GSN Elko Chapter Meeting

Description

Contact: justin.b.milliard@gmail.com

The Elko GSN Chapter is excited to have Grant McKnight of UNR’s Center for Research in Economic Geology giving the October presentation the fall season on the Monitor-Mogul mining district. Geotemps/Geopros is generously sponsoring the meeting.

LOCATION:  Western Folk Life Center, 501 Railroad St., Elko, NV

DATE:  Thursday, October 20th

TIME:  Food and drinks @ 6 pm and talk to begin at 7 pm.

SPONSOR:  GEOTEMPS/GEOPROS INC.

Presenter:  Grant McKight, Ralph J. Roberts Center for Research in Economic Geology, University of Nevada, Reno

Title: “Volcanic Stratigraphy and Varietal Au-Ag-Cu-Hg-S˚ Epithermal Deposits in the Monitor-Mogul Mining District, Alpine County, California”

Abstract: 

The Monitor-Mogul mining district hosts diverse Au, Ag, Cu, Hg, and S° deposits in ~11-8 Ma dacite and andesite flows, intrusions, and tuffs and ~5 Ma rhyolite intrusions. These Miocene to early Pliocene volcanic rocks, some mineralized, predominate in the western andesite assemblage of the ancestral Cascades magmatic arc and the Walker Lane. Other mining districts in this region possess similar precious metal and elemental sulfur resources to the Monitor-Mogul district. Production at Monitor totaled around 16,404 oz. Au and 728,275 oz. Ag with associated Cu, Zn, and Pb, tens of flasks of Hg, and 0.5 Mt S°. Temporal, stratigraphic, and mineralogic relationships suggest at least two periods of mineralization at ~9 and ~5 Ma. The earlier mineralization event includes the Mogul Peak Hg mine, Morning Star/Curtz and other Au-Ag-Cu mines, and likely the Leviathan S° mine. These mines typify classic high sulfidation epithermal deposits and mineralized quartz-alunite alteration cells with diverse mineralization modes including residual quartz steam-heated caps, breccia pipes, and stratiform deposits. The later mineralization event includes the Zaca Au-Ag mine and other prospects on Colorado Hill, a rhyolite plug emplaced at 4.8 Ma. Deposits associated with this intrusion align closely with low-intermediate sulfidation epithermal systems common to the western andesite assemblage and Walker Lane. These two disparate sulfidation states imply different environments of formation for the two deposit types. However, these varietal and asynchronous deposits may still be intimately related as one long-lived eruptive center with multiple pulses of mineralization similar to the Bodie Hills volcanic field of the central Walker Lane.