Barite Mineralization Research Articles

228Th/ 228Ra ages of a barite-rich chimney from the Endeavour Segment of the Juan de Fuca Ridge

Ages in the range 1–15 yr for chimneys deposited from hydrothermal vents from the Endeavour Segment of the Juan de Fuca Ridge are estimated based on the ingrowth of 228Th from 228Ra. Cleaning samples by digestion in an acid bath confirms that the mineral barite is the phase being dated. A detailed examination of sample ALV 2463 R7 collected from the Clam Bed Site yielded a vertical growth rate of 5.8 cm/yr and a radial growth rate of 2.6 cm/yr. This investigation revealed that this chimney did not grow in a regular layer by layer accretion. Therefore, an average of ages obtained from several barite crystals a few centimeters apart (<10 cm) was used to define the age of each segment. Ages obtained from the sulfide-rich Main Field Site sample ALV 2466 R5 suggest that the barite in this sample is from late-stage precipitation, in contrast to the Clam Bed sample where barite formed the primary matrix. These samples conform to different models of barite incorporation into hydrothermal chimneys.

Genesis of sediment-hosted Zn-Pb-Ba deposits in the Irankuh District, Esfahan area, west-central Iran

The results of isotopic studies on carbonates and sulfur-bearing minerals of the Irankuh deposit occurring in Lower Cretaceous carbonate strata provide information concerning the nature of the fluids responsible for Zn-Pb-Ba mineralization and associated dolomitization. An epigenetic model for the Irankuh deposits is supported by their discordant nature, emplacement along the Irankuh fault, progressive depletion in stable carbon isotope ratios of the host dolostones as mineralization is approached, and isotopic characteristics of the ore-stage dolomites and barites. The host-rock dolostones show extensive depletion in 18 O (delta 18 O = -4.9 to -12.7ppm) due to diagenetic modification and/or recrystallization at increased temperatures. Based on isotopic and fluid inclusion data, the ore-stage dolomites in the deposits are interpreted as having formed from warm ( approximately 100 degrees C) saline, 87 Sr-enriched fluids similar to oil field brines. The overlap in delta 18 O values and 87 Sr/ 86 Sr ratios between host dolostones and sucrosic and saddle dolomites implies that these rocks have been isotopically modified and precipitated by similar fluids.The delta 34 S values of metal sulfides range from -3.6 to -9.6 per mil whereas barite values, ranging from 14.3 to 18.9 per mil, fall within the range of Cretaceous-age sulfate values. It is inferred that seawater sulfate acted as the source of the sulfides and barite mineralization. The reduced sulfur was generated by partial reduction of seawater sulfate by organic matter under hydrothermal conditions. The presence of a hydrocarbon (i.e., traces of bitumen) and saddle and fracture-filling dolomite with low delta 13 C values (ranging to -6.4ppm), in conjunction with the temperature of ore deposition, provides evidence for thermochemical sulfate reduction. Carbonates and barites show 87 Sr/ 86 Sr ratios enriched in 87 Sr which is atypical of derivation from normal seawater. The enrichment of 87 Sr is explained by extensive interaction of fluids with the underlying siliciclastic rock evolving toward more radiogenic compositions. The release of the overpressurized fluids appears to have been due to dehydration reactions and regional tectonism. The metal-bearing fluids responsible for mineralization migrated along the major Irankuh fault and mixed with sulfate-bearing fluids at the ore depositional site. Hydrologic considerations demonstrate that the proposed model is feasible.

The Porgera gold mine, Papua New Guinea; magmatic hydrothermal to epithermal evolution of an alkalic-type precious metal deposit

The Porgera gold mine, Papua New Guinea; magmatic hydrothermal to epithermal evolution of an alkalic-type precious metal deposit

The Lokve Barite Deposit, Croatia: an Example of Early Diagenetic Sedimentary Ore Deposits

Syngenesis versus epigenesis in the Kupferschiefer genetic model is still a matter of controversy. The title of the article seems to be a paraphrase of a well-known paper by WEDEPOHL (1971), “Kupferschiefer as a prototype of syngenetic sedimentary ore deposits”. It is intended, however, more as a paradigm for the genesis of the hydrogen-sulphide geochemical barrier, an important ore formation episode prior to heavy metal accumulation, which shows the utility of RENFRO’s (1974) epigenetic model. Barite mineralization in Lokve is a stratabound ore deposit conformably situated at the Permian-Triassic boundary. It bears only two ore minerals, barite and pyrite exclusively, separated into two distinct, juxtaposed horizons stretching for tens of kilometers. The discovery of cryptalgal fabrics and other conspicious sedimentary features in underlying siliciclastics with massive pyrite and surmounting barite-bearing dolomites supports their affiliation to a tidal flat facies and sabkha environment. Barite and pyrite accumulation were formed by an early diagenetic, bacteriogenic sulphate reduction in a peritidal muddy environment, concommitant to a widespread process of evaporative dolomitization. The early diagenetic model is supported by an analysis of the sedimentary facies, trace element geochemistry and sulfur isotope distribution along two vertical profiles across the stratabound barite and pyrite mineralization.

Origin of barite in Tertiary marine sedimentary rocks from Lefkas Island, Greece

Siliceous and calcareous biogenic rocks host pervasive, although volumetrically minor, authigenic barite on Lefkas Island, Greece. The barite composes up to 10 percent of the carbonate-free fraction of samples. In decreasing order of abundance, authigenic barite occurs as infilled foraminifera and radiolarian tests, disseminated grains and aggregates in porcelanite and siliceous limestone, replaced siliceous and calcareous biogenic tests, and thin laminae and lenses. The laminae form anastomosing networks that were probably originally rich in organic matter. Barite abundance shows a good correlation with the abundance of skeletal biogenic components. Biogenic silica diagenesis produced opal-CT and clinoptilolite, which compose the cement of porcelanite, replaced radiolarians, diatoms, and echinoderms and filled in some foraminifera tests. Subsequent silica diagenesis produced chalcedony at deeper stratigraphic levels, which also filled in pore space and calcareous microfossils in siliceous limestones and formed chert beds. Textural evidence shows that barite mineralization postdated opal-CT formation and preceded chalcedony formation. Barite precipitated in microenvironments including microfossil chambers, fecal pellets, and areas rich in organic matter. The source of the barium was probably from the decomposition of organic matter derived from plankton and bacteria and from the diagenesis of silica and carbonate tests. The source of the sulfate ion was seawater; possibly additional sulfate was produced and utilized in microenvironments from degradation of organic matter.

Anomalous elemental composition of aquatic bryophytes near barite zones in the Sowie Mts. (Poland)

In a number of aquatic bryophytes the accumulation of Ba and associated elements originating from barite zones in the Sowie Mts. in the Sudeten mountains in Poland was determined and up to (in μg g −1 dry plant weight) 12500 Al, 3510 Ba, 30 Cd, 469 Co, 13 Cr, 67 Cu, 52580 Fe, 216000 Mn, 17 Mo, 660 Ni, 215 Pb, 105 V and 2830 Zn was found. As aquatic bryophytes concentrate elements and integrate temporal fluctuations in water chemistry it was possible to recognize in this investigation the mean distribution over a longer period of concentrations of metals near the detection limit in streams, corresponding with the distribution pattern of the mineralization zones in the investigated area, while the water data did not allow for such a reconnaissance. Compared to other elements, the concentrations of Ba, Co and Ni in the majority of the bryophytes downstream of the barite mineralization zones were significantly higher (0.001 ≤ P ≤ 0.05) in comparison with the corresponding concentrations in bryophytes upstream of these zones.

Induction of barite mineralization in the Asiatic clam Corbicula fluminea

Barite crystals were formed on the inner shell surface in 1 week by specimens of Corbicula fluminea exposed to dissolved Ba concentrations of 140–559 µg liter‒1. Prevalences of barite crystals increased directly with initial Ba concentrations over the course of a 28‐d experiment. Barite crystals were not observed on the shell exteriors of any clams analyzed. Results suggest that Ba was concentrated by C. fluminea and periodically purged from the soft tissues into the extrapallial fluids, where it heterogeneously coprecipitated with aragonite on the inner shell surface.

Origin of the Atrevida Vein (Catalonian coastal ranges, Spain); mineralogic, fluid inclusion, and stable isotope study

Atrevida is a Ba-F base metal vein located in the Catalonian coastal ranges of Spain about 100 km southwest of Barcelona. The vein cuts Paleozoic metasediments and granites of the Hercynian basement and Triassic red beds at the base of an overlying transgressive sequence. The Atrevida vein can be divided into three parts on the basis of mineralogy. The lower level contains sugarlike quartz + fluorite + minor barite. The middle level contains a breccia of banded barite + basement rocks cemented by a complex sulfide-arsenide assemblage with galena, Ni sulfide, Ag sulfosalt, and native silver veinlets. The upper level contains symmetrical bands of white barite. Late calcite and marcasite are found in geodes. The only alteration observed is quartz + sericite + chlorite after K feldspar and biotite where the vein cuts granite host rocks.Fluid inclusions in fluorite homogenize at 110 degrees C and have salinities of 21 wt percent NaCl equiv. Inclusions in sphalerite homogenize at 90 degrees C and have salinities of 22 wt percent NaCl equiv. Eutectic results in both minerals are as low as -59 degrees C, indicating that the trapped fluids are complex CaCl 2 -bearing polysaline brines. Fluid inclusions in late calcite homogenize at -0.3 degrees C, indicating that low-salinity waters invaded the vein system during calcite deposition.Sulfur and oxygen isotope analyses reveal that vein barites have delta 34 S values of 14 to 17.9 per mil (CDT) and delta 18 O values of 9.5 to 12.2 per mil (SMOW). Barite also occurs as cement in the Triassic red beds with delta 34 S = 15.3 per mil and delta 18 O = 10.6 per mil. Both the sulfur and the oxygen isotope compositions are within the ranges reported for Lower Triassic- to Lower Jurassic-age evaporites.Banded galena from the middle level of the vein has delta 34 S values between -6.3 and -8.9 per mil, and rimming anglesite has delta 34 S values of -21 to -30.9 per mil. Galena from the central breccia has delta 34 S values of -14.9 to -16.1 per mil and coexisting sphalerite is about -10 per mil. Quartz in the lower level of the vein has delta 18 O in the range 20.7 to 22.7 per mil.We infer that sulfate in the vein was derived directly from seawater or from a solution which dissolved evaporites as it descended through the Triassic section along the fault zone. Barite and sulfides were precipitated where the sulfate-bearing solution mixed with an ascending, Ba-rich brine. The reduced sulfur found in the vein may have been carried by the ascending brine (banded galena) and may also have been produced by bacterial reduction of sulfate from a surficial source (galena in breccia). Oxidizing, nonmarine waters were introduced into the hydrothermal system giving rise to anglesite rims on galena.Mineralization took place in the Late Triassic during an extensional tectonic regime characterized by a high-geothermal gradient. Atrevida, and similar barite veins found throughout the Catalonian coastal ranges, formed along basin margin faults near a paleosurface formed on Hercynian basement. On a broader scale, low-temperature veins are known to occur throughout western Europe and northern Africa. If Atrevida is representative of the group, then the formation of these veins may be linked to Mesozoic extensional tectonics.

A sulphur isotopic investigation of the potential sulphur sources for Lower Palaeozoic-hosted vein mineralization in the English Lake District

Current models for Cu–Fe–As (Devonian), Pb–Zn (Carboniferous) and barite (Upper Carhoniferous/Permian) vein mineralization in the Lake District invoke a variety of sources for fluids and metals including the Skiddaw Group sediments, the Borrowdale Volcanic Group, the Lake District batholith, meteoric water and Carboniferous seawater. This study isotopically characterizes the sulphur reservoirs within the Lower Palaeozoic sedimentary and igneous sequences and Late Caledonian intrusives, and assesses their importance as sources of sulphur for the vein mineralization. The Ordovician Skiddaw Group is a reservoir of isotopically heavy sulphur with a range of δ 34 S from +11‰ to +29‰ [&amp; x~ (1 σ ) = 18.53 ±6.7‰ ( n = 10)]. Four analyses of Borrowdale Volcanic Group rocks yielded values of +1‰ to +15‰. Such positive values are thought to be the result of closed system bacteriogenic reduction of Ordovician seawater sulphate in the case of the Skiddaw Group, and mixing of mantle-derived magmatic sulphur with Ordovician seawater sulphate for the Borrowdale Volcanic rocks. The sulphides in the vein systems hosted by the Skiddaw Group in the Vale of Newlands formed from fluids with δ 34 S H 2 S signatures ranging from +16.7‰, to +22.5‰: partially homogenized Skiddaw Group sulphur is considered to be the source. Mineralization at Coniston, hosted by the Borrowdale Volcanic Group, shows similar sulphur isotopic characteristics, and Skiddaw Group at depth is considered to be the predominant source of sulphur with a possible minor input from the wallrock volcanic rocks at the site of deposition. Although the Lake District batholith provided a heat source for the Cu–Fe–As vein mineralization, the granite did not supply any sulphur to those systems. However, magmatic sulphur was an important constituent in mineralization associated with the Shap and Skiddaw granites. The δ 34 S values for barite mineralization at Force Crag, Greenside, Skiddaw and Shap ranges from +13‰ to +18‰, and Carboniferous seawater provides the most reasonable source for sulphate.

Isotopic evidence of the depositional environment of Late Proterozoic stratiform barite mineralisation, Aberfeldy, Scotland

Sulfur, carbon and oxygen stable isotope analyses of sulfides, barite, quartz, magnetite and carbonate and initial 87Sr/ 86Sr ratios ( I Sr) of barite have been undertaken on representative samples from barite horizons mainly in the Foss sector of the Late Proterozoic, Middle Dalradian stratiform mineralisation, near Aberfeldy in the central Scottish Highlands. The main objective of the study was to use new isotope studies to test a SEDEX depositional model which involved mixing of reduced hydrothermal solution with contemporaneous anoxic and oxygenic seawater. The assemblages studied were: massive pyrrhotite+pyrite +sphalerite+galena (scarce, and probably formed sub-seafloor only); barite +pyrite (common); and barite +magnetite (relatively uncommon). The sulfur isotope results (gd 18 SCDT) for the Foss samples, mainly from the open pit area, are: pyrrhotite and associated sulfides ( + 21 to + 24‰); pyrite (+ 27‰) with barite (+40‰); and barite (+35 to +38‰) with magnetite. Oxygen isotope analyses (δ 180 VSMOW) are: about + 14‰ for barite with pyrite and about + 16‰ for barite with magnetite. The variation in I Sr is small; I Sr being about 0.715 for barite with pyrite and about 0.714 for barite with magnetite. δ 18O of magnetite is around +7.5‰. The observed assemblages and the analytical results are considered to be reasonably consistent with the mixing model but with oxygenic seawater playing a very minor and localised role. The massive sulfide has inherited a δ 34S value of about +22‰ from hydrothermal sulfide. The end-member isotopic compositions of the sulfate resulting from mixing are likely to have been: sulfate from hydrothermal sulfide oxidised using oxygen dissolved in seawater, δ 34 S=+22‰ and δ 18 O = +25±5‰ and seawater sulfate, δ 34 S = +40‰ and δ 18 O = +14‰ . A plot of δ 34S against δ 18O for barite sulfate gives a line with a correlation coefficient of 0.766 ( n=10), which is significant above the 99% level although most points cluster close to the seawater end of the expected variation. The I Sr values of the barite suggest that the dominant source for this Sr was from the hydrothermal solution. There is no evidence for a significant contribution to sulfide by bacterial reduction of sulfide and this lack of a geochemical barrier of bacteriogenic sulfide could account for the dispersal of hydrothermal Pb and Zn and thus the apparent lack of economic base metal concentration.

Biomineralization of barite in the shell of the freshwater Asiatic clam Corbicula fluminea (Molluscs: Bivalvia)

Rosette‐shaped clusters of barite crystals were found on the depositional surface and in the inner, complex crossed‐lamellar shell layer of Corbicula fluminea collected from the Maurice River, New Jersey. Morphological analyses revealed that barite crystallized directly from the extrapallial fluid onto the inner shell layer in summer and was covered by inner shell‐layer aragonite in fall. Ba, S, and Sr were detected in energy‐dispersive X‐ray analyses of rosettes, while X‐ray diffraction of the heavy fraction of finely ground shells revealed the presence of a barite mineral composed of ∼75 mol% BaSO4 and 25 mol% SrSO4. It is suggested that barite formation resulted from the purging of soluble Ba from the tissue into the extrapallial fluid where it crystallized onto the shell in a biologically inert form.

SUBSURFACE FRACTURE ANALYSIS, PALM VALLEY GAS FIELD

A comprehensive set of directional fracture data was obtained from the Palm Valley-7 well, central Australia, which has greatly added to the knowledge of the open fracture system which is present in and largely determines production rate from the Palm Valley gas field. The high quality of the Palm Valley-7 fracture data is attributed to the use of the recently introduced tools and techniques of recording down-hole core orientation data with an electronic survey tool, of measuring core fracture orientation at surface with an electronic goniometer linked to a lap-top computer and of acquiring wire-line microresistivity (dipmeter) data which can be analysed interactively to identify fractures and calculate their orientation. Open fractures at Palm Valley-7 have measured apertures of up to 3 mm. Inferred apertures of up to 10 mm are thought to exist. Open fractures occur to depths of at least 1800 m and dip at angles variably greater than 40° towards the south-southwest and west. Many fractures are wholly or partly mineralised; the mineral assemblage is complex, with dominant ankerite (ferroan dolomite), subordinate calcite and quartz, minor barite and traces of pyrite and iron oxides. Fracture orientation and density may vary considerably laterally between wells, vertically within a well and, at a particular point in a well, between different types of fractures. This variability is to some extent controlled by host rock lithology; for example, open fractures are largely confined to highly competent sandstones and dolomitic limestones and bedding plane fractures appear to be confined to less competent shales and shaley siltstones. Results of this study, when incorporated into an ongoing, larger field fracture study, should lead to an improved structural model for the field and an improved ability to site development wells to maximise the likelihood of such wells encountering open fractures in the reservoir section.

Formation of Carboniferous Pb-Zn and barite mineralization from basin-derived fluids, Nova Scotia, Canada

Lead-zinc and barite deposits in central Nova Scotia generally occur at the Tournaisian-Visean (Mississippian) clastic carbonate-evaporite disconformity overlying Cambrian to Devonian metasedimentary and granitic rocks. The deposits are located at the southern margin of the > 10-km-deep Carboniferous Maritimes (Fundy-Magdalen) basin.Fluid inclusion homogenization temperatures of ore-stage to postore minerals range from 230 degrees to 130 degrees C and fluid salinity is > or = 24 equiv wt percent NaCl. A mineralization age of ca. 300 to 330 Ma is suggested by: (1) fission-track dates on zircon from clastic host rock at Gays River, (2) K-Ar dates on clays from altered clastic rock in close proximity to mineralization, and (3) Rb-Sr data on illite from samples collected over a 10-m section of Tournaisian sandstone (far away from mineralization). Lead and strontium isotope data indicate that Tournaisian rock of the Horton Group could have been a source (at ca. 300 Ma) of lead and radiogenic strontium in the ore-stage minerals at the larger deposits. Visean carbonate carbon and sulfate were the dominant sources of carbon and sulfur, respectively. Hydrogen and oxygen isotope data suggest that the mineralizing fluids were basinal brines. Nonbiogenic sulfate reduction at the deposits is the likely sulfide precipitation mechanism.The ore-forming fluids may have originated at a >5-km depth under Visean evaporites in the Magdalen basin and migrated rapidly through Tournaisian clastic rocks and the immediately overlying Pembroke breccia to the basin margins. A pulse of regional tectonism may have set off at least one massive, hydrofracturing, compaction-driven, fluid expulsion event by about 300 Ma.

The Kupferschiefer; an overview with an appraisal of the different types of mineralization

The Kupferschiefer; an overview with an appraisal of the different types of mineralization

Genetic studies of red bed mineralization in the Triassic of the Cheshire Basin, northwest England

The Triassic sediments of the Cheshire Basin are host to a number of small mineral deposits characteristic of red beds. The mineralization comprises Cu and Pb with minor Zn, Ag, CO, V, Ni, As, Sb and Mn which, together with widespread barite mineralization, is closely associated with basin margin faults. The Wilmslow Sandstone Formation is cemented by authigenic quartz overgrowths enclosing iron sulphides, which predate the main sulphide cements of tennantite, bornite and sulpharsenides. Studies on late calcite-hosted fluid inclusions show homogenization temperatures ranging between 60–70 o C (regarded as the minimum temperature of mineralization) and salinities of 9–22 wt% equivalent NaCl (mean = 17wt%), indicating that the mineralizing fluids were warm and saline. Consideration of the basin history suggests that fluid temperatures in the Permo-Triassic sequence may have reached 150 °C at the time of mineralization. New data significantly constrain the genetic hypothesis for the deposits, refuting a magmatic origin. A basin brine expulsion model is favoured. The sulphur isotope data from the barite mineralization (mean δ 34 S = +17‰) suggest that the bulk of the barite sulphur was derived directly from the Upper Triassic evaporites (mean δ 34 S = +19‰), whilst the distribution of δ 34 S values for sulphides (–1.8‰ to +16.2‰) is consistent with ultimate derivation of sulphur from the evaporites by closed system reduction of a sulphate-bearing brine. It seems likely that the reducing agent was organic material (methane) derived from the underlying Coal Measures, but it is uncertain at present whether the principal mechanism was thermochemical or bacterial reduction. The pattern of sulphide δ 34 S favours the former process.

Perturbation of the KAr age system in the Cleveland dyke, U.K.: Evidence of an Early Eocene age for barite mineralisation in the Magnesian Limestone of County Durham

Conventional K-Ar ages (34 in all) measured along a 300-km-long section of the Lower Tertiary Cleveland-Armathwaite dyke, of the North Atlantic Tertiary Igneous Province, U.K., range from 43.8 to 62.6 Ma. Interpreted by a model of single-stage K/Ar exchange, the best estimates for the emplacement age and age of K/Ar exchange are 59.3 ± 2.0 and 52.3–50.6 Ma, respectively. K and Ba contents are correlated and show greatest enrichment where the dyke intersects the Lunedale-Butterknowle Fault system (at the boundary between the Alston Block and adjacent basin). A seismic pumping mechanism, driven by Lower Eocene movements on this fault system, is argued to be responsible for transporting K and Ba waters to the near surface. The post-Permian barite mineralisation occurring elsewhere along the fault system may therefore be, at least in part, of Tertiary age.

Distribution, mineralogy, and geochemistry of gold and silver in the north end orebody, Rosebery, Tasmania

Study of the spatial and mineralogical distribution of gold and silver in the Rosebery north end orebody indicates that both silver and gold are concentrated in massive sphalerite-galena-pyrite ore and barite mineralization. Six styles of gold mineralization have been recognized: (1) in massive sphalerite-galena-pyrite ore (the dominant occurrence), (2) in massive barite mineralization, (3) in the upper parts of pyrite-chalcopyrite pods (in general, pyrite-chalcopyrite pods are gold poor), (4) in distal pyrite mineralization (at the edges of sphalerite-galena-pyrite mineralization and in the overlying host rocks), (5) in footwall mineralization (poorly sampled and understood), and (6) in remobilized quartz-carbonate veins.Mineralogically, gold occurs as electrum which is commonly associated with pyrite in sphalerite-galena-pyrite ore and distal pyrite mineralization. A lesser association of gold with tetrahedrite has been noted by Brathwaite (1969). The grain size of electrum has a lognormal distribution, with most grains having dimensions of less than 25 mu m.Silver occurs dominantly in tetrahedrite, and to a lesser extent, in galena (Henley and Steveson, 1978). Remobilized tetrahedrite is silver and antimony rich, whereas in tetrahedrite from both sphalerite-galena-pyrite ore and massive barite mineralization the silver contents increase with the antimony contents.

Mineralogy and paragenesis of the cupriferous deposits of the Acton Vale-Upton sector, Klippen Belt, Quebec

Mineralogical and paragenetic studies of the metallic and nonmetallic constituents of the carbonate-hosted cupriferous ores of the Acton Vale-Upton sector, Klippen Belt, Quebec, have revealed the following. The deposits are characterized by a simple mineralogy and a complex paragenesis. Several generations of pyrite and chalcopyrite are associated with sphalerite, galena, pyrrhotite, covellite, bornite, idaite, djurleite, malachite, azurite, Fe oxides, and minor barite. The deposits are characterized by three discrete mineral assemblages which are composed of syndiagenetic minerals, epigenetic minerals, and supergene minerals. They are hosted by concordantly interbedded lithologies that have been hydrothermally altered by intrusions. The deposits are characterized by massive lenticular bodies, stockworks, vugs, veins, and by cockade and replacement textures, solution collapse breccias, and karst phenomena. The deposits have been enriched in recent times by supergene processes. Considering that the lithostratigraphic sequence constitutes an ideal structural trap for ascending mineralizing fluids, it is the authors' opinion that the deposits are unconventional epigenetic, carbonate-hosted, Cu-dominant and/or Pb-Zn-Ba bodies which in their original form were too low grade to be economic. They required postdepositional remobilization and concentration to upgrade their protores. Based on the assumption that the ores were derived from the expulsion of metal-rich formation waters during compaction and that they were, at one point, contaminated and set in motion by magmatic solutions emanating from rising plutons of post-Taconic age, it is inferred that the thermal energy necessary to remobilize the ores was provided by the intrusions of the Acton Vale-Upton sector.

Use of strontium isotopes to determine the sources of hydrothermal fluorite and barite from northwestern Sicily (Italy)

Fluorite and barite mineralizations outcrop in several localities in the Western Madonie Mts. (NW Sicily, Italy). The still active mineralizing event particularly affected calcareous lithotypes belonging to the Mesozoic formations of the “Termini Imerese facies”. The samples analyzed in this work come from the Poggio Balate area where fluorite and barite seem to be more abundant than in the other localities. These minerals mainly occur in brecciated limestones of Tithonian age. The Sr isotope composition of barite, fluorite and host rocks have been determined. The fluorites show a 87 Sr 86 Sr ratio ranging from 0.70785 to 0.70790, significantly lower than that of the barites, ranging from 0.70861 to 0.70879. This difference suggests that fluorite and barite mineralizations may be the result of two isotopically different fluids. As for fluorite, the bulk of the Sr may have originated from the Tithonian limestones ( 87 Sr 86 Sr ratio range = 0.70752–0.70789), whereas the Miocene-Oligocene Numidian Flysch and Lower Jurassic bedded cherts ( 87 Sr 86 Sr ratio = 0.71646 and 0.72040, respectively) may have been sources of Sr in the barites.

Geologic and geochemical controls of mineralization in the Southeast Missouri barite district

Residual barite deposits of the Southeast Missouri barite district were derived from the weathering of lower Paleozoic dolostones, chiefly the Upper Cambrian Potosi and Eminence Dolomites. Open-space, Mississippi Valley-type mineralization in the bedrock was controlled by the intersection of permeable lithologies with late Paleozoic near-vertical faults or linear zones of intense jointing. Linear trends of residual deposits are the surface expression of these bed-rock controls. A consistent mineralogical and barite textural zonation is disposed about the central structures. Sulfide mineralization is concentrated about the central structures, whereas barite is more widespread. Barite textures vary systematically from coarse bladed near the central structures to fine plumose more distally. Such zoning indicates outward ore fluid flow from the central faults and joint zones.Fluid inclusions in sphalerite indicate that warm Na-Ca-Cl brines (69 degrees -105 degrees C, 20-25.5 equiv wt % NaCl) were present during early mineralization. Salinity data for fluid inclusions in barite (0-14 equiv wt % NaCl) may be representative of the barite mineralizing fluid, but contamination by later fluids is possible. Sulfur isotope studies show that the paragenetically early sulfides are isotopically lighter than later barite. Individual minerals involved in mainstage mineralization have the following ranges of delta 34 S values: pyrite-marcasite, 8.4 to 34.7 per mil; galena, 3.2 to 11.8 per mil; sphalerite, 7.2 to 15.8 per mil; barite, 20.5 to 32.2 per mil. Barite delta 34 S values show enrichment in 34 S away from the central fault. This spatial distribution is due to the incorporation of sulfate from two reservoirs. Isotopically light sulfate, developed most strongly about the central fault, originated from the oxidation of H 2 S in the ore fluid emanating from the central fault. The heavy sulfate that prevailed distally was indigenous to the host dolostone formation water. The delta 18 O values of main-stage barite vary from 17.0 to 19.6 per mil and the range is attributed to mixing of two fluids of different oxygen isotope composition and to variable isotopic fractionation between sulfate and water due to changing temperature. The light sulfur and oxygen isotope composition of supergene barite (delta 34 S = 15.8ppm, delta 18 O = 9.0ppm) is due to incorporation of isotopically light sulfate produced locally during the oxidation of sulfide minerals in the soil environment.Barite precipitation was caused by fluid mixing, in which a Ba-Pb-Zn-H 2 S-bearing brine discharged from faults and joints into lower Paleozoic dolostones and mixed with an oxidizing, sulfate-bearing, dilute fluid. Increased supersaturation of barite with progressive mixing caused the systematic spatial variation of barite textures from coarse bladed near the central structures to fine plumose more distally. Similar barite-sulfide mineralization in the Central Missouri barite district probably formed in the same manner. Barite mineralization across the north flank of the Ozark dome postdates local Appalachian-Ouachita-Marathon orogenic deformation and suggests the existence of dilute sulfate-bearing water, probably shallow meteoric ground water, in the Paleozoic section during barite mineralization. Uplift of the Ouachitas in late Paleozoic time apparently initiated Mississippi Valley-type mineralization of the Ozark region.