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Overview

USGS LA-ICPMS laboratory
USGS laser ablation inductively coupled plasma mass spectrometer (LA-ICPMS) in Denver, CO.

A new double-focusing single-collector inductively coupled plasma mass spectrometer (SC-ICPMS) at USGS has the ability to perform rapid in situ isotopic analyses of geological materials by laser ablation (LA). This laser ablation single-collector inductively coupled plasma mass spectrometer (LA-SC-ICPMS) is ideally suited for geochronological and isotopic tracer studies related to the timing, duration, and rates of mineralization and the sources of ore-forming fluids. Several ongoing Mineral Resources Program projects rely on geochronology (e.g., uranium-lead (U-Pb) dating of zircon), and most of these studies would also benefit from lead and strontium isotopic data on the mineral scale. We anticipate that the ability to obtain precise and accurate in situ age and isotopic tracer information for USGS minerals-related projects will continue to be vitally important in the future.

Our LA-SC-ICPMS has the capability of providing cost-effective in situ geochronological and mineral isotope tracer data, but the analytical techniques need to be developed further to reach their full potential. Our facility and research scientists are well-positioned to open exciting new frontiers related to in situ geochronology and mineral isotope tracer research, and these new avenues of research will be fully available to the USGS research.

The primary goal of this project is to improve the precision and accuracy of routine uranium-lead dating of zircon, expanding our LA-SC-ICPMS dating technique to other uranium-rich minerals (e.g., monazite, apatite, xenotime), and developing novel LA-ICPMS in situ lead and strontium isotopic tracer methods applicable to studies of ore mineralization and the framework geology of Mineral Resources Program research study areas. The development of the most precise geochronologic and novel isotope tracer methods would open new avenues for minerals-related research including, for example, geochronology of monazite, apatite, and titanite and lead-isotope studies of ore-related feldspar.

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Project Activities

Instrumentation

  • Double-focusing mass spectrometer with low noise discrete dynode electron multiplier detector
    • Beam attenuation capacity (~ factor of 500 reduction)
    • Faraday for larger dynamic range (~1012)
  • Continuiously variable high resolution capabilities
    • From 300 to > 10,000 (10% valley definition)
  • Fast electrostatic scanning / jumping
    • Up to 40% of the mass range
    • No mass discrimination effects
  • Fully laminated, large radius magnet
    • High scan speed - m/z 6 to 250 in < 220 ms

Uranium-Lead (U-Pb) Geochronology

  • High precision and spatial resolution uranium-lead dating of zircon and other uranium-enriched minerals
    • Precise and accurate age determination of high-uranium and -thorium zircon (>2000 ppm) with no apparent matrix effects
    • Uranium-Lead geochronology of monazite micro-inclusions
    • Precise Uranium-Lead geochronology of sub-25µm across zircon
U-Pb dating of zircon
Age determination of zircon sample. Photo by USGS.

Lead-isotope Studies

  • In situ Pb-isotope ratio determination of feldspar, pyrite, and glass materials
    • Precision and accuracy within accepted values of natural and reference materials in both raster and spot mode
    • Determination of Pb-isotope ratios of individual grains of eolian potassium feldspar from Greeley dune field (NE CO)-LA-ICPMS vs bulk TIMS analysis
    • Pb-isotope ratios for pyrites from the Pea Ridge iron oxide-apatite deposit directly measured by LA-ICPMS
apatite and pyrite sample being analyzed
In situ U-Pb dating of apatite and Pb-isotope analysis of co-existing pyrite. Photo by USGS.

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Products

Charts shoping lead and lead-uranium isotopic data
Dating apatite from Pea Ridge iron oxide-apatite deposit, southeast Missouri. Presented by Neymark and others at Goldschmidt 2015 conference. View Neymark Goldschmidt abstract. Image by USGS.

Posters and Presentations

Bala, S.A., Holm-Denoma, C.S., Neymark, L.A., Taylor, C.D., Pietruszka, A.J., and Driscoll, R.L., 2014, U-Pb zircon ages and mineralogy of the Dora Bay instrusive complex and heavy REE-bearing pegmatite dikes: Geological Society of America Abstracts with Programs, Vol. 46, No. 6, p. 782. View Bala 2014 GSA abstract.

Barineau, C.I., Tull, J.F., and Holm-Denoma, C.S., 2015, Ordovician events in the southern Appalachians: Synthesizing the igneous, sedimentary and metamorphic record of the Taconic orogeny: Geological Society of America Abstracts with Programs, Vol. 47, No. 2, p. 22. View Barineau 2015 Southeast Section GSA abstract.

Barineau, C.I., Tull, J.F., Mueller, P.A., Sagul, D.A., and Holm-Denoma, C.S., 2015, Tectonic implications of Ordovician-Silurian magmatic-volcanic sequences in the eastern Blue Ridge and inner Piedmont, southern Appalachian orogen: Geological Society of America Abstracts with Programs, Vol. 47, No. 7, p. 863. View Barineau 2015 GSA abstract.

Holm-Denoma, C.S., McClellan, E., and Southworth, S., 2014, Three episodes of volcanism and erosion during Neoproterozoic extension in eastern Laurentia revealed by U-Pb dating of zircon from clasts of rhyolite and detrital zircon from sedimentary rocks of the Mount Rogers Formation, southwest Virginia: Geological Society of America Abstracts with Programs, Vol. 46, No. 6, p. 90. View Holm-Denoma 2014 GSA abstract.

Holm-Denoma, C.S., Southworth, C.S., Merschat, A.J., and McClellan, E., 2015, The detrital record of Neoproterozoic to Cambrian rocks from the southern Appalachian Blue Ridge: Protracted rifting, rapid unroofing, and stabilization of the margin: Geological Society of America Abstracts with Programs, Vol. 47, No. 7, p. 859. View Holm-Denoma 2015 GSA abstract.

Jones III, J.V., Caine, J.S., Holm-Denoma, C.S., Lease, R.O., Saltus, R.W., and Todd, E., 2015, Refining the characteristics, age, and extent of the Permian Klondike assemblage in eastern Alaska: Geological Society of America Abstracts with Programs, Vol. 47, No. 4, p. 18. View Jones 2015 Cordilleran Section GSA abstract.

Jones III, J.V., Holm-Denoma, C.S., and O'Sullivan, P.B., 2015, Using detrital zircon to correlate and reconstruct Neoproterozoic and early Paleozoic components of peri-Laurentian terranes in the northern Cordillera and Alaska: Geological Society of America Abstracts with Programs, Vol. 47, No. 7, p. 860. View Jones 2015 GSA abstract.

Karl, S.M., Box, S.E., Lease, R.O., Jones III, J.V., Holm-Denoma, C., Bradley, D., and Haeussler, P.J., 2015, Formation of the Kahiltna Basin, Alaska, by time-transgressive Early to Late Cretaceous dextral-oblique juxtaposition of two independent depositional systems: Geological Society of America Abstracts with Programs, Vol. 47, No. 4, p. 53. View Karl GSA abstract.

McClellan, E., and Holm-Denoma, C.S., 2014, Neoproterozoic geologic history of eastern Laurentia: Evidence from U-Pb dating of zircon from rhyolite clasts in Mount Rogers Formation conglomerates, SW VA, USA: Geological Society of America Abstracts with Programs, Vol. 46, No. 6, p. 89. View McClellan 2014 GSA abstract.

McClellan, E., Holm-Denoma, C.S., Gazel, E., Risso, B.R., and Brown, E., 2015, Breaking up Rodinia: Magmatic and sedimentological evidence for a mantle plume trigger: Geological Society of America Abstracts with Programs, Vol. 47, No. 7, p. 859. View McClellan 2015 GSA abstract.

Merschat, A.J., Holm-Denoma, C.S., Southworth, S., and Mundil, R., 2015, Late Pre-Cambrian continental rifting in the southern Blue Ridge, VA-NC-TN, revisited: Honoring 50 years of Doug Rankin's contributions to Appalachian geology: Geological Society of America Abstracts with Programs, Vol. 47, No. 3, p. 61. View Merschat 2015 Northeast Section GSA abstract.

Merschat, A.J., Southworth, S., Rankin, D.W., Holm-Denoma, C.S., Tollo, R.P., and Aleinikoff, J.N., 2015, Preliminary geologic map of the Mount Rogers area, VA-NC-TN: Field relationships of Neoproterozoic volcanism and glaciation in the Blue Ridge: Geological Society of America Abstracts with Programs, Vol. 47, No. 7, p. 121. View Merschat 2015 GSA abstract.

Neymark, L., Aleinikoff, J., Holm-Denoma, C., Pietruszka, A., Pillers, R., and Moscati, R., 2015, High Spatial Resolution SHRIMP and LA-ICPMS U-Pb Geochronology of Pea Ridge Fe-Ree-Au Deposit, USA: Goldschmidt Abstracts, 2015 2264. View Neymark Goldschmidt abstract.

Pietruszka, A., and Neymark, L., 2014, Methods Development for In Situ Laser-Ablation Pb and Sr Isotopic Analyses Using a Double-Focusing Single-Collector ICPMS: American Geophysical Union Fall Meeting, 15-19 December 2014, San Francisco, CA. View Pietruszka AGU abstract.

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