the selective dissolution process could be measured. Selective dissolutions were performed sequentially: Na-pyrophosphate (organo-Al and Fe complexes) followed by hydroxylamine (SRO Al and Fe hydroxides) followed by dithionite-HCl (crystalline Fe hydroxides). Carbon, Al, and Fe concentrations, as well as radiocarbon abundance were measured in the solutions yielded by each stage of the selective dissolution process. Results suggest that precipitation of organo-metal complexes (Na-pyrophosphate extractable C) often accounts for the largest pool of stabilized C among the three selectively dissolved pools, but these complexes were 14 C enriched in comparison to C from the other selectively dissolved pools and the residual C left on crystalline mineral surfaces after all three stages of selective dissolution. Hydroxylamine and dithionite-HCl extractable C pools were, on average, small and often below detection level in temperate soils. However, radiocarbon values for these C pools were generally depleted in comparison to other pools. These results suggest variation in organo-mineral complex stability is associated with degree of crystallinity of the mineral phase. Overall, this work suggests that sequential selective dissolution methods are a promising tool for characterizing the content and isotopic composition of soil C associated with distinct organo-mineral and organo-metal associations.

Geoderma↗

USGS2024

Use of Doppler velocity radars to monitor and predict debris and flood wave velocities and travel times in post-wildfire basins

The magnitude and timing of extreme events such as debris and floodflows (collectively referred to as floodflows) in post-wildfire basins are difficult to measure and are even more difficult to predict. To address this challenge, a sensor ensemble consisting of noncontact, ground-based (near-field), Doppler velocity (velocity) and pulsed (stage or gage height) radars, rain gages, and a redundant radio communication network was leveraged to monitor flood wave velocities, to validate travel times, and to compliment observations from NEXRAD weather radar. The sensor ensemble (DEbris and Floodflow Early warNing System, DEFENS) was deployed in Waldo Canyon, Pike National Forest, Colorado, USA, which was burned entirely (100 percent burned) by the Waldo Canyon fire during the summer of 2012 ( MTBS, 2020 ). Surface velocity, stage, and precipitation time series collected during the DEFENS deployment on 10 August 2015 were used to monitor and predict flood wave velocities and travel times as a function of stream discharge (discharge; streamflow). The 10 August 2015 event exhibited spatial and temporal variations in rainfall intensity and duration that resulted in a discharge equal to 5.01 cubic meters per second (m 3 /s). Discharge was estimated post-event using a slope-conveyance indirect discharge method and was verified using velocity radars and the probability concept algorithm. Mean flood wave velocities – represented by the kinematic celerity ( c k = 2.619 m e t e r s p e r s e c o n d , m / s ± 0.556 p e r c e n t "> 𝑐 𝑘 = 2.619 𝑚𝑒𝑡𝑒𝑟𝑠 𝑝𝑒𝑟 𝑠𝑒𝑐𝑜𝑛𝑑, m/s ± 0.556 𝑝𝑒𝑟𝑐𝑒𝑛𝑡) and dynamic celerity ( c d = 3.533 m / s ± 0.181 p e r c e n t a n d t h e i r u n c e r t a i n t i e s "> 𝑐 𝑑 = 3.533 m/s ± 0.181 𝑝𝑒𝑟𝑐𝑒𝑛𝑡) and their uncertainties were computed. L-moments were computed to establish probability density functions (PDFs) and associated statistics for each of the at-a-section hydraulic parameters to serve as a workflow for implementing alert networks in hydrologically similar basins that lack data. Measured flood wave velocities and travel times agreed well with predicted values. Absolute percent differences between predicted and measured flood wave velocities ranged from 1.6 percent to 49 percent and varied with water slope, hydraulic radius, and depth. The kinematic celerity was a better predictor for steep slopes and wide flood plains associated with the Upper Waldo and Middle Waldo radar streamgages; whereas, the dynamic celerity was a better surrogate for shallow slopes and incised channels such as the Lower Waldo radar streamgage. The method demonstrates the potential extensibility of a post-wildfire warning system by (1) leveraging multiple systems (i.e., weather radar, near-field velocity and stage radars, and rain gages) for accurate and timely warnings of debris and floodflows, (2) establishing an order of operations to site, install, and operate near-field radars and conventional rain gages to record floodflows, forecast travel times, and document geomorphic change in this basin and hydrologically similar basins that lack data, and (3) communicating data operationally with the Colorado Department of Transportation engineering staff, National Weather Service forecasters, and emergency managers.

Colorado↗

USGS2011

Mid Holocene lake level and shoreline behavior during the Nipissing phase of the upper Great Lakes at Alpena, Michigan, USA

The Nipissing phase was the last pre-modern high-water stage of the upper Great Lakes. Represented as either a one- or two-peak highstand, the Nipissing occurred following a long-term lake-level rise. This transgression was primarily an erosional event with only the final stage of the transgression preserved as barriers, spits, and strandplains of beach ridges. South of Alpena, Michigan, mid to late Holocene coastal deposits occur as a strandplain between Devils Lake and Lake Huron. The landward part of this strandplain is a higher elevation platform that formed during the final stage of lake-level rise to the Nipissing peak. The pre-Nipissing shoreline transgressed over Devils Lake lagoonal deposits from 6.4 to 6.1 ka. The first beach ridge formed ~ 6 ka, and then the shoreline advanced toward Lake Huron, producing beach ridges about every 70 years. This depositional regression produced a slightly thickening wedge of sediment during a lake-level rise that formed 20 beach ridges. The rise ended at 4.5 ka at the Nipissing peak. This peak was short-lived, as lake level fell > 4 m during the following 500 years. During this lake-level rise and subsequent fall, the shoreline underwent several forms of shoreline behavior, including erosional transgression, aggradation, depositional transgression, depositional regression, and forced regression. Other upper Great Lakes Nipissing platforms indicate that the lake-level change observed at Alpena of a rapid pre-Nipissing lake-level rise followed by a slower rise to the Nipissing peak, and a post-Nipissing rapid lake-level fall is representative of mid Holocene lake level in the upper Great Lakes.

Michigan↗

USGS2024

First documentation of grass carp spawning in Lake Erie’s Central Basin

Grass carp ( Ctenopharyngodon idella ) are non-indigenous to North America having been translocated to the United States in the 1960s as a potential non-chemical solution for nuisance aquatic vegetation. Reproductively viable grass carp now exist in many watersheds in the United States. In the Great Lakes basin, grass carp were first discovered in the 1980s with direct confirmation of successful reproduction in 2015 via collection of fertilized grass carp eggs in the Sandusky River. Early life stage monitoring also confirmed reproduction in the Maumee River in 2017. During 2018–2021, no new spawning tributaries were discovered (18 total sampling events in five Great Lakes tributaries). In 2022, fourteen eggs with characteristics similar to grass carp were identified from the Huron River which is a tributary to Lake Erie’s Central Basin. Eggs were identified to species via DNA sequencing and were determined to be grass carp eggs. The confirmation of spawning in the Huron River represents a third spawning tributary in the Lake Erie basin and expands eastward the geographic extent of known grass carp spawning locations. Presently, the ability of the Huron River to support hatching and survival of larval grass carp is unknown. Discovery of the Huron River as a grass carp spawning tributary identifies the value of continued surveillance in Great Lakes tributaries for early life stages and conducting scientific inquiries evaluating the consistency of tributary use and survival of early life stages.

Ohio↗

USGS2026

Controlling invasive carp ichthyoplankton dispersion using a streamwise-oriented bubble screen: A proof-of-concept validation in a laboratory flume

Recent evidence of invasive grass carp ( Ctenopharyngodon idella ) reproducing in tributaries to the Laurentian Great Lakes has highlighted the need for control efforts targeting multiple life stages. Initial attempts to control dispersal of downstream-drifting invasive carp ichthyoplankton (i.e., eggs and larvae) using an oblique bubble screen (OBS) revealed that nearly neutrally buoyant grass carp eggs and larvae enter helical-like motions driven by the OBS, preventing aggregation within a single capture location. To improve dispersal control methods for such early-life stage carp, we used a laboratory flume to investigate the efficacy of a streamwise-oriented bubble screen to facilitate their near-bank capture. Five early-life stages of grass carp were tested: live water-hardened eggs, pre- and post-gas bladder inflation larvae, dead larvae, and dead eggs (preserved in formalin solution and later rehydrated). A range of mean channel velocities (0.23, 0.45, and 0.75 m/s) was tested for all drifters. Capture percentages increased with increasing airflow. Preserved eggs, for instance, showed capture percentages up to 95 %, 87 %, and 69 % at low, medium, and high water velocities for the highest airflow rate, respectively, in contrast with the lower than 5 % capture measured for zero airflow cases. Symmetric secondary flow structures on either side of the bubble screen induced helical trajectories of drifters and facilitated their capture in net-arrays along each wall. Velocity data were used to estimate helical recirculation timescales, enabling calculation of optimal bubble diffuser and net-array lengths for desired capture rates. This study provides useful guidance for the design of effective systems to control dispersal of downstream-drifting ichthyoplankton of invasive carp in streams.

Journal of Great Lakes Research↗

USGS2023

Incorporating temperature into seepage loss estimates for a large unlined irrigation canal

Quantifying seepage losses from unlined irrigation canals is necessary to improve water use and conservation. The use of heat as a tracer is widely used in quantifying seepage rates across the sediment–water interface. In this study, field observations and two-dimensional numerical models were used to simulate seepage losses during the 2018 and 2019 irrigation season in the Truckee Canal system. Nineteen transects were instrumented with temperature probes and stage recording devices for inverse modeling to derive seepage flux and volumetric losses over the 39 km length of canal. The numerical models for each transect were calibrated and validated using the two-year dataset. Soil zones and observation data were used in each numerical model to help guide calibration of vertical and lateral heat and fluid fluxes. Model simulations were used to derive multivariable regression equations that consider stage, temperature, and hydraulic gradient. The results demonstrate the value of long-term datasets that illustrate the seasonality of groundwater levels, siltation, stage, and temperature on seepage rates. Seepage rates estimated by the numerical models range from 0.16 to 4.6 m 3 /d m −1 . Total annual volumetric losses estimated for 2018 and 2019 were 1.6 × 10 -2 to 1.2 × 10 -2 km 3 , respectively. The seepage losses estimated by this study account for 32 % to 41 % of the inflow volumes. Regression models were able to reproduce seepage time-series simulated by the numerical models reasonably well. In arid environments, water diverted into irrigation canals may be influenced by seasonal variations in temperature sufficient to influence the water accounting of conveyed surface flows.

Nevada↗

USGS2016

Paleozoic magmatism and porphyry Cu-mineralization in an evolving tectonic setting in the North Qilian Orogenic Belt, NW China

The NWW-striking North Qilian Orogenic Belt records the Paleozoic accretion–collision processes in NW China, and hosts Paleozoic Cu–Pb–Zn mineralization that was temporally and spatially related to the closure of the Paleo Qilian-Qinling Ocean. The Wangdian Cu deposit is located in the eastern part of the North Qilian Orogenic Belt, NW China. Copper mineralization is spatially associated with an altered early Paleozoic porphyritic granodiorite, which intruded tonalites and volcaniclastic rocks. Alteration zones surrounding the mineralization progress outward from a potassic to a feldspar-destructive phyllic assemblage. Mineralization consists mainly of quartz-sulfide stockworks and disseminated sulfides, with ore minerals chalcopyrite, pyrite, molybdenite, and minor galena and sphalerite. Gangue minerals include quartz, orthoclase, biotite, sericite, and K-feldspar. Zircon LA-ICPMS U–Pb dating of the ore-bearing porphyritic granodiorite yielded a mean 206 Pb/ 238 U age of 444.6 ± 7.8 Ma, with a group of inherited zircons yielding a mean U–Pb age of 485 ± 12 Ma, consistent with the emplacement age (485.3 ± 6.2 Ma) of the barren precursor tonalite. Rhenium and osmium analyses of molybdenite grains returned model ages of 442.9 ± 6.8 Ma and 443.3 ± 6.2 Ma, indicating mineralization was coeval with the emplacement of the host porphyritic granodiorite. Rhenium concentrations in molybdenite (208.9–213.2 ppm) suggest a mantle Re source. The tonalities are medium-K calc-alkaline. They are characterized by enrichment of light rare-earth elements (LREEs) and large-ion lithophile elements (LILEs), depletion of heavy rare-earth elements (HREEs) and high-field-strength elements (HFSEs), and minor negative Eu anomalies. They have ε Hf ( t ) values in the range of +3.6 to +11.1, with two-stage Hf model ages of 0.67–1.13 Ga, suggesting that the ca. 485 Ma barren tonalites were products of arc magmatism incorporating melts from the mantle wedge and the lithosphere. In contrast, the 40-m.y.-younger ore-bearing porphyritic granodiorite is sub-alkaline and peraluminous. They are enriched in LREEs and LILEs, depleted in HFSEs, and show weak negative Eu anomalies. They display ε Hf ( t ) values of captured or inherited zircons in the range of +8.5 to +10.0, and younger two-stage Hf model ages of 0.78 Ga and 0.86 Ga, similar to those of ca. 485 Ma tonalite. The ca. 445 Ma zircons have ε Hf ( t ) values of −2.1 to +9.9, with two-stage Hf model ages of 0.75–1.27 Ga. Moreover, they have relatively high oxygen fugacity than that of the precursor barren tonalite. The ca. 445 Ma magmas at Wangdian thus formed in a subduction setting, and incorporated melts from the subduction-modified lithosphere that had previously been enriched by additions of chalcophile and siderophile element-rich materials by the earlier magmatism and metasomatism during the Paleo Qilian-Qinling Ocean subduction event.

North Qilian Orogenic Belt↗

USGS2026

Is new actually better? A structural comparison of collaborative governance structures for the management of Atlantic salmon (Salmo salar) in Maine

Collaborative governance structures (CGS) have been increasingly adopted to address joint-jurisdictional management challenges. While the establishment of CGSs has been widely studied, their practical development has remained a conspicuous gap. CGSs are variable systems with several developmental stages (activation, collectivity, and institutionalization) which eventually lead to stabilization, decline, re-creation, or re-orientation. CGSs in decline may need to revisit earlier developmental stages if members choose to re-create or re-orient the structure. The Atlantic Salmon Recovery Framework (ASRF) was the CGS responsible for managing the Gulf of Maine Distinct Population Segment of Atlantic Salmon ( Salmo salar ) from 2011 until 2019 when it was replaced by the Collaborative Management Strategy (CMS) pilot program. The CMS was designed to address concerns identified in the ASRF; 1. slow and ineffective decision-making, 2. confusion surrounding leadership, and 3. low adaptive capacity. Building upon a previous evaluation of the ASRF, we used a parallel design to compare the structural components and participant perceptions of the two structures using a comparative case study methodology. The changes that occurred between the ASRF and the CMS constitute a re-creation, providing a unique opportunity to study this developmental phase of a CGS. The issues observed in the CMS may result from a misalignment between participant expectations and the current developmental stage of the re-created CGS. The CMS reorganized ASRF members and created roles for participants without direct management jurisdiction. The implementation of the CMS addressed many concerns identified in the ASRF while others remained (i.e., high membership uncertainty and confusion surrounding decision-making procedures). Formal leadership roles have created more equal representation, but participants still reported uncertainty regarding status and formalization of non-leadership roles.

Maine↗

USGS2008

Gold deposits and occurrences of the Greater Caucasus, Georgia Republic: Their genesis and prospecting criteria

The south-central part of the Greater Caucasus region, Georgia Republic, represents an extremely prospective region for significant orogenic gold deposits. Gold-bearing quartz veins are concentrated in two extensive WNW-trending belts, the Mestia-Racha and Svaneti districts, within the northern margin of the Southern Slope Zone of the Great Caucasus orogen. This metalliferous region is dominated by Early to Middle Jurassic slates, which are part of a terrane that likely accreted to the continental margin from late Paleozoic to Jurassic. The slates were subsequently intruded by both Middle to Late Jurassic and Neogene granitoids. Quartz veins in the more carbonaceous slate units are most consistently enriched in As, Au, Hg, Sb, and W, and show mineralization styles most consistent with typical orogenic gold deposits. Quartz veins in the Mestia-Racha district were mined in Soviet times for As, Sb, and W, but many of these are now being recognized as gold resource targets. The veins occur in the footwall of a thrust fault between the Southern Slope zone and an earlier accreted terrane, the Main Zone, to the north. Many veins in the district continue along strike for > 1??km and some cut Neogene intrusions, constraining ore formation to the most recent 4 to 5??million years. Gold deposition thus correlates with final collision of the Arabian plate to the south and uplift of the ore-hosting Greater Caucasus. The Zopkhito deposit, previously mined for antimony, contains an estimated 55??t Au at a cutoff grade of 0.5??g/t. The veins are localized in an area where smaller-order structures show a major change in strike from N-S to more E-W trends. A pyrite-arsenopyrite ore stage includes gold concentrated in both sulfide phases; it is overprinted by a later stibnite-dominant stage. Fluid-inclusion studies of ore samples from the Zopkhito deposit indicate minimum trapping temperatures of 300 to 350????C and 200 to 300????C for the two stages, respectively, and minimum trapping pressures of 0.2 to 0.5??kbar. Ore-forming fluids, with approximately 5 to 20??mol% non-aqueous gas, evolved from N2-dominant to CO2-dominant during evolution of the hydrothermal system. ??34S values of + 1 to + 4??? for ore-related sulfides at Zopkhito are consistent with a sedimentary rock source for the sulfur, and ??18O quartz measurements of 16 to 21??? are consistent with either a magmatic or metamorphic fluid. More than 60 gold-bearing lodes and placers in the Svaneti district occur along the thrust between the Southern Slope and Main Zones. Lode gold potential was first recognized in the historic placer district in the 1980s, with many auriferous quartz veins cutting Middle Jurassic igneous rocks. Brecciated veins in the 18??t Au Lukhra deposit cut a small granodioritic to dioritic stock; the latter intrudes Devonian schist immediately north of the thrust. Presently, there are three recognized ore zones in the deposit, with the most significant occurring over an area 140??m in length and 12??m-wide, with typical grades of 7 to 9??g/t Au. Reconnaissance fluid-inclusion studies of ore samples from the Lukhra deposit indicate minimum trapping temperatures of 220????C. Measurements of ??18Oquartz of about 10??? suggest buffering of isotopic composition by the igneous host rocks.

Ore Geology Reviews↗

USGS2018

Two-event lode-ore deposition at Butte, USA: 40Ar/39Ar and U-Pb documentation of Ag-Au-polymetallic lodes overprinted by younger stockwork Cu-Mo ores and penecontemporaneous Cu lodes

The ore-genesis model for world-class deposits of the Butte mining district, Montana, USA, is deep pre-Main Stage porphyry Cu-Mo and overlying Main Stage Ag-Zn-Cu zoned-lode deposits, both of which formed from hydrothermal fluids driven by minor volumes of rhyolitic magma. The lode-specific model is that hydrothermal processes diminished in intensity outward from district center along lode veins, synchronously forming metal zones. The accepted models are controverted by new geologic and multi-method geochronologic studies. The new data reveal the following sequence of events: (1) Thermal study of country rock indicates that the 76.9-Ma Butte Granite cooled to 350–400 °C by 4 m.y. after emplacement. (2) Five quartz porphyry rhyolite dikes were emplaced at 67–65 Ma and another at 60 Ma (SHRIMP U-Pb) into the cooled Butte Granite without resetting 40 Ar/ 39 Ar ages in country rock. (3) Fifty-eight white mica and K-feldspar samples from alteration envelopes adjacent to Ag-Au-polymetallic lodes in outer parts of the district, Zn-rich lodes in intermediate parts, and Cu-rich lodes in the district center yield 40 Ar/ 39 Ar ages of 73–70 Ma for Ag-rich lodes, 65–64 Ma for Cu-rich lodes, and complex age spectra of 69–65 Ma for Zn-rich lodes. The data show that Ag-Au-polymetallic lodes occupied cross-district fractures by about 73 Ma, forming the greater Butte mining district. At 67–65 Ma, minor quartz porphyry dikes were emplaced into central and eastern parts of the rejuvenated fracture system but without evidence of related cupola or volcanic rocks or of thermal disturbance in the country rock. At 64.5 Ma, overlapping hydrothermal cells formed two stockwork Cu-Mo domes in deep parts of the fracture system. At 65–64 Ma and closely related to late-stage stockwork Cu-Mo activity, a penecontemporaneous hydrothermal pulse formed a high-sulfidation hydrothermal plume that (1) utilized the large re-opened fractures to cannibalize and remobilize Cu from autologous, stockwork, and older Ag-Au-polymetallic lodes, (2) deposited the rich, high-sulfidation Cu lodes, and (3) mobilized metals from early Ag-Au-polymetallic veins in middle parts of the district, transported the metals outward and redeposited them, enriching early veins, especially in the intermediate Zn plus Cu areas. Metals zones in lodes of the Butte district are the result of an intensely focused, Cu-rich hydrothermal plume that variably reworked the center of significantly larger, 10 m.y. older, Ag-Au-polymetallic lodes.

Montana↗

USGS2018

Timing and genesis of ore formation in the Qarachilar Cu-Mo-Au deposit, Ahar-Arasbaran metallogenic zone, NW Iran: Evidence from geology, fluid inclusions, O–S isotopes and Re–Os geochronology

In the Qarachilar Cu-Mo-Au deposit of the Ahar–Arasbaran metallogenic zone (AAMZ), northwest Iran, mineralization occurs as three quartz-sulfide veins that cut granodiorite-quartz monzodiorite rocks of the Qaradagh batholith (QDB). Ore formation can be divided into three stages, with chalcopyrite, molybdenite, and gold-bearing pyrite appearing mainly in the first two stages. The main wall-rock alteration is silicification, and intermediate argillic, carbonate, and propylitic alteration. Fluid inclusion microthermometry indicates trapping of medium- to high-salinity (9.2–55 wt% NaCl equiv.) fluids at Qarachilar. Fluid inclusion trapping conditions are estimated to be 190 °C–530 °C and 0.1–3 kbar. The variable phase ratios as well as spatial coexisting of liquid- and vapor-rich two-phase and halite-bearing multiphase fluid inclusions homogenizing over the same temperatures are consistent with fluid boiling during ore formation. Obtained δ 18 O H2O values of quartz from ore-stage veins are +5.7‰ to +9.7‰, signifying that the ore–fluid system was predominantly magmatic water. The average calculated δ 34 S H2S values are 1 ± 1‰ for pyrite, chalcopyrite and molybdenite, consistent with a magmatic source for sulfur. Combined, the fluid inclusion and stable isotope data indicate that the ore-forming fluids at Qarachilar were magmatic in origin and were subsequently cooled and diluted by meteoric water. Fluid boiling and mixing facilitated hydrothermal alteration and mineralization. Molybdenite Re–Os dating shows that mineralization occurred at 42.35 ± 0.16 Ma, coincident with formation of porphyry Cu-Mo mineralization at Agarak deposit, and Hanqasar, Aygedzor and Dastakert prospects in the Lesser Caucasus. However, Qarachilar is older than all porphyry Cu-Mo mineralization in the AAMZ and Urumieh-Dokhtar magmatic arc (UDMA), which suggests that collision between Arabia and Eurasia were oblique and thus diachronous. Our data suggest that mineralization at Qarachilar is related to collisional Eocene magmatic–hydrothermal activity related to Neo-Tethys subduction, and shares a number of similarities with the vein-type Cu-Mo-Au mineralization related to Cu-Mo porphyries.

Ore Geology Reviews↗

USGS2018

Experimental investigation of the role of rock fabric in gas generation and expulsion during thermal maturation: Anhydrous closed-system pyrolysis of a bitumen-rich Eagle Ford Shale

Gold-tube pyrolysis experiments were conducted on miniature core plugs and powdered rock from a bitumen-rich sample of Eagle Ford Shale to investigate the role of rock fabric in gas generation and expulsion during thermal maturation. The samples were isothermally heated at 130, 300, 310, 333, 367, 400, and 425 °C for 72 h under a confining pressure of 68.0 MPa, corresponding to six levels of induced thermal maturity: pre-oil generation (130 °C/72 h), incipient oil/bitumen generation (300 and 310 °C/72 h), early oil generation (333 °C/72 h), peak oil generation (367 °C/72 h), early oil cracking (400 °C/72 h), and late oil cracking (425 °C/72 h). Experimental results show that gas retention coupled with compositional fractionation occurs in the core plug experiments and varies as a function of thermal maturity. During the incipient oil/bitumen generation stage, yields of methane through pentane (C 1 –C 5 ) from core plugs are significantly lower than those from rock powder, and gases from core plugs are enriched in methane. However, the differences in C 1 –C 5 gas yield and composition decrease throughout the oil generation stage, and by the oil cracking stage no obvious compositional difference in C 1 –C 5 gases exists. The decrease in the effect of rock fabric on gas yield and composition with increasing maturity is the result of an increase in gas expulsion efficiency. Pyrolysis of rock powder yields 4–16 times more CO 2 compared to miniature core plugs, with δ 13 C CO2 values ranging from −2.9‰ to −0.6‰, likely due to carbonate decomposition accelerated by reactions with organic acids. Furthermore, lower yields of gaseous alkenes and H 2 from core plug experiments sugge

Organic Geochemistry↗