Article from
VOL. 44  NO. 2     FEBRUARY  2003

 

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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