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Base and precious metal occurrences along the San Andreas Fault, Point Delgada, California

January 1, 1979

Previously unrecognized veins containing lead, zinc, and copper sulfide minerals at Point Delgada, Calif., are associated with late Mesozoic(?) and Tertiary volcanic and sedimentary rocks of the Franciscan assemblage. Sulfide minerals include pyrite, sphalerite, galena, and minor chalcopyrite, and galena-rich samples contain substantial amounts of silver. These minerals occur in a quartz-carbonate gangue along northeast-trending faults and fractures that exhibit (left?) lateral and vertical slip. The sense of fault movement and the northeasterly strike are consistent with predicted conjugate fault sets of the present San Andreas fault system. The sulfide mineralization is younger than the Franciscan rocks of Point Delgada and King Range, and it may have accompanied or postdated the inception of San Andreas faulting. Mineralization largely preceded uplift, the formation of a marine terrace, and the emplacement of landslide-related debris-flow breccias that overlie the mineralized rocks and truncate the sulfide veins. These field relations indicate that the sulfide mineralization and inception of San Andreas faulting were clearly more recent than the early Miocene and that the mineralization could be younger than about 1.2 m.y.

The sulfide veins at Point Delgada may be of economic significance. However, prior to any exploitation of the occurrence, economic and environmental conflicts of interest involving private land ownership, the Shelter Cove home development, and proximity of the coast must be resolved.

Publication Year 1979
Title Base and precious metal occurrences along the San Andreas Fault, Point Delgada, California
DOI 10.3133/ofr79584
Authors Robert J. McLaughlin, D. H. Sorg, H.N. Ohlin, Chris Heropoulos
Publication Type Report
Publication Subtype USGS Numbered Series
Series Title Open-File Report
Series Number 79-584
Index ID ofr79584
Record Source USGS Publications Warehouse
USGS Organization Geology, Minerals, Energy, and Geophysics Science Center