morphological thermoelectrical geochemical and isotopic anatomy of auriferous pyrite from the bagrote valley placer deposits north pakistan implications for ore genesis and gold exploration abstract the bagrote valley in north pakistan belonging to the kohistan island arc is well known for regional placer gold mining however no economically feasible in situ hydrothermal gold deposits have been discovered in this region due to rugged terrain and remote nature of its location in the western himalaya the streams draining the main karakoram thrust mkt shyoke suture zone carry placer gold in sediments as well as old river terraces although the primary source remains unknown in this paper we employ a multiparametric approach including x ray diffraction xrd analysis thermoelectricity major and trace element geochemistry and isotopic characteristics of pyrite associated with placer gold with a view to identify the nature of the unknown deposits and ore forming fluids on the catchment of the bagrote valley pyrite in the bagrote valley placers is euhedral to subhedral indicating the proximal gold sources the high rate of occurrence of n type thermoelectric coefficients 89 with low p type 11 and crystallization temperature 290 c 380 c combined with chemical features indicate that the pyrite was derived from porphyry or epithermal type of magmatic hydrothermal gold deposits from the hinterlands of the bagrote valley the x ray elemental maps show that fe as mo and ni are homogenously distributed from core to rim suggesting stable crystallization condition without any alteration by later fluids the calculated chemical formula of pyrite of our samples is au0 0006fe s2 004 plots of au as and au fe shows that gold occurs in pyrite as micro to nano inclusion as au 0 the 34 s v cdt values of pyrite range from 0 6 to 0 9 with an average of 0 02 indicating the derivation of sulfur from a homogeneous magmatic source the pb isotope data indicates that the pb was sourced from orogenic type source with minor contribution of lower crust the narrow variations in 206 pb 204 pb and 208 pb 204 pb values suggest a single lead source the low medium and high mo ni ratios reflect a mixed provenance for the auriferous pyrite the average value of 71 8 of pyrite computed from thermoelectric parameters xnp suggests that the dominant part of the primary source that contributes to the placers might have already been eroded however the proximal source and with high content of gold in the pyrite grains up to 1160 ppm suggest the possibility of significant economic mineralisation below the present erosion level of the deposits in the hinterlands of bagrote valley

a review of te and se systematics in hydrothermal pyrite from precious metal deposits insights into ore forming processes abstract pyrite is one of the most common minerals in many precious and base metal hydrothermal ore deposits and is an important host to a range of trace elements including au and co and the semi metals as se sb te and bi as such in many hydrothermal ore deposits where pyrite is the dominant sulphide phase it can represent a major repository for these elements furthermore the concentrations and ratios of au as and co in pyrite have been used to infer key ore forming processes however the mechanisms controlling the distribution of te and se in pyrite are less well understood here we compare the te and se contents of pyrite from a global dataset of carlin type orogenic au and porphyry epithermal deposits to investigate 1 the potential of pyrite to be a major repository for these elements and 2 whether te and se provide insights into key ore forming processes pyrite from carlin type low sulphidation and alkaline igneous rock hosted epithermal systems is enriched in te and se compared to pyrite from high sulphidation epithermal and porphyry cu deposits orogenic au pyrite is characterised by intermediate te and se contents there is an upper solubility limit for te as a function of as in pyrite similar to that established for au by reich et al 2005 and this can be used to identify te present as telluride inclusions which are common in some epithermal porphyry and orogenic au deposits physicochemical fluid parameters such as ph redox and temperature as well as crystal chemistry control the incorporation and concentration of se and te in pyrite neutral to alkaline fluids have the ability to effectively mobilise and transport te fluid boiling in porphyry epithermal systems as well as wall rock sulphidation and oxidation in carlin type and orogenic au deposits can effectively precipitate te in association with pyrite and au in contrast se concentrations in pyrite apparently vary systematically in response to changes in fluid temperature irrespective of ph and f o 2 hence we propose that the se contents of pyrite may be used as a new geo thermometer for hydrothermal ore deposits furthermore the comparison of bulk ore and pyrite chemistry indicates that pyrite represents the major host for te and se in carlin type and some epithermal systems and thus pyrite can be considered to be of economic interest as a potential source for these elements

sulfur isotopes trace element and textural analyses of pyrite arsenopyrite and base metal sulfides associated with gold mineralization in the pataz parcoy district peru implication for paragenesis fluid source and gold deposition mechanisms in the pataz parcoy district current mining activity is focused on the mesothermal quartz carbonate sulfide veins hosted by the pataz batholith total gold production yielded approximately 8 moz with grades in the mined ore shoots varying between 7 and 15 g t au and locally reaching up to 120 g t au high grade ore shoots are extraordinarily enriched in sulfides representing 10 to 20 modal vol of the vein ore mineralogy is characterized by a complex paragenesis of pyrite arsenopyrite galena sphalerite chalcopyrite and gold gold occurs mostly as electrum in equilibrium with base metals sulfides filling fractures of pyrite and arsenopyrite a novel combination of secondary ion mass spectrometry laser ablation inductively coupled plasma mass spectrometry and electron probe microanalysis is used to track the compositional evolution of ore fluid s and to investigate the mineralization processes occurring in the pataz parcoy district contrasting with the classical two stage ore sequence previously proposed for the pataz parcoy district we suggest a revised paragenetic sequence i e 1 deposition of pyrite core pyi with homogeneously distributed base metal sulfide inclusions 2 progressive replacement of pyi by arsenian pyrite pyii and arsenopyrite associated with invisible gold deposition and 3 deposition of sphalerite galena chalcopyrite electrum in fractured pyrite and arsenopyrite we propose two models for the formation of base metal sulfide inclusions in pyi i e 1 co precipitation of base metal sulfide with pyi and later redistribution in cracks driven by partial as replacement of pyi to pyii and arsenopyrite and 2 preferential replacement of the pyi along crystallographic planes by percolation of the fluid responsible for base metal sulfide deposition in fractured pyrite and arsenopyrite

sequence architecture and heterogeneities of a field scale vaca muerta analog neuquen basin argentina from outcrop to synthetic seismic abstract the quintuco vaca muerta system in the neuquen basin argentina has received much attention due to its potential as a major unconventional play this study combines field geology with satellite imagery interpretation to document the sequence architecture of the prograding mixed carbonate siliciclastic system over several kilometers from the shelf to the basin detailed sections allow the allocation of bed scale lithofacies changes within this sequence stratigraphic framework synthetic seismograms are constructed from the observed facies distribution and petrophysical properties in order to compare this architecture with subsurface seismic data the field area the sierra de la vaca muerta shows a prograding system along a 10 km long and 1 km thick cross section the studied interval can be subdivided into eight depositional sequences based on the facies distribution representing a very similar scale as the seven sequences documented in the global sea level chart in this time interval this suggests a eustatic control on the system the depositional sequences are dominated by calcareous shale and siliciclastics but have variable amounts of carbonates admixed both temporally and laterally leading to different motifs of cyclicity and geometry shales and calcareous silt and sandstones are the dominant facies pure carbonate or pure siliciclastic portions are very rare and restricted to sequence tops carbonate rich portions are characterized by abrupt lateral facies transitions and breaks within their steep depositional profile whereas siliciclastic rich intervals show gently inclined profiles with no breaks and more gradual facies changes in the temporal scale heterogeneities occur both as cycles and events meter scale alternations of pure shale with calcareous shale are the typical cyclic expressions which occur down slope of carbonate dominated systems mixed turbidites commonly follow just after carbonate sequences triggered by the steeper depositional gradients this distribution indicates that carbonate rich intervals offer both more brittle volumes for fracturing calc shales and silty wackestones and potential relatively permeable layers turbidites within the surrounding tight shale these sweet spots follow the sequence stratigraphic framework and typically occur in close relation with tops of carbonate dominated cycles these carbonate cycles prove to be easy to detect in the synthetic seismograms due to their strong acoustic impedance and geometrical expressions these findings could offer a way to identify sweet spots for unconventional exploration in the basinal transition since they are laterally related to carbonate sequence tops which have a distinct seismic signature

origin of the wangpingxigou pb zn deposit in east qinling orogenic belt china distal response to the giant donggou porphyry mo system abstract the southern margin of the north china craton ncc hosts many world class porphyry mo and vein type pb zn ag deposits forming an important polymetallic metallogenic belt in china even over the world although the mo and pb zn ag mineralization are temporarily and spatially associated with each other their possible genetic links are still unclear to delineate the relationships between the two types of ore mineralization we carried out in situ geochemical and s pb isotopic analyses on sulfides from the two spatially associated deposits i e the wangpingxigou pb zn and donggou porphyry mo deposits in the ore district based on field and microscopic observations on the crosscutting relationships of various veins and paragenetic relationships of various hydrothermal minerals three i iii and four i iv stages of hydrothermal veins have been identified in the wangpingxigou and donggou deposits respectively pyrite grains from stage ii of the wangpingxigou deposit have high co ni ratios mostly 1 and au and as contents similar to those of typical epithermal systems moreover sulfides from this deposit have in situ 206pb 204pb 17 345 17 417 207pb 204pb 15 454 15 514 and 208pb 204pb 38 138 38 364 ratios similar to those of sulfides from the donggou deposit indicating that the two deposits were relevant to a common source the concentrations of many elements i e pb ag sn zn sb mn au and as in pyrite decrease gradually from the stage ii of the wangpingxigou deposit to the stage ii of the donggou deposit consistent with metal zonation typically observed in porphyry related metallogenic systems further considering similar ages of the two deposits we propose that the wangpingxigou pb zn deposit is likely distal to the donggou porphyry mo system the range of 34s values of pyrites 7 63 8 76 from the stage ii in the donggou deposit is similar to those of the ancient strata xiong er group 7 31 8 17 in the ore district indicating that the sulfur in ore forming fluids may be mainly derived from the ancient strata however the 34s values 9 20 9 70 of stage iii sulfides in the donggou deposit are higher than those of stage ii sulfides in the donggou deposit and stage ii sulfides in the wangpingxigou deposit 7 34 9 29 the different sulfur isotopic compositions may be related to varied physicochemical conditions of the ore forming fluids confirmation of a mo pb zn metallogenic system in the region provides important clues on further prospecting of mo and pb zn resources in the southern margin of the north china craton

geochemistry and textures of gold bearing arsenian pyrite twin creeks nevada implications for deposition of gold in carlin type deposits this study relates morphology size texture and chemistry of arsenian pyrite in the twin creeks carlin type gold deposits to the chemical position and amount of gold that it contains arsenian pyrite is confirmed as the most important gold hosting mineral and four types of gold bearing arsenian pyrite are recognized among these four types the lowest amount of gold and arsenic 1 wt as 17 60 ppm au is contained in arsenian pyrite with relatively large grain sizes 10 30 mu m it formed at relatively high temperatures 250 degrees c and k super h super ratios adularia stable probably relatively slowly the largest amount of gold and arsenic 1 05 2 43 wt as 595 1 465 ppm au is contained in arsenian pyrite with small grain sizes up to 2 mu m that formed at low temperatures 120 degrees 200 degrees c and moderate k super h super ratios illite stable probably by relatively rapid deposition xanes exafs and sims analyses show that gold in arsenian pyrite is both structurally bound au i and in submicroscopic inclusions of free gold au highest amounts of structurally bound gold were observed in the relatively coarse grained arsenian pyrite noted above whereas most inclusions of free gold were observed in fine grained arsenian pyrite in general there is a good correlation between gold and arsenic in arsenian pyrite although au as ratios vary from one pyrite to another it is suggested that gold in arsenian pyrite was deposited by direct deposition of native gold and by adsorption of au i from hydrothermal solutions adsorption of gold by arsenian pyrite can take place from solutions that are not saturated with respect to native gold relative volumes of gold bearing pyrite from different paragenetic stages at twin creeks suggest that as much as 50 percent of the total gold in the deposit could have formed from solutions that were not saturated with respect to native gold because both au and au i are found together in arsenian pyrite it is likely that they were deposited by the same process consideration of possible depositional reactions suggests that a decrease in the activity of reduced sulfur is most likely to cause gold deposition

gold remobilisation and formation of high grade ore shoots driven by dissolution reprecipitation replacement and ni substitution into auriferous arsenopyrite abstract both gold rich sulphides and ultra high grade native gold oreshoots are common but poorly understood phenomenon in orogenic type mineral systems partly because fluids in these systems are considered to have relatively low gold solubilities and are unlikely to generate high gold concentrations the world class obuasi gold deposit ghana has gold rich arsenopyrite spatially associated with quartz veins which have extremely high localised concentrations of native gold contained in microcrack networks within the quartz veins where they are folded here we examine selected samples from obuasi using a novel combination of quantitative electron backscatter diffraction analysis ion microprobe imaging synchrotron xfm mapping and geochemical modelling to investigate the origin of the unusually high gold concentrations the auriferous arsenopyrites are shown to have undergone partial replacement 15 by au poor nickeliferous arsenopyrite during localised crystal plastic deformation intragranular microfracture and metamorphism 340 460 c 2 kbars our results show the dominant replacement mechanism was pseudomorphic dissolution reprecipitation driven by small volumes of an infiltrating fluid that had relatively low s 2 and carried aqueous nicl 2 we find that arsenopyrite replacement produced strong chemical gradients at crystal fluid interfaces due to an increase in s 2 during reaction which enabled efficient removal of gold to the fluid phase and development of anomalously gold rich fluid potentially 10 ppm or more depending on sulphur concentration this process was facilitated by precipitation of ankerite which removed co 2 from the fluid increasing the relative proportion of sulphur for gold complexation and inhibited additional quartz precipitation gold re precipitation occurred over distances of 10 m to several tens of metres and was likely a result of sulphur activity reduction through precipitation of pyrite and other sulphides we suggest this late remobilisation process may be relatively common in orogenic belts containing abundant mafic ultramafic rocks which act as a source of ni and co scavenged by chloride bearing fluids both the preference of the arsenopyrite crystal structure for ni and co rather than gold and the release of sulphur during reaction can drive gold remobilisation in many deposits across broad regions

nano mineralogy and geochemistry of high grade diasporic karst type bauxite from parnassos ghiona mines greece abstract in the present work a combination of various techniques is utilized for the study of nano mineralogy and geochemistry of high grade karst type bauxite al rich and fe depleted samples al2o3 ca 80 wt from the parnassos ghiona mines located in greece initial characterization using pxrd and electron microscopy in microscale and mesoscale sem eds including stem mode proved the presence of fe cr ti containing diaspore anatase and minor rutile the study by means of 57fe mossbauer spectroscopy in correlation with magnetic susceptibility measurements and complemented with synchrotron based spectroscopies at the microscale sr micro xrf and micro xanes exafs indicated that fe3 in contrast to 6 cr3 is not exclusively a component of the diaspore structure while cr3 substitutes al3 in octahedral sites of diaspore 6 cr3 6 al3 the electron microscopy in nanoscale tem eds eels revealed that fe exists in the form of peculiar fe3 bearing nanominerals most likely maghemite type phases between 25 and 45 nm in size in addition to the fe3 ions substituting al3 in the diaspore structure moreover it was proven that tio2 polymorph mineral nanoparticles particularly rounded anatase mesocrystals and nanocrystals and individual needle shaped rutiles are dispersed into the diaspore matrix thus diaspore in the studied bauxite concerns in fact a distinct fe3 cr3 alooh low t authigenic phase demonstrated for the first time in literature on the other hand the observed tio2 mineral nanoparticles formed together with diaspore during diagenesis and fe nanominerals formed during epigenesis were hitherto unknown not only for the allochthonous karst type bauxite deposits of greece but also for the overall bauxite deposits worldwide

astronomical frequencies for pre quaternary palaeoclimate studies the sensitivity of the earth s orbital frequencies involved in the astronomical theory of palaeoclimates to the earth moon distance and consequently to the length of the day and to the dynamical ellipticity of the earth has been investigated for the last billion years the shortening of the earth moon distance and of the length of the day back in time induces a shortening of the fundamental astronomical periods for the obliquity and the precession a shortening which is larger for the longer periods these periods of precession and obliquity influenced by the changing earth moon distance length of the day and dynamical ellipticity of the earth have been recomputed for the last 440 million years

cyclostratigraphy orbital tuning and inferred productivity for the type kimmeridge clay late jurassic southern england three independently measured variables magnetic susceptibility photoelectric factor and total gamma ray obtained from throughout the type kimmeridge clay fm in dorset southern england were used to identify regular metre scale sedimentary cycles spectral analysis demonstrates that for long stratigraphical intervals the cycles are expressed as large amplitude cycles of 1 87 4 05 m wavelength and smaller amplitude cycles of around half that wavelength these cycles are interpreted to record orbital obliquity and precession respectively the much larger amplitude of the inferred obliquity cycles compared with the precession cycles may indicate a high latitude climatic forcing transferred to lower latitudes via sea level variations orbital tuning indicates that the early kimmeridgian sensu anglico lasted at least 3 6 ma 95 longer wavelength cycles and the late kimmeridgian at least 3 9 ma 103 longer wavelength cycles the first detailed productivity estimates for the kimmeridge clay fm on a cycle by cycle calculation indicate that average productivity of the type kimmeridge clay 220 g m 2 a 1 was less than the average productivity on modern continental shelves the high average organic carbon content of the type kimmeridge clay 3 8 total organic carbon cannot be attributed to high average productivity however the average organic carbon content is consistent with low siliciclastic mineral dilution of organic matter and or elevated preservation linked to reduced bottom water oxygenation

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

new evidence of magmatic fluid related phyllic alteration implications for the genesis of porphyry cu deposits the phyllic alteration in a number of circum pacific porphyry cu au deposits is related to high temperature saline magmatic fluids this contradicts the widely used genetic models wherein phyllic alteration formed as the result of mixing between magmatic and meteoric fluids at the endeavour 26 north porphyry deposit in eastern australia the transition from early potassic to the main stage phyllic alteration is associated with fluids that with time decline in total salinity nacl kcl and temperature from 600 to 550 degrees c calculated and measured delta 18 o and delta d compositions of fluids 5 1 8 5 parts per thousand 57 to 73 parts per thousand delta d confirm a primary magmatic origin for both the early potassic and main stage phyllic alteration these results are consistent with other recent studies e g el salvador chile far southeast philippines and panguna and porgera papua new guinea and suggest that rather than these results being unusual a major revision of porphyry cu genetic models is required

gold mineralization at the syenite hosted beattie gold deposit duparquet neoarchean abitibi belt canada le gisement de beattie est situe dans la ceinture de roches vertes de l abitibi a proximite de la faille porcupine destor et est associe a une syenite porphyrique les corps mineralises ont une ressource totale inferee de 2 77moz contenu dans 56 2mt de minerai a 1 53g t d or dans le gisement de beattie deux styles de mineralisation sont presents a controle lithologique et a controle structural la mineralisation a controle lithologique est limitee exclusivement a la syenite alteree en carbonates de fer cette mineralisation represente du minerai a basse teneur mais fort tonnage dans lequel l or est porte par la pyrite arsenifere et l arsenopyrite l or est invisible il se presente sous la forme de solution solide dans le c ur poreux et riche en arsenic des pyrites la mineralisation a controle structural est presente uniquement dans des zones de cisaillement adjacentes et incluses dans la syenite le minerai est a haute teneur dans des zones de breches silicifiees a caractere hydraulique et tectonique dans des veines de quartz cherteux dans des veines polymetalliques intensement silicifiees et dans des dykes de syenite trachytique tres alteree l or y est visible sous forme d electrum dans les microfractures des pyrites brechifiees les deux styles de mineralisation et les alterations font partie d une evolution paragenetique commune dans un environnement magmatique hydrothermal des phases initiales oxydantes ont evolue en conditions reduites a la faveur de fluides magmatiques et externes riches en co2 ce changement d etat d oxydation a entraine la precipitation des sulfures et la cristallisation de l or invisible dans la pyrite arsenifere et l arsenopyrite une phase d alteration ulterieure dominee par des fluides hydrothermaux riches en silice a pour resultat la brechification des sulfures et leur redistribution dans des corridors siliceux ainsi que la remobilisation de l or dans les microfractures des pyrites brechifiees les compositions calculees de 18o et d sur les veines de quartz associees a cet evenement tardif sont respectivement 7 67 o et 66 o indiquant une dominance des fluides magmatiques avec une probable composante metamorphique cet evenement syn metamorphique transition d2 d3 est associe a un fort enrichissement en hg te mo ag sb as et se le style de cristallisation de l or dans le gisement de beattie est une consequence de la dominance des regimes en systemes ouverts tant au niveau de l incorporation dans le magma de l arsenic qui controle la precipitation de l or invisible que de la circulation tardive de fluides hydrothermaux riches en silice qui sont a l origine de la remobilisation de l or le gisement de beattie partage des affinites avec des gisements associes aux intrusions intrusion related gold deposit des gisements epithermaux a tendance neutre a intermediaire et des gisements de type mesothermaux mots cles de l auteur gisement d or porphyre archeen or invisible remobilisation de l or

new constraints on the jurassic cretaceous boundary in the high andes using high precision u pb data abstract the jurassic cretaceous j k boundary is poorly constrained and is the only phanerozoic system boundary that lacks an internationally accepted reference stratigraphic section gssp precise radio isotopic u pb data are unavailable for the earliest stage of the cretaceous the berriasian the age of the jurassic cretaceous boundary was based on several assumptions including the relative duration of ammonite zones the constant spreading rates of magnetic anomalies and the extrapolation of rb sr or k ar isotopic data this paper discusses a site in an andean basin of western gondwana showing the j k boundary interval with geographically widespread nannofossil markers which are here uniquely combined with precise radiometric dates the recent finding of a sequence of marine black shales in the high andes of argentina interbedded with ash fall tuffs provides important constraints on this boundary this succession bears calcareous nannofossils and ammonites which allow correlation with well established tethyan floras and faunas in the northern hemisphere the tithonian berriasian transition in the andes was recognized on the basis of ammonite zones and nannofossil bioevents for the first time in the southern hemisphere the new ages obtained are 137 9 0 9 ma by sensitive high resolution ion microprobe shrimp and 139 55 0 09 0 18 ma by chemical abrasion isotope dilution thermal ionization mass spectrometry tims near the base of the berriasian these new ages can be interpreted in two different ways the first alternative would indicate that the present geological time table is correct and the fossil levels should be late berriasian the second alternative is that the j k boundary is 5 ma younger than the recently published geological time scale the authors support the last alternative and propose that the j k boundary should be close to 140 ma

the cyclic hierarchy of the purbeckian sierra del pozo section lower cretaceous berriasian southern spain the lowermost cretaceous berriasian sierra del pozo formation is divisible into metre scale cycles that are bundled in a four tiered hierarchy of cycles and cyclic sequences at the smallest scale sixth order cycles thought to be the product of precessionally forced sea level fluctuations c 20 ka average less than a metre in thickness shallow upward and are bounded by surfaces where deeper facies abruptly overlie shallower facies bundles of sixth order cycles called fifth order sequences are recognized by two types of asymmetric patterns in facies distribution first more pronounced facies changes occur at sixth order cycle boundaries lower in a sequence whereas smaller facies changes occur at cycle boundaries higher in a sequence secondly subtidal marine limestones i e biomicrites and biosparites are the dominant facies lower in a cyclic sequence whereas more restricted or shallower water facies i e mud cracked microbial laminites dolomites shale and clay are more predominant higher in a cyclic sequence the bundling of sixth order cycles is explained as a product of periodic change 100 ka in the eccentricity of the earth s orbit the degree of orbital eccentricity modulates the magnitude of precessional sea level fluctuations which in turn determine the relative facies contrasts at sixth order cycle boundaries larger scale fourth and third order sequences are defined by similar patterns in facies contrast at successive sequence boundaries and by a change in predominant facies type from bottom to top these patterns are explained as the product of 400 ka and 2 ma periodic variations in the eccentricity of the earth s orbit in summary the strength of the precessional signal varies in consort with periodic changes in orbital eccentricity at three time scales producing a stacked hierarchy of cycles and sequences of cycles change in obliquity of the earth s axis may modulate the effects of the precessional signal and thereby modify patterns of preserved cyclic structure this interpretation of cyclicity in the sierra del pozo section is markedly different from that of

sequence stratigraphy of a tidally dominated carbonate siliciclastic ramp the tithonian early berriasian of the southern neuquen basin argentina the tithonian berriasian vaca muerta carrin cura and picun leufu formations in the southern neuquen basin were deposited on a tidally dominated mixed carbonate siliciclastic ramp basinal outer middle shallow and back ramp facies associations are recognized and a sequence stratigraphic analysis reveals that the ramp record consists of three shallowing upwards sequences ti1 ti2 and ti3 set within a lower order progradational cycle a higher order of cyclicity is superimposed on to the middle ti2 sequence the majority of the ramp facies belong to the transgressive and highstand systems tracts however at the base of ti2 a lowstand systems tract is identified characterized by a basal unconformity and an abrupt basinward shift of the shallow marine lithofacies transgressive systems tracts were characterized by slow sedimentation rates and rapid sea level rises that affected carbonate productivity highstand systems tracts show the greatest carbonate productivity and an increased progradation rate on account of a reduction in accommodation space generation palaeogeography played a major role in the development of the depositional systems partial isolation from the pacific ocean reflecting the growth of the andean magmatic arc and geographic restriction due to tectonic inversion in the central part of the basin resulted in a meso macrotidal regime that produced a tidally dominated sedimentary record in the shallow and back ramp environments coeval anoxic conditions in the central part of the neuquen basin favoured distal ramp and basinal black shale deposition during episodes of relative sea level rise

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

sedimentology and sequence stratigraphy of a tithonian valanginian carbonate ramp vaca muerta formation a misunderstood exceptional source rock in the southern mendoza area of the neuquen basin argentina abstract the vaca muerta formation early tithonian early valanginian is a rhythmic succession of marls and limestones cropping out in the neuquen basin west central argentina this lithostratigraphic unit was traditionally interpreted as basinal to slope deposits detailed facies analysis allows to differentiate seven facies associations representing basinal to middle ramp facies of a homoclinal ramp system prograding westward from the eastern margin and slope facies attributed to a distally steepened ramp system that progrades eastward from the andean volcanic arc in the west two sequence hierarchies are recognized five third order depositional sequences and fifteen fourth order high frequency sequences fluctuations in organic matter content within the vaca muerta formation suggest relationship with depositional sequences finding the highest values associated with transgressive system tracts this work represents an important advance in the understanding of the sedimentary and stratigraphic evolution of this exceptional unconventional reservoir our sequence stratigraphic approach contributes to the understanding of the relationship between organic matter facies and sea level changes

multiple element mapping and in situ s isotopes of au carrying pyrite of shuiyindong gold deposit southwestern china using nanosims constraints on au sources ore fluids and mineralization processes abstract this study employed high sensitivity and high resolution secondary ionizing mass spectrometry nanosims to determine the distribution of au as cu se and s isotopes of pyrite from the shuiyindong au deposit southwestern china nanosims maps show that au occurs as solid solution and heterogeneously distributes at micron scale in the ore pyrite which is the overgrowth of the preexisting synsedimentary or hydrothermal pyrite core commonly rimmed again by the as and au poor outermost zone there is no detectable au in the synsedimentary pyrite invisible au was observed to fill in the submicron scale cracks of the ore pyrite meanwhile element line profile analysis shows that au occurs in three discrete climaxes in the ore pyrite in situ s isotopic analyses identified two types of s sources the synsedimentary pyrites have large negative 34s values ranging from 38 3 to 18 8 which is a typical biogenetic s generated by bacterial reduction of sea water sulfate the hydrothermal pyrites with zoned texture have a narrow 34s range of 3 5 7 4 with a median of 2 3 similar to the recently published sulfur isotope data of the southwest china s carlin type gold deposits except for the lannigou mine combining the distribution of au and s isotopes in pyrite indicates that the au carrying zones have lower 34s values than that of the ore unrelated zones these nanosims observations indicate that the au mineralization was closely associated with strong deformation of the host rock the au forming the deposit was exotic instead of the reactivated au in the preexisting pyrite formed in the synsedimentary basin the mineralization progress was multistage the distribution of au and s isotopes is hard to interpret by the viewpoint of metamorphic fluid or fluid pressure fluctuation instead it is more consistent with magmatic fluid likely contaminated by sedimentary sulfur during its ascending to the surface in addition the multistage ore formation pattern discovered in this study poses new challenges to determine the mineralization age of the au deposits in southwestern china

implications of pyrite geochemistry for gold mineralisation and remobilisation in the jiaodong gold district northeast china abstract the jiaodong gold district of eastern china the largest gold producing district in china is located on the eastern margin of the north china craton it consists of three mineralisation belts the western zhao ye belt the middle qixia belt and the eastern muping rushan muru belt over 85 of mineralisation is hosted in the zhao ye belt which is bordered by the mantle tapping tan lu fault zone pyrite crystals from three deposits in the zhao ye belt and three deposits in the muru belt were studied using a combination of optical petrography bulk pyrite geochemistry and in situ laser ablation icp ms results show that although mineralisation is broadly similar between the two belts there are significant differences in ore and gangue mineral textures pyrite geochemistry and style of gold mineralisation texturally pyrite grains from the zhao ye belt are generally cubic and do not exhibit zoning in contrast muru pyrite grains are more often pyritohedral commonly exhibit well defined concentric zoning and display textures in ore and gangue minerals indicative of open space growth bulk pyrite geochemistry suggests a distinct enrichment in pb bi au ag and te in the zhao ye belt whereas the muru belt pyrite is significantly enriched in as cu and co in situ pyrite geochemistry indicates that au and as are variably correlated in the zhao ye belt typically only exhibiting correlation at low au concentrations most gold occurs as visible electrum along pyrite fractures and grain boundaries with a minor generation of invisible gold formed through as facilitated uptake into pyrite in the muru belt au and as have a strong correlation and there is limited occurrence of gold particles indicating that most gold in the muru belt is invisible gold contained in the crystal structure of as rich pyrite the differences in style of gold mineralisation between the belts indicates an inherent difference in timing of gold introduction in the zhao ye belt the visible electrum accounting for most of the gold endowment is formed post pyrite whereas the invisible gold in the zhao ye and muru belts is formed syn pyrite the heterogeneity in gold distribution in the jiaodong district is attributed to melting of metallogenically fertile archean crust at the base of the well endowed zhao ye belt and the lack of a similarly fertile source region beneath the muru belt

an assessment of the suitability of individual rhythmic carbonate successions for astrochronological application abstract a manual is presented to assist in assessing the suitability of individual calcareous rhythmites for high resolution stratigraphic applications and orbital dating while the astrochronological approach offers an unprecedented high temporal resolution for stratigraphy caution is required to carefully choose suitable rhythmites for the analysis diagenesis is known to distort or mimic primary signals in particular in carbonate rhythmites to keep orbital dating a reliable method the choice of sedimentary successions has to be undertaken with utmost scrutiny here we review and evaluate the methods that have been used for assessing the record of primary signals in calcareous rhythmites the goal is to provide the orbital stratigrapher with tools for a straightforward and systematic assessment of such successions

the vaca muerta quintuco system tithonian valanginian in the neuquen basin argentina a view from the outcrops in the chos malal fold and thrust belt the vaca muerta quintuco system uppermost lower tithonian lower valanginian is a thick shallowing upward sedimentary cycle consisting of dark bituminous shales marlstones limestones and sandstones cropping out in the neuquen basin west central argentina this paper analyzes three outcrop sections in chos malal area northem neuquen province detailed facies analysis allows us to differentiate six facies associations representing basinal to proximal outer ramp facies of a homoclinal carbonate ramp system vaca muerta formation and basinal to shoreface facies of a mixed carbonate siliciclastic shelf system quintuco formation prograding westward from the eastern margin of the basin two sequence hierarchies were recognized 5 composite depositional sequences third order and 15 high frequency sequences fourth order fluctuations in organic matter content within the vaca muerta formation suggest a relationship with depositional sequences finding the highest values associated with transgressive systems tract whereas the transition to the quintuco formation shows a strong decrease in total organic carbon the x ray diffraction studies show an increase of clay minerals and quartz in the transgressive systems tract of the vaca muerta formation and an increase in the content of calcite in highstand systems tracts this pattern is reversed in the quintuco formation our sequence stratigraphic approach contributes to the understanding of the relationship between organic matter clay minerals facies stacking pattern and relative sea level changes in this exceptional shale oil and shale gas unconventional reservoir this study may be helpful for a better postulate of petrophysical and geomechanical models for unconventional exploration

detecting magmatic derived fluids using pyrite chemistry example of the chibougamau area abitibi subprovince quebec abstract magmatic fluids are an important carrier of precious and base metals in many mineralized systems porphyry deposits intrusion related gold systems irgs volcanogenic massive sulfides vms recognizing magmatic inputs is essential for understanding metallogenic processes and for developing accurate exploration models and the importance of fluids exsolved from magmas remains a source of much debate for some contexts such as irgs and orogenic gold deposits this study aims to identify magmatic fluids in the chibougamau area northeastern corner of the neoarchean abitibi subprovince canada using pyrite chemistry this is achieved by comparing the chemistry of pyrites recovered from the cu au magmatic hydrothermal porphyry systems of the chibougamau area to background compositions i e the chemistry of pyrites from weakly mineralized rocks from the same area analyses of quantitative laser ablation inductively coupled plasma mass spectrometry la icp ms are processed in three distinct manners to better evaluate the trace elements controlled by silicates oxides sulfides and sulfosalt inclusions and the trace elements that are structurally bound to pyrite detailed investigation of the trace element content of pyrite indicates that most elements are controlled by silicate inclusions some reflect the composition of the host rock others correlate with the mineralizing style and only te and bi are discriminant of the porphyry systems of the chibougamau area tellurium is structurally bound to pyrite or forms telluride nanoparticles in the study area while the distribution of bi is controlled by galena and chalcopyrite inclusions and pyrite chemistry is interpreted using absolute te values and bi ratios bi pb and bi cu this study provides insight into the cu au magmatic hydrothermal systems of the chibougamau area it also has implications for the way pyrite chemistry can be used to probe for magmatic fluids in other mineralized contexts

relationship between microstructures and grain scale trace element distribution in komatiite hosted magmatic sulphide ores komatiite hosted nickel sulphides from the yilgarn craton australia consist of two main sulphide phases pyrrhotite fe7s8 and pentlandite fe ni 9s8 two minor sulphide phases chalcopyrite cufes2 and pyrite fes2 and trace arsenides samples of massive sulphides from three deposits with diverse deformation and metamorphic histories the silver swan perseverance and flying fox deposits have been studied by electron backscatter diffraction and laser ablation inductively coupled plasma mass spectrometry and nano scale secondary ion mass spectrometry these ore bodies were selected to investigate the relationship between microstructures and mineral trace element chemistry in three dominant sulphide species in each deposit in all three samples pyrrhotite preserves a strong evidence of crystal plasticity relative to both pentlandite and pyrite the trace element composition of pyrrhotite shows significant variation in specific elements pb bi and ag this variation correlates spatially with intragrain pyrrhotite microstructures such as low angle and twin boundaries minor signatures of crystal plasticity in pyrite and pentlandite occur in the form of rare low angle boundaries pentlandite and mild lattice misorientation pyrite trace element compositions of pentlandite and pyrite show no correlation with microstructures variations in pyrrhotite are interpreted as a result of intragrain diffusion during the syn and post deformation history of the deposit intragrain diffusion can occur either due to bulk diffusion dislocation impurity pair diffusion or by pipe diffusion i e along fast diffusion pathways at high and low angle and twin boundaries this contribution examines three different diffusion models and suggests that dislocation impurity pair diffusion and pipe diffusion are the most likely processes behind increased trace element concentration along the microstructures in pyrrhotite the same phenomenon is observed in samples from three different deposits that experienced widely different metamorphic conditions implying that the final disposition of these elements reflects a post peak metamorphic stage of the geological history of all three deposits

origin of high grade gold ore source of ore fluid components and genesis of the meikle and neighboring carlin type deposits northern carlin trend nevada the meikle mine exploits one of the world s highest grade carlin type gold deposits with reserves of ca 220 t gold at an average grade of 24 7 g t locally gold grades exceed 400 g t several geologic events converged at meikle to create these spectacular gold grades prior to mineralization a devonian hydrothermal system altered the bootstrap limestone to fe rich dolomite subsequently the rocks were brecciated by faulting and late jurassic intrusive activity the resulting permeability focused flow of late eocene carlin type ore fluids and allowed them to react with the fe rich dolomite fluid inclusion data and mineral assemblages indicate that these fluids were hot ca 220 c of moderate salinity 2 s rich gold rich pyrite formed by dissolution of dolomite and sulfidation of its contained fe where dissolution and replacement were complete ore stage pyrite and other insoluble minerals were all that remained locally these minerals accumulated as internal sediments in dissolution cavities to form ore with gold grades 400 g t petrographic observations geochemical data and stable isotope results from the meikle mine and other deposits at the goldstrike mine place important constraints on genetic models for meikle and other carlin type gold deposits on the northern carlin trend the ore fluids were meteoric water d 135 18 o 5 that interacted with sedimentary rocks at a water rock ratio of ca 1 and temperatures of ca 220 c the absence of significant silicification suggests that there was little cooling of the ore fluids during mineralization these two observations strongly suggest that ore fluids were not derived from deep sources but instead flowed parallel to isotherms the gold was transported by h 2 s 34 s 9 which was derived from paleozoic sedimentary rocks the presence of auriferous sedimentary exhalative mineralization in the local stratigraphic sequence raises the possibility that preexisting concentrations of gold contributed to the carlin type deposits taken together our observations suggest that meteoric water evolved to become an ore fluid by shallow circulation through previously gold and sulfur enriched rocks carlin type gold deposits formed where these fluids encountered permeable reactive fe rich rocks

the late jurassic tithonian a greenhouse phase in the middle jurassic early cretaceous cool mode evidence from the cyclic adriatic platform croatia well exposed mesozoic sections of the bahama like adriatic platform along the dalmatian coast southern croatia reveal the detailed stacking patterns of cyclic facies within the rapidly subsiding late jurassic tithonian shallow platform interior over 750 m thick ca 5 6 myr duration facies within parasequences include dasyclad oncoid mudstone wackestone floatstone and skeletal peloid wackestone packstone shallow lagoon intraclast peloid packstone and grainstone shoal radial ooid grainstone hypersaline shallow subtidal intertidal shoals and ponds lime mudstone restricted lagoon fenestral carbonates and microbial laminites tidal flat parasequences in the overall transgressive lower tithonian sections are 1 4ae5 m thick and dominated by subtidal facies some of which are capped by very shallow water grainstone packstone or restricted lime mudstone laminated tidal caps become common only towards the interior of the platform parasequences in the regressive upper tithonian are dominated by peritidal facies with distinctive basal oolite units and well developed laminate caps maximum water depths of facies within parasequences estimated from stratigraphic distance of the facies to the base of the tidal flat units capping parasequences were generally 4 m and facies show strongly overlapping depth ranges suggesting facies mosaics parasequences were formed by precessional 20 kyr orbital forcing and form parasequence sets of 100 and 400 kyr eccentricity bundles parasequences are arranged in third order sequences that lack significant bounding disconformities and are evident on accommodation fischer plots of cumulative departure from average cycle thickness plotted against cycle number or stratigraphic position modelling suggests that precessional sea level changes were small several metres as were eccentricity sea level changes or precessional sea level changes modulated by eccentricity supporting a global hot greenhouse climate for the late jurassic tithonian within the overall cool mode of the middle jurassic to early cretaceous

evidence of precessional and eccentricity orbital cycles in a tithonian source rock the mid outer carbonate ramp of the vaca muerta formation northern neuquen basin argentina basin to mid ramp cyclic facies of the tithonian vaca muerta formation are exposed in the loncoche creek section of the neuquen basin mendoza province argentina this unit is characterized by a decimeter scale rhythmic alternation of marls shales and limestones and extends from the lower tithonian to the upper berriasian cyclostratigraphic studies based on a detailed facies analysis allowed the identification of cyclic patterns with frequencies within the milankovitch band according to biostratigraphic data the dominant cycle in the studied section has a period of 20 k y which correlates with the earth s axis precession element spectral analysis based on a series of compacted and decompacted cycle thickness identified a subordinate frequency of about 90 to 120 k y which we interpret as the modulation of the precessional cycle caused by the earth s orbital eccentricity the strength of the precession signal together with the absence of a well defined cyclicity attributable to the obliquity orbital cycle i e 40 k y is in agreement with previous data from the northern hemisphere

ore forming processes of the daqiao epizonal orogenic gold deposit west qinling orogen china constraints from textures trace elements and sulfur isotopes of pyrite and marcasite and raman spectroscopy of carbonaceous material

the fluid evolution of the nimbus ag zn au deposit an interplay between mantle plume and microbial activity abstract the nimbus ag zn au volcanic hosted massive sulfide vhms deposit represents an exceptional orebody in the yilgarn craton of western australia it is located in a zone of juvenile crust running n s through the eastern goldfields superterrane however unlike most other vhms occurrences associated with the 2690 2680 ma rift sequence teutonic bore jaguar bentley erayinia it is hosted by the ca 2705 ma plume related stratigraphy which is more typically associated with komatiite hosted nickel sulfide mineralization the nimbus deposit displays hybrid vhms epithermal characteristics resulting from low temperature and shallow water conditions which developed a quartz carbonate sericite dominated alteration assemblage in the dacite host rocks sulfide mineralization comprises pyrite sphalerite galena arsenopyrite ag sb pb bi sulfosalts and rare chalcopyrite in this study we applied a combination of in situ analytical techniques to monitor the evolving sulfur isotope signature of the mineralizing fluids and propose that the nimbus vhms deposit developed as a result of a bimodal fluid history in the first stage the hydrothermal system powered by plume related magmatism deposited a series of barren pyrite lenses with colloform textures their variable but consistently negative mass independent sulfur isotope fractionation signature 33s 0 81 reflects the interaction between mantle derived magmatic fluids and archean seawater the ubiquitous presence of carbon rich porous textures and the remnants of carbonaceous nests in colloform pyrite also indicate a significant contribution of microbial sulfate reducers during the incipient stages of sulfide precipitation the gradual formation of colloform lenses eventually sealed the hydrothermal system establishing a physical barrier that limited the interaction with seawater this process promoted the onset of higher temperature and pressure conditions required to form the high grade zn ag mineralization sourcing sulfur and fluids largely from a magmatic reservoir 33s 0 09 whereas the identification of a predominantly magmatic sulfur source is supported by sulfur isotope signatures the recognition of a magmatic origin of the fluid may only be inferred indirectly it is consistent with the observed quartz sericite alteration style and the proposed mechanism of sulfide deposition via decompression which does not require any interaction with seawater the trace element distribution of the ore related sulfides also supports a closed hydrothermal system developed through multiple fluid pulses indeed this ore forming scenario is commonly favored by high confining pressures which at nimbus were established following the deposition of the colloform pyrite lenses that progressively sealed the hydrothermal system creating the favorable conditions for mineralization

tectonic control on hydrocarbon generation in the northwestern neuquen basin argentina the petroleum systems of the malargue fold thrust belt in the northwestern neuquen basin argentina comprise multiple reservoir and seal rocks and three major source rocks of the lower jurassic los molles formation fm the lower tithonian to lower valanginian vaca muerta fm and the lower hauterivian to lower barremian agrio fm the thermal history of the mesozoic source rocks has been reconstructed using one dimensional and two dimensional modeling the most important factors that affected the source rock maturation are the timing of maximum late cretaceous to paleogene burial and the heat flow during back arc extension we postulate that synclines have been buried over longer periods and source rock maturation ceased earlier in anticlines accordingly hydrocarbon generation from the vaca muerta fm and agrio fm has started during the campanian despite late stage magmatic activity causing local thermal perturbations the models suggest that the thermal field has been dominated by conductive heat transport and that heat flow has been a response to the evolution from back arc extension to orogenic shortening high heat flows of 85 mw m2 during back arc extension between the latest cretaceous and paleogene have been modeled two main source pods supply hydrocarbons until the present they are related to structurally deep footwall positions of thrust faults active since the late cretaceous and to deep frontal synclines having formed through late stage thick skinned tectonics since the neogene modeling of hydrocarbon fluid type is consistent with existing oil fields exhibiting light and medium oils with api between 22 api and 39 api charged from early to peak mature source rocks

geochemical and isotopic signature of pyrite as a proxy for fluid source and evolution in the candelaria punta del cobre iron oxide copper gold district chile

uncloaking invisible gold use of nanosims to evaluate gold trace elements and sulfur isotopes in pyrite from carlin type gold deposits one hundred nm resolution secondary ionizing mass spectrometry nanosims was used to determine the distribution of au cu as sb and s and stable isotopes of s 34s 32s in gold bearing pyrite from two refractory carlin type gold deposits west banshee northern carlin trend and turquoise ridge getchell trend located in northern nevada nanosims maps reveal that gold occurs in two discrete episodes in each deposit elevated gold concentrations correlate with elevated concentrations of as sb cu te and lower 34s 32s ratios compared to periods when gold was not deposited precipitation of elevated gold and trace elements at west banshee was followed by precipitation of pyrite with lower gold concentrations whereas at turquoise ridge precipitation of trace element rich pyrite was followed by precipitation of late ore stage minerals these nanosims results are consistent with formation of the deposits by the episodic incursion of gold rich fluids into hydrothermal systems otherwise dominated by gold poor fluids such gold rich fluid pulses may be related to incursions of magmatic fluid which have been shown to have high concentrations of gold arsenic and copper in porphyry and high sulfidation epithermal systems

source of ore forming fluids of the yangshan gold field western qinling orogen china evidence from microthermometry noble gas isotopes and in situ sulfur isotopes of au carrying pyrite abstract the yangshan gold ore belt contains a series of sediment hosted disseminated gold deposits in the southern subzone of the western qinling orogen the ore deposits formed in the middle devonian carbonaceous clastic carbonate sequences that underwent strong deformation and low greenschist facies regional metamorphism the shapes and distribution of the ore bodies are strictly confined by the e w trending anchanghe guanyinba thrust fault zone pyrite and arsenopyrite are the major au carrying minerals microthermometric results show that the ore forming fluids are co2 rich aqueous solutions the homogenization temperatures range from 221 to 303 5 c and salinities range from 2 0 to 7 2 wt nacl equiv these characteristics are consistent with orogenic gold deposit noble gas isotopic measurement shows that 3he 4he ratios of pyrite and quartz grains inherited from the mineralized carbonaceous phyllite ranging from 0 033 to 0 081 ra implying that the origins of ore fluids are restricted within the crustal regime the 40ar 36ar ratios range from 434 to 863 indicating 34 to 68 crust derived radiogenic 40ar in the ore fluids based on the backscattered electron bse maps of pyrite three generations i e core mantle rim are distinguished pre ore pyrite including framboidal pyrites and the cores of zoned pyrites both in the phyllite and plagiogranite dikes ore stage pyrites including the middle zones of the three zoned pyrites in the granitic dikes and the outer zones of the zoned pyrites in the phyllite post ore pyrites i e the outermost rims of the zoned pyrites in the dikes the arsenopyrite in the phyllite has similar texture to the pyrite and is regarded as the peak of the mineralization due to its highest au concentrations high spatial resolution nanosims multi elemental maps of the pyrites reveal that i gold is distributed heterogeneously as lattice bounded au in the zoned pyrites with higher au as in the middle zones and lower au as in the inner and outermost zones no nano particles of native gold was identified in pyrite ii gold mineralization occurred in a single event instead of multistage ore formation iii gold precipitation event is followed by an overgrown zone with low au and as concentrations in situ sulfur isotopes of au bearing pyrite identified two types of sulfur sources one is framboidal pyrite and the barren core of pyrite in the carbonaceous phyllite which have very negative 34s values combining au concentrations with the corresponding 34s values in the pyrites reveals that the zones with high au have lower 34s values and vice versa this coupling relation between au and s isotope has been also identified in other orogenic and carlin type gold deposits the oxidation of ore fluid is taken as the key for gold precipitation during formation of orogenic gold deposit however the oxidation of ore fluids accompanied by the escape of reduced gas e g h2s should result in high au coupled with high 34s therefore we propose that the yangshan gold deposit forms through partitioning aqueous vapor with high au as and lower 34s from a deep magma chamber under the ore field which leads to overgrowth of the pre existing pyrites based on the geological features texture of pyrite and sulfur isotopic characteristics we suggested that the yangshan gold deposits have the characteristics between carlin type and orogenic gold deposits they are the product of the western qinling orogeny during the late triassic

genesis and evolution of framboidal pyrite and its implications for the ore forming process of carlin style gold deposits southwestern china abstract southwestern guizhou an indispensable component of the golden triangle area of southwestern china is famous for its numerous carlin style gold deposits unlike other sulfides in the deposits that have been well studied the genesis of framboidal pyrite is still controversial because of its tiny size here we first determined the chemical and in situ sulfur isotopic compositions of framboidal pyrites from three typical carlin style gold deposits namely shuiyindong taipingdong and nibao using secondary electron image sei back scattered electron bse electron probe micro analysis epma and nanometer scale secondary ion mass spectroscopy nano sims methods our epma data show that the framboidal pyrites contain a minor amount of trace elements ni

trace fossil model for reconstruction of paleo oxygenation in bottom waters recognition of fluctuations in the degree of paleo oxygenation of bottom waters recorded in fine grained pelagic strata is important for interpretation of paleoceanographic and paleoclimatologic conditions general sedimentary fabric composition of trace fossil assemblages and burrow size and crosscutting relationships have been incorporated into a trace fossil tiering model that permits detailed reconstruction of changes in paleo oxygenation of bottom waters applications of this model to the miocene monterey formation california and the cretaceous niobrara formation colorado indicate that the ichnologic approach is more sensitive to both magnitude and rates of change in oxygenation levels compared to macrobenthic body fossil information

evolution of porosity and pore types in organic rich calcareous lower toarcian posidonia shale low and high resolution petrographic studies have been combined with mineralogical toc rockeval and porosity data to investigate controls on the evolution of porosity in stratigraphically equivalent immature oil window and gas window samples from the lower toarcian posidonia shale formation a series of 26 samples from three boreholes wickensen harderode and haddessen in the hils syncline was investigated the main primary components of the shales are microfossiferous calcite 30 50 clay minerals 20 30 and type ii organic matter toc 7 15 hi 630 720 mg gc in immature samples characteristic sub centimetric light and dark lamination reflects rapid changes in the relative supply of these components total porosities decrease from 10 to 14 at ro 0 5 to 3 5 at ro 0 9 and then increase to 9 12 at ro 1 45 these maturity related porosity changes can be explained by a the primary composition of the shales b carbonate diagenesis c compaction and d the maturation micro migration local trapping and gasification of heterogeneous organic phases calcite undergoes dissolution and reprecipitation reactions throughout the maturation sequence pores quantifiable in sem ca 50 nm account for 14 25 of total porosity at ro 0 5 sem visible macropores1 are associated mainly with biogenic calcite at this maturity clays and organic matter are not visibly porous but nevertheless hold most of the shale porosity porosity loss into the oil window reflects a compaction b carbonate cementation and c perhaps the swelling of kerogen by retained oil in addition porosity is occluded by a range of bituminous phases especially in microfossil macropores and microfractures in the gas window mineral hosted porosity is still the primary form of macroporosity most commonly observed at the organic inorganic interface increasing porosity into the gas window also coincides with the formation of isolated spongy and complex meso and macropores within organic particles related to thermal cracking and gas generation this intraorganic porosity is highly heterogeneous point counted macroporosity of individual organic particles ranges from 0 to 40 with 65 of organic particles containing no macropores we suggest that this reflects the physicochemical heterogeneity of the organic phases plus the variable mechanical protection afforded by the mineral matrix to allow macroporosity to be retained the development of organic macroporosity cannot alone account for the porosity increase observed from oil to gas window major contributions also come from the increased volume of organic micro and meso porosity and perhaps by kerogen shrinkage

evaluation of the role of sulfidation in deposition of gold screamer section of the betze post carlin type deposit nevada this study was undertaken to evaluate the relation between sulfidation and gold deposition in the screamer section of the betze post carlin type deposit we also attempted to determine the source of sulfur in the deposit and the possibility that more than one gold depositing event contributed metal to the screamer system gold ore at screamer forms a generally stratiform body hosted largely by the wispy member of the devonian popovich formation and lacks obvious alteration of wall rock gangue minerals gold at screamer is hosted by arsenian pyrite that forms disseminated grains and overgrowths on diagenetic pyrite a strong correlation is observed between the gold content of rock samples and their proportion of ore related arsenian pyrite as determined by point counts isocon plots show that mineralization at screamer involved addition of both sulfur and iron along with gold arsenic antimony tungsten and local silica barium and phosphorus fe al vs s al plots show that most ore samples at screamer do not contain enough sulfur to account for all of their iron as pyrite petrographic examination shows that the iron occurs in pyrite ferroan dolomite and iron bearing micas in order of decreasing abundance the fe al vs s al plots also show that screamer samples with high gold contents contain more pyrite than samples with low gold contents and that samples inside the ore zone have more pyrite than those in the surrounding area these relations are interpreted to indicate that screamer has undergone at least two pyrite forming events the first event which probably took place during diagenesis involved incomplete sulfidation that left some iron in carbonate and silicate minerals the second event which probably took place during gold mineralization sulfidized most remaining iron and added pyrite in the screamer ore zone the 34 s values of chemically extracted sulfur from disseminated pyrite at screamer range from 13 8 to 16 5 per mil and 34 s values for hand picked separates of pyrite and other sulfides in veins cutting these rocks range from 21 2 to 11 7 per mil a significant fraction of samples with high gold contents and of samples in the ore zone regardless of gold content have 34 s values between 1 and 5 per mil these data suggest that early diagenetic sulfur with a wide range of 34 s values was overprinted by sulfur with isotopic compositions in the 1 to 5 per mil range that was associated with gold mineralization the 34 s values for gold related sulfur at screamer are lower than those reported for bulk mineral separates from most other carlin type deposits and from sims analyses of sulfides from the proximal post part of the betze post system and could be magmatic limited evidence can be found for multiple gold forming events in the screamer zone tungsten which might have been introduced by the jurassic age goldstrike stock is widespread in the deposit and correlates closely with gold a few samples with high tungsten gold ratios found along fault zones might be part of an earlier phase of mineralization related to the goldstrike stock a 34 s value for pyrite in one of these samples is similar to the high values reported for sulfides in auriferous polymetallic mineralization in the post section of the deposit but this mineralization is not reported to contain tungsten other veins containing sphalerite have lower 34 s values and lack consistent gold values whereas there is no correlation between gold values and the degree to which the host rocks have undergone sulfidation there is a strong and highly significant correlation between gold values and the abundance of ore related pyrite this shows that simple sulfidation of immediately adjacent wall rock cannot account alone for gold deposition at screamer and it might not be the only ore depositing process in some other carlin deposits a more general extended sulfidation process could be important however one likely process involves mixing of an invading mineralizing fluid containing sulfur and gold with a wall rock fluid containing iron derived from adjacent or distal wall rocks recognition of the source s for this iron and fluid flow pathways responsible for introducing it to the ore zone could provide useful guidance in exploration for the next carlin trend

cyclostratigraphy of an orbitally driven tithonian valanginian carbonate ramp succession southern mendoza argentina implications for the jurassic cretaceous boundary in the neuquen basin we conducted detailed sedimentological sequence stratigraphic and cyclostratigraphic analyses on four sections of the vaca muerta formation this unit is characterized by a decimetre scale rhythmic alternation of marls and limestones it consists of five facies associations which represent basin to middle carbonate ramp deposits the rhythmic vertical organization shows a well ordered hierarchy of cycles where elementary cycles bundles of cycles and superbundles within the milankovitch frequency band are recognized cyclostratigraphic data allowed us to build a floating orbital scale for the lower tithonian lower valanginian interval in the neuquen basin orbital calibration of these sections is consistent with riccardi s biostratigraphic scheme which places the jurassic cretaceous boundary within the substeueroceras koeneni ammonite zone equivalent to durangites spp jacobi grandis and initial occitanica standard zones

cenomanian sequence stratigraphy and sea level fluctuations in the tarfaya basin sw morocco we investigated the sequence architecture of two expanded cenomanian successions along a depth transect in the tarfaya basin sw morocco and correlated these successions to published records from northwest europe and india changes in terrigenous material carbonate and organic carbon content carbonate microfacies and foraminiferal biofacies as well as nondepositional and erosional surfaces were used to define depositional sequences and systems tracts we identified two main transgressive cycles in the lower and middle upper cenomanian separated by a major regression at the early middle cenomanian transition sequence boundary ce 3 this regressive interval is characterized by lagoonal low stand deposits indicating an overall sealevel fall of more than 30 m superimposed on the two main transgressive cycles there are 11 third order depositional sequences that correlate to globally recognized sealevel fluctuations and appear to be paced by long eccentricity variations 400 ka period positive carbon isotope excursions in the middle cenomanian 96 0 ma and latest cenomanian 94 0 ma following sealevel lowstands together with planktonic foraminiferal and ammonite datums provide a robust framework for stratigraphic correlation we suggest that the onset of these excursions was triggered by eccentricity minima during periods of low variability in obliquity nodes which probably coincided with glacioeustatic lowstands

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

timing of gold and arsenic sulfide mineral deposition at the getchell carlin type gold deposit north central nevada pregold mineralization at the getchell carlin type gold deposit includes quartz and base metal vein mineralization associated with intrusion of a cretaceous granodiorite stock the veins contain minor pyrite and trace chalcopyrite arsenopyrite galena and sphalerite the pyrite is moderately coarse and in thin section has high relief is well polished and is fractured and locally cemented by the gold ore assemblage white micas are associated with veins near the granodiorite intrusion gold was not observed or detected by fire assay analyses of samples or electron microprobe analyses of pyrites microprobe analyses show that pregold pyrites have near stoichiometric compositions variable low arsenic is present in pyrite in samples overprinted by gold mineralization secondary ion mass spectrometry sims analyses detected trace gold in the coarse near stoichiometric pyrite in overprinted samples the pregold vein assemblage was fractured and cemented by gold ore stage mineralization the gold ore stage assemblage consists of gold and arsenic enriched pyrite and marcasite encompassed by jasperoid and drusy quartz and local late fluorite orpiment and galkhaite the consistent spatial association of jasperoid and ore pyrite reflects their near contemporaneous formation the ore pyrite occurs as either fine irregularly shaped grains or rims on earlier gold free pyrite in thin section the pyrite is visibly distinct and has a low polishing relief and a poor polish sims and electron microprobe analyses show that ore pyrites commonly contain 8 to 11 wt percent arsenic and as much as 2 400 ppm gold near the end of the ore stage fluorite orpiment and galkhaite precipitated locally in open space created by faulting or limestone dissolution late ore stage mineralization consists dominantly of open space filling realgar and calcite with minor quartz stibnite and framboidal pyrite realgar conforms to euhedral crystal faces of ore stage quartz fluorite and galkhaite calcite filled most remaining open space and conforms to euhedral crystal faces of quartz fluorite and realgar significant textural observations argue against an earlier interpretation that the gold mineralization and arsenic minerals formed as two discrete events separated by 40 m y in a few areas where calcite and realgar are in contact with ore stage quartz containing gold bearing pyrite realgar and calcite enclose gold bearing pyrite grains massive realgar and calcite distal from these contacts do not contain the gold bearing pyrite the presence of ore pyrite in realgar calcite and jasperoid requires close timing of these minerals and shows that there is no major time break separating ore stage and late ore stage mineral deposition textures indicate instead that the ore stage and late ore stage formed as part of a single evolving hydrothermal system the consistent successive overgrowth of younger minerals on perfectly preserved euhedral faces of older minerals supports the continuous evolution of the gold ore stage into the late ore stage these results are consistent with fluid inclusions that indicate that paragenetically successive minerals precipitated from an aqueous ore fluid with consistent salinity and gas contents but at declining temperatures results show that within error the 34 39 and 42 ma ages determined for fluorite and galkhaite at getchell and adularia at the nearby twin creeks mine respectively most closely approximate the timing of gold deposition at getchell

sulfur isotope and trace element systematics of zoned pyrite crystals from the el indio au cu ag deposit chile we present a comparative study between early massive pyrite preceding cu ag sulfosalt mineralization in high temperature feeder zones early pyrite and late pyrite that formed during silicic alteration associated with au deposition late pyrite at the el indio high sulfidation au ag cu deposit chile we use coupled in situ sulfur isotope and trace element analyses to chronologically assess geochemical variations across growth zones in these pyrite crystals early pyrite that formed in high temperature feeder zones shows intricate oscillatory zonation of cu with individual laminae containing up to 1 15 wt cu and trace co as bi ni zn se ag sb te au pb and bi late pyrite formed after cu ag sulfosalt mineralization it contains up to 1 14 wt as with trace cu zn pb v mn co ni ge se ag sb te pb and bi as well as colloform cu rich growth bands containing vugs toward the outer edges of some crystals plotting the trace element data in chronological order i e from core to rim revealed that co and ni were the only elements to consistently co vary across growth zones other trace elements were coupled in specific growth zones but did not consistently co vary across any individual crystal the 34s of early pyrite crystals in high temperature feeder zones range from 3 19 to 1 88 0 5 consistent with sublimation directly from a high temperature magmatic vapor phase late pyrite crystals are distinctly more enriched in 34s than early pyrite 34s 0 05 4 77 0 5 as a consequence of deposition from a liquid phase at lower temperatures it is unclear whether the late pyrite was deposited from a small volume of liquid condensate or a larger volume of hydrothermal fluid both types of pyrite exhibit intracrystalline 34s variation with a range of up to 3 31 recorded in an early pyrite crystal and up to 4 48 in a late pyrite crystal variations in 34spyrite at el indio did not correspond with changes in trace element geochemistry the lack of correlation between trace elements and 34s as well as the abundance of microscale mineral inclusions and vugs in el indio pyrite indicate that the trace element content of pyrite at el indio is largely controlled by nanoscale syn depositional mineral inclusions co and ni were the only elements partitioned within the crystal structure of pyrite cu rich oscillatory zones in early pyrite likely formed by nanoscale inclusions of cu rich sulfosalts or chalcopyrite evidence of deposition from a fluid cyclically saturated in ore metals this process may be restricted to polymetallic high sulfidation like deposits

data for distinguishing generations of quartz and a distinct gas signature of deep high grade carlin type gold mineralization using quadrupole mass spectrometry abstract carlin type gold deposits in north central nevada occur in a region that was the locus of igneous and or hydrothermal activity over time and the overprinting of silicification associated with metamorphism base metal mineralization barren jasperoid and post ore alteration hinders exploration efforts therefore the potential to distinguish unrelated generations of quartz using the results of quadrupole mass spectrometer qms gas analyses was evaluated for the getchell trend and compared to results from the goldstrike property in the carlin trend and a carlin type gold occurrence in the huijiabao trend china the results of fluid inclusion petrography qms analyses and interpretation of gas data using n 2 ar he ternary diagrams and co 2 ch 4 vs n 2 ar plots indicate that different generations of quartz in the getchell trend were deposited by hydrothermal fluids having distinct characteristics metamorphic quartz containing one phase ch 4 and halite bearing liquid water dominant vapor poor inclusions has the highest gas content 37 6 mol and highest n 2 ar values 3250 which are suggestive of an evolved magmatic fluid pre ore and quartz base metal veins contain co 2 bearing inclusions base metal veins have n 2 ar values 675 and a positive correlation between h 2 s ar vs n 2 ar that is suggestive of a magmatic fluid carlin type quartz contains liquid dominant vapor poor inclusions and is characterized by total gas contents 10 mol and n 2 ar values 300 that are suggestive of mixed crustal meteoric magmatic fluid sources post ore quartz and barren jasperoid formed from mixtures of gas poor meteoric water and crustal fluids samples of deep high grade mineralization from the goldstrike property have total gas contents up to 10 5 mol and n 2 ar values 300 fluid sources include crustal meteoric and magmatic gas data from the goldstrike property turquoise ridge deposit and metamorphic quartz of the getchell trend plot near the n 2 apex of n 2 ar he diagrams which is indicative of a magmatic fluid end member carlin type mineralization in the huijiabao trend is unique because fluids were ch 4 rich and there is a correlation between ch 4 and hydrocarbons gas analyses commonly record 2 is the dominant gas specie together the results show that fluid inclusion gases can be used to distinguish different generations of quartz in mining districts with complex origins

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

genesis of the bangbu gold deposit in the southern tibet evidenced from in situ sulfur isotopes and trace element compositions of pyrite abstract the bangbu orogenic gold deposit in the north himalaya of the southern tibet contains more than 40 t au at an average grade of 7 0 g t in this deposits gold bearing quartz veins were controlled by nearly e trending qusong cuogu zhemulang shear zone and occurred within the secondary faults which crosscut late triassic greenschist facies rocks to further understand the sulfur source and ore forming process we have conducted a compressive study of in situ sims sulfur isotopes and la icp ms trace element compositions of two stages of pyrite at bangbu early stage pyrite py1 is coarse grained mostly 0 2 2 mm and euhedral and has gold concentrations of less than 0 3 54 ppm mean of 20 ppm and 34s values of 1 6 5 1 mean of 3 2 late stage pyrite py2 is generally fine grained mostly

sequence stratigraphy and bedding rhythms of an outer ramp limestone succession late kimmeridgian northeast spain facies stratal and spectral analyses of an outer ramp lime mudstone succession aguilon north iberian ranges spain are presented in this work the studied succession is late kimmeridgian eudoxus and beckeri zones in age and comprises the transgressive and highstand deposits of a third order depositional sequence a number of higher order sequences bundles and sets of bundles have been identified based on the comparative analysis of the bedding planes the bundles and sets of bundles show a well defined stratal pattern spectral analysis has provided further independent confirmation of the cyclical nature of the bundles and sets of bundles defined from field analysis the bundles have variable thickness from 1 to 2 m and are formed by up to 10 micritic beds they have been related to sea level changes controlled by the orbital precession cycle affecting the shallow productivity area a significant amount of the lime mudstones accumulated in outer ramp settings were derived from resedimentation of the shallow carbonate production areas many of the bundles show a lower interval with a thinning and fining up trend indicating a progressive decrease of the carbonate production and carbonate export during periods of high frequency sea level rise the late transgressive and highstand deposits show sets of bundles groups of five bundles from 5 to 8 m probably related to sea level changes controlled by the short eccentricity cycle the overall thickness and the stacking pattern observed in the sets of bundles are controlled by the long term sea level variation the sets of bundles located in the late transgressive deposits show thinner micritic beds in their lower or middle part the sets of bundles found in the highstand deposits are thinner and show a thickening up and thinning up trend on the studied carbonate ramp during periods of long term sea level rise the overall carbonate production and carbonate export is high although the superposition of the high frequency sea level rises may result in episodic flooding and drowning of the shallow ramp areas during periods of long term early highstand of sea level the overall carbonate production and carbonate export is more reduced but it has maximum peaks during the transgressive and early highstand intervals of the high frequency sea level cycles sedimentation during the long term sea level fall late highstand was scarce and discontinuous in the outer ramp area and resulted in the overall thickness reduction of the sets of bundles d 2003 elsevier science b v all rights reserved

muscovite 40ar 39ar and in situ sulfur isotope analyses of the slate hosted gutaishan au sb deposit south china implications for possible late triassic magmatic hydrothermal mineralization abstract the gutaishan deposit is a slate hosted au sb deposit in the xiangzhong metallogenic province south china the deposit has proven reserves of ca 9 tonnes t of gold with an average grade of 13 g t and 2 500 t of sb with an average grade of 10 in this study muscovite 40ar 39ar and in situ sulfur isotope analyses of pyrite and arsenopyrite were performed to determine the mineralization age and the plausible source of s and au the 40ar 39 ar dating result of muscovite limits the formation age of the gutaishan deposit to ca 223 6 5 3 ma coeval with the adjacent baimashan granite 223 204 ma the in situ 34 s values of pyrite and arsenopyrite coexisting with native gold lie in a range between 3 7 and 2 1 with a mean value of 0 8 and these values are markedly different from those of sedimentary pyrite 7 0 to 23 3 indicating a contribution from magmatic sulfur a magma derived genetic model may therefore be suitable for the gutaishan deposit integrating the available ages of the au sb and sb au deposits and granites in the xiangzhong metallogenic province we propose that a widespread late triassic magmatic hydrothermal au sb mineralization event occurred

organic petrography and pore structure characterization of low mature and gas mature marine organic rich mudstones insights into porosity controls in gas shale systems analyses of both type ii organic rich low mature mudstones from the kimmeridge clay formation yorkshire england and gas mature mudstones from the vaca muerta formation argentina were performed using petrographic and sem observations to characterize the organic and inorganic components of the rocks and their relationship with porosity the porosity analyses using nitrogen adsorption measurements and mercury intrusion porosimetry were then evaluated as a function of both composition and thermal maturity despite the absence of variation in the pore size distribution and the total pore volume with maturity which is controlled by total organic carbon content toc this study demonstrates that the pore network of these marine mudstones varies considerably with thermal maturity contrary to low mature samples whose porosity depends essentially on mineral interparticle pores the porosity of thermally mature rocks is mainly influenced by organic matter hosted pores located within secondary solid bitumen organic matter om porosity which is rare in the low mature stage appears to increase during thermal maturation in response to the thermal cracking of kerogen and oil to become predominant in gas mature rocks it can therefore be considered that thermal maturation is a major process for the development of the om porosity however the om of high toc 5 5 wt gas mature samples contains smaller pores than gas mature low toc mudstones probably due to a difference in the original om composition between these high and low toc samples by analogy with the kimmeridge clay formation which is often considered as time equivalent in terms of om composition uliana et al 1999 the high toc vaca muerta samples appear to have originally contained greater proportions of oil prone amorphous om and thus a better om intrinsic quality for oil generation this difference of om composition and petroleum potential between vaca muerta marine mudstones appears to have dramatically influenced the om hosted pore genesis during maturation consistent with other studies these results show that thermal maturity is not the only process that can explain om hosted pore genesis in gas shale systems the om composition can greatly influence the evolution of this porosity during maturation organic composition and om thermal maturity may therefore have a complementary effect explaining the diversity of trends observed on porosity in natural formations

cyclostratigraphy and the early jurassic timescale data from the belemnite marls dorset southern england time series based on determinations wt of calcium carbonate and total organic carbon have been generated for the entire lower jurassic hemipelagic belemnite marls dorset southern britain this formation was deposited during early pliensbachian time at a paleolatitude of about 35 n in an epicontinental sea that was largely enclosed by the supercontinent of pangea the sequence contains compositionally diverse light and dark marl bedding couplets the thicknesses of which are notably reduced in the upper third of the section the regularity of the couplets in segments of the sequence combined with a regular amplitude modulation indicates an origin that is related to the orbital precession cycle i e one of the milankovitch parameters a timescale is developed by assigning a duration of 20 k y per couplet and this suggests that the entire formation represents at least 1 78 m y using the new timescale bundles of bedding couplets are shown to have periods consistent with the 123 k y component of the orbital eccentricity variations the amplitude of the couplets varies at the same frequencies as the bundle cycles in accordance with the interpretation that the couplets record precession and the bundles record eccentricity however despite having the same frequency of variation there is no consistent relationship coherence between the variations in amplitude of the couplet cycle and the bundle cycles as would be predicted by the eccentricity precession relationship this mismatch can be explained in terms of nonlinear behavior of a climatic system characterized by a varying response time or nonlinear response of the sedimentary system itself the data contain no evidence for orbital obliquity cycles because the obliquity cycle affects insolation principally at high latitudes the climatic factors that indirectly controlled the sedimentary cyclicity must have arisen at relatively low latitudes the belemnite marls timescale indicates highly variable minimum durations for ammonite zones and subzones true durations cannot be determined because it is possible that the succession is incomplete as a result of undetected erosion and or nondeposition a combination of the new results with cyclostratigraphic data from yorkshire northeast england and the southern alps switzerland indicates based on cycle counts that the pliensbachian stage lasted at least 4 82 m y marine sr isotope ratios appear to have decreased linearly from the start of jurassic time until the end of pliensbachian time the rate of decrease in 87 sr 86 sr established using the belemnite marls timescale was 0 000042 m y or less if the main part of the formation is incomplete using this rate with the observed changes in sr isotope ratios gives minimum durations of 2 86 m y for hettangian time 7 62 m y for sinemurian time and 6 67 m y for pliensbachian time

new insights into the genesis of iocg deposits from a case study of the yinachang deposit in sw china abstract the yinachang fe cu au u ree deposit is hosted by the lower part of the paleoproterozoic kunyang group in the central yunnan province of sw china in an area known to contain iron oxide cu au mineralisation the deposit includes i the sulphide assemblage chalcopyrite pyrite magnetite cobaltite molybdenite cassiterite ii rare earth element assemblage bastnaesite parasite fergusonite xenotime monazite iii the uranyl hydroxide mineral vandendriesscheite iv gold commonly hosted by ankerite and v the gangue mineral assemblage apatite biotite fluorspar quartz calcite the ore is commonly massive disseminated banded or in calcite veins the banded mineralisation contains high concentration of au co mo u fe cu and ree and the vein type mineralisation has abundant ree minerals of bastnaesite parisite fergusonite and xenotime monazite exists as inclusions in apatite or as discrete grains on the surface of magnetite and the uranium is associated with chalcopyrite the mineralising process can be divided into an initial na alteration followed by the ore forming assemblages of fe ree and cu au u ree mineralisation the average 18oh2o values in the quartz and calcite change are between 3 5 and 10 7 with dv smow values ranging between 98 2 and 47 7 the calcite siderite and ankerite have 13c isotope composition ranges from 14 to 1 and 18o compositions of 6 9 to 22 the h o c isotope systematics indicate that the mineralising fluids have mixed magmatic and metamorphic sources whereas the carbon is sourced from marine carbonate and the low temperature alternation of polyphase mantle material in situ 34s sulphide value ranges between 1 1 and 11 9 and the bulk 34s value ranges between 4 7 and 10 5 in situ pb isotopes of sulphide samples have 206pb 204pb values of 18 58 18 76 207pb 204pb values of 15 51 15 66 and 208pb 204pb values of 37 47 38 06 these values plot in the upper crust pb evolution curve indicative of a complex source of pb in the deposit the pb is interpreted to have a deep seated magmatic source with a contribution from the crust it is also proposed that the ree mineralised fluids are derived from a late stage of alkaline magma differentiation the 40ar 39ar biotite date indicates that the precambrian rocks in the kangdian region were regionally metamorphosed at ca 900 ma the yinachang fe cu au u ree deposit is interpreted as an iocg deposit based on geological and isotopic studies the banded ore and vein type ore are the main exploration targets for uranium gold and ree this study helps us better understand iocg deposits in china

sulfur isotope and trace element compositions of pyrite determined by nanosims and la icp ms new constraints on the genesis of the shuiyindong carlin like gold deposit in sw china the shuiyindong carlin like gold deposit the largest one of this type in china is located in the late paleozoic early mesozoic youjiang basin the pyrites in the studied ore bodies no i to v can be divided into four main types plus several sub types 1 as poor pyrites include py1 py1a and py1b py2 and py3 and 2 as rich pyrite py4 py4a and py4b in situ la icp ms analyses show that the as rich pyrite also contains higher au cu sb and tl than the other pyrite types in situ nanosims analyses show the 34s variation of py1 48 1 67 5 py2 2 4 7 6 py3 9 2 14 2 and py4 3 0 6 6 with the average values of 58 1 5 1 11 4 and 3 1 respectively the large 34s variations of as poor pyrites may reflect a sedimentary source however the narrow ranges of 34s values for the as rich pyrite py4 may not reflect a sedimentary but a magmatic or metamorphic origin a metamorphic sulfur source of py4 is favored due to paucity of coeval magmatism in the region and decreasing variations of 34s values from py1 to py4 integrated transmission electron microscope tem and nanosims element mapping show that the distribution and concentration of au are discordant with as and cu at the submicron scale also implied by the occurrence of some of au as nano submicron particles in py4 overall our new data indicate that the ore fluids were not only enriched in au but also in as cu and s taking an alternative of fluid oxidation probably resulting in the decreasing 34s values of py4 our result of i to v orebodies indicates the mixing between the underlying metamorphic fluid and meteoric water integrated variations in 34s and as au cu correlations across individual pyrite grains infer the physicochemical changes of aqueous and or aqueous carbonic fluids along migration paths