Barite Veins Research Articles

Evolution of diagenetic fluid of ultra-deep Cretaceous Bashijiqike Formation in Kuqa depression

Diagenetic fluid types of the Cretaceous Bashijiqike formation are restored based on the analysis of petrographic, electron microprobe composition, inclusions homogenization temperature, salinity and vapor composition and laser carbon and oxygen isotope of diagenetic mineral, and regional geological background. Diagenetic fluid evolution sequence is analyzed on this basis. The crystalline dolomite cement has a low concerntration of Sr, high concerntration of Mn and higher carbon isotope, showing that the crystalline dolomite is affected by meteoric fresh water, associated with the tectonic uplift of late Cretaceous. Similar δ13CPDB, negative transfer of δ18OPDB and the differentiation of the concerntration of Fe and Mn indicate that the diagenetic fluid of the vein dolomite cement is homologous with the diagenetic fluid of the crystalline dolomite cement, temperature and depth are the dominant factors of differential precipitation between these two carbonate cements. Anhydrite cements have high concerntration of Na, extremely low concerntration of Fe and Mn contents. Based on these data, anhydrite cements can be thought to be related to the alkaline fluid overlying gypsum-salt layer produced by dehydration. The barite vein has abnormally high concerntration of Sr, ultra-high homogenization temperature and high-density gas hydrocarbon inclusions, which is speculated to be the forward fluid by intrusion of late natural gas. Coexistence of methane inclusions with CO2 gas proves existence of acid water during the accumulation of natural gas in the late stages. Therefore, the alkaline environment and associated diagenesis between the meteoric fresh water in epidiagentic stage and carbonic acid in the late diagenesis have dominated the process of diagenesis and reservoir, the secondary porosity and fracture zone formed by gas accumulation is a favorable play for the exploration of ultra-deep reservoirs.

Geological, geochemical and fluid inclusion studies on the evolution of barite mineralization in the Badroud area of Iran

A sequence of andesitic to dacitic volcanic and volcano-sedimentary rocks from the Late Eocene in the central part of the Urumieh–Dokhtar Magmatic Arc (UDMA) hosts a number of barite occurrences. The Badroud barite deposit is economically important deposit in the study area. The petro-geochemical characteristics of the deposit indicate that the least-altered volcanic host rock was produced as orogenic volcanic rock in the continental margin arc setting. It displays characteristics of a high-K and calc-alkaline series. Mineralized host rock mostly consists of barite crystals, and subordinate quartz, calcite, gypsum, fluorite and rare pyrite, chalcopyrite, galena, stibnite and cinnabar minerals. Petrographic studies revealed three types of barite. The early stage barite occurs as stockworks of large tabular and bladed crystals trending NW-SE in dextral strike-slip faults. The second stage barite precipitated as thick lensoid veins (50 × 3 m) of medium tabular crystals extending in a N-S direction. The third stage of barite mineralization occurs as thin acicular veins trending in a NW-SE direction. Chemically, the barite deposit is characterized by the low amounts of Sr, K, Ca and low Sr/Ba ratio. Fluid inclusion studies, applied to the first stage of bladed crystals of barite veinlets, show a high homogenization temperature of 256–338 °C and 8–13% (wt.) NaCl eq. salinity. Fluid inclusions in the second stage of barite mineralization are characterized by low salinity of 1–9% (wt.) NaCl eq. at a 160–214 °C homogenization temperature. The fluid inclusions occurring in the third stage of thin barite veins revealed high salinity of 19% (wt.) NaCl eq. with a 166–212 °C homogenization temperature. The fluid inclusion characteristics of the first stage barite show a hydrothermal origin with a deeper-seated source on the seafloor associated with a lower sequence of the Late Eocene felsic rock. The second stage barite, exposed beneath the upper sequence of Late Eocene andesite, was formed due to increased dilution, possibly with seawater. The third stage barite mineralization is associated with saline water and the interaction of fluid with volcanic and conglomerate host rocks. The obtained data show that the mineralization at Badroud barite deposit is similar to the Kuroko-type massive sulfide deposits in an arc setting.

Low enthalpy Na-chloride waters from the Lunigiana and Garfagnana grabens, Northern Apennines, Italy: Tracing fluid connections and basement interactions via chemical and isotopic compositions

The Na-Cl waters from NW Tuscany (central Italy) record similar water isotopic and major chemical compositions, which demonstrate their meteoric origin and interactions with Upper Triassic evaporites and the metamorphic units of the Paleozoic basement. Slight differences are found in the deep temperature-pressure conditions of the Lunigiana graben (39–42°C/143–145bar) and the Garfagnana graben (73–78°C/250–256bar). In particular, the thermal fluids outpouring from Garfagnana are probably related to a common deep reservoir or interconnected fluids. Their differences are mainly evidenced by strontium isotopic ratio data (87Sr/86Sr), which combined with previously published sulfur isotope ratios (34S/32S) demonstrate the involvement of vein barites in water-rock interactions. Most likely, these minerals formed during Upper Oligocene-Miocene tectogenesis due to the mixing of fluids from the Verrucano Group and Upper Triassic units. The results of this hydrogeochemical study of the deep Na-Cl fluids could better clarify the distribution of the Verrucano Group within this area and the related discrepancies in the stratigraphic interpretations of the Palaeozoic-Mesozoic transition. Furthermore, the possible presence of an interconnected reservoir could be used to help interpret data produced by the local geochemical monitoring of seismic activity.

Contrasting styles of lead-zinc-barium mineralization in the Lower Benue Trough, Southeastern Nigeria

In the Lower Benue Trough of Southeastern Nigeria, lead-zinc-barium mineralization occurs as widely distributed epigenetic fracture-controlled vein deposits which are restricted to Albian – Turonian sediments. Detailed field studies carried out in Ishiagu, Enyigba-Ameki-Ameri, Wanikande-Wanakom, and Gabu-Oshina which together constitute the four main areas of mineralization in the Lower Benue Trough, show that mineralization appears restricted to NW-SE and N-S fractures while the more common NE-SW fractures are barren. Apart from the Enyigba area, igneous bodies are found in the vicinity of the ore deposits while in the Wanikande area, barite veins and veinlets were observed to be closely interwoven with intrusive bodies. The host lithologies are highly varied, ranging from shales to siltstones, sandstones and occasionally igneous bodies. The ore assemblage also varies remarkably, with lead:zinc:barium ratios ranging from approximately 3:1:0 at Ishiagu, to 2:1:0 at Enyigba, 1:0:2 at Wanikande and nearly 100% barite at Gabu-Oshina. Thus, there is a remarkable increase in barite content from the southwest (Ishiagu) to the northeast (Gabu). The characteristics of the ore deposits roughly fit the base metal type mineralization known as clastic dominated lead-zinc-barium deposits. This study forms part of a mineral potential database which is invaluable for any detailed exploration venture in the area. Contraste de estilos de mineralización de plomo-zinc-bario en la parte baja de la Formación Benue Trough, en el sudeste de NigeriaResumenEn la parte baja de la Formación Benue Trough, en el sudeste de Nigeria, la mineralización de plomo-zinc-bario ocurre en depósitos epigenéticos de fractura controlada ampliamente distribuidos pero que se restringen a sedimentos Albian-Turonian. Estudios de campo detallados realizados en Ishiagu, Enyigba-Ameki-Ameri, Wanikande-Wanakom y Gabu-Oshina (que conforman las cuatro áreas principales de mineralización en la parte baja de Benue Trough) muestran que la mineralización aparece restringida a fracturas NW-SE y N-S, mientras que las fracturas NE-SW, que son más comunes, aparecen estériles. Aparte del área Enyigba, los cuerpos ígneos se encontraron junto a los depósitos de minerales, mientras en el área Wanikande se observaron vetas y vetillas de baritina que están prácticamente entretejidas con cuerpos intrusivos. Las litologías sede son ampliamente variadas, y van desde esquistos a limolitas, areniscas y ocasionalmente cuerpos ígneos. El ensamble de la mena también varía con proporciones de plomo:zinc:bario que van aproximadamente desde 3:1:0 en Ishiagu, 2:1:0 en Enyigba, 1:0:2 en Wanikande y cerca del 100 % de baritina en Gabu-Oshina. Por ende, hay un incremento importante en el contenido de baritina desde el suroeste (Ishiagu) hacia el noroeste (Gabu). Las características de los depósitos minerales se enmarcan aproximadamente en el tipo de mineralización de base metálica, conocido como depósitos plomo-zinc-bario de dominación clástica. Este estudio hace parte de una base de datos de minerales potenciales que es invaluable para una exploración detallada en el área.

Hercynian Granite and Related Mineralisation in Beni Snouss, Western Algeria

The purpose of this research is to describe the mineralisation related to the Hercynian granite located in western Algeria by combining geologic, tectonic, mineralogical and fluid inclusion studies. Quartz veins bearing sulphides occur in close spatial association with granitoids, which, representing hydrothermal activities associated with them. Visible but rare gold occurs in a very small quantity connected with arsenopyrite. Barite veins and stock works are developed in the granites where are observed at Mallal and Bouabdous. The vein varies in thickness from a few centimetres up to 2 meters, and their length varies from 10 up to up 100 m. Most of veins are N50 - N75 and 60 to 90 dip.

The vein-type barite mineralization of the Draïssa ore field, Ougarta; SW- Algeria: mineralogy, trace elements and halogens

The Draissa barite vein system in the Ougarta district is located in southwestern Algeria. It is the principal mineral deposit of economic interest of the area. The mineralization is hosted by Cambrian sedimentary rocks that unconformably overlie Precambrian formations. The mineralized structures consist mostly of barite and quartz with minor sulfide minerals and trend dominantly NE-SW, NW-SE, and E-W. Siliceous alteration zones are associated with the vein system. Samples of barite ore are characterized by low total REE contents ranging from 9 to 50 ppm and positive Eu (2–2.15 ppm) and Y (1.2–11.1 ppm) anomalies, indicating hydrothermal activity during mineralization. Halogen data of the barite show that the Cl/Br molar ratio is 189:571 and the Na/Br ratio is 34:376, indicating that the sulfur was derived from seawater. The Ba-enrichment trend in the volcanic rocks of Draissa is interpreted as possible probable source of the Ba (424–3039 ppm Ba). It appears that the barite-quartz deposits were formed in two stages. Endogenous fluids deposited the primary vein materials, consisting of quartz associated with copper sulfides. Exogenous fluids (cold seawater) became heated during ascendant fluid movement. Mineralization was governed by convective motions and the barite and galena fillings were deposited in openings created by normal faulting.

Fluid evolution and mineralogy of Mn-Fe-barite-fluorite mineralizations at the contact of the Thuringian Basin, Thüringer Wald and Thüringer Schiefergebirge in Germany

Abstract Numerous small deposits and occurrences of Mn-Fe-fluorite-barite mineralization have developed at the contact of the Thuringian Basin, Thüringer Wald and Thüringer Schiefergebirge in central Germany. The studied mineralizations comprise the assemblages siderite+ankerite-calcite-fluorite-barite and hematite-Mn oxides-calcite-barite, with the precipitation sequence in that order within each assemblage. A structural geological analysis places the origin of the barite veins between the Middle Jurassic and Early Cretaceous. Primary fluid inclusions contain water vapour and an aqueous phase with NaCl and CaCl2 as the main solutes, with salinities mostly between 24–27 mass. % CaCl2 eq. Th measurements range between 85 °C and 160 °C in barite, between 139 °C and 163 °C in siderite, and between 80 °C and 130 °C in fluorite and calcite. Stable isotopes (S, O) point to the evaporitic source of sulphur in the observed mineralizations. The S,C,O isotopic compositions suggest that barite and calcite could not have precipitated from the same fluid. The isotopic composition of the fluid that precipitated barite is close to the sea water in the entire Permo–Mesozoic time span whereas calcite is isotopically distinctly heavier, as if the fluids were affected by evaporation. The fluid evolution in the siliciclastic/volcanic Rotliegend sediments (as determined by a number of earlier petrological and geochemical studies) can be correlated with the deposition sequence of the ore minerals. In particular, the bleaching of the sediments by reduced Rotliegend fluids (basinal brines) could be the event that mobilized Fe and Mn. These elements were deposited as siderite+ankerite within the Zechstein carbonate rocks and as hematite+Mn oxides within the oxidizing environment of the Permian volcanic and volcanoclastic rocks. A Middle-Jurassic illitization event delivered Ca, Na, Ba, and Pb from the feldspars into the basinal brines. Of these elements, Ba was deposited as massive barite veins.

مطالعات کانی سازی، ژئوشیمی، سیالات درگیر و ایزوتوپ پایدار گوگرد کانسار Cu-Zn-As باقرق با سنگ میزبان کربناته (شمال شرق انارک)

کانسار Cu-Zn-As باقرق در شمال شرق شهر انارک و در استان اصفهان قرار دارد. کانی‌سازی به‌صورت دیرزاد، ماهیت چینه‌کران و بافت و ساخت پرکننده فضای خالی در سنگ میزبان کربناتی رخداده است. کانی‌شناسی بخش درون‌زاد شامل کالکوسیت، کالکوپیریت، پیریت، اسفالریت، گالن، انارژیت، باریت و کلسیت و کانیهای بخش برون‌زاد شامل مالاکیت، آزوریت، کوولیت، کریزوکولا، کالکوسیت، سروزیت، اسمیت‌زونیت، مس طبیعی، هماتیت، گوتیت و لیمونیت می‌باشد. سنگ میزبان کربناتی در اطراف زون‌های کانه‌دار متحمل دگرسانیهای دولومیتی‌شدن و کلسیتی‌شدن شده است. مس به‌عنوان عنصر اصلی ذخیره (با میانگین 28/20 درصد وزنی) و پس از آن عناصر روی (با میانگین تقریبی 1 درصد وزنی) و آرسنیک (با میانگین تقریبی 1 درصد وزنی) می‌باشند. مطالعات سیالات‌درگیر روی کانی باریت نشان می‌دهد سیال کانه‌دار سولفیدی دارای محدوده دمای همگن شدن بین 259 تا 354 درجه سانتی‌گراد و میزان شوری بین 8 تا 13 درصد وزنی معادل NaCl می‌باشد. سیال کانه‌دار در مراحل پایانی کانی‌سازی با آبهای جوی دچار اختلاط شده و فاز تأخیری غیر سولفیدی کلسیتی با محدوده دمای نسبتا پایین ‌(78 تا 112 درجه سانتی‌گراد) و درجه شوری پایین (بین 3 تا 6 درصد وزنی معادل NaCl) را تشکیل داده است. محدوده مقادیر 34Sδ کانی‌ باریت کانسار باقرق بین 13+ تا 14+ در هزار بوده در حالی‌که محاسبه مقدار 34Sδ مربوط به سیال کانه‌دار پس از تصحیح دمایی بین 7- تا 8- در هزار به‌دست آمد. منشأ گوگرد باقرق با توجه به شباهت ایزوتوپ باریت با سولفات‌های دریایی کرتاسه، احتمالا از لایه‌های تبخیری این دوره زمانی تأمین شده است. این سولفا‌ت‌ها توسط فرآیند‌های ترموشیمیایی به‌صورت بخشی به گوگرد احیایی با مقدار ایزوتوپی سبک‌تر (حدود 21 در هزار) تبدیل و جهت ته‌نشست سولفیدها مورد استفاده قرار گرفته است. کانسار باقرق با توجه به خصوصیاتی همچون سنگ میزبان کربناته، غیاب فعالیت آذرین، بافت پرکننده فضای خالی، دگرسانی دولومیتی،کانی‌شناسی، ژئوشیمی ماده‌معدنی (وجود As و Sb بالا و عدم حضور Bi)، داده‌های دماسنجی و مقادیر ایزوتوپ گوگرد، شباهت زیادی با کانسارهای مس با سنگ میزبان کربناته در افریقا و به‌ویژه نوع سومب (Tsumeb) در نامیبیا نشان می‌دهد. کانسار باقرق احتمالا مرتبط با سیالات دگرگونی آزاد شده در حین فازهای کوه‌زایی مرتبط با بسته‌شدن اقیانوس نئوتتیس می‌باشد.

Argentopentlandite from barite vein in Zagórze Śląskie, Lower Silesia; a first occurrence in Poland

Abstract Argentopentlandite has been found in samples collected on the dump of the Michael mine, an old silver mine in Zagórze Śląskie in the northern part of the Góry Sowie mountains. Though argentopentlandite is not a very common mineral, it is well known from high-temperature hydrothermal veins and from Ni-Cu deposits hosted in ultramafic rocks also containing platinum-group minerals. The argentopentlandite has been recognized in a sulphide nest in association with pyrrhotite and chalcopyrite in massive barite. In comparison to other occurrences (see Table 2), this mineral is characterized by a low Ni content (ave. 16.02wt% - EDS; 16.43wt% - WDS), a lack of cobalt and a relatively high copper content (ave. 2.13wt% - EDS; 1.55wt% - WDS). Based on these data, it can be concluded that the argentopentlandite, and the associated sulphides, were precipitated from hydrothermal fluids shortly after barite, the major vein constituent. As the optical properties of the argentopentlandite in reflected light are rather similar to those of bornite, it can be overlooked during routine observations. Thus, argentopentlandite or associated ore mineralization may also occur in other barite veins in the area.

From deep to shallow fluid reservoirs: evolution of fluid sources during exhumation of the Sierra Almagrera, Betic Cordillera, Spain

AbstractThe combination of structural, geochemical and palaeotopographic data proves to be an efficient tool to understand fluid transfers in the crust. This study discriminates shallow and deep fluid reservoirs on both sides of the brittle–ductile transition under an extensional regime and points out the role of major transcurrent fault activity in this palaeohydrogeological setting. Palaeofluids trapped in quartz and siderite–barite veins record the transfer of fluids and metal solute species during the Neogene exhumation of the Sierra Almagrera metamorphic belt. Ductile then brittle–ductile extensional quartz veins formed from a deep fluid reservoir, trapping metamorphic secondary brines containing low‐density volatile phases derived from the dissolution of Triassic evaporites. During exhumation, low‐salinity fluids percolated within the brittle domain, as shown by transgranular fluid inclusion planes affecting previous veins. These observations indicate the opening of the system during Serravalian to early Tortonian times and provide evidence for the penetration of surficial fluids of meteoric or basinal origin into the upper part of the brittle–ductile transition. During exhumation, synsedimentary transcurrent tectonic processes occurred from late Tortonian times onwards, while marine conditions prevailed at the Earth's surface. At depth in the brittle domain, quartz veins associated with haematite record a return to high‐salinity fluid circulation suggesting an upward transfer fed from a lower reservoir. During the Messinian, ongoing activity of the trans‐Alboran tectono‐volcanic trend led to the formation of ore deposits. Reducing fluids caused the formation of siderite and pyrite ores. The subsequent formation of galena and barite may be related to an increase of temperature. The high salinity and Cl/Br ratio of the fluids suggest another source of secondary brine derived from dissolved Messinian evaporites, as corroborated by the δ34S signature of barite. These evaporites preceded the main sea‐level drop related to the peak of the salinity crisis (5.60–5.46 Ma).

Pangea rifting and onward pre-Central Atlantic opening as the main ore-forming processes for the genesis of the Aouli REE-rich fluorite–barite vein system, Upper Moulouya District, Morocco

The Aouli fluorite–barite±sulphides vein system in the Upper Moulouya District of Central Morocco is hosted in a folded and low to medium grade sedimentary and volcanic rocks, unconformably overlaid by Permo-Triassic to Cretaceous red beds and limestones. Intrusion of the hydrothermally altered multiphase ca. ∼330–319Ma Aouli granite batholith has contact metamorphosed the host rocks to a metamorphic assemblage of cordierite, andalusite, chlorite, muscovite, and biotite±sillimanite±garnet.The mineralized structures that consist mostly of quartz, fluorite, and barite occur principally as ENE–WSW, WNW–ESE, and E–W-trending trans-tensional steeply dipping veins, veinlets and en echelon tension gash fillings. Irrespective of colour, location, paragenesis and textural position within the mineralized vein structure, the fluorite is characterized by high total REY contents ranging from 250 to 662ppm, distinctive positive Eu and Y anomalies, and middle rare-earth element enrichment.Fluid inclusion data indicate that the ore-forming fluids correspond to evolved NaCl–CaCl2+other cations sedimentary (94–174°C), saline (14–24wt% NaCl equiv.) brines. The strontium isotopic compositions of fluorite (87Sr/86Sr=0.710155–0.712293) and barite (0.710215–0.701401), along with the Liassic dolomitized limestones (0.707867–0.708140) are more radiogenic than the Cambro-Ordovician and Triassic–Early Jurassic seawater values, with the Aouli Late Variscan granite (0.70814±12) and the Triassic arkoses (0.709839–0.712313) displaying the highest 87Sr/86Sr ratios. Barite separates show uniform δ34S ratios of +11‰ to +13.4‰ consistent with Permian–Triassic seawater sulphate.The calculated REY fluid compositions along with fluid inclusion, strontium and sulphur isotope data point to the role of hot sedimentary brines with fluid–rock interaction at high fluid/rock ratios. The fluid system is likely related to the Pangea rifting and subsequent Central Atlantic opening during Permian–Triassic time. The fluorite–barite mineralization is likely due to mixing at the basement–cover interface of an ascending deep-seated fluid that equilibrated with Variscan crystalline basement rocks and cooler more dilute formation water.

Metallogeny of the Triassic‐Jurassic Rift‐Related Mineralizations in Argentina

The Triassic-Jurassic NNW-SSE extensional phase affected the western margin of Gondwana and marked the beginning of the fragmentation of this supercontinent. Extensional faulting began in the Late Permian in the northern areas, becoming younger to the south, i.e. Jurassic in Patagonia. During this stage extensive rhyolitic ignimbrite magmatism developed. The rift system, was filled with continental sediments that locally have intercalated bimodal, predominantly mafic, volcanic rocks. The region affected by the Triassic-Jurassic rifting in the Argentine territory hosts a number of deposits that have no direct link with magmatic activity and whose age has previously been attributed, in general, to the Mesozoic (Zappettini, 1999), or are herein ascribed to this event. These include the Se-rich polymetallic deposits, five elements deposits, Pb-Zn-Ag simple veins, epithermal Mn, fluorite and barite veins. The various types of deposits analyzed have a wide regional distribution reflecting the extent of the processes of rifting that started during the Triassic and reached the Cenozoic, generating thermal and fluid flow anomalies leading to hydrothermal mineralizing processes. Where there was a favorable source, fluids collected selected elements resulting in a mineralogical specialization and inhomogeneities in the distribution of the mineralization types along the belt affected by rifting. Characteristically, where the rifting affected Paleozoic or older sedimentary sequences, polymetallic and barite type deposits were generated. Where rifting affected acidic Triassic-Jurassic volcanic and volcaniclastic sequences the fluids originated fluorite mineralization. In the cases where there was an associated restricted basic magmatism or by leaching or volcanic sequences Mn ore bodies were formed. In all cases, this rift environment has been favorable for the emplacement of alkaline to subalkaline acid magmatic rocks. In these cases, besides the presence of fluorine and fluorine-rich fluids, evidenced by the presence of fluorite and / or topaz, there are associated REE mineralizations (Rodeo de los Molles, Sierras Pampeanas of San Luis and Rangel district, Puna of Salta), Mo-rich stockworks (Elsiren and German) and epithermal gold deposits (Pantanito, and, in general, the Au-Ag epithermal deposits of the Deseado Province). In this context the Pb-Ag polymetallic mineralization of the Navidad deposit formed in relation to a rift-related magmatism represented by volcanic and pyroclastic deposits associated with biochemical and epiclastic sediments deposited within the Canadon Asfalto hemigraben (e.g. Fernandez et al., 2008). From a global point of view, the fluorine, manganese and polymetallic deposits related to extensional environments may be associated with precious metal mineralization (Au-Ag) and Mo-rich porphyries, so that their presence can be used regionally as an exploration guide (e.g. Wallace, 2010).

Geology, geochemistry, sulfur isotope composition, and fluid inclusion data of Farsesh barite deposit, Lorestan Province, Iran

Farsesh barite in the central part of Iranian Sanandaj-Sirjan zone is a sample of epigenetic hydrothermal mineralization in dolomitized limestone, which provides appropriate chemicophysical conditions making the passage of mineral-bearing fluids possible. Barite veins may range from a few centimeters to 2 m in thickness that increases downward. The microthermometry measurements obtained from more than 30 fluid inclusions show relative homogenization temperatures ranging from 125 to 200 °C with an average of 110 °C for Farsesh barite deposits. The mean salinity measured proves 16 times as much as weight percentage of NaCl for barite. Coexistence of liquid- and vapor-rich fluid inclusions in barite minerals may provide an evidence of boiling in ore veins. Moreover, occurrence of bladed calcite, high-grade ore zones, and presence of hydrothermal breccia are all consistent with boiling. Thermometric studies indicate that homogenization temperatures (Th) for primary and pseudosecondary fluid inclusions in barite range from 125 to 200 °C with an average of 1,100 °C. The δ34S values of barite also lie between 8.88 and 16.6 %. The relatively narrow spread in δ34S values may suggest uniform environmental conditions throughout the mineralization field. Thus, δ34S values are lower than those of contemporaneous seawater, which indicates a contribution of magmatic sulfur to the ore-forming solution. Barite is marked by total amounts of rare Earth elements (REEs) (6.25–17.39 ppm). Moreover, chondrite-normalized REE patterns of barite indicate a fractionation of light REEs (i.e., LREEs) from La to Sm, similar to those for barite from different origins. The LaCN/LuCN ratios and chondrite-normalized REE patterns reveal that barite in Farsesh deposit is enriched in LREEs compared with heavy rare Earth elements (HREEs). Similarity between Ce/La ratios in barite samples and those found in deep-sea barite supports its marine origin. Lanthanum and Gd exhibit positive anomalies, which are common features of chemical marine sediments. Cerium shows a negative anomaly in most samples inherited from the negative Ce anomaly of hydrothermal fluid that is mixed with seawater at barite precipitation. The available data including tectonic setting, host rock characteristics, REE geochemistry, and sulfur isotopic compositions may support a hydrothermal submarine origin for Farsesh barite deposit.

First data on the chemical composition and morphology of gold in the Tuba Kain deposit (South Urals)

926 The Tuba Kain deposit discovered in the early 20th century is located in the southwestern part of the Eastern Baymak ore-bearing zone confined to the western slope of the Magnitogorsk megastructure of the Southern Urals (Fig. 1). The ore field is composed of volcanogenic and volcano-sedimentary rocks of the Devonian Irendyk, Yarlykap, and Ulutau formations intruded by subvolcanic bodies of dacite porphyrites [1–3]. The rocks of the Eifelian Irendyk Formation distributed in the northwestern and central parts of the ore field are represented by lapilli and agglomerate tuffs of mixed composition with subordinate intercalations of gravel to psammitic tuffs. The lithological– petrographic composition of rock fragments is highly variable imparting variegated coloration to rocks: quartzites, hematite–quartz varieties, quartz porphyries, amygdaloid basalt porphyrites, and diorites. The overlying cherts of the Upper Eifelian Yarlykap Formation are approximately coeval with the Karamyltash Formation and Bugulygyr Horizon of the eastern areas. The rocks of the Givetian–lower Frasnian Ulutau Formation are developed in the western and southern parts of the ore field. The rock composition is relatively uniform with the dominant share of tuffstones and, less commonly, tuffaceous siltstones. The subvolcanic bodies occurring in the central, northern, and eastern parts of the ore field are represented by massive compact plagioclase and hornblende–plagioclase andesite–dacite and dacite porphyrites. At the beginning of the Tuba Kain deposit exploitation, it represented a submeridional gold–barite vein up to 5 m thick occurring among foliated rocks. The vein became exhausted and the residual ore-bearing complex is now represented by secondary quartzites with tourmaline and chlorite–sericite–quartz metasomatites. Their composition is as follows (wt %): SiO 2, 26.74–58.38; TiO 2, 0.35–0.76; Al 2O3, 8.41– 12.18; F 2O3, 7.28–10.06; MnO, 0.0; MgO, 3.93–4.15; CaO, 0.12–0.16; Na 2O, 2.38–2.55; K 2O, 1.24–2.92; P2O5, 0.02–0.11; S tot , 0.32–5.02; Ba, 1.59–28.05; Zn, 0.0051–0.0218; Cr, 0.0–0.0092; V, 0.0142–0.170; Sr, 0.0023–0.0634; Zr, 0.0076–0.0270. The rocks confined usually to contacts of subvolcanic dacite porphyrites are characterized by the following composition (wt %): SiO 2, 69.91; TiO 2, 0.36; Al 2O3, 14.02; F2O3, 3.84; MnO, 0.05; MgO, 1.87; CaO, 1.54; Na 2O, 4.87; K 2O, 0.09; P 2O5, 0.08; S tot , 0.01; Ba, 00233; Zn, 0.0011; Cr, 0.0011; Ni, 0.0085; V, 0.0003; Sr, 0.0306; Zr, 0.0148, Nb, 0.0011; Rb, 0.0010. These rocks are accompanied by tuffs of the Irendyk and Ulutau formations with mixed compositions (wt %): SiO 2, 59.09–67.86; TiO 2, 0.32–0.45; Al 2O3, 11.91–19.23; F2O3, 2.05–5.24; MnO, 0.02–0.13; MgO, 2.19–5.39; CaO, 0.11–2.71; Na 2O, 1.10–4.26; K 2O, 1.80–3.63; P2O5, 0.05–0.10; S tot , 0.06–1.15; Ba, 0.57–9.51; Zn, 0.0069–0.0596; Cr, 0.0015–0.0110; Ni, 0.0005– 0.0032; V, 0.0024–0.0081; Sr, 0.0027–0.0620; Zr, 0.0112–0.0245; Nb, 0.0006–0.0010; Rb, 0.0012–

Regional sulfate–hematite–sulfide zoning in the auriferous Mariana anticline, Quadrilátero Ferrífero of Minas Gerais, Brazil

The distribution of mineral deposits, characterised as barite deposits, hematite-rich auriferous deposits and auriferous tourmaline–sulfide deposits, displays a regional sulfate–hematite–sulfide zoning along the thrust-delineated limbs of the Mariana anticline, in the south-eastern part of the Quadrilatero Ferrifero of Minas Gerais, Brazil. Cross-cut relationships of barite veins and sulfide lodes indicate that sulfidation occurred in a late-tectonic context, which is here attributed to the collapse of the ∼0.6-Ga Brasiliano thrust front. Reconnaissance S-isotopic data from barite and pyrite (Antonio Pereira barite deposit and its adjacent gold deposit, respectively), and arsenopyrite (Passagem de Mariana gold deposit), suggest a new interpretation for the hydrothermal fluid overprint in the Mariana anticline. The Antonio Pereira barite has Δ33S values that are near zero, constraining the sulfate source to rocks younger than 2.45 Ga. The barite-δ34S values are between +19.6 and +20.8 ‰. The Passagem arsenopyrite and tourmaline have Co/Ni ratios that define a positive linear trend with the Antonio Pereira pyrite. The latter has homogenous δ34S values, between +8.8 and +8.9 ‰, which are compatible with thermochemical reduction of aqueous sulfate with the S-isotopic composition of the Antonio Pereira barite.

The North Cycladic Detachment System and associated mineralization, Mykonos, Greece: Insights on the evolution of the Aegean domain

AbstractIn the Aegean back‐arc domain, some 30–35 Ma ago, an increase of the rate of slab retreat led to the initiation of post‐orogenic extension, largely accommodated by large‐scale structures such as the North Cycladic Detachment System (NCDS). Although this extension is still active nowadays, an E–W compressional regime developed in the Late Miocene with the propagation of the North Anatolian Fault. On Mykonos island (Cyclades), the NE–SW back‐arc extension is particularly well expressed with the Livada and Mykonos detachments that belong to the NCDS and that are associated with NW–SE barite veins emplaced during the synkinematic cooling of the Mykonos intrusion. This study shows that the formation of the mineralization occurred when the pluton crossed the ductile‐to‐brittle transition during its exhumation below the NCDS at ~11–10 Ma. In addition, the kinematics of mineralized structures evolved with time: (1) most of the displacement was accommodated by the top‐to‐the‐NE Livada and Mykonos detachments accompanied by the formation of mineralized normal faults that were (2) reworked in a strike‐slip regime with an E–W direction of shortening and a persistent NE–SW stretching and (3) a late post‐mineralization E–W compressional stage with a minor reworking of shallow‐dipping faults (locally including the detachments themselves). We interpret this increase of the E–W shortening component recorded during the mineral deposition as a consequence of the initiation of the westward motion of Anatolia from 10 Ma, thus 4 Ma before the propagation of the North Anatolian Fault in the Dardanelles Strait and the localization of the strain on the Aegean Sea margins.

Ore mineralization in the Miedzianka area (Karkonosze-Izera Massif, the Sudetes, Poland): new information

AbstractThe Miedzianka mining district has been known for ages as a site of polymetallic ore deposits with copper and, later, uranium as the main commodities. Although recently uneconomic and hardly accessible, the Miedzianka ores attract Earth scientists due to the interesting and still controversial details of their ore structure, mineralogy and origin. Our examination of the ore mineralization from the Miedzianka district was based exclusively on samples collected from old mining dumps located in the vicinity of Miedzianka and Ciechanowice, and on samples from the only available outcrop in Przybkowice. In samples from the Miedzianka field, chalcopyrite, pyrite, galena, bornite, chalcocite, digenite, arsenopyrite, magnetite, sphalerite, tetrahedrite-tennantite, bornite, hematite, martite, pyrrhotite, ilmenite, cassiterite and covellite are hosted in quartz-mica schists and in coarse-grained quartz with chlorite. In the Ciechanowice field, the ore mineralization occurs mainly in strongly chloritized amphibolites occasionally intergrown with quartz and, rarely, with carbonates. Other host-rocks are quartz-chlorite schist and quartzites. Microscopic examination revealed the presence of chalcopyrite, pyrite, sphalerite, galena, tetrahedrite-tennantite, bismuthinite, native Bi, arsenopyrite, löllingite, cassiterite, cobaltite, gersdorffite, chalcocite, cassiterite, bornite, covellite, marcasite and pyrrhotite. Moreover, mawsonite and wittichenite were identified for the first time in the district. In barite veins cross-cutting the greenstones and greenschists in Przybkowice, we found previously-known chalcopyrite, chalcocite and galena. The composition of the hydrothermal fluids is suggested to evolved through a series of consecutive systems characterized, in turn, by Ti-Fe-Sn, Fe- As-S, Fe-Co-As-S, Cu-Zn-S and, finally, Cu-Pb-Sb-As-Bi compositions.

Barite Veins in the Benue Trough: Field Characteristics, the Quality Issue and Some Tectonic Implications

The Benue trough is Nigeria’s main, but not exclusive source of barite mineralisation. There are at least ten barite fields in the trough, each containing swarms of veins or concordant stratiform minerals flats of hydrothermal origin. There are only two vein trends in the trough: the NW-SE trend, which tends to be orthogonal to the axis of the trough; and the N-S to NNE-SSW trend, which is younger than the former. Both vein sets are formed from ac tension joints reflecting different post-sedimentary deformation phases in the trough. The NW-SE veins are also more frequent than the N-S veins, almost in the ration of 2:1. Although 86 veins have been studied, not one was found oriented parallel to the axis of the trough, a good indication of structural control on mineral vein orientations. The dips of the veins tend to be high (>80o), a condition that favours manual mining. Veins tend to display a simple block profile and their widths vary from a few centimetres to as much as 6m, though the most frequently occurring widths are between 50cm and 1m. The implication of this is that BaSO4 concentrations in hydrothermal fluids in the trough were probably low during the Cretaceous period. In many veins, there is barite quality contrast between the top part and the lower portions. Higher quality barite tends to come from the lower portions. Hence it is expected that much of the low quality stigma associated with Nigerian barite from the trough would be relieved when mining gets down to good depths. For this reason, mining in those veins of low quality barite should proceed by vertical stripping.

Shear Zone-Hosted Base Metal Mineralization near Abraha Weatsebaha-Adidesta and Hawzein, Tigray Region, Northern Ethiopia

Low-grade basement rocks of Neoproterozoic age with well developed shear zones and posttectonic granitic intrusives from Hawzien area of northern Ethiopia were studied for field characteristics, mineralogy, textures, alteration assemblages and geochemistry to explore theirpotential for base metal mineralization. The basement rocks includes metavolcanic (mafic to felsic), metavolcaniclastic and metasedimentary rocks. The intrusive post-tectonic granitoids mark the end of Proterozoic. Field observation and petrographic data indicate the presence of NS, NE-SW trending shear zones; hydrothermal quartz (±calcite) veins of different generations; malachite stains; alterations like chloritisation, kaolinization, epidotization, sericitization; and presence of base metal sulfides in association with quartz and calcite veins. Geochemistry of surface and drill core samples indicate enrichment of zinc in shear zones with low concentrations of copper, lead, gold, arsenic and silver. Zn-rich base metal mineralization with Pb-Cu-Fe (±Ag-As-Au) is related to D2 deformation. Barite veins are although common, conspicuously occurring in E-W trending veins. Post-tectonic granitoids are facilitating the  hydrothermal activity and the source rock compositions controlling the  nature of the mineralization. A paragenetic scheme is suggested on the basis of texture, mineral association, alteration and deformation. Keywords: Abraha-Weatsebaha, Tigray, Ethiopia, Neoproterozoic, Shear zones, Paragenesis, Sulfide mineralization

Geology and geochemistry of the Jurassic carbonate hosted barite deposits, Northeast Zakho, Iraq

Barite deposits located in Marsis locality of about 25km northeast of Zakho City were hosted in Jurassic dolomitic rocks. The barite is extending for about 6km and limited within about 38m thickness of dolomitic rocks. The thickness of the barite veins varies between few centimeters to 2.5m which increases downward. The major mode of occurrence of barite is as vein and cavity-filling. The barite and other minerals of vein and cavity-filling deposits are typical of suite precipitated from low-temperature hydrothermal solutions associated with igneous activity. Carbonate-hosted barite deposits contain 0.237% BaO, 103ppm Zn, and 83 ppm Pb. These rocks are deficit in Fe and F. Most of carbonate rocks are dolomitized, which provide appropriate physical and chemical conditions that permitted the passage of mineral-bearing fluids. These deposits are formed in carbonate platform setting and commonly developed in foreland thrust belt.