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At least 1,225 records · Page 68Linked to original sources
USGS2022

Juvenile continental crust evolution in a modern oceanic arc setting: Petrogenesis of Cenozoic felsic plutons in Fiji, SW Pacific

Viti Levu, Fiji, provides one of the best exposed Phanerozoic analogues for the formation of juvenile continental crust in an intra-oceanic setting. Tonalites and trondhjemites are present in several large (75–150 km 2 ) adjacent, mid-Cenozoic plutons. We report major and trace element data including rare earth element (REE) and high-precision high field strength element (HFSE) compositions, new Hf-Nd-Sr-Pb isotope data, and zircon U/Pb-ages, O-Hf isotopes, and trace elements, from five different plutons. The Eocene Yavuna pluton and the Miocene Colo plutons are mainly composed of tonalites and trondhjemites and represent the exposed middle crust of the former Vitiaz island arc. The plutons can be divided into three suites. One suite is light REE (LREE) depleted with some trace element ratios lower than average normal mid-ocean ridge basalts (N-MORB). A second suite has flat REE patterns similar to local island arc basalts. Both suites occur near the coast of Viti Levu, include a wide compositional spectrum from gabbro to tonalite, and can be produced mostly by fractional crystallization of mafic precursor melts. The third suite is characterized by LREE enrichments with higher La N /Yb N (2.3–4.9), higher Zr/Y (4.3–7.1), and lower Nb/Ta (9.6–12.4). They occur closer to the center of the island and are bimodal trondhjemite-gabbro intrusions. These characteristics are consistent with formation mostly by partial melting of mafic crust. Trace element modeling shows that the trace element ratios of the third suite can be produced by 10–20 % melting of the mafic crust in the presence of residual amphibole, resulting in the retention of the medium REE (MREE) and diagnostic trace element ratios including low Nb/Ta and high Zr/Y. Geochemical similarities of the LREE enriched suite to typical “low”-pressure Archean tonalites-trondhjemites-granodiorites (TTGs) imply a common petrogenetic origin and similar mechanisms for the generation of juvenile Archean and modern differentiated crust by partial melting of mafic crust with residual amphibole. In modern oceanic arcs, genetically unrelated felsic plutonic as well as volcanic rocks co-exist, and in this regard, the Fijian plutons accompany major tectonic disruptions to arc processes.

Geochimica et Cosmochimica Acta↗
USGS2009

Comparison of humus and till as prospecting material in areas of thick overburden and multiple ice-flow events: An example from northeastern New Brunswick

Thirty-nine elements in humus and till matrix were compared at 109 sites overlying Ag-As-Cu-Mo-Pb-Zn mineralized occurrences in northeastern New Brunswick to assess humus for anomaly identification. Humus element concentrations were not consistently correlative with maximum or minimum concentrations found in the underlying till or bedrock. The humus demonstrated significantly higher mean elemental concentrations than the till for six specific elements: 9 times greater for Mn, 6 times greater for Cd, 5 times greater for Ag and Pb, 3 times greater for Hg, and double the concentration of Zn. Spatial dispersal patterns for these elements were much larger for humus content than that exhibited by the till matrix analysis, but did not delineate a point source. For elements in till, the highest concentrations were commonly found directly overlying the underlying mineralized bedrock source or within one km down-glacier of the source. The complexity of the humus geochemical patterns is attributed to the effects of post-glacial biogenic, down-slope hydrodynamic and solifluction modification of dispersed mineralization in the underlying till, and the greater capacity of humus to adsorb cations and form complexes with some elements, relative to the till matrix. Humus sampling in areas of glaciated terrain is considered to be mostly valuable for reconnaissance exploration as elements can be spatially dispersed over a much larger area than that found in the till or underlying bedrock. ?? 2009 Elsevier B.V. All rights reserved.

Journal of Geochemical Exploration↗
USGS1998

Geochemical and isotopic (Nd-Pb-Sr-O) variations bearing on the genesis of volcanic rocks from Vesuvius, Italy

Alkaline volcanism produced by Monte Somma-Vesuvius volcano includes explosive plinian and subplinian activity in addition to effusive lava flows. Pumice, scoria, and lava (150 samples) exhibit major- and trace-element gradients as a function of SiO2 (58.9-47.2 wt%) and MgO (0-7.8 wt%); Mg value are ???50. Internally gradational chemical groups or cycles are distinguished by age: (1) 25 000 to 14 000 yr B.P.; (2) 8000 yr B.P. to A.D. 79; and (3) A.D. 79 to 1944. A small number of lavas, dikes and scora were also analysed from the Somma formation (~ 35 000 to 25 000 yr B.P.). Within each group, contents of Na2O + K2O increas with decreasing MgO along distinct rocks. Nb/Y values are variable from 0.66 to 3.14 (at SiO2 ??? 50 wt%) generally in the range of alkaline and ultra-alkaline rocks. Variations in contents of some majro elements (e.g., P and Ti), and trace elements (e.g., Th, Nb, Ta, Zr, Hf, Pb, La, and Sc), as well as contrasting trends in ratios of various elements (e.g., Ta/Yb, Hf/U, Th/Ta, Th/Hf, Th/Yb, etc.) are also generally consistent with the group subdivisions. For example, Th/Hf increases from ??? 5 to ??? 10 with decreasing age for the Vesuvius system as a whole, yielding similar compositions in the least evolved rocks (low-silica, high-MgO, imcompatible element-poor) erupted at the end of each cycle. Internal variations within individual eruptions also systematically changed generally towards a common mafic composition at the end of each cycle, thus reflecting the dominanit volume in the magma chamber. At the start of a new eruptive cycle, the rocks are relatively enriched in incompatible elements; younger groups also contain higher abundances than other groups. N-MORB-normalized multielement diagrams exhibit selective enrichments of Sr, K, Rb, Th, and the light rare-earth elements; deep Nb and Ta negative anomalies commonly seen in rocks generated at orogenic margins are absent in the light rare-earth elements; deep Nb and Ta netgative anomalies commonly seen in rocks generated at orogenic margins are absent in our samples. Sr isotopic compositions are known to be variable within some of the units, in agreement with our data (87Sr/86Sr ~ 0.70699 to 0.70803) and with contributions from several isotopic components. Isotopic compositions for ??18O (7.3 to 10.2%), Pb for mineral separates and whole rocks (206Pb/204Pb ~ 18.947 to 19.178, 207Pb/204/Pb ~ 15.617 to 15.769, 208Pb/204Pb ~38.915 to 39.345), and Nd (143Nd ~ 0.51228 to 0.51251) also show variability. Oxygen isotope data show that pumices have higher ??18O values than cogenetic lavas, and that ??18O values and SiO2 are correlated. Radiogenic and stable isotope data plot within range of isotopic compositions for the Roman comagmatic province. Fractional crystallization cannot account for the radiogenic isotopic compositions of the Vesuvius magmas. We favor instead the combined effects of heterogeneous magma sources, together with isotopic exchange near the roof of the magma chamber. We suggest that metasomatized continental mantle lithosphere is the principal source of the magmas. This kind of enriched mantle was melted and reactivated in an area of continental extension (incipient rift setting) without direct reliance on contemporaneous subduction processes but possibly with input from mantle sources that resemble those that produce ocean island basalts.

Journal of Volcanology and Geothermal Research↗
USGS2024

A multidisciplinary approach that considers occurrence, geochemistry, bioavailability, and toxicity to prioritize critical minerals for environmental research

Critical minerals (or critical elements) are minerals or elements that are essential to global security and development and have supply chains vulnerable to disruption. In general, knowledge of the environmental behavior and health effects of critical elements is needed to support the development of safe and environmentally responsible supplies. This knowledge includes identifying potential consequences of increased critical element production and use, alternative critical element sources such as mine wastes, and adverse effects of critical elements on ecosystem condition and organismal health. Here we identify significant data gaps in the understanding of critical elements in surficial and aquatic environments, and the need, given the large number of commodities (50) identified on the 2022 critical minerals list for the United States, for an approach to prioritize them for study of their environmental fate and effects. We propose a multidisciplinary approach for this prioritization, considering measures of occurrence, geochemistry, bioavailability, and toxicity. We describe relatively easy-to-obtain metrics for each of these topic areas and demonstrate the utility of this integrated prioritization approach using indium and zinc as examples. This approach facilitates prioritizing research with a focus on those critical elements that are most mobile in the environment, bioavailable, toxic, or simply lacking data in these categories.

Environmental Science & Technology↗
USGS2004

Ultramafic xenoliths from the Bearpaw Mountains, Montana, USA: Evidence for multiple metasomatic events in the lithospheric mantle beneath the Wyoming craton

Ultramafic xenoliths in Eocene minettes of the Bearpaw Mountains volcanic field (Montana, USA), derived from the lower lithosphere of the Wyoming craton, can be divided based on textural criteria into tectonite and cumulate groups. The tectonites consist of strongly depleted spinel lherzolites, harzbugites and dunites. Although their mineralogical compositions are generally similar to those of spinel peridotites in off-craton settings, some contain pyroxenes and spinels that have unusually low Al2O3 contents more akin to those found in cratonic spinel peridotites. Furthermore, the tectonite peridotites have whole-rock major element compositions that tend to be significantly more depleted than non-cratonic mantle spinel peridotites (high MgO, low CaO, Al2O3 and TiO2) and resemble those of cratonic mantle. These compositions could have been generated by up to 30% partial melting of an undepleted mantle source. Petrographic evidence suggests that the mantle beneath the Wyoming craton was re-enriched in three ways: (1) by silicate melts that formed mica websterite and clinopyroxenite veins; (2) by growth of phlogopite from K-rich hydrous fluids; (3) by interaction with aqueous fluids to form orthopyroxene porphyroblasts and orthopyroxenite veins. In contrast to their depleted major element compositions, the tectonite peridotites are mostly light rare earth element (LREE)-enriched and show enrichment in fluid-mobile elements such as Cs, Rb, U and Pb on mantle-normalized diagrams. Lack of enrichment in high field strength elements (HFSE; e.g. Nb, Ta, Zr and Hf) suggests that the tectonite peridotites have been metasomatized by a subduction-related fluid. Clinopyroxenes from the tectonite peridotites have distinct U-shaped REE patterns with strong LREE enrichment. They have 143Nd/144Nd values that range from 0??5121 (close to the host minette values) to 0??5107, similar to those of xenoliths from the nearby Highwood Mountains. Foliated mica websterites also have low 143Nd/144Nd values (0??5113) and extremely high 87Sr/86Sr ratios in their constituent phlogopite, indicating an ancient (probably mid-Proterozoic) enrichment. This enriched mantle lithosphere later contributed to the formation of the high-K Eocene host magmas. The cumulate group ranges from clinopyroxene-rich mica peridotites (including abundant mica wehrlites) to mica clinopyroxenites. Most contain >30% phlogopite. Their mineral compositions are similar to those of phenocrysts in the host minettes. Their whole-rock compositions are generally poorer in MgO but richer in incompatible trace elements than those of the tectonite peridotites. Whole-rock trace element patterns are enriched in large ion lithophile elements (LILE; Rb, Cs, U and Pb) and depleted in HFSE (Nb, Ta Zr and Hf as in the host minettes, and their Sr-Nd isotopic compositions are also identical to those of the minettes. Their clinopyroxenes are LREE-enriched and formed in equilibrium with a LREE-enriched melt closely resembling the minettes. The cumulates therefore represent a much younger magmatic event, related to crystallization at mantle depths of minette magmas in Eocene times, that caused further metasomatic enrichment of the lithosphere. ?? Oxford University Press 2004; all rights reserved.

Journal of Petrology↗
USGS1956

Geochemistry of sphalerite from the Star Mine, Coeur d'Alene district, Idaho

Forty sphalerite samples from the Star mine, Coeur d'Alene district, Idaho, and 19 sphalerite samples from other Coeur d'Alene mines have been quantitatively analyzed by spectrographic methods for Fe, Cu, Pb, Cd, Ga, Ge, In, Mn, Co, and Hg. The samples from the Star vein were collected over a strike length of 2,000 feet and a vertical distance of 5,300 feet.It is believed that Star mine sphalerite formed in equilibrium with Fe; consequently, following Kullerud's work, the Fe content may be used as a relative temperature scale. Relative Fe temperatures suggest that the lower portions of the Star ore body formed at lower temperatures than the upper portions of the ore body.Distribution of the minor elements in sphalerite is random within the ore body. Also, there is no correlation of Fe with minor elements other than Mn; therefore we believe temperature has had no influence on the distribution of minor elements, except Mn, in this ore body.The principal reason for this seems to be that equilibrium concentrations of the minor elements were not reached. Minor-element concentrations in sphalerite from the Coeur d'Alene district are similar to those in other districts throughout the world; consequently, the writers suggest that in general the minor-element content of sphalerite, other than perhaps Mn, cannot be an indicator of formation temperatures because equilibrium concentrations are rarely, if ever, attained.The average minor-element content in a district is probably that of the ore-forming solutions. Specific minor-element content in sphalerite is random.

Idaho↗
USGS2008

Analytical Results for Municipal Biosolids Samples from a Monitoring Program near Deer Trail, Colorado (U.S.A.), 2007

Since late 1993, the Metro Wastewater Reclamation District of Denver (Metro District), a large wastewater treatment plant in Denver, Colorado, has applied Grade I, Class B biosolids to about 52,000 acres of nonirrigated farmland and rangeland near Deer Trail, Colorado (U.S.A.). In cooperation with the Metro District in 1993, the U.S. Geological Survey (USGS) began monitoring ground water at part of this site. In 1999, the USGS began a more comprehensive monitoring study of the entire site to address stakeholder concerns about the potential chemical effects of biosolids applications to water, soil, and vegetation. This more comprehensive monitoring program recently has been extended through 2010. Monitoring components of the more comprehensive study include biosolids collected at the wastewater treatment plant, soil, crops, dust, alluvial and bedrock ground water, and streambed sediment. Streams at the site are dry most of the year, so samples of streambed sediment deposited after rain were used to indicate surface-water effects. This report will present only analytical results for the biosolids samples collected at the Metro District wastewater treatment plant in Denver and analyzed during 2007. We have presented earlier a compilation of analytical results for the biosolids samples collected and analyzed for 1999 through 2006. More information about the other monitoring components is presented elsewhere in the literature. Priority parameters for biosolids identified by the stakeholders and also regulated by Colorado when used as an agricultural soil amendment include the total concentrations of nine trace elements (arsenic, cadmium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc), plutonium isotopes, and gross alpha and beta activity. Nitrogen and chromium also were priority parameters for ground water and sediment components. In general, the objective of each component of the study was to determine whether concentrations of priority parameters (1) were higher than regulatory limits, (2) were increasing with time, or (3) were significantly higher in biosolids-applied areas than in a similar farmed area where biosolids were not applied. Previous analytical results indicate that the elemental composition of the biosolids from the Denver plant was consistent during 1999-2006 and this consistency continues with the samples for 2007; total concentrations of regulated trace elements remained consistently lower than the regulatory limits for the entire monitoring period. Our previously reported data (1999-2006) and data presented in this report were used to compile an inorganic-chemical biosolids signature that can be contrasted with the geochemical signature for this site. The biosolids signature and an understanding of the geology and hydrology of the site can be used to separate biosolids effects from natural geochemical effects. Elements of particular interest for a biosolids signature include bismuth, copper, silver, mercury, phosphorus, and silver. An alternative method of digestion of biosolids was also recently investigated, and the results are presented in this report. A microwave digestion using only nitric acid at controlled elevated temperature and pressure was tested to replace the much more time-consuming and labor-intensive, traditional four-acid, hotplate method for the preparation of solutions to be analyzed by inductively coupled plasma-mass spectrometry (ICP-MS). Elements of concern determined by ICP-MS following digestion include cadmium, copper, lead, molybdenum, nickel, and zinc. The microwave 'digestion' proved to be a strong acid leach, and it was less efficient at digesting the biosolids samples with consistently lower recoveries (compared to the four-acid digestion value) for most elements, but especially for the elements of concern - copper, nickel, and zinc. Other elements traditionally associated with the silicate or oxide minerals demonstrated low recoveries, especially titaniu

Open-File Report↗
USGS2023

A novel non-destructive workflow for examining germanium and co-substituents in ZnS

A suite of complementary techniques was used to examine germanium (Ge), a byproduct critical element, and co-substituent trace elements in ZnS and mine wastes from four mineral districts where germanium is, or has been, produced within the United States. This contribution establishes a comprehensive workflow for characterizing Ge and other trace elements, which captures the full heterogeneity of samples through extensive pre-characterization. This process proceeded from optical microscopy, to scanning electron microscopy and cathodoluminescence (CL) imaging, to electron microprobe analysis, prior to synchrotron-based investigations. Utilizing non-destructive techniques enabled reanalysis, which proved essential for verifying observations and validating unexpected results. In cases where the Fe content was <0.3 wt% in ZnS, cathodoluminescence imaging proved to be an efficient means to qualitatively identify trace element zonation that could then be further explored by other micro-focused techniques. Micro-focused X-ray diffraction was used to map the distribution of the non-cubic ZnS polymorph, whereas micro-focused X-ray fluorescence (μ-XRF) phase mapping distinguished between Ge 4+ hosted in primary ZnS and a weathering product, hemimorphite [Zn 4 Si 2 O 7 (OH) 2 ·H 2 O]. Microprobe data and μ-XRF maps identified spatial relationships among trace elements in ZnS and implied substitutional mechanisms, which were further explored using Ge and copper (Cu) X-ray absorption near-edge spectroscopy (XANES). Both oxidation states of Ge (4+ and 2+) were identified in ZnS along with, almost exclusively, monovalent Cu. However, the relative abundance of Ge oxidation states varied among mineral districts and, sometimes, within samples. Further, bulk XANES measurements typically agreed with micro-focused XANES (μ-XANES) spectra, but unique micro-environments were detected, highlighting the importance of complementary bulk and micro-focused measurements. Some Ge μ-XANES utilized a high energy resolution fluorescence detector, which improved spectral resolution and spectral signal-to-noise ratio. This detector opens new opportunities for exploring byproduct critical elements in complex matrices. Overall, the non-destructive workflow employed here can be extended to other byproduct critical elements to more fully understand fundamental ore enrichment processes, which have practical implications for critical element exploration, resource quantification, and extraction.

Frontiers in Earth Science↗
USGS2026

The mineral chemistry networks of tin and tungsten reflect metallogenic eras of the Mesozoic

Continental remobilization is a crucial driver of metallogenesis and the formation of ore deposits. Some of the world’s largest mineral deposits of the economically valuable elements tin (Sn), tungsten (W), gold (Au), copper (Cu), lead (Pb), and zinc (Zn) formed during the Mesozoic Era. Additionally, the chemistry and distribution of the elements Sn and W have been investigated in previous studies to understand planetary formation and differentiation processes. These two elements are largely co-located during certain South China Mesozoic metallogenic events but are not co-located during other time periods in the same regions. Here, we investigated the mineral chemistry network similarities and dissimilarities of Sn and W to understand their mineral formation and distribution during the Mesozoic Era and throughout Earth history. Mineral chemistry network community detection analysis and electronegativity associations among mineral constituent elements of Sn minerals and W minerals indicate that the elements have similar chemistry among their oxide minerals. However, Sn forms a much wider range of minerals that also contain S compared to W, which occurs in a limited number of S-containing minerals. The divergent constituent element interactions among S-containing Sn minerals and W minerals reflect the redox sensitivity and importance of oxygen (O) fugacity in Sn mineral formation. Conversely, extensive W mineral deposits are known to form at both high and low O fugacities. The similarities and differences between the mineral chemistry networks of Sn and W reflect the mineral distribution of the two elements in the Sn-W mineralization event from 160 to 139 Ma vs. the Sn–uranium (U) mineralization event from 125 to 98 million years ago (Ma). The mineral chemistry and distribution of Mesozoic Sn and W deposits illustrate the contrasting importance of redox and O fugacity on the mineral formation of different elements, and the dynamic crustal evolution that took place during this period of Earth history.

Geosciences↗
USGS1982

Chemical and mineralogical analysis of devonian black-shale samples from Martin County, Kentucky; Carroll and Washington counties, Ohio; Wise County, Virginia; and Overton County, Tennessee, U.S.A.

Core samples of Devonian shales from five localities in the Appalachian basin have been analyzed chemically and mineralogically. The amounts of major elements are similar; however, the minor constituents, organic C, S, phosphate and carbonate show ten-fold variations in amounts. Trace elements Mo, Ni, Cu, V, Co, U, Zn, Hg, As and Mn show variations in amounts that can be related to the minor constituents. All samples contain major amounts of quartz, illite, two types of mixed-layer clays, and chlorite in differing quantities. Pyrite, calcite, feldspar and kaolinite are also present in many samples in minor amounts. Dolomite, apatite, gypsum, barite, biotite and marcasite are present in a few samples in trace amounts. Trace elements listed above are strongly controlled by organic C with the exception of Mn which is associated with carbonate minerals. Amounts of organic C generally range from 3 to 6%, and S is in the range of 2-5%. Amounts of trace elements show the following general ranges in ppm (parts per million): Co, 20-40; Cu, 40-70; U, 10-40; As, 20-40; V, 150-300; Ni, 80-150; high values are as much as twice these values. The organic C was probably the concentrating agent, and the organic C and sulfide S together created an environment that immobilized and preserved these trace elements. Closely spaced samples showing an abrupt transition in color also show changes in organic C, S and trace-element contents. Several associations exist between mineral and chemical content. Pyrite and marcasite are the only minerals found to contain sulfide-S. In general, the illite-chlorite mixed-layer clay mineral shows covariation with organic C if calcite is not present. The enriched trace elements are not related to the clay types, although the clay and organic matter are intimately associated as the bulk fabric of the rock. ?? 1982.

Chemical Geology↗
USGS1953

Systematic variation of rare earths in monazite

Ten monazites from widely scattered localities have been analyzed for La, Ce, Pr, Nd, Sm, Gd, Y and Th by means of a combined chemical and emission spectrographic method. The analytical results, calculated to atomic percent of total rare earths (thorium excluded), show a considerable variation in the proportions of every element except praseodymium, which is relatively constant. The general variation trends of the elements may be calculated by assuming that the monazites represent different stages in a fractional precipitation process, and by assuming that there is a gradational increase in the precipitability of rare earth elements with decreasing ionic radius. Fractional precipitation brings about an increase in lanthanum and cerium, little change in praseodymium, and a decrease in neodymium, samarium, gadolinium, and yttrium. Deviations from the calculated lines of variation consist of a simultaneous, abnormal increase or decrease in the proportions of cerium, praseodymium, and neodymium with antipathetic decrease or increase in the proportions of the other elements. These deviations are ascribed to abnormally high or low temperatures that affect the precipitability of the central trio of elements (Ce, Pr, Nd) relatively more than that of the other elements. The following semiquantitative rules have been found useful in describing the composition of rare earths from monazite: 1. The sum of lanthanum and neodymium is very nearly a constant at 42 ± 2 atomic percent. 2. Praseodymium is very nearly constant at 5 ± 1 atomic percent. 3. The sum of Ce, Sm, Gd, and Y is very nearly a constant at 53 ± 3 atomic percent. No correlation could be established between the content of Th and that of any of the rare earth elements.

Geochimica et Cosmochimica Acta↗
USGS1996

Characterizing coal beds in western Kentucky with the Al-La-Sc coherent triad

Cyclic sedimentation and lateral facies changes make coal bed correlations inconclusive and difficult. This uncertainty can be further complicated if a coal basin has been structurally deformed. Coal macerals can be studied to indicate the nature and degree of coalification. Their use in coal bed correlation, however, is limited. Most of the trace elements and their ratios that have been studied show significant within-bed lateral and stratigraphic variations, and thus are not effective in correlating coal beds regionally. Geochemically coherent groups of elements, such as rare earth elements (REE) and platinum group elements (PGE), appear to be highly differentiated in coal-forming environments. Geochemical coherent elemental triads appear to be useful for coal bed identification or fingerprinting. The best triad which was demonstrated to be effective in coal bed characterization in western Kentucky, is that of Al, La and Sc. These three elements are highly correlated with one another and they can be determined accurately and simultaneously with instrumental neutron activation analysis (INAA). The elemental triad Al-La-Sc is used to identify and fingerprint three key coal beds in western Kentucky: the Springfield (western Kentucky No. 9), the Davis (western Kentucky No. 6), and the Mining City and Dawson Springs are both considered to be the No. 4 coal bed in western Kentucky). Four distinct groupings can be recognized by use of the Al-La-Sc triad. The Dawson Springs coals have the highest Al/(La + Sc) ratios, followed by the Springfield, the Davis and the Mining City. The Mining City coal bed generally has the highest La/Sc ratio. However, the Dawson Springs is not correlated with the Mining City using the triad analysis, even though they have reportedly similar stratigraphic positions in the western Kentucky coal basin. The Al-La-Sc triad appears to be effective in discriminating between the Springfield and the Davis coal beds throughout the entire Illinois Basin. Furthermore, the range of concentration variation of the AL-La-Sc triad suggests individual groupings of the No. 4 coal in western Kentucky. In addition to characterizing these coal beds, the Al-La-Sc triad may be used to confirm stratigraphic correlations.

International Journal of Coal Geology↗
USGS2009

Fractionation of the platinum-group elments and Re during crystallization of basalt in Kilauea Iki Lava Lake, Hawaii

Kilauea Iki lava lake formed during the 1959 summit eruption of Kilauea Volcano, then crystallized and differentiated over a period of 35??years. It offers an opportunity to evaluate the fractionation behavior of trace elements in a uniquely well-documented basaltic system. A suite of 14 core samples recovered from 1967 to 1981 has been analyzed for 5 platinum-group elements (PGE: Ir, Os, Ru, Pt, Pd), plus Re. These samples have MgO ranging from 2.4 to 26.9??wt.%, with temperatures prior to quench ranging from 1140????C to ambient (110????C). Five eruption samples were also analyzed. Osmium and Ru concentrations vary by nearly four orders of magnitude (0.0006-1.40??ppb for Os and 0.0006-2.01??ppb for Ru) and are positively correlated with MgO content. These elements behaved compatibly during crystallization, mostly likely being concentrated in trace phases (alloy or sulfide) present in olivine phenocrysts or included chromite. Iridium also correlates positively with MgO, although less strongly than Os and Ru. The somewhat poorer correlation for Ir, compared with Os and Ru, may reflect variable loss of Ir as volatile IrF6 in some of the most magnesian samples. Rhenium is negatively correlated with MgO, behaving as an incompatible trace element. Its behavior in the lava lake is complicated by apparent volatile loss of Re, as suggested by a decrease in Re concentration with time of quenching for lake samples vs. eruption samples. Platinum and Pd concentrations are negatively, albeit weakly, correlated with MgO, so these elements were modestly incompatible during crystallization of the major silicate phases. Palladium contents peaked before precipitation of immiscible sulfide liquid, however, and decline sharply in the most differentiated samples. In contrast, Pt appears to have been unaffected by sulfide precipitation. Microprobe data confirm that Pd entered the sulfide liquid before Re, and that Pt is not strongly chalcophile in this system. Occasional high Pt values in both eruption and lava lake samples suggest the presence of unevenly distributed, unidentified Pt-rich trace phases in some Kilauea Iki materials. Estimated mineral (olivine + chromite)/melt D values for Os, Ir, Ru and Pt for equilibrium crystallization for samples from ~ 7 to 27??wt.% MgO are 26, 8.2, 19 and 0.55, respectively. These Os, Ir and Ru estimates are somewhat higher than previous estimates for similar systems. If fractional crystallization is instead assumed, D values are much more similar. Results confirm many prior observations in other mafic systems that olivine (together with included phases) has a major effect on absolute and relative abundances of Re and the PGE. The relatively linear correlations between these elements and MgO potentially permit accurate estimation of the concentrations of these elements in the primary melts of comparable systems, especially in instances where the MgO content of the primary melt is well constrained. ?? 2008 Elsevier B.V.

Chemical Geology↗
USGS2025

Geochemistry and radiogenic isotopes constrain the mantle source region of the Mountain Pass Intrusive Suite, California

The Mountain Pass carbonatite stock is the largest rare earth element (REE) deposit and only active REE mine in the United States. The carbonatite intrusion and spatially associated alkaline silicate intrusions constitute the Mountain Pass Intrusive Suite, which is located within the Mojave Province in California. Both the carbonatite and the alkaline silicate rocks are enriched in large ion lithophile elements and light REEs, and less enriched to depleted in high field strength elements, indicating the mantle source region was metasomatically enriched in incompatible trace elements. The cause of this metasomatic mantle enrichment and the genetic relationship between the carbonatite and the alkaline silicate stocks are poorly understood. In this study, major and trace element geochemical data and isotopic (Rb-Sr, Sm-Nd, and Lu-Hf) data are presented to constrain genesis of the Mountain Pass Intrusive Suite, from mantle source region to the intrusion of the stocks. Our geochemical data are consistent with derivation of the alkaline silicate and carbonatite melts through partial melting from a shared mantle source region rather than through liquid immiscibility or fractional crystallization and separation of a carbothermal fluid. Although the Rb-Sr isotopic system in the Mountain Pass Intrusive Suite is disturbed at the whole-rock scale, the isotopic systems for whole-rock Sm-Nd (εNd i = ‐2.2 ± 0.8) and zircon Lu-Hf (εHf i = 0.1 ± 1.1) are robust and support mantle derivation of the magmas. Geochemical modeling using experimentally derived partition coefficients was used to identify possible causes of enrichment in incompatible elements through metasomatism in the mantle source region. Modeling of metasomatism by melts derived by partial melting of deeply subducted carbonated sediments approximates observed Mountain Pass Intrusive Suite trace element chemistry. Scattered εHf i in inherited zircon (2.8 ± 2.6) is consistent with derivation from an arc-related environment with substantial crustal contamination. Paleotectonic studies in the Mojave Province indicate that regional subduction preceded emplacement of the Mountain Pass Intrusive Suite by ∼300 Ma. Melting of the Mountain Pass source region may have been caused by post-collisional thermal relaxation and extension.

California↗
USGS2004

The geochemical and magnetic record of coal combustion products in West Virginia reservoir sediments and soils

Western West Virginia lies downwind from numerous coal-fired power plants along the Ohio River Valley. To test whether geochemical and mineralogical impacts from these power plants are detectable on the West Virginia landscape, we obtained reservoir cores, soils, and rocks from two separate sites in West Virginia, one in Harrison County (Hinkel and Deegan Reservoirs) and the other in Roane County (Miletree Run Reservoir). Both have small drainage basins that have the effect of maximizing atmospheric inputs relative to weathering inputs. Sediments from Hinkel Reservoir were dated using the 137 Cs method, and by knowledge of the age of the base of the sedimentary section. Major elements in Hinkel Reservoir sediments do not vary systematically over time, suggesting that the depositional history of these sediments has been relatively constant. In contrast, minor elements and sulfur do show dramatic shifts. Zn, Pb, As, S, Cd, Ge, and Hg all peak during the late 1960s and early 1970s. Polyaromatic hydrocarbons associated with combustion processes likewise show this same behavior. Coincident with these maxima is a peak in isothermal remnant magnetization (IRM), a parameter that is proportional to magnetite abundance. We separated the magnetic fraction of the sediments and examined this fraction petrographically. It is dominated by magnetite with a spherical morphology, which is characteristic of magnetite produced by combustion processes. Chemical analyses on local rocks showed that they were not the likely source for the trace element and magnetite enrichments. To compare soils and reservoir sediments, we normalized geochemical data to Ti; the underlying assumption is that Ti will track physical inputs of soil materials into the reservoir sediments. The normalized sediment data for the elements Zn, Pb, As, and S are all higher for sediments deposited during the late 1960s and early 1970s compared to normalized soil data, implying that soils are not the source for the element enrichments. We thus attribute the enrichment to atmospheric inputs. However, a coal-burning zinc smelter within 10 km of the reservoir site that operated until 1971 may have supplied some or all of the anomalous input: There are no nearby major atmospheric pollution sites near Miletree Run Reservoir. A core from this reservoir was dated based on knowledge of the time it was impounded. Like Hinkel Reservoir, there are no systematic shifts in major element contents over its depositional history. Like Hinkel Reservoir, there are also significant shifts in trace elements and IRM that cannot be explained by local soil sources. Magnetic separates from this reservoir are also dominated by spherical combustion-produced magnetite. Covariance over the period 1930-1980 between magnetite and sulfur with US SO 2 production (which comes dominantly from coal combustion) is strongly suggestive of a significant atmospheric input into Miletree Run Reservoir sediments. The nearest upwind power plants are between 50 and 75 km distant. Thus, relatively long distance transmission of particulate matter from the power plants of the Ohio River Valley is likely in this case.

West Virginia↗
USGS2012

Pillow basalts of the Angayucham terrane: Oceanic plateau and island crust accreted to the Brooks Range

The Angayucham Mountains (north margin of the Yukon-Koyukuk province) are made up of an imbricate stack of four to eight east-west trending, steeply dipping, fault slabs composed of Paleozoic (Devonian to Mississippean), Middle to Late Triassic, and Early Jurassic oceanic upper crustal rocks (pillow basalt, subordinate diabase, basaltic tuff, and radiolarian chert). Field relations and geochemical characteristics of the basaltic rocks suggest that the fault slabs were derived from an oceanic plateau or island setting and were emplaced onto the Brooks Range continental margin. The basalts are variably metamorphosed to prehnite-pumpellyite and low-greenschist facies. Major element analyses suggest that many are hypersthene-normative olivine tholeiites. Classification based on immobile trace elements confirms the tholeiitic character of most of the basalts but suggests that some had primary compositions transitional to alkali basalt. Although field and petrographic features of the basalts are similar, trace element characteristics allow definition of geographically distinct suites. A central outcrop belt along the crest of the mountains is made up of basalt with relatively flat rare earth element (REE) patterns. This belt is flanked to the north and south by LREE (light rare earth element)-enriched basalts. Radiolarian and conodont ages from interpillow and interlayered chert and limestone indicate that the central belt of basalts is Triassic in age, the southern belt is Jurassic in age, and the northern belt contains a mixture of Paleozoic and Mesozoic ages. Data for most of the basalts cluster in the “within-plate basalt” fields of trace element discriminant diagrams; none have trace-element characteristics of island arc basalt. The Triassic and Jurassic basalts are geochemically most akin to modern oceanic plateau and island basalts. Field evidence also favors an oceanic plateau or island setting. The great composite thickness of pillow basalt probably resulted from obduction faulting, but the lack of fault slabs of gabbro or peridotite suggests that obduction faults did not penetrate below oceanic layer 2, a likely occurrence if layer 2 were anomalously thick, as in the vicinity of an oceanic island. The presence of basaltic tuff interbeds indicates proximity to an explosive basaltic eruptive center. The juxtaposition of submarine basalts of differing chemical affinity and age, adjacent to higher-grade Paleozoic metamorphic rocks of the Brooks Range to the north, may be explained by obduction of internally complex (thickened) oceanic crust formed in an ocean plateau setting. Emplacement and rotation of thrust plates to steep attitudes occurred during accretion of the Brooks Range passive margin, probably beginning in the Late to Middle Jurassic.

Journal of Geophysical Research Solid Earth↗
USGS1997

Some thoughts on problems associated with various sampling media used for environmental monitoring

Modern analytical instrumentation is capable of measuring a variety of trace elements at concentrations down into the single or double digit parts-per-trillion (ng l-1) range. This holds for the three most common sample media currently used in environmental monitoring programs: filtered water, whole-water and separated suspended sediment. Unfortunately, current analytical capabilities have exceeded the current capacity to collect both uncontaminated and representative environmental samples. The success of any trace element monitoring program requires that this issue be both understood and addressed. The environmental monitoring of trace elements requires the collection of calendar- and event-based dissolved and suspended sediment samples. There are unique problems associated with the collection and chemical analyses of both types of sample media. Over the past 10 years, reported ambient dissolved trace element concentrations have declined. Generally, these decreases do not reflect better water quality, but rather improvements in the procedures used to collect, process, preserve and analyze these samples without contaminating them during these steps. Further, recent studies have shown that the currently accepted operational definition of dissolved constituents (material passing a 0.45 ??m membrane filter) is inadequat owing to sampling and processing artifacts. The existence of these artifacts raises questions about the generation of accurate, precise and comparable 'dissolved' trace element data. Suspended sediment and associated trace elements can display marked short- and long-term spatial and temporal variability. This implies that spatially representative samples only can be obtained by generating composites using depth- and width-integrated sampling techniques. Additionally, temporal variations have led to the view that the determination of annual trace element fluxes may require nearly constant (e.g., high-frequency) sampling and subsequent chemical analyses. Ultimately, sampling frequency for flux estimates becomes dependent on the time period of concern (daily, weekly, monthly, yearly) and the amount of acceptable error associated with these estimates.

Conference Paper↗
USGS2006

Analysis of trace metals in water by inductively coupled plasma emission spectrometry using sodium dibenzyldithiocarbamate for preconcentration

Since concentrations of trace elements in most natural waters seldom exceed the μg/L level, analysis of trace elements in natural waters by inductively coupled plasma emission spectrometry (ICP) requires a preconcentration procedure. The elements Ag, Bi, Cd, Co, Cu, Fe, Mo, Ni, Pb, Sn, V, W, and Zn were separated and concentrated from 500 mL of water by coprecipitating them with sodium dibenzyldithiocarbamate (NaDBDTC) using nickel or silver as a carrier. The precipitated trace elements were collected on a membrance filter, redissolved from the filter with hot nitric and hydrochloric acids, and analyzed using ICP. Recoveries for all the trace elements except tungsten exceeded 80%. Coprecipitation of trace elements with NaDBDTC eliminated the use of difficult-to-inject organic solvents, and NaDBDTC coprecipitated a wider array of trace elements than ammoniumpyrrolidinedithiocarbamate (APDC), another commonly used coprecipitate.

Analytical Letters↗