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

variscan tectonics of central europe postaccretionary intraplate deformation of weak continental lithosphere the area occupied by the variscan belt of central europe forms part of gondwana derived microplates essentially avalonia and armorica that according to paleomagnetic data juxtaposed baltica and laurentia from the upper ordovician to the lower devonian the actual structure of this area is a puzzle of rather small fault bounded crustal blocks different in p t t histories which was created by later tectonic processes at around 360 to 320 ma according to a common view and by contrast to paleomagnetic data the structural record of fault bounded blocks is interpreted in terms of mid devonian to lower carboniferous amalgamation of narrow continental plates represented by the fault bounded blocks themselves however this is not supported in this article instead it will be shown that fault systems and fault bounded blocks were created by intraplate deformation of a weak domain of gondwana derived continental lithosphere significantly after its accretion deformation was partitioned into newly formed deep seated strike slip and kinematically connected reverse or normal detachment systems large translation magnitudes caused juxtaposition of crustal areas of variable thickness until they were emplaced along the fault systems the various categories of fault bounded complexes record different tectonic events category 1 metamorphic complexes represent deep seated parts of thickened crust some time before unroofing on the detachment systems between about 340 360 and 320 ma however the record of subduction and extreme crustal thickening during earlier stages of the collision history was erased to a high degree and is only preserved by mineral and structural relics strike slip and detachment systems propagated across and dismembered tectonic boundaries formed during these early events category 2 metamorphic complexes and the barrandian basin recording predominant pre late devonian metamorphic or stratigraphic events represent the brittle upper crustal parts during continuing metamorphism in the category 1 complexes weakly or unmetamorphosed lower paleozoic category 3 basins represent areas of thinned continental crust and record subsidence before and to some degree during activity of detachment systems the complex overall kinematic pattern of block bounding strike slip and detachment systems indicates compression and extension acting simultaneously this probably reflects the effects of continuing oblique plate convergence rotation and wsw extrusion of fault bounded blocks in addition to heating and extensional flow of previously thickened crustal areas

quaternary grabens in southernmost illinois deformation near an active intraplate seismic zone abstract narrow grabens displace quaternary sediments near the northern edge of the mississippi embayment in extreme southern illinois east central united states grabens are part of the fluorspar area fault complex fafc which has been recurrently active throughout phanerozoic time the fafc strikes directly toward the new madrid seismic zone nmsz scene of some of the largest intra plate earthquakes in history the nmsz and fafc share origin in a failed cambrian rift reelfoot rift every major fault zone of the fafc in illinois exhibits quaternary displacement the structures appear to be strike slip pull apart grabens but the magnitude and direction of horizontal slip and their relationship to the current stress field are unknown upper tertiary strata are vertically displaced more than 100 m illinoian and older pleistocene strata 10 to 30 m and wisconsinan deposits 1 m or less no holocene deformation has been observed average vertical slip rates are estimated at 0 01 to 0 03 mm year and recurrence intervals for earthquakes of magnitude 6 to 7 are on the order of 10 000s of years for any given fault previous authors remarked that the small amount of surface deformation in the new madrid area implies that the nmsz is a young feature our findings show that tectonic activity has shifted around throughout the quaternary in the central mississippi valley in addition to the nmsz and southern illinois the wabash valley illinois indiana benton hills missouri crowley s ridge arkansas missouri and possibly other sites have experienced quaternary tectonism the nmsz may be only the latest manifestation of seismicity in an intensely fractured intra plate region

replacement dolomites and ore sulfides as recorders of multiple fluids and fluid sources in the southeast missouri mississippi valley type district halogen 87sr 86sr δ18o δ34s systematics in the bonneterre dolomite replacement dolomites may continue to recrystallize in the presence of subsequent diagenetic and hydrothermal fluids during recrystallization they can change both their solid geochemistry and that of their included fluids by releasing older fluids and entrapping younger fluids thus it may be possible to decipher a complex fluid history by analyzing both the composition of the dolomite 18o 87sr 86sr and its contained fluids cl br as the former reflects temperature and or fluid rock interactions whereas the latter reflects salinity source regions of the last fluid to affect the dolomite applying this approach to the bonneterre dolomite of southeast missouri which hosts the world class viburnum trend mississippi valley type mvt pb zn district reveals the presence of two geochemically distinct types of brines whose influence varied temporally during the bonneterre s history of dolomitization and ore deposition a plot of cl br molar ratios of included fluids versus 87sr 86sr ratios of the enclosing dolomite indicates distinct salinity sources for early halite dissolution and later extreme evaporation of seawater dolomitizing brines comparison with fluids in ore sulfides may permit us to relate replacement dolomites to ore forming events early stage copper and zinc bearing sulfides 34s 0 have fluids with cl br molar ratios 150 1 050 reflecting a similar importance of halite dissolving brine during ore deposition main stage cuboctahedral galena 34s 15 has fluids with cl br molar ratios 100 400 similar to extremely evaporated seawater brines responsible for late replacement dolomites we suggest that resident brines which gained salinity in part through halite dissolution sulfur and metals from local sedimentary and igneous rocks were important for early replacement dolomitization and early stage ore deposition this fluid type was supplanted by later main stage brines that acquired salinity through seawater evaporation and metals in a more distal basinal setting late stage vug filling cubic galena records a renewed importance of the halite dissolving brine as the influence of the more distal basinal brine waned halogen sulfur isotope systematics of sulfides indicate that fluid mixing likely was a dominant ore depositing mechanism during all stages of ore mineralization in the viburnum trend

the paleohydrology of southeast missouri mississippi valley type deposits interplay of faults fluids and adjoining lithologies observations and geochemical data provide insight into the paleohydrology influencing development of mississippi valley type deposits in southeast missouri and provide clarification and justification of flow paths in light of proposals of fault hydrodynamics versus a continuous aquifer model faults are recognized as pathways for as well as horizontal barriers to fluid flow in a hydrologically compartmentalized region these relations also indicate that at least two geochemically distinct fluids mineralized late cambrian hosts and that these fluids had a similar history of progressive undersaturation with respect to galena an overview of the synthesis indicates that one of the fluids may have originated in the reelfoot rift whereas the other evolved in a recharge area stretching along the ouachita front and exploited the reelfoot rift northwest striking faults in the precambrian basement acted as channels of discharge for flow out of or through the reelfoot rift fluid movement along these pathways was rapid and allowed fluids to reach ore hosts during a migration interval related to the late paleozoic ouachita orogeny vertical circulation along faults and fracture systems introduced fluids into the existing paleozoic section dispersion into the lamotte sandstone resulting from relative permeability differences between discordant subvertical faults and the adjoining quartzarenite was restricted to a northwest trending fault bounded corridor and was concentrated at the base of the bonneterre formation continued vertical movement of fluids maintained fracture networks as vertical pathways during the period that circulation localized mississippi valley type deposits in the late cambrian section

experimental determination of the compositional limits of immiscibility in the system cacl2h2oco2 at high temperatures and pressures using synthetic fluid inclusions abstract using the synthetic fluid inclusion method the temperature pressure and compositional limits of fluid immiscibility in the binary system cacl 2 h 2 o have been determined at 600 and 700 c at pressures between 1 and 2 kbar the limits of the immiscible regions were determined by observation of two different inclusion types in the samples and by measurements of the depression of ice melting temperatures the region of immiscibility in this system extends to much higher pressures than that of the nacl h 2 o system with similar compositional ranges a similar study was done on the cacl 2 h 2 o co 2 system at 500 600 and 700 c at pressures of 1 1 5 2 and 3 kbar in the ternary system the presence of two different inclusion types and the measurement of clathrate melting temperatures were used to delineate the compositional regions of immiscibility the presence of co 2 extends the regions of immiscibility shown in the binary system study to much higher pressures tie lines in the two phase regions were determined by measuring the homogenization temperatures of co 2 vapor and liquid phases and the volume ratios of inclusion bubble to total inclusion in vapor rich type inclusions the locations of these tie lines indicate that the cacl 2 is heavily partitioned towards the more liquid rich phase the experimental results show that with even relatively small amounts of a divalent salt such as cacl 2 immiscibility can exist to very high temperatures and pressures from these results immiscibility should be a very common phenomenon in geologic processes ranging from sedimentary to quite high grade metamorphic environments and that it should have a very important effect on reactions between hydrothermal fluids and rocks and the resulting mineral assemblages

fluid migration and associated diagenesis in the greater reelfoot rift region midcontinent united states the sources and pathways of basinal fluid flow on the north american craton have been the subjects of intense debate regional dolomitization and the distribution of petroleum and sulfide mineralization on the southern midcontinent are believed to be related to migration of warm basinal fluids from and within the arkoma and illinois basins because of its hydrologic connection with these two basins the reelfoot rift has been postulated as a potential source and or conduit for one or more of these fluids cathodoluminescence petrography has revealed nine distinct carbonate cement microstratigraphies in the reelfoot rift and on its adjacent carbonate platforms in missouri western platform and tennessee eastern platform temporal geochemical trends within each of the three areas are distinct eastern platform carbonate cements and their fluid inclusions exhibit decreasing 13c 18o homogenization temperatures t h and last ice melting t m values with decreasing age reelfoot rift dolomite and calcite cement and their fluid inclusions define a trend of decreasing 13c and 18o values and increasing t h and t m values western platform dolomite cements including those in the nearby southeast missouri mississippi valley type mineral district display a paragenetic trend of increasing 13c and 18o values followed by a return to lower values during the final stage of cement deposition distinct geochemical patterns indicate that stratigraphically controlled fluid flow through carbonate aquifers in the reelfoot rift was restricted within individual fault blocks that had limited communication with the adjacent carbonate platforms lateral fluid migration between fault blocks and vertical migration within fault blocks in the reelfoot rift likely was restricted by faults stratigraphic offset and impermeable units if significant fluid movement occurred from the reelfoot rift onto the adjacent western carbonate platform it likely occurred along northwest striking strike slip faults

lead and sulfur isotope microstratigraphy in galena crystals from mississippi valley type deposits the development of an analytical procedure for lead and sulfur isotope analysis by secondary ion microprobe mass spectrometry allowed us to provide in situ isotopic microanalyses of galena crystals we performed analyses across the growth zones of two crystals of galena from mississippi valley type ore deposits with a spatial resolution of 50 mu m and a spacing of 250 mu m these analyses show frequent variations for both lead and sulfur isotope compositions which occurred during the time of the crystal growth we can demonstrate that for both elements these variations involved changes in the sources of the brines which formed the ore deposits the comparison of lead and sulfur isotope behavior suggests that for the picher deposit lead and sulfur originated from common sources whereas for the buick mine deposit lead and sulfur had separate sources the two galenas exhibit rapid and frequent changes in isotopic composition this suggests numerous and discontinuous inputs of lead and sulfur to the ore deposits this model agrees well with a physical model for mississippi valley type deposits proposed by cathles and smith 1983 the isotopically different sources were probably different sedimentary layers and perhaps basement rocks in the same basin whose formation waters were channeled in preferred water conduits to the ore deposit location during the subsidence of the basin allowing mixing between the different sources to occur during the brines travel

evolution of a carboniferous carbonate hosted sphalerite breccia deposit isle of man a newly discovered extensive sphalerite bearing breccia 7 5 wt zn is hosted in dolomitised carboniferous limestones overlying ordovician silurian metasedimentary rocks on the isle of man although base metal sulphide deposits have been mined historically on the island they are nearly all quartz vein deposits in the metamorphic basement this study investigates the origin of the unusual sphalerite breccia and its relationship to basement hosted deposits through a combination of petrographic cathodoluminescence fluid inclusion stable isotope and hydrogeologic modelling techniques breccia mineralisation comprises four stages marked by episodes of structural deformation and abrupt changes in fluid temperature and chemistry in stage i high temperature t h 300 c high salinity 20 45 wt equiv nacl fluid of likely basement origin deposited a discontinuous quartz vein this vein was subsequently dismembered during a major brecciation event stages ii iv are dominated by open space filling sphalerite quartz and dolomite respectively fluid inclusions in these minerals record temperatures of 105 180 c and salinities of 15 20 wt equiv nacl the 34s values of sphalerite 6 5 6 9 vienna canyon diablo troilite are nearly identical to those of ore sulphides from mines in the lower palaeozoic metamorphic rocks the 18o values for quartz and dolomite indicate two main fluid sources in the breccia s hydrothermal system local carboniferous hosted brines 0 5 6 0 vienna standard mean ocean water and basement involved fluids 5 5 11 5 ore sulphide deposition in the breccia is compatible with the introduction and cooling of a hot basement derived fluid that interacted with local sedimentary brines

sulfur isotope evidence for penetration of mvt fluids into igneous basement rocks southeast missouri usa previous studies of galena and sphalerite from paleozoic mvt deposits in the viburnum trend southeast missouri documented large variations in 34s values throughout the ore forming event the present study of cu fe sulfides reveals a similar 34s variation that reflects two end member sulfur reservoirs whose relative importance varied both temporally and spatially more 34s enriched sulfides 34s approaching 25 indicate introduction of sulfur from basinal sedimentary sources whereas more 32s enriched sulfides 34s 600 m vertically through underlying precambrian igneous rocks such basement involvement has been suggested for other carbonate hosted base metal districts e g irish base metal deposits and should be considered an integral part of the ore forming process in southeast missouri

geochemistry of metal rich brines from central mississippi salt dome basin u s a abstract oil field brines are the most favored ore forming solutions for the sediment hosted mississippi valley type ore deposits detailed inorganic and organic chemical and isotope analyses of water and gas samples from six oil fields in central mississippi one of the very few areas with high metal brines were conducted to study the inorganic and organic complexes responsible for the high concentrations of these metals the samples were obtained from production zones consisting of sandstone and limestone that range in depth from 1900 to 4000 m 70 120 c and in age from late cretaceous to late jurassic results show that the waters are dominantly bittern brines related to the louann salt the brines have extremely high salinities that range from 160 000 to 320 000 mg l total dissolved solids and are na ca cl type waters with very high concentrations of ca up to 48 000 mg l and other alkaline earth metals but with low concentrations of aliphatic acid anions the concentrations of metals in many water samples are very high reaching values of 70 mg l for pb 245 mg l for zn 465 mg l for fe and 210 mg l for mn the samples with high metal contents have extremely low concentrations 2 s samples obtained from the smackover formation limestone have low metal contents that are more typical of oil field waters but have very high concentrations up to 85 mg l of h 2 s computations with the geochemical code solmineq 87 give the following results 1 both pb and zn are present predominantly as aqueous chloride complexes mainly as pbcl 4 2 and zncl 4 2 respectively 2 the concentrations of metals complexed with short chained aliphatic acid anions and reduced s species are minor 3 organic acid anions are important in controlling the concentrations of metals because they affect the ph and buffer capacity of the waters at subsurface conditions and 4 galena and sphalerite solubilities control the concentrations of pb and zn in these waters

limist on the metal content of fluid inclusions in gangue minerals from the viburnum trend southeast missouri determined by laser ablation icp ms the hydrothermal fluids that deposited the ores of the viburnum trend of the southeast missouri district have long been recognized to be sedimentary basinal brines the major element composition of these brines has been well characterized however there have been no attempts to measure their metal content which is only loosely constrained by theoretical solubility relations the present study is an effort to assess the metal content of these mineralizing brines by analyzing fluid inclusions from gangue minerals in the viburnum trend using laser ablation inductively coupled plasma mass spectrometry la icp ms and microthermometry by focusing on gangue minerals instead of metal sulfide minerals interferences from the mineral matrix are avoided a high priority was to determine whether brines of anomalously high metal content were circulating through southeast missouri during the time of mississippi valley type mineralization fluid inclusions in dolomite quartz and calcite gangue from throughout the viburnum trend and representative of the entire paragenesis were analyzed none of the inclusions contained measurable quantities of pb zn or cu and only a few contained measurable quantities of ba which ranged from about 100 to 500 ppm where detection limits were not exceeded they indicated maximum possible concentrations of the element in the fluid inclusion maximum possible concentrations varied from inclusion to inclusion and were controlled by the mass of analyte within the fluid volume the larger or more saline the inclusion the lower the detection limit these results showed that the fluid that deposited quartz calcite and most of the dolomite gangue in the viburnum trend is unlikely to have had order of magnitude concentrations of pb and zn higher than 102 ppm or order of magnitude concentrations of cu higher than 101 ppm concentrations of pb and zn during deposition of stage 3 dolomite could not have been higher than 103 ppm and concentrations of cu could not have been higher than 102 ppm these upper limits on possible metal concentrations with the principal exception of those in stage 3 dolomite fluid inclusions are of magnitude similar to the highest measured concentrations of pb zn cu and ba found in typical sedimentary brines thus the brines responsible for depositing gangue minerals in the viburnum trend are unlikely to have had higher ore metal concentrations than typical basinal brines the lack of temporal overlap between gangue and metal sulfide deposition and the higher k na and lower ca mg ratios in fluid inclusions in the gangue minerals compared with fluid inclusions in the metal sulfides leaves open the possibility that the metal content of the fluid that deposited the sulfides was different from that responsible for depositing gangue however the data show that fluid entering the southeast missouri district was not pervasively metal rich throughout time and that if metal enriched fluid ever entered the district it did so at discrete intervals

development of in situ sulfur four isotope analysis with multiple faraday cup detectors by sims and application to pyrite grains in a paleoproterozoic glaciogenic sandstone abstract an in situ sulfur four isotope analysis technique with multiple faraday cup detectors by ion microprobe was developed and applied to detrital pyrite grains in 2 4 ga glaciogenic sandstone from the meteorite bore member of the turee creek group western australia data are standardized with the uwpy 1 pyrite standard 34s 16 04 0 18 33s 0 003 0 009 and 36s 0 21 0 24 2 sd whose sulfur four isotopes were newly determined by gas source mass spectrometry typical reproducibility at two standard deviations 2 sd of spot to spot analyses of standard uwpy 1 pyrite with a primary beam size of 20 m were 0 23 0 05 and 0 86 for 34s 33s and 36s respectively the measured 36s 32s ratio 1 6641 27 is approximately 19 lower than the published ratio for vcdt and we propose a revision of the 36s abundance in vcdt pyrite grains in 2 4 ga glaciogenic sandstone have wide ranging sulfur isotope ratios 32 7 to 13 5 for 34s 3 03 to 11 66 for 33s and 9 7 to 4 6 for 36s respectively some pyrite grains are zoned in 34s values within a grain sulfur isotope ratios of most pyrite grains are distributed along a line with slope 0 9 for 33s vs 36s suggesting that pyrite grains mostly derived from a limited range of source rocks and near surface sulfur reservoirs one pyrite aggregate has a distinct texture from other pyrite grains in the same sandstone and yields a significant mass independent deficit in 36s with a small excess in 33s 36s 33s 4 this is used to suggest that this grain authigenically formed by biological activity during or after sedimentation this work demonstrates that the use of multiple faraday cup detectors provides improved accuracy and precision for in situ sulfur four isotope analysis with secondary ion mass spectrometry

the origin of a mississippi valley type deposit in the viburnum trend southeast missouri petrologic and isotopic studies of the base metal sulfide mineralization in the buick mine have established the following paragenesis an early stage of fine grained pyrite and marcasite replaced the dolostone host rock the iron disulfides and dolostone were replaced by sphalerite during the main stage of sphalerite precipitation delta 34 s sp 16 5 to 19 0ppm following the sphalerite two main stages of galena were precipitated a cuboctahedral stage delta 34 s gn 21 3 to 10 0ppm during which galena replaced dolostone and sphalerite and grew in vugs in the dolostone and in the sphalerite and a cubic stage delta 34 s gn 10 5 to 0 9ppm the two stages of galena precipitation were separated by a period during which the main stage of sphalerite and the cuboctahedral galena were partially dissolved and bladed marcasite delta 34 s mc 2 3 to 4 1ppm was precipitated and followed by a period of mild etching of the cubic galena minor amounts of pale sphalerite delta 34 s sp 14 0 to 16 5ppm were then precipitated white and colorless rhombs of dolomite were precipitated at the same time as some of the main stage of sphalerite the cubic galena and the pale sphalerite after the pale sphalerite was precipitated chalcopyrite quartz and siegenite were precipitated followed by calcite and finally kaolinite the paragenetic and textural data for both galena and sphalerite in the buick mine strongly suggest that these minerals were precipitated and dissolved repetitively during ore formation similar textural evidence for galena reported by other workers for different mines in the viburnum trend implies that repetitive precipitation and dissolution of galena was probably an important process during the formation of the entire viburnum trend fluid inclusions in late quartz crystals coprecipitated with chalcopyrite have filling and freezing temperatures within the ranges reported for sphalerite from other parts of the viburnum trend demonstrating that the ore forming solutions in the viburnum trend were probably at temperatures in the range 105 degrees to 141 degrees c assuming a maximum pressure correction of about 11 degrees c and were extremely saline containing about 4 0 to 5 0 molal chloride consideration of typical chemical analyses of fluid inclusions from other mississippi valley type deposits suggests that the maximum likely concentration of dissolved co 2 in the ore forming solutions was about 0 05 molal at these concentrations the ore forming solutions that travelled to the site of deposition could have had ph9s about two units less than neutral and still have been in equilibrium with dolomite or calcite the ranges of sulfur and lead isotopic compositions of galena from the buick mine are very similar to those established by earlier studies of the old lead belt and adjacent subdistricts however the correlation of isotopically lighter sulfur with more radiogenic lead is much stronger for the viburnum trend suggesting that galena was precipitated from many solutions each of which carried lead and sulfur together and had different lead and overall sulfur isotopic compositions the textural paragenetic and isotopic data for the buick mine cannot be easily explained either by a sulfate reduction model in which sulfate was reduced by organic matter or methane or mixing models in which base metals and reduced sulfur were transported separately to the site of deposition instead the data strongly support a reduced sulfur model for ore formation according to which the base metals were transported together with reduced sulfur as h 2 s in the same solutions to the sites of deposition the reduced sulfur model is also supported by a theoretical calculation of the solubilities of galena and sphalerite which demonstrate that low but economically significant concentrations of lead or zinc could have been transported as chloride complexes together with equivalent concentrations of reduced sulfur at temperatures of 100 degrees to 150 degrees c and ph9s of one to two units less than neutral and could have been precipitated by ph increases cooling or dilution at the sites of deposition

microscopic sulfur isotope variations in ore minerals from the viburnum trend southeast missouri a shrimp study mississippi valley type ore samples from two mines in the viburnum trend of southeast missouri have been examined with the shrimp ion microprobe to determine the extent of their microscopic sulfur isotope variations approximately 140 shrimp delta 34 s values were obtained microscopic delta 34 s variations within and among the intergrown fe cu pb zn sulfides are very large 10 to 25 and indicate an extremely complex history of mineral deposition textures record the general paragenesis fe sulfide galena and sphalerite chalcopyrite and bornite and covellite early fes 2 delta 34 s 10 to 10 is generally much more depleted in 34 s than later galena or chalcopyrite delta 34 s 0 25 both early fes 2 and late chalcopyrite growth sequences exhibit large zonations in delta 34 s typically from light to heavy values over a 15 per mil range isotopic zoning in galena crystals is comparatively negligible but variations among different galena crystals encompass a large total range in delta 34 s values 0 25 that is similar in magnitude to the total ranges observed in early fes 2 and late chalcopyrite where later sulifides crosscut and replace earlier sulfides the shrimp data indicate that there has been negligible local recycling of s from earlier sulfides in the ore forming zone each generation of metal appears to have brought in its own isotopically distinct and evolving batch of sulfur during successive deposition of each metal generation the observed delta 34 s variations require mixing among two or more isotopically distinct distal source fluids feeding already reduced sulfur to the ore forming zone and or the existence of in situ sulfur isotope fractionation mechanisms producing reduced sulfur whose isotopic composition varied progressively with time in the ore forming zone

origin characteristics and distribution of fault related and fracture related dolomitization insights from mississippian carbonates isle of man abstract the southwest davis zinc field sdzf is among the westernmost mvt districts associated with the allegheny ouachita orogeny in the midcontinent u s it consists of a series of small zinc sulfide deposits and associated dolomitization covering an area of 16 km2 6 mi2 adjacent to the arbuckle anticline in southern oklahoma mineralization occurs within the royer dolomite upper cambrian and the butterly dolomite lower ordovician of the arbuckle group and is associated with faults and breccia bodies that parallel the trend of the anticline mining activity in the sdzf was restricted to the early part of the 20th century ore mineralization consists chiefly of sphalerite and subordinate smithsonite with minor galena chalcopyrite and pyrite as well as supergene alterations of these minerals homogenization temperatures th of fluid inclusions in gangue dolomite cement range from 88 to 101 c and have salinities of 6 5 to 20 9 wt nacl equivalent rarer fluid inclusions in sphalerite have an average th value of 105 c and average salinity of 19 2 wt nacl equivalent gangue dolomite cements have 18o values of 6 9 to 9 1 vpdb and 13c values of 0 2 to 1 1 vpdb the 87sr 86sr ratios for these dolomites range from 0 7088 to 0 7105 mineralization likely occurred from a flow system in which basement influenced brines entered the host formations through faults and circulated through the brecciated zones as the ore hydrothermal system waned the relative importance of local brines within the carbonate section increased and resulted in precipitation of late dolomite cements

new constraints on carbonate diagenesis from integrated sr and s isotopic and rare earth element data jurassic smackover formation u s gulf coast a reply isotopic sr s o c and trace element including rare earth element ree compositions of calcite cements metal sulfides and sulfate minerals from oolitic carbonate grainstones of the smackover formation jurassic southwest arkansas shelf constrain the mechanism of sulfate reduction and establish temporal relations between sulfur and carbonate diagenesis strontium isotopic values of calcite cements range from near jurassic age sea water values 0 7068 up to values of 0 7096 this evidence coupled with variation in o and c isotopic compositions and in cement zoning under cathodoluminescence suggests that calcite cement precipitated over the course of burial diagenesis strontium isotopic compositions of pyrite marcasite and native s range up to maximum values observed for calcite cements but galena and sphalerite are less radiogenic the sr contents of sulfides and native s are 30ppm but the rb content is sufficiently low that in situ growth of87sr would not dramatically alter the initial sr isotope ratio diagenetic sulfate minerals also exhibit a range of sr isotopic compositions anhydrites range from 0 7071 to 0 7081 while celestites are more radiogenic 0 7096 the ree patterns of early and late calcite cements and framework grains differ using sm yb ratios as an indicator of heavy vs light ree enrichment early calcites have sm yb ratios 1 whereas late calcite cements have ratios of 1 8 3 2 importantly both cement signatures differ from framework grain ratios 1 3 1 7 indicating lack of rock buffering in fluids from which the cements precipitated furthermore the sympathetic increase in sm yb and sr isotopic ratios from early to late calcites is consistent with input of light ree from siliciclastic sources sulfur isotopic compositions of metal sulfide minerals range from 32 to 8 cdt native s and anhydrite values 18 are near jurassic age sulfate values while celestites are heavier 28 although thermochemical sulfate reduction has been proposed to explain h2s in deeply buried carbonate units associated with evaporite s lack of s isotopic homogenization between sulfate and sulfide minerals lack of s isotopic equilibration of oil with reservoir so4 and the limited distribution of h2s rich brines in southwest arkansas demand a more complex origin

stable isotope and fluid inclusion studies of early zn cu ni co rich ores lower ore zone of brushy creek mine viburnum trend mvt district missouri u s a products of multiple sulfur sources and metal specific fluids abstract mississippi valley type mvt deposits of the viburnum trend are typically lead dominant and occur in the upper portion of the cambrian bonneterre dolomite unusual zinc and copper rich ores with notable enrichments in ni co and ag have been discovered within the lower bonneterre dolomite more than 30 m below the district s main ore bearing horizon these ores appear to be localized along fault fracture zones within the lamotte sandstone which promoted extreme dissolution of the base of the overlying bonneterre dolomite and resulted in pronounced vertical zoning of early ni co cu zn and pb ores above the sandstone dolomite contact stable isotope and fluid inclusion studies were undertaken to assess whether the deep ores resulted from a single fluid reservoir that evolved from cu ni co rich to zn rich to pb rich or are instead products of distinct fluids unrelated to the stratigraphically higher main pb rich ores of the district sphalerite hosted fluid inclusions from the lower orebody appear to be geochemically distinct from those that formed the upper orebodies they record the highest k na and mg na ratios in the southeast missouri mvt district suggesting dominance of siliceous lithologies arkose and or felsic igneous rocks over limestones along their ore fluid pathways paragenetic trends indicate that distinct fluid compositions are associated with specific generations of sphalerite which likely reflects the presence of multiple fluids the 34s values of ore minerals early pyrite and chalcopyrite 7 to 5 early sphalerite 6 to 15 main sphalerite 7 to 17 v cdt indicate deposition from fluids that utilized isotopically distinct sulfide reservoirs low 34s sulfur sources for early ores likely included sulfide in local brines within the lamotte sandstone and diagenetic sulfide minerals within the basal units of the bonneterre dolomite a trend of increasing 34s values of ore sulfides from 5 toward 17 with vertical distance above the lamotte sandstone bonneterre dolomite contact indicates that as the deep ore fluid system worked its way upward it breached less permeable units in the lower bonneterre dolomite allowing incorporation of high 34s sulfide from brines present higher in the stratigraphic section a concomitant up section pattern of decreasing 18o values of dolomite cement and recrystallized remnant host rock from 3 toward 9 v pdb is also consistent with a localized deep mineralizing fluid system which interacted progressively with the stratigraphically higher regional scale pb rich fluid system the episodic nature of metal sulfide deposition in the lower ore zone points to a system in which fluid mixing would have been highly variable both temporally and spatially reaction path models require mixing of multiple ore metal specific and sulfide bearing fluids in order to form the orebody the sequence and concentrations of metal sulfides are inconsistent with ore formation from a single evolving metal bearing fluid this study indicates that faults localized early metal and sulfide bearing fluids facilitating mixing of fluids that resulted in the accumulation of high grade ores near the bonneterre dolomite lamotte sandstone contact recognition of fault fracture patterns beneath more typical pb rich orebodies in the viburnum trend may be a viable exploration strategy for similar zn cu co ni rich deposits

mafic and ultramafic plutons associated with the new madrid rift complex a possible major source of the copper cobalt nickel mineralization of southeast missouri the main rift structure of the new madrid rift complex the reelfoot rift strikes northeast ward extending from northeastern arkansas through the missouri boot heel and western kentucky into southern illinois the recently discovered bloomfield lineament zone transects the reelfoot rift in the boot heel area and strikes north northwest passing through the mine la motte fredericktown subdistrict of the southeast missouri lead zinc copper mining district studies suggest a strong relationship between the proximity of the new madrid rift complex to the southeast missouri district and the anomalously high amounts of cu co and ni in the region particularly in the mine la motte fredericktown subdistrict supporting evidence comes from three sources 1 mineral zoning and paragenetic sequence 2 geotectonics of the new madrid rift complex and 3 regional variations of 87 sr 86 sr and 18 o 16 o isotope ratios a detailed microscopic and sem eds study of the pb zn cu ores from the viburnum no 28 brushy creek and goose creek mines in the southeast missouri district indicates a complicated paragenetic sequence characterized by repeated periods of mineral deposition the sequence is composed of 19 minerals including abundant galena sphalerite chalcopyritc pyrite marcasite dolomite calcite and quartz as well as minor siegenite bornite bravoite blaubleibender covellite covellite gersdorffite digenite enargite tennantite dickite and malachite in addition to the mineralogy and paragenetic sequence a number of significant findings resulted from a comprehensive microscopic study of ore textures from the three mines the paragenetic sequence of the main colloform stage of deposition indicates that the ore solutions evolved in the following general order 1 cu rich 2 co ni rich 3 pb zn rich and 4 fe rich the general depositional sequence corresponds with mineral zoning and is similar throughout the entire lead district most importantly the paragenetically early cu co ni sulfides may represent a regional early development of the cu co ni rich mineralization similar to that in the mine la motte fredericktown subdistrict and the southern extension of the viburnum trend this early cu co ni rich zone always lies at the lowest stratigraphic level and in the mine la motte fredericktown subdistrict indicates a southerly source for the ore fluids it is proposed that the source of at least part of the cu co ni and some siderophile elements of the southeast missouri lead deposits may be the result of basinal brine leaching of a series of probably multiaged mafic and ultramafic intrusions or their sediments controlled by the new madrid rift complex one such branch of the complex observed on landsat 2 imagery is expressed as a fracture zone that extends north northwest from the reelfoot rift toward fredericktown missouri namely the bloomfield lineament zone strong 87 sr 86 sr and 18 o 16 o isotope anomalies show respectively a consistent decrease and a consistent increase from south to north in southeast missouri with the contour lines strikingly tracking the bloomfield fracture zone this suggests that the lineament zone was a channel for ore fluids entering southeast missouri via the mississippi embayment the fracture zone may represent a series of transform faults or a portion of a failed continental rifting event the zone is an epicenter trend and a distinct first order lineament which appears to form part of the northeast boundary of the northwest trending missouri gravity low

sulfur isotope variability in biogenic pyrite reflections of heterogeneous bacterial colonization the top 20 cm of sediments at active cold seeps in monterey bay coastal california contain framboidal pyrite that occurs as infillings and pseudomorphs of the chambers of the tests of foraminifera and rarely as irregularly shaped grains sulfur isotope compositions obtained with the ion microprobe show depletions in 34 s d 34 s 52 41 to 25 cdt and large variations both within and among these pyrite grains intergranular differences in d 34 s values in the same sediment are as large as 35 and intragranular zoning reaches 15 zoning is regular in some grains with systematic isotope changes from core to rim or from one foraminiferal chamber to another but irregular in others the regular zoning is consistent with an increase in 34 s through time backscattered electron imaging reveals three types of pyrite isolated framboids in a porous aggregation pf pyrite agglomerated framboids with cementing interstitial pyrite f 1i pyrite and recrystallized pyrite with isolated relicts of framboids rf pyrite in individual grains rf pyrite cores grade into f1i pyrite toward grain rims and f1i pyrite grades into pf pyrite at the grain edges these textures are consistent with a paragenetic sequence whereby framboids first agglomerate pf pyrite then cement f1i pyrite and finally recrystallize rf pyrite the d 34 s values of rf pyrite are generally lower than that of f1i pyrite if the paragenetic sequence is correct then this trend parallels the regular core rim isotopic zoning observed in some grains the implied increase in d 34 s with time is consistent with rayleigh fractionation of sulfur in a closed system bacteria are intimately involved in the production of pyrite from our samples and heterogeneous colonization by bacteria provides a simple explanation for the sulfur isotope heterogeneity among and within grains the foraminifera provide open space for colonization and local nutrients for bacterial growth whereas the cell walls of the bacteria may provide a local nucleation site for sulfides if so then initial colonization is reflected in lower d 34 s values whereas later bacterial emigration to other foraminifera chambers is indicated by higher d 34 s values

geochemistry of mississippi valley type mineralizing fluids of the ozark plateau a regional synthesis the compositions of fluid inclusions hosted in ore and gangue minerals from mississippi valley type mvt pb zn ba deposits of the ozark plateau region were measured to develop a regional hydro geochemical conceptual model for ore emplacement this model may explain the diverse compositions of fluids involved in mineral precipitation the ore precipitation mechanism and the temporal change in composition of fluids invading the ore districts the conceptual model additionally provides evidence for what factors may have controlled deposit size stratigraphic location and zn pb ratio high pb concentrations up to 1 0009s of ppm were identified in sphalerite hosted fluid inclusions from all of the region9s districts if these high pb concentrations were transported in the same fluid with sulfide then total sulfur concentration in the fluid must have been low mass balance calculations demonstrate that the arkoma basin a presumed source basin for the mineralizing fluids is too small to have contained enough fluid to precipitate the observed masses of sulfur in the larger mvt districts given the low sulfide concentrations that could coexist in the fluid with such high concentrations of pb high methane concentrations in sphalerite hosted fluid inclusions from all of the region9s districts in dolomite hosted fluid inclusions from the tri state and northern arkansas districts and quartz hosted fluid inclusions from the northern arkansas district suggest that the prevailing redox conditions during mvt mineralization were reducing making it unlikely that sulfate was transported in large concentrations in the fluids during sphalerite precipitation assuming saturation with respect to carbon dioxide measured methane concentrations in sphalerite hosted fluid inclusions would have required oxygen fugacity to have been at least two log units below the sulfate predominance field boundary fluid inclusion methane concentrations can also be used to estimate minimum burial depths of mineralization of about 0 08 to 1 2 km available evidence indicates that sulfide mineral precipitation in the ozark plateau mvt districts most likely occurred primarily as a result of the introduction of sulfide into a pb and zn rich ore fluid in the two larger mvt districts sulfide may have been supplied by local organic and sulfur rich carbonate facies an apparent mixing line between high ca na ratio and low ca na ratio fluids hosted predominantly in main stage sulfide minerals and paragenetically late minerals respectively indicates the ore fluid was relatively ca enriched the lack of continuity in high pb concentrations in fluid inclusions in sulfide and nonsulfide minerals from across the mineral parageneses suggests that the ore fluids entered the districts intermittently and or had variable metal contents over time

porosity evolution of the cambrian bonneterre dolomite south eastern missouri usa the cambrian bonneterre dolomite of south eastern missouri usa hosts the large mississippi valley type mvt lead zinc copper ore deposits of the region the bonneterre dolomite consists of dolomitized algal bioherms oolitic grainstone and associated lithologies that were deposited on a carbonate platform surrounding the precambrian age st francois mountains porosity was determined by point counting thin sections from cores and mines in the bonneterre dolomite and by gas porosimetry volumes of epigenetic cements were estimated by point counting cement filling micro and mesoporosity using cathodoluminescence cement volumes were added to present porosity to estimate porosities during various stages of mineralization prior to the onset of mineralization micro and mesoporosity in the bonneterre dolomite averaged approximately 19 precipitation of early dolomite cement roughly concurrent with the main period of sulphide deposition reduced average porosity to approximately 7 and closed off much of the intercrystalline pore space later cementation by dolomite prior to late stage sulphides reduced porosity to approximately 5 and late cementation by quartz further reduced porosity to the present average value of 4 periods of carbonate dissolution during mvt mineralization enhanced large scale megaporosity associated with fractures and breccias but did not significantly increase smaller scale porosity dolomite cementation associated with mvt mineralization porosity and permeability were facies controlled today as a result of mineralization large scale fractures and breccias control porosity and permeability this study indicates that dolomite porosity may undergo significant change during basinal brine migrations associated with mvt mineralization