Reflectance spectra and AVIRIS-NG airborne hyperspectral data analysis for mapping ultramafic rocks in igneous terrain

The Hemingway property, located 1.3 km due north of the Kidd Creek volcanogenic massive sulfide deposit in Kidd township, Ontario, is part of the Kidd Creek volcanic complex. Ore reserves and past production of the mine total 130 million metric tons of ore at 2.86 percent Cu, 6.14 percent Zn, 0.22 percent Pb, and 85 g/t Ag. Felsic volcanic rocks and ultramafic flows and sills intercalated with the felsic rocks have been overprinted by extensive hydrothermal-metasomatic alteration at the Hemingway property and at the Kidd Creek mine. The earliest significant alteration identified in the ultramafic rocks is serpentinization, and in the rhyolite, silicification. Pervasive CO 2 metasomatism of the serpentinized ultramafic rocks and the silicified rhyolite resulted in extensive carbonate alteration of both rock types. Late sericite-fuchsite, chlorite, and minor (second generation) carbonate alteration overprinted the first generation carbonates. It is suggested that silicification and carbonate alteration may represent an early synvolcanic hydrothermal episode associated with ore deposition, whereas the sericite-fuchsite, chlorite and late carbonate alteration was superimposed on the deposit during later metamorphism-metasomatism.Pervasive CO 2 metasomatism at the Hemingway property was a relatively low temperature event. Microthermometric measurements were obtained on primary fluid inclusions in carbonates and quartz from the ultramafic rocks. Since phase separation was observed, the mean homogenization temperature of fluid inclusions provides a formation temperature estimate of 248 degrees + or - 12 degrees C. The CO 2 content of the fluid ranges from <0.85 mole percent in the talc-carbonate-altered ultramafic rocks to 10 to 75 mole percent in the quartz-carbonate-altered ultramafic rocks. Fluid inclusions in the quartz-carbonate rocks contain liquid CO 2 and up to 1 mole percent CH 4 . The salinity of the fluid ranges from 1 to 6 wt percent NaCl equiv. The calculated oxygen isotope composition of the fluid in equilibrium with the carbonates ranges from 0 to 3.5 per mil; delta 13 C values of carbonates define a narrow range of 0 to 1 per mil. The oxygen isotope composition of the fluid is consistent with a modified seawater source, but the presence of liquid CO 2 in the inclusions precludes seawater as the source of the CO 2 . One possible explanation for the high CO 2 concentration may be that CO 2 had a volcanic source and was produced during magma degassing. Although the delta 13 C composition of magmatically derived CO 2 is -3 to -5 per mil, delta 13 C values could have increased as CH 4 was generated from the interaction of the fluid with carbonaceous sediments.The hydrothermal-metasomatic evolution of the rocks at the Hemingway property and the Kidd Creek massive sulfide deposit is comparable to some ultramafic rock-hosted gold deposits in the Abitibi belt. The similarity in previously reported ages of secondary accessory minerals such as monazite, titanite, rutile, fuchsite, and sericite at gold deposits and at Kidd Creek suggests that the hydrothermal and metasomatic evolution of these deposits occurred on a regional scale and should be evaluated in a regional context. Early, pervasive carbonate alteration may have been contemporaneous with the syngenetic deposition of massive sulfides at Kidd Creek, and pervasive carbonate alteration of ultramafic host rocks in gold deposits, such as Dome, Kerr Addison, and Aquarius, may have predated subsequent alteration events (quartz-carbonate veins, fuchsite, chlorite + or - rutile) associated with gold.

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) image interpretation methods such as colour composite images (false colour composite, true colour composite) were adapted to capture the image for interpreting the visible and shortwave infrared raw bands and thus generating the mapping for the ultramafic terrain. ASTER colour composite image generated from shortwave infrared (SWIR) bands 8 and 4 and NIR band 3 shows contrast signature for the presence of rock types in the ultramafic terrain. The low and high silica percentages to be interpreted through the absorption features of the spectral range from 8.1 to 12 μm. The combinations used to map silica index are of bands 10, 11 and 7 as RGB. PCA was applied to SWIR and visible and near-infrared spectral bands and from PCA output PC 6, 2 and 1 used in the generation of RGB colour composite. Hence, the results of PCA processed image highlights the magnesite mining area by dark red colour. The minimum noise fraction transform (B1, B2, B4) in RGB applied to ASTER image to focus on the overlapped rock types inclusive of magnesite and the same achieved as sharp image output. ASTER band ratios (R3/1, G4/5 and B6/8) in RGB calculated in which the numerator represents shoulders of absorption, and the denominator represents nearest absorption band. Thus, this combination indicates clearly the magnesite mining area in blue colour. The relative band depth in thermal infrared (TIR) bands (B13 and B14) correlated to find the carbonate index is high, medium and low through the pixel ratio output of the ultramafic terrain. Preprocessing of ASTER data involved atmospheric correction using FLAASH algorithm. The minimum noise fraction transform reduces the spectral dimensionality of data in a linear combination of bands. Spectral angle mapper and support vector machines are supervised classification technique adopted that are key learning models with the aid of analyse and categorization of data. The classification defends user, producer, overall accuracy and kappa coefficient. The magnesite mining area and adjust rock samples were field observed, and the mapping of the ultramafic terrain supports the output achieved through chosen ASTER band colour composite, band ratios, relative band depth, silica index, PCA, minimum noise fraction and pixel classification. Thus, a more informative lithological map for the ultramafic terrain generated to discriminate magnesite-mining region.

Lithological Discrimination and Mapping using ASTER SWIR Data in the Udaipur area of Rajasthan, India

Spatial distribution of altered minerals in rocks and soils in the Gadag Schist Belt (GSB) is carried out using Hyperion data of March 2013. The entire spectral range is processed with emphasis on VNIR (0.4–1.0 μm) and SWIR regions (2.0–2.4 μm). Processing methodology includes Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes correction, minimum noise fraction transformation, spectral feature fitting (SFF) and spectral angle mapper (SAM) in conjunction with spectra collected, using an analytical spectral device spectroradiometer. A total of 155 bands were analysed to identify and map the major altered minerals by studying the absorption bands between the 0.4–1.0-μm and 2.0–2.3-μm wavelength regions. The most important and diagnostic spectral absorption features occur at 0.6–0.7 μm, 0.86 and at 0.9 μm in the VNIR region due to charge transfer of crystal field effect in the transition elements, whereas absorption near 2.1, 2.2, 2.25 and 2.33 μm in the SWIR region is related to the bending and stretching of the bonds in hydrous minerals (Al-OH, Fe-OH and Mg-OH), particularly in clay minerals. SAM and SFF techniques are implemented to identify the minerals present. A score of 0.33–1 was assigned for both SAM and SFF, where a value of 1 indicates the exact mineral type. However, endmember spectra were compared with United States Geological Survey and John Hopkins University spectral libraries for minerals and soils. Five minerals, i.e. kaolinite-5, kaolinite-2, muscovite, haematite, kaosmec and one soil, i.e. greyish brown loam have been identified. Greyish brown loam and kaosmec have been mapped as the major weathering/altered products present in soils and rocks of the GSB. This was followed by haematite and kaolinite. The SAM classifier was then applied on a Hyperion image to produce a mineral map. The dominant lithology of the area included greywacke, argillite and granite gneiss.

The present work aims to evaluate the advantages of the ASTER sensor to detect Brazilian Savanna vegetation types over ultramafic or mafic rocks from spectral mixture analysis. The study area, the Niquelandia Complex, lies in the central portion of the State of Goias in Brazil. The Niquelandia Complex is a well-exposed heavily layered intrusion in central Brazil that comprises an area of about 1,800 square km and is approximately 15 km thick. Geology and petrology studies show many similarities between the Niquelandia Complex and well-known Precambrian layered intrusions such as Bushveld and Stillwater. The distribution and physiognomy of vegetation in the Niquelandia Massif show strong geological control. In this site, extensive areas of ultramafic rocks are covered by herbaceous vegetation dominated by grasses. The fires that occur during the driest months (June-August), might influence the physiognomy of the vegetation. However, not only fires can explain the abrupt limit among the gabroic rocks (mafic) and the ultramafic substrate. Different types of forests can be found along the streams and valleys. Their existence demonstrates the ability of many species to tolerate soils originating from ultramafic rock if soil depth and humidity are appropriate and some fire protection exists. The methodology used can be divided into three stages: (a) pre-processing, (b) endmember identification and (c) spectral mixture analysis (SMA). The images were acquired with atmosphere correction relative to the AST07 product. The Level 2 surface reflectance data set (AST07) contains surface reflectance for each of the nine VNIR and SWIR bands at 15-m and 30-m resolutions, respectively. Duplicating the pixels size from the SWIR image the spatial dimensions between VNIR and SWIR images. Endmembers were detected in three steps: (1) spectral reduction by the minimum noise fraction (MNF) transformation, (2) spatial reduction by the Pixel Purity Index (PPI) and (3) manual identification of the endmembers using the N-dimensional visualizer. The spectral classification was made using the Spectral mixture analysis (SMA). The amount of nonphotosynthetic vegetation (NPV) and photosynthetic vegetation (PV) is preponderant in the distinction between the vegetation types. These procedures allowed the identification of the main scenarios in the study area. For the Niquelandia area it was possible to separate for the SMA components vegetation patterns in soils from ultramafic or mafic rocks

The weathering of mafic and ultramafic rocks in soil environment was investigated in weakly developed soil profiles in order to determine the origin of phyllosilicate association in the soils formed in humid cold climate of the mountainous tundra of the Polar Urals. The objects of the study are represented by soils formed (i) on and underlain by the ultramafic rock and (ii) on the moraine composed of the mafic rock with an admixture of the ultramafic rock fragments. The minerals found in the clay fraction (<1 µm) of the profiles are the same, characterized by the presence of smectite (saponite), which is absent in both mafic and ultramafic rocks; serpentine and talc identified in ultramafic rock; and chlorite. Chlorite was found in both types of rocks. It was shown that the appearance of smectite (saponite) in the weakly developed soil is not related to pedogenesis. But these soil profiles illustrate the possibility of soil formation on “mature” fine earth formed from a high-sensitive ultramafic rock due to chemical weathering. In cold soil environment the more weatherable ultramafic material plays the more important role as a prerequisite for the weathering trends and soil formation than a mafic rock. The admixture of ultramafic materials mitigates the development of Entic Podzols which were earlier found in the Polar Urals on the pure mafic materials. So, the presence of ultramafic materials either predominating or even in admixture results in the “extreme lithological environment” for a pedogenesis and in the formation of weakly developed soils—Regosols and Leptosols.

In connection with a Geological Survey project to investigate the occurrence of nickel, chromium, and refractory-grade olivine in southeastern Alaska, the authors examined several ultrabasic rock bodies during the summer of 1943. Among these were the bodies in the Lituya Bay-Mount Crillon area, central Baranof Island, Red Bluff Bay, the Blashke Islands, Kane Peak, and Mount Burnett

In the past three years there have been major advancements in our ability to identify clay minerals by remote sensing. Two different technologies have been used--imaging broad-band multispectral scanners and non-imaging narrow-band radiometers and spectrometers. Multispectral scanners, including NASA's Thematic Mapper Simulator (analog for Landsat-D Thematic Mapper) have had several broad-band channels in the wavelength region of 1.0 to 2.5 µm. In particular, the wavelength region 2.0 to 2.5 µm contains diagnostic spectral-absorption features for most layered silicates. Computer processing of image data obtained with these scanners has allowed the identification of the presence of clay minerals, without, however, being able to identify specific mineralogies. Studies of areas with known hydrocarbon deposits and porphyry copper deposits have demonstrated the value of this information for rock-type discrimination and recognition of hydrothermal alteration zones. Non-imaging, narrow-band radiometers and spectrometers have been used in the field, from aircraft, and from space to identify individual mineralogical constituents. This can be done because of diagnostic spectral absorption features in the 2.0 to 2.5 µm region characteristic of different clay types. The Shuttle Multispectral Infrared Radiometer (SMIRR), flown on the second flight of the space shuttle Columbia in 1981, had 10 narrow-band channels specifically chosen to evaluate the ability to identify directly clay minerals and carbonates. Preliminary analysis of SMIRR data over Egypt showed that kaolinite, carbonate rocks, and possibly montmorillonite, could be identified directly. Plans are currently under way for development of narrow-band imaging systems which will be capable of producing maps showing the surface distribution of individual clay types. This will represent a major step in remote sensing, by allowing unique identification of minerals rather than the current ability only to discriminate among materials. Applications of this technology will provide geologists with a powerful new tool for resource exploration and general geologic mapping problems. The research described in this abstract was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. End_of_Article - Last_Page 1442------------

In the past three years there have been major advancements in our ability to identify clay minerals by remote sensing. Two different technologies have been used--imaging broad-band multispectral scanners and non-imaging narrow-band radiometers and spectrometers. Multispectral scanners, including NASA's Thematic Mapper Simulator (analog for Landsat-D Thematic Mapper) have had several broad-band channels in the wavelength region of 1.0 to 2.5 µm. In particular, the wavelength region 2.0 to 2.5 µm contains diagnostic spectral-absorption features for most layered silicates. Computer processing of image data obtained with these scanners has allowed the identification of the presence of clay minerals, without, however, being able to identify specific mineralogies. Studies of areas with known hydrocarbon deposits and porphyry copper deposits have demonstrated the value of this information for rock-type discrimination and recognition of hydrothermal alteration zones. Non-imaging, narrow-band radiometers and spectrometers have been used in the field, from aircraft, and from space to identify individual mineralogical constituents. This can be done because of diagnostic spectral absorption features in the 2.0 to 2.5 µm region characteristic of different clay types. The Shuttle Multispectral Infrared Radiometer (SMIRR), flown on the second flight of the space shuttle Columbia in 1981, had 10 narrow-band channels specifically chosen to evaluate the ability to identify directly clay minerals and carbonates. Preliminary analysis of SMIRR data over Egypt showed that kaolinite, carbonate rocks, and possibly montmorillonite, could be identified directly. Plans are currently under way for development of narrow-band imaging systems which will be capable of producing maps showing the surface distribution of individual clay types. This will represent a major step in remote sensing, by allowing unique identification of minerals rather than the current ability only to discriminate among materials. Applications of this technology will provide geologists with a powerful new tool for resource exploration and general geologic mapping problems. The research described in this abstract was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. End_of_Article - Last_Page 410------------

In the present study, The Landsat 7 ETM satellite data was collected for the Sittampundi anorthosites complex and digital image analysis was carried out. The anorthositic rocks available at Sittampundi complex is considered as an equivalent of lunar highland rocks. Hence, a remote sensing study comprises of image analysis and spectral profile analysis was carried out. The satellite data was digitally processed and generated various outputs like band combinations, color composites, stretched outputs, and PCA. The suitable processed outputs were identified for delineating the anorthosite complex. The diagnostic absorption features of reflectance spectra are the sensitive indicators of mineralogy and chemical composition of rocks, which are interest to the planetary scientists. The spectral profile of Landsat ETM plotted for pure and mixed anorthosite pixels and compared with the field and lab reflectance spectra. The percentages of image spectra vary from 30% to 60% for Sittampundi anorthosite. The spectral bands 2, 4 and 6 have low reflectance and bands 3 and 5 have high reflectance. The spectral range of bands 2,3,4,5 and 6 are 525 nm–605 nm, 630 nm–690 nm, 750 nm–900 nm, 1550 nm–1750 nm and 10400 nm–12500 nm respectively. The field spectral curve has weak absorptions at 650 nm and 1000 nm due to the iron transition absorption and low ca- pyroxene respectively available in the anorthosite, matching with the image spectra. However, hyperspectal image with narrow bandwidth could be more useful in selecting the suitable spectrum for remotely mapping the anorthosite region, as equivalent test site for lunar highland region.

Mélanges through time: Life cycle of the world's largest Archean mélange compared with Mesozoic and Paleozoic subduction-accretion-collision mélanges

SUMMARY (1) A quantitative survey of the bryophyte and macrolichen vegetation of outcrops of Durness limestone, Torridonian sandstone, basalt and ultrabasic rocks on Skye and Rhum was undertaken to examine correlations between flora and rock type. (2) Analysis of rock leachates confirmed that the solubility of calcium from Durness limestone greatly exceeded that of all other elements from all rocks. Detectable quantities of Ca, Mg, Fe, Al and K were leached in 24 h from basalt and ultrabasic rocks by distilled water and EDTA solution, but levels of these elements in Torridonian sandstone leachates were extremely low. The major trend in the non-calcareous rocks was an increase in availability of Fe, Al and Mg in the order sandstone < basalt < ultrabasic rocks. (3) The major floristic feature, revealed by comparison of species-abundances on each rock type using a modified principal coordinates analysis of the vegetation samples, was the uniqueness of the limestone flora compared with that of the other rocks. Overlap of the limestone flora with that of the non-calcareous substrata was due to a few relatively uncommon species, and no taxon was abundant on both calcareous and non-calcareous rocks. (4) The total Ca concentration of limestone bryophytes was consistently higher than that of the calcifuges, on average by a factor of 17. Fe and Al, although generally present at low concentration in calcicoles, were not consistently high in calcifuges, indicating that elevated levels of these elements may not be a general feature of the chemical environment on non-calcareous rocks. (5) Floristic ordination also partially separated vegetation samples on the Torridonian sandstone from those on basalt and ultrabasic rocks. This separation was mainly due to differences in the relative frequencies of the calcifuge species, and is thought to reflect chemical rather than physical and climatic factors. The basalt and ultra-basic rocks may provide generally higher levels of mineral nutrients, more potentially toxic metals, and/or a higher Mg: Ca balance than the sandstone.

The Surficial Geochemistry Case Studies Project in the Lake Nipigon region involved detailed Quaternary mapping and multimedia geochemical sampling within five case study areas. Two of these areas, Lac des Iles and Tib Lake, contain known platinum group element (PGE) mineralization. The other three case study areas feature drainage catchments with lakes that contain anomalous levels of PGEs in bottom sediment. Surficial media sampled included till, soils, stream sediment, lake sediment, peat, surface water, and groundwater. Over Archean terrain, such as at Lac des Iles and Tib Lake, there is excellent geochemical contrast between the PGE prospective rock type (mafic to ultramafic intrusive) and the surrounding rock type (e.g., granitoid rocks). This geochemical contrast is mirrored in the geochemistry of most surficial media sampled during this project. Over the Nipigon Embayment, the geochemical contrast between mafic and ultramafic rocks (e.g., “Seagull”-type intrusions) and the surrounding diabase sill rocks is inherently weaker due to the relatively high background levels for copper, palladium, and gold in the Nipigon diabase sills. However, the results of stream-water geochemistry over the Seagull and Disraeli ultramafic intrusions highlight their unique geochemical footprint on the surficial landscape, in particular with respect to Cr, Mg, and Ni, compared with the surrounding Nipigon diabase. In addition, lake sediments underlain by the Seagull, Disraeli, and Hele intrusions have distinctly elevated Cr concentrations and Gd/Yb ratios compared with the surrounding areas underlain by Nipigon diabase sills or Sibley Group rocks. Therefore, exploration value can be maximized over the Nipigon Embayment by exploiting these geochemical contrasts in surficial media to discriminate between ultramafic rocks and the surrounding Nipigon diabase sills. The results of this study highlight the importance of chromium concentrations in surficial media as a diagnostic feature for the presence of ultramafic rocks, regardless of their age or location. In general, a cost-effective exploration strategy for PGE mineralization includes targeting the associated metals (Cr, Ni) within drift deposits (C-horizon till) and drainage media (stream sediment, lake sediment) to vector to prospective mafic–ultramafic intrusive rocks, prior to detailed (property scale) follow-up, involving the determination of base metals and PGEs within soil, till, stream sediment, and peat samples. Relative to the metals copper, nickel, and chromium (ppm levels), the PGEs have significantly lower initial concentrations (ppb levels), are less mobile in the surficial environment, have significantly shorter glacial dispersion trains, and are less reliably determined at the laboratory.

Located in the northwestern part of the Charlotte terrane of the Carolina zone in central North Carolina, the Mocksville complex is a tabular body which trends NE-SW and covers an area of approximately 500 km2. It consists of late Proterozoic to early Paleozoic, moderately metamorphosed and variably deformed, mainly plutonic ultramafic, mafic and felsic rocks. The ultramafic rocks are pyroxenites, wehrlites, and hornblendites; the mafic rocks are metagabbros and amphibolites; and, the felsic rocks are granites and diorites. Field, geochemical, and geothermobarometry studies suggest that the igneous and metaigneous rocks of the Mocksville complex are likely to be genetically related, formed by calc-alkaline differentiation of mafic magma, and originated in a moderate pressure environment (~8 kbar). Based mainly on the study of volcanic rocks, the terranes of the Carolina zone have been interpreted as magmatic arc terranes in most tectonic models concerning the evolution of the southern Appalachian orogen. The geochemical features of the mafic and ultramafic plutonic rocks of the Mocksville complex corroborate the arc origin of the Charlotte terrane.

Airborne gamma-ray and magnetic anomaly signatures of serpentinite in relation to soil geochemistry, northern California