limited availability of sulfur promotes copper rich mineralization in hydrothermal pb zn veins a case study from the schwarzwald sw germany abstract mixing of compositionally contrasting fluids is widely accepted as the major ore forming process in unconformity related hydrothermal pb zn fluorite barite veins although the general process is relatively well understood the temporal evolution of such fluid systems which may result in distinct mineralogical changes of the ore and gangue minerals precipitating are insufficiently constrained one specific example is the occurrence of late stage siderite chalcopyrite gersdorffite mineralization in 28 hydrothermal veins of the schwarzwald sw germany post dating the major fluorite barite galena sphalerite phase which is very common in the whole area to investigate the underlying process for this late stage cu ni stage published fluid inclusion data have been complemented by detailed confocal raman micro spectroscopy of fluid inclusions petrographic observations and electron microprobe analyses petrography as well as mineral compositions of sphalerite gersdorffite pyrite arsenopyrite fahlore and galena record a gradual but significant influx of cu and ni into a prevailing pb zn hydrothermal system this influx caused a distinct shift towards lower fo2 and pb zn sb ag s in the hydrothermal system at the transition from the pb zn to the cu ni mineralization stage this transition in mineralogy and the related gradual change of the hydrothermal fluid can be explained by changes in the relative proportion of involved fluid components however the transition to the cu ni mineralization stage by fluid influx is significantly different compared to the common rapid fluid mixing from below which is thought to be responsible for the typical pb zn veins and probably records the gradual transition from long term stable deep fluid reservoirs with constant chemical compositions towards more shallow and perturbed fluid reservoirs during rifting and exhumation

multi stage ag bi co ni u and cu bi vein mineralization at wittichen schwarzwald sw germany geological setting ore mineralogy and fluid evolution the wittichen co ag bi u mining area schwarzwald ore district sw germany hosts several unconformity related vein type mineralizations within variscan leucogranite and permian to triassic redbeds the multistage mineralization formed at the intersection of two fault systems in the last 250 ma a permo triassic ore stage i with minor u bi quartz fluorite mineralization is followed by a jurassic to cretaceous ore stage ii with the main ag and co mineralization consisting of several generations of gangue minerals that host the sub stages of u bi bi ag ni as bi and co as bi important ore minerals are native elements co and ni arsenides and pitchblende sulphides are absent the miocene ore stage iii comprises barite with the cu bi sulfosalts emplectite wittichenite and aikinite and the sulphides anilite and djurleite besides native bi chalcopyrite sphalerite galena and tennantite the mineral forming fluid system changed from low salinity 5 wt nacl at high temperature around 300 c in permian to highly saline around 25 wt nacl cacl2 at lower temperatures 50 150 c in triassic to cretaceous times thermodynamic calculations and comparison with similar mineralizations worldwide show that the mesozoic ore forming fluid was alkaline with redox conditions above the hematite magnetite buffer we suggest that the precipitation mechanism for native elements pitchblende and arsenides is a decrease in ph during fluid mixing processes ree patterns in fluorite and the occurrence of bi in all stages suggest a granitic source of some ore forming elements whereas e g ag co and ni probably have been leached from the redbeds the greater importance of cu and isotope data indicates that the miocene ore stage iii is more influenced by fluids from the overlying redbeds and limestones than the earlier mineralization stages

mixing of metamorphic and surficial fluids during the uplift of the hercynian upper crust consequences for gold deposition a detailed geochemical study of fluids from representative quartz sealed faults hosting late hercynian gold concentrations shows that fluids percolating the mineralised faults had two main distinct reservoirs one was a quite shallow and the other rather deep seated both fluids have lost a great part of their original geochemical signature through interactions with host metamorphic formations early fluids present during the primary sealing of the faults by quartz are considered to have effectively equilibrated with the metamorphic pile and then predominantly flowed upwards along the faults they are characterised by ch4 co2 h2o ratios rather typical of fluids equilibrated with graphite and moderate to medium chlorinities with a high br cl ratio the striking feature of the gold bearing quartz is that gold is not synchronous within any quartz deposition and appears located in late microfractures and associated with pb bi sb sulphosalts and sulphides these late stages are characterised by fluids whose salinities decrease to very low values indicating their progressive dilution by waters of more surficial origin in the fault system the long lived activity of the fault favoured the connection between two distinct fluid reservoirs at a critical time during the basement uplift the fluids evolved through two main driving mechanisms which were responsible for the au deposition i decrease in temperature accompanying decompression from supra lithostatic to hydrostatic conditions which yielded in some instances volatile unmixing in the faulted systems ii mixing of the resulting fluids with waters entering the hydrological systems from shallower reservoirs in addition to dilution and fluid mixing which are favourable factors for decreasing the gold solubility the presence of microfractured sulphides could have enhanced gold precipitation through electrochemical processes d 2002 elsevier science b v all rights reserved

sources of basinal and mississippi valley type mineralizing brines mixing of evaporated seawater and halite dissolution brine abstract origins of basinal brines and mississippi valley type mvt mineralizing fluids have been separately attributed to evaporation of seawater or dissolution of halite although brines originating from the two processes are not mutually exclusive in basins this study shows that the na br cl br diagram cannot distinguish between evaporated seawater and halite dissolution fluid using the na deficit ca excess diagram which was previously proposed to characterize fluid rock interactions of basinal brines it is shown that most basinal brines including wt mineralizing fluids of the viburnum trend deposits were probably initially a mixture of halite dissolution fluid and evaporated seawater using the same diagram we suggest that the mineralizing brines of the gays river mvt deposit were derived from an aquifer of clastics underlying a thick succession of evaporites where halite dissolution fluid and evaporated seawater could have mixed

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

double vein ore bearing vs ore free structures in the xitian ore field south china implications for fluid evolution and mineral exploration abstract two types of spatially and temporally associated hydrothermal veins ore bearing and ore free occur as double vein structures in the xitian ore field south china here we investigated the genetic relationship material provenance fluid properties and prospecting significance of the co developed veins in the granite related fault controlled vein type xiangdong w goudanlan w chaling pb zn and xinggao fluorite deposits of the xitian ore field focusing on two common minerals quartz and zircon petrographic cl microthermometric and h o isotopic analyses of stage i and stage ii quartz in both the ore bearing and ore free veins of these deposits document two episodes of hydrothermal activity the first episode involved a high temperature up to 370 high salinity up to 28 nacl equiv high 18o 2 1 to 7 2 and high 2h 82 to 54 mean 68 n 13 fluid that corresponds to the main magmatic hydrothermal stage of the deposits and the second episode involved a low temperature down to 90 low salinity down to 1 nacl equiv low 18o 8 8 to 5 3 and low 2h 83 to 60 mean 73 n 6 fluid that represents an accessary mineralization stage variations in fluid inclusion types and compositions indicate that the processes of fluid mixing boiling cooling and degassing played important roles in mineralization and that magmatic fluid became less important than meteoric water along during the formation of ore free veins la icpms u pb dating reveals totally different age populations for these veins zircons from the ore bearing quartz veins yield older and more variable ages pre devonian 400 ma n 68 that are similar to that of the local basement sedimentary rocks whereas zircons from the ore free quartz veins yield younger and less variable ages triassic 250 200 ma n 31 and jurassic 170 140 ma n 13 that are identical to those of the host granite zircons in addition the ore free veins show lower temperatures salinities and total rees as recorded by quartz but greater alteration as reflected by cl and trace element features of hydrothermally altered zircons and wider vein size than the ore bearing veins we propose a mineral water separation model to explain the formation of the double vein structures in this model ore bearing veins and ore free veins formed in succession during faulting events ore bearing veins formed first in the smaller fractures and were the dominant sites of mineralization whereas the ore free veins served as dissipating passageways for residual water and silica in larger fractures we suggest that the mineral water separation model has good application prospects in mineral exploration and that zircons can be applied as an indicative mineral to differentiate the mineralization potential of different types of quartz veins

fluid transfers at a basement cover interface part ii large scale introduction of chlorine into the basement by mesozoic basinal brines significant fracture and porosity sealing characterizes the sedimentary cover basement interface in the northwestern margin of the aquitaine basin france dolomite and calcite and sometimes fluorite barite and quartz constitute most of the fracture fillings they contain primary inclusions of brines having chlorinities in the range of 3 3 to 5 5 mol cl kg solution with total homogenization temperatures in between 65 and 130 c for quartz and slightly lower for dolomite barite fluorite and calcite crush leach analyses indicate that brines are characterized by na k ratios of 5 to 40 na li ratios of 20 to 530 and cl br ratios of 200 to 1000 which are rather typical of deep basinal brines the fluid 18o signature is estimated to be 6 6 1 8 smow for a crystallization temperature of 100 20 c between 80 and 120 c and the d value is 30 10 smow the fluid source for the fracture filling mineral is interpreted as a deep sedimentary brine expelled during a period of maximum subsidence in the aquitaine basin which migrated along the sediment cover basement interface which is characterized by high permeabilities below the toarcian shales the sealing is likely to be linked to the mixing of the brines with dilute ascending hot waters these dilute waters infiltrated from emerged zones convected and heated at depth reaching temperatures of 100 c up to 150 c on the basis of cation geothermometry extensional activity of probable cretaceous age related to the gascogne gulf rifting could be considered as the most likely cause of a significant fluid migration event at the basement cover interface all along the margins of the french massif central these processes are large scale as shown by the similarities of mineral sequences fluid types and general features of most of the f ba pb zn deposits located at the basement sedimentary cover interface the mass transfer of cl linked to this stage is significant and accounts for the early introduction of large amounts of chlorine in the granitoid microporosity this probably explains the significant chlorine concentrations of the present day fluids recovered in the granitoid aquifer

the role of the kupferschiefer in the formation of hydrothermal base metal mineralization in the spessart ore district germany insight from detailed sulfur isotope studies the spessart district sw germany located at the southwestern margin of the permian kupferschiefer basin in central europe hosts abundant stratabound and structurally controlled base metal mineralization the mineralization styles identified are 1 stratabound cu pb zn ag ores in zechstein sedimentary rocks 2 structurally controlled cu as ag ores in zechstein sedimentary rocks 3 crosscutting co ni bi as and cu fe as veins 4 stratabound metasomatic fe mn carbonate ores in zechstein dolomite 5 barren barite veins and 6 fe mn as veins in permian rhyolites building on previous work that involved mineralogical textural and chemical characterization of the major mineralization types we have performed a comprehensive sulfur isotope study that applied both conventional and novel laser ablation multi collector inductively coupled plasma mass spectrometry techniques the 34s values of sulfide minerals from the different ore types are consistently negative and highly variable in the range between 44 5 and 3 9 whereas the 34s values of barite are all positive in the range between 4 7 and 18 9 remarkably stratabound and structurally controlled mineralization in zechstein sedimentary rocks has the least negative 34s values whereas vein type deposits have consistently more negative 34s values the observed pattern of sulfide 34s values can be best interpreted in terms of fluid mixing at the basement cover interface hydrothermal fluids originating from the crystalline basement migrated upward along subvertical fault zones and were periodically injected into groundwaters that were flowing in the post variscan sedimentary cover these groundwaters had interacted with the zechstein sedimentary rocks resulting in fluids characterized by elevated concentrations of reduced sulfur with negative 34s values and alkaline ph repeated mixing between both chemically contrasting fluids caused rapid and efficient precipitation of sulfide ore minerals in hydrothermal veins with highly variable but distinctly negative 34s values

the manganese and iron shuttle in a modern euxinic basin and implications for molybdenum cycling at euxinic ocean margins a meaningful application of mo as a paleo redox proxy requires an understanding of mo cycling in modern reducing environments stagnant euxinic basins such as the black sea are generally regarded as model systems for understanding euxinic systems during early earth history however drawing direct parallels between the black sea and open marine euxinic margins is somewhat complicated by differences in the seawater residence time between these two environments we report sediment and pore water mo u mn and fe data for a euxinic basin with a short seawater residence time the weakly restricted gotland deep in the baltic sea here prolonged periods of euxinia alternate with brief inflow events during which well oxygenated saline water penetrates into the basin during these inflow events dissolved mn and fe that has accumulated within the euxinic deep water can be oxidized and precipitated co variations of mo and u within the sediment suggest that these inflow and oxygenation events may favor mo accumulation in the sediment through adsorption to freshly oxidized mn and fe solid phases once mo is sequestered within the deeper euxinic water and sediments mo retention can be further facilitated by conversion to thiomolybdate species and interactions with organic matter and metal sulfides by comparing our data with those from previous studies where a mn and fe shuttle for mo has been demonstrated we identify two prerequisites for the occurrence of this mechanism first there must be a water column oxic anoxic redox boundary this provides a solubility contrast for mn and fe second the residence time of seawater in the system has to be short weeks to a few years the latter criterion can be met through regular inflow in weakly restricted basins or upwelling in oxygen minimum zones at open marine continental margins based on prior work we suggest that similar conditions to those currently represented by the gotland deep may have prevailed at euxinic ocean margins during the proterozoic a boundary between euxinic and oxic water masses overlying the continental shelf may have resulted in accelerated mo transport through the water column with mn and fe oxyhydr oxides we propose that this mechanism along with mo isotope fractionation during adsorption could contribute to the light mo isotope composition observed in open marine euxinic sediment facies of the proterozoic

late stage anhydrite gypsum siderite dolomite calcite assemblages record the transition from a deep to a shallow hydrothermal system in the schwarzwald mining district sw germany abstract the majority of hydrothermal vein systems of economic interest occur at relatively shallow crustal levels although many of them formed at significantly greater depths their present position is a consequence of uplift and erosion although many aspects of their formation are well constrained the temporal chemical evolution of such systems during uplift and erosion is still poorly understood these vein minerals comprise calcite dolomite ankerite siderite magnesite anhydrite and gypsum forming the last gangue assemblages in jurassic and tertiary sulphide fluorite quartz barite veins of the schwarzwald mining district sw germany mineral textures of samples from nine localities reveal that in these sequences mineral precipitation follows a recurring pattern early calcite is followed by anhydrite or gypsum siderite and or dolomite this succession may repeat up to three times in situ la icp ms u pb age dating of 15 carbonates from three subsequent generations of the late stage vein assemblage yield robust ages between 20 and 0 6 ma each mineral sequence forms in a distinctive period of about 2 5 ma these ages clearly relate these late stage mineral phases to the youngest geological episode of the schwarzwald which is associated with the cenozoic rhine graben rifting and basement uplift based on thermodynamic modelling the formation of the observed mineral assemblages required an deeply sourced mg fe and so4 rich fluid b which was episodically mixed with a shallow crustal hco3 rich fluid a as a consequence of fluid mixing concentrations of mg fe and so4 temporarily increased and initiated the formation of the observed sulphate carbonate mineral sequences this discontinuous large scale vertical fluid mixing was presumably directly related to episodes of active tectonics associated with the cenozoic strike slip regime of the upper rhine graben analogously episodic fluid mixing is a major key in the formation of older jurassic to early tertiary pb zn fluorite quartz barite assemblages in the same specific vein systems albeit involving different fluid compositions late stage hydrothermal 20 70 c vein assemblages reported in this study record the transition from deep 2 km to very shallow 0 1 km crustal conditions as a consequence of successive uplift increasing proportions of shallower and cooler 50 70 c fluids could take part in such mixing processes associated changes in the fluid composition caused the vein mineralogy to change from sulphide quartz fluorite barite to calcite anhydrite gypsum siderite dolomite as the system passively ascended closer to the surface

gangue mineral 87 sr 86 sr ratios and the origin of mississippi valley type mineralization the 87 sr 86 sr ratio measurements in mississippi valley type gangue minerals and host marine carbonates ranging in age from upper cambrian to mississippian show that in northwestern ohio where the mineralization is sparse the minerals precipitated from fluids in local isotopic equilibrium with the host carbonates in which the minerals were emplaced in contrast most gangue minerals from districts of major mineralization in illinois kentucky virginia and tennessee contain strontium with higher 87 sr 86 sr ratios than the carbonate hosts and appear to have crystallized from fluids containing strontium from silicate minerals in the sedimentary succession no evidence has been found for a magmatie component in the ore fluid strontium data from elmwood tennessee show that the early ore fluids like those of northwestern ohio were in isotopic equilibrium with the host carbonates but that they were mixed with and displaced by introduced fluids containing more radiogenic strontium these findings are consistent with the two fluid mixing model for the mississippi valley mineralization where a fluid indigenous to the host carbonates and containing reduced sulfur was mixed with introduced fluids analogous to metal bearing and low sulfide oil field brines with an extensive history of chemical exchange with clays and other silicate minerals in the sedimentary succession

metal rich fluid inclusions provide new insights into unconformity related u deposits athabasca basin and basement canada the paleoproterozoic athabasca basin canada hosts numerous giant unconformity related uranium deposits the scope of this study is to establish the pressure temperature and composition p t x conditions of the brines that circulated at the base of the athabasca basin and in its crystalline basement before during and after uo2 deposition these brines are commonly sampled as fluid inclusions in quartz and dolomite cementing veins and breccias associated with alteration and u mineralization microthermometry and laser ablation inductively coupled plasma mass spectrometry la icp ms data from five deposits rabbit lake p patch eagle point millennium and shea creek complement previously published data for the mcarthur river deposit in all of the deposits investigated fluid inclusion salinity is between 25 and 40 wt nacl equiv with compositions displaying a continuum between a nacl rich brine end member cl na ca mg k and a cacl2 rich brine end member cl ca mg na k the cacl2 rich brine has the highest salinity and shows evidence for halite saturation at the time of trapping the continuum of compositions between the nacl rich brine and the cacl2 rich brine end members combined with p t reconstructions suggest anisothermal mixing of the two brines nacl rich brine 180 30 c and 800 400 bars cacl2 rich brine 120 30 c and 600 300 bars that occurred under fluctuating pressure conditions hydrostatic to supra hydrostatic however because the two brines were u bearing and therefore oxidized brine mixing was probably not the driving force for uo2 deposition several scenarios are put forward to account for the cl na ca mg k composition of the brines involving combinations of seawater evaporation halite dissolution mixing with a halite dissolution brine mg ca exchange by dolomitization na ca exchange by albitization of plagioclase na k exchange by albitization of k feldspar and mg loss by mg rich alteration finally the metal concentrations in the nacl rich and cacl2 rich brines are among the highest recorded compared to present day sedimentary formation waters and fluid inclusions from basin hosted base metal deposits up to 600 ppm u 3000 ppm mn 4000 ppm zn 6000 ppm cu 8000 ppm pb and 10 000 ppm fe the cacl2 rich brine carries up to one order of magnitude more metal than the nacl rich brine though the exact origin of major cations and metals of the two brines remains uncertain their contrasting compositions indicate that the two brines had distinct flow paths and fluid rock interactions large scale circulation of the brines in the athabasca basin and basement was therefore a key parameter for metal mobility including u and formation of unconformity related u deposits

tracing element sources of hydrothermal mineral deposits ree and y distribution and sr nd pb isotopes in fluorite from mvt deposits in the pennine orefield england fluorite from mississippi valley type mvt deposits in the south pennine orefield england displays significantly different distributions of rare earths and yttrium rey compared to fluorite from similar mvt deposits in the north pennine orefield samples from the south pennine orefield display negative ce and positive gd and y anomalies but lack any eu anomaly indicating that the rey were mobilized from relatively pure marine sedimentary carbonates in marked contrast fluorite from the north pennine orefield lacks any ce and gd anomalies but shows a pronounced positive eu anomaly suggesting that the rey were provided by different source rock s that the mineralizing hydrothermal fluid had experienced higher temperatures prior to fluorite precipitation and that it was derived from deeper crustal levels in the north compared to the south the isotopic composition of sr in blue john fluorite from the south pennine orefield suggests that sr was mobilized from lower carboniferous tournaisian limestones whereas pb isotopes suggest that in contrast to rey and sr pb was derived from aluminosilicate rocks neither nd nor sr or pb isotopes can be used to radiometrically date the formation of blue john fluorite all isotope systems studied indicate that the limestone host rock of this fluorite mineralization did not contribute to the trace element budget of the hydrothermal fluid our results show that different solutes in a natural water hydrothermal fluid groundwater etc may be derived from different sources and that the study of a small set of elements or isotope ratios may not provide full insight into the genesis or history of a mineralization or a hydrothermal fluid our data provide evidence for the uncoupling of sr nd and pb during fluid rock interaction and fluid migration and show that the use of plots such as 87sr 86sr vs end to learn about mixing relationships as is commonly done in igneous geochemistry is unreliable when applied to natural waters and their precipitates

hydrothermal fluids during mesozoic reactivation of the st lawrence rift system canada c o sr and pb isotopic characterization calcite veins with accessory galena sphalerite barite and fluorite are abundant within the ottawa bonnechere and the charlevoix saguenay failed arms of the st lawrence rift system which developed during early paleozoic times within gneisses of the grenville province of canada the mineral assemblages paragenesis and precipitation temperatures of the veins resemble the mississippi valley deposits crosscutting relationships with carbonate rocks of the st lawrence lowlands and deformed carbonate rock slivers of the charlevoix astrobleme show that the ottawa graben and saguenay graben veins are younger than mid ordovician or post devonian respectively 18o and 13c values for vein calcite are positively correlated and range from 11 to 24 and 9 to 3 respectively 87sr86sr in calcite and barite range from 0 7129 to 0 7081 the fluids that precipitated calcite were part of a hydrothermal system dominated by meteoric water enriched in 18o by exchange with silicate minerals and deep seated carbon either from mantle outgassing deep seated brines of the canadian shield or from oxidation of reduced carbon in high grade metamorphic rocks veins cutting marbles of the grenville supergroup have lower 87sr86sr and higher 18o and 13c values than those hosted in quartzofeldspathic gneisses of the grenville province showing that the fluids were modified by interaction at depth with the marbles stable and sr isotope compositions are also correlated with layb ratios in calcite supporting the fact that the veins formed within similar hydrothermal systems in both the ottawa and saguenay grabens the pb isotopic compositions of vein galena are radiogenic 206pb204pb 18 0 19 7 207pb204pb 15 5 15 7 208pb204pb 37 9 41 0 and positively correlated in conventional pb pb diagrams pb isotope and ree data strongly suggest that the fluids leached selectively at the mineral scale gneisses of the grenville province the basinal fluids within the shelf sequence of the western appalachians had 208pb204pb ratios in the lower paleozoic significantly lower than those of vein galena this excludes the basin brine model of formation for the vein deposits like suggested for the mississippi valley deposits the veins rather formed in the mesozoic in response to the rifting of northeastern north america and the reactivation of the st lawrence rift

the rand granite in the southern schwarzwald and its geodynamic significance in the variscan belt of sw germany the rand granite is a heterogeneous metamorphosed granitoid rock complex with numerous wallrock inclusions situated in the moldanubian zone at the southern margin of the central schwarzwald gneiss complex it is a largely mylonitized elongated body and is thrust over the badenweiler lenzkirch zone forming a nappe with shear zones along its northern and southern boundaries it comprises meta granites meta trondhjemites and biotite augen gneisses derived from monzogranites to granodiorites mineral behaviour indicates that the magmatic body has been deformed under upper greenschist facies conditions nappe thrusting which also affected the south schwarzwald gneiss complex occurred in visean time during high temperature low pressure metamorphism kinematic indicators in the mylonites document e to ese directed nappe transport highly transpressive relative to the trend of the nappe boundaries and the foliation the trondhjemites formed at 351 5 4 ma predating the variscan ht metamorphism they have initial end values of 6 6 to 6 7 and relatively low initial 87sr 86sr ratios 0 7042 to 0 7063 indicating a predominant mantle origin the granites and protoliths of the biotite augen gneisses probably crystallised between 436 and 377 ma suggested by u pb zircon model ages they are different from the trondhjemites with low initial end values 4 7 to 3 3 and higher initial 87sr 86sr ratios 0 7068 0 7077 indicating that large part of the rand granite originated from anatexis of continental crust internal structure of zircons from the rand granite reveals mixing of magmas derived from both mantle and crust sources these new data support an interpretation that the rand granite developed along an active continental margin and therefore represents a possible root of a variscan magmatic arc

chlorine isotopes in fluid inclusions determination of the origins of salinity in magmatic fluids abstract thermal ionisation mass spectrometry tims of the cs 2 cl ion has been used to determine the 37 cl value of paleofluids trapped in fluid inclusions modifications to the existing published method have lowered the precision by a factor of 2 0 09 1 thereby allowing real differences to be measured with greater certainty the method has been applied to determine 37 cl of two sets of magmatic fluids trapped in fluid inclusions samples were studied from the capitan pluton in new mexico and the sw england batholith both of which have high temperature fluids whose d and 18 o signatures are distinctly magmatic relative to standard mean ocean chloride smoc the 37 cl values of the capitan samples cluster around 0 whereas those from sw england cluster around 1 8 the br cl ratios of the capitan fluid inclusions are low indicative of halite dissolution and are comparable to local high salinity waters derived from leaching permian evaporites the br cl ratios of the sw england fluid inclusions are much higher and within the range of values normally considered to be magmatic we conclude that the 37 cl value of the capitan magmatic fluids confirms the evidence from br cl ratios that cl was derived from an evaporite source whereas the 37 cl value of the sw england fluids appears to be more representative of a deep magmatic source

origin of the okrouhla radouň episyenite hosted uranium deposit bohemian massif czech republic fluid inclusion and stable isotope constraints the okrouhla radou shear zone hosted uranium deposit is developed along the contact of variscan granites and high grade metasedimentary rocks of the moldanubian zone of the bohemian massif the pre ore pervasive alteration of wall rocks is characterized by chloritization of mafic minerals followed by albitization of feldspars and dissolution of quartz giving rise to episyenites the subsequent fluid circulation led to precipitation of disseminated uraninite and coffinite and later on post ore quartz and carbonate mineralization containing base metal sulfides the fluid inclusion and stable isotope data suggest low homogenization temperatures 50 140 c during pre ore albitization and post ore carbonatization up to 230 c during pre ore chloritization variable fluid salinities 0 25 wt nacl eq low fluid 18o values 10 to 2 v smow low fluid 13c values 9 to 15 v pdb and highly variable ionic composition of the aqueous fluids especially na ca br cl i cl so4 cl no3 cl ratios the available data suggest participation of three fluid endmembers of primarily surficial origin during alteration and mineralization at the deposit 1 local meteoric water 2 na ca cl basinal brines or shield brines 3 so4 no3 cl h co3 playa like fluids pre ore albitization was caused by circulation of alkaline oxidized and na rich playa fluids whereas basinal shield brines and meteoric water were more important during the post ore stage of alteration

major element compositions of fluid inclusions from hydrothermal vein type deposits record eroded sedimentary units in the schwarzwald district sw germany mixing of sedimentary formation fluids with basement derived brines is an important mechanism for the formation of hydrothermal veins we focus on the sources of the sediment derived fluid component in ore forming processes and present a comprehensive fluid inclusion study on 84 jurassic hydrothermal veins from the schwarzwald mining district sw germany our data derive from about 2300 fluid inclusions and reveal differences in the average fluid composition between the northern central and southern schwarzwald fluids from the northern and southern schwarzwald are characterised by high salinities 18 26 wt nacl cacl2 low ca ca na mole ratios 0 1 0 4 and variable cl br mass ratios 30 1140 in contrast fluids from the central schwarzwald show even higher salinities 23 27 wt nacl cacl2 higher ca ca na mole ratios 0 2 0 9 and less variable cl br mass ratios 40 130 these fluid compositions correlate with the nature and thickness of the now eroded sedimentary cover rocks compared to the northern and the southern schwarzwald where halite precipitation occurred during the middle triassic the sedimentary basin in the central schwarzwald was relatively shallow at this time and no halite was precipitated accordingly cl br ratios of fluids from the central schwarzwald provide no evidence for the reaction of a sedimentary brine with halite whereas those from the northern and southern schwarzwald do instead elevated ca ca na high so4 contents and relatively low cl br imply the presence of a gypsum dissolution brine during vein formation in the central schwarzwald which agrees with the reconstructed regional triassic geology hence the information archived in fluid inclusions from hydrothermal veins in the crystalline basement has the potential for reconstructing sedimentary rocks in the former overburden

polyphase enrichment and redistribution processes in silver rich mineral associations of the hydrothermal fluorite barite ag cu clara deposit sw germany the silver copper sulfide mineralization associated with the fluorite barite vein system at the clara deposit in sw germany shows large scale vertical zoning low to moderate silver contents prevail in the upper 350 m whereas high silver contents occur in the subsequent 450 m of the currently known vein system this change in ag tenor is related to conspicuous mineralogical changes with depth a detailed petrographic and fluid inclusion study identifies evidence for five subsequent hydrothermal and one alteration stage all contributing to mineralogical diversity the vertical ag zoning however is attributed only to the first of these stages during this first stage increasing oxidation of ascending hydrothermal fluids 90 160 c 24 2 26 7 wt nacl cacl2 led to the formation of high ag tetrahedrite tennantite in the lower parts and basically ag free enargite in the upper parts of the vein system the subsequent hydrothermal stage led to significant mineralogical changes but inherited the pre existing ag zonation in this second hydrothermal stage which was related to fluids similar in composition to those of the first stage 70 125 c 23 1 26 5 wt nacl cacl2 dissolution of high ag tetrahedrite tennantite resulted in the formation of complex ag sulfosalts together with moderately ag bearing tetrahedrite tennantite and chalcopyrite the first two stages were formed by fluid mixing of a sedimentary and a hot basement fluid the influx of fluids with high ag bi and pb activity during stage 3 and 5 resulted in the local replacement of earlier ag sulfosalts by galena and ag bi sulfosalts the fourth stage is marked by partial dissolution of sulfides and sulfosalts by a late hot undiluted basement fluid 250 c 18 7 20 9 wt nacl cacl2 precipitating fluorite barite and quartz finally supergene alteration lead to the dissolution of silver bearing phases and the precipitation of acanthite and native silver the study illustrates how metal tenor and mineralogy are decoupled in vertically extensive polyphase hydrothermal vein systems this may be pertinent to similarly zoned polymetallic vein systems

fluid mixing and recycling during pyrenean thrusting evidence from fluid inclusion halogen ratios abstract syntectonic fluids have been sampled through fluid inclusion microthermometry and crush leach analyses cations and halogens from a 50 km n s transect through the central southern pyrenees the fluid inclusions are contained in syntectonic quartz veins in triassic redbeds cretaceous carbonates and hercynian basement rocks with some calcite and dolomite data from limestones and evaporites in more external parts of the belt the main datasets come from 1 alpine shear zones cutting the neouvielle granodiorite in the hercynian axial zone at the north end of the transect 2 an imbricate zone beneath the alpine gavarnie thrust at the pic de port vieux 3 several localities in the footwall and hangingwall of the gavarnie thrust on the southern margin of the axial zone the inclusion fluids generally decrease in salinity from 27 35 at the northern end of the transect to 7 22 on the southern margin of the axial zone the majority of the inclusions have cl br ratios lower than seawater and are interpreted as relict fluids after seawater evaporation and halite precipitation in the upper trias this interpretation is supported by cl br na systematics which are consistent with a change from halite to halite sylvite precipitation with progressive evaporation fluids in the basement shear zones are interpreted to have essentially the same evaporitic origin as those still contained in sedimentary formations although it is possible that final concentration of brines in the neouvielle massif involved retrograde hydration reactions with removal of water by precipitation of hydrous minerals the fluids are also very similar in salinity and halogen chemistry to those found in veins associated with mesozoic pb zn f deposits which predate the thrusting the lower salinities seen at the southern margin of the axial zone are interpreted to reflect mixing of the brines with a higher level fluid connate or meteoric water circulating within the mesozoic carbonates of the higher thrust sheets at one locality where triassic evaporites are still present high cl br ratios at relatively low salinities are present in inclusions within the underlying triassic redbeds but low cl br ratios at higher salinities are seen lower in the sequence this is consistent with dissolution of halite by a dilute fluid but with limited penetration downwards we suggest that the fluid history of the pyrenees evolved through a series of stages 1 upper triassic evaporite formation with sinking of brines into underlying redbeds and fractured basement rocks 2 circulation of brines with formation of pb zn deposits along faults at some time between the triassic and the upper cretaceous 3 renewed extension with erosion of triassic rocks in many areas and further drawing down of triassic brines into the basement 4 deposition of u cretaceous and palaeocene carbonates containing connate waters of marine origin 5 formation of the pyrenean thrust belt with overpressuring and expulsion of the brines along shear zones and faults 6 creation of topography with a high level circulation system in the mesozoic thrust sheets driven largely by topography at the southern margin of the axial zone there was limited mixing of the deeper overpressured brines with these more dilute hydrostatically pressured fluids an important point is that because of their density hypersaline brines are difficult to expel from the upper crust and may be involved in a succession of alteration and mineralisation events in the same general area over hundreds of millions of years

the relationship of strain and preferred orientation of phyllosilicate grains in rocks a review abstract the calculation of strain from the preferred orientation of platy phyllosilicate grains taking strain to be homogeneous is surprisingly often successful from a pragmatic point of view although numerous theoretical objections to this procedure can be and have been raised for the calculation to succeed the original distribution of mica or clay mineral grains must be known or assumed the usual assumption that the starting distribution was random and therefore nearly uniform implies that the strain history of pelitic sediments is taken to start when the watery sediment was last stirred by waves or bioturbation or if it was laid down in still anoxic waters from the moment of first deposition it therefore includes compaction as part of the strain history which is usually neglected by structural geologists originally random distribution of clay flake orientations has been observed in recently deposited sediments in many instances and has been theoretically explained in various ways exceptions probably exist but their frequency has not been estimated biologically disturbed sediments may be brought nearer to a state of random orientation of clay flakes than they were at deposition with the exception of whole beds or concretions in which pores are early filled with cement mudrocks are almost always compacted by the weight of later deposits the strain so induced is axially symmetric about the vertical and thus about the pole of the bedding planes compaction acts on soft unconsolidated rocks but may continue with increasing overburden on rocks strengthened by cementation and by increasing interlocking of grains tectonic deformation may start early before the rock is fully compacted or it may begin only much later and the mechanisms of deformation increase in complexity with the increasing temperature and hydrostatic stress of deeper burial up to a certain level of mild metamorphism however phyllosilicate grains seem to be rather permanent if not as mineral species then at least by preservation of their constituent sheets of silica tetrahedra given this permanence the mechanisms of rock deformation whether intergranular slip cataclasis or dissolution and reprecipitation and various intragranular processes in the non phyllosilicate matrix hardly matter as far as the recording of strain is concerned even a certain amount of stress solution at especially heavily loaded points of the phyllosilicate grains themselves does not destroy their value as strain markers as long as the dissolved material is disposed of mainly by crystallographically continuous overgrowth on existing grains the same holds for local dissolution of phyllosilicates in portions of old grains that have become thermodynamically unstable by bending widespread irregular or random nucleation and growth of newly nucleated phyllosilicate grains at intermediate or high grades of metamorphism can reduce the reliability of the strain record and so can domainal structure of the deformed rock if both the volume fraction of phyllosilicate grains and the intensity of total strain differ sharply from one domain to another if distinct domains are not equant and have themselves a strong preferred orientation of shape nevertheless rocks containing an anastomosing network of zones rich in phyllosilicate grains as slates and other deformed mudrocks commonly do have in many cases been found to have average preferred orientations of mica or chlorite which if used to estimate the strain give results similar to those obtained from independent strain markers in the same rocks thus the most significant verification of the usefulness of strain estimates by measurement of preferred orientation is the mutual confirmation with independently determined strain the limit to such verification is the rarity of strain markers so that the coexistence of two independent ones is exceptionally rare for this reason however it is important to make full use of the orientation of phyllosilicate grains where they are available the alternative to have no strain measurements at all causes structural geologists to miss potential information

quartz veins with associated sb pb ag au mineralization in the schwarzwald sw germany a record of metamorphic cooling tectonic rifting and element remobilization processes in the variscan belt a combination of textural observations from 38 permian sb pb ag au bearing quartz veins in the schwarzwald sw germany with isotopic fluid inclusion and geochemical data allows to refine genetic models for this common type of mineralization to understand the origin of mineralogical diversity and the correlation with large scale tectonic events textures record four main mineralization stages i fe as sb au ii pb zn cu iii pb sb and iv ag sb stage i sulfides dominated by pyrite and arsenopyrite formed due to cooling of low salinity metamorphic fluids during the permian with maximum homogenization temperatures of 400 c invisible gold in arsenopyrite pyrite marcasite and stibnite was remobilized and locally precipitated as electrum at the end of stage i minerals of stages ii and iii comprise a rich diversity of sb bearing sulfosalts including e g bournonite zinkenite and jamesonite this assemblage formed during jurassic times due to mixing of high salinity mid and upper crustal fluids up to 27 wt nacl cacl2 with homogenization temperatures between 50 and 250 c stage iii is marked by a rich variety of pb sb sulfosalts its local abundance is directly related to the presence of stage i mineralization and its extent of remobilization during a significant influx of pb in the jurassic cretaceous the formation of the upper rhine graben during the tertiary reactivated especially ne sw oriented veins percolating ag rich fluids reacted with earlier stage iii pb sb sulfosalts forming ag rich minerals stage iv such as miargyrite pyrargyrite and stephanite the transition from metamorphic fluids to basinal saline e g pb bearing brines over hundreds of millions of years as is shown in this study and present in other variscan occurrences indicates a possibly typical poly stage characteristic of sb deposits worldwide which has however not been investigated in detail so far

trace and minor element variations and sulfur isotopes in crystalline and colloform zns incorporation mechanisms and implications for their genesis abstract various models have been proposed to explain the formation mechanism of colloform sphalerite but the origin is still under debate in order to decipher influences on trace element incorporation and sulfur isotope composition crystalline and colloform sphalerite from the carbonate hosted mississippi valley type mvt deposit near wiesloch sw germany were investigated and compared to sphalerite samples from 52 hydrothermal vein type deposits in the schwarzwald ore district sw germany to study the influence of different host rocks formation mechanisms and fluid origin on trace element incorporation trace and minor element incorporation in sphalerite shows some correlation to their host rock and or origin of fluid gangue paragenetic minerals and precipitation mechanisms e g diagenetic processes fluid cooling or fluid mixing furthermore crystalline sphalerite is generally enriched in elements like cd cu sb and ag compared to colloform sphalerite that mainly incorporates elements like as pb and tl in addition sulfur isotopes are characterized by positive values for crystalline and strongly negative values for colloform sphalerite the combination of trace element contents typical minerals associated with colloform sphalerite from wiesloch sulfur isotopes and thermodynamic considerations helped to evaluate the involvement of sulfate reducing bacteria in water filled karst cavities sulfate reducing bacteria cause a sulfide rich environment that leads in case of a metal rich fluid supply to a sudden oversaturation of the fluid with respect to galena sphalerite and pyrite this however exactly coincides with the observed crystallization sequence of samples involving colloform sphalerite from the wiesloch mvt deposit

major and trace element compositions including ree of mineral thermal mine and surface waters in sw germany and implications for water rock interaction abstract the near surface water cycle in a geologically complex area comprises very different sources including meteoric metamorphic and magmatic ones fluids from these sources can react with sedimentary magmatic and or metamorphic rocks at various depths the current study reports a large number of major minor and trace element analyses of meteoric mineral thermal and mine waters from a geologically well known and variable area of about 200 150 km in sw germany the geology of this area comprises a variscan granitic and gneissic basement overlain in parts by triassic and jurassic shales sandstones and limestones in both the basement and the sedimentary rocks hydrothermal mineralization occurs including pb cu as zn u co and many others which were mined in former times mineral waters thermal waters and meteoric waters flowing through abandoned mines mine waters are distributed throughout the area although the mine waters concentrate in and around the schwarzwald the present analyses show that the major element composition of a particular water is determined by the type of surrounding rock e g crystalline or sedimentary rocks and the depth from which the water originates for waters from crystalline rocks it is the origin of the water that determines whether the sample is na cl dominant deeper origin or ca hco3 dominant shallow origin in contrast compositions of waters from sedimentary rocks are determined by the availability of easily soluble minerals like calcite ca hco3 dominant halite na cl dominant or gypsum ca so4 dominant major element data alone cannot therefore be used to trace the origin of a water however the combination of major element composition with trace element data can provide further information with respect to flow paths and fluid rock interaction processes accordingly trace element analyses showed that ce anomalies can be used as an indicator for the origin of a water whereas surface waters have negative or strongly negative ce anomalies waters originating from greater depths show no or only weak negative ce anomalies eu anomalies can be used to differentiate between host rocks waters from gneisses display positive eu anomalies whereas waters from granites have negative ones waters from sedimentary rocks do not display any eu anomalies rb and cs can also be indicators for the rock with which the fluid interacted rb and cs correlate positively in most waters with rb cs ratios of 2 which suggests that these waters are in equilibrium with the clay minerals in the rocks rb cs ratios 5 indicate reaction of a water with existing clay minerals whereas rb cs ratios the chemical compositions of carbonate precipitates from thermal waters indicate that rare earth elements rees rb and cs concentrations in the minerals are controlled by the incorporation of clay particles that adsorb these elements

chemical evolution of ore forming brines basement leaching metal provenance and the redox link between barren and ore bearing hydrothermal veins a case study from the schwarzwald mining district in sw germany abstract six mineralogically exemplary barren and mineralized hydrothermal veins with pb and zn ores of jurassic cretaceous and cenozoic age in the schwarzwald mining district sw germany were chosen to shed light on the origin of their mineralogical diversity the selection of the veins was guided by the fact that they represent the largest number of veins in the region are very well known mineralogically and geochemically and they provide nice examples of barren and mineralized veins of similar age fluid inclusion data from the individual veins overlap implying their diverse mineralogy is not caused by different fluid compositions participating during fluid mixing la icpms data of single fluid inclusions indicate no systematic variations in major elements but significant changes in fluid mixing ratios which caused variable trace element concentrations of different fluid inclusion assemblages in one sample we suggest that different ore gangue assemblages can be produced by mixing of identical fluid endmembers but variable mixing ratios la icpms analyses of single fluid inclusions in barren and mineralized veins record similar base metal and sulfur concentrations hence sulfide mineralization in the veins appears not to be controlled by metal solubility thermodynamic modeling based on the fluid data indicates that the presence of a reducing phase during fluid mixing is required for sulfide mineralization to precipitate la icpms trace element analyses of feldspars biotites chlorites and clay minerals in granites and paragneisses which are the source of the metal content in the ore forming fluids demonstrate that the dominant provenance for pb zn as sb ba tl mo fe and mn are probably paragneisses while co cu and ni are probably sourced from s type granite a rough quantification indicates that

age and genesis of polymetallic veins in the freiberg district erzgebirge germany constraints from radiogenic isotopes the freiberg mining district in the erzgebirge hosts three principal types of polymetallic veins these are 1 the quartz bearing polymetallic sulfide type 2 the carbonate bearing polymetallic sulfide type and 3 the barite fluorite sulfide type we investigated the genesis of each vein type using rb sr sphalerite geochronology sm nd fluorite geochronology and pb sr and nd isotope systematics of ore and gangue minerals field relationships and the rb sr and pb isotope systematics of sulfides from quartz bearing polymetallic sulfide veins and carbonate bearing polymetallic sulfide veins confirm their close genetic affiliation and yield a combined rb sr errorchron age of 276 16 ma the high mean squared weighted deviation mswd value of 42 on the regression is considered to reflect initial isotopic heterogeneity which is probably related to fluid rock interaction during the hydrothermal mineralization process although some sphalerites from barite fluorite sulfide veins have strongly disturbed rb sr isotope systematics six sphalerites and one co genetic fahlore yield a robust isochron age of 121 3 4 2 ma with an mswd of 2 9 this age is supported by a fluorite sm nd isochron age of 101 18 ma mswd 1 3 the new ages and radiogenic isotope data place robust constraints on the long held hypothesis that veins in the freiberg district formed during two hydrothermal events the lower permian age of first stage quartz bearing polymetallic sulfide veins and carbonate bearing polymetallic sulfide veins coincides with post variscan crustal reorganization and rotliegend volcanism the mid cretaceous age of second stage barite fluorite sulfide veins coincides with opening of the north atlantic ocean during the break up of pangea

zinc isotope variation in hydrothermal systems preliminary evidence from the irish midlands ore field little is known about the range or controls on the zinc isotope composition of terrestrial materials and no systematic studies have been carried out on ore forming systems we have obtained zinc isotope data from 19 sphalerite samples formed over a range of well constrained precipitation conditions from the irish zn pb ore field the results reveal variation in 66zn where 66zn 66zn 64zn sample 66zn 64zn standard 1 1000 from 0 17 to 1 33 per mil relative to the lyon jmc 3 0749l zinc standard this variation is significant compared to the external reproducibility 0 12 2 and the data show very good mass dependency with 67zn and 68zn values thus natural variations in the zinc isotope composition of these ore minerals can be resolved our results span the entire range of 66zn values measured on terrestrial geologic samples to date the data suggest that variations in the primary source rock composition or precipitation temperature are unlikely to be important controls on the zinc isotope composition of sphalerite in the ore field we suggest that the variation is most likely due to a kinetic fractionation involving the preferential incorporation of light zinc isotopes in sphalerite precipitated rapidly under disequilibrium conditions however we cannot rule out the possibility of mixing of zinc derived from two isotopically distinct sources the significant variation in zinc isotope compositions we have observed in the irish ore field confirms that such fractionations can provide new insights into mineralizing processes in the earth s crust

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

petrofabric and dielectric anisotropy in rock there is a systematic relationship between anisotropy in the fabric of rocks and anisotropy in their dielectric properties although the relationship is difficult to express in any quantitative sense in general the dielectric constant k the dielectric loss k and the real conductivity are a maximum when measured along the lineation axis l of rock and a minimum when measured along the foliation normal f in this study rocks were measured both vacuum dried and with varying degrees of water present the anisotropy of wet rocks is greater than when vacuum dried due presumably to anisotropic distribution of water parallel to the petrofabric the effects of water however can be eliminated by means of measurements in vacuum or more simply by heat drying the sample and subsequent impregnation of the rock with a hydrophobic low loss dielectric material paraffin wax this is particularly significant since it greatly reduces the cost and time involved in this type of study dielectric anisotropy

the evaporation path of seawater and the coprecipitation of br and k with halite brines and salt were sampled at the morton bahamas solar salt production facility on great inagua island in the bahamas the brines were analyzed by ion chromatography to define more precisely than heretofore the evaporation path of seawater to the end of the halite facies at inagua calcium carbonate begins to precipitate at a brine concentration factor of 1 8 times that of seawater gypsum begins to precipitate at a brine concentration of 3 8 times seawater and halite at a concentration factor of 10 6 three of the most concentrated brines from inagua 40 times seawater were evaporated further in the laboratory magnesium sulfate first precipitated at brine concentrations about 70 times those of seawater and potassium bearing phases began to precipitate for these brines at concentrations greater than 90 times those of seawater the distribution of coefficients of br and k between brines and halite were determined by combining analytical data for the inagua brines with measurements of the br and k content of halites from inagua and of halite which had precipitated from inagua brines during storage the observed average value of dbr is 0 032 in good agreement with some of the previous measurements the measured values of dk are highly variable 0 001 to 0 021 dk for halite precipitated early in the halite facies is in the vicinity of 0 015

formation of u rich mineralizing fluids through basinal brine migration within basement hosted shear zones a large scale study of the fluid chemistry around the unconformity related cigar lake u deposit saskatchewan canada abstract the evolution of basinal brines through percolation into basement rocks is studied in the paleo to mesoproterozoic athabasca basin and its underlying basement this specific geological context includes the evolution of a nacl rich basinal brine to a u mineralizing cacl2 rich brine that is of particular importance for the understanding of the formation of giant u deposits the objective of this study is to determine the physico chemical parameters p t x of the basinal brines and their changes both within the athabasca group sandstones and the underlying basement lithologies on the scale of several km around the world class unconformity related cigar lake u deposit particularly this study focuses on the basement hosted fault systems that are considered to be the main fluid flow pathways a comprehensive study including microthermometry raman spectroscopy and la icp ms analyses was carried out on fluid inclusions as was a semi quantitative estimation of the microfracture paleoporosity based on the surface density of fluid inclusion planes initial nacl rich brines were trapped during early diagenesis c a 1 7 1 65 ga in dickite rich sandstones under a three to seven kilometers thick sedimentary cover at around 90 to 150 c under hydrostatic pressure or at 120 210 c assuming lithostatic conditions at the time of u deposits formation ca 1 46 1 29 ga these brines percolated through the entire basement but preferentially within the damage zones of some graphite rich faults formed during the ca 1 8 ga trans hudson orogeny and active during the subsequent retrograde metamorphism and exhumation ca 1 8 1 72 ga the circulation of the basinal brines into these structures was enhanced and structurally controlled by the microfracture network inherited from earlier brittle reactivation during basement uplift the resulting high microfracture paleoporosity in the vicinity of some but not all of these structures favored intense interaction between the brines and basement rocks that induced the formation of illite sudoite alteration haloes in the basement the percolating brines scavenged mn k ba sr and especially u and evolved from the original nacl dominant composition toward a higher salinity cacl2 rich composition the resulting u bearing brine mixed with the unmodified diagenetic nacl rich brine in above and all along the reactivated faults either during thermal convection in isobaric settings and higher temperatures 110 200 c or through episodic tectonic reactivation in isothermal settings through episodic pressure fluctuation in direct vicinity of the u deposits the interactions between the brines and the basement rocks were the strongest which is marked by the highest intensity of alteration of the host rocks thus the formation of ore forming fluids resulted from the interaction between nacl rich basinal brines and highly microfractured basement rocks this study reinforces the hypothesis that interaction with basement rocks enhanced by strong fluid flow in cataclastic zones can significantly modify the physico chemical characteristics of basin derived brines leading to the formation of mineralizing fluids and the genesis of giant ore deposits such as the unconformity related u deposits

red bed and basement sourced fluids recorded in hydrothermal mn fe as veins sailauf germany a la icpms fluid inclusion study the hydrothermal mn fe as vein mineralization at sailauf germany hosts a complex sequence of oxide and carbonate minerals that record a protracted fluid history the mineralization is related to a major unconformity that separates permian zechstein sedimentary rocks from underlying variscan crystalline basement the hydrothermal veins contain two principal mineralization stages which are mn oxides associated with calcite and hematite associated with mn calcite the fluid evolution of the hydrothermal system has been reconstructed from fluid inclusion petrography microthermometry and la icpms microanalysis coupled with stable isotope geochemistry of carbonate and oxide minerals the fluid inclusions are high salinity sodic calcic brines and the bulk fluid properties show no major differences between the mn oxide and the hematite stage la icpms analysis of major and trace elements demonstrates that the mineralization formed from chemically distinct fluid pulses characterized by variations in their k li b pb and zn concentrations the fluid that precipitated the mn oxide stage has anomalous pb zn and li b ratios which closely resemble fluids found in fracture fillings in red beds of the permian rotliegend basin by contrast the fluids associated with the hematite stage have pb zn and li b ratios typical of crustal fluids that were derived from interaction with crystalline basement both fluids possess characteristic element ratios including cl br but variable absolute concentrations of most metals this suggests that both fluids were modified by mixing with a common metal depleted brine that had a similar cl br ratio most likely a formation water from the overlying zechstein sedimentary rocks the sailauf mineralization provides insight into the protracted post variscan fluid evolution at the basement cover interface the compositionally anomalous fluid that precipitated the mn oxides is comparable to brines derived from interaction with red beds and likely represents the ore fluid of kupferschiefer type sediment hosted cu deposits conversely the fluid that deposited the hematite mineralization resembles fluids that typically form basement and sediment hosted pb zn deposits

the effect of temperature and cataclastic deformation on the composition of upper crustal fluids an experimental approach abstract we investigated the potential of common crystalline rocks to facilitate the geochemical evolution of continental basement brines and to serve as a metal source for hydrothermal ore deposits we performed leaching experiments on typical crystalline basement rocks granite and gneiss a redbed sandstone and their mineral separates feldspar quartz and biotite at variable t 25 180 275 and 350 c p ambient pressure 0 9 1 4 and 1 9 kbar grain size fractions the modification of the fluid chemistry during water rock interaction strongly depends on grain size leachates using pure h 2 o of fine grained rock powders have lower na cl and cl br ratios but much higher chlorinities by a factor of up to 40 compared to leachates from coarse grained rock powders the cl br ratios of all leachates are lower than that of their respective whole rocks smaller grain sizes of the starting materials yield element ratios cl br and na cl similar to those found in natural fluids emphasizing the influence of cataclastic deformation on the fluid chemistry of crustal fluids during our leaching experiments pb zn cu and w are released by felsic minerals while biotite alteration releases ni as and additional zn and cu our experiments confirm that crystalline rocks may serve as metal source for hydrothermal ore deposits short term water rock interactions along cataclastic fault zones in the brittle crust may influence the geochemical evolution of upper crustal fluids this is further suggested by low f cl and cl br ratios in some of the leachates being very similar to halogen systematics in natural fluid samples

sulfate brines in fluid inclusions of hydrothermal veins compositional determinations in the system h2o na ca cl so4 sulfate is among the most abundant ions in seawater and sulfate bearing brines are common in sedimentary basins among other environments however the properties of sulfate bearing fluid inclusions during microthermometry are as yet poorly constrained restricting the interpretation of fluid inclusion compositions where sulfate is a major ion the schwarzwald mining district on the eastern shoulder of the upper rhinegraben rift is an example of a geologic system characterized by sulfate bearing brines and constraints on the anion abundances chloride versus sulfate would be desirable as a potential means to differentiate fluid sources in hydrothermal veins in these regions here we use the pitzer type formalism to calculate equilibrium conditions along the vapor saturated liquidus of the system h2o na ca cl so4 and construct phase diagrams displaying the predicted phase equilibria we combine these predicted phase relations with microthermometric and crush leach analyses of fluid inclusions from veins in the schwarzwald and upper rhinegraben to estimate the compositions of these brines in terms of bulk salinity as well as cation and anion loads sodium versus calcium and chloride versus sulfate these data indicate systematic differences in fluid compositions recorded by fluid inclusions and demonstrate the application of detailed low temperature microthermometry to determine compositions of sulfate bearing brines thus these data provide new constraints on fluid sources and paleo hydrology of these classic basin hosted ore forming systems moreover the phase diagrams presented herein can be applied directly to compositional determinations in other systems