Mother
Lode Field Trip Report
by Jim Barton
On
Saturday January 18, twelve RRR members and their guests met at the
Sutter Gold Mine off Hwy. 49 near Sutter Creek for a guided
underground tour of the mine. We descended a 12 per cent grade
in an open mine buggy about a quarter mile and 400 vertical feet into
the workings. From there, we hiked up a series of stairs and
through a tunnel, where we viewed the contact of the Melones, AKA
"Mother Lode" Fault. We viewed visible gold ore,
Mariposa Formation slate and schist, and Mariposite - a pale green
chromium phengite, or high silica muscovite, mica1.
Upon
our return to the surface, and as a special favor to the club, mine
operations staff provided cored rock samples of the Mariposa
Formation. Afterwards, we traveled to Jackson and the Kennedy
Mine, and toured the surface workings of an abandoned vertical shaft
mine with surface structures undergoing restoration. Docent Dee
Davis entertained us with many hours of stories about local mines and
miners of the Mother Lode District. We finished the day visiting
three road cut geologic sites in Almador County, where serpentine is
available for collecting along the western Melones Fault system.
Serpentine is a regional, low-grade metamorphic rock and a mineral,
which is a part of the zeolite and upper greenschist facies2.
The
road cuts exhibited progressively higher grades of metamorphism as we
traveled north.
Thanks
to all attendees for participating in this interesting field trip.
My special thanks to Geologist Mike Flynn, who provided assistance
through his contacts at Sutter Gold Mine, maps with excellent
directions, and staked the geologic road cuts. Mike is the
principal and manager of the Geotechnical Research and Development
office in Sutter Creek.
1
Minerals of California, Femberton. 2 Simon & Schuster's
Guide to Rocks and Minerals, NewYork
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