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USGS2024

Sulphide petrology and ore genesis of the stratabound Sheep Creek sediment-hosted Zn–Pb–Ag–Sn prospect, and U–Pb zircon constraints on the timing of magmatism in the northern Alaska Range

The Sheep Creek prospect is a stratabound Zn–Pb–Ag–Sn massive sulfide occurrence in the Bonnifield mining district, northern Alaska Range. The prospect is within a quartz–sericite–graphite–chlorite schist unit associated with Devonian carbonaceous and siliceous metasedimentary rocks. Volcanogenic massive sulfide (VMS) deposits in the district are hosted in felsic metavolcanic rocks (362 ± 2 Ma) associated with siliciclastic and carbonaceous sedimentary rocks that overlie the stratigraphic sequence hosting the Sheep Creek prospect. Felsic metaigneous rocks in underlying units are 372 ± 4 to 366 ± 4 Ma. Sheep Creek is atypical of the other sulfide deposits in the district in (1) having Sn grades up to 1.2%; (2) being contained in fine-grained, quartz-rich rocks and quartz–pebble conglomerate that likely originated as chert and chert-clast sediment, respectively; and (3) showing minimal evidence of volcanic components in the host rocks. Comparison of immobile trace-element proportions for graphitic and siliceous rocks from the Sheep Creek area with those for argillite associated with the Bonnifield VMS deposits indicates a continental volcanic-arc provenance for the former and a within-plate and passive margin provenance for the latter. In contrast to previously published interpretations, our data analysis supports a clastic-dominated (CD) rather than a VMS affinity for the Sheep Creek prospect. In our model, Zn–Pb–Ag–Sn mineralization formed by syngenetic or early diagenetic processes on or beneath the seafloor, possibly in the shallow-water environment of an outer continental shelf setting. Potential analogues are the Paleozoic CD deposits in the Canadian Selwyn Basin outboard of the Laurentian continental margin.

Alaska↗

USGS2003

Flood flows, leaf breakdown, and plant-available nitrogen on a dryland river floodplain

We tested the hypothesis that decomposition in flood-inundated patches of riparian tree leaf litter results in higher plant-available nitrogen in underlying, nutrient-poor alluvium. We used leafpacks ( n = 56) containing cottonwood ( Populus deltoides ssp. wislizenii ) leaf litter to mimic natural accumulations of leaves in an experiment conducted on the Yampa River floodplain in semi-arid northwestern Colorado, USA. One-half of the leafpacks were set on the sandy alluvial surface, and one-half were buried 5 cm below the surface. The presence of NO 3 − and NH 4 + presumed to result from a leafpack's submergence during the predictable spring flood pulse was assessed using an ion-exchange resin bag (IER) placed beneath each leafpack and at control locations. Leafpacks and IERs were collected one week after flood peak (71 days total exposure) at half the stations; the remainder were collected three weeks later (93 days exposure). A multi-peaked spring flood with above-average maximum discharge inundated leafpacks for total time periods ranging from 133 to 577 hours. Litter lost from 43 to 68 percent of its initial organic matter (OM) content. Organic matter loss increased with total time inundated and total time of exposure on the floodplain. Burial retarded OM loss if the total time inundated was relatively long, and substrate texture (sand vs. silt) affected OM loss in a complex manner through interactions with total time inundated and total time of exposure. No pulse of N attributable to leaf breakdown was detected in the IERs, and leafpack litter showed no net change in the mass of nitrogen present. Patterns of leafpack and IER nitrogen levels suggested that litter removed N from floodwater and thereby reduced N availability in underlying sediment. Immobilization of floodwater-N by litter and N mineralization outside the flood period may be important components of N flux in semi-arid and arid floodplain environments.

Colorado↗

USGS1999

Environmental processes that affect mineral deposits in the eastern United States

A thorough understanding of the environmental processes that affect mineral deposits and mine wastes has become increasingly important as the Nation wrestles with how to meet our current demand for metals without compromising the environment and how to mitigate the damage caused by the mining practices of previous generations. Regulatory requirements are dominated by empirical approaches to environmental problems associated with mining, but mitigation and reclamation can be enhanced greatly by a theoretical and conceptual understanding of the processes that affect the availability, transport, and fixation of metals and the generation of acidic waters. U.S. Geological Survey (USGS) research efforts in the Eastern United States are concentrating on environmental processes that affect a class of mineral deposits known as massive sulfide deposits. These occurrences were valued historically for their sulfur content and recently for their metals. This deposit type is a research priority because of its economic significance and high potential for adverse environmental impact due to its high sulfide content and the low acid-buffering capacity of host rocks. Numerous examples of these deposits are found in the East, including reclaimed mine sites, abandoned mines, active mines, and sites currently in the permitting process for future production. Published studies of mine drainage chemistry from the Iron Mountain massive sulfide deposit in California have documented extreme conditions of very low pH and high heavy-metal concentrations. These extreme conditions are attributed to the unique hydrologic and climatic settings of the deposit and probably are independent of the mineral deposit type. Areas currently under study include Bald Mountain, Maine, the Great Smoky Mountains National Park, the Vermont copper belt, Contrary Creek, Virginia, and Prince William Forest Park, Virginia (fig.1). Goals of the research are (1) to give land-use planners and the mining industry a better empirical framework from which to assess potential environmental impacts of mining, particularly under eastern climatic conditions, and (2) to provide a better theoretical and conceptual framework from which to design more effective and cost efficient mitigation and reclamation programs.

Information Handout↗

USGS2024

Decoding paleomire conditions of Paleogene superhigh-organic-sulfur coals

Superhigh-organic‑sulfur (SHOS) coals (coals with organic sulfur content >4 wt%) are unique coal deposits found at a few notable locations in the world. Specific peat accumulation and preservation conditions must be met to form SHOS coals. Organic sulfur is a major constituent of such coals, and it may have various sources depending on the prevailing paleomire conditions. Understanding such paleomire conditions sheds light on the formation mechanisms of SHOS coals. This investigation decodes the paleomire conditions of the Paleogene SHOS coals from Meghalaya, India, using sulfur isotopic compositions ( δ 34 S) of organic sulfur ( δ 34 S OS ) and pyritic sulfur ( δ 34 S Py ) along with organic petrography, pyrite morphology and trace element ratios. Thirty coal samples were collected from the Jaintia Hills in the east, Khasi Hills in the middle, and Garo Hills in the west of Meghalaya. The organic sulfur content in the Garo, Khasi, and Jaintia coals varies from 1.0 to 3.3 wt%, 1.4 to 13.8 wt%, and 1.0 to 7.2 wt%, respectively. Further, after separation from pyritic sulfur and sulfate sulfur phases, the organic sulfur content ranges from 54.4 to 69.2%, 63.8 to 79.9%, and 59.3 to 73.8%, in the Garo, Khasi, and Jaintia Hills, respectively, suggesting the SHOS nature of these coal samples. The δ 34 S Py varies from −29.3 ‰ to +5.7 ‰, −21.3 ‰ to +27.3 ‰, and −12.1 ‰ to −4.3 ‰, in the Jaintia, Khasi, and Garo Hills, respectively, while the δ 34 S OS fluctuates from −4.6 ‰ to +3.7 ‰, −9.3 ‰ to +7.8 ‰, and − 9.0 ‰ to −5.0 ‰, respectively. The δ 34 S values of pyrite and organic sulfur (OS) in Jaintia coals are 34 S depleted compared to seawater sulfate (+22 ‰), leading to fractionations in the range of −51.3 ‰ to −16.3 ‰ (mean − 31.6 ‰) and − 26.6 ‰ to −18.3 ‰ (mean − 23.1 ‰) for pyritic and organic sulfur (OS), respectively. Pyrite in Khasi coals show a relatively heavier δ 34 S composition averaging at −20.5 ‰, whereas organic sulfur (OS) isotope compositions range from −31.3 ‰ to −14.2 ‰ with a mean of −22.6 ‰. Pyrite and OS in the Garo coals are depleted compared to seawater sulfate. Isotope variations in the Jaintia, Khasi, and Garo coals indicate microbial sulfate reduction (MSR) of seawater sulfate. Large isotopic fractionations between Eocene seawater sulfate and pyritic sulfur ( Δ 34 S SO4Eocene – pyrite = up to −51.3 ‰; mean − 31.6 ‰) in Jaintia coals indicate their possible formation in the water column/near the sediment-seawater interface (open system) and also hint toward dissimilatory sulfate reduction pathways that prevailed under anoxic redox conditions. However, mean values of Δ 34 S SO4Eocene – pyrite (−20.5 ‰) in the Khasi coals imply pyrite formation deeper in the sediments (more closed system) under dysoxic conditions. The dominance of OS over pyritic sulfur, framboidal pyrite, and its microcrystal size distributions in Jaintia coals may suggest syngenetic pyrite formation in open water reducing/anoxic conditions under paralic environments. Elevated Sr/Ba and U/Th values in these coals further confirm the anoxic conditions. Nevertheless, the presence of euhedral pyrite with the alleviated pyrite framboids in the Khasi coals and their complete absence in the Garo coals may suggest dysoxic-suboxic and suboxic-oxic depositional conditions, respectively. The isotopic signatures of the Garo coals suggest sulfur contribution from the parent paleobiota and MSR under a freshwater-oxic environment. Insignificant fractionations between δ 34 S Py and δ 34 S OS indicate limited iron and sulfate availability for additional sulfur cycling and disproportionation reactions, typical of oxic conditions. The absence of framboidal pyrite, elevated sulfate concentration, and mean Sr/Ba and U/Th values of 0.5 and 0.3, respectively, further suggest the freshwater peat deposition in the Garo Hills under limnotelmatic to telmatic freshwater conditions. Moreover, high inertinite content (I mmf = 9.77–33.16 vol%), possibly induced by atmospheric peat exposure, supports the interpretation of suboxic-oxic paleomire conditions in Garo Hills. Gradually decreasing mineral matter content from Jaintia (mean 13.6 vol%) to Garo coals (mean 7.4 vol%) additionally projects a transition from mesotrophic brackish to freshwater limnotelmatic environment, complementing the shift in the paleomire condition from eastern (Jaintia) to western (Garo) Meghalayan Hills.

International Journal of Coal Geology↗

USGS2015

Petrology and diagenetic history of the upper shale member of the Late Devonian-Early Mississippian Bakken Formation, Williston Basin, North Dakota

The organic-rich upper shale member of the upper Devonian–lower Mississippian Bakken Formation (Williston Basin, North Dakota, USA) has undergone significant diagenetic alteration, irrespective of catagenesis related to hydrocarbon generation. Alteration includes precipitation of numerous cements, replacement of both detrital and authigenic minerals, multiple episodes of fracturing, and compaction. Quartz authigenesis occurred throughout much of the member, and is represented by multiple generations of microcrystalline quartz. Chalcedonic quartz fills radiolarian microfossils and is present in the matrix. Sulfide minerals include pyrite and sphalerite. Carbonate diagenesis is volumetrically minor and includes thin dolomite overgrowths and calcite cement. At least two generations of fractures are observed. Based on the authigenic minerals and their relative timing of formation, the evolution of pore waters can be postulated. Dolomite and calcite resulted from early postdepositional aerobic oxidation of some of the abundant organic material in the formation. Following aerobic oxidation, conditions became anoxic and sulfide minerals precipitated. Transformation of the originally opaline tests of radiolaria resulted in precipitation of quartz, and quartz authigenesis is most common in more distal parts of the depositional basin where radiolaria were abundant. Because quartz authigenesis is related to the distribution of radiolaria, there is a link between diagenesis and depositional environment. Furthermore, much of the diagenesis in the upper shale member preceded hydrocarbon generation, so early postdepositional processes were responsible for occlusion of significant original porosity in the member. Thus, diagenetic mineral precipitation was at least partly responsible for the limited ability of these mudstones to provide porosity for storage of hydrocarbons.

North Dakota↗

USGS2026

Guide and data requirements for submission of mineral deposit mineral chemistry data in the Critical Minerals in Ores - Mineral Chemistry (CMiO-MIN) database

The Critical Minerals in Ores - Mineral Chemistry (CMiO-MIN) database (Hawkins et al., 2026) is designed to capture ore and ore-related mineral compositional data from critical mineral-bearing deposits across the globe. Samples included within this database must be well-characterised and come from localities that have been sufficiently studied to have a reasonable constraint on their deposit type and environment of formation. As such, only samples analysed by modern geochemical methods, and with certain minimum metadata attribution, can be accepted. Data that is submitted to the CMiO-MIN database will also be published via the Geoscience Australia Portal (portal.ga.gov.au) and Critical Minerals Mapping Initiative Portal (www.criticalminerals.org). The CMiO-MIN database is a companion database for the Critical Minerals in Ores (CMiO) database (Champion et al., 2021) that was first published in 2021. This guide draws heavily from the submission guide for CMiO (Case et al., 2024) to ensure similar processes for each database. For more information about the CMiO database please refer Champion et al. (2021) and Case et al. (2024; 2025).

Report↗

USGS1990

Fine-grained rutile in the Gulf of Maine: Diagenetic origin, source rocks, and sedimentary environment of deposition

The Gulf of Maine, an embayment of the New England margin, is floored by shallow, glacially scoured basins that are partly filled with late Pleistocene and Holocene silt and clay containing 0.7 to 1.0 wt percent TiO 2 , chiefly in the form of silt-size rutile. Eleven basins in the gulf are estimated to contain 479 X 10 6 metric tons of TiO 2 (to a depth of 10 m) in the U.S. exclusive economic zone and 168 X 10 6 in Canada, based on analyses of surface sediment and of cores 10 to 20 m long. The U.S. annually consumes approximately 1 X 10 6 metric tons of TiO 2 , of which 73 percent is imported. The inferred amount of fine-grained TiO 2 in the basins is large, and we interpret it to be predominantly rutile; but no attempt has been made yet to mine and beneficiate the fine-grained ore.Sedimentary rocks of Nova Scotia, New Brunswick, and northern Maine contain fine-grained rutile crystals and have been the major source of the fine-grained sediment in the Gulf of Maine basins during and after the Wisconsinan glaciation. We conclude that much of the rutile in the Gulf of Maine mud formed diagenetically in poorly cemented Carboniferous and Triassic coarse-grained sedimentary rocks of Nova Scotia and New Brunswick after the dissolution of titanium-rich detrital minerals (ilmenite, ilmenomagnetite). Another major source of rutile is the generally finer grained Paleozoic sedimentary rocks of northern Maine (and possibly northwestern New Brunswick) which contain recycled diagenetic rutile that most likely originated in sandstones. Additional Wisconsinan sources of fine-grained, diagenetic TiO 2 probably include sedimentary rocks of inferred Triassic age that underlie the Gulf of Maine.The diagenesis of rutlie in coarse sedimentary rocks (especially arkose and graywacke) followed by erosion, segregation, and deposition (and including recycling of fine-grained rutile from shales) can serve as a model for predicting and prospecting for unconsolidated deposits of fine-grained TiO 2 .Gulf of Maine mud is comparable in TiO 2 content to typical shale. A determination of whether the fine-grained TiO 2 in shales primarily occurs as detrital titanium minerals from metamorphic and igneous sources or as recycled, diagenetic titanium oxides from sedimentary sources may assist in interpreting shale provenance and environment of deposition.

Economic Geology↗

USGS1994

Petrology of gabbroic xenoliths in 1960 Kilauea basalt: crystalline remnants of prior (1955) magmatism

The 1960 Kapoho lavas of Kilauea's east rift zone contain 1-10 cm xenoliths of olivine gabbro, olivine gabbro-norite, and gabbro norite. Textures are poikilitic (ol+sp+cpx in pl) and intergranular (cpx+pl??ol??opx). Poikilitic xenoliths, which we interpret as cumulates, have the most primitive mineral compositions, Fo82.5, cpx Mg# 86.5, and An80.5. Many granular xenoliths (ol and noritic gabbro) contain abundant vesicular glass that gives them intersertal, hyaloophitic, and overall 'open' textures to suggest that they represent 'mush' and 'crust' of a magma crystallization environment. Their phase compositions are more evolved (Fo80-70, cpx Mg# 82-75, and An73-63) than those of the poikilitic xenoliths. Associated glass is basaltic, but evolved (MgO 5 wt%; TiO2 3.7-5.8 wt%). The gabbroic xenolith mineral compositions fit existing fractional crystallization models that relate the origins of various Kilauea lavas to one another. FeO/MgO crystal-liquid partitioning is consistent with the poikilitic ol-gabbro assemblage forming as a crystallization product from Kilauea summit magma with ???8 wt% MgO that was parental to evolved lavas on the east rift zone. For example, least squares calculations link summit magmas to early 1955 rift-zone lavas (???5 wt% MgO) through ???28-34% crystallization of the ol+sp+cpx+pl that comprise the poikilitic ol-gabbros. The other ol-gabbro assemblages and the olivine gabbro-norite assemblages crystallized from evolved liquids, such as represented by the early 1955 and late 1955 lavas (???6.5 wt% MgO) of the east rift zone. The eruption of 1960 Kapoho magmas, then, scoured the rift-zone reservoir system to entrain portions of cumulate and solidification zones that had coated reservoir margins during crystallization of prior east rift-zone magmas. ?? 1994 Springer-Verlag.

Bulletin of Volcanology↗

USGS2021

Uranium(VI) attenuation in a carbonate-bearing oxic alluvial aquifer

Uranium minerals are commonly found in soils and sediment across the United States at an average concentration of 2–4 mg/kg. Uranium occurs in the environment primarily in two forms, the oxidized, mostly soluble uranium(VI) form, or the reduced, sparingly soluble reduced uranium(IV) form. Here we describe subsurface geochemical conditions that result in low uranium concentrations in an alluvial aquifer with naturally occurring uranium in soils and sediments in the presence of complexing ligands under oxidizing conditions. Groundwater was saturated with respect to calcite and contained calcium (78–90 mg/L) with elevated levels of carbonate alkalinity (291–416 mg/L as HCO 3 − ). X-ray adsorption near edge structure (XANES) spectroscopy identified that sediment-associated uranium was oxidized as a uranium(VI) form (85%). Calcite was the predominant mineral by mass in the ultrafine fraction in uranium-bearing sediments (>16 mg/kg). Groundwater geochemical modeling indicated calcite and/or a calcium-uranyl-carbonate mineral such as liebigite in equilibrium with groundwater. The δ 13 C (0.57‰ ± 0.15‰) was indicative of abiotic carbonate deposition. Thus, solid-phase uranium(VI) associated with carbonate is likely maintaining uranium(VI) groundwater levels below the maximum contaminant level (MCL; 30 µg/L), presenting a deposition mechanism for uranium attenuation rather than solely a means of mobilization.

Nebraska↗

USGS2004

In situ evidence for an ancient aqueous environment at Meridiani Planum, Mars

Sedimentary rocks at Eagle crater in Meridiani Planum are composed of fine-grained siliciclastic materials derived from weathering of basaltic rocks, sulfate minerals (including magnesium sulfate and jarosite) that constitute several tens of percent of the rock by weight, and hematite. Cross-stratification observed in rock outcrops indicates eolian and aqueous transport. Diagenetic features include hematite-rich concretions and crystal-mold vugs. We interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history. The environmental conditions that they record include episodic inundation by shallow surface water, evaporation, and desiccation. The geologic record at Meridiani Planum suggests that conditions were suitable for biological activity for a period of time in martian history.

Science↗

USGS2014

Science applications of a multispectral microscopic imager for the astrobiological exploration of Mars

Future astrobiological missions to Mars are likely to emphasize the use of rovers with in situ petrologic capabilities for selecting the best samples at a site for in situ analysis with onboard lab instruments or for caching for potential return to Earth. Such observations are central to an understanding of the potential for past habitable conditions at a site and for identifying samples most likely to harbor fossil biosignatures. The Multispectral Microscopic Imager (MMI) provides multispectral reflectance images of geological samples at the microscale, where each image pixel is composed of a visible/shortwave infrared spectrum ranging from 0.46 to 1.73 μ m. This spectral range enables the discrimination of a wide variety of rock-forming minerals, especially Fe-bearing phases, and the detection of hydrated minerals. The MMI advances beyond the capabilities of current microimagers on Mars by extending the spectral range into the infrared and increasing the number of spectral bands. The design employs multispectral light-emitting diodes and an uncooled indium gallium arsenide focal plane array to achieve a very low mass and high reliability. To better understand and demonstrate the capabilities of the MMI for future surface missions to Mars, we analyzed samples from Mars-relevant analog environments with the MMI. Results indicate that the MMI images faithfully resolve the fine-scale microtextural features of samples and provide important information to help constrain mineral composition. The use of spectral endmember mapping reveals the distribution of Fe-bearing minerals (including silicates and oxides) with high fidelity, along with the presence of hydrated minerals. MMI-based petrogenetic interpretations compare favorably with laboratory-based analyses, revealing the value of the MMI for future in situ rover-mediated astrobiological exploration of Mars.

Astrobiology↗

USGS1958

Equilibrium distribution of dissolved sulphur species in water at 25°C and 1 atm total pressure

The E h -pH diagrams for the equilibrium concentrations in aqueous solution at 25°C of native sulphur and all the various sulphur-containing ions and acids from which the ions are produced have been constructed for systems having a total sulphur concentration of 0.1 molar. The composite of these diagrams indicates that elemental sulphur, H 2 S, HS − HSO 4 − and SO 4  are the species that predominate in the environments that might be found in nature. This indication is in agreement with the composition of all sulphur-containing minerals.

Geochimica et Cosmochimica Acta↗

USGS2007

The geology of asbestos in the United States and its practical applications

Recently, naturally occurring asbestos (NOA) has drawn the attention of numerous health and regulatory agencies and citizen groups. NOA can be released airborne by (1) the disturbance of asbestos-bearing bedrocks through human activities or natural weathering, and (2) the mining and milling of some mineral deposits in which asbestos occurs as an accessory mineral(s). Because asbestos forms in specific rock types and geologic conditions, this information can be used to focus on areas with the potential to contain asbestos, rather than devoting effort to areas with minimal NOA potential. All asbestos minerals contain magnesium, silica, and water as essential constituents, and some also contain major iron and/or calcium. Predictably, the geologic environments that host asbestos are enriched in these components. Most asbestos deposits form by metasomatic replacement of magnesium-rich rocks. Asbestos-forming environments typically display shear or evidence for a significant influx of silica-rich hydrothermal fluids. Asbestos-forming processes can be driven by regional metamorphism, contact metamorphism, or magmatic hydrothermal systems. Thus, asbestos deposits of all sizes and styles are typically hosted by magnesium-rich rocks (often also iron-rich) that were altered by a metamorphic or magmatic process. Rock types known to host asbestos include serpentinites, altered ultramafic and some mafic rocks, dolomitic marbles and metamorphosed dolostones, metamorphosed iron formations, and alkalic intrusions and carbonatites. Other rock types appear unlikely to contain asbestos. These geologic insights can be used by the mining industry, regulators, land managers, and others to focus attention on the critical locales most likely to contain asbestos.

Environmental & Engineering Geoscience↗

USGS2006

Intensity of quartz cathodoluminescence and trace-element content in quartz from the porphyry copper deposit at Butte, Montana

Textures of hydrothermal quartz revealed by cathodoluminescence using a scanning electron microscope (SEM-CL) reflect the physical and chemical environment of quartz formation. Variations in intensity of SEM-CL can be used to distinguish among quartz from superimposed mineralization events in a single vein. In this study, we present a technique to quantify the cathodoluminescent intensity of quartz within individual and among multiple samples to relate luminescence intensity to specific mineralizing events. This technique has been applied to plutonic quartz and three generations of hydrothermal veins at the porphyry copper deposit in Butte, Montana. Analyzed veins include early quartz-molybdenite veins with potassic alteration, pyrite-quartz veins with sericitic alteration, and Main Stage veins with intense sericitic alteration. CL intensity of quartz is diagnostic of each mineralizing event and can be used to fingerprint quartz and its fluid inclusions, isotopes, trace elements, etc., from specific mineralizing episodes. Furthermore, CL intensity increases proportional to temperature of quartz formation, such that plutonic quartz from the Butte quartz monzonite (BQM) that crystallized at temperatures near 750 ??C luminesces with the highest intensity, whereas quartz that precipitated at ???250 ??C in Main Stage veins luminesces with the least intensity. Trace-element analyses via electron microprobe and laser ablation-ICP-MS indicate that plutonic quartz and each generation of hydrothermal quartz from Butte is dominated by characteristic trace amounts of Al, P, Ti, and Fe. Thus, in addition to CL intensity, each generation of quartz can be distinguished based on its unique trace-element content. Aluminum is generally the most abundant element in all generations of quartz, typically between 50 and 200 ppm, but low-temperature, Main Stage quartz containing 400 to 3600 ppm Al is enriched by an order of magnitude relative to all other quartz generations. Phosphorous is present in abundances between 25 and 75 ppm, and P concentrations in quartz show little variation among quartz generations. Iron is the least abundant of these elements in most quartz types and is slightly enriched in CL-dark quartz in pyrite-quartz veins with sericitic alteration. Titanium is directly correlated with both temperature of quartz precipitation, and intensity of quartz luminescence, such that BQM quartz contains hundreds of ppm Ti, whereas Main Stage quartz contains less than 10 ppm Ti. Our results suggest that Ti concentration in quartz is controlled by temperature of quartz precipitation and that increased Ti concentrations in quartz may be responsible for increased CL intensities.

American Mineralogist↗

USGS2008

Geochemical data for samples collected in 2007 near the concealed pebble porphyry Cu-Au-Mo deposit, southwest Alaska

In the summer of 2007, the U.S. Geological Survey (USGS) began an exploration geochemical research study over the Pebble porphyry copper-gold-molydenum (Cu-Au-Mo) deposit in southwest Alaska. The Pebble deposit is extremely large and is almost entirely concealed by tundra, glacial deposits, and post-Cretaceous volcanic and volcaniclastic rocks. The deposit is presently being explored by Northern Dynasty Minerals, Ltd., and Anglo-American LLC. The USGS undertakes unbiased, broad-scale mineral resource assessments of government lands to provide Congress and citizens with information on national mineral endowment. Research on known deposits is also done to refine and better constrain methods and deposit models for the mineral resource assessments. The Pebble deposit was chosen for this study because it is concealed by surficial cover rocks, it is relatively undisturbed (except for exploration company drill holes), it is a large mineral system, and it is fairly well constrained at depth by the drill hole geology and geochemistry. The goals of the USGS study are (1) to determine whether the concealed deposit can be detected with surface samples, (2) to better understand the processes of metal migration from the deposit to the surface, and (3) to test and develop methods for assessing mineral resources in similar concealed terrains. This report presents analytical results for geochemical samples collected in 2007 from the Pebble deposit and surrounding environs. The analytical data are presented digitally both as an integrated Microsoft 2003 Access? database and as Microsoft 2003 Excel? files. The Pebble deposit is located in southwestern Alaska on state lands about 30 km (18 mi) northwest of the village of Illiamna and 320 km (200 mi) southwest of Anchorage (fig. 1). Elevations in the Pebble area range from 287 m (940 ft) at Frying Pan Lake just south of the deposit to 1146 m (3760 ft) on Kaskanak Mountain about 5 km (5 mi) to the west. The deposit is in an area of relatively subdued topographic relief with an elevation of around 300 m (1000 ft). This portion of Alaska is part of the subarctic regime mountains division, Yukon intermontane plateaus-tayga-meadow province ecoregion, as defined by Bailey (U.S. Forest Service, 2007). Between June 28th and July 12th, 2007, scientists from the USGS collected soil, water, stream sediment, vegetation, heavy-mineral concentrate, till, and rock samples from the deposit area. This report contains analytical results for soil, water, stream sediment, and vegetation samples. Analyses for the heavy-mineral concentrate, till, and rock samples are still in progress. The sampling was undertaken during relatively dry and stable weather conditions. Only minor scattered rain showers occurred during the sampling period, so surface conditions were largely unaffected by weather. The predominant sample media collected were soils and surface waters. Soil and water (mostly from ponds and springs, some from small creeks) samples were collected along a single 7.8 km-long (4.8 mi) east-west traverse across the Pebble East and Pebble West zones and from more distal background areas around Koktuli and Kaskanak Mountains. Sample sites are shown on figure 2 and plate 1, and locality coordinates are provided in the accompanying Access and Excel files named FieldSite. Water samples were analyzed by USGS laboratories with one subset analyzed by Activation Laboratories (Actlabs), as indicated below. Soils and stream sediments were analyzed for their total content by SGS Minerals Services under a contract with the USGS. Soil samples were also leached by selected partial-extraction leaching procedures and then analyzed by several commercial laboratories, as described below. Vegetation samples were analyzed as indicated below.

Alaska↗

USGS2020

Natural attenuation can lead to environmental resilience in mine environment

Four streams flowing in the Iglesiente and Arburese mine districts (SW Sardinia, Italy), exploited for zinc (Zn) and lead (Pb) extraction from sulphides and secondary non-sulphide mineralization (calamine ores), have been studied combining investigations from the macroscale (hydrologic tracer techniques) to the microscale (X-ray powder diffraction, scanning electron microscopy, X-ray absorption spectroscopy). In the investigated area, concerns arise from release of metals to water during weathering of ore minerals and mine-waste. Specifically, Zn is observed at extremely high concentrations (10s of mg/L or more) in waters in some of the investigated catchments. The results from synoptic sampling campaigns showed marked differences of Zn loads, from 6.3 kg/day (Rio San Giorgio) to 2000 kg/day (Rio Irvi). Moreover, natural attenuation of metals was found to occur i) through precipitation of Fe compounds (Fe oxy/hydroxides and “green rust”), ii) by means of the authigenic formation of metal sulphides promoted by microbial sulphate reduction, iii) by metal intake in roots and stems of plants ( Phragmites australis and Juncus acutus ) and by immobilization in the rhizosphere, and iv) by cyanobacterial biomineralization processes that lead to formation of Zn-rich phases (hydrozincite and amorphous Zn-silicate) The biologically mediated natural processes that lead to significant abatement and/or reduction of metal loads, are the response of environmental systems to perturbations caused from mine activities, and can be considered part of the resilience of the system itself. The aim of this study is to understand the effect of these processes on the evolution of the studied systems towards more stable and, likely, resilient conditions, e.g. by limiting metal mobility and favoring the improvement of the overall quality of water. The understanding of how ecosystems adapt and respond to contamination, and which chemical and physical factors control these natural biogeochemical barriers, can help to plan effective remediation actions.

Sardinia↗

USGS2002

Data set of world phosphate mines, deposits, and occurrences: Part A. Geologic data. Part B. Location and mineral economic data

An inventory of more than 1,600 world phosphate mines, deposits, and occurrences was compiled from smaller data sets collected as part of multiple research efforts by Carlotta Chernoff, University of Arizona, and Greta Orris, U.S. Geological Survey. These data have been utilized during studies of black shale depositional environments and to construct phosphate deposit models. The compiled data have been edited for consistency and additional location information has been added where possible. The database of compiled phosphate information is being released in two sections; the geologic data in one section and the location and mineral economic data in the second. This report, U.S. Geological Survey Open-File Report 02–156–A, contains the geologic data and is best used with the complimentary data contained in Open-File Report 02–156–B. U.S. Geological Survey Open-File Report 02–156–B contains commodity data, location and analytical data, a variety of mineral economic data, reference information, and pointers to related records in the U.S. Geological Survey National mineral databases—MASMILS and MRDS.

Open-File Report↗

USGS2000

Petrology of arkosic sandstones, Pennsylvanian Minturn Formation and Pennsylvanian and Permian Sangre de Cristo Formation, Sangre de Cristo Range, Colorado - data and preliminary interpretations

This report describes the mineral and chemical composition of immature, arkosic sandstones of the Pennsylvanian Minturn and Pennsylvanian and Permian Sangre de Cristo Formations, which were derived from the Ancestral Rocky Mountains. Located in the Sangre de Cristo Range of southern Colorado, the Minturn and Sangre de Cristo Formations contain some of the most immature, sodic arkoses shed from the Ancestral Rocky Mountains. The Minturn Formation was deposited as fan deltas in marine and alluvial environments; the Sangre de Cristo Formation was deposited as alluvial fans. Arkoses of the Minturn and Sangre de Cristo Formations are matrix-rich and thus may be properly considered arkosic wackes in the terminology of Gilbert (Williams and others, 1954). In general, potassium feldspar and plagioclase are subequal in abundance. Arkose of the Sangre de Cristo Formation is consistently plagioclase-rich; arkose from the Minturn Formation is more variable. Quartz and feldspar grains are accompanied by a few percent rock fragments, consisting mostly of intermediate to granitic plutonic rocks, gneiss, and schist. All of the rock fragments seen in sandstone are present in interbedded conglomerate, consistent with derivation from a Precambrian terrane of gneiss and plutonic rocks much like that exposed in the present Sangre de Cristo Range. Comparison of mineral and major oxide abundances reveals a strong association of detrital quartz with SiO2, all other detrital minerals (totaled) with Al2O3, potassium feldspar plus mica with K2O, and plagioclase with Na2O. Thus, major oxide content is a good predictor of detrital mineralogy, although contributions from matrix and cement make these relationships less than perfect. Detrital minerals and major oxides tend to form inverse relationships that reflect mixtures of varying quantities of minerals; when one mineral is abundant, the abundance of others declines by dilution. In arkose of the Minturn and Sangre de Cristo Formations, the abundance of quartz (and SiO2) is enhanced by weathering and transport, which destroys feldspar and rock fragments. Weathering also preferentially destroys plagioclase (and removes Na2O) over potassium feldspar. Thus, as fresh sodic arkose detritus is weathered and transported in the fluvial environment, it becomes potassic and quartz-rich. Stratigraphic profiles of mineral and major oxide abundance reveal that weathering and transport, including reworking by marine currents, was most effective in reducing plagioclase and enhancing quartz content of arkosic sediment in the Minturn Formation near Marble Mountain. In general, the quartz-poor, sodic arkoses of the Sangre de Cristo Formation indicate little weathering in the source area or during transport. Iron-titanium oxides and other heavy minerals, notably zircon and sphene, tend to be most abundant in the Sangre de Cristo Formation. Although concentrated locally as fluvial placers, the overall abundance of heavy minerals probably reflects lack of weathering and proximity to source. The degree of weathering and destruction of unstable grains (feldspar and rock fragments) in the Minturn and Sangre de Cristo Formations of the Sangre de Cristo Range was dependent on rates of uplift and erosion as much as climate (wet versus dry). Reworking by marine currents further reduced the proportion of unstable grains during Minturn time. Sodic (plagioclase-rich), quartz-poor arkose in the coarse, conglomeratic Sangre de Cristo Formation is the product of rapid uplift and erosion.

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