Summary of Micrographic Analysis of Fracture Coating Phases on Drill Cores from Pahute Mesa, Nevada Test Site, Revision 1

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BEST AVAILABLE COPY Summary of Micrographic Analysis of Fracture Coating Phases on Drill Cores from Pahute Mesa, Nevada Test Site BEST AVAILABLE COPY

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BEST AVAILABLE COPY Available to the public from - U.S. Department of Commerce National Technical Information Service 5285 Port Royal Road Available electronically at http://www. doe, pov/bridee. Available to U.S. Department of Energy and its contractors in paper from - U.S. Department of Energy Office of Scientific and Technical Information BEST AVAILABLE COPY

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BEST AVAILABLE COPY DOE/NV/13052--05CH SUMMARY OF MICROGRAPHIC ANALYSIS OF FRACTURE COATING PHASES ON DRILL CORES FROM PAHUTE MESA, NEVADA TEST SITE North Las Vegas, Nevada 89030 Prepared for U.S. Department of Energy. Nevada Operations Office under contract No. DE-AC08-97NV13052 BEST AVAILABLE COPY

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BEST AVAILABLE COPY This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or use fulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any spe cific commercial product, process, or service by trade name, trademark, manufac turer, or otherwise does not necessarily constitute or imply its endorsement, recom mendation. or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the. United States Government or any agency thereof. BEST AVAILABLE COPY

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BEST AVAILABLE COPY Portions of this document may be illegible in electronic image products. Images are produced from the best available original BEST AVAILABLE COPY

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BEST AVAILABLE COPY SUMMARY OF MICROGRAPHIC ANALYSIS OF FRACTURE COATING PHASES ON DRILL CORES FROM PAHUTE MESA, NEVADA TEST SITE Janet N. Wide, Project Manager BEST AVAILABLE COPY

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BEST AVAILABLE COPY Table of Contents List of Figures................................................................................................................................ iii List of Acronyms and Abbreviations............................................................................................ vii 4.1.3 Sample from 1,399 Feet................................................. 4-7 4.2.1 Sample from 173 Feet.................................................................... 4-20 4.3.2 Sample from 13,674 Feet........................................................................ 4-25 4.4.1 Sample from 290 to 330 Feet.................................................................. 4-31 4.5.1 Sample from 320 Feet........................................................ 4-31 4.5.3 Sample from 5,893 Feet.......................................................... 4-35 BEST AVAILABLE COPY

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BEST AVAILABLE COPY Table of Contents (Continued) 4.6.1 Sample from 1,750 Feet.......................................................................... 4-45 4.6.2 Sample from 1,790 to 1,810 Feet............................................................ 4-45 4.6.3 Sample from 2,860 to 2,870 Feet............................................................ 4-45 Appendix A - HRTEM Study of Coating Materials of Fe-Mn Oxides and Clays BEST AVAILABLE COPY

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BEST AVAILABLE COPY List of Figures Number Title Page 3-1 Pahute Mesa Area, Showing Drill Holes from which Archived Materials were Sampled............................................... ........................... 3-2 4-1 SEM Image Showing Bladed Calcite from UE-18t (1,378 foot depth).....................4-2 4-2 SEM Image Showing Heulandite (h). Opal (o), and Smectite (s) 4-3 SEM Image Showing Delicate Smectite Web Structure 4-4 Electron Microprobe (BSE) Image of Thin Section from UE-18t (1,378 foot depth) Showing Potassium Feldspar (f), 4-5 SEM Image Showing Platy Apatite Crystals from 4-6 SEM Image Showing Fine-Grained Calcite Rhombs with Opaline Silica and Smectite from UE-18t (1,399 foot depth)............................ 4-9 4-7 SEM Image Showing Coarse Crystalline Analcime with Opaline Silica from UE-18t (1,399 foot depth)................................................... .. 4-10 4-8 SEM Image Showing Corroded Analcime Crystals with Infilling by Opaline Silica and Calcite Rhombs from 4-9 BSE Image of UE-18t (1,399 foot depth) Showing Apatite (ap) with Eroded Analcime (a)........................................................................................ 4-12 4-10 SEM Image Showing Eroded Calcite (Cc) with Local Smectite (s) 4-11 BSE Image of UE-18t (2,002 foot depth) (Fracture A) and Iron Oxide (Fe).................................................................. 4-15 4-12 SEM Image Showing Pitted and Eroded Calcite (Cc) Adjacent to Mixed Hematite and Smectite from UE-18t (2,002 foot depth) 4-13 SEM Image Showing Smectite (s) Web Between Eroded Calcite (Cc) 4-14 BSE Image of UE-18t (2,002 foot depth) (Fracture B) Showing Calcite (Cc) and Quartz (q) with Iron Oxide (Fe) Coating on Fracture............................. 4-18 4-15 Electron Microprobe (BSE) Image of Thin Section (2,020 foot depth) BEST AVAILABLE COPY

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BEST AVAILABLE COPY Number Title Page 4-16 SEM Image Showing Ragged IIHte Plates from UE-18t 4-17 SEM Image Showing Thin Veil of Smectite Clay on Glass from 4-18 SEM Image Showing Incipient Smectite Growth on Glassy Lapilli Fragment from U-19ar (1,560 foot depth)......................................4-24 4-19 SEM Image Showing Very Fine-Grained Nature of Mixed Fracture Coating Material Comprised of Hematite, Quartz, Hlite, Manganese Oxides, and Alkali Feldspars from UE-20f 4-20 SEM Image Showing a Shallow Crack and the Layering in the Fracture Coating Material from UE-20f (8,668 foot depth)..................................4-27 4-21 SEM Image Showing Blocky, Uneroded Calcite (Cc) with Overgrowth of Illite/Smectite (i/s) Mixed with Goethite from 4-22 SEM Image Showing Euhedral to Subhedral Pyrite Cubes in Vein Matrix of Massive to Sugary Quartz from UE-120f (13,674 foot depth).............. 4-29 4-23 BSE Image of UE-20f (13,674 foot depth) Showing Calcite (Cc) with an Eroded Iron-Rich Rim, and Quartz (q) on Fracture Surface, 4-24 SEM Image Showing Botryoidal Opaline Silica (with later opaline overgrowths) and Eroded Calcite from PM-2 (320 foot depth)..............................4-32 4-25 BSE Image of PM-2 (320 foot d epth) Showing Growth Bands in Botryoidal Opaline Silica with Calcite (Cc)....................................................... 4-33 4-26 Electron Microprobe Elemental Map for Silica in PM-2 (320 foot depth)............ 4-34 4-27 SEM Image Showing Barite Coating Partially Open Fracture Aperture from PM-2 (4,180 foot depth)................................................................. 4-36 4-28 SEM Image Showing Eroded Calcite on Fracture from PM-2 4-29 SEM Image Showing Chlorite on Pitted Calcite from PM-2 4-30 BSE Image of PM-2 (8,050 foot depth) Showing Calcite (Cc), 4-31 SEM Image Showing Eroded Calcite (Cc) and Quartz (q) with Mixed Illite/Smectite Mat (i/s) from PM-2 (8,403 foot depth)................................. 4-41 BEST AVAILABLE COPY

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BEST AVAILABLE COPY List of Figures (Continued) Number Title Page 4-32 SEM Image Showing Close-Up View of Eroded Quartz Crystals with Coating of Mixed Illite/Smectite from PM-2 (8,403 foot depth)....................4-42 4-33 SEM Image Showing Locally Well Developed Mixed Illite/Smectite Clay 4-34 SEM Image Showing Coarse, Blocky, Eroded and Etched Carbonate with Spotty Local Growths of Illite/Smectite from PM-2 4-35 BSE Image of PM-2 (8,403 foot depth) Showing Calcite (Cc), BEST AVAILABLE COPY

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List of Tables BEST AVAILABLE COPY Number Title Page 3-2 Drill Hole Identification, Depths to Groundwater, Sampling Intervals, Lithostratigraphic Description, and Hydrostratigraphic Descriptions for Fracture Coating and Calcite Samples Collected from Pahute Mesa..............3-3 4-1 Electron Microprobe Results (in weight percent oxide) for Point Analyses of Selected Specific Phases in Drill Core Samples from Pahute Mesa..................4-6 5-1 Summary of Fracture Coating Phase Distribution as a Function BEST AVAILABLE COPY

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BEST AVAILABLE COPY List of Acronyms and Abbreviations HRTEM High-resolution transmission electron microscope IT IT Corporation LLNL Lawrence Livermore National Laboratory NTS Nevada Test Site SAED Sleeted area electron diffraction SEM Scanning electron microscope USGS U.S. Geological Survey U.S. Department of Energy Desert Research Institute Energy dispersive spectroscopy BEST AVAILABLE COPY

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BEST AVAILABLE COPY List of Acronyms and Abbreviations (Continued) WDS Wavelength dispersive spectroscopy ZAF Atomic number-absorbtion- fluoresence BEST AVAILABLE COPY

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Fracture Coating Phases BEST AVAILABLE COPY Fracture coating mineral phases on 14 archived core samples from three drill holes in the Pahute Mesa area were analyzed using micrographic techniques. Six additional samples (cuttings and percussion gun sidewall cores) of non-fractured, calcite-bearing materials from three other drill holes on Pahute Mesa were collected primarily for isotopic evaluation. Three of the principal volcanic aquifers hosting groundwater flow are represented by the samples collected. Fracture coating phases within the Timber Mountain Aquifer system are characterized by calcite + mixed illite/smectite + opaline silica in the unsaturated and Mn-oxyhydroxides in the saturated zone. A single sample from the saturated portion of the Belted Range Aquifer is characterized by intense fracturing and the feldspars + mixed illite/smectite. This suggests the presence of a significant transmissive hydrogeologic feature or stratigraphic interval. The predominance of secondary oxide phases in this sample also has important connotations for the potential adsorption of dissolved solutes. Fracture coating phases within the Basal Aquifer are characterized by phases more indicative of an active hydrothermal environment (such as quartz + pyrite + barite) rather than precipitation from a groundwater system. The distinct fracture coating phase assemblages in the three aquifer systems have the potential to impart a geochemical signature to resident groundwaters. This may result in isotopic exchange during water-rock interaction, adsorption of solutes by zeolites and/or Fe- and Mn-oxyhydroxides, or dissolution of relatively soluble phases such as sulfides, volcanic glass, and feldspars. Calcite textures in these samples indicate that carbonate dissolution and precipitation is widespread. The presence of multiple generations of calcite along with other carbonate minerals suggests that these aquifer systems are near equilibrium with respect to carbonate. These geochemical processes should be reflected in the water chemistry of Pahute Mesa groundwaters and will be evaluated as part of the Oasis Valley geochemical modeling conducted during FY 1999. BEST AVAILABLE COPY

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BEST AVAILABLE COPY Fracture Coating Phases The flow path between Pahute Mesa and the groundwater discharge area in Oasis Valley (approximately 18 miles to the southwest) is of concern due to the relatively short travel distance between a recharge area where underground nuclear testing has been conducted and the off-site water users. Groundwater flow and transport modeling by IT Corporation (IT) has shown rapid tritium transport in the volcanic rock aquifers along this flow path (DOE/NV, 1997). The resultant estimates of rapid transport were based on water level data, limited hydraulic conductivity data, estimates of groundwater discharge rates in Oasis Valley, assumed porosities, and estimated retardation rates. Many of these parameters are poorly constrained and may vary considerably. Sampling and analytical techniques are being applied as an independent means to determine transport rates by providing an understanding of the geochemical processes that control solute movement along the flow path. Collaborative geochemical investigations include participants from the U.S. Geological Survey (USGS), Desert Research Institute (DRI), IT, and Lawrence Livermore National Laboratory (LLNL). The intent of these investigations is to use geochemical and isotopic constraints to independently verify the Pahute Mesa - Oasis Valley numerical groundwater flow model, and to determine the age, related travel time, and solute attenuation characteristics for groundwater moving along this flow path. As part of these geochemical investigations, this report summarizes the analysis of fracture coating mineral phases from drill core samples from the Pahute Mesa area of the Nevada Test Site (NTS). Archived samples were collected based on the presence of natural fractures and on the types and abundance of secondary mineral phases present on those fracture surfaces. Mineral phases present along fracture surfaces are significant because, through the process of water-rock interaction, they can either contribute (as a result of dissolution) or remove (as a result of precipitation or adsorption) constituents from solution. Particular attention was paid to secondary calcite occurrences because they represent a potential source of exchangeable carbon and can interact with groundwater resulting in a modified isotopic signature and apparent water age. A companion report by Rose et al. (1998) discusses the results of the stable isotope and radiocarbon analyses of the calcite from these samples. BEST AVAILABLE COPY

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BEST AVAILABLE COPY Fracture Coating Phases Sample properties that were evaluated include: • Sample mineralogy, specifically secondary phases on fi-acture • The chemical composition of selected mineral phases that are assumed to be relatively soluble (e.g., volcanic glass or feldspars) or phases (such as zeolites or iron and manganese oxyhydroxides) that are assumed to be effective substrates for the adsorption of dissolved solutes The sample analysis activities were performed using a combination of optical petrographic, scanning electron micrographic, electron microprobe, and high-resolution transmission electron micrographic techniques. The scanning electron microscope (SEM) and electron microprobe analyses were conducted using the U.S. Geological Survey Microbeam Laboratory, at the Denver Federal Center in Lakewood, Colorado, with the assistance of Greg Meeker. The SEM used is a JEOL 5800LV coupled with an Oxford ISIS energy dispersive spectroscopy(EDS) system. Typical accelerator voltage used on the SEM was 20 kilovolts. Due to the size constraints of the SEM sample chamber, portions (up to 3x3 centimeters) of the natural exposed open fracture surfaces were separated from the main sample and gold-coated for textural and mineralogical evaluation in the SEM. The electron microprobe is a JEOL 8900. Microprobe analyses were corrected using wavelength dispersive spectroscopy (WDS) and ZAF procedures. Backscattered electron (BSE) images and quantitative, using wavelength spectrometers (for Si) by rastering the stage under a stationary electron probe. A single elemental map was obtained from one sample of an area of 4 square millimeters, using 1,000 by 1,000 pixels and a pixel size of 2 microns. analyses were conducted under contract by Huifang Xu, manager of the Transmission Electron Microscopy Laboratory, at the University of New Mexico in Albuquerque, New Mexico. Four separate sub-samples were sent to the University of New Mexico for the preparation of BEST AVAILABLE COPY

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Fracture Coating Phases BEST AVAILABLE COPY ion-milled thin sections and powder samples as summarized in the report by Xu (1998), which is attached as Appendix A. All HRTEM analyses were conducted using a JEOL 2010 HRTEM and associated Link ISIS EDS system with an ultra-thin window for the detector. HRTEM parameters are specified in Appendix A. BEST AVAILABLE COPY

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BEST AVAILABLE COPY Fracture Coating Phases Twenty sub-samples were collected from drill core, cuttings, and percussion gun sidewall core archived at the USGS Core Library in Mercury, Nevada. A preference was given to core samples, due to the high quality preservation of mineral phase relationships on fracture surfaces. However, cuttings and percussion gun sidewall cores were also collected for the isotopic analysis of calcite based on information contained in Warren et al. (1998). The locations of the six drill holes that were sampled are shown in Figure 3-1. Sampling was conducted in April 1998, after sample selection and the sampling plan had been approved by the custodial agency for each drill hole of interest. Samples were collected from the drill holes and depth intervals shown Hydrology and Radionuclide fractured drill core Los Alamos National Laboratory 1,560 percussion gun sidewall core Lawrence Livermore National 290 to 300 drill cuttings from 10-foot intervals Lawrence Livermore National 13,674 fractured drill core Hydrology and Radionuclide fractured drill core Hydrology and Radionuclide percussion gun sidewall core drill cuttings from 10-foot intervals drill cuttings from 10-foot intervals BEST AVAILABLE COPY

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Fracture Coating Phases BEST AVAILABLE COPY U.S. Department of Energy Nevada Test Site, Nevada Pahute Mesa Area, Showing Drill Holes From Which Archived Materials Were Sampled Pahute Mesa Area, Showing Drill Holes from which Archived Materials were Sampled BEST AVAILABLE COPY

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BEST AVAILABLE COPY Fracture Coating Phases Drill hole information including standing water level (from Laczniak et al., 1996), depth interval sampled, and lithostratigraphic (from drill logs on file at the USGS Core Library and from Warren et al., 1998) and hydrostratigraphic (from Prothro and Drellack, 1997) descriptions of sample intervals are summarized in Table 3-2. Additional data comes from a report summarizing a fracture analysis conducted on Pahute Mesa (Drellack et al., 1997), which includes drill holes UE-18t and Drill Hole …