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David I. Norman 1 and Joseph N. Moore 2

Evolution and source of supercritical fluids in the Iceland Deep Drilling Project borehole in light of fluid inclusion quantitative mass spectrometry and microthermometry. David I. Norman 1 and Joseph N. Moore 2 1.Dept. of Earth and Environmental Science, New Mexico Tech

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David I. Norman 1 and Joseph N. Moore 2

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  1. Evolution and source of supercritical fluids in the Iceland Deep Drilling Project borehole in light of fluid inclusion quantitative mass spectrometry and microthermometry David I. Norman1 and Joseph N. Moore2 1.Dept. of Earth and Environmental Science, New Mexico Tech 2.Energy & Geoscience Institute, U. of Utah

  2. Objectives • Characterize past fluid chemical and physical properties • Determine fluid sources and processes • Characterize mineralization and wall rock alteration in s supercritical geothermal system • Understand the evolution of a supercritical geothermal system

  3. Approach Study splits mineral veins and wall rocks (or cuttings) samples by • Petrographic study • Fluid inclusion petrology and microthermometry • Fluid inclusion gas analysis • Fluid inclusion stable isotope analysis • Make supercritical fluid inclusions

  4. Fluid inclusion microthermometry Petrography Fluid inclusion gas analyses Clay mineral analyses (if any) Fluid inclusion stable isotope analyses (with A. Campbell) Division of Labor Moore Norman

  5. Trapping temperatures Trapping pressures Fluid salinities Boiling and fluid mixing Compare temperatures to thermal gradients and boiling curves Types of mineralization and wall rock alteration Paragenesis and evolution Temperature estimates Compare mineralization and alteration to that predicted by reaction –path modeling Petrographic and Fluid Inclusion Studies Fluid Inclusion Microthermometry Petrographic studies

  6. Will There be Vein Quartz? bars (calculated by SUPPCRT ’92)

  7. Trapped Supercritical Fluids -Working with Isochores • Isochores best calculated knowing fluid gas chemistry and fluid salinity • Constrain P-T trapping estimates

  8. Making Fluid Inclusions • Using the method pioneered by Bob Bodnar, we will make fluid inclusions in Brazilian quartz. • This will allow us to “calibrate” our isochore and gas analysis methodology. • We will be able to supply high temperature, supercritical fluid inclusion standards to the fluid inclusion community.

  9. < 0.1 gm mineral grain or wall-rock chip

  10. Is there significant methane in supercritical fluids? Comparison of Fluid Inclusion Analyses to Vent Fluids, Mothra Black Smoker

  11. The CO2/N2-Total Gas Diagram 1000 Condensation trend 100 Boiling-trend CO2/N2 10 Excess gas boiling Gas cap 1 0.1 0.1 1 10 100 Total Gas (mol.%)

  12. Examples: Coso fluid inclusions

  13. Locality: New Mexico MVT deposit Salinity ~8 eq.wt.% NaCl Th ~ 182 ºC

  14. Ar/He-N2/Ar Diagram Andesite Basalt

  15. Karaha-Telaga Bodes (Indonesia) fluid inclusions: Wall rocks include lake beds Average of 89 analyses T-8 well Ralkane/alkene= 23

  16. H2S Saturation The Geysers Broadlands

  17. Example of how we integrate our work Petrographic observation: Calcite is replacing K-feldspar • Supporting Data: • Fluid inclusions indicate no boiling, lower salinity, lower Th fluid • Gas analyses suggest no boiling • Gas analyses indicate shallow meteoric water • Conclusion: Calcite resulted from • an influx of shallow, cooler slightly more acidic or lower salinity meteoric water into the geothermal system. meteoric water fault

  18. Stable Isotopes Will be Done on a New Finnigan Mat 253 Instrument with TC/EA High Temperature Conversion Apparatus • Will analyze dD and d18O on inclusions in mineral and wall rock chips • Analyses will be performed on splits of samples used for fluid inclusion gas analysis

  19. Preparation • Practice gas and microthermometry analyses on Drammen Granite (Norway) miarolitic quartz • Solve problem of how to measure CO by CFS gas analytical method • Develop stable isotope analytical methods • Find best equation of state for isochore calculations

  20. Needed for Our Studies About 25 samples of veins or veinlets taken from about every 200 meters, and an alike number of 5 gm samples of wall rock from near the interval from which the veins samples are obtained. We can work on cuttings. We will need to be able to lower a wire “bucket” to near bottom of the drill hole and keep it there for several days.

  21. FUNDING DOE grant DE-F007-00ID13953

  22. Questions • Do inclusions fluids represent present fluids? • How have fluids evolved in the present supercritical zone? • What types of alteration assemblages are associated with supercritical fluids and how have these evolved? • Do the supercritical fluids have N2-Ar-He ratios similar to MORB basalt? • How do fluid sulfur species gases and concentrations change with time, depth and temperature? • Is there significant methane in Iceland deep geothermal fluids like is seen in MOR geothermal vents, and if so, is the methane generated by inorganic processes or by pyrolysis of biological material? • How do gas chemistry and fluid processes change with depth?

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