fluid inclusion characteristics of intrusion related gold mineralization tombstone tungsten magmatic belt yukon territory canada intrusion hosted low sulfide sheeted vein systems are common within many plutons and stocks of the middle cretaceous tombstone tungsten magmatic belt yukon territory and host significant gold mineralization fluid inclusion characteristics of five such systems namely emerald lake dublin gulch scheelite dome mike lake and mactung constrain the vein forming fluid composition formation temperatures and pressures hydrothermal fluid processes and potential fluid sources the veins contain a wide range of fluid inclusion types ubiquitous type 1a and 1b inclusions are low salinity 1a xnacl 1 kbar at emerald lake and dublin gulch and 2 kbar at mactung and scheelite dome that potentially control fluid composition and evolution a variety of fluid processes may have been responsible for gold precipitation including immiscibility and or release of an evolving magmatic fluid

environmental responses of the northeast antarctic peninsula to the holocene climate variability in this study we present a unique high resolution holocene record of oceanographic and climatic change based on analyses of diatom assemblages combined with biomarker data from a sediment core collected from the vega drift eastern antarctic peninsula eap these data add to the climate framework already established by high resolution marine sedimentary records from the palmer deep western antarctic peninsula wap heavy sea ice conditions and reduced primary productivity were observed prior to 7 4 ka b p in relation with the proximity of the glacial ice melt and calving subsequent holocene oceanographic conditions were controlled by the interactions between the westerlies antarctic circumpolar current acc weddell gyre dynamics a warm period characterized by short seasonal sea ice duration associated with a southern shift of both acc and westerlies field persisted until 5 ka b p this warm episode was then followed by climate deterioration during the middle to late holocene 5 to 1 9 ka b p with a gradual increase in annual sea ice duration triggered by the expansion of the weddell gyre and a strong oceanic connection from the eap to the wap increase of benthic diatom species during this period was indicative of more summer autumn storms which was consistent with changes in synoptic atmospheric circulation and the establishment of low to high latitude teleconnections finally the multicentennial scale variability of the weddell gyre intensity and storm frequency during the late holocene appeared to be associated with the increased el nino southern oscillation frequency

alligator ridge district east central nevada carlin type gold mineralization at shallow depths carlin type deposits in the alligator ridge mining district are present sporadically for 40 km along the north striking mooney basin fault system but are restricted to a 250 m interval of devonian to mississippian strata their age is bracketed between silicified ca 45 ma sedimentary rocks and unaltered 36 5 to 34 ma volcanic rocks the silicification is linked to the deposits by its continuity with ore grade silicification in devonian mississippian strata and by its similar 18 o values 17 and trace element signature as sb tl hg eocene reconstruction indicates that the deposits formed at depths of 300 to 800 m in comparison to most carlin type gold deposits they have lower au ag au grades and contained au more abundant jasperoid and textural evidence for deposition of an amorphous silica precursor in jasperoid these differences most likely result from their shallow depth of formation the peak fluid temperature 230 c and large 18 o h2o value shift from the meteroric water line 20 suggest that ore fluids were derived from depths of 8 km or more a magnetotelluric survey indicates that the mooney basin fault system penetrates to mid crustal depths deep circulation of meteoric water along the mooney basin fault system may have been in response to initial uplift of the east humboldt ruby mountains metamorphic core complex convection also may have been promoted by increased heat flow associated with large magnitude extension in the core complex and regional magmatism ore fluids ascended along the fault system until they encountered impermeable devonian and mississippian shales at which point they moved laterally through permeable strata in the devonian guilmette formation devonian mississippian pilot shale mississippian joana limestone and mississippian chainman shale toward erosional windows where they ascended into eocene fluvial conglomerates and lake sediments most gold precipitated by sulfidation of host rock fe and mixing with local ground water in zones of lateral fluid flow in reactive strata such as the lower devonian mississippian pilot shale

redox chemistry of west antarctic peninsula margin surface sediments abstract continental margin sediments are commonly studied using trace metal enrichments as proxies for characterizing their modern redox conditions and tracking past changes in bottom water ventilation and marine primary productivity currently little is known about the sedimentary redox history of the continental shelf west of the antarctic peninsula yet environmental conditions in the antarctic peninsula region have changed rapidly in recent decades in response to global warming paleoclimate archives including bulk sediment trace metal enrichments can provide insight into both past and future environmental changes in this climatically sensitive region and characterization of redox conditions in surface modern sediments is essential for establishing a framework for paleoredox interpretations in this study we measured concentrations of trace metals ag cd re and mo and productivity proxies total ba organic carbon and biogenic silica in surface sediments from the marguerite bay gerlache strait and bransfield strait areas proxy concentrations suggest that sediments are generally suboxic due to seasonally high export of organic carbon from surface waters comparison of west antarctic peninsula trace metal al ratios to trace metal data from continental margins outside the antarctic region demonstrates that although the west antarctic peninsula water column differs from other locations e g it lacks a strong oxygen minimum zone sedimentary redox chemistry is similarly controlled by organic matter decomposition through slow recycling of highly seasonal export production falling through a cold water column

variability of upwelling off nw africa during the latest quaternary diatom evidence diatom abundance and species composition were quantitatively studied in two latest quaternary 130 ka to the present sequences from the continental margin of northwest africa off this region coastal upwelling is well developed under the influence of the ne trade winds variations in diatom abundance in these cores are inferred to represent changes caused by varying degrees of the upwelling fertility times of high productivity are marked by high relative frequencies of chaetoceros while low productivity is marked by the dominance of aulacoseira granulata upwelling increased during glacial episodes isotopic stages 2 4 and 6 relative to isotopic stages 1 and 5 during the late holocene primary productivity levels are similar to those for stage 5 but in the early holocene upwelling intensities seem to have been weaker than today the paleoproductivity reconstruction based on the diatom record is supported by paleoproductivity estimations based on the organic carbon content of the sediments sarnthein et al 1987a

sediment distribution and sedimentary processes across the antarctic wilkes land margin during the quaternary the study of existing cores collected across the wilkes land margin provides us with a better understanding of the sediment distribution and processes across this margin during the holocene and during pleistocene glacial and interglacial cycles holocene depositional rates are high in deep 1000 m inner shelf basins where diatomaceous ooze is deposited at estimated minimum sedimentation rates ranging from 40 to 60 cm kyr in the shelf troughs holocene sediment has a patchy distribution or is totally absent this is also the case on the shelf banks due to differential deposition because of the irregular relief of the continental shelf and the erosion and redistribution by bottom currents pleistocene interglacial sedimentation is well represented in sediment from the continental rise and is dominated by hemipelagic deposition of massive mud with the highest biogenic content as indicated by opal and with a high abundance of clasts ird during the pleistocene glacial cycles diamictons were deposited in the continental shelf troughs and on the banks reworking e g by bottom currents and remobilization e g gravity flows of these diamictons is a common process along the shallow continental shelf banks on the continental slope and the continental rise gravity flows are one of the most important sedimentary processes sediment from continental slope cores with a texture that greatly resembles the diamictons on the shelf is interpreted to represent either part of a slump block or the start of a debris flow downslope crudely stratified to laminated intervals represent the transition between an end member of a debris flow and a turbidity flow some of the laminated intervals in cores from the continental rise represent sediment deposited from a turbidity flow ages obtained from cores further support that slumps and gravity flows are dominant processes in this margin because numerous hiatuses apparently are present in cores from the base of the slope one of these cores extends into the miocene elsewhere on the continental rise massive and laminated sediments in cores of similar length record near continuous pleistocene sedimentation r 2003 elsevier science ltd all rights reserved

oxygen isotope trends of granitic magmatism in the great basin location of the precambrian craton boundary as reflected in zircons the 18 o values of magmas in the great basin help to decipher the tectonic assembly of north america and to determine the magmatic source and potentially the composition of the crust at depth igneous zircons from precambrian jurassic cretaceous and tertiary intrusive bodies of the northern great basin best preserve the rec ord of magmatic oxygen isotope ratios the variation of 18 o values in zircon with age reconciles previous differences in interpretation based on 18 o wr and radiogenic isotope data the new 18 o zrc data support the results of previous radiogenic isotope studies documenting the increased availability of crustal and sedimentary components to magmas in the cretaceous during the sevier orogeny and a return to a larger proportion of mantle derived components in the tertiary during basin and range extension in the great basin 18 o zrc values also vary systematically with crustal structure as determined by radiogenic isotope systematics plutons emplaced east of the 87 sr 86 sr i 0 706 isopleth have higher 18 o zrc values than plutons intruded west of the 0 706 line however analyses of 18 o values in quartz do not show the bimodal distinction across the 0 706 line owing to subsolidus alteration on the basis of 18 o zrc plutons intruding the walker lane belt are indistinguishable from other plutons emplaced west of the 0 706 line despite significant tectonic displacement and rotation of the belt the difference in 18 o values across the 0 706 line reflects the involvement of high 18 o precambrian and paleozoic sedimentary rocks of the continental margin and precambrian craton in magmas intruded east of the 0 706 line whereas magmas west of the 0 706 line are dominated by lower 18 o rocks derived from juvenile volcanic arcs crustal boundaries and discontinuities in the great basin determined by radiogenic isotope systems agree with discontinuities observed in 18 o zrc values this agreement indicates that the 0 706 line marks a geochronologic and compositional discontinuity in the basement rocks

quasi geostrophic 3d circulation and mass transport in the western bransfield strait during austral summer 1995 96 in the framework of the fruela carbon flux study two oceanographic surveys december 1995 and january 1996 were conducted by b i o hesperides in the western basin of the bransfield strait and southern drake passage the horizontal geostrophic velocity field is characterized by two jet like features linked to frontal hydrographic structures a meandering current off the continental shelf edge of the southern drake passage corresponding to the southern front of the antarctic circumpolar current and the bransfield current related to the bransfield front the first jet shows some changes in the meandering pattern from december 1995 to january 1996 whereas the second has a very stationary location and structure the estimated horizontal circulation and mass transports are compared with available current meter data and with previous geostrophic estimates in the context of a sensitivity analysis that takes into account the choice of the reference level and the station distribution the vertical velocity field has been computed by integrating the quasi geostrophic omega equation maximum estimated values are of the order of 1 m day which suggests that a phytoplankton bloom observed in the northern part of the study area in december and vanished one month later should not be attributed to frontal dynamic instabilities inducing upward motion and nutricline related lifting but rather to other hydrographic factors

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

geology fluid inclusions and isotope geochemistry of the herenping gold deposit in the southern margin of the yangtze craton china a sediment hosted reduced intrusion related gold deposit abstract the herenping gold deposit is a typical gold deposit in the xuefengshan arcuate tectonic zone in the southern margin of the yangtze craton and the major feature of the gold mineralisation in the zone is the varying degrees of tungsten and antimony mineralisation in the ore deposits the herenping gold deposit occurs in the reddish purple sandy slate in the middle section of the madiyi formation of the neoproterozic banxi group and is controlled by the fault fold zone associated with the liulincha anticlinorium and f8 fault zone however its sources of mineralisation and relationships between hydrothermal fluids and magmatic rocks are unclear which similar to those of many gold deposits in metasedimentary terranes in the worldwide the mineralisation can be divided into four stages an albite quartz stage i an albite quartz pyrite gold stage ii a quartz gold polymetallic sulphide stage iii and a quartz carbonate stage iv the gold mineralisation occurred in albite quartz veins in stage ii and in sulphide rich quartz veins in stage iii in the deposit a study of the fluid inclusions reveals that the homogenisation temperature and salinity were slightly higher in stage ii th 186 348 c w 5 2 17 43 wt nacl equiv than in stage iii th 145 249 c w 2 9 15 57 wt nacl equiv indicating that the temperature and salinity of the ore forming fluid are gradually decreasing the h o d 62 3 to 53 0 18o 4 2 11 8 isotope characteristics reveals that the ore forming fluid is a magmatic hydrothermal source the sulphur 34s 4 8 2 0 isotope characteristics and the alteration mineral assemblage sericite chlorite pyrite indicates that the ore forming fluids was reduced the lead 206pb 204pb 17 419 17 436 207pb 204pb 15 519 15 535 and 208pb 204pb 37 86 37 90 isotope characteristics reflect the ore forming materials were likely derived from a deep magmatic source in addition the geochemical characteristics of albitite veins show that they are silicon rich 64 02 66 26 wt and significantly reduced notably the herenping gold deposit is located in the western portion of the tungsten tin metallogenic provinces in south china is host in epimetamorphic detrital rocks and was formed at least two stages of mineralisation typical gold bearing albite quartz veins developed during the primary stage these characteristics are consistent with those of reduced intrusion related deposits such as the muruntau kumtor and telfer deposits thus the herenping gold deposit may be a sediment hosted intrusion related gold deposit based on the phase transition pattern from sulphide rich quartz veins to albite quartz veins to albitite veins with increasing depth in the deposit we propose that reduced intrusions deep in the herenping gold deposit could be discovered in the future which implies the possible existence of a reduced intrusion related gold system in the xuefengshan arcuate tectonic zone

paleoatmospheric consequences of co2 released during early cenozoic regional metamorphism in the tethyan orogen the eocene was the warmest epoch of the cenozoic with published estimates of eocene atmospheric co2 content ranging from two to six times the current value calculations of co2 consumption by silicate weathering show that co2 fluxes to the atmosphere of ca 1018 myr could account for inferred paleocene eocene atmospheric co2 contents and the resulting greenhouse effect would have contributed to eocene warmth extensive portions of the tethyan orogen underwent regional metamorphism culminating in the eocene prograde metamorphism may have been contemporaneous with the late paleocene global warming we calculated the amount of metamorphic co2 produced at depth in the himalayan orogen with data on the timing of the india asia collison duration of prograde regional metamorphism and proportions and bulk compositions of metamorphic co2 source rocks if co2 was generated at a constant rate over a 10 myr period of prograde metamorphism in the himalayan orogen we estimate that ca 1018 1019 moles myr of metamorphic co2 were produced at depth significant expulsion of metamorphic co2 to the atmosphere may have occurred by focused fluid flow along shear zones such as the extensive main central thrust in the himalayan orogen an additional ca 1018 myr could have been contributed by eocene regional metamorphism in the mediterranean tethys i e from the alps to turkey the extensive metamorphism associated with the india asia collision and the closing of tethys may have contributed to co2 greenhouse warming in the early to mid cenozoic

geology and geochemistry of listwaenite related gold mineralization in the sayi gold deposit xinjiang nw china abstract the sayi gold deposit is part of the sartohay ophiolitic melange in west junggar xinjiang china and is hosted by listwaenite which was transformed from serpentinite in a shear zone via fluid rock reaction gold mineralization is hosted by mylonitized listwaenites and quartz veins within listwaenite lenses formed during shearing our study demonstrates that fluid concentrated au ag as sb cu cr ni and co during transformation from serpentinite to listwaenite and ductile deformation deformation due to shearing played an important role in focusing ore forming fluid along the shear zone gold mineralization accompanied formation of hydrothermal minerals in the following stages carbonate quartz pyrite cqp stage i mariposite gersdorffite gold mgg ii quartz carbonate pyrite qcp iii gold bearing quartz iv and dolomite calcite stage v geological characteristics of mgg in mylonitized listwaenite demonstrate that gold mineralization formed during the transition from ductile to brittle deformation which was followed by gold bearing quartz veins filling brittle fractures the au contents show a positive correlation with ag as cu and sb contents in mylonitized listwaenite samples consistent with the coexistence of native gold gersdorffite arsenian pyrite and chalcopyrite in mylonitized listwaenite pressure decrease due to hydraulic fracturing during the transition from ductile to brittle deformation induced gold deposition in the sayi deposit

eocene magmatism the heat source for carlin type gold deposits of northern nevada the origin of carlin type or sediment hosted disseminated gold deposits of the great basin the major source of gold in the united states is poorly understood we propose that eocene magmatism was the heat source that drove the hydrothermal systems that generated these deposits in the carlin trend and independence mountains in northern nevada this interpretation is based on a strong spatial and temporal association of eocene intrusive volcanic centers with the gold deposits of this region our new work and published 40 ar 39 ar dates indicate that magmatism was particularly intense between 39 and 40 ma throughout northeastern nevada especially in and around the area of gold deposits carlin type deposits may have formed preferentially during eocene magmatism because it was 1 more intense in the area than other magmatic episodes 2 somehow compositionally distinct or 3 accompanied by extension that promoted hydrothermal flow however large scale extension does not appear to have been a factor in generating carlin type deposits

glacial contourites on the antarctic peninsula margin insight for palaeoenvironmental and palaeoclimatic conditions deep sea finely laminated and barren glacial sediments occur in the sediment drift field offshore the pacific margin of the antarctic peninsula where a weak contour current flows at present to the sw atypical sedimentary facies were related to the coexistence and interaction of different sedimentary processes three end members of radiograph facies were defined to represent the sedimentary sequences controlled by a dominant process as follows 1 direct influence of turbidity currents on sedimentation is observed in the area surrounding the alexander channel system with silty layers interbedded with laminated mud free of ice rafted debris ird 2 distal meltwater turbid flows dominate the more proximal area of the top plateau with structureless and coarser grained sediments containing ird 3 along the crest of the drift persistent weak bottom currents control the deposition of fine grained sediments conveyed into the system through other processes these laminated sediments contain ird and are atypically not bioturbated because of unusual climatically related environmental conditions of suppressed primary productivity and oxygen reduced deep waters these glacial contourites were observed on most of the antarctic margin with the exception of the areas in which polynyas were maintained during the glacial stages glacial contourites can be used as a proxy to define temporal and spatial extension of the antarctic sea ice deep sea sediments of the sediment drifts offshore the pacific margin of the antarctic peninsula were investigated within the sedano sediment drifts of the antarctic offshore and mogam morphology and geology of antarctic margins antarctic peninsula and wilkes land projects of the italian programma nazionale di ricerche in antartide fig 1 the continental shelf of the pacific margin of the antarctic peninsula is dissected by a number of modern u shaped troughs that reflect the neogene path of large ice streams rebesco et al 1998 2002 sediments across the continental shelf were transported mainly by ice streams and delivered to the continental slope and rise during the periods of maximum glacial expansion the continental rise hosts a number of large sediment drifts separated by dendritic deep sea channel systems that originated on the lower continental slope in alignment with the reaches of each glacial trough amblas et al 2006 rebesco et al 2007 two main alternating lithologies related to climatic changes were initially distinguished pudsey camerlenghi 1998 pudsey 2000 interglacial brown bioturbated mud containing sparse icerafted debris ird and glacial grey laminated mud further detailed studies consisting of over 1000 sedimentological compositional and biostratigraphic analyses diatoms foraminifers and nannofossils allowed lucchi et al 2002a to distinguish four distinctive sets of sedimentary facies connected to a sequence of four climatic stages each characterized by the onset of typical sedimentary processes fig 2 as follows 1 strongly bioturbated mud with abundant ird and aeolian sediment input was produced during the interglacial phase fig 2a the increased bioactivity is matched by insignificant downand along slope processes negligible suspended load and sediment transport by the southwesterly flowing bottom currents is occurring at present on the continental rise giorgetti et al 2003 2 terrigenous structureless mud including a series of close spaced ird layers was produced during the deglaciation transition from glacial to interglacial conditions by the disintegration of the retreating grounded ice sheet fig 2b the absence of calcareous microfossils is related to strong carbonate dissolution and rise of the carbonate compensation depth ccd as a result of major meltwater discharge which in turn caused water stratification with less oxygenated and nutrient enriched conditions at the sea bottom 3 a large variety of from viana a r rebesco m eds economic and palaeoceanographic significance of contourite deposits geological society london special publications 276 111 127 0305 8719 07 15 00 the geological society of london 2007

metamorphic origin of ore forming fluids for orogenic gold bearingquartz vein systems in the north american cordillera constraints froma reconnaissance study of δ15n δd and δ18o the western north american cordillera hosts a large number of gold bearing quartz vein systems from the mother lode of southern california through counterparts in british columbia and southeastern alaska to the klondike district in central yukon these vein systems are structurally controlled by major fault zones which are often reactivated terrane bounding sutures that formed in orogens built during accretion and subduction of terranes along the continental margin of north america mineralization ages span mid jurassic to early tertiary and encompass much of the evolution of the cordilleran orogen nitrogen contents and 15n values of hydrothermal micas from veins are between 130 and 3 500 ppm and 1 7 to 5 5 per mil respectively these values are consistent with fluids derived from metamorphic dehydration reactions within the phanerozoic accretion subduction complexes which have 15n values of 1 to 6 per mil the 18o values of gold bearing vein quartz from different locations in the cordillera are between 14 6 and 22 2 per mil but are uniform for individual vein systems the d values of hydrothermal micas are between 110 and 60 per mil ore fluids have calculated 18o values of 8 to 16 per mil and d values of 65 to 10 per mil at an estimated temperature of 300 c d values of ore fluids do not show any latitudinal control these results indicate a deep crustal source for the ore forming fluids most likely of metamorphic origin low dh2o values of 120 to 130 per mil for a hydrous muscovite from the sheba vein in the klondike district reflect secondary exchange between recrystallizing mica and meteoric waters collectively the n h and o isotope compositions of ore related hydrothermal minerals indicate that the formation of these gold bearing veins involved dilute aqueous carbonic and nitrogen bearing fluids that were generated from metamorphic dehydration reactions at deep crustal levels these data are not consistent with either mantle derived fluids or granitoid related magmatic fluids nor do they support a model involving deeply circulated meteoric water

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

mineralogic fluid inclusion and stable isotope studies of several gold mines in the mother lode tuolumne and mariposa counties california gold bearing quartz veins in the southern part of the mother lode california formed from fluids which contained si k co 2 ca s and metals and which were focused into permeable fault zones in the coulterville district of the mother lode these fluids altered serpentinite to a talc chlorite magnesite quartz assemblage which is crosscut by veins containing quartz dolomite sericite sulfides tellurides and gold textural relationships among the vein filling minerals reveal that galena tellurides pb ni ag au ag and native gold precipitated last among the vein minerals observations from the oro rico and mcalpine mines coulterville district indicate that these deposits were subjected to deformation during and after their formation fluid inclusions in the milky vein quartz exhibit only a narrow range in t sub m ice but a large range in t h which probably reflects posttrapping deformation microthermometry of fluid inclusions from vug filling quartz in the alleghany district in the northern portion of the mother lode reveals low salinity 2 h 2 o fluids with t sub mco 2 56 7 degrees c t sub m clathrate 9 5 degrees c and t sub h total 150 degrees to 200 degrees c visual estimates of co 2 content indicate a maximum of 10 mole percent co 2 in contrast inclusions from vug filling quartz in the coulterville district are filled with low salinity low t h 110 degrees 140 degrees c h 2 o rich fluids which were probably later than and unrelated to the gold mineralizing fluids oxygen isotope values of vein quartz from the southern mother lode indicate formation by 18 o enriched fluids in the range 6 to 11 per mil vs smow these values are similar to estimates of 8 to 15 per mil from vein quartz of the alleghany district taylor 1981 boehlke and kistler 1986 the average delta 13 c values for magnesite and dolomite of 4 5 or 0 6 per mil vs pdb from the southern mother lode are identical to results from the alleghany district 200 km to the north rosenbaum and taylor 1984 these data suggest either a single or well mixed source of oxidized carbon for the fluids oxygen isotope compositions of magnesite calculated using an experimentally derived phosphoric acid fractionation factor at 50 degrees c of 1 0096 are enriched in 18 o relative to coexisting dolomite as predicted for isotopic equilibrium the chemistry of the mother lode ore forming fluids is characterized by several approaches with an x sub co 2 estimate of 0 1 from fluid inclusions quartz magnesite assemblages in the coulterville serpentinite alteration zones limit the temperature of formation to below 325 degrees c for p 2 h 2 o fluid coupled with the assumption of trapping temperatures of 300 degrees c suggests minimum trapping pressures of 1 000 to 2 000 bars assuming equilibrium the assemblage of daughter minerals described by coveney 1981 indicates neutral ph conditions of 5 5 to 6 0 at the prevailing p t conditions sulfide mineral stabilities imply that h 2 s was the dominant sulfur species and that a sub o 2 of the mineralizing fluids was in the range 10 super 32 to 10 super 35 our preferred model for the formation of the mother lode vein system involves magmatic activity associated with a subducting slab in this model generation of ore forming fluids is possible by a variety of mechanisms including metamorphic devolatilization reactions in rocks adjacent to the plutons direct magmatic input and deep circulation of meteoric water any of these mechanisms is possible given the available data on the mother lode deposits

modeling fluid transfer along california faults when integrating pressure solution crack sealing and compaction processes 1 several models pertaining to earthquake cycles imply intermittent fluid flow through fault during the interseismic period increase in fluid pressure from hydrostatic to lithostatic values is a crucial parameter in mechanisms leading to earthquakes to achieve such pressures geodynamic processes gouge compaction fluid flow and changes in permeability are required previous models have postulated that changes in permeability by self healing are faster than the effects of geodynamic processes we consider the different mechanisms and rates of crack sealing near active fault on the examples of uplifted californian faults we find that natural crack sealing is normally not achieved by a rapid self healing process pressure solution with mass transfer from solution cleavage to cracks appears to be a more important mechanism for crack sealing and creep during postseismic deformation the geometry of transfer path and experimental data have been used to model crack sealing rates by pressure solution which are estimated to be rather slow similar to the recurrence time of some earthquakes such slow changes in permeability may be crucial factors in controlling the increase in fluid pressure and consequently the mechanism of critical failure in faults then numerical modeling of fluid pressure and transfer around active faults has been performed integrating a slow change in permeability by crack sealing gouge compaction and fluid flow from depth this modeling shows various location and evolution of fluid overpressure during the interseismic period depending on these processes and allows one to estimate the amount of fluid transferred from depth during interseismic periods

bald mountain gold mining district nevada a jurassic reduced intrusion related gold system the bald mountain mining district has produced about 2 million ounces moz of au geologic mapping field relationships geochemical data petrographic observations fluid inclusion characteristics and pb s o and h isotope data indicate that au mineralization was associated with a reduced jurassic intrusion gold deposits are localized within and surrounding a jurassic 159 ma quartz monzonite porphyry pluton and dike complex that intrudes cambrian to mississippian carbonate and clastic rocks the pluton associated dikes and au mineralization were controlled by a crustal scale northwest trending structure named the bida trend gold deposits are localized by fracture networks in the pluton and the contact metamorphic aureole dike margins high angle faults and certain strata or shale limestone contacts in sedimentary rocks gold mineralization was accompanied by silicification and phyllic alteration argillic alteration at shallow levels although au is typically present throughout the system exhibits a classic concentric geochemical zonation pattern with mo w bi and cu near the center ag pb and zn at intermediate distances and as and sb peripheral to the intrusion near the center of the system micron sized native au occurs with base metal sulfides and sulfosalts in peripheral deposits and in later stages of mineralization au is typically submicron in size and resides in pyrite or arsenopyrite electron microprobe and laser ablation icp ms analyses show that arsenopyrite pyrite and bi sulfide minerals contain 10s to 1 000s of ppm au ore forming fluids were aqueous and carbonic at deep levels and episodically hypersaline at shallow levels due to boiling the isotopic compositions of h and o in quartz and sericite and s and pb in sulfides are indicative of magmatic ore fluids with sedimentary sulfur together the evidence suggests that au was introduced by reduced s bearing magmatic fluids derived from a reduced intrusion the reduced character of the intrusion was caused by assimilation of carbonaceous sedimentary rocks tertiary faults dismember the area and drop down the upper part of the mineralizing system to the west the abundant and widespread kaolinite in oxide ores is relatively disordered 1a polytype and has d and 18o values suggestive of a supergene origin the deep weathering and oxidation of the ores associated with exhumation made them amenable to open pit mining and processing using cyanide heap leach methods

from serpentinization to carbonation new insights from a co2 injection experiment abstract we injected a co2 rich hydrous fluid of seawater chlorinity into an ongoing mildly reducing h 2 a q 3 mmol kg serpentinization experiment at 230 c and 35 mpa to examine the changes in fluid chemistry and mineralogy during mineral carbonation the chemistry of 11 fluid samples was measured speciated and compared with mgo sio2 h2o co2 mshc phase equilibria to approximate the reaction pathway from serpentinization to carbonation although the overall system was in apparent disequilibrium the speciated activities of dissolved silica a sio 2 a q and carbon dioxide a co 2 a q evolved roughly along mshc equilibrium phase boundaries indicative of 4 distinct mineral assemblages over time 1 serpentine brucite magnesite before the injection to 2 serpentine talc magnesite 2 h after the injection to 3 quartz magnesite 48 h after injection and 4 metastable olivine magnesite 623 h after injection until the experiment was terminated inspection of the solid reaction products revealed the presence of serpentine magnesite minor talc and magnetite in addition to relict olivine although quartz was saturated over a short segment of the experiment it was not found in the solid reaction products a marked and rapid change in fluid chemistry suggests that serpentinization ceased and precipitation of magnesite initiated immediately after the injection a sharp decrease in ph after the injection promoted the dissolution of brucite and olivine which liberated sio 2 a q and dissolved mg dissolved mg was efficiently removed from the solution via magnesite precipitation whereas the formation of talc was relatively sluggish this process accounts for an increase in a sio 2 a q to quartz saturation shortly after the injection of the co2 rich fluid molecular dihydrogen h 2 a q was generated during serpentinization of olivine by oxidation of ferrous iron before the injection however no additional h 2 a q was generated after the injection speciation calculations suggest a strong affinity for the formation of methane ch 4 a q at the expense of co 2 a q and h 2 a q after the injection but increased ch 4 a q formation was not observed these findings suggest that kinetically fast mineral carbonation dominates over sluggish ch 4 a q formation in mildly reducing serpentinization systems affected by injection of co2 rich fluids

global variations of surface ocean productivity in low and mid latitudes influence on co2 reservoirs of the deep ocean and atmosphere during the last 21 000 years based on detailed reconstructions of global distribution patterns both paleoproductivity and the benthic 13c record of co2 which is dissolved in the deep ocean strongly differed between the last glacial maximum and the holocene with the onset of termination i about 15 000 years ago the new export production of low and mid latitude upwelling cells started to decline by more than 2 4 gt carbon year this reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric co2 as recorded in ice cores and with a slight delay of more than 1000 years to a large scale gradual co2 depletion of the deep ocean by about 650 gt c this estimate is based on an average increase in benthic 13c by 0 4 0 5 the decrease in new production also matches a clear 13c depletion of organic matter possibly recording an end of extreme nutrient utilization in upwelling cells as shown by sarnthein et al 1987 the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades which in turn was linked via a shrinking extent of sea ice to a massive increase in high latitude insolation i e to orbital forcing as primary cause

carbonate sulfide equilibria and stratabound disseminated epigenetic gold mineralization a proposal based on examples from alleghany california u s a abstract stratabound disseminated pyritic au ore bodies were produced by reactions between wall rocks and through flowing fluids in mesozoic epigenetic au quartz vein systems in the sierra nevada metamorphic belt equilibrium relations among fe bearing carbonate and sulfide minerals were critical in determining which rock types were likely to host disseminated mineralization along portions of discordant veins the compositions of metasomatic carbonates in hydrothermally altered wall rocks at alleghany california u s a were larely predetermined by the relative proportions of fe mg and ca in the unaltered wall rocks thus coexisting solid solutions in the magnesite siderite and dolomite ankerite series from a variety of different wall rocks yield an empirical phase diagram for a large part of the ca co 3 mgco 3 feco 3 system at the temperature of metasomatism 325 50 c because fe mg silicates were unstable in alteration zones adjacent to the veins wall rock fe was partitioned between carbonates and sulfides pyritization and disseminated au mineralization occur in a variety of igneous and metasedimentary wall rocks in which the initial molar fe fe mg 0 5 in altered wall rocks with initial molar fe fe mg 0 5 fe was incorporated almost entirely within mg rich carbonates x feco 3 0 6 in magnesite siderite solutions it is proposed that the co 2 rich vein fluid responsible for the alteration and mineralization was partially buffered with respect to h 2 s co 2 h 2 ratios by equilibrium between pyrite and mg 0 4 fe 0 6 co 3 graphite as it traversed and altered intermediate volcanic and sedimentary rocks this fluid then locally reacted with lower fe fe mg rocks to form fe bearing dolomite magnesite assemblages and reacted with higher fe fe mg rocks to form ankerite pyrite assemblages gold precipitated from saturated solutions of bisulfide complexes partly in response to fluid desulfidation and reduction caused by the pyritization reactions in terranes dominated by intermediate metavolcanic and metasedimentary rocks favorable host rocks for this type of mineralization need not have high fe contents but do require high fe fe mg ratios they may include felsic volcanic and plutonic rocks fe rich tholeiitic differentiates banded fe formations and a variety of siliceous and argillaceous sedimentary rocks rocks which tend not to be heavily sulfidized because they have low initial fe fe mg ratios include ultramafic and mafic igneous rocks and some argillaceous sedimentary rocks exploration guidelines based on these principles may be useful elsewhere in the sierra nevada and in other comparable heterogeneous metamorphic terranes if modified to reflect the dominant buffering rock types in a given fluid flow path carbonate sulfide equilibria are capable of approximately buffering the carbonate sulfide ratios of co 2 rich vein fluids f co 2 10 2 8 at 325 c 200mpa or 2000 bar the alleghany fluid f co 2 10 3 2 or 10 mol co 2 had a molar co 2 h 2 s ratio of approximately 10 3 assuming graphite saturation at lower co 2 fugacities fe bearing silicates entered the buffering assemblages carbonatization reactions could potentially de sulfidize some wall rocks releasing s and associated metals to the fluid this would be most likely to occur in pyrite bearing mafic and ultramafic rocks and some argillites

increased upwelling off portugal during the last glaciation diatom evidence abstract quantitative studies have been carried out on opaline microfossils and diatom assemblage composition and preservation in two latest quarternary 100 ka to p d cores from the continental slope of portugal the sites are located in an area of modern summer coastal upwelling created by northerly trade winds the spatial patterns and intensity of this upwelling system are accurately recorded by the diatom abundances and taxonomic composition in the surface sediments the diatom record in these sequences indicates that coastal upwelling intensity was similar to present day during late holocene interglacial stage 3 and late stage 5 higher during stage 2 and lower in the early holocene paleoproductivity estimates are consistent with the diatom accumulation rates from stage 3 to the recent this indicates that both the diatom and the organic carbon content of the sediments mainly reflect the biological productivity in the euphotic zone

lead in the getchell turquoise ridge carlin type gold deposits from the perspective of potential igneous and sedimentary rock sources in northern nevada implications for fluid and metal sources lead isotope compositions of bulk mineral samples fluorite orpiment and realgar determined using conventional techniques and of ore stage arsenian pyrite using the sensitive high resolution ion microprobe shrimp in the getchell and turquoise ridge carlin type gold deposits osgood mountains require contribution from two different pb sources one pb source dominates the ore stage it has a limited pb isotope range characterized by 208pb 206pb values of 2 000 to 2 005 and 207pb 206pb valuesof 0 8031 to 0 8075 as recorded by 10 mm diameter spot shrimp analyses of ore stage arsenian pyrite these values approximately correspond to 206pb 204pb of 19 3 to 19 6 207pb 204pb of 15 65 to 15 75 and 208pb 204pb of 39 2 to 39 5 this pb source is isotopically similar to that in average neoproterozoic and cambrian clastic rocks but not to any potential magmatic sources whether those clastic rocks provided pb to the ore fluid cannot be unequivocally proven because their pb isotope compositions over the same range as in ore stage arsenian pyrite are similar to those of ordovician to devonian siliciclastic and calcareous rocks the pb source in the calcareous rocks most likely is largely detrital minerals since that detritus was derived from the same sources as the detritus in the neoproterozoic and cambrian clastic rocks the second pb source is characterized by a large range of 206pb 204pb values 18 34 with a limited range of 208pb 204pb values 38 1 39 5 indicating low but variable th u and high and variable u pb values the second pb source dominates late and postore stage minerals but is also found in preore sulfide minerals these pb isotope characteristics typify ordovician to devonian siliciclastic and calcareous rocks around the carlin trend in northeast nevada petrologically similar rocks host the getchell and turquoise ridge deposits lead from the second source was either contributed from the host sedimentary rock sequences or brought into the hydrothermal system by oxidized ground water as the system collapsed late ore and postore stage sulfide minerals pyrite orpiment and stibnite from the betze post and meikle deposits in the carlin trend and from the jerritt canyon mining district have pb isotope characteristics similar to those determined in getchell and turquoise ridge this observation suggests that the pb isotope compositions of their ore fluids may be similar to those at getchell and turquoise ridge two models can explain the pb isotope compositions of the ore stage arsenian pyrite versus the late ore or postore sulfide minerals in either model pb from the ordovician to devonian siliciclastic and calcareous rock source enters the hydrothermal system late in the ore stage but not to any extent during the main stage of ore deposition in one model ore stage pb was derived from a source with pb isotope compositions similar to those of the neoproterozoic and cambrian clastic sequence transported as part of the ore fluid and then deposited in the ore stage arsenian pyrite and fluorite the second model is based on the observation that the pb isotope characteristics of the ore stage minerals also are found in some ordovician to devonian calcareous and siliciclastic rocks hence ore stage pb could have been derived locally and simply concentrated during the ore stage critical to the second model is the removal of all high 206pb 204pb 20 material during alteration it also requires the retention of only the low 206pb 204pb component of the ordovician to devonian sedimentary rocks this critical step is possible only if the high 206pb 204pb values are contained in readily dissolvable mineral phases whereas the low 206pb 204pb values are found only in refractory minerals that released pb during a final alteration stage just prior deposition of auriferous arsenian pyrite distinguishing between pb transported with the ore fluid or inherited from the site of mineral deposition is not straightforward however it is simpler to explain the pb isotope compositions of ore stage arsenian pyrite and fluorite in two different but spatially related carlin type deposits getchell and turquoise ridge with different host rocks by input of pb with the ore fluid once the limited pb in the hydrothermal fluid was exhausted by incorporation in ore stage arsenian pyrite or other ore stage minerals pb from the second source the ordovician to devonian sedimentary rock sequences became available for incorporation in some but not all of the late stage sulfide minerals

productivity cycles of 200 300 years in the antarctic peninsula region understanding linkages among the sun atmosphere oceans sea ice and biota compared to the rest of the world9s oceans high resolution late holocene paleoclimatic data from the southern ocean are still rare we present a multiproxy record from a sediment core retrieved from a deep basin on the western side of the antarctic peninsula that reveals a dramatic perspective on paleoclimatic changes over the past 3700 yr analyses completed include measurement of magnetic susceptibility and granulometry bed thickness particle size percent organic carbon bulk density and microscopic evaluation of diatom and benthic foraminiferal assemblages and abundances downcore variability of these parameters demonstrates the significance of both short term cycles which recur approximately every 200 yr and longer term events 2500 yr cycles that are most likely related to global climatic fluctuations in the upper 600 cm of the core lower values of magnetic susceptibility ms are correlated with lower bulk density the presence of thinly laminated units specific diatom assemblages and generally higher total organic carbon content below 600 cm magnetic susceptibility is uniformly low though variability in other parameters continues the magnetic susceptibility signal is controlled primarily by dilution of ferromagnetic phases with biosiliceous material this signal may be enhanced further by dissolution of magnetite in the magnetic susceptibility lows high total organic carbon the role of variable primary productivity and its relationship to paleoclimate is assessed through the diatom data in particular magnetic susceptibility lows are characterized by higher than normal abundances of chaetoceros resting spores corethron criophilum and or rhizosolenia spp also are found as is a higher ratio of the most common species of fragilariopsis versus species of thalassiosira these assemblages are indicative of periods of high primary productivity driven by the presence of a meltwater stabilized water column the 200 yr cyclicity noted in other paleoclimatic records around the world suggests a global forcing mechanism possibly solar variability in addition to the cyclic changes in productivity overall elevated productivity is noted below 600 cm or prior to ca 2500 yr b p this increased productivity may represent the tail end of a holocene climatic optimum which is widely recognized in other parts of the world but as yet is poorly documented in antarctica

regional variations in bulk chemistry mineralogy and the compositions of mafic and accessory minerals in the batholiths of california we define regional variations in mafic and accessory mineral assemblages and compositions and expand the current understanding of spatial variations in whole rock geochemistry in the batholiths of california in so doing we gain new insights into the nature of magmatic source rocks and mechanisms of magma generation in volcano plutonic arcs of active continental margins little studied metaluminous to strongly peraluminous granites containing fe rich biotite with log x mg x fe f oh and mn in biotite and amphibole increase on a regional scale from western i wc types to eastern i mc and i sc types parallel to eastward increases in incompatible elements and decreases in compatible elements in the plutons in contrast the belts of western i scr granites and eastern i wc quartz diorites and granodiorites disrupt the regional west to east systematics in both mineral and whole rock geochemistry spatial variations in the al content of amphibole are regional in scale and reflect pressures of pluton crystallization we conclude that significant previously unrecognized complexity exists in regional geochemical systematics in the california batholiths

bransfield basin fine grained sediments late holocene sedimentary processes and antarctic oceanographic conditions the antarctic peninsula is sensitive to climatic change due to its northerly position and to the relatively reduced volume and character of its ice cover high resolution palaeoclimatic records from the ant arctic peninsula ice cores extend back only 500 years a climatic record of 2850 years in the bransfield basin is investigated through the analysis of sediment gravity cores from the floor of the central subbasin core gebra 1 and the slope of the eastern subbasin core gebra 2 sedimentological mineralogical and geo chemical properties have been systematically measured together with accelerator mass spectrometry ams radiocarbon dating the fine grained sediments result from two main processes hemipelagic settling from resuspensions and primary productivity and turbidity currents hemipelagic sediments were selected to investi gate the oceanographic and climatic conditions of the northern antarctic peninsula region during the last three millennia cold climatic periods are characterized by millimetric laminations and or black layers with higher organic carbon nitrogen and opal contents warm periods are recorded as massive to diffuse laminated facies with lower biogenic contents the results include the little ice age lia cold pulse as well as several 200 300 year long fluctuations within the lia and before this major climatic event of the holocene

diatom distribution in southern ocean surface sediments atlantic sector implications for paleoenvironmental reconstructions abstract a study of 230 surface sediment samples collected in the atlantic sector of the southern ocean between the southernmost weddell sea and the subtropical zone documents the modern distribution of diatoms revealing patterns of paleoenvironmental significance estimations of diatom valves per gram dry sediment display numbers of 50 200 106 in the zone of high opal burial located between the mean position of the winter sea ice edge and the polar front and maximum values of greater than 200 106 in the near shore sedimentary basins off the antarctic peninsula lowest diatom concentrations and assemblages strongly affected by dissolution were encountered in the weddell basin despite alteration of the diatom assemblages prior to their incorporation into the sediment record the biogeographic distribution and the abundance pattern of most of the 35 studied diatom species shows a close relationship with the surface hydrography water temperature these relationships can be used to estimate past surface water temperatures based on statistical treatments of the assemblages or on simple relations of species occurrences in the geological record another close link occurs between the distribution of sea ice and sea ice related diatoms

recent deep water sedimentation trace metal and radioisotope geochemistry across the southern ocean and northern weddell sea antarctica abstract a wide variety of deep water depositional environments were examined across 12 sampling stations in the southern ocean and northern weddell sea antarctica in order to provide a depositional context for the benthic biodiversity studies of andeep antarctic benthic deep sea biodiversity colonisation history and recent community patterns here we present a diverse dataset comprising sub bottom profiles seabed photographs sediment profile images and box and multicore samples in order to investigate the recent depositional environments across the region the sediments were investigated using texture structure trace metal mn fe u mo ba and pb stable 206pb 207pb and radionuclide excess 210pb isotopes the sediments of the agulhas basin are interpreted as siliceous pelagites the product of enhanced surface productivity the eastern weddell continental rise is characterised by diverse depositional environments with hemipelagic turbiditic and contouritic sedimentation in contrast the northern weddell abyssal plain is dominated by hemipelagites with fine grained turbidites a single sampling station from the central powell basin contained hemipelagites and a fine grained turbidite a core from the central bransfield strait recovered hemipelagites with a silt turbidite the seabed photographs display a seabed dominated by biogenic mud balls formed by cirratulid polychaetes trace metal pb isotope and excess 210pb data all reveal the central bransfield strait to be a region of enhanced productivity with a mass accumulation rate of 0 073 g cm2 two stations in the bellingshausen sea recovered hemipelagites and turbidites mn fe and mo data suggest a degradation of organic matter in the sediments leading to redox cycling

the last 100 000 years in the western mediterranean sea surface water and frontal dynamics as revealed by coccolithophores a quantitative analysis was carried out on coccolith assemblages from two pleistocene cores k1 and k10 from the western mediterranean the distribution of selected coccolithophore species provides new paleoclimatic and paleoceano graphic data a continuous sequence from the top of isotope stage 5 to the holocene was recorded the reversal in dominance between gephyrocapsa muellerae and emiliania huxleyi was dated in both cores at ca 73 ka at about 47 ka e huxleyi shows a regular increase whereas g muellerae progressively decreases in abundance during interglacial periods high concentrations of coccoliths are observed whereas in glacial times coccoliths are more diluted and the percentage of reworked forms increases as a consequence of the higher terrigenous input after taking careful account of the dilution factor we conclude that the production of coccolithophores was higher during warm periods maxima in coccolith concentrations coincide with highstand episodes probably as a result of the intensification of the atlantic flux into the mediterranean across the gibraltar strait this intensification could have produced an increase in nutrient content in the surface mediterranean waters during cold periods the western mediterranean front underwent a reduction in activity probably due to an increase in the saline and or thermal gradients between the superficial waters and intermediate waters in the liguro provencal basin

the cause of the glacial to interglacial atmospheric co2 change a polar alkalinity hypothesis in an attempt to create a scenario for the cause of the glacial to interglacial co2 change recorded in air trapped in polar ice we call on an increase in the alkalinity of polar surface waters in this way we circumvent a major deficiency of the polar nutrient scenarios of sarmiento and toggweiler 1984 siegenthaler and wenk 1984 and knox and mcelroy 1984 namely our scenario does not require a drop in the nutrient content of polar surface waters in conformity with the demonstration by boyle 1988a b that the cadmium content of planktonic foraminifera from polar regions did not decrease from late glacial to holocene time the rise in alkalinity required by our model is a natural consequence of the demise during glacial time of north atlantic deep water as a major force in ocean circulation and of the nutrient maximum deepening of boyle 1988b rather than being original our hypothesis builds on the concept basic to the polar nutrient hypotheses namely that the co2 partial pressure in polar waters controls that for both the atmosphere and warm surface ocean it also requires the alkalinity increase in surface waters produced by boyle s nutrient deepening

trace element contents and in situ sulfur isotope analyses of pyrite in the baiyun gold deposit ne china implication for the genesis of intrusion related gold deposits abstract trace elements distribution in minerals and formation mechanism of visible gold are poorly understood in intrusion related gold systems here we choose the baiyun gold deposit which is hosted within the paleoproterozoic metamorphic rocks in the liaodong peninsula ne north china craton ncc as a case study to address these issues the ore deposit geology characteristics and paragenesis are described in details in situ geochemical and sulfur isotopic compositions of pyrite and bulk pb isotopic ratios of pyrite were presented to define the genesis of pyrite that is closely associated with gold mineralization three generations of pyrite were recognized based on petrographic studies metamorphic pyrite py0 hydrothermal pyrite py1 coexisting with milky quartz and hydrothermal pyrite py2 coexisting with smoky quartz in situ laser ablation inductively coupled plasma mass spectrometer la icp ms spot analysis suggests that both py0 and py1 contain low contents of invisible gold mean 0 19 ppm and 0 17 ppm respectively however py1 is low in most other trace element contents and contains au ag cu pb bi micro inclusions in contrast py2 contains both invisible gold mean 0 50 ppm and au ag cu pb bi micro inclusions furthermore la icp ms mapping reveals the distributions of ag cu pb bi and te closely mimic that of au indicating an episode of ore forming fluid rich in au ag cu pb bi and te in situ sulfur isotope analysis of pyrite shows that py0 has significantly positive 34s values 11 74 17 33 suggesting that sulfur was derived from sedimentary sources py1 and py2 have negative 34s values 8 53 6 19 10 44 6 86 respectively indicating that sulfur was derived from oxidized magmatic fluids the magmatic fluids are concluded to be released from the early cretaceous microdiorite magmas providing most of the sulfur and ore forming metals proofs include the close spatial association of the ore bodies and the dykes as well the uniform pb isotopic ratios of py1 and the early cretaceous microdiorite lines of geological mineralogical geochemical and isotopic evidence consistently suggest that the gold mineralization in the baiyun deposit is intrusion related and was resulted from the 126 ma magmatic hydrothermal activities in the region visible gold precipitating in pyrite and fractures was from metal rich magmatic fluids rather than being remobilized from the metamorphic pyrite

oxygen isotope δ18o evidence of holocene hydrological changes at signy island maritime antarctica a record of holocene hydrological changes has been produced from variations in oxygen isotope composition delta 18 o preserved in freshwater lake sediments from maritime antarctica small amounts 5 of authigenic carbonate have been extracted from a non marl sediment core from sombre lake signy island 60 degrees 43 s 45 degrees 38 w oxygen isotope and particle size analysis provide a sensitive record of hydrological events in the lake arising from local and regional climate phenomena the climate affects delta o 18 through snowpack volume and glacier activity in the catchment lakewater temperatures the input versus evaporation balance and the duration of seasonal lake ice cover the most depleted negative delta o 18 values are associated with influxes of meltwater at times of glacier advance or retreat enriched positive delta o 18 values occur during more arid warmer conditions with longer periods of open water in summer this isotope record can be used to determine century scale to decadal variability in air circulation and moisture origin strong similarities with other holocene proxy records from the weddell sea and antarctic peninsula region are apparent including the mid holocene climate optimum followed by the neoglacial and most recently late twentieth century climatic warming the oxygen isotope record from sombre lake illustrates the importance of remote islands in contributing to our understanding of teleconnections in atmospheric and oceanographic circulation sea ice extent air temperatures and precipitation in the southern ocean

sediment accumulation rates and carbon fluxes to bottom sediments at the western bransfield strait antarctica abstract mean sediment and carbon accumulation rates in the western bransfield strait during the last ca 100 years were determined at three sites by using 210 pb as a radiotracer of sedimentation processes rates 210 pb profiles showed moderate mixing in the upper 8 5 12 cm which was attributed to bioturbation sediment accumulation rates calculated assuming no mixing below the surface mixed layer sml were found to be relatively high between 0 03 and 0 09 g cm 2 yr 1 in good agreement with previously reported data based on both 210 pb and 14 c dating in surrounding areas these results together with the calculated excess 210 pb fluxes to the bottom sediments and the 210 pb and 210 po distributions in the water column indicated the presence of a large net advective flux of material in the area highlighting the importance of glacial related sedimentation processes in this semi enclosed sea carbon in bottom sediments was mainly organic and its content was moderately low 0 65 1 25 being slightly higher within the sml reflecting the presence of inhabiting organisms however organic carbon oc accumulation fluxes 3 1 6 7 g c m 2 yr 1 were considerable due to the high sediment accumulation rates 210 pb dated profiles allowed us to estimate the amount of carbon exported from the water column and buried in the bottom sediment which represents about 3 7 of the mean annual primary production in the euphotic layer of the bransfield strait the burial efficiency of oc in the sediment was estimated to be approximately 60 80

geology and geochemistry of the vantage gold deposits alligator ridge bald mountain mining district nevada geologic relationships major element data and isotopic geochemistry of a group of carlintype au deposits in the alligator ridge bald mountain district of east central nevada were investigated to help constrain the origin and relative timing of au mineralization and associated alteration the vantage gold deposits were the largest of 18 known sediment hosted disseminated gold deposits and prospects that are distributed over a strike length of 40 km the district consists predominantly of paleozoic carbonate and siliciclastic sedimentary rocks minor amounts of tertiary volcanic and volcanic related sedimentary rocks and a small granitic stock in the northern end of the district are also present the intrusion and its surrounding aureole also host gold mineralization but most gold deposits in the district are not spatially associated with intrusive rocks the vantage au deposits formed at the contact between the devonian devils gate limestone and the devonian mississippian pilot shale adjacent to a major fault zone herein referred to as the vantage fault gold mineralization was accompanied by silver antimony and arsenic and showed a strong preference for the pilot shale alteration related in time and space to au mineralization was the replacement of host rock carbonates by quartz replacement in the pilot shale closely followed the ore waste boundary whereas replacement in the devils gate limestone occurred as a stratiform jasperold not confined to the ore zones quartz kaolinite stibnite veins were common within the central high grade portion of each orebody peripheral to silicification diagenetic dolomite in the pilot shale was replaced by hydrothermal calcite and calcite veins constituted as much as 10 percent of the rocks two oxidation events that destroyed organic matter and sulfides occurred after au deposition and silicification the early oxidation event was accompanied by the destruction of detrital illite in the pilot shale and deposition of alunite or barite veins this event was barren of au but did redistribute metals introduced during silicification the spatial distribution of this alteration was similar to that of the silicification k ar dating of this alunite indicates an age of 11 ma for its formation following a period of erosion weathering related oxidation overprinted much of the earlier alteration and deposited jarosite and goethite but it did not affect metal distribution patterns or the matrix of the pilot shale whole rock chemical analyses indicate that silica and sulfur were the only major components introduced during silicification and that very little material other than iron and organic matter was removed during the intense oxidation oxygen isotope compositions determined for jasperoid and vein quartz varied from 15 9 to 18 2 per mil and from 16 1 to 20 1 per mil respectively carbonate from whole rock samples peripheral to silicification showed an increase in their carbon isotope values of up to 3 per mil to 1 4ppm and a decrease in their oxygen isotope values of up to 12 per mil to 12 7ppm in comparison with unaltered samples vein calcite had even more extreme values of up to 3 1 per mil for delta 13 c and 3 8 per mil for delta 18 o sulfur isotope measurements on stibnite and orpiment varied from 5 5 to 10 per mil and from 2 5 to 12 3 per mil respectively vein alunite and barite associated with intense oxidation had sulfur isotope compositions that generally varied from 3 8 to 13 4 per mil and from 21 0 to 29 2 per mil respectively barite that appeared to be sedimentary in origin yielded values of 25 9 to 47 1 per mil hydrothermal fluids that formed the deposits ascended from depth along the vantage fault near the level of the deposits fluids were displaced into minor faults in the footwall limestone at the contact between the devils gate limestone and the pilot shale fluids spread laterally and deposited au ag sb and as and quartz following au deposition hypogene oxidizing fluids using the same conduits destroyed reduced components in the pilot shale and produced major textural modifications the distribution of the elements within the deposits appears to be related to 1 proximity to hydrothermal conduits 2 composition of the host lithologies and 3 extent of postmineralization oxidation oxygen isotope data of jasperoid and vein quartz indicate that the ore fluids were evolved meteoric waters isotopic data for epigenetic sulfides indicate that sulfur was derived from sedimentary sulfides local stratigraphic considerations suggest that cambrian siliciclastic rocks were the source the deposits were geochemically similar to other sediment hosted gold deposits in the great basin e g carlin but they were uncomplicated by extraneous geologic features such as paleozoic thrusts or premineralization intrusions thus the vantage deposits may be more easily understood examples of this class of ore deposits

listvenite and related rocks perspectives on terminology and mineralogy with reference to an occurrence at cregganbaun co mayo republic of ireland the rock listvenite is named and defined by reference to historical observations and recommendations are made so that listvenite s s can be distinguished from related carbonate rich alteration products of ultramafic rocks the mineralogy and tectonic setting of listvenite are reviewed taking into account the descriptions and classifications used in the literature the petrography of listvenite and related rocks at cregganbaun serves as a reference to illustrate the characteristics of true listvenite and closely related products of listvenitic alteration

geology and in situ sulfur and lead isotope analyses of the jinlongshan carlin type gold deposit in the southern qinling orogen china implications for metal sources and ore genesis abstract the jinlongshan gold deposit shaanxi province central china is a large deposit 150 t au in the southern qinling orogen gold mineralization is hosted in upper devonian to lower carboniferous carbonaceous clastic carbonate sequences four stages of pyrite and paragenetic sulfides have been identified based on morphology and paragenesis laser ablation inductively coupled plasma mass spectrometry la icp ms and laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms analyses were conducted to determine the chemical and s pb isotopic composition of the sulfides pre ore stage pyrites py1 and py2 contain relatively high concentrations of mn co ni cu zn sb and pb exhibiting a wide range of 34s values ranging from 29 9 to 48 4 these two pyrites were formed by bacterial and thermochemical sulfate reduction of upper devonian marine sulfate respectively main ore stage pyrite py3 and arsenopyrite apy contain high concentrations of au as cu sb hg and tl with restricted ranges of 34s values from 9 6 to 15 3 which is interpreted as resulting from the underlying low grade metamorphic paleozoic sedimentary rocks by the decomposition of pyrite and or inorganic reduction of sulfate late or post ore stage pyrite py4 is characterized by low concentrations of au ag sn hg and bi and exhibited variable 34s values ranging from 4 4 to 27 7 that may reflect the mixing of metamorphic fluids with meteoric water similarly the pb isotope composition of ore stage sulfides resembles those of underlying low grade metamorphic paleozoic sedimentary rocks whereas differs from precambrian metamorphic basement rocks and granitoids around the basin indicating that the metals of the jinlongshan gold deposit were sourced from the underlying paleozoic sedimentary rocks detailed fieldwork revealed that the deposit has mainly undergone four deformation events the ore bodies developed in ne trending dextral oblique slip reverse faults of d3 that crosscut wnw trending shear zones of d2 the timing and corresponding stress regimes of the d3 event suggest that it formed in a local extensional environment of yanshanian intracontinental orogeny of qinling orogenic belt gold metallogenesis of the jinlongshan gold deposit occurred during the transition of tectonic setting from compression to extension which reactivated the shear zones and migrated deep ore bearing fluids to ne trending brittle faults the geological and geochemical features of the jinlongshan gold deposit are more analogous to the carlin type deposits than other orogenic gold deposits worldwide therefore we propose it is a typical carlin type gold deposit in south qinling orogen

palaeoclimatic significance of late quaternary diatom assemblages from southern windmill islands east antarctica abstract the late quaternary palaeoenvironmental history of the southern windmill islands east antarctica has been reconstructed using diatom assemblages from two long well dated sediment cores taken in two marine bays the diatom assemblage of the lowest sediment layers suggests a warm climate with mostly open water conditions during the late pleistocene during the following glacial the windmill islands were covered by grounded ice preventing any in situ bioproductivity following deglaciation a sapropel with a well preserved diatom assemblage was deposited from 10 500 cal yr bp between 10 500 and 4000 cal yr bp total organic carbon corg and total diatom valve concentrations as well as the diatom species composition suggest relatively cool summer temperatures hydrological conditions in coastal bays were characterised by combined winter sea ice and open water conditions this extensive period of glacial retreat was followed by the holocene optimum 4000 to 1000 cal yr bp which occurred later in the southern windmill islands than in most other antarctic coastal regions diatom assemblages in this period suggest ice free conditions and meltwater stratified waters in the marine bays during summer which is also reflected in high proportions of freshwater diatoms in the sediments the diatom assemblage in the upper sediments of both cores indicates neoglacial cooling from 1000 cal yr bp which again led to seasonally persistent sea ice on the bays the holocene optimum and cooling trends in the windmill islands did not occur contemporaneously with other antarctic coastal regions showing that the here presented record reflects partly local environmental conditions rather than global climatic trends

developing sediment geochronologies for high latitude continental shelf deposits a radiochemical approach during january and february of 1986 47 box cores and 55 piston cores were collected from the bransfield strait gerlache strait and marguerite bay antarctica apparent sediment accumulation rates established for 100 yr time scales with excess 210pb chronologies range from 0 08 to 0 34 cm yr in the bransfield strait 0 15 to 0 51 cm yr in gerlache strait and from 0 10 to 0 27 cm yr in marguerite bay for the antarctic peninsula continental shelf 137cs appears to have a limited usefulness in assessing the effects of deep sediment mixing by benthic fauna on seabed excess 210pb profiles because the observed activities for the regions examined are close to counter detection limits conventional 14c ages of surface sediments from the peninsula region range from 1370 to 2820 yr the spatial variations in the conventional 14c surface ages are thought to be influenced predominantly by inputs of older eroded sediment from lateral transport current winnowing mass wasting and or a variable carbon source on a 1000 yr time scale 14c measurements of five piston cores from the bransfield strait yielded sediment accumulation rates ranging from 0 06 to 0 49 cm yr these data support the assertion by nelson 1988 that the excess 210pb sediment accumulation rates range of 0 08 to 0 34 cm yr for this region represent true rates the two sediment accumulation rates of 0 01 and 0 08 cm yr for the gerlache strait are significantly lower than the observed apparent 210pb accumulation rates mean 0 27 0 12 cm yr for this region likewise two piston cores from marguerite bay yielded 14c sediment accumulation rates of 0 02 and 0 05 cm yr which also are considerably lower than the excess 210pb apparent accumulation rates mean 0 17 0 06 cm yr for this area the one dimensional advection diffusion equation of goldberg and koide geochim cosmochim acta vol 51 1962 was solved simulatneously with 210pb and 14c data for bc18 and bc113 to resolved the effects of sediment mixing and accumulation in bransfield strait and marguerite bay box core samples respectively this model indicates that 210pb and 14c sediment accumulation rates agree within a factor of 2 in the bransfield strait whereas in marguerite bay the apparent 210pb accumulation rates may be as much as an order of magnitude too high in the southern high latitude environments of the antarctic peninsula radiocarbon measurements in the seabed are a better approach than 210pb for establishing accurate rates of sediment accumulation the 14c chronologies when coupled with 210pb data provide more reliable assessments of biological deep mixing and sediment accumulation rates than do excess 210pb data coupled with measurements of bomb produced 137cs the sediment accumulation rates for both 100 yr and 1000 yr time scales tend to decrease southward from the bransfield strait to marguerite bay which is consistent with glacial marine sedimentation processes as modulated by climate for the western antarctic peninsula seabed measurements of 210pb 137cs and 14c also provides valuable insights on water circulation and upwelling atmospheric inputs and sediment depositional processes for the antarctic peninsula region

subjacent crustal sources of sulfur and lead in eastern great basin metal deposits sulfide minerals in mesozoic replacement skarn porphyry and vein deposits in lower paleozoic rocks in central and eastern nevada have sulfur isotope compositions 10 34 s 206 pb 204 pb 19 that are elevated relative to the range of s and pb isotope compositions in eastern great basin metal deposits the s and pb isotope compositions of central and eastern nevada mesozoic metal deposits e g eureka are similar to the s and pb isotope compositions of pyrite disseminated in the thick is less than or equal to 8 km terrigenous detrital succession tds of siliciclastic rocks of late proterozoic early cambrian age subjacent to the deposits tds rocks are therefore a possible source for most if not all s and pb in these deposits to the south and east in southern nevada southeastern california and western utah progressively thinner tds rocks correlate with lower 34 s values 206 pb 204 pb ratios s and pb isotope compositions of sulfide minerals in metal deposits that are temporally related to middle tertiary granitic intrusions also vary geographically and are generally lower than isotope compositions of mesozoic metal deposits regardless of paleozoic host rock age compared to the mesozoic deposits middle tertiary deposits in central and eastern nevada apparently derived significant but mostly smaller amounts of s and pb from tds rocks and or paleozoic rocks tertiary metal deposits in western utah may have obtained nearly all their s and pb from older precambrian crystalline rocks or from magmas and virtually none from tds and paleozoic rocks semiquantification of source rock contributions of s and pb to metal deposits is based on average s and pb isotope compositions of possible source rocks and simple mixing calculations possible source rocks are somewhat isotopically inhomogeneous but their s and pb isotope compositional ranges largely bracket the s and pb isotope compositions of metal deposits in the eastern great basin thus facilitating determination of end member contributions geologic factors that cause isotope inhomogeneity in both source rocks and metal deposits include different source rock provenances particularly for pb isotopes isotope mixing and fractionation by unrecognized hydrothermal processes metamorphism and tectonism that has juxtaposed potential source rocks of differing ages and isotope compositions tds pyrite formed from processes that produced s with high 34 s values including diagenesis involving seawater sulfate and at higher temperatures and greater depths thermochemical sulfate reduction radiogenic pb in tds pyrite was derived from leaching of quartzofeldspathic sedimentary rocks granitic melts acquired s and pb and possibly other ore forming components by bulk assimilation of tds and or paleozoic sedimentary rocks proterozoic crystalline rocks and possibly older precambrian rocks by volatilization of disseminated pyrite in source rocks during ascent and by hydrothermal circulation near the sites of ore deposition the high density of eastern great basin metal deposits and the sources of s and pb for these deposits appear to be a function not only of the large number of granitic intrusions but also of intrusion age and the thickness and type of precambrian crust s and pb isotope compositions in eastern great basin metal deposits support a proposed origin for jurassic cretaceous and tertiary intrusions that involves generation of magmas at different crustal levels and variable amounts of magmatic contamination by precambrian rocks

arsenic associated with historical gold mining in the sierra nevada foothills case study and field trip guide for empire mine state historic park california the empire mine together with other mines in the grass valley mining district produced at least 21 3 million troy ounces 663 tonnes of gold au during the 1850s through the 1950s making it the most productive hardrock au mining district in california history clark 1970 the empire mine state historic park empire mine shp or emshp established in 1975 provides the public with an opportunity to see many well preserved features of the historic mining and mineral processing operations cdpr 2014a a legacy of au mining at empire mine and elsewhere is contamination of mine wastes and associated soils surface waters and groundwaters with arsenic as mercury hg lead pb and other metals at emshp as has been the principal contaminant of concern and the focus of extensive remediation efforts over the past several years by the state of california department of parks and recreation dpr and newmont usa ltd in addition the site is the main focus of a multidisciplinary research project on as bioavailability and bioaccessibility led by the california department of toxic substances control dtsc and funded by the u s environmental protection agency s usepa s brownfields program this chapter was prepared as a guide for a field trip to emshp held on june 14 2014 in conjunction with a short course on environmental geochemistry mineralogy and microbiology of arsenic held in nevada city california on june 15 16 2014 this guide contains background information on geological setting mining history and environmental history at emshp and other historical au mining districts in the sierra nevada followed by descriptions of the field trip stops regional geology empire mine shp is located in the grass valley mining district on the western sloping foothills of the sierra nevada fig 1 the sierra nevada foothills snfh orogenic gold province stretches 150 miles 240 km from the town

sea ice seasonality during the holocene adelie land east antarctica abstract thin sections of laminated cores from different antarctic coastal areas have demonstrated the potential of diatom species to document climate change at the seasonal scale here we present the relative abundances of four diatom species and species groups fragilariopsis curta group as a proxy for yearly sea ice cover f kerguelensis as a proxy for summer sea surface temperature chaetoceros hyalochaete resting spores as a proxy for spring sea ice melting and the thalassiosira antarctica group as a proxy for autumn sea ice formation in core md03 2601 retrieved off adelie land on the antarctic continental shelf these abundances were compared to surface temperatures and sea ice cover modelled over the last 9000 years both the marine records and the simulated climate demonstrated a cooler early holocene 9000 7700 years bp a warmer mid holocene 7700 4000 years bp and a colder late holocene 4000 1000 years bp yearly sea ice cover followed an inverse pattern to temperatures with less sea ice during the mid holocene hypsithermal than during the late holocene neoglacial however diatom census counts and model output indicate that sea ice spring melting happened earlier in the season as expected but that autumn sea ice formation also occurred earlier in the season during the hypsithermal than during the colder neoglacial thereby following seasonal changes in local insolation

is the palea kavala bi te pb sb au district northeastern greece an intrusion related system abstract intrusion related gold systems are generally characterized by a au bi te sn w metal assemblage genetically linked to the emplacement of granitoids the palea kavala ore system greece consists of 150 minor fe mn pb zn ag fe mn au fe as au fe cu au and bi te au occurrences that occur primarily in quartz calcite sulfide veins hypogene mineralization or as supergene bodies in overlapping zones centered on the 21 22 ma granodioritic kavala pluton which intrudes metamorphic rocks of the paleozoic rhodope metamorphic core complex the pluton consists mostly of granodiorite with lesser amounts of diorite tonalite and monzodiorite which was emplaced along the regional e w trending kavala komotini fault the recently discovered 4 km long e w trending so called kavala vein is a sheeted quartz vein system of bi te pb sb au mineralization that crosscuts the kavala pluton and the schists and gneisses of the rhodope massif the kavala vein system is comprised of quartz with lesser amounts of k feldspar plagioclase and muscovite quartz sericite pyrite alteration is pervasive but minor kaolinite is also present pyrite 5 of vein volume contains inclusions of tetradymite some gold bearing bismuthinite and cosalite sulfur isotope values n 27 of pyrite from the kavala and chalkero veins as well as pyrite and galena from garizo hill fe mn pb vein range from 1 9 to 1 0 with one outlier of 4 6 and suggest a magmatic sulfur source homogenization temperatures th of type i two phase aqueous liquid vapor and type ii three phase h2o co2 rich fluid inclusions that homogenize into the liquid phase in quartz from the kavala and chalkero veins range from 216 0 to 420 0 c n 216 and 255 7 to 414 0 c n 112 respectively the th of type iii two phase aqueous liquid vapor which homogenize into the vapor phase ranges from 210 4 to 323 4 c n 28 the salinities of type i and type ii inclusions range from 15 9 to 22 6 wt nacl equiv and 5 5 to 11 2 wt nacl equiv respectively eutectic temperatures of 58 5 to 44 3 c for type i inclusions suggest the presence of appreciable cacl2 in addition to nacl clathrate melting temperatures for type ii inclusions of 56 7 c indicate that co2 is the major component of the gaseous phase however up to 6 ch4 is present in some inclusions the presence of a zoned metallogenetic district centered on bi te pb sb au mineralization within the kavala pluton the presence of both magnetite and ilmenite in the kavala pluton and the two high temperature high salinity immiscible carbonic and aqueous fluids associated with the kavala and chalkero veins are consistent with them being part of an intrusion related gold system that formed along the ilmenite magnetite buffer

part 1 regional studies and epithermal deposits northern nevada is one of the earth s premier gold and silver producing regions and gold and silver are mined from a wide range of deposit types table 1 current production largely comes from carlin type sedimentary rock hosted disseminated gold deposits christensen 1995 teal and jackson 1997 bettles 2002 many of which lie along linear trends fig 1 roberts 1960 1966 berger and bagby 1991 the small area of the carlin trend approximately 8 x 65 km is north america s most prolific gold mining district producing nearly 125 t 4 moz of gold annually since large scale mining began in 1965 with the opening of the carlin mine the carlin trend has produced more than 1555 t 50 moz of gold during 2001 gold production from the entire state of nevada was nearly 253 t 8 13 moz which accounted for approximately 76 percent of the united states and 10 percent of the world production price and meeuwig 2002 in 2001 only the countries of south africa and australia produced more gold than the state of nevada in addition nevada produced 543 t 17 4 moz of silver in 2001 about 31 percent of the united states production and 3 percent of the world production in 1996 the mineral resources program of the u s geological survey began a multidisciplinary project to investigate the origin of gold deposits in northern nevada this project was undertaken in collaboration with the nevada bureau of mines and geology the ralph j roberts center for research in economic geology at the university of nevada reno several other universities and numerous mining companies active in the region in addition several universities and mining companies were conducting research on the origin of gold deposits in northern nevada this research built on more than a century of studies by the

oceanographic control of biogenic opal and diatoms in surface sediments of the southwestern atlantic based on 66 surface sediment samples collected in the sw atlantic ocean between 27 and 50 s this study presents an overview of the spatial distribution of biogenic opal and diatom concentrations and diatom assemblages biogenic opal has highest values in the deepest pelagic stations and decreases toward the slope diatoms closely follow the spatial trend of opal diatom assemblages reflect the present day dominant hydrographical features antarctic diatoms are the main contributors to the preserved diatom community in core top sediments with coastal planktonic and tropical subtropical diatoms as secondary components dominance of antarctic diatoms between 35 and 50 s in the pelagic realm mirrors the northward displacement of antarctic source water masses characterized by high nutrient content and low salinity northward of ca 35 s the highest contribution of tropical subtropical pelagic diatoms typical for nutrient poor and high salinity waters matches the main southward path of the brazil current mixing of antarctic and tropical waters down up to 45 s is clearly illustrated by the diatom assemblage concentrations of biogenic opal and diatoms rather reflect the path of predominant water masses but are less correlated with surface water productivity in the sw atlantic

strains and structures associated with a terrane bounding stretching fault the melones fault zone central sierra nevada california abstract an examination of the structures total strains and rock types across the melones fault zone indicates that in the central sierra nevada this fault separates and locally imbricates two distinct terranes east of the fault a widespread early jurassic cleavage displays west northwest to northwest strikes and is associated with moderate to high strain intensities these structures form in jura triassic metasedimentary rocks in part derived from a continental source a weak northwest striking cleavage and low strain intensities occur west of the fault in lower jurassic volcanic rocks and upper jurassic slates and sandstones the fault zone itself consists of steep east dipping ductile brittle shear zones or stretching faults along which the early jurassic structures are transposed parallel to the jura cretaceous and fault related structures large flattening type strains are common in the fault zone and may be the result of heterogeneous strains developed when the shear zones bend around resistant blocks or by volume losses total strains in the eastern hanging wall reflect the superposition of fault related on older strains therefore stretching lineations in this hanging wall do not reflect directions of fault motion stretching lineations in the footwall and fault zone kinematic indicators in the fault zone and a small eastward jump in metamorphic grade suggest an east over west or reverse sense of movement no evidence for significant strike slip or oblique slip motion was found removal of footwall strains indicates that the jura cretaceous shortening across the fault was responsible for both the transposition of older structures east of the fault and the rotation of the fault to its present steep dips thus the melones fault is a large ductile brittle shear zone along which the eastern hanging wall merced river terrane moved to the southwest over the western footwall eastern foothills terrane

high resolution diatom stratigraphy of quaternary sediments from the scotia sea upper quaternary pelagic and hemipelagic sediments from the scotia sea and south scotia ridge range from diatom ooze to diatom bearing mud diatom content increases northwards and at most sites diatom rich and diatom poor sediments alternate downcore on a scale of metres a local stratigraphy is based on relative abundance of six prominent diatom taxa eucampia antarctica rhizosolenia spp thalassiosira spp chaetoceros spores nitzschia kerguelensis and othernitzschia species and one silicoflagellate species distephanus speculum these stratigraphic units defined using diatoms are correlated with radiolarian abundance stratigraphy cycladophora davisiana and with palaeomagnetic stratigraphy information from modern environments phytoplankton and sediment trap studies indicates that changes in diatom species composition are related to n s movement of the winter ice edge and of the antarctic convergence

bioaccumulation record and paleoclimatic significance in the western bransfield strait the last 2000 years abstract two gravity cores a 3 and a 6 from the western basin of the bransfield strait antarctica were recovered during the bio hesperides expedition fruela 96 both cores consist mainly of hemipelagic and laminated muds with black layers rich in sand sized volcanic ash geochemical analyses toc and opal radiometric dating techniques ams 14 c and 210 pb and micropaleontological analyses diatoms were performed on both cores ams analyses on toc yielded 14 c ages older than expected 3960 50 yr bp for the core top of a 3 and 3410 50 yr bp for a 6 210 pb analyses revealed that core top age for both gravity cores could be estimated to be about 100 15 yr bp the results of diatom analyses were related to the sequence of neoglacial events that have occurred over the last two millennia the abundance patterns of chaetoceros rs the biogenic silica content and the abundance of diatom valves agree with the high productivity values previously reported for the bransfield strait waters the significant recent reduction in resting spores of the diatom chaetoceros suggests as a reduction in surface productivity trend differences between chaetoceros resting spore abundance and toc contents are explained in terms of organic matter preservation diatom communities from the bransfield strait did not play an important role in the global co 2 cycle during cold periods bio and geochemical changes have an overprinted high frequency cyclicity at about 200 300 yr which might be related to the 200 yr solar cycle

sedimentation of biogenic siliceous particles in antarctic waters from the atlantic sector abstract sediment traps were deployed in the drake passage bransfield strait and west of south orkney islands powell basin during december 1980 january 1981 december 1983 and between march and december 1983 respectively most of the trapped material is biogenic opal except in the lower half of the water column in bransfield strait where large amounts of resuspended aluminosilicates and quartz grains were present frustules and skeletons of siliceous microorganisms diatoms silicoflagellates radiolarians chrysophycean cysts fragments and moults of crustaceans and tests of foraminifera were found quantitatively diatoms are the dominant constituent of the trapped biogenic material alteration of diatom assemblages in the water column is due to mechanical breakdown by grazing zooplankton it mainly affects large frustules e g corethron criophilum castracane in the uppermost part of the water column dissolution of frustules occurs mostly at the sediment water interface and leads to the enrichment of strongly silicified valves e g nitzschia kerguelensis o meara hasle thalassiosira antarctica comber resting spores at the bransfield strait site a large part of biogenic opal was incorporated into fecal pellets of krill and copepods the bulk of pellet content consists of fragmented diatom frustules 1 10 m in size most intact valves found in the sediments have settled through the water column by means other than fecal pellet transport e g settling as solitary particles or incorporated into or attached to marine snow or large amorphous aggregates

magmatic arc asymmetry and distribution of anomalous plutonic belts in the batholiths of california effects of assimilation crustal thickness and depth of crystallization in order to better understand geologic fac tors controlling pronounced regional variations in whole rock chemistry mineralogy and mineral chemistry in the batholiths of california we calculate the magmatic intensive variables f hf f h 2 o f hf f hcl and f o 2 regional scale west to east increases in f oh in mafic silicates corresponding to the systematic i wc to i mc and i sc progression reflect orders of magnitude increase in f hf f h 2 o attending pluton crystallization low f hf f h 2 o of formation of western i wc types is consistent with their derivation from low fluorine source rocks in subducted oceanic slabs or the upper mantle in contrast higher f hf f h 2 o of crystallization of i mc and i sc types to the east implies the involvement of 1 progressively greater amounts of continental crustal source material such as biotite bearing metamorphic rocks their unweathered sedimentary derivatives retaining f rich mafic minerals or their fusion products and or 2 source materials which become more f rich toward the continental interior the regional distribution of i mc and i sc types suggests that the precambrian craton of western north america or derivative sediments may extend farther north in california and be morphologically more complex than previously thought from seemingly out of place occurrences of i wc plutons on the eastern slopes of the sierra nevada batholith we infer the existence of regions where precambrian basement was thin or absent in mesozoic time which prevented extensive cratonal contamination of subducted slab or upper mantle derived magmas new methods for estimating t f o 2 relations in the magmas demonstrate that i scr granites crystallize at oxygen fugacities as much as five orders of magnitude lower than those of i wc i mc and i sc types under conditions at or below the maximum stability limit of graphite in equilibrium with a c o h s gas phase the local scale formation of i scr granites in plutonic belts within specific wall rock terranes containing highly reducing sediments or metasediments may occur by contamination of i types with graphitic pelite or in some cases by the direct fusion of this reducing pelitic wall rock the spatial distribution of i scr granite provinces therefore is controlled simply by wall rock lithology amphibole geobarometry demonstrates a general west to east decrease in crystallization pressure across the sierra nevada batholith in contrast the peninsular ranges batholith displays a west to east crystallization pressure increase the bulk of the california batholiths crystallized at pressures less than 4 5 kb and depths less than about 15 19 km in the southern sierra nevada batholith the san gabriels and the eastern peninsular ranges however plutons crystallized at pressures exceeding 6 kb at deep crustal levels 23 km reconstruction of the pre erosion top of the batholith shows that in an east west cross section the central sierra nevada batholith was a horizontal tabular body with an aspect ratio of at least five to one

evidence of a high productivity area off the coast of malaga from studies of diatoms in surface sediments abstract the assemblages of diatoms contained in nineteen surface sediment samples recovered off the coast of malaga province spain between 5 w and 4 38 w have been analysed the variations observed in the diatom assemblage point to the presence of nutrient enriched waters transported laterally from the centre of an upwelling that occurs to the west of the study area the utility of species such as paralia sulcata thalassionema nitzschioides and the spores of chaetoceros spp in the reconstruction of physico chemical and biological characteristics and of the spatial structure of the upwelling is confirmed

the tuscarora au ag district eocene volcanic hosted epithermal deposits in the carlin gold region nevada the tuscarora mining district contains the oldest and the only productive eocene epithermal deposits in nevada the district is a particularly clear example of association of low sulfidation deposits with igneous activity and structure and it is unusual in that it consists of two adjoining but physically and chemically distinct types of low sulfidation deposits moreover tuscarora deposits are of interest because they formed contemporaneously with nearby giant carlin type gold deposits the tuscarora deposits formed within the 39 9 to 39 3 ma tuscarora volcanic field along and just outside the southeastern margin of the caldera like mount blitzen volcanic center both deposit types formed at 39 3 ma contemporaneous with the only major intrusive activity in the volcanic field no deposits are known to have formed during any of the intense volcanic phases of the field intrusions were the apparent heat source and structures related to the mount blitzen center were conduits for hydrothermal circulation the ore forming fluids interacted dominantly with eocene igneous rocks the two deposit types occur in a northern silver rich zone that is characterized by relatively high ag au ratios 110 150 narrow alteration zones and quartz and carbonate veins developed mostly in intrusive dacite and in a southern gold rich zone that is typified by relatively low ag au ratios 4 14 more widespread alteration and quartz fissure and stockwork veins commonly developed in tuffaceous sedimentary rocks the deposit types have similar fluid inclusion and pb and s isotope characteristics but different geochemical signatures quartz veins from both zones have similar thermal and paragenetic histories and contain fluid inclusions that indicate that fluids cooled from between 260 and 230 c to less than 200 c fluid boiling may have contributed to precious metal deposition veins in both zones have relatively high as and sb and low bi te and w the silver zone has high ca pb mn zn cd tl and se the gold zone has high hg and mo a few samples from an area of overlap between the two zones share chemical characteristics of both deposit types the deposit types could represent a single zoned or evolving system in which hydrothermal fluids rose along structures within the silver zone preferentially deposited ag and base metals and then spread into the gold zone alternatively the deposit types could represent two distinct but temporally indistinguishable hydrothermal cells that only narrowly overlapped spatially as noted in previous studies the hydrothermal fluids that generated the tuscarora and other epithermal deposits could have evolved from carlin type fluids by boiling and mixing with meteoric water if so the tuscarora deposit may represent epithermal conditions above carlin type deposits and carlin type deposits may lie beneath the district

recent diatom record of mcmurdo sound antarctica implications for history of sea ice extent analyses of diatom assemblages within surface sediments from mcmurdo sound antarctica document the regional circulation patterns in this large embayment in the southwestern ross sea thalassiosira spp indicative of water column primary productivity is most common in eastern and portions of northwestern mcmurdo sound as a result of its advection into these regions from areas of open water primary productivity surface sediments from southwestern mcmurdo sound are composed mainly of nitzschia curta a small pennate form commonly found both as a member of the sea ice microbial community as well as a dominant component in ice edge blooms in the ross sea the northward advection of oligotrophic water into the western sound from beneath the mcmurdo ice shelf results in the dominance of an autochthonous flora in the southwestern sound sediments deposited during the past 500 years also have been dominated by thalassiosira spp and nitzschia curta thalassiosira spp concentrations reached a maximum between 1600 and 1875 a d corresponding to the time of the little ice age more persistent winds may have been responsible for more prevalent polynyas at that time resulting in greater amounts of open water primary productivity and subsequent higher percentages of thalassiosira spp increased areal extent and or duration of coastal polynyas during the little ice age suggests that within the southwestern ross sea the production of high salinity shelf water and hence antarctic bottom water may have been greater at that time

a fluid inclusion study of au bearing quartz vein systems in the central and north deborah deposits of the bendigo gold field central victoria australia the central and north deborah gold deposits with a production of about 7 tons au are located in one of 15 domes in the bendigo gold field central victoria australia an important mesothermal lode gold province the gold bearing quartz vein systems are hosted predominantly by reverse faults in lower ordovician turbidites which underwent lower greenschist facies metamorphism in the central and north deborah mines there are six stages of quartz veins that developed in the following sequence 1 laminated veins with a metal association of au as sb pb zn ni 2 spurs au 3 massive barren veins main dilation stage 4 brecciated veins with au as 5 quartz ankerite veinlets and 6 late pure quartz or calcite veinlets of the three mineralized vein stages 1 2 and 4 only the first one predated or was coeval with the main deformation event whereas stages 2 and 4 postdated the main deformation the vein structures indicate that vein development was controlled by repeated fluctuations of fluid pressure inducing hydraulic fracturing fluid inclusions in vein quartz contain c o h fluids of variable compositions three main types of fluid inclusions are recognized at room temperature type i two phase primary ch4 v h2o l fluid inclusions type ii two or three phase primary pseudosecondary co2 v or l ch4 v or l h2o l fluid inclusions including iia ch4 co2 h2o and iib co2 h2o fluid inclusions and type iii h2o v h2o l fluid inclusions type iii fluid inclusions are further divided into three groups iiia primary pseudosecondary vapor rich iiib primary pseudosecondary liquid rich and iiic secondary liquid rich data from fluid inclusion distribution microthermometry and raman spectroscopy indicate that fluids associated with au mineralized quartz veins stages 1 2 and 4 have moderate salinity ranging from 0 to 12 wt percent nacl equiv modeled salinities around 7 8 wt nacl equiv these veins formatted at temperatures from 325 to 375 c and pressures of 200 to 300 mpa with emplacement depths of about 8 to 12 km fluids associated with barren quartz veins stages 3 5 and 6 have a low salinity of about 0 to 3 wt percent nacl equiv modeled salinities about 2 3 wt nacl equiv and lower temperatures there is evidence of fluid immiscibility in all vein stages and mixing between fluids of the same souce but differing fo2 may also have influenced gold deposition cox et al 1995 hydrothermal ore forming fluids responsible for gold mineralization are in the ch2 co2 h2o nacl system whereas those of massive barren veins stage 3 and veinlets stages 5 and 6 are in the co2 h2o nacl and h2o nacl systems respectively the carbonic phases of type i and ii fluid inclusions range from pure ch4 through mixed ch4 and co2 to pure co2 gold ore forming fluids were weakly acidic with f o2 estimated to have been 10 25 to 10 37 bars and generally above the co2 ch4 and below the so2 h2s buffer boundaries throughout gold mineralization the relatively reduced mineralizing fluids are similar to those of other turbidite hosted lode gold deposits and counterparts in volcanic plutonic terranes

crustal structure of the ruby mountains and southern carlin trend region nevada from magnetotelluric data abstract we have collected about 150 magnetotelluric mt soundings in northeastern nevada in the region of the ruby mountains metamorphic core complex uplift and southern carlin mineral trend in an effort to illuminate controls on core complex evolution and deposition of world class gold deposits the region has experienced a broad range of tectonic events including several periods of compressional and extensional deformation which have contributed to the total expression of electrical resistivity most of the soundings reside in three east west profiles across increasing degrees of core uplift to the north bald mountain harrison pass and secret pass latitudes one short cross line was also taken to assess an east west structure to the north of the northern profile model resistivity cross sections were derived from the mt data using a 2 d inversion algorithm which damps departures of model parameters from an a priori structure geological interpretation of the resistivity combines previous seismic potential field and isotope models structural and petrological models for regional compression and extension and detailed structural stratigraphic interpretations incorporating drilling for petroleum and mineral exploration to first order the resistivity structure is one of a moderately conductive phanerozoic sedimentary section fundamentally disrupted by intrusion and uplift of resistive crystalline rocks late devonian and early mississippian shales of the pilot and chainman formations together form an important conductive marker sequence in the stratigraphy and show pronounced increases in conductance conductivity thickness product from east to west these increases are attributed to graphitization caused by elko sevier era compressional shear deformation and possibly by intrusive heating the resistive crystalline central massifs adjoin the host stratigraphy across crustal scale steeply dipping fault zones the zones provide pathways to the lower crust for heterogeneous upper crustal induced electric current flow resistive core complex crust appears steeply bounded under the middle of the neighboring grabens and not to deepen at a shallow angle to arbitrary distances to the west the numerous crustal breaks imaged with mt may contribute to the low effective elastic thickness t e estimated regionally for the great basin and exemplify the mid crustal steeply dipping slip zones in which major earthquakes nucleate an east west oriented conductor in the crystalline upper crust spans the east humboldt range and northern ruby mountains the conductor may be related to nearby graphitic metasediments with possible alteration by middle tertiary magmatism lower crustal resistivity everywhere under the profiles is low and appears quasi one dimensional it is consistent with a low rock porosity

thermochronologic evidence of major tectonic denudation associated with detachment faulting northern ruby mountains east humboldt range nevada fission track ft thermochronology studies on igneous and metamorphic rocks from the ruby mountains east humboldt range metamorphic core complex provide important constraints on the timing and nature of major mid tertiary extension in northeast nevada rocks from within the ruby east humboldt detachment brittle ductile normal sense shear zone were analyzed the dominant lithology studied was variably mylonitic mafic orthogneiss nonmylonitic amphibolite from the top of the structurally lower migmatitic core and porphyritic biotite granodiorite from the oligocene circa 36 ma harrison pass pluton were also studied ft ages on apatite zircon and sphene except one 18 4 ma apatite from the basal portion of the detachment zone are concordant and range in age from 26 5 ma to 23 6 ma all ages overlap at 1 between 25 4 ma and 23 4 ma these data suggest that rocks of the upper and middle portions of the detachment zone cooled rapidly from temperatures above 285 c sphene closure temperature to below 70 c lower temperature limit of track stability in apatite near the beginning of the miocene minimum cooling rate of 40 c ma the length distribution of confined fission tracks in apatites from these exhumed middle crustal rocks is strikingly similar to those of rocks known to have cooled rapidly fish canyon ash flow tuff the lower part of the detachment zone as well as the underlying migmatitic core also cooled through sphene and zircon closure temperatures during this time interval but apparently only cooled to a temperature within the zone of partial annealing of apatite 70 130 c residence of these rocks in this zone led to a partial retention of fission tracks thus resulting in a reduced age confined track length distributions from apatite provide independent evidence of very rapid cooling but also indicate that the rocks of the lower detachment zone experienced a more protracted cooling history remained hotter longer than structurally higher levels of the zone ft data firmly establish the lower limit on the timing of mylonitization during detachment faulting in this area as 23 4 ma rapid cooling of the region is considered to reflect large scale tectonic denudation intracrustal thinning the vertical complement to crustal extension rocks originating in the middle crust 10 15 km were quickly brought near the surface along the ruby east humboldt detachment fault brittle ductile simple shear zone and juxtaposed against brittlely extended rocks deformed under upper crustal conditions

effects of mother lode type gold mineralization on 187os 188os and platinum group element concentrations in peridotite alleghany district california osmium isotope compositions and concentrations of re platinum group elements pge and au were determined for host peridotites serpentinites and harzburgites and hydrothermally altered ultramafic wall rocks associated with mother lode type hydrothermal gold quartz vein mineralization in the alleghany district california the host peridotites have os isotope compositions and re pge and au abundances typical of the upper mantle at their presumed formation age during the late proterozoic or early paleozoic the hydrothermally altered rocks have highly variable initial os isotope compositions with os values deviation of 187os 188os from the chondritic average calculated for the approx 120 ma time of mineralization ranging from 1 4 to 8 3 the lowest os isotope compositions are consistent with re depletion of a chondritic source e g the upper mantle at ca 1 6 ga most of the altered samples are enriched in au and have depleted and fractionated abundances of re and pge relative to their precursor peridotites geochemical characteristics of the altered samples suggest that re and some pge were variably removed from the ultramafic rocks during the mineralization event in addition to re the pt and pd abundances of the most intensely altered rocks appear to have been most affected by mineralization the 187os depleted isotopic compositions of some altered rocks are interpreted to be a result of preferential 187os loss via destruction of re rich phases during the event for these rocks os evidently is not a useful tracer of the mineralizing fluids the results do however provide evidence for differential mobility of these elements and mobility of 187os relative to the initial bulk os isotope composition during hydrothermal metasomatic alteration of ultramafic rocks

deformation and regional carbonate metasomatism of turbidite hosted cretaceous alkaline lamprophyres northwestern papua new guinea abstract a suite of variably metasomatised camptonite dykes and rare stocks named the fu intrusives has been recognised within thrust plates of mesozoic slates in a 3000 km2 portion of the new guinea thrust belt the intrusions were emplaced prior to oligo miocene fold deformation and low grade regional metamorphism of their host and consequently have foliated margins and are cross cut by metamorphic quartz veins samples from the less altered stocks display primary cumulophyric aggregates of kaersutite titansalite titanbiotite set in a matrix of albite salite apatite olivine quartz calcite ocelli are occasionally present ree patterns la cn lu cn 10 la 100 chondrite and initial sr ratios 0 7042 are typical of alkaline lamprophyres kaersutite and titanbiotite separates from such samples have yielded concordant k ar ages of 75 ma campanian which we accept as the age of intrusion however the dykes have suffered heavy texture destructive carbonate sericite alteration though relict cumulophyric texture and globular structures are sometimes observed composition volume calculations suggest that metasomatism was accompanied by loss of na ti and p and systematic addition of ca fe and co2 as well as progressive lree depletion and fe reduction alteration carbonates exhibit a narrow range of 18o values 13 8 to 14 9 indicating uniform conditions of metasomatism throughout the terrain the calculated fluid 18o at a model temperature of 300 50 c is 8 2 which corresponds with that deduced from the 18o value 12 3 of the cleanest sericite separate the four analysed sericite separates have a mean d of 64 12 implying an hydrogen isotopic composition for the alteration fluid of 58 30 at 300 50 c the calculated fluid composition therefore overlaps the normal range of metamorphic and magmatic waters however c and sr isotopic ratios of the alteration carbonates 13c 7 3 to 0 4 87 sr 86 sr 0 7076 0 7126 strongly support a crustal source for the metasomatic fluids this is corroborated by field evidence that country rock slates adjacent to the dykes are unaffected by carbonate metasomatism and hence were in equilibrium with the alteration fluid we therefore conclude that regional carbonate metasomatism of the fu intrusive suite occurred as a result of metamorphic dewatering of their host rocks during slaty cleavage development

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

new sr nd and pb isotopic data from plutons in the northern great basin implications for crustal structure and granite petrogenesis in the hinterland of the sevier thrust belt the influence of tectonic setting and age on the variation of isotopic signatures of granitic plutons in the northern great basin has in general not been apparent from previous investigations although elison et al pointed out isotopic differences between jurassic and younger plutons near the 0 706 sr isopleth and farmer and depaolo noted that there might be a difference between cenozoic vs mesozoic plutonic rocks in the eastern part of the northern great basin neither of these studies revealed the remarkable correlation between isotopic signature age and tectonic setting shown by our expanded sr nd and pb isotopic data base jurassic early cretaceous plutons in the northern great basin have a limited range of sr and nd isotopic values that cluster near bulk earth all but one of these plutons have nd values less negative than 7 despite their location both to the west and east of the nd 7 line construction of sr 0 706 and nd 7 isotopic boundaries is virtually impossible for plutons of this age range in contrast upper cretaceous peraluminous granites east of the nd 7 line have very negative nd values and high initial sr ratios and they appear to represent essentially pure crustal melts the data favor a model that equates generation of these plutons via crustal thickening associated with the sevier thrust belt cenozoic plutons appear to be mixtures of mantle and crustal reservoirs and their isotopic systematics along with those of the late cretaceous age plutonic suite define a previously unrecognized approximately east west trending crustal boundary between predominantly archean crust to the north and predominantly proterozoic crust to the south the isotopic data from the jurassic early cretaceous plutonic suite do not reflect the presence of this boundary suggesting that the isotopic systematics of this plutonic suite may not have been controlled by the same variations in crustal and or mantle lithospheric structure at depth

water masses and distribution of physico chemical properties in the western bransfield strait and gerlache strait during austral summer 1995 96 in the framework of the fruela project two oceanographic surveys were conducted by r v hesperides in the eastern bellingshausen sea western basin of the bransfield strait and gerlache strait area during december 1995 and january 1996 the main hydrographic structures of the study domain were the southern boundary of the acc and the bransfield front the characteristics and zonation of local water masses are discussed in terms of temperature salinity dissolved oxygen nutrient and inorganic carbon concentrations concentration intervals for water mass labelling on the basis of chemical parameters in addition to the common s based classification are defined silicate seems to be a very good discriminator for local water masses

gold mineralization in the okanagan valley southern british columbia fluid inclusion and stable isotope studies two styles of precious metal vein mineralization epithermal and mesothermal occur in the okanagan valley of southern british columbia the epithermal deposit dusty mac is composed of quartz stockwork mineralization in eocene volcanic and volcaniclastic rocks the mesothermal deposits fairview and oro fino consist of thick 1 10 m quartz veins in paleozoic and mesozoic metamorphic rocks fluid inclusion and stable isotope studies indicate that two distinct hydrothermal fluids were responsible for the mineralization events at dusty mac the epithermal fluid had a relatively low temperature 230 degrees 250 degrees c extremely low salinity 18 o 7 to 9ppm and delta d 133ppm values at fairview and oro fino the mesothermal fluids had higher temperatures 280 degrees 330 degrees c significant co 2 contents and higher salinities 3 6 equiv wt nacl stable isotope data show that the mesothermal fluids had low delta d 121 to 148ppm and delta 13 c 8 5ppm values but high delta 18 o 4 to 6ppm values the data indicate that the fluids involved in both styles of mineralization are 18 o shifted meteoric water with shallow circulation responsible for the epithermal deposits and deep circulation involved in the formation of the mesothermal deposits although both styles of mineralization occur in the same tectonic regime it appears that they are not temporally or genetically related to each other

shoshonitic lamprophyre dykes and their relation to mesothermal ausb veins at hillgrove new south wales australia abstract the hillgrove mineral field in the southern part of the new england orogen of northeastern new south wales australia contains numerous mesothermal au sb vein systems calc alkaline shoshonitic lamprophyre cal dykes are also associated with mineralisation with dilational lode structures acting as conduits for dyke intrusion which has occurred before and after major quartz stibnite veining dykes include minette and vogesite compositions and were emplaced in the late permian 247 255 ma at the same time as regionally extensive i type magmatism in the new england orogen least altered dykes are enriched in mg k ba rb sr zr th cr and ni relative to i type intrusives although chemical affinities are evident between lamprophyres and the more mafic members of the high k moonbi plutonic suite hillgrove lamprophyres are commonly enriched in sb as hg au w and bi with respect to average cal compositions evidence indicates this is most likely due to contamination of magma during intrusion through mineralised structures rather than a primary magmatic feature partially resorbed xenocrystic stibnite occurs in dykes which have intruded lode structures probably facilitated by the low melting point of stibnite 550 c and its incorporation into the magma carbon and oxygen isotopic data from carbonates in least altered post lode lamprophyres are indistinguishable from carbonate in altered dykes and veins implying that hydrothermal interaction continued after dyke intrusion although it is unlikely that lamprophyre dykes have been a direct source for mineralisation at hillgrove the close temporal and spatial relation of dykes mesothermal au sb veins and i type intrusions are interpreted to be manifestations of the post collisional setting and influx of mantle derived heat and partial melts into the new england orogen during the late permian

geology and geochemistry of the deep star gold deposit carlin trend nevada deep star is a high grade carlin type gold deposit located in the northern part of the carlin trend the deposit averages 34 0 g t au and by year end 2000 had produced 37 8 t 1 217 000 oz gold with a remaining reserve of 16 0 t 513 698 oz gold the deposit is primarily hosted in brecciated calc silicate rocks of the devonian popovich formation with a minor amount of gold in the jurassic goldstrike diorite intrusion of the syn and postore deep star rhyolite constrains the age of the mineralization the postore rhyolite is compositionally and mineralogically similar to the synore dike and yielded an average 40ar 39ar isochron age of 38 3 ma eocene rhyolite dikes intruded active dilatant north to northeast striking faults and or fractures providing an important age constraint on the local stress regime at deep star during mineralization essentially horizontal west northwest directed eocene extension 291 is consistent with dextral normal oblique slip observed on north south striking east dipping portions of the gen post fault system and dilation and sinistral shear on dike filled northeast striking structures a right stepping releasing bend in the deep star fault at its intersection with northwest and north northwest striking subsidiary structures created a deep tapping dilatant conduit for gold bearing hydrothermal fluids five stages of hydrothermal alteration are present at deep star stages 1 and 2 are related to thermal metamorphism metasomatism and possibly retrograde alteration associated with intrusion of the goldstrike stock stage 3 consists of preore quartz carbonate alteration the carbonate minerals are zoned both laterally and vertically with dolomite as the dominant mineral closest to ore stage 3 overlaps with stage 4 quartz kaolinite alteration associated with the introduction of gold and is therefore interpreted to be part of the eocene mineralizing event gold is hosted in as rich rims on marcasite and pyrite within a kaolinite and quartz matrix postore stage 5 is dominated by calcite with lesser siderite and barite a three dimensional geochemical model of the deep star deposit and its environs reveals that carlin type systems may have a geochemical expression involving a much broader suite of elements than previously recognized elements with distribution patterns considered to be related to the mineralizing event include ag as au ba bi ca cd co cu fe hg mg mo mn ni p pb s sb se te tl u v w and zn the multielement anomaly associated with the deep star deposit is best described as a vertical plume that is 1 focused between the deep star and post faults below the deposit 2 present in the footwall of the deep star fault and the deep star post fault corridor at the level of the deposit and 3 broadly dispersed above and to the west of the deposit under the influence of northeast and northwest trending structural fabrics most closely associated with gold deposition are enrichments in as sb hg tl ag and zn within a halo of ca mg ba and sr depletion the elements fe mn co ni and p are most elevated in the immediate hanging wall of the deep star fault and above the deposit in a region where secondary carbonate veins ankerite kutnahorite and mn rich dolomite open space filling carbonate minerals siderite calcite have been observed some lateral zonation is evident at levels above the deposit with increases of pb and bi on its eastern margin and more mo u v and w west of the deposit isotopic analyses of kaolinite are interpreted to indicate that gold mineralizing fluids originated from either a magmatic or possibly a deep metamorphic source fluids range from near the magmatic water field for those near the center of the deep star orebody along a mixing path toward exchanged mid tertiary meteoric water as represented by the fluids near the eastern orebody margin

geology mineralization stable isotope and fluid inclusion characteristics of the vostok 2 reduced w cu skarn and au w bi as stockwork deposit sikhote alin russia abstract the large 180 kt wo 3 and at least 10 15 t au vostok 2 deposit is situated in a metallogenic belt of w sn w au and au w deposits formed in late to post collisional tectonic environment after cessation of active subduction the deposit is related to an ilmenite series high k calc alkaline plutonic suite that by its petrologic signatures is transitional between those at w dominant and au dominant reduced intrusion related deposits consistently besides large w cu skarns of the reduced type the deposit incorporates quartz stockworks with significant au w bi mineralization also formed in a reduced environment the hydrothermal stages include prograde and retrograde essentially pyroxene skarns hydrosilicate amphibole chlorite quartz alteration and phyllic quartz sericite albite apatite and carbonate alteration assemblages these assemblages contain abundant scheelite associated with pyrrhotite chalcopyrite and at the phyllic stage also with bi minerals as bi sb te pb zn sulfides and sulfosalts as well as au mineralization the fluid evolution included hot high pressure 420 460 c 1 1 1 2 kbar low salinity 5 4 6 0 wt nacl equiv aqueous fluids at the retrograde skarn stage followed by lower temperature cyclic releases of high carbonic low salinity to non carbonic moderate salinity aqueous fluids at the hydrosilicate stage a high carbonic ch 4 dominated hot 350 380 c low salinity fluid was followed by cooler 300 350 c non carbonic moderate salinity 5 7 14 9 wt nacl equiv fluid at the phyllic stage a high carbonic co 2 dominated moderately hot 330 355 c 0 9 kbar low salinity fluid was followed by cooler 230 265 c non carbonic moderate salinity 6 6 12 0 wt nacl equiv fluid a homogenized magmatic source of water 18 o h2o 8 3 to 8 7 and a sedimentary source of sulfur 34 s 6 9 to 6 2 and carbon 13 c fluid 20 1 to 14 9 at the hydrosilicate stage are suggested a magmatic source of water 18 o 8 6 to 9 2 and a sedimentary source of sulfur 34 s 9 3 to 4 1 but a magmatic mantle to crustal derived source of carbon 13 c fluid 6 9 to 5 2 are envisaged for fluids that formed the early mineral assemblage of the phyllic stage then the role of sedimentary carbon again increased toward the intermediate 13 c fluid 16 4 to 14 5 and late 13 c fluid 16 3 to 14 7 phyllic mineral assemblages the magmatic differentiation was responsible for the fluid enrichment in w whereas au and bi could also have been sourced from mafic magma the decreasing temperatures together with elevated ca content in non boiling fluids promoted scheelite deposition at the early hydrothermal stages the most intense scheelite deposition at the phyllic stage was caused by co 2 removal due to boiling of co 2 rich fluids further cooling of non boiling fluids favoured joint deposition of scheelite bi and au

palaeoclimatic and archaeological evidence for a 200 yr recurrence of floods and droughts linking california mesoamerica and south america over the past 2000 years conspicuous grey clay rich flood deposits in the predominantly olive varved sediment in the central santa barbara basin california were dated via varve counting to c ad 212 440 603 1029 1418 and 1605 the 200 yr quasi periodicity and the timing of individual floods match time periods of known supraregional climatic changes and the documented 200 yr periodicity in palaeoclimate records elsewhere the floods of c ad 440 and ad 1418 occurred during global reorganizations of atmospheric circulation cold spells seem to have accompanied the floods of c ad 1029 and ad 1605 california floods and other palaeoclimate records suggest that expressions of regional climates are modulated by solar variability with a 200 yr periodicity our compilation of palaeoclimatic and mesoamerican and south american archaeological records provides evidence that palaeoenvironmental and cultural changes were often coincident within their respective dating uncertainties and occurred in 200 yr steps the matching patte