Barite Deposits Research Articles

A Special Issue Devoted to Barite and Zn-Pb-Ag Deposits in the Red Dog District, Western Brooks Range, Northern Alaska

The Brooks Range in northern Alaska (Fig. 1) contains an enormous accumulation of zinc and barite. The four deposits at Red Dog (Qanaiyaq, Main, Aqqaluk, and Paalaaq) have reserves and resources totaling 140.6 Mt at 16.6 percent Zn and 4.6 percent Pb (Jennings and King, 2002), which surpass most deposits worldwide in terms of grade and size (Fig. 2). Including resources of the unmined Su-Lik (38 Mt at 9% Zn + Pb; Jennings and King, 2002) and Anarraaq deposits (18 Mt at 23% Zn + Pb; King et al., 2002) northwest of Red Dog, the district has about 40 Mt of contained Zn + Pb (Fig. 2). For comparison, both the Broken Hill deposit and the Mt. Isa district (including the George Fisher, Hilton, and Mt. Isa deposits) in Australia contain more than 50 Mt Zn + Pb (Large et al., 2002). The Australian deposits are lead rich compared with the Brooks Range deposits. In terms of total zinc content, the combined deposits of the Red Dog district (~31 Mt) rival that of the Mt. Isa district (~36 Mt) and surpass Broken Hill (~25 Mt). In terms of zinc concentrate production, the Red Dog mine has the world’s largest—almost 600,000 tonnes (t) per year. The Brooks Range barite deposits are extraordinarily large. The barite body at the Anarraaq deposit alone is estimated to be as much as 1 billion metric tonnes (King et al., 2002). The Wulik, Moil, and Gull barite deposits (Fig. 1) are interpreted to be the lateral equivalents of the Anarraaq barite body (J. Clark, Teck Cominco, pers. commun., 2003), making the total area underlain by these deposits a minimum of 20 km2. Owing to a lack of published information, it is uncertain how this deposit compares with the giant barite bodies in south China, but …

Formation of modern and Paleozoic stratiform barite at cold methane seeps on continental margins: Comment and Reply

[Maynard and Okita (1991)][1] divided ancient bedded barite deposits into two major types: (1) continental margin type, which lacks significant accumulations of base metals, such as the Nevada and Arkansas deposits; and (2) cratonic rift type, which contains significant Pb and Zn, such as the Meggen

Age determination of submarine hydrothermal barite deposits by the 210Pb/226Ra method

An age determination and the chemical composition of hydrothermal barite, collected from an Okinawa Trough hydrothermal field, were studied. Initially contaminated 210Pb in sulfide and other minerals were leached by a chemical treatment. After the treatment, the radioactivity and chemical composition were determined by gamma spectrometry and neutron activation analysis, respectively. The following results were obtained: 1. An accurate and reproducible age was obtained by a chemical treatment of barite samples. 2. A matrix effect of barite samples on gamma-ray measurement was significantly observed, and was calibrated with mixed NaCl-BaSO4 references. 3. The precipitation age, calculated by the 210Pb/226Ra method after correction was concordant with the 228Th/228Ra and 228Ra/226Ra methods. 4. The Sr/Ba weight ratios were in the range of 0.007∼0.053, which seems to have positive relationship with the temperature of the hydrothermal vent fluid. 5. A chronological study of barite in sample No. 974R1 showed that Sr/Ba weight ratio seems to be high in older samples, and tends to decrease in young samples, which would suggest a possible alteration of the hydrothermal activity in this field.

Comparison of some sediment-hosted, stratiform barite deposits in China, the United States, and India

Shifts in world barite production since the 1980s have resulted in China becoming the world's largest barite-producing country followed by the US and India. Most barite produced for use in drilling fluids is derived from black shale- and chert-hosted, stratiform marine deposits. In China, Late Proterozoic to Early Cambrian marine barite deposits occur on the oceanic margins of the Yangtze platform, in the Qinling region in the north and the Jiangnan region in the south. Most US ore-grade deposits are in the Nevada barite belt; most commercial deposits occur in Ordovician and Devonian marine rocks along the western margin of the early Paleozoic North American continent. Production in India is predominantly from a single Middle Proterozoic deposit in a sedimentary basin located on Archean basement in Andrah Pradesh. The geologic and geochemical characteristics of the deposits are consistent with origins from a variety of sedimentary-exhalative processes, with biogenic processes contributing to the concentration of some seafloor barite. Linear distributions of clusters of lenticular deposits suggest a geographic relationship to syndepositional seafloor fault zones. Sulfur isotope data of the barite deposits range from values that are similar to coeval seawater sulfate to significantly higher δ 34S values. Strontium isotope values of continental-margin-type deposits in Nevada and China are less radiogenic than those of cratonic-rift deposits (e.g. Meggen and Rammelsberg). Comparison of La n /Ce n ratios of barite in the Qinling region of China with marine chert ratios suggests a relationship to hydrothermal fluids, whereas ratios from the Jiangnan region and Nevada can be interpreted as reflecting a biogenic influence. The California Borderland provides a potential modern analog where hydrothermal barium is being deposited on the seafloor in fault-block-bounded basins. Anoxic to dysaerobic conditions on some marine basin floors result from upwelling, nutrient-rich currents and high productivity in surface waters. In this setting, biogenic processes could contribute to the concentration of barium from hydrothermal sources.

The antiquity of microbial sulfate reduction

The phylogenetic positions of sulfate-reducing organisms, as revealed from comparisons of small-subunit ribosomal RNA (SSU rRNA), are spread over both the Archaeal and Bacterial domains, though when they evolved is uncertain. The low-branching positions of some of these groups on the Tree of Life have inspired the hypothesis that the metabolic innovation of microbial sulfate reduction is of great antiquity. Only recently, however, have sulfur isotope data from Precambrian rocks begun to emerge that clearly demonstrate sulfate-reducing microbes had evolved by the early Archean. The large spread of δ 34S values of microscopic pyrites aligned along growth faces of former gypsum crystals in the ∼3.47-Ga North Pole barite deposit of northwestern Australia provide the oldest evidence of microbial sulfate reduction and the earliest indication of a specific microbial metabolism. The distinct expression of microbial sulfate reduction in this localized and cool sulfate-rich environment provides the oldest date for calibrating the temporal progress of early evolution on the Tree of Life.

A NEW FOSSIL VENT BIOTA IN THE BALLYNOE BARITE DEPOSIT,SILVERMINES, IRELAND: EVIDENCE FOR INTRACRATONIC SEA-FLOOR HYDROTHERMALACTIVITY ABOUT 352 Ma

Considerable controversy exists as to the timing of the important Mississippian carbonate-hosted Irish-type Zn + Pb ± Ba ± Ag deposits. The Silvermines deposits have been defined as an end member of this style in that they have been interpreted to display textures indicative of sea-floor deposition. One of the strongest arguments in favor of this interpretation was the report of a hydrothermal vent field, including pyritic chimneys in the Ballynoe open-pit barite deposit. This paper adds to that body of evidence by describing a hydrothermal vent fauna from the same vent field, consisting of a delicately pyritized worm tube hosted by massive pyrite and hematized filaments of apparent microbial origin. The worm tube is remarkably similar to fossil worm tubes from modern and ancient volcanic-hosted massive sulfide deposits, and the filamentous microfossils have similarities to modern Fe-oxidizing bacteria. We have found no correlation between the worm tube and normal Mississippian fossils such as crinoids, whose replacement by pyrite in the immediately underlying Ballynoe footwall destroys original morphology. The sulfur isotope composition of the worm tube and host pyrite is essentially identical to that of the vent field pyrite and the main sulfide ore stage of Silvermines sulfides, all having a mean value about –20 per mil, indicating an open-system bacteriogenic sulfide source. These discoveries provide additional evidence for the exhalative nature of parts of the Silvermines orebodies, and imply that mineralization had begun in the Irish ore field by the late Tournaisian (~352 Ma).

Stratigraphy and sedimentary petrology of an Archean volcanic–sedimentary succession at Mt. Goldsworthy in the Pilbara Block, Western Australia: implications of evaporite (nahcolite) and barite deposition

Abstract A approximately 3.3 Ga sedimentary succession at Mt. Goldsworthy in the northeastern Pilbara Block, Australia contains beds composed of silicified pseudomorphs of nahcolite (NaHCO3) or barite (BaSO4). This sedimentary succession correlates with the Corboy Formation and consists of lower, middle and upper sedimentary units, which conformably overlie mafic to ultramafic volcanic and volcaniclastic rocks. The lower and middle units are predominantly siliciclastic, whereas the upper unit is characterized by ferruginous cherts and banded iron-formations with minor proportions of intercalated mature sandstone. The succession defines an overall upward fining and deepening trend. The detrital materials were derived from older greenstone successions, volcaniclastics and reworked precipitative beds. Silicified pseudomorphs of nahcolite crystals up to 40 cm in length occur in a 20 m thick bed in the upper portion of the lower unit. The formation of this unit was initiated by deposition of immature terrigenous clastic sediments and followed by the precipitation of nahcolite from Na+-HCO3− brines in a closed or semi-closed evaporitic basin. Bladed barite deposits occur mainly in the middle unit, which was deposited in a sub-aerial to shallow marine environment. Barite may have precipitated as a result of mixing of SO42−-rich seawater and Ba2+-rich hydrothermal fluids. The Mt. Goldsworthy sedimentary succession records an Archean shallow to sub-aerial sedimentary environment that probably developed in a continental margin setting.

Formation of modern and Paleozoic stratiform barite at cold methane seeps on continental margins

Stratiform (bedded) Paleozoic barite occurs as large conformable beds within organic- and chert-rich sediments; the beds lack major sulfide minerals and are the largest and most economically significant barite deposits in the geologic record. Existing models for the origin of bedded barite fail to explain all their characteristics: the deposits display properties consistent with an exhalative origin involving fluid ascent to the seafloor, but they lack appreciable polymetallic sulfide minerals and the corresponding strontium isotopic composition to support a hydrothermal vent source. A new mechanism of barite formation, along structurally controlled sites of cold fluid seepage in continental margins, involves barite remobilization in organic-rich, highly reducing sediments, transport of barium-rich fluids, and barite precipitation at cold methane seeps. The lithologic and depositional framework of Paleozoic and cold seep barite, as well as morphological, textural, and chemical characteristics of the deposits, and associations with chemosymbiotic fauna, all support a cold seep origin for stratiform Paleozoic barite. This understanding is highly relevant to paleoceanographic and paleotectonic studies, as well as to economic geology.

Massive barite deposits and carbonate mineralization in the Derugin Basin, Sea of Okhotsk: precipitation processes at cold seep sites

An area of massive barite precipitations was studied at a tectonic horst in 1500 m water depth in the Derugin Basin, Sea of Okhotsk. Seafloor observations and dredge samples showed irregular, block- to column-shaped barite build-ups up to 10 m high which were scattered over the seafloor along an observation track 3.5 km long. High methane concentrations in the water column show that methane expulsion and probably carbonate precipitation is a recently active process. Small fields of chemoautotrophic clams (Calyptogena sp., Acharax sp.) at the seafloor provide additional evidence for active fluid venting. The white to yellow barites show a very porous and often layered internal fabric, and are typically covered by dark-brown Mn-rich sediment; electron microprobe spectroscopy measurements of barite sub-samples show a Ba substitution of up to 10.5 mol% of Sr. Rare idiomorphic pyrite crystals (∼1%) in the barite fabric imply the presence of H2S. This was confirmed by clusters of living chemoautotrophic tube worms (1 mm in diameter) found in pores and channels within the barite. Microscopic examination showed that micritic aragonite and Mg-calcite aggregates or crusts are common authigenic precipitations within the barite fabric. Equivalent micritic carbonates and barite carbonate cemented worm tubes were recovered from sediment cores taken in the vicinity of the barite build-up area. Negative δ13C values of these carbonates (>−43.5‰ PDB) indicate methane as major carbon source; δ18O values between 4.04 and 5.88‰ PDB correspond to formation temperatures, which are certainly below 5°C. One core also contained shells of Calyptogena sp. at different core depths with 14C-ages ranging from 20 680 to >49 080 yr. Pore water analyses revealed that fluids also contain high amounts of Ba; they also show decreasing SO42- concentrations and a parallel increase of H2S with depth. Additionally, S and O isotope data of barite sulfate (δ34S: 21.0–38.6‰ CDT; δ18O: 9.0–17.6‰ SMOW) strongly point to biological sulfate reduction processes. The isotope ranges of both S and O can be exclusively explained as the result of a mixture of residual sulfate after a biological sulfate reduction and isotopic fractionation with ‘normal’ seawater sulfate. While massive barite deposits are commonly assumed to be of hydrothermal origin, the assemblage of cheomautotrophic clams, methane-derived carbonates, and non-thermally equilibrated barite sulfate strongly implies that these barites have formed at ambient bottom water temperatures and form the features of a Giant Cold Seep setting that has been active for at least 49 000 yr.

Fluid seepage along the San Clemente Fault scarp: basin-wide impact on barium cycling

Material fluxes associated with fluid expulsion at cold seeps and their contribution to oceanographic budgets have not been accurately constrained. Here we present evidence that the barium released at cold seeps along the San Clemente Fault zone may significantly impact the geochemical budget of barium within the basin. Barium fluxes at seep localities on the fault scarp, measured with benthic chambers, reach values as high as 5 mmol m−2 day−1. This is the largest dissolved barium flux measured to date at a cold seep. The discharge of barium-rich fluids results in formation of massive barite deposits along the escarpment wall. The deposits are young (approximately 8 yr) and appear to grow at a minimum rate of 0.2 cm yr−1. This rapid growth rate requires a barium efflux rate that is about two orders of magnitude higher than the measured dissolved flux. We believe that the discrepancy reflects a highly localized seepage system and that chambers positioned as close as possible to the growing chimneys did not sample the foci of fluid discharge. Transport of fine barite particles from the seeps may be responsible for excess rates of barium accumulation throughout the San Clemente Basin, relative to other basins in the California Margin. Based on a preliminary budget, we estimate that cold-seep barite is accumulating at the basin floor in San Clemente at a rate of 2 μmol m−2 day−1, a value that is comparable to the total barium accumulation rates driven by detrital and biogenic components in neighboring basins. Remobilization of cold-seep barite on the basin floor adds to that driven by the biogenic barium flux and results in benthic barium recycling rates (effluxes) within the San Clemente Basin that are as much as seven times higher than the effluxes from surrounding borderland basins. Our estimates imply that processes associated with fluid seepage along the San Clemente Fault significantly contribute to the basin’s barium cycle. The strontium isotopic composition of the seep barite is significantly different from marine ‘biogenic’ barite, which is known to accurately record seawater composition. In addition, the seep deposits are depleted in 226Ra relative to their modern biogenic counterparts, and are likely to be a source of radium-depleted particulate barium to the basin. Thus the impact of barite transport from seeps on the San Clemente escarpment to the basin floor might also have implications for the geochemistry of elements other than barium.

Geology and geodynamic setting of Archaean silicic metavolcaniclastic rocks of the Bien Venue Formation, Fig Tree Group, northeast Barberton greenstone belt, South Africa

Mapping of the northeastern part of the Barberton greenstone belt (BGB) has delineated a new lithostratigraphic unit, the Bien Venue Formation, within the Fig Tree Group, Swaziland Supergroup, South Africa. The formation is composed mainly of quartz–muscovite (±andalusite±chlorite±chloritoid±pyrophyllite) schists derived from a sequence of quartz-phyric, dacitic-to-rhyodacitic volcaniclastic protoliths dated at 3256±1 and 3259±5 Ma. Subordinate rock types include banded chert, phyllite, biotite–plagioclase (±chlorite±carbonate) schists derived from plagioclase-phyric dacitic volcaniclastic assemblages, and chlorite (±carbonate±amphibole) schists representing altered basalt or basalt-andesite. These rocks were deposited on deep-water shales, turbiditic greywackes, banded iron-formations (BIFs) and silicic metavolcaniclastic assemblages correlated with the Belvue Road Formation, and are, in turn, overlain by alluvial to shallow-marine sandstones and conglomerates of the Moodies Group along a regional unconformity. In places, the quartz–muscovite schists host subeconomic massive sulphide (Zn–Cu–Pb–Ag) and barite deposits of probable volcanogenic origin. The sedimentary structures, lithologies, stratigraphic associations, and mineral deposits suggest that the Bien Venue Formation represents a proximal volcaniclastic succession formed in a largely subaqueous depositional environment that may have varied from deep (>1 km depth) to shallow water. The protoliths of the Bien Venue schists were geochemically similar to calc-alkaline and transitional tholeiitic-calc-alkaline suites formed at Phanerozoic mature active continental margins. Variably fractionated rare earth element (REE) profiles, moderate abundances of Yb and Y, and relative depletions at Ta–Nb, P and Ti on normalised immobile multi-element diagrams are consistent with hydrous fusion of upper mantle material above steeply subducted oceanic crust undergoing dehydration. The features suggest that the Bien Venue Formation records Early Archaean continental arc volcanism along the north-east flank of the BGB. The lithochemical signatures of the Bien Venue rocks are distinctly different from those of silicic volcanic suites hosting major syngenetic polymetallic massive sulphide deposits in Canada. The host rocks of the Bien Venue massive sulphide deposit do not appear to have undergone significant fractionation in a high-level magma repository which could have supplied heat for the development of a major mineralising hydrothermal fluid system. These observations suggest low potential for the discovery of economic base-metal massive sulphide deposits in the rocks of the Bien Venue Formation. The Bien Venue rocks were previously included in the Theespruit Formation of the Onverwacht Group, however, the isotopic age data indicate that they are some 290 million years younger than the oldest assemblages within the lower Onverwacht. The schists are also 30 million years older than plagioclase-phyric dacitic rocks within the Schoongezicht Formation (ca. 3226 Ma), uppermost formation of the Fig Tree Group along the northwest flank of the BGB, precluding direct correlation with this unit. Published ages indicate that the Bien Venue Formation is a temporal correlative of proximal volcaniclastic rocks making up the Auber Villiers Formation (3256 Ma), and possibly also some distal dacitic tuffaceous sequences within the Mapepe Formation (3258–3227 Ma), both of which form part of the southern Fig Tree facies.

Geochemical Investigations of Stratabound Gunga Barite Deposits of Khuzdar (Balochistan), Pakistan

Abstract: The Gunga barite deposits occur in carbonate clastic marine sequence of Jurassic age. These rocks are widely spread in Khuzdar‐Lasbela belt which host important stratabound barite and zinc‐lead deposits of Pakistan. These rocks are intricately folded and extensively faulted. The Gunga are low temperature hydrothermal deposits occurring as a series of disconnected lenses a few meters thick. Two mineralized horizons are recognized: barite in the upper zone, sphalerite and galena in the lower zone. Four types of barite mineralization occurs in Gunga stratabound replacement associated with 1) fracture filling, 2) open space fillings in solution collapsed breccia, 3) replacement in fault, and 4) veinlets associated with all these three types. The wall rocks of the Gunga deposits have also been altered by silicification, leaching and ferruginization.The sulfur isotope values of most of the Gunga barite samples range from 23.8 to 27.8 per mil with an average of 26.4 per mil, which is very close to the average of isotopic values of epigenetic carbonate hosted Late Paleozoic Missouri barite deposits. The Gunga like other barite and sulfide deposits of Khuzdar‐Lasbela belt are Mississippi Valley type, stratabound and of replacement origin precipitated from connate brines expelled during the incipient rifting of India from Gondwana land in the Late Jurassic and Early Cretaceous periods. The low content of copper, lead and zinc in the Gunga barite deposits suggests that these deposits were not formed in proximity to an igneous source of the ore solution.The Gunga deposits are epigenetic and stratabound as their mineralization is structure controlled. There is an evidence of transgressive nature of host rock and wall rock alteration which are absent in stratiform or bedded deposits.

Origin of marine barite deposits: Sr and S isotope characterization

Barite can precipitate in microenvironments in the water column (marine barite), from supersaturated pore fluids at the oxic-anoxic boundary within marine sediments and where Ba-rich pore fluids are expelled and come into contact with sulfate-rich seawater (diagenetic barite), or from hydrothermal solutions (hydrothermal barite). Barite is relatively resistant to alteration after burial and has been used in paleoceanographic studies to reconstruct seawater chemistry and productivity through time. For such applications it is very important to determine the origin of the barite used, because both diagenetic and hydrothermal barite deposits may not accurately record the open-ocean contemporaneous seawater chemistry and productivity. We show here that it is possible to distinguish between the different types of barite by using Sr and S isotopes along with crystal morphology and size characteristics.

Mineral chemistry of barium- and titanium-bearing biotites in calc-alkaline volcanic rocks from the Mezitler area (Balikesir-Dursunbey), western Turkey.

Barium- and titanium-bearing biotites from Miocene volcanic rocks of Mezitler area, eastern Balikesir, western Turkey are studied. The chemical composition of volcanic rocks range from andesite to rhyodacite. The iron-enrichment index of micas (average I.E. = 0.40) is intermediate between annite and phlogopite. The biotite phenocrysts contain up to 1.72 wt.% BaO and 5.90 wt.% TiO2, with the average formulae (K0.807Na0.131Ca0.036Ba0.027) (Mg1.404Fe2+0.800 Fe3+0.131 Ti0.303Al0.056Mn0.023) (Si2.832Al1.167)O10[(OH)1.976Cl0.024]. The BaO content of electron-microprobe micas is positively correlated with the Al2O3, TiO2, and FeO contents, and with the I.E., and is negatively correlated with the SiO2, K2O, and MgO contents. Ba- and Ti-rich micas are generally found in potassic igneous rocks, in subalkaline and alkaline gabbroic rocks and in contact metamorphic rocks, whereas Ba- and Ti-bearing micas in this study occur in calc-alkaline volcanic rocks that hosted manganese-oxide and barite deposits. Most of the phenocrysts analyzed have deficiencies in their octahedral and partly interlayer sites. Deficiencies in the octahedral sites may arise from the Ti-vacancy and partly the Ti-tschermakite substitution. On the other hand, deficiencies in the interlayer-site are due to the replacement of K by Ba. The substitution mechanism in the Mezitler micas is characterized by Ba + 2Ti + 3Al = (K + Na + Ca) + 3(Mg + Fe + Mn) + 3Si, with an excellent correlation coefficient. In terms of aluminum and titanium contents, micas from the Mezitler area lie on a similar trend parallel to that for metasomatic phlogopites from Canary Island xenoliths, which overlap the field for micas from the Ilha da Trindade xenolith, South Atlantic. Biotite compositions from the Mezitler area fall between the quartz-fayalite-magnetite (QFM) and nickel-nickel oxide (NNO) oxygen fugacity buffers. All these show that Mezitler micas with low to moderate Ba- and Ti-contents may be formed from magmas in a subduction-enriched sub-continental lithospheric mantle environment.

CELSIAN, (Ba,K)-FELDSPAR AND CYMRITE FROM SEDEX BARITE DEPOSITS OF ZAMORA, SPAIN

(Ba,K)-feldspars occur with cymrite as thin layers of massive fine-grained celsian interbedded with apatite, sulfides and barite, or diseminated in the thin-bedded barite-bearing siliceous and carbonate beds ranging in thickness from 0.15 to 0.40 m in three barite deposits in Zamora, Spain. The (Ba,K)-feldspars, which include celsian, hyalophane and K-feldspar, vary from 1.3 t o 96.4 mole % BaAl2Si2O8, but exhibit two discontinuities, at 8–24 and 40–92 mol.%. The associated cymrite shows 1.3–3 mol.% KAlSi3O8 in solid solution. Relict celsian has a similar K content, 1.2–2.8 mol.% KAlSi 3O8. The Ba-rich feldspars may have been deposited i) as an authigenic phase, or ii) by replacement of authigenic barite during a later diagenetic or metamorphic event. Cymrite and celsian were formed under low-grade dynamothermal metamorphism that affected Paleozoic sedex barite deposits of Zamora. Fluid-inclusion studies indicate 350 °–370°C and 1.5 kbars as conditions of equilibration. Those data, and the presence of vitrinite (350°C), indicate the upper limit of P–T reached. These conditions are close to the reaction curve for celsian + H 2O = cymrite. The stability field of cymrite confirms that this mineral can be stable in low-P – low-T metasedimentary environments. That reaction has geobarometric and tectonothermal importance.

Characterization and Testing of Saudi Barite for Potential Use in Drilling Operations

There are huge drilling operations in most areas of the Kingdom of Saudi Arabia nowadays searching for potential hydrocarbon reservoirs. While drilling for oil and gas, formations of high pore fluid pressure may be encountered (up to 20 ppg equivalent). Normal drilling fluid can control formation pressure up to 10 to 12 ppg. Therefore, it is necessary to increase mud pressure to correct this imbalance, otherwise a blowout may occurs. Barite is preferred upon the other weighting materials for its low price, purity, availability and its non-toxicity. Barite expenditure is estimated to be one half of the total mud cost. The expenses of importing barite from outside the area, necessitate the testing of local sources of barite which are cheap to utilize and are abundantly available. Therefore, samples of barite deposits were collected from Rabiqh area in the Western Province of Saudi Arabia. The collected samples were investigated for mineralogy, chemical analysis, physical properties, water requirement and its effect on common water-based drilling mud properties. For comparison, commercial barite was as well tested for the same properties. Based on the analysis performed in this study, it was found that the local barite is identical to commercially available one. Therefore, it is recommended to perform an economical feasibility study for the utilization of this local mineral.

Mineralogy, Geochemistry, and Age Constraints on the Zn-Pb Skarn Deposit of Maria Cristina, Quebrada Galena, Northern Chile

The Maria Cristina Zn-Pb skarn deposit, hosted by carbonate rocks of the Lower Cretaceous Chanarcillo Group in northern Chile, is described to provide a basis of comparison to adjacent (~2 km) barite deposits and regional Pb-Zn and Ba deposits with Mississippi Valley-type affinities. Strongly retrograded garnet (andradite to Ad30Gr70), diopsidic pyroxene, and epidote skarn, and barite-bearing massive sulfides (sphalerite-pyrite-galena-marcasite-magnetite) occur at the contact of potassically altered diorite porphyry of mid-Cretaceous age. The skarn mineral compositions, similar to those of Cu skarns, may reflect emplacement in a high f O2 context. Sulfur isotope values of sulfides (–8.8 to +7.1‰) and barite (14.0–26.1‰) indicate disequilibrium conditions and different sulfur sources, including magmatic sulfur. Lead isotope ratios of galena and strontium isotope ratios of barite indicate a similar metal reservoir for the different ore deposit types, constituted by the intercalated Lower Cretaceous volcanic rocks or mid-Cretaceous intrusive rocks. 40Ar/39Ar dating of hydrothermal K feldspar suggests an age between 94 and 90 Ma for the mineralization.

Trace metal-rich Quaternary hydrothermal manganese oxide and barite deposit, Milos Island, Greece

The Cape Vani Mn oxide and barite deposit on Milos Island offers an excellent opportunity to study the three-dimensional characteristics of a shallow-water hydrothermal system. Milos Island is part of the active Aegean volcanic arc. A 1 km long basin located between two dacitic domes in northwest Milos is filled with a 35-50 m thick section of Quaternary volcaniclastic and pyroclastic rocks capped by reef limestone that were hydrothermally mineralized by Mn oxides and barite. Manganese occurs as thin layers, as cement of sandstone and as metasomatic replacement of the limestone, including abundant fossil shells. Manganese minerals include chiefly δ-MnO2, pyrolusite and ramsdellite. The MnO contents for single beds range up to 60%. The Mn oxide deposits are rich in Pb (to 3.4%), BaO (to 3.1%), Zn (to 0.8%), As (to 0.3%), Sb (to 0.2%) and Ag (to 10 ppm). Strontium isotopic compositions of the Mn oxide deposits and sulphur isotopic compositions of the associated barite show that the mineralizing fluids were predominantly sea water. The Mn oxide deposit formed in close geographical proximity to sulphide-sulphate-Au-Ag deposits and the two deposit types probably formed from the same hydrothermal system. Precipitation of Mn oxide took place at shallow burial depths and was promoted by the mixing of modified sea water (hydrothermal fluid) from which the sulphides precipitated at depth and sea water that penetrated along faults and fractures in the Cape Vani volcaniclastic and tuff deposits. The hydrothermal fluid was formed from predominantly sea water that was enriched in metals leached from the basement and overlying volcanogenic rocks. The hydrothermal fluids were driven by convection sustained by heat from cooling magma chambers. Barite was deposited throughout the time of Mn oxide mineralization, which occurred in at least two episodes. Manganese mineralization occurred by both focused and diffuse flow, the fluids mineralizing the beds of greatest porosity and filling dilatational fractures along with barite.

Magmatic Arc and associated gold, copper, silver, and barite deposits in the State of Goias, Central Brazil: characteristics and speculations

In the western portion of the State of Goias, Central Brazil, base-met al deposits typical of volcanic-plutonic arcs occur. Up- to-date studies suggest that porphyry Cu-Au, (volcanogenic ?) hydrothermal exhalative Cu-Au and stratiform, submarine exhalative Au-Ag-Ba are present. Although restricted, the present state of knowledge on the geology and mineralizations of the magmatic arc indicates potential resources for met allic mineral deposits in the Brasilia Belt.

Vein and Karst Barite Deposits in the Western Jebilet ofMorocco: Fluid Inclusion and Isotope (S, O, Sr) Evidence for Regional FluidMixing Related to Central Atlantic Rifting

Numerous vein and karst barite deposits are hosted by Hercynian basement and Triassic rocks of the western Jebilet in Morocco. Sulfur, oxygen, and strontium isotope analyses of barite, combined with fluid inclusion microthermometry on barite, quartz, and calcite were used to reveal the nature and source of the ore-forming fluids and constrain the age of mineralization. The δ 34S values of barite between 8.9 and 14.7 per mil are intermediate between the sulfur isotope signatures of Triassic evaporites and Triassic-Jurassic seawater and lighter \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(SO_{4}^{2{\mbox{--}}}\) \end{document}, probably derived from the oxidation of dissolved H2S and leaching of sulfides in the Hercynian basement. The 87Sr/86Sr ratios of barite between 0.7093 and 0.7130 range between the radiogenic strontium isotope compositions of micaceous shale and sandstone and the nonradiogenic isotopic signature of Triassic to Jurassic seawater and Cambrian limestone. The δ 18O values of barite between 11 and 15 per mil (SMOW) support mixing between two or more fluids, including Late Triassic to Jurassic seawater or a water dissolving Triassic evaporites along its flow path, hot basinal, or metamorphic fluids with δ 18O values higher than 0 per mil and/or meteoric fluids with δ 18O values lower than 0 per mil. The general trend of decreasing homogenization temperatures and initial ice melting temperatures with increasing salinities of H2O-NaCl ± CaCl2 fluid inclusions trapped in barite, quartz, and calcite indicates that a deep and hot basinal fluid with salinities lower than 6 wt percent NaCl equiv might have mixed with a cooler surficial solution with a mean salinity of 20 wt percent NaCl equiv. Calcium was leached from the Cambrian limestone and the clastic and mafic volcanic rocks of the Hercynian basement. Alkali feldspars and micas contained in the Cambrain sandstones provided most of the Ba to the hydrothermal system. Vein and karst deposits are modeled as a two-component mixing process in which the temperature and the S and Sr isotope composition of the end members changed during the 220 to 155 Ma interval. The hot basinal fluid remained volumetrically dominant during the entire mineralization process. Differences in mean S, O, and Sr isotope compositions among the barite families are interpreted as reflecting differences in mineralization age. Most barite deposits formed before the Kimmeridgian, except for north-south-oriented vein barite, karst barite, and barite cement in the conglomeratic Upper Jurassic, which were deposited later, possibly around 155 Ma. Similar genetic processes have been described for late Paleozoic to Mesozoic F-Ba vein deposits in western Europe. The vein and karst barite in the western Jebilet of Morocco reveals a wide-scale regional mineralization event related to Central Atlantic rifting.