Geochemical data for samples of rock, stream sediment, and nonmagnetic heavy-mineral concentrate from the South Sierra Wilderness and the South Sierra Roadless Area, southern Sierra Nevada, California

Abstract

helped perform the geochemical sampling. GEOLOGIC SETTING South Sierra Wilderness and the South Sierra Roadless Area are underlain mostly by granitic rocks of the Sierra Nevada batholith, that were emplaced during at least three major periods of intrusive activity (Evernden and Kistler, 1970). These consist of Cretaceous leucocratic, nonfoliated rocks of granitic to granodioritic composition; an older set of slightly more mafic granodioritic to tonalitic rocks of Jurassic age that often have stromatic to schlieric textures; and gabbroic to dioritic rocks with schistose to gneissic textures that are probably of Triassic and (or) Jurassic age. The granitic rocks intruded and metamorphosed Paleozoic to Mesozoic sedimentary and volcanic rocks to quartz-mica schist, quartzite, marble, and minor greenschist. Zones of garnet-epidote-wollastonite calc-silicate hornfels developed near contacts with granitic rocks. Monache Mountain, a Tertiary rhyolite volcanic cone was erupted in the northwestern part of the study area. SAMPLE COLLECTION AND PREPARATION Sampling stations were located at bedrock outcrops and first-order (unbranched) and second-order (below the junction of two first-order) streams as shown on 1:62,500-scale U.S. Geological Survey topographic maps. Availability permitting, at each sampling site, a rock sample, a streamsediment sample, and a bulk stream-sediment sample to be used for panning were collected. When water was available, the bulk sample was pan-concentrated at the sampling site. At some sites only one or two of the three sample types were collected, depending upon their availability. Duplicate samples were collected at about 10 percent of the sites in order to control sampling and analytical variation. A total of 44 rock samples, 59 stream-sediment samples, and 56 nonmagnetic heavy-mineral-concentrate samples were analyzed. The analytical data for these samples are listed in tables 7 through 9. The approximate sampling density was 1 sample per 3*62 mi for rocks, 1 sample per 2.70 mi for stream sediments, and 1 sample per 2.85 mi for nonmagnetic heavy-mineral concentrates. Station and sample numbers Sampling sites were assigned a station number composed of a two-letter prefix and a sample number. The prefix denotes the U.S. Geological Survey 15minute quadrangle of the sampling site; HR for Haiwee Reservoir, MO for Monache Mountain, and OL for Olancha. The prefix is followed by a three digit sample number. Rocks that were not collected at stream sites have numbers in the series 001-099; samples collected in stream drainages have numbers in the series 901-999. Sample numbers used in tables 7 through 9 are composed of a station number to which a sample-type suffix has been added; A for rock samples, S for stream-sediment samples, and P for nonmagnetic heavy-mineral concentrate samples. For samples collected in duplicate, the letter suffix has a duplicate pair number (1 or 2) added. The station location map (pi. 1) shows the stations and station numbers of all sampling sites in the study area. Rock sam...