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USGS2012

Modeling groundwater flow and quality

In most areas, rocks in the subsurface are saturated with water at relatively shallow depths. The top of the saturated zone—the water table—typically occurs anywhere from just below land surface to hundreds of feet below the land surface. Groundwater generally fills all pore spaces below the water table and is part of a continuous dynamic flow system, in which the fluid is moving at velocities ranging from feet per millennia to feet per day (Fig. 33.1). While the water is in close contact with the surfaces of various minerals in the rock material, geochemical interactions between the water and the rock can affect the chemical quality of the water, including pH, dissolved solids composition, and trace-elements content. Thus, flowing groundwater is a major mechanism for the transport of chemicals from buried rocks to the accessible environment, as well as a major pathway from rocks to human exposure and consumption. Because the mineral composition of rocks is highly variable, as is the solubility of various minerals, the human-health effects of groundwater consumption will be highly variable.

Book chapter↗

USGS2008

Characteristics, extent and origin of hydrothermal alteration at Mount Rainier Volcano, Cascades Arc, USA: Implications for debris-flow hazards and mineral deposits

Hydrothermal alteration at Mount Rainier waxed and waned over the 500,000-year episodic growth of the edifice. Hydrothermal minerals and their stable-isotope compositions in samples collected from outcrop and as clasts from Holocene debris-flow deposits identify three distinct hypogene argillic/advanced argillic hydrothermal environments: magmatic-hydrothermal, steam-heated, and magmatic steam (fumarolic), with minor superimposed supergene alteration. The 3.8 km 3 Osceola Mudflow (5600 y BP) and coeval phreatomagmatic F tephra contain the highest temperature and most deeply formed hydrothermal minerals. Relatively deeply formed magmatic-hydrothermal alteration minerals and associations in clasts include quartz (residual silica), quartz–alunite, quartz–topaz, quartz–pyrophyllite, quartz–dickite/kaolinite, and quartz–illite (all with pyrite). Clasts of smectite–pyrite and steam-heated opal–alunite–kaolinite are also common in the Osceola Mudflow. In contrast, the Paradise lahar, formed by collapse of the summit or near-summit of the edifice at about the same time, contains only smectite–pyrite and near-surface steam-heated and fumarolic alteration minerals. Younger debris-flow deposits on the west side of the volcano (Round Pass and distal Electron Mudflows) contain only low-temperature smectite–pyrite assemblages, whereas the proximal Electron Mudflow and a < 100 y BP rock avalanche on Tahoma Glacier also contain magmatic-hydrothermal alteration minerals that are exposed in the avalanche headwall of Sunset Amphitheater, reflecting progressive incision into deeper near-conduit alteration products that formed at higher temperatures. The pre-Osceola Mudflow alteration geometry is inferred to have consisted of a narrow feeder zone of intense magmatic-hydrothermal alteration limited to near the conduit of the volcano, which graded outward to more widely distributed, but weak, smectite–pyrite alteration within 1 km of the edifice axis, developed chiefly in porous breccias. The edifice was capped by a steam-heated alteration zone, most of which resulted from condensation of fumarolic vapor and oxidation of H 2 S in the unsaturated zone above the water table. Weakly developed smectite–pyrite alteration extended into the west and east flanks of the edifice, spatially associated with dikes that are localized in those sectors; other edifice flanks lack dikes and associated alteration. The Osceola collapse removed most of the altered core and upper east flank of the volcano, but intensely altered rocks remain on the uppermost west flank. Major conclusions of this study are that: (1) Hydrothermal–mineral assemblages and distributions at Mount Rainier can be understood in the framework of hydrothermal processes and environments developed from studies of ore deposits formed in analogous settings. (2) Frequent eruptions supplied sufficient hot magmatic fluid to alter the upper interior of the volcano hydrothermally, despite the consistently deep (≥ 8 km) magma reservoir which may have precluded formation of economic mineral deposits within or at shallow depths beneath Mount Rainier. The absence of indicator equilibrium alteration-mineral assemblages in the debris flows that effectively expose the volcano to a depth of 1–1.5 km also suggests a low potential for significant high-sulfidation epithermal or porphyry-type mineral deposits at depth. (3) Despite the long and complex history of the volcano, intensely altered collapse-prone rocks were spatially restricted to near the volcano's conduit system and summit, and short distances onto the upper east and west flanks, due to the necessary supply of reactive components carried by ascending magmatic fluids. (4) Intensely altered rocks were removed from the summit, east flank, and edifice interior by the Osceola collapse, but remain on the upper west flank in the Sunset Amphitheater area and present a continuing collapse hazard. (5) Visually conspicuous rocks on the lower east and mid-to-lower west flanks are not intensely altered and probably have not significantly weakened the rock, and thus do not present significant collapse hazards. (6) Alteration developed most intensely within breccia units, because of their high permeability and porosity. Volcanoes with abundant near-conduit upper-edifice breccias are prone to alteration increasing the possibility of collapse, whereas those that are breccia-poor (e.g., massive domes) are less prone to alteration.

Journal of Volcanology and Geothermal Research↗

USGS2021

Zirconium-bearing accessory minerals in UK Paleogene granites: Textural, compositional, and paragenetic relationships

The mineral occurrences, parageneses, textures, and compositions of Zr-bearing accessory minerals in a suite of UK Paleogene granites from Scotland and Northern Ireland are described. Baddeleyite, zirconolite, and zircon, in that sequence, formed in hornblende + biotite granites (type 1) and hedenbergite–fayalite granites (type 2). The peralkaline microgranite (type 3) of Ailsa Craig contains zircon, dalyite, a eudialyte-group mineral, a fibrous phase which is possibly lemoynite, and Zr-bearing aegirine. Hydrothermal zircon is also present in all three granite types and documents the transition from a silicate-melt environment to an incompatible element-rich aqueous-dominated fluid. No textures indicative of inherited zircon were observed. The minerals crystallized in stages from magmatic through late-magmatic to hydrothermal. The zirconolite and eudialyte-group mineral are notably Y + REE-rich (REE signifies rare earth element). The crystallization sequence of the minerals may have been related to the activities of Si and Ca, to melt peralkalinity, and to local disequilibrium.

European Journal of Mineralogy↗

USGS2007

Geological assessment of cores from the Great Bay National Wildlife Refuge, New Hampshire

Geological sources of metals (especially arsenic and zinc) in aquifer bedrock were evaluated for their potential to contribute elevated values of metals to ground and surface waters in and around Rockingham County, New Hampshire. Ayotte and others (1999, 2003) had proposed that arsenic concentrations in ground water flowing through bedrock aquifers in eastern New England were elevated as a result of interaction with rocks. Specifically in southeastern New Hampshire, Montgomery and others (2003) established that nearly one-fifth of private bedrock wells had arsenic concentrations that exceed the U.S. Environmental Protection Agency (EPA) maximum contamination level for public water supplies. Two wells drilled in coastal New Hampshire were sited to intersect metasedimentary and metavolcanic rocks in the Great Bay National Wildlife Refuge. Bulk chemistry, mineralogy, and mineral chemistry data were obtained on representative samples of cores extracted from the two boreholes in the Kittery and Eliot Formations. The results of this study have established that the primary geologic source of arsenic in ground waters sampled from the two well sites was iron-sulfide minerals, predominantly arsenic-bearing pyrite and lesser amounts of base-metal-sulfide and sulfosalt minerals that contain appreciable arsenic, including arsenopyrite, tetrahedrite, and cobaltite. Secondary minerals containing arsenic are apparently limited to iron-oxyhydroxide minerals. The geologic source of zinc was sphalerite, typically cadmium-bearing, which occurs with pyrite in core samples. Zinc also occurred as a secondary mineral in carbonate form. Oxidation of sulfides leading to the liberation of acid, iron, arsenic, zinc, and other metals was most prevalent in open fractures and vuggy zones in core intervals containing zones of high transmissivity in the two units. The presence of significant calcite and lesser amounts of other acid-neutralizing carbonate and silicate minerals, acting as a natural buffer to reduce acidity, forced precipitation of iron-oxyhydroxide minerals and the removal of trace elements, including arsenic and lead, from ground waters in the refuge. Zinc may have remained in solution to a greater extent because of complexing with carbonate and its solubility in near-neutral ground and surface waters. The regional link between anomalously high arsenic contents in ground water and a bedrock source as established by Ayotte and others (1999, 2003) and Montgomery and others (2003) was confirmed by the presence of some arsenic-bearing minerals in rocks of the Kittery and Eliot Formations. The relatively low amounts of arsenic and metals in wells in the Great Bay National Wildlife Refuge as reported by Ayotte and others (U.S. Geological Survey Water Resources Data, 2005) were likely controlled by local geochemical environments in partially filled fractures, fissures, and permeable zones within the bedrock formations. Carbonate and silicate gangue minerals that line fractures, fissures, and permeable zones likely limited the movement of arsenic from bedrock to ground water. Sources other than the two geologic formations might have been required to account for anomalously high arsenic contents measured in private bedrock aquifer wells of Rockingham County.

New Hampshire↗

USGS1969

The geographic applications program of the U. S. Geological Survey

The fundamental objective of modern Geography is to improve man's level of living through a better understanding of man-environment inter actions. Related goals of the USGS program for applications of remote sensor data to Geographical research are: (1) the analysis and improvement of land use, with special emphasis on urban problems; and (2) more effective use of the total available energy budget, including insolation, mineral fuels, atomic energy, human resources, and mental energy, all of which are integrated into man-environment interactions. The collection of data through remote sensors in air craft and spacecraft is financed largely by funds from NASA, and is part of the much broader EROS Program of the Department of the Interior. Results to date have achieved much toward the identification of remote sensor signatures for Earth features and human activities, and toward evaluation of instruments for collecting essential information.

Photogrammetric Engineering↗

USGS1963

Geology of the Anlauf and Drain quadrangles, Douglas and Lane counties, Oregon

The Anlauf and Drain quadrangles, Oregon, lie about 20 miles south of the City of Eugene, in Douglas and Lane Counties. They constitute an area of about 435 square miles that includes parts of both the Cascade Range and Coast Range physiographic provinces. A sequence of lower Tertiary sedimentary and volcanic rocks with a maximum thickness of about 20,000 feet is exposed in the area. The oldest part of this sequence is the Umpqua formation of early Eocene age consisting of a lower Member of vesicular and amygdaloidal olivine basalt flows, a middle member of water-laid vitric and lapilli crystal tuff, and an upper member of interbedded fissile siltstone and basaltic sandstone which contains a 300-foot tongue of massive to thick-bedded basaltic sandstone near its top. These rocks are predominantly of marine origin, although the general absence of pillow structures Which are common in basaltic lavas of equivalent age elsewhere in the Coast Ranges suggests that some of the flows were poured out subaerially. The overlying tuff member, however, contains Foraminifera and in places has a lime content slightly in excess of 10 percent. Mollusca and Foraminifera indicate that the Umpqua formation is of early Eocene age and is a correlative of the Capay formation of California. The Tyee formation of middle Eocene age overlies the Umpqua formation and consists of more than 5,000 feet of rhythmically deposited sandstone and siltstone in beds 2 to 30 feet thick. The basal part of each bed consists of medium- to coarse-grained sandstone that grades upward into line-grained sandstone and siltstone. The principal constituents of the sandstone are quartz, partly altered feldspar, mica, clay, and fragments of basalt, fine-grained argillaceous rocks, and mica schist. Other detrital minerals include epidote, garnet, blue-green hornblende, tourmaline, and zoisite. The depositional environment of the Tyee formation is poorly known, although the rhythmic-graded bedding suggests turbidity currents. About 500 feet of sandstone and siltstone assigned to the Spencer formation of late Eocene age unconformably overlies the Tyee formation. The Spencer formation, better exposed in the east-central part of the Coast Ranges, contains marine fossils but also has thin impure coal beds, indicative of strand-line accumulation. The sandstone in the Spencer formation is very similar to that in the Tyee formation, from which it was probably derived. The Fisher formation contains about 5,500 feet of nonmarine pyroclastic and Volcanic rocks that are related to the volcanic rock sequences of the western Cascade Range. The formation is characterized by a wide variety of rock types, including conglomerate, tuffaceous sandstone and siltstone, vitric and crystal tuff, waterlaid and mudflow breccia, and andesitic lava flows. These rocks generally occur in lenticular beds that have little stratigraphic significance. The rocks apparently accumulated on a plain slightly above sea level that was subjected alternately to flooding by running water and to desiccation. Fossil leaves from the lowermost part of the Fisher formation are of late Eocene age; the upper part of the formation is of early, and possibly middle, Oligocene age. A few exposures of olivine basalt were mapped in the extreme northern part of the Anlauf quadrangle. The flows, more extensively exposed to the north, overlie the Fisher formation, and, therefore, are tentatively considered to be post-Oligocene in age. All these stratigraphic units, but principally the Fisher formation, are cut by dikes, sills, and stocklike bodies of porphyritic basalt, diabase, and norite. Contemporaneously with the emplacement of most of these rocks, in late Miocene(?) time, hydrothermal solutions locally altered the sedimentary and extrusive igneous rocks and deposited cinnabar and other sulfide minerals, carbonates, and silica. Three parallel northeastward-trending anticlines in the older marine rocks are the most conspicuous structural features in the area. These folds plunge both to the northeast and southwest and expose in their central parts basalt flows of the Umpqua formation. The rocks along the west margin of the area dip westward into a structural basin in the adjacent Elkton quadrangle, whereas to the east the Fisher formation generally has an easterly dip typical of the nonmarine rocks in the western Cascade Range. Geologic studies in the Anlauf and Drain quadrangles were undertaken principally to evaluate the petroleum possibilities of the area. Available data indicate that source beds and reservoir rock suitable for the formation and accumulation of petroleum are absent in this part of the Coast Ranges, but because of the lack of subsurface information, this evaluation is only tentative. Mineral deposits of economic value in the area include quicksilver and alumina clay.

Oregon↗

USGS1963

Geology of the Anlauf and Drain Quadrangles, Douglas and Lane Counties, Oregon

The Anlauf and Drain quadrangles, Oregon, lie about 20 miles south of the city of Eugene, in Douglas and Lane Counties. They constitute an area of about 435 square miles that includes parts of both the Cascade Range and Coast Range physiographic provinces. A sequence of lower Tertiary sedimentary and volcanic rocks with a maximum thickness of about 20,000 feet is exposed in the area. The oldest part of this sequence is the Umpqua formation of early Eocene age consisting of a lower member of vesicular and amygdaloidal olivine basalt flows, a middle member of water-laid vitric and lapilli crystal tuff, and an upper member of interbedded fissile siltstone and basaltic sandstone which contains a 300-foot tongue of massive to thick-bedded basaltic sandstone near its top. These rocks are predominantly of marine origin, although the general absence of pillow structures which are common in basaltic lavas of equivalent age elsewhere in the Coast Ranges suggests that some of the flows were poured out subaerially. The overlying tuff member, however, contains Foraminifera and in places has a lime content slightly in excess of 10 percent. Mollusca and Foraminifera indicate that the Umpqua formation is of early Eocene age and is a correlative of the Capay formation of California. The Tyee formation of middle Eocene age overlies the Umpqua formation and consists of more than 5,000 feet of rhythmically deposited sandstone and siltstone in beds 2 to 30 feet thick. The basal part of each bed consists of medium- to coarse-grained sandstone that grades upward into fine-grained sand- stone and siltstone. The principal constituents of the sandstone are quartz, partly a1tered feldspar, mica, clay, and fragments of basalt, fine-grained argillaceous rocks, and mica schist. Other detrital minerals include epidote, garnet, blue-green hornblende, tourmaline, and zoisite. The depositional environment of the Tyee formation is poorly known, although the rhythmic-graded bedding suggests turbidity currents. About 500 feet of sandstone and siltstone assigned to the Spencer formation of late Eocene age unconformably overlies the Tyee formation. The Spencer formation, better exposed in the east-central part of the Coast Ranges, contains marine fossils but also has thin impure coal beds, indicative of strand-line accumulation. The sandstone in the Spencer formation is very similar to that in the Tyee formation, from which it was probably derived. The Fisher formation contains about 5,500 feet of nonmarine pyroclastic and volcanic rocks that are related to the volcanic rock sequences of the western Cascade Range. The formation is characterized by a wide variety of rock types, including conglomerate, tuffaceous sandstone and siltstone, vitric and crystal tuff, waterlaid and mudflow breccia, and andesitic lava flows. These rocks gen- erally occur in lenticular beds that have little stratigraphic significance. The rocks apparently accumulated on a plain slightly above sea level that was subjected alternately to fiooding by running water and to desiccation. Fossil leaves from the lowermost part of the Fisher formation are of late Eocene age; the upper part of the formation is of early, and possibly niiddle, Oligocene age. A few exposures of olivine basalt were mapped in the extreme northern part of the Anlauf quadrangle. The flows, more extensively exposed to the north, overlie the Fisher formation, and, therefore, are tentatively considered to be post-Oligocene in age. All these stratigraphic units, but principally the Fisher formation, are cut by dikes, sills, and stocklike bodies of 'porphyritic basalt, diabase, and norite. Contemporaneously with the emplacement of most of these rocks, in late Miocene (?) time, hydrothermal solutions locailly altered the sedimentary and extrusive igneous racks and deposited cinnabar and other sulfide minerals, carbonates, and silica. Three parallel nartheastward-trending

Bulletin↗

USGS1992

Predicting sizes of undiscovered mineral deposits; an example using mercury deposits in California

A critical part of the exploration for mineral deposits or of quantitative mineral resource assessments is the estimation of how large undiscoveredeposits might be. Typically, this problem is addressed using grade and tonnage models in which a major source of variation in possible sizes is accounted for by the differences in types of deposits (Cox and Singer, 1986; Mosier and Page, 1988; Bliss, 1992). It is clear from studies of petroleum exploration that larger oil fields tend to be found early in the process (Arps and Roberts, 1958). If the same behavior exists in mineral exploration, then tonnage models constructed from local data may be biased estimators of the tonnages of any remaining undiscoveredeposits in the area. Although Singer and Mosier (1981) showed that larger porphyry copper deposits should be found earlier than smaller deposits in a given geologic and exploration environment, there are no definitive studies that we could find which actually test the hypothesis that larger mineral deposits are discovered early in the exploration of a region. In this paper the hypothesis that larger mineral deposits are discovered early in the exploration of a region is tested by examining the relationship between discovery order and size of known mercury deposits in the California Coast Ranges. We then present a new maximum likelihood approach to modeling the size distribution of undiscovered mineral deposits by examining the sizes of the mercury deposits discovered early in the exploration process.

Economic Geology↗

USGS1996

Iron and manganese oxide mineralization in the Pacific

Iron, manganese, and iron-manganese deposits occur in nearly all geomorphologic and tectonic environments in the ocean basins and form by one or more of four processes: (1) hydrogenetic precipitation from cold ambient seawater, (2) precipitation from hydrothermal fluids, (3) precipitation from sediment pore waters that have been modified from bottom water compositions by diagenetic reactions in the sediment column and (4) replacement of rocks and sediment. Iron and manganese deposits occur in five forms: nodules, crusts, cements, mounds and sediment-hosted stratabound layers. Seafloor oxides show a wide range of compositions from nearly pure iron to nearly pure manganese end members. Fe/Mn ratios vary from about 24 000 (up to 58% elemental Fe) for hydrothermal seamount ironstones to about 0.001 (up to 52% Mn) for hydrothermal stratabound manganese oxides from active volcanic arcs. Hydrogenetic Fe-Mn crusts that occur on most seamounts in the ocean basins have a mean Fe/Mn ratio of 0.7 for open-ocean seamount crusts and 1.2 for continental margin seamount crusts. Fe-Mn nodules of potential economic interest from the Clarion-Clipperton Zone have a mean Fe/Mn ratio of 0.3, whereas the mean ratio for nodules from elsewhere in the Pacific is about 0.7. Crusts are enriched in Co, Ni and Pt and nodules in Cu and Ni, and both have significant concentrations of Pb, Zn, Ba, Mo, V and other elements. In contrast, hydrothermal deposits commonly contain only minor trace metal contents, although there are many exceptions, for example, with Ni contents up to 0.66%, Cr to 1.2%, and Zn to 1.4%. Chondrite-normalized REE patterns generally show a positive Ce anomaly and abundant ΣREEs for hydrogenetic and mixed hydrogenetic-diagenetic deposits, whereas the Ce anomaly is negative for hydrothermal deposits and ΣREE contents are low. However, the Ce anomaly in crusts may vary from strongly positive in East Pacific crusts to slightly negative in West Pacific crusts, which may reflect the redox conditions of seawater. The concentration of elements in hydrogenetic Fe-Mn crusts depends on a wide variety of water column and crust surface characteristics, whereas concentration of elements in hydrothermal oxide deposits depends of the intensity of leaching, rock types leached, and precipitation of sulphides at depth in the hydrothermal system.

Geological Society Special Publication↗

USGS2005

Origin of secondary sulfate minerals on active andesitic stratovolcanoes

Sulfate minerals in altered rocks on the upper flanks and summits of active andesitic stratovolcanoes result from multiple processes. The origin of these sulfates at five active volcanoes, Citlalte??petl (Mexico), and Mount Adams, Hood, Rainier, and Shasta (Cascade Range, USA), was investigated using field observations, petrography, mineralogy, chemical modeling, and stable-isotope data. The four general groups of sulfate minerals identified are: (1) alunite group, (2) jarosite group, (3) readily soluble Fe- and Al-hydroxysulfates, and (4) simple alkaline-earth sulfates such as anhydrite, gypsum, and barite. Generalized assemblages of spatially associated secondary minerals were recognized: (1) alunite+silica??pyrite??kaolinite?? gypsum??sulfur, (2) jarosite+alunite+silica; (3) jarosite+smectite+silica??pyrite, (4) Fe- and Al-hydroxysulfates+silica, and (5) simple sulfates+silica??Al-hydroxysulfates??alunite. Isotopic data verify that all sulfate and sulfide minerals and their associated alteration assemblages result largely from the introduction of sulfur-bearing magmatic gases into meteoric water in the upper levels of the volcanoes. The sulfur and oxygen isotopic data for all minerals indicate the general mixing of aqueous sulfate derived from deep (largely disproportionation of SO2 in magmatic vapor) and shallow (oxidation of pyrite or H2S) sources. The hydrogen and oxygen isotopic data of alunite indicate the mixing of magmatic and meteoric fluids. Some alunite-group minerals, along with kaolinite, formed from sulfuric acid created by the disproportionation of SO2 in a condensing magmatic vapor. Such alunite, observed only in those volcanoes whose interiors are exposed by erosion or edifice collapse, may have ??34S values that reflect equilibrium (350??50 ??C) between aqueous sulfate and H2S. Alunite with ??34S values indicating disequilibrium between parent aqueous sulfate and H2S may form from aqueous sulfate created in higher level low-temperature environments in which SO2 is scrubbed out by groundwater or where H2S is oxidized. Jarosite-group minerals associated with smectite in only slightly altered volcanic rock are formed largely from aqueous sulfate derived from supergene oxidation of hydrothermal pyrite above the water table. Soluble Al- and Fehydroxysulfates form in low-pH surface environments, especially around fumaroles, and from the oxidation of hydrothermal pyrite. Anhydrite/gypsum, often associated with native sulfur and occasionally with small amounts of barite, also commonly form around fumaroles. Some occurrences of anhydrite/gypsum may be secondary, derived from the dissolution and reprecipitation of soluble sulfate. Edifice collapse may also reveal deep veins of anhydrite/gypsum??barite that formed from the mixing of saline fluids with magmatic sulfate and dilute meteoric water. Alteration along structures associated with both hydrothermal and supergene sulfates, as well as the position of paleo-water tables, may be important factors in edifice collapse and resulting debris flows at some volcanoes. ?? 2004 Elsevier B.V. All rights reserved.

Chemical Geology↗

USGS1967

Shock effects in certain rock-forming minerals

Shock effects in quartz, plagioclase, biotite, amphibole, and some accessory minerals have been observed in rocks subjected to various degrees of meta morphism by meteoritic impact. The shock features described are unique; they are never observed in rocks from normal geologic environments. Such features are described: 1) Multiple sets of closely spaced planar microstructures occur in quartz, plagioclase, and other rock-forming minerals. Those characteristic of shock consist of alternating platelets, with a range of reduced mean index of re fraction and birefringence; they con sist of platelets that have been partially or completely transformed to an amor phous phase. 2) Quartz and plagioclase are selec tively and completely transformed to silica glass and plagioclase glass in the solid state, whereas the associated mafic minerals remained crystalline. There is no reaction between adjacent minerals. 3) High-pressure polymorphs occur, such as coesite or stishovite. Coesite oc Curs exclusively within silica glass; it has not been observed as a reaction or breakdown product. 4) Nickel-iron spherules occur in the fused glass or impactites. 5) The occurrence of droplets of ilmenite, rutile, pseudobrookite, and baddaleyite in impactites indicates a temperature of formation exceeding 150°C. 6) Dense glass occurs, similar in composition to bulk rock, in which iron oxide, such as fine particles of mag netite, is completely dissolved. All these features are characteristic of a process involving the rapid rise and fall of extremiiely high pressures and temperatures. Minerals and mineral as semblages experiencing such high strain rates and sudden changes of pressures and temperatures react and change in dependently to the bulk chemical com position, under nonequilibrium condi tions. Many aspects of shock features re quire careful study. Kink bands in biotite and deformation lamellae in quartz occur in tectonically deformed rocks. These features should be studied with great care in order to determine whether reduction in mean index of refraction and total birefringence along the planar structures have resulted from vitrification or phase transition; their presence is additional evidence in favor of a shock mechanism. Vitreous phases or glasses formed by shock also have many unique prop erties; they have not been studied by such methods as thermoluminescence, electron spin resonance, low-angle x ray diffraction, or infrared spectroscopy. Shock-fused glass of high density needs to be studied in detail in carefully con trolled laboratory conditions. Experimental shock-wave studies of the equation-of-state of single minerals and mineral assemblages, under care fully controlled conditions, must pre cede estimates of peak pressures and peak and residual temperatures of shocked natural mineral assemblages. Detailed petrographic and mineralogic studies, however, have provided useful and definitive criteria for characteriza tion of impact events. Such data should be of paramount importance in the study of samples brought back from Moon.

Science↗

USGS1982

The depositional environment and petrology of the White Rim Sandstone Member of the Permian Cutler Formation, Canyonlands National Park, Utah

The White Rim Sandstone Member of the Cutler Formation of Permian age in Canyonlands National Park, Utah, was deposited in coastal eolian and associated interdune environments. This conclusion is based on stratigraphic relationships primary sedimentary structures, and petrologic features. The White Rim consists of two major genetic units. The first represents a coastal dune field and the second represents related interdune ponds. Distinctive sedimentary structures of the coastal dune unit include large- to medium-scale, unidirectional, tabular-planar cross-bedding; high-index ripples oriented parallel to dip direction of the foresets; coarse-grained lag layers; avalanche or slump marks; and raindrop impressions. Cross-bedding measurements suggest the dunes were deposited as transverse ridges by a dominantly northwest to southeast wind. Distinctive sedimentary structures of the interdune pond unit include wavy, horizontally laminated bedding, adhesion ripples, and desiccation polygons. These features may have been produced by alternate wetting and drying of sediment during water-table fluctuations. Evidence of bioturbation is also present in this unit. Petrologic characteristics of the White Rim helped to define the depositional environment as coastal. A crinoid fragment was identified at one location; both units are enriched in heavy minerals, and small amounts of well rounded, reworked glauconite were found in the White Rim throughout the study area. Earlier work indicates that the White Rim sandstone is late Wolfcampian to early Leonardian in age. During this time, the Canyonlands area was located in a depositional area alternately dominated by marine and nonmarine environments. Results of this study suggest the White Rim represents a coastal dune field that was deposited by predominantly on-shore winds during a period of marine transgression.

Open-File Report↗

USGS2017

Sedimentology, sequence-stratigraphy, and geochemical variations in the Mesoproterozoic Nonesuch Formation, northern Wisconsin, USA

We use core descriptions and portable X-ray fluorescence analyses to identify lithofacies and stratigraphic surfaces for the Mesoproterozoic Nonesuch Formation within the Ashland syncline, Wisconsin. We group lithofacies into facies associations and construct a sequence stratigraphic framework based on lithofacies stacking and stratigraphic surfaces. The fluvial-alluvial facies association (upper Copper Harbor Conglomerate) is overlain across a transgressive surface by the fluctuating-profundal facies association (lower Nonesuch Formation). The fluctuating-profundal facies association comprises a retrogradational sequence set overlain across a maximum flooding surface by an aggradational-progradational sequence set comprising fluctuating-profundal, fluvial-lacustrine, and fluvial-alluvial facies associations (middle Nonesuch through lower Freda Formations). Lithogeochemistry supports sedimentologic and stratigraphic interpretations. Fe/S molar ratios reflect the oxidation state of the lithofacies; values are most depleted above the maximum flooding surface where lithofacies are chemically reduced and are greatest in the chemically oxidized lithofacies. Si/Al and Zr/Al molar ratios reflect the relative abundance of detrital heavy minerals vs. clay minerals; greater values correlate with larger grain size. Vertical facies association stacking records depositional environments that evolved from fluvial and alluvial, to balanced-fill lake, to overfilled lake, and returning to fluvial and alluvial. Elsewhere in the basin, where accommodation was greatest, some volume of fluvial-lacustrine facies is likely present below the transgressive stratigraphic surface. This succession of continental and lake-basin types indicates a predominant tectonic driver of basin evolution. Lithofacies distribution and geochemistry indicate deposition within an asymmetric half-graben bounded on the east by a west-dipping growth fault. While facies assemblages are lacustrine and continental, periodic marine incursions are probable, especially across maximum transgressive surfaces. We demonstrate a sequence-stratigraphic approach may be applied to fine-grained Precambrian sediments using traditional rock description and supporting lithogeochemistry. Identification of a characteristic lithofacies succession in Mesoproterozoic sediments demonstrates fundamental controls commonly interpreted for Phanerozoic lake systems may be extended into the Precambrian. These controls result in a predictable association of lithofacies, with distinct physical, biological, and geochemical properties. This has regional significance for carbon sequestration and the distribution of mineral and hydrocarbon resources and broader significance for addressing Mesoproterozoic paleogeographic reconstructions and questions related to the evolution of terrestrial life.

Wisconsin↗

USGS1989

Geochemistry of intrusive rocks associated with the Latir volcanic field, New Mexico, and contrasts between evolution of plutonic and volcanic rocks

Plutonic rocks associated with the Latir volcanic field comprise three groups: 1) ???25 Ma high-level resurgent plutons composed of monzogranite and silicic metaluminous and peralkaline granite, 2) 23-25 Ma syenogranite, and alkali-feldspar granite intrusions emplaced along the southern caldera margin, and 3) 19-23 Ma granodiorite and granite plutons emplaced south of the caldera. Major-element compositions of both extrusive and intrusive suites in the Latir field are broadly similar; both suites include high-SiO2 rocks with low Ba and Sr, and high Rb, Nb, Th, and U contents. Moreover, both intermediateto siliciccomposition volcanic and plutonic rocks contain abundant accessory sphene and apatite, rich in rare-earth elements (REE), as well as phases in which REE's are essential components. Strong depletion in Y and REE contents, with increasing SiO2 content, in the plutonic rocks indicate a major role for accessory mineral fractionation that is not observed in volcanic rocks of equivalent composition. Considerations of the rheology of granitic magma suggest that accessory-mineral fractionation may occur primarily by filter-pressing evolved magmas from crystal-rich melts. More limited accessory-mineral crystallization and fractionation during evolution of the volcanic magmas may have resulted from markedly lower diffusivities of essential trace elements than major elements. Accessory-mineral fractionation probably becomes most significant at high crystallinities. The contrast in crystallization environments postulated for the extrusive and intrusive rocks may be common to other magmatic systems; the effects are particularly pronounced in highly evolved rocks of the Latir field. High-SiO2 peralkaline porphyry emplaced during resurgence of the Questa caldera represents non-erupted portions of the magma that produced the Amalia Tuff during caldera-forming eruption. The peralkaline porphyry continues compositional and mineralogical trends found in the tuff. Amphibole, mica, and sphene compositions suggest that the peralkaline magma evolved from metaluminous magma. Extensive feldspar fractionation occurred during evolution of the peralkaline magmas, but additional alkali and iron enrichment was likely a result of high halogen fluxes from crystallizing plutons and basaltic magmas at depth. ?? 1989 Springer-Verlag.

Contributions to Mineralogy and Petrology↗

USGS1990

A comparison of geochemical exploration techniques and sample media within accretionary continental margins: an example from the Pacific Border Ranges, Southern Alaska, U.S.A.

The Pacific Border Ranges of the southern Alaskan Cordillera are composed of a number of allochthonous tectonostratigraphic terranes. Within these terranes are widespread volcanogenic, massive sulfide deposits in and adjacent to portions of accreted ophiolite complexes, bands and disseminations of chromite in accreted island-arc ultramafic rocks, and epigenetic, gold-bearing quartz veins in metamorphosed turbidite sequences. A geochemical pilot study was undertaken to determine the most efficient exploration strategy for locating these types of mineral deposits within the Pacific Border Ranges and other typical convergent continental margin environments. High-density sediment sampling was carried out in first- and second-order stream channels surrounding typical gold, chromite and massive sulfide occurrences. At each site, a stream-sediment and a panned-concentrate sample were collected. In the laboratory, the stream sediments were sieved into coarse-sand, fine- to medium-sand, and silt- to clay-size fractions prior to analysis. One split of the panned concentrates was retained for analysis; a second split was further concentrated by gravity separation in heavy liquids and then divided into magnetic, weakly magnetic and nonmagnetic fractions for analysis. A number of different techniques including atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry and semi-quantitative emission spectrography were used to analyze the various sample media. Comparison of the various types of sample media shows that in this tectonic environment it is most efficient to include a silt- to clay-size sediment fraction and a panned-concentrate sample. Even with the relatively low detection limits for many elements by plasma spectrometry and atomic absorption spectrometry, anomalies reflecting the presence of gold veins could not be identified in any of the stream-sediment fractions. Unseparated panned-concentrate samples should be analyzed by emission spectroscopy and atomic absorption spectrometry for Ag and Au. If, however, magnetic and nonmagnetic concentrate fractions are used in a reconnaissance program, semiquantitative emission spectrography is adequate for all analytical work.

Journal of Geochemical Exploration↗

USGS2021

Zircon surface crystallization ages for the extremely reduced magmatic products of the Millennium Eruption, Changbaishan Volcano (China/North Korea)

The Millennium Eruption (ME) of Changbaishan volcano (Baitoushan, Paektu) at 946 CE (Common Era) is one of the largest explosive eruptions on Earth during Holocene times. We date unpolished zircon crystal faces from diverse ME products collected from the southern side of Changbaishan volcano where the ME pumice and welded and non-welded pyroclastic flow deposits (PFD) are better exposed. All zircons from a pumice sample of the southern caldera rim and the youngest (Group 1) zircons from a welded pumiceous PFD sample yield an isochron crystallization age of 0.7 ± 1.8 ka (2σ). Zircons from the welded pumiceous PFD sample yield additional two age groups at ~10 ka and ~ 100 ka. Zircons from a non-welded charcoal-containing PFD have only one age population at 100 ka. Our work shows that different eruption products from ME have different zircon surface age distributions and may tap different levels of a zoned felsic magma chamber. In addition, the results indicate that ion microprobe U-Th dating of zircon crystal surfaces from ME pumices can effectively date the Millennium eruption age. Previously reported zircon U-series ages for Qixangzhan eruption (12.2 ± 1.1 ka, 2σ) and Yuanchi eruption (7.3 ± 1.8 ka, 2σ) at Changbaishan are also likely to date their respective eruption ages. The occurrence of 100 ka zircons in welded and non-welded PFDs reveals an important magmatic event for the Changbaishan volcano. Zircon and Fe-rich clinopyroxene crystallized at similar temperature at 770–750 °C, indicative of early zircon crystallization in peralkaline magmas. Another important result is the extremely low oxygen fugacity (fO 2 = ΔFMQ-2) of the Changbaishan samples. Minerals in ME magmas were crystallized under some of the most reducing magmatic environments on Earth. Highly reducing conditions of magmas from Changbaishan supports a continental rift setting and argues against significant involvements of subduction-related oxidizing fluids during magma genesis.

Changbaishan Volcano↗

USGS1985

Mission, goals, and authorities of the U.S. Geological Survey, June 1985

We live in a society which depends on natural resources. Our high standard of living requires use of the land, water, and mineral endowment of the Earth. In using these resources, we may affect our environment and alter our options for land and resource use in the future. How can we ensure an adequate supply of this natural wealth in the future? In what ways are we irreversibly altering our natural environment? How can we avoid undesirable or unacceptable side effects of man's use of the land and prevent or mitigate earth-related hazards? To respond to these and other similar questions, knowledge about the Earth, its structure, its resources, and its dynamics is essential.

Report↗

USGS2025

Critical Minerals in Ores (CMiO) database

Critical minerals are commodities essential to modern industrial and strategic technologies and are highly vulnerable to supply chain disruption. The Critical Minerals Mapping Initiative (CMMI) is a collaboration among the U.S. Geological Survey (USGS), the Geological Survey of Canada, and Geoscience Australia that aims to deepen global understanding of where critical minerals are located. A key output of this initiative is the Critical Minerals in Ores (CMiO) database that is advancing our collective understanding of critical minerals distributions. For instance, publicly available data on the concentrations of many critical minerals are sparse because these commodities can only be produced in small, yet essential, quantities compared to the primary commodities like copper and zinc. The CMiO database helps bridge this gap by offering high-quality, multielement geochemical data from a wide variety of critical mineral-bearing deposits around the world. Importantly, it uses a novel consensus deposit environment, group, and type classification scheme developed by the agencies that allows comparisons among ore deposits from different regions. The CMiO database contains geochemical data for more than 20,000 samples from more than 100 deposit types comprising 10 deposit environments.

Fact Sheet↗