Inclusions In Barite Research Articles

Phase separation and fluid mixing in subseafloor back arc hydrothermal systems: A microthermometric and oxygen isotope study of fluid inclusions in the barite‐sulfide chimneys of the Lau Basin

Fluid inclusions in barite and sulfide in chimneys (both active and inactive) from three hydrothermal sites of the back arc Lau basin were studied with microthermometric and isotopic methods to determine the chemistry and evolution of hydrothermal aqueous fluids. Strontium isotope compositions of sulfides from the Lau basin reflect the presence of anhydrite and barite inclusions. The 87Sr/86Sr ratios of these two sulfate minerals vary from 0.7045 to 0.7078 and are interpreted as the result of mixing between various proportions of the hydrothermal end‐member and pure seawater. The microthermometric study of fluid inclusions reveals that mixing with seawater involved different kinds of aqueous fluid end‐members. A high‐temperature Mg‐depleted end‐member of high salinity (≥5.5 wt % eq NaCl) was found at the Vai Lili site. A uncommon low‐temperature Mg‐rich end‐member was also identified at the Hine Hina site in association with barite deposition. At the Vai Lili site, very low salinity fluids were produced in addition to a very saline brine (≥30 wt % NaCl) that was trapped inside anhydrite precipitated from an active vent at a temperature of 342°C. Oxygen isotope ratios of water inclusions range from 2‰ to 4.4‰ for chalcopyrite, barite, and sphalerite minerals. The 18O enrichment and the high salinities of many fluids from the Lau basin are accounted for by the specificity of the back arc setting. This non mid‐ocean ridge setting is characterized by the shallow depth of the hydrothermal systems that allows frequent unmixing of high‐temperature liquids. The abundance of silicic magmas also provided magmatic fluids (including brines) that mixed with seawater‐derived aqueous fluids.

Aqueous and liquid petroleum inclusions in barite from the Walton Deposit, Nova Scotia, Canada; a Carboniferous, carbonate-hosted Ba-Pb-Zn-Cu-Ag deposit

The Walton Ba-Pb-Zn-Cu-Ag deposit, with a historical (1941-1978) production of 4.4 Mt of barite and 0.36 Mt of massive sulfide ore, is hosted by sideritized, Visean carbonates of the Macumber Formation which forms the basal member of the marine Windsor Group in southern Nova Scotia. Strata-bound mineralization occurs as massive barite which gives way to barite and sulfide mineralization at depth; locally, mineralization transects bedding and may occur within the underlying terrestrial clastics of the Tournaisian Horton Group. Barite occurs in a variety of forms (massive to bladed, fine to coarse grained) and colors (white, red, orange, and shades of these) and overlaps the deposition of sulfide minerals.All barite types are characterized by the presence of abundant aqueous and liquid petroleum fluid inclusions that are of dominantly equant shape, of primary and secondary origin, and < or = 100- to 150-mu m size. Inclusions are classified as (1) L- and V-rich aqueous with rare solid phases, (2) mixed CO 2 and CH 4 (rare), and (3) liquid petroleum with rare bitumen. It is not possible to establish a chronology for the different fluids and all types may, in fact, be closely related temporally and spatially. The occurrence of three-phase aqueous-petroleum inclusions, indicative of heterogeneous trapping, indicates contemporaneity of the aqueous and petroleum inclusions. The aqueous inclusions are dominated by high-salinity types (20-28 wt % NaCl equiv), but intermediate- and low-salinity types also occur. Observations of first melting (eutectics at -55 degrees and -35 degrees C) and final melting (ice and hydrohalite) indicate that fluid compositions varied in terms of NaCl/(NaCl + CaCl 2 ) (< or = 0.1-1.0) and NaCl/(NaCl + MgCl 2 ) (0.2-0.84) ratios. Preliminary SEM-EDS analysis of decrepitate mounds confirms the presence of Na, Ca, and Mg and also indicates K, Fe, and Mn in solution. The lack of clathrate phases suggests that, if present, condensed gases (e.g., CH 4 , CO 2 ) occur in only minor to trace amounts in aqueous inclusions. Homogenization temperatures cover a broad range with maximum temperatures of ca. 300 degrees C.Liquid petroleum inclusions, with a blue-white color under ultraviolet light, occur in isolated populations with uniform L/V ratios characterizing a particular group. Homogenization temperatures range from ca. 100 degrees to 300 degrees C, similar to the range for aqueous inclusions but within a group a much narrower range is recorded. The high homogenization temperatures and rare occurrence of bitumen in the inclusions predicates rapid, postentrapment cooling of the area (i.e., within a few kiloyears), otherwise degradation of the petroleum would have occurred. The delta 34 S signatures of sulfides at Walton suggest that mineralization occurred in the presence of liquid petroleum with the petroleum causing reduction of aqueous sulfate to H 2 S.Collectively the fluid inclusion data indicate that mineralization occurred at ambient conditions of 250 degrees to 300 degrees C and pressures of ca. 400 bars, as constrained for different inclusion types. The liquid petroleum is considered to have been generated by thermogenic processes via interaction of the heated, highly saline mineralizing fluid with organic-rich beds within the Horton Group (Horton Bluff Formation) and was subsequently entrained as an immiscible phase within the aqueous fluid. Generation of the hydrothermal petroleum at Walton is analogous to the present-day occurrence of liquid petroleum vented from black smokers on the ocean floor (e.g., Guaymas basin).

Barite Inclusions in Fluorite

Barite Inclusions in Fluorite

Volcanic‐hosted sulfide‐barite deposit from the Kita‐Bayonnaise submarine caldera, Izu‐Ogasawara arc, northwestern pacific

Volcanic‐hosted sulfide and barite mineralization with high Au content (19.3 ppm) was discovered by submersible study (Shinkai 2000) on the eastern floor of the Kita‐Bayonnaise submarine caldera on the Shichito‐Iwojima Ridge, Izu‐Ogasawara Arc, northwestern Pacific. The hydrothermally mineralized rhyolitic tuff is partly coated by Mn oxyhydrox‐ide, and associated with hydrothermal Mn crusts and debris of mussel shells in the vicinity of the hydrothermally altered tuff‐breccias. The minearlized rhyolitic tuff occurs as a fragment of a large block (about 2 ×1 ×1 m) on talus, while the crusts occur on the caldera floor as a few thin patches several meters across or smaller. Ore‐mineral composition of the mineralized rhyolitic tuff consists mainly of sulfides and barite. Randomly interstratified seriate and montmorillonite is the only hydrothermal clay mineral from glass shards in the mineralized rhyolitic tuff. The mineralized tuff is significantly enriched in Zn, Fe, Cu, Ba, Au, Ag, and As, and has high Au /Ag ratio (0.036 to 0.071) compared with other marine volcanogenic sulfides. Au is probably present as submicrometer‐sized particles within sulfide minerals or is contained within the crystal lattice of the sulfide minerals. The δ34S values of sulfides of subsamples from the mineralized rhyolitic tuff indicate a fairly narrow range between +3.4 and +4.8% but are characterized by lighter isotopes in a drusy cavity compared with vein and disseminated sulfides. The sulfide sulfur is mainly from volcanic rocks of the caldera basement. A single barite sulfur isotopic value (+20.7%o) and salinity of fluid inclusions in barite are close to modern seawater values, suggesting a major contribution of seawater sulfate to the barite precipitation.

Origin of ‘exotic’ minerals in Mississippi salt dome cap rocks: results of reaction-path modeling

Shallow salt domes in central Mississippi pierce Mesozoic formations hosting regionally extensive metal-rich brines. This association, coupled with the multiple fluid-migration pathways around salt domes, suggests that these brines were the source of Fe and base-metal sulfide, Sr, and Ba minerals in salt dome cap rocks. Fluid inclusions in barite and celestite indicate that the brines had a relatively constant average composition of approximately 200,000 mg/I total dissolved solids, which is similar to present-day oil field brines from central Mississippi. Geochemical reaction-path modeling indicates that the suite of observed cap rock minerals can be produced by alternating periods of biogenic SO 4 reduction with inorganic anhydrite dissolution (or by mixing with seawater). Sulfide-rich portions of cap rock at Hazlehurst salt dome have molar Fe:Pb and Fe:Zn ratios similar to present-day oil field brines, indicating that mixing of brines with abundant amounts of H 2S produced by biogenic SO 4 reduction led to rapid precipitation of virtually all dissolved metals as relatively insoluble sulfide minerals.

Fluid inclusions and preliminary studies of hydrothermal alteration in core hole PLTG-1, Platanares geothermal area, Honduras

Abstract The Platanares geothermal area in western Honduras consists of more than 100 hot springs that issue from numerous hot-spring groups along the banks or within the streambed of the Quebrada de Agua Caliente (brook of hot water). Evaluation of this geothermal area included drilling a 650-m deep PLTG-1 drill hole which penetrated a surface mantling of stream terrace deposits, about 550 m of Tertiary andesitic lava flows, and Cretaceous to lower Tertiary sedimentary rocks in the lower 90 m of the drill core. Fractures and cavities in the drill core are partly to completely filled by hydrothermal minerals that include quartz, kaolinite, mixed-layer illite-smectite, barite, fluorite, chlorite, calcite, laumontite, biotite, hematite, marcasite, pyrite, arsenopyrite, stibnite, and sphalerite; the most common open-space fillings are calcite and quartz. Biotite from 138.9-m depth, dated at 37.41 Ma by replicate 40 Ar/ 39 Ar analyses using a continuous laser system, is the earliest hydrothermal mineral deposited in the PLTG-1 drill core. This mid-Tertiary age indicates that at least some of the hydrothermal alteration encountered in the PLTG-1 drill core occured in the distant past and is unrelated to the present geothermal system. Furthermore, homogenization temperatures ( T h ) and melting-point temperatures ( T m ) for fluid inclusions in two of the later-formed hydrothermal minerals, calcite and barite, suggest that the temperatures and concentration of dissolved solids of the fluids present at the time these fluid inclusions formed were very different from the present temperatures and fluid chemistry measured in the drill hole. Liquid-rich secondary fluid inclusions in barite and caicite from drill hole PLTG-1 have T h values that range from about 20°C less than the present measured temperature curve at 590.1-m depth to as much as 90°C higher than the temperature curve at 46.75-m depth. Many of the barite T h measurements (ranging between 114° and 265°C) plot above the reference surface boiling-point curve for pure water assuming hydrostatic conditions; however, the absence of evidence for boiling in the fluid inclusions indicates that at the time the minerals formed, the ground surface must have been at least 80 m higher than at present and underwent stream erosion to the current elevation. Near-surface mixed-layer illite-smectite is closely associated with barite and appears to have formed at about the same temperature range (about 120° to 200°C) as the fluid-inclusion T h values for barite. Fluid-inclusion T h values for calcite range between about 136° and 213°C. Several of the calcite T h values are significantly lower than the present measured temperature curve. The melting-point temperatures ( T m ) of fluid-inclusion ice yield calculated salinities, ranging from near zero to as much as 5.4 wt. % NaCl equivalent, which suggest that much of the barite and calcite precipitated from fluids of significantly greater salinity than the present low salinity Platanares hot-spring water or water produced from the drill hole.

Temperature, pressure, burial history, and paleohydrology of the Les Malines, Pb-Zn deposit; reconstruction from aqueous inclusions in barite

Aqueous inclusions in oil-bearing vug-filling barite which postdates the karstic and fissural ore stages at Les Malines, one of the largest Mississippi Valley-type Zn-Pb deposits in Europe, have been studied by microthermometry and Raman spectrometry. The correlative variations of the melting points of ice (T (sub m ice ) and of the homogenization temperatures (T h define three main stages: (1) stage I, gas-rich inclusions characterized by T (sub m ice ) = -7 degrees + or - 1 degrees C and T (sub h (sub L-V(V)) ) = 180 degrees to 380 degrees C, (2) stage II, liquid-rich and gas-rich inclusions homogenized in the temperature range of 160[degree to 175 degrees C, with T (sub m ice ) = -8.2 degrees to -4.1 degrees C--stage I and stage II inclusions contain CO 2 and no CH 4 , N 2 , or H 2 S detectable by Raman spectrometry, and (3) stage III, liquid-rich inclusions, characterized by T (sub m ice ) which increased from -8 degrees to -1.7 degrees C as their T (sub h (sub L-V(L)) ) decreased from 160 degrees to 130 degrees C. They are essentially aqueous.The H 2 O-CO 2 -NaCl vapor-dominant stage I inclusions in barite cannot have leaked because their gas content is distinct from air. They are interpreted to have trapped a hot (T approximately 300 degrees C), CO 2 -bearing vapor which was cooling. Oil was thermally degraded during trapping in barite. The source of heat and CO 2 is considered to be volcanism contemporaneous with the major uplift of the horst during the Upper Jurassic, Dissolution of the carbonated wall rock is related to stage I. Stage II inclusions are interpreted to represent the end-product of the mixing of pore fluid with the hot vapor. The temperature of the pore fluid exceeded 150 degrees prior to the addition of magma-heated fluids. Such anomalous pore fluid temperatures are tentatively related to the steady dewatering of the Terres Noires shales from below, with the fluids moving up along the east-west fault of Les Malines near adiabatic conditions. The formation waters were probably responsible for the migration of the oil and for the recrystallization of the basement. Gas-rich and liquid-rich stage II inclusions are compatible with minor unmixing of the H 2 O-CO 2 -NaCl liquid with precipitation of calcite. The V-X properties calculated for a stage II liquid-rich inclusion (96.1 mole percent H 2 O, 1.85 mole percent NaCl, and 2 + or - 0.2 mole percent CO 2 ; V = 21.5 + or - 1.3 cm 3 mole (super -1) fix the pressure of unmixing at 175 degrees C in the range 285 + or - 45 bars. The T h -V-X properties of secondary CO 2 -bearing inclusions in barite from the earlier fissural stage (Charefand Sheppard, 1988) point to higher fluid pressures in the horst, in the range of 365 + or - 45 bars minimum. CO 2 -rich inclusions in the two barite generations imply that the metamorphosed Cambrian basement at Les Malines has been transiently geopressured below the Triassic shales. The addition of a small amount of magma-derived CO 2 to the pore fluid probably accounts for the rapid increase of pressure. The fluid pressure in the horst reached near-lithostatic values repetitively, first at the end of the Middle Jurassic subsidence, when the burial depth was around 1,600 + or - 200 m, then at a later stage, probably during the Upper Jurassic, when the sedimentary cover was partly eroded to around 1,200 + or - 200 m. The overpressuring, with a possible structural deformation resulting from the rising magma, probably caused the opening of the vertical, late barite-filled veins by hydraulic fracturing. Stage III inclusions are interpreted to indicate the influx of colder diluted fluid to the horst under hydrostatic pressure conditions, i.e., after decompression.

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.

Synthesis of barium-strontium sulphate solid solution and some considerations on the genesis of barite-celestite deposits in Neuquen province, Argentina.

Experiments on the synthesis of barium-strontium sulphate solid solution were performed. The results showed that the cell constants a0 and c0 of the solid solution series vary linearly with respect to chemical composition and corresponding changes in b0 follow a curve with gentle slope. Since the synthesized mineral was richer in barium than the solution, the [Sr2+]:[Ba2+] ratio of the solution became gradually higher as crystallization of the mineral progressed. The results also showed that the distribution coefficient kBaSr increased with increasing temperature. It was observed that crystallization of the mineral with intermediate [BaSO4]:[SrSO4] molar ratio ranging from about 1:1 to 1:4 at 270°C and from about 3:1 to 1:9 at 170°C, was extremely more difficult than the minerals outside these ranges. This indicates a possibility that at these ranges an immiscibility area exists. It appears that the area is enlarged with decrease in temperature. Many barite-celestite deposits are found in Neuquen province, Argentina. Some of them are of vein-type traversing stratified rocks. Others have bedded shapes, roughly concordant with stratification and formed by selective replacement of limestone seams by barite and celestite. Measured homogenization temperature of liquid inclusions in barite and celestite, their chemical compositions, wall-rock alterations, the associated sulphide minerals and the results of the present synthesis experiments suggest that these deposits were formed under the following conditions: (1) Some of the ore deposits were formed by hydrothermal solutions poor in strontium at rather high temperatures; (2) Some others were formed by hydrothermal solutions rich in strontium at rather high temperatures; and (3) the rest of the deposits were formed by hydrothermal solutions rich in strontium at rather low temperatures.