post eocene extensional tectonics in southern new caledonia sw pacific insights from onshore fault analysis and offshore seismic data ductile to brittle extensional deformation following thrusting of the peridotites nappe during the upper eocene has been shown to play a major role in the tertiary tectonic evolution of the northern part of the main island of new caledonia and its eastern and western margins in this study we provide new tectonic data from southern new caledonia that allow to better constrain the tectonic evolution of the southern part of the main island we present a kinematic analysis of faults and striations obtained mainly from exposures of sedimentary rocks in the region of noumea with complements from measurements made farther north at nepoui within post obduction middle miocene deposits we also present additional results of an interpretation of seismic lines from the lagoon south of the noumea peninsula which provide constraints on the current tectonic regime of southern new caledonia extensional faults in the noumea region have been studied within terranes of various ages including pre and syn obduction deposits and ophiolites hence we demonstrate that important extensional events have affected the southern part of the new caledonia block after the obduction of the peridotite nappe the direction of maximum extension is variable at the scale of the region both high angle and low angle normal faults are present and block rotation is observed at some localities this suggests that detachments accommodating significant displacements are cutting through the sedimentary pile the average final strain pattern of the region can be regarded as the results of a multidirectional flattening a hypothesis consistent with vertical uplift associated with regional extension these results are in good agreement with conclusions of earlier workers showing late extensional evolution of the ophiolites along

the metamorphic sole of new caledonia ophiolite 40ar 39ar u pb and geochemical evidence for subduction inception at a spreading ridge amphibolite lenses that locally crop out below the serpentinite sole at the base of the ophiolite of new caledonia termed peridotite nappe recrystallized in the high temperature amphibolite facies and thus sharply contrast with blueschists and eclogites of the eocene metamorphic complex amphibolites mostly display the geochemical features of morb with a slight nb depletion and thus are similar to the youngest late paleocene eocene babb components of the allochthonous poya terrane thermochronological data from hornblende 40ar 39ar zircon and sphene u pb suggest that these mafic rocks recrystallized at 56ma using various geothermobarometers provides a rough estimate of peak recrystallization conditions of 0 5gpa at 800 950c the thermal gradient inferred from the metamorphic assemblage 60 ckm 1 geometrical relationships and geochemical similarity suggest that these mafic rocks belong to the oceanic crust of the lower plate of the subduction obduction system and recrystallized when they subducted below young and hot oceanic lithosphere they were detached from the down going plate and finally thrust onto unmetamorphosed poya terrane basalts this and the occurrence of slab melts at 53ma suggest that subduction inception occurred at or near to the spreading ridge of the south loyalty basin at 56ma 2012 american geophysical union all rights reserved

salt karst and tectonics sinkholes development along tension cracks between parallel strike slip faults dead sea jordan this work deals with the tectonic interpretation of an alignment of more than 300 sinkholes stretching along the jordanian coast of the dead sea ghor al haditha area its dimensions are 6 km long with a width of 600 m sinkholes appeared during the last decades as a consequence of the very rapid lowering of the lake level the linear shape was inferred from ground collapse inventories carried out between 1991 and 2008 the lineament is replaced and analyzed in its structural setting at regional and local scales its direction n 24 e is sub parallel to the ones displayed by many focal mechanisms especially the one associated with the earthquake of the 23 april 1979 mb 5 1 n 20 e 5 which is representative of all focal mechanisms calculated on a fault plane compatible with the general direction of the jordan dead sea transform fault system for the east coast of the dead sea area the alignment of sinkholes is constituted by 13 minor linear segments separated by as many empty spaces four minor linear units present an en echelon arrangement from which one can deduce the presence of a local extensional stress field in this context the sinkhole locations provide information of subsurface discontinuities interpreted as hidden fractures in a close future such results could support the work of decision makers and engineers in the projected development of the area copyright 2009 john wiley sons ltd

a drastic lower miocene regolith evolution triggered by post obduction slab break off and uplift in new caledonia a lower miocene coarse conglomerate that crops out in the nepoui peninsula does not represent the base of the marine transgression that followed obduction in new caledonia instead the conglomeratic alluvial fan that contains peridotite cobbles and reworked weathering products records a short lived episode of terrestrial erosion intercalated between two intervals of subsidence marked by marine carbonate deposition considering the miocene sea level evolution reported in the literature it is concluded that neither lower miocene transgression nor erosion were driven by sea level variation in contrast a southeastward propagating slab tear that initiated at the latitude of the high pressure low temperature metamorphic complex of northern new caledonia likely generated east to west tilting of new caledonia subsidence along the west coast and hence fringing reef development together with moderate erosion of older regolith coincidence between conglomerate deposition and hence prominent erosion that closely followed emplacement of postobduction granitoids influenced by a slab window suggests a genetic link therefore it is concluded that short lived lower miocene erosion was due to slab breakoff and subsequent uplift that occurred at 22 ma lower miocene erosion profoundly dissected the peridotite nappe and in the northern half of new caledonia only left isolated klippes along the west coast

mineral paragenesis alteration and geochemistry of the two types of gold ore and the host rocks from the carlin type deposits in the southern part of the goldstrike property northern nevada implications for sources of ore forming elements ore genesis and mineral exploration this study was undertaken to characterize the mineral paragenesis and metal zoning at the property scale evaluate the potential sources of ore related metals quantify the relationship between intensity of alteration and gold grade and propose a comprehensive genetic model for the carlin type au deposits at the southern part of the goldstrike property nevada mineralogy textural relationships whole rock composition and spatial distribution of the studied samples revealed two types of gold ore ore i and ii the former which is hosted by the roberts mountains and rodeo creek formations and the wispy planar and upper mud units of the popovich formation is the most abundant and widespread in the property ore i is characterized by intense hydrothermal alteration e g carbonate dissolution silicification and precipitation of pyrite and high amounts of trace elements e g ag as au ba cd cu hg mo ni s sb se te tl and zn on the other hand ore ii which is hosted in the wispy planar and soft sediment deformation units of the popovich formation is mainly confined to the central north northwest portion of the screamer deposit and is weakly altered with low concentration of trace elements both ores i and ii contain similar average concentrations of au in whole rock 14 and 19 g t au respectively and in pyrite 290 and 540 ppm respectively however auriferous pyrite from ore i has higher trace element as ag cu hg ni sb se and tl au ratios than ore ii the sedimentary units are interpreted to be the major local source of cd mo ni u v and zn and minor as cu hg and se as denoted by the composition of least altered samples and diagenetic pyrite and sphalerite this study reveals that al2o3 and tio2 are the most immobile compounds and their distribution indicates a homogeneous source for the detrital components in the sedimentary rocks among the ore related trace elements tl best correlates with au grade r 2 0 69 and shows some relationship with the calculated amount of pyrite r 2 0 49 indicating that tl would be the best element to vector toward zones of high grade carlin type au mineralization gold grades do not correlate with the amount of pyrite degree of alteration or organic c our results integrated with available thermodynamic data for au ore related elements and sio2 lead us to suggest that the formation of ore i occurred more proximal to the major mineralizing conduits as the hot more acid sio2 and trace element rich auriferous fluids interacted with fe bearing impure carbonate host rocks intensely dissolving the carbonate rocks and precipitating quartz and auriferous pyrite in the betze post and rodeo deposits as the fluids moved laterally throughout the favorable host rocks the ph increased leading to a decreasing in the rate of carbonate dissolution and in the solubility of silica favoring the formation of more distal ore ii in the central northern part of the screamer deposit significantly the gold concentrations in whole rock and in pyrite are in some way very similar in both ore types being slightly higher in ore ii suggesting that less acidic conditions were still favorable for the incorporation of gold in the structure of pyrite even at lower concentrations of other trace elements

a special issue devoted to gold deposits in northern nevada part 2 carlin type deposits this is the second of two special issues of economic geology devoted to gold deposits in northern nevada readers interested in a general overview of these deposits their economic significance their context within the tectonic evolution of the region and synoptic references on each gold deposit type are directed to the preface of the first special issue john et al 2003 volume 98 issue 2 contains five papers that address regional aspects important to the genesis of gold deposits in northern nevada and five papers that present detailed studies of epithermal deposits and districts all of the regional papers are pertinent to carlin type gold deposits because they address the age of mineralization arehart et al 2003 origin and evolutionary history of the northwest striking mineral belts that localize many deposits grauch et al 2003 nature of the middle and lower crust below these mineral belts howard 2003 district to deposit scale stream sediment and lithogeochemical anomalies theodore et al 2003 and stratigraphy and structure of a district located along a northeast striking lineament peters et al 2003 the nine papers in this second special issue focus on an array of problems pertinent to genetic and exploration models for carlin type deposits in northern nevada fig 1 these investigations sort out and characterize the sequence of deformational igneous and hydrothermal events in mining districts constrain the age of mineralization map paleothermal gradients identify structures and lithologies that are preferentially mineralized ascertain processes of ore formation determine sources of ore fluid components and define fluid flow paths a common theme among these papers is inheritance whereby older features in the mineral belts influence ore formation in subsequent carlin type hydrothermal systems three types of inheritance are inferred by one or more of these investigations 1 structural inheritance where older faults are reactivated during subsequent contractional and or

local to regional scale structural controls on mineralisation and the importance of a major lineament in the eastern mount isa inlier australia review and analysis with autocorrelation and weights of evidence although major crustal lineaments may play an important role in mineralisation the relationship between lineaments and mineral deposits can be quite cryptic and structural controls may vary as a function of scale along lineaments major lineaments alone may be of limited use for detailed target generation the cloncurry lineament in the eastern part of the mount isa inlier is a crustal scale structure defined by potential field derived worms weights of evidence quantifies the association between mineral occurrences and this lineament autocorrelation is used to recognise structural controls on mineralisation at different scales by progressively limiting the lengths of the vectors between mineral occurrence points in the autocorrelation plot the weights of evidence analysis shows that au au cu cu au and cu deposits have a positive spatial correlation to the cloncurry lineament which suggests it that acted as a primary crustal scale control on the localisation of cu and au through focussing mineralisation systems on a broad scale however autocorrelation defines a variety of local structural controls which can be interpreted as shear zones variably oriented fault sets en echelon fault arrays and potentially the orientation of bedding and or iron formations which localise fluid flow and mineral deposition at finer scales the results suggest that major lineaments defined by geophysical contrasts can be used in conjunction with techniques of spatial analysis for targeting structurally controlled mineralisation in areas under thin cover adjacent to mineralised terrains such as the mt isa inlier

tectonic stresses seaward of an aseismic ridge trench collision zone a remote sensing approach on the loyalty islands sw pacific abstract the loyalty islands are a series of limestone karstified islands on the australian plate that are presently approaching the vanuatu subduction zone sw pacific they are deformed due to the combined effects of the bulging of the subducting lithosphere and the beginning collision between the loyalty ridge and the vanuatu subduction zone therefore they constitute a series of markers for early phases of ridge arc collision lineaments deduced from remote sensing images aerial photos spot3 spot4 and envisat data termed here as fractures are analyzed by comparison with planar structures measured during field studies and termed as geological data fracture data indicate a stable main n110 direction with a large variance of nearly 15 in rms and two minor directions 45 apart which may constitute shear directions associated to the major one a scale dependent analysis shows that fractures longer than 2000 m are close to the n110 direction and that their orientation shifts progressively to reach the n125 direction for l

resolving the nature and geometry of major fault systems from geophysical and structural analysis the palmerville fault in ne queensland australia abstract the palmerville fault in northeastern queensland australia forms a major terrane bounding structure that probably had a major influence on the evolution of the adjacent palaeozoic hodgkinson province the northernmost part of the tasman fold belt system in eastern australia the nature and subsurface expression of the palmerville fault remain poorly constrained and models for contrasting geometries exist in addition to structural field and microscopic observations we have combined results from multi scale wavelet edge analysis worming forward modelling of regional magnetic and gravity data and geochemical data sets to develop an improved understanding of the nature and subsurface geometry and depth extent of the palmerville fault results from worming suggest a steeply dipping geometry for the palmerville fault based on constraints from field observations and worming we have generated a number of sections across the palmerville fault and forward modelled their magnetic and gravity response to compare with the observed magnetic and gravity response our results show that the palmerville fault represents a steeply eastward dipping structure that may become listric at depth suggesting the presence of proterozoic basement underneath the hodgkinson province our findings suggest that the palmerville fault was a first order normal fault that controlled early middle palaeozoic basin development in the hodgkinson province subsequently the fault acted as a mid crustal decollement zone accommodating basin inversion in the hodgkinson province during the late palaeozoic these results provide important constraints on the tectonic evolution of the hodgkinson province in northeastern australia and importantly demonstrate the strength of combining geological observations with geophysical analysis in particular multi scale wavelet edge analysis in resolving the surface geometry and evolution of major fault systems especially in areas of low data density

on the formation of collapse dolines a modelling perspective abstract collapse dolines are among the most striking surface features in karst areas although they can be the result of different formation mechanisms evidence suggests that large collapse dolines form due to chemical and mechanical removal of material at and below the level of groundwater we have applied a genetic model of a two dimensional fracture network to calculate the rate of dissolutional bedrock removal in the heavily fractured crushed zone intersecting a karst conduit in the phreatic zone to account for infilling and breakdown processes in the crushed zone two simple rules were added to the basic model 1 continuous infilling of dissolutionally created voids prevents fractures from growing beyond some limited aperture although the dissolution proceeds 2 discontinuous collapsing causes sudden closure of a fracture once some critical aperture has been reached both rules limit the transmissivity of the network and the related flow rates therefore the constant head difference between the input and the output points is sustained and the flow remains distributed over the entire crushed zone provided that restrictions posed by the two rules permit turbulent flow dissolution rates also remain high in the entire region high surface area of water rock contact and high dissolution rates result in high overall removal rates of rock from the crushed zone one of the necessary conditions for the formation of large closed depressions despite the fact that the model neglects some processes and dynamics that would increase the removal rate the results suggest that large closed depressions could form in the order of 1 million years

morphometric indices as indicators of tectonic fluvial and karst processes in calcareous drainage basins south menorca island spain this study proposes using morphometric indices to discriminate the processes that shape calcareous drainage basins to illustrate this a dem of the southern part of menorca island migjorn was created and basin slope drainage density hypsometric curve and integral and the area occupied by open and closed dolines were extracted from it these indices show an important dependence on tectonics which govern the morphology of these drainage basins and encourage the predominance of karst and or fluvial processes in the different sectors the morphometric indices are clearly influenced by the geological migjorn structure a carbonate upper miocene reef platform gently folded as an asymmetrical anticline the hypsometric integral and curve discriminate the influence of tectonics and structure whilst the drainage density and the proportion of open dolines are associated with basins with more pronounced fluvial processes a cluster analysis based on these indices discriminated three sectors where different forms and processes are found in the western and eastern sectors rounded basins without major fractures predominate the basins slope at less than 5 and karst processes outweigh fluvial processes the central sector however has steeper slopes a clearly defined drainage system and a predominance of fluvial over karst processes greater uplift in this sector has facilitated the formation of elongated basins that follow the main fracture lines copyright 2007 john wiley sons ltd

geophysical and isotopic constraints on crustal structure related to mineral trends in north central nevada and implications for tectonic history we combined information from sr and pb isotope data and magnetotelluric models to develop a new magnetic and gravity interpretation of the crustal structure of north central nevada to better understand the origin of mineral trends the new interpretation suggests a crustal structure that is composed of precambrian continental crust transitional crust and primarily oceanic crust that are separated by northwest and northeast striking fault zones the magnetic expression of the buried precambrian continental crust is recognized for the first time low magnetic values primarily reflect magnetite poor crystalline crust rather than elevated temperatures at depth northwest and northeast striking crustal boundaries are defined by isotopic data and abrupt gradients in gravity and magnetic data the carlin and battle mountain eureka mineral trends are associated with two of three northwest striking boundaries the carlin boundary is primarily defined by a change in density and isotopic character of the lower to middle crust the battle mountain eureka boundary coincides with a density contrast in the upper crust and a change in isotopic character in the lower to middle crust magnetotelluric models suggest that the battle mountain eureka boundary represents a crustal fault zone for most of its extent but that deep rooted faulting is more complex near and northwest of battle mountain crustal fault zones inferred from the magnetotelluric models near the carlin trend are oblique to it suggesting that they may not have been controlled by the deep boundary seen in the gravity and isotopic data the third northwest trending boundary is related to the western edge of the buried precambrian continent in west central nevada but lacks an associated mineral trend a northeast striking boundary forms the northern limit of precambrian continental and transitional crust the boundaries may have originated as rift or transform faults during precambrian breakup of rodinia or as faults accommodating lateral movements or accretion during later paleozoic tectonic events comparing the crustal structure to tectonic elements produced by successively younger events shows that it had a profound influence on subsequent sedimentation deformation magmatism extension and most important mineralization

geologic and isotopic constraints on the crustal structure of the northern great basin geophysical data do not define the western limit of north american continental crust in the northern great basin because phanerozoic deformation particularly cenozoic extension has overprinted original gravity magnetic and seismic signatures stratigraphic and structural analyses of north central nevada however allow location of the continental oceanic crustal boundary on the basis of recognition of continental slope deposits the stratigraphically defined location of the continental edge corresponds to the position of an isotopically defined boundary between granitic plutons with initial sr isotopic ratios less than 0 706 to the west and greater than 0 706 to the east three generally north south trending subprovinces with different sr and nd isotopic character can be defined in the northern great basin the boundary between the western and central subprovinces is defined by the 87 sr 86 sr initial 0 706 isopleth and corresponds to the stratigraphically defined western edge of transitional north american continental crust the boundary between the central and eastern subprovinces is defined by the nd 7 line farmer and depaolo 1983 in north eastern nevada and may be entirely within north american crust a third isotopically defined boundary imprecisely located in western utah marks the western boundary of the largely undeformed north american craton

age constraints on jerritt canyon and other carlin type gold deposits in the western united states relationship to mid tertiary extension and magmatism carlin type gold deposits are difficult to date and a wide range of ages has been reported for individual deposits therefore several methods were employed to constrain the age of the gold deposits in the jerritt canyon district dated igneous rocks with well documented crosscutting relationships to ore provided the most reliable constraints k ar and 40 ar 39 ar dates on igneous rocks are as follows andesite dikes 324 ma sericitic alteration in andesite dikes 118 ma basalt dikes 40 8 ma quartz monzonite dikes 39 2 ma and calc alkaline ignimbrites 43 1 to 40 1 ma of these only the andesite and basalt dikes are clearly altered and mineralized the gold deposits are therefore younger than the 40 8 ma basalt dikes the sericitic alteration in the andesite dikes is unrelated to the gold deposits a number of dating techniques did not work k ar and 40 ar 39 ar dates on mica from mineralized ordovician to devonian sedimentary rocks gave misleading results the youngest date of 149 ma from the smallest 187 os 188 os initial 0 9 3 6 but did not yield a meaningful isochron due to very low re and os concentrations and large analytical uncertainties paleomagnetic dating techniques failed because the hydrothermal fluids sulfidized nearly all of the iron in the host rocks leaving no remnant magnetism when published isotopic dates from other carlin type deposits in nevada and utah are subject to the rigorous evaluation developed for the jerritt canyon study most deposits can be shown to have formed between 42 and 30 ma k ar and 40 ar 39 ar dates on the youngest preore igneous rocks range from 41 to 32 ma whereas the oldest postore igneous rocks range from 35 to 33 ma hydrothermal adularia from the twin creeks deposit yields similar 40 ar 39 ar dates of 42 ma k ar dates on supergene alunite range from 4 to 30 ma k ar and 40 ar 39 ar dates on micas separated from sedimentary 395 43 ma and igneous 145 38 ma rocks are usually much older than the gold deposits and most are suspect because they are from incompletely reset preore micas or from mixtures of preore and ore stage mica fission track dates on zircons are also generally older than the deposits 169 35 ma and are not completely reset by mineralization apatites are likley to be reset by the hydrothermal systems and by younger thermal events and yield dates 83 22 ma that are younger than those from zircon independent support of a mid tertiary age is provided by the low delta d sub h 2 o values of hydrothermal fluids from 10 widely separated carlin type deposits 134 or 23ppm the low delta d sub h 2 o values are consistent with a mid tertiary age when the climate was cool but are inconsistent with the cretaceous and jurassic ages favored by some workers when the climate was warm the age and distribution of carlin type deposits coincides with areas that underwent extension and calc alkaline magmatism over the same time period despite this relationship the deposits lack clear spatial or genetic relationships to mid tertiary epizonal plutons rather many deposits are localized along preexisting crustal fault zones in the getchell trend structures tapped deep sourced metamorphic or magmatic fluids and subsequently variably exchanged meteoric water in the other trends and districts only variably exchanged meteoric water has been detected these relationships suggest either that all of the deposits formed from deep sourced fluids and were subsequently flooded by meteoric water or that fluids from different sources evolved to produce deposits with similar charateristics

long term tropical morphogenesis of new caledonia southwest pacific importance of positive epeirogeny and climate change extensive mapping of relict lateritic landsurfaces over the 1600 m of relief of mainland new caledonia is used to evaluate long term morphogenesis of the island since its emergence in the oligocene the results support the interpretation of the lateritic levels as abandoned stepped remnant landsurfaces that may be grouped into eight island scale erosion levels recording episodic lowering of base level the separation of the erosion levels results from the combination of positive epeirogenic movements of the new caledonia continental ridge and long term neogene climate variability which is recorded by the contrasted erosion and weathering patterns of the three youngest levels and tentatively correlated with known global and regional paleoclimatic events

evidence for a battle mountain eureka crustal fault zone north central nevada and its relation to neoproterozoic early paleozoic continental breakup 1 combined evidence from gravity radiogenic isotope and magnetotelluric mt data indicates a crustal fault zone that coincides with the northwest trending battle mountain eureka bme mineral trend in north central nevada usa the bme crustal fault zone likely originated during neoproterozoic early paleozoic rifting of the continent and had a large influence on subsequent tectonic events such as emplacement of allochthons and episodic deformation magmatism and mineralization throughout the phanerozoic mt models show the fault zone is about 10 km wide 130 km long and extends from 1 to 5 km below the surface to deep crustal levels isotope data and gravity models imply the fault zone separates crust of fundamentally different character geophysical evidence for such a long lived structure likely inherited from continental breakup defies conventional wisdom that structures this old have been destroyed by cenozoic extensional processes moreover the coincidence with the alignment of mineral deposits supports the assertion by many economic geologists that these alignments are indicators of buried regional structures

fusion of multi resolution surface terrestrial laser scanning and subsurface geodata ert srt for karst landform investigation and geomorphometric quantification a multi method research design based on terrestrial laser scanning gis geophysical prospecting electrical resistivity tomography refraction seismics and sedimentology is applied for the first time to investigate enclosed karst depressions in an integrated way fusing multi resolution surface and subsurface geodata provides profound insights into the formation geometry and geomorphologic processes of dolines the studied landforms which are located in the dikti mountains of east crete are shown to be filled by loose sediments of thicknesses of up to 30 m that mainly consist of fine grained material overlying solid bedrock at depths below 35 to 45 m by combining subsurface observations with geomorphometric calculations local doline genesis can be traced back to initial collapse of fractured bedrock followed by subsequent infilling with colluvials in order to define crucial methodological requirements and guidelines for data fusion both the impact of different elevation models and the influence of data resolution are assessed surface volumes of depressions derived by the digital surface model are 7 21 higher than the results obtained from the terrain model due to vegetation similarly estimates of infill volume calculated on the basis of geophysical outcomes and elevation data differ by up to 13 calculations of the landforms current volumes i e total surface and subsurface volume however are fairly insensitive to raster resolution hence the distinct geomorphologic properties of landforms e g shape terrain roughness slope inclination substantially determine the geomorphometric analysis of both surface and subsurface data as shown by the findings data fusion to integrate digital terrain geophysical and sedimentological datasets of varied resolutions benefits geomorphologic studies and helps provide a comprehensive image of landforms copyright 2013 john wiley sons ltd

climate change and the formation of nickel laterite deposits one of the major controls on nickel laterite deposit formation is climate a comparison of climatic data for regions where ultramafic rocks are exposed shows that areas currently conducive to nickel laterite formation receive 1000 mm yr precipitation have cold month mean cmm temperatures between 15 and 27 c and warm month mean wmm temperatures between 22 and 31 c using a compilation of paleoclimatic data and the defined climatic window of nickel laterite deposit formation allows an assessment of the timing and duration of paleo nickel laterite formation in ancient terrains to illustrate the potential of this technique we show that the formation of the caldag nickel laterite deposit of western turkey most likely initiated when the ultramafic protolith of cretaceous age was exposed in the early eocene and that the majority of the deposit formed during the eocene in contrast the formation of the bitincke deposit south albania was mostly complete by the early eocene after which cmm temperatures dropped below the optimum for laterite formation

carlin style gold deposits youjiang basin china tectono thermal and structural analogues of the carlin type gold deposits nevada usa the triassic gold deposits of the youjiang basin southern china have been variously correlated to carlin style and orogenic gold deposits or classified as a new intermediate deposit type however in terms of a multi scale mineral system approach they show remarkable similarities to the tertiary carlin type deposits of nevada and distinct contrasts to orogenic gold deposits both the nevada and youjiang deposit groups formed in a continent scale post orogenic extension event on fragmented continental crust underlain by metasomatized lithosphere both form roughly orthogonal deposit trends that subparallel near orthogonal margins of a continental crustal block with deposits controlled by gentle anticlines monoclines or half horsts and extensional faults not tight locked up anticlines and shear zones the mineralogy and ore geochemistry of the two groups are similar with differences consistent with slightly deeper and higher temperature of formation of the older chinese deposits commensurate with deeper erosional levels the youjiang gold deposits should be classified as carlin type rather than carlin like or other terminologies with their lower gold endowment probably related to a more distal thermal and fluid source than the nevada carlin type deposits

regional surficial geochemistry of the northern great basin the regional distribution of arsenic and 20 other elements in stream sediment samples in northern nevada and southeastern oregon was studied in order to gain new insights about the geologic framework and patterns of hydrothermal mineralization in the area data were used from 10 261 samples that were originally collected during the national uranium resource evaluation nure hydrogeochemical and stream sediment reconnaissance hssr program in the 1970s the data are available as u s geological survey open file report 02 0227 the data were analyzed using traditional dot maps and interpolation between data points to construct highresolution raster images which were correlated with geographic and geologic information using a geographic information system gis wavelength filters were also used to deconvolute the geochemical images into various textural components in order to study features with dimensions of a few kilometers to dimensions of hundreds of kilometers the distribution of arsenic antimony gold and silver is different from distributions of the other elements in that they show a distinctive high background in the southeast part of the area generally in areas underlain by the pre mesozoic craton arsenic is an extremely mobile element and can be used to delineate structures that served as conduits for the circulation of metal bearing fluids it was used to delineate large crustal structures and is particularly good for delineation of the battle mountain eureka mineral trend and the steens lineament which corresponds to a post miocene fault zone arsenic distribution patterns also delineated the black rock structural boundary northwest of which the basement apparently consists entirely of miocene and younger crust arsenic is also useful to locate district sized hydrothermal systems and clusters of systems most important types of hydrothermal mineral deposit in the northern great basin appear to be strongly associated with arsenic this is less so for low sulfidation epithermal deposits in addition to individual elements the distribution of factor scores that resulted from principal component studies of the data was used the strongest factor is characterized by fe ti v cu ni and zn and is used to map the distribution of distinctive basalts that are high in cu ni and zn and that appear to be related to the steens basalt the other important factor is related to hydrothermal precious metal mineralization and is characterized by sb ag as pb au and zn the map of the distribution of this factor is similar in appearance to the one for arsenic and we used wavelength filters to remove regional variations in the background for this factor score the resulting residual map shows a very strong association with the most significant precious metal deposits and districts in the region this residual map also shows a number of areas that are not associated with known mineral deposits illustrating the utility of the method as a regional exploration tool a number of these prospective areas are distant from known significant mineral deposits the deconvolution of the spatial wavelength structure of geochemical maps combined with the use of large regional geochemical data sets and gis permits new possibilities for the use of stream sediment geochemistry in the study of large scale crustal features as well as the isolation of mineral district scale anomalies

spatial analysis of a karst depression population clues to genesis a detailed analysis of depression spatial distribution on the parts of the western highland rim and pennyroyal plain underlain by the st louis and ste genevieve limestones indicates the presence of a depression infrastructure the major geomorphic elements of the infrastructure include depression density no km 2 doline swallet order and interdoline spacing a multigenerational diffusion and competition process model best explained 1 the presence of two lognormally distibuted depression density subpopulations 2 discrete clustered depression sets containing second order swallet dolines surrounded by first order swallet depressions 3 geomorphic competition between adjacent second order swallet dolines for runoff and catchment area and 4 a positive correlation between interdoline rim spacings of the small swallet order and the sum of their respective major axial lengths

regional crustal structures and their relationship to the distribution of ore deposits in the western united states based on magnetic and gravity data upgraded gravity and magnetic databases and associated filtered anomaly maps of western united states define regional crustal fractures or faults that may have guided the emplacement of plutonic rocks and large metallic ore deposits fractures igneous intrusions and hydrothermal circulation tend to be localized along boundaries of crustal blocks with geophysical expressions that are enhanced here by wavelength filtering in particular we explore the utility of regional gravity and magnetic data to aid in understanding the distribution of large mesozoic and cenozoic ore deposits primarily epithermal and porphyry precious and base metal deposits and sediment hosted gold deposits in the western united states cordillera on the broadest scale most ore deposits lie within areas characterized by low magnetic properties the mesozoic mother lode gold belt displays characteristic geophysical signatures regional gravity high regional low to moderate background magnetic field anomaly and long curvilinear magnetic highs that might serve as an exploration guide geophysical lineaments characterize the idaho montana porphyry belt and the la caridad mineral park belt from northern mexico to western arizona and thus indicate a deep seated control for these mineral belts large metal accumulations represented by the giant bingham porphyry copper and the butte polymetallic vein and porphyry copper systems lie at intersections of several geophysical lineaments at a more local scale geophysical data define deep rooted faults and magmatic zones that correspond to patterns of epithermal precious metal deposits in western and northern nevada of particular interest is an interpreted dense crustal block with a shape that resembles the elliptical deposit pattern partly formed by the carlin trend and the battle mountain eureka mineral belt we support previous studies which on a local scale conclude that structural elements work together to localize mineral deposits within regional zones or belts this study of mineral deposits of the western united states demonstrates the ability of magnetic and gravity data to elucidate the regional geologic framework or structural setting and to contribute in locating favorable environments for hydrothermal mineralization

first palaeomagnetic dating of ferricrete in new caledonia new insight on the morphogenesis and palaeoweathering of grande terre terra nova 24 77 85 2012 abstract comparing palaeolatitudes estimated from remanent magnetization data of ferricrete developed over laterite at two sites goro and tiebaghi against the apparent polar wandering path of australia provides new time constraints for the peridotite weathering in new caledonia the tiebaghi massif of the west coast klippes displays a single episode of ferricrete development during latest oligocene times by contrast the goro site in the southern part of the massif du sud reveals a more complex history with several episodes of ferricrete development from latest oligocene to pliocene quaternary times these data have made it possible to constrain the post obduction geodynamics and associated morphogenesis of new caledonia since related uplift probably prevented regolith development until latest oligocene times moreover the later uplift and deep erosion of the west coast klippes during the early miocene probably prevented further regolith preservation

genesis of middle miocene yellowstone hotspot related bonanza epithermal au ag deposits northern great basin usa epithermal deposits with bonanza au ag veins in the northern great basin ngb are spatially and temporally associated with middle miocene bimodal volcanism that was related to a mantle plume that has now migrated to the yellowstone national park area the au ag deposits formed between 16 5 and 14 ma but exhibit different mineralogical compositions the latter due to the nature of the country rocks hosting the deposits where host rocks were primarily of meta sedimentary or granitic origin adularia rich gold mineralization formed where glassy rhyolitic country rocks host veins colloidal silica textures and precious metal colloid aggregation textures resulted where basalts are the country rocks clay rich mineralization with silica minerals adularia and carbonate developed oxygen isotope data from quartz originally amorphous silica and gels from super high grade banded ores from the sleeper deposit show that ore forming solutions had 18o values up to 10 heavier than mid miocene meteoric water the geochemical signature of the ores including their se rich nature is interpreted here to reflect a mantle source for the epithermal suite elements au ag se te as sb hg and that signature is preserved to shallow crustal levels because of the similar volatility and aqueous geochemical behavior of the epithermal suite elements a mantle source for the gold in the deposits is further supported by the pb isotopic signature of the gold ores apparently the host rocks control the mineralization style and gangue mineralogy of ores however all deposits are considered to have derived precious metals and metalloids from mafic magmas related to the initial emergence of the yellowstone hotspot basalt derived volatiles and metal loid s are inferred to have been absorbed by meteoric water dominated geothermal systems heated by shallow rhyolitic magma chambers episodic discharge of volatiles and metal loid s from deep basaltic magmas mixed with heated meteoric water to create precious metal ore forming fluids colloidal nanoparticles of au ag alloy electrum naumannite ag2se silica and adularia likely nucleated at depth traveled upward and deposited where they grew large enough to aggregate along vein walls silica and gold colloids have been reported in hot springs from yellowstone national park suggesting that such processes may continue to some extent to the present however it is possible that the initial development of the mantle plume led to a major but short lived distillation process which led to the mid miocene bonanza ore forming event

the initiation and growth of gullies in madagascar are humans to blame abstract lavaka madagascar s unusual gullies require thick lateritic regolith on smoothly convex hills and they are initiated locally by a variety of cultural and natural proximate causes such as paths roads defensive trenches around hillforts steep fields unchanneled to slightly concentrated storm run off springs mass movements etc growth continues by rain attack incision by run off earthfalls caused by wetting and drying cycles and especially basal sapping by diffuse groundwater flow above bedrock somewhat in that order lavaka are less directly permitted and promoted by 1 hardening of exposed laterite surfaces which creates a hard soft hard profile from bedrock to laterite which favors incision relative to lateral erosion 2 the superimposition of concave run off profiles onto convex hills and locally 3 re equilibration of watersheds after stream piracy and faulting run off and hardening are interrelated with devegetation because hardening results from exposure following devegetation because both hardening and devegetation increase run off relative to infiltration and because hardening rain attack and run off impede vegetation devegetation is certainly worsened by harmful human activities such as range burning forest cutting and or overgrazing but tectonism and natural climatic aridification are probably ultimately more important given that many lavaka are simply a natural part of the landscape s evolution and that some lavaka clearly predate primary uncut rain forest

geologic and geophysical evidence for the influence of deep crustal structures on paleozoic tectonics and the alignment of world class gold deposits north central nevada usa abstract geologic data concur with geophysical and isotopic data that suggest the presence of deep crustal fault zones along the battle mountain eureka bme trend and elsewhere in nevada the fault zones may have originated during proterozoic rifting of the continent and were likely substantially reactivated and modified during paleozoic tectonism five distinct paleozoic structural and stratigraphic domains are defined that demonstrate the complexity of paleozoic tectonic events and also lead to hypotheses about ways in which the margin could have been modified the current locations of these domains adjacent to the geophysically and isotopically defined indicators of the buried continent edge corroborate their interactions with the continental margin during the tertiary preexisting crustal fault zones were intersected and reopened during episodes of extension and served as the conduits for deep sourced gold rich fluids which were disseminated into paleozoic slope facies sedimentary rocks forming sediment hosted carlin type and other deposits multiple factors including the locations of these deep seated structures the original configuration of the lower paleozoic continental margin of nevada and its subsequent reactivation during the paleozoic all were fundamental controls on the location of younger mineral deposits a clearer understanding of the original configuration of the margin and of the effects of subsequent paleozoic and mesozoic tectonic events on the margin would provide insight into the locations of these and other prospective mineral belts

morphometric analysis of sinkholes in a karst coastal area of southern apulia italy salento the southern portion of apulia region se italy is a narrow and elongated peninsula in carbonate rocks with prevailing low coastlines locally interrupted by high rock cliffs the long stretches of low coasts are marked by typical karst landforms consisting of collapse sinkholes as observed in many other karst coastal settings worldwide development of sinkholes may be particularly severe along the coasts where both natural and anthropogenic processes contribute to accelerate the dissolution of carbonate rocks and subsidence processes even influencing the coastline evolution following a previous study where the main features of sinkholes at torre castiglione taranto province were investigated and described and a preliminary susceptibility map produced at the light of updated data and elaborations in the present paper we perform a detailed morphometric analysis on the sample of identified sinkholes the main morphometric parameters generally used for sinkhole characterization have been considered in this study shape of the sinkhole azimuth and length of maximum and minimum axes depth elongation ratio and distance from the shorelines each of them is described both as individual parameter and in conjunction with the others in the attempt to identify the main factors controlling development of sinkholes in the area and their evolution as well with regard to this latter aspect beside simple morphometry of the sample of sinkholes at torre castiglione we also focused our attention on the likely relationships existing between distribution and shape of the sinkholes and the tectonic discontinuities to investigate the matter a three stage analysis has been carried out in this study by means of field measurements of the fractures bounding the sinkholes field measurement of the long axes azimuth of the elongated sinkholes comparison of the previously described sets with the strikes of the main regional geological structures the obtained results show in addition to the coincidence of the main regional discontinuity systems with the major axis of elongated sinkholes a clear control exerted by development and evolution of the sinkholes on the formation of coastal inlets and bays eventually the approach here presented may be applied in other karst coastal sinkhole prone areas to gain new knowledge on the genesis and evolution of coastal sinkholes and to properly evaluate the hazard they pose to the anthropogenic environment

applying spatial prospectivity mapping to exploration targeting fundamental practical issues and suggested solutions for the future abstract despite many decades of development spatial prospectivity modelling is not yet widely used or accepted throughout the global mineral exploration industry a common criticism of the method is that it is not practically useful because it has a bias to mature well known areas and generates excessively large areas of high prospectivity it is suggested that the reason for this is not primarily related to limitations in the prospectivity mapping algorithms but rather to issues relating to the use of input data sets specifically it is common that the input data such as geological interpretations do not uniformly and objectively represent the search space of interest omit critical targeting relevant geoscientific elements such as major deep seated ore controlling structures and have a large degree of unrecognised dependence it is considered that these problems are not in principle barriers to the eventual successful deployment of this technology however future approaches to spatial prospectivity modelling need to explicitly address these concerns it is suggested that the most effective method may be a hybrid of subjective human geological interpretation and objective machine based analysis that captures the best aspects of these alternative approaches i e an intelligence amplification ia rather than an artificial intelligence ai approach a roadmap is proposed for improving the effectiveness of spatial prospectivity modelling that has implications for the broader community interested in mineral exploration targeting

large scale fractures related to inception of the yellowstone hotspot during middle miocene time western north america was subject to flood basalt volcanism dike swarm injection and broad scale fracturing and folding of the crust we propose a simple model to account for these events and for a regional pattern of geologic and geophysical features aeromagnetic maps reveal some of the most important elements of this pattern which are several narrow arcuate anomalies here referred to as the northern nevada rifts these rifts extend hundreds of kilometers across nevada and are likely caused by highly magnetic middle miocene mafic dikes with the aid of filtering techniques the anomalies can be traced into oregon together with other geologic features such as fold axes dike swarms and faults they produce a spoke like pattern fanning over 2208 of arc that converges toward a point near the oregon idaho border lat 448n a possible cause for this pattern is a point source of stress at the base of the crust related to the formation of the yellowstone hotspot the spoke like pattern however does not persist at large distances from the emerging hotspot several hundred kilometers to the south the northern nevada rifts deviate significantly 308 from a radial trend we show that a simple model imposing a point source of stress at the base of the crust and a regional stress field aligned with the presumed middle miocene stress direction fits the observed fracture pattern it thus accounts for both the radial pattern present near the nascent hotspot and the far field pattern due to regional stresses

geological characteristics and ore forming process of the gold deposits in the western qinling region china the western qinling belonging to the western part of the qinling dabie sulu orogen between the north china block and south china block is one of the most important gold regions in china isotopic dates suggest that the mesozoic granitoids in the western qinling region emplaced during the middle late triassic and the deposits formed during the late triassic almost all gold deposits in the western qinling region are classified as orogenic carlin type and carlin like gold deposits and they are the products of qinling orogenesis caused by the final collision between the north china block and the south china block the early subduction of the mian lue oceanic crust and the latter collision between south qinling terrane and the south china block along the mian lue suture generated lithosphere scale thermal anomalies to drive orogen scale hydrothermal systems the collision related magmatism also provided heat source for regional ore forming fluids in the carlin like gold deposits orogenic gold deposits such as huachanggou liziyuan and baguamiao lie between the shang dan and mian lue sutures and are confined to wnw trending brittle ductile shear zones in devonian and carboniferous greenschist facies metasedimentary rocks that were highly deformed and regionally metamorphosed these deposits are typical orogenic gold deposits and formed within a late triassic age the deposits show a close relationship between au and ag ores contain mainly microscopic gold and minor electrum and visible gold along with pyrite the ore forming fluids were main metamorphic fluids intensive tectonic movements caused by orogenesis created fluid migrating channels for precipitation locations although some orogenic gold deposits occur adjacent to granitoids mineralization is not synchronous with magmatism that is the granitoids have no genetic relations to orogenic gold deposits as ore forming fluids converged into dilated fractures during the extension stage of orogenesis changes of physico chemical conditions resulted in fluid immiscibility that played a key role in gold and sulfide deposition the geochemical and mineralogical characteristics of the carlin type deposits in the western qinling region are similar to those in the carlin trend nevada usa gold deposits such as la erma and jinlongshan occur mostly in the southeastern margin of the western qinling regionic region whereas some deposits occur in its eastern part these deposits are hosted in slightly metamorphosed cambrian to triassic sedimentary rocks showing structurally and stratigraphically controlled features the deposits mainly contain submicroscopic and microscopic gold in arsenian pyrite and arsenopyrite with characteristic ore forming elements of au as sb ba the ore forming fluids are early stocked formation water and later recharged meteoric water meteoric water apparently evolved in ore forming fluids by circulation indicating the extensional setting and led to the deposition of au and other elements in cool reactive permeable rocks at shallow levels forming the disseminated ores carlin like gold deposits occur between the shang dan suture and the fengxian zhen an fault the host rocks are mainly sedimentary rocks that underwent reconstruction through reworking by structural metamorphism these deposits are structurally controlled by brittle ductile shear zone and occur adjacent to granitoid plutons the most important characteristic that differ to the orogenic and carlin type gold deposits is the genetic relationship with the synchronous magmatism gold occurs mainly as microscopic gold pyrite and arsenian pyrite can be recognized as gold bearing minerals the ore forming fluids are main magmatic water mixed with metamorphic and or formation water similar to orogenic gold deposits fluid immiscibility caused the deposition of gold carlin like gold deposits

regional study of mineral resources in nevada insights from three dimensional analysis of gravity and magnetic anomalies a three dimensional interpretation of the basins of nevada was developed based on statewide data bases of digital gravity magnetic geologic well and topographic information an iterative technique was applied to isostatic residual gravity anomalies in nevada in order to define the location and shape of pre tertiary basement and to produce a gravity map that reflects variations of density within the pre tertiary basement the dominant feature of the basement gravity of nevada is an enormous area of low gravity that spans the entire state between latitudes 37 n and 40 5 n this regional low strongly correlates with the distribution of middle and late tertiary volcanic rocks and may reflect silicic intrusions within the mid crust and upper crust that are the counterparts of volcanic rocks at the surface although 80 of nevada is covered by cenozoic deposits these deposits are thicker than 1 km over only about 20 of the state the remaining 60 of nevada may have pre tertiary basement rocks within reach of current mineral exploration techniques aeromagnetic profiles from the national uranium resource evaluation nure were analyzed in order to produce a map showing the location of shallow magnetic sources in nevada this analysis shows that 46 of the state has magnetic sources generally mesozoic and cenozoic igneous rocks within 1 km of the surface a linear magnetic anomaly in north central nevada has been interpreted by others as a rift zone active during middle miocene time the rift also is evident in nure magnetic profiles but our interpretation suggests that the magnetic expression of the rift continues south southeast with similar strike to at least 38 n and perhaps to the amagmatic zone lat 37 n the survival since the middle miocene of this narrow crustal feature essentially linear over a distance of 500 km is difficult to interpret in light of later basin and range deformation our analysis of gravity anomalies shows that many deep cenozoic basins are located near the rift yet only two basins cut across it and at least five others change strike near the rift as if to avoid it the rift may have remained linear because it is associated with crustal structures that acted to resist subsequent deformation

part 1 regional studies and epithermal deposits northern nevada is one of the earth s premier gold and silver producing regions and gold and silver are mined from a wide range of deposit types table 1 current production largely comes from carlin type sedimentary rock hosted disseminated gold deposits christensen 1995 teal and jackson 1997 bettles 2002 many of which lie along linear trends fig 1 roberts 1960 1966 berger and bagby 1991 the small area of the carlin trend approximately 8 x 65 km is north america s most prolific gold mining district producing nearly 125 t 4 moz of gold annually since large scale mining began in 1965 with the opening of the carlin mine the carlin trend has produced more than 1555 t 50 moz of gold during 2001 gold production from the entire state of nevada was nearly 253 t 8 13 moz which accounted for approximately 76 percent of the united states and 10 percent of the world production price and meeuwig 2002 in 2001 only the countries of south africa and australia produced more gold than the state of nevada in addition nevada produced 543 t 17 4 moz of silver in 2001 about 31 percent of the united states production and 3 percent of the world production in 1996 the mineral resources program of the u s geological survey began a multidisciplinary project to investigate the origin of gold deposits in northern nevada this project was undertaken in collaboration with the nevada bureau of mines and geology the ralph j roberts center for research in economic geology at the university of nevada reno several other universities and numerous mining companies active in the region in addition several universities and mining companies were conducting research on the origin of gold deposits in northern nevada this research built on more than a century of studies by the

the use of gis based digital morphometric techniques in the study of cockpit karst cockpit karst landscapes are among the most distinctive landscapes in the world and have been the focus of long standing scientific interest early researchers used largely descriptive techniques to categorize the terrain and subsequent work has not attempted to critically re evaluate descriptions of landscapes using more sophisticated methods the distinctive surface topography of cockpit karst areas can be characterized in order to compare them with other karst as well as non karst areas and to determine geological and or climatic conditions that are responsible for the observed terrain process models of the rate of karst denudation or evolution can only be accurate if the contemporary morphology of the landscape is quantitatively and unambiguously defined a detailed analysis of cockpit karst terrain is carried out using the latest gis based digital morphometric techniques in order to assess the nature of such terrain and provide further information for subsequent modelling as well as other non geomorphological applications such as environmental management and conservation issues the paper presents the methodology used for the digital analysis of terrain and landforms in the distinctive cockpit country area of jamaica and its environs the results indicate that cockpit karst may be categorized based on its vertical horizontal and shape characteristics as well as by looking at the semivariogram slope characteristics and landscape relief scale which combine measures of vertical and horizontal scales copyright 2006 john wiley sons ltd

the moho in the northern basin and range province nevada along the cocorp 40 n seismic reflection transect cocorp seismic reflection profiles across nevada at about 40 n image a prominent essentially continuous band of reflectors at a two way traveltime of 9 to 11 s the approximate correspondence of this reflection time with estimates of the two way traveltime to the moho in this area provided by seismic refraction data suggests that the prominent reflections are from the moho the relief on these reflectors the reflection moho beneath nevada across a latitudinal transect of

special paper major gold deposits and belts of the north and south american cordillera distribution tectonomagmatic settings and metallogenic considerations a compilation of economically viable gold concentrations containing 10 moz in the north and south american cordillera reveals the existence of 22 discrete belts in addition to five major isolated deposits most formed over the last 150 m y the gold concentrations are attributed to eight widely recognized deposit types of which porphyry sediment hosted and high sulfidation epithermal are economically the most important individual gold belts are typically several tens to hundreds of kilometers long dominated by single deposit types and metallogenically active for relatively brief periods 5 20 m y many of the gold belts and major isolated deposits were generated under extensional or transtensional tectonic conditions in either arc or back arc settings nevertheless the two main high sulfidation epithermal gold belts were generated in thickening or already thickened crust during low angle subduction eight other gold belts or districts also accompanied compression or transpression with two of them the main orogenic gold belts occupying fore arc sites there is a strong suggestion that the preeminent cordilleran gold concentrations formed either during or immediately following prolonged contraction the major gold deposits and belts occur along the craton edge as well as in adjoining accreted terranes but almost all are of postaccretionary timing many of the gold belts and isolated deposits were localized by crustal scale faults or lineaments which may be either parallel or transverse to the cordilleran margin the gold concentrations accumulated during active subduction commonly in close spatial and temporal association with intermediate to felsic medium to high k calc alkaline igneous rocks by contrast the low sulfidation epithermal gold deposits accompany bimodal volcanic pulses of calc alkaline tholeiitic or alkaline affinity however a gold alkaline rock association is uncommon a genetic link between gold mineralization and coeval magmatism is widely accepted for most of the deposit types the exceptions being the sediment hosted and orogenic gold deposits notwithstanding the small cumulative extent of the gold concentrations relative to the entire cordilleran margin there is a marked tendency for two or more belts or isolated deposits of different ages and genetic types to occur in close proximity within relatively restricted arc including fore and back arc segments in the case of the western united states for example six belts and four isolated major deposits make up a particularly prominent cluster if fortuity is discounted this clustering or pairing of gold concentrations must imply a predisposition of certain arc segments to gold mineralization an analogous situation is evident for other metals particularly copper and tin the reason for the recurrent generation of major deposits and belts dominated by one or more metals remains uncertain although heterogeneously distributed metal preconcentrations favorable redox conditions or other parameters somewhere above the subducted slab between the mantle wedge and upper crust are widely contemplated possibilities elucidation of the reason s for this metallogenic inheritance at the scale of limited arc segments poses an important and challenging series of research questions as well as being critical to the planning of potentially successful greenfield exploration programs

gold in turkey a missing link in tethyan metallogeny abstract the gold metallogeny of turkey constitutes a sector of the tethyan eurasian metallogenic belt temb within the alpine himalayan orogenic system that formed from jurassic cretaceous to the present this orogenic system produced many different types of deposits related to subduction collision post collision and rifting processes gold deposits as well as other mineral deposits of turkey are mainly concentrated in late mesozoic and tertiary rocks evaluation of the gold metallogeny of turkey is based on a gis database compilation of known gold deposits and prospects currently available data show that turkey has a gold endowment including reserves and resources of approximately 31 5 m oz 979 tonnes in 51 deposits 21 of which contain more than 0 2 m oz gold the other 30 deposits contain a total of approximately 1 m oz 31 tonnes gold resources two recent discoveries kisladag and copler currently contain total resources of 17 6 m oz au 549 tonnes more than 50 of the total turkish gold endowment turkey possesses a wide spectrum of gold deposits related to mesozoic and cenozoic volcanoplutonic arcs however porphyry gold copper epithermal gold including both high and low sulfidation styles and gold rich volcanic associated massive sulfide including both kuroko and cyprus types are the most economically important to date orogenic gold including listwanite hosted placer gold and skarn hosted gold are relatively less important or abundant deposit types other potential gold systems for exploration include carlin type gold detachment fault related gold iron oxide copper gold and gold in carbonate replacement and manganese deposits

crustal structure in the elko carlin region nevada during eocene gold mineralization ruby east humboldt metamorphic core complex as a guide to the deep crust the deep crustal rocks exposed in the ruby east humboldt metamorphic core complex northeastern nevada provide a guide for reconstructing eocene crustal structure 50 km to the west near the carlin trend of gold deposits the deep crustal rocks in the footwall of a west dipping normal sense shear system may have underlain the pinon and adobe ranges about 50 km to the west before tertiary extension close to or under part of the carlin trend eocene lakes formed on the hanging wall of the fault system during an early phase of extension and may have been linked to a fluid reservoir for hydrothermal circulation the magnitude and timing of paleogene extension remain indistinct but dikes and tilt axes in the upper crust indicate that spreading was east west to northwest southeast perpendicular to a paleozoic and mesozoic orogen that the spreading overprinted high geothermal gradients associated with eocene or older crustal thinning may have contributed to hydrothermal circulation in the upper crust late eocene eruptions upper crustal dike intrusion and gold mineralization approximately coincided temporally with deep intrusion of eocene sills of granite and quartz diorite and shallower intrusion of the harrison pass pluton into the core complex rocks stacked mesozoic nappes of metamorphosed paleozoic and precambrian rocks in the core complex lay at least 13 to 20 km deep in eocene time on the basis of geobarometry studies in the northern part of the complex the presently exposed rocks had been even deeper in the late mesozoic to 30 km depths before losing part of their cover by eocene time nappes in the core plunge northward beneath the originally thicker mesozoic tectonic cover in the north part of the core complex mesozoic nappes and tectonic wedging likely occupied the thickened midlevel crustal section between the deep crustal core complex intrusions and nappes and the overlying upper crust these structures as well as the subsequent large displacement cenozoic extensional faulting and flow in the deep crust would be expected to blur the expression of any regional structural roots that could correlate with mineral belts structural mismatch of the mineralized upper crust and the tectonically complex middle crust suggests that the carlin trend relates not to subjacent deeply penetrating rooted structures but to favorable upper crustal host rocks aligned within a relatively coherent regional block of upper crust

surface seismic and electrical methods to detect fluids related to faulting in the absence of drilling surface based geophysical methods are necessary to observe fault zones and fault zone physical properties at seismogenic depths these in situ physical properties can then be used to infer the presence and distribution of fluids along faults although such observations are by nature indirect and become less exact with greater depth multiple observations of a range of such geophysical properties as compressional and shear seismic velocity vp and vs vp v5 ratio related to poisson s ratio resistivity and attenuation in and adjacent to fault zones offer the greatest hope of making inferences of the fault zone geometry fluids in the fault zone and fluid reservoirs in the surrounding crust for simple geometries fault zone guided waves can provide information on fault zone width and velocities for faults of the order of 200 m wide to address the question of whether a narrow fault zone can be imaged well enough at depths of seismic rupture to infer the presence of anomalously high fluid rock ratios we present synthetic seismic tomography and magnetotelluric examples for an ideal case of a narrow fault zone with a simple geometry large changes in material properties and numerous earthquakes within the fault zone a synthetic 0 5 km wide fault zone with 20 velocity reduction is well imaged using local earthquake tomography when sequential velocity inversions are done the true fault width is found even to 9 km depth although the calculated amplitude of the velocity reduction is lower than the actual amplitude vp vs is as well determined as vp magnetotelluric imaging of a synthetic fault zone shows that a conductive fault zone can be well imaged within the upper 10 km further a narrow 1 km very low resistivity 3 ohm m fault core can be imaged within a broad 5 km low resistivity 10 ohm m fault zone illustrating that regions of a fault containing large quantities of interconnected fluids within a broader conductive fault zone should be detectable thus variations in fluid content and fluid pressure can be inferred from electrical and seismic methods but there will always be uncertainty in these inferences due to the trade off with other factors such as intrinsic variations in porosity mineralogy and pore geometry the best approach is combined modeling of varied seismic and electrical data

array tracking of infrasonic sources at stromboli volcano 1 infrasonic arrays are a powerful tool for volcanic monitoring and hazard assessment explosions were recorded at stromboli using a small aperture array of 4 infrasonic stations allowing precise vent location the acoustic signals were delayed and summed revealing the existence of two main groups of infrasonic waves the ne crater produces short 3 s high amplitude 20 80 pa pressure waves while the sw crater produces small acoustic pressure 10 30 pa with long 5 15 s coda the two groups reflect different in explosive styles and similar spectral content centered on 5 6 hz when stacked together acoustic waveforms for each crater reveal the same pressure pulse which indicates a common source process we infer that the acoustic onset at both craters is generated by the burst of a large gas bubble while the acoustic coda is controlled by a sustained pressure release

tectonic accretion and underplating of mafic terranes in the late eocene intraoceanic fore arc of new caledonia southwest pacific geodynamic implications this paper deals with the tectonic events that result in the accretion of mafic terranes in the fore arc region and a close juxtaposition of ultramafic rocks low grade and high grade mafic terranes in many collisional orogens the example is taken from new caledonia where tectonic accretion subduction underplating and obduction of mafic terranes took place during the late eocene in an intra oceanic forearc setting the late eocene tectonic complex comprised three major terranes an overlying ultramafic mainly harzburgitic allochthon named the ophiolitic nappe an intermediate mafic mainly basaltic off scraped melange composed of kilometre scale slices of oceanic upper crust called the poya terrane parts of which have been metamorphosed into an eclogite blueschist facies complex the pouebo terrane and a lower continental basement formed by the norkolk ridge terranes based upon exhaustive sampling of the mafic terranes and field surveys our tectonic micropaleontologic and geochemical data reveal that poya and pouebo terranes rocks originally formed within one single campanian to late paleocene oceanic basin floored by tholeiitic basalt associated with some minor seamount related intraplate alkali basalt the tholeiitic basalt displays a continuous range of compositions spanning between undepleted and depleted end members the former being volumetrically predominant the overall geochemical and isotopic features indicate an origin from a prominently heterogeneous mantle source during the opening of a marginal basin the south loyalty basin which almost completely disappeared during eocene convergence the opening of this basin originally located to the east of the norfolk ridge was synchronous with that of tasman sea basin as a consequence of oceanward migration of the west dipping pacific subduction zone establishing the origin of the ultramafic ophiolitic nappe is beyond the scope of this paper however it appears to be genetically unrelated to the mafic poya and pouebo terranes although it was located in the late eocene fore arc the ophiolitic nappe and the corresponding oceanic lithosphere originated before the late cretaceous to the east of the south loyalty basin in a back arc setting or alternatively in a much older trapped basin for reasons that remain unclear a new east dipping subduction started in the eocene and consumed most of the south loyalty basin forming the intra oceanic loyalty arc due to a changing subduction regime underplating of the diahot terrane the mafic slices that now form the poya terrane were tectonically accreted in the loyalty fore arc region and remained under low pressure low temperature conditions possibly at the subsurface until the norfolk ridge reached the subduction zone diachronously this resulted in the final obduction of the fore arc area the two step obduction involved first the mafic complex forming the poya terrane and thereafter the lithospheric mantle that now forms the ophiolitic nappe in contrast pieces of the accretionnary complex were dragged down into the subduction zone underplated at depth ca 70 km and metamorphosed into high temperature eclogite to form the pouebo terrane metamorphics that display the same geochemical features as the poya terrane basalt a mid to late eocene syntectonic piggy back sedimentary basin the nepoui flysch basin mainly filled with mafic clastic material and shallow water carbonates that record the progressive uplift of the fore arc region due to the accretion and underplating of mafic ocean related and other material in contrast a slightly younger foreland basin located upon the norfolk ridge the priabonian bourail flysch basin received a massive input of detrital material derived from the norfolk ridge itself and a time increasing amount of mafic poya derived material that recorded the first step of obduction thereafter the bourail flysch was overthrust by the poya terrane and finally by the ophiolitic nappe at the same time buoyancy driven uplift and exhumation of the high pressure metamorphic complex occurred as a consequence of the diachronous blocking of the subduction zone finally for a short time a new subduction started along the west coast of new caledonia and generated small amounts of active margin related magmas these events have resulted in the close juxtaposition of unmetamorphosed and highly metamorphosed mafic and ultramafic terranes that may represent a good pre collision analogue of mafic ultramafic belts found in many collisional mountain ranges

geochemical and geochronological constraints on mineralization within the hilltop lewis and bullion mining districts battle mountain eureka trend nevada the hilltop lewis and bullion mining districts located within the northern shoshone range lander county nevada are part of the greater battle mountain eureka trend historic production of mostly ag with au cu pb and zn from all three districts exploited 3 m wide quartz veins hosted mainly within upper plate ordovician devonian siliceous and siliciclastic rocks of the roberts mountains allochthon eocene felsic intrusive rocks located both proximal and distal to the vein deposits were emplaced throughout the northern shoshone range along a west northwest trend molybdenite mineralization is associated with some intrusive rocks and some intrusive rocks host vein type mineralization new and previously published radiometric ages for primary igneous minerals from unaltered rocks within and or proximal to mineralized areas are nearly coincident with published re os ages for several northern shoshone range molybdenite occurrences 40 1 0 6 ma avg supporting a relationship between pluton emplacement and molybdenite mineralization age differences between quartz vein hosted gold base metal mineralization e g 38 3 0 1 ma gray eagle mine bullion district and nearby intrusive rocks e g 39 0 0 1 ma granite mountain imply that vein mineralization probably formed during prolonged hydrothermal activity synchronous with or subsequent to igneous rock emplacement or from heat associated with a second slightly younger phase of intrusive igneous activity primary fluid inclusion salinity 0 6 4 wt nacl equiv and th 115 425 c data from ore bearing vein quartz in conjunction with measured 18ovsmow data 0 97 to 17 3 indicate that vein forming fluids contained variable mixtures of magmatic and meteoric components calculated 18ovsmow values of 16 0 to 13 3 and spanned the epithermal porphyry temperature continuum new and previously published stable isotope c o and s data from vein hosted ore and gangue minerals unaltered and altered siliceous upper plate host rocks and unaltered carbonate lower plate and upper plate rocks indicate mixed and variable sources of vein hosted ore and gangue components and variable interaction between some vein forming fluids and nonsiliceous rock types carbonates bedded barite that underlie the northern shoshone range large vein widths high vein densities and lack of evidence supporting fluid boiling in primary fluid inclusions suggest that vein deposits of the northern shoshone range probably formed at shallow depths 1 km under lithostatic conditions geochronology and stable isotope data support a temporal and genetic link between eocene magmatism quartz vein hosted precious and base metal mineralization and molybdenite porphyry mineralization within the hilltop lewis and bullion mining districts

approximating edges of source bodies from magnetic or gravity anomalies cordell and grauch 1982 1985 discussed a technique to estimate the location of abrupt lateral changes in magnetization or mass density of upper crustal rocks the final step of their procedure is to identify maxima on a contoured map of horizontal gradient magnitudes we attempt to automate their final step our method begins with gridded magnetic or gravity anomaly data and produces a plan view of inferred boundaries of magnetic or gravity sources the method applies to both local surveys and to continent wide compilations of magnetic and gravity data e g zietz 1982 simpson et al 1983a kane et al 1982

relationship of epithermal gold deposits to large scale fractures in northern nevada geophysical maps of northern nevada reveal at least three and possibly six large scale arcuate features one of which corresponds to the northern nevada rift that possibly extends more than 1 000 km from the oregonidaho border to southern nevada these features may reflect deep discontinuities within the earth s crust possibly related to the impact of the yellowstone hot spot because mid miocene epithermal gold deposits have been shown to correlate with the northern nevada rift we investigate the association of other epithermal gold deposits to other similar arcuate features in northern nevada mid miocene and younger epithermal goldsilver deposits also occur along two prominent aeromagnetic anomalies west of the northern nevada rift here we speculate that mid miocene deposits formed along deep fractures in association with mid miocene riftrelated magmatism and that younger deposits preferentially followed these preexisting features statistical analysis of the proximity of epithermal gold deposits to these features suggests that epithermal gold deposits in northern nevada are spatially associated with large scale crustal features interpreted from geophysical data

earliest eocene 53 ma convergence in the southwest pacific evidence from pre obduction dikes in the ophiolite of new caledonia uncertainty about the timing and location of the initiation of convergence in the western and south western pacific greatly hinders accurate plate tectonic reconstructions of subduction systems in that area the chemistry and age of dikes intruding mantle peridotite in the ophiolite of new caledonia infer that subduction related magmatism began before 53 ma these new results infer that obduction in the south west pacific is unrelated to the reorientation of the pacific plate motion that occurred c 43 ma and confirm new interpretations showing that changes in mantle flow hotspot and plate motion may have occurred as soon as late paleocene or early eocene

a relation among geology tectonics and velocity structure western to central nevada basin and range in the northwestern to central nevada basin and range there are correlations between velocity and specific geologic structures of the crust mapped range bounding faults at the surface can be traced to appreciable 10 km depths based on velocity variations and are consistent with subsurface projections of the faults based on seismic reflection images the limiting depth of the faults as indicated by the velocity variations corresponds to the maximum depth of earthquakes along the seismic profile correlations between velocity and the surface geology show that in the upper crust the pre cenozoic rocks are underlain by high velocity 6 0 km s rocks whereas the tertiary ranges are underlain by lower velocity 4 0 5 7 km s rocks to depths as great as 10 km although the tertiary rocks differ in composition from the mesozoic rocks the lower velocity tertiary rocks may also be attributed to rock masses which are broken 4 0 5 7 km s and the higher velocity mesozoic rocks 6 0 km s may be attributed to largely unbroken rock masses the regional seismicity pattern is consistent with this interpretation as earthquakes are largely confined within or near the base of the low velocity rocks these low velocity highly fractured rocks are laterally distributed in discrete zones suggesting that extension is not uniformly distributed but occurs in discrete highly extended zones beneath these highly extended zones the lower crustal layers show structural evidence of extension and velocity measurements suggest that the lowermost crust has been magmatically underplated the superposition of tertiary volcanic rocks highly fractured upper crust and lower crustal magmatic underplating suggests that the tertiary volcanic rocks originated from lower crustal magmas that migrated to the surface via the highly extended zones the velocity structure of one of the highly extended zones and the lahonton basin resembles that of many continental rifts the velocity structure beneath central nevada however is much more like normal continental crust on the basis of isotopic studies it is concluded that the transition between highly extended crust and more normal crust occurs in the area inferred to be the edge of the north american craton

constraints of deep crustal structures on large deposits in the cloncurry district australia evidence from spatial analysis abstract deep structures are commonly recognized as critical factors for controlling the formation of large hydrothermal deposits it is of great importance for the metallogenic studies to quantitatively describe the spatial associations of deep structures with mineral deposits in the cloncurry district of the mt isa province australia many large deposits have been discovered and district scale deep structures have also been recognized from the magnetic gravity seismic and magnetotelluric data in this paper we delineate the 3d configuration of the deep structures by 3d geometric modeling and gaussian curvature analysis and quantify spatial associations of the deep structures with the large deposits by the weights of evidence method the results demonstrate that the configuration of deep structures has a positive spatial constraint on the distribution of deposits many deposits are located close to the high curvature portion of the deep structures according to this rule there are some potential target areas where curvature of the deep structural surfaces is high but no deposits have been discovered such results can be used to identify targets with potential for finding undiscovered deposits

morphology and distribution of dolines on ultramafic rocks from airborne lidar data the case of southern grande terre in new caledonia sw pacific dolines are closed geomorphological depressions which are surface manifestations of karstic systems usually developed on limestones they also typify the morphology of the new caledonian landscape particularly on the southern massif of the main island known as massif du sud the specificity of dolines here lies in their development on ultramafic rocks they are evidences of subsidence suffosion and collapse phenomena resulting from dissolution weathering of peridotites however extensive underground drainage systems are still not yet recognized copyright 2016 john wiley sons ltd semi automatic mapping of dolines is carried out on a 148 km2 area of the massif du sud from a high accuracy lidar digital elevation model in this area 8601 dolines ranging from 1 m2 to 2 km2 are identified and morphologically characterized with precision most are small shallow and round shaped yet more complex shapes are locally observed size distribution analysis allows the setting of a threshold of 20 000 m2 above which surface processes rather than chemical weathering control doline evolution doline density analysis reveals high concentrations on flat areas where ferricrete overlies the complete weathering profile especially in the case of elevated rainy watersheds dolines are aligned and elongated along a north 135 5 major fracture direction which is inherited from the obduction of the pacific plate upper mantle in the late eocene copyright 2016 john wiley sons ltd finally we propose a pioneering morphometric typology of dolines that provides important clues as to pseudokarstic activity we define collapse bowl shaped and flat bottom dolines collapse and bowl shaped dolines are assumed to denote active pseudokarst they may widen and deepen or eventually be filled by sediments they are distinguished from flat bottom dolines that are partially to completely filled which suggests that they are associated with paleo pseudokarsts however the groundwater flow paths associated with the genesis and evolution of dolines must be clarified thus collapse and bowl shaped dolines should be hydrologically monitored copyright 2016 john wiley sons ltd

prospectivity analysis of orogenic gold deposits in saqez sardasht goldfield zagros orogen iran abstract diverse deposit types or mineral systems form by diverse geological processes so translation of knowledge about the controls of mineralization acquired from the 4d geological modeling into 2d spatial predictor maps is a major challenge for prospectivity analysis in this regard mathematical functions have been used to model the conceptual or perceived spatial relationships between geological variables and targeted type or system of mineralization in this paper due to the different models of spatial relationships between predictors and mineral deposits we investigated the performance of different fuzzification functions to quantify the relationships we demonstrated that various types of relationships between exploration features and a mineralization type sought could be quantified using different fuzzification functions for prospectivity analysis we illustrated the process of the prospectivity analysis by using a data set of orogenic gold deposits in saqez sardasht goldfield iran prospectivity modeling of orogenic gold mineralization in the study area showed that the ne sw trending targets have priority for further prospecting of the deposits

spatial distribution and alignments of volcanic centers clues to the formation of monogenetic volcanic fields monogenetic basaltic volcanic fields occur worldwide in tectonic environments ranging from extensional to convergent understanding similarities and differences between these fields may help to characterize key controls on their generation such volcanic fields consist of numerous volcanic centers each of which represents a pathway of magma from its source to the surface we analyzed the spatial distribution of volcanic centers in 37 monogenetic volcanic fields and assuming that the distribution of volcanic centers relative to each other is matched by a similar source pattern within the mantle applied the following methods for each 1 the poisson nearest neighbor pnn analysis representing the degree to which the distribution of the volcanic centers departs from a predicted poisson distribution and 2 a volcanic alignment analysis to ascertain the preferential pathways if any used by the magma to reach the surface this is the first comprehensive global comparison of such analyses magma pathways within the brittle upper crust are influenced to various degrees by two end member situations 1 formation of new extension fractures perpendicular to the least compressive stress 3 and 2 re activation of pre existing fractures that are near parallel to the maximum principal stress 1 the results of the pnn analysis show that independently of the tectonic environment most volcanic fields display a clustered distribution of their volcanic centers alignment analysis shows that either the ambient tectonic environment exerts a strong influence on the preferential orientations of the volcanic alignments or that it is in competition with other factors e g pre existing structures local stress changes due to older intrusions overall these results indicate that the propagation of the magma and therefore the spatial distribution of the volcanic centers within volcanic fields is the product of an interplay between deep level influences i e nature of the magma source and shallow level influences i e stress field pre existing crustal structures of the lithosphere

the northern nevada rift regional tectono magmatic relations and middle miocene stress direction as defined by the most recent aeromagnetic surveys the north northwest trending northern nevada rift zone extends for at least 500 km from southern nevada to the oregon nevada border at several places along the rift the magnetic anomaly is clearly related to north northwest trending dikes and flows that based on new radiometric dating erupted between 17 and 14 ma and probably during an even shorter time interval the tectonic significance of the rift is dramatized by its length its coincidence in time and space at its northern terminus with the oldest silicic caldera complex along the yellowstone hot spot trend and its parallelism with the subduction zone along the north american coast prior to the establishment of the san andreas fault the northern nevada rift is also equivalent in age trend and composition to feeder dikes that fed the main eruptive pulse 95 volumetrically off the columbia river flood basalts in northern oregon 15 5 16 5 ma because of these similarities both regions are considered to be part of an enormous lithospheric rift that propagated rapidly south southeast and north northwest respectively from a central mantle plume the site of the initial breaching of the north america plate by this plume is probably the mcdermitt volcanic center at the north end off the rift near the oregon nevada border the present north northwest trend of the rift and its internal elements such as dikes and lava filled grabens record the orientation of the arc normal extensional stress in this back arc region at the time of emplacement paleomagnetic evidence presented by others and interpreted to indicate block rotations at three sample localities is not consistent with either a rotation of dikes within the rift or with a regional rotation of the entire rift the present north northwest trend of the rift reflects the state of stress in the basin and range during middle miocene time and is consistent with stress indicators of similar age throughout the basin and range and rio grande rift provinces