sequence age and source of silicic fallout tuffs in middle to late miocene basins of the northern basin and range province the latest cenozoic 6 ma ash beds in the western united states have been intensively studied for several decades the more widespread of these ash beds are well documented event horizons that are of great value in studies of the timing and pace of geological climatological and biological events throughout the region because explosive volcanism was not restricted to latest neogene time in this region many older ash beds are likely to prove as useful as younger beds as event horizons once they are located characterized and dated as a first step in developing a useful chronology of older cenozoic ash beds in the western united states we have sampled and analyzed silicic fallout tuffs in middle to late miocene sedimentary basins across the northern basin and range province the northern basin and range basins ideally situated in the vicinity of major coeval silicic volcanic centers contain numerous relatively unaltered silicic fallout tuffs we have correlated tuffs between all sampled sections on the basis of glass shard composition the composite stratigraphic sequence established by the correlations contains more than 200 individual tuffs including 59 widely distributed tuffs termed correlative tuffs the tuffs vary widely in composition but most are in one of two compositional groups gray metaluminous vitric tuffs gm tuffs or white metaluminous vitric tuffs wm tuffs distribution patterns compositional characteristics and correlation with ash flow tuffs show that the source for most gm tuffs was the snake river plain volcanic province along the northern edge of the northern basin and range and the source for most wm tuffs was the southwestern nevada volcanic field in the southern part of the northern basin and range the northern basin and range tuffs range in age from ca 16 6 ma the ages of individual tuffs are determined variously by direct isotopic dating by correlation to previously dated fallout and ash flow tuffs or by interpolation age estimation ages for most tuffs are known to within 0 25 m y 1 or less and for many tuffs to within 0 1 m y or less the sequence and ages of tuffs established in this study provide insights into the evolution of the northern basin and range basins and patterns of explosive volcanism in coeval volcanic centers and contribute to the development of a high resolution stratigraphy and chronology of coeval sedimentary deposits throughout the western united states

mesozoic plate motion history below the northeast pacific ocean from seismic images of the subducted farallon slab the high resolution seismic imaging of subducted oceanic slabs1 2 has become a powerful tool for reconstructing palaeogeography3 the images can now be interpreted quantitatively by comparison with models of the general circulation of the earth s mantle4 here we use a three dimensional spherical computer model of mantle convection5 6 to show that seismic images of the subducted farallon plate provide strong evidence for a mesozoic period of low angle subduction under north america such a period of low angle subduction has been invoked independently to explain rocky mountain uplift far inland from the plate boundary during the laramide orogeny7 the computer simulations also allow us to locate the largely unknown kula farallon spreading plate boundary the location of which is important for inferring the trajectories of suspect terrain across the pacific basin8

spatial and temporal distribution of gold deposits in the urals during the past 10 years the paleozoic urals mountain belt has been the subject of internationally based deep seismic and ancillary geologic studies aimed at improving our knowledge of the lithospheric evolution of the orogenic belt in general and its prominent crustal root in particular in view of its wide ranging mineral endowment especially for gold this work also provides important keys to help clarify relationships between collisional tectonic processes and gold mineralization following an outline of current ideas on the tectonic evolution of the urals we present an overview of the distribution of the majority of known gold deposits this information together with the available isotopic and geologic age data of associated alteration assemblages is compared to available geochronological data for various magmatic and deformation episodes spatial and temporal relationships suggest that hydrothermal mineralizing processes and the geodynamic evolution of the orogen are linked in an attempt to analyze the deep structural framework of the orogen down to the mantle we have also examined a number of subcontinental and regional scale continuous geophysical datasets the urals have been subdivided traditionally into a series of north south striking tectonic zones but more recently into three principal tectono magmatic sectors which comprise a suture sector along the main uralian fault zone and two sectors with tectonically imbricated island arc transitional viewed as active continental margin and continental zones gold deposits are found in all tectono magmatic sectors of the orogen minor gold occurs in siluro devonian volcanic hosted massive sulfide deposits magnetite copper skarns and porphyry copper deposits in a number of cases younger structures shear zones faults and their intersections have controlled the deposition of higher gold grades in the urals this has led to the concept of progressive concentration of gold during later tectonic overprinting and the understanding that regional deformation and hydrothermal fluid rock interaction in the late carboniferous to early triassic upgraded gold contents of earlier deposits during the late carboniferous to early triassic gold bearing quartz vein lodes which effectively encompass the majority of the larger gold deposits in the urals were also formed in structural chemical traps some deposits such as mindyak that is hosted by tectonic melanges along the main uralian fault zone are clearly typical late orogenic lode gold deposits others occur within and along the margins of early to middle carboniferous older granite and although local orthomagmatic relationships have been described most recent observations now favor a strong structural control on the lodes and no direct genetic association with granite intrusion in the two largest gold deposits kochkar and berezovskoe gold mineralization was controlled by structural and combined structural chemical traps in dilational jogs in both shear and contact zones locally gold mineralization has been shown to occur during a change from orthogonal to transpressional compression the inferred ages of the lode gold deposits suggest they are mostly coeval with the generally undeformed permian early triassic younger granites however a spatial relationship with gold mineralization has not been observed the younger granites were formed in an extensional regime following ural wide magma generation caused by a thermal flux attributed to underplating of the crust by mantle derived mafic magmas the widespread distribution of this late thermal event during changes in stress regime and the involvement of magma generating mantle processes suggest regional delamination in the lithosphere and concomitant upwelling of the asthenosphere these processes may have largely occurred prior to the formation of the prominent crustal root of the urals which formed during subsequent transpressional convergence another triassic ural wide phase of hydrothermal alteration has been recognized but associated gold deposits have been documented in only two cases we tentatively attribute this phase to destabilization of the lithosphere of the wider altaids reflected by the formation of the west siberian and central asian basins east of the urals during the mesozoic the integrated analysis of magnetic bouguer gravity heat flow and crustal thickness data suggests that a major indenter of the east european craton is responsible for a singular transcrustal sidewall ramp in the subsurface of the middle urals this ramp may extend into the mantle and formed the principal conduit zone for mineralizing fluids the world class kochkar and berezovskoe gold deposits are adjacent to this proposed conduit

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

origin of the columbia plateau and snake river plain deflection of the yellowstone plume previous models relating the snake river plain and columbia river basalt northwest united states to the yellowstone plume have not taken into account the effects of the subducted farallon and juan de fuca plates not only did subduction shield the surface from mantle plume activity but it deflected the plume in the direction of plate motion a variety of geophysical and geologic evidence suggests that the plume penetrated the subducted slab at 17 5 ma causing eruption of the columbia river basalt the plate boundary then migrated over the plume and the yellowstone plume has recovered to a more nearly vertical conduit forming the snake river plain and yellowstone plateau

geodynamic setting of the mineral deposits of the urals the first order geodynamic domains of the uralide orogen constitute a relatively simple pattern across the orogenic belt continental rifting along the western margin is expressed by a system of vendian early palaeozoic structures with shale hosted siderite and magnesite and basalt hosted base metals it is superimposed on a middle riphean rift system with layered mafic ultramafic complexes with chromite and ilmenite titano magnetite and subordinate ophiolite massifs with gold and magnetite an oceanic spreading domain immediately east of the main uralian fault is associated with chromite titano magnetite and massive sulphide deposits dombarovsky or cyprus type further east bimodal volcanic associations in island arcs with oceanic crust have formed copper zinc massive volcanic sulphide deposits uralian type subsequently complex volcanic sulphide deposits are associated with belts of andesite dacite and co magmatic diorite baymak or kuroko type the eastern destructive margin of the orogen is characterized by magnetite and copper magnetite skarns and porphyry systems relatively small plagiogranite to granodiorite complexes related to oceanic crust carry scheelite and gold calc alkaline granitic massifs have formed associations of tungsten tantalum and beryllium this pattern was dissected by major thrusts and transcurrent shear zones increased fluid activity in the course of deformation inferred to have been involved in complex multi phase gold mineralization was most probably controlled by deep reaching faults and shears although the recognition of the first order domains represents a guideline for exploration detailed structural geological studies of the kinematics of the major faults and shear zones are required in conjunction with radiometric dating of suitable fault and ore associated minerals in association with on going deep reaching geophysical investigations

local magnitude determinations for intermountain seismic belt earthquakes from broadband digital data the university of utah seismograph stations uuss earthquake catalogs for the utah and yellowstone national park regions contain two types of size measurements local magnitude m l and coda magnitude m c which is calibrated against m l from 1962 through 1993 uuss calculated m l values for southern and central intermountain seismic belt earthquakes using maximum peak to peak p p amplitudes on paper records from one to five wood anderson w a seismographs in utah for m l determinations of earthquakes since 1994 uuss has utilized synthetic w a seismograms from u s national seismic network and uuss broadband digital telemetry stations in the region which numbered 23 by the end of our study period on 30 june 2002 this change has greatly increased the percentage of earthquakes for which m l can be determined it is now possible to determine m l for all m 3 earthquakes in the utah and yellowstone regions and earthquakes as small as m to maintain continuity in the magnitudes in the uuss earthquake catalogs we determined empirical m l station corrections that minimize differences between m l s calculated from paper and synthetic w a records application of these station corrections in combination with distance corrections from richter 1958 which have been in use at uuss since 1962 produces m l values that do not show any significant distance dependence m l determinations for the utah and yellowstone regions for 1981 2002 using our station corrections and richter s distance corrections have provided a reliable data set for recalibrating the m c scales for these regions our revised m l values are consistent with available moment magnitude determinations for intermountain seismic belt earthquakes to facilitate automatic m l measurements we analyzed the distribution of the times of maximum p p amplitudes in synthetic w a records a 30 sec time window for maximum amplitudes beginning 5 sec before the predicted sg time encompasses 95 of the maximum p p amplitudes in our judgment this time window represents a good compromise between maximizing the chances of capturing the maximum amplitude and minimizing the risk of including other seismic events

p wave attenuation of the yellowstone caldera from three dimensional inversion of spectral decay using explosion source seismic data using explosion source seismic refraction data recorded in the 1978 and 1980 yellowstone snake river plain seismic experiments a three dimensional inversion of differential p wave attenuation was used to assess the relative variations in q 1 in and around the volcanically active 45 km by 70 km yellowstone caldera northwestern wyoming differential attenuation was derived from spectral decay of upper crustal pg phases observed from six explosions and recorded at 90 temporary stations because of the relatively short time windows used to determine the spectral content a maximum entropy technique was employed to estimate the spectra that yielded an optimally small variance differential p wave attenuation was calculated from least squares determinations of the spectral ratios corrected for source and path effects the observed differential attenuation parameters were then inverted using a weighted least squares technique for a discretized 70 105 km three dimensional surface and upper crustal q 1 model of the yellowstone caldera and surrounding region results showed that the surface layer to depths of 2 km within the yellowstone caldera is characterized by relatively high attenuation with low q values less than 30 compared to values of 38 to 50 outside the caldera the higher attenuation in the caldera s surface layer is thought to be associated with quaternary lake sediments highly altered rhyolites and the possible influence of steam in areas of hydrothermal activity in the crystalline upper crust at depths of 2 km to 12 km q values of 40 to 70 were observed in areas of thick sedimentary fill northwest of the caldera and in areas of hydrothermal activity within the caldera upper crustal attenuation generally corresponded to q of 200 in areas that are interpreted to be associated with hot but now solidified granitic material in comparison relatively high attenuation q 40 was observed in the upper crust of the northeastern yellowstone caldera in an area that also corresponds to a 20 reduction in pg velocity a prominent negative bouguer gravity low of 20 mgal near yellowstone s largest area of hydrothermal activity and near a quaternary volcanic resurgent dome on the basis of constitutive models of velocity and density this zone of high attenuation is likely a product of unusual hydrothermal activity highly altered upper crustal rocks a shallow magmatic source or a highly porous steam saturated body outside the caldera the upper crust is relatively unaffected by high temperatures and thermal alteration and the corresponding attenuation is low with q values greater than 200

the late paleozoic porphyry epithermal spectrum of the birgilda tomino ore cluster in the south urals russia abstract the birgilda tomino ore cluster in the east uralian zone south urals russia hosts a variety of late paleozoic porphyry copper deposits birgilda tomino kalinovskoe etc high and low sulfidation epithermal deposits bereznyakovskoe michurino and skarn related base metal mineralization biksizak in carbonate rocks the deposits are related to quartz diorite and andesite porphyry intrusions of the k na calc alkaline series associated to a subduction related volcanic arc we report microprobe analyses of ore minerals tetrahedrite tennantite sphalerite bi tellurides and sulfosalts au and ag tellurides as well as fluid inclusion data and mineral geothermometry on the basis of these data we propose that the birgilda tomino ore cluster represents a porphyry epithermal continuum with a vertical extent of about 2 3 km controlled by temperature decreases and fs2 and fte2 increase from deeper to shallow levels

structural controls of lode gold mineralization by mafic dykes in late paleozoic granitoids of the kochkar district southern urals russia the kochkar gold district in the east uralian zone of the southern urals is located in late paleozoic granite gneisses of the plast massif gold mineralization is associated with tabular quartz lodes that are preferentially developed along the margins of easterly trending mafic dykes fabric development indicates that dykes had a profound influence on the development of shear zones in granitoids ene and se trending dykes have been reactivated as dextral and sinistral oblique strike slip shear zones respectively forming a set of approximately conjugate shear zones related to the permian regional scale e w directed shortening dyke shear zone relationships in the plast massif are the result of strain refraction due to the presence of biotite rich incompetent dykes in more competent granite gneisses deformation and the formation of associated gold quartz lodes occurred close to peak metamorphic upper greenschist to lower amphibolite facies conditions strain refraction has resulted in partitioning of the bulk strain into a component of non coaxial mainly ductile shear in mafic dykes and a component of layer normal pure shear in surrounding granitoids where deformation was brittle ductile brittle fracturing in granitoids has resulted in the formation of fracture permeabilities adjacent to sheared dykes that together with the layer normal dilational component promoted the access of mineralizing fluids both ore controlling dykes and gold quartz lodes were subsequently overprinted by lower greenschist facies mainly brittle fault zones and associated hydrothermal alteration that post date gold mineralization

crustal deformation and source models of the yellowstone volcanic field from geodetic data 1 geodetic observations comprising interferometric synthetic aperture radar insar global positioning system gps and precision leveling measurements are used to infer volume change in the subsurface associated with the dynamics of the yellowstone volcanic system we focus primarily on the yellowstone caldera and its related magmatic hydrothermal and fault systems it appears that known faults play a significant role in controlling crustal volume increases and decreases due to the migration of volcanic and hydrothermal fluids for example over 5 cm of subsidence from 1992 to 1995 is associated with source volume changes 6 10 km beneath the nw trending elephant back fault zone and a north trending fault cutting across the caldera furthermore we are able to image an episode of fluid intrusion near the northern edge of the caldera the intrusion is elongated in the north south direction and is parallel to the north trending volume decrease the primary intrusion and related hydrothermal activity occurred between 1996 and 2000 though the volume changes appear to have continued shallowed and changed shape between 2000 and 2002 there is evidence that the intrusive activity influenced extensional faults to the north of the caldera

the fate of the juan de fuca plate implications for a yellowstone plume head beneath the pacific northwest the juan de fuca plate a remnant of the farallon plate continues subducting beneath the north american continent to the east of the cascadia subduction zone lies the yellowstone hotspot track the origins of this track can be traced back to the voluminous basaltic outpourings in the columbia plateau around 17 ma if these basalts are the result of a large melting anomaly rising through the mantle to the base of the north american continent such as a mantle plume head the anomaly would need to punch through the subducting juan de fuca slab here we use teleseismic body wave travel time tomography to investigate the fate of the subducted slab and its possible interaction with a plume head our dataset is derived from the oregon array for teleseismic study oats deployment in oregon and all other available seismic data in this region during the same period in our jdf07 models we image the subducted juan de fuca plate in the mantle east of the cascades beneath oregon where the slab has not been imaged before to a depth of 400 km but no deeper the slab dips similar to 50 degrees e and has a thickness of similar to 75 km immediately beneath the slab we image a low velocity layer with a similar geometry to the slab and extending down to at least similar to 575 km depth in the v model the total length of the high velocity slab is similar to 660 km about 180 km longer than the estimated length of slab subducted since 17 ma assuming similar slab geometry to today this 180 km length of slab would reach similar to 60 km depth comparable to the thickness of continental lithosphere we propose that the absence of the slab below 400 km today is due to the arrival of the yellowstone plume head similar to 17 ma which destroyed the juan de fuca slab at depths greater than the thickness of the continental lithosphere given this scenario the low velocity anomaly beneath the slab is likely the remnant plume head material which has been pulled down by traction with the subducting plate the amplitude of the observed low velocity anomaly is comparable with that expected for plume head material 100 300 degrees c hotter than the surrounding asthenosphere c 2007 elsevier b v all rights reserved

ignimbrites of the eastern snake river plain evidence for major caldera forming eruptions the eastern snake river plain is a predominantly rhyolitic province analogous to the present day yellowstone plateau volcanic field but older and further evolved the widespread quaternary basaltic lavas that now blanket the eastern snake river plain appear to have erupted after major rhyolitic activity ceased and represent less than 20 of the total volume of volcanic rock near the north central margin of the plain the rhyolites show a general age progression that becomes younger northeastward toward yellowstone three major ignimbrite sheets comparable in magnitude to those of the yellowstone plateau field have been correlated on both sides of the eastern snake river plain from the arco and pocatello areas to margins of the yellowstone plateau these 4 3 to 6 5 ma old ignimbrites are referred to herein as the heise volcanic field studies of facies changes and lateral variations in the three major ignimbrites of the heise field permit identification of related calderas that are now buried beneath the plain petrologic studies suggest that although the ignimbrites overlap compositionaliy each was derived from an isotopicaliy distinct magma that contained a significant component of crustal material

a deep low velocity body under the yellowstone caldera wyoming delineation using teleseismic p wave residuals and tectonic interpretation in previously published papers iyer 1975 iyer and stewart 1977 iyer 1979 evidence was presented for the presence of a large body of anomalous material with compressional velocities considerably lower than normal from the surrounding rock in the crust and upper mantle under yellowstone national park wyoming in this paper we give a detailed analysis of p residual data from the 26 element telemetered seismic array and three groups of portable stations operated by the u s geological survey in the yellowstone region using a variety of analytical techniques we delineate the shape of the low velocity body determine the velocity structure inside the body and interpret the nature of the material that constitutes the body we will also outline some tectonic implications of our model the spectacular surface geothermal phenomena for which yellowstone is famous result from deep seated volcanism the volcanic evolution of yellowstone is discussed by christiansen and blank 1972 and summarized by eaton and others 1975 briefly the geothermal manifestations in yellowstone are results of three cycles of quaternary volcanism each culminating in a devastating pyroclastic eruption and resulting in large collapse calderas and predominantly rhyolitic flows the oldest cycle ended about 1 9 m y ago forming a caldera from island park to perhaps the central part of the present yellowstone caldera the second cycle climaxed about 1 2 m y ago and was confined to the island park caldera the third cycle began soon after the second and is responsible for the 75 by 45 km yellowstone caldera as it is outlined today this caldera is the result of a catastrophic eruption approximately 600 000 yr ago the most recent episode of volcanism probably began about 150 000 yr ago in the western half of the caldera near old faithful geyser and the youngest flows in yellowstone about 70 000 yr old are probably associated with this episode

the gold content of volcanogenic massive sulfide deposits volcanogenic massive sulfide deposits contain variable amounts of gold both in terms of average grade and total gold content with some vms deposits hosting world class gold mines with more than 100 t au previous studies have identified gold rich vms as having an average gold grade expressed in g t exceeding the total abundance of base metals expressed in wt however statistically meaningful criteria for the identification of truly anomalous deposits have not been established this paper presents a more extensive analysis of gold grades and tonnages of 513 vms deposits worldwide revealing a number of important features in the distribution of the data a large proportion of deposits are characterized by a relatively low gold grade 2 g t with a gradual decrease in frequency towards maximum gold grades defining a log normal distribution in the analysis presented in this paper the geometric mean and geometric standard deviation appear to be the simplest metric for identifying subclasses of vms deposits based on gold grade especially when comparing deposits within individual belts and districts the geometric mean gold grade of 513 vms deposits worldwide is 0 76 g t the geometric standard deviation is 2 70 g t au in this analysis deposits with more than 3 46 g t au geometric mean plus one geometric standard deviation are considered auriferous the geometric mean gold content is 4 7 t au with a geometric standard deviation of 26 3 t au deposits containing 31 t au or more geometric mean plus one geometric standard deviation are also considered to be anomalous in terms of gold content irrespective of the gold grade deposits with more than 3 46 g t au and 31 t au are considered gold rich vms a large proportion of the total gold hosted in vms worldwide is found in a relatively small number of such deposits the identification of these truly anomalous systems helps shed light on the geological parameters that control unusual enrichment of gold in vms at the district scale the gold rich deposits occupy a stratigraphic position and volcanic setting that commonly differs from other deposits of the district possibly due to a step change in the geodynamic and magmatic evolution of local volcanic complexes the gold rich vms are commonly associated with transitional to calc alkaline intermediate to felsic volcanic rocks which may reflect a particularly fertile geodynamic setting and or timing e g early arc rifting or rifting front at the deposit scale uncommon alteration assemblages e g advanced argillic aluminous strongly siliceous or potassium feldspar alteration and trace element signatures may be recognized e g au ag as sb bi hg te suggesting a direct magmatic input in some systems

lithospheric topography tilted plumes and the track of the snake river yellowstone hot spot 1 the trace of the snake river yellowstone hot spot is the world s best example of a mantle plume that has been overridden by continental lithosphere the standard model calls for the plume head to rise under northern nevada and be forced northward to form basalts of the columbia plateau subsequent movement of north america to the southwest over the plume tail created a hot spot trace on the surface we present a new conceptual model for the origin of this feature that resolves inconsistencies in the current standard model and explains the recent documentation of a thermal anomaly in the mantle below yellowstone today that plunges 65 wnw our model implies that the plume tail was forced beneath thinned cratonic lithosphere to the se along with part of the plume head and has remained in this orientation for the last 12 ma we infer that almost all of the volcanism in se oregon and sw idaho prior to 12 ma results from overriding the southern extension of the plume head not the plume tail and that a distinct plume tail hot spot track was not established until formation of the bruneau jarbidge eruptive center around 12 ma the plume tail track may also be controlled by a preexisting structural boundary in lithosphere that is thinner than adjacent lithosphere this model demonstrates the potential importance of lithospheric topography on controlling the surface manifestation of plume volcanism and the complexity that may arise when lithospheric thickness is nonuniform

typomorphic features of placer gold of vagran cluster the northern urals and search indicators for primary bedrock gold deposits abstract the vagran placer cluster is located on the eastern slope of northern urals during 100 years of gold mining history approximately 40 tons of gold have been extracted from the placer deposits bedrocks of the region consist of high metamorphic upper proterozoic and paleozoic terrigeneous terrigeneous volcanogenic and igneous rocks gold placer deposits are mostly alluvial genesis deposits and of quaternary to oligocene age the alluvial deposits consist of gravel with pebbles boulders and sandy clay covered by sandy silt and a soil layer the thickness of the alluvial sequence is usually 5 10 m and reaches 18 m in the main watercourses of the third order nearly all of the alluvial sediments are gold bearing but concentrations of economic importance prevail in the bottom part of the sequence above the bedrock there are four different types of gold particles i rounded and well rounded particles of high fineness and homogeneous inner structure ii rounded to sub rounded high fineness particles with a pure gold rim developed over a core iii crystallomorphic idiomorphic high fineness with a homogeneous inner structure and iv irregular angular and subangular particles of medium fineness with a significant content of ag 10 40 wt and elevated hg up to 1 15 wt the first type is prevalent and comprises up to 65 of the total gold particles it is uniformly distributed throughout the territory there are features with initially complicated dendritic and laminar shaped particles which were rounded during transportation the second and third types have a propensity for zones of the inherited erosion tectonic depressions apparently types i ii and iii are related with orogenic mesothermal gold sulfide quartz mineralization the differences of these types depend on the primary zonation of ore bodies and supergenic transformation of the alloys they were connected with middle depth ore bodies of an orogenic gold sulfide quartz formation the fourth type is evident of nearby transportation from primary sources and a short duration of supergenic influence it is controlled by a zone of nw se orientation diagonal to the main structures of ural fold belt the plot of au content vs coefficient of heterogeneity ratio of the au content in the core and in the rim of the grains is the distinguishing factor between the four types of gold grains both by primary hypogenetic characteristics and supergenetic features no corresponding lode occurrence of gold sulfide quartz mineralization has been identified to date in this region placer gold concentrations are related to the intermediate hosts of the mesozoic cenozoic surfaces of the ural peneplain uplift in the oligocene and eroded in miocene quaternary time this factor determines the widespread distribution of placer gold in the territory of the vagran cluster the large carlin type vorontsovsk gold deposit is located 60 km south east from the vagran area it has a shallow erosional level small size of native gold and its distal location from the placer deposits makes it an unlikely primary source for the vagran placers however mineralization of this type of deposit is noted within the cluster gold of the fourth type nearly resembles the gold of the vorontsovsk deposit and apparently the source is related to the same hydrothermal mineralization event icp ms analyses of the quartz sulfide lodes in the floor of gold bearing valleys revealed a gold content of 2 0 6 9 g t in the zone of type iv distribution therefore gold of the fourth type can be used as an indicator for the exploration of primary bedrock mineralization the geological setting and typomorphic features of this placer gold shows that the primary gold mineralization is similar to the vorontsovsk deposit and within the zone of distribution of the placer gold of the fourth type

the 1978 yellowstone eastern snake river plain seismic profiling experiment data and upper crustal structure of the yellowstone region eleven in line refraction profiles recorded to distances of 300 km and one azimuthal fan plot were constructed from data recorded with a 150 station array in the yellowstone national park area during the 1978 yellowstone snake river plain seismic experiment interpretations of the data suggest that the crustal p wave velocity model for the yellowstone region is characterized by 1 an averaged 10 km thick upper crustal layer v sub p 6 0 km s 2 an average crustal velocity of 6 3 km s and 3 a total crustal thickness of 44 km velocity models are presented for profiles that emphasize the upper crust and show 1 a decrease in the depth to the top of the upper crustal crystalline basement from 5 km in southwestern yellowstone near island park to 1 km at the northeast side of the yellowstone plateau that is interpreted as a progressive thinning of the silicic surface volcanic layer to the northeast and 2 evidence for a large lateral inhomogeneity interpreted to be a low velocity body with a decrease of at least 10 in p wave velocity located beneath the northeast corner of the yellowstone plateau the low velocity zone coincides with a local 30 mgal residual gravity anomaly and is located beneath partmore of the sour creek resurgent dome and part of the hot springs basin the largest hydrothermal system in yellowstone the low velocity body has a maximum depth to the top of 3 km and a minimum depth to the bottom of 9 km and may represent a zone of partial melt in comparison to the thermally undisturbed upper crust of the surrounding rocky mountains the upper crust of the northeastern yellowstone plateau appears laterally inhomogeneous in velocity and layer thickness suggesting effects of thermal and magma intrusion whereas the lower crust appears relatively homogeneous less

mineralogical and microtextural parameters in metals ores traceability studies abstract the demand in mineral resources is increasing rapidly but there is a lack of transparency in the trade of concentrated raw mineral materials because of speculation and involvement in the finance of armed conflicts because of the distance between primary extraction and the final production sites it is difficult to check the origin of these products an identity card is required for mineral commodities so that trading in the industry can be verified and the traceability of concentrates ensured this problem may be considered as an inversion process studying the products sold to identify the original ore the discriminant parameters are mineralogical composition identification of textural microfacies of the target minerals pseudo paragenetic sequence and the contents and distribution of minor elements of target minerals for base metal the selected target minerals are pyrite for its ubiquity sphalerite for its ability to host numerous discriminant and potentially valuable minor elements in its lattice and chalcopyrite for its proximity with the two other minerals the kolmogorov smirnov distance and the colin white test are used to compare the chemical composition of the three target minerals the application to volcanic massive sulfide ore deposits shows that it is possible to distinguish pyrite sphalerite and chalcopyrite between two ore deposits in the iberian pyrite belt province and seven ore deposits from the urals province using the selected characteristics ore deposits from different provinces may be discriminated using the identity cards as well as different deposits in the same province

metamorphism of volcanogenic massive sulphide deposits in the urals ore geology abstract the urals vms province comprises a broad spectrum of variably metamorphosed deposits from unmetamorphosed to those without any primary ore textures which are the results of high grade metamorphic processes contact metamorphism near large granite and granodiorite plutons caused the most significant changes of ores with coarse grained to pegmatoidal ores with magnetite closest to its contact with the intrusion followed by pyrrhotite enriched copper ores and more distal zinc pb ag mineralisation koktau tarnyer and vesenneye deposits are metamorphosed to the hornblende hornfels and pyroxene hornfels facies t 400 800 c p 1 6 kbar metamorphism of tash yar dzhusinskoe and krasnogvardeiskoe deposits corresponds to the greenschist and albite epidote hornfels facies t 250 450 c p 1 4 kbar the regional metamorphism of vms ores varies from prehnite pumpellyite facies t 150 300 c p 0 5 4 kbar in the south urals to the epidote amphibolite and amphibolite facies t 400 600 c up to 700 c p 1 6 kbar in the karabash area in the middle urals in the magnitogorsk zone the metamorphism of host rocks and vms bodies increases to the north reaching its peak near the ufa promontory of the east european platform with increased metamorphism the morphology of orebodies evolves from gently dipping thick lenses alexandrinskoe and uzelga fields to subvertical and folded uchaly and novo uchaly deposits and pseudomonoclinal steeply dipping vein like bodies karabash district the massive sulphide transformation in ptx gradient fields led to partial redistribution of ore material an enrichment in cu zn ag and au pb occur in the uppermost parts of large steeply dipping massive sulphide lenses in wide tectonic zones e g gai deposit or as gold sulphide disseminated bodies near large metamorphosed vms lenses distal to a granite pluton tarnyer deposit partial melting probably occurred in some highly metamorphosed deposits tarnyer koktau and mauk redeposition of base metals sulphides chalcopyrite tennantite sphalerite bornite galena as well as the presence of visible gold and tellurides took place during retrograde metamorphism which produced a transfer of ore matter towards the low stress areas such as the outer parts of shear zones the uppermost parts of steeply dipping ore lenses pressure shadows hinge zones of small folds and small extension fractures i e alpine type veins in deformed ore body or its immediate surroundings

chimneys in paleozoic massive sulfide mounds of the urals vms deposits mineral and trace element comparison with modern black grey white and clear smokers in the urals a wide range of well preserved chimneys are found in vms deposits which are associated with ultramafic atlantic type dergamysh mafic cyprus type buribay bimodal mafic uralian type yubileynoye sultanovskoye yaman kasy molodezhnoye uzelga 4 valentorskoye and bimodal felsic kuroko or baymak type oktyabrskoye tash tau uselga 1 talgan alexandrinskoye sequences chimneys have also been found in the safyanovskoye deposit altay type that is hosted by intercalated felsic lavas and carbonaceous shales a combination of geological mineralogical and trace element data provide a general outline for comparison between chimneys from the urals deposits and modern vent sites the chimneys from the dergamysh deposit show a broad affinity with those from the rainbow and other vent sites associated with serpentinites of the mid atlantic ridge the chimneys from the buribay deposit are similar to the black smokers of the epr vent sites including the scarcity of rare minerals the chimneys from the urals type of the vms deposits show some similarities with grey smokers from the brother volcano and pacmanus sites the chimneys from the baymak type of the vms deposits resemble grey and white smokers of the pacmanus and grey smokers of the suiyo vent sites the chimneys from the safyanovskoye deposit are similar to the black and clear smokers from the okinawa trough mineral assemblages are controlled by the combination of host rock composition and physico chemical conditions of the ore forming processes amount of colloform pyrite isocubanite and pseudomorphic pyrite and marcasite after pyrrhotite decreases in the chimneys across the range from ultramafic and mafic to felsic hosted deposits and is concomitant with increase in the contents of sphalerite galena bornite fahlores native gold and barite across this range the chimneys from the urals type contain abundant tellurides and sulfoarsenides while these minerals are rare except for hessite in the baymak type deposits in the same range the buffering capacity of host rocks decreases in contrast to the increase in s2 and o2 with the exception of the safyanovskoye deposit trace element assemblages in chalcopyrite vary to reflect the host rock ultramafic high se sn co ni ag and au mafic high co se mo and low bi au and pb bimodal mafic high te au ag bi pb co moderate se and variable as and sb bimodal felsic high as sb mo pb moderate bi and low co te and se in sphalerite of the same range the contents of bi pb ag au and sb increase versus fe se and o the variations in trace elements in colloform pyrite coincide with these changes the specific mineral changes in the local ranges from cu to zn rich chimneys in each vms deposit are similar to the general changes in the range of host rock classes of the deposits however the local t s2 and o2 changes can broadly be interpreted in terms of contribution of variable oxygenated cold seawater to the subseafloor and seafloor hydrothermal processes

shore platform downwearing in eastern canada micro tidal gaspe quebec abstract work has been conducted in the laboratory and field on a micro tidal subhorizontal shore platform in argillaceous rocks at mont louis in gaspe quebec surface downwearing rates for 450 rock samples were measured over 3 years in the laboratory at the neap low mid and high tidal levels under semi diurnal tidal conditions de ionized water was used to determine the role of wetting and drying and artificial sea water for the additional effect of salt and possibly chemical weathering another 300 samples were immersed in de ionized water or artificial sea water for 90 min every 1 2 or 3 weeks representing conditions between the neap and spring high tidal levels and exposed in air for 90 min every 1 2 or 3 weeks to represent conditions between the neap and spring low tidal levels surface downwearing was recorded in the field at 34 transverse micro erosion meter tmem stations most of which were installed along 4 shore normal profiles in 2004 and 2005 mean downwearing rates in the laboratory ranged from 1 25 mm yr 1 at the neap high tidal level to 0 63 mm yr 1 at the neap low tidal level downwearing was much slower between the neap and spring tidal levels and it was uniformly slow below the neap low tidal level the presence of salts inhibited downwearing within the neap tidal range where wetting and drying was dominant and promoted it between the neap and spring high and low tidal levels surface swelling was fairly common in the field and the mean downwearing rate 0 242 mm yr 1 was much lower than in the laboratory possibly because the tmem stations were installed in harder rocks modeling supports the contention that the mont louis platform was cut initially by waves at a higher elevation and then lowered by weathering in the last few thousand years as relative sea level fell to its present elevation

the berezovsk giant intrusion related gold quartz deposit urals russia evidence for multiple magmatic and metamorphic fluid reservoirs abstract the berezovsk gold deposit in the middle urals has been mined for 270 years its endowment past production and gold reserves is estimated to be 490 t of gold the deposit is located in the greenschist metamorphosed silurian volcanogenic sedimentary rocks intruded by granitoid dykes to the north east of late carboniferous shartash granite massif mineralisation is represented by sulphide quartz veins in the granitoid dykes ladder veins and in the host rocks krassyk veins formed in the following four stages ankerite quartz quartz pyrite gold polymetallic and carbonate ore veins are accompanied by halos of gumbeite quartz orthoclase carbonate beresite quartz sericite ankerite pyrite and listvenite quartz fe mg carbonate fuchsite pyrite the veins mainly consist of quartz with sulphide minerals commonly 3 5 vol about 180 minerals have been identified in ores but the most abundant minerals are quartz calcite ankerite pyrite galena tennantite chalcopyrite aikinite native gold and sphalerite native gold was deposited during quartz pyrite au i and gold polymetallic au ii stages fineness of gold ranges from 863 to 984 and from 723 to 848 for au i and au ii respectively the mineral and metal zoning was identified relative to the roof of the shartash granite massif the fluid inclusion study revealed that the gold mineralisation at the berezovsk deposit was formed at 300 230 c and 0 3 2 3 kbar mostly 0 5 1 2 kbar from a h2o co2 nacl fluid with salinity of 7 3 18 2 wt nacl equiv the fluid was separated into h2o co2 nacl and co2 rich fluids due to temperature and or pressure drop at the deposition site calculated 18o and d values are 5 2 8 1 and 39 to 63 respectively for the fluid in equilibrium with alteration assemblages the average 13c value for the fluid equilibrated with carbonates from the inner zones of metasomatic halos is 5 3 the calculated 18o and 13c values are 3 0 9 6 and 3 to 9 respectively for ore forming fluids the 34s values are 1 4 12 9 and 1 6 to 11 7 for the fluid in equilibrium with early and late sulphides respectively in addition to the isotopic data the geological mineralogical and fluid inclusion data confirmed the predominant contribution of the magmatic fluid to formation of the berezovsk hydrothermal system the light c o and s isotope enrichment of the fluid was mainly caused by fluid phase separation fluids generated by decarbonation and dehydration reactions due to the contact metamorphism of the host rocks during the shartash massif emplacement were responsible for additional 34s input the ore forming fluid was enriched in the light 16o isotope on the deposit flanks indicating the mixing with heated meteoric water

p and s wave velocity and vp vs in the wake of the yellowstone hot spot 1 seismic vp vs and vp vs structure is imaged across the yellowstone hot spot swell including the hot spot track where magmatism occurred at the eastern snake river plain 6 10 m y b p data are teleseismic p and s travel time delays that have been corrected for the well understood upper mantle anisotropy and crustal structure amplitude variations in the imaged structures are 6 2 11 2 and 8 for vp vs and vp vs respectively the dominant structure is a zone which extends beneath the snake river plain to a depth of 190 km that is high in vp vs and low in vp and vs the physical state of the upper mantle is inferred by assuming isostasy using the volume of melt segregated from the mantle that is inferred from estimates of magma addition to the crust and using relations that scale changes in temperature partial melt fraction and composition to density specifically we infer that the low velocity mantle beneath the snake river plain is partially molten up to 1 0 and the high velocity yellowstone swell mantle away from the snake river plain is 80 k cooler and 5 depleted in basaltic component the imaged large seismic velocity variations occur under near isothermal conditions

gold and platinum group minerals in placers of the south urals composition microinclusions of ore minerals and primary sources abstract gold and platinum group minerals from the gold placers of the south urals are studied in order to identify the metal sources in placers from the main uralian fault zone muf the primary gold contains ag up to 29 wt cu up to 2 wt and hg up to 4 wt and its fineness ranges from 538 to 997 tetra auricupride and cupriferous gold up to 20 wt cu are common for the nizhny karabash placer of the muf zone in the eastern part of the south urals the placer gold is mainly characterized by high fineness of 900 1000 and low cu contents max 1 38 wt most of the placer gold grains consist of the primary domains which are rimmed by secondary high fineness gold with diffuse and clear boundaries the secondary gold also develops along the shear dislocations of primary gold gold contains microinclusions of geerite balkanite chalcopyrite se bearing galena sphalerite pyrite pyrrhotite arsenopyrite and hematite twenty four including five unnamed platinum group minerals pgms were found in 28 placers those from the kialim and maly iremel placers of the miass placer zone were studied in details in the kialim placer ruthenium is most abundant pgm which hosts microinclusions of isoferroplatinum ferroan platinum laurite cupriferous gold a mineral similar in composition to tolovkite heazlewoodite and unnamed rhsbs phase the osmium contains microinclusions of erlichmanite and laurite the iridium grains hosts various sulfides and arsenides of platinum group elements pges the inclusion free pgms form ru compositional trend in contrast to os ru trend of the ir depleted inclusion hosted pgms the isoferroplatinum from the maly iremel placer hosts laurite rhodarsenite bowieite a mineral similar in composition to miassite and unnamed sulfide of pt pt 1 11 s 2 00 and antimonide of pd pd 2 41 rh 0 43 fe 0 17 3 01 sb 0 91 te 0 09 1 00 ruthenium is a host to isoferroplatinum pge sulfides and arsenides and heazlewoodite osmium contains microinclusions of ferroan platinum iridium is a host to a mineral similar in composition to hongshiite three types of pgm intergrowths were identified in the maly iremel samples 1 the intergrowths of platy grains of ruthenium with isoferroplatinum and a mineral similar in composition to tulameenite 2 the open latticework intergrowths of platy crystals of ruthenium with interstitial aggregates made up of gold isoferroplatinum and a mineral similar in composition to xingzhongite and 3 the intergrowths of osmium and irarsite and iridarsenite which are developed along cleavage of the osmium grains nickel sulfides associated with some pgms contain ru 11 32 wt and rh 2 21 wt in millerite and ir 31 00 wt ru 5 81 wt and rh 2 87 wt in vaesite the primary metal sources were determined on the basis of the mineral assemblages and composition of minerals taking into account the nearby mineral deposits and directions of rivers the rodingite associated gold gold bearing massive sulfide and chromite deposits are major sources of gold and pgms in placers of the miass placer zone confined to the muf structure of the south urals in the southern part of this structure gold was mainly originated from orogenic gold sulfide deposits associated with volcanic volcaniclastic rocks and listvenite associated gold deposits the placer pgms were derived from the adjacent ultramafic massifs of ophiolitic origin the distance between the placers and primary deposits varies from 2 to 5 km up to 20 km in the extended valley of the miass river usage of ore microinclusions and associated pgms in study of placer gold is far more advanced than an ordinary consideration of gold composition alone this approach allowed us to identify the concrete sources for individual placers and to predict some mineralogical findings in already known primary occurrences

crustal structure of the eastern snake river plain determined from ray trace modeling of seismic refraction data ray trace travel time modeling of the seismic refraction record sections for a profile from near soda springs idaho to near mckay idaho was used to derive a crustal model across the eastern snake river plain esrp the derived crustal model is consistent with the velocity structure interpreted from a profile along the axis of the esrp the interpretation also indicates that significant lateral inhomogeneities exist in the upper crust beneath the esrp when compared with the upper crust beneath the adjoining northern rocky mountain and basin and range provinces the most prominent features of the crustal structure inferred by the ray trace modeling are as follows 1 the northwest margin of the esrp was modeled as a fault structure downthrown on the srp side se with an offset of greater than 4 km the southeast margin conversely appears to be downwarped with possible minor faulting paleozoic sedimentary rocks are present beneath the cenozoic volcanics of the esrp possibly to and beyond 40 km from the southeastern margin of the esrp near blackfoot idaho 2 the modeling indicates no abrupt variation in the depth to the top of the lower crustal layer near the margins of the esrp 3 an intermediate 6 5 km s layer occurring beneath the esrp interpreted from a refraction profile located along the axis of the esrp was found to be localized within the esrp margins this layer is interpreted as a pervasive intrusion of higher velocity material from the upper mantle into the highly fractured upper crustal layer in this region 4 a density model of the crust across the esrp was prepared with the densities selected using the interpreted seismic velocities as a constraint the gravity field calculated from this model resulted in a good match to observed gravity data over the eastern snake river plain

plume formation in the d double prime layer and the roughness of the core mantle boundary numerical simulations of the formation of thermal plumes in the d layer at the base of the earth s mantle show that plumes are initiated by coalescence of small scale convective instabilities within the low viscosity region immediately above the core mantle boundary cmb these instabilities support topographic roughness on the cmb having horizontal scales of 20 50 km and provide a source for scattered p waves seen as precursors to the phases pkikp and pkkp the calculated structure of fully developed plumes emerging from d consists of 5 50 cm yr 1 flow confined to 50 100 km thick vertical conduits with strongly temperature dependent viscosity plumes exhibit time dependent behaviour including upward propagating solitary conduit waves which may contribute to episodicity in hotspot volcanism

contemporary vertical surface displacements in yellowstone national park relative vertical displacements and average relative vertical velocities have been determined for bench marks located throughout yellowstone national park ynp by comparing geodetic leveling measurements made in 1923 second order 1936 third order 1941 third order 1955 third order 1960 first order and 1975 1977 first order the 1923 1975 data indicate uplift greater than 400 mm 7 7 mm yr of an area approximately 15 20 km wide and at least 40 km long which is centered along the northeast trending axis of the 600 000 year old yellowstone caldera the maximum 1923 1975 vertical displacement in this area is 726 mm 14 0 mm yr the existence of a well defined and untilted yellowstone lake terrace implies that the 1923 1975 average vertical velocities cannot have been maintained for more than a few hundred years the 1955 1977 data from central ynp indicate that the northeastern caldera half has risen relative to the southwestern half at an average velocity of about 8 mm yr a similar bias is present in the 1923 1975 data but it is less pronounced the 1923 1960 and 1960 1975 data from northwestern ynp and a 200 mm depression in the 1923 1975 data near norris junction may be interpreted in terms of deformation associated with the 1959 hebgen lake earthquake and the 1975 yellowstone park earthquake a composite profile of the 1936 1977 and 1941 1977 average vertical velocity data which skirts the edge of the yellowstone caldera in northeastern ynp is most easily explained as the result of random leveling error and or bench mark instabilities the apparent youth of the 1923 1975 yellowstone uplift and its close association with the yellowstone caldera suggest that the most likely cause of the uplift is a recent not more than 500 years ago influx of molten material into the upper crust beneath the caldera

the yellowstone hotspot in space and time nd and hf isotopes in silicic magmas abstract over the course of its 16 m y history the yellowstone hotspot has produced silicic magmas exhibiting systematic and often sympathetic variations in isotopic and chemical composition temperature and frequency of eruption nd and hf isotopic ratios vary systematically from initial eruptions at 16 ma contemporaneous with basaltic volcanism in eastern oregon and washington to the present day yellowstone volcanic plateau nd and hf isotopic ratios co vary and span the range of most terrestrial samples reflecting mixing of mantle and crustal sources earliest erupted silicic magmas were hot in excess of 1050 c relatively less evolved and have isotopic ratios within the range of contemporaneous columbia river flood basalts the transit of the hotspot across the lithospheric boundary between the western accreted oceanic terrain and the precambrian craton at 15 ma is marked by shifts in e nd from 4 to 11 and in e hf from 10 to 10 the duration of the transit yields a crustal magma source diameter of 70 km in the interval from 14 to 9 ma e nd systematically increases from 11 to 7 recording a minimum increase in the mantle component from 5 to 30 the mantle component could be twice as great depending upon the isotopic composition of crust and mantle reservoirs in this same interval peak temperatures of 1000 c occurred at 9 ma the last 8 m y are characterized by less frequent eruption of lower temperature 830 900 c and more compositionally evolved magmas

geodynamics of the yellowstone hotspot and mantle plume seismic and gps imaging kinematics and mantle flow abstract integration of geophysical and geological data show that the yellowstone hotspot resulted from a mantle plume interacting with the overriding north america plate a process that has highly modified continental lithosphere by magmatic and tectonic processes and produced the 16 17 ma 700 km long yellowstone snake river plain ysrp silicic volcanic system accessibility of the ysrp allowed large scale geophysical projects to seismically image the hotspot and evaluate its kinematic properties using geodetic measurements seismic tomography reveals a crustal magma reservoir of 8 to 15 melt 6 km to 16 km deep beneath the yellowstone caldera an upper mantle low p wave velocity body extends vertically from 80 km to 250 km beneath yellowstone but the anomalous body tilts 60 wnw and extends to 660 km depth into the mantle transition zone we interpret this conduit shaped low velocity body as a plume of up to 3 5 vp and 5 5 vs perturbation that corresponds to a 1 2 partial melt models of whole mantle convection reveal eastward upper mantle flow beneath yellowstone at relatively high rates of 5 cm yr that deflects the ascending plume into its west tilted geometry a geodynamic model of the yellowstone plume constrained by vp and vs velocities and attenuation parameters suggests low excess temperatures of up to 120 k corresponding to a maximum 2 5 melt and a small buoyancy flux of 0 25 mg s i e properties of a cool weak plume the buoyancy flux is many times smaller than for oceanic plumes nonetheless plume buoyancy has produced a 400 km wide 500 m high topographic swell centered on the yellowstone plateau contemporary deformation derived from gps measurements reveals sw extension of 2 3 mm yr across the yellowstone plateau one fourth of the total basin range opening rate which we consider to be part of basin range intraplate extension locally decadal episodes of subsidence and uplift averaging 2 cm yr characterize the 80 year yellowstone caldera monitored history and are modeled as hydrothermal magmatic sources moreover a recent episode 2004 2009 of accelerated uplift of the yellowstone caldera at rates up to 7 cm yr has been modeled as resulting from magmatic recharge of a 10 km deep sill at the top of the crustal magma reservoir regionally gravitational potential energy of the yellowstone swell drives the lithosphere southwest and downhill from the yellowstone plateau 400 km where it coalesces with basin range province wide westward extension based on the geometry and its assumed 660 km depth we extrapolate the plume source southwest to its original location at 17 ma and 600 km southwest and 200 km north of the ysrp importantly this location is beneath the southern part of the columbia plateau flood basalt field of the same age and implies that the yellowstone mantle plume may be the common source for both of these large volcanic fields our time progression model suggests that the original plume head rose vertically behind the juan de fuca plate but at 12 ma it lost the protection of the subducting plate from eastward mantle flow and encountered cooler thicker continental lithosphere becoming entrained in eastward upper mantle flow these results reveal that yellowstone plume plate processes have had a profound effect on late cenozoic geologic evolution and topography of a large part of the western u s

crustal velocity structure across the eastern snake river plain and the yellowstone swell teleseismic receiver functions are used to estimate the crustal structure beneath a 36 station 500 km long nw oriented linear array centered on the eastern snake river plain and crossing the yellowstone hotspot swell 250 km sw of yellowstone structure derived previously for this region from wide angle reflection data is used as an initial model and this structure explains most features observed in our receiver functions based on a combination of forward and inverse modeling our data require several modifications to the initial structure 1 moho depth is 42 km beneath most of the snake river plain shallows to 37 km to either side and thickens abruptly to 47 km beneath sw wyoming 2 a midcrustal layer interpreted previously as a 9 km thick gabbroic sill is flat topped across the entire 90 km width of the snake river plain and 3 a low velocity layer is found beneath and southeast of the snake river plain which probably is partially molten lower most crust using the seismic structure of the crust to estimate the crustal load upon the mantle and assuming local isostasy we calculate that mantle beneath the yellowstone swell is approximately uniformly as buoyant as 12 million year old ocean mantle and more buoyant than the adjacent wyoming mantle by an amount equivalent of 1 5 km of elevation the transition between these regions of greatly different mantle occurs across a major paleozoic boundary that now separates the basin and range from the rocky mountains

vorontsovka carlin style gold deposit in the north urals mineralogy fluid inclusion and isotope data for genetic model abstract the vorontsovka gold deposit in the tagil zone north urals hosts 101 t au averaging 7 g t au and including 30 t au in the regolith and 120 t ag averaging 8 g t ag early skarn magnetite mineralisation related to a dioritic intrusion of the shoshonitic series was formed in the late emsian water and volatiles mainly co2 released from host metapelites and limestones were mixed with the metalliferous magmatic fluid during catagenesis to contact metamorphism the modified fluid extracted ore components from host rocks and syn volcanic stratiform mineralisation and became enriched in fe mn ba zn pb au ag and s to deposit these components as sulphide dissemination in the footwall of siliciclastic unit and underlying limestone both brecciated along the trust at the final early eifelian stage there was an additional inflow of deep mantle magmatic fluid enriched in au hg as sb and tl the mixing of this fluid with metamorphic water resulted in carlin style gold realgar stibnite tl minerals mineralisation mainly in carbonate breccia the main gold endowment associates with gold arsenic ores located in brecciated silicified limestone jasperoid and argillised tuff siltstone early ore assemblages were formed at 510 240 c including magnetite skarn whereas overprinting carlin style gold fe as sb hg tl sulphide mineralisation was deposited at decreasing temperatures mainly from 260 to 110 c fluid inclusion data revealed aqueous carbonic ca na mg and k chloride compositions of ore bearing fluid of 4 8 9 3 wt eq nacl changing fluid pressure corresponded to near lithostatic 0 5 0 6 kb to hydrostatic 0 15 0 2 kb conditions based on the 34s ranges of sulphides determined for siliciclastic rocks 2 3 1 8 and skarns 2 1 6 it is assumed that most of the sulphur derived from magmatic reservoir associated with the mantle the lead isotopic compositions of sulphides show a relatively narrow range and continue the linear trend of the early silurian vms deposits corresponding to the mixing line of mantle and crustal lead sources model pb pb ages for the vorontsovka sulphides are grouped into two clusters 425 416 and 398 388 ma the second period is close to the u pb isotope age of the final stage of the auerbakh pluton as well as in a good agreement with the ar ar isotope age of 391 1 4 9 ma of hydromica from the late gold arsenopyrite assemblage the specific features of the vorontsovka deposit indicative of the carlin style mineralisation are as follows the paleo continental margin and trust related position causing high k shoshonitic igneous activity the fine disseminated sulphide mineralisation in the highly brecciated carbonate clastic sequence jasperoid and argillic alteration accompanying gold orebodies with assay boundaries multiple fluid source au as hg tl geochemical association the abundance of as and as fe sulphides and as sb sulphosalts the occurrence of hg tl sulphides and sulphosalts the association of gold with arsenian pyrite and arsenopyrite overgrowing previously forming pyrite and the predominance of submicroscopic gold in the ores a la icp ms analysis of pyrite confirms that elevated concentrations of au regularly correlate with higher contents of as ag sb or tl

regional implications of heat flow of the snake river plain northwestern united states abstract the snake river plain is a major topographic feature of the northwestern united states it marks the track of an upper mantle and crustal melting event that propagated across the area from southwest to northeast at a velocity of about 3 5 cm yr the melting event has the same energetics as a large oceanic hotspot or plume and so the area is the continental analog of an oceanic hotspot track such as the hawaiian island emperor seamount chain thus the unique features of the area reflect the response of a continental lithosphere to a very energetic hotspot the crust is extensively modified by basalt magma emplacement into the crust and by the resulting massive rhyolite volcanism from melted crustal material presently occurring at yellowstone national park the volcanism is associated with little crustal extension heat flow values are high along the margins of the eastern and western snake river plains and there is abundant evidence for low grade geothermal resources associated with regional groundwater systems the regional heat flow pattern in the western snake river plains reflects the influence of crustal scale thermal refraction associated with the large sedimentary basin that has formed there heat flow values in shallow holes in the eastern snake river plains are low due to the snake river plains aquifer an extensive basalt aquifer where water flow rates approach 1 km yr below the aquifer conductive heat flow values are about 100 mw m 2 deep holes in the region suggest a systematic eastward increase in heat flow in the snake river plains from about 75 90 mw m 2 to 90 110 mw m 2 temperatures in the upper crust do not behave similarly because the thermal conductivity of the plio pleistocene sedimentary rocks in the west is lower than that in the volcanic rocks characteristic of the eastern snake river plains extremely high heat loss values averaging 2500 mw m 2 and upper crustal temperatures are characteristic of the yellowstone caldera

global comparisons of volcanic associated massive sulphide districts although volcanic associated massive sulphide vms deposits have been studied extensively the geodynamic processes that control their genesis location and timing remain poorly understood compar

seismic gravity and petrological evidence for partial melt beneath the thickened central andean crust 21 23 s on the basis of seismic refraction investigations and gravimetric data we have modelled the crustal structure of the southern central andes 21 23 s a pronounced variation in crustal parameters is seen in n s and w e crossing seismic profiles over the entire andean orogene characterized by a crustal thickness of up to 70 km under the magmatic arc and backarc strongly reduced seismic velocities and a bouguer minimum of 450 mgal anomalously low velocities of 5 9 6 0 km s in the deeper crust of the western cordillera and altiplano regions lead to an over compensation of the bouguer minima resulting in values of crustal densities higher than estimates based purely on seismic velocity measurements in an attempt to reconcile these differences the behavior of crystalline rocks based on published laboratory data was studied under varying pressure and temperature conditions up to the range of partial melting if the temperature is increased above the melting point a rapid decrease in seismic velocity is accompanied by a slow decrease in density for the central andes a good fit of the observed and calculated bouguer anomalies is obtained if the densities of the rocks from the low velocity zone lvz beneath the western cordillera and the altiplano are varied model calculations lead to a velocity density relation for partial molten rocks that allows the melt proportions of rocks to be estimated model calculations indicate that 15 20 vol of basaltic to andesitic melt at depth is necessary to explain the lvz and bouguer anomaly beneath the arc and parts of the backarc high heat flow values 100 mw m2 support the idea that large areas of the deeper andean crust are strongly weakened by the presence of partially molten rocks resulting in reduced seismic velocities with the western cordillera the active volcanic arc of the andean mountain range acting as a ductile buffer between the two more rigid crustal blocks of the forearc and backarc regions

the shaimerden supergene zinc deposit kazakhstan a preliminary examination the shaimerden supergene zinc deposit in the southern urals mountains is located in the province of kostanai in northwest kazakhstan it lies at the southern end of the kostanai megasyncline a north northeast trending structurally controlled area of lower paleozoic clastic and carbonate sedimentary rocks and volcanic rocks a zinc lead resource estimated at 4 645 100 tonnes at 21 06 percent zn has been defined the deposit is hosted within a sequence of intertidal to open marine carbonates and evaporites of visean early carboniferous age although drilling to date has not intersected a fault significant faulting in the area is suggested by the presence of polymict debris flows comprising a wide range of carbonate facies and by large variations in micropaleontologic dates sulfide deposits replaced hydrothermally dolomitized carbonates and were subsequently reworked into polymict conglomerates of probable carboniferous age that were deposited in a marine environment weathering of the sulfide mineral deposits took place during the triassic period following uplift during the late paleozoic the weathering occurred in situ and small intervals of relict sulfides were preserved in the center of the deposit the degree of weathering increases outward from the center of the deposit which passes from massive sulfide to massive hemimorphite smithsonite to weathered clays with hemimorphite smithsonite fragments the supergene minerals are overlain by bauxitic clays of cretaceous age and quaternary silty soils and sands

ferruginous and manganiferous haloes around massive sulphide deposits of the urals proximal brecciform ferruginous and manganiferous rocks related to vms deposits of the urals are subdivided into jasperites gossanites and umbers in addition to thin bedded jaspers and cherts the coherence of host rock composition and mn fe fertility of the sediments have been established fe poor pink hematitic and gray sulphidic chert are typical of the felsic class of vms deposits in contrast the contents of fe vary from high to moderate in ferruginous rocks enclosed in basaltic units associate with vms deposits fe and mn rich ferruginous rocks and umbers occur in association with limestones and calcareous sedimentary rocks in both types of volcanic sequences a common feature of jasperites and umbers is the abundance of replacement textures of hyaloclastites and carbonates by hematite and silica in addition replacement of clastic sulphides by hematite and magnetite is a characteristic genetic feature of gossanites all of these sedimentary rocks are accompanied by pseudomorphs of hematite and quartz formed after bacterial filaments the abundance of replacement textures are supportive of the halmyrolysis model in addition to hydrothermal sedimentary and sub seafloor hydrothermal replacement theories study of chemical zonation of altered hyaloclasts shows depletion of their rims not only in mobile na k mg but also in immobile al ti and ree whereas si and fe are concentrated in situ the halmyrolysis model presented here involving organic rich calcareous hyaloclastic sediments resolves the problem of subtraction of al ti ree and other elements which are commonly immobile under hydrothermal conditions the evolution of the halmyrolysis process from acidic reducing to alkaline oxidized conditions infers a possible range in transformation from fe ii mg smectites to fe silicates and fe si oxides as precursors of brecciform jasperite and thin bedded jasper the higher acidic initial stage of gossanite formation seems to be required for oxidation of organic matter and or pyrite the acidic condition facilitates the temporal preservation of immobile elements al ti ree in immature chlorite hematite gossanites another peculiarity of the gossanite forming processes is the likely sorption of p u and v by iron hydroxides displacing sulphides the general evolution of all ferruginous sediments results in complete fe 2 oxidation and silicification accompanied by subtraction of other elements the vertical diagenetic differentiation leads to concentration of mn carbonates silicates and oxyhydroxides into the tops of jasperite and gossanite layers mn oxyhydroxides scavenge positively charged hydrated cations like co and ni near vent bacterial communities may activate the processes of volcanic glass and sulphide degradation the proposed processes of halmyrolysis followed by silicification in situ may resolve the enigma of silica rich sediment formation in a silica undersaturated ocean the discrimination between gossanite and jasperite is useful for elaboration of new criteria for local exploration of vms and mn deposits halo dispersion of gossanites covering an area about two to three times that of the massive sulphide deposit is a good vector for ore body discovery proximal gossanites can be differentiated from jasperites by presence of relic sulphide clasts or elevated contents of chalcophile elements cu fe zn pb bi te as sb ba noble metals au ag and distinct ree patterns with la and eu positive anomalies the development of halmyrolysis and biomineralization models merit further elaboration and testing in on going research in order to add or revise theories of iron and manganese deposit formation 2012 elsevier b v