Arizona Geological Society


Upcoming events

    • 07 Jun 2016
    • 6:00 PM - 9:00 PM
    • Sheraton, 5151 E Grant Rd. (& Rosemont), Tucson AZ 85712


    Sponsored by: Boart Longyear

    Collisions, Slab Failure Magmatism and the Development of Cordilleran Batholiths

    by Robert Hildebrand

    Abstract:  Cordilleran batholiths are generally considered to form beneath arc terranes in thickened crust, but a survey of modern continental arcs reveals most to be regions of normal to thinned crust, not zones of crustal thickening. Thus, the origin of Cordilleran batholiths is enigmatic.  I suggest that these batholiths form mostly during and after arc-continent collision as the result of slab failure. Slab failure is a natural consequence of arc-continent collision, and explains the age difference between continental and oceanic lithosphere, because oceanic lithosphere is readily subducted, whereas continents are buoyant and difficult to subduct. Once the subducting slab tears, rocks of the partially subducted continental margin rise due to buoyancy and the collision zone is exhumed. The failure also allows asthenosphere to upwell through the tear, melt adiabatically, and rise into the collision zone, where it interacts especially with subcontinental lithosphere and crust of the upper plate. Slab failure magmas are geochemically and isotopically distinct from arc magmas because slab failure magmas form from melting of garnet peridotite whereas arc magmas are derived from melting of spinal peridotite.

    Cretaceous exmples of slab failure magmatism include the La Posta and Sierran Crest magmatic suites of the Peninsular Ranges and Sierran batholiths, which formed due to closure of the Bisbee-Arperos seaway, a marginal basin that opened along the western margin of the Cordilleran Ribbon Continent at about 135 Ma and closed at ~100 Ma. This seaway likely extended from southern Mexico to the Arctic ocean.

    Slab failure rocks of the 125-105 Ma Sevier event, which occurred in the Great Basin sector of the US, outcrop in the Omineca belt and Selwyn basin of Canada where they were transported after 70 Ma during the 82-58 Ma Laramide event. The Laramide event also had a period of slab failure magmatism that extended from southern Mexico to Alaska. Slab failure magmas were emplaced into a zone of uplift and exhumation in the Sonoran batholith of Mexico and Arizona, the Transverse Ranges of southern California, the Idaho and Boulder batholiths, and the Coast Range batholith of British Columbia.

    Most of the Cretaceous plutons in the North American Cordillera appear to be slab failure bodies, not arc plutons. Commonly associated with slab failure magmatism are porphyry Cu±Au deposits and Li-Cs-Ta pegmatites. Lastly, most of the world's diamonds may owe their origin to subduction and foundering of carbonate on subducted continental margins.

    Bio:  Robert Hildebrand is a field geologist who grew up in Marblehead, Massachusetts, and spent his first complete summer working in the high Sierra in 1971. He received a B.A. in geology at UC Santa Barbara and a PhD from Memorial University of Newfoundland. He spent 20 years mapping in the Northwest Territories of Canada for the Territorial Government and the Geological Survey of Canada where he was a research scientist.

    Subsequently, he managed gold exploration projects in Venezuela, Mexico, and the Dominican Republic.

    About 10 years ago he turned his attention to the North American Cordillera and has published his research in several journal articles and two stand-alone GSA special papers on the Cordillera.

    Hildebrand is a Fellow of the Geological Society of America, was a Visiting Scholar at the University of Arizona and is currently a Research Associate at the University of California, Davis.

    • 05 Jul 2016
    • 6:00 PM - 9:00 PM
    • Sheraton, 5151 E Grant Rd. (& Rosemont), Tucson AZ 85712

    Sponsored by: Available

    Genesis of the Chilito Porphyry Copper Deposit

    by Donald Applebee, Corporate Exploration Manager, ASARCO LLC

    Abstract:  Chilito Porphyry Copper Deposit is located in the Dripping Springs mountains 4 miles N-NW of Asarco’s Hayden facility which includes both a concentrator and smelter. The site can be accessed by a dirt road along HWY 177 or from another dirt road via the back gate of the Hayden facility.

    Early mining activities and prospecting began in the late 1880’s. Larger mining operations in the early 1900’s included the London Arizona Mine, Schneider Mine, Apex Mine, 79. Mine. London Arizona Mine mined the O’Carroll bed of the Martin formation for copper 15,000 tons @ avg. grade Tcu 4.5%.  Schneider Mine for smelter flux in the Troy quartzite. Apex Mine mined for gold in the Martin formation valued at$20,000 worth of gold. 79 Mine mined for lead and copper estimated at 3,000 tons of ore 24% Pb, and 1.75% Cu.

    Chilito deposit is bounded by the Keystone fault to the west and the O’Carroll fault to the east. Both are normal high angle faults and the Chilito deposit is the horst block between the two faults. The Paleozoic section at Chilito has been eroded away leaving only the Precambrian section in place at the surface. Those Precambrian units exposed in outcrop include Troy quartzite, Mescal limestone, Apache group, and a Precambrian Diabase. Drill core has intersected the lower Apache group, Pioneer formation, Pinal Schist, and Ruin Granite. East of the O’Carroll fault, and west of the Keystone fault the Paleozoic section is exposed at surface within the grabens.

    The Chilito Quartz Diorite was emplaced during the Laramide (66+/- ma.) which provide the hydrothermal fluids for mineralization. Favorable units within the Precambrian section became the host rocks for the pyrite, chalcopyrite, and minor molybdenum mineralization. Those favorable are the Mescal, Diabase, sub-units in the Apache group, Pinal Schist, and Ruin Granite. Drilling over the last 50 plus years has demonstrated this mineralization does exist. Recent land acquisitions have opened up exploration potential in the Paleozoic section and that exploration work is ongoing.    

    Bio:  Don Applebee began his geological career working for the U.S. Geological Survey’s Astrogeology Branch in Flagstaff, Arizona while pursuing a Master’s Degree in Geological Sciences from Northern Arizona University. After completing his degree in 1989 Don accepted a mine geologist position at the Oracle Ridge Mine in the Santa Catalina Mountains northeast of Tucson, AZ. His position entailed geologic mapping of development drifts in a copper skarn deposit, along with short range mine planning and mine site exploration. In 1996 he accepted a geologist position at Asarco’s Mission Mine a copper porphyry skarn deposit. His duties at Mission included both underground and open pit mapping, along with mine site exploration programs. In 2003 he became the Senior Geologist at the Silver Bell Mine, in addition to mine geology and exploration, he assisted faculty from the University of Arizona in numerous field trips and short courses. In 2007 Don took a Senior Geologist Position with Freeport-McMoRan, Morenci Operation to manage the deep sulfide exploration program. In 2009 Don accepted a Senior Mine Geologist position with Kinross Gold Corp. Buckhorn Mine in Republic, WA, and a gold skarn deposit where he was responsible for geologic modeling and short range mining. In 2011 Don returned to Tucson to work for Asarco’s Exploration Department, eventually becoming Corporate Exploration Manager and oversees both mine site exploration along with advance stage exploration projects. His interests include porphyry copper deposits and structural modeling of these deposits.

    • 02 Aug 2016
    • 6:00 PM - 9:00 PM
    • Sheraton, 5151 E Grant Rd. (& Rosemont), Tucson AZ 85712

    Sponsored by: Available

    The Politics of Geology in Arizona

    Lee Allison, State Geologist and Director, Arizona Geological Survey


Past events

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

AGS By Laws: "The object of the society shall be the promotion and encouragement of interest in the science of geology and in the geology of the State of Arizona."                                                                         Contact:

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