Arizona Geological Society

Sarah E. Baxter presents "Treasures and Formation of Arizona's Sky Islands: Geology and Mineral Resources of Coronado National Forest

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

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    Please cancel by 11 a.m. on the Friday prior to the meeting, if you are unable to attend - no shows and late cancellations will result in the forfeiture of their payment, if AGS is unable to sell your dinner.
  • Members RSVP here. Registration requires online prepayment via credit card. The reservation process will no be complete without prepayment.

    Please cancel by 11 a.m. on the Friday prior to the meeting, if you are unable to attend - no shows and late cancellations will result in the forfeiture of their payment, if AGS is unable to sell your dinner.
  • Free to Student members thanks to Freeport-McMoRan, Inc. Full-time students may join online free - click "Join or Renew"

    Please cancel by 11 a.m. on the Friday prior to the meeting, if you are unable to attend - no shows and late cancellations will be invoiced, if AGS is unable to sell your dinner.

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Sponsored by:  Basin Wells Associates PLLC


Treasures and Formation of Arizona's Sky Islands:  Geology and Mineral Resources of Coronado National Forest

by Sarah E. Baxter, Mineral Resources Project Manager and Zone Geologist of Nogales Ranger District, Coronado National Forest 

Abstract:  Coronado National Forest (“Forest”) contains approximately 1.853 million acres (7,200 km2); dominantly occurring in the high mountain ranges of south to southeastern Arizona and southwestern New Mexico.  The Forest occupies parts of Cochise, Graham, Greenlee, Pima and Santa Cruz Counties of Arizona and Hidalgo County New Mexico.  The geology of the Forest is very diverse and highly variable, which reflects the complex geologic history of this region.  Much of the geologic record of the region, which is part of the Basin and Range geologic province, contains intercalated sedimentary and volcanic rocks composing seven (7) major sequences that have been intruded during at least five (5) magmatic events; a geologic record stretching from the Precambrian to the late-Tertiary.  This region’s high mountains and broad-flat low valleys gave rise to its unique nickname: Arizona’s Sky Islands.  Not surprisingly, because of the Sky Island’s unique geologic nature and evolution, Coronado National Forest is the most biologically diverse of all lands managed by the USDA – Forest Service.

The mineral resources of the Forest have been investigated and mined by various inhabitants, visitors and prospectors for thousands of years.  Silver (Ag) has been produced from mantos vein deposits and epithermal deposits.  Gold (Au), Ag, and lead (Pb) have been produced by fissure-hosted and carbonate replacement deposits as well as contact metasomatic deposits known as skarns.  The largest and richest deposits on the Forest are world-class porphyry Copper (Cu) deposits, which have produced Pb, Cu, zinc (Zn), Au, Ag, and molybdenum (Mo).  Most of these porphyry-Cu deposits reside outside of the Forest, except in the Patagonia, Pajarito, Santa Rita, and Chiricahua Mountains.  Other productive mineral resources occur within the Dragoon, Whetstone, Huachuca and Santa Catalina mountains.  The Forest contains a diverse list of mineral resources and potential ore deposits including the following: tungsten skarn, tungsten vein, porphyry-Cu, porphyry-related Cu skarn, polymetallic replacement, porphyry Cu-Mo, polymetallic vein, Creede-type epithermal vein, rhyolite-hosted tin (Sn), and placer Au.  It is the treasures of Arizona’s Sky Islands that continue to tempt the small prospector as well as large international mining companies to explore; not only in the Forest’s past but also into the future.

Bio:  Sarah is 6th-generation native Californian (her family established residency in California as early as 1850) originally from Torrance, California.  At the age of 5, she learned mineral prospecting and geology while working the family placer claim in San Bernardino National Forest. In 1999, she graduated from the University of California, Davis with a degree in Political Science and worked for five years in Law, Government Administration and Environmental Policy.

In 2008, Sarah sought to redefine her career and graduated from Oregon State University (OSU) with a Bachelor’s of Science in Geology. Her undergraduate research thesis focused on an underground orogenic gold deposit and was entitled: Mineralogy of Gold-Quartz Veins of the French Gulch District, Shasta County, California. Her work was funded by a department scholarship for academic excellence.

Following graduation from OSU, Sarah worked as a brownfields exploration geologist for Freeport-McMoRan in Morenci, Arizona. Following work in Alaska for Pathfinder Mineral Services and Sumitomo Metal Mining in 2009, she formed Klondike Mountain Geological Services and worked as an independent geologist, awarded contracts with Kinross Gold Corporation, Hudbay Minerals, and ASARCO.

In 2015, Sarah earned her Professional Science Master’s degree in Economic Geology from the University of Arizona. As a graduate student, she was awarded the 2013-2014 SRK Consulting Scholarship for Academic Excellence and her Master’s thesis was entitled: Calc-Silicate Alteration and Ore Characterization, ASARCO Mission Complex: Implications for the Optimization of Molybdenum Recovery.

In January 2017, Sarah joined the US Forest Service where she administers several minerals projects including the Rosemont Copper Project.  Her diverse career ranges from helicopter-supported reconnaissance field geologist in the Alaskan Interior, near mine-site exploration and being a production geologist at both underground and open pit operations in Nevada, Alaska, Washington, and Arizona to Minerals Administration for the US Forest Service.


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