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At least 37 records · Page 2Linked to original sources
USGS2022

Mercury contamination from historic mining in water and sediment, Guadalupe River and San Francisco Bay, California

The New Almaden mercury mines in California (USA), which collectively represent the largest historic producers of mercury in North America, are a persistent source of mercury contamination to the San Francisco Bay estuary. An estimate based on total mercury concentration (HgTOT) and provisional stream flow data measured at a gauging station in the Guadalupe River during base flow conditions yields a base flow flux of 30 g of mercury for the month of October 2000. In contrast to this base flow estimate, one 2-day rain event in October 2000 resulted in a flux of 22 g of mercury past this site. An estimate of mercury transport from the entire Guadalupe River watershed based on a sediment transport model and our measured suspended particulate HgTOT (0.5-4 ??g g-1) results in a total of 4-30 kg year-1 transported to the southern reach of the estuary. Sediments in the southern reach have lower HgTOT (most ??? 0.4 ??g g-1 dry wt) and monomethyl-mercury (MMHg, c. 1 ng g-1 dry wt) concentrations than those in the Guadalupe River (HgTOT, 0.41-33 ??g g-1 dry wt; MMHg, 1-10 ng g-1 dry wt). Because the most elevated methylmercury concentrations (8-12 ng g-1 dry wt) were found in sediments deposited immediately upstream of hydraulic structures (e.g. diversion dams and weirs) within the river, it is proposed that such physical structures may represent important zones of MMHg production and fluxes to San Francisco Bay.

Geochemistry: Exploration, Environment, Analysis↗
USGS2022

Mercury in vegetation and soils at abandoned mercury mines in southwestern Alaska, USA

We chemically analysed vegetation (willow and alder) and soil samples collected at three abandoned mercury (Hg) mines and at background sites in southwestern Alaska and compared Hg concentrations, speciation and distribution. Total Hg and methylmercury (MeHg) concentrations were higher in vegetation and soil samples from all the mine sites compared to samples from the background sites, but there was no correlation between total-Hg concentrations in vegetation and total-Hg concentrations in soil or between total-Hg and MeHg concentrations. However, the percent MeHg of the total Hg was higher in samples from the background sites compared to samples from the mine sites and is higher in vegetation samples than in corresponding soil samples. The percent MeHg is an order of magnitude higher in the willow samples than in corresponding alder or soil samples. The percent of divalent Hg [Hg(II)] is highest in soil samples from the retort and background areas. The higher percent MeHg in vegetation and soil in samples from background sites may be explained by the higher proportions of reactive Hg species, such as Hg(II), at these sites compared to the surface mined and tailings areas where most of the Hg is in the elemental and cinnabar (HgS) forms. Dissolved gaseous Hg species are more readily accumulated in vegetation and are more readily methylated than solid phases like HgS and liquid Hg.

Geochemistry: Exploration, Environment, Analysis↗
USGS2022

Effects of acidic recharge on groundwater at the St. Kevin Gulch site, Leadville, Colorado

The acid rock drainage-affected stream of St. Kevin Gulch recharges the Quaternary sand and gravel aquifer of Tennessee Park, near Leadville, Colorado, lowering pH and contributing iron, cadmium, copper, zinc and sulphate to the ground-water system. Dissolved metal mobility is controlled by the seasonal spring runoff as well as oxidation/reduction (redox) reactions in the aquifer. Oxidizing conditions occur in the unconfined portions of the aquifer whilst sulphate-reducing conditions are found down gradient where semi-confined groundwater flow occurs beneath a natural wetland. Iron-reducing conditions occur in the transition from unconfined to semi-confined groundwater flow. Dissolved iron concentrations are low to not detectable in the alluvial fan recharge zone and increase in a down gradient direction. The effects of low-pH, metal-rich recharge are pronounced during low-flow in the fall when there is a defined area of low pH groundwater with elevated concentrations of dissolved zinc, cadmium, copper and sulphate adjacent to St. Kevin Gulch. Dissolved metal and sulphate concentrations in the recharge zone are diluted during spring runoff, although the maximum concentrations of dissolved zinc, cadmium, copper and sulphate occur at selected down gradient locations during high flow. Dissolved zinc, cadmium and copper concentrations are low to not detectable, whereas dissolved iron concentrations are greatest, in groundwater samples from the sulphate-reducing zone. Attenuation of zinc, cadmium and copper beneath the wetland suggests sulphide mineral precipitation is occurring in the semi-confined aquifer, in agreement with previous site investigations and saturation index calculations. Adsorption of dissolved zinc, cadmium and copper onto iron hydroxides is a minor attenuation process due to the low pH of the groundwater system.

Colorado↗
USGS2022

Water-quality trends for a stream draining the Southern Anthracite Field, Pennsylvania

Stream flow, chemical and biological data for the northern part of Swatara Creek, which drains a 112 km 2 area in the Southern Anthracite Field of eastern Pennsylvania, indicate progressive improvement in water quality since 1959, after which most mines in the watershed had been flooded. Drainage from the flooded mines contributes substantially to base flow in Swatara Creek. Beginning in 1995, a variety of treatment systems and surface reclamation were implemented at some of the abandoned mines. At Ravine, Pa., immediately downstream of the mined area, median SO 4 concentration declined from about 150 mg l −1 in 1959 to 75 mg l −1 in 1999 while pH increased from acidic to near-neutral values (medians: c. pH 4 before 1975; c. pH 6 after 1975). Fish populations rebounded from non-existent during 1959–1990 to 21 species identified in 1999. Nevertheless, recent monitoring indicates (1) episodic acidification and elevated concentrations and transport of Fe, Al, Mn, and trace metals during storm flow; (2) elevated concentrations of Fe, Mn, Co, Cu, Pb, Ni, and Zn in streambed sediments relative to unmined areas and to toxicity guidelines for aquatic invertebrates and fish; and (3) elevated concentrations of metals in fish tissue, notably Zn. The metals are ubiquitous in the fine fraction (<0.063 mm) of bed sediment in mining-affected tributaries and the main stem of Swatara Creek. As a result of scour and transport of streambed deposits, concentrations of suspended solids and total metals in the water column are correlated, and those for storm flow typically exceed base flow. Nevertheless, the metals concentrations are poorly correlated with stream flow because concentrations of suspended solids and total metals typically peak prior to peak stream stage. In contrast, SO 4 , specific conductance and pH are inversely correlated with stream flow as a result of dilution of poorly buffered stream water with weakly acidic storm runoff derived mainly from low-pH rainfall. Declines in pH to values approaching 5.0 during storm flow events or declines in redox potential during burial of sediment could result in the remobilization of metals associated with suspended solids and streambed deposits.

Pennsylvania↗
USGS2015

Soil geochemical survey of abandoned mining sites in the Eastern-Central Peloritani Mountains, Sicily, Italy

This investigation focused on topsoils ( n = 122) and vertical profiles ( n = 6) distributed over an area of 250 km 2 in the eastern-central Peloritani Mountains, northeastern Sicily. Georeferenced concentration of 53 elements (including potentially harmful ones), determined by ICP-MS after an aqua regia leach, were used to produce geochemical maps by means of a GIS-aided spatial interpolation process. Results show that there are two distinct areas: the larger, located between the Fiumendinisi, Budali and Ali villages, and the other between C. Postlioni and Femmina Morta, which contain anomalous As (up to 727 mg/kg), Sb (up to 60 mg/kg), Ag (up to 1 mg/kg) and Au (up to 0.1 mg/kg) concentrations. Most of the investigated areas have high contamination levels for As, Zn, Sb, and Pb that exceed the threshold values (As = 20 mg/kg, Zn = 150 mg/kg, Sb = 10 mg/kg and Pb = 100 mg/kg) established for soils by the Italian Environmental Law ( Decreto Legislativo 2006 , number 152). The isotopic ratios of 206 Pb/ 207 Pb and 208 Pb/ 207 Pb have been measured in selected soils on both leaches [using 1M HNO 3 –1.75M HCl (50:50)] and residues thereof. Soil leach reflects possible anthropogenic contamination, whereas soil residues indicate geogenic contributions. Results suggest that most of contamination in the soils is related to the presence of sulphide and sulphosalt rock-forming minerals in the surveyed area. The soil fraction contains a Pb value >1600 mg/kg and has ratios of 1.1695 for 206 Pb/ 207 Pb and 2.4606 for 208 Pb/ 207 Pb. Only one soil leach isotopic composition could reflect possible anthropogenic contamination. The correlation among As, Zn, Pb contents v. Pb isotopic signatures of 206 Pb/ 207 Pb indicates that surface and deep soils collected from profiles are dominated by geogenic compositions.

Peloritani Mountains, Sicily↗
USGS2017

Arsenic and mercury contamination related to historical goldmining in the Sierra Nevada, California

Arsenic (As) is a naturally occurring constituent in low-sulphide gold-quartz vein deposits, the dominant deposit type for lode mines in the Sierra Nevada Foothills (SNFH) gold (Au) province of California. Concentrations of naturally occurring mercury (Hg) in the SNFH Au province are low, but extensive use and loss of elemental Hg during amalgamation processing of ore from lode and placer Au deposits led to widespread contamination of Hg in the Sierra Nevada foothills and downstream areas, such as the Sacramento–San Joaquin Delta and San Francisco Bay. This review paper provides an overview of As and Hg contamination related to historical Au mining in the Sierra Nevada of California. It summarizes the geology, mineralogy, and geochemistry of the Au deposits, and provides information on specific areas where detailed studies have been done in association with past, ongoing, and planned remediation activities related to the environmental As and Hg contamination. Arsenic is a naturally occurring constituent in low-sulphide Au-quartz vein deposits, the dominant deposit type for lode mines in the Sierra Nevada Foothills (SNFH) Au province ( Ashley 2002 ). Because of elevated concentrations of As in accessory iron-sulphide minerals including arsenopyrite (FeAsS) and arsenian pyrite (Fe(S,As) 2 ), As is commonly a contaminant of concern in lode Au mine waste, including waste rock and mill tailings. The principal pathways of human As exposure from mine waste include ingestion of soil or drinking water, and inhalation of dust in contaminated areas ( Mitchell 2014 ). Concentrations of naturally occurring Hg in the SNFH Au province are low, but extensive use and loss of elemental Hg during amalgamation processing of ore from lode and placer Au deposits ( Churchill 2000 ) led to widespread contamination of Hg in the Sierra Nevada foothills and downstream areas, such as the Sacramento–San Joaquin Delta and San Francisco Bay ( Alpers et al. 2005 a ). Conversion of Hg to monomethylmercury (MeHg) by sulphate-reducing and iron-reducing microbes facilitates its bioaccumulation ( Wiener et al. 2003 ). The human Hg exposure pathway of main concern is ingestion of MeHg from sport (non-commercial) fish, especially higher trophic levels such as bass species ( Davis et al. 2008 ). Wildlife exposure to MeHg is also a concern because of chronic and reproductive effects, for example in fish-eating and invertebrate-foraging birds (e.g. Wiener et al. 2003 ; Eagles-Smith et al. 2009 ; Ackerman et al. 2016 ).

California↗
USGS2023

Stream sediment geochemistry in mineral exploration: A review of fine-fraction, clay-fraction, bulk leach gold, heavy mineral concentrate and indicator mineral chemistry

Stream sediment surveys support early-stage reconnaissance mineral exploration and regional assessment programmes, enhanced by recent improvements in analytical method detection limits, continuously improving mineral chemistry, and new approaches to the interpretation of geochemical data. Sediment surveys may be used to predict catchment basin lithology, mineralization type based on pathfinder geochemistry, and geological features based on indicator mineral chemistry. Sediment surveys that target a finer-fraction sediment sample led to the discovery of the La Colosa gold deposit, Colombia. The Batu Hijau porphyry Cu–Au deposit in Indonesia was discovered based on an anomalous clay-sized fraction sample 12 km downstream. In an arid region with poorly developed drainages and minor topographic relief, the Ag-base-metal Navidad District in Argentina was discovered with clay-fraction sediment geochemistry. Heavy mineral concentrate (HMC) sediment surveys that include mineral chemistry determinations have led to global diamond discoveries. HMC surveys contributed to discovery of the Ring of Fire Ni–Cu–PGE and chromite district, Ontario, Canada. Discoveries and geochemical mapping can assist advancement of the application of stream sediment geochemistry in those global areas for which lithologies and deposits are exposed. Stream sediment surveys continue to be one of the most cost-effective geochemical methods for covering large areas for mineral exploration.

Geochemistry: Exploration, Environment, Analysis↗
USGS2023

Anthropogenic influence on groundwater geochemistry in Horn Creek Watershed near the Orphan Mine in Grand Canyon National Park, Arizona, USA

Breccia pipe deposits of the Grand Canyon region contain ore grade copper and uranium. Horn Creek is located near the Orphan Mine mineralized breccia pipe deposit and groundwater emerging from the bedrock in the headwaters of Horn Creek has the highest uranium concentrations in the region. Uranium decreases an order of magnitude between the groundwater at the top of the watershed and the groundwater emerging from the alluvial material lower in the watershed. Horn Creek water has low sulfur and uranium isotopic ratios which may suggest interaction with sulfide and uranium minerals found in mineralized breccia pipe deposits. Per- and polyfluoroalkyl substances (PFBA and PFBS) were found in low concentrations in groundwater from the bedrock and may be related to mining process materials or other anthropogenic activities. PHREEQC modeling suggests that water that is elevated in uranium emerging from the bedrock in the upper watershed may mix with other groundwater and atmospheric precipitation infiltrated into the alluvial material in the lower watershed. Tritium is elevated in Horn Creek groundwaters suggesting a component of modern water, some of which may have interacted with Orphan Mine workings. Additional studies could build on this understanding of chemistry changes in waters of Horn Creek to provide more direct evidence of contribution of water moving through the Orphan Mine.

Arizona↗
USGS2025

Tracing metal sources and groundwater flow paths in the Upper Animas River watershed using rare earth elements and stable isotopes

Groundwater flow paths and processes that govern metal mobility and transport are difficult to characterize in mountainous bedrock watersheds. Despite the difficulty in holistic characterization, conceptual understanding of subsurface hydrologic and geochemical processes is key to developing remediation plans for locations affected by acid mine drainage, such as the Upper Animas River watershed in southwestern Colorado, USA. Stable isotopes of water and rare earth elements were utilized to evaluate groundwater flow and metal sources within this complex catchment. Stable isotope samples collected from draining mine adits and springs display systematic spatial variation wherein sample sites at higher elevations have greater seasonal variability than sites at lower elevations. The Upper Cement Creek watershed, where multiple draining mines are present, displays the lowest seasonal variation in stable isotopic signatures, potentially indicating the presence of a large, well-mixed volume of groundwater storage or interbasin groundwater flow. Rare earth elements display statistically significant variation between different alteration styles in the catchment. Overprinting of regional propylitic alteration is evident based on enrichment of middle rare earth elements in acidic springs and mines that are not spatially associated with surficial exposures of acid generating alteration styles. Europium anomaly and middle rare earth enrichment signatures from two flooded mine tunnels on opposite sides of a watershed divide indicate connections to the same subsurface flooded mine workings.

Colorado↗
USGS2025

Tracking the sources of metals to the San Juan River, Four Corners Region, USA: An introduction to the thematic issue

Surface water quantity and quality is important for arid and semi-arid regions where many people, including underserved and Indigenous communities, rely on a scarce resource for drinking water, irrigation, livestock and ceremonial uses. The southwestern United States, and specifically the Four Corners Region (Colorado, Arizona, New Mexico and Utah), is an example of this situation. Elevated concentrations of metals including aluminium, arsenic and lead were identified in previous studies and this study in the San Juan River from below the Navajo Dam, through the Navajo Nation to Mexican Hat, Utah. An interdisciplinary team applied approaches and principles of geology, geochemistry, geomorphology, hydrology and statistics to gain a better understanding of the tributaries supplying the source(s) of metals to the San Juan River. This introductory paper provides an overview of the ‘Metal geochemical fingerprinting to identify sub-watershed source contributions to surface water at a regional arid watershed scale, Four Corners Region, USA’ thematic collection . An overview of sampling sites, techniques and potential sources of metals is provided. Approaches used in this study could be applied to investigations in similar systems globally.

Four Corners region↗
USGS2025

Adaptive instrument design strategy for collecting water, sediment samples and stage data in remote, ephemeral arroyos in the arid southwestern United States

Methods for collecting water, suspended sediment samples, and streamflow from rivers and streams have been documented in the literature by various science agencies. However, some projects may require data collected in difficult conditions including remote sites, sites that have limited accessibility during storms, and streamflow that occurs rarely. For these studies, adaptive approaches to sampler instrument design can yield valuable sample and streamflow data previously unobtainable. Tracking the source(s) of metals to the San Juan River required water chemistry samples, suspended sediment samples, and streamflow data collected on 28 ephemeral arroyos and five perennial streams. These tributaries to the San Juan River presented many challenges because of their remote locations, inaccessibility during storms, and ephemeral nature. A novel design, following on previous adaptive instrument designs, was created for this specific project. The design includes readily available materials (i.e. sourced from hardware stores), low cost, and allows for ease of replacement. Three instruments were designed following these design goals: a siphon sampler (water chemistry), sediment trap (suspended sediments), and a stage sensor (water level). These instruments were mounted to a t-post array in the stream channel. This installation approach, collectively named the “sed-chem gage”, was operated at each ephemeral arroyo for two consecutive field seasons. The instrument design approach, parts list, and results of operation are presented herein. This approach will be useful to scientists, water managers, and communities who need to evaluate water flow and water and sediment chemistry in a large, remote area where traditional techniques and methods may be cost prohibitive.

Arizona, Colorado, New Mexico, Utah↗
USGS2025

Applying geological unit distribution and chemical weathering indices to evaluate potential lithological sources of Al, As and Pb to the San Juan River, Four Corners region, USA

In arid to semi-arid landscapes, sporadic monsoonal events, varying widely in scale and distribution, can generate overland flow resulting in streamflow in ephemeral channels. These channels may contain metal-laden sediments that are a by-product of the weathering and erosion of local geological units. To evaluate the potential for local geology to contribute aluminium (Al), arsenic (As) and lead (Pb) to the San Juan River, northwestern New Mexico, USA, the distributions of geological units were delineated for 12 hydrological basins within the greater San Juan River watershed. Concentrations of Al, As and Pb in the predominant geological units were compiled from data in the National Geochemical Database. Chemical indices of weathering (CIW) were calculated for geological units with greater than 5% coverage in the entire San Juan River watershed. Based on CIWs of the major geological units, the Mesaverde Group (CIW = 95.2), Chinle and Dolores Formations ( combined ) (CIW = 93.3), and Mancos Shale ( combined ) (CIW = 82.6) are the most likely units to weather, erode and contribute sediments with elevated concentrations of Al, As and Pb to the San Juan River. The results of this study show the importance of understanding geological sources of sediments because they could be substantial contributors of constituents of concern to water, especially in arid environments where surface water may be the only source of water in the region.

Arizona, Colorado, New Mexico, Utah↗
USGS2025

Morphometric and geological characterization with statistical correlations for 33 tributary drainage basins of the San Juan River watershed in the Four Corners region, USA

Basin morphometry, climate and geology control how a hydrological network evolves over time, controlling the efficiency of weathering of elements from geological materials, and ultimately the input of sediment and dissolved constituents to river systems. Exceedances to the Navajo Nation surface water quality standards for trace metals have been reported in the San Juan River watershed. Because metals are transported adsorbed to fine-grain sediment, the identification of areas with elevated sources of trace metals and/or areas with increased erosion and sediment transport potential is an important first step in protecting water quality. Physical factors such as elevation, slope, relief and stream order were used to quantify morphometric parameters that effect the contribution of trace metals into the stream network. By correlating these parameters with water quality data that were collected from tributaries along the San Juan River, we identified statistically significant regressions between morphometric parameters and total Al, Pb, U, Fe and Mn in surface water. Positive correlations with trace metals include tributary drainage basin perimeter, pour point elevation and total number of streams, while negative correlations include stream length ratio, ruggedness number and longest basin axis. Stream reach measurements within geological units that contain known trace metal constituents reveal that Gallegos Canyon and Desert Creek are the most susceptible to sediment mobilization and transport, while other tributary drainage basins, such as Desert, Recapture and Salt creeks, are associated with naturally elevated concentrations of Al, As, Pb and U.

Arizona, Colorado, New Mexico, Utah↗
USGS2025

Evaluating sediment transport and metal sorption in the San Juan River watershed

The physical and chemical characteristics of sediment influence the transport of metals in rivers. The San Juan River and its tributaries are located in the Four Corners Region in the southwestern United States and the watershed contains a wide variety of potential metal sources. Comparisons of past and present sediment data provide insight into the effects of seasonality and storm events on the transport of sediment within a watershed. Comparisons suggest finer (<0.63 µm) sediment particles increase at a greater rate during intense storm events than coarser sediment particles. These fine, clay-sized sediments have a greater potential for metal sorption. Statistical analyses compared upper and lower portions of the San Juan River. Results show that total elemental concentration decreases in sediments (1785.15 μ g l −1 ) and that concentrations increase in the aqueous phase (2063.08 μ g l −1 ) downstream in the San Juan River. Analyses using geochemical and scanning electron microscopy with energy dispersive spectroscopy suggest that sediment clay particles are the most likely constituent to transport metals in the San Juan River. Metal transport is further aided by metal oxide coatings that develop on the surfaces of larger particles. Increases in aggregation of fine-grained particles in the downstream portions of the San Juan River are also likely to bind elements within sediments, which can act as both a source and sink for metals in the lower watershed. CEC , geochemistry , PSD

Arizona, Colorado, New Mexico, Utah↗
USGS2025

Geochemical processes related to mined, milled, or natural metal deposits in a rapidly changing global environment

The demand for metals and raw materials, such as nickel and copper, has been projected to expand in the coming decades, driven by the global energy transition, the need for green technologies, and expanding infrastructure. Consequently, the increasing extraction and production of mining waste can have adverse impacts on surrounding environments and human health. The aim of this thematic collection is to fill critical knowledge gaps in the present-day cycles of metal(loid)s from source to larger sinks, and the effect of environmental management, anthropogenic development, and climate change. Altogether, the studies have been conducted in different natural settings around the world and comprise investigations in laterites, a soil-medicinal plant system, watersheds, and banded iron formations, among others. The geochemical applications in tracing mineralization, its secondary products, and/or potential impact on the immediate environment are highly diverse with applied tools ranging from isotope tracers to major and trace element systematics. Particularly the use of rare earth elements, their patterns and anomalies are methods employed by several studies in this collection. We summarize the findings to offer a potential future direction for the use of geochemical tracing techniques in resource exploration in the context of climate change and environmental challenges.

Geochemistry: Exploration, Environment, Analysis↗
USGS2017

Origin and evolution of mineralizing fluids and exploration of the Cerro Quema Au-Cu deposit (Azuero Peninsula, Panama) from a fluid inclusion and stable isotope perspective

Cerro Quema is a high sulfidation epithermal Au-Cu deposit with a measured, indicated and inferred resource of 35.98 Mt. @ 0.77 g/t Au containing 893,600 oz. Au (including 183,930 oz. Au equiv. of Cu ore). It is characterized by a large hydrothermal alteration zone which is interpreted to represent the lithocap of a porphyry system. The innermost zone of the lithocap is constituted by vuggy quartz with advanced argillic alteration locally developed on its margin, enclosed by a well-developed zone of argillic alteration, grading to an external halo of propylitic alteration. The mineralization occurs in the form of disseminations and microveinlets of pyrite, chalcopyrite, enargite, tennantite, and trace sphalerite, crosscut by quartz, barite, pyrite, chalcopyrite, sphalerite and galena veins. Microthermometric analyses of two phase (L + V) secondary fluid inclusions in igneous quartz phenocrysts in vuggy quartz and advanced argillically altered samples indicate low temperature (140–216 °C) and low salinity (0.5–4.8 wt% NaCl eq.) fluids, with hotter and more saline fluids identified in the east half of the deposit (Cerro Quema area). Stable isotope analyses (S, O, H) were performed on mineralization and alteration minerals, including pyrite, chalcopyrite, enargite, alunite, barite, kaolinite, dickite and vuggy quartz. The range of δ 34 S of sulfides is from − 4.8 to − 12.7‰, whereas δ 34 S of sulfates range from 14.1 to 17.4‰. The estimated δ 34 S ΣS of the hydrothermal fluid is − 0.5‰. Within the advanced argillic altered zone the δ 34 S values of sulfides and sulfates are interpreted to reflect isotopic equilibrium at temperatures of ~ 240 °C. The δ 18 O values of vuggy quartz range from 9.0 to 17.5‰, and the δ 18 O values estimated for the vuggy quartz-forming fluid range from − 2.3 to 3.0‰, indicating that it precipitated from mixing of magmatic fluids with surficial fluids. The δ 18 O of kaolinite ranges from 12.7 to 18.1‰ and δD from − 103.3 to − 35.2‰, whereas the δ 18 O of dickite varies between 12.7 and 16.3‰ and δD from − 44 to − 30. Based on δ 18 O and δD, two types of kaolinite/dickite can be distinguished, a supergene type and a hypogene type. Combined, the analytical data indicate that the Cerro Quema deposit formed from magmatic-hydrothermal fluids derived from a porphyry copper-like intrusion located at depth likely towards the east of the deposit. The combination of stable isotope geochemistry and fluid inclusion analysis may provide useful exploration vectors for porphyry copper targets in the high sulfidation/lithocap environment.

Azuero Peninsula↗
USGS2019

Links between tectonics, magmatism, and mineralization in the formation of Late Cretaceous porphyry systems in the Yukon-Tanana upland, eastern Alaska, USA

Cretaceous-Paleocene porphyry Cu(±Mo±Au) occurrences are scattered throughout the Yukon-Tanana upland in eastern Alaska. Known occurrences in eastern Alaska are poorly characterized, despite a resurgence in exploration. Porphyry deposits in the upland are emplaced into structurally complex metamorphic rocks representing a variety of tectonic environments, resulting in diverse alteration and mineralization assemblages. New mapping, drill core logging, petrography, geochemistry, geochronology, and structural analysis allow improved characterization of the parameters of porphyry systems and identify key linkages to regional tectonic and magmatic events. New sericite 40 Ar/ 39 Ar and zircon U/Pb dates constrain porphyry systems to the Late Cretaceous-earliest Paleocene (ca. 71-63 Ma). Zircon Hf-isotope ratios and Ce and Eu concentrations indicate that Late Cretaceous-Paleocene intrusions emplaced into basement dominated by Triassic and Jurassic plutons are more isotopically juvenile, reflecting more oxidized conditions. In contrast, those emplaced into basement dominated by mid-Cretaceous plutons are more reduced crustal geochemical-affinity. Diversity in mineral assemblages in contrasting systems may reflect emplacement into crustal domains of varying compositions and oxidation states. Those formed within a domain containing more-oxidized Triassic and Jurassic plutons are molybdenite-rich and apparently lack gold. In contrast, systems formed within domains dominated by more reduced mid-Cretaceous plutons contain lower-sulfidation state mineral assemblages with reported gold.

Alaska, Yukon↗
USGS2002

Porphyry copper deposits of the world: Database, maps, and preliminary analysis

Mineral deposit models are important in exploration planning and quantitative resource assessments for two reasons: (1) grades and tonnages among deposit types are significantly different, and (2) many types occur in different geologic settings that can be identified from geologic maps. Mineral deposit models are the keystone in combining the diverse geoscience information on geology, mineral occurrences, geophysics, and geochemistry used in resource assessments and mineral exploration. Far too few thoroughly explored mineral deposits are available in most local areas for reliable identification of the important geoscience variables or for robust estimation of undiscovered deposits—thus we need mineral-deposit models. Globally based deposit models, such as those presented here, allow recognition of important features because the global models demonstrate how common different features are. Well-designed and -constructed deposit models allow geologists to know from observed geologic environments the possible mineral deposit types that might exist, and allow economists to determine the possible economic viability of these resources in the region. Thus, mineral deposit models play the central role in transforming geoscience information to a form useful to policy makers. The foundation of mineral deposit models is information about known deposits—the purpose of this publication is to make this kind of information available in digital form for a group of porphyry copper deposits. This publication contains a computer file of information on porphyry copper deposits around the world. It also presents new grade and tonnage models for three subtypes of porphyry copper deposits, maps showing locations and general ages of these deposits, and a preliminary analysis with a number of figures summarizing many of the properties of these porphyry-style deposits. These summaries can be considered a new, quantified, form of most parts of descriptive models such as those in Cox and Singer (1986). The value of this information and analyses depends critically on the consistent manner of data gathering. For this reason, we first discuss the rules used in this compilation. Next the fields of the data file are considered. Finally, we discuss some of the things that can be done with the data.

Open-File Report↗