Effects of Hydrothermal Alteration on the Geomechanics of Degradation at the Bagdad Mine, Arizona Item Type text; Electronic Thesis Authors Coutinho, Paulo Citation Coutinho, Paulo. (2020). Effects of Hydrothermal Alteration on the Geomechanics of Degradation at the Bagdad Mine, Arizona (Master's thesis, University of Arizona, Tucson, USA). Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction, presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 05/10/2021 14:56:11 Link to Item http://hdl.handle.net/10150/648603 EFFECTS OF HYDROTHERMAL ALTERATION ON THE GEOMECHANICS OF DEGRADATION AT THE BAGDAD MINE, ARIZONA by Paulo Coutinho ______________________________________________________________________________ Copyright © Paulo Coutinho 2020 A Thesis Submitted to the Faculty of the DEPARTMENT OF MINING AND GEOLOGICAL ENGINEERING In Partial Fulfillment of the Requirements For the Degree of MASTER OF SCIENCE WITH A MAJOR IN MINING, GEOLOGICAL, AND GEOPHYSICAL ENGINEERING In the Graduate College THE UNIVERSITY OF ARIZONA 2020 2 3 Acknowledgements I would like to extend my sincere gratitude to my advisors, Dr. John Kemeny and Dr. Isabel Barton, for their crucial role in guiding me through my graduate studies. I would also like to thank my thesis committee members, Mr. Keith Taylor, for his valuable support and enlightening comments. Dr. Sergio Castro Reino for his resources and experience involving rock mass degradation. Furthermore, I would like to thank my coworkers at Freeport McMoRan Inc. for providing me geology and geological engineering knowledge pertaining to the Bagdad deposit, and Call & Nicholas for their constructive criticisms regarding my modeling techniques. Finally, I would like to extend a special thank you to Mr. David Streeter for his guidance in running the geotechnical analysis at the University of Arizona. 4 Table of Contents List of Illustrations ........................................................................................................................................ 5 List of Tables ................................................................................................................................................ 7 Abstract ......................................................................................................................................................... 8 Chapter 1 – Introduction ............................................................................................................................. 10 Background ............................................................................................................................................. 10 Rock Mechanics and Mineralogy ....................................................................................................... 10 Types of Failures and Quantifying Failure Conditions ....................................................................... 12 Modeling How Rock Mass Characteristics Affect Slope Stability ..................................................... 15 Porphyry Deposit Geology and Alteration and Relationship to Geomechanics ................................. 16 Geology of the Study Site ................................................................................................................... 20 Pregnant Leaching Solution Infiltration .............................................................................................. 25 Chapter 2 – Literature Review .................................................................................................................... 26 Chapter 3 – Problem Definition and Methodology ..................................................................................... 31 Geotechnical Tests .............................................................................................................................. 35 Rock Characterization and Short-Wave Infrared Spectrometry (SWIR) Data ................................... 38 Petrographic and SEM Characterization ............................................................................................. 40 Slope Stability Finite Element Model ................................................................................................. 41 Chapter 4 – Results ..................................................................................................................................... 44 Geotechnical Tests .............................................................................................................................. 44 Shortwave Infrared Imagery (SWIR) Data ......................................................................................... 49 Petrographic Characterization ............................................................................................................. 51 Slope Finite Element Modeling .......................................................................................................... 62 Chapter 5 – Conclusion and Future Work .................................................................................................. 72 Recommendations for Future Projects ................................................................................................ 73 Chapter 6 – Reference ................................................................................................................................. 74 5 List of Illustrations Figure 1: Diagram illustrating different circular failure mechanisms. From left to right: slope failure, toe failure, and base failure. ............................................................................................. 14 Figure 2: Outcrop illustrating the change in joint spacing with type of hydrothermal alteration between a zone of intense sodic-calcic alteration (A) and a zone of intense potassic alteration with a propylitic overprint (B) at the Yerington district (Nevada). Joint spacing increases in the zone of sodic-calcic alteration. ..................................................................................................... 18 Figure 3: Cross-section of an idealized porphyry alteration zoning system (Berger et al., 2008; Lowell and Guilbert, 1970). .......................................................................................................... 19 Figure 4: Geographic location of the Bagdad mine in the United States...................................... 21 Figure 5: Schematic illustration of typical vein formed during multiple stages of alteration. The white zone consists of vein of quartz-sulfide-Cu (±Carbonate) with fixation of SiO2 released due to hydration, carbonatization, and sulfidation of silicates. The green zone is the proximal zone of sulfide (sericite, ± Carbonate) with fixation of S and Cu. The yellow zone is the intermediate zone of carbonate (±chlorite, some sulfide) with CO2 fixation. Finally, the red zone is the distal zone with chlorite (±carbonate, less sulfide content) and fixation of H2O. .................................. 22 Figure 7: Geologic Map of the Bagdad Pit with local structures separated into West (1), North (2), East (3), and Southeast (4) where geotechnical test and thin section samples were collected based on map from Rathkopf et al., 2017. .................................................................................... 23 Figure 6: Geologic map indicating the major formations and structures around the Bagdad area. (Rathkopf et al., 2017 and sources therein). ................................................................................. 24 Figure 8: Illustration of the same core from the Grasberg mine, 3 years apart. The RQD of the section below 102 m changed through time, probably due to the oxidation of pyrite in the core generating sulfuric acid. ................................................................................................................ 32 Figure 9: Diagram illustrating the workflow for this project. ....................................................... 34 Figure 10: Example of Load Cell Versa stress through time for the Brazilian test. ..................... 36 Figure 11: Samples soaking under PLS and tap water for 5 days. ............................................... 40 Figure 12: Example of meshed slope and boundary conditions along slope. ............................... 42 Figure 14: UCS data from the Bagdad mine displaying their average (green) and -1-standard deviation (red). Samples with XRD and Strain Gauges are broken out as shown. ....................... 46 6 Figure 15: Tensile strength data from the Bagdad Mine displayed with the average line (green) and the -1 standard deviation line (red). ....................................................................................... 48 Figure 16: The effective vertical stress compared to the effective confining pressure using the average uniaxial compressive strength of all data points. ............................................................. 48 Figure 17: Example of hydrothermal alteration as a potential source of degradation, as the alteration of primary micas to chlorite causes the core to break along the alteration zone. ......... 50 Figure 18: Illustration of SWIR spectra of montmorillonite (A) and muscovitic-illite (B) from the East wall, and phengite (C) and muscovite (D)