Analytical results and sample locality map of stream-sediment, heavy-mineral-concentrate, rock, and water samples from the Chemehuevi Mountains Wilderness Study Area (CDCA-310), San Bernardino County, California

Abstract

Stream-sediment samples Analyses of the stream-sediment samples represent the chemistry of the rock material eroded from the drainage basin upstream from each sample site. Such information is useful in identifying those basins which contain concentrations of elements that may be related to mineral deposits. The stream-sediment samples consisted of alluvium collected primarily from first-order (unbranched) and second-order (below the junction of two first-order) streams as shown on USGS topographic maps (scale = 1:24,000). Each sample was composited from several localities within an area that may extend as much as 150 ft from the site plotted on the map. Heavy-mi neral-concentrate samp]es We panned heavy-mineral-concentrate samples from drainages having two or more first-order streams. Collection was intentionally biased by selection of material from points of natural concentration of heavy minerals by stream processes. The material selected was panned until most of the quartz, feldspar, organic material, and clay-sized material was removed. The sample was air dried. Rock samples We collected rock samples from outcrops or exposures in the vicinity of the plotted site location. Most samples were collected from unaltered rock. Rock samples provide information on elements in rocks that have not been affected by alteration or mineralization. In addition, some altered and(or) mineralized rocks were collected. Water samples We collected water samples from four springs. A 500-mL sample was taken at each site and stored in a new untreated plastic bottle. In addition, a 200-mL sample was filtered through a 0.45-micrometer filter, was acidified with reagent-grade concentrated nitric acid to pH 2, and was stored in an acid-rinsed polyethylene bottle. Sample Preparation Only the stream-sediment samples required extensive preparation. Rock samples were simply crushed and then pulverized with ceramic plates to less than 0.15 mm. Water samples required no preparation beyond that done in the process of collecting them. The samples were air dried and sieved through an 80-mesh sieve using stainless steel sieves. The portion of the sediment passing through the sieve was split and a representative fraction was saved for analysis. Panned-concentrates were air-dried and examined to determine mineral composition. A small split of each sample was separated and hand-ground for spectrographic analysis. The entire remainder of each concentrate was saved for analysis. Sample Analysis Spectrographic method We analyzed the stream-sediment, heavy-mineral-concentrate, and rock samples for 31 elements using a semiquantitative, direct-current arc emission spectrographic method (Grimes and Marranzino, 1968). The elements analyzed and their lower limits of determination are listed in Table 1. Spectrographic results were obtained by visual comparison of spectra derived from the sample against spectra obtained from standards made from pure oxides and carbonates. Standard concentrations are geometrically spaced over any given order of magnitude of conc...