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USGS1971

Fluid inclusion studies on the porphyry-type ore deposits at Bingham, Utah, Butte, Montana, and Climax, Colorado

Data are given on the composition, temperature, pressure, and density of the hydrothermal fluids present in the central Cu-Mo core of the deposit at Bingham, Utah, and in its related but not necessarily coeval peripheral Pb-Zn deposits. These data are based on a study of primary and secondary fluid inclusions in transparent ore and gangue minerals that included the use of freezing, heating, and crushing microscope stages. The composition of the hydrothermal fluids at various stages in the mineralization and repeated later fracturing and rehealing ranged from nearly fresh water to water containing more than 60 weight percent salts in solution--virtually a hydrous saline melt--in some quartz-molybdenite-chalcopyrite veins from the core. Most of these salts have crystallized out as daughter minerals on cooling, forming major amounts of halite and sylvite and minor amounts of anhydrite (?), hematite (?) and several unidentified phases. These highly saline fluids occur only in the core. Some of them have apparently boiled, forming bubbles of a relatively low density CO 2 -rich "steam" containing only a few percent NaCl. These low-density fluids have also been trapped as inclusions. The fluids that formed the peripheral deposits had low salinities, and some of these also have apparently boiled. A few were very high in hydrogen sulfide. Inclusions from a quartz pod and in the quartz-molybdenite-chalcopyrite veins from the core yield the highest temperatures, 640 ° -725 ° C; most inclusions from the core homogenize at temperatures above 400 ° C. Samples from the peripheral deposits were uniformly lower, in the range 294 ° -330 ° C. The abundant evidence of intermittent boiling of these solutions is important because it places limits on the pressure at the time of trapping, it results in there being little or no need for a pressure correction to the homogenization temperatures, and it indicates that the pressure has varied with time. Although some of the homogenization temperatures are very high, the high salinity causes the vapor pressures at homogenization to be relatively low, from about 80 to a maximum of about 1,100 atmospheres. The density of the hydrothermal fluids is of great concern in any consideration of flow patterns, and particularly in the inevitable mixing with possibly heated ground waters. Steam inclusions from the core had gross densities of 0.3 to 0.1 g · cm -3 , but many of the highly saline inclusions in the core contain fluids whose density at trapping was as high as 1.3 g · cm -3 . The fluids trapped in inclusions in the peripheral deposits had densities of 0.75-0.95 g · cm -3 , well below that of the surrounding cold ground water. Hydraulic pressure gradients from these density differences, and the vapor pressures involved, must also have varied with time in any given location, particularly when boiling occurred, and thus the circulation patterns could have been very complex. The more highly saline fluids are believed to be of truly magmatic origin, and not merely heated ground water from the area at the time of the intrusion. The great abundance throughout the core of planes of secondary inclusions in which individual planes are uniform but adjacent planes have widely varying composition, density, and homogenization temperature, is evidence of thorough and repeated fracturing of these rocks under hydrothermal conditions. Inclusions were also examined in some samples from Butte, Montana, Climax, Colorado, and several Arizona porphyry copper deposits. The ranges of temperature, composition, and density found were similar but smaller than at Bingham. This might be simply a result of insufficient sampling.

Arizona, Colorado, Montana, Utah↗

USGS2021

Calcite U-Pb dating unravels the age and hydrothermal history of the giant Shuiyindong Carlin-type gold deposit in the Golden Triangle, south China

The ages of Carlin-type gold deposits in the Golden Triangle of South China have long been questioned due to the general lack of minerals unequivocally linked to gold deposition that can be precisely dated using conventional radiogenic isotope techniques. Recent advances in U-Pb methods show that calcite can be used to constrain the ages of hydrothermal processes, but few studies have been applied to ore deposits. Herein, we show that this approach can be used to constrain the timing of hydrothermal activity that generated and overprinted the giant Shuiyindong Carlin-type gold deposit in the Golden Triangle. Three stages of calcite (Cal-1, Cal-2, and Cal-3) have been recognized in this deposit based on crosscutting relationships, cathodoluminescence colors, and chemical (U, Pb, and rare earth element [REE]) and isotope (C, O, Sr) compositions. Cal-1 is texturally associated with ore-stage jasperoid and disseminated Au-bearing arsenian pyrite in hydrothermally altered carbonate rocks, which suggests it is synmineralization. Cal-2 fills open spaces and has a distinct orange cathodoluminescence, suggesting that it precipitated during a second fluid pulse. Cal-1 and Cal-2 have similar carbonate rock-buffered chemical and isotopic compositions. Cal-3 occurs in veins that often contain realgar and/or orpiment and are chemically (low U, Pb, and REE) and isotopically (higher δ 13 C, lower δ 18 O and Sr i values) distinct from Cal-1 and Cal-2, suggesting that it formed from a third fluid. U-Pb isotope analyses, by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) for U-rich Cal-1 and Cal-2 and by LA-multicollector (MC)-ICP-MS for U-poor Cal-3, yield well-defined age constraints of 204.3 to 202.6, 191.9, and 139.3 to 137.1 Ma for Cal-1, Cal-2, and Cal-3, respectively. These new ages suggest that the Shuiyindong gold deposit formed in the late Triassic and was overprinted by hydrothermal events in the early Jurassic and early Cretaceous. Given the association of Cal-3 with orpiment and realgar, and previous geochronologic studies of several other major gold deposits in the Golden Triangle, we infer that the latest stage of calcite may be associated with an early Cretaceous regional gold metallogenic event. Combined with existing isotopic ages in the region, these new ages lead us to propose that Carlin-type gold deposits in the Golden Triangle formed during two metallogenic episodes in extensional settings, associated with the late Triassic Indochina orogeny and early Cretaceous paleo-Pacific plate subduction. This study shows that the calcite U-Pb method can be used to constrain the timing of Carlin-type gold deposits and successive hydrothermal events.

Golden Triangle, south China↗

USGS2013

The interplay of evolved seawater and magmatic-hydrothermal fluids in the 3.24 Ga panorama volcanic-hosted massive sulfide hydrothermal system, North Pilbara Craton, Western Australia

The ~3240 Ma Panorama volcanic-hosted massive sulfide (VHMS) district is unusual for its high degree of exposure and low degree of postdepositional modification. In addition to typical seafloor VHMS deposits, this district contains greisen- and vein-hosted Mo-Cu-Zn-Sn mineral occurrences that are contemporaneous with VHMS orebodies and are hosted by the Strelley granite complex, which also drove VHMS circulation. Hence the Panorama district is a natural laboratory to investigate the role of magmatic-hydrothermal fluids in VHMS hydrothermal systems. Regional and proximal high-temperature alteration zones in volcanic rocks underlying the VHMS deposits are dominated by chlorite-quartz ± albite assemblages, with lesser low-temperature sericite-quartz ± K-feldspar assemblages. These assemblages are typical of VHMS hydrothermal systems. In contrast, the alteration assemblages associated with granite-hosted greisens and veins include quartz-topaz-muscovite-fluorite and quartz-muscovite (sericite)-chlorite-ankerite. These vein systems generally do not extend into the overlying volcanic pile. Fluid inclusion and stable isotope studies suggest that the greisens were produced by high-temperature (~590°C), high-salinity (38–56 wt % NaCl equiv) fluids with high densities (>1.3 g/cm 3 ) and high δ 18 O (9.3 ± 0.6‰). These fluids are compatible with the measured characteristics of magmatic fluids evolved from the Strelley granite complex. In contrast, fluids in the volcanic pile (including the VHMS ore-forming fluids) were of lower temperature (90°–270°C), lower salinity (5.0–11.2 wt % NaCl equiv), with lower densities (0.88–1.01 g/cm 3 ) and lower δ 18 O (−0.8 ± 2.6‰). These fluids are compatible with evolved Paleoarchean seawater. Fluids that formed the quartz-chalcopyrite-sphalerite-cassiterite veins, which are present within the granite complex near the contact with the volcanic pile, were intermediate in temperature and isotopic composition between the greisen and volcanic pile fluids (T = 240°–315°C; δ 18 O = 4.3 ± 1.5‰) and are interpreted to indicate mixing between the two end-member fluids. Evidence of mixing between evolved seawater and magmatic-hydrothermal fluid within the granite complex, together with the lack of evidence for a magmatic component in fluids from the volcanic pile, suggest partitioning of magmatic-hydrothermal from evolved seawater hydrothermal systems in the Panorama VHMS system. This separation is interpreted to result from either the swamping of a relatively small magmatic-hydro-thermal system by evolved seawater or density contrasts precluding movement of magmatic-hydrothermal fluids into the volcanic pile. Variability in the salinity of fluids in the volcanic pile, combined with evidence for mixing of low- and high-salinity fluids in the massive sulfide lens, is interpreted to indicate that phase separation occurred within the Panorama hydrothermal system. Although we consider this phase separation to have most likely occurred at depth within the system, as has been documented in modern VHMS systems, the data do not allow the location of the inferred phase separation to be determined.

Pilbara↗

USGS1990

Genetic implications of regional and temporal trends in ore fluid geochemistry of Mississippi Valley-type deposits in the Ozark region

Fluids extracted from aqueous fluid inclusions in epigenetic gangue and ore minerals record the migration of huge volumes of highly saline fluids throughout the stratigraphic section of the Ozark region. The extracted fluids share many similarities regionally, but there are significant temporal differences which define two geochemically distinct end-member ore-forming fluids that we refer to as the Viburnum Trend main stage or Viburnum Trend type and the Tri-State type.Viburnum Trend-type fluids are enriched in potassium and are associated only with deposits close to the basal Lamotte Sandstone. The main-stage octahedral galena ore of the Viburnum Trend and much of the Old Lead Belt ore is thought to be derived from this type of ore fluid. Galena deposited by Viburnum Trend-type fluids contains less radiogenic lead than galena deposited by Tri-State-type fluids. Sulfides deposited by Viburnum Trend-type fluids also contain isotopically heavier sulfur and significant amounts of copper, cobalt, nickel, and silver.Tri-State-type fluids have a low potassium content when compared with Viburnum Trend-type fluids and are characteristic of deposits where ore-forming fluids migrated through large volumes of carbonate rock. These fluids are thought to have formed the ore deposits of the Tri-State, Northern Arkansas, and Central Missouri districts, the cubic galena-stage ore of the Viburnum Trend, and the many trace occurrences of sphalerite throughout the Ozark region. Galena deposited by Tri-State-type fluids has more radiogenic lead and the sulfides have isotopically lighter sulfur than sulfides deposited by Viburnum Trend-type fluids. A systematic south to north increase of potassium in the Tri-State-type fluids suggests that they migrated from a southerly source such as the Arkoma basin.Possible explanations for the origins of these two end-member fluids include: (1) a single parent brine evolved into two distinct fluids due to reactions with geochemically distinct aquifers during migration, (2) the two distinct fluids reflect normal fluid evolution within a single source basin of a bittern and of later halite dissolution, and (3) the Viburnum Trend and Tri-State-type brines migrated to southeast Missouri from two different source basins. Our data does not preclude any of these possibilities; however, the geochemical similarity of the Viburnum Trend end-member fluid to a bittern may be accounted for by water-rock modifications of the brine during migration. Other evidence strongly supports a southerly source for the ore-forming brines thus limiting possible sources for the Viburnum Trend-type fluid to the Arkoma and/or Black Warrior basins of the Ouachita foreland trough. Viburnum Trend-type fluid flow was probably funneled northward through basal sandstones within the Reelfoot rift and water-rock modifications occurring there may have resulted in its unique geochemistry.

Economic Geology↗

USGS1985

Regional setting and new information on some critical geologic features of the West Shasta district, California

The West Shasta massive sulfide district is in the easternmost of a series of accreted island-arc and oceanic crust terranes that comprise the Klamath Mountains. A sequence of submarine volcanic rocks of predominantly Early Devonian age is the principal component of the island-arc terrane in which the sulfide deposits are hosted. The Copley Greenstone, consisting mainly of andesitic and basaltic pillow lavas and breccias totaling at least 1,800 m in thickness, is the oldest rock unit in the sequence. It is overlain and also intruded by dikes of the Balaklala Rhyolite. Northeast of the West Shasta district, greenstone also overlies the Balaklala Rhyolite, suggesting that a major greenstone unit may overlie potentially mineralized rhyolite east of the district. However, recent studies have shown that the complex relations in that area can be explained by folding.The Balaklala sequence consists of silicic flows, breccias, and tuffs having a maximum thickness somewhat in excess of 1,000 m. The Balaklala has been divided by Kinkel et al. (1956) into three units: a lower nonporphyritic to slightly porphyritic unit containing large amounts of breccia and tuff; a middle unit characterized by rhyolite containing quartz phenocrysts 1 to 4 mm in diameter but also containing a complex assortment of tuff, breccia, and pyritic massive sulfide bodies in its upper part; and an upper unit typically containing dark quartz phenocrysts in excess of 4 mm in diameter. Much of the lower part of the upper unit is pyroclastic material, whereas most of the upper part of the unit appears to be a massive volcanic-flow rock. At least half a dozen eruptive centers for the Balaklala Rhyolite are identified, three of them within an area measuring 17 X 3 km that constitutes the limits of the former mining district.The youngest unit in the arc sequence is the Kennett Formation consisting of black shale and chert containing radiolarians, which indicate fairly deep-water deposition in its lower part, and limestone containing a shallow water fauna of probable Middle Devonian age in the upper part. A 400-m.y.-old trondhjemite stock, named the Mule Mountain stock, intrudes the Copley Greenstone and Balaklala Rhyolite and is considered to be essentially coeval with these volcanic units.The pyritic massive sulfide deposits occur in clusters of individual bodies owing in large part to disruption by postmineral faults. The deposits are stratigraphically confined to the upper part of the subhorizontal middle unit of the Balaklala, and their horizontal distribution is here interpreted to have been controlled by an extensional tectonic regime that prevailed during Early Devonian time. The major geologic evidence for such a regime is the marked preferred elongations exhibited by the distribution of the afore-mentioned eruptive centers, the eight or nine massive sulfide clusters in the district, and the geometrically similar distribution of the clusters in relation to each other. The preferred directions of elongation in both the detailed and broader senses may be generalized to N 20 degrees to 25 degrees E, N 37 degrees E, N 60 degrees to 80 degrees E, and N 40 degrees to 60 degrees W. The three northeast trends dominate throughout the district, whereas the northwest trend is evident mainly in the northern part and is more speculative. The major deposit clusters fall at intersections of the major trends, some of which may have been grabens. Trend intersections having no known deposits may be good exploration targets in localities where the stratigraphically favorable middle unit of the Balaklala is still present.

Economic Geology↗

USGS1993

The Geysers-Clear Lake area, California: Thermal waters, mineralization, volcanism, and geothermal potential

Manifestations of a major thermal anomaly in the Geysers-Clear Lake area of northern California include the late Pliocene to Holocene Clear Lake Volcanics, The Geysers geothermal field, abundant thermal springs, and epithermal mercury and gold mineralization. The epithermal mineralization and thermal springs typically occur along high-angle faults within the broad San Andreas transform fault system that forms the western boundary of the North American plate in this area. The young volcanic rocks overlie Mesozoic marine rocks of the Great Valley sequence which have been thrust above the coeval Franciscan Complex and penecontemporaneously dropped back down along low-angle detachment faults.Many of the waters of the region are nonmeteoric as defined by their isotopic signature. One type of isotopically shifted water emerges from or near Great Valley sequence rocks and is the most chloride rich. It is interpreted to be evolved connate in origin. A second type, evolved meteoric water, has moderate chloride contents, high boron contents, and high B/Cl ratios and is found locally in Franciscan rocks, notably at the Sulphur Bank mercury mine, where it probably results from near-closed-system, repeated boiling of meteoric water in host rocks that also contribute organic components to the water. At the Sulphur Bank mine fracturing of otherwise impermeable Franciscan rocks by faulting has created a localized zone of permeability in which thermal water boils repeatedly with limited venting to the surface. Boron-rich fluids were apparently present at depth in The Geysers geothermal field when intrusion of silicic magma occurred, because the concealed intrusion of felsite is surrounded by a halo of tourmaline-bearing hornfels. The volume of this poorly dated early to middle Quaternary intrusive body probably exceeds the 100 km 3 of erupted Clear Lake Volcanics. Similar intrusions may have occurred in the eastern part of the area at Wilbur Springs and the McLaughlin mine, where gold deposition and evidence of hydrothermal phenomena suggest more magmatic activity than is indicated by the small exposed bodies of early Quaternary basaltic lava. The Clear Lake Volcanics are the present locus of volcanism in the northern Coast Ranges and progressively older volcanic centers occur to the south. Geophysical data suggest that a large silicic magma body may be centered north of The Geysers steam field, providing the heat for the geothermal field.Geothermal power production has peaked at The Geysers and pressure declines indicate significant depletion of the fluid resource. The vapor-dominated field evolved from a preexisting hydrothermal system within fractured, otherwise impermeable Franciscan metamorphic rocks. A deep water table of saline fluid has been postulated to be present under the steam field, but no chloride-rich water has been found at drillable depth. We propose that recently discovered, isotopically shifted steam in the northwest Geysers area indicates the presence not of deep connate water but xather of boiled-down, boron-rich Franciscan evolved meteoric water. This water is likely to be present in limited quantities and will not provide a significant hot water resource for geothermal power production at The Geysers field or from the main Clear Lake volcanic field.

Economic Geology↗

USGS1994

Chemical reaction path modeling of ore deposition in Mississippi Valley-type Pb-Zn deposits of the Ozark region, US midcontinent

The Ozark region of the U.S. midcontinent is host to a number of Mississippi Valley-type districts, including the world-class Viburnum Trend, Old Lead Belt, and Tri-State districts and the smaller Southeast Missouri barite, Northern Arkansas, and Central Missouri districts. There is increasing evidence that the Ozark Mississippi Valley-type districts formed locally within a large, interconnected hydrothermal system that also produced broad fringing areas of trace mineralization, extensive subtle hydrothermal alteration, broad thermal anomalies, and regional deposition of hydrothermal dolomite cement. The fluid drive was provided by gravity flow accompanying uplift of foreland thrust belts during the Late Pennsylvanian to Early Permian Ouaehita orogeny.In this study, we use chemical speciation and reaction path calculations, based on quantitative chemical analyses of fluid inclusions, to constrain likely hydrothermal brine compositions and to determine which precipitation mechanisms are consistent with the hydrothermal mineral assemblages observed regionally and locally within each Mississippi Valley-type district in the Ozark region. Deposition of the regional hydrothermal dolomite cement with trace sulfides likely occurred in response to near-isothermal effervescence of CO 2 from basinal brines as they migrated to shallower crustal levels and lower confining pressures. In contrast, our calculations indicate that no one depositional process can reproduce the mineral assemblages and proportions of minerals observed in each Ozark ore district; rather, individual districts require specific depositional mechanisms that reflect the local host-rock composition, structural setting, and hydrology.Both the Northern Arkansas and Tri-State districts are localized by normal faults that likely allowed brines to rise from deeper Cambrian-Ordovician dolostone aquifers into shallower carbonate sequences dominated by limestones. In the Northern Arkansas district, jasperoid preferentially replaced limestones in the mixed dolostone-limestone sedimentary packages. Modeling results indicate that the ore and alteration assemblages in the Tri-State and Northern Arkansas districts resulted from the flow of initially dolomite-saturated brines into cooler limestones. Adjacent to fluid conduits where water/rock ratios were the highest, the limestone was replaced by dolomite. As the fluids moved outward into cooler limestone, jasperoid and sulfide replaced limestone. Isothermal boiling of the ore fluids may have produced open-space filling of hydrothermal dolomite with minor sulfides in breccia and fault zones. Local mixing of the regional brine with locally derived sulfur undoubtedly played a role in the development of sulfide-rich ore runs.Sulfide ores of the Central Missouri district are largely open-space filling of sphalerite plus minor galena in dolostone karst features localized along a broad anticline. Hydrothermal solution collapse during ore deposition was a minor process, indicating dolomite was slightly undersaturated during ore deposition. No silicification and only minor hydrothermal dolomite is present in the ore deposits. The reaction path that best explains the features of the Central Missouri sulfide deposits is the near-isothermal mixing of two dolomite-saturated fluids with different H 2 S and metal contents. Paleokarst features may have allowed the regional brine to rise stratigraphically and mix with locally derived, H 2 S-rich fluids. The Viburnum Trend and Old Lead Belt ores are galena rich with lesser amounts of sphalerite; they replace the most permeable dolostone facies in the Bonneterre Dolomite. Hydrothermal dissolution of host dolostone was concurrent with sulfide deposition, but dolomite deposition occurred episodically between periods of sulfide deposition. The important ore controls in these districts are a variety of sedimentary and geologic features that allowed cross-stratigraphic fluid flow and provided opportunities for fluid mixing. The reaction path which best reproduces the broad features of the Viburnum Trend and Old Lead Belt ores is one in which a dolomite-saturated, lead-rich, zinc- and H 2 S-poor brine mixes with a less saline, H 2 S-rich fluid. The brine became enriched in K, Mg, and Pb and depleted in H 2 S as it flowed through sandstone and redbed aquifers prior to entering the district. This mixing model is consistent with the abundant fluid inclusion and stable isotope evidence for fluid mixing in the districts. Small amounts of cooling associated with the mixing may have contributed to sulfide deposition.

Alabama, Arkansas, Illinois, Indiana, Kansas, Kent↗

USGS1988

Cyclic development of igneous features and their relationship to high-temperature hydrothermal features in the Henderson porphyry molybdenum deposit, Colorado

The Henderson porphyry molybdenum deposit was formed by the superposition of coupled alteration and mineralization events, of varying intensity and size, that were associated with each of at least 11 intrusions. Deposition of molybdenite was accompanied by time-equivalent silicic and potassic alteration. High-temperature alteration and mineralization are spatially and temporally linked to the crystallization of compositionally zoned magma in the apex of stocks. Differences in hydrothermal features associated with each intrusion (e.g., mass of ore, orientation and type of veins, density of veins, and intensity of alteration) correlate with differences in primary igneous features (e.g., composition, texture, morphology, and size). The systematic relations between hydrothermal and magmatic features suggest that primary magma compositions, including volatile contents, largely control the geometry, volume, level of emplacement, and mechanisms of crystallization of stocks. These elements in turn govern the orientations and densities of fractures, which ultimately determine the distribution patterns of hydrothermal alteration and mineralization.Based on primary igneous features, intrusions are grouped into four types, 1 to 4. The first three types define a potassic series of compositions (normarive orthoclase/albite greater than 1) and form a continuum from texturally and compositionally simple intrusions (type 1) to complex intrusions (type 3). Intensity and volume of high-temperature alteration and mineralization associated with a given stock increase from type 1 (2% of total ore) to type 3 (77% of total ore). Complex and strongly mineralizing intrusions (type 3) are separated from one another in time by relatively simple and weakly mineralizing intrusions (type 1). Stocks of type 4, the youngest intrusions, define a sodic series of compositions (normative orthoclase/albite less than 1) and are associated with the waning stages of mineralization.A number of textural features indicate that highly mineralizing type 3 stocks contained high primary concentrations of volatile components, e.g., the presence of unidirectional solidification textures, aplitic rather than aphanitic groundmass, extreme local textural variability, low percentages of phenocrysts in apices, brecciation of apices, and low volumes of dikes. From apex to root zone, textural units within the Seriate stock (type 3), the most productive stock in the deposit, include: (1) a Brain Rock unit with abundant quartz + or - fluorite crenulate layers, (2) a Border unit of generally low but variable phenocryst content (0-25%), (3) a transition zone, 5 to 10 m wide, of unidirectional solidification textures, (4) an Intermediate unit of moderate phenocryst content (25%), (5) another transition zone, 5 to 10 m wide, of unidirectional solidification textures, (6) a Porphyry unit of high phenocryst contents (40%), and (7) a Granite Porphyry or Granite unit. Crystals in layers of unidirectional textures always project toward the interior of the stock and indicate progressive inward solidification of magma along the walls of a chamber. Variations in texture are accompanied by variations in primary composition: the apex of the Seriate stock (the region above the deepest transition zone of unidirectional textures) is enriched in K 2 O and SiO 2 and depleted in Na 2 O, F, Nb, and Y relative to deeper units.Mineralization in the deposit is controlled by moderately outward-dipping concentric veins of both replacement and open-space origin, and by steeply dipping radial veins of replacement origin. Both sets of veins were formed nearly simultaneously about a stock and are focused in a systematic manner on the apex. A classic stockwork of veins occurs only in regions where vein sets associated with spatially separated intrusions overlap. Fluids that filled outward-dipping concentric structures flowed downward and outward from a stock. Fluid pressures in excess of lithostatic pressures, generated during crystallization of magma, were required to open and fill concentric structures. As magma solidified progressively inward, the zone of fluid evolution also migrated downward and inward. With time, the volume of evolved fluids decreased: vein densities decrease from greater than 200/m in the Seriate Brain Rock unit to less than 0.1/m immediately below the last transition zone separating the Seriate Intermediate unit from Seriate Porphyry unit. Crosscutting relations between veins and high-level dikes associated with the Seriate stock establish that most of the ore related to the Seriate stock was deposited prior to solidification of its deepest transition zone of unidirectional solidification textures.The absence of high-temperature veins and associated hydrothermal alteration in deep cores of stocks, the distribution of ore about the high levels of stocks, the orientation of veins about the apex of stocks, and the crosscutting relations between veins and dikes of the same stock are suggestive of initially high concentrations of molybdenum and volatiles in the apex of a stock immediately prior to the onset of significant crystallization. Additional accumulation of ore components, if any, ceased after solidification of the apex. Assignment of molybdenum in the ore shell about the Seriate stock to the volume of solid occupied by the apex of the Seriate stock yields concentration levels in the apical magma of approximately 13,000 ppm Mo.

Economic Geology↗

USGS2015

Hydrothermal, biogenic, and seawater components in metalliferous black shales of the Brooks Range, Alaska: Synsedimentary metal enrichment in a carbonate ramp setting

Trace element and Os isotope data for Lisburne Group metalliferous black shales of Middle Mississippian (early Chesterian) age in the Brooks Range of northern Alaska suggest that metals were sourced chiefly from local seawater (including biogenic detritus) but also from externally derived hydrothermal fluids. These black shales are interbedded with phosphorites and limestones in sequences 3 to 35 m thick; deposition occurred mainly on a carbonate ramp during intermittent upwelling under varying redox conditions, from suboxic to anoxic to sulfidic. Deposition of the black shales at ~335 Ma was broadly contemporaneous with sulfide mineralization in the Red Dog and Drenchwater Zn-Pb-Ag deposits, which formed in a distal marginal basin. Relative to the composition of average black shale, the metalliferous black shales ( n = 29) display large average enrichment factors (>10) for Zn (10.1), Cd (11.0), and Ag (20.1). Small enrichments (>2–<10) are shown by V, Cr, Ni, Cu, Mo, Pd, Pt, U, Se, Y, and all rare earth elements except Ce, Nd, and Sm. A detailed stratigraphic profile over 23 m in the Skimo Creek area (central Brooks Range) indicates that samples from at and near the top of the section, which accumulated during a period of major upwelling and is broadly correlative with the stratigraphic levels of the Red Dog and Drenchwater Zn-Pb-Ag deposits, have the highest Zn/TOC (total organic carbon), Cu/TOC, and Tl/TOC ratios for calculated marine fractions (no detrital component) of these three metals. Average authigenic (detrital-free) contents of Mo, V, U, Ni, Cu, Cd, Pb, Ge, Re, Se, As, Sb, Tl, Pd, and Au show enrichment factors of 4.3 × 10 3 to 1.2 × 10 6 relative to modern seawater. Such moderate enrichments, which are common in other metalliferous black shales, suggest wholly marine sources (seawater and biogenic material) for these metals, given similar trends for enrichment factors in organic-rich sediments of modern upwelling zones on the Namibian, Peruvian, and Chilean shelves. The largest enrichment factors for Zn and Ag are much higher (1.4 × 10 7 and 2.9 × 10 7 , respectively), consistent with an appreciable hydrothermal component. Other metals such as Cu, Pb, and Tl that are concentrated in several black shale samples, and are locally abundant in the Red Dog and Drenchwater Zn-Pb-Ag deposits, may have a partly hydrothermal origin but this cannot be fully established with the available data. Enrichments in Cr (up to 7.8 × 10 6 ) are attributed to marine and not hydrothermal processes. The presence in some samples of large enrichments in Eu (up to 6.1 × 10 7 ) relative to modern seawater and of small positive Eu anomalies (Eu/Eu* up to 1.12) are considered unrelated to hydrothermal activity, instead being linked to early diagenetic processes within sulfidic pore fluids. Initial Os isotope ratios ( 187 Os/ 188 Os) calculated for a paleontologically based depositional age of 335 Ma reveal moderately unradiogenic values of 0.24 to 0.88 for four samples of metalliferous black shale. A proxy for the ratio of coeval early Chesterian seawater is provided by initial ( 187 Os/ 188 Os) 335 Ma ratios of four unaltered black shales of the coeval Kuna Formation that average 1.08, nearly identical to the initial ratio of 1.06 for modern seawater. Evaluation of possible sources of unradiogenic Os in the metalliferous black shales suggests that the most likely source was mafic igneous rocks that were leached by externally derived hydrothermal fluids. This unradiogenic Os is interpreted to have been leached by deeply circulating hydrothermal fluids in the Kuna basin, followed by venting of the fluids into overlying seawater. We propose that metal-bearing hydrothermal fluids that formed Zn-Pb-Ag deposits such as Red Dog or Drenchwater vented into seawater in a marginal basin, were carried by upwelling currents onto the margins of a shallow-water carbonate platform, and were then deposited in organic-rich muds, together with seawater- and biogenically derived components, by syngenetic sedimentary processes. Metal concentration in the black shales was promoted by high biologic productivity, sorption onto organic matter, diffusion across redox boundaries, a low sedimentation rate, and availability of H 2 S in bottom waters and pore fluids.

Alaska↗

USGS1993

Origin and significance of tourmaline-rich rocks in the Broken Hill district, Australia

Tourmaline-rich rocks are widespread minor lithologies within the Early Proterozoic Willyama Supergroup in the Broken Hill district, Australia. Tourmaline concentrations occur in strata-bound and local stratiform tourmalinites, clastic metasedimentary rocks, quartz-gahnite lode rocks, stratiform Pb-Zn-Ag sulfide ores, garnet quartzites, strata-bound scheelite deposits, quartz-tourmaline nodules, discordant quartz veins, and granitic pegmatites. Most of the tourmaline-rich rocks are within the Broken Hill Group that hosts the main Pb-Zn-Ag ores.At the Globe mine along the northeast end of the main lodes, tourmalinites are closely associated with Pb-Zn-Ag mineralization and in places are interbedded with Mn-rich garnet quartzites. Galena and other ore minerals occur locally in the cores of recrystallized tourmaline grains in these tourmalinites, indicating that tourmaline and sulfides were present together prior to deformation and high-grade metamorphism. Electron microprobe analyses of tourmalines intergrown with Fe sulfides at the Globe mine show Mg-rich compositions relative to tourmalines in sulfide-free assemblages from the same area, suggesting early (premetamorphic) introduction of boron and Mg enrichment of tourmaline by sulfide-silicate reactions during metamorphism.Combined field and geochemical data indicate that the district tourmalinites represent normal clastic sediments that were metasomatically altered by boron-rich hydrothermal fluids at or below the sediment-water interface. Whole-rock chemical analyses of 33 tourmaline-rich rocks show linear trends of data for major and trace elements that closely resemble the trends observed for unmineralized elastic metasedimentary rocks of the district. Average Fe/Al, Mg/Al, Na/Al, and Ti/Al molar ratios of the tourmaline-rich rocks and clastic metasediments are very similar; the average K/Al molar ratio of the tourmaline-rich rocks is significantly lower than that of the clastic metasediments, reflecting the loss of K during tourmalinite formation. Chondrite-normalized patterns of rare earth elements (REE) in the quartz-rich tourmalinites are generally similar to those of the clastic metasediments, except for minor depletions of light REE; local positive and negative Ce anomalies suggest tourmalinite formation in the presence of seawater or a seawater-derived pore fluid. The geochemical data imply relative immobility of Al, Ti, Cr, and heavy REE during hydrothermal alteration and later metamorphism. Boron isotope analyses of 52 tourmaline separates show a total range of delta 11 B values from -26.8 to -17.0 per mil. Fine-grained, euhedral, nonpoikilitic tourmalines from tourmalinites in the andalusite-muscovite zone in the northern part of the district (e.g., Black Prince mine) have delta 11 B values from -21 to -17 per mil, whereas coarse granoblastic and poikilo-blastic tourmalines from the sillimanite and two-pyroxene granulite zones in the southern part of the district (e.g., Globe mine) have delta 11 B values of-24 to -19 per mil. Tourmalines in strongly retrogressed tourmalinites have delta 11 B values from about -27 to -20 per mil. The observed variations in delta 11 B are consistent with prograde and retrograde metamorphic fractionation of boron isotopes, in which the fluid phase is preferentially enriched in the heavier isotope ( 11 B). Premetamorphic hydrothermal fluids that deposited the Black Prince tourmalinites had delta 11 B values of-8 to -5 per mil at 200 degrees to 300 degrees C, suggesting a boron source from nonmarine evaporite borates.Tourmalinites in the Broken Hill district apparently formed by the same submarine hydrothermal processes as the main Pb-Zn-Ag lodes and the siliceous ferromanganese protoliths of the garnet quartzites. In our model, the hydrothermal system(s) acquired abundant boron by leaching evaporitic borates within the Thackaringa Group, the stratigraphic sequence that underlies the Broken Hill Group and most of the tourmaline concentrations. We suggest that evaporites of the Thackaringa Group provided a source of readily extractable boron for formation of the tourmalinites and also the source of the fluoride, sulfur, and perhaps the carbonate in the main lodes; such evaporites may have been critical for increased metal chloride complexing and transport necessary for deposition of the high-grade Pb-Zn-Ag ores. The Broken Hill deposit may have formed contemporaneously with the Mount Isa and McArthur River Pb-Zn-Ag deposits in similar evaporite-bearing sequences during widespread Early Proterozoic continental rifting.

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USGS2012

USGS Environmental health science strategy: providing environmental health science for a changing world: Public review release

America has an abundance of natural resources. We have bountiful clean water, fertile soil, and unrivaled national parks, wildlife refuges, and public lands. These resources enrich our lives and preserve our health and wellbeing. These resources have been maintained because of our history of respect for their value and an enduring commitment to their vigilant protection. Awareness of the social, economic, and personal value of the health of our environment is increasing. The emergence of environmentally driven diseases caused by environmental exposure to contaminants and pathogens is a growing concern worldwide. New health threats and patterns of established threats are affected by both natural and anthropogenic changes to the environment. Human activities are key drivers of emerging (new and re-emerging) health threats. Societal demands for land and natural resources, a better quality of life, improved economic prosperity, and the environmental impacts associated with these demands will continue to increase. Natural earth processes, climate trends, and related climatic events will add to the environmental impact of human activities. These environmental drivers will influence exposure to disease agents, including viral, bacterial, prion, and fungal pathogens, parasites, natural earth materials, toxins and other biogenic compounds, and synthetic chemicals and substances. The U.S. Geological Survey (USGS) defines environmental health science broadly as the interdisciplinary study of relations among the quality of the physical environment, the health of the living environment, and human health. The interactions among these three spheres are driven by human activities, ecological processes, and natural earth processes; the interactions affect exposure to contaminants and pathogens and the severity of environmentally driven diseases in animals and people. This definition provides USGS with a framework for synthesizing natural science information from across the Bureau and providing it to environmental, natural resource, agricultural, and public-health managers. The USGS is a Federal science agency with a broad range of natural science expertise relevant to environmental health. USGS provides scientific information and tools as a scientific basis for management and policy decision making. USGS specializes in science at the environment-health interface, by characterizing the processes that affect the interaction among the physical environment, the living environment, and people, and the resulting factors that affect ecological and human exposure to disease agents. This report describes a 10-year strategy that encompasses the portfolio of USGS environmental health science. It summarizes national environmental health priorities that USGS is best suited to address, and will serve as a strategic framework for USGS environmental health science goals, actions, and outcomes for the next decade. Implementation of this strategy is intended to aid coordination of USGS environmental health activities and to provide a focal point for disseminating information to stakeholders. The "One Health" paradigm advocated by the World Health Organization (WHO, 2011), and the American Veterinary Medicine Association (AVMA, 2008), among others, is based on a general recognition that the health of humans, animals, and the environment are inextricably linked. Thus, successful efforts to protect that health will require increased interdisciplinary research and increased communication and collaboration among the broader scientific and health community. This strategy is built upon that paradigm. The vision, mission, and five cornerstone goals of the USGS Environmental Health Science Strategy were developed with significant input from a wide range of stakeholders. Vision - The USGS is a premier source of the environmental health science needed to safeguard the health of the environment, fish, wildlife, and people. Mission - The mission of USGS in environmental health science is to contribute scientific information to environmental, natural resource, agricultural, and public-health managers, who use that science to support sound decision making. USGS provides the science to: - Goal 1: Identify, prioritize, and detect contaminants and pathogens of emerging environmental concern. - Goal 2: Reduce the impact of contaminants on the environment, fish, wildlife, and people. - Goal 3: Reduce the impact of pathogens on the environment, fish, wildlife, and people. - Goal 4: Discover the complex interactions and combined effects of exposure to contaminants and pathogens. - Goal 5: Prepare for and respond to environmental impacts and related health threats of natural and anthropogenic disasters. Goals 1 through 4 are intended to provide science to address environmental health threats in a logical order, from informing prevention and preparedness, to supporting systematic management response to environmental health issues. Goal 4 addresses the interaction among contaminants and pathogens, an issue of emerging concern in environmental health science. Goal 5 acknowledges the fact that natural and anthropogenic disasters can cause immediate and prolonged adverse environmental health threats. This strategy proposes that USGS take the following strategic science actions to achieve each of the five goals of this strategy: Goal 1: Identify, prioritize, and detect contaminants and pathogens of emerging environmental concern. - Strategic Science Action 1. - Prioritize contaminants and pathogens of emerging concern to guide research, detection, and management activities. - Strategic Science Action 2. - Conduct surveillance and monitoring to provide early warning of emerging health threats. - Strategic Science Action 3. - Develop approaches and tools that identify vulnerable environmental settings, ecosystems, and species. Goal 2: Reduce the impact of contaminants on the environment, fish, wildlife, and people. - Strategic Science Action 1. - Systematically characterize the sources, occurrence, transport and fate of environmental contaminants to guide efforts to manage and mitigate contamination. - Strategic Science Action 2. - Evaluate the threats of contamination on the health of the environment, fish, wildlife, and people, and inform the associated management and protection efforts. - Strategic Science Action 3. - Characterize potential human exposure to support establishment of health-based standards or guidelines and contamination-reduction efforts. Goal 3: Reduce the impact of pathogens on the environment, fish, wildlife, and people. - Strategic Science Action 1. - Determine the biotic and abiotic factors that control the ecology of infectious diseases affecting natural populations of aquatic and terrestrial species and potential transmission to other animals and humans. - Strategic Science Action 2. - Establish how natural and anthropogenic environmental changes affect the distribution and severity of infectious diseases in natural populations of aquatic and terrestrial species and potential transmission to other animals and humans. - Strategic Science Action 3. - Develop surveillance systems to identify changing patterns of disease activity in priority geographic areas. Goal 4: Discover the complex interactions and combined effects of exposure to contaminants and pathogens. - Strategic Science Action 1. - Identify how exposure to one class of disease agents (contaminants or pathogens) can make an organism more susceptible to effects from exposure to the other class of disease agents. - Strategic Science Action 2. - Implement interdisciplinary studies that characterize the effects of combined exposure to pathogens and contaminants. Goal 5: Prepare for and respond to the environmental impacts and related health threats of natural and anthropogenic disasters. - Strategic Science Action 1. - Establish a formal interdisciplinary science capability to rapidly assess the environmental health risks associated with disasters. - Strategic Science Action 2. - Enhance methods to anticipate, prepare for, and identify environmental, ecological, and related health impacts of future disasters. This strategy is one of seven USGS science strategies developed concurrently: - Climate and Land Use Change - Core Science Systems - Ecosystems - Energy and Mineral Resources - Environmental Health - Natural Hazards - Water. This strategy describes how USGS will address the highest priority environmental health issues facing the Nation. The ultimate intended outcome of this science strategy is prevention and reduction of adverse impacts to the quality of the environment, the health of our living resources, and human health. Communication with, and receiving input from, partners and stakeholders regarding their science needs is essential for successful implementation of this strategy. It is incumbent on USGS to reach out to all stakeholders to ensure that USGS efforts are focused on the highest priority environmental health issues and that products are provided in the most timely and usable form to all those who can use them. USGS must reach out to the scientific community, internally and externally, to ensure that our efforts are integrated with and take full advantage of the activities of others.

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