Porphyry Deposits of the Great Basin

INTRODUCTION
Welcome to the Geological Society of Nevada’s 2005 Symposium Field Trip which will visit the Battle
Mountain and Yerington mining districts. The goal of this trip is to initially provide a lecture-style
overview of the four ages of porphyry activity that have affected the Great Basin: Miocene, Eocene-
Oligocene, Cretaceous and Jurassic. The trip will also visit two mining districts: The Battle
Mountain district, which is an example of the Eocene-Oligocene and Cretaceous porphyry event;
and, the Yerington Mining District, which is an example of the Jurassic porphyry event in Nevada. In
the overview session, six industry and academic representatives will present the following:
• Dr. Jeremy Richards: Tectono-magmatic precursors for porphyry Cu-(Mo-Au) deposit
formation.
• Dr. William Chavez: Supergene leaching processes in the porphyry environment with
applications to the Great Basin.
• Ken Krahulec: Great Basin porphyry deposits with an emphasis on Bingham and the
Stockton discovery.
• Richard Lorson: Epithermal precious metal and related porphyry gold mineralization at
Paradise Peak, Nevada.
• Dr. Eric Seedorff: The Ruth-Robinson porphyry Cu-Au system.
• Dr. John Dilles: Magmatic and hydrothermal features of the Yerington Batholith with
emphasis on the porphyry Cu-(Mo) deposit in the Ann-Mason area.
We will begin at 8:00 am on May 19th at the Nugget Hotel conference room with presentations by the
above speakers. At about 3:00 p.m., the presentation will be concluded and we will drive to
Winnemucca where the tour will overnight for two nights (see Itinerary for motel details).
May 20th will include initially a trip to the Copper Basin deposit for an explanation of the regional
geology and historic production, followed by a visit to Newmont’s mine office located at Copper
Canyon (Phoenix-Fortitude deposits). We will be accompanied by the group from field trip #7.
Newmont geologists Fred Breit and Eric Saderholm will provide maps and rock samples as well as
discuss the geology and ore controls. A brief tour of the Copper Canyon porphyry will follow. After
the visit to Copper Canyon, our group will depart the Newmont facilities at Phoenix-Fortitude (and
from field trip #7) and travel southwest to the Buffalo Valley Mo system, which is both outcropping
and exposed by trenches. It is a low-grade, Cretaceous, low-fluorine, porphyry Mo system. Other
stops will include at least a drive by stop and discussion of the Buffalo Valley gold system, which is
an Eocene-Oligocene porphyry-related gold system that produced about 52,000 ounces of gold.
Pending a drill rig being active, the final stop will be at the Converse-Redline project of Metallic
Ventures where Pete Chapman will review maps, possibly core and drilling results. Converse-
Redline is an Eocene-Oligocene porphyry-related Au system that is currently in the advanced
exploration stage. Converse-Redline has no outcrop, but Metallic Venures may have core to review
at that time.
May 21st will depart Winnemucca early and arrive in late morning for a field visit to the Yerington
District where Dr. John Dilles will lead the tour to representative locations. The Yerington district
has both outcrop and trenches to visit. Dr. Dilles as well as Anaconda geologists including John
Proffett and Dr. Marco Einaudi have extensively mapped the district. The tour will provide
excellent examples of porphyry and dike textures and relationships to copper mineralization.