surface geostrophic currents across the antarctic circumpolar current in drake passage from 1992 to 2004 the southern ocean plays an important role in the global overturning circulation as a significant proportion of deep water is converted into intermediate and deeper water masses in this region recently a secular trend has been reported in wind stress around the southern ocean and it is thought theoretically that the strength of the acc is closely related to wind stress so one consequence should be a corresponding increase in acc transport and hence changes in the rate of the global overturning there are no long term data sets of acc transport and so we must examine other data that may also respond to changing wind stress here we calculate surface currents in drake passage every seven days over 11 25 years from 1992 to 2004 we combine surface velocity anomalies calculated from satellite altimeter sea surface heights with measured surface currents since 1992 the uk has regularly occupied woce hydrographic section sr1b across the acc in drake passage from seven hydrographic sections surface currents are estimated by referencing relative geostrophic velocities from ctd sections with current measurements made by shipboard and lowered acoustic doppler current profilers combining the seven estimates of surface currents with the altimeter data reduces bias in the estimates of average currents over time through drake passage and we show that surface current anomalies estimated by satellite and in situ observations are in good agreement the strongest surface currents are found in the subantarctic and polar fronts with average speeds of 50 cm s and 35 cm s respectively and are inversely correlated so that maximum westward flow in one corresponds to minimum westward flow in the other the average cross sectional weighted surface velocity from 1992 to 2004 is 16 7 0 2 cm s a spectral analysis of the average surface current has only weakly increasing energy at higher frequencies and there is no dominant mode of variability the standard deviation of the seven day currents is 0 68 cm s and a running 12 month average has only a slightly smaller standard deviation of 0 52 0 16 cm s the southern annular mode sam measures the circumpolar average of wind stress and like the surface currents its spectrum has slightly increased energy at frequencies greater than 1 cpy a cospectral analysis of these averaging cospectra of five slightly overlapping 36 month segments improve statistical reliability suggests that there is coherence between them at 1 cpy with the currents leading changes in the southern annular mode we conclude that the sam and average drake passage surface currents are weakly correlated with no dominant co varying modes and hence predicting southern ocean transport variability from the sam is not likely to give significant results and that secular trends in surface currents are likely to be masked by weekly and interannual variability

a history of cleavage and folding an example from the goldenville formation nova scotia temporal relationships between cleavage formation and folding in sedimentary rock sequences can vary from either phenomena preceding the other to both occurring simultaneously knowledge of this relationship however is required to understand fully the relationship of cleavage orientation to finite strain and the origin of cleavage refraction across competent incompetent layers evidence from the goldenville formation provides an example of cleavage formed before folding by 50 pressure solution removal of material resulting in cleavage planes normal to bedding during active folding this layer parallel shortening was accompanied by excess pore pressure that in some cases exceeded lithostatic pressure causing formation of bedding parallel quartz veins with crack seal textures folds developed by a mechanism of differential flexural flow with no loss of coherence across bedding surfaces en echelon veins formed sequentially across some beds during active folding and subsequently were deformed by various increments of bedding parallel shear after folds reached 80 limb dips continued horizontal shortening was accommodated by additional pressure solution but no recognizable new cleavage was formed because cleavage in the goldenville formation formed perpendicular to bedding before folding and was passively rotated and extended by bedding parallel simple shear during fold amplification the resulting cleavage planes cannot lie in the xy plane of the finite strain ellipsoid differential shear between metagray wacke and slate beds accounts for the observed cleavage refraction and the bedding cleavage angle provides a good estimate of the shearing across these beds during active folding if cleavage can be shown to postdate folding in other examples it is possible that cleavage planes will lie in the xy plane of the finite strain ellipsoid

vertical mixing in the ocean the thermohaline circulation of the ocean results primarily from downwelling at sites in the nordic and labrador seas and upwelling throughout the rest of the ocean the latter is often described as being due to breaking internal waves here we reconcile the difference between theoretical and observed estimates of vertical mixing in the deep ocean by presenting a revised view of the thermohaline circulation which allows for additional upwelling in the southern ocean and the separation of the north atlantic deep water cell from the antarctic bottom water cell the changes also mean that much less wind and tidal energy needs to be dissipated in the deep ocean than was originally thought

residual mean solutions for the antarctic circumpolar current and its associated overturning circulation abstract residual mean theory is applied to the streamwise averaged antarctic circumpolar current to arrive at a concise description of the processes that set up its stratification and meridional overturning circulation on an f plane simple solutions are found in which transfer by geostrophic eddies colludes with applied winds and buoyancy fluxes to determine the depth and stratification of the thermocline and the pattern of associated residual meridional overturning circulation

a middle cambrian trilobite faunule from the meguma group of nova scotia the meguma group of southern nova scotia is a thick succession of mostly deep water siliciclastic sedimentray rocks of uncertain age previous fossil finds have been in the halifax formation of the upper part of the sequence and have provided early ordovician ages a newly discovered trilobite bearing bed from the underlying goldenville formation yields middle cambrian taxa of acado baltic affinity specimens belonging to paradoxides s l agraulos dorypyge and ellipsocephalidae indicate that the meguma group is an exotic succession with faunal similarity to the adjacent avalon terrane and to middle cambrian successions in europe the middle east and west africa

direct characterization of airborne particles associated with arsenic rich mine tailings particle size mineralogy and texture windblown and vehicle raised dust from unvegetated mine tailings can be a human health risk airborne particles from as rich abandoned au mine tailings from nova scotia canada have been characterized in terms of particle size as concentration as oxidation state mineral species and texture samples were collected in seven aerodynamically fractionated size ranges 0 5 16 micro m using a cascade impactor deployed at three tailings fields all three sites are used for recreational activities and off road vehicles were racing on the tailings at two mines during sample collection total concentrations of as in the 8 micro m fraction varied from 65 to 1040 ng m sup 3 of air as measured by proton induced x ray emission pixe analysis the same samples were analysed by synchrotron based microfocused x ray absorption near edge spectroscopy micro xanes and x ray diffraction micro xrd and found to contain multiple as bearing mineral species including fe as weathering products the as species present in the dust were similar to those observed in the near surface tailings the action of vehicles on the tailings surface may disaggregate material cemented with fe arsenate and contribute additional fine grained as rich particles to airborne dust results from this study can be used to help assess the potential human health risks associated with exposure to airbornemore particles from mine tailings less

stability of the atlantic meridional overturning circulation and stratification in a zonally averaged ocean model effects of freshwater flux southern ocean winds and diapycnal diffusion the atlantic meridional overturning circulation amoc is a crucial component of the global climate system in this study using a zonally averaged ocean model we reexamine the sensitivity of this circulation and ocean density structure in general to several types of external forcing the basin of the model extends from northern high latitudes to antarctica and includes an implicit representation of a circumpolar channel in the south and ocean circulation is driven by surface buoyancy fluxes and wind forcing in contrast to earlier two dimensional studies of the amoc our approach involves a careful treatment of the residual mean circulation comprising the eulerian mean and eddy induced flows which is especially important for the southern ocean dynamics using boundary conditions consistent with present day observations the model reproduces realistic ocean stratification and meridional overturning the structure intensity and stability of the overturning are then extensively studied using three control parameters the strength of westerly wind stress over the southern ocean the magnitude of freshwater fluxes imposed on the northern atlantic and ocean diapycnal diffusivity in a realistic parameter range we estimate the amoc sensitivity to changes in the southern ocean winds on the order of 1 sv per 20 increase in the wind stress the overturning also increases with diapycnal diffusivity but the dependence is weaker than in the absence of the winds the model can undergo a shutdown of the overturning subject to a hysteresis when either the freshwater forcing gradually increases or the wind stress decreases the hysteresis loop disappears for large values of isopycnal diffusivity changes in the amoc intensity are accompanied by changes in the volume transport of the antarctic circumpolar current specifically the amoc collapse leads to a strengthening of this transport ultimately our calculations produce stability maps for the steady states of the meridional overturning circulation and provide a general framework that potentially can be used to compare different models or to understand past abrupt climate changes related to reorganization of the amoc

eddy advective and diffusive transports of heat and salt in the southern ocean there are two distinct mechanisms by which eddies provide systematic transport of tracer on isopycnals the advective transport associated with the slumping of isopycnals and the diffusive transport associated with down gradient diffusion depending on the large scale tracer distribution eddy advective transport has either the same direction as or opposite direction to eddy diffusive transport as a consequence eddy advection and eddy diffusion can reinforce each other for some tracers but oppose each other for other tracers using scaling analysis it is argued that the relative directions of eddy advective and diffusive transports can be determined simply from the relative slopes of tracers and isopycnals an eddy resolving 1 12 global ocean model is used to illustrate the two eddy transport mechanisms for temperature and salinity in the southern ocean applications to other tracers such as oxygen are discussed the diagnosed eddy diffusivity for temperature and salinity is found to be considerably different from the eddy diffusivity for eddy advective transport velocity

the onaman prospect ontario an unusual occurrence of cu bearing au mineralization in a shear zone the onaman prospect is an unusual example of mesothermal gold mineralization in which native gold electrum and minor chalcopyrite are disseminated in metavolcaniclastic rocks in shear zones or concentrated in felsite dikes that intrude the metavolcaniclastic rocks mineralization was contemporaneous with carbonatization and involved early replacement of iron bearing minerals in the wall rock by ankerite and pyrite and later replacement of pyrite by arsenopyrite pyrrhotite chalcopyrite electrum and native gold oxygen isotope ratios of ankerite suggest a metamorphic origin for the fluid and carbon isotope ratios are similar to those of large mesothermal gold deposits in the superior province for which a mantle origin has been proposed sulfur isotope ratios correlate positively with gold grades and may reflect decreasing f o2 during mineralization a model is proposed in which deformation of the volcanic pile led to the formation of a shear zone and created dilational zones allowing dike intrusion metamorphic fluids rose along the shear zones and the dikes pyritization of the host rock was the major control on gold and chalcopyrite deposition reducing a h 2 s and destabilizing the bisulfide complexes of au and cu the onaman occurrences provide an uncommon example of a mesothermal system in which ph was relatively low and the correspondingly low solubility of copper allowed the fluid to saturate with and deposit chalcopyrite in most other mesothermal gold systems copper is too soluble to saturate the fluid with a copper mineral and is therefore flushed through the system

234u 238u mass spectrometry of corals how accurate is the uth age of the last interglacial period direct measurement of u and th by mass spectrometry recently provided a spectacular improvement in the precision of coral dating by the uth disequilibrium method 1 mass spectrometric data also provide a much better resolution for the examination of subtle diagenetic effects revealed by small variations of the 234u 238u ratio such perturbations may strongly affect the accuracy of the uth chronometer a compilation of all the corals analyzed to date by mass spectrometry shows that most of the corals from terraces of the last interglacial have initial 234u 238u ratios higher than present day seawater in contrast to modern holocene and last glacial corals some samples that have very high 234u 238u initial ratios up to 1 2 and high u concentrations up to 4 ppm were probably contaminated by continental groundwaters however even apparently pristine samples have 234u 238u initial ratios which are still slightly higher than present day seawater mean value 1 160 compared to 1 140 1 150 2 with little overlap between the two distributions this difference in the u initial ratio raises some uncertainty about the accuracy of the uth age determinations of these corals in spite of the fact that the 234u230th ages cluster in a narrow range between 122 and 133 kyr the data could also be interpreted as resulting from slight contamination of corals that are significantly older than 125 kyr two possible explanations may explain these data 1 all these samples may have been diagenetically altered since they all come from surface outcrops which have been directly exposed to precipitations or soil waters for 125 kyr in this case the true age of these corals remains uncertain depending on the timing of the alteration process i e initial late or continuous 2 the second possibility is that some of the differences in 234u 238u ratios measured in 125 kyr cold corals compared to modern seawater may be due to a higher 234u 238u ratio in seawater 125 kyr ago this could result from temporal variations in the weathering regimes of continental land masses

sulphur isotopic composition of sulphides from the beaver dam and other meguma group hosted gold deposits nova scotia implications for genetic models sulphur isotopic compositions were determined for sulphide mineral phases in meguma group hosted gold deposits nova scotia in order to resolve i potential source regions for sulphur in these de

platform drowning leading to cool water carbonate deposition evolution of a late ordovician turinian chatfieldian mixed sediment platform within the taconic orogen long point group newfoundland appalachians late ordovician turinian chatfieldian drowning of a mixed carbonate siliciclastic platform within the taconic orogen newfoundland appalachians is recorded by net deepening of an initial warm shallow water platform succession lourdes formation culminating in a metre scale thick condensed interval that characterizes a drowning succession punctuated by storm deposits composition of transported material suggests that seaward drowning was coupled with back stepping of a high energy carbonate factory related to hinterland uplift and erosion that would eventually lead to drowning of the outer platform beneath marine transported siliciclastic sediments winterhouse formation in the new offshore shelf setting a sparse reciprocal stratigraphy of fine to very coarse grained phosphatic carbonate and mixed sediment is interpreted to document gravity flow deposition downgradient from either a sustained or episodically developed high energy cool water carbonate source along the inner shelf transported carbo

integrated model for meguma group lode gold deposits nova scotia canada meguma group lode gold deposits represent concentrations of a variety of auriferous quartz veins in lower paleozoic metaturbidites of the meguma terrane of southern nova scotia our studies incorporating extensive field regional and detailed mapping and laboratory petrography fluid inclusions geochemistry isotopes studies of 30 of these deposits in the eastern meguma terrane suggest that mineralization occurred at ca 370 ma 40 ar 39 ar dating of hydrothermal vein minerals during widespread incursion of mafic and felsic magmatism into the crust concurrent with subvertical shear zone development thus postdating regional acadian deformation by some 30 40 m y isotopic data s c o sr indicate that vein forming fluids were not solely magmatic and were in part exotic to the meguma group thus earlier magmatic and metamorphogenic lateral secretion models that considered either late stage magmatic fluids or the enveloping meguma group metasedimentary rocks as the sole source of vein components are invalidated

ore shoots in folded and fractured rocks insights from 3d modelling of the fosterville gold deposit victoria australia abstract at the fosterville gold deposit high concentrations of visible and refractory gold are hosted in arrays of quartz and quartz carbonate veins they are distributed in elongate zones to form south plunging ore shoots within a folded and fractured turbidite sequence here we distinguish the influence of faults versus folds at fosterville by assessing the deposit scale structural framework and hydrothermal fluid flow using a combination of 3d implicit modelling structural analysis and 3d fault slip dilation tendency analyses gold assay and bedding trend data from a large drillhole dataset were spatially interpolated and used to analyse and measure the orientation of ore bodies and folded host rocks field measurements of fold axis orientations were compared to bedding measurements in oriented drillcore bingham axial analysis of bedding trends and orientation data from a 3d implicit model both field and drill core structural data show that ore shoots at fosterville do not parallel the first order gently 10 south plunging folds instead the orientation of the ore shoots is coincident with an intersection lineation between steeply west dipping bedding parallel faults and moderately dipping linkage faults that obliquely cut across the main structural grain resulting in ore shoot plunges larger than 20 slip and dilation tendencies suggest that linkage faults had a higher likelihood of activity in the inferred far field stress regimes at the time of mineralisation relative to other structures at fosterville these linkage faults are therefore interpreted to have been preferential fluid flux conduits in the system despite appearing to be subordinate structures at the scale of the deposit this new structural model for fosterville highlights that fluid flow and ore shoot formation are strongly controlled by obliquely oriented structures that are unlike the main structural grain of first order folds and faults

aspects of the antarctic circumpolar current dynamics investigated with drifter data interactions between eddies and mean flow are essential to close the momentum budget of the southern ocean as well as to determine the structure of the global meridional overturning circulation both the structure of the antarctic circumpolar current and the eddy dynamics arising at its heart are importantfor water mass circulation and global ocean ventilation and therefore for the global climate however the characterization of the eddy fields of heat and momentum are still poorly sampled by direct observations and are difficult to accurately resolve or parameterize in numerical models here we present observation based eddy statistics and eddy heat flux ehf from a consistent dataset and estimate southern ocean surface ehf from direct measurements without any parameterization assumption observations obtained from near surface drifters represent a very useful dataset to analyze the eddy field because of their ability to catch a large number of scales of motion while providing a quasi synoptic coverage of the investigated area differences between winter and summer distributions of mean velocities mean kinetic energy and eddy kinetic energy are shown to be strongly constrained by bottom topography and suggest a winter shift of the polar front in specific areas around the circumpolar belt overall the flow follows the contours of constant planetary vorticity set by the depth of the ocean and creates anisotropy in eddy dispersion with maximum dispersion along these contours furthermore eddy mean flow interactions are strongly influenced by topography with eddies having a tendency to accelerate jets upstream of ridges and decelerate them further downstream these strong regional variabilities introduced by topography affect the flux of heat induced by eddies and therefore affect formation and subduction of the main surface and intermediate southern ocean water masses integrated over the southern ocean subduction of water masses induced by ehf appears as an order on component for the southern ocean thermocline ventilation our results based on direct observations emphasizes once more the importance of continuing sustained effort to better represent the effect of mesoscale eddies in a coarse climate model if we are to represent and predict future climate

drowned coralline algal dominated deposits off lanai hawaii carbonate accretion and vertical tectonics over the last 30 ka we present detailed bathymetry remotely operated vehicle rov and submersible observations and sedimentary and radiocarbon age data from carbonate deposits recovered from two submerged terraces at 150 m t1 and 230 m t2 off lanai hawaii the tops of the terraces are veneered by relatively thin b5 m in situ accumulations of coralline algal nodule coralgal nodule halimeda and a derived oolitic facies deposited in intermediate 30 60 m to deep fore reef slope settings 60 120 m the data are used to develop a sedimentary facies model that is consistent with eustatic sea level variations over the last 30 ka both nodule facies on t1 and t2 initiated growth 30 29 ka following a fall in sea level of 50 m and increase in bottom currents during the transition from marine isotope stage 3 to 2 the nodules accreted slowly throughout the last glacial maximum when sea level was relatively stable drowning occurred during the early deglaciation 17 16 ka and was marked by the complete drowning of coralline algal nodules facies on t2 and incipient drowning of coralgal facies on t1 abrupt sea level rise during the middle deglaciation perhaps associated with global meltwater pulse 1a 14 15 ka finally drowned the coralgal facies on t1 which in turn was overlain by a deep water halimeda facies or an oolitic facies derived from upslope our data indicates that lanai has experienced relatively little vertical tectonic movement over the last 30 ka using paleobathymetric data derived from the sedimentary facies age vs depth relationships and published sea level curves we estimate that lanai could be either slowly uplifting or subsiding but at rates b0 1 m kyr uplift or b0 4 m kyr subsidence over this 30 kyr period d 2005 elsevier b v all rights reserved

a review of the mesothermal gold deposits of the meguma group nova scotia canada abstract the gold province of the meguma terrane in nova scotia contains several classic examples of turbidite hosted mesothermal gold deposits there are over 300 gold occurrences and deposits hosted by the cambro ordovician meguma group rocks in southern nova scotia canada the meguma group consists of two formations 1 a lower sand dominated flysch goldenville formation and 2 an upper shaley flysch halifax formation subdivision of the goldenville formation into several map units is leading to a better understanding of the stratigraphic constraints on the gold mineralization although detailed stratigraphic investigations in all of the major gold producing areas is still ongoing it is evident that the steve s road beaverbank and the mt uniacke stratigraphic intervals contain most of the major past gold producers in the province the meguma group rocks are variably deformed into upright gently to moderately doubly plunging folds with multiple cleavages the strata are metamorphosed from greenschist to amphibolite facies and are subsequently intruded by ca 370 ma peraluminous granites and minor mafic intrusions the gold deposits can be divided into three main types 1 high grade approximately 15 g t au narrow gold bearing quartz veins 2 low grade 0 5 4 g t au slate argillite hosted and 3 low grade meta sandstone hosted a combination of two or more of the above can also occur almost all of the historic production 47 million g au has come from the high grade veins within 200 m of surface a variety of vein types occur although most of the gold produced came from bedding concordant stockwork and fissure veins isotopic investigations and dating of the vein minerals indicate that the mineralization was related to migration of metamorphic fluids from multiple reservoirs in the waning stages of the acadian orogeny disseminated low grade gold with minor electrum and associated intermetallic compounds and metal alloys have recently been recognized in host rocks at several of the former gold mining areas in nova scotia the presence of disseminated gold in combination with high grade vein mineralization greatly enhances the economic viability of gold deposits in the meguma group the association of disseminated gold and narrow vein hosted deposits has important exploration implications for similar mesothermal gold districts elsewhere

hydrothermal alteration in metasedimentary rock hosted orogenic gold deposits reefton goldfield south island new zealand orogenic or mesothermal quartz lodes in lower palaeozoic greenland group metasedimentary rocks of the reefton area have produced 67 tonnes t of gold prior to 1951 and recent exploration has identified new gold resources in several deposits including the largest past producers blackwater and globe progress the metasedimentary rocks consist of alternating sandstone and mudstone beds that were metamorphosed to lower greenschist facies prior to being hydrothermally altered adjacent to the quartz lodes the sandstones are feldspathic litharenites averaging q65 f10 r25 with detrital grains of quartz rock fragments muscovite and plagioclase and biotite that were altered to albite and chlorite respectively during metamorphism accessory minerals are graphite apatite zircon tourmaline and titanite hydrothermal alteration of the sandstones has developed a mineral assemblage of k mica carbonate dolomite ankerite ferroan magnesite and magnesian siderite chlorite pyrite and arsenopyrite the abundance of hydrothermal chlorite is greater at blackwater than at the other prospects studied hydrothermal alteration associated with the quartz lodes is marked by bleaching magnesian siderite spots disseminated arsenopyrite and pyrite and thin carbonate quartz and sulphide veins these trends are accompanied by increasing concentrations of s as and sb and decreasing na and a decrease of fe and mg in k mica the alkali alteration indices 3k al representing k mica and na al representing albite generally show antipathetic trends with 3k al increasing near the lodes and na al decreasing these trends reflect the replacement of albite by k mica carbonate alteration indices co2 ca mg fe and co2 ca mg fe 0 5 s as quantify the abundance of hydrothermal carbonates but they show variable correlation with the lodes they increase the width of the alteration halo in the hanging wall of the lodes at the globe progress and general gordon prospects but the peak values are as far as 150 m from the lodes by contrast peak values of the carbonate alteration indices are within 10 and 2 m of the lodes respectively at the merrijigs and blackwater deposits data show that for deposits with wide hydrothermal alteration halos such as at the globe progress and general gordon prospects the use of a suite of geochemical indicators can assist exploration by indicating trends in hydrothermal alteration that provide vectors to mineralisation they also increase the size of the exploration target by contrast the alteration halo of the blackwater deposit is restricted to within less than 5 m of the quartz lode and therefore the geochemical indicators are of more limited assistance to exploration

application of la icp ms analysis of arsenopyrite to gold metallogeny of the meguma terrane nova scotia canada abstract investigation of gold metallogeny in the paleozoic meguma terrane canada is conducted through la icp ms analysis of arsenopyrite collected from eight slate belt style vein gold deposits using a novel approach integrating elemental distribution maps and their derived elemental paragenesis with multi element binary plots the data reveal two distinct gold events 1 an early event characterized by a co ni mo sb se elemental association related to initial growth of arsenopyrite that reflects the presence of invisible gold 10 ppm and 2 a second event spatially associated with late fracture sets that is characterized by an al ti v mn element association and reflects either remobilization or upgrading of primary invisible gold and is manifest as visible gold the results of this study indicate a complex and protracted history of gold mineralization which has important ramifications for the meguma gold deposits as well as other orogenic gold districts globally in the case of the meguma terrane it involves an initial gold event that is followed by element mobilization and in the case of precious metals au ag an upgrading through a zone refining process in addition the variable coupling and decoupling of elements is only revealed using in situ derived la icp ms data

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

paleozoic orogenic gold deposits in the eastern central andes and its foreland south america abstract in the eastern central andes and its foreland 6 34 s abundant quartz veins emplaced along brittle ductile deformation zones in ordovician to carboniferous granites and gneisses and in saddle reefs in lower paleozoic turbidites represent a coherent group of middle to late paleozoic structurally hosted gold deposits that are part of three major au sb w metallogenic belts these belts extending from northern peru to central argentina along the eastern andean cordillera and further south in the sierras pampeanas include historical districts and mines such as pataz parcoy ananea santo domingo yani aucapata amayapampa sierra de la rinconada and sierras de cordoba on the basis of the available isotopic ages two broad mineralization epochs have been identified with devonian ages in the sierras pampeanas au belt 26 to 33 30 s and carboniferous ages for the pataz maranon valley au belt in northern peru 6 50 to 8 50 s the absolute timing of the southeastern peruvian bolivian and northwestern argentinian turbidite hosted lodes which form the au sb belt of the southern eastern andean cordillera 12 to 26 s is poorly constrained field relationships suggest overlap of gold veining with carboniferous deformation events the northernmost belt which includes the pataz province is over 160 km long and consists of sulfide rich quartz veins hosted by brittle ductile shear zones that have affected carboniferous granitic intrusions gold mineralization at least in the pataz province occurred a few million years after the emplacement of the 329 ma host pluton and an episode of molassic basin formation during a period of rapid uplift of the host units the two southern belts are associated with syn to post collisional settings resulting from the accretion of terranes on the proto andean margin of south america the au sb belt of the southern eastern andean cordillera presumably formed in the final stages of the collision of the arequipa antofalla terrane and the sierras pampeanas au belt is considered concurrent with the late transpressional tectonics associated with the accretion of the chilenia terrane the three devono carboniferous andean belts are the south american segments of the trans global orogenic gold provinces that were formed from late ordovician to middle permian in accretionary or collisional belts that circumscribed the gondwana craton and the paleo tethys continental masses a paleogeographic map of the gondwana supercontinent in its middle cambrian configuration appears as a powerful tool for predicting the location of the majority of the paleozoic orogenic gold provinces in the world as they develop within mobile belts along its border the three south american belts are sited in the metallogenic continuation of the paleozoic terranes that host the giant eastern australian goldfields such as bendigo ballarat and charters towers with which they share many features when compared to deposits in the french massif central direct counterparts of the andean deposits such as pataz and ananea yani are respectively the saint yrieix district and the salsigne deposit considering the ubiquity of the au sb w vein type deposits in the eastern cordillera and sierras pampeanas and the relatively little attention devoted to them the devonian and carboniferous orogenic gold deposits in the eastern section of the central andes constitute an attractive target for mineral exploration

rhenium osmium geochronology of arsenopyrite in meguma group gold deposits meguma terrane nova scotia canada evidence for multiple gold mineralizing events rhenium osmium geochronology using arsenopyrite was undertaken for three gold deposits in the meguma terrane nova scotia canada in order to better constrain their age of formation and to assess the utility of arsenopyrite for dating similar deposits globally analyses of arsenopyrite from bedding concordant veins from the ovens locality southwest meguma terrane yield a precise re os isochron age of 409 5 ma arsenopyrite analyses from a bedding discordant vein at this locality indicate an identical re os age of 407 4 ma saddle reef veins from the dufferin deposit northeast meguma terrane contain arsenopyrite with a precise re os isochron age of 380 3 ma the lack of common os in some arsenopyrite samples from both the ovens and dufferin permit calculation of single mineral model ages for each deposit which are identical to those determined using the isochron method initial os compositions for the two vein types at the ovens suggest a predominately crustal source of os in the mineralizing fluids whereas a less radiogenic initial os composition for arsenopyrite from dufferin does not as clearly define a crustal metal source at a third locality the touquoy deposit the re os systematics of arsenopyrite associated with disseminated gold mineralization do not define a precise formation age possibly as a result of mixing of re and os derived from the mineralizing fluid and the shale host rock the re os ages of arsenopyrite indicate that there were at least two distinct periods of gold deposition in the meguma terrane coinciding with widespread tectonothermal events regional deformation and metamorphism associated with acadian orogenesis and widespread generation of meta and peraluminous granites and high grade metamorphism within the basement rocks under the meguma terrane the ca 407 ma age for the ovens arsenopyrite provides the best estimate for the timing of regional acadian deformation in the meguma terrane and is slightly older than previous estimates based solely on 40ar 39ar dating

eddy variability and energetics from direct current measurements in the antarctic circumpolar current south of australia two year time series measurements of current velocity and temperature in the subantarctic front saf south of australia from 1993 to 1995 provide estimates of eddy fluxes of heat and momentum across the antarctic circumpolar current acc and further insight into the variability of the acc the saf was found to be an energetic meandering jet with vertically coherent fluctuations varying on a timescale of 20 days with typical amplitude 30 cm s21 at 1150 dbar a daily varying coordinate frame that follows the direction of flow allowed mesoscale variability of the saf to be isolated from variability due to meandering of the front and proved very successful for examining eddy fluxes vertically averaged cross stream eddy heat flux was 11 3 kw m 22 poleward and significantly different from zero at 95 for fluctuations in the 2 90 day band zonally integrated this eddy heat flux 50 9 pw is more than large enough to balance heat lost south of the polar front and is as large as cross saf fluxes found in drake passage cross stream eddy momentum fluxes were small not significantly different from zero and of indeterminate sign but tending to decelerate the mean flow a relationship between vertical motion and meander phase identified in the gulf stream was found to hold for the acc eddy kinetic energy levels were similar to those in drake passage and southeast of new zealand eddy potential energy was up to an order of magnitude larger than at other acc sites most likely because meandering of the front is more common here baroclinic conversion was found to be the dominant mechanism by which eddies grow south of australia typical eddy growth time is estimated to be 30 days approximately twice as fast as in drake passage consistent with eddy energy growing rapidly downstream

carbonate platforms along the southeast bahamas hispaniola collision zone the southeast bahama banks have been colliding with the island of hispaniola along a restraining bend within the northern caribbean plate boundary zone since the late miocene a seamarc ii seismic reflection investigation was conducted along the deep water flanks of mouchoir bank and navidad bank to evaluate the response of these carbonate platforms to active plate tectonic collision overall our data provide evidence of large scale platform margin retreat which contrasts sharply with the prograding platform margins in the tectonically passive northwest bahamas north of silver bank there is a large 5 000 km2 deep water 3 000 4 000 m plateau that records the drowning and step back 50 km of an early cretaceous carbonate platform margin intact uneroded segments of this cretaceou platform margin may occur along the seaward edge of the deep water plateau bahama escarpment separated by large 20 km across erosional reentrants a coalescing system of broad up to 10 km shallow 200 m relief canyons akin to mountainous avalanche chutes funnel debris into the reentrants from the flank of silver bank the reentrants are interpreted as zones of structural weakness produced by passage of the atlantic spreading center along a transform plate boundary during the late jurassic early cretaceous drowning and step back appear to be part of a global response of carbonate platforms to a mid cretaceous tectonic pulse of ocean crust formation and relative sea level rise the southern margin of mouchoir bank has also been drowned and has stepped back by about 30 km this event occurred during the late tertiary prior to the mid pliocene and is attributed to tectonic tilting and subsidence resulting from oblique underthrusting of the southeast bahamas beneath hispaniola the southern margin of mouchoir bank is also characterized by large 20 km across amphitheater shaped scallops that expose tertiary shallow water limestones along their deep water flanks seaward of one scallop is a large 25 km wide 50 km long mass movement with flow lines preserved on the seafloor we interpret these scallops as catastrophic collapse structures triggered by large earthquakes generated along the collision zone since the late tertiary south of navidad and silver banks is a very complex seafloor morphology resulting in part from the accretion of a portion of the bahamas onto hispaniola there is also a series of e w oriented down to basin normal faults that have caused the platform margin to retreat extensional stress along this predominantly transpressive plate boundary may be a consequence of rotation of the nearby puerto rico block or lithospheric bending during oblique subduction this study provides an initial framework within which to view the actualistic response of carbonate platforms to plate tectonic collision

platform sedimentation and collapse in a carbonate dominated margin of a foreland basin jaca basin eocene southern pyrenees the eocene jaca basin is a foreland basin with well exposed carbonate platforms in the distal margin this margin underwent alternating periods of stable platform growth and platform drowning periods of drowning were accompanied by large scale collapses with generation of shelf edge truncations and resedimentation of carbonate megabreccias into a terrigenous turbiditic trough these features caused a stepped retreat of the platforms and are related to episodic variations of tectonic loading in the hinterland and correlative flexural bending of the distal basin

reef drowning during the last deglaciation evidence for catastrophic sea level rise and ice sheet collapse elevations and ages of drowned acropora palmata reefs from the caribbean atlantic region document three catastrophic metre scale sea level rise events during the last deglaciation these catastrophic rises were synchronous with 1 collapse of the laurentide and antarctic ice sheets 2 dramatic reorganization of ocean atmosphere circulation and 3 releases of huge volumes of subglacial and proglacial meltwater this correlation suggests that release of stored meltwater periodically destabilized ice sheets causing them to collapse and send huge fleets of icebergs into the atlantic massive inputs of ice not only produced catastrophic sea level rise drowning reefs and destabilizing other ice sheets but also rapidly reduced the elevation of the laurentide ice sheet flipping atmospheric circulation patterns and forcing warm equatorial waters into the frigid north atlantic such dramatic evidence of catastrophic climate and sea level change during deglaciation has potentially disastrous implications for the future especially as the stability of remaining ice sheets such as in west antarctica is in question

thermal history of the southwestern meguma zone nova scotia from an 40ar 39ar and fission track dating study of intrusive rocks two geologically distinct regions within the meguma terrane have been studied in detail and are shown to have contrasting thermal histories this conclusion is based on 31 new 40ar 39ar age spectra on micas k feldspars and hornblendes from several of the plutons in southern nova scotia which are satellites to the much larger south mountain batholith smb in addition we report four k feldspar age spectra from a locality in the northeastern part of the smb and seven fission track ages from both the southern and northern areas the complex age spectrum of hornblende from a mafic phase associated with the bamngton passage pluton suggests a minimum intrusive age of 385 ma a result consistent with geologic evidence that this pluton represents an early less evolved magmatic pulse later intrusive activity appears to have been coeval with the intrusion of the smb at ca 370 ma ago in the southern region argon clocks in feldspars were completely reset and mica clocks variably reset by a later thermal event the cumulative geochronologic and geologic evidence constrains this event to 300 320 ma ago in the smb this alleghanianl hercynian thermal disturbance is much less pronounced and appears to be localized to small areas that are often associated with economic mineralization k feldspars from the southern plutons record an episode of argon loss 220 230 ma ago which is less evident in the smb to the north upper triassic dike injection in the southern region associated with the initial rifting phase of the canadian atlantic margin accompanied this milder thermal pulse apatites in the two regions record a mean fission track age of ca 180 ma which we attribute to the final cooling of the terrane below about 100 c the timing of this event coincides with regional uplift recorded in sedimentary sequences along much of the maritime continental shelf deux kgions gtologiques distinctes inttgkes au terrane de meguma ont ctt ctudites en dctai1 et leurs histoires thermales

the touquoy zone deposit an example of unusual orogenic gold mineralisation in the meguma terrane nova scotia canada the touquoy zone deposit is host to disseminated gold mineralisation in metasiltstones of lower palaeozoic age from the close correlation between ore grades and the intersection of favourable stratigraphy and bounding faults it is apparent that mineralisation is controlled by both structural and lithological influences within the ore zone disseminated gold arsenopyrite pyrite and rare base metal sulphides are associated with a network of widely spaced millimetre scale quartz carbonate veinlets quasi pervasive fluid flow and prolonged interaction with the host rocks resulted in a diffuse but pronounced halo of wall rock alteration that is characterized by the breakdown of detrital feldspar and metamorphic chlorite and the development of hydrothermal carbonate phases k mica and disseminated sulphides these mineralogical changes are accompanied by enrichment in co2 k au as and s and depletion in na across the ore zone vein formation occurred at between 250 and 350 c and pressures of less than 1 2 kbar 1 kbar 100 mpa corresponding to an estimated depth of between 2 8 and 6 km mineralisation resulted from the unmixing of an overpressured low salinity co2 rich fluid in response to decreasing pressure during its ascent and penetration into permeable host rocks geological and geochemical features of mineralisation in the touquoy zone deposit are seen as convincing evidence for a close genetic association between disseminated style and lode gold mineralisation in orogenic terrains with the resulting style of mineralisation largely controlled by the overall structural geometry of the mineralising site rheological properties permeability and chemical receptiveness of the host rock and structural level of emplacement

a holistic model for the origin of orogenic gold deposits and its implications for exploration the term orogenic gold deposits has been widely accepted but there has been continuing debate on their genesis early syn sedimentary or syn volcanic models and hydrothermal meteoric fluid models are now invalid magmatic hydrothermal models fail because of the lack of consistent spatially associated granitic intrusions and inconsistent temporal relationships the most plausible models involve metamorphic fluids but the source of these fluids is equivocal intra basin sources within deeper segments of the hosting supracrustal successions the underlying continental crust subducted oceanic lithosphere with its overlying sediment wedge and metasomatized lithosphere are all potential sources several features of precambrian orogenic gold deposits are inconsistent with derivation from a continental metamorphic fluid source these include the presence of hypozonal deposits in amphibolite facies domains their anomalous multiple sulfur isotopic compositions and problems of derivation of gold related elements from devolatilization of dominant basalts in the sequences the phanerozoic deposits are largely described as hosted in greenschist facies domains consistent with supracrustal devolatilization models a notable exception is the jiaodong gold deposits of china where ca 120 ma gold deposits are hosted in precambrian crust that was metamorphosed over 2000 million years prior to gold mineralization other deposits in china are comparable to those in the massif central and elsewhere in france in that they are hosted in amphibolite facies domains or clearly post date regional metamorphic events imposed on hosting supracrustal sequences if all orogenic gold deposits have a common genesis the only realistic source of fluid and gold is from devolatilization of a subducted oceanic slab with its overlying gold bearing sulfide rich sedimentary package or the associated metasomatized mantle wedge with co2 released during decarbonation and s and ore related elements released from transformation of pyrite to pyrrhotite at about 500 c although this model satisfies all geological geochronological isotopic and geochemical constraints and is consistent with limited computer based modeling of fluid release from subduction zones the precise mechanisms of fluid flux are model driven and remain uncertain from an exploration viewpoint the model re emphasizes the ubiquitous occurrence of orogenic gold deposits in subduction related orogenic belts and importance of continental scale lithosphere tapping fault and shear zones to focus large volumes of auriferous fluid it confirms the importance of the consistent spacing between world class deposits broadly equivalent to the depth of the moho as derived from empirical observations

structural evolution of the orogenic gold deposits in central victoria australia the role of regional stress change and the tectonic regime abstract this review synthesizes the main characteristics of the orogenic gold deposits in western and central victoria australia and presents new insights into the relationships between orogen scale deformation and the 12 hard rock gold deposits that have each produced 30 t au we examine five of these large deposits stawell ballarat bendigo fosterville and costerfield from the start of the delamerian orogeny at ca 515 ma to the end of the tabberabberan orogeny at ca 370 ma the eastern continental margin of gondwanan australia experienced both accretionary growth and the development of the lachlan orocline central western victoria lies on the western edge of this oroclinal structure and is partly underlain by a proterozoic continental fragment the selwyn block all of the 30 t orogenic gold deposits in the region lie either on or to the west of the selwyn block from the delamerian orogeny onwards the deformation front progressively moved eastwards and the principal stress direction rotated clockwise from ne sw through e w and ultimately to n s so that the initial faulting and folding created pathways and traps for the subsequent mineralizing fluids through the brittle to brittle ductile crust thus the 455 440 ma benambran orogeny was the major mineralizing event at stawell and resulted in some early mineralization in the bendigo zone the 420 410 ma bindian orogeny gave rise to significant additional mineralization at ballarat bendigo and fosterville while the 385 370 ma tabberabberan orogeny drove mineralization at costerfield and a second bonanza event at fosterville the largest gold deposits formed where the fluid pathways either remained open or reopened in this rotating stress field allowing multiple pulses of gold rich fluids

control of lower limb overturning circulation in the southern ocean by diapycnal mixing and mesoscale eddy transfer a simple model is developed of the lower limb of the meridional overturning circulation in the southern ocean based on residual mean theory it is hypothesized that the strength of the lower limb overturning is strongly controlled by the magnitude of abyssal diapycnal mixing and that of mesoscale eddy transfer k in particular it is argued that k the scaling and associated theory find support in a suite of sensitivity experiments with an idealized ocean general circulation model this study shows that intense diapycnal mixing is required to close the buoyancy budget of the lower limb overturning circulation in contrast to the upper limb where air sea buoyancy fluxes can provide the required diabatic forcing

link between gold provinces low salinity high temperature 200 degrees c reducing fluids are poorly represented in ore forming processes yet appear to account for 90 percent of the primary gold mined to date such fluids have been implicated in the formation of many archcan greenstone witwatersrand slate belt and epithermal gold deposits these low salinity auriferous fluids occur in variable time space lithological sequence and tectonic settings and are most easily explained by metamorphic devolatilization of mafic and or graywacke successions metamorphism of chlorite calcite albite quartz assemblages e g mafic or graywacke at the greenschist amphibolite facies boundary occurs around 480 degrees or 20 degrees c for 3 5 kbars and produces large volumes of low salinity h 2 o co 2 fluid similar in composition to those recorded in many gold deposits widespread pyrite in the above assemblage typically leads to elevated levels of dissolved sulfur such conditions are ideal for gold transport as a molecular au s complex and can lead to deposits rich in gold relative to silver and base metals deposition of gold occurs in the temperature range of 250 degrees to 400 degrees c and can be facilitated by lower temperature lower sulfur activity and changes in oxygen activity lower sulfur activity is most readily achieved by fluid interaction with fe rich host rocks with the formation of pyrite or pyrrhotite whereas lower oxygen activity is readily achieved by interaction with carbonaceous metasediments low salinity fluids produced by metamorphic devolatilization provide a common theme embracing the formation of many archcan greenstone slate belt witwatersrand and potentially epithermal gold deposits it involves the common features of high geothermal gradient low salinity fluid high au ag high au base metals and broad synchroneity with metamorphism it also accounts for the considerable variability in hosting structures detailed timing relations host rocks alteration assemblages and geologic age of different deposits interestingly the similarities are explained by deeper processes the differences by processes at or near the depositional sites

volcanogenic upwelling of anoxic nutrient rich water a possible factor in carbonate bank reef demise and benthic faunal extinctions the middle cretaceous oceans were characterized by widespread anoxia high sea levels reef carbonate bank extinctions and at least in the pacific by intense widespread mid plate volcanism the demise of reefs on numerous pacific atolls has left a large number of guyots this synthesis explores the possibility that the middle cretaceous demise of mid pacific and other carbonate bank communities and related extinctions elsewhere reflects sporadic possibly volcanogenic upwelling of anoxic water the upwelling would have had to be rapid enough to overwhelm surface reoxygenation and frequent widespread enough to suppress recolonization according to the hallock schlager hypothesis upwelling of nutrient rich waters destroyed the carbonate bank communities nutrient excess and anoxia may well have worked together the globally widespread presence of at least mid depth anoxia h 2 s is reasonably well established the cenomanian turonian oceanic anoxic event perhaps was an extreme example as is the mortality of modern benthic invertebrates at o 2 levels below about 0 15 ml l recolonization times for modern reef corals imply that upwelling catastrophes if localized need have recurred on approximately decade time scales previously postulated cretaceous sea level fluctuations raising sea level at rates on the order of 5 10 m in 10 4 10 5 yr would then have sufficed to carry the intermittently stressed reef surfaces below the 5 to 10 m deep high carbonate production zone below which reef recovery chances diminish thus the episode of frequent localized but widespread upwelling events need have lasted only about 10 4 10 5 yr although intermittent deep water ventilation is known to have occurred on milankovitch time scales during the cretaceous thereby bringing anoxic and or nutrient rich waters to the surface geologic and ocean modeling evidence is necessary to establish whether a significant amount of rapid upwelling did or could occur because mid plate submarine volcanism was widespread and intense in the middle cretaceous pacific volcanogenic hydrothermal heating and entrainment of nutrient rich anoxic waters is one possible mechanism for catastrophic buoyant upwelling rudistid bank extinction and guyot formation the efficacy of this process depends principally on the buoyancy that is heat energy flux and the buoyancy brunt vaisala frequency typical hydrothermal plumes along the mid oceanic ridge axis rise only to 150 to 400 m heights above the sea floor but megaplumes rising 1 000 m are known simple plume models imply that only basalt eruptions comparable to the largest historically known would be sufficiently energetic 10 12 10 14 j s to bring bottom water to the ocean surface from normal mid oceanic ridge axial depths 3 km over much of the present ocean however these models are conservative through neglect of momentum overshoot and gas exsolution to the extent that higher eruption rates and lower brunt vaisala frequencies due to lower vertical temperature gradients prevailed in the middle cretaceous pacific anoxic deep waters would more readily have reached the ocean surface most cretaceous guyots are now in the north pacific but were carried across the equator by pacific plate motion normal tendencies to upwelling and oxygen deficiency along the equator would have made the carbonate banks most vulnerable during their equatorial transit

structural and geochemical controls on the development of turbidite hosted gold quartz vein deposits wattle gully mine central victoria australia gold quartz vein deposits in the wattle gully mine arefault related structures developed in a low grade metamorphosed ordovician quartz rich flysch sequence the major mineralization is associated with a high angle reverse fault wattle gully fault that has a maximum displacement of 40 m over 10 6 metric tons t of vein quartz averaging 10 5 g t au occur within a dilatant jog in this structure fold geometry has controlled fault geometry and resulted in the localization of the jog segment where the wattle gully fault traverses an east dipping fold limb to link two more steeply dipping bedding parallel fault sediments on adjacent west dipping fold limbs gold mineralization is also associated with several minor east clipping reverse faults and a bedding parallel fault whose development is related to flexural slip during fold tightening mineralization occurs within fault fill veins and extension veins adjacent to faults the geometry and internal structures of veins indicate that vein growth has been controlled by repeated fluctuations in fluid pressure and shear stress associated with fault valve behavior vein mineralogy is dominated by quartz with minor carbonates chlorite white mica albite and apatite arsenopyrite and pyrite are the major sulfide phases but sphalerite galena chalcopyrite and pyrrhotite are also present the highest au grades tend to be localised in vein systems that are in proximity to carbonaceous slates wall rock alteration is minor and restricted mainly to narrow zones adjacent to major vein systems sulfur isotope fractionation between galena and sphalerite indicates mineralization occurred at temperatures around 300 degrees c the delta 34 s compositions of pyrite and arsenopyrite are nearly uniform throughout the mine 1 5 2 8 but are generally not in equilibrium with the delta 34 s values of associated base metal sulfides 0 7 5 3 the delta 18 o values for vein quartz vary between 15 6 and 18 0 per mil and correspond to delta 18 o values

stratigraphic constraints on the development and timing of arc continent collision in northern papua new guinea abstract the finisterre mountains of northern papua new guinea are the site of an active southeast propagating collision between the finisterre terrane and the australian continental margin the clastic sedimentary sequence on the southern flank of the range records the history of the collision the age of initial collision can be deduced from the second of two provenance shifts that occur in the sequence as revealed by a study of 69 dated sandstones the first shift at about 16 18 ma was from volcanolithic sediments to mixed provenance sediments rich in quartz and metasedimentary lithic fragments these latter sediments were probably derived from the orogenic belt active along the australian continental margin at that time at 3 0 3 7 ma the volcanic source was rejuvenated initial collis on at this time uplifted the finisterre terrane causing the provenance shift here we break the stratigraphic sequence into three units the sarawaget beds the erap structural complex and the leron formation the sarawaget beds are middle eocene to early miocene volcanolithic sandstones that were deposited as clastic aprons un the flanks of the finisterre volcanic are volcanic activity ceased in the early miocene the erap complex is divided into two clastic subunits the sukurum and nariawang units and one basaltic subunit the gorambampan unit the sukurum unit consists of turbidites deposited south of the extinct finisterre arc from the latest early miocene through the early pliocene much of the sediment in the unit was derived from low to medium grade metasedimentary units on the active northern margin of the australian continent renewed subduction i the late miocene or pliocene occurred along the new britain trench just south of the remnant finisterre arc closing an eastward widening small ocean basin the sukurum unit probably represents an accretionary prism that formed at this subduction zone scattered seamounts that were scraped off the downgoing plate are preserved as the gorambampan unit initial collision of the finisterre terrane with the continental margin at 3 0 3 7 ma uplifted the paleogene volcanic rocks which were rapidly eroded and deposited as the volcanolithic turbidites of the nariawang unit southeastward propagation of the collision tip caused incorporation of the nariawang unit into the accretionary wedge rapid uplift raised the terrane foreland above sea level sometime after 1 3 mo the fluvial lacustrine and marginal marine deposits of the leron formation accumulated in a terrane foreland basin that developed south of the collision zone further propagation of the thrust front toward the foreland incorporated the leron formation into the fold and thrust belt rapid uplift of the finisterre range and voluminous volcanolithic sedimentation continue to the present in the finisterre range arc continent collision is marked by a provenance shift from metasedimentary and quartzose detritus to volcanic detritus in another modern arc continent collision on taiwan collision has caused a shift from volcanic to metasedimentary detritus we attribute this discrepancy to the presence of the finisterre terrane an extinct arc in the forearc region of the finisterre arc continent collision and the absence of a similar terrane in the forearc area on taiwan the very different evolution of sandstone provenance in the active taiwan and finisterre collision zones shows that local factors can profoundly influence the provenance histories of collision zones no one model of sediment provenance evolution can characterize all collision zones whether modern or ncient

water mass conversion fluxes and mixing in the scotia sea diagnosed by an inverse model abstract an inverse box model of the scotia sea is constructed using hydrographic tracer and velocity data collected along the rim of the basin during the antarctic large scale box analysis and the role of the scotia sea albatross cruise the model provides an estimate of the time mean three dimensional circulation as the antarctic circumpolar current acc crosses the region it concurrently solves for geostrophic and wind driven ekman transports across the boundaries of the basin air sea driven diapycnal fluxes and interior diapycnal fluxes below the ocean surface an increase is diagnosed in the acc volume transport from 143 13 sv sv 106 m3 s 1 at drake passage to 149 16 sv on leaving the scotia sea supplied by the import of 5 9 1 7 sv of weddell sea deep water wsdw over the south scotia ridge there is a lateral redistribution of the transport primarily in response to a topographically induced branching of the 70 80 sv polar front pf jet and an increase in the transport associa

active arc continent collision earthquakes gravity anomalies and fault kinematics in the huon finisterre collision zone papua new guinea the huon finisterre island arc terrane is actively colliding with the north edge of the australian continent the collision provides a rare opportunity to study continental accretion while it occurs we examine the geometry and kinematics of the collision by comparing earthquake source parameters to surface fault geometries and plate motions and we constrain the forces active in the collision by comparing topographic loads to gravity anomalies waveform inversion is used to constrain focal mechanisms for 21 shallow earthquakes that occurred between 1966 and 1992 seismic moment 1017 to 3 1020 n m twelve earthquakes show thrust faulting at 22 37 km depth the largest thrust events are on the north side of the huon peninsula and are consistent with slip on the ramu markham thrust fault zone the northeast dipping thrust fault system that bounds the huon finisterre terrane thus much of the terrane s crust but little of its mantle is presently being added to the australian continent the large thrust earthquakes also reveal a plausible mechanism for the uplift of pleistocene coral terraces on the north side of the huon peninsula bouguer gravity anomalies are too negative to allow simple regional compensation of topography and require large additional downward forces to depress the lower plate beneath the huon peninsula with such forces plate configurations are found that are consistent with observed gravity and basin geometry other earthquakes give evidence of deformation above and below the ramu markham thrust system four thrust events 22 27 km depth directly below the ramu markham fault outcrop are too deep to be part of a planar ramu markham thrust system and may connect to the north dipping highlands thrust system farther south two large strike slip faulting earthquakes and their aftershocks in 1970 and 1987 show faulting within the upper plate of the thrust system the inferred fault planes show slip vectors parallel to those on nearby thrust faults and may represent small offsets in the overriding plate these faults along with small normal faulting earthquakes beneath the huon finisterre ranges and a 25 along strike rotation of slip vectors demonstrate the presence of along strike extension of the accreting terrane and along strike compression of the lower plate

nitrogen distribution in lower palaeozoic slates phyllites of the meguma supergroup nova scotia canada implications for au and zn pb mineralisation and exploration abstract major and trace elements and nitrogen were analysed in 59 cambrian and ordovician slates phyllites of various lithostratigraphic levels within the meguma supergroup 14 ordovician slates phyllites of the ovens gold mineralisation and 16 ordovician slates phyllites of the eastville pb zn cu mineralisation the fixed nitrogen content and the normative n fix k 2 o ratio of muscovite separates members of the goldenville sandstone greywacke quartzite dominated and halifax formation slate phyllite dominated low fixed nitrogen concentration is related to high manganese concentration black slates phyllites of the saddle reef type au mineralisation in the ovens area are characterised by high fixed nitrogen and a high normative n fix k 2 o ratio of muscovite the nitrogen is of secondary hydrothermal origin therefore it might be possible to use the fixed nitrogen as an exploration tool for black slates phyllite hosted gold mineralisation in nova scotia mineralised slates phyllites of the eastville stratabound pb zn mineralisation cannot be distinguished from nonmineralised time equivalent lithologies on the basis of the fixed nitrogen distribution or the n fix k 2 o ratio of muscovite

genesis of the shangxu orogenic gold deposit bangong nujiang suture belt central tibet china constraints from h o c si he and ar isotopes abstract shangxu is an orogenic gold deposit in the bangong nujiang suture zone central tibet china formed in the early cretaceous orogene related to convergence and collision between the qiangtang and lhasa terranes the mineralization at shangxu is hosted by jurassic turbidite sedimentary rocks of the mugagangri group and is associated with a regional fault system hydrothermal minerals develop muscovite carbonate sulfides and chlorite hydrothermal fluids record three main hydrothermal stages based on mineral paragenesis the earliest is barren quartz stage h1 which is pre ore during the early mineralization quartz pyrite stage h2a defined by massive quartz veins with minor euhedral pyrite and gold hydrothermal fluids had a 18ofluid of 6 1 6 4 d of 74 to 116 13cco2 of 5 4 to 7 6 and 30si of 0 1 in the quartz pyrite sulfides stage h2b characterized by abundant quartz granular pyrite muscovite with minor chalcopyrite galena sphalerite and gold fluids had a 18ofluid of 7 8 2 d of 109 to 120 13cco2 of 9 6 and 30si of 0 1 to 0 2 during the ankerite sulfide stage h3a distinguished by abundant ankerite muscovite sulfides with minor quartz and chlorite hydrothermal system had a fluid with 18ofluid of 4 9 5 3 d of 125 3 30si of 0 1 13cco2 of 12 4 in quartz inclusion fluid and 13cco2 of 2 7 in ankerite the calcite sulfide stage h3b is characterized by calcite sulfides with minor quartz and chlorite quartz formed earlier than calcite from a fluid having a 18ofluid of 6 4 d of 112 6 30si of 0 1 and 13cco2 of 7 4 after which calcite precipitated from a hydrothermal fluid with 18ofluid of 5 5 9 13cco2 of 0 5 to 2 8 hydrothermal fluids in h2b pyrite have 3he 4he ratios of 0 27 0 42ra and 40ar 36ar ratios of 313 372 the stable isotope composition of hydrothermal fluids from the shangxu gold deposit is similar to that of typical orogenic gold deposits the early stage h1 methane bearing fluids were probably sourced from the basin sediments leading to precipitation of early barren quartz veins and siderite alteration from the quartz sulfide stage h2 to carbonate sulfide stage h3 hydrothermal fluids were likely derived from dissolution of the marine carbonate cement from sedimentary host rocks during metamorphism at depth the decreasing d and 13c of the ore forming fluids from early to late suggests mixing with 13c depleted oxidized graphite in sedimentary rocks meteoric waters or reation between d depleted organic matters generally these fluids were likely generated at depth through prograde metamorphic devolatilization of hydrous minerals in the deeper equivalents of the sedimentary rocks of the mugagangri group sulfur and gold by inference likely originated from sedimentary diagenetic pyrite or the metasedimentary rocks between the greenschist and amphibolite facies and migrated with the metamorphic fluids during transportation to the site of deposition gold bearing fluids variably reacted with country rocks

retreat of carbonate platforms response to tectonic processes a seamarc ii and seismic reflection investigation of the deep water margins of carbonate banks in the southeast bahamas has documented the retreat of these isolated platforms since mid cretaceous time this retreat is in sharp contrast to prograding carbonate platforms in the passive northwest bahamas and provides an initial framework within which to view the response of carbonate platforms to tectonic processes processes of retreat include large scale 50 60 km step back of platform margins during the mid cretaceous tectonic subsidence and downfaulting during the late tertiary and large scale collapse of platform margins which may be an active process step back during the mid cretaceous correlates with a global tectonic pulse of ocean crust formation and relative sea level rise downfaulting may be a response to either late tertiary lithospheric bending during subduction and or block rotation along the north american caribbean plate boundary and collapse may be related to earthquake shocks generated by active plate tectonic collision between the southeast bahamas and hispaniola

the role of flexural slip during the development of multilayer chevron folds abstract flexural slip has long been recognized as a crucial mechanism during the development of chevron folds and a conceptual understanding of its role has been presented by analogue and kinematic models and field studies this study uses 2d finite element analysis to provide a thorough quantitative evaluation of flexural slip based on buckling of effective single layers1 and true multilayers1 the analysis of the results describes the spatial and temporal evolution of flexural slip and documents the resulting fold shapes the results show that effective single layer buckle folds amplifying the dominant wavelength d do not result in chevron folds in any of the situations considered varying initial perturbation viscosity contrast and friction coefficient slip initiates early and a transition from sinusoidal or parabolic to box folds is common reducing the amplified wavelength 10 of d results in systematic chevron folds for true multilayer buckle folds systematic chevron folds featuring hinge collapse develop regardless of the initial perturbation used the ratio of incompetent to competent layer thickness s h is a crucial parameter for s h 1 flow dominates and slip is not initiated for s h 53 and that sinusoidal or parabolic folds nearly instantaneously change shape to chevron folds during a short period of slip initiation and termination thus confirming the phenomenon of limb lock up for models incorporating permeability contrasts the development of deformation induced overpressure leads to an earlier initiation of flexural slip

the timing of sea level high stands during marine isotope stages 7 5 and 9 constraints from the uranium series dating of fossil corals from henderson island direct dating of fossil coral reefs using the u series chronometer provides an important independent test of the milankovitch orbital forcing theory of climate change however well dated fossil corals pre dating the last interglacial period 130 thousand years ago ka are scarce due to 1 a lack of sampling localities 2 insufficient analytical precision in u series dating methods and 3 diagenesis which acts to violate the assumption of closed system u series isotopic decay in fossil corals here we present 50 new high precision u series age determinations for fossil corals from henderson island an emergent coral atoll in the central south pacific u series age determinations associated with the marine isotope stage mis 9 interglacial and mis 7 5 interstadial periods are reported the fossil corals show relatively little open system u series behaviour in comparison to other localities with fossil coral reefs formed prior to the last glacial cycle however open system u series behaviour is still evident in most of the dated corals in particular percent level shifts in the 230th 238u act composition are observed leading to conventional u series ages that are significantly younger or older than the true sample age this open system u series behaviour is not accounted for by any of the open system u series models indicating that new models should be derived the new u series ages reported here support and extend earlier findings reported in stirling et al 2001 providing evidence of prolific coral reef development on henderson island at not vert similar320 ka most likely correlated with mis 9 3 and subsequent reef development at not vert similar307 ka during mis 9 1 while relative sea level was potentially not vert similar20 m lower than during mis 9 3 the u series ages for additional well preserved fossil corals are suggestive of minor reef development on henderson island during mis 7 5 245 230 ka at 240 3 0 8 and 234 7 1 3 ka all u series observations are consistent with the milankovitch theory of climate change in terms of the timing of onset and termination of the dated interglacial and interstadial periods the best preserved samples also suggest that the oceanic 234u 238u during mis 9 and mis 7 5 was within five permil of the modern open ocean composition

spatial and temporal patterns of small scale mixing in drake passage temperature and salinity profiles obtained with expendable ctd probes throughout drake passage between february 2002 and july 2005 are analyzed to estimate turbulent diapycnal eddy diffusivities to a depth of 1000 m diffusivity values are inferred from density temperature inversions and internal wave vertical strain both methods reveal the same pattern of spatial variability across drake passage diffusivity estimates from inversions exceed those from vertical strain by a factor of 3 over most of drake passage the polar front pf separates two dynamically different regions strong thermohaline intrusions characterize profiles obtained north of the pf south of the pf stratification is determined largely by salinity and temperature is typically unstably stratified between 100 and 600 m depth in the upper 400 m turbulent diapycnal diffusivities are o 10 3 m2 s 1 north of the pf but decrease to o 10 4 m2 s 1 or smaller south of the pf below 400 m diffusivities typically exceed 10 4 m 2 s 1 diffusivities decay weakly with depth north of the pf whereas diffusivities increase with depth and peak near the local temperature maximum south of the pf the meridional pattern in near surface mixing corresponds to local maxima and minima of both wind stress and wind stress variance near surface diffusivities are also found to be larger during winter months north of the pf wind driven near inertial waves strong mesoscale eddy activity and double diffusive convection are suggested as possible factors contributing to observed mixing patterns

a carbonaceous sedimentary source rock model for carlin type and orogenic gold deposits this paper presents evidence and arguments that carbonaceous sedimentary rocks were a source for au and as in sediment hosted orogenic and carlin type gold deposits and develops a corresponding genetic model in this two stage basin scale model gold and arsenic are introduced early into black shale and turbidite basins during sedimentation and diagenesis stage 1 and concentrated to ore grades by later hydrothermal structural or magmatic processes stage 2 in reduced continental margin basin settings organic matter sedimented under anoxic to euxinic conditions immobilizes and concentrates gold arsenic and a range of trace elements particularly v ni se ag zn mo cu u present in marine bottom waters into fine grained black mudstone and siltstone of slope and basin facies during early diagenesis gold and certain other trace elements ni se te ag mo cu pge are preferentially partitioned into arsenian pyrite that grows in the muds these processes produce regionally extensive black shale and turbidite sequences enriched in syngenetic gold and arsenic commonly from 5 to 100 ppb au and 10 to 200 ppm as rare organic and sulfide rich metalliferous black shales may contain up to 1 to 2 ppm au and over 1 000 ppm as present as refractory gold in arsenian pyrite and nanoparticles of free gold during late diagenesis and early metamorphism stage 2 the diagenetic arsenian pyrite is recrystallized to form coarser grained pyrite generations and the organic matter is cooked to bitumen under higher grade metamorphism lower greenschist facies and above arsenian pyrite in carbonaceous shales is converted to pyrrhotite these processes release gold arsenic sulfur and other elements sb te cu zn mo bi tl and pb from the source rocks to become concentrated by hydrothermal processes locally to produce gold ores in structural sites such as fold hinge zones shear or breccia zones within or above the black shale sequence la icp ms analyses of diagenetic pyrite in carbonaceous sediments both associated and not associated with gold deposits suggests that invisible gold contents of greater than 250 ppb in diagenetic pyrite are indicative of carbonaceous shale source rocks with the potential to produce economic gold deposits application of this sedimentary source rock model enables a systematic exploration approach for sediment hosted gold deposits based on the distribution composition and structure of carbonaceous shale sequences and their contained diagenetic pyrite

isopycnal averaging and the residual mean circulation abstract the zonally averaged circulation in the atmosphere or ocean can be misleading if the averaging is performed at constant height in the ocean there is apparently anomalously large diapycnal motion forming the so called deacon cell the atmospheric equivalents are the ferrel cells there are two zonal averaging techniques commonly used to avoid these spurious cells one involves averaging at constant density and this technique has been used in both fluids the other technique which has so far been applied only in the atmosphere involves taking into account perturbation correlation terms to form the residual mean circulation using a taylor series expansion we show that these apparently dissimilar techniques are formally equivalent at leading order in perturbation amplitude the equivalence is demonstrated using output from the fram southern ocean numerical model

the three dimensional overturning circulation of the southern ocean during the woce era a box inverse model of the southern ocean during the world ocean circulation experiment is constructed to investigate the three dimensional structure of the regional overturning circulation in that era the model has many features in common with various preceding inverse studies but also contains several novel elements that make it well suited for addressing many of the significant uncertainties that surround the circulation at present the net overturning circulation of the southern ocean is found to consist of two well defined cells of similar strength the upper cell consists of a northward transport of 18 8 5 5 sv of surface mode and intermediate waters lighter than the 27 5 kg m 3 isoneutral and an equivalent southward flow in the approximate 27 5 27 9 kg m 3 neutral density range encompassing the bulk of the upper circumpolar deep water the lower cell involves the northward export of 18 6 0 9 sv of antarctic bottom water and lower circumpolar deep water denser than 28 08 kg m 3 and an opposing transport in the lighter classes of that water mass substantial structural differences between the overturning circulations of the atlantic indian and pacific basins are indicated by the model s solution overall the diagnosed southern ocean circulation shares many qualitative and some quantitative features with previous inverse estimates particularly as regards the large scale depth integrated lateral circulation and associated energy fluxes in the subtropics and in the antarctic circumpolar current and the strength of the upper overturning cell however it also suggests several significant adjustments to current views of the regional circulation most notable amongst these are the subpolar circulation of the southern ocean is more vigorous and zonally interconnected than generally thought the associated lower overturning cell is more intense than indicated by most preceding estimates contrary to common perception sub surface mixing processes play a role of comparable importance to air sea ice exchanges of buoyancy in underpinning the dianeutral closure of the southern ocean overturning even at shallow mode and intermediate water levels and the connection between north atlantic deep water formation and southern ocean upwelling is fundamentally three dimensional such that deep waters from the north atlantic must upwell dianeutrally before being returned to the permanent pycnocline of the northern oceans

a rare phanerozoic amphibolite hosted gold deposit at danba yangtze craton china significance to fluid and metal sources for orogenic gold systems the danba gold deposit is located in a poorly documented gold province on the north western margin of the yangtze craton it is sited in devonian sequences in a high grade metamorphic terrane that includes an extensional metamorphic core complex around the deposit peak metamorphic conditions of 6 0 5 kbar and 650 50 c at ca 193 ma were followed by retrograde sillimanite grade conditions of 4 5 0 5 kbar and 550 50 c the deposit is hosted in a broadly strata bound ductile brittle shear zone with high t proximal alteration assemblages of biotite amphibole plagioclase and ore assemblages dominated by pyrrhotite but with a strong association between gold and bismuth tellurides alteration mineral thermobarometers together with heating freezing studies of low salinity h2o co2 ch4 fluid inclusions indicate p t conditions of early ore deposition of approximately 4 5 kbar and 500 650 c at around 185 9 ma indicated by re os geochronology on ore related molybdenite in conjunction all data demonstrate that danba represents a lower jurassic hypozonal orogenic gold deposit that formed during post peak metamorphic retrogression the primary high p t nature of the deposit combined with its late metamorphic timing negate that the ore fluid was sourced via devolatilization of the hosting supracrustal sequences a deep externally derived ore fluid source is required the most likely source is the k h2o co2 and ore metal fertilized lithospheric mantle that was metasomatized during neoproterozoic subduction it is proposed that transition from lithospheric transpression to extension in the jurassic triggered the devolatilization of this metasomatized lithosphere to cause the formation of this rare phanerozoic amphibolite hosted gold deposit at danba

thrust loads and foreland basin evolution cretaceous western united states two dimensional modeling of loading during the formation of the idaho wyoming thrust belt shows that regional isostatic compensation by flexure of an elastic lithosphere is sufficient to control the formation of a foreland basin the flexural rigidity of the lithosphere is inferred to have been approximately 1023 nm 1030 dyne cm on the basis of palinspastic comparison of predicted downwarping due to the thrust plate loads to the shape of the sedimentary wedge on the west side of the cretaceous western interior seaway erosion of part of the uplifted thrust plates redistributed the load depositing it farther to the east thereby causing subsidence over a much wider area than could have been accomplished only by the loading by thrust plates paleotopography after major cretaceous thrust events was calculated the resulting mountainous terrain gentle alluvial plain and flat sea floor correspond well with the topography of the modern foreland thrust belt and basin system in the andes of south america and to paleogeographic reconstructions in the western united states thrust belt topography is controlled by the subsurface geometry of the thrust faults particularly the positions of ramp zones and by isostatic subsidence

a comparison of orogenic gold mineralisation in central victoria aus western south island nz and nova scotia can implications for variations in the endowment of palaeozoic metamorphic terrains abstract the palaeozoic western lachlan orogen in victoria se australia the buller terrane western south island new zealand and the meguma terrane nova scotia canada are remarkably similar in regard to their geological age and history structural make up and the setting and formation of orogenic lode and disseminated style gold deposits within these fold belts a comprehensive review of the principal characteristics of orogenic gold deposits in each of the three historically important gold provinces illustrates the many similarities but it also reveals several major geological structural tectonic geochemical and geochronological differences that may account for the disparity in contained gold and overall endowment between the three fold belts aspects that stand out as potentially playing a critical role in the generation of a phanerozoic world class orogenic gold province include 1 the presence of a hydrated oceanic character substrate that can provide a fertile source rock for both fluids and metals 2 asthenospheric thermal input to trigger and sustain crustal devolatilisation and melting 3 the existence of a number of near vertical deep seated faults 4 substantial transcurrent movement and 5 evolution of an accretionary subduction system that promotes development of an extensive fore arc system with prolonged fluid generation and circulation quantification of these controlling factors provide a significantly improved understanding of the processes that control the genesis of orogenic gold deposits and also have the potential to enable discrimination between more and less gold favourable orogens and parts of orogens

the deacon cell and the other meridional cells of the southern ocean abstract the meridional circulation cells of the southern ocean are investigated using the results from a fine resolution primitive equation model zonal integration along depth levels shows the classical series of meridional cells but integration along density layers shows a number of differences including the virtual disappearance of the deacon cell to investigate the differences the meridional transport is calculated as a function of both density and depth the results show that the deacon cell is associated with systematic changes in the depth of density surfaces between the western boundary current region off south america and the return flow in the interior of the ocean water flowing on each density surface produces a meridional cell with a vertical excursion of a few hundred meters thew cells combine without water crossing density surfaces to produce a single integrated deacon cell extending from the surface to below 2000 m the results also show that at each latitude water on each of the

subsurface variations in arsenic mineralogy and geochemistry following long term weathering of gold mine tailings abstract variations in arsenic as mineralogy and geochemical controls on its mobility were evaluated in subsurface tailings at the historical montague and goldenville mine sites in nova scotia canada tailings at these sites contain some of the highest as concentrations in nova scotia and are located in close proximity to local communities pore water in the subsurface tailings is characterized by circumneutral to alkaline ph 6 2 to 8 7 and mildly reducing to oxidizing redox conditions 130 mv to 347 mv bulk chemistry scanning electron microscopy and synchrotron micro x ray diffraction analyses showed as mineral hosts differ with depth the deepest tailings max 2 m are in direct contact with partially decomposed vegetation which supports reducing conditions and the precipitation of authigenic as and fe sulfides under reducing conditions dissolved as concentrations are also controlled by desorption of as from dissolution of fe and mn oxides and the sorption or co precipitation of as with carbonates these geochemical controls differ from those influencing dissolved as concentrations under oxidizing conditions in the near surface as mobility is controlled by oxidative dissolution of primary arsenopyrite precipitation of secondary fe arsenates fe oxyhydroxides and mn oxides secondary ca fe arsenates and sorption onto fe oxyhydroxides and gangue minerals some of these mineral species are stable under different conditions yet occur in close association indicating the importance of microenvironments the results of this study show that the weathering characteristics of these tailings vary with depth leading to the formation of new as hosts that are distinct from those observed in the near surface identification of these as hosts provides an understanding of current controls on as mobility and has implications for future reprocessing and or remediation efforts

geology mineralogy and geochemistry of the shangxu orogenic gold deposit central tibet china implications for mineral exploration abstract shangxu is an orogenic gold deposit within the bangong nujiang suture zone central tibet china it is hosted by turbidite sedimentary rocks of the jurassic mugagangri group the host rocks were metamorphosed to subgreenschist facies prior to being hydrothermally altered adjacent to mineralization hydrothermal minerals in wall rocks consist of muscovite carbonate sulfides and chlorite whole rock geochemistry indicates hydrothermal alteration is characterized by the introduction of k2o co2 and s and leaching of na2o increasing 3 k al and decreasing na al alteration indexes approaching the ore correlate to muscovitization co2 concentration reflects the degree of carbonation which in conjunction with molar mn fe fe ca mg mn and co2 cao can be used to distinguish siderite from ankerite in carbonate alteration mass transfer analysis shows gains in as au co2 w ca cd ni cr sr rb k and losses in na pb cu during hydrothermal alteration in the muscovite alteration zone muscovite within shear zones ms1 shows an increase in fe mg and na towards the ore whereas metamorphic muscovite along cleavage planes and in pressure shadows ms2 and hydrothermal muscovite ms3 change in composition from phengitic mg fe distal to mineralization to paragonitic na adjacent to gold in carbonate alteration the composition in carbonate phases changes from early magnesian siderite to ankerite and then to calcite and dolomite during the evolution of the hydrothermal system siderite spots in host rocks and ankerite in veins wall rock or its replacement of siderite are all enriched in fe mn and depleted in mg from proximal to distal alteration zones pyrite is a dominant mineral in sulfide alteration of the shangxu deposit the earliest framboidal pyrite py1 formed during diagenesis and overprinted by py2 which is recrystallized pyrite associated with burial metamorphism py3 rims and enlarges previous pyrite aggregates or recrystallizes into cubic grains with cracks and quartz pressure shadows during deformation py4 is ore related euhedral pyrite disseminated near gold and formed in hydrothermal stage vein pyrite py5 coexists with marcasite and fills cracks in quartz veins hydrothermal alteration minerals form overlapping alteration haloes surrounding the main auriferous lodes distal muscovitization carbonatization and proximal sulfidation constitute a progressive alteration front from gold the alteration envelope is tabular in shape following the strike and dip of the mineralization and tends to be the widest around the thickest parts of the ore such that the occurrence and thickness of the alteration envelope can be used as an approximate guide to the size of gold mineralization shangxu shares many diagnostic features with turbidite hosted orogenic gold deposits such as bendigo reefton and meguma districts in deposit geology alteration mineralogy and lithogeochemistry

methods for making point estimates of eddy heat flux as applied to the antarctic circumpolar current yearlong measurements of current and temperature are used to examine the characteristics of eddy heat flux and its distribution in drake passage this seemingly straightforward calculation can produce misleading results when measurement errors are not corrected and when careful consideration is not given to the nature of the time series under study and the coordinate system used when moorings blow over during periods of high current speeds eddy heat fluxes produced from the resulting records may be overestimated by as much as 20 if not corrected by using concomitant pressure time series and vertical temperature gradients although short time scale processes such as tides internal waves and inertial oscillations are routinely eliminated from heat flux estimates by low pass filtering low frequency contamination of eddy heat fluxes is not usually considered long period events can impose unwanted dominating cross correlation eddy heat flux between fluctuation temperature and velocity in drake passage low frequency variability in some current records is associated with sporadic lateral shifts of the fronts within the antarctic circumpolar current defining an effective eddy time scale 40 hours to 90 days and band passing the current records before calculating eddy heat flux results in values that are more homogeneous consistent with one another in direction and have higher statistical significance finally we consider the coordinate system used for the eddy heat flux calculations relative to the dynamic processes under study for the circumpolar current we define poleward eddy heat flux as that component perpendicular to the axis of the current that forms a continuous but distorted band encircling antarctica since the current direction varies in time across stream eddy heat flux is calculated relative to the 90 day low pass direction the resulting heat fluxes from all deep instruments are small about 1 kw m2 whereas those at depths less than 1000 m in the northern passage are an order of magnitude larger the average across stream flux for all available instruments is 3 7 kw m2 and directed to the right poleward of the 90 day low pass current cospectra of fluctuation temperature and velocity show that heat flux is separated on the average into two frequency bands with corresponding periods between 100 and 40 days and 16 and 10 days this pattern is strongly influenced by the records from shallow instruments and those in the northern passage and compares favorably with the cospectrum from a 5 year bridged record from the central passage comparison with previous estimates in this region shows considerable differences partly as a result of the use of different techniques however analysis of five 1 year records from a single location shows that interannual variability is large which urges caution when interpreting the significance of isolated short term estimates of eddy heat flux

lithospheric controls on the formation of provinces hosting giant orogenic gold deposits ages of giant gold systems 500 t gold cluster within well defined periods of lithospheric growth at continental margins and it is the orogen scale processes during these mainly late archaean palaeoproterozoic and phanerozoic times that ultimately determine gold endowment of a province in an orogen a critical factor for giant orogenic gold provinces appears to be thickness of the subcontinental lithospheric mantle sclm beneath a province at the time of gold mineralisation as giant gold deposits are much more likely to develop in orogens with subducted oceanic or thin continental lithosphere a proxy for the latter is a short pre mineralisation crustal history such that thick sclm was not developed before gold deposition in constrast orogens with protracted pre mineralisation crustal histories are more likely to be characterised by a thick sclm that is difficult to delaminate and hence such provinces will normally be poorly endowed the nature of the lithosphere also influences the intrinsic gold concentrations of potential source rocks with back arc basalts transitional basalts and basanites enriched in gold relative to other rock sequences thus segments of orogens with thin lithosphere may enjoy the conjunction of giant scale fluid flux through gold enriched sequences although the nature of the lithosphere plays the crucial role in dictating which orogenic gold provinces will contain one or more giant deposits the precise siting of those giants depends on the critical conjunction of a number of province scale factors such features control plumbing systems traps and seals in tectonically and lithospherically suitable terranes within orogens

isopycnal diffusivities in the antarctic circumpolar current inferred from lagrangian floats in an eddying model average 750 250 m 2 s 1 around the polar frontal zone the results imply that parameterizations that only use eddy kinetic energy to parameterize the diffusivities are incomplete we suggest that dominant correlations of lagrangian eddy diffusivities with eddy kinetic energy found in previous studies may have been due to the use of too short time lags in the integration of the velocity autocovariance used to infer the diffusivities we find evidence that strong mean flow inhibits cross stream mixing within the acc but there are also areas where cross stream diffusivities are large in spite of strong mean flows for example in regions close to topographic obstacles such as the kerguelen plateau

vertical structure and transport of the antarctic circumpolar current in drake passage from direct velocity observations 1 the structure of the antarctic circumpolar current acc in drake passage is examined using 4 5 years of shipboard acoustic doppler current profiler adcp velocity data the extended 1000 m depth range available from the 38 khz adcp allows us to investigate the vertical structure of the current the mean observed current varies slowly with depth while eddy kinetic energy and shear variance exhibit strong depth dependence objectively mapped streamlines are self similar with depth consistent with an equivalent barotropic structure vertical wavenumber spectra of observed currents and current shear reveal intermediate wavenumber anisotropy and rotation indicative of downward energy propagation above 500 m and upward propagation below 500 m the mean observed transport of the acc in the upper 1000 m is estimated at 95 2 sv or 71 of the canonical total transport of 134 sv mean current speeds in the acc jets remain quite strong at 1000 m 10 20 cm s 1 vertical structure functions to describe the current and extrapolate below 1000 m are explored with the aid of full depth profiles from lowered adcp and a 3 year mean from the southern ocean state estimate sose a number of functions including an exponential are nearly equally good fits to the observations explaining 75 of the variance fits to an exponentially decaying function can be extrapolated to give an estimate of 154 38 sv for the full depth transport

critical depth for the survival of coral islands effects on the hawaiian archipelago coral islands drown when sea level rise exceeds the maximum potential of coral reefs to grow upward about 10 millimeters per year during the holocene transgression 18 000 years ago to present sea levels rose at rates of up to 10 to 20 millimeters per year and most coral island reefs situated deeper than a critical depth of30 to 40 meters below present day sea level drowned coral islands that did not drown during the holocene transgression apparently all developed on antecedent foundations shallower than critical depth during low stands in sea level during the pleistocene these islands were elevated and subject to subaerial erosion today in the hawaiian archipelago the depth of drowned banks is inversely related to summit area smaller banks are progressively deeper evidently because of erosional truncation during low sea level stands bank summit area may therefore be an important factor determining the failure or success of coral islands

tectonic controls on carbonate platform evolution in southern papua new guinea passive margin to foreland basin the middle oligocene collision of the northern margin of the australian craton with a complex subduction system resulted in emplacement of a thrust mass and formation of a foreland basin that extended from the coral sea to the indian ocean the distribution of carbonate platform facies in southwestern papua new guinea reflects the transition from an eocene passive margin setting to the early stages of foreland basin evolution the initial basin configuration with terrigenous sedimentation confined to the proximal foredeep allowed carbonate deposition in the shallow environment adjacent to the peripheral forebulge subsequent southward migration of the basin resulted in a rapid increase in the area and thickness of carbonate platform deposition when the proximal foredeep became filled by detritus shed from the emerging orogen clastic sediments buried the platform and terminated carbonate deposition the history of the southern papua new guinea carbonate platform illustrates the paradox of carbonate deposition within the foreland basin whereby basin configuration initially encourages thick and extensive carbonate deposition but inevitably leads to terrigenous inundation and the demise of the carbonate platform

what sets the mean transport through drake passage twelve experiments with two coarse resolutions of a global ocean model using a variety of surface forcings are analyzed to address the question of what sets the mean transport through drake passage seven of the experiments do not have an active sea ice model but the remaining five do previous theories have suggested that the drake passage transport is governed by the cape horn sverdrup transport or alternatively is proportional to the square root of the meridional ekman transport at the latitude of drake passage the results presented here do not support either of these theories the drake passage transport depends quite strongly on the isopycnal diffusivity parameter in the model and less strongly on the background vertical diffusivity and horizontal viscosity parameters however when the magnitudes of these parameters are fixed the results show a very strong correlation between drake passage transport and both the strength of the meridional ekman transport at the latitude of drake passage and the thermohaline circulation off the antarctic shelf the relationships are monotonic but not linear the best estimate is that the meridional ekman transport drives 100 sv of drake passage transport while the remaining 30 sv are driven by the global thermohaline circulation

sense of displacement on the cobequid chedabucto fault system nova scotia canada the cobequid chedabucto fault system of the canadian appalachians is a major anastomosing fault system over 300 km in length it separates the meguma terrane of southern nova scotia from the avalon terrane to the north these terranes are distinct tectonic and lithological entities in the appalachian orogen two areas at either end of this fault system have been examined in detail to determine the sense and history of offset along it both areas are situated on major component fault zones of the system and both exhibit structures due to early intense ductile shearing that are overprinted by semi brittle to brittle structures caused by later faulting along the eastern chedabucto fault zone area a ductile structures were examined this area is characterized by the progressive development of s c textures and shear bands rotated syntectonic porphyroblasts and asymmetric minor folds features indicative of and caused by ductile shearing along the western cobequid fault zone area b semi brittle and b

the timing of high sea levels over the past 200 000 years the 230 th ages and 234 u 238 u ratios were determined for barbados corals that grew during periods of high sea level within the last 200 000 years the similarity of the initial 234 u 238 u ratios of some of the corals to the modern marine value suggests that these samples are pristine and that the marine 234 u 238 u ratio 83 000 and 200 000 years ago was within 2 per mil of the modern value the accuracies of the 230 th ages are evaluated on the basis of the 234 u 238 u values and a model of the behavior of uranium and thorium isotopes during diagenesis for the last three interglacial and two intervening interstadial periods sea level peaked at or after peaks in summer insolation in the northern hemisphere this overall pattern supports the idea that glacial interglacial cycles are caused by changes in earth9s orbital geometry the sea level drop at the end of the penultimate interglacial the last interglacial and a subsequent interstadial period lagged behind the decrease in insolation by 5 000 to 10 000 years

a large drop in atmospheric 14c 12c and reduced melting in the younger dryas documented with 230th ages of corals paired carbon 14 14 c and thorium 230 230 th ages were determined on fossil corals from the huon peninsula papua new guinea the ages were used to calibrate part of the 14 c time scale and to estimate rates of sea level rise during the last deglaciation an abrupt offset between the 14 c and 230 th ages suggests that the atmospheric 14 c 12 c ratio dropped by 15 percent during the latter part of and after the younger dryas yd this prominent drop coincides with greatly reduced rates of sea level rise reduction of melting because of cooler conditions during the yd may have caused an increase in the rate of ocean ventilation which caused the atmospheric 14 c 12 c ratio to fall the record of sea level rise also shows that globally averaged rates of melting were relatively high at the beginning of the yd thus these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the mississippi to the st lawrence river triggered the yd event

foredeep tectonics and carbonate platform dynamics in the huon gulf papua new guinea hawaii mr1 side scan sonar and six channel seismic reflection data reveal a history of carbonate platform growth drowning and back stepping in the huon gulf papua new guinea this is one of the few modern sites where active carbonate platform development and foredeep subsidence are linked 230 th methods date aragonitic shallow water corals recovered from a modern depth of 2000 m at 348 10 ka this documents rapid subsidence of the huon gulf in response to the encroaching finisterre mountains at an average rate of 5 7 mm yr for the past 348 k y the highest subsidence rate reported from any foredeep setting carbonate deposition has moved toward the foreland at an average rate of 110 mm yr over the same period comparisons of the measured age with sea level history derived from the oxygen isotope record suggest that the reefs may have formed during sea level lowstands and drowned during rapid rates of sea level rise

paleoproterozoic turbidite hosted gold deposits of the ashanti gold belt ghana west africa comparative analysis of turbidite hosted gold deposits and an updated genetic model abstract the paleoproterozoic gold deposits of the ashanti gold belt ghana occur mainly as auriferous quartz veins in graphitic shears proximal to contacts between deformed and metamorphosed turbidites and tholeiitic volcanics alternately block faulted tarkwaian sediments they are suggested in this article to belong to that class of gold deposits recognized as turbidite hosted hence evidence from previous investigations of turbidite hosted and turbidite associated gold deposits occurring in circumstances roughly similar to the ashanti deposits are used where relevant to produce an updated genetic model for the latter given the relatively significant amounts of graphite associated with the major ashanti deposits the role of non carbonate carbon is assessed in the light of conclusions reached by work on other turbidite hosted and turbidite associated gold belts conclusions as to the origins of mineralizing fluids and temporary repositories of gold auriferous interflow sediments reached by work on these other belts are also analysed a concept of the tectonic development of the ashanti belt kumasi basin area introduced in this article is deemed to be critical to the origin of the ashanti gold deposits it encompasses the role of non carbonate carbon turbidites and the primary sources and secondary repositories of au and as in the genesis of the major ashanti gold deposits it examines the significance of the intimate relationship between calc alkaline volcanism and the basin sediments the occurrences of felsic metasandstones in transition zone sediments and ttg granitic material and fragments of chemical sediments in turbidites all of which are incompatible with one or the other of existing concepts of tectonic development in the area

an oxygen isotope study of two contrasting orogenic vein gold systems in the meguma terrane nova scotia canada with implications for fluid sources and genetic models sampling of quartz vein material from two gold deposits of similar geological setting but different ages the ovens 408 ma dufferin 380 ma in the meguma terrane of nova scotia has been done to compare and contrast their 18oquartz signatures despite different ages of formation quartz from all vein types in each of the deposits i e saddle reef bedding concordant leg reefs en echelon discordant shows limited intra deposit variation with similar average 18o values of 15 2 0 9 n 16 for the ovens and 15 7 0 6 n 12 for dufferin using an average 18o value of 15 4 for the two deposits the corresponding 18oh2o values calculated for 400 c and 350 c based on constraints from mineral assemblages and fluid inclusion studies indicate averages of 11 4 0 2 and 10 2 0 2 respectively the isotopic data indicate that 1 the vein forming fluids have a metamorphic signature 2 all vein types in the two deposits represent formation from a single isotopically homogeneous fluid and 3 a fluid of similar isotopic signature was generated by two contrasting tectono thermal events in the meguma terrane that were separated by 30 ma integration of these results with previously published data for 14 meguma gold deposits indicate a general stratigaphic dependence in 18oh2o values for deposits when arranged in their relative stratigraphic position such that 18oh2o values increase upwards in the stratigraphy this apparent trend cannot be explained by models involving either fluid mixing or cooling of the vein forming fluids but instead is modelled using fluid rock interaction taking into account a change in the modal mineralogy of the metasedimentary rocks upwards in the stratigraphy

how wind forcing and air sea heat exchange determine the meridional temperature gradient and stratification for the antarctic circumpolar current mesoscale oceanic eddies have a profound effect on the meridional circulation in the antarctic circumpolar region previous studies have shown that eddies transport heat poleward to balance the heat lost by the ocean to the atmosphere in the waters around antarctica and also transport eastward momentum downward at a rate comparable to the amount of momentum put into the water column by the wind stress using the poleward eddy heat fluxes to relate air sea heat loss and wind stress we find that the meridional temperature gradient in the circumpolar region is determined by the ratio of the air sea heat loss to the zonal wind stress including a widely used parameterisation where poleward eddy heat fluxes are proportional to the mean meridional temperature gradient we find that the slope of isotherms or isopycnals across the circumpolar zone is determined by the wind stress further assuming no cross isopycnal mixing in the interior ocean we find that the stratification in the deep ocean is determined by the ratio of air sea heat loss to zonal wind stress squared the poleward eddy heat fluxes also represent a southward eddy mass transport in the upper water column in density coordinates the vertical gradient of this eddy mass transport is the meridional component of the eddy stokes drift which is equal to the difference between the lagrangian and eulerian mean velocities in the circumpolar region because there can be no zonally averaged geostrophic eulerian meridional velocity across the circumpolar region above the topography this southward eddy stokes drift provides a mechanism by which circumpolar deep water can flow southward across the circumpolar zone eddy heat fluxes which are central to the mass momentum heat and energy balances in the circumpolar region provide a catalyst for relating the roles of wind and buoyancy forcing in setting the overall circulation for the southern ocean

mechanics of formation of gold bearing quartz veins nova scotia canada abstract the meguma terrane of nova scotia canada is composed largely of low grade clastic metasediments swarms of structurally complex bedding concordant quartz veins are found across the whole terrane partly or wholly outlining anticlinal domes these veins exhibit spectacular features due to intermittent hydraulic fracturing and healing crack seal such as phyllosilicate inclusion bands columnar quartz grains and included sheets of host rock overprinting all the precipitation features are a suite of deformation structures which include pinch and swell tectonic stylolites and cross cutting extension and hybrid fractures the veins were formed syntectonically in folded and foliated strata the vein precipitating fluids pooling beneath less permeable beds in anticlinal domes fluid migration paths were controlled by the two fundamental mechanical anisotropies in the host rocks bedding and foliation a simple two dimensional vein model is considered using fracture propagation and quartz precipitation rates estimates of rates of vein formation are determined for example it seems possible that a quartz vein 100 m long and 175 cm wide could form in less than 10 yrs such times are effectively geologically instantaneous and have considerable implications with respect to physical and chemical processes in deformation and metamorphism

orogenic disseminated gold in phanerozoic fold belts examples from victoria australia and elsewhere abstract orogenic gold mineralisation in the lachlan orogen of southeastern australia and in other phanerozoic fold belts has generally been assumed to be confined entirely to quartz veins however an improved understanding of the tectonic structural and geochronological framework in which these occurrences form and recent advances towards the extent of wallrock alteration around these veins cast doubt on the validity of this deeply entrenched lode gold paradigm ore grade orogenic disseminated gold mineralisation has been recognised in a number of fold belts that are known to host significant orogenic lode gold deposits lachlan orogen australia buller terrane and otago schist new zealand meguma terrane canada tien shan mountains in uzbekistan and kyrgyzstan yana kolyma province baikal verhoyansk and allakh yun fold belts in north central mongolia and far east russia disseminated mineralisation in these collisional belts is invariably hosted by pervasively altered greenschist to subgreenschist facies rocks these occurrences also share a number of characteristics with some carlin type gold deposits in the great basin of western north america e g getchell regarding structural relationships fluid composition mineral paragenesis and a common association of carbonaceous matter with mineralisation features of alteration physico chemical characteristics of the ore bearing fluids and strong structural control in all of the studied occurrences point to a close genetic association with lode gold mineralisation the two styles are considered to represent end members of a crustal continuum of orogenic gold emplacement in phanerozoic fold belts with disseminated mineralisation more likely to develop at shallower levels and within more permeable units during the waning stages of uplift and exhumation these conditions facilitate ground preparation via brittle fracturing and the development of intricate stockwork systems efficient gold segregation from bisulphide complexes is largely controlled by fluid mixing of an evolved metamorphic fluid with either more oxidised ascending fluids or meteoric fluids and accelerated by the presence of carbonaceous matter at the site of deposition

simple models for the geochemical response of the ocean to climatic and tectonic forcing abstract simple models for the geochemical response of the ocean to periodic forcing are used as a framework to discuss the shortest periods of change resolvable by present analytical precision of elemental or isotopic ratio measurements of the chemical evolution of seawater for chemical properties whose budget is dominated by fluxes into and out of the ocean we show that the geochemical response to changing fluxes is strongly attenuated at periods shorter than the residence time and that the response at these periods is also phase shifted so as to lag the forcing by one quarter cycle the amplitude response as a function of period is used to estimate the periods of forcing resolvable by present analytical precision in measuring the 87sr 86sr and 234u 238u evolution of seawater and we find that the shortest periods resolvable are of the order of 1 myr if variations at periods shorter than this are found we would argue that these are very likely of local as opposed to global origin we illustrate the importance of phase shifts as a function of forcing period by discussing some recently published data that show a high degree of correlation over the last 300 kyr between changes in 87sr 86sr and 18o measured in the same sediment core at first sight this correlation might be taken as good evidence that both 87sr 86sr and 18o are responding to some common climatic forcing but given the long residence time of sr in the ocean sr and o should in fact have different phase shifts relative to any proposed common forcing thus the apparent correlation between 87sr 86sr and 18o over the past several 100 ma is not necessarily an indication that they are responding to a common cause amplitude response curves are also used to place limits on permissible global seawater 234u 238u variations and these are then compared with published data to identify local diagenetic effects application to 187os 186os and u records in seawater detectors is proposed

late kinematic timing of orogenic gold deposits and significance for computer based exploration techniques with emphasis on the yilgarn block western australia abstract orogenic gold deposits are a widespread coherent group of epigenetic ore deposits that are sited in accretionary or collisional orogens they formed over a large crustal depth range from deep seated low salinity h2o co2 ch4 n2 ore fluids and with au transported as thio complexes regional structures provide the main control on deposit distribution in many terranes first order faults or shear zones appear to have controlled regional fluid flow with greatest ore fluid fluxes in and adjacent to lower order faults shear zones and or large folds highly competent and or chemically reactive rocks are the most common hosts to the larger deposits focusing of supralithostatic ore fluids into dilatant zones appears to occur late during the evolutionary history of the host terranes normally within d3 or d4 in a d1 d4 deformation sequence reactivation of suitably oriented pre existing structures during a change in far field stress orientation is a factor common to many deposits and repeated reactivation may account for multiple mineralization episodes in some larger deposits absolute robust ages of mineralization support their late kinematic timing and in general suggest that deposits formed diachronously towards the end of the 100 to 200 m y long evolutionary history of hosting orogens for example in the yilgarn block a region specifically emphasised in this study orogenic gold deposits formed in the time interval between 40 and 90 m y with most about 60 to 70 m y after the youngest widespread basic ultrabasic volcanism and towards the end of felsic magmatism the late timing of orogenic gold deposits is pivotal to geologically based exploration methodologies this is because the present structural geometries of i the deposits ii the hosting goldfields and iii the enclosing terranes are all essentially similar to those during gold mineralization at least in their relative position to each other thus interpretation of geological maps and cross sections and three dimensional models can be used to accurately simulate the physical conditions that existed at the time of ore deposition it is particularly significant that the deposits are commonly related to repetitive and predictable geometries such as structural heterogeneities within or adjacent to first order structures around rigid granitoid bodies or in specific locked up fold thrust structures importantly the two giant greenstone hosted goldfields kalgoorlie and timmins show a remarkably similar geometry at the regional scale computer based stress mapping and gis based prospectivity mapping are two computer based quantitative methodologies that can utilize and take advantage of the late timing aspect of this deposit type to provide important geological aids in exploration both in broad regions and more localized goldfields both require an accurate and consistent solid geology map stress mapping requires knowledge of the far field stresses during mineralization and the empirical prospectivity mapping requires data from a significant number of known deposits in the terrane the kalgoorlie terrane in the yilgarn block meets these criteria and illustrates the potential of these methodologies in the exploration for orogenic gold deposits low minimum stress anomalies interpreted to represent dilational zones during gold related deformation coincide well with the positions of known goldfields rather than individual gold deposits in the terrane and there are additional as yet unexplained anomalies the prospectivity analysis confirms that predictable and repetitive factors controlling the siting of deposits are i proximity to and orientation and curvature of granitoid greenstone contacts ii proximity to segments of crustal faults which strike in a preferred direction iii proximity to specific lithological contacts which have similar preferred strike iv proximity to anticlinal structures and v the presence of preferred reactive host rocks e g dolerite the prospectivity map defines a series of anomalous areas which broadly conform to those of the stress map 78 correspondence the most prospective category on this map covers less than 0 3 of the greenstone belts and yet hosts 16 of the known deposits which have produced 80 of known gold thus it discriminates in favour of the larger economically more attractive deposits in the terrane the successful application of stress mapping and prospectivity mapping to geology based exploration for orogenic gold deposits indicates that more quantitative analysis of geological map data is a profitable line of research the computer based nature of these methodologies is ideal for the production of an ultimate integrated deposit target map which can be compared to other more conventional targeting parameters such as geophysical and geochemical anomalies such an integrated strategy appears the way forward in the increasingly difficult task of cost effective global exploration for orogenic gold deposits in poorly exposed terranes

geology geochronology and fluid characteristics of the pingqiu gold deposit southeastern guizhou province china abstract the junction of the southeastern guizhou the southwestern hunan and the northern guangxi regions is located within the southwestern jiangnan orogen and forms a ne trending 250 km gold belt containing more than 100 gold deposits and occurrences the pingqiu gold deposit is one of the numerous lode gold deposits in the southeastern guizhou district gold mineralization is hosted in neoproterozoic lower greenschist facies metamorphic rocks and controlled by fold related structures vein types present at pingqiu include bedding parallel and discordant types with saddle reefs and their down limb extensions dominating but with lesser discordant types the major sulfide minerals are arsenopyrite and pyrite with minor sphalerite galena chalcopyrite and rare pyrrhotite marcasite and tetrahedrite much of the gold is m to mm sized grains and occurs as fracture controlled isolated grains or filaments in quartz galena sphalerite pyrite and wallrock three types of fluid inclusions are distinguished in hydrothermal minerals type 1 aqueous inclusions have homogenization temperatures of 171 396 c and salinities of 1 4 9 8 wt nacl equiv type 2 aqueous carbonic inclusions yield final homogenization temperatures of 187 350 c with salinities of 0 2 7 7 wt nacl equiv type 3 inclusions are carbonic inclusions with variable relative content of co2 and ch4 and minor amounts of n2 and h2o the close association of co2 rich inclusions and h2o rich inclusions in groups and along the same trail suggests the presence of fluid immiscibility the calculated 18oh2o values range from 4 3 to 8 3 and dh2o values of fluid inclusions vary from 55 8 to 46 9 a metamorphic origin is preferred on the basis of geological background and analogies with other similar deposit types two ore related sericite samples yield well defined 40ar 39ar plateau ages of 425 7 1 7 ma and 425 2 1 3 ma respectively these data overlap the duration of the caledonian gold mineralization along the jiangnan orogen and suggest that gold mineralization was post peak regional metamorphism and occurred during the later stages of the caledonian orogeny overall the pingqiu gold deposit displays many of the principal characteristics of the bendigo gold mines in the western lachlan orogen se australia and the dufferin gold deposit in the meguma terrane nova scotia canada but also some important differences which may lead to the disparity in gold endowment however the structural make up at deposit scale and the shallow mining depth at present indicate that the pingqiu gold deposit may have considerable gold potential at depth

active deformation in the new guinea fold and thrust belt seismological evidence for strike slip faulting and basement involved thrusting the new guinea fold and thrust belt forms a 1000 km long mountain chain running the length of new guinea but its trend is oblique to the predicted convergence direction a large component of left lateral shear across the mountain belt is expected but geological evidence for such motion is ambiguous surface structures in the fold and thrust belt show mountain building by folding and thrusting supposedly thin skinned of pre pliocene continental shelf sediments although some evidence indicates that active faulting penetrates the basement we examine the active deformation of this mountain belt by using teleseismic long period p and sh waveforms short period p waveforms and p wave first motions to determine reliable focal mechanisms and source depths for the 18 largest earthquakes in the new guinea fold and thrust belt since 1964 eight thrust events with seismic moments m0 between 1017 and 2 1018 n m are distributed throughout the thrust belt at depths ranging from 0 5 to 45 km and have steeply dipping fault planes that strike parallel to surface structural trends six of the eight events are between 11 and 25 km deep the steep dips of nodal planes the depths of these earthquakes and the known thicknesses of the sedimentary section show that thrust faulting is not exclusively thin skinned i e confined above a shallow detachment surface but penetrates the crystalline basement at high angles most earthquakes in the western half of the thrust belt including the three largest earthquakes examined m0 5 1018 n m show strike slip faulting with the probable fault plane oriented east west so that displacement is left lateral the nine strike slip earthquakes account for almost 90 of the observed seismic moment in the period 1964 1985 and indicate a seismic slip rate of 5 25 mm a all but one of these strike slip earthquakes are shallower than the thrust earthquakes suggesting that east northeast convergence across the fold and thrust belt is accommodated by a decoupled system of strike slip and dip slip faults while the great height of the mountain belt is an obvious indication that crustal thickening is an important consequence of plate motion in new guinea seismological evidence suggests that translation by strike slip faulting may play a much greater role than previously recognized by analogy in older collisional orogens whose motions can be inferred only from remnant structures and not from seismicity strike slip faulting may have been equally important in accommodating convergence we estimate from seismic moments of earthquakes and from the volume of the mountains that deformation of the new guinea highlands may account for 5 20 of the total convergence between the pacific plate and australia in new guinea

the ventilated ocean abstractadiabatic theories of ocean circulation and density structure have a long tradition from the concept of the ventilated thermocline to the notion that deep ocean ventilation is controlled by westerly winds over the southern ocean this study explores these ideas using a recently developed lagrangian ocean model lom which simulates ocean motions by computing trajectories of water parcels a unique feature of the lom is its capacity to model ocean circulations in the adiabatic limit in which water parcels exactly conserve their densities when they are not in contact with the ocean surface the authors take advantage of this property of the lom and consider the circulation and stratification that develop in an ocean with a fully adiabatic interior with both isopycnal and diapycnal diffusivities set to zero the ocean basin in the study mimics that of the atlantic ocean and includes a circumpolar channel the model is forced by zonal wind stress and a density restoring at the surface despite the

40ar 39ar dating of hydrothermal biotite from high grade gold ore tangier gold deposit nova scotia further evidence for 370 ma gold metallogeny in the meguma terrane a hydrothermal biotite carbonate alteration zone adjacent to a high grade multi ounce gold vein in the tangier gold deposit meguma terrane nova scotia has given an 40 ar 39 ar plateau age of 374 ma the alteration halo is part of a vein package in the hinge zone of the tangier anticline which contains abundant auriferous quartz veins formed during flexural slip folding during a late stage reactivation of the regional fold belt the 374 ma age is similar to 40 ar 39 ar ages determined for hydrothermal vein minerals at seven other meguma gold districts thereby suggesting a terrane wide metallogenic event a similar age of vein formation and by inference gold mineralization and granite emplacement across the meguma terrane suggest that the cospatial and cotemporal nature of the two geological events may be related an integrated model including anatexis and devolitization of the lower crust possibly as a consequence of overriding a mantle plume in concert with late stage reactivation of the fold belt owing to continued transpression along a terrane bounding fault is proposed

the role of eddy transfer in setting the stratification and transport of a circumpolar current abstract high resolution numerical experiments of a circumpolar current are diagnosed to study how lateral and vertical transfer of buoyancy by geostrophic eddies balances advection by a meridional circulation driven by surface wind stresses and buoyancy fluxes a theory is developed in the framework of the residual circulation to relate the vertical and horizontal stratification set up to the transfer properties of eddies and the patterns of imposed wind and buoyancy forcing simple expressions are found for the depth of penetration stratification baroclinic transport and residual circulation of the current finally the ideas are applied to the antarctic circumpolar current acc and yield predictions for how its properties depend on wind and buoyancy forcing