Crustal Geophysics and Geochemistry Science Center

Isotope and chemical methods for mineral and geoenvironmental assessments

Noble gas isotope and active gas chemistry of studies of mineral deposits


Task Objectives

Noble gas isotope chemistry of fluid inclusions is a emerging field that when combined with stable isotope, active gas species and multi-element chemistry data has the potential to result in a quantum leap in the understanding of ore forming processes. Noble gases are inert and conservative gas species whose isotopes provide tracers on the origin of components in hydrothermal ore-forming fluids from mantle, deep crustal, shallow crustal and atmospheric sources. Consequently noble gas data provide the opportunity to understand ore formation in a larger context of crustal evolution and magma generation than is possible with other isotope and chemical data.

The task will provide high precision fluid inclusion gas analyses of the active gas species (N2, CO2, CH4, H2, H2S, SO2, HCl, HF, H2O, and light hydrocarbons) and noble gases and their isotopes (He, Ne, Ar, Kr, Xe). Compositions and isotopes will be used to identify volatile evolution, magma degassing, and gas-rock buffering processes leading to mineralization in several metal deposit environments. The thermodynamics versus kinetics of key reactions will be examined. Geochemical and model driven paradigms of ore-forming processes will be advanced based upon new insights constrained by active and noble gas chemistry.

Statement of Work

This year the focus will be on completion of manuscripts and papers. Carlin NV Eocene volcanics and study of mantle-crust-magmatic volatiles evolution into metals transport and deposition will continue. To facilitate this, new Matlab software has been developed to reduce by least squares residual numerical methods all quad mass spec data, using an interactive GUI interface within Matlab. High temperature and pressure H2O-CO2 volatile equilibration experiments with basalts are being performed. We are developing methods of opening and analyzing the experimental capsules within the ultrahigh vacuum manifold for analysis of residual volatile components and then to thermodynamically re-speciate the gas chemistry back to PT conditions. The task will continue support of work on Sleeper, pegmatites, ancient hydrothermal-geothermal systems, Oyu Tolgoi, and Chinese deposits with colleagues and visitors.

Products

Abstracts

  • Hofstra, A.H., Landis, G.P., 2009, Analysis of gases in single melt or fluid inclusions by quadrupole mass spectrometry [QMS] and ion trap-time of flight mass spectrometry [IT-TOF-MS] – Application to mineral resource investigations: Geological Society of America Abstracts with Program, v. 41, no. 7, p. 332.
  • Hofstra, A.H., Rye, R.O., Landis, G.P., Johnson, C.A., Emsbo, P., Koenig, A.E., Marsh, E.E.,Todorov, T.I., and Adams,D.T., 2009, Overview of the USGS Denver Inclusion Analysis Laboratory [DIAL] and applications to mineral resource investigations. Geological Society of America Abstracts with Program, v. 41, no. 7, p. 254.
  • Hofstra, A.H., Todorov, J.I., Marsh, E.E., Emsbo, P., and Landis, G.P., 2010, Chemical composition of fluid inclusions, U.S. Antimony Mine, MT–Relation to giant silver veins in the Coeur d'Alene district, ID, USA: Pan-American Current Research on Fluid Inclusions, Abstract with Program, pp. 45-46.
  • Hunt, A.G., Breit, G.N., Bergfeld, D., Rytuba, J., Wolf, R.E., and Landis, G.P., 2009, Use of noble gas geochemistry and trace element analysis to determine if modern geothermal waters are responsible for associated epithermal Au deposits: Geological Society of America Abstracts with Program, v. 41, no. 7, p. 526.
  • Landis, G.P., and Rye, R.O., 2009, Fluid inclusion active and noble gases in coarse-banded alunite veins at Alunite Ridge, Marysvale, Utah, and implications for crust-mantle magmatic volatile evolution: Geological Society of America Abstracts with Programs, v. 41, no. 7, p. 525.
  • Marsh, E.E., Landis, G.P., Emsbo, P., Todorov, T.I., and Goldfarb, R.J., 2009, Geochemistry of fluid inclusions from orogenic and intrusion-related gold deposits in the Tintina gold province, Alaska and the Yukon Territory: Geological Society of America Abstracts with Program, v. 41, no. 7, p. 256.
  • Rusk, B.G., Hofstra, A.H., Emsbo, P., Hunt, A.G., Landis, G.P., and Rye, R.O., 2009, Low salinity fluids from large open system magma chambers form porphyry-Cu (Mo-Au) deposits: Geological Society of America Abstracts with Program, v. 41, no. 7, p. 523.

Presentations

  • Johnson, C.A., Landis, G.P., and Bookstrom, A.A., 2007, Sulfur and helium isotopes in the cobalt+copper +/- gold deposits of the Idaho Cobalt Belt: Geological Society of America Abstracts with Programs, v. 39, no. 6, p. 412.

Articles and Reports

  • Hofstra, A.H., Landis, G.P., Premo, W.R., Ressel, M.W., and Henry, C.D., 2010, Evaluation of the role of magmatic volatiles from Eocene mafic to flesic igneous rocks in the formation of Carlin-type gold deposits of the Carlin trend and Jerritt Canyon district as constrained by preliminary He, Pb, Sr, Nd isotopic data: Proceedings of the Geol. Soc. Nevada, 12 p.
  • Hunt, A.G., Breit, G., Bergfeld, D., Rytuba, J.J., Landis, G.P., and Wolf R.E., 2010, Clarification of the roles of magmatic versus amamgmatic sources for modern geothermal systems associated with epithermal mineralization using noble gas geochemistry: Proceedings of Geol. Soc. Nevada, 20 p.

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