Mapping advanced argillic alteration at Cuprite, Nevada, using imaging spectroscopy

• Published in: Economic geology and the bulletin of the Society of Economic Geologists Vol. 109; no. 5; pp. 1179 - 1221
• Main Authors: Swayze, Gregg A, Clark, Roger N, Goetz, Alexander F. H, Livo, K. Eric, Breit, George N, Kruse, Fred A, Sutley, Stephen J, Snee, Lawrence W, Lowers, Heather A, Post, James L, Stoffregen, Roger E, Ashley, Roger P
• Format: Journal Article
• Language: English
• Published: Economic Geology Publishing Company 01-08-2014
• Subjects: absolute age; alteration; applied (geophysical surveys & methods); Ar/Ar; AVIRIS; calibration; Cenozoic; Cuprite Nevada; D/H; dates; Esmeralda County Nevada; faults; geophysical surveys; Geophysics; hydrogen; hydrothermal alteration; igneous and metamorphic rocks; isotope ratios; isotopes; mapping; metasomatism; mineral composition; Miocene; Neogene; Nevada; O-18/O-16; oxygen; Petrology; Pliocene; reflectance; remote sensing; S-34/S-32; spectra; stable isotopes; Stonewall Flat Tuff; sulfur; surveys; Tertiary; United States
• ISSN: 0361-0128; 1554-0774
• DOI: 10.2113/econgeo.109.5.1179

Mineral maps based on Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data were used to study late Miocene advanced argillic alteration at Cuprite, Nevada. Distributions of Fe-bearing minerals, clays, micas, sulfates, and carbonates were mapped using the Tetracorder spectral-shape matching system. The Al content of white micas increases toward altered areas and near intrusive rocks. Alunite composition varies from pure K to intimate mixtures of Na-K endmembers with subpixel occurrences of huangite, the Ca analogue of alunite. Intimately mixed Na-K alunite marks areas of relatively lower alteration temperature, whereas co-occurring Na-alunite and dickite may delineate relict hydrothermal conduits. The presence of dickite, halloysite, and well-ordered kaolinite, but absence of disordered kaolinite, is consistent with acidic conditions during hydrothermal alteration. Partial lichen cover on opal spectrally mimics chalcedony, limiting its detection to lichen-free areas. Pods of buddingtonite are remnants of initial quartz-adularia-smectite alteration. Thus, spectral maps provide a synoptic view of the surface mineralogy, and define a previously unrecognized early steam-heated hydrothermal event. Faulting and episodes of hydrothermal alteration at Cuprite were intimately linked to upper plate movements above the Silver Peak-Lone Mountain detachment and growth, collapse, and resurgence of the nearby Stonewall Mountain volcanic complex between 8 and 5 Ma. Isotopic dating indicates that hydrothermal activity started at least by 7.61 Ma and ended by about 6.2 Ma. Spectral and stable isotope data suggest that Cuprite is a late Miocene low-sulfidation adularia-sericite type hot spring deposit overprinted by late-stage, steam-heated advanced argillic alteration formed along the margin of the Stonewall Mountain caldera.