re os dating of pyrite confirms an early diagenetic onset and extended duration of mineralization in the irish zn pb ore field the irish midlands region contains one of the world s largest hydrothermal zn pb ore districts but uncertainty exists in the timing of mineralization relative to host rock ages consequently genetic models for ore formation are poorly constrained and remain controversial here we use re os geochronology to show that ore stage pyrite from the lisheen deposit formed at 346 6 3 0 ma shortly after host rock deposition pyrite from the silvermines deposit returns an age of 334 0 6 1 ma indicating that at least some mineralization occurred during later burial these age determinations show that the much younger paleomagnetic ages reported for the irish zn pb deposits reflect remagnetization during the variscan orogeny a process that we suggest affects paleomagnetic dating more widely the re os ages overlap with the ages of lower carboniferous volcanic rocks in the midlands which are the product of magmatism that has been invoked as the driving force for hydrothermal activity the relatively low initial os ratios for both lisheen 0 253 0 045 and silvermines 0 453 0 006 are compatible with derivation of os from these magmas or from the caledonian basement that underlies the ore deposits

on diagenesis dolomitisation and mineralisation in the irish zn pb orefield marine calcite cementation and lithification of carboniferous carbonate sediments hosting zn pb mineralisation in the irish orefield occurred at or near the seafloor a relatively early fine grained grey replacive dolomite preferentially developed in micrite is widely developed in the waulsortian limestone formation the main host to mineralisation and is pervasive in the southeastern midlands in proximity to the leinster massif this dolomite formed after the first four main stages of calcite cementation but probably also developed within tens of metres of the seafloor as evidenced by incorporation of clasts of dolomite in intraformational sedimentary breccias later coarse grained white dolomite preferentially replaced coarser components of the waulsortian limestone and infilled residual vuggy porosity whilst some of this coarse dolomite may be related to the fine replacive dolomite event a common spatial association with fault zones coupled with primary fluid inclusion data suggest that a significant proportion of this phase precipitated during the onset of fault controlled subsidence and widespread hydrothermal circulation within the irish midlands area fluids up to 250 c and 10 15 wt nacl equivalent sourced from a lower palaeozoic basement equilibrated fluid reservoir infiltrated the carbonate sequence via faults and fractures the more localised development of dolomite cemented breccias white matrix breccias that are frequently associated spatially with mineralisation was a consequence of the increased focusing of these hydrothermal fluids ore formation was broadly synchronous with development of the white dolomite breccias but only happened where mixing occurred between the hydrothermal ore fluids and localised near surface reservoirs of low temperature h2s rich brine in the waulsortian this process led to the precipitation of a distinctive black dolomite that forms a broad halo to massive sulphides although ore stage sulphides postdate significant diagenesis of the host rocks and often display epigenetic textures the fact that much of the cementation occurred soon after carbonate deposition means that mineralisation does not have to have formed after significant burial in fact the occurrence of clasts of hydrothermal dolomite and sulphides in intraformational debris flow breccias is only consistent with mineralising processes occurring in the near seafloor environment relatively soon after host rock deposition the regional development of a distinctive pink dolomite associated with faults and fractures was a post ore event and is considered to mark a regional brine migration linked to the onset of the variscan orogeny the development of this new tectonic and flow regime may have been responsible for the cessation of economic mineralisation in ireland

burial of organic carbon and pyrite sulfur in sediments over phanerozoic time a new theory in present day marine sediments almost all of which are deposited in normal oxygenated seawater rates of burial of organic carbon c and pyrite sulfur s correlate positively and bear a constant ratio to one another c s 3 on a weight basis by contrast calculations based on the isotopic model of garrels and lerman 1981 indicate that at various times during the phanerozoic the worldwide burial ratio must have been considerably different than the present day value this ratio change is caused by the requirement that increases in the worldwide mass of organic carbon must be accompanied by equivalent decreases in the mass of sedimentary pyrite sulfur in order to maintain a roughly constant level of o2 in the atmosphere such apparently contradictory behavior can be explained if the locus of major organic carbon burial has shifted over time from normal marine environments as at present to non marine freshwater or to euxinic environments in the geologic past a shift to predominantly freshwater burial can help explain predicted high c s ratios in permo carboniferous sediments and a shift to euxinic environments can help explain predicted low c s ratios during the early paleozoic it is demonstrated that the three environments today exhibit distinguishably different average c s ratios

regional dolomitization of the waulsortian limestone in southeastern ireland evidence of large scale fluid flow driven by the hercynian orogeny the lower carboniferous waulsortian limestone has been affected by late diagenetic regional burial dolomitization over an area of 7000 km 2 extending 170 km northeastward from the hercynian front the dolostone is composed of two components 1 a very fine crystalline replacive component and 2 a coarse crystalline baroque component that fills vuggy porosity developed within the replacive dolostone fluid inclusions within the coarse crystalline component of the regional dolostone indicate that the dolomitizing solutions were warm 100 c and moderately saline 10 13 wt nacl equivalent the replacive dolomite displays systematic decreases in crystal size and degree of xenotopic texture northward both components of the regional dolostone display a regular northward increase in mean 18 o values the replacive dolomite has 87 sr 86 sr values that decrease northward these laterally variable characteristics suggest that regional dolomitization resulted from large scale north directed fluid flow of heated brines developed in response to topographic uplift associated with collapse of the continental margin south of ireland during the hercynian variscan orogeny

alteration and mineralization at the zhibula cu skarn deposit gangdese belt tibet abstract the zhibula cu skarn deposit contains 0 32 mt cu metal with an average grade of 1 64 and is located in the gangdese porphyry copper belt in southern tibet the deposit is a typical metasomatic skarn that is related to the interaction of magmatic hydrothermal fluids and calcareous host rock stratiform skarn orebodies occur at the contact between tuff and marble in the lower jurassic yeba formation alteration zones generally grade from a fresh tuff to a garnet bearing tuff a garnet pyroxene skarn and finally to a wollastonite marble minor endoskarn alteration zonations are also observed in the causative intrusion which grade from a fresh granodiorite to a weakly chlorite altered granodiorite a green diopside bearing granodiorite and to a dark red brown garnet bearing granodiorite prograde minerals which were identified by electron probe microanalysis include andradite grossularite of various colors e g red green and yellow and green diopside retrograde metamorphic minerals overprint the prograde skarn and are mainly composed of epidote quartz and chlorite the ore minerals consist of chalcopyrite and bornite followed by magnetite molybdenite pyrite pyrrhotite galena and sphalerite three types of fluid inclusions are recognized in the zhibula deposit including liquid rich two phase inclusions type l vapor rich two phase inclusions type v and daughter mineral bearing three phase inclusions type s as the skarn formation evolved from prograde stage i to early retrograde stage ii and later retrograde stage iii the ore forming fluids correspondingly evolved from high temperature 405 667 c high salinity up to 44 0 wt nacl equiv and high pressure 500 600 bar to low moderate temperature 194 420 c moderate high salinity 10 1 18 3 and 30 0 44 2 wt nacl equiv and low moderate pressure 250 350 bar isotopic data of 34 s 0 1 to 6 8 estimated 34 s fluids 0 7 d h2o 91 to 159 and 18 o h2o 1 5 to 9 2 suggest that the ore forming fluid and material came from magmatic hydrothermal fluids that were associated with miocene zhibula intrusions fluid immiscibility likely occurred at the stage i and stage ii during the formation of the skarn and mineralization fluid boiling occurred during the stage iii which is the most important cu deposition mechanism for the zhibula deposit

sulfide mineral chemistry investigation of sediment hosted stratiform copper deposits nahand ivand area nw iran abstract copper mineralization in nahand ivand area nw iran appears as disseminated copper sulfides along a redox boundary between gray sandstone and microconglomerate and hematitic sandstones siltstones and shaly marl geochemical analyses of the nahand ivand deposits show as much 35 wt cu and 730 ppm ag in the gray sandstone electron probe micro analysis epma was used to determine the mineralogical composition and distribution patterns of copper and silver bearing phases mainly in pyrite and cu bearing sulfides the epma data were essential for evaluating the distribution and partitioning of potential economically valuable components between co existing minerals furthermore they contribute to a better understanding of the genesis of the nahand ivand copper deposits and will guide further exploration in the region the epma results from different types of pyrite reveal cu contents as high as 0 32 wt 1 10 wt and 2 88 wt for framboidal pyrite pyi overgrowths on framboidal pyrite pyii and diagenetic pyrite pyiii respectively this successive increase of copper from pyi to pyiii is attributed to a continuous supply of copper that replaces framboidal pyrite in turn by the more copper rich digenetic pyrite because of hydrothermal overprinting pyrite has been replaced by djurleite roxbyite and other nonstoichiometric cu s minerals that include covellite the epma study indicates that covellite contains significant concentrations of ag locally 1 wt in contrast only trace amounts of silver have been detected in pyrite and other copper sulfides indicating that covellite is the major ag carrier in the ore according to textural relationships such open space filling impregnation and replacement textures and the epma results later stage copper bearing fluids were responsible for the silver enrichment in the nahand ivand deposits

ree activated cathodoluminescence of calcite and dolomite high resolution spectrometric analysis of cl emission hrs cl abstract cathodoluminescence cl investigations of phanerozoic marine limestones sinter calcites and saddle dolomites of hydrothermal veins indicate that in contrast to previous knowledge rare earth element ree activated cl in sediments is common the methods of high resolution spectrometric analysis of cl emission hrs cl combined with hot cathode cl microscopy are able to prove qualitatively some ree below the detection limits of electron microprobe and proton induced x ray emission analysis pixe our investigations document sm3 dy3 tb3 and probably ho3 activated cl in calcite and eu3 activated cl in a saddle dolomite of hydrothermal veins sometimes the ree activated cl is hidden by dominant mn 2 emission in such cases the ree emission spectrum may be obtained by subtracting a spectrum of luminescence produced only by mn2 the occurrence of only one ree in natural samples is uncommon in all observed samples ree are present in groups

dolomitization of the waulsortian limestone lower carboniferous in the irish midlands the waulsortian limestone lower carboniferous of the southern irish midlands is dolomitized pervasively over a much larger region than previous studies have documented this study indicates a complex multistage multiple fluid history for regional dolomitization partially and completely dolomitized sections of waulsortian limestones are characterized by finely crystalline 0 01 0 3 mm planar dolomite planar replacive dolomite is commonly followed by coarse 0 5 mm nonplanar replacive dolomite and pervasive void filling saddle dolomite cement is frequently associated with zn pb mineralization planar dolomite has average 18o and 13c values pdb of 4 8 and 3 9 respectively these are lower oxygen and slightly higher carbon isotope values than averages for marine limestones in the waulsortian 18o 2 2 13c 3 7 mean c and o isotope values of planar replacive dolomite are also distinct from those of nonplanar and saddle dolomite cement 7 0 and 3 3 7 4 and 2 4 respectively fluid inclusions indicate a complex history involving at least three chemically and thermally distinct fluids during dolomite cementation the petrography and geochemistry of planar dolomites are consistent with an early diagenetic origin possibly in equilibrium with modified carboniferous sea water where the waulsortian was exposed to hydrothermal fluids 70 280 c planar dolomite underwent a neomorphic recrystallization to a coarser crystalline planar and nonplanar dolomite characterized by lower 18o values void filling dolomite cement is isotopically similar to nonplanar replacive dolomite and reflects a similar origin from hydrothermal fluids this history of multiple stages of dolomitization is significantly more complex than earlier models proposed for the irish midlands and provides a framework upon which to test competing models of regional vs localized fluid flow

structural and paleotopographic controls of lead zinc mineralization in the silvermines orebodies republic of ireland occurrence in lower carboniferous and devonian strata in northern tipperary the deposits comprise lower discordant zones deposited epigenetically along the channelways of the ascending ore solutions and upper late tournaisian stratiform syngenetic syndiagenetic zones of sedimentary exhalative origin mineralization occurs in a variety of sediments whose composition reflects the nature of the exhaled fluids and the variable physiochemical conditions in their depositional sites as a result of periodic tectonism on the fault zone these mineralized sediments were subjected to varying degrees of brecciation in a very unstable depositional environment the stratiform deposits of silvermines are synsedimentary products of the exhalation of mineralizing fluids from northwest trending feeder zones on to a late tournaisian sea floor of highly irregular paleotopography modified journal abstract

diagenetic evidence for an epigenetic origin of the courtbrown zn pb deposit ireland mineralisation at the courtbrown deposit in south western ireland is concentrated in the basal section of the chadian waulsortian limestone immediately above the courceyan ballysteen limestone two episodes of sulphide deposition have been identified an early stage of minor pyrite precipitation and a later base metal rich mineralisation event sphalerite galena and pyrite of the later mineralisation event occur predominantly as replacement phases along stylolites dissolution seams and within the micritic matrix of the host limestone these sulphide minerals also occur as cements within late stage fractures

mid dinantian waulsortian buildups in the dublin basin ireland abstract the sedimentary history and biostratigraphic setting of waulsortian carbonate buildups of the feltrim limestone formation late courceyan to early chadian within the dublin basin are described there is no unique precursor or successor facies to this formation and the massive waulsortian banks are composed predominantly of peloidal skeletal wackestones and lime mudstones with packstones near the tops of banks these banks form tabular bodies of moderate relief and are interbedded with thin shales and argillaceous crinoidal limestones of inter bank facies in the southwest of the basin inter bank facies are rare and the bank facies have abundant stromatactis cavities and uniquely at roselawn a fauna of rugose corals all buildups in the dublin basin have phase c and or d component assemblages of lees and miller 1985 and are interpreted as accumulating in moderately shallow water depths near or within the photic zone isopachs for the feltrim limestone formation show a ne sw trending axial depocentre where the waulsortian facies is in excess of 400 m thickness deposition appears to have taken place on this double sided ramp in a manner similar to the model of lees 1982 for belgium and southern britain soft sediment deformation such as large scale slumping shale injections and water escape structures not previously recorded from these rocks is widespread the upper surface of the feltrim limestone formation is fissured and displays a prominent erosion surface termination of waulsortian facies deposition and influx of terrigenous sediment was caused by rapid uplift attributed to chadian tectonism however eustatic sea level fall cannot be ruled out as a partial cause of the demise of the waulsortian

remobilization and mineralization of selenium tellurium in metamorphosed red beds evidence from the munster basin ireland abstract selenium and tellurium are vital elements for the ongoing development of carbon free energy generation but are only recovered in small volumes as by products of base and precious metal processing security of supply of these commodities is of high importance as their demand is forecast to increase in the near future thus more research is required on the varying mineralization systems where their occurrence and behavior are poorly understood such as sedimentary basins and metasedimentary terranes the munster basin of southern ireland is a good study area for sedimentary se te in such environments as it has a regionally high soil selenium anomaly and is characterized by devonian terrestrial red beds which were metamorphosed during the hercynian variscan orogeny the area also contains ore grade biogenic sediment hosted copper and remobilized vein hosted copper sulfides which are prospective for chalcophile selenium and tellurium quartz vein hosted se te mineralization was identified across the munster basin accompanied by trace gold silver mercury accessory phases new sulfur isotope data reinforces the model of sulfur and selenium remobilized from a biogenic red bed source which reflects a wider association of selenium deposits with oxidizing environments the co occurrence of tellurium mineralization suggests that it too may be concentrated in oxidizing environments associated traces of gold add to a growing body of evidence that gold is also transported and precipitated in oxidizing conditions in continental basins

characterization and discrimination of paleokarst breccias and pseudobreccias in carbonate rocks insight from ordovician strata in the northern tarim basin china abstract ordovician carbonates in the central and southern halahatang area of the tarim basin host highly productive hydrocarbon reservoirs previous studies suggest that the yingshan and yijianfang formations the primary producing intervals have been extensively karstified however the current author has not observed significant karst features in the formations based on the detailed study of 380 m long cores from 16 wells in the current study true breccias are only identified in two wells in the lianglitage formation including crackle and mosaic breccias as well as chaotic clast supported breccias the breccias are interpreted as karst related breccias that formed in near surface environments during pre silurian subaerial exposure and timing of karstification probably coincided with eustatic sea level fall caused by the middle katian glaciation widespread karst features of the yijianfang and yingshan formations identified as breccias or sediment filled cavities in many previous studies are actually only a mottled fabric pseudobreccia caused by selective diagenetic alteration and infiltration of bitumen in the deeper subsurface the color difference between pseudoclasts and pseudomatrix does not reflect a mixture of clasts and cave sediments but instead is characterized by distinct nevertheless commonly subtle variations in the limestone texture and whether bitumen is present one the basis of core and thin section observations sem scanning electron microscope and xrd x ray diffraction analyses the author presents criteria to distinguish karst breccias and pseudobreccias that can be applied to other similar carbonate deposits discrimination between karst breccias and nodular limestones is also presented differentiation of karst and pseudokarst features serves not only an academic interest but also has important applications for the exploration and development of carbonate reservoirs

timing of mineralization at the navan zn pb deposit a post arundian age for irish mineralization navan is the largest of the irish zn pb deposits and contains some of the most important evidence for the inferred early timing of mineralization in ireland clasts of ore above a middle carboniferous erosion surface we have examined diagenetic fabrics within the main ore pale beds and the overlying erosion surface boulder conglomerate in order to determine the timing of mineralization this diagenetic analysis and particularly the presence of premineralization dolomite in the boulder conglomerate has revealed that all of the mineralization postdates the erosion surface and therefore must be post arundian 345 ma in age furthermore the navan mineralization must be entirely epigenetic in origin i e similar to mississippi valley type deposits and is likely to be holkerian 343 ma in age or younger this conclusion disagrees with the previous model of at least partially syngenetic mineralization and has important implications for the age of other deposits in ireland and the nature of irish type deposits in general

chemical mass transfer during hydrothermal alteration of carbonates controls of seafloor subsidence sedimentation and zn pb mineralization in the irish carboniferous abstract petrographic and geochemical data were acquired to evaluate models for the formation of hydrothermal dolomite breccias that host zinc lead orebodies in the rathdowney trend of the irish orefield and assess element mobility during hydrothermal alteration of carbonates macroscopic and microscopic textures indicate that the breccias largely formed by a pseudobrecciation process involving dissolution and replacement of precursor waulsortian dolomite of diagenetic origin during subseafloor hydrothermal fluid flow geochemical analyses show that compared with the waulsortian dolomite precursor breccia clasts and matrix contain respectively higher concentrations of al ti and light rare earth elements which are linearly correlated indicative of mass loss during hydrothermal interaction bulk rock mass loss estimates average 33 indicating extensive dissolution of carbonate although petrographic evidence and limited clast rotation or translation rule out the development of significant open space this supports a mechanism of alteration whereby hydrothermal fluids migrating along grain boundaries microcracks and solution seams drove dissolution and replacement of the surrounding host rock with partial collapse of the transient microporosity produced progressive interaction led to the gradual isolation of domains clasts surrounded by replacement dolomite matrix massive sulfide mineralization formed subsequently by stratabound replacement of the dolomite pseudobreccia by hydrothermal fluids preferentially focused within the more permeable and possibly more reactive lithology this process involved further volume loss 30 of the replaced rock quantitative mass transfer analysis indicates that during hydrothermal interaction net loss of na p mn sr and sometimes cu and net gain in li k fe as well as the ore associated elements typically occurred marked fractionation of the ree is observed eu was added implicating elevated temperature acidic and reduced hydrothermal fluids ce was also added possibly derived from remobilization of pre sulfide oxide mineralization the lree were typically immobile or partially removed and the hree were preferentially mobilized and transported beyond the scale of sampling thus the hree together with na p mn sr and possibly cu may form a distal chemical anomaly at the base of the waulsortian limestone formation the net addition of li k and be in dolomite breccia matrix samples combined with their increase in concentration due to dolomite dissolution produced a broad anomaly of these elements extending for at least 1 5 km from the center of the lisheen deposit these various geochemical anomalies have potential utility in mineral exploration a total volume loss of up to 68 at lisheen is consistent with a marked thinning of the waulsortian biomicrite facies above massive sulfide the observed thickening of upper and supra waulsortian facies in the trough developed above this zone is interpreted to reflect infill of a seafloor depression up to 90 m deep developed in response to underlying hydrothermal dissolution this model implies mineralization initiated during the latter stages of waulsortian deposition in the late courceyan early chadian at a depth of approximately 150 m below the seafloor

the carbonate hosted lisheen zn pb ag deposit county tipperary ireland the lisheen zn pb ag deposit located in county tipperary in southeast central ireland consists of a group of strata bound pyritic sulfide lenses containing 22 mt of ore with an overall grade of 11 5 percent zn 1 9 percent pb 26 g t ag and 16 percent fe hosted in lower carboniferous early mississippian carbonate rocks sulfide bodies at lisheen are restricted to the waulsortian mudbank complex and the lisduff oolite unit of the ballysteen limestone which compose the stratigraphically lowest nonargillaceous carbonate horizons in the local lower carboniferous succession the deposit is located within a major right stepping relay zone of a segmented normal fault system sulfide bodies occur adjacent to the normal faults thickest development of sulfides generally occurs at points of maximum throw metal zoning is well developed relative to these structures the waulsortian mudbank complex and portions of the overlying succession were subjected to an early premineralization regional scale dolomitizing event that increased permeability the regional dolostone produced by this event is cut and replaced by hydrothermal dolomite referred to as black matrix breccia and white matrix breccia associated with mineralization hydrothermal dolomitization was most intense in the waulsortian mudbank complex though it locally affected rocks from the silurian basement to more than 200 m above the level of major sulfide precipitation the majority of the lisheen deposit consists of fe zn pb ag sulfides hosted in the black matrix breccia regional dolomite and to a much lesser extent undolomitized limestone of the waulsortian complex sulfide bodies at lisheen consist of pyrite marcasite sphalerite and galena with subsidiary sulfosalt minerals arsenopyrite and copper sulfides sulfides replace carbonate minerals and infill dissolution cavities gangue minerals intergrown with sulfides include dolomite calcite barite and quartz mineral textures indicate a regular paragenetic sequence of sulfide deposition from early precipitation of colloform iron sulfide containing minor sphalerite and galena through deposition of a complex assemblage of sphalerite galena iron sulfides sulfosalt minerals and copper sulfides distribution of alteration and sulfide zones indicates that the lisheen deposit formed as a prograding hydrothermal system textural and mineralogic evidence suggests that the hydrothermal fluids were relatively acidic and that reaction with the carbonate host rocks was a primary reason for sulfide precipitation on the basis of the probable age of faulting and crosscutting relationships of the regional and hydrothermal dolomite the maximum age of mineralization at lisheen was at least 10 m y after host rock deposition

macrotextures microtextures and carbonate sulfide relationships in stratiform carbonate hosted zn pb orebodies of silvermines ireland ore stage carbonates of the silvermines stratiform orebodies have increased zn and pb and high fe and mn content a major microtexture observed is produced by the replacement of carbonate allochems by dolomite fe dolomite and siderite followed by the replacement of carbonates by sulfides generally the process of replacement took place while the former fabric of the host carbonates was preserved the reactivity of metal carbonates with sulfur favored the concentration of pb and zn in the sulfide and of fe and mn in the carbonate form sulfide carbonate reactions probably maintained a high permeability in the ore zone over an extended period of time eventually producing a high grade ore from solutions rich in fe and mn but poor in zn and pb initial porosity and permeability created by gravity flows controlled the mineralizing process at the beginning but later stages were probably controlled by replacements i e sulfide carbonate reactions

high precision u pb zircon age calibration of the global carboniferous time scale and milankovitch band cyclicity in the donets basin eastern ukraine 1 high precision id tims u pb zircon ages for 12 interstratified tuffs and tonsteins are used to radiometrically calibrate the detailed lithostratigraphic cyclostratigraphic and biostratigraphic framework of the carboniferous donets basin of eastern europe chemical abrasion of zircons use of the internationally calibrated earthtime mixed u pb isotope dilution tracer and improved mass spectrometry guided by detailed error analysis have resulted in an age resolution of 0 05 or 100 ka for these carboniferous volcanics this precision allows the resolution of time in the milankovitch band and confirms the long standing hypothesis that individual high frequency pennsylvanian cyclothems and bundles of cyclothems into fourth order sequences are the eustatic response to orbital eccentricity 100 and 400 ka forcing tuning of the fourth order sequences in the donets basin to the long period eccentricity cycle results in a continuous age model for the middle to late pennsylvanian moscovian kasimovian ghzelian strata of the basin and their record of biological and climatic changes through the latter portion of the late paleozoic ice age detailed fusulinid and conodont zonations allow the export of this age model to sections throughout euramerica additional ages for mississippian strata provide among the first robust radiometric calibration points within this subperiod and result in variable lowering of the base ages of its constituent stages compared to recent global time scale compilations

cementation hydrothermal alteration and zn pb mineralization of carbonate breccias in the irish midlands textural evidence from the cooleen zone near silvermines county tipperary a reply sir we are delighted to respond to the comments of reed and wallace on our paper on the origin of breccia hosted base metal mineralization in the irish ore field lee and wilkinson 2002 reed and wallace s thesis is that the mineralized breccias we have described within the mississippian waulsortian limestone formation at cooleen are not of sedimentary origin and therefore by extension that synsedimen tary breccias do not exist elsewhere in the ore field if correct one of a number of lines of evidence that have been used to infer a near sea floor origin for at least a component of sulfide mineralization in ireland that of reworked clasts of sulfide within sedimentary breccias would be invalidated contrary to the suggestion of reed and wallace the existence of sedimentary breccias spatially associated with mineralization in the waulsortian is universally accepted in the literature mine based investigations that include underground observations as well as drill core data and sedimentological studies have concluded that the stratiform wedge shaped breccia bodies commonly developed within the waulsortian limestone facies are sedimentary debris flows of courceyan age boyce et al 1983 taylor 1984 andrew 1986 clifford et al 1986 somerville et al 1992 submarine fault scarp sedimentary breccias are common in sediment hosted zn pb deposits e g goodfellow et al 1993 and display the same characteristics as the breccias at cooleen hitzman and beaty 1996 p 125 also recognized that synsedimentary breccias are present within the waulsortian at both silvermines and lisheen but went on to state that textural and field relationships clearly show that the principal episode of brecciation postdated regional burial dolomiti zation inferring a hydrothermal origin for the ore hosting breccias while we would not agree with this conclusion particularly in relation to the silvermines area we accept that the ore hosting breccias at lisheen galmoy and silvermines have been

quantifying the origin and geometry of circular sag structures in northern fort worth basin texas paleocave collapse pull apart fault systems or hydrothermal alteration three dimensional seismic data reveal numerous subcircular sag structures in the northern fort worth basin the structures are defined by concentric faults that extend vertically upward 760 1060 m 2500 3500 ft from the lower ordovician ellenburger group the largest structures remained active into the lower desmoinesian strawn group criteria are outlined for defining seismically resolvable sag structures and a detailed quantitative analysis of the geometries of these circular features was undertaken results are compared and contrasted with reviews of subsurface collapse mechanisms and strike slip processes that are known to produce subsurface circular to subcircular sag geometries in plan view in this manner we develop several constraints for differentiating collapse related sag structures from strike slip related sag structures qualitative analyses indicate that the geometries observed are strongly analogous to subsurface collapse features where material is removed at depth to create a void into which the overburden subsequently sags and collapses quantitative analyses support the formation of these features by incremental collapse and suprastratal deformation above a linked system of coalesced collapsed paleocaves within the ellenburger group observations and criteria presented herein provide valuable information in defining seismically resolvable collapse features worldwide and help distinguish sag features of collapse affinity from those of other origins

paleomagnetic evidence for an early permian age of the lisheen zn pb deposit ireland the lisheen zn pb deposit is one of the major lower carboniferous carbonate hosted base metal deposits of the irish midlands the timing of ore mineralization and therefore its genesis remains much debated because of a lack of absolute age determinations paleomagnetic analysis of 432 specimens from 12 sites in ore mineralization and 10 sites in host rocks at lisheen isolated a well defined stable characteristic remanent magnetization chrm direction using af step demagnetization except in one site of massive sulfide mineralization and two sites of postore pink dolomite thermal step demagnetization and saturation remanence tests show that the chrm is carried dominantly by single domain magnetite a paleomagnetic fold test is negative indicating that the chrm postdates burial lithification and deformation the chrm directions from eight host rock and 12 zn pb mineralized sites are indistinguishable at 95 percent confidence the combined chrm directions give a mean paleopole at 41 6 s 18 8 w semiaxes of the oval of 95 confidence along and perpendicular to the site pole great circle dp 1 7 dm 3 3 that when compared to the robust apparent polar wander path for laurentia rotated into european coordinates gives an age of 277 7 2 ma for the chrm this 277 7 ma age is close to the paleomagnetic ages of 290 9 2 ma for zn pb mineralization at galmoy and 269 4 2 ma for the ba mineralization at silvermines which are 10 km northeast and 30 km west of lisheen respectively this early permian magnetization postdates peak variscan orogenic heating that is observed in all carboniferous strata in ireland our preferred interpretation is that the paleomagnetic data in conjunction with other thermal data support an entirely epigenetic origin in contrast to the pre variscan syn genetic or syndiagenetic models favored by previous authors we propose a topographically driven fluid flow either from the south of ireland or from closer to the deposit which was modified by localized convection during the variscan orogeny

genesis of sediment hosted copper mineralization in south central kansas sulfur carbon and sulfur isotope systematics copper sulfide mineralization occurs within reduced sedimentary rocks of the permianage wellington formation and ninnescah shale in south central kansas there are two distinct sulfide assemblages pyrite digenite is found in gray green shale units within red beds of the ninnescah shale chalcopyrite bornite and chalcocite occur in carbonate units within the upper wellington formation to lower ninnescah shale transition digenite occurs as a replacement of pyrite whereas copper sulfides in carbonate units occur in vugs and small fractures chalcocite and barite fill vugs in carbonates occurring within red bed dominated stratigraphy whereas the assemblage calcite chalcopyrite bornite is prevalent in veinlets within carbonate units situated near a major stratigraphic color change from underlying gray units to red beds sulfide sulfur and organic carbon concentrations are generally low 0 2 wt for both in cu sulfide bearing rocks it is possible that initial organic carbon and sulfide sulfur contents were low prior to copper mineralization or that there was interaction between an oxidized cu bearing fluid and reduced organic carbon bearing sediments the delta 34 s values for pyrite range from 40 to 26 per mil digenite replacing pyrite is characterized by a similar range in delta 34 s values whereas chalcopyrite bornite and chalcocite in carbonate hosts are significantly heavier with a range in delta 34 s values of 19 to 7 per mil textures of mineralized rocks s c relationships and delta 34 s values probably reflect digenite pyrite mineralization involving sulfur conserving replacement reactions whereas sulfide deposition in carbonates followed partial reduction of sulfate delta 34 s value near 11ppm contained in the cu bearing fluid sulfide mineral distribution and copper contents of reduced and oxidized sedimentary rocks suggest that large scale fluid infiltration was minimal and that mineralization resulted from small scale fluid migration within the sedimentary column

yttrium and rare earth elements in fluids from various deep sea hydrothermal systems rare earth element ree and yttrium y concentrations were measured in fluids collected from deep sea hydrothermal systems including the mid atlantic ridge mar i e menez gwen lucky strike tag and snakepit the east pacific rise epr i e 13 n and 17 19 s and the lau vai lili and manus vienna woods pacmanus desmos back arc basins bab in the south west pacific in most fluids y is trivalent and behaves like ho chondrite normalized y ree y reen concentrations of fluids from mar epr and two bab sites i e vai lili and vienna woods showed common patterns with lree enrichment and positive eu anomalies ree analysis of plagioclase collected at lucky strike strengthens the idea that fluid ree contents are controlled by plagioclase phenocrysts other processes however such as ree complexation by ligands cl f so42 secondary phase precipitation and phase separation modify ree distributions in deep sea hydrothermal fluids ree speciation calculations suggest that aqueous ree are mainly complexed by cl ions in hot acidic fluids from deep sea hydrothermal systems ree concentrations in the fluid phases are therefore influenced by temperature ph and duration of rock fluid interaction unusual y reen patterns found in the pacmanus fluids are characterized by depleted lree and a positive eu anomaly the demos fluid sample shows a flat y reen pattern which increases regularly from lree to hree with no eu anomaly these manus basin fluids also have an unusual major element chemistry with relatively high mg so4 h2s and f contents which may be due to the incorporation of magmatic fluids into heated seawater during hydrothermal circulation ree distribution in pacmanus fluids may stem from a subseafloor barite precipitation and the ree in demos fluids are likely influenced by the presence of sulfate ions

a model for the diagenetic formation of sandstone hosted copper deposits in tertiary sedimentary rocks aragon ne spain s c ratios and sulphur isotope systematics abstract numerous small noneconomic copper deposits are associated with syntectonic sandstones of tertiary age campodarbe and uncastillo formations in the south pyrenean foreland basin spfb sulphides native metal and their oxidation products occur within elongate lenses in fluvial sandstones and conglomerates in all cases the geometry of the ore is highly consistent with the primary depositional and biogenic structures of the host sandstones copper ores replace wood debris and diagenetic pyrite or more frequently appear as intergranular cement replacing previous diagenetic calcite cement sulphide sulphur and organic carbon distribution shows that pyrite rich sandstones are the copper ore precursor and that mineralizing processes provoked the depletion of both reduced s and organic c as a consequence of interaction with an oxidized cu bearing fluid on the other hand low 34s values are consistent with bacteriogenic derivation of sulphur after pyrenean evaporites petrographic studies sulphide sulphur and organic carbon concentrations and 34s values suggest that cu rich fluids were introduced into reduced sediments during diagenesis mineralizing processes took place in two different periods the first one related to the filling of the jaca basin during erosion of the pyrenean basement and the second one related to the emplacement of a thrust ramp which initiated the erosion of the previously formed cupriferous sandstones

sedimentary basins formed and carried piggyback on active thrust sheets small sedimentary basins that formed on the apennine southern margin of the po basin complex northern italy have been studied using borehole and seismic reflection information and their evolution can be dated using the largely marine biostratigraphy of the miocene to quaternary sediments these studies show that the basins formed and were filled while being carried on moving thrust sheets and they are therefore named piggyback basins each of these basins corresponds to the active phase of a different thrust front ramp on the pyrenean northern margin of the ebro basin complex northern spain similar piggyback basins formed between eocene and mid miocene time they have since been uplifted and eroded and may therefore be studied in outcrop in northern spain much of the basin fill sediment was deposited in nonmarine environments

constraints on the origins of fluids forming irish zn pb ba deposits evidence from the composition of fluid inclusions the numerous zn pb deposits in the irish midlands together with the quantity and grade of the ore make this a world class base metal province despite significant exploration and research there is still disagreement on the origin of the mineralizing fluids in this study we have measured the composition of fluid inclusions using a crush leach technique these data constrain the possible sources of the fluids both during and after mineralization chloride and br concentrations indicate that the main ore fluid at tynagh and silvermines was seawater that had evaporated until the salinity was between 12 and 18 wt percent however na k and li data show that water rock interactions have resulted in the depletion of na and the enrichment of k and li relative to the concentrations expected for evaporated seawater the fluids that produced postore dolomitization were also derived from seawater that had evaporated to higher salinities and had precipitated halite the concentrations of na k and li are what would be expected for seawater at this degree of evaporation and show that these fluids did not interact with the same lithologies as the ore fluids the major change to their fluid composition was exchange of mg for ca during dolomitization we suggest that the ore fluids could only have reached their high salinity by evaporation of seawater on the extensive shallow water shelf regions that existed over much of the irish midlands

site formation at kudu koppie a late earlier and middle stone age site in northern limpopo province south africa in the mapungubwe national park near the confluence of the shashe and limpopo rivers along south africa s northernmost borders with botswana and zimbabwe the site of kudu koppie is characterized by three lithologically and archaeologically distinct stone age units from bottom to the top these units are 1 the lower kudu koppie unit lkku which includes large tools such as handaxes picks and cleavers characteristic of a late earlier stone age phase 2 the middle kudu koppie unit mkku which contains bifacially retouched points characteristic of a middle stone age msa industry and 3 the upper kudu koppie unit ukku which has sporadic segments and other tools characteristic of the later stone age lsa a refitting and nodule analysis which matches lithic pieces based on microscopic similarities in colour texture and other visible characteristics demonstrates that site formation processes have caused some vertical displacement of material within but not between the lkku and mkku within the national park the kudu koppie sandstone outcrop is unusual in that it has an overhanging structure which undoubtedly contributed to the initial formation and eventual preservation of the archaeological deposits this paper presents several lines of evidence indicating that stratigraphic integrity at kudu koppie has been preserved and that the three horizons are in primary or near primary context

ore textures within the u lens of the navan zn pb deposit ireland recent exploration in the vicinity of the giant 90 mt navan orebody has resulted in the discovery of ore grade mineralisation to the southwest of the deposit much of which occurs within the upper pale beds a horizon that is only weakly mineralised above the main orebody within this new u lens mineralisation preferentially occurs within bioclastic carbonate grainstones and calcareous quartz sandstones and is dominated by sulphide replacement of the carbonate component of the host sequence much of the replacive mineralisation is spatially associated with hydrothermal cavities which are filled by a variable mixture of brecciated replacement sulphide minerals space filling sulphide and gangue cements and internal sediments mineralisation also occurs within veins and dissolution seams and as disseminated sulphide minerals massive mineralisation is typically a complex chaotic combination of replacement cavity and fracture filling sulphides fluid inclusion analyses of ore stage saddle dolomite indicate temperatures at the time of sulphide precipitation of 90 150 c with a maximum of 175 c these temperatures are lower than those typically proposed for irish type deposits

origin and reservoir characteristics of upper ordovician trenton black river hydrothermal dolomite reservoirs in new york in the past decade more than 20 new natural gas fields have been discovered in laterally discontinuous dolomites of the upper ordovician black river group in south central new york the dolomites form around basement rooted wrench faults that are detectable on seismic data most fields occur in and around elongate fault bounded structural lows interpreted to be negative flower structures away from these faults the formation is composed of impermeable limestone and forms the lateral seal for the reservoirs in most cases the faults die out within the overlying trenton limestone and utica shale most porosity occurs in saddle dolomite coated vugs breccias and fractured zones matrix porosity is uncommon in the black river cores described for this study the patchy distribution around basement rooted faults and geochemical and fluid inclusion analyses supports a fault related hydrothermal origin for the saddle and matrix dolomites this play went for many years without detection because of its unconventional structural setting i e structural lows versus highs using the appropriate integrated structural stratigraphic diagenetic model more hydrothermal dolomite natural gas reservoirs are likely to be discovered in the black river of new york and in carbonates around the world

rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments abstract analyses have been made of ree contents of a well characterized suite of deep sea 4000 m principally todorokite bearing ferromanganese nodules and associated sediments from the pacific ocean ree in nodules and their sediments are closely related nodules with the largest positive ce anomalies are found on sediments with the smallest negative ce anomalies in contrast nodules with the highest contents of other rare earths 3 ree are found on sediments with the lowest 3 ree contents and vice versa 143 nd 144 nd ratios in the nodules 0 51244 point to an original seawater source but an identical ratio for sediments in combination with the ree patterns suggests that diagenetic reactions may transfer elements into the nodules analysis of biogenic phases shows that the direct contribution of plankton and carbonate and siliceous skeletal materials to ree contents of nodules and sediments is negligible inter element relationships and leaching tests suggest that ree contents are controlled by a p rich phase with a ree pattern similar to that for biogenous apatite and an fe rich phase with a pattern the mirror image of that for sea water it is proposed that 3 ree concentrations are controlled by the surface chemistry of these phases during diagenetic reactions which vary with sediment accumulation rate processes which favour the enrichment of transition metals in equatorial pacific nodules favour the depletion of 3 ree in nodules and enrichment of 3 ree in associated sediments in contrast ce appears to be added both to nodules and sediments directly from seawater and is not involved in diagenetic reactions

world class base and precious metal deposits a quantitative analysis over 62 percent of the 193 000 metric tons of gold discovered to date is located in four countries and more than 68 percent occurs in four types of mineral deposits about 55 percent of the 1 740 000 metric tons of silver found is in four countries and 45 percent is in four types of deposits fifty six percent of the 1 52 billion metric tons of discovered copper is from four countries and four types of deposits contain 88 percent of the total over 50 percent of both the 713 000 000 metric tons of zinc and 349 000 000 metric tons of lead discovered to date come from four countries and 70 percent of both metals occur in four types of deposits all discovered gold would fit in a cube with a height of 22 m silver in a 55 m cube copper in a 550 m cube zinc in a 460 m cube and lead in a 310 m cube at least 74 percent of gold silver zinc and lead is in deposits having average grades above the respective median grades and 44 percent of copper is in deposits with average grades above the median grade of all deposits lower grade deposits contain less total metal than higher grade deposits tonnage of mineralized rock is an even better predictor of contained metal with over 96 percent of each metal s total residing in deposits having greater than median size and between 47 and 79 percent of metal contained in the largest 10 percent of deposits world class deposits defined as the upper 10 percent of deposits in terms of contained metal account for over 86 percent of all gold 79 percent of silver 84 percent of copper 71 percent of zinc and 73 percent of lead these giant deposits contain at least 100 metric tons 3 2 moz gold 2 400 metric tons 77 moz silver 2 million metric tons copper 1 7 million metric tons zinc or 1 million metric tons lead mineral deposits occur rarely in the earth s crust and large ones are especially uncommon this analysis shows that only the unusually large deposits can significantly affect supply

compositional multivariate statistical analysis of thermal groundwater provenance a hydrogeochemical case study from ireland abstract thermal groundwater is currently being exploited for district scale heating in many locations world wide the chemical compositions of these thermal waters reflect the provenance and circulation patterns of the groundwater which are controlled by recharge rock type and geological structure exploring the provenance of these waters using multivariate statistical analysis msa techniques increases our understanding of the hydrothermal circulation systems and provides a reliable tool for assessing these resources hydrochemical data from thermal springs situated in the carboniferous dublin basin in east central ireland were explored using msa including hierarchical cluster analysis hca and principal component analysis pca to investigate the source aquifers of the thermal groundwaters to take into account the compositional nature of the hydrochemical data compositional data analysis coda techniques were used to process the data prior to the msa the results of the msa were examined alongside detailed time lapse temperature measurements from several of the springs and indicate the influence of three important hydrogeological processes on the hydrochemistry of the thermal waters 1 salinity and increased water rock interaction 2 dissolution of carbonates and 3 dissolution of sulfides sulfates and oxides associated with mineral deposits the use of msa within the coda framework identified subtle temporal variations in the hydrochemistry of the thermal springs which could not be identified with more traditional graphing methods or with a standard statistical approach the msa was successful in distinguishing different geological settings and different annual behaviours within the group of springs this study demonstrates the usefulness of the application of msa within the coda framework in order to better understand the underlying controlling processes governing the hydrochemistry of a group of thermal springs in a low enthalpy setting

the ree content of some hydrothermal fluids ree concentrations were determined in solutions from submarine hydrothermal vents on the east pacific rise and for the first time from continental geothermal fields in tibet and bulgaria they indicate that in hydrothermal systems ree are immobile at temperatures below 350 c and for water rock ratios of 105 nd values of submarine solutions and anhydrites 4 7 to 6 2 suggests recharge on the sedimentcovered flanks of the ridge carbonate anions as measured by alkalinity appear to increase the solubility of heavy ree somewhat but not to the extent that substantial amounts of ree could be driven out from rocks by hydrothermal activity

stratiform copper deposits hosted by low energy sediments i timing of sulfide precipitation an hypothesis published interpretations on the timing of copper and copper iron sulfide deposition in stratiform copper deposits hosted by low energy sediments range from those postulating deposition during sedimentation to those postulating deposition later in the diagenetic history of the host sediments with most favoring deposition during diagenesis interpretations of sulfide precipitation during diagenesis of the host sediments commonly favor a sulfide replacement of biogenic pyrite and in some instances replacement of anhydrite as well a qualitative reexamination was made of published data on 1 sulfur isotopes sulfide textures and sulfide nonsulfide mineral relationships in stratiform copper deposits hosted by low energy sediments and on 2 timing of bacterial sulfate reduction timing of pyrite formation and timing of authigenic mineral formation in modern analogues of host sediments to ore the reexamination is permissive of the hypothesis that chalcocite but not necessarily copper iron sulfides in stratiform copper deposits was precipitated within 50 cm of the sediment surface and that most precipitated within a few centimeters of the surface as a result of bacterial sulfate reduction the reexamination reveals that evidence for a pyrite replacement origin of chalcocite is based upon equivocal interpretations of sulfide textures textures displayed by most bornite chalcopyrite and digenite can be interpreted to indicate an origin by replacement of preexisting pyrite chalcocite composite grains limited porosity and permeability data on modern analogues of the host sediments and on clays are compatible with the hypothesis the porosity and permeability data and published models of compacting shale and sandstone sequences indicate that flow of copper transporting water was probably along rather than across the host rock bedding

ore depositional process in the navan zn pb deposit ireland the navan zn pb deposit in ireland is hosted by a lower carboniferous carbonate dominated sedimentary sequence in excess of 97 percent of the ore is hosted by a courceyan shallow water succession termed the pale beds the ore occurs as complex strata bound tabular lenses often dislocated by faulting and truncated by a submarine erosional slide structure above this surface unconformity lies the economically minor but genetically important conglomerate group ore hosted by a complex debris flow termed the boulder conglomerate timing constraints on the mineralization can be defined by the relationship to the erosion surface and style of mineralization suggesting a late chadian or early arundian age approximately 345 ma the bulk of the ore formed below the erosion surface in the semilithified to lithified pale beds ore the mineralogy of the economic ores is relatively simple being dominated by sphalerite and galena in a 5 1 ratio pyrite and marcasite are present in subordinate amounts in the majority of the pale beds ore but dominate the conglomerate group ore and the pale beds ore immediately below the erosion surface particularly lens 2 1 gangue minerals are dominated by calcite dolomite and barite the morphology of the mineralization reflects subsea floor emplacement the orebody occurs as numerous strata bound horizons ranging from intense high grade massive sulfides to lower grade sulfide layers separated by barren limestone in all cases there is strong evidence for tectonic disruption during ore deposition sulfides were dominantly deposited as open space growth and replacement of host rock open space textures include dendritic skeletal stalactitic internal sediment geopetal and coarse bladed forms the general absence of coarse euhedral cavity lining textures or substantial collapse brecciation suggests that large cavities were not present prior to mineralization replacement textures range from delicate pseudomorphs of biodasts to more destructive granular styles sulfide sulfur isotope analyses exhibit two dominant groupings of delta 34 s from around 23 to 5 and 0 to 15 per mil respectively and a third minor grouping around 32 to 28 per mil at least two sources of sulfur are invoked values around 23 to 15 per mil are considered to be the result of bacteriogenic reduction of lower carboniferous seawater sulfate approximately 20ppm with a characteristic fractionation around 35 to 45 per mil away from sulfate this is the most common range of delta 34 s in the deposit values around 8 to 15 per mil are interpreted to be hydrothermal sulfide transported with the metal bearing fluid mixing of these two components is inferred from the isotopic data and trends in the mineral paragenesis barite has a mean of delta 34 s 21 or 2 per mil which falls within the range generally recognized for lower carboniferous seawater sulfate we consider that contemporaneous seawater sulfate was the dominant source of sulfur in the barite at navan implying that seawater accessed the pale beds at the time of mineralization

structurally controlled hydrothermal dolomite reservoir facies an overview structurally controlled hydrothermal dolomite htd reservoir facies and associated productive leached limestones are major hydrocarbon producers in north america and are receiving increased exploration attention globally they include multiple trends in the ordovician locally silurian and devonian of the michigan appalachian and other basins of eastern canada and the united states and in the devonian and mississippian of the western canada sedimentary basin they also occur in jurassic hosts along rifted atlantic margins in the jurassic cretaceous of the arabian gulf region and elsewhere hydrothermal dolomitization is defined as dolomitization occurring under burial conditions commonly at shallow depths by fluids typically very saline with temperature and pressure t and p higher than the ambient t and p of the host formation the latter commonly is limestone proof of a hydrothermal origin for htd reservoir facies requires integration of burial thermal history plots fluid inclusion temperature data and constraints on timing of emplacement hydrothermal dolomite reservoir facies are part of a spectrum of hydrothermal mineral deposits that include sedimentary exhalative lead zinc ore bodies and htd hosted mississippi valley type sulfide deposits all three hydrothermal deposits show a strong structural control by extensional and or strike slip wrench faults with fluid flow typically focused at transtensional and dilational structural sites and in the hanging wall transtensional sags above negative flower structures on wrench faults are favored drilling sites for htd reservoir facies saddle dolomite in both replacive and void filling modes is characteristic of htd facies for many reservoirs matrix replacive dolomite and saddle dolomite appear to have formed near contemporaneously and from the same fluid and temperature conditions the original host facies exerts a major influence on the lateral extent of dolomitization resultant textures pore type and pore volume breccias zebra fabrics shear microfractures and other rock characteristics record short term shear stress and pore fluid pressure transients particularly proximal to active faults high temperature hydrothermal pulses may alter kerogen in host limestones a process designated forced maturation basement highs underlying sandstone and or carbonate aquifers probably overpressured and overlying and internal shale seals and aquitards also may constrain or influence htd emplacement although many questions and uncertainties remain particularly in terms of mg and brine source and mass balance recognition and active exploration of the htd play continues to expand increasing use of three dimensional seismic imagery and seismic anomaly mapping combined with horizontal drilling oblique to linear trends defined by structural sags helps to reduce risk