mineralogy and geochemistry of gold bearing arsenian pyrite from the shuiyindong carlin type gold deposit guizhou china implications for gold depositional processes arsenian pyrite in the shuiyindong carlin type gold deposit in guizhou china is the major host for gold with 300 to 4 000 ppm au and 0 65 to 14 1 wt as electron miroprobe data show a negative correlation of as and s in arsenian pyrite which is consistent with the substitution of as for s in the pyrite structure the relatively homogeneous distribution of gold in arsenian pyrite and a positive correlation of as and au with au as ratios below the solubility limit of gold in arsenian pyrite suggest that invisible gold is likely present as au1 in a structurally bound au complex in arsenian pyrite geochemical modeling using the laser ablation inductively coupled plasma mass spectrometry la icp ms analysis of fluid inclusions for the major ore forming stage shows that the dominant au species were au hs 2 77 and auhs aq 0 23 gold hydroxyl and gold chloride complexes were negligible the ore fluid was undersaturated with respect to native au with a saturation index of 3 8 the predominant as species was h3aso30 aq pyrite in the shuiyindong deposit shows chemical zonation with rims richer in as and au than cores reflecting the chemical evolution of the ore bearing fluids the early ore fluids had relatively high activities of as and au to deposit unzoned and zoned arsenian pyrite that host most gold in the deposit the ore fluids then became depleted in au and as and formed as poor pyrite overgrowth rims on gold bearing arsenian pyrite arsenopyrite overgrowth aggregates on arsenian pyrite indicate a late fluid with relatively high activity of as the lack of evidence of boiling and the low iron content of fluid inclusions in quartz suggest that iron in arsenian pyrite was most likely derived from dissolution of ferroan minerals in the host rocks with sulfidation of the dissolved iron by h2s rich ore fluids being the most important mechanism of gold deposition in the shuiyindong carlin type deposit

solution weathering rate and origin of karst landforms and caves in the quartzite of auyan tepui gran sabana venezuela abstract the paper reports the results of sio 2 analyses in the aonda cave system located on the auyan tepui one of the widest table mountains of the gran sabana south venezuela characterised by karst landforms developed in siliceous rock chemical analyses underline the very low concentration of sio 2 of the surface water percolation and cave drip waters have a sio 2 concentration of about 1 mg l the mean silica load of the cave stream is 184 mg s mainly derived from surface solution removal in the allogenic recharge area in the aonda cave system the mean sio 2 dissolved load is 40 mg s in part from surface solution 15 and mainly from underground processes 85 the low solubility of sio 2 in slightly acidic water implies the importance of the time factor in the formation of cave systems with the present dissolution rate about 10 ma would be necessary to form the known karst system this estimation can be significant only if we assume that climate has been stable in the last few tens of millions of years furthermore this age can be taken as a minimum estimate while according to the geomorphic evolution of the area the origin of the aonda cave system could be reasonably dated back to at least 20 30 ma that is to the oligocene

natural and induced sinkholes of the obruk plateau and karapinar hotamis plain turkey abstract the number of sinkholes locally known as obruks has increased rapidly in recent years near karapinar located in the semi arid konya closed basin in central anatolia nineteen sinkholes have formed in the last 33 years 1977 2009 as a result of the collapse of cavity roofs in the neogene lacustrine limestone in the obruk plateau and beneath quaternary lake sediments in the karapinar hotamis plain of these 13 have formed within the past 4 years 2006 2009 the obruk plateau takes its name from the presence of several hundred paleo sinkholes which formed as a result of natural processes during the quaternary period more recently human activity has induced the formation of new sinkholes which presents a hazard to life and property changing agricultural patterns have led to the opening of thousands of deep wells in recent years and increased water pumping currently exceeds the sustainable yield of the aquifer thus the formation of sinkholes has been triggered by a combination of natural and human causes the groundwater level has dropped almost 24 m in the vicinity of karapinar during the last 26 years 1983 2008 approximately 8 m of this drop occurred within the 4 years prior to the study 2005 2008 legally binding precautions must be taken to prevent further water table decline in order to decrease sinkhole formation within the basin in the years to come

la icpms and epma studies of pyrite arsenopyrite and loellingite from the bhukia jagpura gold prospect southern rajasthan india implications for ore genesis and gold remobilization abstract the bhukia jagpura gold prospect is hosted by a paleoproterozoic metasedimentary rock sequence that constitutes the lowermost part of the aravalli supergroup lying in close proximity to the basement cover contact a combined ore petrographic la icpms and epma studies of iron sulfides and sulfarsenides from the prospect has revealed four varieties of pyrite and two varieties of arsenopyrite with different trace element compositions the data indicates a sedimentary diagenetic origin for the earliest pyrites py i and ii which are devoid of any gold in contrast to hydrothermal py iii and iv with a minor but significant content of invisible gold 0 3 1 6 ppm associated loellingite 35 51 ppm and arsenopyrite aspy i 0 28 10 ppm contain the maximum concentration of invisible gold while it is substantially lower in aspy ii 0 06 1 5 ppm the compositions of the gold bearing pyrites low ni co ratios arsenopyrites and loellingite rich in co and the presence of au bi te mineral phases within arsenopyrite support a magmatic hydrothermal model for the origin of gold sulfide mineralization which appears to have taken place during the peak of regional metamorphism or at an earlier stage the different stages of deformation and metamorphism released and remobilized gold in invisible and discrete forms from the sulfarsenides during prograde metamorphism of aspy i gold was partially incorporated and relatively enriched within the structure of loellingite later during retrograde metamorphism gold was exsolved as visible grains at the interface of loellingite and aspy ii and or within loellingite

african easterly waves and convection part i linear simulations abstract a linearized version of a nonhydrostatic model is used to study the normal mode selection and the structure of the african easterly waves in dry and moist environments associated with an idealized african easterly jet structure the dry mode reproduces the principal observed characteristics of the lower troposphere in particular the low level ascent and convergence in the trough a simple cisk type parameterization improves the upper level circulation a budget of kinetic energy shows barotropic and baroclinic contributions and adequately reproduces the analysis of norquist et al the scale selection and the structure of the most unstable mode appears sensitive to the jet structure in particular to the meridional and vertical shear several discrepancies between observations and these linear modes emphasize the importance of an accurate description of convection

a strategy for frequency spectra of quaternary climate records the paleoclimatic variability at frequencies ranging from 10 4 cycle per year cpy to 10 5 cpy is investigated using a set of four deep sea cores from the atlantic pacific and indian oceans dominant features are the presence of orbital frequencies corresponding to mean periods of 117 7 43 6 24 9 and 19 3 kyr these are statistically significant according to such advanced spectral tools as blackman tukey maximum entropy and the highly efficient thomson technique however the main purpose of this paper is methodological describing the statistical analyses of time series with modern methods in order to stress their relative power advantages and disadvantages the more advanced statistical methods confirm the coincidence of the dominant periods in the deep sea cores and those in the astronomical elements including combination tones three frequency bands of high paleoclimatic variability centred at 15 4 13 and 10 8 kyr are indeed also detected these two last periods are very close to those predicted by the climatic non linear model of ghil and le treut and found by pestiaux et al and yiou et al

ore genesis of the bake gold deposit southeastern guizhou province china constraints from mineralogy in situ trace element and sulfur isotope analysis of pyrite abstract the bake gold deposit is exceptional for its high native gold abundance relative to the other orogenic gold deposits in the southeastern guizhou district the grades of gold can be up to 2 to 3 wt in bonanza ore and native gold preferentially occurs within voids and fractures in pyrite arsenopyrite and quartz gold content can be up to 6 9 ppm in hydrothermal pyrite however the majority of the pyrite analyses have au contents less than 1 ppm mean 0 32 ppm based on la icpms analyses meanwhile empa reveals that arsenopyrite has a maximal au content of up to 0 14 wt but most analyses are below detection limit 0 01 wt moreover native gold grains in cataclastic pyrite and arsenopyrite are commonly high purity with fineness ranging from 949 to 977 given that paragenetically early hydrothermal pyrite and arsenopyrite contain variable but relatively high gold concentrations than later generations of sulfide it is suggested that early invisible gold may have been remobilized to form at least part of the microscopic visible gold post mineralization shear zones which cut the vein bearing anticline may have led to the deformation of the lode quartz vein system on the macro level and microscopically sulfide fragmentation and elemental remobilization although diagenetic pyrite from unaltered host rocks is enriched in invisible gold with mean values at 0 83 ppm evidence supporting the release of au from them is weak corresponding evidence comes from the distinct sulfur isotope signatures in different pyrite generations diagenetic pyrite has 34s values in the narrow range of 9 27 to 10 75 whereas hydrothermal pyrite shows a broad range 6 81 to 17 42 based on la mc icpms analyses the mesoproterozoic lengjiaxi group underlying the xiajiang group is most likely the source region on the basis of geological background and assuming the metamorphic devolatilization model

sensitivity of equatorial convection to horizontal resolution in aquaplanet simulations with a variable resolution gcm abstract climate simulations using idealized zonally symmetric boundary conditions an aquaplanet are performed in order to highlight possible deviations from zonality introduced by the spatial variations in resolution caused by the variable resolution technique simulations at three different uniform resolutions with spectral truncations t21 t63 and t106 are used as control simulations and analyzed in order to describe the zonal climate simulated by this version of the arpege climat general circulation model and establish its sensitivity to varying spatial resolution the model simulates a single equatorial precipitation maximum in which the activity of the convective cells is modulated by westward and eastward propagating equatorial waves depending on the resolution a simulation with the variable resolution technique using a truncation t63 and a stretching factor of 3 with the maximum resolution pole placed at the equator is then compared to the uniform resolution simulations deviations from the

easterly wave regimes and associated convection over west africa and tropical atlantic results from the ncep ncar and ecmwf reanalyses ncep ncar and ecmwf daily reanalyses are used to investigate the synoptic variability of easterly waves over west africa and tropical atlantic at 700 hpa in northern summer between 1979 1995 1979 1993 for ecmwf spectral analysis of the meridional wind component at 700 hpa highlighted two main periodicity bands between 3 and 5 days and 6 and 9 days the 3 5 day easterly wave regime has already been widely investigated but only on shorter datasets these waves grow both north and south of the african easterly jet aej the two main tracks noted over west africa at 5 n and 15 n converge over the atlantic on latitude 17 5 n these waves are more active in august september than in june july their average wavelength phase speed varies from about 3000 km 8 m s 1 north of the jet to 5000 km 12 m s 1 south of the jet rainfall convection and monsoon flux are significantly modulated by these waves convection in the inter tropical convergence zone itcz being enhanced in the trough and ahead of it with a wide meridional extension compared to the 3 5 day waves the 6 9 day regime is intermittent and the corresponding wind field pattern has both similar and contrasting characteristics the only main track is located north of the aej along 17 5 n both over west africa and the atlantic the mean wavelength is higher about 5000 km long and the average phase speed is about 7 m s 1 then the wind field perturbation is mostly evident at the aej latitude and north of it the perturbation structure is similar to that of 3 5 days in the north except that the more developed circulation centers moving more to the north lead to a large modulation of the jet zonal wind component south of the aej the wind field perturbation is weaker and quite different the zonal wind core of the jet appears to be an almost symmetric axis in the 6 9 day wind field pattern a clockwise circulation north of the aej being associated with a counter clockwise circulation south of the jet and vice versa these 6 9 day easterly waves also affect significantly rainfall convection and monsoon flux but in a different way inducing large zonal convective bands in the itcz mostly in the trough and behind it as opposed to the 3 5 day wave regime these rainfall anomalies are associated with anomalies of opposite sign over the guinea coast and the sahelian regions over the continent these waves are more active in june july and in august september over the ocean gate phase i gave an example of such an active 6 9 day wave pattern considered as a sequence of weak easterly wave activity this phase was also a sequence of high 6 9 day easterly wave activity we suggest that the 6 9 day regime results from an interaction between the 3 5 day easterly wave regime maintained by the barotropic baroclinic instability of the aej and the development of strong anticyclonic circulations north of the jet over west africa and both north and south of the jet over the atlantic significantly affecting the jet zonal wind component the permanent subtropical anticyclones azores libya st helena could help initiation and maintenance of such regime over west africa and tropical atlantic based on an a priori period band criterion our synoptic classification has enabled us to point out two statistical and meteorological easterly wave regimes over west africa and tropical atlantic ncep ncar and ecmwf reanalyses are in good agreement the main difference being a more developed easterly wave activity in the ncep ncar reanalyses especially for the 3 5 day regime over the atlantic

fluid wall rock interaction in an archean hydrothermal gold deposit a thermodynamic model for the hunt mine kambalda gold mineralization at the hunt mine kambalda is situated in a 20 m thick steeply dipping shear zone within a sequence of rather uniform metabasalts zonal alteration of the host rocks occurred around fractures which acted as conduits during gold mineralization limited major element mobility ensured assemblages of low variance over most of the alteration zone providing a suitable environment for the application of thermodynamics in conjunction with detailed petrographic geochemical electron microprobe analysis of mineral compositions and fluid inclusion studies microthermometry equilibrium equations involving fluid components and alteration minerals are used to determine conditions during the alteration event and in particular activity gradients of components profiles across the schist zone show increasing f sub h 2 s around auriferous quartz veins log f sub h 2 s 0 6 but constant f sub o 2 log f sub o 2 29 7 these results are near the magnetite pyrrhotite pyrite triple point for the inferred temperature of 350 degrees c and explain the pyrite pyrrhotite magnetite zonation sequence outward from veins the profile of x sub co 2 is very close to the value of 0 25 determined independently from fluid inclusions the k super h super profile shows increases adjacent to auriferous veins corresponding to the zone of biotite stability using a value for fluid salinity of 2 equiv wt percent nacl ph was calculated to be around 6 9 the solubility of gold in solution was estimated for the calculated conditions for the complex au hs super 2 the maximum solubility is around 0 5 mg kg super 1 i e 0 5 ppm for au cl super 2 it is close to 10 super 6 mg kg super 1 indicating the efficacy of sulfide transport of gold compared to chloride transport under these conditions the calculated decrease in f sub h 2 s away from the auriferous quartz veins results in an 80 percent or greater decrease in gold solubility suggesting hat the sulfidation of fe rich wall rocks is a geologically reasonable and very efficient mechanism for precipitating gold from solution at elevated temperatures

application of seismic velocity tomography in investigation of karst collapse hazards guangzhou china this paper describes seismic velocity tomography applied to the investigation and assessment of karst collapse hazards to facilitate accurate characterization of geological conditions of karst sinkhole formation in the survey areas of xiamao guangzhou china and huangchi foshan china seismic velocity tomography was used to explore the structures of rock and soil associated with karst collapse the results show that sand intercalated with clay or clay intercalated with soft soil dominates the cover of these two areas the overburden is 20 33 m thick and underlain by carboniferous limestone in the limestone there are well developed karst caves and cracks as well as highly fluctuating bedrock surfaces the seismic velocities are less than 2500 m s in the cover 2500 4500 m s in the karst fracture zones and caves of xiamao and 1500 2000 m s in the huangchi collapse area the karst fracture zones relief of bedrock surfaces and variations of soil thicknesses revealed by seismic velocity tomography are well constrained and in agreement with those in the drilling borehole profiles this paper demonstrates that seismic velocity tomography can delineate anomalies of rock and soil with the advantages of speed intuitive images and high resolution

gold mineralization in as rich mesothermal gold ores of the bogosu prestea mining district of the ashanti gold belt ghana remobilization of invisible gold the bogosu prestea mining district of southwestern ghana is a 33 km section of the early proterozoic ashanti gold belt greenschist facies carbonaceous and carbonate bearing turbidites and greywackes and mafic dikes host numerous economic mesothermal gold deposits structurally higher ores in the bogosu concession have brittle deformation and consist of disseminated sulphide lodes in tectonically disrupted sedimentary rocks and carbonate altered mafic dikes most gold occurs as micrometre size particles in arsenian pyrite and as invisible gold in arsenian pyrite and arsenopyrite the structurally deeper ores of the adjoining prestea concession are associated with brittle ductile deformation and consist of extensive crack seal quartz veins and graphitic shear zones only minor amounts of invisible gold were detected in these deeper lodes gold occurs dominantly as abundant microscopic and larger particles in sulphide arsenide minerals and in gangue the gold distribution patterns revealed by sims microprobe analysis and ion maps emp and colour staining suggest that most of the primary gold in the bogosu prestea system precipitated in solid solution with sulphide arsenide minerals however post depositional concentration and redistribution occurred in increasing degree with 1 increase in metamorphic hydrothermal gradients in the gold system depth 2 decrease in the refractory properties of the host mineral and 3 increase in the amount of post depositional host mineral recrystallization and deformation gold evolved from primary solid solution within sulphide arsenide minerals to colloidal and micrometre size particles concentrated in voids fractures and internal grain boundaries and finally to microscopic and larger particles at sulphide arsenide grain margins and in the gangue assemblage the general conclusions presented here are applicable to as rich gold deposits of all ages worldwide the presence of gold in late fractures is insufficient evidence for late stage introduction of gold in mesothermal gold systems

a reexamination of the genesis of african waves abstract the problem of genesis of easterly african waves is reexamined as a linear eigenvalue instability problem of a supposedly realistic basic zonal shear flow with and without a cumulus heating evidence will be presented to show how the growth rate the propagation speed and the overall composite structure of the observed tropical easterly waves can he well reproduced in the model in conjunction with a cisk representation of the latent heating the degree of resemblance between the structure of the model unstable wave and the observed african waves is found to be significantly dependent upon the secondary features of the basic shear flow this finding is based on a detailed comparison of the results using different structures for the basic flow including the one used by mass much of the kinetic energy of the unstable wave is generated via the barotropic instability process associated with the horizontal shear of the sahara jet centered at the 650 mb level but the vertical shear of the zonal flow

organization of rainfall by an unstable jet with an application to african waves abstract african waves are believed to originate as shear instabilities although in certain cases rainfall is organized so that latent heating contributes to wave growth what determines whether the shear instability can organize rainfall is considered here in particular why african waves organize rainfall mainly during the late summer despite the regular occurrence of shear instability and rainfall throughout the season during gate moisture convergence by the waves was also largest toward the late summer it is assumed that an african wave will organize rainfall if it converges moisture as measured by the ascent at the top of the moist layer with sufficient amplitude the wave amplitude is specified at some level beneath the 600 mb african jet whose instability is a plausible source of the wave the ascent is calculated using the quasigeostrophic potential vorticity and thermodynamic equations and depends on the zonal wind separating the unstable jet from the top of the moist layer before turning

evidence of two regimes of easterly waves over west africa and the tropical atlantic synoptic scale easterly waves at 700 hpa have been studied over west africa and the tropical atlantic for the summers of 1979 1995 spectral analyses fast fourier and wavelet transforms of 700 hpa meridional wind component along 17 5 n enable to point out two band periods between 3 and 5 days and between 6 and 9 days an example of each wave is shown composite analysis confirms the evidence of two such regimes of easterly waves during summer over west africa and the tropical atlantic the 6 9 day wave regime differ from the 3 5 day wave regime by larger anticyclonic cells originated from the libyan and the azores areas and by more northern tracks

a multidisciplinary study of invisible gold in arsenopyrite from four mesothermal gold deposits in siberia russian federation characterization of gold in four siberian mesothermal gold deposits was done through a multidisciplinary investigation including ore microscopy inaa sims epma and 197 au moessbauer spectroscopy the deposits are olympiada and veduga in the enisei mountain range and nezhdaninskoye and sentachan in the verkhoyansk kolyma area in which vein and disseminated orebodies are hosted by sedimentary sequences metamorphosed to amphibolite olympiada and greenschist facies ore minerals include arsenopyrite and pyrrhotite or pyrite as major constituents with minor scheelite and sphalerite chalcopyrite and native gold as minor constituents with or aurostibite galena gudmundite tetrahedrite stibnite and berthierite some of the gold mineralization is metallurgically refractory in all four deposits largely due to the presence of invisible gold in arsenopyrite and to a lesser extent in pyrite several generations of arsenopyrite are recognized in the auriferous zones of the veduga nezhdaninskoye and sentachan deposits textural observations indicate late deposition of native gold with respect to arsenopyrite no evidence was found of arsenopyrite recrystallization and the crystallization of native gold is considered to result from an evolution of fluids rather than redeposition of gold wide variations in the gold contents of arsenopyrite occur within deposits within samples and within individual grains inna analyses of individual arsenopyrite grains 30 70 mu m in size show that the gold concentration ranges from 197 au moessbauer spectra of arsenopyrite concentrates from the veduga nezhdaninskoye and sentachan deposits exhibit mainly a component with isomer shifts between 3 3 and 3 6 mm s which is interpreted as strong evidence of the presence of chemically bound gold in the arsenopyrite crystal structure the spectra of samples from the veduga deposit also contain minor amounts of native gold for which negative isomer shifts near 1 2 mm s are expected metallic gold dominates in the 197 au moessbauer spectra of samples from the olympiada deposit but varying amounts of chemically bound gold are also visible in the spectra some attributed to aurostibite it is concluded that the ores from these deposits are refractory partly because the gold occurs in arsenopyrite as chemically bound gold as well as submicroscopic metallic particles probably as small as 2 nm this study also shows that au bearing arsenopyrite is usually depleted in as with respect to its stoichiometric composition but correlation of au enrichment to fe deficiency was not found it is inferred from 197 au moessbauer spectroscopy that substitution of fe super 3 for au super 3 is most likely the temporal change in different modes of gold occurrence i e as native gold or invisibly in sulfides in the mineralized zones and veins is interpreted to result from an evolution of fluids rather than to be a recrystallization phenomenon dissemination of au bearing sulfides within the altered halos infers that a pervasive fluid rock interaction was an effective mechanism for deposition of minerals and gold absorption of gold complexes onto sulfide surfaces is also suggested to have played an important role in the deposition of native gold during the latest episodes in the formation of the deposits

imaging regional geology and au sulphide mineralization over dhanjori greenstone belt implications from 3 d inversion of audio magnetotelluric data and petrophysical characterization abstract the 2 1 ga old paleoproterozoic dhanjori group of rocks covers 800 sq km area within the singhbhum crustal province of eastern india and is composed of siliciclastic metasedimentary sequence interlayered with mafic to ultramafic rocks the meta volcanosedimentary sequence is deformed and is of low grade greenschist metamorphic facies the gold occurrences within the study area are confined to the sulphide hosted mafic ultramafic volcanic rocks and also in the basal quartz pebble conglomerates qpc within the dhanjori formation gold mineralization within the mafic ultramafic meta volcanics formations occurs within the quartz carbonate vein i e lode gold and as detrital gold within the qpc 0 5 7 ppm of phuljhari formations regional audio magnetotelluric amt measurements across the geological domains of dhanjori group and iron ore group iog were carried out in the frequency range of 10 khz 10 hz this work discusses the conductivity model from 3 d inversion along with geology and petrophysical properties in mapping the regional geological features associated sulphide mineralization and influence of texture grain and bulk properties on mineralization dimensionality and strike analysis of the amt data indicate complex conductivity structures 3 d inversion of off diagonal component of impedance was performed for obtaining an optimum value of uniform half space initial resistivity and error floor for off diagonal component of impedance data these were used to perform 3 d inversion of full impedance to produce a conductivity model of the study area the conductivity model delineated major geological boundaries and the sulphide bearing mineralized zone a major conductor is observed which extends to a depth of 250 m within meta volcanics on comparison with the available borehole adjacent to this it is confirmed that the conductor corresponds to sulphide mineralization the resistivity low at a depth of 150 m coincides with metabasalts pyrite present which extends to 159 m with arsenopyrite another mineralized zone is observed at the boundary of iron ore group volcanics and proterozoic gabbro anorthosite ultramafics pgau it starts appearing from a depth of 400 m and can be seen which extends to a depth of 800 m it is worth mentioning that there lies kundarkocha gold mine in the same geological domain in addition near surface conductor to a maximum depth of 50 m is observed all along the amt profile the sediments and fluids could account for this conducting feature this is in agreement with available electrical resistivity tomography section the borehole within dhanjori volcanics also detected sulphide mineralization for 50 m thus it can be inferred that the near surface conductor indicates the presence of gold in association with other sulphide minerals the petrophysical studies helped to estimate the concentration of minerals within the rocks high density and low susceptibilities in the area is an indicative of low grade metamorphism and low level of serpentenization combined density and susceptibility scatter diagram and component proportion phase diagram suggests 20 vol 78 vol and 2 vol of haematite sulphides barren rocks and magnetite respectively the high value of chargeability and negligible value of susceptibility indicates the presence of disseminated sulphides rather than haematites and or massive sulphides in the rocks ternary plot suggest that the mineralization is controlled by texture and grain properties petrophysical analysis suggests that the lithotypes of the study area are similar to those of greenstone terrain in the abitibi subprovince integrating inverted section geology and petrophysical properties has a substantial impact on the study area in terms of predicting the mineralization prospect and at the same time substantially reduces the drilling cost thus the study provides a new orientation and advancement to the exploration strategy for deeper deposits

understanding and simulating the link between african easterly waves and atlantic tropical cyclones using a regional climate model the role of domain size and lateral boundary conditions using a suite of lateral boundary conditions we investigate the impact of domain size and boundary conditions on the atlantic tropical cyclone and african easterly wave activity simulated by a regional climate model irrespective of boundary conditions simulations closest to observed climatology are obtained using a domain covering both the entire tropical atlantic and northern african region there is a clear degradation when the high resolution model domain is diminished to cover only part of the african continent or only the tropical atlantic this is found to be the result of biases in the boundary data which for the smaller domains have a large impact on tc activity in this series of simulations the large scale atlantic atmospheric environment appears to be the primary control on simulated tc activity weaker wave activity is usually accompanied by a shift in cyclogenesis location from the mdr to the subtropics all era40 driven integrations manage to capture the observed interannual variability and to reproduce most of the upward trend in tropical cyclone activity observed during that period when driven by low resolution global climate model gcm integrations the regional climate model captures interannual variability albeit with lower correlation coefficients only if tropical cyclones form in sufficient numbers in the main development region however all gcm driven integrations fail to capture the upward trend in atlantic tropical cyclone activity in most integrations variations in atlantic tropical cyclone activity appear uncorrelated with variations in african easterly wave activity

la icp ms trace element analysis of pyrite from the chang an gold deposit sanjiang region china implication for ore forming process abstract the chang an gold deposit yunnan province is one of five large gold deposits in the ailaoshan gold belt that is the most important ore belt of the sanjiang tethyan metallogenic domain geochemical study of pyrite in the deposit was conducted using laser ablation inductively coupled plasma mass spectroscopy three types of hydrothermal pyrite were identified in the ores and wall rocks i e the coarse euhedral crystals in syenite py1 the coarse grains disseminated in altered sandstones or sandstone ores py2 and the fine grained euhedral pyrite in sandstone ores py3 their trace elements exhibit different concentrations associations and rim core zoning implying different geneses and crystallization processes the cores of py1 were formed by magmatic fluids and have the lowest concentrations of au as cu and zn the cores of py2 were formed by metamorphic fluids and have relatively high au ag ni pb and cu concentrations the py3 grains and the growth rims of py1 and py2 show consistently high contents of au as pb and co suggesting that all of them were rapidly deposited from a mixing fluid system that was probably composed of fluids of metamorphic and magmatic origins this interpretation is supported by the observation that the high grade ores generally contain lots of py2 and py3 hence we consider that the deposit was formed during india asia collision slightly postdate the 33 35 ma tectono magmatism

african easterly wave activity in a variable resolution gcm the role of large scale conditions on african easterly waves variability and associated rainfall is investigated in simulations with the variable resolution version of the arpege climat general circulation model gcm easterly waves are identified from the 850 hpa meridional winds the simulated waves characteristics and their frequency response are compared with that in the reanalyses of the european center for medium range weather forecasts ecmwf during summer 1992 the zonal wavelength of the simulated waves increases toward the equator this increase found also in previous works is explained by the increase in 850 hpa mean zonal winds toward the equator as a result of low level monsoon flow a pronounced seasonal variability indicating a late summer enhancement of wave activity and related precipitation is found in both simulations and reanalyses this feature which has been found from observation campaigns is explained by the variability of the large scale circulation which gives favorable conditions for the penetration of the easterly waves into the moist layer in the late summer a shift of the spectra towards low frequencies is found in the simulated waves when compared to the reanalysis the shift is explained by the relatively weak westward winds within the african easterly jet in the model which tend to generate waves with low phase speed and frequency we suggest that the weakness of the winds in the jet is caused by the strong eastward monsoon flow in the model which may be due to surface condition parameterizations

bimodal distribution of gold in pyrite and arsenopyrite examples from the archean boorara and bardoc shear systems yilgarn craton western australia this study investigates the microstructures geochemistry and hydrothermal evolution of gold bearing pyrite and arsenopyrite from six orogenic gold deposits in the archean eastern goldfields province western australia scanning electron microscope sem electron microprobe emp and laser ablation inductively coupled plasma mass spectroscopy la icp ms analyses show that the gold bearing minerals possess a number of similar textural features including the occurrence of invisible gold within initial phases of growth and later stage visible gold associated with alteration rims the alteration rims are characterized by a higher than average atomic mass mainly owing to arsenic enrichment and are preferentially located along fractures and grain boundaries in the pyrite and arsenopyrite these observations suggest that visible gold formation is associated with hydrothermal alteration of preexisting pyrite and arsenopyrite textural observations and la icp ms data suggest that some invisible gold was remobilized from early formed pyrite and arsenopyrite to form visible gold during development of these alteration rims gold may also have been added by hydrothermal fluids during a later stage of mineralization in situ geochemistry and phase relationships of alteration rims are used to further constrain the hydrothermal process responsible for formation of alteration rims and visible gold in fractures based on sulfide stability relations our data indicate that development of arsenopyrite alteration rims associated with late stage visible gold formation was related to an increase in temperature maximum increase from 310 to 415 c and up to of sic orders of magnitude increase in sulfur fugacity whereas changes in oxygen fugacity were less important la icp ms analyses show that the relative and absolute variations in selected trace element au ag sb bi ba te pb co and mo concentrations can also be used to distinguish between unaltered and altered pyrite and arsenopyrite in general trace elements within pyrite and arsenopyrite have a relatively uniform distribution whereas later stage alteration rims have more variable trace element distributions although the observed textures are typical of prograde metamorphic coronae we suggest that they are the consequence of variations in fluid conditions and chemistry and that mineralization occurred in response to syn and or postpeak metamorphic fluid infiltration

constraints of mineralogical characterization of gold ore implication for genesis controls and evolution of gold from kundarkocha gold deposit eastern india abstract gold mineralization in kundarkocha gold deposit occurs in the eastern indian craton that is hosted by sheared quartz carbonate sulfide veins emplaced within the graphitic schist carbonaceous phyllite and talc chlorite serpentine schist belongs to gorumahisani badampahar schist belt of iron ore group gold mineralization exhibits both lithological and structural controls in the study area albeit the stratigraphic control is more ubiquitously observed detailed mineralogical characterization coupled with electron probe microanalysis of the sulfide phases reveal the occurrences of gold in three distinct forms i as lattice bound form within sulfides especially enriched in arsenopyrite loellingite pyrite pyrrhotite and chalcopyrite in decreasing order of abundance ii as micro inclusions or nano scale gold inclusions within pyrite and arsenopyrite especially along the growth zones and micro fractures as substrates and iii as free milling nugget gold grains either along the grain boundaries of sulfides or within the host rocks three generations of pyrite py i py ii and py iii and arsenopyrite asp i asp ii asp iii have been identified based on textural morphological characteristics and mineral chemistry the lattice bound gold content in pyrite and arsenopyrite varies from 600 to 2700 ppm and 900 to 3600 ppm respectively and increase in concentration of such refractory gold is seen in the order of chalcopyrite pyrrhotite pyrite loellingite arsenopyrite the evolutionary stages of different forms of gold include remobilization of the lattice bound grains in pyrite and arsenopyrite py i and asp i and re concentration along the zoned pyrite and arsenopyrite py ii and asp ii and ultimately as native gold nuggets surrounding the sulfides as well as within the main mineralized zone lattice bound gold distribution could have resulted due to metamorphic devolatilization reactions which are further aided by the influx of hydrothermal fluids these reactions along with additional input of hydrothermal fluid paved the way for expulsion of lattice bound gold from sulfides to concentrate as nuggets main lode within shear fractures channelizing the fluid flow thermometry results of the arsenopyrite pyrite pyrrhotite assemblage yielded a temperature range from 375 to 390 c which is the ideal condition for gold precipitation native silver gersdorffite and arsenian ullmannite are being reported for the first time from this deposit indicating the complexity and wide variety of mineral phases associated with gold implying magmatic hydrothermal input of the source fluid

mesoarchaean crustal history of the eastern indian craton smnd and upb isotopic evidence abstract a variety of xenoliths representing high al trondhjemites and supracrustal lithologies occur within mesoarchaean granitoid rocks of the eastern indian craton a trondhjemitic xenolith from the bonai pluton yields a u pb age of 3380 6 4 ma for magmatic zircon and a minimum age of 3448 ma for xenocrystic zircon grains this sample also shows an nd value of 4 2 and t dm of 3 9 ga whereas four other xenoliths yield nd values ranging from 0 3 to 1 8 and t dm of 3 54 to 3 37 which are consistent with published data from the region and suggest a derivation from protoliths with relatively short lived crustal residence times

neoarchean paleoproterozoic stratigraphy of the dhanjori basin singhbhum craton eastern india and recording of a few u pb zircon dates from its basal part abstract the stratigraphy of the dhanjori basin placed at the northeastern margin of the paleo mesoarchean singhbhum craton has been revised a mainly quartz pebble conglomerate qpc and volcani clastics bearing unit at the base of the dhanjori basin and intruded by the mayurbhanj granite has been named phuljhari formation the dhanjori volcani sedimentary sequence with quartzite polymictic conglomerate at its base disconformably overlies the phuljhari formation and non conformaby over the mayurbhanj granite the dhanjori group is inferred to broadly range in age from 2 6 2 1 ga detrital zircons from qpc belonging to the phuljhari formation have yielded oldest chemical ages of 3 09 3 04 ga thus fixing the upper age limit of the formation the 3 09 ga old zircons recovered earlier from the mayurbhanj granite which is intrusive into the relatively younger phuljhari fm therefore appears to be xenocrystic in nature a fine grained variety of the mayubhanj granite close to its intrusive contact with the phuljhari fm was sampled during the present study it has recorded strong impress of acid magmatic event around 1 0 0 8 ga by its lower intercept and an upper intercept age of 2 8 ga the latter might record the inherited age of protolith to the mayurbhanj granite and correspond to widespread granite magmatic activity affecting the margin of the singhbhum craton signature of 1 0 0 08 ga old thermal perturbation also affected lower parts of the dhanjori basin and the singhbhum shear zone detrital au u bearing qpc in the phuljhari formation represent neoarchean sedimentation at the margin of the peneplained craton the dhanjhori group comprising mafic ultramafic volcanics and siliciclastics was hosted in rift induced intracratonic basin around neoarchean palaeoproterozoic threshold

invisible gold within sulfides from the archean hutti maski schist belt southern india abstract the hutti maski schist belt is an important gold producing archean greenstone belt in india mesothermal gold mineralization occurs within smoky quartz sulfide veins occupying brittle ductile shear zones principal ore minerals observed are arsenopyrite pyrite pyrrhotite chalcopyrite sphalerite loellingite and gold although most of the gold occurs in native form a substantial amount of gold is also present in the sulfides especially within arsenopyrite in invisible form two stages of gold deposition occur in this area 1 lattice bound invisible gold within sulfides restricted to the shear fractures a part of the primary gold depositional history 2 native gold within sulfides as inclusions and as separate grains which may belong to another phase of hydrothermal fluid influx remobilization reconstitution and concentration of the early phase might have formed the later phase the substitution of fe by au within the sulfidic sites adsorption reduction and fluid rock interaction phase immiscibility may be the plausible mechanisms for the invisible gold microscopic substrates and visible gold respectively

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

structure and evolution of collapse sinkholes combined interpretation from physico chemical modelling and geophysical field work abstract in karst rocks limestone anhydrite gypsum etc water flowing through fissures and bedding partings can enlarge voids either by physical or chemical dissolution within a geologically short period of time the increase in void space creates a large secondary porosity typical for soluble rocks which is responsible for preferential flow through the karst rock often through cave systems with passages reaching the meter scale and more this large scale voids in the sub surface can initiate collapse of the overburden either through wall or roof breakdown and the initial void created by dissolution can migrate upwards and finally cause a surface collapse and create a collapse sinkhole while the dissolution part of this evolution is in the order of 10 000 100 000 years the final mechanical collapse can occur on time scales of days we have studied a typical collapse sinkhole site in the southern harz mountains in germany with anhydrite partly converted to gypsum as soluble rock in the sub surface we discuss geophysical measurements gravity electrical resistivity tomography self potential magnetics from the location to identify the local collapse sinkhole signal and the possibility to separate the collapse sinkhole signal from the broader geological signal of the study site we model the initiation of sub surface voids with our numerical tool karstaquifer a 3d karst evolution model describing flow and dissolution in karst rocks we apply this numerical model to predict collapse sinkholes in a locality in the harz mountains

age and source of the kure odemis arsenopyrite gold mineralization menderes massif turkey determined by re os he isotopes abstract the menderes massif mm is considered to be one of the principal regions hosting vein type quartz arsenopyrite orogenic gold deposits and occurrences in turkey gold mineralizations in the mm can be grouped into i schistosity conformable e trending veins and ii shear controlled nw trending veins arsenopyrite is one of the major gold bearing minerals in these deposits or occurrences rhenium osmium isotopic dating of two types of arsenopyrite from the schistosity conformable and vein type kure odemis gold deposit has yielded two groups of model ages maximum ages at 557 574 ma and 246 250 ma respectively the data suggested that the quartz arsenopyrite gold deposit formed in the neoproterozoic and early triassic with the former and the latter corresponding to pan african compressional orogenesis and palotethys rifting respectively fluid inclusions in kure arsenopyrite have 3he 4he ratios of 0 08 0 09 ra ra 1 39x10 6 the 3he 4he ratio of air being within the range of middle to upper crustal values a minor helium contribution of mantle fluids to the kure gold deposit is possible because the 4he concentrations in arsenopyrite are enriched 170 to 9520 times relative to argon and typical atmospheric values indicating that contribution of atmospheric he to the mineralizing fluids is negligible and 0 08 0 09 ra is slightly above typical crustal 3he 4he ratios arsenopyrite yields relatively non radiogenic initial os isotopic compositions also indicating possiblecontribution from mantle fluids carbonic fluid inclusion type 2 h2o co2 nacl ch4 in quartz of nw trending veins at kure are gas liquid hydrate crystal rich and their homogenization temperatures th range from 244 to 387 c salinity values range from 0 2 to 5 7 wt nacl equiv the homogenization temperatures th of aqueous fluid inclusions type 1 h2o nacl in quartz from nw trending veins at kure vary between 237 and 358 c whereas salinity values range from 1 7 to 7 7 wt nacl equiv quantitative epma spot analyses on arsenopyrite minerals have shown that as concentrations in ew trending and nw trending veins range from 32 5 to 33 8 and 32 3 33 8 respectively based on a phase diagram for the fe as s system along with the arsenopyrite geothermometer the ranges of temperature and corresponding logf s2 at which arsenopyrite is in equilibrium with pyrite are between 380 and 480 c and 7 4 and 4 3 for apy 1 respectively these values are between 390 and 475 c and 7 0 and 4 5 for apy 2 respectively

comparison of metasomatic reactions between a common co 2 rich vein fluid and diverse wall rocks intensive variables mass transfers and au mineralization at alleghany california the gold deposits at alleghany california are typical of many epigenetic gold bearing hydrothermal vein systems in metamorphic terranes worldwide detailed analyses of alteration halos in serpentinite mafic amphibolite and granite wall rocks at alleghany indicate that widely contrasting deposit types ranging from fuchsite carbonate schists to pyrite albitites resulted when different wall rocks interacted with the same externally derived co 2 rich hydrothermal vein fluid patterns of element redistribution within halos and among lithologic units suggest a complex process involving fluid flow along vein fractures and diffusion or infiltration normal to the veins wall rocks locally controlled both the directions and magnitudes of chemical fluxes across vein walls vein fluids at constant temperature and pressure with relatively constant ratios of mobile species na super k super h super and co 2 h 2 s h 2 caused contrasting divergent reactions in proximal alteration zones because the wall rocks controlled the ratios of relatively immobile species al cr fe mg and fe mg and the component activities of hydrothermal mineral solid solutions thus pyrite and albite were stable with respect to the relatively pure siderite and k mica that occur sparingly in proximal granite zones but they were not stable with respect to the relatively impure siderite and k mica that characterize proximal serpentinite zones partly as a result of divergent reactions altered rocks exhibit contrasting mobile element concentration gradients e g ca ba sr rb na k c s and imply local sources and sinks and possibly short residence times for some of these components along discordant fluid flow paths calculated reaction coefficients for h super h 2 and h 2 s indicate that different wall rocks at different stages of alteration may have inhibited or promoted gold precipitation the distribution of gold and its calculated solubility are consistent with its having been precipitated from au hs 2 super complexes in response to pyritization of granite fluid desulfidation and reduction and possibly in part in response to dolomitization and sericitization of serpentinite fluid acidification strata bound disseminated orebodies may be expected in a variety of other host rocks with higher than average fe mg ratios where pyrite was stable with respect to intermediate magnesite siderite as in the granite it is proposed that the co 2 rich vein fluids approached partial equilibrium with alteration assemblages in the average or dominant rocks along their flow paths simpler but radically different proximal assemblages were then produced where the fluids encountered chemically extreme rock types fluid rock interaction equilibria can account for much of the diversity in the mineralogy and chemistry of gold deposits in heterogeneous metamorphic terranes while maintaining a simple genetic classification based on the distinctive chemistry of the hydrothermal fluids comparative studies of multicomponent phase equilibria and mass exchanges can provide both rationalizations and predictions of local wall rock effects on geochemical anomalies and the locations of ore deposits in lithologically heterogeneous terranes simultaneous consideration of contrasting high variance phase deficient assemblages along discordant veins is suggested as a general method for quantifying fluid intensive variables in metasomatic systems

a genetic classification of sinkholes illustrated from evaporite paleokarst exposures in spain this contribution analyses the processes involved in the generation of sinkholes from the study of paleokarst features exposed in four spanish tertiary basins bedrock strata are subhorizontal evaporites and in three of the basins they include halite and glauberite in the subsurface our studies suggest that formation of dolines in these areas results from a wider range of subsidence processes than those included in the most recently published sinkhole classifications a new genetic classification of sinkholes applicable to both carbonate and evaporite karst areas is thus proposed with the exception of solution dolines it defines the main sinkhole types by use of two terms that refer to the material affected by downward gravitational movements cover bedrock or caprock and the main type of process involved collapse suffosion or sagging sinkholes that result from the combination of several subsidence processes and affect more than one type of material are described by combinations of the different terms with the dominant material or process followed by the secondary one e g bedrock sagging and collapse sinkhole the mechanism of collapse includes any brittle gravitational deformation of cover and bedrock material such as upward stoping of cavities by roof failure development of well defined failure planes and rock brecciation suffosion is the downward migration of cover deposits through dissolutional conduits accompanied with ductile settling sagging is the ductile flexure of sediments caused by differential corrosional lowering of the rockhead or interstratal karstification of the soluble bedrock the paleokarsts we analysed suggest that the sagging mechanism not included in previous genetic classifications plays an important role in the generation of sinkholes in evaporites moreover collapse processes are more significant in extent and rate in areas underlain by evaporites than in carbonate karst primarily due to the greater solubility of the evaporites and the lower mechanical strength and ductile rheology of gypsum and salt rocks

sinkhole structure imaging in covered karst terrain 1 ground penetrating radar gpr and resistivity techniques have been widely used to map the locations of sinkholes in covered karst terrain to determine whether a sinkhole is a likely preferential conduit for groundwater flow however requires higher resolution imaging than that used in conventional sinkhole mapping surveys field observations combined with simulated surveys for a 15 m diameter 3 m deep sinkhole in west central florida are used to assess the resolution of gpr and resistivity surveys targeting the semiconfining unit that floors the sinkhole depression 2d resistivity surveys clearly show the central depression as well as resistivity contrasts between the cover sediments within and outside of the sinkhole but are inadequate for resolving breaches in the semiconfining unit or underlying conduits a 3d gpr survey resolves vertical structure on the order of tens of centimeters within the semiconfining unit as well as indicators of conduits that extend several meters beneath the central depression 3d gpr thus holds promise for imaging hydrologically significant features of sinkholes

self formed waterfall plunge pools in homogeneous rock waterfalls are ubiquitous and their upstream propagation can set the pace of landscape evolution yet no experimental studies have examined waterfall plunge pool erosion in homogeneous rock we performed laboratory experiments using synthetic foam as a bedrock simulant to produce self formed waterfall plunge pools via particle impact abrasion plunge pool vertical incision exceeded lateral erosion by approximately tenfold until pools deepened to the point that the supplied sediment could not be evacuated and deposition armored the pool bedrock floor lateral erosion of plunge pool sidewalls continued after sediment deposition but primarily at the downstream pool wall which might lead to undermining of the plunge pool lip sediment evacuation and continued vertical pool floor incision in natural streams undercutting of the upstream pool wall was absent and our results suggest that vertical drilling of successive plunge pools is a more efficient waterfall retreat mechanism than the classic model of headwall undercutting and collapse in homogeneous rock

sandstone caves on venezuelan tepuis return to pseudokarst abstract venezuelan table mountains tepuis host the largest arenite caves in the world the most frequently used explanation of their origin so far was the arenization theory involving dissolution of quartz cement around the sand grains and subsequent removing of the released grains by water new research in the two largest arenite cave systems churi tepui system in chimanta massif and ojos de cristal system in roraima tepui showed that quartz dissolution plays only a minor role in their speleogenesis arenites forming the tepuis are not only quartzites but they display a wide range of lithification and breakdown including also loose sands and sandstones speleogenetic processes are mostly concentrated on the beds of unlithified sands which escaped from diagenesis by being sealed by the surrounding perfectly lithified quartzites only the so called finger flow pillars testify to confined diagenetic fluids which flowed in narrow channels leaving the surrounding arenite uncemented another factor which influenced the cave forming processes by about 30 was lateritization it affects beds formed of arkosic sandstones and greywackes which show strong dissolution of micas feldspars and clay minerals turning then to laterite barro rojo the main prerequisite to rank caves among karst phenomena is dissolution as the dissolution of silicate minerals other than quartz appears to play not only a volumetrically important role but even a trigger role these arenitic caves may be ranked as karst

invisible gold in arsenian pyrite and arsenopyrite from a multistage archaean gold deposit sunrise dam eastern goldfields province western australia the sunrise dam gold mine 11 1 moz au is the largest deposit in the archaean laverton greenstone belt eastern goldfields province yilgarn craton western australia the deposit is characterized by multiple events of fluid flow leading to repeated alteration and mineralization next to a major crustal scale structure the au content of arsenian pyrite and arsenopyrite from four mineralizing stages d1 d3 d4a and d4b and from different structural and lithostratigraphic environments was measured using in situ laser ablation inductively coupled plasma mass spectrometry pyrite contains up to 3 067 ppm au n 224 whereas arsenopyrite contains up to 5 767 ppm n 19 gold in arsenopyrite d4a stage was coprecipitated and remained as invisible gold nanoparticles and or lattice bound during subsequent deformation events in contrast gold in pyrite is present not only as invisible gold but also as micrometer size inclusions of native gold electrum and au ag tellurides pristine d1 and d3 arsenian pyrite contains relatively low au concentrations 26 ppm the highest au concentrations occur in d4a arsenian rich pyrite that has recrystallized from d3 pyrite textures show that this recrystallization proceeded via a coupled dissolution reprecipitation process and this process may have contributed to upgrading au grades during d4a in contrast au in d4b pyrite shows grain scale redistribution of invisible gold resulting in the formation of micrometer scale inclusions of au minerals the speciation of au at sunrise dam and the exceptional size of the deposit at province scale result from multiple fluid flow and multiple au precipitating mechanisms within a single plumbing system

multi stage growth and invisible gold distribution in pyrite from the kundarkocha sediment hosted gold deposit eastern india abstract gold mineralization at kundarkocha india is hosted in sheared gray quartz veins that were emplaced in carbonaceous pyritic phyllite gold occurs as enclosed grains within sulfides and free grains in quartz based on characteristic textural and chemical features documented by x ray element imaging electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry analyses four pyrite types were identified in carbonaceous phyllites and auriferous veins rock hosted fine grained syn sedimentary to early diagenetic pyrite framboids pyi have lower contents of co and as but consistently high gold values pyrite of the next generation pyii has numerous silicate and rare sulfide inclusions lower contents of co and ni moderate as values the highest mean value of invisible gold and maximum concentrations of trace elements such as li ti zn rb sr y zr nb la ce ta th u and cr pyrite of the third generation pyiii shows evidence of overgrowth over pyii contains both silicate and sulfide inclusions and are characterized by moderate contents of co high ni and low au values and higher concentrations of large ion lithophile elements but lesser amount of high field strength elements pyrites of the latest type pyiv occur as polycrystalline aggregates that contain inclusions of gold sulfides and rare silicates show oscillatory zoning of co and as and the lowest concentrations of all other trace elements successive decrease in contents of majority of trace elements from pyii to pyiv is attributed to fluid assisted recrystallization during diagenesis and low grade metamorphism later generation pyrites pyii through pyiv exhibit higher au contents regardless of their as values indicating occurrence of invisible gold mostly as nanoparticles at times reaching up to 500 ppm unlike the majority of trace elements that underwent large scale remobilizations gold was somehow locked up in pyrite resulting in a rather lean deposit at kundarkocha

evolution of the proterozoic rift margin sediments north singhbhum mobile belt jharkhand orissa india abstract the proterozoic north singhbhum mobile belt nsmb a proterozoic rift basin registered a complex interplay of tectonism and sedimentation the siliciclastic sedimentary succession developed along the southern margin of the nsmb offers a deep insight into the changing pattern of sedimentation in response to crustal dynamism along a rift margin stratigraphic sedimentologic structural and tectonic studies of the proterozoic sedimentary succession bisrampur formation indicate deposition in a series of half grabens developed successively along the margin of the rift basin under the influence of lithospheric stretching analyses of the sedimentary facies attributes and the architecture of the studied sedimentary succession and paleocurrent patterns indicate filling of the half grabens by archean basement derived siliciclastic sediments in an alluvial fan fan delta environment the structural elements developed in these sediments and neighboring rock units suggest that deformation and final collapse of the half graben basins took place during a terminal orogeny on the basis of an integrated analysis of the dataset generated in the present study and the database available in published work a comprehensive evolutionary model of the north singhbhum mobile belt is reconstructed

gold and trace element zonation in pyrite using a laser imaging technique implications for the timing of gold in orogenic and carlin style sediment hosted deposits laser ablation icp ms imaging of gold and other trace elements in pyrite from four different sedimenthosted gold arsenic deposits has revealed two distinct episodes of gold enrichment in each deposit an early synsedimentary stage where invisible gold is concentrated in arsenian diagenetic pyrite along with other trace elements in particular as ni pb zn ag mo te v and se and a later hydrothermal stage where gold forms as either free gold grains in cracks in overgrowth metamorphic and or hydrothermal pyrite or as narrow goldarsenic rims on the outermost parts of the overgrowth hydrothermal pyrite compared to the diagenetic pyrites the hydrothermal pyrites are commonly depleted in ni v zn pb and ag with cyclic zones of co ni and as concentration the outermost hydrothermal pyrite rims are either as au rich as in moderate to highgrade deposits such as carlin and bendigo or co ni rich and as au poor as in moderate to low grade deposits such as sukhoi log and spanish mountain the early enrichment of gold in arsenic bearing syngenetic to diagenetic pyrite within black shale facies of sedimentary basins is proposed as a critical requirement for the later development of carlin style and orogenic gold deposits in sedimentary environments the best grade sediment hosted deposits appear to have the gold climax event toward the final stages of deformation related hydrothermal pyrite growth and fluid flow

studies of african wave disturbances with the giss gcm abstract simulations made with the general circulation model of the nasa goddard institute for space studies giss gcm run at 4 latitude by 5 longitude horizontal resolution are analyzed to determine the model s representation of african wave disturbances waves detected in the model s lower troposphere over northern africa during the summer monsoon season exhibit realistic wavelengths of about 2200 km however power spectra of the meridional wind show that the waves propagate westward too slowly with periods of 5 10 days about twice the observed values this sluggishness is most pronounced during august consistent with simulated 600 mb zonal winds that are only about half the observed speeds of the midtropospheric jet the modeled wave amplitudes are strongest over west africa during the first half of the summer but decrease dramatically by september contrary to observational evidence maximum amplitudes occur at realistic latitudes 12 20 n but not as observed near the atlantic coast spectral

geomorphic and geophysical evidence of a collapse origin for large sandstone depressions atop the western cumberland plateau in tennessee abstract for over 70 years closed topographic depressions developed in siliciclastic rocks of the cumberland plateau have been hypothesized to form via collapse of rock into caverns formed in the carbonate rich rocks below we made observations of surface characteristics and applied geophysical methods across two of these depressions on the western part of the plateau to collect subsurface information and test the cave collapse hypothesis electrical resistivity tomography ert and seismic refraction tomography srt were conducted at both sites 1 and 2 and two dimensional 2d multi channel analysis of surface waves masw was conducted at site 2 three zones of material are interpreted at both sites based on field observations and variations in density velocity and resistivity characteristics a relatively thin cover of organic matter and colluvium sandstone bedrock primarily observed at the rims and upper slopes of the depression and a possible boulder rubble zone identified towards the centers of the depressions details derived from lidar data field observations and collected geophysical data for site 2 allow for the projection of a circular breccia pipe in the subsurface a 3 stage model of development is proposed for these features a youthful stage occurs after initial collapse of surface material into a subsurface cavity in which the depression has a cylindrical form in the mature stage the slopes have shallowed and slope adjustments are made as the breccia pipe fills and settles bedrock cliffs are mechanically weathered and influenced by gravity forming talus that covers slopes and the floor with colluvium mixed with organic matter the degraded stage is entered when the breccia pipe has settled the bedrock exposures are covered and the depression begins to fill the depressions studied for this research are classified as being in the mature stage future geophysical surveys and additional geologic mapping and field work at these and other depressions on the plateau will add to our understanding of their development and evolution over time

the archaean nucleus of singhbhum the present state of knowledge abstract the supracrustal rocks of the older metamorphic group omg consisting of metasediments and ortho amphibolite constitute the oldest unit in the archaean nucleus of singhbhum however there are indications that still older 3 4 3 8 ga crust of both sialic and mafic composition existed in this region the omg ortho amphibolites were formed by partial melting of mantle with near chondritic composition ca 3 3 ga ago probably as a result of plume activity shortly afterwards partial melting of the underplated mafic material produced a tonalitic melt older metamorphic tonalitic gneiss omtg which intruded the omg supracrustals and the entire suite was deformed and metamorphosed to upper amphibolite facies subsequent to this melting of the omg ortho amphibolites and the lower crustal material of probable andesitic composition produced melts varying in composition from tonalite to granite and these intruded in different phases to produce plutons of singhbhum granite bonai granite and kaptipada granite which together form volumetrically the major part of the archaean nucleus the older omg and omtg occur as enclaves within these younger granitoids the time difference between the emplacements of the omtg and the early phases of younger granitic intrusion was of the order of 100 200 ma thus serial additions of juvenile material led to the formation of a stable microcontinent by 3 2 ga thermally triggered stretching in this microcontinent produced basins peripheral to the present day singhbhum granite pluton and in these basins the younger supracrustal rocks of the iron ore group iog consisting of bif associated argillaceous and subordinate arenaceous rocks and mafic lavas were laid down there is inadequate field or geochronological evidence to resolve the issue of whether the different iron ore basins were coeval or not meagre geochronological data suggest that some of the bifs are older than ca 3 1 ga post iog activity is confined to the intrusion of mafic dyke swarms and formation of intracratonic basins the ages of both being uncertain

the coupled geochemistry of au and as in pyrite from hydrothermal ore deposits the ubiquity of au bearing arsenian pyrite in hydrothermal ore deposits suggests that the coupled geochemical behaviour of au and as in this sulfide occurs under a wide range of physico chemical conditions despite significant advances in the last 20years fundamental factors controlling au and as ratios in pyrite from ore deposits remain poorly known here we explore these constraints using new and previously published empa la icp ms sims and pixe analyses of as and au in pyrite from carlin type au epithermal au porphyry cu cu au and orogenic au deposits volcanogenic massive sulfide vhms witwatersrand au iron oxide copper gold iocg and coal deposits pyrite included in the data compilation formed under temperatures from 30 to 600 c and in a wide variety of geological environments the pyrite au as data form a wedge shaped zone in compositional space and the fact that most data points plot below the solid solubility limit defined by reich et al 2005 indicate that au1 is the dominant form of au in arsenian pyrite and that au bearing ore fluids that deposit this sulfide are mostly undersaturated with respect to native au the analytical data also show that the solid solubility limit of au in arsenian pyrite defined by an au as ratio of 0 02 is independent of the geochemical environment of pyrite formation and rather depends on the crystal chemical properties of pyrite and post depositional alteration compilation of au as concentrations and formation temperatures for pyrite indicates that au and as solubility in pyrite is retrograde au and as contents decrease as a function of increasing temperature from 200 to 500 c based on these results two major au as trends for au bearing arsenian pyrite from ore deposits are defined one trend is formed by pyrites from carlin type and orogenic au deposits where compositions are largely controlled by fluid rock interactions and or can be highly perturbed by changes in temperature and alteration by hydrothermal fluids the second trend consists of pyrites from porphyry cu and epithermal au deposits which are characterised by compositions that preserve the au as signature of mineralizing magmatic hydrothermal fluids confirming the role of this sulfide in controlling metal ratios in ore systems

invisible gold in ore and mineral concentrates from the hillgrove gold antimony deposits nsw australia vein hosted mesothermal stibnite gold mineralisation at the hillgrove au sb mine in northeastern new south wales has a halo of veinlet and disseminated auriferous arsenopyrite and arsenian pyrite in metasedimentary and granitic host rocks about 50 55 of the gold produced at hillgrove occurs invisibly in arsenopyrite and pyrite gold losses of 20 into tailings are due to this mineral chemical factor from pixe probe analyses it has been found that arsenopyrite contains 255 1500 ppm au and pyrite 24 223 ppm au with au contents of each mineral correlating moderately with as content arsenopyrite and pyrite also contain anomalous values of cu ag and sb whereas paragenetically later stibnite contains little invisible gold but minor fe as ag cu and pb the precipitation of invisible gold in arsenopyrite and pyrite by a possible fe au 3 as s 3 substitution mechanism may have been facilitated by rapid non equilibrium conditions involving pressure decreases and wall rock reaction sulphidation carbonatisation as a prelude to the main stage of stibnite and gold deposition

climate simulations of african easterly waves the three dimensional structure and propagation characteristics of african easterly waves for the 1986 94 period are studied with june august european centre for medium range weather forecasts ecmwf operational analyses national centers for environmental prediction ncep reanalyses and canadian centre for climate modelling and analysis gcm output specific consideration is given to the differences in the timemean circulation synoptic scale variance covariance and principal oscillation patterns the african easterly waves derived from the ecmwf and ncep analyses are very similar with both providing a reasonably realistic depiction of african easterly waves given the agreement with one another earlier station data studies and theory where significant differences exist between the results from the two data assimilation systems they expectably do so over the tropical atlantic and in fields that are not directly observed such as vertical velocity the situation with the gcm is not as favorable but there are some encouraging areas of agreement despite the gcm s relatively coarse resolution and absence of observed data to constrain it selected points of agreement and disagreement between the gcm and the analyses include the following i the gcm african easterly wave energetics are comparable with the analyses in terms of the sign and magnitude of the energy transfers from the time mean state to the waves ii the northern track of easterly waves seen in the analyses terminates prematurely in the gcm at the african coast iii the southerly track of moist easterly waves seen in the analyses near the seasonal rainband is absent in the gcm possible reasons for the deficiencies are discussed the sensitivity of the gcm simulated african easterly waves to co2 doubling is investigated together with significant mean warming and moistening over the northern sahara the level of simulated african easterly wave activity increases with co 2 doubling

combined microgravity electrical resistivity tomography and induced polarization to detect deeply buried caves algaidilla cave southern spain abstract the suitability of the combined microgravity and electrical tomography to detect and characterize caves deeply buried in limestones is tested we have selected the buried algaidilla cave in the estepa range western betic cordillera which is partially submerged below the water table and which was intersected between 26 and 66 m in depth by two boreholes at that location microgravity electrical resistivity tomography ert and induced polarization ip data was collected along four profiles algaidilla cave is associated with a 0 5 mgal residual gravity anomaly minimum microgravity models reveal an approximately horizontal n s elongated shape with a maximum length of 150 m and a width of 40 m resistivity variations provide information on the cave sectors remaining above as well as below the water table forward modeling and depth of investigation doi support the suitability of ert to constrain the cave geometry the cave is identified as having an intermediate to low resistivity feature which approximately matches the 250 m contour line along its ceiling in addition induced polarization models show high chargeability anomalies probably associated with decalcification clays the location and approximately geometry of algaidilla cave estimated from geophysical modeling suggests that nearby overburden may develop cave ins and collapse sinkholes microgravity is proved as a powerful tool to detect caves at this depth but this method alone fails to estimate the geometry ert results delineate the cavity both above and below the water table although the deepest sectors of the models should be interpreted with caution since they are less constrained by the data below the water table the cavity shows great resistivity contrast with regard to the background carbonate in addition this study points out the usefulness of the ip method for detecting decalcification clays often present at the base of karstic caves

study of out of plane effects in the inversion of refraction wide angle reflection traveltimes abstract in the presence of three dimensional 3d inhomogeneous structure the results of 2d traveltime inversion will be in error since the effects of out of plane or 3d ray sampling are ignored we have inverted synthetic data using 2d and 3d algorithms to examine the errors caused by 3d inhomogeneities which produce significant out of plane ray bending the results of inverting data from 2d experiments are compared with vertical slices through 3d models obtained by inverting data using a number of recently employed 3d recording geometries our results show that even for strong 3d inhomogeneities out of plane effects are relatively small with crustal velocity errors of less than 0 15 km s and intra crustal boundary depth errors generally less than 2 km these errors are approximately equal to the uncertainties commonly assigned to crustal models derived from traveltime inversion the artifacts are also similar in magnitude to the lateral smearing that occurs in 3d models when using relatively coarse 3d geometries only for a dense network of profiles will a 3d inversion using off and in line data provide greater lateral resolution than a 2d independent or simultaneous inversion of in line data along each profile 2d and 2 5d inversion of crooked line data in the presence of strong velocity variations produces erroneous small scale velocity structure we conclude that most 3d crustal experiments cannot be justified on the basis that the results from a 2d experiment or a network of 2d profiles will be significantly in error due to out of plane effects 3d experiments can be justified when a dense grid of shots and receivers is used or if a volume image as opposed to a cross sectional image is required

dating the oldest greenstone in india a 3 51 ga precise u pb shrimp zircon age for dacitic lava of the southern iron ore group singhbhum craton abstract this article reports a precise 3506 8 2 3 ma u pb shrimp zircon age for dacitic lava in a well preserved low grade metamorphic and low strained greenstone belt succession of the southern iron ore group singhbhum craton india this age makes the succession the oldest known greenstone belt succession in india and one of the oldest low strain greenstone successions in the world after the 3 51 ga coonterunah group of the pilbara craton western australia and the moderately deformed 3 54 ga theespruit formation of the barberton greenstone belt kaapvaal craton south africa the geochemical composition of the dacitic lava and related volcanic rocks suggests that they formed in a volcanic arc setting the succession also contains a major 120 m thick oxide facies banded iron formation that distinguishes it from the slightly older successions of the pilbara and kaapvaal cratons this banded iron formation may well be one of the oldest and most well preserved and together with associated volcanics

formation of gold deposits a metamorphic devolatilization model a metamorphic devolatilization model can explain the enrichment segregation timing distribution and character of many goldfields such as those found in archean greenstone belts slate belts and other gold only provinces in this genetic model hydrated and carbonated greenschist facies rocks particularly metabasic rocks are devolatilized primarily across the greenschist amphibolite facies boundary in an orogenic setting devolatilization operates on the scale of individual mineral grains extracting not just h2o and co2 but also s and in turn au elevated gold in solution is achieved by complexing with reduced s and by h2co3 weak acid buffering near the optimal fluid ph for gold solubility the buffering is more important than being at the point of maximum gold solubility low salinity ensures low base metal concentrations in the auriferous metamorphic fluid migration of this fluid upwards is via shear zones and or into hydraulic fracture zones in rocks of low tensile strength the geometry of the shear zones dictates the kilometre scale fluid migration paths and the degree of fluid focusing into small enough volumes to form economic accumulations of gold deposition of gold from solution necessitates breakdown of the gold thiosulphide complex and is especially facilitated by fluid reduction in contact with reduced carbon bearing host rocks and or by sulphidation of wallrocks to generate iron bearing sulphide and precipitated gold as such black slate carbon seams banded iron formation tholeiitic basalt magnetite bearing diorite and differentiated tholeiitic dolerite sills are some of the important hosts to major goldfields gold deposition is accompanied by carbonation sulphidation and muscovite biotite alteration where the host rock is of suitable bulk composition the correlation of major gold deposits with rock type even when the gold is primarily in veins argues for rock dominated depositional systems not fluid dominated ones as a consequence a general role in gold deposition for fluid mixing temperature decrease and or fluid pressure decrease and boiling is unlikely although such effects may be involved locally several geological features that are recorded at gold only deposits today reflect subsequent modifications superimposed upon the products of this generic metamorphic devolatilization process overprinting by higher grade metamorphism and deformation and or palaeo weathering may provide many of the most obvious features of goldfields including their mineralogy geochemistry geometry small scale timing features geophysical response and even mesoscopic gold distribution

summer synoptic scale waves over west africa observed by trmm 1 a 5 year daily rainfall dataset 3b42 from trmm is used to investigate the activity and properties of westward propagating synoptic scale waves i e african easterly waves aew over tropical west africa evident wave signals appearing in wavenumber frequency space show their modulations on the surface rainfall pattern during the boreal summer interannual variability exists in both their intensity and spectral properties i e dominant frequency and wavenumber ranges these variabilities can be ascribed in part to year to year variations of their embedded large scale environment especially the mid tropospheric african easterly jet aej generally a stronger weaker aej indicates more less instability energy yielding a stronger weaker wave activity season both seasonal mean rainfall and aews were weak in 2001 but not in 1999 consequently there may exist a nonlinear relationship between the aej aews and mean rainfall to fully understand interannual variability of synoptic scale waves over tropical west africa including the variability in the waves preferred frequencies and wavenumbers it is necessary to examine possible intra seasonal variations in both wave activity and large scale fields in addition to their structure propagation and associated convection

assessment of doline geometry using geophysics on the quercy plateau karst south france in the protection of karstic aquifers the role played by dolines is of interest as these shallow structures can be preferential infiltration pathways for groundwater recharge in this study three depressions in south france orniac lot were identified and characterized using combined geophysical methods apparent conductivity mapping allows precise definition of dolines corresponding to topographic depressions it also reveals other dolines that are hidden by soil cover electrical resistivity and seismic refraction tomography provide detailed cross sections even though the dolines studied are close one to another they exhibit great variability in shape and content moreover time lapse data show that the most saturated regions are on the edges of the first doline such information helps to evaluate human impacts and forecast potential groundwater contamination