geology u pb geochronology and stable isotope geochemistry of the tunca semi massive sulfide mineralization black sea region ne turkey implications for ore genesis abstract upper cretaceous volcano sedimentary sequences of the eastern pontide orogenic belt ne turkey are host to significant vms mineralization including near tunca the initial stages of felsic volcanism within the mineralized area are marked by the eruption of dacitic lavas and breccias of the kizilkaya formation this was accompanied by the emplacement of domelike hematitic dacites autobrecciated and volcaniclastic rocks both in situ and resedimented were likely generated from extrusive portions of these dacite bodies basaltic volcanism is marked by the eruption of the lava flows and pillow lavas of the caglayan formation hiatuses in basaltic activity are marked by thin horizons of volcaniclastics and mudstones the uppermost felsic volcanic units were accompanied by resedimentation of autoclastic facies from previous volcanism and represent the latest phase of upper cretaceous volcanism in the area the semi massive sulfide mineralization is associated with a late stage of the initial felsic volcanism u pb la icp ms zircon dating of a dacitic tuff breccia yielded an age of 88 1 1 2 ma coniacian upper cretaceous which is interpreted to be the age of the sulfide occurrences a concentric zoned alteration pattern is observed in the footwall rocks the alteration pattern is considered to have formed by lateral migration of hydrothermal fluids which had ascended along the discharge conduit fluid inclusion data indicate precipitation or mobilization processes within a relatively narrow temperature range of 152 255 c avg 200 c the low salinity fluids in the fluid inclusions less than 5 9 wt nacl equivalent are consistent with typical modified seawater dominant hydrothermal vent fluids sulfur isotope analysis of the tunca sulfides yields a narrow range of 1 5 4 1 per mil these 34 s values are also typical of many vms deposits most of the recorded 18 o values 7 1 to 14 0 per mil are greater than 9 per mil the most intensely hydrothermally altered rocks tend to have lower 18 o values relative to the less altered rocks collectively the geologic relationships mineralization style and the lack of seafloor ore facies suggest that mineralization is principally of sub seafloor origin the most geologically reasonable interpretation of the genesis of the tunca mineralization is the continuous interaction between the host rocks and seawater derived fluids without significant involvement of a magmatic fluid

change in climate ocean and ice sheet conditions in the ross embayment antarctica at 6 ka evidence from the ross embayment antarctica suggests an abrupt cooling and a concomitant increase in sea ice cover at about 6000 sp 6 ka stable isotope delta d concentrations in the taylor dome ice core at the western edge of the ross embayment decline rapidly after 6 ka and continue to decline through the late holocene methanesulfonic acid concentrations at taylor dome show opposite trends to delta d sediment cores from the western ross sea show a percentage minimum for the sea ice diatom fragilariopsis curta between 9 and 6 ka when taylor dome delta d values are highest followed by an increase through the late holocene radiocarbon dates from raised beach deposits indicate that the retreat of ice shelves in the ross embayment ceased atabout 6 ka coincident with the environmental changes inferred from the sediment and ice core records the similarity in timing suggests an important role for climate in controlling the evolution of ice shelf margins following the end of the last 9 glaciation

timing of millennial scale climate change at siple dome west antarctica during the last glacial period using atmospheric methane and the isotopic composition of o2 as correlation tools we place the dd record of ice from the siple dome west antarctica ice core on a precise common chronology with the gisp2 greenland ice core for the period from 9 to 57 ka the onset of major millennial warming events in siple dome preceded major abrupt warmings in greenland and the pattern of millennial change at siple dome was broadly similar though not identical to that previously observed for the byrd ice core also in west antarctica the addition of siple dome to the database of well dated antarctic paleoclimate records supports the case for a coherent regional pattern of millennial scale climate change in antarctica during much of the last ice age and glacial interglacial transition

orebody geometry fluid and metal sources of the omitiomire cu deposit in the ekuja dome of the damara belt in namibia the omitiomire cu deposit resource of 137 mt at 0 54 cu in the ekuja dome of the damara belt in namibia is hosted by an anastomosing low angle pan african ca 520 ma shear zone system developed around an older ca 1100 1060 ma late mesoproterozoic intrusive breccia between a suite of mafic rocks originally lava flows and later tonalitic gneisses high grade ore shoots preferentially formed along contacts between tectonically interleaved biotite epidote quartz chalcocite schists and felsic gneisses and are directly related to an increase in the number and cumulative thickness of thin contact parallel mineralized shear zones alteration and mineralization are associated with elevated concentrations of k2o cr rb s and cu and a loss of na2o cao and mgo oxygen isotope fractionation for quartz biotite quartz feldspar and quartz amphibole mineral pairs support equilibrium temperatures of between 500 and 650 c during the fluid rock interaction mineral separates from amphibole biotite gneisses and mineralized schists have similar ranges in 18o values of about 1 2 to 2 relative to vsmow coexisting minerals are arranged in an order of increasing 18o values from biotite to epidote amphibole and quartz suggesting that the omitiomire shear zone was a rock dominated system similarly h isotope results for mineral separates from biotite epidote schists and amphibole gneisses do not show any reversals for d h fractionations with d values of between 48 and 82 typical of metamorphic magmatic rocks the homogeneous and low 34s values 6 1 to 4 7 cdt are compatible with a local redistribution of sulfur from magmatic rocks and interaction with sulfur derived from metamorphic fluids of metasedimentary origin the relatively low fluid rock ratios and elevated cu values 1500 ppm from unaltered amphibolite point to a local redistribution of an earlier late mesoproterozoic keweenaw type cu mineralization into later pan african shear zones during the exhumation of the ekuja dome the timing polyphase evolution and tectonic setting of the omitiomire deposit show remarkable similarities with the large cu deposits of the domes region in the adjoining lufilian arc of northern zambia this suggests the presence of a much larger regionally significant cu province extending from central namibia through northern botswana and into zambia

evaluation of the role of cambrian granites in the genesis of world class vhms deposits in tasmania abstract an analysis of the distribution composition and alteration zonation of cambrian granites which intrude the mt read volcanics of western tasmania provides evidence that there may have been a direct input of magmatic fluids containing fe cu au and p to form the copper gold volcanic hosted massive sulphide vhms mineralisation in the mt lyell district interpretation of regional gravity and magnetic data indicates that a narrow discontinuous body of cambrian granite 2 4 km wide extends along the eastern margin of the mt read volcanic belt for over 60 km the cambrian granites are altered magnetite series types which show enrichment in barium and potassium and contrast markedly with the fractionated ilmenite series devonian granites related to tin mineralisation elsewhere in the dundas trough copper mineralisation occurs in a linear zone above the apex of the buried cambrian granite body at the southern end of the belt from mt darwin to the mt lyell district over a strike length of 25 km gold and zinc mineralisation are concentrated higher in the volcanic stratigraphy more distant from the granite overlapping zones of alteration extend from the granite into the surrounding volcanic rocks an inner zone of k feldspar alteration is overprinted by chlorite alteration which passes outwards into sericite alteration magnetite pyrite chalcopyrite apatite mineralisation is concentrated in the chlorite alteration zone as veins and low grade disseminations the mt lyell copper gold stringer and disseminated mineralisation is hosted in felsic volcanic rocks 1 to 2 km west of the interpreted buried granite position magnetite apatite pyrite veins in the prince lyell deposit at mt lyell are very similar to the veins in the halo of the granite further south and provide evidence for magmatic fluid input during the formation of the copper gold vhms deposits a model involving deeply penetrating convective seawater mixing with a magmatic fluid released from the cambrian granites best explains the features of vhms mineralisation in the mt lyell district

the archean cu zn magnetite rich gossan hill volcanic hosted massive sulfide deposit western australia genesis of a multistage hydrothermal system the gossan hill volcanic hosted massive sulfide vhms deposit is an archean cu zn magnetite rich deposit located in the warriedar fold belt of the yilgarn craton western australia the deposit is hosted by redeposited rhyodacitic tuffaceous volcaniclastics of the golden grove formation and is overlain by felsic volcanic rocks of the scuddles formation the deposit consists of two separate subvertical ore zones the stratigraphically lower cu rich ore zone 7 0 mt 3 4 cu is strata bound and varies from podiform massive pyrite chalcopyrite pyrrhotite magnetite to sheetlike massive magnetite carbonate chlorite talc the upper zn cu ore zone 2 2 mt 11 3 zn 0 3 cu 1 5 g t au and 102 g t ag contains strata bound massive sphalerite pyrite chalcopyrite that overlies discordant moundlike massive pyrite pyrrhotite chalcopyrite magnetite sulfide stockwork connects the upper and lower ore zones metal zonation varies from cu au in the lower ore zone to zn cu at the base of the upper ore zone which grades upward and laterally to zn ag au cu pb multiphase deformation and greenschist facies metamorphism overprint the deposit the relationship between host rocks and sulfide indicates that mineralization was broadly codepositional with sedimentation of the golden grove formation however gradational and interdigitating contacts between these volcaniclastic rocks and magnetite support the formation of massive magnetite by subsea floor replacement sulfides replace and vein the massive magnetite with inferred synchronous formation of the upper and lower sulfide ore zones although these sulfide ore zones formed mainly by subsea floor replacement stratiform hydrothermal chert sulfide sediment layers within and adjacent to the upper zn rich ore zone attest to some local exhalation the thickest development of massive magnetite massive sulfide and stringer stockwork occurs in the north of the deposit and supports a common feeder during massive magnetite and sulfide formation furthermore local chlorite quartz hydrothermal alteration massive magnetite massive sulfide and stockwork all form asymmetric zones that thin southward these attributes indicate strong synvolcanic structural control during mineralization the relict synvolcanic growth structure is obscured and probably occupied and by a dacite dome of the hanging wall scuddles formation thermodynamic considerations suggest that massive magnetite and sulfide formed from similar high temperature 300 degrees celsius slightly acidic low fo2 hydrothermal fluids massive magnetite formed from h2s poor fluids whereas massive sulfide formed from relatively rich h2s fluids physicochemical changes associated with interaction between upwelling h2s bearing fluids and preexisting massive magnetite may have resulted in the subsea floor precipitation of sulfide in the lower cu rich ore zone the gossan hill vhms deposit represents a multistage hydrothermal system within an environment characterized by rapid volcaniclastic sedimentation and changing structural and magmatic processes the six main stages were as follows 1 initiation of the hydrothermal system 2 sedimentation metasomatism and progressive heating of convecting fluids 3 deposition of massive magnetite from h2s poor fluids by subsea floor replacement above a buried synvolcanic conduit 4 structural reactivation tapping deeper h2s and metalbearing fluids 5 subsea floor replacement and minor exhalative sulfide mineralization with 6 burial and preservation of the deposit resulting from proximal felsic volcanism

alteration characteristics of the archean golden grove formation at the gossan hill deposit western australia induration as a focusing mechanism for mineralizing hydrothermal fluids the archean golden grove formation is a 550 m thick rhyodacitic tuffaceous volcaniclastic succession that hosts the cu zn rich gossan hill volcanic hosted massive sulfide vhms deposit in the yilgarn craton western australia the golden grove formation consists of volcanic quartz and altered pumice and shards which were deposited during successive episodes of subaqueous mass flow coherent volcanics are absent from the golden grove formation at gossan hill but form the main rock type in the hanging wall scuddles formation a massive dacite dome that overlies its volcanic feeder dike is inferred to occupy a synvolcanic structure that focused mineralizing fluids during the formation of the gossan hill deposit the gossan hill deposit consists of two stratigraphically separate ore zones interconnected by stockwork the cu rich lower ore zone and the zn rich upper ore zone occur in the middle and upper parts of the golden grove formation respectively podiform zones of massive magnetite occur in the cu rich ore zone where the formation of magnetite predates massive sulfide the asymmetry of massive sulfide massive magnetite and alteration zones at the gossan hill deposit attest to synvolcanic structural control during mineralization the principal lithofacies of the golden grove formation are sandstone and pebble breccia which have a regionally extensive quartz fe rich chlorite and lesser muscovite alteration at gossan hill this alteration has resulted in near complete replacement of tuffaceous components causing substantial chemical modification of the primary lithologies quartz chlorite muscovite alteration is characterized by severe k2o na2o and cao depletion with rocks consisting principally of sio2 feo al2o3 and mgo along a quartz chlorite mixing trend widespread preservation of pumice and shard volcanic textures within the golden grove formation indicates that quartz chlorite muscovite alteration occurred soon after or possibly during sedimentation the absence of diagenetic compaction textures further suggests induration of the succession during this early alteration stage with the tuffaceous succession largely sealed from the texturally destructive effects of subsequent hydrothermal alteration except where mineralizing fluids were locally channeled along synvolcanic feeder conduits local intense hydrothermal alteration zones surround the gossan hill deposit and overprint earlier quartz chlorite muscovite alteration these local alteration zones have the same extent as the sulfide vein envelope and represent hydrothermal alteration formed during sulfide magnetite mineralization intense fe rich chlorite ankerite siderite alteration occurs as a strata bound envelope around massive magnetite cu rich veins and massive sulfide in the lower ore zone this chlorite rich alteration has strong feo and mgo enrichment with minor chloritoid and andalusite that reflect intense acid leaching during hydrothermal alteration iron chlorite ankerite siderite alteration grades upward into discordant to strata bound intense quartz alteration intense quartz alteration forms an envelope around zn rich veins and massive sulfide in the stockwork and upper ore zone the trend from fe chlorite ankerite siderite to quartz alteration toward the top of the deposit is consistent with the cooling of hydrothermal mineralizing fluids nearing the sea floor rhyodacite and dacite volcanics of the hanging wall scuddles formation have a pervasive muscovite calcite alteration muscovite calcite alteration led to na2o depletion and cao and k2o enrichment associated with burial of the gossan hill mineralizing system we propose that the gossan hill sulfide magnetite vhms deposit formed during an evolving archean hydrothermal system that began as part of a regional scale low temperature seawater convection alteration system initially this system caused extensive replacement of the golden grove formation by quartz and fe chlorite muscovite a process that sealed and indurated the volcaniclastic rocks by infilling of primary porosity and permeability structures due to subsequent impermeability of the host rock succession later and hotter mineralizing fluids that generated alteration and massive magnetite and sulfide at the gossan hill deposit were constrained to and focused upward along a synvolcanic feeder structure

textures of the hellyer volcanic hosted massive sulfide deposit tasmania the aging of a sulfide sediment on the sea floor the relatively undeformed polymetallic massive sulfide ore of the hellyer deposit retains many textures developed during the early crystallization history common textures in the least modified ore away from the main feeder zone include pyrite framboids concentric and radial textured spheres dendritic and fibrous forms breccias mineral banding veins and reniform and crustification textures many are typical of early crystallization within a medium at high degrees of supersaturation some result from open space filling and others indicate disturbances of the sulfide mass possibly due to tectonic activity and volume adjustment the banding could be due to current winnowing most of these textures are found in modern midocean ridge and kuroko massive sulfide deposits but at hellyer the framboids are much more common hexagonal outlines in ore sphalerite indicate derivation of much of the sphalerite by inversion of wurtzite the high content of chalcopyrite in the wurtzite derived sphalerite appears in most cases to have developed by exsolution rather than replacement or coprecipitation although there is local evidence of both processes having operated possibly resulting from early asymmetrical crystal growth comparison of hellyer ore and typical kuroko ores reveals other differences than framboid abundance e g metal contents and ratios mineralogy and sulfur isotope compositions the most significant of which are the relatively high salinities of the hellyer ore fluids these together with evidence of a coeval basin imply sulfide deposition in a brine pool as previously proposed the development of a quenched sulfide mud at the bottom of a basin filled with spent ore fluid with little or no involvement of seawater explains the different mineral content e g lack of fe oxides scarcity of barite in the massive sulfide and the pyrite arsenopyrite assemblage the high metal content lack of chimney structures and differences in sulfur isotope compositions the sulfide mud dominated by fe s phases would be an ideal growth medium for framboidal pyrite the weight of experimental evidence concerning the development of framboidal pyrite points to involvement of metastable precursor fe s phases such as mackinawite and greigite in a weakly oxidized environment oxygen may have been added to the reduced acid brine pool as a result of inward diffusion of oxygen from overlying seawater which is shown to have been oxic by the presence of sessile benthic dendroids in the shales overlying the ore deposit however the level of oxidation was insufficient to form marcasite

mineralization of an intra oceanic arc in an accretionary orogen insights from the early silurian honghai volcanogenic massive sulfide cu zn deposit and associated adakites of the eastern tianshan nw china the honghai volcanogenic massive sulfide vms deposit occurs in the kalatage inlier of the dananhu haerlik arc eastern tianshan in the southern altaids the deformed deposit hosted in a suite of early paleozoic basic to intermediate volcanic volcaniclastic and sedimentary rocks consists of lenticular massive to semimassive and sulfide silicate stockwork orebodies the orebodies are characterized by zoning of metallogenic elements and sulfide minerals outward from a central stockwork zone as follows fe cu fe cu zn au ag cu zn fe zn cu au ag zn cu and fe cu zn a typical vms hydrothermal alteration zone that formed around the foot of the massive orebodies is several times larger than the lenticular massive orebody the hydrothermally altered rocks contain sericite chlorite and epidote zones from the core outward re os and argon dating of pyrite and sericite shows that the honghai vms deposit formed in the early silurian 436 2 ma and was deformed in the early devonian 410 4 ma this is the first documented early paleozoic vms deposit in the eastern tianshan our multidisciplinary data indicate that the honghai cu zn deposit formed in an immature nascent island arc where early tholeiitic lavas evolved into transitional basic andesitic volcanic rocks and calc alkaline intrusions with relatively high epsilon nd t values 6 2 8 4 and low sr 87 sr 86 i ratios 0 70412 0 70541 the sr nd pb s isotopic and geochemical data suggest that the ore forming melts started in mantle derived volcanic rocks and deep subvolcanic intrusions and some alteration was influenced by seawater the deposit formed in a high level subvolcanic intrusion driven by sub seafloor co2 rich nacl cacl2 h2o hydrothermal fluids temperatures 99 377 degrees c salinities 6 18 nacl equivalent circulating in active extensional faults in a submarine caldera extension of the immature nascent intra oceanic arc was one of the important factors that controlled the development and preservation of the vms deposit future work will benefit from this improved understanding of the vms deposits formed in immature nascent intra oceanic arcs especially in early paleozoic island arcs in the eastern tianshan in the southern altaids

alteration zonation and short wavelength infrared swir characteristics of the honghai vms cu zn deposit eastern tianshan nw china abstract the honghai vms cu zn deposit is located in the dananhu tousuquan arc eastern tianshan northwestern china orebodies of the honghai deposit are buried 300 m underground and hosted by the middle ordovician upper silurian daliugou formation felsic to intermediate volcanic sedimentary rocks at the footwall and hanging wall of the massive sulfide lens intensive and pervasive phyllic alterations were found detailed drill core logging petrographic study and electron microprobe analyses had delineated six alteration mineralization zones namely from top to bottom zone i chlorite albite white mica carbonate ii epidote chlorite albite white mica carbonate iii quartz white mica pyrite iv massive sulfide v chlorite pyrite white mica and vi chlorite quartz white mica our new data supported the sub seafloor replacement influence for the honghai vms deposit as evidenced by the presence of 1 sulfide breccias in the immediate host rocks 2 rapid emplacement of host rocks 3 strong phyllic alteration in the immediate hanging wall 4 replacement textures of the massive sulfides 5 barite as gangue minerals moreover intensive chlorite and epidote alterations and vein mineralization are present in the hanging wall which are comparable with porphyry related propylitic alteration besides different mineralogy and mineral chemistry are present between chlorites from the hanging wall and footwall at honghai which probably suggested porphyry style alteration and mineralization overprinting at honghai short wavelength infrared swir spectral analysis had identified mainly white mica chlorite and epidote and minor montmorillonite calcite gypsum kaolinite and prehnite the wavelengths of the aloh absorption feature for white mica range from 2194 to 2221 nm suggesting compositions from paragonite through muscovite to phengite the wavelengths of feoh absorption feature for chlorite range from 2249 to 2261 nm indicating compositions from mg rich to fe rich chlorite according to swir measurements and electron microprobe analyses empa areas proximal to the massive sulfides are characterized by short wavelength of the aloh absorption feature and high alvi content of white mica petrography and empa showed that chlorite in the ore proximal zones are more mg rich than that in ore distal zones these findings indicated high temperature for the white mica formation and more seawater influx during the chlorite formation in areas near the massive sulfides this study suggested that swir analysis supported by petrographic study and empa can serve as an effective tool in alteration mapping and mineral geochemical variations are potential deposit scale exploration vectoring tools

major features of glaciochemistry over the last 110 000 years in the greenland ice sheet project 2 ice core major chemical species cl no3 so42 na nh4 k mg2 ca2 and 18o covering the last 110 000 years from the greenland ice sheet project 2 gisp2 ice core were utilized in this study in order to reconstruct the soluble chemistry of the atmosphere over greenland and interpret major climate events that have affected the region during the holocene the major chemical species and 18o do not display any significant relationship however a strong inverse correlation was found between concentrations of the major chemical species and 18o a proxy for temperature during the last glacial period suggesting that in general during periods of decreased temperature there is an increase in atmospheric chemical loading examination of changes in major chemical composition over the last 110 000 years of the gisp2 ice core reveals that during the holocene the atmosphere was acidic during inters t adials the atmosphere was neutral or alkalescent and during stadials the atmosphere was alkaline in addition the relative abundance of major chemical species varied during the holocene stadials and interstadials during the holocene nh4 and no3 are the dominant cations and anions while ca2 and so42 are the dominant cations and anions during the stadials and inters t adials this suggests that source regions or types differed between the holocene and the last glacial period in addition changes in chemical composition and changes in chemical ratios also indicate that source regions differed during the holocene stadials and interstadials twenty four previously identified dansgaard oeschger stadial interstadial events dansgaard et al 1993 were in the gisp2 chemical series the duration of the stadials is inversely correlated with variations in sea level over the last glacial period i e the more extensive the northern hemisphere ice sheet the longer the duration of the stadial there is also a close correspondence between the duration of interstadials and the timing of heinrich events massive icebergs discharged into the ocean in the gisp2 ice core long up to 2000 years warm periods follow each heinrich event suggesting perhaps that enhanced deep water circulation is re initiated following heinrich events

proterozoic accretionary tectonics in the east kimberley region australia abstract the east kimberley region contains well preserved tectonic structure dating back to the earth s most significant stage of continental growth the assembly of the nuna supercontinent an integrated geological geophysical investigation of this region has been conducted and reveals insight into its tectonic evolution including potential influence of significant crustal scale structures in the development of regional architecture the emplacement of magma and the relationship of these structures to large scale deformation some newly interpreted features include a north trending structure and three north west trending structures that segment the north east trending orogen the central segment of the orogen is a zone of higher metamorphic grade and is host to a distinct gravity high this gravity high can be explained by excess mass in the mid crust this anomaly is consistent with either a large mafic ultramafic intrusion or a high density crustal fragment possible tectonic models to explain the geophysical and metamorphic anomalies involve in the latter case the accretion of a crustal fragment to the kimberley craton prior to the 1865 1850 ma hooper orogeny or in the former case intrusion of voluminous mafic magmas into the middle crust whether by igneous or structural means we consider the development of this anomalous region to be a result of along strike variations in subduction dynamics these were perhaps driven by variations in slab geometry accommodated by the orogen normal structures we identify the orogen normal structures are interpreted to be crustal scale faults along which significant vertical displacement occurred when a crustal fragment collided with kimberley craton and exhumed high grade metamorphic rocks to the surface

hydrothermal fluids associated with seafloor mineralization at two southern kermadec arc volcanoes offshore new zealand massive sulfide samples have been recovered from brothers and rumble ii west volcanoes of the southern kermadec frontal arc northeast of new zealand both are caldera forming volcanoes with brothers largely dacitic and rumble ii west basaltic to basaltic andesite in composition the sulfide samples are considered to be pieces of chimneys from near the base of the caldera walls and are dominated by cu fe ba pb chalcopyrite pyrite barite galena and to a lesser extent zn fe ba pb sphalerite pyrite barite galena mineralization gold is present in the samples up to 6 1 ppm paragenetic relationships suggest that the two hydrothermal systems have heated up and later cooled down oxidation of the sulfides is common and suggests that parts of the deposits are relatively old fluid inclusion microthermometric data show salinities fall predominantly in the range 3 0 to 3 4 wt nacl equivalent similar to seawater values 3 2 wt about 15 of the brothers salinity data range to both lower 2 2 wt and higher 3 9 wt than seawater values homogenization temperatures for type i inclusions in barite range between 175 and 322 c for the brothers samples and between 205 and 268 c for one rumble ii west sample a dramatic decrease in temperature and or change in the oxidation state of the hydrothermal fluid are considered the main mechanisms responsible for gold deposition at the kermadec vent sites this was achieved by mixing the hydrothermal fluid with ambient seawater within what are inferred to have been 300 c white smoker chimneys consistent with s isotope results fluid inclusion volatiles are dominated by h2o 99 81 99 98 mol followed by co2 0 03 0 17 and lesser amounts of n2 0 004 0 023 ch4 0 002 0 026 and trace cos and c2 c3 hydrocarbons fluid inclusions hosted by barite contain noticeably lesser amounts of gas than those within sulfides consistent with mixing the source of the relatively high concentrations of ch4 is enigmatic although may be related to the thermal degradation of organic rich sediments intercalated within the volcanic pile addition of a pressure correction and the effect of dissolved gases show that the hydrothermal fluids did not boil at the chimney depths however the range of measured salinities in the brothers field combined with slightly positive trends in fluid inclusion co2 ch4 versus co2 n2 plots suggest sub seafloor phase separation may have occurred in the hydrothermal system prior to venting

cu and mo re enrichment during ductile deformation a case study of the yuleken porphyry cu deposit eastern junggar nw china abstract porphyry cu deposits can be strongly deformed during subsequent tectonic evolution to date research pertaining to the deformation and the enrichment of mineralization in porphyry deposits has suffered from a paucity of proof here we describe the diagnostic petrologic and geochemical signatures of the yuleken porphyry cu deposit from stages of metallogenic overprinting the rocks studied in this work are from deformation metallogenic structures that have 1 a distinguished metallogenic and tectonic evolution 2 a three layer spatial deformation metallogenic structure 3 distinguishably different fluid components within protomylonite mylonite and ultramylonite zones and 4 variational geochemical characteristics of coexisting chalcopyrite and magnetite integrated sulfide and oxide mineral investigations pertaining to the mineral deformation and the trace element variation of the minerals chalcopyrite and magnetite in the yuleken porphyry cu deposit indicated that cu and mo can be enriched during ductile deformation through physical analogous geochemical characteristics of chalcopyrite from different stages and chemical migrations the elemental variation of magnetite magnetites from deformed stages have higher contents of ti v co mn and ga than those from other stages and the variation of the fluid components within the protomylonite mylonite and ultramylonite zones reveal that the migration and precipitation of cu mo and fe were influenced by oxygen fugacity fluid components and temperature variation in conclusion the arc related porphyry deposits were able to become involved in the ductile deformation zone inducing areas of cu and mo enrichment in theory units subjected to ductile deformation may have great potential for porphyry cu mo deposit formation under the influence of magmatism

sulfur isotope and trace element data from ore sulfides in the noranda district abitibi canada implications for volcanogenic massive sulfide deposit genesis we examine models for volcanogenic massive sulfide vms mineralization in the 2 7 ga noranda camp abitibi subprovince superior province canada using a combination of multiple sulfur isotope and trace element data from ore sulfide minerals the noranda camp is a well preserved vms deposit rich area that is thought to represent a collapsed volcanic caldera due to its economic value the camp has been studied extensively providing a robust geological framework within which to assess the new data presented in this study we explore previously proposed controls on mineralization within the noranda camp and in particular the exceptional au rich horne and quemont deposits we present multiple sulfur isotope and trace element compositional data for sulfide separates representing 25 different vms deposits and showings within the noranda camp multiple sulfur isotope data for this study have 34sv cdt values of between 1 9 and 2 5 and 33sv cdt values of between 0 59 and 0 03 we interpret the negative 33s values to be due to a contribution of sulfur that originated as seawater sulfate to form the ore sulfides of the noranda camp vms deposits the contribution of seawater sulfate increased with the collapse and subsequent evolution of the noranda caldera an inference supported by select trace and major element analyses in particular higher concentrations of se occur in samples with 33s values closer to 0 as well as lower fe zn ratios in sphalerite suggesting lower pressures and temperatures of formation we also report a relationship between average au grade and 33s values within au rich vms deposits of the noranda camp whereby higher gold grades are associated with near zero 33s values from this we infer a dominance of igneous sulfur in the gold rich deposits either leached from the volcanic pile and or directly degassed from an associated intrusion

geochemical modeling of the zoned footwall alteration pipe hellyer volcanic hosted massive sulfide deposit western tasmania australia the mineralogy of hydrothermal alteration assemblages siliceous core chlorite zone sericite zone in the footwall pipe of the hellyer volcanic hosted massive sulfide vhms deposit is controlled mainly by the temperature ph and redox state of the hydrothermal fluids based on the results of our numerical modeling the zoned alteration system could have formed by a combination of water rock interaction and cooling with a siliceous core predicted to form at the center of the conduit passing outward to a chlorite dominated zone a sericite rich zone and finally grading out to unaltered andesite these mineralogical changes relate to a gradual evolution of fluid chemistry water rock ratio ph and temperature from the core to the margin of the system initial temperatures were probably close to 350 degrees c and the hydrothermal fluids were reduced h2s dominated at low temperatures 200 degrees c a peripheral alteration zone consisting mostly of k feldspar chlorite sericite and hematite is predicted to form this low temperature zone has not been recognized at hellyer but elevated k2o contents and local k feldspar development have been noted at other vhms deposits suggesting that this zone might form at low temperatures and low water rock ratios in the footwall of vhms deposits if the existence of barren outer k feldspar alteration zones is confirmed the findings could have important implications for exploration specifically with regards to distinguishing ore related alteration zones from barren alteration systems

sulphur and lead isotope geochemistry of sulphide minerals from the zn pb cu ag au lemarchant volcanogenic massive sulphide vms deposit newfoundland canada abstract the lemarchant zn pb cu ag au volcanogenic massive sulphide vms deposit in the newfoundland appalachians canada is an important example of a precious metal bearing vms deposit the deposit contains vms and sulphosalt rich mineral assemblages which are paragenetically distinct initial zn pb sulphosalt mineralization was deposited from low temperature 300 c less oxidized hydrothermal fluids with lower sulphur activity in situ microanalyses of pyrite chalcopyrite and galena yield a wide range of 34s values 6 4 to 15 1 sulphides from paragenetically early lower temperature zn pb sulphosalt assemblages have the lowest average 34s values 4 6 whereas the highest 34s values occur in the late stage high temperature cu rich sulphide assemblages variability in 34s occurs in all styles of mineralization and is consistent with s derived from thermochemical reduction of seawater sulphate igneous leaching and potentially disproportionated magmatic so2 although it is difficult to distinguish explicitly between leached igneous and magmatic sources of sulphur mineralogical and geochemical data from lemarchant suggest a possible contribution of magmatic so2 during the deposition of epithermal style mineralization at the earlier stages of deposit formation lead isotope compositions of galena show little variability with style of mineralization suggesting similar pb sources throughout ore deposition most pb at lemarchant is derived from underlying neoproterozoic sandy brook group volcanic rocks with potential input of juvenile pb from the lake ambrose basaltic rocks of the tally pond group and or from more juvenile neoproterozoic basement rocks

geochemistry of metamorphosed volcanic rocks in the neoarchean qingyuan greenstone belt north china craton implications for geodynamic evolution and vms mineralization abstract the qingyuan greenstone belt qgb situated in the northeastern section of the north china craton ncc is considered to be the unique metallogenic province in china that hosts both banded iron formations bifs and volcanogenic massive sulfide vms deposits traditionally the qgb is divided into the hunbei and hunnan terranes separated by the hunhe fault and grouped into the lower shipengzi middle hongtoushan and upper nantianmen formations which have undergone amphibolite to granulite facies metamorphism exposed supracrustal rocks are composed of plagioclase amphibolite and biotite plagioclase gneiss with minor amounts of bif marble and schist in this study detailed field and petrographic observations lithogeochemical u pb geochronological as well as whole rock sm nd isotope analyses were conducted on the metamorphosed mafic and felsic volcanic rocks i e plagioclase amphibolite and biotite plagioclase gneiss respectively in the qgb in order to discuss implications for tectonic evolution and comitant vms mineralization the supracrustal rocks of both hunbei and hunnan regions were formed synchronously from 2 57 to 2 53 ga and then had undergone 2 52 2 48 ga regional metamorphism specifically the lower section of the shipengzi formation is composed dominantly of transitional tholeiitic basalts with negative nb anomalies suggesting that they were likely generated by partial melting of a mantle source that was previously altered by variable amounts of slab derived fluids or melts in contrast the lithologic assemblages grade upward into interlayered bimodal volcanic rocks i e n morb type tholeiitic basalts and fi to fii type dacites of transitional to calc alkalic affinities representing a change in tectonic regime related to subduction from compression to extension among them all the basalts are characterized by consistently positive initial nd compositions end t 2 7 to 3 4 further indicate a depleted mantle source whereas those dacites possess negative to positive initial nd values end t 4 6 to 3 0 suggesting they were formed by partial melting of depleted mafic source likely lower mafic crust and accompanied with variable addition of old crustal material significantly vms deposits are genetically linked to this extensional event and closely associated with the fii type dacites that were generated by higher melting degree at high temperature conditions and shallow crustal level likely 10 15 km in all geochemical features e g negative nb anomalies and end value together with contamination from continental crusts for tholeiitic mafic rocks and inherited zircons from these volcanic rocks imply a continental arc setting where the qgb was evolved

evolution of the subseafloor hydrothermal system associated with the ming vms deposit newfoundland appalachians and its controls on base and precious metal distribution the 487 ma ming volcanogenic massive sulfide vms deposit consists of four subparallel elongated semi massive to massive sulfides lenses the 1807 1806 ming north and ming south zones hosted in rhyodacite of the rambler rhyolite formation newfoundland appalachians a discordant cu rich lower footwall zone underlies the semi massive to massive sulfide lenses alteration associated with mineralization can be divided into nine facies that formed in three paragenetic stages 1 weak quartz calcite spessartine quartz sericite and quartz sericite chlorite alteration stage 1 2 quartz chlorite quartz chlorite sulfide and quartz chlorite sericite assemblages stage 2 and 3 quartz sericite sulfide and localized mn rich carbonate assemblages stage 3 a thin syngenetic silica rich layer immediately overlies part of the vms deposit and likely formed during the early stages the volcanic architecture and synvolcanic faults controlled the lateral distribution of extrusive rocks and hydrothermal alteration precipitation of the high temperature discordant to semi conformable cu rich chloritic assemblages stockwork was laterally restricted to one of these synvolcanic faults and the transition from coherent to volcaniclastic dominated lithofacies lower temperature sericitic assemblages stages 1 and 3 are controlled by the distribution of volcaniclastic rocks and generally form the immediate footwall to the semi massive to massive sulfide lenses lithogeochemical mass balance calculations illustrate the alteration minerals and mineralization chlorite rich assemblages gains in sio2 fe2o3t mgo cr ni and cu and losses in na2o mno and cao and sericite rich assemblages gains in k2o zn and ag and losses in mno mgo cao na2o and y calcium and magnesium rich alteration assemblages are restricted to the northwest fringe of the deposit distal to the main chloritic and sericitic alteration and have elemental gains in p2o5 y and losses in k2o the late stage 3 quartz sericite sulfide assemblage overprints most assemblages hosts sphalerite galena sulfosalt ag au rich veins and is spatially associated with coherent volcanic rocks the less permeable nature of these rocks is interpreted to have acted as a physical barrier for ascending metal rich hydrothermal fluids results from the detailed reconstruction of the hydrothermal architecture and paragenetic evolution of the ming deposit suggest that precious metals were introduced during the waning stage of the hydrothermal system associated with decreases in temperature and ph of the hydrothermal fluids

bismuth and cobalt minerals as indicators of stringer zones to massive sulphide deposits iberian pyrite belt the stringer zones and commonly the interaction zone at the base of the massive sulphide mounds in the iberian pyrite belt contain bismuth and cobalt minerals that are not found in the overlying massive sulphides these are fairly rare cobalt sulphoarsenides cobaltite alloclasite galucodot that were formed at the beginning of the massive sulphide genesis and fairly common bismuth sulphides bismuthinite hammarite wittichenite cosalite kobellite joseite etc including species rare at world scale nuffieldite giessenite jaskolskiite that were deposited from last stage high temperature 300 c copper bearing fluids containing bi te se the last stage fluids precipitated chalcopyrite containing cu bi te se sulphosalts at the base of the sulphide mound to form a high cupriferous zone their interaction with the massive sulphides is reflected by the formation of an exchange zone a few metres thick showing chalcopyrite disease textures at the base of the mound this zone forms the upper limit of potentially economic copper enrichment and of bismuth minerals gold is undoubtedly in part if not totally related to this last phase the bismuth concentrations being equivalent in the massive sulphides and the stringers the presence of bismuth minerals in the stringer zones results from high temperature conditions combined with a rarity of galena which impedes absorption of available bi the distribution of these bismuth minerals provides a basic mineralogical zoning in the stringer zone with a deep low as2 zone containing native bismuth and tellurides and a shallow higher as2 zone in contact with the massive ore sensu stricto and containing complex bismuth sulphides these results make it possible to distinguish between sulphide veinlets belonging to stockwork zones of massive orebodies and veinlets of an ambiguous nature and provide mineralogical criteria for the proximity of copper rich zones they enrich the very complex mineralogy of the iberian pyrite belt

stratigraphy petrography and paleogeography of the late paleozoic diamictites of the lesser himalaya abstract the late paleozoic diamictites of the lesser himalaya are one of its most important stratigraphic horizons because they are very useful in stratigraphic correlation of its unfossiliferous rocks and in paleogeographic reconstruction the clast petrography of the diamictites from garhwal and the eastern himalaya as well as of other diamictites clearly indicates a provenance from largely late precambrian early paleozoic rocks of the lesser himalaya a widespread glacio marine environment with occassional volcanism and probably turbidity currents in certain parts of the diamictite association has been postulated for their origin paleogeographic reconstruction of the lesser himalaya during the late paleozoic has revealed a homotaxial relationship between its diamictites and the gondwana diamictites of peninsular india these were extensively though unevenly deposited upon the eroded surface of orogenically deformed late precambrian early paleozoic rocks of the lesser himalaya and they belong to different tectonic units which are superposed upon each other as a consequence of the himalayan orogeny

alteration mineralogy lithochemistry and stable isotope geochemistry of the murgul artvin ne turkey volcanic hosted massive sulfide deposit implications for the alteration age and ore forming fluids abstract the murgul artvin ne turkey massive sulfide deposit is hosted dominantly by late cretaceous calc alkaline to transitional felsic volcanics the footwall rocks are represented by dacitic flows and pyroclastics whereas the hanging wall rocks consist of epiclastic rocks chemical exhalative rocks gypsum bearing vitric tuff purple vitric tuff and dacitic flows multi element variation diagrams of the hanging wall and footwall rocks exhibit similar patterns with considerable enrichment in k rb and ba and depletion in nb sr ti and p the chondrite normalized rare earth element rees patterns of all the rocks are characterized by pronounced positive negative eu anomalies as a result of different degrees of hydrothermal alteration and the semi protected effects of plagioclase fractionation mineralogical results suggest illite illite smectite chlorite kaolinite and chlorite in the footwall rocks and illite smectite kaolinite and chlorite illite in the hanging wall rocks overall the alteration pattern is represented by silica sericite chlorite and chlorite carbonate epidote sericite and quartz albite zones increments of ishikawa alteration indexes resulting from gains in k 2 o and losses in na 2 o and the chlorite carbonate pyrite index towards to the center of the stringer zone indicate the inner parts of the alteration zones calculations of the changes in the chemical mass imply a general volume increase in the footwall rocks abnormal volume increases are explained by silica and iron enrichments and a total depletion of alkalis in silica zone relative k increments are linked to the sericitization of plagioclase and glass shards and the formation of illite smectite in the sericite zone in addition fe enrichment is always met by pyrite formation accompanied by quartz and chlorite illite is favored over chlorite smectite and kaolinite in the central part of the ore body due to the increase in the al k na ca ratio although the rees were enriched in the silicification zone light rees show depletion in the silicification zone and enrichment in the other zones in contrast to the heavy rees behavior hydrothermal alteration within the hanging wall rocks apart from the gypsum bearing vitric tuffs is primarily controlled by chloritization with proportional fe and mg enrichments and sericitization the 18 o and d values of clay minerals systematically change with increasing formation temperature from 6 6 to 8 7 and 42 to 50 for illites and 8 6 and 52 for chlorite respectively the o and h stable isotopic data imply that hydrothermal alteration processes occurred at 253 332 c for illites and 136 c for chlorite with a temperature decrease outward from the center of the deposit the positive 34 s values 20 3 to 20 4 for gypsum suggest contributions from seawater sulfate reduced by fe oxide hydroxide phases within altered volcanic units thus the hydrothermal alteration possibly formed via a dissolution precipitation mechanism that operated under acidic conditions the k ar dating 73 62 ma of the illites indicates an illitization process from the maastrichtian to early danian period

distribution mineralogy and geochemistry of selenium in felsic volcanic hosted massive sulfide deposits of the finlayson lake district yukon territory canada three significant base metal deposits were recently discovered in the finlayson lake district yukon territory canada however widely varying selenium contents e g 1 100 ppm avg se at wolverine 200 ppm avg se at kudz ze kayah and 7 ppm avg se at gp4f have hindered their rapid exploitation observations and data from the deposits in the finlayson lake district show a strong positive correlation between high temperature 300 c copper rich sulfide assemblages at the base of volcanic hosted massive sulfide vhms and the selenium content of all sulfide minerals thermodynamic calculations for selenide and sulfide minerals indicate significantly higher temperatures of formation and lower solubilities of selenide versus sulfide minerals which is consistent with petrographic observations and can explain the distribution of selenium in zone refined vhms and volcanic sediment hosted massive sulfide deposits volumetric mass balance calculations indicate that some selenium could be sourced from contemporaneous volatile degassing of seo 4 its rapid reduction to h 2 se and subsequent entrainment into hydrothermal ore fluid however estimates for the kudz ze kayah and wolverine deposits suggest an additional large se reservoir volumetric mass balance estimates indicate that contemporaneous volcanic rocks and black shales are likely selenium reservoirs for the kudz ze kayah and wolverine deposits respectively

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

bipolar changes in atmospheric circulation during the little ice age annually dated ice cores from siple dome west antarctica and central greenland indicate that meridional atmospheric circulation intensity increased in the polar south pacific and north atlantic at the beginning 1400 a d of the most recent holocene rapid climate change event the little ice age lia as deduced from chemical concentrations at these core sites the lia was characterized by substantial meridional circulation strength variability and this variability persists today despite strong evidence for an end to lia cooling thus increased late 20th century storm variability may be in part a result of the continuation of these climatic fluctuations

silicic acid leakage from the southern ocean a possible explanation for glacial atmospheric pco2 1 using a simple box model we investigate the effects of a reduced si n uptake ratio by antarctic phytoplankton on the marine silica cycle and atmospheric pco2 recent incubation experiments demonstrate such a phenomenon in diatoms when iron is added hutchins and bruland 1998 takeda 1998 franck et al 2000 the southern ocean may have supported diatoms with reduced si n uptake ratios compared to today during the dustier glacial times petit et al 1999 a similar reduction in the uptake ratio may be realized with an increased production of nondiatom phytoplankton such as phaeocystis our model shows that reduced si n export ratios in the southern ocean create excess silicic acid which may then be leaked out to lower latitudes any significant consumption of the excess silicic acid by diatoms that leads to an enhancement in their growth at the expense of coccolithophorids diminishes caco3 production and therefore diminishes the carbonate pump in our box model the combination of a reduced carbonate pump and an open system carbonate compensation draw down steady state atmospheric co2 from the interglacial 277 to 230 242 ppm depending on where the excess silicic acid is consumed by comparison the atmospheric pco2 sensitivity of general circulation models to carbonate pump forcing is 3 5 fold greater which combined with carbonate compensation can account for peak glacial atmospheric pco2 we discuss the importance of the initial rain ratio of caco3 to organic carbon on atmospheric pco2 and relevant sedimentary records that support and constrain this silicic acid leakage scenario

glacial interglacial variations in methanesulfonate msa in the siple dome ice core west antarctica methanesulfonate msa in the siple dome ice core is a record of the deposition of biogenic sulfur to the west antarctic ice sheet covering the past 100 kyr siple dome msa levels were low during the last glacial maximum and increased to higher holocene levels with a several kyr lag relative to the deglacial warming the positive correlation between msa and temperature at siple dome is similar to that in greenland ice cores renland gisp2 and grip and stands in contrast to the negative correlation observed at vostok east antarctica the siple dome msa data suggest that the sign of the high latitude dust sulfur climate feedback is negative at least for the pacific sector of the high latitude southern ocean these results challenge the idea that fertilization by increased dust deposition led to widespread increased dms emissions from this region of the glacial southern ocean

the generation of a stratiform skarn and volcanic exhalative pb zn deposit sawusi in the southern chinese altay mountains the constraints from petrography mineral assemblage and chemistry abstract numerous pb zn and fe ore deposits occur in the volcanic sedimentary basins along the southern chinese altay mountains the mineralization of these deposits is hosted by early middle devonian volcanics and sedimentary rocks and is directly associated with skarns the genesis of these deposits is uncertain or hotly debated this study considers the sawusi pb zn deposit from the southern chinese altay the host rock of the sawusi deposit is rhyolitic crystal tuff with intercalated bands of fe mn calcic carbonates and a small amount of rhyolite within the upper section of the early devonian kangbutiebao formation on the basis of a field investigation the petrographic features of the skarn were described detailed electron microprobe analysis was performed on the skarn minerals and the o h and c isotopic compositions of quartz and its fluid inclusions were determined petrographic observation revealed a progressively intensifying alteration from the tuff and its intercalated bands to the stratiform skarn characterized by alternate bands of dark garnet biotite skarn and light grunerite biotite skarn mineral chemical analysis shows that the stratiform skarn of the sawusi deposit consists mainly of spessartine almandine mn rich grunerite biotite and fe mn calcic carbonate minerals a mass balance consideration of the cations in the skarn minerals suggests that the stratiform skarn formed through dimetasomatism between the tuff and intercalated bands of sedimentary fe mn calcic carbonates however the scale of the metasomatism is limited to a few centimeters laser 40 ar 39 ar dating was performed on the skarn grunerite yielding an isochron age of 412 15 ma the 40 ar 39 ar age is identical within analytical error to the zircon u pb age 401 2 7 ma of the rhyolite from the kangbutiebao formation that hosts the skarn and pb zn mineralization and the age 401 3 1 ma of the biesisala porphyry sawusi deposit the o h and c isotopic compositions show that the ore forming fluid includes two components one is h 2 o co 2 which has volatilized from carbonate and dehydrated from tuff and the other is meteoric derived surface water carrying minor meteoric co 2 or organic matter derived co 2 therefore the stratiform skarn and pb zn mineralization of the sawusi deposit are quite different from the contact metasomatic skarn and related deposits and suggest a volcanic exhalation sedimentation origin instead this study has broad relevance to the pb zn and fe deposits along the southern altay mountains in the areas of ore genesis study and ore prospecting

earthquakes and deformational structures seismites in holocene sediments from the himalayan andaman arc india soft sediment deformational structures from the himalayan arc caused by episodic earthquake recurrences during the holocene recent are produced by the ongoing tectonic processes these small scale subtle structures occur along some major thrusts in the garhwal himalaya and vary from normal faults in the lower zone to compressional structures in the middle zone along the main central thrust in the tons valley the latter includes isoclinal angular kink and disharmonic folds with discrete displacements along their axial surfaces thrusts with decollement listric and overstep thrusts in duplex style and load slumping the upper zone is marked by very low angle thrusts with left lateral displacement and associated displacement shears d riedel shears r and thrust shears p as well as small scale sporadic kinks three zones reveal changing tectonic character from gravity tectonics in the lower zone to compression in both the middle and upper zones with the maximum principal stress 1 oriented n60 to n110 respectively along the tons thrust post depositional structures include drag along normal fault zone characterized by d r and p shears and conjugate fractures that provide localized orientation of stresses 1 at 75 n60 2 at 12 n280 and 3 at 12 n290 earthquake induced liquefaction and subtle variations in physiomechanical properties of soft sediments have primarily controlled the deformational pattern due to localized tectonic stresses ground and sediment deformations during two earthquakes in the himalayan andaman arc provide additional support for the seismogenic origin of such structures preserved in loose or consolidated sediments

tianzhushania spinosa and other large acanthomorphic acritarchs of ediacaran period from the infrakrol formation lesser himalaya india covering a time span from ediacaran base of blaini pink carbonates to early cambrian base of tal group the krol belt in the lesser himalaya india occurs as a series of synclines from solan himachal pradesh in the north west to nainital uttarakhand in the south east various lithostratigraphic divisions of this belt reveal many palaeobiological entities namely cyanobacteria algae acritarchs small shelly fossils and trace fossils globally large acanthomorphic acritarchs of the ediacaran period are used as significant biostratigraphic tools for global correlation in the krol belt reports of acanthomorphic acritarchs from the infrakrol and krol a formations of the krol group have further supported this notion this paper reports well preserved microfossils including acanthomorphic acritarchs sphaeromorphic acritarchs coccoids namely tianzhushania spinosa t polysiphonia papillomembrana compta schizofusa sp gloeodiniopsis lamellosa sphaerophycus medium and the unnamed forms a b and c from the chert nodules of the infrakrol formation exposed in the nainital syncline of the kumaun lesser himalaya a biostratigraphic correlation based on acanthomorphic acritarchs suggests that the infrakrol formation is coeval to the lower tianzhushania assemblage zone of the doushantuo formation of south china tianzhushania and papillomembrana are significant additions to the previous record of the ediacaran acanthomorphic acritarchs from the lesser himalaya of india and provide an independent evidence for construction of both biozonation scheme and paleogeography

methanesulfonate in the greenland ice sheet project 2 ice core in this paper we present measurements of methanesulfonate in the greenland ice sheet project 2 gisp2 ice core methanesulfonate is an atmospheric oxidation product of dimethylsulfide the gisp2 methanesulfonate record contains information about the atmospheric loading of biogenic sulfur over the past 110 kyr and its relationship to climate change the gisp2 data set supports the inferences made from the renland ice core from greenland that the glacial atmosphere over greenland had reduced concentrations of biogenic sulfur compared with the present day hansson and saltzman 1993 we conclude that the flux of biogenic sulfur from the north atlantic ocean must have been lower during glacial times and speculate that this decrease may have been related to differences in phytoplankton speciation the data suggest that changes in direct radiative forcing from biogenic sulfur aerosols would act as negative feedback to the glacial interglacial climate cycles in this region

australian volcanic hosted massive sulfide deposits features styles and genetic models the cambro ordovician period has yielded the major development of volcanic hosted massive sulfide vhms deposits in australia resulting in about 12 million metric tons of contained metal copper lead and zinc concentrated in the mount read volcanics tasmania and the mount windsor volcanics queensland the archean 4 million metric tons of metal and the silurian 3 5 million metric tons of metal constitute the next important episodes while the devonian and permian have produced isolated deposits the deposits range from cu type to zn cu type to zn pb cu type the zn cu type deposits are restricted to the archean and silurian whereas the cu type and zn pb cu type occur sporadically throughout the time span from early archean to permian in general terms the major vhms bearing districts are calc alkaline in character and display a thick basal pile of rhyolitic volcanics 1 3 km thick including lavas epiclastics and subvolcanic intrusions which is overlain by a polymodal sequence containing various proportions of rhyolite dacite andesite basalt and sediments the major deposits are commonly located at the top contact of the rhyolite pile or within the lower part of the overlying polymodal sequence there is a wide range in variability of styles of australian vhms deposits including mounds pipes sheets layered deposits stacked deposits stockwork and disseminated deposits distal reworked deposits and cyclic layered deposits although these various styles show a range of features there is a consistent theme across the spectrum of metal zonation alteration mineralogy alteration chemistry sulfur isotopes macrotextures microtextures and host volcanic relationships which strongly suggests that they all belong to the one genetic group of ore deposit the classic mound style deposits such as hellyer have a series of key features subsets of which are represented in the other deposit styles the mound deposits are considered to form from deposition of metal sulfides on the sea floor immediately around the hydrothermal vent growth of the mound occurs by upward replacement of sulfide assemblages stable at higher fluid temperatures leading to zone refining and lead zinc silver gold enrichment in the outer and upper parts of the mound departure from the classic mound style of deposit is related principally to three key factors the chemistry of the ore fluid salinity temperature f02 and ah2s the nature permeability and chemistry of the volcanic pile and the sea hoor environment sea hoor topography and seawater depth these factors control the aspect ratio of the deposit the extent of stringer zone development the degree of subsea floor replacement mineralization the nature and spatial development of footwall alteration and the development and style of related distal mineralization sulfur isotope studies of australian vhms deposits indicate that reduced seawater sulfate is a major source of sulfur in the deposit whereas lead and strontium isotope results are compatible with the metals being derived by seawater convection and leaching from the volcanic pile and basement rocks this conclusion is supported by the application of various leaching models which demonstrate the availability of an adequate source of both base and precious metals in the footwall volcanic sequences the input of metals directly from volcanic magma chambers is not precluded by the available data and one likely scenario involves the contribution of gold and copper from a magmatic vapor plume rising to mix with convective seawater fluids which contribute lead zinc silver and gold leached from the footwall volcanics and basement rocks the relative importance of the magmatic input compared with the seawater convective input may help to explain the spectrum of deposit styles arid their spatial relationship to volcanic centers or adjacent sedimentary basins

the antarctic ice sheet during the last glacial maximum and its subsequent retreat history a review abstract an emerging body of evidence from studies of the last glacial interglacial cycle suggests that the east and west antarctic ice sheets have not advanced and retreated in concert the west antarctic ice sheet advanced to the outer shelf in most regions during the last glacial maximum lgm the retreat from the shelf commenced shortly after the lgm and continued into the late holocene the west antarctic ice sheet in ross and amundsen seas slid across a deforming bed at least during the final phases of extended glaciation this implies that at this time the ice sheet had a low profile differences in the number and locations of grounding zone wedges and smaller grounding zone features from trough to trough imply that individual west antarctic ice sheet ice streams retreated episodically details concerning the expansion retreat and behavior of the east antarctic ice sheet eais are more sparse the picture emerging is that the eais did not expand to the continental shelf edge during the lgm rather it achieved a maximum extent of a mid shelf position in some locations while in other areas the ice terminus was situated near its present location the timing of retreat along sectors within the eais appears diachronous and in places occurred prior to the lgm the antarctic peninsula shelf contained considerably more ice during the lgm than previously proposed the results presented in this paper support more recent published ice sheet models that call for greater contributions of melting ice from west antarctica including the antarctic peninsula to the post glacial rise in sea level

a revised stratigraphic and tectonic framework for the ashele volcanogenic massive sulfide deposit in the southern chinese altay evidence from stratigraphic relationships and zircon geochronology abstract the ashele volcanogenic massive sulfide vms deposit is the largest and most representative vms deposit in the chinese altay metallogenic belt but its stratigraphic sequence tectonic framework and morphology are debated in this paper on the basis of previous research field investigations excavation pits drill core sampling and new la icp ms u pb analyses of zircons from mafic and felsic volcanic rocks we show that the main structure of the ashele deposit is an overturned tightly closed syncline and that the primary orebody is controlled by this structure moreover we show that the ashele vms deposit displays a double layer structure made up of a feeder zone of veinlet disseminated and stockwork orebodies overlain by massive stratiform orebodies that are folded we revise the stratigraphy of the ashele formation into five conformable sedimentary subsequences based on new field investigations and the zircon geochronology of each subsequence from bottom to top we divide the formation into a siliceous tuff layer 405 1 1 8 ma a dacitic layer 395 9 403 ma a rhyolitic layer 390 9 0 83 ma an orebody layer ca 387 ma and a basalt layer 387 377 ma the early to middle devonian ashele formation unconformably underlies the late devonian qiye formation

genesis of the wolverine volcanic sediment hosted massive sulfide deposit finlayson lake district yukon canada mineralogical mineral chemical fluid inclusion and sulfur isotope evidence the wolverine deposit is a high grade 6 2 mt at 12 7 zn 1 3 cu 1 6 pb 370 9 g t ag and 1 8 g t au volcanic and sedimentary rock hosted massive sulfide deposit in the finlayson lake area yukon territory the area has the potential to become an important mining camp and currently contains more than 30 million tons mt of massive sulfide ore in five deposits a succession of metamorphosed early mississippian felsic volcanic and sedimentary rocks that are interpreted to have formed on the margin of an ensialic back arc ocean basin between the yukon tanana terrane and the ancestral north american craton hosts the wolverine deposit the massive sulfide ore occurs at a single horizon that marks a significant change in the character of the volcanism from quartz and feldspar phyric rhyolite of the footwall to aphyric rhyolite and chemical sedimentary exhalative rock of the hanging wall the deposit consists of two discrete zn pb ag massive sulfide lenses situated at the same stratigraphic level connected by strata bound semimassive replacement style zn pb ag mineralization copper rich massive sulfide commonly replaces the zn pb ag massive sulfide at the base of the lenses and in the footwall replacement zones beneath the massive mineralization several zones of sulfide stringer veins and chlorite sericite carbonate alteration occur within permeable footwall volcaniclastic rocks alteration minerals preferentially associated with massive sulfide mineralization include ba rich phengitic mica biotite mg rich chlorite and siderite microthermometric measurements of fluid inclusions in the massive sulfide bodies and accompanying stringer zones indicate formation at temperatures of 235 to 353 c primary aqueous liquid rich fluid inclusions in hydrothermal quartz from quartz sulfide stringer veins contain low salinity fluids 2 1 8 5 wt nacl equiv mean 6 0 there is no evidence of fluid boiling in the inclusions and based on the average fluid salinity and temperature of homogenization mineralization took place under a minimum water depth of 1 000 m in situ analyses of 34sv cdt in sulfide minerals from massive sulfide lenses means 0 8 and sulfide stringer veins mean 12 0 display a bimodal distribution lower 34s values characterize sulfides near the top of the lenses versus higher more positive values in underlying veins may reflect different processes of reduction of seawater sulfate sulfur in sulfides from the tops of the lenses was likely derived mainly from bacterial reduction of seawater sulfate whereas sulfur in the stringer veins and at the base of the lenses was mainly from inorganic reduction of seawater sulfate sulfide minerals precipitated both on the sea floor and in the subsea floor from hydrothermal fluids that vented from multiple mounds the presence of black shales and the strongly positive sulfur isotope compositions of the sulfides provide evidence that the ambient bottom water in the basin in which the wolverine deposit formed was likely anoxic this environment may have contributed to the preservation of the sulfide mounds based on its tectonic setting host rock types local geologic setting metal grades age and source s of sulfur the wolverine deposit best exemplifies the volcanic sediment hosted massive sulfide vshms class of syngenetic massive sulfide deposits in the district

characteristics of water soluble inorganic and organic ions in aerosols over the southern ocean and coastal east antarctica during austral summer 1 to characterize the concentrations and size distributions of water soluble organic and inorganic aerosol species including na non sea salt sulfate nss so42 methane sulfonate msa oxalate and succinate over the southern ocean so and coastal east antarctica cea bulk and size segregated aerosols were collected from 40 s 100 e to 69 s 76 e and between 69 s 76 e and 66 s 110 e during a cruise from november 2010 to march 2011 results show that sea salt was the major component of the total aerosol mass accounting for 72 over the so and 56 over cea the average concentrations of nss so42 varied from 420 ng m 3 over the so to 480 ng m 3 over cea the concentrations of msa ranged from 63 to 87 ng m 3 over the so and from 46 to 170 ng m 3 in cea the average concentrations of oxalate were 3 8 ng m 3 over the so and 2 2 ng m 3 over cea the concentrations of formate acetate and succinate were lower than those of oxalate a bimodal size distribution of aerosol mass existed over cea peaking at 0 32 0 56 m and 3 2 5 6 m msa was accumulated in particles of 0 32 0 56 m over cea high chloride depletion was associated with fine mode particles enriched with nss so42 msa and oxalate higher cation to anion and nh4 nss so42 ratios in aerosols over cea compared to that over the so imply the higher neutralization capacity of the marine atmosphere over cea

mineralogy and mineral chemistry of the metamorphosed and precious metal bearing ming deposit canada abstract the ming deposit in the northwestern canadian appalachians is a metamorphosed bimodal mafic precious metal au ag bearing and cu rich volcanogenic massive sulfide vms deposit consisting of several spatially proximal lenses in a sericite to chlorite altered rhyodacitic footwall the various lenses 1807 zone 1806 zone ming south up plunge ming south down plunge and the lower footwall zone have variations in cu au ag and zn grades that reflect varying physico chemical conditions of ore formation this study describes the complex ore mineralogy of the orebodies and constrains the genesis of the deposit using field methods mineralogy whole rock sulfide geochemistry and micro analytical methods the orebodies are predominantly pyrite chalcopyrite with lesser sphalerite pyrrhotite and trace galena and arsenopyrite with the exception of the lower footwall zone which consists of a high temperature 320 c chalcopyrite pyrrhotite pyrite cubanite assemblage the other orebodies 1806 1807 ming south up plunge and down plunge contain trace amounts of tellurides hessite altaite tsumoite unnamed bismuthtelluride sulfosalts ag poor and ag rich tennantite tetrahedrite meneghinite agsb phases stannite and precious metal phases electrum aghg au alloys the 1807 zone is enriched in te bi and se whereas the 1806 zone is telluride free and contains as sb hg au and ag mineral chemistry of sphalerite shows strong variations in fe content 1 12 11 04 wt intermediate fe 4 33 6 33 wt fe and fe rich 7 327 11 04 wt fe sphalerite are common in all orebodies whereas fe poor sphalerite 1 12 3 57 wt fe occurs exclusively in the 1807 and 1806 zones tennantite tetrahedrite is typically ag poor 0 25 2 19 wt in the 1807 zone but is significantly enriched in ag up to 29 3 wt in the 1806 zone galena in the 1807 zone and ming south orebodies is commonly myrmekitically intergrown with tellurides and has high concentrations of te bi se and ag in contrast galena in the 1806 zone is less enriched in te bi and se but high in ag variations in mineralogy epithermal elements as bi hg sb se sn te and precious metal ag au content and mineral chemistry between the different orebodies indicate that they were formed from predominantly reduced acidic hydrothermal fluids with varying te2 s2 se2 s2 and mbi msb ratios as temperatures steadily decreased from 300 c to

consonorm_lg new normative minerals and alteration indexes for low grade metamorphic rocks the consonorm lg method provides a standardized solution for approximating metamorphic parageneses as well as indexes for estimating chemical and mineralogical changes caused by hydrothermal alteration consonorm lg is designed for rocks dominated by silicates fe ti oxides and or carbonates and it approximates the main parageneses of greenschist and lower amphibolite grade metamorphic rocks for three sets of temperature and pressure conditions 350 c and 2 5 kbars 450 c and 2 5 kbars 575 c and 2 kbars for each model the norm calculates the main paragenesis using an acfmnk tetrahedron a convenient way of representing a large number of silicate assemblages in addition to silicate minerals consonorm lg calculates fe ti oxides and other accessory minerals from minor elements as well as sulfides from analyzed s or from analyzed metals and carbonates from analyzed co2 or from normative co2 estimated from loss on ignition loi consonorm lg also calculates several alteration indexes to estimate fe mg e g chloritization ca e g propylitic alteration na and k acid alterations e g sericitization phyllic alterations and al gain e g argillization carbonatation indexes are also calculated using the amount of normative minerals formed by this type of alteration i e carbonates chlorite and muscovite the normative calculation is validated using published whole rock analyses and petrographic descriptions alteration indexes are validated using several natural samples of alteration halos around base metal and gold deposits

alteration of felsic volcanics hosting the thalanga massive sulfide deposit northern queensland australia and geochemical proximity indicators to ore thalanga is an early ordovician stratiform zn pb cu ag rich massive sulfide deposit in northern queensland australia with a total resource of 6 6 mt of ore the host rock succession consists of variably altered rhyolite in the footwall and a dacite dominated volcano sedimentary sequence in the hanging wall the sulfide deposit and the enclosing volcanic sequence were metamorphosed under upper greenschist conditions a laterally continuous footwall alteration zone extends beneath the entire deposit 3 000 m and to a stratigraphic depth of at least 300 m below the ore lenses the bulk of this zone is occupied by feldspar destructive muscovite biotite chlorite rich mottled alteration facies with disseminated pyrite representing the metamorphic equivalent of phyllosilicate dominated hydrothermal alteration discordant zones of intense quartz pyrite alteration represent the principal fluid pathways during mineralizing hydrothermal activity locally quartz k feldspar alteration facies exist on the fringes of the system and calcareous alteration and chlorite pyrite alteration facies exist in the upper part of footwall rhyolite proximal to sulfide lenses quartz feldspar porphyritic rhyolite laterally surrounding the footwall alteration zone and feldspar porphyritic dacite in the hanging wall are unaltered or weakly altered the compositional diversity of altered footwall rhyolite implies that hydrothermal alteration at thalanga was a complex processes this paper presents a model for the evolution of the footwall alteration zone calcareous alteration probably represents the initial phase of hydrothermal activity this was followed by diffuse upwelling of acidic seawater dominated fluids causing destruction of primary feldspar precipitation of pyrite and formation of hydrothermal sericite chlorite and clay minerals subsequent intense quartz pyrite alteration was directly associated with mineralization the thalanga footwall alteration zone has several geochemical characteristics that show systematic changes with increasing proximity to ore these include na depletion and elevated mg s alteration index ai chlorite carbonate pyrite index ccpi mo bi and as furthermore the x mg of chlorite and biotite increases systematically from values of 0 45 to 0 5 in least altered rhyolite to values 0 9 immediately below ore these geochemical features can be used in exploration for massive sulfide deposits as vectors to ore at the prospect scale and in discrimination of prospective hydrothermal from unprospective diagenetic alteration systems at the regional scale

post collisional crustal extension setting and vhms mineralization in the jinshajiang orogenic belt southwestern china abstract the jinshajiang orogenic belt job of southwestern china located along the eastern margin of the himalayan tibetan orogen includes a collage of continental blocks joined by paleozoic ophiolitic sutures and permian volcanic arcs three major tectonic stages are recognized based on the volcanic sedimentary sequence and geochemistry of volcanic rocks in the belt westward subduction of the paleozoic jinshajiang oceanic plate at the end of permian resulted in the formation of the chubarong dongzhulin intra oceanic arc and jamda weixi volcanic arc on the eastern margin of the changdu continental block collision between the volcanic arcs and the yangtze continent block during early middle triassic caused the closing of the jinshajiang oceanic basin and the eruption of high si and al potassic rhyolitic rocks along the permian volcanic arc slab breakoff or mountain root delamination under this orogenic belt led to post collisional crustal extension at the end of the triassic forming a series of rift basins on this continental margin arc significant potential for vhms deposits occurs in the submarine volcanic districts of the job mesozoic vhms deposits occur in the post collisional extension environment and cluster in the late triassic rift basins

3 26 ga black smoker type mineralization in the strelley belt pilbara craton western australia early archaean 3 26 ga volcanogenic massive sulphide vms deposits located within the low strain and very low metamorphic grade strelley greenstone belt east pilbara western australia contain exceptionally well preserved sulphide textures which are directly analogous to those formed in black smoker chimneys at present day submarine hydrothermal vents the vms deposits are associated with seafloor alteration zones in and below silicacarbonate laminites at the top of a pile of tholeiitic to calc alkaline intermediate and felsic volcanic rocks with trace element abundances indicative of modem subduction related processes vms mineralization comprises zn rich sulphide lenses with significant cu and barite and variable pb and ag above cu rich stringer zones all of which are similar to phanerozoic vms deposits sulphide sulphate mineralization implicates hydrothermal discharge into sulphate bearing ocean waters

ice core evidence for antarctic sea ice decline since the 1950s the instrumental record of antarctic sea ice in recent decades does not reveal a clear signature of warming despite observational evidence from coastal antarctica here we report a significant correlation p

himalaya the northern frontier of east gondwanaland abstract the himalayan province which represents the northern platform of the peninsular india belonging to east gondwanaland was strongly affected by pan african diastrophism 500 25 ma ago this brought to an end the protracted purana cycle of sedimentation throughout the peninsular india and the lesser himalaya and interrupted basin filling in its northern tethyan domain but the sea returned in the early permian along a narrow depression formed due to rifting of the himalayan crust in what is today the southern lesser himalaya in the rift valley was deposited tillites by glaciers of the gondwana continent under grip of refrigeration along with the glacigene conglomerates were emplaced diamictites generated by submarine slides triggered presumably by earthquakes originating from faults delimiting the rift the diamictities are admixed with lava agglomerate and tuff indicating widespread volcanism in the rift valley the rifting culminated in the breaking away of the tibetan part of the himalaya in the late permian and formation of neotethys between the gondwanaland and the cimmerian microcontinent embodying tibet iran and turkey rivers of the northern peninsular india flowed in the northerly directions since the middle proterozoic through early eocene in the late eocene there was a drastic drainage reversal to south and southeast when the himalaya emerged in the northern front of the gondwanaland

erratum to variations of sulphur isotope signatures in sulphides from the metamorphosed ming cu au volcanogenic massive sulphide deposit newfoundland appalachians canada the ming deposit is an early ordovician bimodal mafic cu au volcanogenic massive sulphide vms deposit in the newfoundland appalachians that was metamorphosed to upper greenschist lower amphibolite facies conditions and deformed in the silurian and devonian the ming deposit consists of several spatially proximal ore bodies of which the 1806 zone 1807 zone ming south up plunge and down plunge and the lower footwall zone are the focus of this paper the ore bodies have similar stratigraphic sequences the ore bodies can be divided into 1 a silicified horizon that caps the massive sulphides 2 semi massive to massive sulphides and 3 sulphide mineralization in a rhyodacitic footwall sulphide mineralization in a rhyodacitic footwall includes a sulphide stringers immediately below the semi massive to massive sulphides and b chalcopyrite pyrrhotite pyrite stringers distally from semi massive to massive sulphides in the lower footwall zone pyrite chalcopyrite pyrrhotite arsenopyrite and galena were analysed by in situ secondary ion mass spectrometry sims for sulphur isotope compositions the isotopic signatures of pyrite chalcopyrite pyrrhotite and arsenopyrite fall within a limited range of 2 8 to 12 0 for semi massive to massive sulphides and sulphide mineralization in the footwall the silicified horizon capping the semi massive to massive sulphides has higher 34s 5 8 19 6 especially for pyrrhotite mean 17 2 2 2 n 8 the sulphur isotope composition of galena is more heterogeneous especially within semi massive to massive sulphides and sulphide stringers ranging from 0 8 to 17 3 mean 6 1 4 3 n 35 and 7 6 to 17 1 mean 13 7 5 3 n 3 respectively geothermometric calculations give insufficient formation and metamorphism temperatures for neighbouring mineral pairs because sulphides were not in isotopic equilibrium while deposited in early ordovician or re equilibrated during silurian devonian metamorphism respectively therefore original isotopic compositions of sulphides at the ming deposit have been preserved modelling of the source of sulphur shows that 1 reduced seawater sulphate and 2 sulphur leached from igneous wall rock and or derived from magmatic fluids are the main sources of sulphur in the ming deposit the influence of igneous sulphur igneous wall rock magmatic fluids increases with temperature and is an important sulphur source for the semi massive to massive sulphides and footwall mineralization in addition to a contribution from thermochemical sulphate reduction tsr of seawater it is difficult to distinguish between sulphur leached from igneous rocks and magmatic fluid related sulphur and it is possible that both sources contributed to the ores at the ming deposit in addition to igneous sulphur the heavy isotopes of the silicified horizon are consistent with the sulphur in this horizon being derived only from thermochemical sulphate reduction of early ordovician seawater sulphate

the origin of chlorite tremolite carbonate rocks associated with the thalanga volcanic hosted massive sulfide deposit north queensland australia the thalanga polymetallic massive sulfide deposit is hosted by felsic volcanics of the cambro ordovician mount windsor subprovince in north queensland the sheetlike sulfide deposit consists of several semiconnected lenses totaling 6 6 million metric tons mt which lie at a single stratigraphic level between underlying subaqueously emplaced rhyolite and overlying dacitic to andesitic lavas sills and volcaniclastic rocks the ores and host rocks have been deformed and metamorphosed to upper greenschist facies associated with the west thalanga orebody are strata bound lenses composed of chlorite tremolite dolomite and calcite that previously have been interpreted as exhalites they extend up to a few hundred meters along the mineralized horizon and locally also exist in the stratigraphic footwall around the fringes of the deposit rhyolitic volcanics beneath the deposit are extensively altered a pervasive sericite chlorite pyrite zone that extends greater than 200 m into the footwall envelops semistratiform proximal quartz pyrite chlorite stringer zones major and trace element geochemical data indicate that zr ti and al remained essentially immobile in the footwall rocks despite intense hydrothermal alteration involving significant mass transfers of mobile elements the chlorite tremolite carbonate assemblages associated with ore lenses have immobile element ratios identical to those of the altered rhyolites carbonate rich assemblages retain some relict spheroidal and rhombic textures in dolomite which suggest formation at an early hydrothermal stage in a matrix of chlorite or in open spaces the chlorite tremolite carbonate rocks probably represent metamorphic equivalents of hydrothermal chlorite quartz dolomite calcite or mg smectite quartz dolomite calcite assemblages the formation of tremolite by metamorphic reaction of quartz and dolomite is consistent with regional metamorphic conditions with allowance for metamorphic decarbonation carbon and oxygen isotope data from dolomite and calcite are consistent with precipitation of primary dolomite at 170 to 250 c from seawater dominated fluid the chlorite tremolite carbonate rocks at thalanga are consequently reinterpreted as altered rhyolitic volcaniclastics containing variable proportions of hydrothermal carbonate they probably formed in a zone of mixing of hydrothermal fluid and seawater in a permeable substrate close to the paleosea floor siliceous ironstones that are present in distal parts of some thalanga ore lenses have very low immobile element contents and are probably true exhalites

brine pool deposition for the zn pb cu massive sulphide deposits of the bathurst mining camp new brunswick canada i comparisons with the iberian pyrite belt abstract the ordovician zn pb cu massive sulphide ore deposits of the bathurst mining camp share many features with those of the devonian carboniferous iberian pyrite belt particularly the tendency to large size tonnage and metal content shape as far as can be determined after allowing for deformation metal content particularly fe cu pb zn and sn mineral assemblages pyrite arsenopyrite pyrrhotite and lack or rarity of sulphates sulphide textures particularly framboidal pyrite lack of chimney structures and rubble mounds irregular metal or mineral zoning and the low degree of zone refining compared to hokuroku ores the major differences between the provinces are the lack of vent complexes and the presence of sn cu ores in the iberian pyrite belt there are also similarities in the geological setting of the two camps both lie within continental terranes undergoing arc continent and continent continent collision and in each case massive sulphide mineralisation followed ophiolite obduction the ore deposits are associated with bimodal volcanic rocks derived from morb and continental crust and marine shales and mineralisation was locally accompanied or followed by deposition of iron formations fluid inclusion data from veins in stockworks from at least six of the iberian massive sulphide deposits point to sulphide deposition having taken place in basins containing mostly spent saline ore forming fluids brine pools and it is suggested that most of the major features of the bathurst deposits can be explained by similar processes the proposed model is largely independent of ocean sulphate and o 2 content whereas low values of each are requisites for the current spreading plume model of sulphide deposition in the bathurst camp

dating the siple dome antarctica ice core by manual and computer interpretation of annual layering the holocene portion of the siple dome antarctica ice core was dated by interpreting the electrical visual and chemical properties of the core the data were interpreted manuallyandwith acomputeralgorithm the algorithm interpretation was adjusted to be consistent with atmospheric methane stratigraphic ties to the gisp2 greenland ice sheet project 2 ice core 10 be stratigraphic ties to the dendrochronology 14 c recordandthedatedvolcanic stratigraphy thealgorithm interpretation ismorecon sistent andbetter quantifiedthanthe tedious and subjective manual interpretation

volcanic and structural reconstruction of the deformed and metamorphosed ming volcanogenic massive sulfide deposit canada implications for ore zone geometry and metal distribution

a switch from si oh 4 to no 3 depletion in the glacial southern ocean 1 phytoplankton in the antarctic deplete silicic acid si oh 4 to a far greater extent than they do nitrate no3 this pattern can be reversed by the addition of iron which dramatically lowers diatom si oh 4 no3 uptake ratios higher iron supply during glacial times would thus drive the antarctic towards no3 depletion with excess si oh 4 remaining in surface waters new 30si and 15n records from antarctic sediments confirm diminished si oh 4 use and enhanced no3 depletion during the last three glaciations the present low si oh 4 water is transported northward to at least the subtropics we postulate that the glacial high si oh 4 water similarly may have been transported to the subtropics and beyond this input of si oh 4 may have caused diatoms to displace coccolithophores at low latitudes weakening the carbonate pump and increasing the depth of organic matter remineralization these effects may have lowered glacial atmospheric pco2 by as much as 60 ppm

the bashkirian fenestella shales and the moscovian chaetetid shales of the tethys himalaya south tibet nepal and india abstract the fenestella shales are a mid carboniferous marker unit which has long been described from classic localities of the nw himalaya kashmir spiti correlative shaly units have recently been traced in central nepal and as far as south tibet where they yielded varied brachiopod assemblages indicative of bashkirian age a second distinct interval of black shales characterized by the abundance of chaetetids and directly underlying the widespread gondwanan diamictites has been dated as moscovian in spiti and represents the youngest fossiliferous horizon hitherto identified in the upper carboniferous of the tethys himalaya the chaetetid shales are recognized also in manang whereas in south tibet the stratigraphic framework still needs improved definition these major fossiliferous black shale units marking repeated transgressive events in the middle part of the himalayan rift sequence have not only major stratigraphic significance but also represent a fundamental landmark in palaeogeographic and palaeoclimatic reconstructions of northern gondwana with the onset of continental rifting arid tropical climates at the close of the tournaisian were replaced by temperate humid conditions in the visean serpukhovian when diamictites were deposited in south tibet after this first cooling stage the fenestella shales mark a widespread transgression at the very beginning of the late carboniferous coupled with reduced tectonic activity and temperate to temperate warm climates after renewed tectonic activity during a second cooling episode marked by local deposition of diamictites in central nepal the chaetetid shales represent another major transgression in the moscovian shortly preceding the final and most intense cooling event marked by deposition of glacio marine diamictites in the whole tethys himalaya from kashmir to south tibet during the latest carboniferous earliest permian two fossiliferous horizons containing very similar brachiopod faunas of early late carboniferous age have recently been found also in north karakorum at lower southern latitudes where climatic conditions always remained temperate and there is no trace of upper palaeozoic glacial deposits or ice rafted debris

subsea floor replacement in volcanic hosted massive sulfide deposits abstract recent research on volcanic hosted massive sulfide vms deposits indicates that syngenetic subsea floor replacement ores form an important component of many deposits in the context of vms deposits subsea floor replacement can be defined as the syn volcanic formation of sulfide minerals within pre existing volcanic or sedimentary deposits by infiltration and precipitation in open spaces fractures inter and intra granular porosity as well as replacement of solid materials there are five criteria for distinguishing subsea floor replacement in massive sulfide deposits 1 mineralized intervals are enclosed within rapidly emplaced volcanic or sedimentary facies lavas intrusions subaqueous mass flow deposits pyroclastic fallout 2 relics of the host facies occur within the mineral deposit 3 replacement fronts occur between the mineral deposit and the host lithofacies 4 the mineral deposit is discordant to bedding and 5 strong hydrothermal alteration continues into the hanging wall without an abrupt break in intensity criteria 1 3 are diagnostic of replacement whereas criteria 4 and 5 may suggest replacement but are not alone diagnostic because clastic sulfide ores contain accessory rock fragments collected by the parent sediment gravity flow s during transport criteria 2 can only be applied to massive semi massive disseminated or vein style deposits and not clastic ores the spectrum of vms deposit types includes deposits that have accumulated largely subsea floor and others in which sedimentation and volcanism were synchronous with hydrothermal activity and precipitation of sulfides occurred at and below the sea floor over the life of the hydrothermal system deposits that formed largely subsea floor are mainly hosted by syn eruptive or post eruptive volcaniclastic facies gravity flow deposits water settled fall autoclastic breccia however some subsea floor replacement vms deposits are hosted by lavas and syn volcanic intrusions sills domes cryptodomes burial of sea floor massive sulfide by lavas or sediment gravity flow deposits can interrupt sea floor mineralization and promote subsea floor replacement and zone refining the distance below the sea floor at which infiltration and replacement took place is rarely well constrained with published estimates ranging from less than 1 to more than 500 m but mainly in the range 10 200 m the upper few tens to hundreds of metres in the volcano sedimentary pile are the favoured position for replacement as clastic facies are wet porous and poorly consolidated in this zone and at greater depths become progressively more compacted dewatered altered and less amenable to large scale infiltration and replacement by hydrothermal fluids furthermore sustained mixing between the upwelling hydrothermal fluid and cold seawater is regarded as a major cause of sulfide precipitation in vms systems and this mixing process generally becomes less effective with increasing depth in the volcanic pile the relative importance of subsea floor replacement in vms systems is related principally to four factors the permeability and porosity patterns of host lithofacies sedimentation rate the relative ease of replacement of host lithofacies especially glassy materials and early formed alteration minerals during hydrothermal attack and physiochemical characteristics of the hydrothermal fluid

problems in applying preservation facies and sequence models to sinian neoproterozoic glacial sequences in australia and asia abstract the sinian 800 530 ma is an extraordinary period of earth history characterized by the transition from simple to complex multicellular organisms and by extreme variations in climate eustasy and possibly tectonics understanding sinian stratigraphy may help interpret the co evolution of life and environment during the period though sinian successions are poorly dated and difficult to correlate preservation facies and sequence models based on mesozoic recent successions may be used to interpret them preservation models based on basin subsidence permit estimates of how thick and complete successions can be in different tectonic settings and how long it took for them to be deposited facies models for rift craton shelf slope and basin environments help in identification of these different tectonic settings sequence models facilitate interpretation of the interplay of tectonic subsidence eustasy rates of sedimentation and climate such models applied to the sinian successions of australia and asia indicate the following great shallowing upwards megacycles occur in sinian successions and each ends with regional glaciations deep rift basins formed around 850 800 ma preserve the oldest megacycles but these basins soon were filled with rapidly deposited glaciogenic sediments relatively complete sequences are found only in deep basins subject to repeated rifting cratons and shallow shelves preserve only the youngest megacycles older deposits have been removed by younger glacial advances deep shelves and slopes preserve one to three megacycles depending on the timing of the start of passive margin subsidence megasequences can be correlated based on limited radiometric dating and inferred regional distribution of unique rock types but these sequences are not developed to the same extent in all blocks problems in correlating the four great megacycles recognized elsewhere with those of asia will persist until the requisite facies analysis and u pb dating of interbedded volcanics are done

a genetic model for the woodcutters pbznag orebodies northern territory australia abstract the woodcutters pb zn ag base metal deposit is hosted by an inverted intracontinental basin sequence of early proterozoic age near darwin australia the 1800 ma inversion event d1 resulted in horizontal upright folds f1 axial plane cleavage s1 and extension lineation le and lowermost greenschist facies metamorphism northwest trending left lateral faults of late proterozoic to cambrian age offset the folds a mine sequence of five dolomitic carbonate units in dominant slate defines the 3 and 5 anticlines with the 3 and 5 faults on their eastern limbs a lamprophyre dyke within the 5 fault is pre s1 a second is oblique and post dates s1 the deposit has two main distributions of sulphide banded pb zn fe massive sulphides which have saddle inverted wishbone and poddy shaped forms in the hinge zones of the 3 and 5 anticlines and laminated crack seal pyrite rich vein type mineralization which partly occupies the 3 and 5 faults the banded layered ore is mainly stratiform and stratigraphically controlled having mimetically replaced bedding in carbonate rich units the fault hosted mineralization comprises the 3 and 5 feeder channels vertically linking the banded sulphide orebodies mine meso and micro scale relationships between the sulphides and the dykes faults and d1 structures such as folds f1 s 1 l e and boudinage strongly suggest that the ore was emplaced pre to early syn d1 there is a compelling case for the ore having been folded overprinted by cleavage and locally remobilized post d1 emplacement of ore is disproved but the possibility of syn deformational genesis that is progressive emplacement of ore during folding and cleavage development remains substantially after syn s1 remobilization the ore underwent left lateral faulting and fault related remobilization followed by intrusion of lamprophyre and intrusion related remobilization the genetic model involves basin dewatering and channelled flow up deep reaching faults reactivated by the onset of basin inversion the ore formed by volume for volume replacement of carbonate rich units and was progressively folded and remobilized during overprinting by cleavage woodcutters is a deformed epidiagenetic deposit comprising replacement ore and attendant feeder mineralization

syngenetic origin for the sediment hosted disseminated gold deposits in nw sichuan china ore fabric evidence abstract sediment hosted disseminated gold deposits in nw sichuan china have many features in common with the well known carlin type deposits in the western united states they are hosted by middle upper triassic turbidites composed of 1300 4300 m of rhythmically interbedded slightly metamorphosed calcareous sandstone siltstone and slate the ore bodies are typically layer or lens like in shape and generally extend parallel to the stratification of the host sedimentary rocks with a strike length of tens to several hundreds of meters the immediate host rocks consist mainly of calcareous slate and siltstone characterized by high contents of organic matter and diagenetic pyrite the main primary ore minerals associated with gold mineralization include pyrite arsenopyrite realgar and stibnite gangue minerals comprise mostly quartz calcite and dolomite gold is extremely fine grained usually less than 1 m and cannot be seen with an electron microscope two types of ore mineralization have been recognized in the deposits the stratiform ores are composed of rhythmical interbeds of sulfides e g pyrite arsenopyrite realgar stibnite interpreted to be authigenic and detrital quartz quartzite sericite and graphite of allogenic origin they were folded and deformed concordantly with host rocks and grade both vertically and laterally into normal country rocks another type of ore forms a network of numerous gold bearing veins and veinlets of quartz calcite sulfides of millimeter centimeter decimeter and even meter scale in width the network ore randomly fills fissures microfissures and cleavages but still is stratabound in character detailed studies on ore fabrics show abundant evidence for synsedimentary origins although subsequent diagenesis metamorphism tectonic deformation and epigenetic hydrothermal activity have significantly remolded the primary fabrics primary fabrics are shown either by rhythmical interbeds of different mineral components parallel to the bedding or by the change of grain size of the same minerals such as pyrite realgar and stibnite the layer inhomogeneity of the stratiform ore is clarified by parallel overprints of later schistosity planes resulting in distinct grain orientation and elongation aggregate polarization and undulating extinction of ore minerals especially of mechanically and chemically extremely mobile ones such as realgar and stibnite it is proposed that the stratiform ores in these chinese deposits were most probably formed concurrently with their host middle upper triassic turbidites in submarine hot spring environments while the network mineralization was formed as a result of complicated processes such as diagenesis weak metamorphism tectonic deformation and epigenetic hydrothermal activity responsible for the remobilization or reworking of the pre existing stratiform ores geochemical data also support this genetic model

mineralogy of gold in the elshitsa massive sulphide deposit sredna gora zone bulgaria the elshitsa volcanic hosted massive sulphide deposit occurs in the central part of the srena gora metallogenic zone in bulgaria the gold bearing massive sulphide mineralization is considered to be the product of an island arc volcano plutonic process and hydrothermal activity that took place during the late cretaceous in addition to the major gold hosted opaque minerals such as pyrite chalcopyrite sphalerite and galena there are minor phases of tennantite goldfieldite se bearing aikinite native silver and bornite in the massive sulphide lenses and stringer zones most of the sulphide minerals are se bearing all of the six mineral assemblages that were deposited during the pyrite and copper pyrite stages of mineralization are gold bearing the gold tenor as a rule is less than 1 g t native gold and electrum occur as blebs or intergranular particles in the sulphide minerals gold in the early massive pyrite is of submicroscopic type 100 m in the late gold sulphide assemblages the electrum fineness in 41 individually studied grains varies between 780 and 992 with a mean of 895 native silver was found in association with bornite cu te sb and bi are the most common trace elements in gold and electrum the cu zn pb association is most important as a au ag carrier a model for gold behaviour during sulphide deformation is proposed involving coarsening of gold grain size from the earlier to the later sulphide mineral assemblages

lithostratigraphic correlation of blaini formation late proterozoic lesser himalaya india with other late proterozoic tillite sequences the blaini formation of the lesser himalaya has long been considered permo carboniferous in age on simple lithological correlation with gondwana tillites in southern india rare and non repeatable finds of fossils from the type area were thought to confirm this recently lower cambrian faunas have been recorded from the overlying tal and krol formations and possible metazoan trails recorded from the blaini itself in addition the blaini formation is even on a lithostratigraphic comparison much more like other late proterozoic glacial sequences the term blaini formation should only be used for rocks of the type area not for widely scattered glacial deposits which may or may not be correlatable with the type section the persistent belief in the paleozoic age of the blaini and adjacent formations has for long retarded unterstanding of lesser himalaya stratigraphy and tectonics

a combined fluid inclusion and s pb isotope study of the neoproterozoic pingshui volcanogenic massive sulfide cu zn deposit southeast china abstract the pingshui cu zn deposit is located in the jiangshan shaoxing fault zone which marks the neoproterozoic suture zone between the yangtze block and cathaysia block in south china it contains 0 45 million tons of proven ore reserves with grades of 1 03 wt cu and 1 83 wt zn this deposit is composed of stratiform massive sulfide ore bodies which contain more than 60 vol sulfide minerals these ore bodies are hosted in altered mafic and felsic rocks spilites and keratophyres of the bimodal volcanic suite that makes up the neoproterozoic pingshui formation metallic minerals include pyrite chalcopyrite sphalerite tennantite tetrahedrite and magnetite with minor galena gangue minerals are quartz sericite chlorite calcite gypsum barite and jasper three distinct mineralogical zones are recognized in these massive sulfide ore bodies a distal zone composed of sphalerite pyrite barite zone i an intermediate zone characterized by a pyrite sphalerite chalcopyrite assemblages zone ii and a proximal zone containing chalcopyrite pyrite magnetite zone iii a thin layer of exhalative jaspilite overlies the sulfide ore bodies except in the proximal zone the volcanic rocks of the pingshui formation are all highly altered spilites and keratophyres but their trace element geochemistry suggests that they were generated by partial melting of the depleted mantle in an island arc setting homogenization temperatures of the primary fluid inclusions in quartz from massive sulfide ores are between 217 and 328 c and their salinities range from 3 2 to 5 7 wt nacl equivalent raman spectroscopy of the fluid inclusions showed that water is the dominant component with no other volatile components fluid inclusion data suggest that the ore forming fluids were derived from circulating seawater the 34 s values of pyrite from the massive sulfide ores range from 3 6 to 3 4 indicating that the sulfur was primarily leached from the arc volcanic rocks of the pingshui formation both pyrite from the massive sulfide ores and plagioclase from the spilites have similar lead isotope compositions implying that the lead was also derived from the pingshui formation the low lead contents of the massive sulfide ores and the geochemistry of their host rocks are similar to many vms cu zn deposits in canada e g noranda and thus can be classified as belonging to the bimodal mafic subtype the presence of magnetite and the absence of jaspilite and barite at the 505 m level in the pingshui deposit suggest that this level is most likely the central zone of the original lateral massive sulfide ore bodies if this interpretation is correct the deep part of the pingshui cu zn deposit may have significant exploration potential

early carboniferous onset of gondwanian glaciation and neo tethyan rifting in south tibet at least four diamictite bearing intervals of early carboniferous age containing faceted pebbles trapezoidal cobbles and boulders up to 1000 m3 in volume have been recognized and traced for over 200 km along the tethys himalayan zone of south tibet from east of everest to west of shishapangma these largely glacio marine sediments intercalated within the rakyang formation which overlies lower tournaisian limestones and underlies lower bashkirian black shales were deposited during the visean to serpukhovian shore ice thus began to form in this region of northern gondwana several tens of million years earlier than previously thought this glacial event occurred at middle southern latitudes and was triggered by basin inversion and tectonic uplift in the first stages of neo tethyan rifting as documented by the close association of diamictites with olistoliths and olistostromes in lower carboniferous units after a transgressive interglacial episode in the bashkirian a much more widespread glaciation occurred in the latest carboniferous and was shortly followed by continental break up and opening of neo tethys in the late early permian

geology and lithogeochemistry of hydrothermal mudstones from the upper block near the duck pond volcanogenic massive sulfide vms deposit newfoundland canada evidence for low temperature venting into oxygenated mid cambrian seawater pyrite and pyrrhotite rich mudstones are spatially associated with cambrian 512 509 ma volcanogenic massive sulfide vms deposits throughout the tally pond group central newfoundland canada at the duck pond mine sulfide rich mudstones are hosted within a weakly mineralized upper block that structurally overlies the deposit but is older 513 versus 509 ma the mudstones are laminated 10 30 cm thick and pyrite and pyrrhotite rich and occur along pillow lava selvages or in between pillow lavas rhyolite flows and volcaniclastic rocks the mudstones are laterally extensive and proximal to the mudstone host rocks are hydrothermally altered to epidote quartz chlorite basalt host and sericite quartz rhyolite host lithogeochemical data for the sulfide rich mudstones reflect the varying contributions of elements from sedimentary detritus hydrothermal discharge and hydrogenous scavenging from middle cambrian seawater the mudstones have minor detrital element abundances and significant hydrothermal element enrichments i e elevated fe2o3 s pb zn cu and ba concentrations high fe al ratios the hydrothermal mudstones are also enriched in oxyanions i e p2o5 u v cr ni co and hg interpreted to have been enriched via oxidative scavenging from seawater by fe oxide oxyhydroxide particles the mudstones also have ree y signatures similar to modern oxygenated seawater with high y ho and negative ce anomalies ce ce 0 40 0 86 average 0 58 which correlate with adsorbed oxyanion concentrations the low eu eu 1 02 1 86 average 1 22 in the mudstones suggest that they were deposited from low temperature 250 c fe rich hydrothermal fluids that likely formed a buoyant plume into an oxygenated water column the ree y oxyanion signatures suggest that the particles within the hydrothermal plume had sufficient residence time to scavenge oxyanions from seawater and inherit a middle cambrian seawater signature the predominant seawater ree y oxyanion signature in the duck pond upper block sulfide rich mudstones suggests that they are distal hydrothermal sedimentary rocks that could have formed up to 10 km from their original vent sources correspondingly to utilize hydrothermal mudstones as vectors to mineralization in the tally pond belt and similar belts globally it is critical to identify vent proximal samples that have hydrothermal signatures i e high fe al base metals ba s with subdued seawater and adsorption signatures i e chondritic y ho low p2o5 ni u co cr v and hg indicating minimal residence time in the water column and deposition proximal to the vent

zn pb cu massive sulfide deposits brine pool types occur in collisional orogens black smoker types occur in backarc and or arc basins volcanic hosted massive sulfide deposits of zn pb cu type were derived either from seawater dominated buoyant fluids that built mounds on the seafloor e g the ores of the hokuroku basin japan or from saline fluids that reversed buoyancy on mixing with seawater and filled basins on the seafloor e g several ores of the iberian pyrite belt and the mount read province in tasmania the hokuroku ores formed above subduction zones during protracted periods of regional extension but both the iberian pyrite belt and the mount read province formed under extensional stress during continent continent iberia or arc continent mount read collision and orogenesis in the iberian pyrite belt oblique convergence resulted in transcurrent faulting and this may also be the case for the mount read province transcurrent faulting may have allowed easy vertical access for the ore related magmas some of which were sourced in the asthenosphere as well as the blueschist and eclogitic facies emplaced in adjacent terrains and possibly also saline fluids exsolved from the magmas

rare earth element geochemistry of the woxi w sb au deposit hunan province south china the woxi w sb au deposit in hunan south china is hosted by proterozoic metasedimentary rocks a turbiditic sequence of slightly metamorphosed greenschist facies gray green and purplish red graywacke siltstone sandy slate and slate the mineralization occurs predominantly 70 as stratabound stratiform ore layers and subordinately as stringer stockworks the former consists of rhythmically interbedded banded to finely laminated stibnite scheelite quartz pyrite and silty clays whereas the latter occurs immediately beneath the stratabound ore layers and is characterized by numerous quartz pyrite gold scheelite stringer veins or veinlets that are typically either subparallel or subvertical to the overlying stratabound ore layers the deposit has been the subject of continued debate in regard to its genesis rare earth element geochemistry is used here to support a sedimentary exhalative sedex origin for the woxi deposit the ree signatures of the metasedimentary rocks and associated ores from the woxi w sb au deposit remained unchanged during post depositional processes and were mainly controlled by their provenance the original ore forming hydrothermal fluids as demonstrated by fluid inclusions in quartz from the banded ores are characterized by variable total ree concentrations 3 5 to 136 ppm marked lree enrichment lan ybn 28 248 lree hree 16 to 34 and no significant eu anomalies eu eu 0 83 to 1 18 they were most probably derived from evolved seawater that circulated in the clastic sediment pile and subsequently erupted on the seafloor the bulk banded ores are enriched in hree lan ybn 4 6 11 4 lree hree 3 to 14 and slightly depleted in eu eu eu 0 63 to 1 14 relative to their parent fluids this is interpreted as indicating the influence of seawater rather than a crystallographic control on ree content of the ores within a single ore layer the degree of hree enrichment tends to increase upward while the total ree concentrations decrease reflecting greater influence and dilution of seawater there is a broad similarity in chondrite normalized ree patterns and the amount of ree fractionation of the bandedoresinthisstudyandexhalitesfromothersedex typepolymetallicoredeposits suggestingasimilargenesisforthesedeposits

the first greenland ice core record of methanesulfonate and sulfate over a full glacial cycle methanesulfonate msa in ice cores has attracted attention as a possible tracer of past oceanic emissions of dimethylsulfide dms after sulfate msa is the second most prevalent aerosol oxidation product of dms but in contrast to sulfate dms oxidation is the only known source of msa the hypothesis by charlson et al 1987 of a climate feedback mechanism with sulfur emissions from marine phytoplankton influencing the cloud albedo adds to the interest in establishing long records of msa and non seasalt sulfate spanning large climatic changes records of msa and non seasalt sulfate covering time periods from a few years to thousands of year have been extracted from antarctic ice cores ivey et al 1986 saigne and legrand 1987 legrand and feniet saigne 1991 mulvaney et al 1992 but only the record from the vostok ice core legrand et al 1991 covers a full glacial cycle the concentrations of msa and non seasalt sulfate in antarctica have been found to increase under glacial conditions here we present the first northern hemisphere record of msa and the first continuous record of non seasalt sulfate both extracted from the renland ice core east greenland the records are extending from the holocene to the eem interglacial 130 000 years b p the contrast to the southern hemisphere records is striking with a decreasing concentration of msa with the advance of glaciation but an increasing concentration of non seasalt sulfate a strong linear relationship is found in the renland ice core between the ratio of msa to non seasalt sulfate and the temperature with higher ratios associated with warmer climatic stages while the opposite relationship to temperature is found in the vostok ice core a more complicated picture is emerging of the use of msa in ice cores as a quantitative tracer which suggests that previous interpretations can have been overly simplistic

volcanogenic related origin of sulfide rich quartz veins evidence from o and s isotopes at the geant dormant gold mine abitibi belt canada the geant dormant gold mine is a sulfide rich quartz vein gold deposit hosted by a volcano sedimentary sequence and an associated felsic endogenous dome and dikes the auriferous quartz sulfide veins were preceded by two synvolcanic gold bearing mineralizing events early sulfidic seafloor related and later disseminated pyrite in the felsic dome this deposit differs from classical archean auriferous quartz vein deposits by the low carbonate and high sulfide contents of the veins and by their formation prior to ductile penetrative deformation the 18o values of quartz associated with seafloor related auriferous sulfides average 11 9 0 6 n 3 the seafloor hydrothermal fluids had a 18o value of 3 2 calculated at 250 c the oxygen isotope composition of quartz and chlorite from veins average 12 5 0 3 n 20 and 5 9 1 1 n 4 respectively assuming oxygen isotope equilibrium between quartz and chlorite the veins formed at a temperature of 275 c which is consistent with the calculated temperature of 269 10 c from chlorite chemistry the gold bearing fluids had a 18o value of 4 7 calculated at 275 c the 34s values of sulfides from the three gold events range from 0 6 to 2 8 n 32 and are close to magmatic values sulfur isotope geothermometry constrains the sulfide precipitation in the gold bearing veins at a temperature of 350 c the similarity of the isotope data the calculated 18o of the mineralizing fluids and the likely seawater fluid source suggest that the three mineralizing events are genetically related to a volcanogenic hydrothermal system the high value of the auriferous fluids 18o 4 7 is attributed to a significant magmatic fluid contribution to the evolved seawater dominated convective hydrothermal system the two stage filling of veins at increasing temperature from quartz chlorite 275 c to sulfides 350 c may reflect the progressive maturation of volcanogenic hydrothermal systems these results together with field and geochemical data suggest that formation of gold rich volcanogenic systems require specific conditions that comprise a magmatic fluid contribution and gold from arc related felsic rocks coeval with the mineralizing events this study shows that some auriferous quartz vein orebodies in archean terranes are formed in volcanogenic rather than mesothermal systems

the interplay of evolved seawater and magmatic hydrothermal fluids in the 3 24 ga panorama volcanic hosted massive sulfide hydrothermal system north pilbara craton western australia the 3240 ma panorama volcanic hosted massive sulfide vhms district is unusual for its high degree of exposure and low degree of postdepositional modification in addition to typical seafloor vhms deposits this district contains greisen and vein hosted mo cu zn sn mineral occurrences that are contemporaneous with vhms orebodies and are hosted by the strelley granite complex which also drove vhms circulation hence the panorama district is a natural laboratory to investigate the role of magmatic hydrothermal fluids in vhms hydrothermal systems regional and proximal high temperature alteration zones in volcanic rocks underlying the vhms deposits are dominated by chlorite quartz albite assemblages with lesser low temperature sericite quartz k feldspar assemblages these assemblages are typical of vhms hydrothermal systems in contrast the alteration assemblages associated with granite hosted greisens and veins include quartz topaz muscovite fluorite and quartz muscovite sericite chlorite ankerite these vein systems generally do not extend into the overlying volcanic pile fluid inclusion and stable isotope studies suggest that the greisens were produced by high temperature 590 c high salinity 38 56 wt nacl equiv fluids with high densities 1 3 g cm3 and high 18o 9 3 0 6 these fluids are compatible with the measured characteristics of magmatic fluids evolved from the strelley granite complex in contrast fluids in the volcanic pile including the vhms ore forming fluids were of lower temperature 90 270 c lower salinity 5 0 11 2 wt nacl equiv with lower densities 0 88 1 01 g cm3 and lower 18o 0 8 2 6 these fluids are compatible with evolved paleoarchean seawater fluids that formed the quartz chalcopyrite sphalerite cassiterite veins which are present within the granite complex near the contact with the volcanic pile were intermediate in temperature and isotopic composition between the greisen and volcanic pile fluids t 240 315 c 18o 4 3 1 5 and are interpreted to indicate mixing between the two end member fluids evidence of mixing between evolved seawater and magmatic hydrothermal fluid within the granite complex together with the lack of evidence for a magmatic component in fluids from the volcanic pile suggest partitioning of magmatic hydrothermal from evolved seawater hydrothermal systems in the panorama vhms system this separation is interpreted to result from either the swamping of a relatively small magmatic hydro thermal system by evolved seawater or density contrasts precluding movement of magmatic hydrothermal fluids into the volcanic pile variability in the salinity of fluids in the volcanic pile combined with evidence for mixing of low and high salinity fluids in the massive sulfide lens is interpreted to indicate that phase separation occurred within the panorama hydrothermal system although we consider this phase separation to have most likely occurred at depth within the system as has been documented in modern vhms systems the data do not allow the location of the inferred phase separation to be determined

role of metalliferous mudstones and detrital shales in the localization genesis and paleoenvironment of volcanogenic massive sulphide deposits of the tally pond volcanic belt central newfoundland canada the cambrian tally pond volcanic belt in central newfoundland contains numerous volcanogenic massive sulphide vms deposits and prospects associated with exhalative metalliferous mudstones deposits in the belt are bimodal felsic vms deposits that are both base metal bearing e g duck pond boundary and base metal and precious metal bearing lemarchant at the lemarchant deposit metalliferous mudstones are stratigraphically and genetically associated with mineralization in the remainder of the tally pond belt detrital shales occur predominantly in the northeastern part of the belt mostly as unrelated mid ordovician structural blocks in the upper sections of the cambrian volcanic stratigraphy but locally also are intercalated with metalliferous mudstones their relationships to massive sulphides are less obvious with many spatially but not necessarily genetically related to mineralization upper cambrian to lower ordovician black shales from bell island which represent pelagic sedimentation not associated with hydrothermal activity and volcanism are compared with the tally pond belt mudstones and shales exhalative mudstones like those at lemarchant have elevated fe al and base metal values and have shale normalized negative ce and positive eu anomalies indicative of deposition from high temperature 250 c hydrothermal fluids within an oxygenated water column mudstones and shales sampled from other tally pond prospects have more variable signatures ranging from hydrothermal to nonhydrothermal black shales no positive eu anomalies flat rare earth element patterns low fe al and base metal contents to those that have mixed signatures accordingly mudstones from areas with a lemarchant like hydrothermal and vent proximal character are more attractive exploration targets than mudstones and shales with predominantly detrital signatures

gold in the brunswick no 12 volcanogenic massive sulfide deposit bathurst mining camp canada evidence from bulk ore analysis and laser ablation icp ms data on sulfide phases the 329 mt brunswick no 12 volcanogenic massive sulfide deposit total resource of 163 mt at 10 4 zn 4 2 pb 0 34 cu and 115 g t ag is hosted within a middle ordovician bimodal volcanic and sedimentary sequence massive sulfides are for the most part syngenetic and the bulk of the sulfide ore occurs as a zn pb rich banded sulfide facies that forms an intimate relationship with a laterally extensive algoma type iron formation and defines the brunswick horizon zone refining of stratiform sulfides is considered to have resulted in the development of a large replacement style cu rich basal sulfide facies which is generally confined between the banded sulfide facies and an underlying stringer sulfide zone complex polyphase deformation and associated lower to upper greenschist facies regional metamorphism is responsible for the present geometry of the deposit textural modification has resulted in a general increase in grain size through the development of pyrite and arsenopyrite porphyroblasts which tend to overprint primary mineral assemblages despite the heterogeneous ductile deformation primary features have locally been preserved such as fine grained colloform pyrite and base and precious metal zonation within the main zone base metal and trace element abundances in massive sulfides from the brunswick no 12 deposit indicate two distinct geochemical associations the basal sulfide facies characterized by a proximal high temperature hydrothermal signature cu co bi se contains generally low au contents averaging 0 39 ppm n 34 conversely au is enriched in the banded sulfide facies averaging 1 1 ppm au n 21 and is associated with an exhalative suite of elements zn pb as sb ag sn finely laminated sulfide lenses hosted by iron formation at the north end of the main zone are further enriched in au averaging 1 7 ppm n 41 and ranging up to 8 2 ppm laser ablation inductively coupled plasma mass spectrometry icp ms analyses of pyrite n 97 from the north end of the main zone average 2 6 ppm au and range from the detection limit 0 015 ppm to 21 ppm overall these analyses reveal a distinct au sb as ag hg mn association within pyrite grains gold is strongly enriched in large pseudo primary masses of pyrite that exhibit relict banding and fine grained cores smaller euhedral pyrite porphyroblasts and euhedral rims of metamorphic origin surrounding the pyrite masses contain much less au sb ag as and sn arsenopyrite occurring chiefly as late porphyroblasts contains less au averaging 1 0 ppm and ranging from the detection limit 0 027 ppm to 6 9 ppm depth profiles for single spot laser ablation icp ms analyses of pyrite and arsenopyrite display uniform values of au and an absence of discrete microscopic inclusions of au bearing minerals which is consistent with chemically bonded au in the sulfide structure the pervasive correlation of au with sn in the zn pb rich banded sulfide facies suggests similar hydrothermal behavior during the waxing stages of deposition on the seafloor under high temperature 350oc and moderate to low ph conditions au and sn in hydrothermal fluids would be transported as chlorocomplexes an abrupt decrease in temperature and ah2s accompanied by an increase in fo2 and ph during mixing with seawater would lead to the simultaneous destabilization of both au and sn chlorocomplexes the enrichment of au in fine grained laminated sulfides on the periphery of the deposit accompanied by sporadic occurrences of barite and fe poor sphalerite supports lower hydrothermal fluid temperatures analogous to white smoker activity on the flanks of a large volcanogenic massive sulfide system in lower temperature 350oc and mildly acidic hydrothermal fluids au would be transported by thiocomplexes which exhibit multifunctional retrograde prograde solubility and a capacity to mobilize au to the outer parts of the sulfide mound the sluggish nature of this low temperature venting together with larger variations in ambient fo2 could lead to a sharp enrichment of au towards the stratigraphic hanging wall of massive sulfide deposits

textural and chemical characteristics of diagenetic and hydrothermal alteration in glassy volcanic rocks examples from the mount read volcanics tasmania the mount black and sterling valley volcanics comprise a complex cambrian succession of originally glassy felsic to mafic submarine volcanic facies in western tasmania the mount black and sterling valley volcanics have been modified by the combined effects of diagenesis hydrothermal alteration and regional metamorphism metamorphosed diagenetic and hydrothermal alteration facies have been distinguished using a combination of alteration mineralogy overprinting relationships texture distribution intensity and whole rock geochemistry alteration facies that are interpreted to be the regionally metamorphosed equivalents of diagenetic clays and zeolites are regionally extensive and overprinted by the regional cleavage although widespread their distribution is patchy and their intensities are highly variable reflecting the complexity of the original textures in glassy volcanic rocks thin films of sericite carbonate and chlorite sericite hematite replace clays that coated original glassy surfaces at the onset of diagenesis prior to compaction feldspar quartz sericite chlorite sericite and chlorite sericite hematite alteration facies replace zeolites and clays that filled pore space and altered glass prior to and synchronous with compaction the final diagenetic alteration facies chlorite epidote began after compaction and continued during metamorphism diagenetic alteration involved significant mineralogical and textural changes but only minor changes in chemistry the chemical changes associated with diagenetic alteration facies are consistent with the interaction of rhyolitic and basaltic glass with seawater during burial alteration facies that are interpreted to be hydrothermal are local in distribution crosscut stratigraphic boundaries and involve significant changes in texture mineralogy and composition early hydrothermal alteration facies quartz sericite and calcite quartz hematite predated compaction and were synchronous with diagenesis chlorite calcite magnetite and chlorite pyrite alteration facies were synchronous with regional deformation and are associated with tectonic breccias faults and shear zones chlorite quartz calcite alteration facies postdated regional deformation