purple haze combined geochemical and pb sr isotope constraints on colourants in celtic glass abstract the composition of 2977 late prehistoric glass objects was investigated to derive information on the nature of the colourants used 2673 late iron age celtic la tene bracelet fragments from the netherlands and austria and 51 early iron age beads from the netherlands were analysed hand held xrf analyses demonstrated that all glass objects were of the soda silica lime type which has a presumed origin in the eastern mediterranean copper was used as colourant in the form of copper filings in most of the early iron age glass beads to give recycled glass a blue green colour the vast majority 98 of the translucent iron age glass was coloured using cobalt blue manganese purple colourless antimony colourless and iron green manganese however was added to all glass contributing additional amounts of elements like copper cobalt and iron opaque decorations were produced using antimony or a combination of tin and lead ree analyses on a selection of representative objects indicate that the manganese ores in translucent glass are of hydrogenetic diagenetic early iron age or hydrothermally influenced diagenetic late iron age types strontium isotope ratios show mixing between a calcite related seawater source 0 709 and manganese ores with isotope ratios of 0 70766 lead isotope ratios are dominated by colourant derived pb the isotope ratios of the manganese used to produce translucent glass and lead used for opaque glass decorations fall in the same range the most likely general provenance of both lies on lavrion or the western cycladic islands although an origin in the central taurus or the sinai mountains cannot be excluded the conclusion is that manganese ore used for colourants contributes significantly to the ree concentration in the glass including nd as well as to sr and pb this needs to be taken into account when using concentrations or isotope ratios of these elements for provenancing other raw materials like sand and calcium carbonate this appears to be the case for all antique soda lime silica glass

delineating alteration footprints from field and aster swir spectra geochemistry and gamma ray spectrometry above regolith covered base metal deposits an example from abra western australia

provenance of polychrome and colourless 8th 4th century bc glass from pieria greece a chemical and isotopic approach abstract glass objects from pydna and methoni in modern day greece dated to the eighth to fourth century bc were chemically investigated the combined use of multiple analytical techniques allowed the elemental and isotopic characterization of these polychrome and colourless glass artefacts in order to examine their provenance all fragments were found to be soda lime silica natron based glass produced from a rather pure silica rich sand containing sea shells and mixed with natron possibly coming from more than one source based on the strontium and neodymium isotopic signatures most glass artefacts likely derive from a syro palestinian production site although the exact location is unknown also the oxygen isotopic signature of most of the samples suggests the manufacturing of the artefacts from raw materials with a primary origin along the syro palestinian coast nevertheless the use of particular raw materials cannot be excluded for some artefacts as some samples show enriched 18 o values pointing to a different glassmaking tradition

potential of sentinel 2 data for alteration extraction in coal bed methane reservoirs abstract this study illustrates the potential of alteration extraction in coal bed methane cbm reservoirs using the recently available sentinel 2 data this study then evaluates the capabilities for mapping the altered minerals and vegetation in the alteration mapping process we separately analyzed the key remote sensing signatures of altered minerals and geobotanical anomalies based on the hydrocarbon micro seepage theory the diagnostic spectral characteristics of irons clays and altered vegetation were concentrated and demonstrated the distribution of hydrocarbon micro seepage in the bare soil region the altered minerals including irons and clays were extracted through band math and principal component analysis pca methods in the vegetation area mapping the diagnostic spectral feature parameters such as the locations and slopes of three feature edges were calculated in addition the mapping accuracy was assessed based on the extraction results of hyperion data through full spectral profile matching method and the x ray diffraction xrd analysis results the results show that 1 compared with band math and pca methods the different extraction methods were suitable for different minerals 2 the extraction results of iron and clay minerals were most accurate 78 33 and 76 67 respectively with xrd analysis 3 the highest rate of change of the feature edge slope was up to 39 with a reference spectrum and 4 the distribution of alteration information was consistent with the hudi coal mining area in jincheng shanxi province the potential geological application of sentinel 2 data was revealed to identify the direction of cbm exploration in a large scale highly efficient convenient and inexpensive way

proximal and remote spectroscopic characterisation of regolith in the albany fraser orogen western australia abstract vast parts of the australian continent are prospective for precious and base metal mineralisation but exploration is hindered by extensive cover of often deeply reaching regolith new operational exploration methods are required that can help to characterise the cover and provide information about bedrock signatures this paper shows how mineral mapping information from a combination of satellite multispectral advanced spaceborne thermal emission and reflection radiometer aster imagery and drill core hyperspectral profiling data hylogging can be used to unravel the regolith stratigraphy and to describe regional variations of regolith landforms delivering important information for mineral exploration the case study is located in the neale tenements in the northeastern albany fraser orogen western australia which is prospective for tropicana style gold mineralisation by interpretation of indicator minerals from hyperspectral drill hole logging data the regolith stratigraphy atop a metamorphic basement comprising saprock ferrugineous saprolite kaolinitic saprolite silcrete and transported cover is recorded in cm detail important mineralogical parameters extracted from the hyperspectral subsurface data and validated by xrd and ftir are 1 the abundance and type of iron oxides 2 the abundance and crystallinity of kaolinite 3 the abundance and composition of primary minerals such as white mica and 4 the abundance of quartz the hylogging data served as ground control points for mineral mapping information provided by csiro s aster geoscience products which are a collection of mineral maps that highlight variations in the abundance type or chemistry of selected mineral groups key aster geoscience products for regolith characterisation were the ferric oxide and aloh abundance and composition images the comparison of the surface with the subsurface data suggests three major different regolith landforms including erosional depositional and relict areas which were used to generate a map showing transported versus relict and erosional areas erosional domains were mapped out in great detail providing important information for exploration in saprolite dominated areas furthermore source areas of transported material could be identified which may help to understand the distribution of geochemical signatures collected during for example geochemical soil sampling projects

hydrothermally altered mineral mapping using synthetic application of sentinel 2a msi aster and hyperion data in the duolong area tibetan plateau china abstract the duolong area is in a strong potential copper mineralization zone associated with felsic intrusions and several porphyry copper deposits pcds have been identified the pcds are characterized by hydrothermal alteration zones in this study sentinel 2a multispectral instrument msi advanced spaceborne thermal emission and reflection radiometer aster and hyperion data are combined to map hydrothermally altered minerals three temporal sentinel 2a msi images are processed by integrating the crosta technique and the anomaly overlaying selection method to map iron oxides and hydroxyl bearing minerals these approaches are implemented to omit interference induced false anomalies the six shortwave infrared swir bands of aster are used to extract information on al oh and mg oh group minerals the distribution of al oh minerals in the aster image map corresponds to that of hydroxyl bearing minerals in the msi image map a combination of minimum noise fraction mnf pixel purity index ppi n dimensional visualizer n d visualizer and matched filtering mf is adopted to process the hyperion image to obtain accurate hydrothermal alteration mapping results the overall accuracy for mineral mapping is 92 75 and the kappa coefficient is 0 89 the results of the hyperion image are spatially consistent with those of the sentinel 2a msi and aster images the image processing results were validated by field investigations and spectral reflectance measurements hydrothermally altered rocks correspond well with the five pcds in the duolong area three mineralization prospects associated with felsic intrusions are discovered in accordance with the results the methodologies and data are effective in detecting porphyry copper mineralization in other arid areas

sub pixel mapping of alunite and jarosite using aster data a case study from north of semnan north central iran abstract a widespread series of volcanic rocks and younger intrusive bodies are exposed in the north and northeastern semnan north central iran they show an intermediate to felsic composition which have undergone various types of alteration including alunite and jarosite in this research aster data were used for sub pixel mapping of these typical minerals using the mixtured tuned matched filtering mtmf algorithm the spectral properties of field samples were measured by an asd spectroradiometer and their spectra were analyzed through a visual comparison to the usgs spectral library however the z profile method was used for extraction of target spectra from pixels in which the occurrence of desired minerals were verified by other methods the mtmf output results revealed pixels with the highest fractions of alunite and jarosite dominantly near the altered rhyolitic and andesitic tuffs as well as in adamelites it is suggested that an integration of mtmf method and the aster data is a powerful approach for sub pixel mapping of alunite and jarosite which could be applicable in mineral exploration projects

equilibrium mineral fluid calculations and their application to the solid solution between alunite and natroalunite in the el indio pascua belt of chile and argentina abstract the effects of temperature and bulk fluid k na on the alunite natroalunite solid solution have been determined at 200 bar and 100 300 c these are conditions typical of magmatic hydrothermal alteration and precious metal mineral deposition in high sulfidation environments which are characterized by the presence of alunite bearing alteration zones our model is based on published experimental parameters which indicate that both alunite and natroalunite are stable over this temperature range and that increased na substitution is favored at higher temperature our calculation results predict that at all temperatures fluids in equilibrium with natroalunite are significantly more na rich than those typical of modern volcanic hydrothermal environments the results also indicate that a large variation in fluid k na is required to precipitate both k and na rich alunite at high temperature assuming near equilibrium conditions at lower temperature much less variation in fluid composition can yield compositions near those of the end members controls on alunite natroalunite solid solution in natural systems were evaluated using electron microprobe data from high sulfidation gold deposits of the el indio pascua belt the results indicate that higher temperatures of deposition correlate with a greater range of na substitution in alunite elevated na content in alunite is also locally attributed to higher concentrations of na in the source fluid as a result of the leaching and alteration of andesitic host rocks dacitic to granitic host lithologies in other regions of the belt are correlative with more k rich alunite compositions the results from this study suggest that the use of alunite k na composition as a guide to mineral exploration should be treated with caution

characterising the hydrothermal alteration of the broadlands ohaaki geothermal system new zealand using short wave infrared spectroscopy abstract hydrothermal clay minerals present in the broadlands ohaaki geothermal field were characterised by field portable short wave infrared spectroscopy three major alteration zones an upper smectite a middle illite and a lower illite chlorite are spectrally separable the zoning pattern is generally consistent with the thermal structure of the geothermal field although occasionally zone boundaries cut present day isotherms the data indicate that temperature is the major control on clay zoning and permeability plays a subordinate role both beidellite and montmorillonite are common in the upper low temperature smectite zone kaolinite mainly of low crystallinity marks the margin of the field where cool acidic ground waters inflow in the middle alteration zone illite dominantly k rich shows a narrow compositional variability some highly permeable zones are characterised by illite with low octahedral al contents ammonium bearing illite and buddingtonite are present locally in permeable horizons within the illite zone where temperatures are above 200 c chlorite is most abundant in the lower alteration zone temperature 250 c although it also occurs unevenly in the upper and middle alteration zones chlorite varies from mg to fe rich varieties but mostly with mg values

reflectance spectroradiometry applied to a semi quantitative analysis of the mineralogy of the n4ws deposit carajas mineral province para brazil abstract quantifying the abundance and physicochemical properties of minerals using reflectance spectroradiometry in the visible near infrared and shortwave infrared 400 2500 nm regions is an important tool in mineral exploration in this study the reflectance spectra of drill cores from the world class n4ws iron deposit located in the carajas mineral province brazil were obtained these spectra were validated using x ray fluorescence xrf geochemical analyses and thin sections the reflectance spectra were collected using a fieldspec 3 spectroradiometer asd boulder colorado usa in 10 drill cores the mineralogy of the deposit is mainly hematite with lesser amounts of magnetite goethite quartz kaolinite gibbsite smectite talc carbonate and chlorite the mineralogy of the iron deposit was extracted from the spectral data using the geometry depth and wavelength of absorption features across the reflectance spectrum removed from the continuum the depth of the absorption features is proportional to the mineral abundance and the wavelength is proportional to the mineral chemical composition the diagnostic absorption features of each mineral were used to determine the mineral abundance and composition the final products include the abundance of iron hydro oxide 11 6 root mean square error rmse fe2o3 abundance of aluminous clays rmse 6 al2o3 abundance of talc 8 rmse mgo identification of clay type kaolinite montmorillonite or gibbsite composition of carbonate dolomite vs calcite and composition of chlorite mg vs fe the mineral abundance and composition results provided an effective characterisation of the ore protore and host rocks and showed variations within the ore body

the first archaeometric data on polychrome iron age glass from sites located in northern italy abstract a large sample set of transparent and opaque glass artefacts recovered from etruscan contexts in northern italy bologna and spina fe necropoleis and dated to a period between the 6th and 4th century bc are analysed in this paper samples of highly decorated beads spindle whorls and vessels of the mediterranean group i alabastron oinochoes amphoriskos were selected in order to determine whether these different glass artefacts were produced at the same manufacturing site while the vessels almost certainly originate from greece the beads could derive from a more ancient local production ascertained at the site of frattesina rovigo italy and dated to the bronze age the aims of this study are i to characterise a set of iron age glass artefacts thus providing new quantitative chemical data and ii to identify possible differences between finds recovered from different localities and between glass vessels and beads in order to establish whether different manufactures were active contemporaneously the chemical analyses of major and minor elements were performed with an electron microprobe the nature of the opacifying and colouring agents was determined by x ray diffraction the sample set is relatively homogeneous and most of the samples can be classified as low magnesium glass the yellow opaque decorations are rich in pb and sb while only sb is present in the white and light blue samples the xrd analyses confirmed the presence of lead antimonates in the yellow decorations and of calcium antimonates in the white and light blue decorations

the application of aster remote sensing data to porphyry copper and epithermal gold deposits abstract this paper reviews the performance characteristics of the advanced spaceborne thermal emission and reflection radiometer aster remote sensor the standard data products and applications of the most recently developed image processing methods applied to aster data as a tool for mapping hydrothermal alteration mineral zones associated with porphyry copper and epithermal gold mineralization and related host rock lithology hydrothermal alteration zones associated with porphyry copper deposit such as phyllic argillic and propylitic mineral assemblages can be discriminated from one another by virtue of their spectral absorption features which are detectable by aster swir spectral bands the identification of the phyllic zone is important in the initial stages of porphyry copper exploration as an indicator of high economic potential for copper mineralization two new crosstalk corrected aster swir reflectance products including ast 07xt and refl1b are more reliable than previous aster data products for regional mineral mapping without use of additional spectral data from the site for calibration four types of algorithms were used to extract spectral information of aster data 1 band ratio indices and logical operator based methods 2 principal components and enhancement based methods such as principal component analysis pca and minimum noise fraction mnf 3 shape fitting based algorithms such as spectral angle mapper sam matched filtering mf and mixture tuned matched filtering mtmf and 4 partial unmixing methods such as linear spectral unmixing lsu and constrained energy minimization cem this review emphasizes that the logical operator algorithms can be best suited for hydrothermal alteration mineral mapping including phyllic and argillic zones associated with porphyry copper mineralization in a regional scale shape fitting based and partial unmixing algorithms are robust and reliable for detecting particular mineral and mineral assemblages in hydrothermal alteration zones in a district scale consequently the integration of the results derived from the logical operator shape fitting based and partial unmixing algorithms can produce comprehensive and accurate information for the reconnaissance stages of copper and gold exploration at both regional and district scales all of the methods and applications reviewed in this paper demonstrate the utility of aster data for exploration of the porphyry copper and epithermal gold deposits around the world

geology and hydrothermal alteration of the chapi chiara prospect and nearby targets southern peru using aster data and reflectance spectroscopy southern peru contains several small and medium sized epithermal au ag base metals deposits related to miocene pliocene metallogenetic belts specifically the characterization of the geology and mapping of hydrothermal alteration zones of the chapi chiara prospect canahuire deposit and cerro millo and san antonio de esquilache targets were done with data acquired by advanced spaceborne thermal emission and reflection radiometer aster spaceborne sensor aster mapping techniques included 1 band ratio and principal component analysis crosta technique applied to the visible and near infrared and short wave infrared bands to produce a regional hydrothermal alteration map alunite and or kaolinite illite muscovite and or smectite iron bearing minerals and 2 spectral indices and selective principal component analysis applied to the thermal infrared bands to detect quartz and carbonates bearing targets respectively these methods were used to establish a hydrothermal zoning pattern in paleostratovolcanoes where the chapi chiara cerro millo and san antonio de esquilache targets are located this zoning pattern was used to infer erosion conditions and the potential for metal deposits based on the mineralogy which was also analyzed using reflectance spectroscopy and petrography in addition aster data were used to characterize the carbonate host rocks the quartz bearing units of the yura group and the quartz poor unit associated with the phreatic and phreatomagmatic breccias in the canahuire deposit region this characterization led to the development of a favorability model for the occurrence of canahuire type deposits based on spatial analysis using the fuzzy logic technique

new constraints on the upper mantle structure of the slave craton from rayleigh wave inversion 1 rayleigh wave phase and amplitude data are analyzed to provide new insight into the velocity structure of the upper mantle beneath the slave craton in the northwestern canadian shield we invert for phase velocities at periods between 20 s 142 s with greatest sensitivity at depths of 28 200 km using crossing ray paths from events recorded by the polaris broadband seismic network and the yellowknife array phase velocities obtained for the slave province are comparable to those from other cratons at shorter periods but exceed the global average by 2 at periods above 60 s suggesting that the slave craton may be an end member in terms of its high degree of mantle depletion the one dimensional inversion of phase velocities yields high upper mantle s wave velocities of 4 7 0 2 km s that persist to 220 65 km depth and thus define the cratonic lithosphere azimuthal anisotropy is well resolved at all periods with a dominant fast direction of n59 e 20 suggesting that upper mantle anisotropy beneath the slave craton is influenced by both lithospheric fabric and sub lithospheric flow

analysis of polychrome iron age glass vessels from mediterranean i ii and iii groups by la icp ms in this work the analytical results obtained by icp ms with laser ablation solid sampling and sem eds for some polychrome glass vessels from the iron age are presented and discussed the samples coming from etruscan sites near adria northern italy belong to the so called mediterranean groups i ii and iii and are dated from the 5th 3rd and 2nd century b c respectively to date analytical data for only two sets of vessels of the iron age have been discussed in the literature in spite of the low number of available samples this is the first time that vessels of all three periods are analytically compared elemental concentration data show that the samples can be classified as low magnesia low potash lmlk soda lime silica glasses with low phosphorus and titanium contents in agreement with data for similar samples of the same age bivariate and multivariate analyses of the contents of many elements characterizing the siliceous sands showed three distinct sets corresponding to the three periods since the sets indicate different provenances of the sands it seems rational to assume that different glassmaking locations were involved chromophores and opacifiers of the blue bodies and the yellow white and turquoise decorations of the vessels were analytically identified while the nature of the corresponding ores was hypothesized

mapping hydrothermally altered rocks at cuprite nevada using the advanced spaceborne thermal emission and reflection radiometer aster a new satellite imaging system the advanced spaceborne thermal emission and reflection radiometer aster is a 14 band multispectral instrument on board the earth observing system eos terra the three bands between 0 52 and 0 86 m and the six bands from 1 60 and 2 43 m which have 15 and 30 m spatial resolution respectively were selected primarily for making remote mineralogical determinations the cuprite nevada mining district comprises two hydrothermal alteration centers where tertiary volcanic rocks have been hydrothermally altered mainly to bleached silicified rocks and opalized rocks with a marginal zone of limonitic argillized rocks country rocks are mainly cambrian phyllitic siltstone and limestone evaluation of an aster image of the cuprite district shows that spectral reflectance differences in the nine bands in the 0 52 to 2 43 m region provide a basis for identifying and mapping mineralogical components which characterize the main hydrothermal alteration zones opal is the spectrally dominant mineral in the silicified zone whereas alunite and kaolinite are dominant in the opalized zone in addition the distribution of unaltered country rocks was mapped because of the presence of spectrally dominant muscovite in the siltstone and calcite in limestone and the tuffaceous rocks and playa deposits were distinguishable due to their relatively flat spectra and weak absorption features at 2 33 and 2 20 m respectively an airborne visible infrared imaging spectrometer aviris image of the study area was processed using a similar methodology used with the aster data comparison of the aster and aviris results shows that the results are generally similar but the higher spectral resolution of aviris 224 bands permits identification of more individual minerals including certain polymorphs however aster has recorded images of more than 90 percent of the earth s land surface with less than 20 percent cloud cover and these data are available at nominal or no cost landsat tm images have a similar spatial resolution to aster images but tm has fewer bands which limits its usefulness for making mineral determinations

alteration mineralogy at the cerro la mina epithermal prospect patagonia argentina field mapping short wave infrared spectroscopy and aster images the cerro la mina prospect located in the los menucos area argentina is currently being explored for epithermal gold mineralization triassic jurassic hydrothermal activity produced intense alteration of rhyolites andesites ignimbrites and tuffs of the late triassic los menucos group in the somun cura massif a detailed surface map of the principal alteration assemblages at cerro la mina was produced employing field mapping supported by short wave infrared swir field spectroscopy petrography x ray diffraction xrd and scanning electron microscopy sem advanced argillic argillic and silicic alteration zones and their internal mineral assemblage variations were recognized at cerro la mina the silicification consists of massive bodies of fine grained quartz and minor vuggy quartz locally containing disseminated aggregates of pyrite and rutile advanced argillic alteration of magmatic hydrothermal origin occurs adjacent to the silicic alteration zones and can be subdivided into three mineral assemblages 1 stage 1 alunite quartz dickite kaolinite pyrophyllite diaspore rutile pyrite barite 2 dickite kaolinite pyrophyllite diaspore pyrite barite and 3 dickite quartz diaspore the advanced argillic and silicic alteration grades to argillic alteration comprising three mineral assemblages 1 kaolinite dickite quartz illite smectite 2 kaolinite illite smectite ferroan clinochlore and 3 illite quartz muscovite kaolinite supergene alteration which locally overprints the prior alteration zones consists of jarosite hematite goethite stage 2 alunite aluminum phosphate sulfate aps poorly crystalline kaolinite consistent discrimination of the main alteration minerals of this prospect was also achieved by means of satellite multispectral remote sensing the application of image processing techniques specifically designed for mineral mapping to selected spectral bands of the terra aster multispectral sensor resulted in a detailed alteration map for the entire prospect comparison between the results achieved through remote sensing with field data on the cerro la mina confirmed the accuracy of the former the silicification and minor vuggy quartz the abundant dickite and the coarse grained hypogene alunite among other advanced argillic alteration assemblages suggest that cerro la mina corresponds to a volcanic hydrothermal leached environment possibly controlled by permeable lithological units these characteristics led us to interpret this prospect as a possible lithocap similar to those that typically host subsequent high sulfidation mineralization

regional mineral mapping of island arc terranes in southeastern mongolia using multi spectral remote sensing data abstract over the last few decades many porphyry cu deposits have been discovered in southeastern se mongolia in particular the gurvansayhan and mandalovoo island arc terranes have high potential for ore deposits regional mineral mapping of these terranes using data from the landsat enhanced thematic mapper plus etm and the advanced spaceborne thermal emission and reflection radiometer aster have provided new geological information on the metallogenic province revealing potential mineral deposits for future explorations iron oxides hydroxides with high etm band 1 3 ratio values occur extensively in quaternary deposits located at the boundary between the gurvansayhan and mandalovoo island arcs terranes and basins the high average band ratios 1 35 registered for the porphyry cu and au deposits and their occurrences are associated with iron oxidation which originates from the erosion and weathering of ore zones regional mapping of the island arc terranes using the aster shortwave infrared swir logical operators showed circular or semicircular alteration patterns which usually cluster along faults the mineral assemblages mapped by the aster swir analysis in five major porphyry cu districts can be divided into two types the first type includes argillic phyllic and propylitic mineral assemblages as exemplified by the shuteen ikh shankhai and oyu tolgoi deposits the second type of assemblage includes phyllic and propylitic mineral assemblages as exemplified by the kharmagtai and tsagaan suvarga deposits within the deposits of the first type quartz was also mapped using the aster thermal infrared tir mineral index the difference between the two types may be related to the presence of a lithocap the results of a field survey including spectral reflectance measurements in the ikh shankhai porphyry cu district showed a good correlation with the image analysis results

short wavelength infrared spectral characteristics of the hw horizon implications for exploration in the myra falls volcanic hosted massive sulfide camp vancouver island british columbia canada short wavelength infrared swir spectrometry has been used to identify previously unmapped hydrothermal alteration zones around volcanic hosted massive sulfide vhms orebodies at myra falls vancouver island british columbia hydrothermal alteration assemblages are uniformly dominated by fine grained white mica with poor development of mineralogical zonation swir spectrometry is an ideal exploration tool for characterizing this fine grained hydrothermal alteration at myra falls swir spectrometry has identified subtle shifts in the wavelengths of the aloh absorption feature of white mica corresponding to compositional changes in altered rhyolite distal and proximal to ore aloh absorption occurs at shorter wavelengths 2 198 nm and corresponds to lower fe fe mg and si al and higher na na k in strongly altered samples proximal to ore slightly sodic muscovites aloh absorption occurs at longer wavelengths 2 206 nm and corresponds to higher fe fe mg and si al and lower na na k in samples distal to ore nonsodic slightly phengitic muscovites white mica in siltstone within a meter of vhms ore has higher zn v fe and mg contents than white mica distal to these altered samples chlorite compositions identified by swir also show systematic changes with intensity of alteration and distance from ore the average wavelength of the feoh absorption feature for chlorite in rhyolitic samples proximal to ore is 2 241 nm intermediate mg chlorite whereas wavelengths in background samples average 2 247 nm intermediate fe chlorite similar changes are observed in footwall and hanging wall andesites with samples near the battle mine containing muscovite to phengitic muscovite average wavelength of the aloh absorption feature of 2 200 nm and mg rich chlorite average wavelength of the feoh absorption feature of 2 245 nm to regional andesite samples with phengitic muscovite average wavelengths of the aloh absorption feature of 2 209 nm and fe rich chlorite average wavelength of the feoh absorption feature of 2 249 nm in weakly altered rocks white mica compositions also vary with host lithology the aloh absorption feature occurs at longer wavelengths in white mica in dacite and andesite compared to adjacent rhyolitic rocks suggesting that higher fe and mg in the host lithology affects the composition of white mica two zones of intense hydrothermal alteration above the battle and hw orebodies have distinctive swir spectral characteristics with the aloh and feoh features occurring at shorter wavelengths 2 197 and 2 240 nm respectively small anomalous zones of alteration were also identified in the thelwood valley area where minor mineralized zones are present as broad zones of fine grained white mica sericite alteration are ubiquitous throughout the myra falls property alteration proximal to ore cannot be identified simply by visual logging of drill core alteration zonation may be determined by subtle shifts in white mica spectral characteristics this study indicates that swir analysis may be an effective field based exploration tool for quantifying the intensity of alteration associated with vhms orebodies and that trends in mineral compositions even in very fine grained rocks can be used as mine scale vectors to ore

short wavelength infrared swir spectral analysis of hydrothermal alteration zones associated with base metal sulfide deposits at rosebery and western tharsis tasmania and highway reward queensland spectral analysis of rock samples by short wavelength infrared swir analysis using the portable infrared mineral analyzer pima spectrometer is a relatively new field method with applications in mineral exploration the technique allows rapid field based identification of hydrothermal alteration minerals and delineation of alteration zones variations in mineral composition crystallinity and relative abundance may also be determined phyllosilicates including white mica and chlorite are particularly amenable to short wavelength infrared analysis these are prominent alteration minerals in the felsic volcanic rocks in the mount read volcanics tasmania and the mount windsor subprovince north queensland they have regional distributions as diagenetic and metamorphic products and exist locally in alteration zones associated with volcanic hosted sulfide deposits a geochemical and spectral investigation of white micas in the least altered rocks in the mount read volcanics has shown considerable background compositional variations the white micas range from phengite to moderately sodic muscovite and swir spectral measurements provide reliable estimates of their compositions chlorites also have a broad compositional range in these rocks however swir spectral analysis has proven to be unreliable in determining chlorite composition in samples where chlorite exists in low proportions relative to white mica or in mixed assemblages with epidote white micas in footwall alteration zones of the rosebery stratiform zn pb deposit tasmania are variably phengitic similar to those in regional background volcanics a unit of relatively unaltered volcaniclastic sandstone in the rosebery hanging wall sequence contains anomalous sodic muscovite in proximity to ore lenses white micas associated with the disseminated to massive pyritic cu au deposits at western tharsis tasmania and highway reward north queensland range in composition from phengite to slightly sodic muscovite in these symmetrically zoned alteration systems white micas grade in composition from phengite in peripheral zones to slightly sodic muscovite in proximal zones near ore in all three cases the white mica compositional variation is a vector to ore that is effectively measured by swir spectrometry with particular application in prospect scale exploration chlorite compositions at rosebery are not strictly spatially related to ore but tend to be most magnesian in zones of high chlorite abundance in the outer alteration zone at western tharsis there is a faint proximal trend to iron rich chlorites however it does not represent a well defined vector to ore in either case attempts at quantitative estimation of the relative abundance of white mica and chlorite in mixed samples by spectral analysis have produced results that are imprecise in comparison to geochemically derived estimates the data scatter relates to the low proportions of chlorite in the majority of the samples analyzed resulting in weak chlorite absorptions better results may be obtainable in specific alteration or lithostratigraphic domains by use of customized spectral unmixing software this investigation has shown that pima based swir spectrometry is a potent field method of mapping compositional variations in white micas that represent empirical vectors to at least some types of volcanic hosted sulfide deposits it has also highlighted its effectiveness in field identification of megascopically difficult or indeterminate alteration minerals such as pyrophyllite zunyite and topaz which may have genetic implications and exploration significance

identifying high potential zones of gold mineralization in a sub tropical region using landsat 8 and aster remote sensing data a case study of the ngoura colomines goldfield eastern cameroon abstract climatic conditions and vegetation constrain the use of optical satellite imagery as an exploration tool for hydrothermal ore mineralization in tropical and subtropical regions in this investigation landsat 8 and aster satellite imagery were used to detect hydrothermal alteration zones associated with gold mineralization in the ngoura colomines region eastern cameroon the study area contains several gold bearing quartz veins associated with zones of pyritization muscovite sericite iron oxides and silicification principal component analysis pca independent component analysis ica and specialized spectral band ratios were used to extract spectral information related to vegetation iron oxide hydroxide minerals al oh fe mg oh carbonate group minerals and silicification using landsat 8 data at regional scale linear spectral unmixing lsu algorithm was implemented to aster vnir swir bands for detailed discrimination of hematite jarosite kaolinite muscovite chlorite and epidote at district scale the automated spectral hourglass ash technique was employed to extract reference spectra directly from the aster bands for producing fraction images of end members using the lsu a comprehensive field survey was used to verify the remote sensing results petrographic study x ray diffraction analysis and reflectance spectroscopy indicated the presence of quartz goethite and sericite as well as the absorption features of fe3 fe2 al oh oh h2o and sio2 in the alteration zones several hydrothermal alteration zones of iron oxide hydroxide clay carbonate minerals and silicification zones were identified which are spatially associated with known mining areas and gold occurrences in the study area high potential prospects were also delineated including the ngoura colomines prospects and the newly discovered yangamo ndatanga and tapare tapondo prospects in the southwestern and southeastern parts of the study area consequently satellite based mineral prospectivity maps at regional and district scales were generated for the study area by implementing the fuzzy logic model to the most informative thematic layers derived from image processing results the satellite based prospectivity maps are reliable for exploration of new gold prospective zones in the ngoura colomines goldfield

spectral characteristics of minerals in alteration zones associated with porphyry copper deposits in the middle part of kerman copper belt se iran abstract visible near infrared and shortwave infrared vnir swir 350 to 2500 nm reflectance spectra obtained from an analytical spectral device asd have been used to define alteration zones adjacent to porphyry copper deposits pcds in the central part of kerman magmatic arc se iran the spectral analysis identified sericite illite halloysite montmorillonite dickite kaolinite pyrophyllite biotite chlorite epidote calcite jarosite and iron oxyhydroxides e g hematite goethite of hydrothermal and supergene origin identified alteration zones are classified into six principal types namely phyllic phyllic propylitic propylitic potassic argillic and advanced argillic the iron oxide minerals in the oxidized zone were also identified using spectral analysis results of spectral analyses of samples are consistent with mineralogical data obtained from x ray diffraction xrd and petrographic studies spectroscopic studies by asd demonstrate that this tool is very useful for semi quantitative and cost effective identification of different types of alteration mineral assemblages furthermore it can provide a valuable tool for evaluating aerial distribution of alteration minerals while coupled with remote sensing data analysis

the aster spectral library version 2 0 abstract the advanced spaceborne thermal emission reflection radiometer aster on nasa s terra platform has been widely used in geological and other science studies in support of aster studies a library of natural and man made materials was compiled as the aster spectral library v1 2 and made available from http speclib jpl nasa gov the library is a collection of contributions in a standard format with ancillary data from the jet propulsion laboratory jpl johns hopkins university jhu and the united states geological survey usgs a new version of the library v2 0 is now available online or via cd which includes major additions to the mineral and rock spectra the aster library provides a comprehensive collection of over 2300 spectra of a wide variety of materials covering the wavelength range 0 4 15 4 m

jurassic epithermal au ag deposits of patagonia argentina abstract important precious metal deposits have been discovered during the last 10 years in the deseado massif region of patagonia argentina this region is a plateau consisting of middle to upper jurassic volcanic rocks that host fracture controlled epithermal au ag mineralization these mineral deposits represent low sulfidation type hydrothermal systems and formed following the main period of volcanism probably during the late jurassic period the presence of silica sinters and veins interpreted to be feeder structures indicates that the tops of some deposits have been preserved with erosion of younger sedimentary and volcanic rocks now exposing these systems these deposits represent diverse erosional levels ranging from sinter formed at the paleosurface to intermediate au ag rich quartz veins to base metal bearing au ag veins that represent deeper levels of the epithermal systems the best known deposits are in the cerro vanguardia district where vein systems occur over a 350 km 2 area and veins can be traced for more than 14 km geological mapping of the district has resulted in the definition of over 140 km of veins current reserves are over 3 2 million ounces au equivalent with grades of 10 g t au and 120 g t ag the geologic characteristics of the region and the presence of major au ag deposits provide targets for continuing exploration in the deseado massif

mapping advanced argillic alteration at cuprite nevada using imaging spectroscopy 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