Bernard E. Hubbard

Comparative alteration mineral mapping using visible to shortwave infrared (0.4-2.4 /spl mu/m) Hyperion, ALI, and ASTER imagery

Advanced Land Imager (ALI), Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), and Hyperion imaging spectrometer data covering an area in the Central Andes between Volcan Socompa and Salar de Llullaillaco were used to map hydrothermally altered rocks associated with several young volcanic systems. Six ALI channels in the visible and near-infrared wavelength range (0.4-1.0 /spl mu/m) were useful for discriminating between ferric-iron alteration minerals based on the spectral shapes of electronic absorption features seen in continuum-removed spectra. Six ASTER channels in the short wavelength infrared (1.0-2.5 /spl mu/m) enabled distinctions between clay and sulfate mineral types based on the positions of band minima related to Al-OH vibrational absorption features. Hyperion imagery embedded in the broader image coverage of ALI and ASTER provided essential leverage for calibrating and improving the mapping accuracy of the multispectral data. This capability is especially valuable in remote areas of the earth where available geologic and other ground truth information is limited.

Environmental geochemistry at Red Mountain, an unmined volcanogenic massive sulphide deposit in the Bonnifield district,Alaska Range, east-central Alaska

The unmined, pyrite-rich Red Mountain (Dry Creek) deposit displays a remarkable environmental footprint of natural acid generation, high metal and exceedingly high rare earth element (REE) concentrations in surface waters. The volcanogenic massive sulphide deposit exhibits well-constrained examples of acid-generating, metal-leaching, metal-precipitation and self-mitigation (via co-precipitation, dilution and neutralization) processes that occur in an undisturbed natural setting, a rare occurrence in North America. Oxidative dissolution of pyrite and associated secondary reactions under near-surface oxidizing conditions are the primary causes for the acid generation and metal leaching. The deposit is hosted in Devonian to Mississippian felsic metavolcanic rocks of the Mystic Creek Member of the Totatlanika Schist. Water samples with the lowest pH (many below 3.5), highest specific conductance (commonly >2500 μS/cm) and highest major- and trace-element concentrations are from springs and streams within the quartz–sericite–pyrite alteration zone. Aluminum, Cd, Co, Cu, Fe, Mn, Ni, Pb, Y, Zn and, particularly, the REEs are found in high concentrations, ranging across four orders of magnitude. Waters collected upstream from the alteration zone have near-neutral pH, lower specific conductance (370 to 830 μS/cm), lower metal concentrations and measurable alkalinities. Water samples collected downstream of the alteration zone have pH and metal concentrations intermediate between these two extremes. Stream sediments are anomalous in Zn, Pb, S, Fe, Cu, As, Co, Sb and Cd relative to local and regional background abundances. Red Mountain Creek and its tributaries do not, and probably never have, supported significant aquatic life.

Mineral information at micron to kilometer scales: Laboratory, field, and remote sensing imaging spectrometer data from the orange hill porphyry copper deposit, Alaska, USA

Using imaging spectrometers at multiple scales, the USGS, in collaboration with the University of Alaska, is examining the application of hyperspectral data for identifying large-tonnage, base metal-rich deposits in Alaska. Recent studies have shown this technology can be applied to regional mineral mapping [1] and can be valuable for more local mineral exploration [2]. Passive optical remote sensing of high latitude regions faces many challenges, which include a short acquisition season and poor illumination due to low solar elevation [3]. Additional complications are encountered in the identification of surface minerals useful for mineral resource characterization because minerals of interest commonly are exposed on steep terrain, further challenging reflectance retrieval and detection of mineral signatures. Laboratory-based imaging spectrometer measurements of hand samples and field-based imaging spectrometer scans of outcrop are being analyzed to support and improve interpretations of remote sensing data collected by airborne imaging spectrometers and satellite multispectral sensors.

Alteration, slope-classified alteration, and potential lahar inundation maps of volcanoes for the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Volcano Archive

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Geospatial compilation of results from field sample collection in support of mineral resource investigations, Western Alaska Range, Alaska, July 2013

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The origins of Late Quaternary debris avalanche and debris flow deposits from Cofre de Perote volcano, México

Cofre de Perote volcano is a compound, shield-like volcano located in the northeastern Trans-Mexican volcanic belt. Large debris avalanche and lahar deposits are associated with the evolution of Cofre. The two best preserved of these debris-avalanche and debris-flow deposits are the ∼42 ka “Los Pescados debris flow” deposit and the ∼11–13 ka “Xico avalanche” deposit, both of which display contrasting morphological and textural characteristics, source materials, origins and emplacement environments. Laboratory X-ray diffraction and visible-infrared reflectance spectroscopy were used to identify the most abundant clay, sulfate, ferric-iron, and silica minerals in the deposits, which were either related to hydrothermal alteration or chemical weathering processes. Cloud-free Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) remote sensing imagery, supporting EO-1 Hyperion image spectra, and field ground truth samples were used to map the mineralogy and distribution of hydrothermally altered rocks on the modern summit of Cofre de Perote. The results were then compared to minerals identified in the two debris-avalanche and debris-flow deposits in order to assess possible source materials and origins for the two deposits. The older Los Pescados debris-flow deposit contains mostly halloysite and hydrous silica minerals, which match the dominant mineralogy of soils and weathered volcanic deposit in the surrounding flanks of Cofre de Perote. Its source materials were most likely derived from initially noncohesive or clay-poor flows, which subsequently bulked with clay-rich valley soils and alluvium in a manner similar to lahars from Nevado del Ruiz in 1985, but on a larger scale. The younger Xico avalanche deposit contains abundant smectite, jarosite, kaolinite, gypsum, and mixed-layered illite/smectite, which are either definitely or most likely of hydrothermal alteration origin. Smectite in particular appears to be the most abundant and spectrally dominant mineral in summit ground truth samples, ASTER mapping results, Xico avalanche deposit, and an older (pre-Xico avalanche) deposit derived from collapse(s) of ancestral Cofre de Perote edifice. However, both Xico avalanche and Los Pescados debris flow deposits show some evidence of secondary, postemplacement weathering and induration, which is evident by the presence of gibbsite, and hydroxyl interlayered minerals, in addition to recently formed halloysite and hydrous silica (i.e., indurating) cements. Field-based, visible infrared image spectroscopy (VIS/IR) spectral measurements offer the possibility of distinguishing primary minerals of hydrothermal alteration origin in debris-avalanche and debris-flow deposits from those produced either by in situ chemical weathering or bulked from weathered source materials.