Arizona Geological Society


Upcoming events

    • 08 Jan 2019
    • 6:00 PM - 9:00 PM
    • Sheraton, 5151 E Grant Rd. (& Rosemont), Tucson AZ 85712

    Sponsored by: 

    Using the Zonation of Trace Metal Geochemistry and Hydrothermal Mineralogy for Porphyry Copper Mineral Exploration

    by John Dilles - SEG Thayer-Lindsley Distinguisted Lecturer and Professor of Geology, College of Earth, Ocean, and Atmospheric Sciences, Oregon State University

    Abstract - The key zonation features of the hydrothermal mineralogy in porphyry copper deposits have been well-known since the early 1970s (USGS workers; Lowell and Guilbert, 1970) and improved by the recognition that during the ~100,000 year timescale of a single magmatic-hydrothermal system the thermal collapse leads to lower temperature veins and alteration cutting earlier high temperature veins and zones (Gustafson and Hunt, 1975). 

    Headframe at Butte, MontanaMagmatic hydrothermal fluids produce spatial zonation from K-silicate alteration near source granitoid intrusions and porphyry dikes upward to sericitic alteration and the near-surface (<1 km) “lithocap” of advanced argillic alteration.  In most porphyry Cu-Mo-Au hydrothermal systems, ore minerals and A-B-style quartz veins are deposited synchronous with K-silicate alteration (700-500°C) and locally into sericitic alteration (~500-300°C), which significantly remobilizes higher temperature ores.  Lithocaps are likely produced where low density magmatic gas condenses into shallow groundwater, and these commonly lack Cu-Au unless added by later low-temperature condensed fluids.  Peripheral propylitic and sodic-calcic alteration in most cases is produced by non-magmatic advecting fluids, and therefore do not generally produce porphyry Cu-Mo-Au ores.

    Progress on understanding trace metal zonation has followed the development of low-cost whole-rock lithogeochemical analyses for a suite of elements (n>44) via ICP and ICP-MS with detection limits near crustal abundances.  Parallel mineralogic studies make use of SWIR data from remote sensing, spot analyses, and core-scanning systems, as well as mineral compositions from EMPA and LA-ICP-MS.

    Trace metal anomalies provide an excellent means of tracking the magmatic-hydrothermal plume via alkali addition in whole rocks and phyllosilicates (K, Rb, Cs, Ba, Li, Tl), from ore zones to the lithocap.  Trace metals are similarly zoned in a sequence from Cu-Mo±Au, Sn, W upward to Se-Te and shallower As-Sb-Bi, where the latter five elements largely occur in pyrite as inclusions and in solid solution.  In the surface environment, these elements form insoluble and immobile oxides so are useful for geochemical vectoring.  Alkalis and Cu-Mo-Au-Sn-W are largely derived from the source magma, and therefore differ based on magma composition.  Many of the elements deposited at lower temperature (Se-Te-As-Sb-Bi) are potentially derived from magma or via wall-rock alteration leaching at >400°C, as is the case of much of Zn, Mn, and Pb deposited in upper zones at <400°C.

    Sericitic alteration associated with pyrite-rich D-type veins remain excellent prospecting tools as they may extend several kilometers upward or outward from ore.  Along both these paths, formation of sericite consumes acid, and therefore mapping the pH gradient may provide a useful vector.  In distal weakly sericitized rock containing relict feldspar, the pH is buffered and muscovite is pale green and phengitic (Fe-Mg-rich), whereas in proximal zones at lower pH muscovite is white and Fe-Mg-poor.  These compositional differences can be mapped using the position of the SWIR 2200 nm, which increases as Fe-Mg content increases.

    Bio - John Dilles was born in California, and earned BS and MS degrees in geology from Caltech (1975, 1976), and a PhD in geology from Stanford University (1984).  During the 1980s he worked as an exploration geologist in the western USA for Hunt, Ware & Proffett and other companies, and operated small gold mines with his brother, Peter.  He joined the faculty of the Oregon State University in 1986, where he is currently Professor of Geology in the College of Earth, Ocean and Atmospheric Sciences.  He advises graduate students and teaches courses in mineralogy, petrology-geochemistry, field geology, and mineral deposits.  His research has been conducted in the USA, South American, and Canadian Cordillera, and focuses on the geology of porphyry copper deposits, magmatic processes that generate metal and sulfur-bearing hydrothermal fluids, field-based structural geology, and isotopic tracers and geochronology.  He has published more than 50 peer-reviewed papers and geologic maps, additional field trip guidebooks and reports.  Google Scholar notes his publications have 3477 citations (h-index = 29).  He has served as a Fellow, Silver Medalist (2017), and Thayer Lindsay Lecturer (2018) of the Society of Economic Geologists, Fellow of the Geological Society of America and is past-chair of the Minerals and Energy Section of the Association of Public and Land-Grant Universities, where he has advocated for federal support for US universities.

    • 05 Feb 2019
    • 6:00 PM - 9:00 PM
    • Sheraton, 5151 E Grant Rd. (& Rosemont), Tucson AZ 85712

    Sponsored by:

    The Hope Diamond and Smithsonian National Gem Collection

    by Dr. Jeffrey E. Post, Smithsonian Institution, Curator of the U.S. National Gem and Mineral Collection 

    Abstract: The Hope Diamond is one of the most famous gemstone in the world.  It is familiar to most people because of its fascinating human history which includes kings and thieves and perhaps a curse or two, but it is also a rare blue diamond, the largest and finest of its kind known.  Despite its long history in the public eye, the diamond still prompts many questions. The United States National Gem Collection at the Smithsonian Institution is also well-known for its many other world-class gems and jewelry pieces such as Polly Logan’s 423 carat sapphire, the historic Napoleon Diamond Necklace and Blue heart Diamond, and the spectacular Carmen Lúcia Ruby.  This beautifully illustrated talk by the Curator-in-charge, Dr. Jeffrey Post, will explore the science and lore behind some of the famous and lesser known gems in the National Collection, as well as highlight some exciting recent additions to the collection. 

    Bio:  Dr. Jeffrey Edward Post, a native of Wisconsin, received Bachelor of Science degrees in geology and chemistry from the University of Wisconsin - Platteville, and his Ph.D. in chemistry, with a specialty in geochemistry, from Arizona State University.  Prior to joining the Department of Mineral Sciences at the Smithsonian Institution in 1984, he was a Postdoctoral Research Fellow for three years in the Department of Geological Sciences at Harvard University.  He is currently Chairman of the Department of Mineral Sciences, and since 1991 has served as Curator of the U.S. National Gem and Mineral Collection. Dr. Post served as the lead Curator for the Janet Annenberg Hooker Hall of Geology, Gems and Minerals that opened in 1997.

    His areas of research interest include mineralogy, gemology, geochemistry, crystallography, and electron microscopy.  He has published more than 100 scientific articles in these fields.  He is the author of The National Gem Collection.



Past events

04 Dec 2018 David (Duff) Gold presents - Deep-Seated Volcanism and the Genesis of Diamonds
06 Nov 2018 William Wilkinson Presents - The Good, The Bad and The Ugly: Three Decades of Exploration
02 Oct 2018 Ihor Kunasz Presents - The Geology and Economics of Lithium
04 Sep 2018 Jim Reed Presents - Applying Geological Exploration Methods Towards the Location of Clandestine Gravesites
07 Aug 2018 Rhodochrosite: Red Treasure of the Rockies - The Story of the Sweet Home Mine
03 Jul 2018 Alison Jones Presents - Rafting through 2 Billion Years of Geologic Time
05 Jun 2018 Gary Huckleberry Presents - The Geoarcheology of Ancient Water Control in the Southwest: Lessons from the Past
01 May 2018 William B. White presents The Science of Caves and Cave Contributions to Science
21 Apr 2018 Spring Field Trip - Jerome - An Early Proterozoic Volcanogenic Massive Sulfide Deposit
03 Apr 2018 Volker Spieth and Stanley Keith Present - Finding Gold in the Kupferschiefer
29 Mar 2018 Future Home of the University of Arizona Gem and Mineral Museum
06 Mar 2018 Joe Wilkins, Jr. Presents - Piedras Verdes and Cuatro Hermanos, Sonora, Mexico - A Tale of Two Porphyries
06 Feb 2018 Paul F. Hlava presents Causes of Color in Minerals and Gemstones
02 Jan 2018 Peter L. Ward presents Bringing Peace to the Climate Wars
05 Dec 2017 Joellen Russell presents The Ocean's Role in the Climate of the Anthropocene
07 Nov 2017 Eric Sundquist presents Geological Perspectives on Carbon Dioxide, the Carbon Cycle and Carbon Management
03 Oct 2017 Lily Jackson presents Andean River Sediments as a Window into the Tectonic History of Ecuador
05 Sep 2017 Vic Baker presents The Influence of the 18th Century Enlightenment on the Natural Sciences
22 Aug 2017 AGS Meet and Greet, A Networking Event
11 Jul 2017 Andrew Zaffos presents Global Tectonics and Marine Animal Diversity
06 Jun 2017 Dan Johnson presents Introduction to the Florence Copper Project and In-Situ Copper Recovery
02 May 2017 Robert Glennon presents America's Water Crisis and What To Do About It
22 Apr 2017 Spring Field Trip - The Laramide-age Chilito Porphyry Copper Deposit
04 Apr 2017 David London presents The Nature and Origins of Internal Zonation within Granitic Pegmatites
07 Mar 2017 Derek J. Thorkelson presents The Precambrian Tectonic Connection between Yukon and Arizona
07 Feb 2017 Daniel Hummer presents Mineral ecology and evolution: Using large datasets to tell the story of the co-evolution of Earth and life
03 Jan 2017 David A. Sawyer presents Dating Geologic Time in the Cretaceous: Integrating Biostratigraphy, Isotope Geochronology, and Astrochronology in Sedimentary Deposits of the Cretaceous Western Interior Seaway
06 Dec 2016 John W. Ewert presents USGS Responses to Some Volcanic Crises and Eruptions Around the World
01 Nov 2016 Alexander Schauss presents Minerals, Trace Elements and Human Health
22 Oct 2016 Fall Field Trip - The Peach Spring Tuff and the Silver Creek Caldera, Northwestern Arizona
04 Oct 2016 Hamish Martin Presents Geology of the Resolution Cu-Mo Deposit, Superior Arizona
06 Sep 2016 Keith R. Long Presents No Bonanza from Cheap Oil
02 Aug 2016 Lee Allison Presents The Future of State Geological Surveys: the Arizona Case Study
05 Jul 2016 Don Applebee Presents Genesis of the Chilito Porphyry Copper Deposit
07 Jun 2016 Robert Hildebrand Presents Collisions, Slab Failure Magmatism and the Development of Cordilleran Batholiths
03 May 2016 Peter Modreski will present "Pegmatites: Mineralogy, Gemstones, Economic Geology, and maybe not quite the same Giant-Crystal Rocks you always thought they were"
30 Apr 2016 Spring Field Trip - An Introduction to the Pinal Schist in Southeastern Arizona
05 Apr 2016 Jordon Bright Presents Looking for an Ocean in the Desert, the Enigmatic Bouse Formation
01 Mar 2016 Peter R. Johnson Presents Tectonics and Mineral Deposits of the Arabian-Nubian Shield
02 Feb 2016 Dr. Karen Wenrich Presents The Ga-Ge Rich Apex Mine, Utah - A Tsumeb, Namibia Analogue
05 Jan 2016 Sarah Baxter Presents Calc-silicate Alteration and Ore Characterization, ASARCO Mission Complex, Pima County, Arizona
01 Dec 2015 Peter Smith Presents The Latest News from Mars
14 Nov 2015 Fall Field Trip - Northern Plomosa Mountains and Bouse Formation in Blythe Basin
03 Nov 2015 Karen Kelley presents The Giant Concealed Pebble Cu-Au-Mo Porphyry Deposit, Southwest Alaska
06 Oct 2015 Caleb King presents Eocene Hydrothermal Systems and Contrasting Hydrothermal Alteration in the Battle Mountain District, Nevada
01 Sep 2015 Carl Bowser presents The Genesis of the Kramer Borax Deposit, Rogers Lake, Mojave Desert, CA:
04 Aug 2015 Dan Lynch presents Volcanoes in the Back Yard
07 Jul 2015 Erik Melchiorre presents The Complex Geological History Recorded by Arizona Placer Deposits:
02 Jun 2015 Jan C. Rasmussen Presents - Arizona Mineralization through Geologic Time
05 May 2015 Gordon Haxel Presents - Alpine peridotite in the desert - Arizona's Laramide subduction complex
02 May 2015 Spring Field Trip - Oak Creek - Mormon Lake Graben
18 Apr 2015 Third Annual Arizona Geological Society Doug Shakel Student Poster Event
03 Mar 2015 Apollo 17 Astronaut and Former Senator Harrison H. Schmitt presents A Geological Visit to a Valley on the Moon
03 Feb 2015 Don Yurewicz Presents Assessing Unconventional (Continuous) Hydrocarbon Resource Plays
06 Jan 2015 Arend Meijer presents: Sulfide-rich Proterozoic Mafic Rocks and Arizona Porphyry Copper Deposits - A Connection?
02 Dec 2014 Victor R. Baker: Megafloods on Earth, Mars, and Beyond
15 Nov 2014 Fall Field Trip - Debris Flows Shape the Sabino Canyon Landscape - look out below!
04 Nov 2014 Isabel F. Barton: Historical Development & Current State of Geological Research in the Central African Copperbelt
07 Oct 2014 Apollo 17 Astronaut and Former Senator Harrison H. Schmitt presents A Geological Visit to a Valley on the Moon
02 Sep 2014 Lewis Land presents Evaluation of Groundwater Residence Time in a Karstic Aquifer System
05 Aug 2014 Jamie Molaro presents Thermal Stress Weathering in the Inner Solar System
01 Jul 2014 Jim Leenhouts presents Surface-water/groundwater Interactions in Arizona
03 Jun 2014 Arend Meijer presents Pinal Schist of So. Arizona--A Paleoproterozoic Fore-Arc Complex
06 May 2014 John C. Lacy presents The Genesis of Mining Law
26 Apr 2014 Spring Field Trip - Geology of the Christmas Porphyry Copper Deposit
24 Apr 2014 Second Annual Arizona Geological Society Doug Shakel Student Poster Event
01 Apr 2014 Eric Seedorff presents, Structural Dismemberment of a Porphyry Molybdenum System, Spruce Mountain District, Northeastern Nevada
04 Mar 2014 John Dreier presents, Copper Deposits of the Coast Ranges of Chile; A trip through time, space, and ore deposit nomenclature
04 Feb 2014 Ralph Stegen presents The Morenci Porphyry Cu-Mo Deposit, Greenlee County, Arizona: A Geologic Summary with Emphasis on Hypogene and Supergene Mineralization
07 Jan 2014 Steve Castor presents, Mountain Pass and other North American Rare Earth Element Deposits
03 Dec 2013 Stephen Jackson, USGS, Looking forward from the past: Ecological impacts of climate change through the lens of history
05 Nov 2013 Malcolm Siegel, PhD, MPH, LJS Consulting, Inc and School of Medicine, University of New Mexico, Albuquerque, NM. 87047: Uranium Mining in the American Southwest: Can Medical Geologists Ask the Right Questions?
04 Oct 2013 Field Trip - H. Wilson Sundt Generating Station
01 Oct 2013 Mark Logsdon, Principal Geochemist, Geochimica, Inc.: What Does “Perpetual” Management and Treatment Mean? Toward a Framework for Determining an Appropriate Period-of-Performance for Management of Reactive, Sulfide-Bearing Mine Wastes
01 Oct 2013 Mark J. Logsdon, Geochimica, Inc., Does acid-rock drainage lead to waste-rock instability? Geological, hydrological, and geochemical framework for the Questa Mine
03 Sep 2013 Pete Reiners, UA, Geosciences Dept., Geochronology of secondary Fe & Mn oxides in bedrock
30 Aug 2013 Field Trip - University of Arizona Tree-Ring Research Laboratory
06 Aug 2013 Bill Stavast, Freeport-McMoRan Copper & Gold, The Safford Mine: What we have learned since production began
02 Jul 2013 Lukas Zurcher, USGS, presents: "Tectono-magmatic evolution of the Central Tethys Region"
04 Jun 2013 Steve Van Nort presents, "Gold Fever! The BRE-X/Busang Story
07 May 2013 Federal lands and mineral resources: Colorado Plateau uranium deposits and the Sonoran Desert Heritage
18 Apr 2013 First Annual Arizona Geological Society Doug Shakel Student Poster Event

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