liquid absent aqueous fluid inclusions and phase equilibria in the system cacl2naclh2o abstract raman spectra and microthermometric data are reported for a new class of aqueous fluid inclusions in quartz from the bushveld complex the inclusions which are approximated by the system cacl2 nacl h2o hold special interest because they display the following properties 1 1 the inclusions do not contain a liquid phase at room temperature but they homogenize to an aqueous liquid at elevated temperatures 2 2 initial melting occurs at a reaction point at 29 c rather than at the cacl2 nacl h2o eutectic point at 52 c as is generally the case for fluid inclusions approximated by this system 3 3 ice is absent in the subsolidus assemblage despite the high h2o contents of the inclusions an aqueous liquid is generated upon heating through decomposition of incongruently melting hydrate daughter minerals 4 4 the most abundant minerals in the subsolidus assemblages are antarcticite cacl2 6h2o and a second hydrate that may be a new mineral probably a polymorph of cacl2 4h2o and 5 5 the fluid compositions fall outside the compositional limits defined by previous studies of natural fluid inclusions the inclusions are characterized by a high ca na ratio and a very high concentration of total dissolved solids greater than 52 wt aqueous fluid inclusions that do not contain a liquid phase at ambient temperature may be commonly overlooked or misinterpreted as mineral inclusions the liquid absent aqueous inclusions from the bushveld complex are spatially associated with a second type of fluid inclusion comprised of antarcticite halite vapor and liquid at 20 c the two types of inclusions have similar bulk compositions but they differ radically in melting behavior because their compositions lie on opposite sides of a subsolidus join given the topology of the cacl2 nacl h2o phase diagram small variations in bulk composition in the vicinity of a phase boundary or subsolidus join can result in large differences in the initial melting temperature equilibrium melting sequence and phase proportions at 20 c conversely significant constraints on fluid composition may be derived from qualitative observations of the equilibrium melting sequence

fluid inclusion studies of regionally extensive epigenetic dolomites bonneterre dolomite cambrian southeast missouri evidence of multiple fluids during dolomitization and lead zinc mineralization sources of basinal fluids that precipitated the dolomite hosted mississippi valley type orebodies of southeast missouri historically have been a subject of debate this study presents microthermometric data for fluid inclusions in the regionally extensive epigenetic dolomite at the base of the ore hosting bonneterre dolomite and in gangue dolomite of the viburnum trend pb zn district samples of epigenetic dolomite cover an area of more than 25 000 km 2 west of the st francois mountains and permit determination of regional variations of temperature and composition of the mineralizing fluids and possible fluid interactions homogenization temperature ice melting relationships temperature salinity among these inclusions document at least two end member fluid components a warmer less saline fluid 120 to 187 c 5 wt equiv nacl and a cooler more saline fluid 60 to 80 c 30 wt equiv nacl intermediate temperatures and fluid compositions indicate that the end member fluids likely mixed as they flowed through the region mixing was not confined to a stationary front but occurred throughout the study area comparison of homogenization temperatures to distance from possible basinal fluid sources indicates no discernible temperature gradient over the 25 000 km 2 study area the data are interpreted to indicate multiple basinal fluid interactions coeval with dolomitization and associated pb zn ore formation

the origin and evolution of canadian shield brines evaporation or freezing of seawater new lithium isotope and geochemical evidence from the slave craton abstract new chemical and isotopic data for deep seated calcium chloride brine from the miramar con gold mine yellowknife n w t strongly suggest that the brine salinity is of marine origin diagnostic marine properties include uniformly elevated br cl ratios typical of seawater concentrated beyond halite saturation and li br ratios 0 0254 0 0325 and 6 li compositions 32 1 to 36 3 similar to seawater 32 3 the mean 6 li for all mine water samples of 35 1 may reflect minor uptake of li by secondary minerals this interpretation is supported by analyses of altered metabasalt from fault zones which is enriched in li but depleted in 6 li 14 7 to 15 6 relative to the unaltered metabasalt 5 4 the mechanism responsible for concentrating the hypersaline brine end member is not unequivocal as evidence exists to support both evaporative and cryogenic processes on the one hand the devonian sedimentary record in the great slave lake region in conjunction with yellowknife brine isotopic compositions 2 h and 34 s so 4 that are similar to various devonian fluids support an evaporative origin on the other hand the na cl br cl relationship in the brine strongly suggests a cryogenic mechanism regardless of the concentrative mechanism the chemical data indicate that the yellowknife parent brine was concentrated 28 to 30 fold relative to seawater the extreme depletion of mg and enrichment of ca in the brines accompanied by sr ca ratios similar to that of seawater are accounted for by dolomitization of an aragonite rich marine sediment by the brine before infiltration into the crystalline basement rocks subsequent alteration of silicate minerals in the shield added additional ca and sr to the brine as indicated by their radiogenic 87 sr 86 sr ratios up to 0 7147 based on mineral balance calculations the major mineral products of the cryogenic and evaporitic concentration and evolution paths are significantly different the cryogenic evolution results in some 15 mirabilite 60 hydrohalite and 18 dolomite whereas the major minerals formed from the evaporitic evolutionary sequence are 36 halite 8 gypsum 17 dolomite and 30 albite the great similarity between the calcium chloride brine from yellowknife and other such canadian shield brines indicates that they may share a common marine origin

migration of brines in the basement rocks of the athabasca basin through microfracture networks p patch u deposit canada abstract the unconformity type uranium deposits of the athabasca basin saskatchewan canada are hosted near the unconformity between a middle proterozoic intracratonic sedimentary basin and an archean to paleo proterozoic metamorphic and plutonic basement these deposits which are considered to be the richest u deposits in the world are the result of massive basinal fluid migrations in the basement rocks this study shows that basinal brines have strongly penetrated into the basement not only through faults and major pathways but also by way of dense networks of microfractures which favoured the percolation of fluids down to considerable depths hundred metres below the unconformity and their chemical modification salinity increase by interaction with basement lithologies these processes are one of the major causes of uranium mobility within the basement rocks and the formation of unconformity type mineralization microfracture networks which opened during the basinal brine stage ca 1600 1400 ma are interpreted as sets of mode i cracks corresponding to a specific stage of deformation and occur as fluid inclusion planes after healing the stress field at that stage 1 n130 150 e subvertical partly reopened the earlier microcrack networks 1 n80 110 e and n130 150 e subvertical issued from the trans hudson orogeny late retrograde metamorphic stage ca 1795 1720 ma the circulation of the two types of fluids carbonic and brines occurs thus at two distinct events trans hudson orogeny late retrograde metamorphism for carbonic fluids and maximal burial diagenesis for brines but the same main microfissure geometry was used by the fluids this demonstrates the existence of a similar stress field direction acting before and after the basin formation moreover the brine circulations in the basement acted in a wider volume than the clay rich alteration halo surrounding the u ores generally considered as the main envelope of fluid percolation outside the fault systems the data on the chemistry of the fluids and on the geometry of their migration at various scales emphasise the fundamental role of the basement in the chemical evolution of highly saline brines linked to unconformity related uranium mineralization in the athabasca basin

numerical model to determine the composition of h2o nacl cacl2 fluid inclusions based on microthermometric and microanalytical data natural fluids approximated by the h2o nacl cacl2 system are common in a wide range of geologic environments including sedimentary basins associated with hydrocarbon occurrences and mvt deposits submarine hydrothermal systems and other metamorphic magmatic and hydrothermal environments we present a comprehensive numerical model and microsoft excel based computer program to determine the compositions of fluid inclusions in the h2o nacl cacl2 system based on microthermometric and microanalytical data the model consists of six polynomial correlation equations that describe liquid salinity as a function of nacl cacl2 ratio and melting temperature on each of the ice hydrohalite halite antarcticite cacl2 4h2o and cacl2 2h2o vapor saturated liquidus surfaces the cotectic and peritectic boundaries are determined from the intersections of the liquidus surfaces the model is implicitly internally consistent and topologically correct the model expands upon the compositional range of applicability and the data types that can be used for compositional determination it reproduces experimental data for all compositions that lie within the h2o nacl cacl2 4h2o compositional triangle in the h2o nacl cacl2 system and yields accurate reproductions of the h2o nacl and h2o cacl2 binaries furthermore in comparison to previously published models the one presented here eliminates systematic errors wavy isotherms and cotectic and peritectic curves with local bumps

a fluid inclusion and stable isotope study of synmetamorphic copper ore formation at mount isa australia earlier structural studies indicate that the dolomitic and siliceous breccias and contained copper mineralization at mount isa queensland australia formed during regional deformation and greenschist facies metamorphism of their host mid proterozoic metasediments the metasomatic breccia body locally called silica dolomite is zoned with an outer halo of sparry dolomitic alteration replacing finely laminated dolomitic pyritic metasediments the core of the dolomitic breccia next to the underlying altered greenstones is overprinted by siliceous breccia containing the bulk of the chalcopyrite ore fluid inclusions in quartz and dolomite were studied by microthermometry micro raman spectrometry and semiquantitative electron microprobe analysis of inclusion salts two types of aqueous inclusions are restricted to dolomitic breccia cacl 2 rich group 1 with a cation ratio na ca k mg nearly equal 30 10 3 1 and salinity approximately 25 wt similar to recent salton sea geothermal brines and low salinity with 10 to 20 mole percent co 2 co 2 rich group 2 these two aqueous inclusion types are intimately associated in the same crystals and have probably both been trapped during dolomitic alteration siliceous alteration superimposed on dolomitic breccia contains nacl rich fluid inclusions group 3 na ca k mg nearly equal 300 10 30 1 minor ch 4 microstructures suggest that earlier higher salinity 10 20 wt and later lower salinity 4 9 wt variants of this nacl rich fluid bracket the main stage of chalcopyrite introduction there are no low density vapor inclusions indicative of any stage of fluid boiling rare high density ch 4 or co 2 rich carbonic inclusions are associated with nacl rich aqueous inclusions in a few samples secondary inclusions of a highly calcic low temperature brine group 4 occur along late healed cracks and postdate all major stages of mineral precipitation the c o and h isotope compositions of dolomites quartz and hydrous silicates and of fluid inclusion extracts from samples of the siliceous alteration zone were imposed by the externally derived weakly ch 4 co 2 bearing nacl rich fluid at high fluid rock ratios and over a small range of temperatures this fluid may have originated as a highly evolved basin brine or an evaporite derived metamorphic fluid the early cacl 2 rich fluid may have had an origin similar to the nacl rich ore fluid but its different delta d and the mass balance constraints arising from its chemical composition suggest that it has not been derived from the nacl rich fluid by progressive rock interaction within the zoned alteration system similarly an independent source is likely for the co 2 rich fluid the absolute pressure temperature ranges for the two alteration processes seem to be slightly different but it is uncertain whether the quartz chalcopyrite mineralization occurred at slightly lower temperature or higher pressure compared with the dolomitic alteration the latter is confined to 270 degrees to 350 degrees c and 700 to 1 500 bars by isochore and mineral stability data the following working hypothesis for the syntectonic and synmetamorphic fluid rock interaction and copper ore formation at mount isa is proposed in an initial stage dolomitic alteration occurred by chemical interaction between the urquhart shale and moderate amounts of two fluids of different chemical and hydrological origin represented by the cacl 2 rich and the co 2 rich fluid inclusions fluid mixing may have been aided by extension on the limb of a regional fold which temporarily lowered fluid pressures thus leading to hydraulic brecciation and fluid influx from two fluid regimes above and below the co 2 rich fluid probably represents the local metamorphic fluid of the urquhart shale whereas the cacl 2 rich brine was introduced from the underlying altered greenstones the initial stage of brecciation and dolomitic alteration was followed by the main stage of silicification and copper introduction by the much more copious nacl rich fluid probably at near lithostatic fluid pressure quartz and chalcopyrite precipitation occurred by a combination of slight cooling a ph increase and possibly an increase in sulfur activity as the initially reduced acid and possibly s deficient nacl rich fluids reacted with the previously dolomitized pyritic and dolomitic urquhart shale

saline groundwaters in the canadian shield a first overview abstract the chemical and isotopic compositions of saline groundwaters and brines in the canadian shield are described the occurrence of such waters is very widespread not related to any specific rock type or mineralization and generally can be expected at depths below 1 km the most saline brines have salinities exceeding 200 g l 1 dissolved solids and their chemistries tend to suggest that in the past saline waters penetrated the canadian shield the original chemistry of these solutions was subsequently modified through strong rock water interactions and it appears that their final chemical compositions are independent of the original chemistries stable isotope analyses indicate that these waters are not simple evaporated seawater sedimentary basin brines hydrothermal solutions or residual ore forming fluids although any of these could be a precursor of the brines secondary isotope exchange reactions and the hydration of primary silicates accompanied by the formation of clay minerals could have modified not only the primary isotopic composition but may have also profoundly influenced the chemistries of these brines to be effective these processes would have had to occur in closed systems

fluid inclusions with nacl cacl2 h2o composition from the cloncurry hydrothermal system nw queensland australia abstract fluid inclusions whose composition can be approximated by the ternary system nacl cacl 2 h 2 o are common in the fe oxide cu au deposits and associated alteration in the cloncurry hydrothermal system nw queensland australia detailed microthermometric work indicates that a multi staged cacl 2 bearing fluid trapping was involved during the formation of mineralization and alteration the fluid evolution history is characterized by early high temperature and low salinity to late low temperature and high salinity which is distinct from many intrusion related hydrothermal systems in the world the ubiquitous presence of low temperature t h 2 bearing inclusions is a remarkable feature of the mid proterozoic cloncurry hydrothermal system and it is interpreted to be a result of the interaction between evaporites and downward penetration of meteoric water the transition from early magmatic and or metamorphic fluids to late meteoric water is ascribed to the shift of the crustal level during exhumation despite the controversies over the mechanisms of mineralization fluid mixing demonstrated by the rapid drop in temperature through addition of cooler meteoric water into the hydrothermal system must have played a significant role with regard to the metal precipitation in some deposits of this type

characteristics and origin of the oak dam east breccia hosted iron oxide cu u au deposit olympic dam region gawler craton south australia oak dam east is a large 560 mt of 41 56 wt fe cu au u bearing massive fe oxide deposit in the northeastern gawler craton south australia it is one of several unmined deposits in the same province as the giant olympic dam deposit and it lies beneath more than 500 m of younger cover rocks the oak dam east breccia complex formed in a near surface environment and was characterized by an early history of skarnlike albite calc silicate magnetite formation from hypersaline 400 500 c fluids large scale brecciation was an early feature and the resulting complex was progressively filled in and replaced by 1 hematite and goethite hematite stage i 2 magnetite apatite quartz actinolite magnetite stage 3 hematite goethite quartz chalcedony pyrite chlorite monazite hematite stage ii and 4 chalcopyrite pitchblende illite hydromus covite florencite carrolite cu u au mineralization stage hematite stage ii assemblages are volumetrically most abundant and were formed from fluids of 1 to10 wt percent nacl equiv that were boiling at 170 to 190 c and had 18o values more negative than 3 7 to 1 7 per mil interpreted as meteoric water the upper 200 m of the breccia complex contains spectacular colloform hematite void fillings interpreted to have replaced hydrothermal goethite the cu u mineralized zones resemble olympic dam ore in terms of geometries being grossly subhorizontal 10 to 70 m thick and crosscutting with respect to the host breccias the mineralization is zoned vertically from pyrite 34s 6 to 0 at depth to shallower chalcopyrite 34s 14 to 7 high grade pitchblende occurs centrally within the chalcopyrite zone e g 10 m of 0 46 cu and 3 700 ppm u3o8 straddling a boundary between k mica illite alteration and underlying fe mg chlorite alteration the deposit is assigned to the 1570 to 1595 ma iron oxide cu au u event in the eastern gawler craton on the basis of its similarity to other cu au u deposits in the province an la icpms pb isotope age for monazite in hematite stage ii was calculated to be 1455 20 ma and possibly as young as 1370 54 ma to explain all isotopic data this is an age of isotopic resetting our preferred model is that cu u mineralization developed within a stratified hydrothermal brine complex analogous to the salton sea geothermal system copper fe and s in the deep brine was sourced from an evolving deep reservoir with local compositional controls on sulfur isotopes including cooling boiling and replacement of previous pyrite chalcopyrite u veins and disseminations formed as a result of mixing with overlying steam heated u rich saline ground water mixing induced cooling and dilution only occurred episodically following hydrofracturing events that ephemerally linked the brine layers within the substantially cemented upper complex by contrast high grade uo2 formation occurred as deep upflow waned via reaction of the upper brine with hematite stage ii fe mg chlorite along an interface that descended with time this resulted in an increase of u grades through time caused by leaching and reprecipitation

mixed messages in iron oxide copper gold systems of the cloncurry district australia insights from pixe analysis of halogens and copper in fluid inclusions proterozoic rocks of the cloncurry district in nw queensland australia are host to giant tens to hundreds of square kilometers hydrothermal systems that include 1 barren regional sodic calcic alteration 2 granite hosted hydrothermal complexes with magmatic hydrothermal transition features and 3 iron oxide copper gold iocg deposits fluid inclusion microthermometry and proton induced x ray emission pixe show that iocg deposits and the granite hosted hydrothermal complexes contain abundant high temperature ultrasaline complex multisolid type 1 inclusions that are less common in the regional sodic calcic alteration the latter is characterized by lower salinity three phase halite bearing type 2 and two phase type 3 aqueous inclusions copper contents of the type 1 inclusions 300 ppm is higher than in type 2 and 3 inclusions 1 000 ppm are found both in the granite hosted systems and in inclusions with br cl ratios that are consistent with a magmatic source the br cl ratios of the inclusions with lower cu contents are consistent with an evaporite related origin wide ranges in salinity and homogenization temperatures for fluid inclusions in iocg deposits and evidence for multiple fluid sources as suggested by halogen ratios indicate fluid mixing as an important process in iocg genesis the data support both leaching of cu by voluminous nonmagmatic fluids from crustal rocks as well as the direct exsolution of cu rich fluids from magmas however larger iocg deposits may form from magmatic derived fluids based on their higher cu content

active ore formation at a brine interface in metamorphosed deltaic lacustrine sediments the salton sea geothermal system california the salton sea geothermal system is an area of active hydrothermal metamorphism of pliocene to pleistocene deltaic lacustrine and evaporitic sediments deposited in a modern continental rift zone temperatures up to 365 degrees c hypersaline metalliferous brines with up to 26 wt percent total dissolved solids and active base metal ore formation accompany low pressure greenschist and amphibolite facies metamorphism at depths less than 3 2 km drill cores recovered by the salton sea scientific drilling project shed new light on the nature and origin of ore formation in the eastern portion of the salton sea geothermal system base metal ore mineralization occurs in vertical fractures that comprise the major form of fluid permeability at 1 to 3 km in the modern geothermal system type 1 veins are dominated by carbonate contain pyrrhotite and other sulfides are completely sealed and occur in wall rock showing minimal alteration fluid inclusion data indicate that they were deposited under a thermal gradient much higher than that now found in the eastern part of the system type 2 veins are dominated by silicates and hematite are permeable and occur in wall rocks showing pervasive chloritization and epidotization fluid inclusion data indicate that they are forming now from the geothermal brines under the modern thermal gradient fluid inclusions record an apparent steep progressive salinity increase in the vein systems in the upper 2 km of the system however fluid production data from salton sea geothermal wells indicate that reduced metalliferous hypersaline brine averaging 23 wt percent total dissolved solids is overlain by more oxidized metal poor fluid averaging 5 wt percent total dissolved solids a sharp interface exists between the fluids at 1 to 2 km paralleling the 250 degrees c isothermal surface a model is developed for type 2 vein ore formation involving mixing at the interface between the two fluids magmatic intrusion induces fracturing heating and the expulsion of reduced connate fluids to cause early type 1 vein mineralization following the rising thermal front deep hypersaline brine rises diapirically and mixes with overlying fluids in vertical fractures transecting the ascending interface forming type 2 veins the hypersaline brine rises to a level of density temperature stabilization causing pervasive greenschist metamorphism of the host sediments the diapir then begins to cool and descend shallow oxidized brine is drawn in as the hypersaline brine descends promoting late stage hematite in type 2 veins the eastern salton sea geothermal system presently appears to be in this latter mode of cooling and retrograde brine descent ore formation in the system is caused by the coincidence of transaxial entry of a major river into an active rift zone deposition of metal bearing deltaic sediments to form a closed basin sedimentary environment episodic lacustrine evaporite formation and injection of heat and elements by rift related magmatic intrusions at depth the presence of an upwelling brine diapir in the system may be analogous to conditions immediately prior to the exhalation of metalliferous fluids that formed stratiform fe zn pb cu sulfide and oxide deposits in paleorift zone environments

fluid and mass transfer during metabasalt alteration and copper mineralization at mount isa australia metabasalts surrounding the metasediment hosted base metal deposit at mount isa have been modified by metamorphism polyphase deformation and several stages of hydrothermal alteration this study aims to understand the large scale hydrothermal processes that determined the chemical composition of syn to postmetamorphic ore brines prior to being focused into chemicaly anomalous metasediments that acted as a chemical trap for localized copper precipitation field mapping of the metabasalts provided the framework to determine the relative timing of district scale alteration events which were then studied by mineralogic observations and bulk mass balance measurements microthermometry raman microspeetrometry and br cl analyses of fluid inclusions and h o c and s stable isotope measurements on vein minerals were used to characterize the hydrothermal fluids associated with the alteration events all fluids are moderately to highly saline variably ca enriched with high br cl compared to modern seawater and isotopiealy most akin to modern evolved basin or low grade metamorphic brines the timing and fluid tracer observations in conjunction with thermodynamic mass transfer modeling permit the following correlation between district scale alteration processes and the mine scale hydrothermal events associated with copper deposition at mount isa district scale epidote sphene alteration of metabasalts temporally overlapped with the peak of greenschist facies metamorphism and deformation and is widely distributed in flow top breccias and as halos around synmetamorphic quartz calcite veins it is associated with calcic brines with 12 to 38 wt percent cacl 2 nacl equiv and thermodynamic modeling suggests that the observed mineralogy and bulk mass changes can be explained by focusing of metabasalt equilibrated fluids and by reaction with similar rocks at somewhat higher temperature similar timing and fluid characteristics are associated with dolomitic alteration at the mount isa mine where mixing of metabasalt derived calcic brine with metamorphic co 2 from the metasediments led to massive dolomite precipitation kilometer scale fracture zones associated with carbonate fe oxide alteration calcite albite magnetite or hematite or biotite or chlorite cut all penetrative foliations in the metabasalts east of mount isa they are locally associated with uranium mineralization and are characterized by medium salinity nacl rich fluid inclusions 8 93 wt nacl equiv carbonate fe oxide alteration is interpreted to mark channelways of infiltration by oxidized sulfate bearing brines from outside the metabasalt sequence possibly from an overlying evaporitic cover sequence fluid characteristics evidence for extreme copper mobility and timing criteria of alteration relative to deformation suggest a temporal and possibly genetic correlation with the main copper and silica deposition stage at the mount isa mine mg chlorite rutile alteration is restricted to metabasalts immediately below the copper deposit and the vicinity of the mount isa fault zone where higher grade amphibolite facies metabasalts were upthrust against the greenschist facies metabasalts and metasediments now hosting the copper ore bodies mg chlorite rutile alteration of metabasalts and copper mineralization in the adjacent reduced sediments can both be explained by fluid focusing along an actively extending contact zone between the oxidized metabasalts and the reducedmetasediments the brines focused into this contact zone were initially oxidized as a result of infiltration through the carbonate fe oxide fracture zones and less altered metabasalts and became reduced by reaction with the metasediments the unusual geochemical and isotopic low 13 c and high 34 s composition of mg chlorite rutile alteration can be explained as a result of back flow of reduced fluids from the metasediments into the metabasalts although mg chlorite rutile alteration of metabasalts probably liberated some of the copper now present in the orebodies this alteration may be a relatively localized effect associated with the site of ore deposition rather than an essential sourcing mechanism for the copper the regional feature of greatest significance to ore formation at mount isa and to exploration for similar high grade copper deposits elsewhere is not the somewhat elevated initial copper content of the metabasalts nor their locally significant copper depletions but their moderately high oxidation state evident from the ubiquitous occurrence of fe rich epidote and the large scale fe oxide altered fracture zones oxidation of the basalts or any other silicate rocks favored high copper solubility along extensive transport paths and provided the essential chemical contrast to the depositional environment which was anomalously reduced and sulfide rich as a result of an earlier process of sedimentary to diagenetic pb zn fe s mineralization

a fluid inclusion study of the suicide ridge breccia pipe cloncurry district australia implication for breccia genesis and iocg mineralization abstract the suicide ridge barren breccia pipe 1527 4 ma is one of numerous breccia occurrences that characterize the cloncurry district australia interest in breccia systems in the cloncurry district is related to their possible link with iron oxide copper gold deposits the suicide ridge barren breccia pipe is temporally and spatially associated with a granite that outcrops at its southwestern boundary and which is ascribed to the williams and naraku magmatic event ca 1550 1500 ma the breccia is characterized by clasts of variable dimensions degree of rounding and composition that includes dominant calc silicate clasts of the corella formation that underlie rocks of the soldiers cap group that host the pipe indicating a dominant upward transport of the fragments other breccia fragments include granite bodies characterized by albite quartz mineralogy and textures typical of the magmatic hydrothermal transition these rocks are interpreted to have formed in a fractionated granite carapace during the exsolution and accumulation of volatiles associated with the cooling magma two dominant types of inclusions have been identified at the suicide ridge barren breccia pipe these include early primary and pseudosecondary carbonic fluid inclusions observed only in magmatic hydrothermal transitional textures of granite breccia clasts and secondary sodic calcic brine inclusions that occur in all the collected samples variable homogenization temperatures in the primary and pseudosecondary pure co2 fluid inclusions indicate that they were trapped under different pressure conditions pressures estimated from the primary co2 fluid inclusions suggest that they were trapped at 4 2 kbar at least 1 kbar above the inferred lithostatic pressure this likely represents the overpressuring produced by release of co2 rich volatiles during the crystallization of magma and which ultimately caused the subsequent brecciation estimated pressures for pseudosecondary co2 fluid inclusions indicate pressure entrapment conditions around 2 7 kbar similar to the lithostatic pressure and 1 5 kbar lower than pressures recorded by type ia fluid inclusions this significant drop of pressure likely represents the sudden pressure depression occurring in response to brecciation evidence from field relationships breccia characteristics mineralogy and textures of granite clasts within the pipe and fluid inclusion studies support an origin of the suicide ridge barren breccia pipe in response to overpressuring generated by the release expansion and possibly phase separation of fluids of dominant carbonic composition from a crystallizing magma beneath and adjacent to the pipe sodic calcic fluid inclusions represent a later influx of fluids in the breccia system that produced widespread albitization significantly high temperature ultrasaline multisolid fluid inclusions abundant in iocg deposits and considered to be samples of the mineralizing fluid were not observed at the suicide ridge breccia pipe their absence in the barren systems suggests that they were critical for the formation of iocg deposits

hydrothermal evolution of the el teniente deposit chile porphyry cu mo ore deposition from low salinity magmatic fluids the magmatic hydrothermal evolution of the el teniente porphyry cu mo deposit in the central andes in chile is reconstructed based on field relationships scanning electron microscopy cathodoluminescence petrography and fluid inclusion analysis by microthermometry and laser ablation inductively coupled plasma mass spectrometry la icpms three major stages of cu mo mineralization are observed following the barren hydrothermal stage 1 the stage 2 mineralization is characterized by quartz anhydrite stockwork veins and breccias with chalcopyrite bornite and molybdenite both stages 1 and 2 are associated with pervasive potassic alteration quartz anhydrite veins with chalcopyrite bornite and molybdenite associated with phyllic alteration represent stage 3 mineralization stage 4 mineralization linked to the formation of the large braden diatreme is characterized by breccias and rare veins containing a lower temperature assemblage with tourmaline sericite and lesser tennantite bornite and chalcopyrite with late gypsum in local vugs ten fluid types are distinguished in this study based on petrographic and microthermometric criteria such as phase proportions daughter minerals homogenization behavior and salinity the hydrothermal evolution across the stages of cu deposition is characterized by the contraction of a vapor phase originating by phase separation during stage 2 overall cooling of the system at pressures fluctuating around the two phase fluid surface led to a transition from a two phase fluid state dominated by vapor at 410 c and 300 bars in stage 2 to a single phase low salinity fluid derived from cooling and contraction of magmatic vapor to a liquid which dominates during stage 3 mineralization at 350 c and 200 bars copper mineralization mainly formed from the vapor phase and its low salinity liquid derivatives representing a large volume of fluid with an initially high cu content 1 2 0 4 wt cu copper sulfides precipitated upon cooling between 410 and 320 c indicated by a drop of cu na k mn fe ratios of over four orders of magnitude through the evolution of the deposit from stage 2 to stage 4 the highest mo concentrations occur in residual brines resulting from extreme boiling as indicated by concurrent halite saturation recent geochronology cannell 2005 maksaev et al 2004 suggests a relatively long lived magmatic hydrothermal system at el teniente our fluid chemical data show no evidence for major crystal fractionation in a large fluid generating upper crustal magma chamber because cs na k mn fe is constant from pre ore to all syn ore fluids however the initiation of copper mineralization was associated with a 4 to 10 fold increase in the concentration of cu mo li and fe in the inferred main ore forming input fluid compared with pre ore fluids of intermediate salinity and otherwise very similar major and trace element ratios these data indicate that injection from depth of an exceptionally cu mo li and probably also s rich volatile phase into an already actively evolving upper crustal magmatic hydrothermal system triggered the formation of this unusually large and rich copper deposit

origin of hydrothermal fluids at olympic dam preliminary results from fluid inclusions and stable isotopes fluid inclusions and stable isotope data provide evidence of the temperature composition and sources of hydrothermal fluids associated with formation of the fe rich breccias that host cu u au ag ore at olympic dam early magnetite associated with pyrite and siderite precipitated from fluids of high delta 18 o content approx 10ppm at temperatures near 400 degrees c and magnetite in k feldspar apatite veins at the nearby acropolis deposit probably formed from similar fluids in contrast hematite associated with ore bearing breccias formed at lower temperatures 200 degrees 400 degrees c from fluids of lower delta 18 o content 9ppm fluid inclusion homogenization temperatures in quartz fragments within hematite breccias overlap with and are lower than those indicated by isotope geothermometry two phase liquid plus vapor inclusions mainly homogenize at temperatures between 130 degrees and 280 degrees c with a mode at 170 degrees to 190 degrees c quartz fragments within rare laminated barite clasts display a larger range of homogenization temperatures from 110 degrees to 420 degrees c and may have preserved evidence of early high temperature hydrothermal events measurement of freezing point depressions in fluid inclusions provides evidence of widely varying salinities and complex solute chemistry indicated salinities vary from a minimum of 7 3 wt percent nacl equiv 1 3 m to a maximum of 23 7 wt percent nacl equiv 4 2 m in two phase fluid inclusions and up to 42 wt percent nacl equiv in halite saturated three phase inclusions all the fluid inclusions studied displayed evidence of additional solutes in addition to nacl all required a high degree of supercooling to induce freezing and displayed initial ice melting at temperatures below 23 degrees c and many formed distinctive brown granular ice in addition several inclusions also formed co 2 clathrates and other metastable solids qualitative assessment of these characteristics indicates fluids carrying multiple solutes probably including nacl kcl cacl 2 fecl 2 caf and co 2 these preliminary results suggest that at least two sources of fluids of contrasting temperature composition and oxygen isotope characteristics were involved in the formation of olympic dam early magnetite was deposited from hydrothermal fluids of deep seated possibly magmatic origin but magnetite bearing rocks are not significant hosts for copper uranium mineralization later hematite associated with ore bearing breccias was deposited by fluids of significantly lower temperature and lower delta 18 o values the geologic setting of the deposit a fault bounded depression at or near the palcosurface implies that waters of surficial origin seawater closed basin water or ground water may have been involved in the later stages of hydrothermal activity that formed the hematite breccias although our preliminary isotopic data do not require such waters they are consistent with this conclusion

chemical evolution of brines during mississippi valley type mineralization evidence from east tennessee and pine point the major element chemical composition of inclusion fluids from mississippi valley type deposits has been evaluated semiquantitatively using scanning electron microscopy and energy dispersive analysis of individual inclusion decrepitates in ore and gangue minerals the volcano shaped decrepitates are produced by heating polished plates above the decrepitation temperature of the inclusions forcing the enclosed fluids to the surface where the nonvolatile components precipitate energy dispersive analyses of these precipitates here called decrepitates are expressed in cation and anion weight ratios and carry errors of or 10 percent application of this technique to fluid inclusions in sphalerite and dolomite from the mascot jefferson city zinc district of east tennessee and the pine point lead zinc district of the northwest territories reveals that fluids attending sulfide deposition in both districts are dominantly na ca chloride brines subordinate but significant amounts of k mg and locally sr and fe are also present cacl 2 cacl 2 nacl weight ratios vary greatly among the samples from both deposits but are consistently lower 0 1 0 3 in gangue dolomites not associated with sulfides than in sphalerite and ore stage dolomite 0 2 0 6 at east tennessee 0 4 0 8 at pine point although cl is the only significant anion detected in the east tennessee analyses a significant proportion of decrepitates from sphalerite and ore associated dolomite at pine point contain appreciable s occasionally in amounts equal to or exceeding cl mass balance calculations show that the increase in the cacl 2 cacl 2 nacl ratio in decrepitates associated with ore from both districts cannot result simply from limestone dissolution at the site of brecciation and mineralization instead they appear to require either fluid mixing or a chemical evolution of the fluids entering the carbonate host rocks the presence of significant ca and s together in the pine point fluid inclusions and the absence of daughter anhydrite requires that most s was reduced which lends support to mixing models involving metal rich brines and sulfur rich waters in ore formation in that district further the presence of excess s in ore stage decrepitates from pine point suggests that sulfide de position there was limited by the amount of metal rich brine entering the h 2 s rich barrier reef complex in contrast the lack of detectable sulfur in the decrepitates from mascot jefferson city ores suggests that mineralization there may have been limited by the availability of s but does not permit selection between mixing and fluid evoluton as a cause of ore deposition

orthogonal switching of ams axes during type 2 fold interference insights from integrated x ray computed tomography ams and 3d petrography abstract we applied x ray computed microtomography ct in combination with anisotropy of magnetic susceptibility ams analysis to study metamorphic rock fabrics in an oriented drill core sample of pyrite pyrrhotite quartz mica schist the sample is extracted from the paleoproterozoic martimo metasedimentary belt of northern finland the ct resolves the spatial distribution shape and orientation of 25 920 pyrrhotite and 153 pyrite grains localized in mm thick metapelitic laminae together with microstructural analysis the ct allows us to interpret the prolate symmetry of the ams ellipsoid and its relationship to the deformation history ams of the sample is controlled by pyrrhotite porphyroblasts that grew syntectonically during d1 in subhorizontal microlithons the short and intermediate axes k3 and k2 of the ams ellipsoid interchanged positions during a subsequent deformation d2 that intensely crenulated s1 and deformed pyrrhotite while the long axes k1 maintained a constant position parallel to the maximum stretching direction however it is likely that all the three ams axes switched similar to the three principal axes of the shape ellipsoid of pyrite porphyroblasts from d1 to d2 the superposition of d1 and d2 produced a type 2 fold interference pattern

measurements and interpretations of36cl in groundwater milk river aquifer alberta canada abstract the 36 cl cl ratios of 12 groundwater samples from the milk river aquifer were determined by accelerator mass spectrometry using known cl concentrations 36 cl concentrations were deduced approximately linear relations were observed between the logarithm of the 36 cl concentration the cl concentration and the distance from the recharge area along two flow paths the results are discussed in two approaches 1 in an interpretation of the linear relation between logarithm of the 36 cl concentration and cl concentration excluding and including in situ production of 36 cl 2 in a diffusion model the increase of the cl concentration with the distance from the recharge area is considered to be due to diffusion of cl from the underlying confining colorado shale to the aquifer flow velocities ranging between 0 04 and 0 14 m a and ages of the groundwater between 0 6 and 2 ma are obtained at a distance of 80 km from the recharge area

ore forming fluids in archean gold bearing quartz veins at the sigma mine abitibi greenstone belt quebec canada archean gold bearing quartz veins at the sigma mine occur in deformed metavolcanics intruded by two generations of preore porphyries the veins were emplaced during a late compressional tectonic event and they consist primarily of quartz tourmaline carbonates pyrite and scheelite vein minerals have been deformed and are also cut by abundant healed fractures outlined by fluid inclusions in the veins gold typically occurs in late fractures and in recrystallized quartz microthermometric sem eda leachate analysis and gas chromatographic techniques were used to study fluid inclusions in quartz most fluid inclusions at sigma occur in late fractures and are secondary the fluid inclusions are commonly found in fractures parallel to or less commonly within gold bearing fractures and are genetically related to the gold three types of fluid inclusions are identified 1 high salinity na ca cl aqueous inclusions 25 34 wt salt with small amounts of co 2 some containing halite calcite and nahcolite as daughter minerals 2 co 2 rich inclusions containing small amounts of h 2 o and ch 4 and 3 low salinity h 2 o co 2 inclusions 10 equiv wt nacl with co 2 contents which are variable but commonly in the range of 15 to 30 mole percent co 2 leachate analyses show that in addition to na and ca the aqueous fluids contain minor amounts of k fe mg and li homogenization temperatures of h 2 o co 2 inclusions with constant phase ratios range from 285 degrees to 395 degrees c those of aqueous inclusions range from 60 degrees to 295 degrees c the aqueous and co 2 rich inclusions are interpreted to have trapped two coexisting fluids resulting from the unmixing of a homogeneous h 2 o co 2 parent fluid itself occasionally trapped in late fractures the ore bearing fluid is interpreted to be a low salinity 10 equiv wt nacl fluid containing 15 to 30 mole percent co 2 at minimum temperatures in the range of 285 degrees to 395 degrees c the relatively low homogenization temperatures of aqueous inclusions are interpreted to be the result of co 2 effervescence from a co 2 saturated aqueous fluid due to pressure fluctuations at the time of entrapment it is also proposed that the onset of gold deposition is related to the onset of fluid unmixing

the chemical and thermal evolution of the fluids in the cave in rock fluorspar district illinois mineralogy paragenesis and fluid inclusions a detailed fluid inclusion and paragenetic study was undertaken on samples from the deardorff and hill mines in the cave in rock fluorspar district illinois fluid inclusion homogenization temperature and salinity data were collected on all available transparent minerals in the paragenetic sequence fluorite sphalerite quartz calcite and barite the bulk of the fluid inclusion data however was from fluorite crystals the fluorite crystals from the bedded replacement deposits are color banded the banding sequence is observable and correlated from crystal to crystal within a mine and either the general sequence or parts of it have been observed in crystals from throughout the district measurements were made on fluid inclusions from each band of several large crystals from the hill mine which contained the entire banding sequence inclusions in these samples yielded homogenization temperatures between 132 degrees and 151 degrees c for most of the sequence and between 115 degrees and 120 degrees c in the outermost band the salinity of the fluids ranged between 18 and 20 equivalent weight percent nacl except in the outermost band where the salinity dropped to 9 to 10 equivalent weight percent nacl a group of purple fluorite bands p3 which are easily recognizable in many deposits was correlated from crystal to crystal at over 40 sample localities in the deardorff mine measurements on inclusions in these bands yielded information on the thermal and salinity variations at a single time plane these measurements denote a series of concentrically zoned hot areas within the mine which were areas of upwelling fluids the temperature of the fluids changed as much as 10 degrees c over 50 to 200 ft the salinity of the inclusions in these samples varied only between 19 and 21 equivalent weight percent nacl and did not correlate with either sample location or temperature fluid inclusion measurements on quartz sphalerite calcite and barite yield temperatures of 68 3 degrees to 165 1 degrees c for early quartz 160 1 degrees to 226 5 degrees c for milky quartz bands 130 4 degrees to 160 0 degrees c for sphalerite 81 9 degrees to 137 2 degrees c for calcite and 115 2 degrees to 157 0 degrees c for barite inclusions in sphalerite and quartz had salinities like those for fluorite of 18 3 to 21 0 equivalent weight percent nacl but the salinity of the fluid dropped during calcite and barite deposition 7 0 to 8 9 equivalent weight percent nacl for calcite and 1 2 to 1 3 equivalent weight percent nacl for barite the fluid inclusion measurements on samples from the hill mine indicate that the fluids stayed at nearly the same temperature and salinity for most of the mineralizing period the drop in temperature and salinity in the final stages of deposition strongly suggests an influx of cooler probably meteoric water the temperature measurements on samples from the deardorff mine indicate that there were thermal variations of as much as 10 degrees c within the ore fluid the narrow salinity range and lack of correlation between salinity and temperature or sample location seem to preclude mixing of two fluids as the deposition mechanism mixing of two or more fluids at depth however is not ruled out a cooling mechanism for fluorite deposition requires rather large quantities of fluid to have passed through the deposit however cooling combined with chemical changes in the fluid is the best working hypothesis

calcium rich brines and other hydrothermal fluids in fluid inclusions from plutonic rocks oceanographer transform mid atlantic ridge abstract fluid inclusions in metagabbro plagiogranite and epidosite from the oceanographer transform mid atlantic ridge were investigated using microthermometric measurements and laser raman spectroscopy inclusions in quartz reveal the presence of a high salinity average 40 wt nacl cacl 2 high temperature 340 c calcium rich na ca about 1 by weight fluid in metagabbro and plagiogranite at room temperature these fluids bear a halite daughter crystal and may also contain small crystals of calcite titanite and hematite a low density vapor rich fluid bearing a small amount of co 2 is closely associated with the briney fluids in one sample all samples contain a population of high temperature 150 to 400 c aqueous liquid dominated fluid inclusions commonly of secondary origin having seawaterlike salinity 3 to 8 wt nacl equivalent we conclude that the calcium rich brines are produced by a combination of two processes fluid phase separation and segregation of brines from vapor prior to trapping to generate the high salinities and extensive fluid mafic rock interaction at low water rock ratio to promote the calcium enrichment later introduction along microfractures of low salinity modified seawater at high water rock ratio is recorded by the secondary fluid inclusions the chemical complexity and association with co 2 may indicate that there is a magmatic component to the brines in addition to a seawater source differences between the oceanographer transform brines and those reported in previous studies of oceanic and ophiolite samples are attributed to variations in the degree of water rock interaction the host rock lithology and the influence of a magmatic fluid component

mixing of sodic and calcic brines and uranium deposition at mcarthur river saskatchewan canada a raman and laser induced breakdown spectroscopic study of fluid inclusions the richest u deposit in saskatchewan canada occurs in the mcarthur river area in the vicinity of the unconformity between the athabasaca sandstones and an archean to lower proterozoic basement paleofluids related to the silicification of the sandstones and the formation of pre and postore cements in breccias were studied using microthermometry raman microspectroscopy and laser induced breakdown spectroscopy libs on individual fluid inclusions a detailed reconstruction of the fluid composition in the system na ca mg cl shows that two types of brines are responsible for the main quartz cements an nacl rich brine 25 wt nacl up to 14 wt cacl 2 and up to 1 wt mgcl 2 which is interpreted as a primary formation water that was expelled from bedded evaporites and a cacl 2 rich brine 5 8 wt nacl 20 wt cacl 2 and up to 11 wt mgcl 2 which is considered to have formed during the interaction between the nacl rich brine and ca rich minerals in the basement and was introduced into the fault system and mixed with the nacl rich brine during the critical stage of u deposition the pressure temperature conditions of formation of the quartz cements are estimated to be 1 200 to1 400 bars and 190 to 235 c for the silicification events during the preore stage and 500 to 900 bars after a pressure decrease from lithostatic conditions and slightly lower temperatures due to the mixing of the nacl rich brine with the cooler approx 140 c cacl 2 rich brine during the main stage of breccia sealing temperature and pressure drops combined with the effects of brine mixing appear to be key factors for the main stages of quartz cementation and u deposition at the mcarthur deposit

accurate and precise quantification of major and trace element compositions of calcic sodic fluid inclusions by combined microthermometry and la icpms analysis abstract determination of absolute trace element concentrations in fluid inclusions using laser ablation la icpms requires an internal standard i e the concentration of one element must be independently known from independent observation microthermometric determination of the last melting temperature of ice hydrohalite or halite is routinely used to calculate apparent salinities in wt nacl equivalent using phase relations in the binary h 2 o nacl system to estimate na concentration calculating the concentrations of all other elements requires an empirical correction if additional salt concentrations are of similar magnitude as that of nacl if cacl 2 is the main additional salt component as in many low temperature basin and basement brines absolute na concentrations wt nacl abs can be obtained by observing two melting temperatures hydrohalite and either ice or halite uniquely defining the major element composition of the fluid in the ternary model system h 2 o nacl cacl 2 and allowing na to be used as internal standard for quantifying all minor and trace elements test results for a range of compositions show that calcium concentration can be determined more precisely by microthermometry than by la icpms analysis but that both methods agree within error the combined approach of microthermometry and la icpms analysis described here permits reliable quantification of major ca na as well as trace element concentrations in sodic calcic brine inclusions even in ca rich host minerals such as fluorite or ca bearing carbonates

fluid inclusion evidence on the origin of some australian unconformity related uranium deposits fluid inclusions in altered and unaltered host rocks and hydrothermal quartz calcite and dolomite from the unconformity related uranium deposits of koongarra nabarlek and jabiluka northern territory australia were examined using standard microthermometry laser raman microprobe and scanning electron microscopy decrepitated gases were analyzed in a mass spectrometer the relationship of fluid inclusions to alteration and mineralization was established by occurrence restricted to the alteration zones around the deposits and the presence in fluid inclusions of solid phases which also occur as megascopic phases in the alteration secondary halite saturated fluid inclusions in altered host rock quartz and in early hydrothermal quartz veins are believed to relate to hydrothermal alteration associated with ore deposition these inclusions are identical to primary inclusions in silicified and boron metasomatized kombolgie formation sandstone above the jabiluka 2 deposit durak et al 1983 and hence sample post kombolgie fluids the trapped fluid is saline and calcium rich ca 23 equiv wt cacl 2 and sulfate poor so super 2 4 0 001 m no gases were detected in the vapor phase of such inclusions and the median vapor disappearance temperature is 140 degrees c primary inclusions in postore dolomite veins and secondary inclusions in host rock and hydrothermal quartz sample postore hydrothermal fluid this fluid is hypersaline and also calcium rich typically 35 equiv wt cacl 2 and is saturated with as many as 11 solid phases including dolomite and iron rich chlorite vapor bubbles in these inclusions contain methane and minor n 2 and the median vapor disappearance temperature is 127 degrees c aromatic hydrocarbons detected by mass spectrometry are possibly related to this population the calcic brines are thought to have been terrestrial in origin and derived from the oxidized red bed sediments overlying the deposits macarthur basin ore deposition was a response either to reduction of the ore bearing fluid by direct interaction with graphite and ferrous iron in the wall rocks or by mixing with a methane and higher hydrocarbon bearing brine represented by postore fluid inclusions ore deposition and related hydrothermal alteration occurred between 200 degrees and 300 degrees c under a depth of cover of ca 2 km this temperature is consistent with independent temperature constraints and suggests an anomalous thermal gradient during ore formation