theoretical models of magnetic anisotropy to strain relationship revisited abstract mathematical modelling of the relationships between the low field magnetic anisotropy and strain are redeveloped and the calculated data are compared with the degree of anisotropy for various rock types it is found that the degree of anisotropy for realistic strain magnitudes is unrealistically high in the passive model the ductile model for which the degree of anisotropy depends on the magnetic grain the matrix viscosity ratio becomes realistic at high viscosity contrasts in the line plane model the theoretical degree of anisotropy corresponds well to the natural degree of anisotropy for rocks in which the carrier of magnetic anisotropy is either magnetite or phyllosilicate minerals by contrast in the case of haematite and pyrrhotite the modelled degree of anisotropy is much higher than the natural values in the viscous model the calculated degree of anisotropy corresponds well to that measured in sedimentary and volcanic rocks in the models imposing pure shear strain the natural logarithm of the degree of anisotropy to natural strain relationship can be approximately represented by a straight line at least for low to intermediate strains the proportionality constant varies according to the specific model and the specific carrier of the anisotropy of magnetic susceptibility

emplacement and deformation of granites during transpression magnetic fabrics of the archean sparrow pluton slave province canada abstract the sparrow pluton is part of the prosperous suite of two mica granites that crop out within amphibolite grade meta greywackes of the southern yellowknife domain in the slave province of the canadian shield the magnetic susceptibility k and the anisotropy of magnetic susceptibility ams were used to systematically map the structural patterns in the pluton and to establish the relationship between plutonism and late archean tectonics in the region paramagnetic fe phyllosilicates biotite chlorite and very fine grained magnetite contribute to k and to the ams the magnetic foliation and the magnetic lineation are predominantly controlled by the biotite fabrics and their orientations are consistent with the regional d 2 strain field the horizontal magnetic lineations in the sparrow pluton suggest a horizontal stretching component associated with the regional d 2 event the zonation defined by k values is compatible with a fold pattern trending parallel to the regional f 2 folds and s 2 foliation and to the magnetic fabric trends in the pluton the intensities and symmetries of the ams also define map patterns that are consistent with d 2 deformation microstructural study indicates the pluton recorded d 2 strain as it crystallized and cooled from the solidus demonstrating syn d 2 emplacement the results indicate the pervasive structural patterns in the sparrow pluton are an integral part of the regional strain field and that they are kinematically consistent with a transpressive d 2 strain regime mapping the fabric patterns within syntectonic plutons provides a useful approach to the kinematic analysis of synemplacement deformation events in multiply deformed metamorphic terranes

magnetic fabric of granitoids from southern corsica and northern sardinia and implications for late hercynian tectonic setting anisotropy of magnetic susceptibility ams data 180 sites from hercynian granitoids from southern corsica france and northern sardinia italy provide a high density net of structural information for this part of the european hercynian belt two main groups of granitoids defined according to petrography and relative chronology provide contrasting ams results for both groups shallowly dipping magnetic foliations and lineations suggest that these granitoids were emplaced as large scale shallowly dipping sheets or open funnel shaped structures at a high structural level in non leucocratic granitoids 305 300 ma foliation and lineation trajectory maps reveal antiforms and synforms with a n130 axial trace intersection of the foliation planes indicates a n120 low plunging fold axis revealing a n120 maximum stretching direction slightly younger leucocratic granitoids 295 285 ma bounded by late hercynian faults display n50 lineations parallel to the elongated shapes of these intrusions this structural pattern is undisturbed by the faults and suggests an intrusion in decakilometre scale tensional fractures indicating a n140 instantaneous stretching direction compatible with the stretching direction evidenced in non leucocratic granitoids a younger c n20 oriented permian dyke swarm confirms the permanence of this stretching direction over at least 35 ma and indicates a coaxial strain regime to integrate these new data within a broader context in the hercynian belt corsica has to be back rotated clockwise by 70 to its permian position which indicates a north to n30 stretching direction for the 305 285 ma interval compatible with the post collisional strain and stress fields of the french massif central at about the same period

magnetic susceptibility of the rock matrix related to magnetic fabric studies non ferromagnetic minerals constitute what is called the rock matrix whose susceptibility k1 is directly accessible using only high magnetic fields measurements on minerals and a wide range of rock types show that k1 is mainly due to paramagnetism and hardly exceeds 10 3 si with an anisotropy degree p less than 1 35 different methods to estimate the role of the matrix component in low field susceptibility k and its anisotropy include petrological and chemical analysis evolution of p vs k low temperature studies and comparison of k with remanent magnetizations

synmagmatic deformation patterns in the old woman mountains se california abstract synmagmatic structures within granitic plutons may provide insight into the interplay between plutonism and regional deformation at mid crustal levels within the late cretaceous old woman pluton mojave desert se california synmagmatic structures include magmatic fabrics parallel to wall rock foliations melt filled shear zones folded gneissic xenoliths and schlieren with axial planar magmatic fabric deformation continued below granite solidus temperatures in shear zones on the pluton margins these structures permit reconstruction of a sheet like pluton that was emplaced under regional extension taken together with published thermochronometric data the synmagmatic structures constrain the role played by magmatic events in the collapse of a thickened crustal section the post plutonic cooling history suggests rapid uplift and denudation ending by 65 ma we argue that extensional deformation overlapped and post dated pluton emplacement and may have contributed to tectonic unroofing we suggest that magma emplacement can trigger subsequent extensional collapse in overthickened crustal blocks

microstructure and magnetic susceptibility applied to emplacement kinematics of granites the example of the foix pluton french pyrenees abstract the variscan foix granite 40 km 2 central pyrenees was subjected to detailed microstructural magnetic susceptibility and anisotropy studies magnetic susceptibility is shown to be of dominant paramagnetic origin its magnitudes clearly define a zoning which compares with the petrographic zoning and reveals that the pluton is the southern remnant of a normally zoned pluton truncated during alpine tectonics magnetic susceptibility anisotropy characterizes the planar and linear preferred orientations of the main iron bearing silicates namely biotite and accessory amphibole it is argued that these fabrics also reflect the flow pattern of the granite microstructural observations aid in distinguishing the magmatic and late magmatic fabric signatures main body from the post magmatic solid state signature leucogranite in order to account for the consistently subhorizontal and ne sw directed magmatic lineations in the northern sector of the foix granite an oblique intrusion is proposed it may be coeval with the early variscan regional sw trending shearing event steepening of the structures in at least part of the southern sector may be coeval with the late development of upright folds and vertical cleavage in the country rocks the utility of combined microstructural and magnetic susceptibility studies is demonstrated as an aid in the structural interpretation of granite intrusions which act as kinematic markers of their host terranes

diagnostic calculations of the circulation in the martian atmosphere the circulation of the martian atmosphere during late southern summer is derived from atmospheric temperature and dust distributions retrieved from a subset of the mariner 9 infrared interferometer spectrometer iris thermal emission spectra ls 343 348 santee and crisp 1993 zonal mean zonal winds are calculated by assuming gradient wind balance and zero surface zonal wind both hemispheres have intense midlatitude westerly jets with velocities of 80 90 m s near 50 km in the southern tropics the winds are easterly with velocities of 40 m s near 50 km the net effect of the zonal mean meridional circulation and large scale waves can be approximated by the diabatic circulation which is defined from the atmospheric thermal structure and net radiative heating rates the radiative transfer model described by crisp 1990 and santee 1993 is used to compute solar heating and thermal cooling rates from diurnal averages of the retrieved iris temperature and dust distributions at pressures below 4 mbar there are large net radiative heating rates up to 5 k d in the equatorial region and large net radiative cooling rates up to 12 k d in the polar regions these net radiative heating rates are used in a diagnostic stream function model which solves for the meridional and vertical components of the diabatic circulation simultaneously we find a two cell circulation with rising motion over the equator poleward flow in both hemispheres sinking motion over both polar regions and return flow in the lowest atmospheric levels the maximum poleward velocity is 3 m s in the tropics at 55 km altitude and the maximum vertical velocity is 2 5 cm s downward over the north pole at 60 km altitude if these large transport rates are sustained for an entire season the martian atmosphere above the 1 mbar level is overturned in about 38 days this diabatic circulation is qualitatively similar to the terrestrial diabatic circulation at the comparable season but is more vigorous

age of the camaguey gold silver district cuba tectonic evolution and preservation of epithermal mineralization in volcanic arcs epithermal precious metal deposits commonly form in middle to late cenozoic volcanic arcs several kilometers above the level at which batholiths are emplaced this relationship has led to the guideline that epithermal deposits should not be sought in volcanic arcs where batholiths are widely exposed the camaguey district in central cuba violates this tenet and provides important insights into arc forming processes that create and expose epithermal deposits the camaguey district hosts the jacinto and florencia low sulfidation vein deposits and the deseada and golden hill high sulfidation prospects all of which are within a few kilometers of the large camaguey batholith some of the deposits such as jacinto lie immediately below a local paleosurface that exposes the batholith and probably formed when rhyolite domes were emplaced onto this surface a second group of deposits such as the deseada high sulfidation system is hosted by volcanic rocks that overlie the camaguey batholith and stand above the paleosurface new ar ar age measurements indicate that jacinto type deposits and prospects cooled through ar ar closure temperatures for adularia and muscovite at about 71 ma and are slightly younger than the widespread granodiorite facies of the camaguey batholith in contrast deseada type deposits and mineralized zones cooled through roughly similar closure temperatures for sericite illite and alunite at about 80 ma which is older than the age of the immediately underlying camaguey batholith these ages are best explained if the camaguey batholith and surrounding volcanic rocks underwent rapid uplift probably by tectonic unroofing to form the paleosurface below which jacinto type deposits formed and if the older deseada type deposits were thrust into place over this surface this tectonic unroofing probably took place in an extensional regime generated during oblique convergence of cuba with yucatan as the greater antilles arc moved north into the caribbean region during late cretaceous time thrusting probably accompanied late stages of this convergence and or later collision with the bahamas bank in eocene time all of the epithermal deposits were covered by late cretaceous eocene sedimentary rocks that have been removed only recently by erosion thus accounting for the preservation of these unusually old epithermal deposits extensional events causing tectonic unroofing are probably common in arcs that undergo oblique convergence and could be an important agent for formation of epithermal deposits in other parts of the world preservation of these deposits might be aided by deposition and later erosion of sedimentary cover related to later collisions

geology and geochemistry of the early permian axi low sulfidation epithermal gold deposit in north tianshan nw china abstract the axi gold deposit containing 12 mt of ore with an average au grade of 5 g t is the largest low sulfidation epithermal gold deposit in chinese tianshan it is hosted by late devonian to early carboniferous continental arc volcanic rocks in the tulasu volcanic sedimentary basin in north tianshan nw china the orebody is controlled by annular and radial faults associated with volcanic crater and later nw trending faults four stages of ore formation could be identified based on petrographic studies i chalcedony ii gold bearing pyrite quartz veins and breccias iii gold bearing marcasite quartz carbonate veins and iv quartz barite calcite veins electrum precipitated in stage ii 285 195 c log f s 2 6 7 to 13 and stage iii 190 95 c log f s 2 15 8 to 25 6 the chalcedony formed in stage i is strongly enriched in lree la yb 4 5 36 2 compared with later gold bearing pyrite quartz veins and quartz barite calcite veins la yb 1 2 2 0 o h isotopic data indicate that fluid mixing is a major mechanism causing electrum precipitation in stage ii hydrothermal breccias consisting of chalcedony altered wall rocks and gold bearing pyrite quartz veins stage ii are cemented by gold bearing marcasite quartz carbonate assemblages stage iii which implies that brecciation plays an important role in stage iii ore formation re os isotopic analyses of gold bearing pyrite samples yield an 187 re 188 os 187 os 188 os isochron age of 299 35 ma with an initial 187 os 188 os ratio of 0 57 0 37 k ar ages of four intensively sericitized andesitic wall rocks range between 286 and 293 ma these early permian ages are much younger than the late devonian early carboniferous host volcanic rocks but overlap the age range of postcollisional granitoid in the tulasu basin the re os isotopic compositions and the ages suggest that mantle derived components were involved in the axi ore forming system in a postcollisional setting

magnetic fabric of the barrington passage pluton meguma terrane nova scotia a two stage fabric history of syntectonic emplacement abstract structural analysis and the anisotropy of magnetic susceptibility ams are used to document the internal magmatic to high temperature subsolidus fabrics of the tonalitic late devonian barrington passage pluton the ams fabric orientations compare favorably with mesoscopic scale fabrics in general the k1 k2 principal plane of the ams is close to the observed mineral foliation defined by biotite and plagioclase and the k1 axis is aligned parallel to a mineral lineation defined by the same minerals and to a locally developed weak extension lineation defined by quartz measurement of the anisotropy of anhysteretic remanence aar and image analysis of biotite preferred orientations confirm that the orientation of the ams is principally controlled by biotite locally anomalous ams orientations are attributed to the influence of fine grained magnetite crystals the presence of which is revealed by measurements of hysteresis and coercivity properties a two stage fabric history is revealed first horizontal fabrics were formed foliation compositional banding during emplacement of a laccolith like pluton the second stage involved synmagmatic folding of the horizontal foliation and banding in response to regional contraction associated with the acadian orogeny with development of a lineation that records stretching parallel to the fold axis the results demonstrate that the barrington passage pluton was emplaced during the main phase of the acadian orogeny a model is proposed that depicts the barrington passage pluton as the folded base of a larger syntectonic pluton that is now largely eroded off

regional scale strain variations in banded iron formations of eastern india results from anisotropy of magnetic susceptibility studies anisotropy of magnetic susceptibility ams data are used as a tool to determine strain variations in different parts of the banded iron formations bifs of the bonai synclinorium eastern india ams data of 88 cylindrical cores drilled from 29 samples collected from the limb and hinge parts of mesoscopic scale folds as well as different parts of the entire synclinorium are presented it is found that the samples from limbs of small scale folds and also from limbs of the regional scale synclinorium have higher degrees of anisotropy than the hinges this is inferred to indicate that the limbs accommodated higher strain than the hinges ams orientation data are analysed in conjunction with field data it is concluded that the magnetic fabric developed in the limbs as well as hinges of the bifs of the study area is related to deformation and is not a manifestation of sedimentary fabric

strain partitioning during partial melting and crystallizing felsic magmas abstract the rheology of partly molten felsic systems changes dramatically during the onset of melting and through crystallization solid to liquid and liquid to solid transitions are not rheologically identical contradicting the concept of a unique rheological critical melt percentage we use four thresholds separating the successive stages according to the melt fraction for the melting transition 1 the liquid percolation threshold connects the melt pockets at about 8 of melt thus allowing local magma displacement at the metric scale and 2 for greater melt percentages 20 25 a melt escape threshold corresponds to the onset of transport over large distances of the melt and part of the residual solid phase leading ultimately to granitic bodies for the solidification transition 3 the first formation of a rigid framework of crystals which can accumulate stress although the melt can still flow corresponds to the rigid percolation threshold 55 solids and 4 the system becomes totally locked at about 72 75 solid which corresponds to the particle locking threshold the present paper focuses on strain partitioning induced by the coexistence of two contrasting rheological phases between these thresholds on a variety of scales non coaxial deformation is preferentially accommodated by the lower viscosity melt which increases the vorticity in the melt phase and reinforces asymmetries in the flow pattern strain partitioning also increases the scale length of the weakest phase during melting and magma ascent whereas strain partitioning decreases the scale length during crystallizing strain partitioning also affects the migration of melt by raising the particle locking threshold and lowering the melt escape threshold for three dimensional deformations such as transpression the direction of melt segregation e g horizontal may differ from the direction of melt migration e g vertical

active sand transport along a fjord bottom channel bute inlet british columbia an underwater channel system is incised in the holocene fjord basin sediments of bute inlet british columbia high resolution side scan sonar swaths and seismic profiles reveal two channels within a zone of extensive rotational sliding on the slopes of a fjord head delta the channels coalesce into a single sinuous channel that extends 14 km downfjord on a 0 9 slope where it splits into two distributaries which continue another 18 km ending within stacked depositional lobes piston cores show sands in the channels and lobes in contrast to deep water silty clays in the basin floor the sea floor features and sediment distributions result from active highly mobile slide generated sediment flows which transport sands via the channels from the delta to the fjord basin

fluid inclusion and stable isotope study of the lubin zardeh epithermal cu au deposit in zanjan province nw iran implications for ore genesis abstract the lubin zardeh deposit is located in the western alborz magmatic belt 45 km ne of zanjan iran this deposit contains polymetallic cu au pb zn mineralization which is hosted by the cenozoic volcanic intrusive rocks of mainly intermediate and acidic composition pyrite chalcopyrite galena sphalerite bornite and tennantite tetrahedrite with native gold and silver are present in the ores quartz adularia and clay minerals illite montmorillonite with minor calcite are the most abundant gangue minerals and generally occur as fine grained assemblages some are however medium and coarse grained assemblages the ore minerals show disseminated vein veinlet replacement and brecciated textures while the gangue minerals represent replacement cockade crustiform colloform comb vein veinlet and plumose textures alteration haloes along the main vein are silicic argillic illite montmorillonite sericitic and pyritic gold contents of the quartz chalcopyrite gold veins range from 0 002 to 10 ppm with an average of 0 52 ppm the average values for total reserve of 0 5 mt of lubin zardeh deposit has been determined 1 3 0 7 and 0 4 for cu pb and zn respectively most of fluid inclusions in the quartz gold sulfide veins consist of two vapor and liquid phases at room temperature the primary fluid inclusions have a low to intermediate homogenization temperature between 127 and 327 c and salinity between 4 07 and 13 98 wt nacl equivalent stable isotope and fluid inclusion studies indicate that mineralization occurred in two stages at lubin zardeh deposit i e stage i along which base metal deposited and stage ii which is associated with copper and gold mineralization the 18oquartz values from stage i and stage ii range from 9 56 to 12 77 and from 7 23 to 9 24 respectively while their 34s values of sulfide minerals range from 0 9 to 6 2 and form 6 6 to 1 9 the isotopic and microthermometric data indicate that the hydrothermal solution evolved through mixing of magmatic fluids with meteoric waters boiling of magmatic fluid and mixing with meteoric waters were the main mechanisms of ore deposition in the lubin zardeh low sulfidation epithermal deposit

origin of the mclaughlin mine sheeted vein complex metal zoning fluid inclusion and isotopic evidence the mclaughlin deposit is a large hot spring type gold deposit located in the northern coast ranges of california at the faulted lithologic contact between the coast range ophiolite and the great valley sequence the mclaughlin deposit is centered around the sheeted vein complex a large multistage vein swarm localized in a dilation zone formed by rheologic contrasts in the footwall polymictic melange the surface expression of the sheeted vein complex is a subaerial sinter terrace which merges into the sheeted vein complex metal zoning in the sheeted vein complex is highly telescoped the sinter is enriched in mercury whereas gold and silver are restricted to the upper 350 m with the proportion of gold to silver decreasing with depth gold is typically present as electrum and is associated with silver and base metal bearing sulfosalts below 350 m mineralization is dominated by small quartz veins with base metal sulfides fluid inclusion studies indicate that nacl is the main dissolved salt in concentrations averaging 2 4 wt percent nacl equiv the bulk of the salinity data can be explained by variable amounts of adiabatic boiling and mixing with steam heated ground water fluid inclusion homogenization data ranges from 121 degrees to 263 degrees c with the deepest portion of the system examined having the highest temperatures and the shallowest samples having the lowest temperatures fluid inclusion gas concentrations vary with depth below the sinter co 2 and to a lesser extent ch 4 shows a systematic increase with depth fluid pressures calculated from fluid inclusion homogenization temperatures and gas analysis are in excess of the hydrostatic pressure and approach or exceed lithostatic pressure self sealing of the system and tectonic dilation most likely resulted in catastrophic phase separation and hydrothermal eruption breccias geothermometry results based on fluid inclusion gas ratios show a reasonable correspondence with the highest fluid inclusion homogenization temperatures there is a strong trend for decreasing delta 18 o quartz values with depth due to the effect of temperature the calculated delta 18 o sub h 2 values are fairly constant at about 9 to 10 per mil oxygen and hydrogen isotope values as well as geologic relationships are consistent with those of hydrothermal fluids originating as meteoric water these evolved to increasingly high ones by interaction with great valley sequence sedimentary rocks lead isotope compositions of sulfides and potential source rocks indicate that lead and by inference other metals was derived from a crustal source the lead source may have been detritus from the sierra nevada batholith that comprises the great valley sequence or alternatively it may have been derived from a thorough mixture of radiogenic lead and nonradiogenic lead that occurred prior to mineralization

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

geochemical fluid inclusion and o h s isotope studies of the milajerd au polymetallic prospect central iran implications for ore genesis abstract the milajerd pb zn au polymetallic prospect in naein qom magmatic zone is a favorable target for exploration geological and geochemical characteristics such as setting alteration assemblages fluid inclusion microthermometry and stable isotopes are consistent with the milajerd pb zn au polymetallic prospect being a typical low sulfidation ls epithermal deposits the au polymetallic mineralization occurs mainly as structurally controlled veins and brecciated dikes hosted by calc alkaline volcanic rocks mineralization at the milajerd prospect is controlled by an annular fault system the sulfide mineralogy of the deposit includes sphalerite galena pyrite arsenopyrite and marcasite the principal gangue minerals are quartz calcite sericite and adularia the alteration assemblages include quartz pyrite quartz sericite pyrite and chlorite calcite epidote fluid inclusions in quartz sulfide veins have homogenization temperatures th of 158 255 c and salinities of 4 7 7 7 wt nacl equiv whereas those in barren quartz carbonate veins yield th values of 135 176 c and salinities of 1 1 4 3 wt nacl equiv the h and o isotopic composition dwater 120 to 92 inferred 18owater 6 2 to 3 5 of fluid inclusions in quartz veins imply that cooling a mixed magmatic and meteoric waters was the main mechanisms of ore deposition at milajerd deposit the 34s values of ore sulfides are mostly close to zero avg 0 1 indicating a magmatic source of sulfur which could have emanated directly from magmatic activity or have been leached from the surrounding volcanic rocks

subepithermal au pd mineralization associated with an alkalic porphyry cu au deposit mount milligan quesnel terrane british columbia canada at the mount milligan cu au porphyry deposit quesnel terrane british columbia canada barren and weakly mineralized late stage hydrothermal veins occur in volcanic rocks adjacent to zones of cu au porphyry mineralization and have overprinted the porphyry stage veins the earliest of the late stage hydrothermal veins are barren and consist of quartz pyrite carbonate chlorite tourmaline these veins are similar to transitional to late stage hydrothermal veins in other alkaline porphyry cu au deposits and we consider these to be the equivalent of transitional post porphyry pre epithermal quartz sericite pyrite veins in calc alkaline porphyry environments a later generation of volumetrically minor mineralized veins are composed of pyrite hg and as bearing quartz carbonate chlorite and contain early electrum arsenopyrite tetra hedrite tennantite platinum group element pge tellurides galena sphalerite barite and chalcopyrite as inclusions in pyrite and a later assemblage of electrum pge tellurides arsenides and antimonides galena sphalerite chalcopyrite and various au ag te bi minerals in annealed fractures and open space infillings in quartz and pyrite metal precipitation in these veins was temporally and spatially associated with the deposition and later recrystallization of pyrite primary fluid inclusions in quartz in the barren and weakly mineralized veins are two phase l v homogenize to liquid over a narrow range in t 170 270 c n 96 12 veins and show a wide range in salinity 4 2 wt nacl equiv to 28 7 wt cacl2 equiv when all samples are considered however individual veins show narrow ranges in salinity and homogenization temperature la icp ms analyses indicate that the fluids were highly enriched in as to 2 260 ppm sb to 230 ppm b to 5 400 ppm au 1 2 ppm and pd 0 5 1 ppm but depleted in cu 80 ppm compared to typical porphyry stage fluids metal ratios in the fluids overlap with bulk rock metal ratios in the mineralized veins the inclusions are interpreted to contain a contracted magmatic vapor produced by boiling that lost cu during the formation of porphyry stage veins at depth fluids show decreasing b as sb and increasing sr ca and salinity with time stable c o and h isotope analyses of vein minerals indicate that mixing of this magmatic fluid with meteoric water was not responsible for metal deposition rather metal precipitation was possibly the result of mixing of the magmatic derived fluid with a heated saline groundwater the precious and accessory metal mineralogy of the hydrothermal veins is similar to that found in low to intermediate sulfidation epithermal systems fluid inclusion microthermometry and chlorite thermometry constrain the approximate formation conditions of the veins between 200 and 1 500 bars and 240 and 280 c after the formation of the mineralized veins circulation of low salinity metal depleted fluids occurred these latest stage fluids may have formed by mixing of the saline magmatic fluid groundwater hybrid with meteoric water the results of this study suggest a genetic link between porphyry stage events and the deposition of au and pge in late stage veins in an alkalic igneous environment recognition of hydrothermal processes involving the transport of au pge as sb bi te b rich fluids in the subepithermal regimes implies that low sulfidation epithermal au deposits may have been present in the shallower parts of the magmatic hydrothermal complex and that there is potential for the discovery of pge rich epithermal veins in less deeply exhumed terranes on the other hand the formation of high grade low sulfidation epithermal au pge deposits may be prohibited if porphyry epithermal transitional fluids precipitate ore metals through mixing with groundwater prior to reaching the level where meteoric water mixing and epithermal boiling normally occur

revisiting hydrocarbon phase mobilization of au in the au hg mclaughlin mine geysers clear lake area california abstract carbonaceous material cm enriched silica is co located with gold au mineralization at the au hg mclaughlin deposit geysers clear lake area california u s a the co location suggests that hydrocarbons hc may be involved in mineralization and metal concentration processes but little is known about the role of hc in the formation of ore deposits previous studies noted liquid oil inclusions in samples from the mclaughlin deposit and proposed that the hc were liquid at the time of ore deposition hydrocarbon materials in the mclaughlin deposit occur as solid and liquid textural evidence suggests that hydrocarbon rich and aqueous silica rich fluids were present simultaneously as well as separately in alternating pulses synchrotron x ray fluorescence microscopy of microscopic silica free carbonaceous material reveals that the cm contains abundant ore metals e g au ag hg and pb the cm could have become metal enriched by scavenging metals from other ore fluids or it could have transported metals when the cm was still liquid with subsequent in situ degradation due to hydrothermal heat gold concentrations of up to 18 ppm were measured via acid digestion of solid and liquid hc material and subsequent inductively coupled plasma mass spectrometry icp ms analyses hydrocarbon material with liquid to medium viscous properties bearing 10 8 ppm au provides evidence that au in liquid hc in the mclaughlin au hg deposit is still mobile and that remobilization and or transport of metals to the deposit by hc liquids cannot be ruled out

stabilization of the aravalli craton of northwestern india at 2 5 ga an ion microprobe zircon study abstract in order to establish the stabilization age of the aravalli craton of northwestern india we have used an ion microprobe to measure 207 pb 206 pb ages of zircons from six samples collected from the southern aravalli mountains our analyses gave precise results for four granitoids whose minimum crystallization ages ranged between 2562 6 and 2440 8 ma 1 a single sample of gneiss gave an age of 2502 4 ma which is unexpectedly younger than an age of 3281 ma which we previously obtained from another gneissic sample we interpret the 2502 ma age as the time of emplacement of the sample s igneous protolith suggesting that the mewar gneiss contains multiple metamorphic components of differing ages based on our data we conclude that the southern segment of the aravalli craton had broadly stabilized by 2 5 ga this stabilized landmass formed the basement on which the younger aravalli supergroup was unconformably deposited this study represents the first application of a small geometry ion microprobe for routine geochronology

variscan dextral transpression in the french pyrenees new data from the pic des trois seigneurs granodiorite and its country rocks abstract new structural data from both the trois seigneurs granodiorite and its country rock lead to new conclusions about the variscan tectonic history of this part of the pyrenees sedimentary rocks of the massif that increase in metamorphic grade from north to south are imprinted by a single major deformation responsible for both the tight upright e w trending folds with vertical to steeply n dipping foliations and the gently w plunging stretching lineations syntectonic emplacement of the pic des trois seigneurs granodiorite is demonstrated by the parallelism between structures of the pluton as determined by magnetic fabric measurements and the foliations and lineations imprinted in the country rocks large deformation of the granodiorite magma during emplacement is indicated by strong anisotropy and ubiquitous magmatic microstructures the high thermal gradients of regional metamorphism which is also syntectonic are attributed to a large thermal aureole provided by deep seated magma reservoirs shear sense criteria in xz thin sections of the metasedimentary country rocks indicate a dextral sense of the non coaxial component of strain throughout the massif and regardless of metamorphic grade the overall structure of the massif is concluded to have derived from a major shearing event that is equated with the d 2 main phase observed in the entire variscan pyrenees as the e w oriented stretch and dextral shear cannot be separated from compressive structures generally considered to be characteristic of d 2 this phase is concluded as representing regional transpression

structural relationships and srnd isotope systematics of polymetamorphic granitic gneisses and granitic rocks from central rajasthan india implications for the evolution of the aravalli craton this paper reviews the state of structural and geochronological knowledge of precambrian cratonic rocks in part of central rajasthan india and contributes new observations and isotopic data on the structural features and age of granitic rocks in the area the granitic rocks comprise plutons of two suites bgc and sendra suites which intrude ortho and paragneisses the archean banded gneiss complex bgc and its inliers as well as the proterozoic delhi supergroup nearly all the plutons show a foliation and a lineation which are mostly the result of solid state deformation although a magmatic component of strain is apparent in some of them the intensity of these structural fabrics varies from weak to extremely strong samples of granitic rocks from the bgc suite yield ages from sm nd isotopic data which scatter around a 2 83 ga reference isochron nd t of 4 1 with depleted mantle model ages ranging from 2 6 to 3 0 ga scatter of the data suggests that the bgc is a composite group of gneisses and confirms the antiquity of the bgc within this part of the aravalli delhi orogenic belt rb sr isotopic data of the bgc suite lie on a 1 7 ga reference isochron indicating a thermal event at that time data from plutons of the sendra suite on the other hand show some scatter but define a model ii isochron with slope equivalent to an age of 0 966 250 ga initial 87sr86sr of 0 70390 0 01889 mswd 311 the scatter of data could reflect open system behavior during a subsequent thermal event malani volcanics although independent evidence for such is lacking in the study area ages calculated from our rb sr data are within the error of published results from previous workers structural observations on granitic rocks within the bgc inlier at ajmer suggest that the inlier could represent a remobilized diapiric ridge emplaced into the delhi supergroup during the 1 7 ga thermotectonic event contemporaneously with formation of d1 structures in the wall rock although the radiometric age of the latter structures is not well constrained microtexture mineralogy and field relations of granitic rocks of the sendra suite point to those plutons being emplaced into the delhi supergroup during the 0 966 ga thermotectonic event late syntectonic relative to d2 indicating that d2 is 0 96 1 0 ga d3 represents retrograde deformation synchronous with cooling of the regional thermal framework and local pluton cooling probably between 0 96 and 0 90 ga further geochronological geochemical and structural work on the plutons and wall rock of both suites is necessary to establish a rigorous thermotectonic chronology by which to accurately model the crustal evolution of this part of central rajasthan

the kohuamuri siliceous sinter as a vector for epithermal mineralisation coromandel volcanic zone new zealand the kohuamuri siliceous sinter is the largest known fossil hot spring system in the hauraki goldfield a 200 40 km volcanic terrain with at least 50 adularia illite epithermal deposits formed 16 3 5 6 ma within the coromandel volcanic zone new zealand the sinter is associated with rhyolite and ignimbrite of the whitianga caldera miocene pliocene and consists of two deposits the kohuamuri deposit itself a large in situ outcrop 47 000 m2 and its associated sinter boulder field 4500 m2 and the kaitoke deposit 900 m to the southwest comprising boulders in a landslide situated on a normal fault the well preserved macroscopic and microscopic textures at kohuamuri are similar to actively forming and ancient hot spring deposits elsewhere derived from deep circulating magmatically heated near neutral ph alkali chloride fluids oversaturated in amorphous silica and that discharge at the earth s surface at 100 c lithofacies petrography mineralogy as well as trace element concentrations of the kohuamuri kaitoke deposits were used to locate likely palaeo thermal conduits from the deep reservoir and to reconstruct the palaeoenvironmental setting of the siliceous sinter as an aid to assessing the economic potential of the ancient geothermal system both deposits contain the high temperature 75 c geyserite lithofacies with the kohuamuri deposit also exhibiting textures affiliated with cooler middle and distal sinter apron areas as well as geothermally influenced marsh facies trace element analysis of sinter lithofacies revealed concentrations and zonations of au ag base metals pb cu zn and pathfinder elements as sb associated with epithermal deposits elevated in the proximal vent area and providing evidence of possible au and ag ore mineralisation at depth the methodology used in this study could be utilised globally to identify and assess as yet unidentified epithermal deposits

geology of the ivanhoe hg au district northern nevada influence of miocene volcanism lakes and active faulting on epithermal mineralization the mercury gold deposits of the ivanhoe mining district in northern nevada formed when middle miocene rhyolitic volcanism and high angle faulting disrupted a shallow lacustrine environment sinter and replacement mercury deposits formed at and near the paleosurface and disseminated gold deposits and high grade gold silver veins formed beneath the hot spring deposits the lacustrine environment provided abundant meteoric water the rhyolites heated the water and the faults flow units and lakebeds provided fluid pathways for the hydrothermal fluids a shallow lake began to develop in the ivanhoe area about 16 5 ma the lake progressively expanded and covered the entire area with fine grained lacustrine sediments lacustrine sedimentation continued to at least 14 4 ma and periodic fluctuations in the size and extent of the lake may have been responses to both climate and nearby volcanism the eruption of rhyolite and andesite flows and domes periodically disrupted the lacustrine environment and produced interfingered flows and lake sediments the major pulse of rhyolitic volcanism took place between 15 16 0 05 and 14 92 0 05 ma high angle faulting began in the basement about 15 2 ma penetrated to and disrupted the paleosurface after 15 10 0 06 ma and largely ceased by 14 92 0 05 ma ground motion related to both faulting and volcanism created debris flows and soft sediment deformation in the lakebeds mercury gold mineralization was coeval with rhyolite volcanism and high angle faulting and it took place about 15 2 to 14 9 ma at and near the paleosurface hydrothermal fluids migrated through tuffaceous sediments above relatively impermeable volcanic and paleozoic units creating chalcedonic cinnabar bearing replacement bodies and sinters disseminated gold was deposited in sedimentary and volcanic rocks beneath the mercury deposits although the hydrologic path between the two ore types is unclear higher grade gold silver deposits formed in massive rhyolites and paleozoic quartzites at deeper levels and these mineralized zones possibly represent the feeder zones for the higher level deposits fluctuations in the ground water table locally produced hydrothermal oxidation of the near surface mercury and disseminated gold deposits the locus of mineralization shifted with time moving south and east from its inception point in the west central part of the district thus although mineralization in the district took place during a span of 300 000 years the duration of mineralization at any one place probably was much shorter the low sulfidation deposits of the ivanhoe district formed at the same time and under similar conditions as those in the nearby midas district 15 km to the northwest which includes the large high grade ken snyder gold silver epithermal vein deposit the exposures in the ivanhoe district are interpreted to represent the near surface example of the paleosurface that originally was present above the midas mineralizing system the resulting combined ivanhoe midas model provides an exploration guide for epithermal deposits in similar geologic environments in northern nevada

magnetic properties of the high himalayan leucogranites structural implications the magnetic properties of the high himalayan leucogranites have been investigated on 527 specimens in three plutons everest makalu 6 sites and manaslu 40 sites in nepal and gangotri 43 sites in india susceptibility varies between 2 and 100 10 6 si with an anisotropy ratio up to 1 16 high field and low temperature magnetic measurements together with comparison with weight percent iron demonstrate that anisotropy of magnetic susceptibility is carried by paramagnetic biotite and tourmaline the latter produces an inverse fabric i e with the minimum axis parallel to mineral lineation the magnetic fabric demonstrates complex patterns of stretching lineations during magmatic emplacement and its usefulness in semi quantitatively estimating petrofabric intensity is demonstrated for the biotite bearing facies natural remanent magnetization was measurable at only two sites in everest makalu where there are well defined reverse directions carried by titanomagnetite and pyrrhotite comparison of these preliminary results with predicted directions for stable india suggests northward tilting of about 10 and a small clockwise rotation of this massif

sm nd evidence for 3 3 ga old rocks in rajasthan northwestern india abstract tonalitic to granodioritic gneisses from the basement gneiss of the aravalli region northwestern india define a sm nd isochron corresponding to an age of 3 31 0 07 ga and an initial nd isotopic ratio that is close to chondritic lenticular bodies of mafic amphibolites within the gneisses however define an isochron corresponding to a younger age of 2 83 0 05 ga and small positive initial nd this age is similar to that reported for a large intrusive granite the untala granite in this area and combined with field evidence suggests that mafic volcanism may have been associated with formation of the granite a highly hree enriched garnet separate from one of the tonalitic gneisses defines a two point garnet wholerock isochron age of 2 45 0 02 ga which also is similar to the age of a known thermal event in the region intrusion of the berach and bundelkhand granites at approximately 2 5 ga these results document in broad outline archean crustal formation events in the northwestern segment of the indian subcontinent and demonstrate the need for more detailed studies of the complex terranes mapped by heron 1953 as a single unit the banded gneiss complex

evidence for deformation induced k feldspar replacement by myrmekite several examples of deformation induced myrmekite have been found in two amphibolite facies mylonites derived from granitic protoliths namely a muscovite poor s c mylonite and a single foliation muscovite poor mylonitic gneiss back scattered sem and conventional optical microscopy show that in both rock types syntectonic myrmekitic intergrowths of oligoclase and quartz formed on the two sides of k feldspar grains that faced the local inferred incremental shortening direction for the mylonite myrmekite does not occur on the two ends of the grain that faced the incremental stretching direction the replacement of k feldspar by plagioclase and quartz results in a volume decrease and is favoured on high normal stress sites around the grains we suggest that the ambient temperature pressure and chemical activities were such that the replacement reaction was favoured but the addition of extra strain energy along the high pressure sides of the grains localized the reaction at these sites this energy could arise from elastic strain or strain associated with tangled dislocations or twin boundaries the relative roles of stress and strain energy concentrations in driving the replacement reaction are not known but both were probably important

geologic setting and genesis of the mule canyon low sulfidation epithermal gold silver deposit north central nevada the mule canyon mine exploited shallow low sulfidation epithermal au ag deposits that lie near the west side of the northern nevada rift in northern lander county nevada mule canyon consists of six small deposits that contained premining reserves of about 8 2 mt at an average grade of 3 81 g au tonne it is an uncommon mafic end member of low sulfidation au ag deposits associated with tholeiitic bimodal basalt rhyolite magmatism the ore is hosted by a basalt andesite eruptive center that formed between about 16 4 to 15 8 ma during early mafic eruptions related to regionally extensive bimodal magmatism hydrothermal alteration and au ag ores formed at about 15 6 ma and were tightly controlled by north northwest to north striking high angle fault and breccia zones developed during rifting emplacement of mafic dikes and eruption of mafic lava flows hydrothermal alteration assemblages are zoned outward from fluid conduits in the sequence silica adularia adularia smectite smectite intermediate argillic and smectite carbonate propylitic all alteration types contain abundant pyrite and or marcasite arsenopyrite field relations indicate that silica adularia alteration is superimposed on argillic and propylitic alteration little or no steam heated acid sulfate alteration is present probably the result of a near surface water table during hydrothermal alteration and ore deposition two distinct ore types are present at mule canyon early replacement and later open space filling replacement ores consist of disseminated and vesicle filling pyrite marcasite and arsenopyrite in argillically altered or weakly silicified rocks ore minerals consist of au bearing arsenopyrite and arsenian pyrite overgrowths on earlier formed pyrite and marcasite open space filling ores include narrow stockwork quartz adularia veins banded and crustiform opaline and chalcedonic silica adularia veins silica adularia cemented breccias and sparse carbonate pyrite and or marcasite veins ore minerals consist mostly of electrum and ag sulfide and selenide minerals with minor to major amounts of pyrite marcasite and arsenopyrite and local stibnite both types of ores have similar geochemical signatures characterized by high au ag as sb and se contents locally high hg mo tl and w contents and low cu pb and zn contents stable isotope data indicate that ore fluids consisted dominantly of meteoric water that evolved by deep circulation through paleozoic sedimentary rocks at low water rock ratios about 1 and high temperatures 200 c calculated isotopic compositions of ore fluids are 18oh2o 3 to 7 per mil dh2o 107 to 124 per mil 13cco2 0 to 6 per mil and 34sh2s 3 to 8 per mil the ore fluids obtained much of their h2s and co2 and probably scavenged ore metals and trace elements from the paleozoic sedimentary rocks some h2s and co2 may have been derived from degassing miocene magmas mule canyon formed at shallow depths probably about 100 m below the paleosurface ore fluids were dilute nearly neutral in ph reduced h2s rich and co2 bearing peak temperatures in ore zones reached 230 to 265 c at nearly lithostatic pressures when some crystalline quartz adularia precipitated but most ore formed at temperatures 200 c at near hydrostatic pressures and was accompanied by precipitation of opaline and chalcedonic silica adularia calcite and dolomite deposition of gold in as rich overgrowths on pyrite and or marcasite in disseminated ores occurred owing to decreasing h2s in the ore fluids resulting from sulfidation reactions later electrum and ag selenide precipitation in open spaces occurred owing to boiling loss of h2s to the vapor phase and cooling mule canyon is similar to most other low sulfidation au ag deposits associated with miocene tholeiitic bimodal basalt rhyolite magmatism in the great basin such as sleeper midas and buckhorn major differences at mule canyon are the high fe sulfide contents of some ores and altered wall rocks the paucity of silicification and the presence of only narrow and discontinuous gold bearing siliceous veins these differences primarily are due to the mafic composition of the host rocks mule canyon differs from low sulfidation deposits associated with subduction related calc alkaline porphyry intrusions such as the comstock lode in that a much smaller proportion of water salts and metals was derived from crystallizing magmas

geochemistry and isotopic characteristics of mafic phulad ophiolite and related rocks in the delhi supergroup rajasthan india implications for rifting in the proterozoic abstract regionally metamorphosed mafic rocks phulad ophiolite in the delhi supergroup n w india have tholeiitic compositions the data indicate that there are two independent rock suites phulad barr jetgarh pbj meta basalts with element abundances and ratios resembling midocean ridge basalts morb and ranakpur desuri r d meta basalts and meta gabbros with relatively high al2o3 and low tio2 for similar mgo and high lil element rb ba sr coupled with low hfs zr nb and ree sm nd abundances the compositions of these rocks are characteristic of ocean arc basalts dioritic rocks at ranakpur exhibit low k tholeiitic differentiation trends and have close chemical affinity with the spatially associated meta basalts ranakpur diorites define a sm nd whole rock isochron corresponding to an age of 1012 78 ma with an initial nd isotopic composition that is similar to bulk earth sm nd mineral isochrons for a meta gabbro diorite and quartz diorite at ranakpur correspond to ages of 838 36 835 43 and 791 43 ma respectively these younger ages reflect metamorphic re equilibration of isotope compositions during widespread granite and granodiorite emplacement in this region during the late proterozoic model sm nd ages for the meta basalts calculated relative to undepleted mantle vary between 1300 1700 ma the chemistry of both mafic rock suites indicates derivation from source regions which had been depleted during previous melting episodes so the model ages are a maximum age constraint ranakpur desuri mafic rocks have negative initial nd 1 0 to 4 5 and low sm nd ratios suggesting crustal contamination or reworking with a few exceptions the pbj meta basalts have positive initial nd 1 5 to 4 8 indicating that they were derived from heterogeneously enriched although longterm depleted mantle the chemical data support the hypothesis that the pbj meta basalts are fragments of proterozoic ocean crust

zircon u pb and galena pb isotope evidence for an approximate 1 0 ga terrane constituting the western margin of the aravalli delhi orogenic belt northwestern india abstract zircon u pb ages of 987 6 4 and 986 3 2 4 ma have been established for rhyolites in the southern and northern parts respectively of the ambaji sendra arc terrane in the western fringe of the aravalli delhi orogenic belt pb isotope data for volcanogenic massive sulphide deposits within this arc terrane define a linear trend which is considered a useful reference palaeoisochron or mixing line at an age of about 990 ma and establish continuity of the terrane between ambaji and sendra these results are in contrast to the traditional and continuing assignment of the ambaji sendra terrane to the 1700 ma delhi supergroup the isotopic composition of galena from an apparently epigenetic occurrence at punagarh hill yields a model age of about 940 ma suggesting that the punagarh group could form part of the same arc sequence the phulad lineament which has been considered by most workers to represent the western boundary of the aravalli delhi orogenic belt appears in terms of this stratigraphic assignment to represent an oblique structure which has not greatly offset the punagarh and ambaji sendra domains within the arc terrane the eastern boundary of the terrane is marked by the sabarmati fault a zircon u pb age of 836 7 5 ma for the siwaya gneissic granite in the southern part of the ambaji sendra belt is in accord with previous age data for felsic erinpura plutons that have intruded the arc sequence a monazite age of 826 5 ma may reflect slow cooling of the siwaya pluton or a younger thermal event a model age of about 820 ma for galena is obtained from the tosham sn cu mineralized zone in haryana state about 280 km north northeast of ajmer which is related to the felsic anorogenic malani volcanism plutonism hence this widespread magmatism found extensively west of the ambaji sendra terrane may have been coeval with erinpura plutonism or followed it very closely the present geochronological data warrant the recognition of the ambaji sendra arc terrane as defined here as a distinct metallogenic province which saw the formation of vms type deposits in the late mesoproterozoic around 1 0 ga the pb isotope compositions of the deposits however do not clearly define the metal sources the lead from danva prospect is most primitive and must have the greatest component from a juvenile mantle source the birantiya khurd deposit on the other hand contains a much greater component of lead from a significantly older crustal source

la josefina au ag deposit patagonia argentina a jurassic epithermal deposit formed in a hot spring environment abstract the la josefina jurassic epithermal au ag deposit located in patagonia argentina developed in an extensional setting of a back arc environment associated with a widespread middle late jurassic calc alkaline volcanism block faulting has juxtaposed shallow level features evidenced by hot spring manifestations hydrothermal eruption breccias and au rich veins which suggest that mineralization in these veins could extend far below the depths already tested by core drilling veins are filled by quartz chalcedony opal and minor adularia and barite with massive comb cockade colloform crustiform bandings and lattice bladed textures ore minerals include electrum ag rich sulfosalts freibergite pyrite galena sphalerite chalcopyrite and specular hematite with minor arsenopyrite marcasite tetrahedrite and bornite four mineralizing stages have been identified the first two s1 and s2 are au and ag rich with temperatures ranging from 225 to 290 and salinities from up to 15 wt in s1 decreasing to 1 wt nacl in s2 the third stage s3 displays higher base metal contents at lower temperatures 200 c finally the last stage s4 is barren with temperatures lower than 100 c veins are surrounded by a proximal alteration halo of quartz pyrite adularia illite followed outwards by illite smectite interstratified clays and smectites with less chlorite to a propylitic zone stable isotope values calculated for the fluids show a mostly meteoric origin for mineralization fluids such distinct features place the la josefina deposits in a hot spring environment with evidences of being formed at a proximal position of the jurassic paleosurface and paleowater level

multistage emplacement of the mount givens pluton central sierra nevada batholith california the ca 90 ma mount givens pluton is one of the largest granodioritic to granitic intrusions in the sierra nevada batholith of california emplacement of the pluton occurred during a critical time in the tectonic evolution of the central sierra nevada magmatic arc marked by a transition from regional contraction to dextral transcurrent shear a model for the emplacement of the intrusion is developed based on detailed mapping of the pluton and its wall rocks and characterization of its internal structure by measurements of the anisotropy of magnetic susceptibility ams at 351 stations one of the key results of the study is documentation of a strong correlation between petrologic and structural fabrics in the pluton and determination that these fabrics reflect internal magma chamber dynamics more than regional tectonic strain the 80 km long 15 30 km wide pluton crystallized from a multiphase three segment magma chamber marked by a bulbous northern lobe and linear central and southern segments the pluton is interpreted to be tabular in shape with a thickness of 5 km most of the space for the pluton was created by piecemeal block downdrop of the magma chamber floor along three principal fracture sets the most important of which were steeply dipping northwest trending fractures formed parallel to the structural grain of the arc and vertical north trending extension fractures formed in response to a component of arc parallel dextral shear some of these fractures acted as magma conduits episodically filling the pluton as source rocks became depleted in melt an initial voluminous intrusive event stage 1 quickly filled the southern chamber with granodiorite magma but only partially filled the northern and central chambers stage 2 magmatism involved underplating of megacrystic granite in the northern chamber and lateral flow of a large batch of this magma from the northern to the central chamber the latter delineated by a 20 km long belt of megacrystic granite containing subhorizontal magnetic lineations that connects the pluton segments floor downdrop eventually ceased to be an effective space making process in the northern lobe and renewed magmatism stage 3 led to expansion and doming of the chamber as the northern lobe cooled a ring fault ruptured within the viscoelastic stage 1 2 carapace allowing ring dike intrusion stage 4 and sinking of a central flap of consolidated material the temporal and spatial variations in emplacement mechanisms demonstrated for the mount givens pluton i e fracture generation floor downdrop underplating inflation ring diking suggest that end member models e g fracture vs diapir are oversimplifications of the pluton assembly process

constraints on the ore fluids in the chah zard breccia hosted epithermal au ag deposit iran fluid inclusions and stable isotope studies the chah zard gold silver deposit in the central part of the urumieh dokhtar magmatic arc udma of iran is a breccia hosted low to intermediate sulfidation epithermal deposit with a resource of 2 5 mt averaging 1 7 g t au and 12 7 g t ag gold and silver mineralization occurs in breccia and veins associated with a 6 2 0 2 ma volcanic complex microthermometric measurements on quartz and sphalerite hosted two phase liquid rich fluid inclusions indicate that the mineralization may have taken place between 260 and 345 c from a moderately saline hydrothermal fluid 8 4 13 7 wt nacl equiv first ice melting temperatures between 37 and 53 c indicate that the aqueous fluids contained nacl cacl2 mgcl2 fecl2 coexisting liquid rich and vapor rich fluid inclusions in quartz and sphalerite provide evidence for boiling in ore stage breccia and veins additionally the occurrence of adularia and bladed calcite in high grade ore zones and the presence of hydrothermal breccias and chalcedonic quartz are consistent with boiling calculated 18o values of water in equilibrium with quartz 3 4 to 13 1 suggest that the fluid may have had a magmatic source but was 18o depleted by mixing with meteoric water the average calculated 34sh2s values are 0 2 for pyrite 0 2 for chalcopyrite 1 0 for sphalerite and 0 2 for galena the 34sh2s values are consistent with a magmatic source for sulfur gold deposition at chah zard is inferred to have been largely caused by boiling although fluid mixing and or wall rock reactions may also have occurred after rising to a depth of between 970 and 440 m the fluid boiled causing deposition of fine grained quartz and sealing of the hydrothermal conduit episodic boiling in response to alternating silica sealing and hydraulic brecciation was responsible for ore deposition gold and silver may have precipitated due to the destabilization of hs complexes caused by the boiling off of h2s to vapor whereas the dilution and or cooling of hydrothermal fluids led to the precipitation of base metals

structure and origin of the gold mineralization in the nacimiento block the los burros deposits central california abstract the los burros gold deposit is located within the franciscan complex of the nacimiento block california although this deposit was mined during the late 19th and early 20th centuries its origin and its relationship with the regional metamorphism and deformation are unclear in order to better understand the mode of formation of the deposit and its possible link with a post subduction thermal anomaly we performed a detailed geological and structural mapping within the los burros district coupled with a u th he thermochronological study on apatite and zircon fluid inclusion and stable isotope o and c analyses of the ore deposit provide constraints on the temperature and potential source of the fluid s responsible for the los burros gold formation our results demonstrate that the los burros au deposit formed from a metamorphic aqueous co2 ch4 fluid at temperatures of 300 c results from raman spectroscopy of carbonaceous materials confirm the presence of a thermal anomaly in the range 260 320 c near the los burros mining district as previously inferred by vitrinite reflectance techniques our structural and preliminary thermochronological analyses show that the los burros au deposit consists of a series of meter wide quartz calcite sulfide en echelon veins formed during a late transpressive event related to san andreas fault activity and the subduction of a slab window during the past 30 ma our new data suggest that the thermal anomaly recorded in the vicinity of the los burros mining district is not associated with a magmatic derived hydrothermal system such as described within the epithermal mclaughlin deposit in northern california but rather with a late transpressive deformation event that uplifted deeply buried metamorphic rocks possibly connected to a local metamorphic overprint

boiling and vertical mineralization zoning a case study from the apacheta low sulfidation epithermal gold silver deposit southern peru the au ag pb zn apacheta deposit is located in the shila district 600 km southeast of lima in the cordillera occidental of arequipa province southern peru the vein mineralization is found in early to middle miocene calc alkaline lava flows and volcanic breccias both gangue and sulfide mineralization express a typical low sulfidation system assay data show element zoning with base metals enriched at depth and higher concentrations of precious metals in the upper part of the veins three main deposition stages are observed 1 early pyrite and base metal sulfides with minor electrum 1 and acanthite 2 brecciation of this mineral assemblage and cross cutting veinlets with subhedral quartz crystals mn bearing calcite and rhombic adularia crystals and finally 3 veinlets and geodal filling of an assemblage of tennantite tetrahedrite colorless sphalerite 2 galena chalcopyrite electrum 2 fluid inclusions in the mineralized veins display two distinct types aqueous carbonic liquid rich lw c inclusions and aqueous carbonic vapor rich vw c inclusions microthermometric data indicate that the ore minerals were deposited between 300 and 225 c from relatively dilute hydrothermal fluids 0 6 3 4 wt nacl the physical and chemical characteristics of the hydrothermal fluids show a vertical evolution with in particular a drop in temperature and a loss of h2s the presence of adularia and platy calcite and of co existing liquid rich and vapor rich inclusions in the ore stage indicates a boiling event strong h2s enrichment in the vw c inclusions observed at 200 m the abundance of platy calcite and the occurrence of hydrothermal breccia at this level may indicate a zone of intense boiling the vertical element zoning observed in the apacheta deposit thus seems to be directly related to the vertical evolution of hydrothermal fluid characteristics precious metal deposition mainly occurred above the 200 m level below the present day surface in response to a liquid vapor phase separation due to an upward boiling front

hydrothermal breccias and veins at the kelian gold mine kalimantan indonesia genesis of a large epithermal gold deposit mineralized hydrothermal breccias and veins formed during and after the waning stages of maar diatreme related volcanic activity at kelian kalimantan indonesia subsurface phreatic explosions occurred around the margins of the diatreme breccia complex focusing high temperature fluid flow and generating several large mineralized hydrothermal breccia bodies tectonic phreatomagmatic and hydraulic processes also contributed to hydrothermal brecciation explosive phreatic brecciation was followed by in situ hydraulic brecciation and then by minor veining as the system returned to steady state geothermal conditions brecciation and mineralization mostly occurred 400 to 700 m below the paleowater table the kelian deposit contained more than 240 t au prior to mining precious metals occur with sulfide minerals as disseminations in sheeted and conjugate veins and as breccia cement there is a progression from pyrite dominated stage 1 to base metal sulfide dominated stages 2 and 3 to sulfosalt dominated hydrothermal breccias and veins stage 4 in terms of gangue minerals the system evolved from illite quartz to adularia and or quartz and or illite dominated and then carbonate dominated boiling produced abundant bladed carbonate during stages 3 and 4 overall carbonate and base metal sulfide minerals are abundant whereas quartz is comparatively minor free gold is most abundant in stages 3 and 4 but also occurs in stages 1 and 2 native gold occurs principally as inclusions in pyrite sphalerite galena arsenopyrite quartz bladed carbonate and sulfosalts hydrothermal alteration assemblages are zoned about contacts faults breccias and veins and consist of secondary quartz illite pyrite chlorite and various carbonate minerals kelian preserves evidence of a magmatic component to the mineralizing fluids fluid inclusion analyses revealed the presence of saline fluid inclusions in particular from stage 3 isothermal mixing of low salinity 0 to 2 wt nacl equiv with moderate salinity fluids 10 to 25 wt nacl equiv rather than boiling resulted in the range of salinity and homogenization temperatures of fluid inclusions in sphalerite carbonate and quartz deposited during stage 3 salinities of 4 to 6 wt percent nacl equiv for inclusions in adularia and quartz from stages 2 and 4 and in rhodochrosite and proustite pyrargyrite from stage 4 may also reflect a component of mixing of low salinity water with a moderately saline fluid sulfur isotope values from kelian sulfides 34s 1 4 to 5 5 per mil are consistent with a magmatic sulfur source both boiling and fluid mixing contributed to high grade au mineralization at kelian rapid formation hundreds of years or less is inferred for the individual hydrothermal breccia bodies 2008 society of economic geologists inc

structure magnetic fabric and emplacement of the archean lebel stock sw abitibi greenstone belt abstract the anisotropy of magnetic susceptibility ams has been determined in a suite of samples from the ca 2680 ma old sub circular syenitic lebel stock which is bound to the north by a major late archean shear zone larder lake cadillac deformation zone lcdz the ams defines a magnetic foliation which is parallel to a strong planar preferred mineral orientation fabric considered to have been acquired during flow of a crystalladen magma during emplacement the geometry of the foliation indicates that the stock has an horizontal dish shape at depth the syenites also contain a well defined magnetic lineation which consistently points toward the lcdz apart from localities in the south where it trends e w parallel to the stock s margin ams ellipsoids are dominantly of oblate type except in samples showing solid state strain and alteration overprints which often have plane to prolate ellipsoids the intensity of the magnetic fabric shows a weak spatial variation being strongest at the southern margin the magnetic and magmatic fabric pattern ams parameter variation and the sense of displacement of the western wall rocks are used to propose an emplacement mechanism involving southward migration of a relatively thin sheet of syenitic magma from a linear source corresponding to the present location of the lcdz

a large and complete jurassic geothermal field at claudia deseado massif santa cruz argentina abstract late jurassic geothermal deposits at claudia argentinean patagonia are among the largest 40 km 2 and most varied in the deseado massif a 60 000 km 2 volcanic province hosting precious metals au ag mineralization generated during diffuse back arc spreading and opening of the south atlantic ocean both siliceous sinter and travertine occur in the same stratigraphic sequence deposits range from those interpreted as fluvially reworked hydrothermal silica gels to extensive apron terraces to a clustering of high temperature subaerial vent mounds paleoenvironmentally diagnostic textures of sinters include wavy laminated bubble mat and nodular fabrics and for travertines comprise fossil terracette rims wavy laminated bubble mat spherulitic oncoidal and peloidal fabrics of special note is the presence of relatively large to 25 cm high inferred subaqueous conophyton structures in travertines which serve as analogs for some precambrian stromatolites and imply the presence of relatively deep pools maintained by voluminous spring discharges the claudia geothermal field is geographically and geologically linked to the cerro vanguardia epithermal project total resource of 7 8 million ounces au equivalent via proximity similar veins and structural linkages making it an especially large and relevant prospect for the region the combined claudia cerro vanguardia hydrothermal system likely represents a fortuitous alignment of focused fluid flow and structure conducive to forming a giant epithermal ore deposit with respect to size ore concentration and potentially duration in the late jurassic of patagonia

deformation of granitic rocks across the brittle ductile transition abstract a microstructural analysis has been carried out on mylonites and mylonitic gneisses of the eastern peninsular ranges mylonite zone which were formed over a range of metamorphic conditions from lower greenschist to amphibolite facies composite planar fabrics in the form of c and s planes are found at all metamorphic grades fractured feldspars kinked biotites and ductile deformation of quartz characterize the lower greenschist facies mylonites at mid upper greenschist grade orthoclase grains show dynamic recrystallization textures whereas plagioclase exhibits low temperature plasticity with only minor recovery biotite ribbons form by progressive rotation and coalescence of kink band segments to produce chevron fold patterns at epidote amphibolite grade and above recovery processes and annealing recrystallization predominate in all minerals residual orthoclase porphyroclasts show strain related myrmekite formation along those sides of the grains that face the instantaneous shortening direction myrmekite formation due to replacement reactions cannot explain this geometry it is proposed that the myrmekites formed due to a combination of exsolution replacement and strain enhanced diffusion

low sulfidation type au ag mineralization at bergama izmir turkey abstract bergama the center of bergama county is located in western turkey and includes the villages of ovacik narlica and saganci the ovacik epithermal gold silver deposit is located in the western anatolian volcanic and extensional province adjacent to the ene trending bergama graben some 100 km north of the city of izmir gold of economic grades at the ovacik deposit reserves 4 19 mt at 7 6 g t occurs in epithermal quartz veins which display low temperature epithermal textures including crustiform banding quartz pseudomorphs after bladed calcite and multiphase hydrothermal breccias alteration minerals at both ovacik and narlica are dominated by smectite mixed layer illite smectite chalcedonic quartz and adularia whereas major kaolinite and minor mixed layer smectite illite 13 4 a occur at saganci the total sulfide content at ovacik is low geochemical variations in altered wall rocks at ovacik and narlica are generally characterized by two fold enrichments in k rb cs and 25 to 93 depletions in sr ca mg na and even higher depletions 96 to 99 decrease in the quartz adularia vein zone lanthanum ce pr hf zr sm eu gd tb and ho also exhibit up to 50 depletions in the wall rock and even more so up to 90 depletion for la and nd in the vein structure wall rock enrichment in au ag as hg and sc is by factors of 60 150 88 8 and 3 respectively the ranges of ree in both the altered volcanic rocks and quartz adularia veins are wide and may reflect either significant mobilization of ree during alteration and mineralization or their dilution by the metasomatic processes from fresh volcanic rocks through montmorillonite illite adularia altered wallrock to quartz adularia veins high rb sr ratios in adularia illite altered areas are closely related to the presence of k rich alteration minerals low rb sr ratios and corresponding low k values at saganci are due to acid leaching of volcanic rocks positive correlation coefficients between au and ag pb zn cd cu and sb in epithermal quartz veins all of which are 0 51 are significant silver and sb are remarkably enriched at higher levels of the deposit no correlation occurs between au and as or ag and as the ovacik quartz in au ag bearing veins has 18o values ranging from 9 5 to 15 7 whereas d values of fluid inclusions in quartz range from 89 to 125 however the narlica quartz in au ag bearing veins returned 18o values ranging from 5 9 to 8 3 whereas the d values of fluid inclusion in quartz range from 82 to 99 18o results indicate that ore forming hydrothermal fluids at ovacik and narlica had 18oh2o values ranging from 2 9 to 3 5 average 0 24 and from 2 96 to 0 6 average 1 6 respectively they are thus 18o enriched in comparison with present day meteoric and hydrothermal meteoric waters 5 4 18o 18oh2o and d values suggest that mineralizing solutions were a mixture of meteoric and magmatic waters the 34s sulfide data at ovacik and narlica range from 2 1 to 5 3 average 1 7 and from 4 6 to 2 7 average 0 36 respectively these 34s sulfide values are consistent with a magmatic source for s

the waihi epithermal gold silver base metal sulfide quartz vein system new zealand temperature and salinity controls on electrum and sulfide deposition the large andesite hosted quartz vein system at waihi contains a major epithermal au ag deposit total production of 6 4 moz au and 39 9 moz ag ag au 6 2 it is notable for a large vertical extent up to 575 m of economic au ag ore a pervasive adularia quartz illite chlorite pyrite alteration zone bounds the larger quartz veins and is associated with veinlets of quartz calcite pyrite adularia illite this zone is enveloped by an illite quartz adularia chlorite calcite pyrite alteration zone which grades out through a transition zone characterized by interlayered illite smectite into a smectite chlorite calcite alteration zone in the least altered andesites the formation of the adularia quartz chlorite calcite pyrite and some illite in these alteration assemblages was associated with an initial stage of vein filling by platy calcite and quartz this was followed by a main stage of quartz and sulfide vein filling with crustiform quartz at deeper levels and colloform quartz plus minor adularia at shallow levels deposition of main stage quartz and sulfides was accompanied by illite overprinting adularia in the wall rock and filling fractures in the quartz calcite pyrite adularia veinlets sulfide bearing bands associated with the main stage quartz show a zonation with decreasing depth from a coarse grained sphalerite galena pyrite chlorite assemblage at deep levels to a finer grained sphalerite galena pyrite chalcopyrite acanthite electrum assemblage at medium to shallow levels fluid inclusion studies indicate that the main stage quartz was deposited from fluids which ranged in temperature and composition from up to 295 c and 1 7 wt percent nacl equiv at depth to 190 c and 0 2 wt percent nacl equiv at shallow levels these are true salinities because the fluids extracted from the fluid inclusions have low co 2 contents 0 05 0 24 wt quartz within electrum poor zn pb fe sulfide bands was deposited at higher temperatures 295 242 c and salinities than quartz in electrum bearing zn pb fe cu ag sulfide bands 260 190 c temperature versus depth profiles for fluid inclusions with evidence of boiling indicate that the paleowater table was located about 160 m above the present erosion level during deposition of the main stage quartz minor amethyst as the final stage of vein filling was locally preceded by inesite and was not associated with sulfides and electrum amethyst was deposited at 253 to 170 c from fluids containing up to 4 5 wt percent nacl equiv these higher salinities are attributed to concentration of salts in the residual liquid by localized open system boiling chloride depth chloride enthalpy and 18 o water enthalpy plots indicate mixing of deep fluids up to 1 7 wt nacl for the main stage quartz with very low salinity steam heated ground water oxygen isotope 18 o values for vein quartz and amethyst range from 6 1 to 11 6 per mil and for vein calcite from 2 29 to 9 4 per mil calculated 18 o water values define a trend from 2 9 per mil at shallow levels to 0 6 per mil at depth extrapolation of the dilution trend on a 18 o water enthalpy plot indicates that the deep fluid 18 o water 0 6 was mixed with heated 160 180 c ground water of local meteoric water composition 5 5 dilution of a deep chloride fluid 1 2 wt nacl equiv carrying zinc and lead as chloride complexes with steam heated ground water is inferred to have been responsible for deposition of the electrum poor zn pb fe sulfide assemblage from 300 to 240 c at a paleodepth below about 500 m deposition of this assemblage may also have been promoted by decrease of sulfur in solution through loss of h 2 s gas by boiling during episodic fracturing the decrease in salinity following dilution favored the transport of gold silver and copper as hydrosulfide complexes and led to the deposition of the electrum bearing zn pb fe cu ag sulfide assemblage over a temperature range of 260 to less than 190 c at paleodepths of 500 to less than 250 m in this assemblage the decrease of sulfur in solution as a result of deposition of the associated chalcopyrite pyrite and galena is a likely mechanism for electrum deposition

early archean hot springs above epithermal veins north pole western australia new insights from fluid inclusion microanalysis the world s most ancient biogenic structures are found in the north pole dome of western australia where 3 47 gyr old algal mats and stromatolites are closely associated with bedding conformable and discordant laminar quartz chalcedony and barite barite rich quartz hydrothermal veins with similar mineralogy occur throughout the stratigraphy below the conformable biogenic structures with the exception of the large volume of barite these bedding conformable and discordant laminar quartz veins exhibit textures and associated hydrothermal alteration quartz chalcedony chlorite illite calcite adularia pyrite typical of epithermal deposits formed from near neutral ph fluids we characterize the physical and chemical conditions of the ancient water responsible for depositing both the discordant and conformable quartz chalcedony barite as it passed through the upper parts of the archean crust field relationships combined with new fluid inclusion data suggest that the best documented stromatolites in the north pole dome occur adjacent to quartz chalcedony bands formed from cool 120 c low salinity 3 wt nacl equiv waters higher temperature up to 300 c more saline up to 10 wt nacl equiv and co2 h2s rich ch4 aqueous fluids occur in deeper level veins rare inclusions that are unusually rich in co2 containing liquid and gaseous co2 and liquid h2o support the existence of multiple batches of hydrothermal fluids with variable densities and gas contents oxygen isotope data 8 7 3 7 suggest that the causative fluids comprised admixtures of deeply circulated surface water with variable input of magmatic components our findings reveal that the earliest life known on earth lived in and around a hydrothermal system with temperatures from 300 c at depth to 120 c near the paleosurface in an environment closely analogous to modern hot springs developed above epithermal veins evidence exists for the introduction of different batches of hydrothermal fluids with variable densities and gas contents during the development of veins these findings support previous studies that demonstrate that the processes that form epithermal deposits have been active throughout geologic time and the present day distribution of epithermal deposits is dominantly a result of preservation not process

granite magma generation ascent and emplacement within a transpressional orogen crustal thickening during transpressive orogenesis may produce anatectic granites which may then localize deformation leading to transcurrent movement granites may be transported from sites of generation through the mid crust in dyke like channelways within relatively narrow strike slip shear zones which link to major fault zones in the upper crust extensional jogs within fault systems provide developing sites for the assembly of plutons from magma arriving from below the model is based upon observations from the cadomian belt of nw france which exposes sections through middle and upper levels of the late precambrian crust within different elements of the orogen the mechanism provides a favourable alternative to diapirism and explains the common collocation of granites and shear zone fault systems within orogenic belts

discovery geology and origin of the fruta del norte epithermal gold silver deposit southeastern ecuador fruta del norte is a completely concealed and extraordinarily well preserved epithermal gold silver deposit located in the remote cordillera del condor mountain ranges of southeastern ecuador currently defined resources in a single steep relatively small body displaying exceptional grade continuity contain 9 81 million ounces moz of gold and 15 0 moz of silver with an indicated resource grade of 9 59 g t au and 12 9 g t ag the deposit was discovered in early 2006 during a greenfields program conducted by aurelian resources a canadian junior explorer discovery resulted from systematic drill testing of a conceptual geologic model which predicted that auriferous veins would be present in andesitic volcanic rocks inferred to underlie a steep silicified rib cutting a fluvial conglomerate sequence the rib is highly anomalous in arsenic antimony and mercury but contains low order gold values the second drill test the discovery hole intersected 230 m of ore grade gold silver mineralization beneath 200 m of the barren conglomerate cover the host andesitic volcanic rocks crosscutting feldspar porphyry and associated phreatic breccias are assigned to the piuntza unit of the santiago formation which along with the zamora batholith and a series of porphyry copper stocks was generated in a continental margin magmatic arc during the middle to late jurassic the deposit is located near the northeastern extremity of the 10 km long suarez pull apart basin where it is linked to the steep west and central faults part of the regionally extensive las penas strike slip fault zone the pull apart basin was progressively filled by fluviatile conglomerate dacitic ignimbrite flows finer grained siliciclastic sedimentary rocks and finally andesite flows all assigned to the chapiza formation the fruta del norte deposit consists of a 1 3 km long and up to 300 m wide vein stockwork associated with quartz illite pyrite alteration the deposit comprises two principal vein types one in the south dominated by quartz manganoan carbonates and abundant base metal sulfides and the other in the north dominated by manganese and base metal poor quartz and calcite adularia is a minor main stage gangue mineral in each both types are abruptly transitional upward and westward to a third ore type marked by intense silicification and chalcedony veining with disseminated and veinlet marcasite pyrite the uppermost part of this silicic zone is sulfide deficient probably the result of a short lived supergene oxidation event prior to initial conglomerate deposition the deposit is notable for the widespread occurrence of fine to coarse visible gold which gives rise to bonanza grades and is closely associated with quartz chalcedony carbonate and sulfide gangue the sulfide free silicic zone is overlain by an extensive silica sinter horizon which may either directly overlie the piuntza volcanic rocks and or occur as interbeds in the basal 20 m of the conglomerate which are invariably silicified and marcasite bearing otherwise the conglomerate above the orebody lacks silicification with one critical exception the steeply inclined zone that is exposed as the silicified rib that led to discovery the sinter horizon containing localized mud pool deposits and hydrothermal eruption breccias is in unusual proximity to the underlying gold silver orebody the northern and southern parts of the fruta del norte deposit possess characteristics that are usually considered typical of low and intermediate sulfidation epithermal deposits respectively they may have required two discrete mineralizing fluids both of which are suspected to have ascended via the west and central faults the upward change to the silicified zone is attributed to cooling of the ascendant fluid on approach to the paleosurface sinter progressive burial of the deposit beneath the suarez basin fill may have contributed to the suppression and eventual extinction of the epithermal system with gold mineralization of the conglomerate being inhibited by rheologic and chemical factors formation of the fruta del norte deposit and complete filling of the suarez basin took place in 3 to 6 m y during the late jurassic 157 154 ma

kinematics of compressional fold development in convergent wrench terranes abstract kinematic models are presented for compressional fold development in wrench and convergent wrench terranes that relate fold shortening axial rotation and axial extension fold shortening may be derived from final fold geometry existing fold geometry and axial orientation two readily measurable quantities provide the data needed to determine the relative components of shearing and convergence within the fold system analyses utilizing these kinematic models indicate that folds developed in sedimentary rocks in the wrench borderlands of both the rineonada and san andreas wrench faults in central california are the product of strongly convergent wrenching the axes of these folds have been rotated no more than a few degrees during the course of their development in contrast folds developed in the alpine schists along the alpine fault in new zealand and in pleistocene sediments along the southern limit of the san andreas fault suggest an almost pure wrench setting and large 25 axial rotations significant axial extension is inherent in wrench related compressional folds this axial extension is commonly manifest in the form of normal and strike slip faults that are internal to the folds and trend at high angles to the fold axes the relative amount of axial extension diminishes as the degree of convergence increases this axial extension and the associated extensional features can be a diagnostic indication of the influence of wrenching

fluid inclusion and stable isotope constraints on ore genesis of the zajkan epithermal base metal deposit tarom hashtjin metallogenic belt nw iran in the zajkan pb zn cu au ag deposit of the tarom hashtjin metallogenic belt thmb northwest iran mineralization occurs as quartz base metal sulfide veins hosted by eocene volcanic and volcaniclastic rocks of the karaj formation four stages of ore formation are identified at zajkan 1 quartz chalcopyrite pyrite veins 2 quartz galena sphalerite chalcopyrite pyrite veins and breccias 3 quartz hematite veins and breccias and 4 barren quartz carbonate veinlets the primary metallic minerals are pyrite chalcopyrite sphalerite galena and trace amounts of hematite gangue minerals are mainly quartz sericite chlorite and calcite the main wall rock alteration is silicification and intermediate argillic and propylitic alteration the coexistence of different types of fluid inclusions lv vl and v in individual fluid inclusion assemblages in quartz and sphalerite suggests boiling and heterogeneous trapping excluding the heterogeneously entrapped fluid inclusions the microthermometric measurements of primary lv fluid inclusion assemblages in quartz and sphalerite indicate that the veins were formed at temperatures between 217 and 273 degrees c from fluids with salinities between 1 7 and 6 4 wt nacl equiv the oxygen isotopic compositions delta o 18 water vsmow of 3 7 to 1 1 parts per thousand indicate that the ore forming fluids were mainly derived from magmatic water with the input of meteoric water in the later ore stages sulfur isotopic values of sulfide minerals vary over a narrow range from 5 0 to 0 9 parts per thousand vcdt averaging 2 2 parts per thousand vcdt suggesting that sulfur was derived from a homogeneous magmatic source the fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at zajkan our data suggest that the zajkan deposit is an intermediate sulficiation style epithermal mineralization the estimated ore formation depth of zajkan indicates minor denudation in the region and may imply a great prospecting potential for other epithermal mineralization in the thmb

the gangotri granite garhwal himalaya laccolithic emplacement in an extending collisional belt the gangotri miocene leucogranite is composed of several laccoliths 6 7 km long 1 5 2 km thick which can be divided into two sets of lenses the southern lenses intruded in the lower part of the high himalaya sedimentary cover and the northern lenses intruded in an older porphyritic biotite bearing granite in both cases the magmatic fabric is commonly weak with no dominant stretching direction although a rough e w trend is present in the northern lenses the magnetic fabric is characterized by the fact that drastic changes in the direction in the magnitude of the magnetic parameters or in the fabric type planar or linear may take place over very short distances measurements of preferred orientations in thin sections indicate that the strain regime was largely dominated by a coaxial component for both sets of lenses in agreement with the large dispersion observed in both the field and magnetic lineations the comparison of the granite and host rock structures shows that the leucogranite emplacement dates the onset of the extensional tectonism in the high himalaya range and is not related to a southward directed thrust event associated with the main central thrust this is exemplified by the vertical attitude of the feeder dikes that intrude the metasedimentary rocks beneath die southern lenses the presence of these dikes indicates in turn that magma ascent occurred by fracture propagation the spatial disposition of the southern lenses could have resulted either from the disruption of a single laccolithic intrusion by crustal scale boudinage due to a northern gravity backslide of the top of the tibetan slab or from the intrusion of independent laccoliths the use of the elastic bending theory of pollard and johnson 1973 shows that in both hypotheses the current laccolith sizes are compatible with a laccolithic mode of magma emplacement however neither the density contrast between the magma and its enclosing rocks nor the lithological boundary between the tibetan slab and the overlying tibetan metasedimentary series controlled the level of magma emplacement rather flat lying collapse structures which intersected the upward propagating magma dikes are the most likely causes of magma arrest such a mechanism was favored by the schist rich lithology of the metasedimentary host rocks in addition field relationships indicate that the melt supply through the dike system was a continuous rather than pulsed process existing numerical treatments on the rates of magma transport through fractures show that in such a case the laccoliths could have been built in less than 100 years this short time of emplacement the small size of the laccoliths and their peripheral disposition relative to the badrinath granite suggest that the gangotri lenses may represent the initial stage of pluton accretion in the high himalaya which ultimately gave rise to a much larger massif such as the manaslu granite

hydrothermal alteration of volcanic rocks at the mclaughlin gold deposit northern california the plio pleistocene mclaughlin mine is a large hot spring gold silver mercury deposit located in the northern coast ranges of california two distinctly different suites of volcanic rocks host mineralization an upper jurassic basalt part of the coast range ophiolite and an upper cenozoic basaltic andesite part of the clear lake volcanic field the two suites of volcanic rocks range from least altered rocks showing primary igneous mineralogy to intensely altered rocks composed of an assemblage of quartz montmorillonite sericite and adularia mass balance calculations indicate almost total loss of na ca mg and sr and large gains in and ba as a result of the hydrothermal alteration the mass flux corresponds to the replacement of plagioclase feldspar with sericite and adularia and mafic minerals with montmorillonite trace elements show no evidence for mobility rocks adjacent to the hydrothermal system have the greatest 18o values and the highest calculated mass flux suggesting the greates

geology geochemistry and genesis of axi a paleozoic low sulfidation type epithermal gold deposit in xinjiang china abstract axi is a low sulfidation type epithermal gold deposit hosted in paleozoic subaerial volcanic rocks in the western tianshan orogenic belt xinjiang china the resource is more than 50 t gold at an average grade of 4 4 ppm the deposit occurs in the tulasu volcanic fault basin in the paleozoic active continental margin on the northern side of the yili central tianshan plate the host rocks are andesitic volcaniclastic rocks of the paleozoic dahalajunshan formation and the orebodies occur as veins in annular faults of a paleocaldera mineralization at axi can be subdivided into five stages quartz and or chalcedony vein quartz vein quartz carbonate vein sulfide vein and carbonate vein there are two types of ore host quartz vein and altered rocks ore minerals are native gold electrum pyrite marcasite arsenopyrite hematite limonite and trace amounts of pyrargyrite polybasite naumannite cerargyrite sphalerite chalcopyrite tetrahedrite galena pyrrhotite and clausthalite gangue minerals are mainly quartz chalcedony illite calcite siderite dolomite adularia and laumontite the main wall rock alteration is silicification and phyllic alteration carbonatization and propylitization the deposit is characterized by an enrichment relative to crustal abundance of au ag as sb bi hg se te and mo depletion in base metals cu pb and zn and a low ag au ratio 0 5 3 7 three types of fluid inclusions were recognized in quartz from the major mineralization stages liquid aqueous inclusions liquid rich two phase inclusions and small amounts of vapor rich two phase inclusions microthermometric measurements indicate that the final ice melting temperatures are 0 3 to 4 4 c corresponding to salinities of 0 5 6 9 wt nacl equiv 2 2 wt nacl equiv in average the peak temperatures of ice melting varies from 0 4 to 1 9 c corresponding to salinities of 0 7 3 1 wt nacl equiv homogenization temperatures range mainly between 120 and 240 c with an average of 190 c and a maximum of 335 c the fluid density is 0 73 to 0 95 g cm 3 and thus the estimated maximum mineralization depth is about 700 m hydrogen and oxygen isotopic compositions of the ore fluids lie within a narrow range d h2o is 98 to 116 and 18 o h2o 1 8 to 0 4 3 he 4 he ranges from 0 0218 to 0 138 ra with an average of 0 044 ra indicating that he derived predominantly from crust with negligible mantle he in the ore fluids by contrast the 40 ar 36 ar ranges from 317 7 to 866 0 suggesting that crust derived radioactive 40 ar accounts for 7 0 to 66 and atmospheric 40 ar about 43 to 93 in the ore fluids hydrogen oxygen carbon sulfur and noble gas isotopes indicate that the ore forming fluids of the axi gold deposit consisted predominantly of circulating meteoric water ore forming metals may have derived mainly from the host volcaniclastic rocks of the dahalajunshan formation and basement rocks the occurrence of adularia platy calcite and quartz or sulfide aggregates as pseudomorphs after bladed calcite in ore veins and occurrence of aqueous liquid and liquid rich and vapor rich two phase inclusions indicates that boiling of the ore forming fluid have occurred leading to supersaturation of the hydrothermal solution and deposition of ore metals this is the main mineralization mechanism for quartz vein type ores in axi the ore forming fluid was buffered to a near neutral ph in a reduced environment during mineralization the preservation of this paleozoic axi deposit and its discovery required a rapid accumulation of sediments in the basin after formation of the deposit and minimal amount of erosion after late cenozoic uplift

intermediate sulfidation type base metal mineralization at aliabad khanchy tarom hashtjin metallogenic belt nw iran abstract the aliabad khanchy epithermal base metal deposit is located in the tarom hashtjin metallogenic belt thmb of northwest iran the mineralization occurs as cu bearing brecciated quartz veins hosted by eocene volcanic and volcaniclastic rocks of the karaj formation ore formation can be divided into five stages with most ore minerals such as pyrite and chalcopyrite being formed in the early stages the main wall rock alteration is silicification and chlorite argillic and propylitic alteration microthermometric measurements of fluid inclusion assemblages show that the ore forming fluids have eutectic temperatures between 30 and 52 c trapping temperatures of 150 290 c and salinities of 6 6 12 4 wt nacl equiv these data demonstrate that the ore forming fluids were medium to high temperature medium to low salinity and low density h2o nacl cacl2 fluids calculated 18o values indicate that ore forming hydrothermal fluids had 18owater ranging from 3 6 to 0 8 confirming that the ore fluid system evolved from dominantly magmatic to dominantly meteoric the calculated 34sh2s values range from 8 1 to 5 0 consistent with derivation of the sulfur from either magma or possibly from local volcanic wall rock combined the fluid inclusion and stable isotope data indicate that the aliabad khanchy deposit formed from magmatic hydrothermal fluids after rising to a depth of between 790 and 500 m the fluid boiled and subsequent hydraulic fracturing may have led to inflow and or mixing of early magmatic fluids with circulating groundwater causing deposition of base metals due to dilution and or cooling the aliabad khanchy deposit is interpreted as an intermediate sulfidation style of epithermal mineralization our data suggest that the mineralization at aliabad khanchy and other epithermal deposits of the thmb formed by hydrothermal activity related to shallow late eocene magmatism the altered eocene volcanic and volcaniclastic rocks especially at the intersection of subvolcanic stocks with faults were the most favorable sites for epithermal ore bodies in the thmb

underground fumaroles excess heat effects in vein formation we examine the heat extracted from a fractured hydrothermal system following the sudden dilation of fractures in the host rock this dilation increases the permeability of the system and veins form along irregular fractures where the opening is localized for simplicity we will consider one such vein in this paper fluid in the system is assumed to be initially close to vapor saturation and in thermal equilibrium with the surrounding host rock the rapid opening of the vein leads to approximately isenthalpic vapor separation and causes a pressure drop to propagate through the system as the two phase fluid in the fracture system is constrained to the vapor pressure curve the depressurization is accompanied by a rapid cooling of the fluid fluid flow is also induced from a hydrothermal reservoir toward the dilated discharge vein the temperature difference between the host rock and the two phase fluid in the fracture system drives heat from the rock into the fluid the excess heat 1 1 derived from the host rock in this manner evaporates additional liquid in the two phase flow which develops substantially larger vapor fractions than those due only to the rapid initial adiabatic depressurization of the fluid such additional vapor separation therefore leads to high solute concentrations in the liquid phase and potentially results in faster deposition of minerals in the fracture system and local veins a model is developed here to describe the minimum excess heat transfer i e the worst case scenario into the two phase saturated liquid vapor mixture as it is drawn horizontally from the hydrothermal reservoir toward the discharge vein excess heat effects are shown to be effective within tens to hundreds of meters of actively forming veins and a principal cause of oscillatory banding and lamination fabrics this transient heat extraction process applies to a wide range of shallow crustal deposit styles associated with brittle and brittle ductile deformation these deposit styles range from epithermal bonanza veins sea floor massive sulfide deposits mesothermal veins in shear zones to the higher temperature veins and stockworks of hypothermal and porphyry mineralization 1 fn 1

the miocene atastra creek sinter bodie hills volcanic field california and nevada 4d evolution of a geomorphically intact siliceous hot spring deposit abstract the atastra creek siliceous hot spring deposit or sinter occurs in the paramount bald peak alteration zone due north of the bodie precious metals mining district in the miocene bodie hills volcanic field california and nevada u s a distinctive features include its geomorphically intact geyser vent mounds the presence of growth fault stepped sinter terraces that developed westward along a nnw trending fault and atypical hg sb and as concentrations high temperature 75 c subaerial proximal apron sinter occurs in two settings 1 radiating botryoidal geyserite in vent mounds and 2 bedded geyserite columnar nodular size sorted geyser eggs intercalated with mid to low temperature

magnetic fabrics in the cabanas granite ne brazil interplay between emplacement and regional fabrics in a dextral transpressive regime the late neoproterozoic cabanas granite northeastern brazil is a tabular body that was emplaced south of the dextral east pernambuco shear zone system anisotropy of magnetic susceptibility ams measurements reveal that the cabanas granite has fabric patterns more complex than usually reported in plutons intruded in similar settings most structures have ew to ene trending magnetic lineations consistent with the overall regional structural direction in the north these structures parallel the mylonitic fabric encountered in shear zones that bound or cross cut the pluton in the central and southern portions of the pluton magnetic foliation trajectories the overall banded disposition of the iso susceptibility lines and shape parameters of the ams ellipsoids suggest that the cabanas granite was subjected to ene trending folding along with its underlying and enclosing country rocks it is concluded that emplacement took place during regional dextral transpression a secondary but well developed family of structures consists of n to nw plunging lineations which is interpreted to represent the trace of the vertical conduits that fed the pluton this study emphasizes the utility of the ams to unravel both the internal structure of low anisotropy plutons and the interplay between emplacement and regional straining during magma crystallization

geyserite in hot spring siliceous sinter window on earth s hottest terrestrial paleo environment and its extreme life siliceous hot spring deposits or sinters typically form in active terrestrial on land volcanic terrains where magmatically heated waters circulating through the shallow crust emerge at the earth s surface as silica charged geothermal fluids geyserites are sinters affiliated with the highest temperature 75 100 c natural geothermal fluid emissions comprising localized lithologically distinctive hydrothermal silica precipitates that develop around geysers spouters and spring vents they demarcate the position of hot fluid upflow zones useful for geothermal energy and epithermal mineral prospecting near vent areas also are extreme environment settings for the growth of microbial biofilms at near boiling temperatures microbial biosignatures e g characteristic silicified microbial textures carbon isotopes genetic material lipid biomarkers may be extracted from modern geyserite however because of strong taphonomic filtering and subsequent diagenesis fossils in geyserite are very rare in the pre quaternary sinter record which in and of itself is patchy in time and space back to about 400 ma only a few old examples are known such as geyserite reported from the devonian drummond basin australia devonian rhynie cherts scotland and a new example described herein from the spectacularly well preserved late jurassic 150 ma yellowstone style geothermal landscapes of patagonia argentina there geyserite is associated with fossil vent mounds and silicified hydrothermal breccias of the claudia sinter which is geologically related to the world class cerro vanguardia gold silver deposit of the deseado massif a part of the chon aike siliceous large igneous province tubular filament like micro inclusions from claudia were studied using integrated petrographic and laser micro raman analysis the results of which suggest a biological origin the putative fossils are enclosed within nodular geyserite a texture typical of subaerial near vent conditions overall this worldwide review of geyserite confirms its significance as a mineralizing geological archive reflecting the nature of earth s highest temperature habitable terrestrial sedimentary environment hot spring depositional settings also may serve as analogs for early earth paleoenvironments because of their elevated temperature of formation rapid mineralization by silica and morphologically comparable carbonaceous material sourced from prokaryotes adapted to life at high temperatures

origin and evolution of hydrothermal fluids in the marshoun epithermal pb zn cu ag deposit tarom hashtjin metallogenic belt nw iran abstract the marshoun epithermal pb zn cu ag deposit is located in the tarom hashtjin metallogenic belt thmb northwest iran the epithermal base metal veins are mainly hosted in eocene volcanic and volcaniclastic rocks of the karaj formation and late eocene pyroxene quartz monzodiorite the mineralization process can be divided into five stages 1 quartz chalcopyrite pyrite veins and breccias 2 quartz calcite sphalerite galena chalcopyrite pyrite veins and breccias 3 barren post ore quartz veinlets 4 barren post ore calcite veinlets and 5 supergene mineral assemblages the primary metallic minerals are pyrite chalcopyrite sphalerite and galena gangue minerals are mainly quartz calcite sericite and chlorite the main wall rock alteration is silicification intermediate argillic carbonate and propylitic alteration microthermometric measurements of primary lv fluid inclusion assemblages in quartz and sphalerite indicate that the veins were mainly formed at temperatures between 173 and 285 c from fluids with salinities between 3 4 and 6 3 wt nacl equiv coexisting lv vl and v inclusions in quartz and sphalerite provide evidence for boiling in ore stage breccia and veins additionally the occurrence of bladed calcite as well as plumose and colloform crustiform banded quartz in the ore zones and the presence of hydrothermal breccias are consistent with boiling obtained oxygen and sulfur isotope compositions 18owater 9 2 to 1 5 34sh2s 10 0 to 5 7 indicate there was a major contribution from a magmatic component to metallogenesis the fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at marshoun the marshoun deposit is interpreted as an intermediate sulfidation style of epithermal mineralization our data suggest that the epithermal mineralization in the thmb are related to late eocene ca 36 37 ma shallow magmatic hydrothermal activity the altered eocene volcanic subvolcanic rocks particularly at the intersection of subvolcanic rocks with faults were the most favorable locus for exploration targeting of epithermal ores at thmb

the great tonalite sill emplacement into a contractional shear zone and implications for late cretaceous to early eocene tectonics in southeastern alaska and british columbia the late cretaceous to early tertiary great tonalite sill of southeast alaska and british columbia is a very long 1 000 km and thin 25 km orogen parallel composite batholith which lies between the insular superter rane including the alexander and wrangellia terranes and the intermontane superterrane including the stikine and cache creek terranes the batholith is delineated by many steep sheet like plutons which are dominated by northwest southeast striking concordant fabrics with steep lineations that formed during deformation in a country rock shear zone prior to the complete crystallization of the magmas deformation in this shear zone is dominated by northeast southwest directed contraction orthogonal to the orogenic strike associated with a component of northeast over southwest high angle shear the steep multiple dike like nature of the body and its emplacement during orogenic contraction imply that ascent and emplacement have been achieved by dike wedging mechanisms along the deep reaching shear zone the remarkable narrowness of the great tonalite sill is probably the result of melting at the base of a very localized zone of thickened crust produced by the associated narrow contractional shear zone extending along the orogen length such a shear zone of late cretaceous to early tertiary age lying along 800 km of the possible boundary between the insular and intermontane superterranes implies that it may represent the actual boundary between them if this hypothesis is correct it implies that the large scale tectonic regime during emplacement of the great tonalite sill was predominantly orthogonal and not obliquely dextral as has been indicated from paleomagnetic data

emplacement of the ardara pluton ireland new constraints from magnetic fabrics rock fabrics and age dating the ardara pluton as part of the donegal batholith was intruded into neoproterozoic metasediments and metadolerites at mid crustal levels the emplacement mechanism of the ardara granite is very controversial and mechanisms ranging from diapirism ballooning and stoping followed by nested diapirism have been proposed magnetic fabrics rock fabrics and k ar dating of micas are used here to constrain the emplacement history the compositional zoning of the ardara pluton is clearly reflected in the different bulk magnetic susceptibilities between the outer quartz monzodiorite and the central granodiorite whereas the intervening tonalite is of intermediate nature the magnetic carriers are characterized by the anisotropy of the magnetic susceptibility ams thermomagnetic measurements and through high field analyses hfa the separation of the ferrimagnetic and paramagnetic contributions revealed that biotite and magnetite control the ams in the quartz monzodiorite both minerals are oriented in such a way that their summed contribution is constructive and originates from the shape fabric of magnetite and the texture of biotite biotite is responsible mainly for the ams in the tonalite and granodiorite the magnetic foliation can be directly related to the macroscopic foliation and also to the d4 structures in the country rocks the foliation is consistent with the geometry of the roughly circular shape and has a mostly steep to vertical dip towards the central granodiorite the magnetic foliation dies out although plagioclase texture measurements indicate a weak magmatic shape fabric with the exception of the tail the kmax axes magnetic lineation vary from steeply to gently plunging the so called lineation factor is approximately 1 01 and therefore points to a less significant axial symmetry these observations coincide with strain estimates on mafic enclaves that show a very consistent pattern of k 0 flattening strain texture analyses of biotite and quartz additionally support the observations made by the strain analyses and the magnetic fabric data microstructural investigations give evidence that the fabrics are associated with the emplacement over a range of temperatures from truly magmatic to high temperature solid state conditions the age of the intrusion is still under discussion but a new cooling age was determined by k ar dating of biotite at 403 7 8 ma corresponding to a temperature range between 450 and 300 c for a mylonite along the southern contact between the ardara pluton and the country rock a k ar muscovite age of 378 8 7 ma indicates a minimum age for the shear zone when the ardara pluton must have already been cooled down below 350 50 c

obliquely convergent tectonics and granite emplacement in the trans saharan belt of eastern nigeria a synthesis abstract the eastern nigeria terrane belongs to the 3000 km long trans saharan belt which was formed in the neoproterozoic between 750 and 500 ma by continental collision between the converging west african craton congo craton and east saharan block the study area consists mostly of gneisses and migmatites that underwent granulite facies metamorphism 800 c 800 mpa in contrast with western nigeria and cameroon no basement cover relationship has been identified which is in agreement with a monocyclic metamorphic history around 640 ma the area underwent a nappe tectonics with eastward displacement emplacement of bt ms granites and granulite facies peak later on around 615 ma nappes were towards the north numerous hbl bt granite plutons were emplaced around 585 ma during north south strike slip regional deformation the anisotropy of magnetic susceptibility fabric helps in defining strain localization along narrow north south to nne ssw vertical shear zones during the exhumation history exhumation of the terrane assessed using u pb ar ar and rb sr methods was presumably slow with uplift rates around 0 2 0 5 mm year preliminary estimates of contemporaneous horizontal movements suggest that they were one order of magnitude larger

the spar lake strata bound cu ag deposit formed across a mixing zone between trapped natural gas and metals bearing brine ore formation at the spar lake red bed associated strata bound cu deposit took place across a mixing and reaction zone between a hot oxidized metals transporting brine and a reservoir of sour h2s bearing natural gas trapped in the host sandstones fluid inclusion volatile analyses have very high ch4 concentrations 1 mol in most samples and a sample from the fringe of the deposit has between 18 and 36 mol ch4 the ratio of ch4 co2 in fluid inclusions appears to vary regularly across the deposit with the lowest ch4 co2 ratios from high grade chalcocite bearing ore and the highest from the chalcopyrite bearing fringe the helium r ra isotope ratios 0 23 0 98 and concentrations define a mixture between crustal and atmospheric helium the volatiles in fluid inclusions ch4 co2 h2s so2 h2 h2o and other organic gases and values of f o2 and temperature calculated from the volatiles data all show gradations across the deposit that are completely consistent with such a mixing and reaction zone other volatiles from the fluid inclusions hcl hf 3he 4he n2 ar characterize the brine and give evidence for only shallow crustal fluids with no magmatic influences the brine entered the gas reservoir from below and along the axis of the deposit and migrated out along bedding to the southwest northeast and northwest metals transporting brines may have been fed into the host sandstones from the east fault but that remains uncertain abundant ore stage fe and mn calcite cements from the reduced fringe have 13c values as low as 18 4 and many values less than 10 which indicate that significant carbonate was generated by oxidation of organic carbon from the natural gas the zone of calcite cements with very low 13c values approximately envelopes chalcocite bearing ore sulfur isotope data of cu pb and fe sulfides and barite indicate derivation of roughly half of the orebody sulfide directly from sour gas h2s that sour gas h2s had developed in steps known from other sedimentary basins starting with 1 bacterial sulfate reduction bsr of seawater sulfate having 34s of about 20 and sequestering of the sulfide in organic matter in source rocks stratigraphically below the deposit host rocks followed by 2 maturation of the sulfide bearing organic matter into liquid petroleum with relatively homogeneous sulfide having 34s of 5 5 then by 3 thermal cracking of the oil to ch4 and h2s with relatively homogeneous sulfide having 34s closely distributed about 6 the ch4 and h2s migrated and were trapped in sandstones of the upper member of the revett formation where they were later met by the 200 c metals transporting brine there was additional contribution of sulfide to ore from later thermochemical sulfate reduction tsr operating on sulfate 34s of 20 to 29 in both formation waters and metals transporting solutions a large range of 34s in sulfides resulted as the 6 sour gas sulfide was supplemented with varying proportions of 20 to 29 sulfide from tsr

evidence of polyphase deformation in gneissic rocks around devgadh bariya implications for evolution of godhra granite in the southern aravalli region india in this paper field evidence documenting the polydeformed nature of banded gneiss that comprises a part of the godhra granite and gneiss in the southern portion of aravalli mountain belt amb india is presented the structural geometry involving an episode of recumbent reclined folding in the gneiss lying in the vicinity of devgadh bariya town is worked out the banded gneiss occurs as enclaves in the granite therefore it is suggested that the banded gneiss of the region is older than godhra granite microstructures preserved in the granitic rocks are documented and it is suggested that the granitic rocks underwent deformation and strain during their evolutionary history variation in the mesoscopic scale fabric of the gneiss and granite along a south to north traverse within the study area is documented and different possibilities for evolution of godhra granite are discussed

prism and basal plane parallel subgrain boundaries in quartz a microstructural geothermobarometer empirical data on quartz subgrain patterns from various metamorphic rocks show that at least up to 10 kbar in the stability field of low quartz prismatic subgrain boundaries are dominant whereas basal subgrain boundaries are not developed in the high quartz stability field both prismatic and basal subgrain boundaries occur and form typical rectangular chessboard patterns the likely reason behind the different occurrence of these subgrain patterns is that in high quartz prismatic glide becomes as easy as or probably even easier than basal glide the two types of subgrain patterns can be clearly distinguished by optical microscopy consequently the occurrence of chessboard subgrain patterns in quartz represents a practicable geothermobarometer the possibilities of its application are far reaching and include the specification of deformation conditions at high grade metamorphism the recognition of syntectonic intrusions and the distinction between pluton emplacement at lower and at higher crustal levels

a review of criteria for the identification of magmatic and tectonic foliations in granitoids abstract foliations in granitoids can form by magmatic flow submagmatic flow high temperature solid state deformation and moderate to low temperature solid state deformation a review of previous work suggests that no single criterion can consistently distinguish foliations in granitoids formed by flow during ascent diapiric emplacement and expansion emplacement during regional deformation or regional deformation post dating emplacement however a magmatic origin is favoured for foliations defined by the alignment of igneous commonly euhedral minerals particularly where the foliation is parallel to internal or external pluton contacts foliations formed during expansion or ballooning of diapirs may be strictly magmatic in origin although some studies suggest that solid state deformation also may occur if so we would hope to find evidence of deformation of crystal melt systems and that the solid state deformation occurred at high temperatures the inference of syntectonic foliations is most convincing where magmatic and high temperature solid state foliations are subparallel these foliations are continuous with regionally developed foliations in the wall rocks synkinematic porphyroblasts are present in the wallrocks and igneous minerals have the same age as metamorphic minerals associated with the regional cleavage a strictly tectonic origin for foliations in granitoids is favoured when the foliation is defined by metamorphic minerals no alignment of igneous minerals occurs the foliation is locally at high angles to pluton wallrock contacts and the foliation is continuous with a regionally developed cleavage

resources of gold in phanerozoic epithermal deposits we have estimated earth s endowment of gold in phanerozoic epithermal deposits using a tectonic diffusion model which simulates the emplacement of deposits at a shallow crustal depth and their subsequent vertical tectonic migration in the crust the calculation was calibrated by least squares comparison of a calculated age frequency distribution to the age frequency distribution for 448 epithermal deposits of phanerozoic age results indicate that 17 percent of the epithermal deposits that formed through phanerozoic time remain in the crust today whereas 83 percent have been removed by erosion assuming a similar age distribution for all 1 181 epithermal deposits in our compilation indicates that 307 000 deposits formed throughout phanerozoic time that 63 000 of these remain in the crust and that 244 000 have been eroded grade and tonnage data of gold in 757 epithermal deposits in the compilation have an arithmetic average of 34 7 t and yield an estimate of 2 2 106 t of gold for epithermal deposits remaining in the crust using the model based vertical distribution of deposits remaining in the crust we estimate that epithermal deposits in the upper kilometer of the united states contain 2 9 104 t of gold adjusting for areas of outcropping volcanic rocks in each continent increases our estimate to 4 0 104 t these estimates are similar to the 1 7 104 t gold resource estimated by the u s geological survey using completely different methods several comparisons based on these results provide insights into the efficiency of processes that form epithermal deposits and the outlook for sustainability for instance all of the epithermal deposits that formed through phanerozoic time represent only about 0 03 percent of the gold in the crust only about 0 007 percent of crustal gold remains in epithermal deposits the rest has been eroded and recycled this is consistent with comparisons based on the flux of gold in the taupo volcanic zone which indicate that epithermal deposits trap only 0 1 to 0 2 percent of the gold that moves through convergent margin hydrothermal systems epithermal gold deposits that remain in the crust can supply current production from them for 1 400 to 5 000 years depending on success of exploration and depth of mining finally we are consuming gold from epithermal deposits about 17 000 times faster than earth is replenishing the supply

magnetic fabric and rheology of co mingled magmas in the nasavrky plutonic complex e bohemia implications for intrusive strain regime and emplacement mechanism abstract the fabrics of mafic microgranular enclaves mme and of the host granodiorite of the old granodiorite intrusion of the nasavrky plutonic complex e bohemia were investigated by means of magnetic anisotropy the magnetic fabric in mme is oriented coaxially with the magnetic fabric of the host granodiorite which is undoubtedly magmatic intrusive in origin consequently the magnetic fabric in mme originated during the same process as the magnetic fabric in granodiorite i e during the granodiorite emplacement in addition also the degree of anisotropy and the shapes of susceptibility ellipsoids are very similar in mme and in granodiorite which probably indicates that the mme had probably a similar viscosity to that of granodiorite and behaved as passive markers whose shapes resembled those of the intrusive strain ellipsoids petrological and geochemical approaches coupled with rheological modelling allow the prediction of the physical states of magmas and of the development of their internal fabrics observed fabrics were compared to the results of numerical modelling of multiparticle systems slowly moving in viscous fluid the steep magnetic foliations and almost vertical magnetic lineations suggest that today s erosion level represents a relatively deep intrusive level where magma flowed vertically and its intrusion was controlled by the shape of the feeder zone used for magma ascension

granite emplacement and its relation with regional deformation in the aravalli mountain belt india inferences from magnetic fabric abstract this contribution presents field microstructural and anisotropy of magnetic susceptibility ams data from the godhra granite a ca 1 ga pluton at the southern margin of the aravalli mountain belt western india that lies near the central indian tectonic zone citz the northern and southern margins of the granite are high strain zones with north dipping e w striking foliations and nw plunging stretching lineations the presence of preferentially oriented feldspars suggests that the granite was subjected to magmatic deformation during its emplacement high temperature solid state deformation fabrics are recorded from microstructural studies which imply that the granite is deformed ams data show magnetic foliations and magnetic lineations in the granite with orientations similar to the field data the magnetic foliation in the granite is parallel to the d 3 foliation in the gneissic host rock both the stretching lineations and the magnetic lineations at the granite margin high strain zones are parallel with the axes of d 3 reclined folds in the gneiss therefore the emplacement of the godhra granite is inferred to have taken place syntectonically while the gneiss was undergoing the d 3 phase of deformation the orientation and character of these lineations and the vergence of the d 3 folds imply oblique simple shear which is inferred to have controlled the emplacement of the granite the magnetic fabric data are compared with the regional structural trends of the metasedimentary rocks of the southern aravalli region and the available geochronological data from rocks of the southern aravalli region are summarised based on this information it is suggested that the emplacement of godhra granite deformation of the southern parts of aravalli mountain belt and tectonothermal events along the citz and rodinia supercontinent assembly were related events

the phillips pluton maine usa evidence of heterogeneous crustal sources and implications for granite ascent and emplacement mechanisms in convergent orogens the phillips pluton age of 403 8 1 3 ma was assembled at a crustal level below the contemporary brittle plastic transition during regional dextral reverse transpressive deformation the pluton is composed dominantly of medium to coarse grained leucogranite sensu lato s l but within its bounds includes decametric massive outcrop of fine to medium grained granodiorite s l in places the leucogranite contains centimetric enclaves apparently of the granodiorite granodiorite is host to more biotite than muscovite and more calcic oscillatory zoned plagioclase compared to the leucogranite pegmatitic granite and composite pegmatite aplite occur as metric sheets within the pluton and as larger bodies outside the pluton to the sw magmatic fabrics defined by biotite schlieren occur locally in the leucogranite the attitude of these fabrics and layering within the leucogranite are concordant with the ne striking steeply dipping country rock foliation k2o contents rb sr ratios rb sr and ba covariations and chondrite normalized rare earth element ree patterns of leucogranite are consistent with high to moderate a h2o muscovite dehydration equilibrium eutectic melting of a predominantly pelite source similar to metasedimentary rocks of the surrounding central maine belt cmb the ree patterns and rb sr ratios of granodiorite also suggest derivation from a metasedimentary source but more likely by moderate to low a h2o muscovite biotite dehydration equilibrium eutectic to non eutectic minimum melting of a protolith dominated by greywacke in which garnet and plagioclase were residual phases both granite s l types have heterogeneous initial nd isotope compositions samples of granodiorite define a range in end 404 ma of 1 8 to 0 1 0 3 2 uncertainty and samples of leucogranite define a range in end 404 ma of 8 0 to 5 3 0 3 2 uncertainty this bimodal distribution suggests that melts were derived from a minimum of two sources the data are consistent with these sources being cmb metasedimentary rocks end 404 ma 4 for the granodiorite the range of nd isotope compositions within each granite type most likely reflects isotopic heterogeneity inherited from the source these data imply that the integrity of individual melt batches was maintained during ascent and that extensive mixing of melt batches during emplacement at this level in the pluton did not occur although centimetric enclaves have intermediate nd isotope compositions consistent with small scale interactions between magmas we infer that the phillips pluton represents the root of a larger pluton and that what remains of this larger pluton is the feeder constructed from multiple melt batches arrested during waning flow of granite magma through a crustal scale shear zone system

fossilised geothermal surface features of the whitianga volcanic centre miocene coromandel volcanic zone new zealand controls and characteristics abstract the late miocene whitianga volcanic centre of the coromandel volcanic zone north island new zealand is host to 18 known siliceous and intensely silicified deposits including silicified volcanics sediments of inferred lacustrine fluvial and mud pool origin siliceous hot spring deposits or sinters and silicic veins collectively these siliceous and silicified deposits indicate past geothermal activity that occurred at the earth s surface and in the shallow subsurface sinters in particular are of interest because they are derived from deep geothermal reservoirs and precipitate from discharged thermal fluids at the intersection of the water table with the land surface however some siliceous and silicified features in hydrothermal paleoenvironments have been misidentified as sinters by studying textural types distributions structural setting mineral paragenesis and trace elemental composition of the siliceous and silicified deposits in the whitianga volcanic centre it is possible to differentiate sinters and identify their spring vent source areas 100 70 c from more distal thermal spring discharge locations ag mineralisation may have occurred at depth this has important implications for the exploration of mineralised epithermal ore deposits at local to regional scales in particular for the hauraki goldfield of the coromandel volcanic zone

the pombal granite pluton magnetic fabric emplacement and relationships with the brasiliano strike slip setting of ne brazil paraiba state abstract the pombal pluton 500 km 2 a suite of diorite syenite and porphyritic granite bodies is here used to constrain kinematics of brasiliano age tectonic episodes in northeast brazil the pluton intrudes high grade to migmatitic gneiss forming the western basement of the serido belt and is located at the intersection between two sets of continental scale dextral strike slip shear zones the northern set of shear zone strikes ne sw and branches southwards into the e w patos mega shear zone a detailed microstructural and low field magnetic susceptibility study was performed to unravel the relationships between solid state deformation in the country rocks and magma emplacement porphyritic granite and syenite have quite high magnetic susceptibilities 10 3 10 2 si units indicative of magnetite as the principal carrier of susceptibility the magnetic fabric is remarkably homogeneous in orientation throughout the pluton it is characterized by a shape preferred alignment of magnetite itself parallel to the shape fabric of mainly biotite amphibole i e to the magmatic fabric even close to the contact with the high temperature mylonites of the patos shear zone south of pombal no imprint of the e w trending structures is observed in the fabrics of either the granite or the host rocks granite emplacement and its internal fabric development is concluded to be independent of the movement of the patos shear zone in the southwestern border of the pluton a low dip foliation bearing a ne sw striking lineation is shared in both the magmatic fabric of the pluton and the solid state fabric farther to the north approaching the ne sw strike slip shear zone the magmatic fabric is characterized by a steeply dipping ne striking foliation carrying a subhorizontal lineation transition from low to steep dips of the planar fabrics is progressive two models are proposed for emplacement of the pombal pluton one considers magma injection during an early episode of tangential tectonics responsible for the gently dipping foliations evolving later to strike slip deformation the other model considers that the pluton was emplaced in a pull apart domain developed in the overlapping sector of a right hand en echelon system of a dextral shear zone compatibility of these models with the tectonic evolution of the serido belt is discussed

self ordering and complexity in epizonal mineral deposits epizonal base and precious metal deposits makeup a range of familiar deposit styles including porphyry copper gold epithermal veins and stockworks carbonate replacement deposits and polymetallic volcanic rock hosted vhms deposits they occur along convergent plate margins and are invariably associated directly with active faults and volcanism they are complex in form variable in their characteristics at all scales and highly localized in the earth s crust more than a century of detailed research has provided an extensive base of obser vational data characterizing these deposits from their regional setting to the fluid and isotope chemistry of mineral deposition this has led to a broad understanding of the large scale hydrothermal systems within which they form low salinity vapor released by magma crystallization and dispersed into vigorously convecting ground water systems is recognized as a principal source of metals and the gases that control redox conditions within systems the temperature and pressure of the ambient fluid anywhere within these systems is close to its vapor liquid phase boundary and mineral deposition is a consequence of short timescale perturbations generated by localized release of crustal stress however a review of occurrence data raises questions about ore formation that are not addressed by traditional genetic models for example what are the origins of banding in epithermal veins and what controls the frequency of oscillatory lamina tion what controls where the phenomenon of mineralization occurs and why are some porphyry deposits for example so much larger than others the distinctive self organized characteristics of epizonal deposits are shown to be the result of repetitive coupling of fracture dilation consequent on brittle failure phase separation boiling and heat transfer between fluid and host rock process cou pling substantially increases solute concentrations and triggers fast far from equilib rium depositional processes since these coupled processes lead to localized transient changes in fluid characteristics paragenetic isotope and fluid inclusion data relate to conditions at the site of deposition and only indirectly to the characteristics of the larger scale hydrothermal system and its longer term behavior the metal concentra 1 the us government has the right to retain a nonexclusive royalty free license in and to any copyright covering this paper

isotope geochemistry of mercury in source rocks mineral deposits and spring deposits of the california coast ranges usa abstract we present here the first study of the isotopic composition of mercury in rocks ore deposits and active spring deposits from the california coast ranges a part of earth s crust with unusually extensive evidence of mercury mobility and enrichment the franciscan complex and great valley sequence which form the bedrock in the california coast ranges are intruded and overlain by tertiary volcanic rocks including the clear lake volcanic sequence these rocks contain two types of mercury deposits hot spring deposits that form at shallow depths the franciscan complex and great valley sequence contain clastic sedimentary rocks with higher concentrations of mercury than volcanic rocks of the clear lake volcanic field mean mercury isotopic compositions 202hg for all three rock units are similar although the range of values in franciscan complex rocks is greater than in either great valley or clear lake rocks hot spring and silica carbonate mercury deposits have similar average mercury isotopic compositions that are indistinguishable from averages for the three rock units although 202hg values for the mercury deposits have a greater variance than the country rocks precipitates from spring and geothermal waters in the area have similarly large variance and a mean 202hg value that is significantly lower than the ore deposits and rocks these observations indicate that there is little or no isotopic fractionation