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USGS Mendenhall Postdoctoral  Research Fellowship Program

14-26. New insights into the genesis and environmental impact of ore deposits from “heavy” metal stable isotopes

We seek a postdoctoral research fellow to apply one or more “heavy” metal stable isotopic systems to studies of the genesis and/or environmental impact of ore deposits and related mineralizing systems.  The formation of an economically important metal-rich ore deposit requires a sequence of extraordinary conditions and/or events, the details of which remain poorly understood in most cases.  The discovery of new ore deposits, and the full production of existing deposits, depends heavily upon clear knowledge of the mineralizing processes and their geologic context.  In addition, the subsequent weathering of an ore deposit, and the related transport of metals through the hydrosphere, is a topic of concern to society, particularly for understanding the natural background of toxic metals and for the mitigation of environmental hazards associated with mining.  Heavy metal stable isotopes are a relatively new tool to aid in efforts to investigate the origin and environmental behavior of ore deposits.

The advent of multiple-collector inductively coupled plasma mass spectrometry (MC-ICPMS) has made it possible to measure variations in the isotopic composition of a wide array of metals from across the Periodic Table from lithium (e.g., Teng et al., 2010) to vanadium (e.g., Prytulak et al., 2013) to uranium (e.g., Weyer et al. 2008).  High-precision isotopic measurements of these elements in geological, hydrological, and biological materials have revealed mass-dependent variations due to a range of natural processes, a development that has revolutionized the field of stable isotope geochemistry.  A small subset of these elements, such as iron (e.g., Dauphas et al., 2009; Roy et al., 2012), copper (e.g., Graham et al., 2004; Borrok et al., 2008), zinc (e.g., John et al., 2008; Paniello et al., 2012), and molybdenum (e.g., Scheiderich et al., 2010; Voegelin et al., 2012), have received most of the attention in recent years, but the stable isotopic variations of these and other heavy elements are incompletely understood, and some elements, such as gallium, germanium, indium, tin, and tellurium, have yet to be investigated in any detail.  Many of the elements that are amenable to stable isotopic investigations are economically or strategically important (directly, or indirectly because they are key elements that are used to understand the origin of mineral and energy resources) or represent significant environmental toxins, such as cerium (a rare-earth element), silver, cadmium, chromium, thallium, and mercury (in addition to the elements mentioned previously).

Variations in the stable isotopic composition of heavy metals may result from a variety of natural and anthropogenic processes, but the links between these processes and isotopic signatures are not well characterized.  Heavy metal stable isotopic systems are particularly well suited to studies of the genesis and environmental impact of ore deposits and related mineralizing systems due partly to the relatively high concentrations of many transition metals and metalloids in these systems.  Many aspects of the formation, weathering, and subsequent dispersion of an ore deposit, commonly known as its “life cycle”, can be investigated using systematic variations in the isotopic composition of heavy elements.

The primary goal for research under this Opportunity is to apply one or more metal stable isotopic systems to studies of the life cycle of ore deposits and related mineralizing systems, including the so-called Strategic and Critical Elements (e.g., lithium, platinum-group elements, rare-earth elements, antimony, tellurium, tungsten, gallium, or germanium).  Ideally, the successful candidate will choose to (1) develop a new analytical technique for measuring mass-dependent variations in the isotopic composition of an understudied or unstudied heavy element, and apply it to a study of the life cycle of an ore deposit or (2) apply one or more well established analytical techniques to one or more detailed studies of natural or experimental systems relevant to the life cycle of an ore deposit.  Applicants are encouraged to propose research that provides innovative approaches, using heavy metal stable isotopes and other geochemical data, to investigate at least one of the following research themes:  (1) the 4-D (three dimensions plus time) compositional variability within different types of ore deposits at a range of length scales; (2) studies of modern (active) natural analogs of potential ore-forming processes, preferably in conjunction with an ancient, spatially and genetically related ore deposit; (3) transport, biogeochemical transformation, and fixation of ore-related metals into the environment; and (4) experimental studies that mimic natural systems to determine the conditions or processes that may lead to compositional variability and isotopic fractionation during the life cycle of an ore deposit.  Proposals can be site specific or of a regional extent, and may involve a significant experimental component.

The USGS is creating a state-of-the-art Laboratory for Isotope Geochemistry in Denver that is expected to come online in early 2014.  This facility will include a new Class 10,000 clean laboratory, enabling low blank, high yield separation and purification of a wide range of elements (Li to U) from geological, hydrological, and biological samples.  The Mendenhall Fellow will have full access to this new laboratory as well as other existing analytical facilities and scientific expertise including a high-resolution MC-ICPMS and a high-resolution single-collector (SC)-ICPMS instrument along with associated laser ablation systems.

REFERENCES.

Borrok, D.M., et al. (2008). Isotopic variations of dissolved copper and zinc in stream waters affected by historical mining. Geochimica et Cosmochimica Acta. 72, 329-344.

Dauphas, N., et al. (2009). Iron isotopes may reveal the redox conditions of mantle melting from Archean to Present. Earth and Planetary Science Letters. 288, 255-267.

Graham, S., et al. (2004). Tracing Cu and Fe from source to porphyry: in situ determination of Cu and Fe isotope ratios in sulfides from the Grasberg Cu-Au deposit. Chemical Geology. 207, 147-169.

John, S.G., et al. (2008). Zinc stable isotopes in seafloor hydrothermal vent fluids and chimneys. Earth and Planetary Science Letters. 269, 17-28.

Paniello, R., et al. (2012). Zinc isotopic evidence for the origin of the Moon. Nature. 490, 376-379.

Prytulak, J., et al. (2012) The stable vanadium isotope composition of the mantle and mafic lavas. 365, 177-189.

Roy, M., et al. (2012). Iron isotope fractionation in a sulfide-bearing subterranean estuary and its potential influence on oceanic Fe isotope flux. Chemical Geology. 300-301, 133-142.

Scheiderich, K., et al. (2010). Century-long record of Mo isotopic composition in sediments of a seasonally anoxic estuary (Chesapeake Bay). Earth and Planetary Science Letters. 289, 189-197.

Teng, F.Z., et al. (2010). Contrasting lithium and magnesium isotope fractionation during continental weathering. Earth and Planetary Science Letters. 300, 63-71.

Voegelin, A.R., et al. (2012). The impact of igneous bedrock weathering on the Mo isotopic composition of stream waters: natural samples and laboratory experiments. Geochimica et Cosmochimica Acta. 86, 150-165.

Weyer, S., et al. (2008). Natural fractionation of 238U/235U. Geochimica et Cosmochimica Acta. 72, 345-359.

Proposed Duty Station: Denver, CO

Areas of Ph.D.:  Isotope or trace element geochemistry, analytical chemistry, chemical petrology or mineralogy, economic geology or related fields (candidates holding a Ph.D. in other disciplines but with knowledge and skills relevant to the Research Opportunity may be considered).

Qualifications: Applicants must meet one of the following qualifications - Research Geologist, Research Chemist.

(This type of research is performed by those who have backgrounds for the occupations stated above.  However, other titles may be applicable depending on the applicant’s background, education, and research proposal. The final classification of theposition will be made by the Human Resources specialist).

Research Advisors: Aaron Pietruszka, (303) 236-5514, apietruszka@usgs.gov; Rich Wanty, (303) 236-1819, rwanty@usgs.gov; Philip Verplanck , (303) 236-1902, plv@usgs.gov, Ian Ridley, (303) 236-1800, iridley@usgs.gov

Human Resources Office Contact: Jennifer Daberkow, (303) 236-9566, jdaberkow@usgs.gov


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U.S. Department of the Interior, U.S. Geological Survey
URL: http://geology.usgs.gov/postdoc/opps/2014/14-26 Pietruszka.htm
Direct inquiries to Rama K. Kotra at rkotra@usgs.gov
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Last modified: 17:58:04 Tue 23 Jul 2013
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