Crustal Geophysics and Geochemistry Science Center

Isotope and chemical methods for mineral and geoenvironmental assessments

Chemical compositions of single melt and fluid inclusions


Task Objectives

Ore genesis studies are often interpreted in terms of the evolution of magmas and hydrothermal fluids that produce them. Melt and fluid inclusions in various minerals record the compositions of such magmas and fluids. Our challenge in the study of ore deposits is to read the complete record at the smallest level of detail. It is now possible to determine the multielement composition of the magmas and fluids of individual inclusions as small as 10 microns using our newly acquired petrographic microscope - laser ablation - induction coupled plasma - mass spectrometer (PM-LA-ICP-MS) system.

To compliment this system we will develop a laser raman microprobe for analysis of water, major gas species, and salinity and an experimental laser ablation- quadrupole ion trap, time of flight mass spectrometer (LA-IT-TOF-MS) system for the analyses of major and minor gas species and possibly noble gas and stable isotope compositions. Data obtained from these systems can be used to calculate the mass of magma and/or ore fluid required to produce a given deposit, identify the metal transporting ligands, characterize the chemical environment of ore formation, precipitation mechanisms, fluid-rock interactions and source(s) of ore components. No other laboratory has such capabilities and the prospect of having such equipment offers an unparalleled opportunity to increase our understanding of the processes that produce ore deposits in a way that will lead to greatly improved mineral assessment models for many deposit types.

Our new PM-LA-ICP-MS system will be tested and methods developed to determine the mulitelement composition of individual silicate melt and aqueous fluid inclusions in igneous and hydrothermal quartz from the full spectrum of magmatic and amagmatic ore deposit types. The laser raman microprobe and LA-IT-TOF-MS system will be brought into operation and methods developed to determine the major and minor gas species in individual fluid inclusions. We will also attempt to determine the isotope composition of noble gases and eventually the isotope composition of carbon in CO2 and hydrogen in water in single fluid inclusions. Such individual fluid inclusion data will be integrated with other bulk stable isotope, noble gas isotope and gas and ionic species data on the same samples to better understand the evolution of ore producing magmas and hydrothermal fluids.

Statement of Work

Continue to develop inclusion analysis methods and apply them to diverse ore deposit problems. Foster collaborations with both internal and external geoscientists. Prepare publications for symposia, journals, and USGS reports.

Products

Abstracts

  • Adams, D., Todorov, T., Premo, W.R., Hofstra, A.H., and Rye, R.O., 2009, The age of zircons and composition of melt inclusions in quartz phenocrysts from an altered dike indicate the ~14 ma Alunite Ridge - Deer Trail system overlies a 30.7 ma silicic intrusion: Geological Society of America, Abstracts with Programs, v. 41, no. 6, p. 20.
  • Adams, D.T., Hofstra, A.H., Cosca, M.A., Todorov, T.I., and Marsh, E.E., 2009, Age of sanidine and composition of melt inclusions in quartz phenocrysts from volcanic rocks associated with large Mo and Be deposits in the western Unites States: Geological Society of America, Abstracts with Programs, v. 41, no. 7, p. 255.
  • 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 Programs, v. 41, no. 7, p. 254.
  • Hofstra, A.H. and 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 Programs, v. 41, no. 7, p. 332.
  • 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 felsic igneous rocks in the formation of Carlin-type gold depositsvin the Carlin trend an Jerritt Canyon district as constraned by He, Pb, Sr, and Nd isotopic data: Geological Society of Nevada 2010 Symposium, Great Basin Evolution & Metallogeny, May 14 - 22, Sparks, Nevada, p. 53.
  • Hofstra, A.H., Todorov, T.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: PACROFI X 2010, June 7-10, 2010, Las Vegas, Nevada, 2 p.
  • 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 Programs, v. 41, no. 7, p. 256.
  • Rusk, B.G., Hofstra, A.H., Emsbo, P., Hunt, A.G., Landis, G.P., Rye, R.O., Reed, M., Dilles, J.H., Valley, J.W., and Kita, N.T., 2009, Low salinity fluids from large open system magma chambers form porphyry Cu (Mo-Au) deposits: Geological Society of America, Abstracts with Programs, v. 41, no. 7, p. 523.
  • Todorov, T., Koenig, A., and Marsh, E.E., 2009, Integrated Raman microspectroscopy laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) system for the analysis of fluid and melt inclusions: Geological Society of America, Abstracts with Programs, v. 41, no. 7, p. 332.
  • Todorov, T., Koenig, A., Marsh, E.E., Adams, D.T., and Hofstra, A.H., 2009, Techniques for elemental quantification of laser ablation-inductively coupled plasma-mass spectrometry [LA-ICP-MS] results for melt and fluid inclusions – Problems and solutions: Geological Society of America, Abstracts with Programs, v. 41, no. 7, p. 255.

Reports

  • Rusk, B.G., Hofstra, A.H., Embso, P., Hunt, A.G., Landis, G.P., and Rye, R.O., 2008, Fluid inclusion insights into the origins of fluids and metals in porphyry copper deposits: PACRIM Congress 2008, The Pacific Rim: Mineral Endowment, Discoveries & Exploration Frontiers, 24-26 November, Gold Coast, Queensland, Australia, 7 p.

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