Crustal Geophysics and Geochemistry Science Center

Isotope and chemical methods for mineral and geoenvironmental assessments

Solute chemistry of fluid inclusions


Task Objectives

Task objectives are to produce chemical analyses of cations and anions in fluid inclusions in hydrothermal minerals to aid in understanding the source of ore-fluid components and geochemical processes that form ore deposits. These data, when integrated with age, isotopic, geologic, fluid inclusion gas, and geochemical data are of fundamental importance in effectively developing robust mineral deposit and geoenvironmental models. Fluid inclusion compositional data are being used to understand fluid-rock reactions, the migrational history of deep crustal fluids, and to develop models for the genesis of a variety of deposit types and assess the regional impact of hydrothermal systems that are geologically and geochemically realistic. Recent results have opened new avenues of study and demonstrate that this new method is an important tool in ore genesis studies.

Statement of Work

This year work will continue collaborative research with James Cook University and the Institute of Geosciences, University of Campinas, to study the brines that form iron oxide-copper-gold (IOCG) deposits in Brazil and Australia. A collaboration with the Center for Ore Deposit Research (CODES), Colorado School of Mines, and AMIRA on the origin of brines that formed the African Copper Belt will continue. This study will be expanded to include samples from sediment hosted copper deposits from around the world. Results will help constrain the origin of the brines, map brine provinces, and identify subsequent compositional modifications resulting from mineral precipitation, fluid-rock reactions, and fluid mixing involved in the formation of sedimentary hosted Cu deposits. This work will provide important constraints for several efforts currently underway for the national Assessment Projects. We will continue to augment data from our current sample with noble gas analyses, which will further characterize sources and genesis of these fluids. The sources of brines that formed sedimentary Cu and IOCG deposits have previously not been established, but might be vital in understanding the geneses of these enormous deposits. Collaborative studies of this deposit type will be pursued this year to gain samples for analyses.

Products

Presentations

  • Emsbo, P., 2009, Fluid Inclusion Cl-Br-Na Ratios Implicate Residual Evaporative Brines in the Formation of Supergiant Sedex Zinc Deposits: Geological Society of America Abstracts with Programs, Vol. 41, No. 7, p. 254.
  • 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, Vol. 41, No. 7, p. 254.
  • 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., 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, Vol. 41, No. 7, p. 523.

Reports

  • Emsbo, P, 2009, Geologic Criteria for the Assessment of Sedimentary Exhalative (Sedex) Zn-Pb-Ag Deposits: U.S. Geological Survey Open-File Report 2009-1209, 21 p.
  • Rusk, B., Hofstra, A., Emsbo, P., Hunt, A.G., Landis, G., and Rye, R., 2008, Fluid Inclusion Insights into the Origins of Fluids and Metals in Porphyry Copper Deposits: PACRIM Congress 2008, The Australian Institute of Mining and Metallurgy, pp. 289 - 293.
  • Xavier, R., Rusk, B., Emsbo P., and Monteiro, L. 2009, Composition and source of salinity of ore-bearing fluids in Cu-Au systems of the Carajás Mineral Province, Brazil, Smart Science for Exploration and Mining.

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