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

paleomagnetic age of the central missouri barite deposits and its genetic implications in the central missouri barite district barite samples were taken from four barite deposits and carbonate samples from the lower ordovician jefferson city and gasconade dolomites in two road cuts and from the mississippian burlington limestone in a quarry the samples were tested paleomagnetically using detailed alternating field and thermal demagnetization and saturation isothermal remanent magnetization methods an a magnetization direction of declination 153 5 degrees inclination 17 6 degrees n 35 k 17 alpha 95 4 8 degrees is carried by pseudosingle domain magnetite in the barite rich zones of three open pit mines as an ore synchronous component in the jefferson city dolomite as a secondary component and in collapse breccia blocks of probable post middle devonian age in the dolomite to give a negative conglomerate test the a paleopole at 121 0 degrees e 36 6 degrees n dp 2 6 degrees dm 4 9 degrees falls within the kiaman reversed magnetic polarity interval on the late pennsylvanian to early early permian part of the apparent polar wander path for north america a b magnetization direction of declination 36 8 degrees inclination 77 8 degrees n 21 k 13 alpha 95 92 degrees is found in the other units it is a hybrid magnetization dominated by hematite produced by weathering and by viscous remanence in magnetite both of quaternary origin the kiaman magnetization in the barite ores and host rocks of the central missouri district agrees with known kiaman magnetizations in the lead zinc ores and host rocks of the adjacent southeastern missouri and northern arkansas districts this agreement provides strong support for the ouachita tectonic uplift model of genesis for the origin of the mississippi valley type ore deposits in the midcontinental region of the united states

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

temporal benchmarks for modeling phanerozoic flow of basinal brines and hydrocarbons in the southern midcontinent based on radiometrically dated calcite fluid inclusion studies of radiometrically dated u pb th pb calcite samples document the presence of hydrothermal fluids at ca 251 137 67 and probably 39 ma within the tri state zn pb mining district of missouri kansas and oklahoma fluid inclusions indicate minimum temperatures and equivalent salinities ranging from highs of 122 c and 24 wt nacl ca 251 ma to lows of 52 c and 0 wt nacl ca 39 ma the two earliest calcites contain primary petroleum inclusions but these are absent in samples younger than ca 137 ma when combined with information on metal rich shales paleomagnetism and modern groundwater flow our results are most readily explained by periodic influxes of hydrothermal fluids of diverse compositions for 200 m y and sporadic migration of hydrocarbons for at least 100 m y in the southern midcontinent

the determination of sulphate in fluid inclusions using the m o l e raman microprobe application to a keuper halite and geochemical consequences sulphate concentrations have been determined in fluid inclusions by raman spectroscopy using the m o l e microprobe after verifying that the sulphate determination is proportional to the total sulphate in the aqueous phase comparison of miso4 values in primary fluid inclusions with associated mother brine from actual solar salt works demonstrates their chemical equivalence keuper halite of marine origin has also been studied the inclusions contain solid phases anhydrite and possibly gypsum and glauberite as well the moiality of the total dissolved sulphate in the aqueous phase is lower than that obtained during present sea water evaporation at the halite stage of precipitation some geochemical hypotheses are proposed to account for this anomaly

ground preparation and zinc mineralization in bedded and breccia ores of the monte cristo mine north arkansas two distinct varieties of mississippi valley type ore occur in the northern arkansas zinc lead district 1 open space fillings in solution collapse breccia and 2 strata bound replacement deposits generally conformable with their carbonate host rocks the relationship between these two types of ore is unusually well exposed in the monte cristo mine as is the relationship between these ores and their host rocks primary pore spaces in the micritic and stromatolitic limestones and dolostones ordovician everton formation were largely occluded by cementation during diagenesis dissolution of limestone sometime after the early mississippian period locally produced solution collapse breccias composed chiefly of dolostone fragments in a quartz sand and dolomite matrix after lithification of this matrix further fracturing opened channels later used by the ore fluid mineralization deposition of sphalerite and pink sparry dolomite was preceded and or accompanied by silicification of limestone in the bedded orebodies and the outer margin of the breccias fluid inclusion and stable isotope c and o data suggest a mixing of two brines during mineralization both of probable deep burial origin the mixtures were hot 90 degrees 150 degrees c and highly saline 19 25 equiv wt nacl and were displaced by cool dilute presumably meteoric waters during deposition of late gangue quartz and calcite it is noteworthy that in the monte cristo mine the bedded and breccia mineralizations are physically and mineralogically continuous and yield indistinguishable fluid inclusion stable isotope and rare earth element signatures hence the bedded ores which possess many characteristics of mississippi valley type deposits attributed to a syngenetic or diagenetic origin elsewhere in the world formed simultaneously with the discordant breccia ore and are at least in northern arkansas epigenetic in origin

interaction of ocean temperature advection surface heat fluxes and sea ice in the marginal ice zone during the north atlantic oscillation in the 1990s a modeling study 1 a moderately fine resolution 0 4 40 vertical levels global coupled ice ocean model was configured and run for 24 years 1979 2002 forced with high frequency national center for environmental prediction national center for atmospheric research ncep ncar atmospheric fluxes the model consists of the los alamos national laboratory parallel ocean program pop and sea ice model cice the fidelity of the simulated mean climatological state and variability of key variables such as ice concentration total ice area ice thickness and drift were compared to observational data sets from satellite and ice drift buoy measurements basin scale changes in the lower atmosphere surface ocean sea ice in the simulated arctic and nordic seas before and after the north atlantic oscillation nao phase switch in 1995 were examined using winter composite analyses over the period 1990 1999 ice cover changes between the two nao phases were consistent with observations in that reduced concentrations were found in the nordic and barents seas and increased values occurred in the labrador sea next we regionally evaluated the relative importance of winter anomalies of upper ocean mixed layer net heat fluxes and of ocean temperature advection on marginal ice zone variability in the irminger greenland and barents seas for this ten year period we found that the net heat flux winter anomaly was at least four times more important than the winter anomaly of ocean temperature advection in the greenland and barents seas while it was twice as important in the irminger sea the ekman ocean temperature advection component generally dominated the geostrophic component in all three regions

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

constraints from fluid inclusions on sulfide precipitation mechanisms and ore fluid migration in the viburnum trend lead district missouri measurements on fluid inclusions in hydrothermal dolomite cements place constraints on sulfide precipitation mechanisms and on the thermal hydrologic processes which formed the viburnum trend mississippi valley type lead district homogenization temperatures and freezing point depressions were determined for fluid inclusions in bonneterre dolomite hosted dolomite cements in mine samples as well as drill core from up to 13 km outside of the district a well defined cathodoluminescent zonation distinguishes dolomite growth zones in the vi burnurn trend as older or younger than main stage mineralization octahedral galena and facilitates correlation with other dolomites outside the viburnum trend homogenization temperatures and salinities in samples from mines are not systematically different from those of samples outside of the district medians of homogenization temperature distributions differ by not more than 25 degrees c so that a temperature gradient if present should not have exceeded approximately 25 degrees c within the study area these observations are interpreted to indicate that the viburnum trend was not strongly thermally anomalous with respect to surrounding country rock and that fluid flow occurred on a broad scale through not only the lamotte sandstone but through the overlying cambrian carbonates as well the absence of a significant recognizable decrease in temperature either vertically within the section or east west across the district coupled with the minor amount of silica in the district argues against cooling as a primary cause of sulfide precipitation fluids whose primary aquifer was the lamotte sandstone predominantly a quartz arenite should have been in equilibrium with quartz quartz in the viburnum trend occurs as a minor drusy vug lining phase but the district lacks the intense silicification found in other mississippi valley type districts such as tri state oklahoma kansas missouri quartz solubility is strongly temperature dependent and under equilibrium conditions a decrease of 10 degrees c or more should have precipitated at least as many moles of silica as galena assuming a galena solubility of between 1 and 10 ppm clearly this is not the case as galena is far more abundant than quartz in the viburnum trend ice final melting temperatures t m in fluid inclusions generally range from 14 degrees to 27 degrees c for primary dolomite hosted inclusions using these t m values and cation ratios for the inclusion fluids absolute concentrations for the individual cations and chloride were calculated using the thermochemical model of spencer et al 1990 the corresponding high but variable salinities 3 9 to 5 9 chloride molality are evidence for the presence of more than one distinct fluid during mineralization in a reduced sulfur mineralization model with pb carried as chloride complexes dilution is also a possible sulfide precipitation mechanism the difference in pb solubility for an equal quantity of reduced sulfur in the extremes of the chloride concentration range 3 9 vs 5 9 molal reaches 1 ppm only for ph values below approximately 4 5 accepting 1 ppm as a minimum metal concentration for a viable ore forming fluid dilution only appears capable of precipitating sulfides in a fluid with ph near the lower limit of values considered geologically reasonable or attainable dolomite cements hosting warm approximately 105 degrees 125 degrees c saline fluid inclusions are ubiquitous in the porous dolomitic facies of the bonneterre dolomite based on stratigraphic reconstructions however it is unlikely that the bonneterre was buried deeper than 1 5 km the distribution of warm inclusions beyond the viburnum trend district implies that fluid migration was regional in scale fluid inclusion temperatures inconsistent with typical basement heat flow controlled geothermal gradients 25 degrees 35 degrees c km may be explained by long distance migration of warm basin derived brines elevated temperatures observed in fluid inclusions at shallow stratigraphic depths are consistent with a gravity flow hydrologic system characterized by rapid flow rates and the capacity for advective heat transport

organic maturation and ore precipitation in southeast missouri the sulfate reduction plus mixing hypotheses for the formation of mississippi valley type deposits have suffered from an inability to show a plausible mass balance between sulfate possible reductants and sulfide ores and a mechanism for mixing the reduced gas h 2 s with the metal bearing fluid both these problems are resolved by focusing on the gases mostly methane generated from the organic matter in the host carbonate rocks during thermal maturation caused by heat from the hydrothermal solutions in southeast missouri it appears that the volume of the bonneterre formation required to produce all the methane needed to reduce enough sulfate to precipitate all the ores is approximately the same as the volume of the brown rock facies which hosts most of the ore therefore it appears that metal and sulfate bearing solutions entered the bonneterre at lamotte sandstone pinchouts then followed permeability trends which coincided mainly with the oolitic grainstones associated with the stromatolite reef most of which are brown evolution of methane and other reducing compounds from the brown rock resulted in sulfate reduction and precipitation of sulfides several other regional and local factors in the geology of the area are found to be compatible with this idea

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

average lithospheric structure of southern africa summary we present a new 1 d earth model for the crust and upper mantle beneath the archaean core of southern africa the crustal structure is constrained by published seismic refraction reflection data and by the modelling of teleseismic receiver function data the mantle structure is constrained by traveltime measurements for p and s waves by waveform inversion of multimode surface waves and by forward modelling of p waveforms for regional earthquakes the 42 km thick crust of southern africa consists of four layers a 2 km thick 5 05 km s surface layer a 5 km thick 6 08 km s upper crust a 20 km thick 6 30 km s l mid crust and a 15 km thick 6 73 km s lower crust below the crust there is an 80 km thick upper mantle lid v and v are 8 09 and 4 62 km s l respectively at the top of the lid and the compressional and shearvelocity gradients through the lid are 0 0008 s l and 0 0013 s respectively below the lid there is a substantial shear wave lvz with the shear wave velocity dropping from 4 72 km s l in the lower part of the lid to 4 32 km s at 250 km depth the shear wave lvz is required to fit both the v measurements and the regional surface waveforms forward modelling of p suggests that no upper mantle p wave lvz exists there is an increase in the p wave velocity gradient at 125 km depth to 0 0015 s and a second increase at 250 km depth to 0 0035 s velocities and densities in the seismic model of the lid agree closely with velocity and density estimates from the geochemical analysis of garnet periodotite nodules from kimberlites of the kaapvaal craton implying that the estimates from kirnberlites are representative of a wider region of the archaean core of southern africa not just of the restricted region beneath which the kimberlites are found a comparison of the southern african seismic model with seismic models for other shield regions where nodule data are not available shows that the nodule results may also be representative of the upper mantle in those regions

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

raman microspectrometry of fluid inclusions abstract for many kinds of fluid inclusions the coupling of microthermometry and raman microspectrometry is still the only viable option to obtain compositions of single fluid inclusions a review is given on the basis of 16 years of experience and helped with about 120 references of the instrumentation analytical conditions and methodology of the application of raman microspectrometry to gaseous aqueous and hydrocarbon inclusions and their daughter minerals

reactive flow models of ore formation in the southeast missouri district two dimensional numerical reactive transport modeling was used to investigate the deposition of pb zn cu ores in the southeast missouri district central united states by two potential mechanisms cooling of a fluid carrying metals and reduced sulfur and mixing of two fluids one enriched in metals but poor in sulfur and the other enriched in reduced sulfur but poor in metals the mechanisms were studied within the context of the topography driven ground water flow regime established in the ozark region by the late paleozoic alleghanian orogeny the models integrated geology fluid flow heat and solute transport and chemical reaction generating the most complete depiction yet of potential ore forming processes in southeast missouri both mechanisms were found capable of generating important characteristics of the mineralization patterns observed in the field but fell short in other respects in models of the cooling hypothesis mineralization was indeed found to be concentrated within the southeast missouri portion of the ozark region this was primarily because of the fact that mineralizing fluid underwent very little temperature change as it traversed the ozark region until it arrived in southeast missouri where its temperature decreased significantly the important association of mineralization with local basement highs within the southeast missouri district was also produced caused by local increases of fluid velocity over the crests of the basement highs smaller scale models however revealed much of the mineralization to be concentrated within the basal lamotte sandstone rather than the overlying bonneterre dolomite where it is actually concentrated in the field this model result stemmed directly from the fact that permeability and therefore fluid velocities were higher in the lamotte than in the bonneterre a further discrepancy with field observations was the high predicted concentrations of quartz which exceeded those of galena by over two orders of magnitude models of the mixing hypothesis also led to the regional concentration of mineralization in southeast missouri provided vertical dispersivities in the lamotte sandstone and bonneterre dolomite the formations that transmitted the two different types of fluids were low when dispersivities were high mineralization was produced more uniformly along the flow path in further conformity with field observations ore was concentrated in the bonneterre dolomite and particularly around the basement highs demonstrating the importance of the lamotte pinch outs in causing the fluids to mix the models reproduced well the observed vertical zonation in metals which was controlled by the relative solubility differences among the primary sulfide ore minerals however though mixing was induced by the configuration of the local geology its intensity was relatively low leading to ore grades that were considerably less than would be expected from geochemical grounds alone because the flow regime is predominantly laminar the two fluids tended to miscibly displace one another rather than vigorously mix with one another while still potentially a viable ore forming mechanism under conditions of high local dispersivity high dissolved metal and sulfur concentrations or high fluid velocity the mixing hypothesis as typically formulated in southeast missouri is nonetheless much less efficient than previously supposed greater efficiency could possibly be generated by reaction of aqueous species with solid phases in the matrix or gas e g h 2 s being generated in the matrix

the mixing hypothesis and the origin of mississippi valley type ore deposits anderson 1991 proposed that methane generated from the heating of kerogen in the wall rocks of mississippi valley type mvt deposits diffuses into the ore zone reducing sulfate and precipitating the ore minerals this hypothesis has been tested by calculating the diffusion of methane from wall rock into a flowing solution at 150 c methane pressures in the ore zone quickly reach a steady state which depends on the assumed methane pressure in the wall rock and the flow velocity calculated methane pressures in the ore solution are not sufficient to generate a gas phase but other dissolved gases such as co 2 may contribute sufficiently to make this happen sulfate reduction and sulfide precipitation will occur whether or not a gas phase forms but many mvt ores have a tabular form or are located in the upper part of breccias suggesting that there was a gas phase control recent experimental results chou and burruss 2007 offer an explanation for the fact that very light carbon isotopes are not commonly found in mvt deposits the main obstacles to further development of these ideas is our lack of understanding of the thermochemical sulfate reduction reaction and the fact that little attention has been paid to possible sources of methane in the vicinity of ore deposits

hydrothermal fluid origins in mississippi valley type ore districts combined noble gas he ar kr and halogen cl br i analysis of fluid inclusions from the illinois kentucky fluorspar district viburnum trend and tri state districts midcontinent united states samples were selected from three of the classic mississippi valley type districts in the midcontinent area of north america the illinois kentucky fluorspar district belongs to the fluoritic subtype of mississippi valleytype districts and the ozark districts of the viburnum trend and tri state are representative of the pb rich and more typical zn rich subtypes of mississippi valley type mineralization respectively noble gas ar kr and halogen cl br i data have been obtained simultaneously by noble gas mass spectrometry of inclusion fluids released by in vacuo crushing of irradiated fluorite quartz carbonate and sphalerite samples additionally he analyses have been obtained from nonirradiated fluorite from the illinois kentucky fluorspar district fluorite from the illinois kentucky fluorspar district has a maximum 3 he 4 he ratio of 0 35 ra where ra atmospheric 3 he 4 he ratio of 1 4 10 6 higher than values typical of crustal fluids and confirming the presence of a minor mantle component equal to less than 6 percent of the total he in the fluids of the illinois kentucky fluorspar district the br cl mol ratios of all the deposits are with one exception higher than the value of seawater 1 54 10 3 ranging from 1 69 to 3 70 10 3 and indicating acquisition of salinity by the evaporation of seawater beyond the point of halite saturation late quartz from the tri state district contains a very minor component of halite dissolution water and has a br cl mol ratio of 1 46 10 3 the i cl mol ratios are typical of oil field brines and are ubiquitously higher than what is attainable by the evaporation of seawater alone i cl mol ratios are in the range of 6 to 270 10 6 indicating that the fluids have interacted with i rich organic matter present in sedimentary rocks in the ozark districts 40 ar 36 ar ratios vary between 320 and 345 in the tri state and between 350 and 420 in the viburnum trend in the illinois kentucky fluorspar district 40 ar 36 ar ratios reach values of 1 200 the corresponding concentrations of 40 arexcess 40 ar not attributable to radiogenic decay of 40 k or an atmospheric source are similarly elevated in the main stage fluorite mineralization of the illinois kentucky fluorspar district 6 8 18 2 10 4 cm 3 cm 3 h2o relative to the viburnum trend and tri state districts mostly 1 3 3 3 10 4 cm 3 cm 3 h2o and 0 3 1 4 10 4 cm 3 cm 3 h2o respectively together the noble gas and halogen data indicate the existence of three brine provinces 1 a regional tristate brine present throughout the ozark region 2 a viburnum trend brine and 3 an illinois kentucky brine furthermore in the viburnum trend the halogen composition of main stage dolomite is distinct from that of the main stage sphalerite but identical to the regional hydrothermal dolomite seen in the tri state district the data imply that mixing relationships in the viburnum trend are highly complex but are compatible with regional models in which the tri state brine present throughout the ozark region was sourced in the arkoma basin

paleomagnetism of the mississippi valley type ores and host rocks in the northern arkansas and tri state districts a paleomagnetic study has been done on 452 specimens from the early ordovician cotter and middle ordovician everton formations in the northern arkansas mississippi valley type mvt lead zinc ore d

a pennsylvanian paleomagnetic pole from the mineralized late cambrian bonneterre formation southeast missouri one hundred eighty eight oriented samples of the late cambrian bonneterre carbonates of southeastern missouri were taken from viburnum trend mines and local surface outcrops initial natural remanent magnetization directions have south southeasterly declinations and downward inclinations progressive demagnetizations using thermal and af techniques give two directions one is a viscous present day field direction and the other is of reversed polarity with south southeasterly declinations and very shallow inclinations the resulting paleopole at 43 n 126 e is located near the pennsylvanian to early permian segment of the north american apparent polar wander path a negative conglomerate test supports this assignment for the magnetization age magnetic extracts from the mineralized as well as unmineralized zones of the bonneterre contain spherical crystal aggregates of pure magnetite of late diagenetic origin the secondary magnetization resides in the magnetite spheroids and we infer that the spheroids formed prior to sulfide mineralization

genetic implications of regional and temporal trends in ore fluid geochemistry of mississippi valley type deposits in the ozark region fluids extracted from aqueous fluid inclusions in epigenetic gangue and ore minerals record the migration of huge volumes of highly saline fluids throughout the stratigraphic section of the ozark region the extracted fluids share many similarities regionally but there are significant temporal differences which define two geochemically distinct end member ore forming fluids that we refer to as the viburnum trend main stage or viburnum trend type and the tri state type viburnum trend type fluids are enriched in potassium and are associated only with deposits close to the basal lamotte sandstone the main stage octahedral galena ore of the viburnum trend and much of the old lead belt ore is thought to be derived from this type of ore fluid galena deposited by viburnum trend type fluids contains less radiogenic lead than galena deposited by tri state type fluids sulfides deposited by viburnum trend type fluids also contain isotopically heavier sulfur and significant amounts of copper cobalt nickel and silver tri state type fluids have a low potassium content when compared with viburnum trend type fluids and are characteristic of deposits where ore forming fluids migrated through large volumes of carbonate rock these fluids are thought to have formed the ore deposits of the tri state northern arkansas and central missouri districts the cubic galena stage ore of the viburnum trend and the many trace occurrences of sphalerite throughout the ozark region galena deposited by tri state type fluids has more radiogenic lead and the sulfides have isotopically lighter sulfur than sulfides deposited by viburnum trend type fluids a systematic south to north increase of potassium in the tri state type fluids suggests that they migrated from a southerly source such as the arkoma basin possible explanations for the origins of these two end member fluids include 1 a single parent brine evolved into two distinct fluids due to reactions with geochemically distinct aquifers during migration 2 the two distinct fluids reflect normal fluid evolution within a single source basin of a bittern and of later halite dissolution and 3 the viburnum trend and tri state type brines migrated to southeast missouri from two different source basins our data does not preclude any of these possibilities however the geochemical similarity of the viburnum trend end member fluid to a bittern may be accounted for by water rock modifications of the brine during migration other evidence strongly supports a southerly source for the ore forming brines thus limiting possible sources for the viburnum trend type fluid to the arkoma and or black warrior basins of the ouachita foreland trough viburnum trend type fluid flow was probably funneled northward through basal sandstones within the reelfoot rift and water rock modifications occurring there may have resulted in its unique geochemistry

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

regional epigenetic dolomitization in the bonneterre dolomite cambrian southeastern missouri a dolomite bed averaging 6 m in thickness forms the base of a limestone and shale facies of the bonneterre dolomite cambrian southeastern missouri the dolomite immediately overlies the lamotte sandstone and covers an area of more than 16 600 km 2 it is proposed that this basal dolomite formed as a result of interaction with warm basin derived water circulating through the underlying lamotte sandstone and that the dolomitization event coincided with the emplacement of mississippi valley type sulfide ores in the nearby viburnum trend this hypothesis is supported by 1 petrographic evidence that suggests an origin at temperatures 50 c 2 cathodoluminescent microstratigraphy of dolomite cements which is correlative with that in gangue dolomite cements in the nearby orebodies and 3 stable oxygen and carbon isotope values that are consistent with a basinal origin of the dolomitizing water the basal dolomite bed may represent one of the most extensive epigenetic dolomites yet documented this implies that a basinal water can alter rocks over a wide area at a considerable distance from its source