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Mapping the carbonate alteration footprint of the Cortez Hills Carlin-type gold deposit, Nevada using… Herron, Christopher Stephen 2018

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MAPPING THE CARBONATE ALTERATION FOOTPRINT OF THE CORTEZ HILLS CARLIN-TYPE GOLD DEPOSIT, NEVADA USING CARBON-OXYGEN STABLE ISOTOPES, AND GEOCHEMISTRY AS A VECTORING TOOLbyChristopher Stephen HerronMEarthSci with B.Sc., (Honours) Geology, The University of Edinburgh, 2014A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF  THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Geological Sciences)THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver)April 2018©Christopher Stephen Herron, 2018iiAbstractThe Cortez Hills deposit is located along the Battle-Mountain Eureka Trend in North-Central Nevada and is a world-class Carlin-type (CTD) gold deposit. Visible and cryptic alteration associated with mineraliza-tion were used to define footprints, alteration haloes, mineralization targets and fluid pathways. Approxi-mately 2,500 carbon and oxygen isotope analyses from a mm- to m-scale using core, chips, pulped rock and surface samples together with geology and geochemistry provided an integrated dataset for evaluating fluid transport and alteration in the Cortez Hills plumbing system.The Cortez Hills plumbing system was described using calcite veins. Timing of calcite veins were based on crosscutting relationships relative to alteration and mineralization events.  Three main vein stag-es were identified which includes ten vein types and two stylolite events. Cross-cutting relationships were supported by vein physical characteristics to improve identification.  Calcite veins at Cortez Hills have distinct physical and chemical characteristics that can be identified with a variety of methods. Chemical characteris-tics were used to understand the processes that formed veins. V2 veins associated with Carlin fluids could be a significant fluid pathway contributing to the hydrothermal plumbing system. Calcite veins have the poten-tial to be used as an exploration tool for Carlin systems.Invisible alteration was described using carbon and oxygen stable isotopes, and Carlin pathfinder elements (As, Au, Hg, Sb, and Tl) as a vectoring tool. Oxygen isotopes represented the most far-field detect-able feature of CTDs and were used to define the cryptic carbonate alteration of Cortez Hills. Defining thresh-olds for carbon and oxygen isotopes, and pathfinder elements were integral to map alteration haloes (lower threshold), define mineralization targets (upper threshold) and map fluid flow pathways. Isotopes and path-finder elements were described in order of greatest distance travelled outboard of economic gold orezones and utilized as a vectoring tool for alteration and mineralization: 18O>As>Hg>Sb>Tl-13C>Au. The defined 18O deposit footprint (lower threshold) was >3.5km and the pathfinder element alteration halo was 2.2km in size. The defined 18O mineralization target (upper threshold) was 1km in width and 0.6km in height. iiiLay SummaryThe metal gold is a major form of wealth exchanged, shared and stored by countries and financial markets globally in addition to applications in electronics, jewellery and medicine. The discovery of giant gold mineral deposits have drastically reduced in the previous 20 years. This has forced the mineral industry to become smarter and increasingly efficient in time and capital at exploring and developing mineral deposits that occur at greater depths. Gold mined from the ground in Nevada represents ~8% of the total annual gold mined globally and in Nevada it dominantly originates from Carlin-type gold deposits. This thesis contributes to developing tools and approaches at Cortez Hills in Nevada to aid the discovery and definition of Carlin-type gold deposits. This thesis widens our perspective on how fluids that transport gold in the Earth’s upper surface flows and the distances they travel to form giant gold deposits in Nevada.ivPrefaceThis thesis is part of the Mineral Deposit Research Unit (MDRU) Carbonate Alteration Footprint Ini-tiative and MDRU project proposal V03122013v2. The thesis addresses three key objectives from the project proposal. The initial project design and objectives were produced by Prof. Gregory Dipple, Prof. Kenneth Hickey, Dr. Shaun Barker, Dr. Andreas Beinlich, and Dr. Craig Hart from MDRU, University of British Columbia (UBC) and Dr. Jeremy Vaughan and Paul Dobak from Barrick Gold Corp. Exploration. The objectives were subsequently changed and improved upon by the author and supervisor Prof. Gregory Dipple.  Chapter 3 is an additional objective outside the initial project design. Contributions to this work include the Barrick Gold Corp. Exploration Group; Paul Dobak, Dr. Jeremy Vaughan, Simon Griffiths, Dr. Francois Robert, Kevin Creel, Meghan Jackson, and Dr. Andrew Wurst.  It also includes support from the following Barrick geology groups; Cortez Hills Open Pit, Cortez Hills Underground, and Cortez District Exploration.The author is responsible for the collection of all field data and samples. The author is not responsi-ble for the production of geological surface maps.Samples were prepared and subsequently analyzed using an Olympus portable x-ray fluorescence intrument, ultra-violet fluorescence, cold-cathode luminescence petrography, stable carbon and oxygen isotope analysis at MDRU, UBC by the author. Polished thin sections for petrographic analysis were prepared at Vancouver Petrographics Ltd. Four-acid and aqua regia digestion I