2010 Mining History Association Field Trip


Geology of the Silver City Region

June 12, 2010

Tour Leader: Virgil W. Leuth, NMBGMR

The MHA field trip route went east on Highway 152 from Silver City to the vicinity of San Lorenzo in the Mimbres Valley.  The route of travel was then reversed and stops were made at road cuts of the various rock formations, starting from the oldest (Proterozoic) to the youngest (Pennsylvanian).  The trip ended at the overlook for the Santa Rita/Chino Mine with its younger-still (Laramide) porphyry copper intrusions.  The New Mexico Bureau of Geology and Mineral Resources (NMBGMR) published an excellent on-line Field Trip Guide that covers the areas visited on the MHA geology field trip. 
Geologic section visited on the MHA field trip (Modified from Jones et al., 1967; NMBGMR, 2009)





View westward going up the geologic section along Highway 152.  The Fusselman Dolomite is the upper cliff.  Upper slopes are the Montoya and El Paso Limestones. Lower slopes are Bliss Sandstone and Proterozoic rocks.

Near San Lorenzo, gravels fill the valley on top of Proterozoic rocks.

Unconformity between the Proterozoic rocks (bottom) and the Bliss Formation (top)

Close-up of Bliss Sandstone with four and two-footed creatures!

MHAers inspect the Percha Shale, keeping an eye out for fossils.

Trip Leader, Virgil Leuth (center), explains the Lake Valley Limestone to the MHA group.  It is the host rock for the Hanover zinc ores.

Oswaldo Limestone north of the Santa Rita/Chino Pit viewpoint.

Freeport-McMoran Copper and Gold’s Santa Rita/Chino Pit mines porphyry copper intrusions in the surrounding sediments.  Local landmark, the Kneeling Nun (in the notch on the far horizon, is composed of the Kneeling Nun Tuff.

Photo Credits: Mike Kaas



William Rich Jones, Robert Mann Hernon, and Samuel L. Moore, “General Geology of the Santa Rita Quadrangle, Grant County, New Mexico,” U. S. Geological Survey, Professional Paper 555, (Washington: Government Printing Office, 1967).


Shari A. Kelly, “Chino Mine,” New Mexico Bureau of Geology and Mineral Resources,  (Accessed 28 December 2011).


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