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

regional geologic and petrologic framework for iron oxide apatite rare earth element and iron oxide copper gold deposits of the mesoproterozoic st francois mountains terrane southeast missouri usa this paper provides an overview on the genesis of mesoproterozoic igneous rocks and associated iron oxide apatite ioa rare earth element iron oxide copper gold iocg and iron rich sedimentary deposits in the st francois mountains terrane of southeast missouri usa the st francois mountains terrane lies along the southeastern margin of laurentia as part of the eastern granite rhyolite province the province formed during two major pulses of igneous activity 1 an older early mesoproterozoic ca 1 50 1 44 ga episode of volcanism and granite plutonism and 2 a younger middle mesoproterozoic ca 1 33 1 30 ga episode of bimodal gabbro and granite plutonism the volcanic rocks are predominantly high silica rhyolite pyroclastic flows volcanogenic breccias and associated volcanogenic sediments with lesser amounts of basaltic to andesitic volcanic and associated subvolcanic intrusive rocks the iron oxide deposits are all hosted in the early mesoproterozoic volcanic and volcaniclastic sequences previous studies have characterized the st francois mountains terrane as a classic a type within plate granitic terrane however our new whole rock geochemical data indicate that the felsic volcanic rocks are effusive derivatives from multicomponent source types having compositional similarities to a type within plate granites as well as to s and i type granites generated in an arc setting in addition the volcanic hosted ioa and iocg deposits occur within bimodal volcanic sequences some of which have volcanic arc geochemical affinities suggesting an extensional tectonic setting during volcanism prior to emplacement of the ore forming systems the missouri iron orebodies are magmatic related hydrothermal deposits that when considered in aggregate display a vertical zonation from high temperature magmatic hydrothermal ioa deposits emplaced at moderate depths 1 2 km to magnetite dominant ioa veins and iocg deposits emplaced at shallow subvolcanic depths the shallowest parts of these systems include near surface iron oxide only replacement deposits surficial epithermal sediment hosted replacement deposits synsedimentary ironstone deposits and mn rich exhalite deposits alteration associated with the ioa and iocg mineralizing systems of the host volcanic rocks dominantly produced potassic with lesser amounts of calcic and sodic rich mineral assemblages no deposits are known to be hosted in granite implying that the mineralizing systems were operative during a relatively short postvolcanic period yet prior to intrusion of the granitoids companion studies in this special issue on mineral chemistry stable isotopes and iron isotopes suggest that the magnetite within the ioa deposits formed from high temperature fluids of magmatic or magmatic hydrothermal origin however the data do not discriminate between a magmatic hydrothermal source fluid exsolved from an fe rich immiscible liquid or an fe rich silicate magma mineral chemical fluid inclusion and stable isotope data from these new studies record the effects of metasomatic fluids that interacted with crustal reservoirs such as volcanic rocks or seawater

salt precipitation in magmatic hydrothermal systems associated with upper crustal plutons magmatic hydrothermal systems associated with upper crustal plutons strongly influence volcanic and geothermal processes and form important mineral deposits fluids released from plutons are commonly saline and undergo phase separation into high salinity brines and low salinity vapors upon ascent while brine vapor immiscibility has been extensively studied precipitation of solid salt during phase separation in magmatic hydrothermal systems has generally been considered a rare phenomenon here we show that most porphyry deposits exhibit fluid inclusion evidence best interpreted by solid salt precipitation from ore forming solutions this interpretation naturally links thermodynamics numerical simulations and independent estimates of porphyry ore formation depths salt precipitation imposes major changes on the permeability of the system moreover salt precipitation has implications for ore formation along the liquid vapor halite curve the recognition of salt saturated systems is challenging but very relevant for understanding the evolution of magmatic hydrothermal systems

iron oxide copper gold iocg deposits through earth history implications for origin lithospheric setting and distinction from other epigenetic iron oxide deposits the iron oxide copper gold iocg group of deposits initially defined following discovery of the giant olympic dam cu u au deposit has progressively become too embracing when associated deposits and potential end members or analogs are included the broader group includes several low ti iron oxide associated deposits that include iron oxide p rich iron oxide f and ree rich fe or cu au skarn high grade iron oxide hosted au cu carbonatite hosted cu ree and f rich and iocg sensu stricto deposits consideration of this broad group as a whole obscures the critical features of the iocg sensu stricto deposits such as their temporal distribution and tectonic environment thus leading to difficulties in developing a robust exploration model the iocg sensu stricto deposits are magmatic hydrothermal deposits that contain economic cu and au grades are structurally controlled commonly contain significant volumes of breccia are commonly associated with presulfide sodic or sodic calcic alteration have alteration and or brecciation zones on a large commonly regional scale relative to economic mineralization have abundant low ti iron oxides and or iron silicates intimately associated with but generally paragenetically older than fe cu sulfides have lree enrichment and low s sulfides lack of abundant pyrite lack widespread quartz veins or silicification and show a clear temporal but not close spatial relationship to major magmatic intrusions these intrusions where identified are commonly alkaline to subalkaline mixed mafic even ultramafic to felsic in composition with evidence for mantle derivation of at least the mafic end members of the suite the giant size of many of the deposits and surrounding alteration zones the highly saline ore fluids and the available stable and radiogenic isotope data indicate release of deep volatile rich magmatic fluids through devolatization of causative mantle derived magmas and variable degrees of mixing of these magmatic fluids with other crustal fluids along regional scale fluid flow paths precambrian deposits are the dominant members of the iocg group in terms of both copper and gold resources the 12 iocg deposits with 100 tonnes t resources are located in intracratonic settings within about 100 km of the margins of archean or paleoproterozoic cratons or other lithospheric boundaries and formed 100 to 200 m y after supercontinent assembly their tectonic setting at formation was most likely anorogenic with magmatism and associated hydrothermal activity driven by mantle underplating and or plumes limited amounts of partial melting of volatile rich and possibly metal enriched metasomatized early precambrian subcontinental lithospheric mantle sclm fertilized during earlier subduction probably produced basic to ultrabasic magmas that melted overlying continental crust and mixed with resultant felsic melts with devolatilization and some penecontemporaneous incorporation of other lower to middle crustal fluids to produce the iocg deposits preservation of near surface deposits such as olympic dam is probably due to their formation above buoyant and refractory sclm which resisted delamination and associated uplift most precambrian iron oxide p rich or magnetite apatite kiruna type deposits have a different temporal distribution apparently forming in convergent margin settings prior to or following supercontinent assembly it is only in the phanerozoic that iocg and magnetite apatite deposits are roughly penecontemporaneous in convergent margin settings the phanerozoic iocg deposits such as candelaria chile occur in anomalous extensional to transtensional zones in the coastal cordillera which are also the sites of mantle derived mafic to felsic intrusions that are anomalous in an andean context this implies that special conditions possibly detached slabs of metasomatized sclm may be required in convergent margin settings to generate world class iocg deposits it is likely that formation of giant iocg deposits was mainly a precambrian phenomenon related to the extensive mantle underplating that impacted on buoyant metasomatized sclm generally smaller and rarer phanerozoic iocg deposits formed in tectonic settings where conditions similar to those in the precambrian were replicated

macrostructure of diagnostic b horizons relative to underlying bc and c horizons in podzols luvisol cambisol and arenosol evaluated by image analysis abstract five soils albic ortsteinic podzol albic podzol and dystric brunic arenosol developed from sand and haplic luvisol and eutric cambisol developed from loess were studied to evaluate morphometric features and selected physico chemical properties of b horizons in relation to bc and c horizons by standard laboratory methods soil texture total organic carbon the amount of carbonates ph particle and bulk density total porosity were measured samples with preserved structure were used to produce for each tested layer 16 resin impregnated 8 9 cm in size opaque soil blocks for qualitative and quantitative soil structure analysis utilizing the scanned images of the opaque blocks the following morphometric parameters were measured the relative area of pore cross section macroporosity the relative length of pore cross sections perimeter the relative number of pore and solid phase element cross sections the mean area of pore and solid phase element cross section and fraction of number of horizontally diagonally and vertically oriented pore cross sections the numerical characteristics of each soil structure revealed that the layers of the b horizons differed from the underlying layers representing bc c and ck horizons in an ambiguous way depending on soil genesis the obtained morphometric parameters and morphological analysis showed that in the b horizons the original structure of sand or loess obliterated due to the processes of enrichment of the b horizons in organic substances al and fe and the soil fauna and flora activity and consequently the development of aggregate structure or pores cutting the soil groundmass the morphometric parameters measured by image analysis corresponded logically with basic soil properties namely the organic carbon content and total porosity increased and the bulk density decreased while the morphometric parameters grew showing the development of more loose soil arrangement no characteristic differences in view of the measured morphometric parameters were found between bhs bs and bt horizons illuvial accumulation and bwo and bw horizons their genesis driven by in situ accumulation the bc horizons were much more similar than the b horizons to the parent material with respect to the values of morphometric parameters it should be stressed that the quantitative image analysis exposed visible in the opaque blocks qualitative dissimilarities between soil layers but due to the innate for soil especially a forest one high heterogeneity of structure the observed differences between the average values of morphometric parameters for the layers were not always validated through statistical tests the orientation analysis provided no characteristic description of soil structure status it helped however to interpret other morphometric parameters our study demonstrated that the quantitative macrostructure analysis could be an indirect method for evaluation of pedogenesis intensity because physico chemical properties of the developed b horizons controlled the occurrence and extent of abiotic and biotic factors regulating soil structure

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

alkaline lake systems with stromatolitic shorelines in the ediacaran volcanosedimentary ouarzazate supergroup anti atlas morocco abstract in the zenaga and saghro inliers of the anti atlas morocco the ediacaran ouarzazate volcanosedimentary supergroup preserves a record of the complex interplay between effusion of lava floods and explosive volcanic activity from numerous separate volcanic centres volcanic units consist of basaltic and andesitic lava flows and subvolcanic sills and dikes and dacitic rhyolitic ignimbrites and tuffs that represent a post collisional high k calc alkaline magmatism volcanic events are separated by erosive and low angle unconformities related to regional tilting which mark significant hiatii in the timing of deposition and are locally marked by carbonate production in palaeoweathered lowlands infill of scattered decametre scale carbonate bearing troughs less than 1 km across started with the dominantly local derivation of weathered and eroded lava debris followed by the migration of scattered subaqueous bottomset and foreset structures and final nucleation of carbonate productivity microbial mats developed along the shorelines of these ponds when bathymetry increased the stromatolites developed domal to columnar morphologies that coalesced laterally to form metre thick biostromes the lack of evidence for significant fluvial and deltaic deposits suggests that the streams that entered the ponds were intermittent and thus not a significant source of water it appears that groundwater rather than surface water was the dominant source of water to sustain the ephemeral ponds in the low lying weathered palaeodepressions preserved in the ouarzazate supergroup fluids passing through the surrounding volcanic landscape and the volcanic ashes interbedded within the lacustrine infill supplied silica enriched fluids giving the ponds the characteristics of alkaline lake systems their lacustrine affinity is supported by the subaerial character of many of the volcanic products that surround them ree composition of partly silicified dolomitized and undolomitized stromatolites is entirely consistent with freshwater lacustrine or shallow lagoonal with a strong freshwater input depositional settings but they also display a strong contamination from the rhyolitic tuffs that overly them

ore genesis constraints on the idaho cobalt belt from fluid inclusion gas noble gas isotope and ion ratio analyses a reply the idaho cobalt belt is a 60 km long alignment of deposits composed of cobaltite co pyrite chalcopyrite and gold with anomalous nb y be and rare earth elements rees in a quartz biotite tourmaline gangue hosted in mesoproterozoic metasedimentary rocks of the lemhi group it is the largest cobalt resource in the united states with historic production from the blackbird mine all of the deposits were deformed and metamorphosed to upper greenschist lower amphibolite grade in the cretaceous they occur near a 1377 ma anorogenic bimodal plutonic complex the enhanced solubility of fe co cu and au as chloride complexes together with gangue biotite rich in fe and cl and gangue quartz containing hypersaline inclusions allows that hot saline fluids were involved the isotopes of b in gangue tourmaline are suggestive of a marine source whereas those of pb in ore suggest a u th enriched source the ore and gangue minerals in this belt may have trapped components in fluid inclusions that are distinct from those in post ore minerals and metamorphic minerals such components can potentially be identified and distinguished by their relative abundances in contrasting samples therefore we obtained samples of co and cu sulfides gangue quartz biotite and tourmaline and post ore quartz veins as well as cretaceous metamorphic garnet and determined the gas noble gas isotope and ion ratios of fluid inclusion extracts by mass spectrometry and ion chromatography the most abundant gases present in extracts from each sample type are biased toward the gas rich population of inclusions trapped during maximum burial and metamorphism all have co 2 ch 4 and n 2 ar ratios of evolved crustal fluids and many yield a range of h 2 ch 4 co 2 h 2 s equilibration temperatures consistent with the metamorphic grade cretaceous garnet and post ore minerals have high r h and r s values suggestive of reduced sulfidic conditions most extracts have anomalous 4 he produced by decay of u and th and 38 ar produced by nucleogenic production from 41 k in contrast some ore and gangue minerals yield significant so 2 and have low r h and r s values of a more oxidized fluid three extracts from gangue quartz have high helium r r a values indicative of a mantle source and neon isotope compositions that require nucleogenic production of 22 ne in fluorite from u th decay two extracts from gangue quartz have estimated 40 k 40 ar that permit a precambrian age extracts from gangue quartz in three different ore zones are biased toward the hypersaline population of inclusions and have a tight range of ion ratios na k nh 4 cl br f suggestive of a single fluid their na cl br ratios suggest this fluid was a mixture of magmatic and basinal brine na k ca temperatures 279 347 c are similar to homogenization temperatures of hypersaline inclusions the high k na of the brine may be due to albitization of k silicate minerals in country rocks influx of k rich brines is consistent with the k metasomatism necessary to form gangue biotite with high cl an extract from a post ore quartz vein is distinct and has na cl br ratios that resemble metamorphic fluids in cretaceous silver veins of the coeur d alene district in the belt basin the results show that in some samples for certain components it is possible to see through the cretaceous metamorphic overprint of great import for genetic models the volatiles trapped in gangue quartz have 3 he derived from a mantle source and 22 ne derived from fluorite both of which may be attributed to nearby 1377 ma basalt rhyolite magmatism the brine trapped in gangue quartz is a mixture of magmatic fluid and evaporated seawater the former requires a granitic intrusion that is present in the bimodal intrusive complex and the latter equatorial paleolatitudes that existed in the mesoproterozoic the results permit genetic models involving heat and fluids from the neighboring bimodal plutonic complex and convection of basinal brine in the lemhi group while the inferred fluid sources in the idaho cobalt belt are similar in many respects to those in iron oxide copper gold deposits the fluids were more reduced such that iron was fixed in biotite and tourmaline instead of iron oxides

iron rich melts magmatic magnetite and superheated hydrothermal systems the el laco deposit chile we propose an integrated model that explains the magmatic and hydrothermal features of the unique el laco iron deposit that is located in a pliocene pleistocene volcano of the chilean andes sub volcanic crystallization of an iron rich melt as massive magnetite promoted the exsolution of a small volume of a hydrosaline melt and of large amounts of vapor that led to the formation of an alkali calcic hydrothermal assemblage replacing the host andesite this assemblage is capped and overprinted by a large zone of acid sulfate steam heated alteration forming as a whole a protracted shallow level magmatic hydrothermal system oxygen isotopic data for the massive magnetite 18o 4 3 5 0 and the alkali calcic altered rock diopside 18o 7 2 8 7 magnetite 18o 4 4 6 7 suggest that these rocks are genetically related to the host andesite 18o 7 4 9 6 the estimated temperature of the mineral assemblage 900 c may be the highest recorded in hydrothermal systems is attributed to exsolution of fluids from the crystallizing iron rich melts and is considered unlikely to reflect the convection of surficial fluids

ti diffusion in quartz abstract we have measured ti diffusion in quartz under dry 1 atm conditions experiments were performed using synthetic and natural quartz and a tio2 powder source with ti profiles obtained by rutherford backscattering spectrometry rbs over the temperature range 700 1150 c the following arrhenius relation was obtained for diffusion parallel to 001 d ti 7 10 8 exp 273 12 kj mol 1 r t m 2 sec 1 similar diffusivities were obtained for both synthetic and natural quartz and for a range of ti source materials including natural titanite powder and rutile quartz single crystal diffusion couples although ti diffusion appears slightly slower in the direction normal to c this difference is not great using these diffusion parameters calculations indicate that distances over which diffusional alteration of ti concentrations in quartz could occur in a million years would be on order of 500 m at 800 c and 15 m at 600 c the arrhenius relation above should be broadly applicable and may find application in constraining metamorphic histories under conditions where the ti in quartz geothermometer can be reasonably applied this relation can also be used to constrain peak temperatures and cooling histories from observations of exsolved rutile needles in quartz and the width of the ti depleted zone that develops around the growing needles finally these findings may find utility in evaluating crystal residence times in magmatic systems when coupled with observations of the sharpness of zoning patterns in quartz

giant kiruna type deposits form by efficient flotation of magmatic magnetite suspensions kiruna type iron oxide apatite ioa deposits are an important source of fe ore and two radically different processes are being actively investigated for their origin one hypothesis invokes direct crystallization of immiscible fe rich melt that separated from a parent silicate magma while the other hypothesis invokes deposition of fe oxides from hydrothermal fluids of either magmatic or crustal origin here we present a new model based on fe and o stable isotopes and trace and major element geochemistry data of magnetite from the 350 mt fe los colorados ioa deposit in the chilean iron belt that merges these divergent processes into a single sequence of events that explains all characteristic features of these curious deposits we propose that concentration of magnetite takes place by the preferred wetting of magnetite followed by buoyant segregation of these earlyformed magmatic magnetite bubble pairs which become a rising magnetite suspension that deposits massive magnetite in regionalscale transcurrent faults our data demonstrate an unambiguous magmatic origin consistent with the namesake ioa analogue in the kiruna district sweden further our model explains the observed coexisting purely magmatic and hydrothermal magmatic features and allows a genetic connection between kiruna type ioa and iron oxide copper gold deposits contributing to a global understanding valuable to exploration efforts

evaporitic subtidal stromatolites produced by in situ precipitation textures facies associations and temporal significance abstract the transition between carbonate platforms or isolated carbonate buildups and overlying evaporites commonly is marked by assemblages of stromatolites and interlaminated carbonates and evaporites stromatolites display lamination textures that vary from peloidal and discontinuous on a scale of a millimeter to a few centimeters to isopachous and continuously laminated on a scale of a centimeter to a few meters the isopachous lamination texture may be composed of either 1 micritic or radial fibrous calcite or 2 dolomite isopachous stromatolitic laminae are remarkably uniform varying little in thickness over a given lateral distance in contrast to stromatolites formed of peloidal laminae which show marked variation in thickness over an equivalent lateral distance these isopachous textures are uncommon on most open marine carbonate platforms and apparently developed in transitional carbonate to evaporite settings because of increasing temperature salinity and anoxia related to water stratification which would have created ecologic restriction and an opportunity for stromatolite growth stromatolites with isopachous lamination are here interpreted to have formed as a result of in situ precipitation of sea floor encrusting calcite and possibly dolomite whereas the stromatolites composed of peloidal discontinuous lamination are inferred to have formed by trapping and binding of loose carbonate sediment in microbial mats while the presence of microbes in almost all near surface environments nullifies use of the term abiotic to describe most precipitated minerals we interpret growth of the isopachous stromatolites to have been dominated by chemogenic precipitation in the absence of microbial mats and the growth of peloidal stromatolites to have been controlled by sedimentation in the presence of microbial mats these transitional stromatolite facies are best developed atop proterozoic and paleozoic carbonate platforms that underlie major evaporite successions however inspection of jurassic and younger evaporite basins such as the messinian of the mediterranean region shows that stromatolites with thin isopachous lamination and radial fibrous textures though present are rare instead these facies may have been replaced by stromatolites with peloidal clastic textures and by low diversity diatomaceous and coccolith mudstones accumulation of the mudstones would have imposed two important effects 1 production of coccoliths would have helped extract calcium carbonate from seawater thus lowering the growth potential for precipitation of sea floor encrusting stromatolites 2 settling of both coccoliths and diatoms would have created a sediment flux to the sea floor which would have served to impede growth of precipitated stromatolites because of smothering of growing crystals

mineral thermometry and fluid inclusion studies of the pea ridge iron oxide apatite rare earth element deposit mesoproterozoic st francois mountains terrane southeast missouri usa mineral thermometry and fluid inclusion studies were conducted on variably altered and mineralized samples from the mesoproterozoic pea ridge iron oxide apatite ioa rare earth element ree deposit in order to constrain p t conditions fluid chemistry and the source of salt and volatiles during early magnetite and later ree mineralization scanning electron microscopy sem cathodoluminescence and sem backscatter electron images show that quartz and rutile precipitated before during and after magnetite and ree mineral growth ti in quartz and zr in rutile equilibration temperatures range from 350 to 750 c in the amphibole magnetite hematite and silicified zones where t increased during magnetite and quartz growth and dropped precipitously after fracturing and brecciation late drusy quartz cements within a ree rich breccia pipe record the lowest t 315 400 c liquid vapor rich and hypersaline hematite calcite fluid inclusions are common and liquid co 2 is present locally salinities define three populations saline 10 27 wt nacl equiv hypersaline 34 60 wt nacl equiv and dilute 0 10 wt nacl equiv the wide range of eutectic melting temperatures 67 to 19 c suggests that saline inclusions trapped variable proportions of a cacl mgcl fecl bearing fluid end member and an nacl kcl fluid end member homogenization temperatures and pressures of these saline inclusions suggest they were trapped when fluids unmixed into brine and vapor at t the na cl na k and cl br ratios of fluid inclusion extracts provide evidence for mixtures of magmatic hydrothermal fluids and evaporated seawater extracts from magnetite hematite and pyrite plot in the magmatic hydrothermal field indicating that fe was derived from a magmatic source their enrichments in mg and ca are consistent with a mafic magmatic source the positive correlation between na mg and na ca ratios may be due to halite saturation or albitization of igneous rocks extracts from barite in the ree rich breccia pipes are enriched in na and br and plot near the seawater evaporation trend he is highly enriched relative to ne and ar in fluid inclusion extracts which precludes air as a source of he although the he is mostly of crustal origin pyrite with a 3 he 4 he r r a of 0 1 contains up to 12 mantle he many extracts have low 20 ne 22 ne ratios due to nucleogenic production of 22 ne in high f o minerals such as fluorapatite or f biotite the arrays of data for 3 he 4 he r r a and 22 ne 20 ne suggest that volatiles were derived from two sources a moderate f mafic magma containing mantle he and a high f silicic magma with crustal he together with other evidence cited in this report these data 1 support a magmatic hydrothermal origin for the mesoproterozoic magnetite apatite deposit with ore fluids derived from a concealed mafic to intermediate composition intrusion 2 suggest that the ree minerals in breccia pipes were either derived from apatite or precipitated in response to decompression and cooling during breccia pipe formation 3 provide evidence for the influx of basinal brine magmatic fluids from granitic intrusions and meteoric water after breccia pipe formation and 4 show that pea ridge was relatively unaffected by the late paleozoic mississippi valley type mvt pb zn system in overlying cambrian sedimentary rocks

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

time scales of porphyry cu deposit formation insights from titanium diffusion in quartz porphyry dikes and hydrothermal veins from the porphyry cu mo deposit at butte montana contain multiple generations of quartz that are distinct in scanning electron microscope cathodoluminescence sem cl images and in ti concentrations a comparison of microprobe trace element profiles and maps to sem cl images shows that the concentration of ti in quartz correlates positively with cl brightness but al k and fe do not after calibrating cl brightness in relation to ti concentration we use the brightness gradient between different quartz generations as a proxy for ti gradients that we model to determine time scales of quartz formation and cooling model results indicate that time scales of porphyry magma residence are 1 000s of years and time scales from porphyry quartz phenocryst rim formation to porphyry dike injection and cooling are 10s of years time scales for the formation and cooling of various generations of hydrothermal vein quartz range from 10s to 10 000s of years these time scales are considerably shorter than the 0 6 m y overall time frame for each porphyry style mineralization pulse determined from isotopic studies at butte montana simple heat conduction models provide a temporal reference point to compare chemical diffusion time scales and we find that they support short dike and vein formation time scales we interpret these relatively short time scales to indicate that the butte porphyry deposit formed by short lived episodes of hydrofracturing dike injection and vein formation each with discrete thermal pulses which repeated over the 3 m y generation of the deposit

titaniq a titanium in quartz geothermometer titanium is one of many trace elements to substitute for silicon in the mineral quartz here we describe the temperature dependence of that substitution in the form of a new geothermometer to calibrate the titaniq thermometer we synthesized quartz in the presence of rutile and either aqueous fluid or hydrous silicate melt at temperatures ranging from 600 to 1 000 c at 1 0 gpa the ti contents of quartz in ppm by weight from 13 experiments increase exponentially with reciprocal t as described by text log left x text qtz text ti right 5 69 pm 0 02 frac 3765 pm 24 t k application of this thermometer is straightforward typically requiring analysis of only one phase quartz this can be accomplished either by epma for crystallization temperatures above 600 c or by sims for temperatures down to at least 400 resulting temperature estimates are very precise usually better than 5 c potentially allowing detailed characterization of thermal histories within individual quartz grains although calibrated for quartz crystallized in the presence of rutile the thermometer can also be applied to rutile absent systems if tio2 activity is constrained

petrogenesis of metaluminous a type rhyolites from the st francois mountains missouri and the mesoproterozoic evolution of the southern laurentian margin abstract predominantly acid volcanic and intrusive rocks of the approximately 1 48 ga eastern granite rhyolite province are exposed only in the st francois mountains inlier missouri combined nd isotopic major and trace element analyses are presented for the predominantly acid volcanic rocks of the st francois mountains they are metaluminous to mildly peraluminous a type compositions with positive initial e nd values of 3 1 5 0 they are interpreted to be the result of crystal fractionation of partially melted calc alkaline igneous rocks formed at a recently active subduction zone the likelihood of a juvenile calc alkaline subduction generated protolith for the st francois mountains rhyolites leads to a hypothesis in which dacitic parental magmas resulted from partial melting in a continental back arc setting basaltic magmatism due to decompression melting of the mantle resulted from lithospheric extension and thinning and provided the heat source for melting in the middle or lower crust penecontemporaneous magmatism elsewhere in laurentia included subduction related calc alkaline rocks in the pinware terrane of labrador some felsic igneous rocks of uncertain plate tectonic setting within the grenville province also have 1 5 1 6 ga t dm ages these are interpreted as magmatic products of approximately 1 5 ga northward dipping subduction beneath much of the length of the southern margin of laurentia the eastern granite rhyolite province is consequently seen as an integral inboard expression of this subduction related igneous activity petrogenetic models involving a mantle plume or the development of a continental rift are not required to explain this granite rhyolite terrane and evidence against their involvement is discussed

a numerical model to estimate trapping conditions of fluid inclusions that homogenize by halite disappearance abstract fluid inclusions fi that homogenize by halite disappearance are common in some geological environments and interpretation of microthermometric data from these inclusions has been limited by the lack of a model describing the pvtx relationships over the complete range of ptx conditions found in nature in this study a system of equations has been developed that can be used to estimate salinity pressure and density of fi that homogenize by halite disappearance the salinity pressure density and d p d t slope of the fi isochore are calculated as functions of liquid vapor homogenization temperature th and halite dissolution temperature tm the equations are based on a numerical model describing the isochoric pressure temperature trajectory followed by halite saturated fluids during heating the model is valid for th and tm from 100 to 600 c and for pressures along the liquid vapor halite curve to 300 mpa

magnetite lava flows in the pleito melon district of the chilean iron belt 1982 concluded that this sequence was deposited in a volcanic island arc setting in the pleito mel n district the bandurrias group is composed principally ofandesitic lavas and volcanic breccias with intercalated rhyolitic tuffs and stratiform iron ores the bandurrias volcanics continues to the east of the area shown in figure 2 an intrusive complex with tonalitic granodioritic and dioritic units crops out to the west and east of the volcanic sequence fig 2 this complex has up to now been regarded as tertiary in age moscoso et al 1982 but our stratigraphic data indicate that parts of it may be cretaceous and constitute a basement for the bandurrias sequence in the berenguela area fig 3 the diorite is younger than the bandurrias andesites which are recrystallized a large number of rhyolitic dikes and a few andesitic ones cut extrusive as well as intrusive rocks and some of the dikes may be feeders of the extrusions structures there are three fault systems in the district all of them part of the atacama megafault cf thiele and pincheira 1987 the most important systems follow north northeast and northwest to north northwest directions and the third one consists of secondary east to east northeast faults the north northeast system is longitudinal and seems to be the oldest it has produced downfaulted blocks for example in the e1 mel n area fig 3 and many of the iron ores in the district are associated with it the north

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

mining and exploration history of the southeast missouri iron metallogenic province mining has been a driving force in the development of missouri for hundreds of years a history of feast and famine success and ruin in southeast missouri the mining history spans times from early crude furnaces and small mines to large modern operations working at depths of more than 730 m below the surface eight major iron orebodies and myriad minor deposits are known in the southeast missouri iron metallogenic province which is hosted in mesoproterozoic igneous rocks of the st francois mountains terrane the first iron furnace west of the mississippi river was opened in missouri in the early part of the 19 th century marking the beginning of a prosperous industry that shaped the fortunes of citizens and the state the industry persevered through the united states civil war including the dramatic battle in 1864 that caused extensive damage to the pilot knob ironworks earlier discovery in 1844 of banded iron formation ores in michigan and depletion of easily accessible surface iron deposits in southeast missouri led to eventual downturn in the local mining industry magnetic surveys in the 1950s resulted in discovery of several large subsurface deposits including the pea ridge iron oxide apatite deposit and the boss iron oxide copper gold deposit ca 52 km to the south iron production in missouri ceased in 2001 when the pea ridge mine closed great potential nevertheless exists for renewed production of iron and other metals in the province

the pilot knob magnetite deposit in the proterozoic st francois mountains terrane southeast missouri usa a magmatic and hydrothermal replacement iron deposit abstract the pilot knob magnetite deposit is located in southeast missouri within the 1380 1480 ma st francois mountains terrane rhyolitic trachytic volcanic rocks the deposit is tabular dips about 45 and is sill like in nature being approximately parallel to the bedding in the host tuffs the deposit was uncovered by erosion and exposed to weathering in the late proterozoic and is overlain in angular unconformity by the cambrian lamotte sandstone this proterozoic weathering cycle apparently had little effect on the deposit with only the updip edge being converted to hematite textural and mineralogical features of the deposit suggest a combined magmatic and hydrothermal replacement origin the magnetite rich ores that make up the bulk of the deposit are interpreted as having crystallized from an iron rich magma and a surrounding envelope of lower to moderate grade ores where magnetite has clearly replaced the tuffaceous host rocks are interpreted as hydrothermal in origin after the development of the higher grade magnetite ores and the envelope of lower to moderate grade ores late hydrothermal minerals were deposited as cross cutting veins and breccia fill the two most abundant minerals in the higher grade portions of the deposit are magnetite and albitic plagioclase and petrologically the higher grade ores could be described as a magnetite sodic syenite the most abundant gangue mineral within the lower grade impregnated envelope of ores around the higher grade ores is k feldspar apparently relict from the rhyolites trachytes thin lenses within the higher grade ores contain calcite as a matrix mineral to the magnetite and are considered to indicate carbonatitic affinity rare earth elements are elevated in one of five whole rock chemical analyses of the ores and the ree bearing mineral ferriallanite has been identified minor portions of the deposit below the proterozoic weathering cap consist of high grade hematite ores having equilibrium textures at depth the deposit is intruded by the shepherd mountain gabbro a 120 m thick near horizontal dike which resulted in minor contact metamorphism of the ore

isotopic composition of lead in galenas from the viburnum trend missouri the isotopic composition of lead in crystals of galena from the no 28 magmont brushy creek fletcher and ozark mines along the viburnum trend has been determined by ion microprobe variations in the isotopic composition of lead along traverses perpendicular to growth zoning are generally complex patterns of lead isotope variation from the center to the edge of galena crystals can be correlated for distances up to 200 m our lead isotope data together with earlier data for galena from the viburnum trend and the old lead belt lie along a linear band on 207 pb 206 pb 208 pb 206 pb diagrams lead in the paragenetically early octahedral galena is less radiogenic than lead in the paragenetically late cubic galena there is no significant geographic variation in the isotopic composition of the galena leads within the viburnum trend most of the isotopic variations can be explained in terms of the mixing of a normal lead isotope component from oil field brines and a radiogenic lead component derived from the precambrian basement the lead in these brines is derived from a source with a lower time integrated th u value than that of the source of the lead for analyzed oil field brines the isotopic composition of the radiogenic component is most consistent with derivation from a grenvillian 1 0 1 2 b y source the composition of lead in the cubic galenas may also be influenced by the admixture of lead derived from the dissolution of earlier octahedral galena

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

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

extremely high solubility of rutile in chloride and fluoride bearing metamorphic fluids an experimental investigation rutile tio 2 is an important high field strength element sequestering phase and thus understanding its solubility in metamorphic fluids is important if we are to understand terrestrial trace element cycling titanium is often assumed to be fluid immobile and previous experimental data suggest that rutile has very low solubility in h 2 o however fluids in high temperature metamorphic rocks are known to be more complex in composition the solubility of rutile in chloride and fluoride rich hydrous fluids was determined experimentally at 0 5 gpa and high temperatures the experimental results indicate much higher rutile solubility in brines compared to pure h 2 o in chloride brines solubility was 2 4 times higher than in h 2 o and in fluoride brines solubility was elevated 20 100 times the results imply that titanium may be much more mobile in metamorphic fluids than previously anticipated as solubility is critically dependent on fluid chemistry we also present a possible mechanism for rutile precipitation in metamorphic veins due to a change in fluid chemistry following the precipitation of halogen rich minerals such as apatite

sea ice thickness retrieval algorithms based on in situ surface elevation and thickness values for application to altimetry 1 in situ measurements of sea ice thickness i snow depth s and snow freeboard fsn from drilling profile lines from 15 cruises into the southern ocean antarctica were analyzed i was calculated from in situ fsn and s using an isostatic approach i was also directly estimated from fsn as can be obtained from laser altimetry the root mean square difference rmsd between observed and calculated i reduces and the correlation between fsn and i increases substantially when 1 using values averaged over the survey lines 50 m instead of single drill hole measurements 1 m and 2 treating positive and negative sea ice freeboard fi separately for small fi however s approximates fsn pointing toward an isostatic balance also between s and i our linear regression analysis between the in situ measurements suggests a direct conversion of fsn into i using a region specific set of equations rmsd values are similar to those obtained employing isostatic balance models and treating positive and negative fi separately however more data would have been needed to obtain significant differences between most of the various models suggested still our new approach gives a viable alternative for antarctic i retrieval from altimetric measurements of fsn alone correlation between in situ observations of fsn and s is high rmsd between observed and calculated s is small this suggests estimation of s from altimetric fsn measurements such s has an estimated precision of 5 cm and is neither affected by snow wetness or grain size nor limited to s 50 cm

long term changes in precipitation recorded by magnetic minerals in speleothems speleothems are important paleoclimate archives researchers typically compile measurements of stable isotopic ratios dated using high precision u th radiometric techniques to reconstruct regional and global climate magnetic material incorporated within speleothems can provide an independent means of connecting large scale climatic changes with their impact on more localized processes in soils overlying cave systems under certain environmental conditions pedogenic processes can produce magnetite nanoparticles enhancement of pedogenic magnetite in soil profiles depends strongly on local precipitation pedogenic magnetite can be subsequently transferred via drip waters into underlying cave systems and incorporated into speleothems as they grow here we employ high resolution magnetic methods to analyze a well dated stalagmite from buckeye creek cave west virginia usa and find that changes in magnetite concentration follow both changes in stable isotopes measured in the same stalagmite and global climate proxies we interpret the changes in magnetite concentration as reflecting variations in local pedogenic processes controlled by changes in regional precipitation this record demonstrates how magnetic measurements on speleothems can constrain interpretations of speleothem climate proxies

neodymium isotopic study of rare earth element sources and mobility in hydrothermal fe oxide fe p ree systems rare earth element ree enriched igneous related hydrothermal fe oxide hosted fe p ree systems from four areas in north america have been analyzed for their neodymium iosotopic composition to constrain ree sources and mobility in these systems the nd isotopic results evidence a common pattern of ree concentration from igneous sources despite large differences in age proterozoic to tertiary tectonic setting subduction vs intraplate and magmatic style mafic vs felsic in the middle proterozoic st francois mountains terrane of southeastern missouri epsilon sub nd for fe p ree apatite monazite xenotime deposits ranges from 3 5 to 5 1 similar to associated felsic to intermediate igneous rocks of the same age epsilon sub nd 2 6 to 6 2 at the mid jurassic humboldt mafic complex in western nevada epsilon sub nd for fe p ree apatite mineralization varies between 1 1 and 2 4 similar to associated mafic igneous rocks minus 1 0 to 3 5 in the nearby cortez mountains in central nevada mid jurassic felsic volcanic and plutonic rocks epsilon sub nd minus 2 0 to minus 4 4 are associated with fe p ree apatite monazite mineralization having similar epsilon sub nd minus 1 7 to minus 2 4 at cerro de mercado durango mexico all assemblages analyzed in this tertiary rhyolite hosted fe oxide deposit have identical isotopic compositions with epsilon sub nd minus 2 5 these data are consistent with coevalmore igneous host rocks being the primary source of ree in all four regions and are inconsistent with a significant contribution of ree from other sources interpretations of the origin of these hydrothermal systems and their concomitant ree mobility must account for nonspecialized igneous sources and varied tectonic settings less