plane stress and plane strain fracture in eocene chalks around beer sheva abstract a distinction has been made between plane strain and plane stress fracture conditions in metals in these materials flat fracture normal to the tensile stress develops in plane strain however the fracture is slanted when conditions change to plane stress analogies with rock mechanics suggest a simple model of en echelon cracking along fringes of vertical joints in thin horizontal sedimentary layers according to this model the en echelon cracking is a result of fracture under plane stress conditions when failure is explained by the coulomb criterion and subject to limited overburden

development of strike slip faults from dikes sequoia national park california abstract faults several kilometers long near pear lake in sequoia national park california nucleated on preexisting dikes weakened by closely spaced echelon joints these joints essentially parallel much more widely spaced regional joints fault nucleation by dike fracturing can explain how a nearly planar fault can grow to lengths of several kilometers or more we suggest that opening mode fractures including dikes might serve more commonly as nuclei for faults than is generally appreciated the longest fault in the study area the pear lake fault has a trace length of 7 km and a maximum measured lateral separation of 86 98 m a sharp decrease in slip occurs near the center of the trace of the pear lake fault where another fault branches from it mechanical analyses demonstrate that a sharp decrease in slip is expected where a fault branches all the faults near pear lake show non elliptical slip distributions based on our mechanical analyses we infer that the observed slip distributions reflect a mechanical interaction among the faults the geometry and distribution of structures that precede faulting i e dikes and joints control to a large extent the structure of a fault network and hence the ultimate slip distribution on faults in the network

mapping the piute mountains california with thermal infrared multispectral scanner tims images thermal infrared multispectral scanner tims data were acquired in 1990 over the piute mountains california to evaluate their usefulness for lithologic mapping in an area of metamorphosed structurally complex igneous and sedimentary rocks the data were calibrated and atmospherically corrected and emissivity variations in the form of alpha residuals were extracted from which color composite images were made there was an excellent visual correlation between the units revealed in the color composite image and the lithologic units mapped in the eastern side of the area it was also possible to correct improve and extend the recent map for example several areas mapped as granodioritic gneiss had tims alpha residual spectra consistent with mafic rocks and were subsequently mapped as amphibolite the presence of a swarm of mafic dikes of which only a few had previously been identified was also revealed the images also showed color variations in granitoid plutons that correlated with compositional variations previously determined by extensive field and geochemical work the western piute mountains is an area that has proven to be especially difficult to map with field and air photographic methods due to heterogeneous nature of certain units and various levels of desert varnish the images permitted the extremely heterogeneous proterozoic schists gneisses and granites to be easily mapped because the small scale compositional variability was averaged to the tims pixel size 12 m 12 m square areal measurements from the images show that the proterozoic rocks in the piute mountains consist of granitoids 50 biotite gneiss 15 pelitic gneiss 15 quartzite 10 and amphibolite 10 tims data can dramatically increase the efficiency and the quality of geologic mapping in well exposed heterogeneous areas with minimal vegetation cover where detailed mapping of lithologic contacts by traditional methods is unusually difficult

geology and magmatic hydrothermal evolution of the giant pebble porphyry copper gold molybdenum deposit southwest alaska the pebble deposit is located 320 km southwest of anchorage alaska it is one of the largest porphyry deposits known with a total resource of 10 78 billion tons bt it comprises the east and west zones which are approximately equal in size with slightly lower grade mineralization in the center of the deposit where the peripheries of the two zones merge the west zone was discovered by cominco america in 1989 and the east zone was discovered by northern dynasty minerals in 2005 the oldest rock in the pebble district is the jurassic cretaceous kahiltna flysch unit which contains basinal turbidites interbedded basalt flows and associated gabbro intrusions these rocks were intruded between 99 and 96 ma by coeval granodiorite and diorite sills followed shortly thereafter by alkalic monzonite intrusions and related breccias subalkalic hornblende granodiorite porphyry plutons of the kaskanak batholith were emplaced at 90 ma similar smaller granodiorite plutons were emplaced around the margins of the batholith and are related to cu au mo mineralization re os dates on molybdenite are between 89 7 and 90 4 ma a late cretaceous volcanic and sedimentary cover sequence completely conceals the east zone whereas the west zone is overlain only by glacial sediments and is exposed in one small outcrop eocene volcanic rocks and subvolcanic intrusions occur east and southeast of the pebble deposit and unconsolidated glacial sediments are widespread the east and west zones represent two coeval hydrothermal centers within a single system the west zone extends from surface to 500 m depth and is centered on four small granodiorite plutons emplaced into flysch diorite and granodiorite sills and alkalic intrusions and breccias the much higher grade east zone extends to at least 1 700 m depth and is hosted by a larger granodiorite pluton and adjacent granodiorite sills and flysch the granodiorite plutons merge with depth on the east side of the deposit high grade mineralization has been dropped 600 to 900 m into the ne trending east graben where the deposit remains undelineated to the east and to depth variations in hypogene grade and metal ratios reflect multiple stages of metal introduction and redistribution hornfels related to the kaskanak batholith formed prior to hydrothermal activity at pebble and is most intensely developed in flysch disseminated and vein hosted cu au mo mineralization dominated by chalcopyrite and locally accompanied by bornite formed with potassic alteration in the shallow part of the east zone and with approximately coeval sodic potassic alteration in the west zone and at depth in the east zone illite kaolinite alteration overprinted potassic and sodic potassic alteration throughout the deposit and variably redistributed copper and gold high grade copper gold mineralization is related to advanced argillic alteration controlled by a synhydrothermal brittle ductile fault zone which overprinted potassic sodic potassic and illite kaolinite alteration in the east zone advanced argillic alteration comprises a core of pyrophyllite alteration associated with chalcopyrite bounded to the west by an upward flaring zone of sericite alteration which contains hypogene bornite digenite covellite and trace enargite and tennantite late quartz veins introduced additional molybdenum in several parts of the deposit grade destructive quartz sericite pyrite alteration forms a halo to the entire deposit and yields outward to propylitic alteration a quartz illite pyrite cap is preserved in the weakly mineralized center of the deposit mineralization at pebble is predominately hypogene a thin incompletely developed zone of supergene mineralization occurs in the west zone and is overlain by a thin leached capping there is no evidence for paleosupergene mineralization or leaching below the cover sequence in the east zone molybdenite contains high concentrations of rhenium throughout the deposit elevated palladium concentrations are associated with pyrophyllite alteration in the east zone the pebble deposit occurs in one of a number of large deep seated magnetic anomalies which are located at the intersection of crustal scale structures both parallel and at high angles to a mid cretaceous magmatic arc this setting is similar to fertile porphyry environments in northern chile and suggests that southwestern alaska is highly prospective for porphyry exploration the large size and high hypogene grades of the pebble deposit may reflect a combination of multiple stages of metal introduction with vertically restricted lateral fluid flow induced by hornfels aquitards in flysch

imaging 3 d fracture networks around boreholes a new method has been developed for building and visualizing three dimensional 3 d subsurface natural fracture networks in rocks surrounding boreholes using image logs such as cast emi fmi fms rosi and others the method correlates fracture patterns with different stages of fracture network development for individual sets of fractures and extrapolates fracture density and connectivity from one dimension 1 d in boreholes to 3 d in the surrounding rocks the application of this work is 3 d visualizations of fracture distributions in volumes close to the boreholes for well planning reservoir scale fracture model building reservoir flow simulation and hydraulic fracture control

synmetamorphic vein spacing distributions characterisation and origin of a distribution of veins from nw sardinia italy abstract the spatial distribution of a single generation of axial planar synmetamorphic veins exposed in greenschist facies rocks on nw sardinia was investigated with the aim of gaining insight into the processes controlling the fracture spacing the vein spacing distribution measured along linear profiles is non uniform and approximately log normal although the vein abundance and absolute vein spacing is strongly influenced by rock type the vein spacing distribution is independent of rock type comparison of the observed data with synthetically generated fracture distributions indicates that the observed distribution can be reproduced by kolmogorov fragmentation but cannot be reproduced by a random even bisection or a fractal cantor dust process these results are interpreted to indicate that the positions of fractures that become veins are interdependent in an attempt to explain the interdependency of fracture positions the perturbations of stress and fluid pressure associated with an isolated underpressured axial planar fracture were investigated simple calculations show that the fluid pressure drop inside a fracture coinciding with failure locally perturbs the stress and fluid pressure fields such that the surrounding rock extending over a lateral extent equivalent to approximately two fracture lengths is instantaneously driven into a critical stress state that satisfies the failure condition numerical simulations demonstrate that this process tends to localise the nucleation of subsequent fractures close to existing fractures this mechanism can explain the existence of non random or clustered fracture or vein spacing distributions forming by hydrofracture

interaction between normal faults and fractures and fault scarp morphology fault slip and geomorphic surface processes create and modify bedrock normal fault scarps our field studies and numerical models show that mechanical interaction between near surface fractures and active faults may diminish scarp slopes and broaden deformation near the surface in our models increasing fracture density and depth reduces and complicates the scarp s topographic expression fracture depth and density and orientation of the structures control the location and magnitude of zones of positive and negative shear displacements along the fractures our field studies of the interaction of active graben bounding normal faults and fractures in northern arizona illustrate the mechanical analysis reduction in scarp slopes and broadening of the deformation field may cause incorrect interpretations of shallow bedrock scarp morphologies as old rather than as the result of slip along fractures around the fault

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

isotopic evidence for the sources of cretaceous and tertiary granitic rocks east central alaska implications for the tectonic evolution of the yukon tanana terrane magnetotelluric traverses across the southern yukon tanana terrane ytt reveal the presence of a thick conductive layer or layers beneath paleozoic crystalline rocks these rocks have been interpreted to be flysch of probable mesozoic age on the basis of the occurrence of jurassic cretaceous flysch in the kahiltna assemblage and gravina nutzotin belt flanking the ytt to the southwest and southeast respectively the pb nd sr and o isotopes in cretaceous and tertiary granitic rocks that crop out throughout the ytt were measured to determine if these rocks do in fact contain a component of flysch previous limited analyses indicated that the pb isotopes of the granitic rocks could be a mixture of radiogenic pb derived from paleozoic crystalline rocks of the ytt with an increasing component of relatively nonradiogenic pb with decreasing age our nd sr and o data along with additional pb isotope data eliminate flysch as a likely source and strongly suggest that the nonradiogenic end member was deri

ree distribution in the clay fraction of pelites from the southern apennines italy abstract in order to evaluate whether clay minerals or accessory phases control the ree pattern of the only illite is correlated with ree while a smectite rich sample is characterized by the lowest content in ree strong correlations exist between ree and tio2 nb zr and a less significant one with sr no correlations exist between these elements and y r mode factor analysis indicated that three factors account for 87 of the total variance the first factor var 43 2 seems to express mainly the tendency of some resistate minerals to concentrate ree in the fine fraction the second factor var 30 0 may be related to the effect of circulating fluids responsible for dickite genesis the third factor may be linked to the weathering of micaceous phases the ree do not have a significant weight in the second and third factors resistate minerals appear dominant in controlling at least the lree and nb it is proposed that in the studied samples illite likely conveyed ree via the included minerals

pb isotopic ratios and elemental abundances for selective leachates from near surface till implications for mineral exploration abstract pb isotope ratios obtained from fine grained fractions in this study pb isotopic measurements and selective leaching of 6 near surface till samples down ice from the chisel lake manitoba and manitouwadge ontario vms deposits were carried out in order to determine the location and nature of the pb within till elemental abundances from selective leachates for all 6 samples display similar patterns and show that chalcophile elements cu ni pb and zn derived predominantly from the underlying vms deposits occur as i adsorbed exchangeable metals ii associated with oxyhydrous fe and mn iii crystalline fe oxides and or iv silicate despite the relative proximity of some of the till samples to the vms deposits only a very small component of the chalcophile elements is present as sulfide this result is consistent with those from studies of weathered oxidized tills which show that labile minerals such as sulfides have been completely destroyed and their chemical constituents reprecipitated or scavenged locally by clay sized phyllosilicates and secondary oxides hydroxides pb isotopic ratios for selective leachates from till samples with vms like anomalous signatures are similar to those from ore galena within the proximal vms deposits this indicates that the pb is of a secondary nature and was probably scavenged and deposited after destruction of original sulfide minerals during till formation the lack of a predominant sulfide held pb component within the selective leachates supports this interpretation in contrast pb isotopic ratios for the same selective leachates from background samples are significantly higher and show that the pb is not derived from proximal vms deposits but from a more radiogenic source till samples were also leached using 2 5 m hcl ldconventional leaching the pb isotope ratios from the conventional leachates are similar to those obtained from the selective leachates and show a large difference in pb isotopic ratios between anomalous and background samples we propose therefore that the conventional leaching rather than selective leaching or complete dissolution of a particular grain size fraction be adopted for mineral exploration purposes using glacial sediments the results from this study support the effective use of pb isotope ratios from near surface till as an exploration tool despite the weathered nature of the latter we feel that this represents a more cost effective technique over traditional geochemical prospecting methods if used in conjunction with pb abundance data

a rock mechanical assessment of mercury s global tectonic fabric abstract mercury s global tectonic history is thought to have been dominated by two major processes tidal despinning and global contraction each process is expected to have produced a distinctive global stress field and resultant fault pattern thousands of thrust fault related landforms documented on mercury can be attributed to global contraction but no global signature of tidal despinning has been conclusively documented because global contraction operated throughout an extended portion of mercury s geologic history any tidal despinning pattern either would have formed together with global contraction or would have been modified by global contraction after despinning was complete here we reassess global fracture patterns predicted to result from tidal despinning and from a combination of tidal despinning and global contraction we specifically make use of rock strength and deformability parameters appropriate for mercury s fractured lithosphere results indicate that a tidal despinning pattern would consist only of a global set of opening mode fractures joints in the upper part of the lithosphere whereas the combination of tidal despinning and global contraction would have produced a global population of thrust faults with no preferred orientations in the polar regions but with an increasing preference for north south orientations toward the equator if an equatorial bulge from an early state of rapid spin was supported by mercury s lithosphere two end member scenarios for the timing and duration of these two processes may be considered in one tidal despinning predated global contraction in the other tidal despinning and global contraction overlapped in time we test the predictions of both scenarios against the distribution and orientations of mercury s tectonic landforms the global pattern of thrust faults is generally consistent with predictions for the scenario under which tidal despinning and global contraction temporally overlapped

estimating natural fracture producibility in tight gas sandstones coupling diagenesis with geomechanical modeling natural fracture attributes important for tight gas reservoir characterization include hydraulic aperture length spacing and connectivity all of these parameters contribute to the permeability of the fractured reservoir but many are difficult to observe and or quantify with core logs or seismic our approach to estimating permeability for fractured layers is to augment direct fracture observation with geomechanical modeling and diagenetic characterization

expert system based mineral mapping in northern death valley california nevada using the airborne visible infrared imaging spectrometer aviris abstract integrated analysis of imaging spectrometer data and field spectral measurements were used in conjunction with conventional geologic field mapping to characterize bedrock and surficial geology at the northern end of death valley california and nevada a knowledge based expert system was used to automatically produce image maps showing the principal surface mineralogy from airborne visible infrared imaging spectrometer aviris data linear spectral unmixing of the aviris data allowed further determination of relative mineral abundances and identification of mineral assemblages and mixtures the imaging spectrometer data show the spatial distribution of spectrally distinct minerals occurring both as primary rockforming minerals and as alteration and weathering products field spectral measurements were used to verify the mineral maps and field mapping was used to extend the remote sensing results geographically referenced image maps produced from these data form new base maps from which to develop improved understanding of the prosesses of deposition and erosion affecting the present land surface

the initiation and growth of en echelon veins abstract numerical models are used to understand the evolution of mode i opening fractures from spatially random distributions in a brittle elastic material en echelon arrays commonly develop because mechanical fracture interaction promotes growth for this geometry this provides a new mechanism for en echelon vein formation in rock which is distinctly different than previously proposed mechanisms it is suggested that some macroscopic en echelon vein arrays may have served as zones of weakness that localized later shear zone development in a manner analogous to that observed by experimentalists examining micro cracking and subsequent shear rupture of rocks loaded under compression sigmoidally shaped veins and vein fillings are explicitly modeled showing that they can form in response to the mechanical interaction of neighboring fractures which redirects the propagation path numerical comparison of sigmoidal veins formed by brittle fracture and by ductile shear zones demonstrates some of the pitfalls of failing to correctly identify the mechanism of formation

mobility of rare earth elements during weathering of till in northern sweden abstract continuous volume controlled sampling from the surface down to a depth of 130 cm was conducted at two stations on weathered till typic haplocryods all the samples were analysed for major and trace elements including the rare earth elements ree eight thousand seven hundred years of weathering since the glacial ice left the area has resulted in a strong depletion of ree in the e horizon this loss decreases as atomic number increases so that 80 85 of the la and 54 60 of the yb have been lost europium has been lost to a greater degree than have the neighbouring elements possible explanations for the release of ree are weathering of common silicates such as hornblende and epidote and plagioclase in the case of eu weathering of apatite weathering of rare but ree rich minerals such as allanite and monazite and release of ree adsorbed on clay minerals further studies on various size fractions and minerals are needed to quantify the importance of the various possible mechanisms of ree release the release of ree continues within and below the bs1 horizon but the results from one station show that light ree can be enriched in the bs1 horizon this secondary enrichment could be caused by adsorption on secondary oxy hydroxides on clay minerals or on organic material however the net result of the weathering is that all ree have been released to the groundwater

characteristics and origins of coal cleat a review abstract cleats are natural opening mode fractures in coal beds they account for most of the permeability and much of the porosity of coalbed gas reservoirs and can have a significant effect on the success of engineering procedures such as cavity stimulations because permeability and stimulation success are commonly limiting factors in gas well performance knowledge of cleat characteristics and origins is essential for successful exploration and production although the coal cleat literature spans at least 160 years mining issues have been the principal focus and quantitative data are almost exclusively limited to orientation and spacing information few data are available on apertures heights lengths connectivity and the relation of cleat formation to diagenesis characteristics that are critical to permeability moreover recent studies of cleat orientation patterns and fracture style suggest that new investigations of even these well studied parameters can yield insight into coal permeability more effective predictions of cleat patterns will come from advances in understanding cleat origins although cleat formation has been speculatively attributed to diagenetic and or tectonic processes a viable mechanical process for creating cleats has yet to be demonstrated progress in this area may come from recent developments in fracture mechanics and in coal geochemistry

lead isotopes in iron and manganese oxide coatings and their use as an exploration guide for concealed mineralization abstract lead isotopes from fe and mn oxides that coat stream pebbles from around the mount emmons porphyry molybdenum deposit in colorado were studied to assess the feasibility of using pb isotopes to detect concealed mineral deposits the fe mn oxide coatings were analyzed to determine their elemental concentrations using icp aes the pb isotope compositions of solutions from a selected suite of samples were measured using both thermal ionization and icp mass spectrometry to compare results determined by the two analytical methods heavy mineral concentrates from the same sites were also analyzed to compare the pb isotope compositions of the fe mn coatings with those found in panned concentrates the fe mn and 206 pb 204 pb ratios of the oxide coatings are related to the lithology of the host rocks fe mn oxide coatings on pebbles of black shale have higher fe mn values than do the coatings on either sandstone or igneous rocks the shale host rocks have a more radiogenic signature e g higher 206 pb 204 pb than the sandstone or igneous host rocks the pb isotope data from sandstone and igneous hosts can detect concealed mineralized rock on both a regional and local scale even though there are contributions from 1 metals from the main stage molybdenite ore deposit 2 metals from the phyllic alteration zone which has a more radiogenic pb isotope signature reflecting hydrothermal leaching of pb from the mancos shale 3 pb rich base metal veins with a highly variable pb isotope signature and 4 sedimentary country rocks which have a more radiogenic pb isotope signature an investigation of within stream variation shows that the pb isotope signature of the molybdenite ore zone is retained in the fe mn oxide coatings and is not camouflaged by contributions from pb rich base metal veins that crop out upstream in another traverse the pb isotope data from fe mn oxide coatings reflect a complex mixing of pb from the molybdenite ore zone and its hornfels margin pb rich base metal veins and sedimentary country rocks stream sediment anomalies detected using oxalic acid leaches can be evaluated using pb isotope analysesof selected geochemical anomalies such an evaluation procedure given regional target pb isotope signatures for concealed mineralization can greatly reduce the cost of exploration for undiscovered ore deposits concealed beneath barren overburden lead isotope measurements on aliquots of the same solutions showed that icp ms determinations are of low precision and vary non systematically when compared with the pb isotope values of the higher precision thermal ionization method these variations and lower precision of the icp ms measurements are attributed to matrix effects

lithologic mapping in the mountain pass california area using advanced spaceborne thermal emission and reflection radiometer aster data abstract evaluation of an advanced spaceborne thermal emission and reflection radiometer aster image of the mountain pass california area indicates that several important lithologic groups can be mapped in areas with good exposure by using spectral matching techniques the three visible and six near infrared bands which have 15 m and 30 m resolution respectively were calibrated by using in situ measurements of spectral reflectance calcitic rocks were distinguished from dolomitic rocks by using matched filter processing in which image spectra were used as references for selected spectral categories skarn deposits and associated bright coarse marble were mapped in contact metamorphic zones related to intrusion of mesozoic and tertiary granodioritic rocks fe muscovite which is common in these intrusive rocks was distinguished from al muscovite present in granitic gneisses and mesozoic granite quartzose rocks were readily discriminated and carbonate rocks were mapped as a single broad unit through analysis of the 90 m resolution five band surface emissivity data which is produced as a standard product at the eros data center three additional classes resulting from spectral angle mapper processing ranged from 1 a broad granitic rock class 2 to predominately granodioritic rocks and 3 a more mafic class consisting mainly of mafic gneiss amphibolite and variable mixtures of carbonate rocks and silicate rocks

geometallurgy of the pebble porphyry copper gold molybdenum deposit alaska implications for gold distribution and paragenesis the pebble cu au mo deposit in southwest alaska is one of the world s largest porphyry deposits the deposit contains over 80 billion pounds blbs cu 107 million ounces moz au and 5 6 blbs mo in all resource categories copper and gold grades vary across diverse hydrothermal alteration assemblages with higher grades associated with sericite and pyrophyllite rich assemblages in an advanced argillic alteration zone moderate grades are associated with the potassic and sodic potassic alteration assemblages that dominate the deposit and low grades are found in quartz illite pyrite assemblages these variations reflect fluctuations in both the temperature and composition of the magmatic hydrothermal fluids in time and space qemscan scanning electron microscope based mineral mapping and in situ laser ablation inductively coupled plasmamass spectrometry methods designed to document the spatial and temporal variations in metal deportment across alteration zones show that gold occurs as inclusions of electrum and high fineness gold in chalcopyrite and pyrite and as free grains hosted by silicate minerals with the proportion of each related to the principal host alteration assemblage gold associated with the earliest high temperature sodic potassic and potassic assemblages occurs as electrum inclusions in chalcopyrite and to a lesser extent pyrite and pyrite trace element signatures have high gold silver and copper concentrations pyrite 1 during cooling of the hydrothermal system lower temperature illite and illite kaolinite alteration overprinted the earlier assemblages with varying degrees of recrystallization and precipitation of more pyrite rich assemblages with pyrite having a gold poor trace element composition pyrite 2 gold released during recrystallization formed high fineness gold inclusions in newly formed pyrite and narrow gold rich pyrite rims pyrite 3 a second magmatic hydrothermal event resulted in a sericite and pyrophyllite rich advanced argillic overprint which introduced more copper and gold to the system and recrystallized preexisting sulfides into both high and low sulfidation assemblages with high fineness gold inclusions in pyrite and chalcopyrite and solid solution gold in bornite a second generation of pyrite 1 with elevated palladium concentrations is associated with this hydrothermal fluid pulse and also possibly high arsenic pyrite pyrite 4 understanding the controls on gold deportment provides genetic constraints on ore deposit genesis alteration and sulfide assemblages and gold compositions provide information on the hydrothermal fluid compositions ph and temperature evolution of the magmatic hydrothermal system the presence of electrum inclusions in chalcopyrite and pyrite in potassic and sodic potassic alteration is consistent with these zones forming from early high temperature magmatic fluids because both gold and silver are transported together in such fluids high fineness gold inclusions in younger pyrite related to low temperature clay alteration are evidence that the gold in early electrum was partially remobilized and reprecipitated the low temperature clay alteration most likely formed from a mixture of h2s rich vapor with meteoric waters conditions where gold is transported as a bisulfide complex and silver is not resulting in the separation of the two metals a second structurally controlled pulse of magmatic fluids formed a well mineralized advanced argillic alteration assemblage containing high fineness gold inclusions in chalcopyrite and pyrite the only part of the deposit where high fineness gold is hosted by chalcopyrite in the pyrophyllite stability field acidic fluid compositions transport gold and silver as different complexes and gold solubility is significantly lower than silver leading to the precipitation of highfineness gold inclusions palladium is transported by the same complex as gold under these conditions consistent with the elevated palladium content of pyrite in the advanced argillic alteration assemblage the temporal and spatial studies of variations in gold deportment across the pebble deposit provide critical inputs to optimization of mineral processing design the greatest influence on metallurgical gold recovery at pebble is the proportion of gold that is hosted by pyrite pyrite hosted gold may require different mineral processing methodologies compared with gold hosted by chalcopyrite therefore defining domains of consistent hydrothermal alteration and sulfide mineralogy and gold deportment is the key to the geometallurgical characterization of the deposit

groundwater in the broken hill region australia recognising interaction with bedrock and mineralisation using s sr and pb isotopes the supergiant pb zn ag broken hill orebody and numerous other minor mineral deposits occur within the limited outcrop of the proterozoic curnamona province of australia the vast majority of this province is concealed by up to 200 m of transported regolith hampering conventional exploration strategies approximately 300 groundwater samples were collected over the southern curnamona province to test whether this medium could be helpful in the search for hidden mineral deposits sulphur sr and pb isotope composition of the groundwaters were determined and s excess s xs i e the amount of s that can be ascribed neither to evaporation nor to mixing was calculated many samples were recognised to have undergone an addition of 34 s depleted s which can be attributed to oxidation of sulfides with a broken hill type 34 s signature average 0 v cdt furthermore sr isotopes identify the broad types of bedrock that the groundwater has been interacting with from the less radiogenic adelaidean rocks and minerals in the west groundwater 87 sr 86 sr ratio as low as 0 708 to the highly radiogenic willyama supergroup in the east 87 sr 86 sr ratio up to 0 737 the groundwaters have 207 pb 204 pb and 206 pb 204 pb ratios comparable to or intermediate between various mineralisation types recognised in the area broken hill rupee thackaringa etc types the few samples taken in the vicinity of known mineralisation yield positive indicators positive s xs low 34 s 87 sr 86 sr signature of bedrock type and pb isotope fingerprinting of mineralisation type this study also highlights several new locations under sedimentary cover where these indicators suggest interaction with mineralisation

the role of the interbed thickness on the step over fracture under overburden pressure multilayer jointing in tight oil and gas reservoirs is a useful indicator for the prediction of fluid mobility since pore pressure balances the principal minor horizontal stress at depth joint nucleations considered as sub vertical are mainly driven by the overburden pressure we demonstrate with a mixed criterion combining necessary conditions of stress and energy how heterogeneity such as an interbed promotes initiation of a fracture by a step over mechanism referring to critical characteristics such as the interbed thickness a specific initiation criterion emerges giving rise to a size effect due to the interbed thickness and is compared to a typical homogeneous rock failure criterion jointing over an interbed is enhanced by large interbed thicknesses even for moderate effective confining stresses size effect is reversed according to the relative importance of singular effects effective minor stress normal to the fracture plane and structural effect parallel loading effective conditions

imaging spectroscopy earth and planetary remote sensing with the usgs tetracorder and expert systems 1 imaging spectroscopy is a tool that can be used to spectrally identify and spatially map materials based on their specific chemical bonds spectroscopic analysis requires significantly more sophistication than has been employed in conventional broadband remote sensing analysis we describe a new system that is effective at material identification and mapping a set of algorithms within an expert system decision making framework that we call tetracorder the expertise in the system has been derived from scientific knowledge of spectral identification the expert system rules are implemented in a decision tree where multiple algorithms are applied to spectral analysis additional expert rules and algorithms can be applied based on initial results and more decisions are made until spectral analysis is complete because certain spectral features are indicative of specific chemical bonds in materials the system can accurately identify and map those materials in this paper we describe the framework of the decision making process used for spectral identification describe specific spectral feature analysis algorithms and give examples of what analyses and types of maps are possible with imaging spectroscopy data we also present the expert system rules that describe which diagnostic spectral features are used in the decision making process for a set of spectra of minerals and other common materials we demonstrate the applications of tetracorder to identify and map surface minerals to detect sources of acid rock drainage and to map vegetation species ice melting snow water and water pollution all with one set of expert system rules mineral mapping can aid in geologic mapping and fault detection and can provide a better understanding of weathering mineralization hydrothermal alteration and other geologic processes environmental site assessment such as mapping source areas of acid mine drainage has resulted in the acceleration of site cleanup saving millions of dollars and years in cleanup time imaging spectroscopy data and tetracorder analysis can be used to study both terrestrial and planetary science problems imaging spectroscopy can be used to probe planetary systems including their atmospheres oceans and land surfaces

experimental determination of subcritical crack growth parameters in sedimentary rock mounting evidence suggests that subcritical crack growth is an important mechanism for the development of natural fractures numerical simulations of fracture patterns are sensitive to the subcritical crack growth index the exponent used to describe the power law dependence of crack velocity on stress intensity few measured values of subcritical indices in sedimentary rocks have been published however and no systematic studies of diagenetic controls of subcritical crack index behavior are available subcritical crack index measurements are especially difficult in weak porous rock primarily because non elastic material response can obscure fracture related behavior we have carried out numerous subcritical crack index measurements with the widely used dual torsion beam test configuration and developed a modified test methodology for subcritical crack index measurements on porous rocks the principal element of the methodology is a specimen pre loading procedure to minimize transient material response measurement reliability is documented in the study by documentation of reproducibility in three sets of sandstone and carbonate specimens

quantitative estimation of granitoid composition from thermal infrared multispectral scanner tims data desolation wilderness northern sierra nevada california we have produced images that quantitatively depict modal and chemical parameters of granitoids using an image processing algorithm called minmap that fits gaussian curves to normalized emittance spectra recovered from thermal infrared multispectral scanner tims radiance data we applied the algorithm to tims data from the desolation wilderness an extensively glaciated area near the northern end of the sierra nevada batholith that is underlain by jurassic and cretaceous plutons that range from diorite and anorthosite to leucogranite the wavelength corresponding to the calculated emittance minimum min varies linearly with quartz content sio2 and other modal and chemical parameters thematic maps of quartz and silica content derived from min values distinguish bodies of diorite from surrounding granite identify outcrops of anorthosite and separate felsic intermediate and mafic rocks

possible effects of pre existing basement topography on thrust fault ramping finite element models show that one way in which thrust ramps may arise is through the mechanical interaction between basement and overlying sediments in the simplest case shear coupling between a planar basement sediment causes the differential stresses in the sediments to die out with depth and distance from the applied load for such cases curved thrust faults may result if the strength of the rock is exceeded basement topography may also affect the location and shape of ramps by acting as a stress concentrator by producing a stress shadow and by changing principal stress orientations modeling suggests that whether or not these basement topographic features cause ramping will depend on the height and angularity of the feature as well as the rock types that overlie it under the assumption of linear elasticity and for given boundary conditions the poisson s ratio plays an important role in determining the orientation and magnitude of the principal stresses calculations using experimentally measured poisson s ratios predict that the earliest maximum compressive stress directions should be nearly vertical in the more cratonward portions of thrust belts however the stress directions which are inferred to have occurred earliest in this part of thrust belts are nearly horizontal this suggests that non elastic or ductile processes have an effect on the propagation of thrust faults

non linear growth kinematics of opening mode fractures abstract fracture aperture is commonly assumed to be a linear function of fracture length stress and elastic material properties under constant stress fracture opening displacement may change without concurrent length or height growth if the material effectively weakens after initial linear elastic fracture growth by changes in elastic properties or by non elastic deformation processes to investigate the kinematics of fracture opening and its dependence on length and height growth we reconstructed the opening history of three opening mode fractures that are bridged by crack seal quartz cement similar crack seal cement bridges had been interpreted to form by repeated incremental fracture opening and subsequent precipitation of quartz cement using scanning electron microscope cathodoluminescence imaging we determined the thickness and number of crack seal cement layers as a function of position along fracture length and height observed trends in crack seal cement layer thickness and number of fracture opening increments are consistent with non linear fracture growth kinematics consisting of an initial stage of fast fracture propagation relative to aperture growth followed by a stage of slow propagation and pronounced aperture growth consistent with earlier fluid inclusion observations indicating fracture opening and propagation occurring over 40 50 m y we interpret the second stage of pronounced aperture growth and slow propagation to result from fracture opening strain accommodated by solution precipitation creep and concurrent slow possibly subcritical fracture propagation

formation of joints in cooling plutons abstract the geometry age and mineralogy of steeply dipping joints in the lake edison granodiorite of california indicate that thermal stresses played a key role in the formation of the joints joint traces curve to approach the pluton boundary at high angles at both large and small scales and they generally terminate at or near the contact with an older pluton radiometric dates and the epidote and chlorite fillings of the joints tie jointing to the initial cooling of the pluton a thermo mechanical stress analysis assuming two dimensional conductive cooling predicts thermal stresses of several tens of mpa the same order of magnitude as plausible fluid pressures regional stresses and lateral normal stresses associated with the overburden the orientation of the joints can be accounted for rather well by the stress field formed by superposing a uniform regional stress field on the predicted thermal stresses the large scale pattern of the early joints in many plutons should be predictable based on a pluton s geometry its age relative to the adjacent rock and knowledge of the regional stress at the time of initial cooling these findings bear on issues pertinent to mining petroleum recovery nuclear waste repository siting and ground water flow

automated lithological mapping using airborne hyperspectral thermal infrared data a case study from anchorage island antarctica the thermal infrared portion of the electromagnetic spectrum has considerable potential for mineral and lithological mapping of the most abundant rock forming silicates that do not display diagnostic features at visible and shortwave infrared wavelengths lithological mapping using visible and shortwave infrared hyperspectral data is well developed and established processing chains are available however there is a paucity of such methodologies for hyperspectral thermal infrared data here we present a new fully automated processing chain for deriving lithological maps from hyperspectral thermal infrared data and test its applicability using the first ever airborne hyperspectral thermal data collected in the antarctic a combined airborne hyperspectral survey targeted geological field mapping campaign and detailed mineralogical and geochemical datasets are applied to small test site in west antarctica where the geological relationships are representative of continental margin arcs the challenging environmental conditions and cold temperatures in the antarctic meant that the data have a significantly lower signal to noise ratio than is usually attained from airborne hyperspectral sensors we applied preprocessing techniques to improve the signal to noise ratio and convert the radiance images to ground leaving emissivity following preprocessing we developed and applied a fully automated processing chain to the hyperspectral imagery which consists of the following six steps 1 superpixel segmentation 2 determine the number of endmembers 3 extract endmembers from superpixels 4 apply fully constrained linear unmixing 5 generate a predictive classification map and 6 automatically label the predictive classes to generate a lithological map the results show that the image processing chain was successful despite the low signal to noise ratio of the imagery reconstruction of the hyperspectral image from the endmembers and their fractional abundances yielded a root mean square error of 0 58 the results are encouraging with the thermal imagery allowing clear distinction between granitoid types however the distinction of fine grained intermediate composition dykes is not possible due to the close geochemical similarity with the country rock

a geometrically based method for predicting stress induced fracture aperture and flow in discrete fracture networks modeling of fluid flow in naturally fractured reservoirs is often done through modeling and upscaling of discrete fracture networks dfns the two dimensional fracture geometry required for dfns is obtained from subsurface and outcropping analog data however these data provide little information on subsurface fracture aperture which is essential for quantifying porosity and permeability apertures are difficult to obtain from either outcropping or subsurface data and are therefore often based on fracture size or scaling relationships but these do not consider the orientation and spatial distribution of fractures with respect to the in situ stress field using finite element simulations mechanical aperture can be modeled explicitly but because changes in fracture geometry require renewed meshing and simulating this approach is not easily integrated into subsurface dfn modeling workflows we present a geometrically based method for calculating the shear induced hydraulic aperture that is an aperture of up to 0 5 mm 0 02 in that can result from shear displacement along irregular fracture walls the geometrically based method does not require numerical simulations but it can instead be directly applied to dfns using the fracture orientation and spacing distributions in combination with an estimate of the regional stress tensor and orientation the frequency distribution of hydraulic aperture from the geometrically based method is compared with finite element models constructed from five real fracture networks digitized from outcropping pavements these networks cover a wide range of possible geometries and spatial distributions the geometrically based method predicts the average hydraulic aperture and equivalent permeability of fractured porous media with error margins of less than 5

the coupled release of ree and pb to the soil labile pool with time by weathering of accessory phases wind river mountains wy abstract rare earth element ree distributions and pb isotope compositions were explored in soils varying in age from ca 0 4 to 300 ka developed on moraines in the wind river mountains wyoming soil extracts 0 6 m hcl were used to examine the soil labile pool while the major element distribution in soil profiles was used to determine the extent of weathering at different soil depths the results show that the chondrite normalized ree patterns of the deepest bulk soil within each profile reflects the composition of the moraine till except for the oldest soil up to ca 12 ka the soil extract fraction is enriched in light ree indicating early release of light ree to the soil labile pool while that of the two oldest soils are relatively enriched in heavy ree in the soil extracts the la sm ratio normalized to the deepest soil la d sm d decreases systematically with soil age similarly the eu anomaly in the deepest soil from each profile eu d eu d decreases slightly with soil age in the three young soils however eu d eu d increases with soil age in the older soils the systematic trends of these two ratios indicate the depletion of light ree in young soils and the enrichment of eu and heavy ree in the older soils based on the pb isotope ratios the relative contribution of pb to the soil labile pool via mineral weathering of u or th rich phases was assessed for the different stages of weathering the whole soil profile 208 pb 204 pb ratio was found to decrease with soil age and with la d sm d whereas it increased with the eu d eu d ratio in each horizon pb isotope ratios 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratio generally decrease with soil age in order to overcome possible effects from parent material heterogeneity the amount of radiogenic pb as compared to the whole soil composition was calculated and this was found to decrease systematically with soil age

a classification of dyke fracture geometry with examples from precambrian dyke swarms in the vestfold hills antarctica a classification of dilational fracture geometry is proposed it applies to structures that can be characterized by the combination of a fracture system and a dilation vector field the classification is illustrated with examples of igneous dykes pegmatites and pseudotachylites segmentation in the form of offsets jogs or bifurcations is common to most fracture systems four basic types of dilational fracture systems are distinguished on the basis of the geometry of segmentation these are irregular braided en echelon and zigzag zigzag fracture systems are further differentiated they consist of newly formed obliquely dilated fractures or alternatively of pre existing planes in the host rock that are reactivated by oblique dilation this paper is the first to actually report an igneous zigzag dyke involving newly formed fractures rotation of the regional stress field in the direction of propagation leads to en echelon segmentation braided fracture systems reflect high local stress intensities probably related to propagation rate two possibilities exist for the formation of zigzag dykes consisting of newly formed fractures that are obliquely dilated they may form by extreme interaction of tensile fracture segments in a regional stress field with a low differential stress alternatively they may form in a regional stress field with high differential stress through the propagation of shear fractures segmentation of dykes characterized by offsets is common such segmentation can be the result of protrusions of the fracture termination offsets also occur where a dyke cuts an older planar structure such offsets are the result of the local inhibition of fracture propagation the resulting apparent offset can lead to a misinterpretation of relative age apophyses form as a result of the dilation of a segmented fracture system

sm nd isotope technique as an exploration tool delineating the northern extension of the thompson nickel belt manitoba canada application of nd isotope mapping to aid mineral exploration has been tested successfully in areas north of the well prospected productive portion of the thompson nickel belt in manitoba canada economic nickel deposits in this main part of the belt are restricted to the ospwagan group cover sequence and ultramafic sills overlying archean basement gneisses distinguishing some units in the ospwagan group from its basement and less prospective paleoproterozoic paragneiss of the burntwood group in the area is difficult based on lithology stratigraphy geochemistry and structure alone however the ospwagan group has a unique nd isotope signature that allows it to be identified with certainty a compilation of nd isotope data from the main portion of the thompson nickel belt and a new dataset from drill core and reconnaissance mapping clearly support early exploration indications that basement gneiss and narrow belts of the ospwagan group typical of the belt extend northeast of the main part of belt for at least 100 km this confirms the presence of a large new area for nickel exploration the limits of which are still unknown in this poorly exposed northern area crustal residence nd model ages t cr are instrumental in clearly separating 1 the ospwagan group supracrustal rocks t cr 2 8 3 2 ga that host the nickel deposits from 2 neoarchean basement gneiss t cr 3 2 3 5 ga 3 juvenile overthrust burntwood t cr 2 2 2 6 ga grass river and sickle t cr 2 0 2 4 ga groups paragneisses and 4 fragments of a mesoarchean gneiss complex t cr 3 5 4 1 ga the latter being the host of precious metal prospects the variation in nd model ages not only distinguishes the different supracrustal successions but the variable inheritance of ancient crustal material in units of archean gneiss reflected in nd model ages serves as a tool to unravelling the complexly interleaved structure of this crust and aids in tracing the potentially nickel hosting ospwagan group in narrow structural keels the robustness of the nd isotope system under the conditions of high grade metamorphism and migmatization attained in the thompson nickel belt makes this an ideal tool for distinguishing between units of economically prospective and barren gneiss in frontier areas where other methods have failed are difficult to apply or have led to erroneous interpretations

rapid determination of coalbed methane exploration target region utilizing hyperspectral remote sensing abstract this study reveals the common surface mineral characteristics over coalbed methane cbm enrichment regions from spaceborne hyperion images and the possibility of hyperspectral remote sensing for prospecting coalbed methane exploration target region with an inexpensive large scale rapid and convenient way for this study a typical scheme including bands removal atmospheric correction snr estimation minimum noise fraction mnf pixel purity index ppi and n dimensional visualization was applied on hyperion image in qinshui basin china to accurately extract mineral endmembers the endmember spectra of carbonate and clay mineral were identified based on the diagnostic absorption feature while no endmember of ferrous iron mineral was found the absorption feature parameters of carbonate absorption position and especially asymmetric factor and clay mineral absorption position left and right shoulder positions were quantitatively estimated which showed the endmember spectra of carbonate and clay mineral from hyperspectral images in this paper were correct in addition this study proposed an interesting research direction measuring the asymmetric absorption factor to facilitate the identification of carbonates furthermore spectral angle mapper sam and spectral feature fitting sff were used to map carbonates and clay minerals two assessment methods visual interpretation based on field spectra and x ray diffraction xrd analysis were utilized to evaluate the mapping accuracy which showed total agreements of 84 03 and 72 58 respectively the results in this paper suggested that both carbonates and clay minerals were rich while there was hardly any ferrous iron mineral on the surface of cbm enrichment regions in addition another similar experiment was carried out in ordos basin and also showed similar surface mineral characteristics on cbm enrichment region

pb sr nd isotopes in surficial materials at the pebble porphyry cu au mo deposit southwestern alaska can the mineralizing fingerprint be detected through cover the cretaceous pebble porphyry cu au mo deposit is covered by tundra and glacigenic sediments pb sr nd measurements were done on sediments and soils to establish baseline conditions prior to the onset of mining operations and contribute to the development of exploration methods for concealed base metal deposits of this type pebble rocks have a moderate range for 206pb 204pb 18 574 to 18 874 207pb 204pb 15 484 to 15 526 and 208pb 204pb 38 053 to 38 266 mineralized granodiorite shows a modest spread in 87sr 86sr 0 704354 0 707621 and 143nd 144nd 0 512639 0 512750 age corrected 89 ma values for the granodiorite yield relatively unradiogenic pb e g 207pb 204pb 15 52 low values of 87sr 86sr and positive values of nd 1 00 4 52 that attest to a major contribution of mantle derived source rocks pond sediments and soils have similar pb isotope signatures and 87sr 86sr and 143nd 144nd values that resemble the mineralized granodiorites glacial events have obscured the recognition of isotope signatures of mineralized rocks in the sediments and soils baseline radiogenic isotope compositions prior to the onset of mining operations reflect natural erosion transport and deposition of heterogeneous till sheets that included debris from barren rocks mineralized granodiorite and sulfides from the pebble deposit and other country rocks that pre and postdate the mineralization events isotopic variations suggest that natural weathering of the deposit is generally reflected in these surficial materials the isotope data provide geochemical constraints to glimpse through the extensive cover and together with other geochemical observations provide a vector to concealed mineralized rocks genetically linked with the pebble deposit

natural fractures in shale a review and new observations natural fractures have long been suspected as a factor in production from shale reservoirs because gas and oil production commonly exceeds the rates expected from low porosity and low permeability shale host rock many shale outcrops cores and image logs contain fractures or fracture traces and microseismic event patterns associated with hydraulic fracture stimulation have been ascribed to natural fracture reactivation here we review previous work and present new core and outcrop data from 18 shale plays that reveal common types of shale fractures and their mineralization orientation and size patterns a wide range of shales have a common suite of types and configurations of fractures those at high angle to bedding faults bed parallel fractures early compacted fractures and fractures associated with concretions these fractures differ markedly in their prevalence and arrangement within each shale play however constituting different fracture stratigraphies differences that depend on interface and mechanical properties governed by depositional diagenetic and structural setting several mechanisms may act independently or in combination to cause fracture growth including differential compaction local and regional stress changes associated with tectonic events strain accommodation around large structures catagenesis and uplift fracture systems in shales are heterogeneous they can enhance or detract from producibility augment or reduce rock strength and the propensity to interact with hydraulic fracture stimulation burial history and fracture diagenesis influence fracture attributes and may provide more information for fracture prediction than is commonly appreciated the role of microfractures in production from shale is currently poorly understood yet potentially critical we identify a need for further work in this field and on the role of natural fractures generally

fracture accommodated strain in the diamond joe stock arizona fractures filled with hydrothermal minerals form a dominantly radial pattern in the diamond joe stock these fractures record a portion of the deformation experienced by the pluton from the time that it was emplaced until it cooled to ambient conditions in individual outcrops fracture orientations are very consistant to within 10 where fractures cross k feldspar phenocrysts no shear offset is observed indicating that the fractures have opened by dilation we have measured the apertures of these veins and define a two dimensional deformation gradient matrix to characterize the uniaxial strain accommodated by each fracture we assume that each fracture represents one increment of strain and superimpose all increments in an individual outcrop to compute the fracture accommodated strain for that outcrop we calculate the orientation and magnitude of the principal strains for each outcrop as well as the area change accommodated by the fractures all of the outcrops have experienced a decrease in area that ranges from 5 a portion of this area change is interpreted as thermal contraction however in the central part of the pluton additional contraction is present in this portion of the pluton the amount of strain and area change correlates well with fracture abundance we interpret this additional contraction to result from volume changes associated with crystallization and or vapor exsolution during crystallization of the pluton

ree fractionation during granite weathering and removal by waters and suspended loads sr and nd isotopic evidence very few studies deal with ree rare earth element mobility within the system soil soil solution streamwater in this article we try to characterize the fractionation and the migration of the ree in a granite derived soil system located in a small catchment of the vosges mountains icp ms and tims measurements were performed on both solid samples fresh granite soil and suspended load of the stream and waters soil solutions springwater and streamwater to determine their respective ree concentrations and sr and nd isotopic compositions the paas normalized ree pattern of the bedrock is characterized by a strong depletion in hree heavy ree and a negative eu anomaly 0 46 similarly the granite normalized ree distribution patterns of the soil samples show hree depletions that become more important with decreasing depth the correlative behavior between p2o5 th and ree with depth indicates that besides apatite other phosphate minerals such as monazite are the most important phases controlling the th and ree budget in the soil profile on the other hand at greater depth zircon seems to be another important mineral phase controlling especially the hree enrichment as shown by the positive relationship between zr content and the yb ho ratio different grain size fractions show similar ree distribution patterns and are only weakly fractionated compared with bulk soil sample however the finest fraction 0 20 m is more enriched in sr and ree suggesting a stronger concentration of ree carrying minerals in this fraction the suspended and dissolved load of the stream show as a whole an enrichment in hree if compared with the granite or with the different soil samples however compared with the uppermost soil samples the suspended load is significantly more enriched in hree its ree distribution pattern is more similar to that of the finest fraction of the deeper soil sample and to the fresh granite thus most probably the ree of the suspended load originated from a source with ree characteristics found in the deep soil horizons this source might have been situated in the uppermost soil profile which is actually ree depleted the weathering process can be compared with a leaching experiment where the waters correspond to the leachate and the soil to the residual phase of the granite the sr isotope data indicate that the suspended load originates from the finest soil fraction the sr and nd isotopic data of the suspended load suggest that it contains up to 3 sr and nd from apatite and up to 97 from feldspar most of the sr and nd in the waters originate from apatite leaching or dissolution

integrating visible near infrared and short wave infrared hyperspectral and multispectral thermal imagery for geological mapping at cuprite nevada this study investigated the potential value of integrating hyperspectral visible near infrared and short wave infrared imagery with multispectral thermal data for geological mapping two coregistered aerial data sets of cuprite nevada were used airborne visible infrared imaging spectrometer aviris hyperspectral data and modis aster airborne simulator master multispectral thermal data four classification methods were each applied to aviris master and a combined set confusion matrices were used to assess the classification accuracy the assessment showed in terms of kappa coefficient that most classification methods applied to the combined data achieved a marked improvement compared to the results using either aviris or master thermal infrared tir data alone spectral angle mapper sam showed the best overall classification performance minimum distance classification had the second best accuracy followed by spectral feature fitting sff and maximum likelihood classification the results of the study showed that sff applied to the combination of aviris with master tir data are especially valuable for identification of silicified alteration and quartzite both of which exhibit distinctive features in the tir region sam showed some advantages over sff in dealing with multispectral tir data obtaining higher accuracy in discriminating low albedo volcanic rocks and limestone which do not have unique distinguishing features in the tir region

rheology of the lithosphere selected topics we review recent results concerning the rheology of the lithosphere with special attention to the following topics 1 the flexure of the oceanic lithosphere 2 deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins 3 the rheological stratification of the continents 4 strain localization and shear zone development and 5 strain induced crystallographic preferred orientations and anisotropies in body wave velocities we conclude with a section citing the 1983 1986 rock mechanics literature by category

precollision tilt of crustal blocks in rifted island arcs structural evidence from the kohistan arc 1 we describe results from field and microstructural investigations in the unusually large chilas plutonic complex which was emplaced within the mesozoic kohistan island arc northern pakistan magmatic and deformational fabrics of the chilas gabbronorite are concordant with magmatic fabrics of associated gabbros diorites and tonalites and show that this reportedly huge intrusion is composed of juxtaposed plutonic bodies with predominantly ssw dipping flow structures over the northeastern part of the complex which turn to sw ne striking subvertical attitudes to the west evidence for multiple intrusions includes concordant and discordant intrusive and or mylonitic contacts between gabbronorites and associated rocks owing to structural and kinematic consistency we attribute transitions from magmatic to more localized mylonitic fabrics to higher finite strain and or strain rate produced from drag of magma against its margin we discuss this structural pattern and conclude that the chilas gabbronorite emplaced incrementally into generally south dipping listric faults that dominated arc extension about 85 ma in addition several sets of hornblende pegmatite indicate that brittle deformation occurred in the presence of residual melt during consolidation of the main body the latest pegmatite set is composed of variably striking vertical extensional veins that show no relationship to the magmatic fabric we argue that the original attitude of these veins along with that of the enclosing chilas complex has been mostly preserved we hypothesize that the northward dip of the southern side of the kohistan is inherited from late cretaceous rotation of crustal blocks in the hanging wall of the listric faults

till geochemical and indicator mineral methods in mineral exploration abstract this paper summarizes advances since 1987 in the application of glacial sediment sampling to mineral exploration drift prospecting in areas affected by continental or alpine glaciation in these exploration programs clastic glacial sediments are tested by geochemical or mineralogical methods to detect dispersal trains of mineral deposit indicators that have been glacially transported from source by mechanical processes in glaciated terrain the key sampling medium till is produced by abrasion crushing and blending of rock debris and recycled sediment followed by down ice dispersal ranging from a few metres to many kilometres as a consequence of the mid 1980s boom in gold exploration the majority of case studies and regional till geochemical surveys published in the past decade deal with this commodity approximately 30 of canada and virtually all of fennoscandia have been covered by regional till geochemical surveys that aid mineral exploration and provide baseline data for environmental agricultural and landuse planning the most profound event in drift prospecting in the last decade however has been the early 1990s explosion in diamond exploration which has dramatically increased the profile of glacial geology and glacial sediment sampling and stimulated changes in sampling and analytical methods

testing a thermal stress origin of fractures in a pluton abstract several factors suggest that mineralized joints in the lake edison granodiorite of the sierra nevada formed as the pluton cooled biotites and hornblendes in the granodiorite yield radiometric ages of 80 m y and 85 m y respectively whereas minerals in fault zones that developed from the joints are dated at 79 m y the age of the joints thus is consistent with cooling of the pluton mineral fillings in the joints consist principally of epidote and chlorite an assemblage consistent with the joints having formed as the pluton cooled the joints approach the boundary of the elongate pluton at nearly right angles the joints usually terminate at or near the pluton boundary rather than extending well into an older adjacent pluton thermoelastic stress analyses suggest conductive cooling of the pluton could have caused the observed joint patterns and the strains accommodated by joints if joints in plutons characteristically form as a result of thermal stresses during cooling then the large scale pattern of joints should be predictable based on pluton geometry practical applications of this work with regard to large scale fluid flow in the crust include petroleum recovery and nuclear waste repository siting

hydrothermal breccias in vein type ore deposits a review of mechanisms morphology and size distribution abstract breccias are among the most widely distributed rock textures found in hydrothermal vein type deposits previous studies have mainly been interested in developing qualitative descriptive approaches leading to a confusing profusion of terms brecciation originates in numerous ways resulting in highly complex classification systems and frequent misinterpretations of facies field observations are difficult to reconcile with physical theories of fragmentation partly due to the fact that few satisfactory quantitative tools have been developed a review of the main brecciation processes occurring in hydrothermal vein type deposits allows for the discrimination between chemical and physical mechanisms including tectonic comminution wear abrasion two types of fluid assisted brecciation hydraulic and critical volume expansion or reduction impact and collapse each of these mechanisms can be distinguished using nonscalar parameters that describe breccia geometry including fragment morphology size distribution of the fragments fabric and dilation ratio the first two parameters are especially important because 1 the morphology of the fragments allows chemical and physical mechanical breccias to be distinguished and 2 the particle size distribution psd is a function of the energy input during breccia formation the slope of the cumulative psd fractal dimension ranges from high values for high energy brecciation processes to low values for low energy processes indicated by an isometric distribution the evolution of a vein system can be divided into three stages propagation wear and dilation these stages are separated by one threshold of mechanical discontinuity and one of hydraulic continuity these two thresholds also mark the transition between different types of brecciation mineralization occurs during all three stages and may display different textures due to pressure variations the use of quantitative parameters in fault related hydrothermal breccias allows a better understanding of the physical parameters related to a vein environment including structural setting and crustal level as well as fluid rock interactions recognition of the different breccia types could also be important during the early stages of mineral exploration

summary of exploration geochemical and mineralogical studies at the giant pebble porphyry cu au mo deposit alaska implications for exploration under cover exploration geochemical and mineralogical studies by the u s geological survey at the pebble porphyry cu au mo deposit were designed to 1 determine whether the concealed deposit can be detected with surface samples 2 better understand the processes of metal migration from the deposit to the surface and 3 test existing methods for assessing concealed mineral resources and or develop new ones surface water ponds streams and springs pond and stream sediment soils subjected to various leaching techniques and glacial till samples were collected the tilted nature of the undisturbed orebody varying depth of cover and later glacial processes strongly influence the geochemical responses and processes active on the various sample media the multimedia approach aids in identifying possible processes that caused the significant geochemical variations within and among the various media these processes include the following 1 in the pebble west zone thin cover and local exposure of the orebody have facilitated the oxidation of pyrite and other sulfides and associated ferrous ferric iron reactions resulting in the local natural acidification of ponds observed in the west zone and in associated metal anomalies in waters sediments and soils 2 in contrast the east zone is concealed by both glacial deposits and underlying thick cover rocks which precludes the oxidation of sulfides in the underlying orebody low level geochemical anomalies in circumneutral spring and pond waters from the east zone are discernible only by using high resolution inductively coupled plasma mass spectrometry with lower limits of determination two and perhaps three orders of magnitude lower than traditional methods a variety of partial leaches of soils over the east zone reveal geochemical anomalies in a similar suite of elements that may be related to upwelling waters from depth along graben bounding faults 3 the indicator minerals gold jarosite and andradite in till reveal a displaced mineralogical anomaly to the west and south of the pebble orebody as ore related minerals were scraped from the orebody and deposited in till downice of the deposit geochemical anomalies in pond water and sediment over the displaced till are attributed to the ore related minerals in till this orientation study demonstrates the strong control of local geologic and geochemical settings on the effectiveness of different traditional and newer reconnaissance geochemical exploration techniques and thus has important implications for exploration

application of lead isotopes to mineral exploration in glaciated terrains the 206pb 204pb ratios of fine grained fractions from glacial tills indicate the presence of known proterozoic volcanogenic massive sulfide deposits at chisel lake near snow lake manitoba canada data from 2 m and other size fractions define a linear array on a 207pb 204pb vs 206pb 204pb diagram with a slope that yields an age similar to the age of the deposits and the surrounding country rocks some of the least radiogenic till samples were found down ice from the deposits suggesting that the pb isotopic compositions from till may provide a new approach to mineral exploration for massive sulfide deposits in glaciated terrains

average lead isotope growth curves for shale hosted zinc lead deposits canadian cordillera average lead isotope growth curves for shale hosted zinc lead deposits have been constructed empirically for a large but well defined tectonic segment of the canadian cordillera the model defined is applicable to the dating of galena lead from shale hosted deposits in the selwyn basin and in the ogilvie richardson wernecke and mackenzie mountains in the eastern fold belt and in much of the omineca crystalline belt this area of the cordillera generally had a coherent geochemical evolution lead for deposits was extracted from sediments which had been deposited along the western margin of the north american craton and which were derived largely from upper crustal crystalline rocks that formed the western part of the canadian shield the average shale growth curves involve three stages of evolution the third most recent stage of the three stage model starts at 1 89 m y and evolves to 0 m y with mu of 12 16 and omega of 49 09 the first two stages follow the two stage model of stacey and kramers 1975 the model allows precise model age estimates with an error generally less than 0 05 m y to be made for deposits of known age this is particularly useful in property evaluation during exploration because in many cases the certainty of a syngenetic or epigenetic origin can control future philosophy about exploration and or evolution of a deposit or an area model ages in concert with stratigraphic information commonly indicate the likelihood of epigenetic or syngenetic origins

mapping white mica alteration associated with the jiama porphyry skarn cu deposit central tibet using field swir spectrometry abstract field measurement of the short wave infrared swir reflectance from drill hole samples proved to be an effective method to map variations in white mica composition tschermak substitution associated with hydrothermal alteration zonation of the jiama porphyry skarn cu deposit tibetan plateau china this swir mineral spectral information provides geological insights into a the possible nature of the related magmatic intrusions b the physicochemistry of the associated hydrothermal fluids c the interactions between these fluids and country rocks and d potential vectors to economic mineralization the results suggest that the al oh band wavelength of white mica can used as an indicator in the subsequent steps of prospecting

mechanisms controlling rupture shape during subcritical growth of joints in layered rocks during joint propagation the orientation of plume lines on joint faces allows for mapping the path taken by the crack tip line during rupture growth rupture shapes in layered clastic sediments of the devonian catskill delta finger lakes district new york indicate joint growth through three stages where velocity of the tip line v tl varies as a function of the crack tip stress intensity k i the initial stage of growth is characterized by a rupture of approximately circular or elliptical shape that expands from an initiation fl aw with a velocity v tl in some cases primary growth involves self correction where an elliptical rupture redistributes the crack tip stress so that the rupture returns to a more stable circular shape the crack tip line eventually propagates to a bedding interface where properties of either a plastic or a noncohesive bedding interface cause v tl 0 along a portion of the tip line the onset of secondary growth occurs when the rupture tip line intersects both bedding interfaces and splits into two discontinuous segments that propagate synchronously as a single coherent rupture nonuniform nonsystematic v tl eventually interferes with the rupture s ability to grow coherently and thus leads to the transition to tertiary growth characterized by the detachment of the coherent rupture into one or more independently propagating noncoherent tip lines throughout all three stages of rupture growth the k i dependent v tl points to subcritical propagation variation from a smooth to rough plume morphology is consistent with propagation through region i of the subcritical regime with a transition at v tl 10 5 m sec rupture velocity may enter region ii of the subcritical regime but such a broad range of k i must be crossed to reach region iii and quasistatic behavior at the critical stress intensity k ic that region ii acts as a barrier through which few joints pass thus greatly limiting the number of postcritical joints in the catskill delta if not in the crust of the earth

a new indicator of glacial dispersal lead isotopes abstract lead isotope ratios from glacigenic sediments have been successfully used as glacial indicators to define dispersal patterns in mineralized areas of the canadian shield and the appalachian orogen sediments adjacent to and down ice from volcanogenic massive sulphide vms deposits have pb isotope ratios that reflect an input of pb from the deposits these ratios are distinctly different from those of the surrounding country rocks vertical sections overlying one of the deposits show that the pb isotope signature is preserved in much of the succession although incursions of pb from other sources are also identified by pb isotope ratios that are much higher than those of the deposit sections away from known deposits have isotopic ratios characteristic of the country rocks pb from some vms deposits can form an ideal glacial indicator the reasons for this are i the deposits can be considered point sources ii the pb in old vms deposits is isotopically different from the country rocks iii the pb abundance in the deposits is significantly enriched relative to average crustal abundances iv the pb isotope ratios are independent of the pb concentration in samples containing low to moderate amounts of pb v isotope ratio measurements can be made on small quantities of material and vi the isotope ratios of till enriched in vms derived pb are not measurably affected by weathering

tectonic setting of the pebble and other copper gold molybdenum porphyry deposits within the evolving middle cretaceous continental margin of northwestern north america the pebble cu au mo deposit in southwestern alaska containing the largest gold resource of any known porphyry in the world developed in a tectonic setting significantly different from that of the present day it is one of a series of metalliferous middle cretaceous porphyritic granodiorite quartz monzonite and diorite bodies evolved from lower crust and metasomatized lithospheric mantle melts which formed along much of the length of the north american craton suture with the peninsular alexander wrangellia arc the porphyry deposits were emplaced within the northernmost two of a series of ca 130 to 80 ma flysch basins that define the suture as well as into arc rocks immediately seaward of the two basins deposits include the ca 100 to 90 ma pebble neacola and other porphyry prospects along the kahiltna basin peninsula terrane boundary and the ca 115 to 105 ma baultoff carl creek horsfeld orange hill bond creek and chisna porphyries along the nutzotin basin wrangellia terrane boundary the porphyry deposits probably formed along the craton margin more than 1 000 km to the south of their present latitude palinspastic reconstructions of plate kinematics from this period are particularly difficult because magmatism overlaps the 119 to 83 ma cretaceous normal superchron a period when sea floor magnetic data are lacking our favored scenario is that ore formation broadly overlaps the cessation of sedimentation and contraction and the transition to a transpressional continental margin regime such that the remnant ocean basins were converted to strike slip basins the basins and outboard peninsular alexander wrangellia composite superterrane which are all located seaward of the deep crustal denali farewell fault system were subjected to northerly dextral transpression for as long as perhaps 50 m y beginning at ca 95 10 ma the onset of this transpression was marked by development of the mineralized bodies along fault segments on the seaward side of the basins geochemical and radiogenic isotopic data for igneous rocks associated with the pebble porphyry deposit suggest continuous melt derivation from enriched lithosphere of a recently metasomatized mantle these geochemical characteristics coupled with the arc continent related collisional setting suggest that lithospheric thickening and postcollisional lithospheric melting are the most likely cause of the ore related magmatism subsequent to translation of the alaskan margin terranes and early tertiary oroclinal bending of alaska the northernmost kahiltna basin and the pebble deposit as well as the other porphyry systems reached their present day locations along southern alaska

kinematic implications of joint zones and isolated joints in the navajo sandstone at zion national park utah evidence for cordilleran relaxation 1 at zion national park znp the landscape is a consequence of differential weathering of the navajo sandstone where closely spaced vertical joints constitute joint zones that erode to form regularly spaced half kilometer slot canyons striking 351 between these joint zones is a set of isolated joints striking 339 fracture interaction and horsetail wing crack development indicate that the 339 striking joint set is younger than the 351 striking joint zones despite the lateral extent of stress reduction shadows in the vicinity of the large scale joint zones in addition to an older less pervasive 020 joint set this sequence of jointing records a counterclockwise rotation of the regional extension directed from wnw to wsw in the navajo sandstone at znp znp is located at the western margin of the colorado plateau 100 km east of the major normal faults of the northeastern central basin and range subprovince extension within the eastern central basin and range initiated during the miocene and exhibited a wsw extension direction anderson 1971 wernicke et al 1988 snow and wernicke 2000 the correlation between nearby basin and range extension and the extension direction for the 351 tending joint zones of znp is so close that the jointing at znp is interpreted as evidence for modest yet pervasive basin and range extension in the western margin of the colorado plateau

the giant pebble cu au mo deposit and surrounding region southwest alaska introduction the pebble deposit is located about 320 km southwest of and 27 km northwest of the village of iliamna in alaska fig 1a it is one of the largest porphyry deposits in terms of contained cu fig 2a and it has the largest au endowment of any porphyry deposit in the world fig 2b the deposit comprises the pebble west and pebble east zones that represent two coeval hydrothermal centers within a single system lang et al 2013 together the measured and indicated resources total 5 942 million metric tons mt at 0 42 cu 0 35 g t au and 250 ppm mo with an inferred resource of 4 835 mt at 0 24 cu 0 26 g t au and 215 ppm mo in addition the deposit contains significant concentrations of ag pd and re northern dynasty minerals 2011 fig 1 a map of southwestern alaska showing extensive cover by tertiary and quaternary deposits and locations of known mineral deposits with outline of the pebble district distribution of tertiary and quaternary deposits is after wilson et al 2006 b map of the pebble district showing locations of deposits all deposits are named as zones for example the 37 zone regional mineral deposit locations are from u s geological survey 2008 descriptions of district deposits are in hawley 2004 and lang et al 2013 boundaries for the pebble west and pebble east zones are based on 0 3 and 0 6 cu equiv respectively fig 2 the 25 largest porphyry copper deposits based on a the tonnage of contained copper metal and b the tonnage of contained gold modified from cooke et al 2005 the classifications of deposits into cu mo cu au mo and cu au types are described in cooke et al 2005 unlike most porphyry deposits in southwest alaska which are 75 ma u s geological survey 2008 re os

magma driven hydraulic fracturing and infiltration of fluids into the damaged host rock an example from dronning maud land antarctica abstract excellent outcrops in dronning maud land antarctica provide unique insight into the mode and extent of fluid infiltration into metamorphic and plutonic rocks in the middle crust the fluids are liberated from pegmatitic veins and give rise to alteration halos in the alteration halos the conspicuous change in colour is correlated with 1 hydration mineral reactions and 2 high density of microcracks in quartz and feldspar exceeding that observed in the unaltered host rock by an order of magnitude the field relations indicate that the veins originated as melt driven hydraulic fractures sealed by pegmatite and aplite crystallising from volatile rich melts with the alteration halo being the wake of the process zone formed at the tip of the propagating fractures it is proposed that 1 the size of the alteration zone and the width of the vein are correlated resulting in higher values of both these quantities for cracks propagating at higher velocities and consequently higher crack propagation toughnesses 2 the damage zone is characterised by a transient state of high permeability which was short lived due to rapid healing and sealing of microcracks 3 the infiltration and retrogression of the high grade rocks can be considered as a quasi instantaneous process on geologic time scales with a duration of hours to weeks

airborne imaging spectrometer data of the ruby mountains montana mineral discrimination using relative absorption band depth images abstract airborne imaging spectrometer data collected in the near infrared 1 2 2 4 m wavelength range were used to study the spectral expression of metamorphic minerals and rocks in the ruby mountains of southwestern montana the data were analyzed by using a new data enhancement procedure the construction of relative absorption band depth rbd images rbd images like bandratio images are designed to detect diagnostic mineral absorption features while minimizing reflectance variations related to topographic slope and albedo differences to produce an rbd image several data channels near an absorption band shoulder are summed and then divided by the sum of several channels located near the band minimum rbd images are both highly specific and sensitive to the presence of particular mineral absorption features further the technique does not distort or subdue spectral features as sometimes occurs when using other data normalization methods by using rbd images a number of rock and soil units were distinguished in the ruby mountains including weathered quartz feldspar pegmatites marbles of several compositions and soils developed over poorly exposed mica schists the rbd technique is especially well suited for detecting weak near infrared spectral features produced by soils which may permit improved mapping of subtle lithologic and structural details in semiarid terrains the observation of soils rich in talc an important industrial commodity in the study area also indicates that rbd images may be useful for mineral exploration

aperture size scaling variations in a low strain opening mode fracture set cozzette sandstone colorado the aperture size distribution of a set of opening mode fractures in the cozzette sandstone is complex and cannot be described uniquely by a single equation this study of horizontal core includes aperture size data of macrofractures measured using a hand lens and microfractures measured using scanning electron microscope based cathodoluminescence sem cl macrofractures are poorly cemented and total fracture strain is an order of magnitude lower than the smallest strain values of most previously described vein sets macrofractures in this set therefore resemble typical joints as opposed to veins in most respects although intragranular microfractures compose about 98 of the microfracture population orientation fracture fill and fracture trace characteristics suggest that only transgranular microfractures can be shown to be genetically related to macrofractures aperture size data below 0 012 mm and above 1 mm follow a log normal distribution intermediate size data though relatively sparse suggest a power law aperture size distribution these results support the notion that this fracture set is an intermediate case between typical veins and joints the results also suggest that processes leading to size distributions commonly associated with veins i e power laws may be present in joint sets but over a more limited range bound at small size scales by grain scale effects and above by mechanical layering effects

first use of an airborne thermal infrared hyperspectral scanner for compositional mapping in may 1999 the airborne thermal infrared hyperspectral imaging system spatially enhanced broadband array spectrograph system sebass was flown over mormon mesa nv to provide the first test of such a system for geological mapping several types of carbonate deposits were identified using the 11 25 m band however massive calcrete outcrops exhibited weak spectral contrast which was confirmed by field and laboratory measurements because the weathered calcrete surface appeared relatively smooth in hand specimen this weak spectral contrast was unexpected here we show that microscopic roughness not readily apparent to the eye has introduced both a cavity effect and volume scattering to reduce spectral contrast the macroroughness of crevices and cobbles may also have a significant cavity effect the diminished spectral contrast is important because it places higher signal to noise ratio snr requirements for spectroscopic detection and identification this effect should be factored into instrumentation planning and interpretations especially interpretations without benefit of ground truth sebass had the required high snr and spectral resolution to allow us to demonstrate for the first time the ability of an airborne hyperspectral thermal infrared scanner to detect and identify spectrally subtle materials

three dimensional fracture distribution in relation to local cooling in a granitic body an example from the toki granitic pluton central japan this paper describes a spatial distribution of fracture frequency fracture number per unit interval in the toki granitic pluton central japan and their evaluation with respect to cooling behavior after solidification of the pluton three dimensional distribution of fracture frequency of all fractures all angle fractures based on borehole television data collected from 19 boreholes shows that 1 the central region of the granite has a high fracture frequency and 2 fracture frequency decreases with decreasing elevation measured from the mean sea level with the exception of the west side of the body the development of sub solidus reaction textures reflects the annealing duration of the pluton after solidification the extent of sub solidus reaction textures was measured at two neighboring positions and the difference was divided by the distance between the two positions the resulting quantity is here defined as a local cooling indicator lci we observed a related pattern between the distribution of fracture frequency and lci the high lci region corresponds to the region with a high frequency of all fractures and vice versa this relation indicates that fracture genesis has been mostly controlled by local cooling after solidification which caused thermal stress thus the three dimensional pattern of lci is a potential diagnostic tool for obtaining the spatial distribution of all fractures

regional fractures i a mechanism for the formation of regional fractures at depth in flat lying reservoirs 1 regional fractures may form slowly at depth in extension and parallel to regional horizontal tectonic compression such fracture sets can be common in reservoirs despite the absence of flexure of the strata and are commonly important contributors to reservoir permeability such fractures make good targets for deviated wells high formation pore pressure is crucial to creating low effective confining stresses and brittle rock properties in the reservoirs conditions conducive to fracturing despite deep burial but pore pressure does not exceed the least principal stress and does not cause tensile fracturing the mechanism of natural hydraulic fracturing is incompatible with the characteristics of most regional fracture sets rather many regional fractures form duri g far field compression initiate at locally induced tensile stresses caused by flaws in the rock and propagate in the plane of the maximum and intermediate compressive stresses the differential stress required for initiation and propagation of regional fractures is well below that necessary for shear failure in the presence of high pore pressure fractures can be held open at depth by a tectonic basinwide dilatancy of the strata and the open void space commonly becomes mineralized

change of sm nd isotope composition during weathering of till weathering of till in northern sweden results in the formation of well developed spodosols the till is dominated by 1 9 1 8 ga granitic material the ree are among the elements most strongly depleted during weathering and the loss of ree from the e horizon decreases as the atomic number increases to study if weathering leads to a change of the nd isotope composition we have analysed the nd isotopic composition of the various horizons including living plants and humus of two profiles of weathered till typic haplocryods in northern sweden as much as between 65 6 and 75 3 of the sm and nd in the 0 2 mm fraction has been lost from the e horizon and between 32 5 and 54 7 from the b horizon nd has been lost to a slightly greater extent than sm the two c horizon samples have end 0 values of 22 1 and 23 2 corresponding e horizon values are 18 1 and 20 2 the b horizon values are intermediate between the values of the e and c horizons it is concluded that the weathering leads to a change in the sm nd ratio resulting in a change of the sm nd isotope composition the plant and humus samples deviate even more from the unweathered till for one station the results could be interpreted as if the sm and nd taken up by the plants had similar isotope characteristics as the amounts of these elements released by weathering in the e horizon for the other station it is probable that the nd isotope composition of the organic samples is dominated by nd released by till weathering which however is mixed with another nd source possibly an airborne component the explanation to the change of isotope compostion in the till is that a larger proportion of the nd released by weathering is released from minerals with a lower sm nd ratio than the bulk soil compared with the amount released from minerals with a higher sm nd ratio although the various ree carrying minerals had the same initial nd isotopic composition 1 8 1 9 ga of decay of 147sm to 143nd has resulted in a higher present 143nd 144nd ratio in the minerals with a higher sm nd ratio

formation and growth of extensional fracture sets naturally occurring extension fractures including some joints and veins form sets consisting of numerous subparallel fractures each with well defined ends in order to correctly interpret these fractures in the field it is necessary to determine which factors control the geometries of fracture sets this requires consideration of the conditions leading to both the initiation and the cessation of fracture propagation a fracture begins to propagate when the crack extension force reaches a critical value which is a property of the rock and of environmental conditions after propagation initiates the crack extension force varies owing to 1 increase in crack length 2 change in remote strain 3 elastic interaction with nearby cracks 4 change in internal fluid pressure and 5 stress relaxation due to growth of cracks in the surrounding rock each fracture continues to propagate as long as its crack extension force exceeds the critical value and terminates when this condition is no longer met neglecting fluid effects the final geometry of the fracture set is a function of the remote strain history and the initial crack geometry which can be characterized by the initial crack density for low initial densities large increases in crack length occur with little or no increase in remote strain however for large initial densities crack lengths increase only if the applied strain increases this analysis is used to estimate the variation in remote strain during formation of a fracture set in granitic rock from observations of the final fracture geometry

a model of fracture nucleation growth and arrest and consequences for fracture density and scaling 1 in order to improve discrete fracture network dfn models which are increasingly required into groundwater and rock mechanics applications we propose a new dfn modeling based on the evolution of fracture network formation nucleation growth and arrest with simplified mechanical rules the central idea of the model relies on the mechanical role played by large fractures in stopping the growth of smaller ones the modeling framework combines in a time wise approach fracture nucleation growth and arrest it yields two main regimes below a certain critical scale the density distribution of fracture sizes is a power law with a scaling exponent directly derived from the growth law and nuclei properties above the critical scale a quasi universal self similar regime establishes with a self similar scaling the density term of the dense regime is related to the details of arrest rule and to the orientation distribution of the fractures the dfn model so defined is fully consistent with field cases former studied unlike more usual stochastic dfn models ours is based on a simplified description of fracture interactions which eventually reproduces the multiscale self similar fracture size distribution often observed and reported in the literature the model is a potential significant step forward for further applications to groundwater flow and rock mechanical issues

rare earth element geochemistry and the origin of andesites and basalts of the taupo volcanic zone new zealand abstract two types of basalt a high al basalt associated with the rhyolitic centres north of taupo and a low al basalt erupted from red crater tongariro volcanic centre and five types of andesite labradorite andesite labradorite pyroxene andesite hornblende andesite pyroxene low si andesite and olivine andesite low si andesite occur in the taupo volcanic zone tvz north island new zealand rare earth abundances for both basalts and andesites are particularly enriched in light rare earth elements high al basalts are more enriched than the low al basalt and have values comparable to the andesites labradorite and labradorite pyroxene andesites all have negative eu anomalies and hornblende andesites all have negative ce anomalies the former is probably due to changing plagioclase composition during fractionation and the latter to late stage hydration of the magma least squares mixing models indicate that neither high al nor low al basalts are likely sources for labradorite labradorite pyroxene andesites high al basalts are considered to result from fractionation of olivine and clinopyroxene from a garnet free peridotite at the top of the mantle wedge labradorite labradorite pyroxene andesites are mainly associated with an older nw trending arc the source is likely to be garnet free but it is not certain whether the andesites result from partial melting of the top of the subducting plate or a hydrated lower portion of the mantle wedge pyroxene low si andesites probably result from cumulation of pyroxene and calcic plagioclase within labradorite pyroxene andesites and hornblende andesites by late stage hydration of labradorite pyroxene andesite magma olivine andesites low si andesites and low al basalts are related to the nne trending taupo hikurangi arc structure although the initial source material is different for these lavas they have probably undergone a similar history to the labradorite labradorite pyroxene andesites all lavas show evidence of crustal contamination

growth of faults by accumulation of seismic slip the accommodation of large strains in the upper crust is largely achieved by the accumulation of displacement on faults observation shows that as a fault accumulates displacement it grows in size i e its surface area and its length increase here we address the question for an increase in the amount of displacement on a fault by how much would the length of the fault change it is argued by cowie and scholz 1992a that the displacement on a fault is linearly related to the length of the fault this simple result is expanded upon in this paper by assuming that a fault accumulates displacement by repeated earthquakes two different approaches are presented the first approach considers the balance that must be achieved between the energy available for deformation and the work involved in creating new fault surface area as the fault grows the available energy is provided by changes in strain energy when the fault slips the second approach is to construct a geometrical model for fault growth using the scaling relationship between the slip during a single earthquake and the length of the rupture the total displacement on a fault is the sum of the slips contributed by many earthquakes the usefulness of these two approaches is that the growth of a fault over geologic time can be described by parameters that can be obtained from earthquake and fault data the models presented here predict that 1 the maximum amount a fault can grow in a single earthquake that ruptures the entire fault is of the order of 1 of its previous length and 2 the work of faulting may account for 10 of the total energy available during an earthquake the energy lost from the system is accounted for by work done against friction and seismic radiation consequences of fault growth for the segmentation and thus seismogenic potential of a fault over geologic time are discussed using predictions of the theory