LA-ICPMS Data Research Articles

Gold and uranium contents in gypsum formed from percolating ground water in a Witwatersrand-like gold deposit, Ouro Fino, Minas Gerais, Brazil: LA-ICPMS data

Gold and uranium contents in gypsum formed from percolating ground water in a Witwatersrand-like gold deposit, Ouro Fino, Minas Gerais, Brazil: LA-ICPMS data

Origin of the Early-Middle Devonian magmatism in the Sakarya Zone, NW Turkey: Geochronology, geochemistry and isotope systematics

A unique example of isotopically-dated Devonian metagranitoid (the Çamlık metagranite; Okay et al., 1996) crops out in the Biga Peninsula, NW Turkey, although its contact relationships with the country rocks and geodynamic setting have remained to be enigmatic so far. Our field work, however, has shown that a number of metagranitoid bodies similar to the Çamlık metagranite intruded the country rocks and developed contact metamorphic zones, consisting of andalusite and calcsilicate hornfelses, garnet–epidote and diopsite–wollastonite skarns. The country rocks of these metagranitoids are made up of regionally metamorphosed metaclastic successions with subordinate metacarbonate–metachert–metabasites (the Kalabak formation), intercalated with tectonic slices of meta-serpentinites. The metagranitoids and the Kalabak formation are collectively termed here the Havran Unit which forms a NE–SW trending, 20 km wide and 80 km long belt in the Biga Peninsula. The Havran Unit is unconformably overlain by the Late Triassic shallow marine sediments and is in tectonic contact with the Permo-Triassic Karakaya Complex, interpreted as the Palaeotethyan subduction–accretion complex. U–Pb SHRIMP-II and LA–ICP–MS dating of the zircons from four individual plutons yielded crystallization ages ranging from 389.1 ± 2.6 to 401.5 ± 4.8 Ma (i.e. Early to Middle Devonian). Based on their geochemical characteristics, the metagranitoids are divided into two groups named the Çamlık and Yolindi metagranitoids. Both granitoids display distinct subduction signature and plot in the volcanic arc granite and post-collisional granite fields on tectonic discrimination diagrams. 87Sr/ 86Sr ( T ) values of these intrusions vary between 0.707367 and 0.715588 while their 143Nd/ 144Nd ( T ) values range from 0.51166 to 0.51187. Very low values of εNd ( T ) (from −5.3 to −9.1) imply that the Lower to Mid-Devonian metagranitoids in the Havran Unit might have been generated by partial melting of lower continental crust, probably driven by a major magma underplating event. Delamination and/or slab-breakoff models are considered to be the most plausible mechanisms for the genesis of these metagranitoids. The data obtained in this study has shown for the first time the widespread existence of Devonian and older basement in NW Turkey. Regional geological correlations imply that this basement may be an exotic terrane in the Sakarya Zone, emplaced during the Late Triassic, prior to its amalgamation with the Palaeotethyan Karakaya Complex.

Elemental Analysis of Desert Varnish Samples in the Vicinity of Coal-Fired Power Plants and the Nevada Test Site Using Laser Ablation ICPMS

Desert varnish is a thin manganese-iron rich dark coating that forms on rocks most often in arid climates. This coating may be up to a few hundred microns in thickness and is thought to grow by approximately one micron per thousand years. Recent research has shown that many elements are incorporated into this coating, and, in spite of its slow growth, it may serve as a passive environmental monitor for recent and historical air pollution. To test this hypothesis, small pieces of varnished rock were probed directly by laser ablation inductively coupled plasma mass spectrometry (LA- ICPMS). Results were obtained for 11 elements (13 isotopes: 9 Be, 107 Ag, 111 Cd, 118 Sn, 121 Sb, 138 Ba, 184 W, 205 Tl, 206 Pb, 207 Pb, 208 Pb, 232 Th, and 238 U) by magnetic sector ICPMS and for 23 elements (25 isotopes: same as before plus 51 V, 52 Cr, 59 Co, 60 Ni, 65 Cu, 66 Zn, 88 Sr, 98 Mo, 115 In, 133 Cs, 197 Au, and 209 Bi) by quadrupole ICPMS. Varnished rock samples were collected mainly in the fallout patterns of two coal-fired power plants and downwind from the Nevada Test Site (NTS). The LA-ICPMS data indicate that many of the elements commonly found in fly ash from coal-fired power plants (e.g., Cr, Co, Ni, Cu, Zn, Cd, Sn, Sb, Tl and Pb) were highly enriched in the rock coatings in relation to the upper continental crust (UCC). For one of the power plants, where tracer plume studies had been carried out, the highest concentrations in the rock varnish coincide with the peak tracer concentration locations. Thus, these elements in rock varnish hold promise for identifying those geographical regions impacted by nearby power plants. Overall, the results indicate that rock varnish can be used as a passive environmental monitor of relatively recent events, and that the trace element fingerprints held in rock varnish may also hold much potential in forensic air pollution studies.

Plešovice zircon — A new natural reference material for U–Pb and Hf isotopic microanalysis

Matrix-matched calibration by natural zircon standards and analysis of natural materials as a reference are the principle methods for achieving accurate results in microbeam U–Pb dating and Hf isotopic analysis. We describe a new potential zircon reference material for laser ablation ICP-MS that was extracted from a potassic granulite facies rock collected in the southern part of the Bohemian Massif (Plešovice, Czech Republic). Data from different techniques (ID-TIMS, SIMS and LA ICP-MS) and several laboratories suggest that this zircon has a concordant U–Pb age with a weighted mean 206Pb/ 238U date of 337.13 ± 0.37 Ma (ID-TIMS, 95% confidence limits, including tracer calibration uncertainty) and U–Pb age homogeneity on the scale used in LA ICP-MS dating. Inhomogeneities in trace element composition due to primary growth zoning prevent its use as a calibration standard for trace element analysis. The content of U varies from 465 ppm in pristine parts of the grains to ~ 3000 ppm in actinide-rich sectors that correspond to pyramidal faces with a high degree of metamictization (present in ca. 30% of the grains). These domains are easily recognized from high intensities on BSE images and should be avoided during the analysis. Hf isotopic composition of the Plešovice zircon (> 0.9 wt.% Hf) is homogenous within and between the grains with a mean 176Hf/ 177Hf value of 0.282482 ± 0.000013 (2SD). The age and Hf isotopic homogeneity of the Plešovice zircon together with its relatively high U and Pb contents make it an ideal calibration and reference material for laser ablation ICP-MS measurements, especially when using low laser energies and/or small diameters of laser beam required for improved spatial resolution.

239, 240, 241Pu fingerprinting of plutonium in western US soils using ICPMS: solution and laser ablation measurements

Sector field inductively coupled plasma mass spectrometry (SF-ICPMS) has been used with analysis of solution samples and laser ablation (LA) of electrodeposited alpha sources to characterize plutonium activities and atom ratios prevalent in the western USA. A large set of surface soils and attic dusts were previously collected from many locations in the states of Nevada, Utah, Arizona, and Colorado; specific samples were analyzed herein to characterize the relative contributions of stratospheric fallout vs. Nevada Test Site (NTS) plutonium. This study illustrates two different ICPMS-based analytical strategies that are successful in fingerprinting Pu in environmental soils and dusts. Two specific datasets have been generated: (1) soils are leached with HNO3-HCl, converted into electrodeposited alpha sources, counted by alpha spectrometry, then re-analyzed using laser ablation SF-ICPMS; (2) samples are completely dissolved by treatment with HNO3-HF-H3BO3, Pu fractions are prepared by extraction chromatography, and analyzed by SF-ICPMS. Optimal laser ablation and ICPMS conditions were determined for the re-analysis of archived alpha spectrometry "planchette" sources. The best ablation results were obtained using a large spot size (200 microm), a defocused beam, full repetition rate (20 Hz) and scan rate (200 microm s(-1)); LA-ICPMS data were collected with a rapid electrostatic sector scanning experiment. Less than 10% of the electroplated surface area is consumed in the LA-ICPMS analysis, which would allow for multiple re-analyses. Excellent agreement was found between (239+240)Pu activities determined by LA-ICPMS vs. activity results obtained by alpha spectrometry for the same samples ten years earlier. LA-ICPMS atom ratios for 240Pu/239Pu and 241Pu/239Pu range from 0.038-0.132 and 0.00034-0.00168, respectively, and plot along a two-component mixing line (241Pu/239Pu = 0.013 [240Pu/239Pu] - 0.0001; r2 = 0.971) with NTS and global fallout end-members. A rapid total dissolution procedure, followed by extraction chromatography and SF-ICPMS solution Pu analysis, generates excellent agreement with certified (239+240)Pu activities for standard reference materials NIST 4350b, NIST 4353, NIST 4357, and IAEA 385. (239+240)Pu activities and atom ratios determined by total dissolution reveal isotopic information in agreement with the LA-ICPMS dataset regarding the ubiquitous mixing of NTS and stratospheric fallout Pu sources in the regional environment. For several specific samples, the total dissolution method reveals that Pu is incompletely recovered by simpler HNO3-HCl leaching procedures, since some of the Pu originating from the NTS is contained in refractory siliceous particles.

U-Pb dating of zircon and rutile from the gold-bearing White Hills Gravel, St Arnaud district, Victoria

The White Hills Gravel is a widespread gold-bearing palaeontology in western and north-central Victoria. Its age is unconsidered by palaeontology but has been considered as Late Cretaceous to early Tertiary. Using coarse (> 1mm) concentrates of heavy minerals from an occurrence of the WHG near St Arnaud, we have obtained evidence for the age and provenance of the formation. U?Pb SHRIMP dating of two populations of zircons gave ages of 74.5 and 68.2 Ma, indicating a maximum age of latest Cretaceous for the WHG. The zircons are believed to have been sourced from basaltic volcaniclastic deposits since removed by erosion. These also provided coloured sapphires, spinel and possibly the sole diamond recovered from the concentrates. Such an assemblage is characteristic of eastern Australian gemfields associated with Cainozoic basaltic lavas. Other minerals in the concentrates include schorl, rutile, andalusite, anatase and metamorphic corundum. U?Pb LA-ICPMS dating of rutile gave an age of 393 Ma, within the age ange of Early Devonian granites in the region, which have intruded Cambro-Ordovician metasediments (St Arnaud Group). Sources within contact metamorphosed pelitic metasediments and associated pegmatites are indicated for the rutile, and probably for schorl, andalusite and natase. Corundum-bearing rocks are unknown in the region, so these may have a more distal and older source. Investigation of heavy mineral concentrates from other occurrences of the White Hills Gravel may enable regional correlation of sources and provide more evidence for particular depositional models.

EPMA and LA-ICPMS dating of hydrothermal REE-minerals from the Estrela Copper Deposit, Carajás, Brazil

EPMA and LA-ICPMS dating of hydrothermal REE-minerals from the Estrela Copper Deposit, Carajás, Brazil

MAJOR- AND TRACE-ELEMENT ANALYSIS OF SULFIDE ORES BY LASER-ABLATION ICP MS, SOLUTION ICP MS, AND XRF: NEW DATA ON INTERNATIONAL REFERENCE MATERIALS

International reference materials representing a diverse suite of sulfide ores and related lithologies have been analyzed for major and trace element concentrations by XRF, solution ICP–MS, and laser-ablation ICP–MS (LA–ICP–MS) after fusion of the sample to a lithium borate glass. Reference materials analyzed for this study include a wide variety of bulk compositions, incl uding ores of Pb–Zn sulfides, Fe sulfides, Cu–Mo sulfides, and silicate matrices. Concentrations of 33 elements were determined, including lithophile and chalcophile elements of particular interest to economic geochemistry and ore deposit studies. The resu lts of LA–ICP–MS analyses were calibrated using a fused glass standard prepared specifically for the analysis of sulfides. Accuracy of the LA–ICP–MS technique is established by comparison with results obtained by the other methods for abundance variations over several orders of magnitude. Replicate analyses demonstrate a precision of 2–8% (1 RSD) for the LA–ICP–MS data at rock-equivalent concentrations >1 ppm. Matrix effects were not a significant problem at the scale of compositional variation represented by these samples, and no significant differences in the results were produced with the laser operating in either fi xedspot or line-scan mode. LA–ICP–MS analysis of fused glasses effectively overcomes problems related to insoluble phases such as cassiterite that are resistant to acid dissolution. Whole-rock analysis of sulfide ores by XRF and LA–ICP–MS provides a fast and convenient approach for determinations of major- and trace-element concentrations in a variety of ores and related material s without the need for wet-chemical dissolutions.

Incompatible trace element partitioning and residence in anhydrous spinel peridotites and websterites from the Ronda orogenic peridotite

We report solution-ICPMS analyses of Rb, Ba, Th, U, Nb, Ta, REE, Sr, Zr and Hf for acid-leached minerals of anhydrous spinel peridotites and websterites from the Ronda peridotite (S. Spain). The same elements were also analyzed by LA-ICPMS in the silicates of three peridotites. The results obtained by solution-ICPMS and LA-ICPMS are similar for the less (HREE) and the most incompatible (Rb–Ba) elements, and provide comparable inter-element distribution coefficients ( D xt/cpx) for these elements. However, moderately incompatible elements (typically LREE) show significant discrepancies between solution and in situ analyses. D opx/cpx and D ol/cpx for these elements are generally lower for solution than for in situ analyses. D xt/cpx for MREE, HREE, Zr and Hf are consistent with experimental values. In contrast, D xt/cpx for highly incompatible elements and LREE are higher than expected from available experimental data and/or crystal-chemical considerations. The observed D xt/cpx for the most incompatible trace elements may be explained by very small amounts of melt/fluid, or solid, inclusions trapped in these minerals. Inclusions would affect both solution- and LA-ICPMS data, but their proportion would be less important for LA-ICPMS analyses. We show with a mixing model that an extremely small amount of equilibrium partial melt (typically 0.01–0.1%) trapped in minerals is sufficient to increase the D opx/cpx for HIE and LREE by a factor of 5–20 and the D ol/cpx by two or three orders of magnitude. Similar effects may be produced by sub-percent amounts of HIE-rich fluids of solid microphases. Such very small volumes of inclusions may pass unnoticed during mineral handpicking and LA-ICPMS analysis. Hence, D xt/cpx for HIE and LREE should be considered cautiously when mineral analyses are used to constrain melt processes and mantle composition. Mass balance calculations were performed for a nominally anhydrous spinel harzburgite sample. Similar to previous studies, the mass balance indicates important discrepancies for HIE between peridotite composition reconstructed from mineral analyses (bulk and in situ) and whole rock composition. The major silicate minerals are the main repositories for REE, Zr and Hf (>75% of the whole rock budget), and also host ≥65% of Th and U. In contrast, more than 80% of the budget of Rb, Ba and Nb, and about 60% of Ta and Sr, is hosted by micro-components in grain boundaries (GBC) or trapped in minerals (inclusions). Alone, the GBC accounts for 50% of the budget of Nb and Ta. The inclusions are an important repository for Rb (39%), Nb (40%) and Sr (49%). The GBC and inclusion repositories display very similar trace element signatures, suggesting that they were once a single repository (<1 wt%) now re-distributed in different textural components. This repository could be a combination of hydrous phases and/or Ti oxides, and/or melt/fluid inclusions of mantle origin.

SULPHIDE MINERALOGY AND CHALCOPHILE/SIDEROPHILE ELEMENT GEOCHEMISTRY OF ABYSSAL PERIDOTITES FROM THE MARK AREA (20-24°N MID-ATLANTIC RIDGE, SOUTH OF THE KANE TRANSFORM)

SULPHIDE MINERALOGY AND CHALCOPHILE/SIDEROPHILE ELEMENT GEOCHEMISTRY OF ABYSSAL PERIDOTITES FROM THE MARK AREA (20-24°N MID-ATLANTIC RIDGE, SOUTH OF THE KANE TRANSFORM)

Corrigendum

Owing to an error in a computer program, some of the LA—ICP—MS data for yttrium presented in Tables 3, 4, 5, 6, 12 and 13 of Bea (1996) are incorrect. The following changes should be made:

Chemical composition of hydrothermal fluids buffered by veinand pegmatite-forming mineral assemblages: An experimental calibration at high temperatures and pressures

The Ning-Wu volcanic basin is an important part of the Middle-Lower Yangtze River Valley metallogenic belt in eastern China, where magnetite–apatite deposits are common. These magnetite–apatite deposits can be classified into two types. The first type includes the Washan, Taocun, Heshangqiao and Dongshan deposits, which are hosted in diorite porphyry and adjacent volcanic rocks. The second type includes Gushan, Baixiangshan and Hemushan deposits, developed at the contact between gabbro–diorite and sedimentary rocks. We used 40Ar–39Ar dating on phlogopite and U–Pb LA-ICP MS dating of zircon in ore-related diorite porphyry and gabbro–diorite to determine the timing of iron mineralization in the basin. The ages of the magnetite–apatite deposits such as Washan, Taocun, Heshangqiao Gushan Baixiangshan Hemushan deposits are from 130 Ma to 131 Ma. Thus the magnetite–apatite deposits in the Ning-Wu volcanic basin all formed at about 130 Ma, later than the skarn and porphyry Cu–Au deposits in the adjacent fault-uplift areas such as Edongnan, Jiu-Rui, Anqing-Guichi and Tongling clusters that are between 146 Ma and 135 Ma. Based on available petrological and geochemical data, the magnetite–apatite deposits in the Ning-Wu volcanic basin are interpreted to have formed under regional lithospheric extension and thinning, and ore-forming elements were derived from basaltic melts sourced from enriched lithospheric mantle and the crust.