OVERVIEW OF THE USGS DENVER INCLUSION ANALYSIS LABORATORY [DIAL] AND APPLICATIONS TO MINERAL RESOURCE INVESTIGATIONS

The chemical and isotopic composition of melt and fluid inclusions is essential to understand how magmas and hydrothermal fluids evolve and generate significant ore deposits. Such data are critical to development of reliable assessment models for mineral resources. The USGS–Denver Inclusion Analysis Laboratory [http://minerals.cr.usgs.gov/dial/] is comprised of a consortium of geoscientists that have optimized an unparalleled array of instruments for single and bulk inclusion analysis. To document petrographic relations among inclusions and their host minerals, DIAL is equipped with supporting sample preparation equipment, petrographic microscopes with UV, IR, or CL capability, SEM-CL, and digital imaging systems. Single inclusion instruments [and analytes] include gas flow and conductive heating/freezing stage microscopes [microthermometry, –196° to 1500°C], electron microprobe [oxides, F, Cl, S, Total], laser Raman spectroscope [salinity, water-gas ratios, aqueous species, daughter minerals], laser ablation or thermal decrepitation -quadrupole mass spectrometer and -ion trap-time of flight-mass spectrometer [gases], and laser ablation-induction coupled plasma-mass spectrometer [major to trace elements]. Bulk analysis methods include dual ion chromatograph [anions & cations], quadrupole mass spectrometer [gases], high resolution static sector mass spectrometer [He, Ne, Ar, Kr, Xe isotopes], and isotope ratio mass spectrometers [H, O, C, N, S isotopes]. The combination of, and normalization between, single and bulk inclusion data enables comprehensive characterization of magmas and hydrothermal fluids [T, P, d, X, isotopes]. The integration of such inclusion data with other information has enabled us to: trace the source of H, O, C, S, He, and salt, quantify ligand and metal concentrations, measure metal partioning between immiscible phases, identify mineral and gas buffers, monitor processes, constrain paleodepths, and calculate the mass of ore fluid and source rock (or magma) involved in the formation of mineral resources. Such data constrain numerical simulations of fluid flow and mineral precipitation/dissolution, and translate into practical assessment criteria.