Hydrothermal alteration and mineralisation of the Glen Eden Mo-W-Sn deposit: a leucogranite-related hydrothermal system,Southern New England Orogen,NSW, Australia

The Glen Eden Mo-Sn-W deposit in north-eastern New South Wales, Australia, is an example of a leucogranite-related, low-grade, large-tonnage hydrothermal system. It occurs in the southern part of the New England Orogen and is hosted within Permian felsic volcanic rocks, intruded at depth by dykes of porphyritic microleucogranite (Glen Eden Granite). The deposit is hosted within a pipe-like quartz-rich greisen breccia body about 500 m in diameter, surrounded by a greisen zone several hundred metres across, zoning out into altered volcanic rocks. The dominant ore minerals, largely hosted as open space fillings and disseminations in quartz and quartz-rich greisen, are molybdenite, wolframite and cassiterite; they are accompanied by minor to trace amounts of muscovite, fluorite, topaz, siderite, pyrrhotite, arsenopyrite, chalcopyrite, sphalerite, bismuth, bismuthinite, joseite A, cosalite, galenobismutite, beryl, anatase and late-stage dickite and kaolinite. Two types of breccia are recognised: (1) greisenised volcanic rock fragments (quartz + muscovite), cemented by hydrothermal quartz ± K-feldspar ± ore minerals, and (2) fragments of hydrothermal quartz ± cassiterite ± wolframite enclosed in quartz ± clay. In both types of breccia and in stockwork veins, there is evidence of early precipitation of Mo-Sn-W phases, followed by Bi minerals and base metal sulfides (± fluorite, siderite).Breccia formation and associated hydrothermal alteration (greisen, potassic, argillic, propylitic) are interpreted to be related to devolatilisation of the highly fractionated Glen Eden Granite of early Triassic age (240±1 Ma based on ⁴⁰Ar/³⁹Ar geochronology of greisen muscovite) as well as to fluid mixing with meteoric waters. The breccia pipe could have formed in part by rock dissolution and collapse, as well as by explosive degassing of boiling fluids. Fluid inclusion evidence is consistent with boiling, with breccia pipe formation and mineralisation having mainly occurred at 250–350 °C from fluids with salinity of 0.4–9 wt% NaCl equivalent in the dilute types and 30–47 wt% NaCl equivalent in the hypersaline types. Stable isotopic evidence (O, D, C, S) indicates a strong magmatic contribution to the hydrothermal fluids and metals in the breccia. The ¹⁸O values of quartz decrease outward from the breccia pipe (10.6–12.3 in the pipe to 3.4–8.7 in the peripheral quartz) indicating that there has been mixing with isotopically light (high latitude) meteoric fluids, mainly after formation of the breccia pipe.     

Fluid Inclusion Studies of Ore and Gangue Minerals from the Piaotang Tungsten Deposit, Southern Jiangxi Province, China

The Piaotang deposit is one of the largest vein-type W-polymetallic deposits in southern Jiangxi Province, South China. The coexistence of wolframite and cassiterite is an important feature of the deposit. Based on detailed petrographic observations, microthermometry of fluid inclusions in wolframite, cassiterite and intergrown quartz was undertaken. The inclusions in wolframite were observed by infrared microscope, while those in cassiterite and quartz were observed in visible light. The fluid inclusions in wolframite can be divided into two types: aqueous inclusions with a large vapor-phase proportion and aqueous inclusions with a small vapor-phase ratio. The homogenization temperature (Th) of inclusions in wolframite with large vapor-phase ratios ranged from 280°C to 390°C, with salinity ranging from 3.1 to 7.2 wt% NaCl eq. In contrast, the Th values of inclusions with small vapor-phase ratios ranged from 216°C to 264°C, with salinity values ranging from 3.5 to 9.3 wt% NaCl eq. Th values of primary inclusions in cassiterite ranged from 316°C to 380°C, with salinity ranging from 5.4 to 9.3 wt% NaCl eq. Th values for primary fluid inclusions in quartz ranged from 162°C to 309°C, with salinity values ranging from 1.2 to 6.7 wt% NaCl eq. The results show that the formation conditions of wolframite, cassiterite and intergrown quartz are not uniform. The evolutionary processes of fluids related to these three kinds of minerals are also significantly different. Intergrown quartz cannot provide the depositional conditions of wolframite and cassiterite. The fluids related to tungsten mineralization for the NaCl-H2O system had a medium-to-high temperature and low salinity, while the fluids related to tin mineralization for the NaCl-H2O system had a high temperature and medium-to-low salinity. The results of this study suggest that fluid cooling is the main mechanism for the precipitation of tungsten and tin.     

Geochemistry of cassiterite and wolframite from tin and tungsten quartz veins in Portugal

Cassiterite and wolframite compositions from Sn > W- and W > Sn-bearing quartz veins in Northern and Central Portugal are compared to provide evidence on fluid compositions. In Sn > W-bearing quartz veins, euhedral cassiterite shows sequences of alternating parallel darker and lighter zones. The darker zones are pleochroic, oscillatory zoned, exhibit exsolutions of columbite and ixiolite and are richer in Nb, Ta and Fe than the lighter zones which consist of nearly pure SnO₂. Cassiterite from W > Sn-bearing quartz veins is usually zoned, with homogeneous and slightly pleochroic darker zones, which are chemically similar to lighter zones. Both zones have inclusions of rutile and rare ilmenite. The darker zones of cassiterite from the former veins are richer in Nb, Ta and Fe contents and poorer in Ti than the darker and lighter zones of cassiterite from the latter veins. This is attributed to differences in the composition of magmatic hydrothermal fluids.Wolframite compositions from Sn > W- and W > Sn-bearing quartz veins do not show any significant distinction, because they precipitate from relatively similar magmatic hydrothermal fluids. In some deposits, most wolframite crystals are homogeneous, but others are heterogeneous. Inner patches, rich in a hübnerite component, rarely occur in crystals from the Filharoso and Panasqueira deposits. Zoned crystals, showing an increase in Fe and a decrease in Mn from core to rim, were found in the Vale das Gatas deposit. Complex oscillatory zoned crystals occur. In the Carris deposit, later wolframite contains inclusions of scheelite, partially replaces it and is richer in Fe and poorer in Mn than earlier wolframite. Wolframite from Sn > W-bearing quartz veins in the Argozelo deposit and W > Sn-bearing quartz veins from Vale das Gatas and Panasqueira deposits has significant Nb content. This does not depend on the Fe and Mn content of the wolframite, but W content is negatively correlated with Nb content. Only very rare single crystals of wolframite show an increase in W and a decrease in Nb from core to rim. Sn > W-bearing quartz veins contain wolframite poorer in Nb than the darker zones of cassiterite, which exsolved columbite and ixiolite. In W > Sn-bearing quartz veins from Panasqueira and Vale das Gatas, the wolframite has a higher Nb content than the cassiterite, which contains rutile inclusions enriched in Nb, because cassiterite and wolframite are derived from two distinct magmatic hydrothermal fluids of different age. The fluid responsible for wolframite precipitation will have a similar composition to that resulting from the evolution of the fluid responsible for cassiterite precipitation in the Sn > W-bearing quartz veins.     

Nature and genesis of a carbonatite-associated fluorite deposit at Speewah, East Kimberley region, Western Australia

Summary The Speewah fluorite deposit (>2.28Mt at 25.5% CaF₂) is sited adjacent to the crustal-scale Greenvale Fault on the western side of the Halls Creek Orogen, in the East Kimberley region of Western Australia. Host rocks are Palaeoproterozoic sedimentary rocks, dolerite and granophyre, Early Cambrian basalt, and the Yungul carbonatite. The deposit comprises mainly fluorite–quartz veins associated with lesser barite, sulfides and calcite, controlled by NNE–SSW and N–S brittle faults and fractures. Cross-cutting field relationships indicate that the fluorite veins were deposited post Early Cambrian.Fluorite–quartz vein textures, including colloform banding and comb texture, combined with microthermometric data from primary fluid inclusions, indicate that fluorite was deposited by the incremental infill of open-space structures in an epizonal, and probably epithermal, environment (<160°C) from complex, Li–Ca–Mg-rich, highly saline ore-fluids.The Yungul carbonatite and intimately-associated replacement-type fluorite have similar levels of REE enrichment and identical chondrite-normalised HREE patterns. Samarium and neodymium isotopic analyses of the fluorite indicate extreme differentiation of the ¹⁴⁷Sm/¹⁴⁴Nd ratio, from 0.0709 to 0.6918. These Sm–Nd isotopic data correspond to a mineral isochron with an age of 122±24Ma, interpreted to represent the age of fluorite deposition.Based on the potentially magmatic fluid composition, the replacement-type fluorite within the carbonatite, the similar HREE patterns of fluorite and carbonatite, and direct, if imprecise, isotopic dating of the fluorite, which confirms that fluorite mineralization is younger than the Early Cambrian basalts, the Speewah fluorite deposit is interpreted to be genetically related to the Yungul carbonatite. The large fluorite resource cannot have been derived from the exposed, low-volume carbonatite dyke. Rather, it must have been sourced from a larger carbonatite body at depth, whose presence is implied from basement-derived xenocrystic zircons in the Yungul carbonatite.     

Sulfide mineralogy in the polymetallic cassiterite deposits of Dachang,P.R. China

Several important mineral deposits of Sn, Zn, Cu, Pb, and other metals associated with Devonian sediments and Yanshanian (Cretaceous) granitic rocks are known in the Dachang district (Guangxi). Early genetic hypotheses related the origin of the deposits entirely to the Yanshanian granites. Recently, it was suggested that in Devonian times an earlier syngenetic metal concentration may have occurred, later overprinted by the Yanshanian metallogeny. This contribution is aimed at placing constraints on the physicochemical conditions during the Yanshanian ore formation-remobilization by studying the sulfide chemistry (arsenopyrite, sphalerite, stannite) and fluid inclusion data on the two major deposits in the area, i.e., the polymetallic cassiterite deposit of Changpo and the Zn-Cu skarn deposit of Lamo. Sphalerite and arsenopyrite are quite abundant in both deposits; stannite is minor, but fairly widespread at Changpo, and quite rare at Lamo. They are accompanied by pyrite, pyrrhotite, galena, chalcopyrite, cassiterite, fluorite, and a large variety of other sulfides and sulfosalts. The main compositional data for sphalerite and arsenopyrite are summarized as follows:Changpo: arsenopyrite associated with pyrrhotite 31.4–36.1 at% As; Associated with pyrite 31.9–33.1 at% As; sphalerite associated with pyrrhotite 18.3–22.2 mol% FeS; associated with pyrite 10.6–18.6 mol% FeS.Lamo: arsenopyrite associated with pyrrhotite 32.9–35.3 at% As; associated with pyrite 30.3–31.7 at% As; sphalerite associated with pyrrhotite, 17.2–24.4 mol% FeS; associated with pyrite 4.2–19.6 mol% FeS.Partitioning of Fe and Zn between coexisting sphalerite and stannite from Changpo indicates temperatures of 300°–350°C. For Lamo, the following fluid inclusion data are available: fluorite, salinities of 0–9.5 equiv. wt% NaCl, and homogenization temperatures between 160°C and 250°C; quartz, moderate salinities (0–4.6 equiv. wt% NaCl), and homogenization temperatures of 208°–260°C. Combining the mineralogical evidence with the compositional and fluid inclusion data, it is suggested that the evolution of the environment during the Yanshanian event was characterized by the following parameters: pressure was relatively low (on the order of 1–1.5 kb); temperature may have been as high as 500°C during deposition of the As-richest arsenopyrites, but eventually dropped below 200°–250°C in the latest stages; with an increase in sulfur activity and/or the decrease in temperature pyrrhotite was no longer stable in the latest stages of mineralization.     

Criteres d'analyse géochimique des gisements de fluorine basés sur l'étude de la distribution des lanthanides — application au gite de Maine (71—Cordesse,France)

59 fluorite samples have been analysed by neutron activation for La, Ce, Sm, Eu, Tb, Dy, Yb and Lu. Two properties of the partition coefficient of the R. E. E. between fluorite and poorly complexing solutions (L. Marchand, 1976) have been used for interpretations: (R. E. E.) CaF₂/(R. E. E.)_solution are always very high so that CaF₂ records with an important magnification and without major distortion in the R. E. E. pattern from the mother solution; the partition coefficients are higher for the heavy earths than for the lighter ones. Consequently, in finite reservoirs where CaF₂ precipitates, the trend for solutions will be a gradual enrichment in ceric earths. Interpretations at different scales of the Maine hydrothermal deposit (D. Joseph, 1974) permit to emphasize: — a constant geochemical signal at the scale of a growth band of homogenous colour; — a possible characterization of the ore-forming solutions dynamic (infinite vs finite reservoirs) by comparison of successive growth bands in a same sample; — distinct source rocks for the formation blanche and formation verte.     

The role of synmetamorphic igneous rocks in the metamorphism and partial melting of metasediments,Northwest Adirondacks

Field and petrologic studies along the Adirondack Lowlands — Highlands boundary near Harrisville, NY, indicate that heat from the synmetamorphic intrusion of the Diana syenite complex (intrusion temperature of 1,050° C) played a major role in the local metamorphic thermal regime and was responsible for extensive partial melting of adjacent metasedimentary units (Major Paragneiss of Engel and Engel). Metamorphic temperatures inferred from two — feldspar and spinel — quartz assemblages decrease from 850–950° C along the Diana — metasediment contact to 650–700° C, 2–3 km away from the contact. Metamorphic pressures are 7±0.5 kb as determined from coexisting plagioclase — garnet — sillimanite — quartz, kyanite — sillimanite, and garnet — rutile — ilmenite — sillimanite — quartz (GRAIL). In the paragneiss, migmatites consisting of quartz — microcline perthite — sodic plagioclase leucosomes are generally concordant with the melanosome consisting of biotite — sillimanite — garnet — spinel — plagioclase ±corundum±cordierite. Qualitatively the amount of partial melt and occurrences of corundum-bearing assemblages decrease away from the Diana contact. Activity of H₂O inferred from coexisting biotite — sillimanite — quartz — garnet — K-feldspar ranges from 0.01 to 0.17 and is five to ten times lower in corundum-bearing rocks.Melting proceeded via vapor-absent reactions involving biotite in response to localized heating by synmetamorphic intrusion of magma. This unusually preserved, synmetamorphic contact aureole in a regional granulite terrane supports the concept that granulites owe their origin to magma intrusion and/or the ponding of magmas at the base of the crust.     

Contrasting evolution of low-P rare metal granites from two different terranes in the Hoggar area, Algeria

Two mineralogically different rare metal granites located in two distinct terranes from the Tuareg area are compared: the Tin-Amzi granite in the north of the Laouni Terrane and the Ebelekan granite in the Assodé–Issalane Terrane.The Tin-Amzi granite is enclosed within Eburnean granulitic gneisses, and consists of albite, quartz, protolithionite, K-feldspar and topaz granite (PG). The accessory minerals include columbite tantalite, U- and Hf-rich zircon, Th-uraninite, wolframoixiolite and wolframite. This facies is characterised by a mineralogical evolution from the bottom to the top underlined by a strong resorption of K-feldspar and albite and the crystalliK-feldspar of more abundant topaz and protolithionite II which is further altered in muscovite and Mn-siderite. It is underlain by an albite, K-feldspar, F-rich topaz, quartz and muscovite granite (MG), with W–Nb–Ta oxides, wolframite, Nb-rutile, zircon and scarce uranothorite as accessories.The Ebelekan granite intrudes into a coarse-grained biotite granite enclosed within upper amphibolite-facies metasediments. It comprises a zinnwaldite, albite, topaz porphyritic granite (ZG) with “snow ball” quartz and K-feldspar. The accessories are zircon, monazite, uranothorite, Ta bearing cassiterite, columbite tantalite and wodginite. It is capped by a banded aplite-pegmatite (AP).The geochemistry of Tin-Amzi and Ebelekan granites is nearly comparable. Both are peraluminous (A/CNK=1.10–1.29; ASI=1.17–1.31), sodolithic and fluorine rich with high SiO₂, Al₂O₃, Na₂O+K₂O, Rb, Ga, Li, Ta, Nb, Sn and low FeO, MgO, TiO₂, Ba, Sr, Y, Zr and REE contents. These rare metal Ta bearing granites belong to the P-poor subclass, relating to their P₂O₅ content ( 0.03–0.15 wt.%). Nevertheless, they are distinguished by their concentration of W, Sn and Ta. The Tin-Amzi granite is W–Ta bearing with high W/Sn ratio whereas the Ebelekan granite is Ta–Sn bearing with insignificant W content.At Tin-Amzi the W–Nb–Ta minerals define a sequence formed by W-columbite tantalite followed by wolframoixiolite and finally wolframite showing the effect of hydrothermal overprinting with an extreme W enrichment of the fluids. At Ebelekan, the Sn–Nb–Ta oxides follow a Mn sequence: manganocolumbite→manganotantalite→wodginite+titanowodginite→cassiterite that represents a trend of primary crystallisation resulting from progressive substitution Fe→Mn and Nb→Ta during the magmatic fractionation.     

Die W-Sn-Lagerstätte Chojlla,Cordillera Real,Bolivien Teil 1: Nebengestein und Tektonik

The W, Sn ore deposit of Mina Chojlla is situated in the Cordillera Real to the NE of La Paz within a thick pile of Lower Paleozoic slates near the contact to the alkaligranitic and granodioritic Taquesi-Mururata Batholith of Upper Triassic age. Due to the intrusion the slates, which during the Paleozoic had slightly been folded, became low grade metamorphic and were metasomatically turmalinized. The slates, which uniformly dip to the NE, are cut at right angle by a system of parallel orebearing quartz veins, which dip to the SW. They evidently are tensional features, but opening of joints was made possible only through a special orientation of stratification parallel to the tensional stress and normal to the compressional stress. The stress pattern was generated in a shear zone as a consequence of an upward motion of the batholith with respect to its surroundings. Younger Andean tectonics first caused frequently repeated small bedding plane faults, and lateron a system of reversed faults.

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Resumen El yacimiento de wolfram y estaño de la mina Chojlla está ubicado en la Cordillera Real al Noreste de la Paz dentro de una secuencia muy potente de pizarras del Paleozoico inferior y cerca del contacto con el granito alcalino y la granodiorita del batolito Taquesi-Mururata de edad triásica superior. Debido a la intrusión, las lutitas ya levemente plegadas durante el ciclo hercínico fueron sometidas a un metamorfismo de bajo grado y a una turmalinización metasomática. Una serie de vetas mineralizadas, que están inclinadas hacia el SW, corta perpendicularmente a las pizarras inclinadas hacia el NE. Resultan de grietas de extensión, las cuales pudieron abrirse sólo por consecuencia de una orientación especial de la estratificación paralela al esfuerzo extensivo y perpendicular al esfuerzo compresivo. Estos esfuerzos pueden explicarse como componentes de un sistema de cizalla producido por un levantamiento tardío del batolito. La tectónica más reciente produjo primero frecuentes fallas en el plano de estratificación y luego un sistema tranversal de fallas inversas.

     

Accessory minerals from the Primorsky rapakivi granite complex, West Baikal Region

The composition of accessory minerals from granites of the second phase, quartz-muscovite (+fluorite), and quartz-muscovite-topaz greisens from the Primorsky rapakivi granite complex, West Baikal region, were studied using backscattered scanning electron microscopy. Ilmenite from granites contains inclusions of cassiterite, titanocolumbite, fergusonite-(Y), polycrase-(Y), and betafite. Allanite-(Ce), bastnaesite-(Ce), xenotime-(Y), Y- and Zr-thorite, zircon, and cyrtolite have been identified in granites. Greisens contain cassiterite, ferrocolumbite (Ta/Nb = 0.02−0.06), pyrochlore-group minerals, ilmenorutile, rutile, wolframite, polycrase-(Y), monazite-(Ce), fluocerite-(Ce), bastnaesite-(Ce), cerphosphorhuttonite, thorite, and other minerals. The ferrocolumbite + ilmenorutile assemblage is typical of quartz-muscovite greisen, whereas the rutile + ilmenorutile + wolframite + W-columbite assemblage is contained in the quartzmuscovite-topaz greisen as a result of an increase in Eh and decrease in pH and potassium activity of solution in the back zone. The compositions of Th- and REE-bearing minerals indicate the important role of phosphate and fluorine complexes in the transport of these elements.     

The Pemali tin deposit,Bangka, Indonesia

The Pemali tin deposit is located in a Triassic granite pluton the magmatic evolution of which is characterized by a decrease of compatible Ca, Mg, Ti, P and Zr in the sequence: medium- to coarse-grained biotite granite, megacrystic medium-grained biotite granite, two-mica granite/muscovite granite. The tin mineralization is confined to the two-mica granite and consists of disseminated cassiterite as well as greisen-bordered veins. The highly evolved muscovite granite is tin-barren and is distinguished from the two-mica granite by its low mica content and low loss-on-ignition values. The fluid inclusions in quartz and fluorite of the two-mica granite and of the greisen homogenize in the 115–410 °C temperature range; the salinities are in the range of 0.4–23 equiv wt% NaCl and the CO₂ concentrations are < 2 mole%.     

Ein Lateritprofil auf klastischen Sedimenten des Mittelmiozäns von Neyveli (Madrasstate — Indien)

Zusammenfassung Mittelmiozäne Deltasedimente aus kaolinitischen Quarzsanden, in die sich Kaolinitlagen, Lignit-Linsen und Lateritoidhorizonte einschalten, werden als Aufarbeitungsdetritus des praemiozän lateritisierten Grundgebirges gedeutet. An ihrer Oberfläche befindet sich ein postmittelmiozäner Laterithorizont. Unter Auflösung von Quarz und Zerstörung eines Teiles der Schwerminerale und Tonminerale wurden Eisen-Konkretionen, Kaolinit und Spuren von AI-Hydroxiden und -Oxidhydraten neu gebildet.Diese hier ausgebildete Delta-Fazies — Verknüpfung von lateritischem Umlagerungsschutt mit autochthonen Lateritisierungsvorgängen — kann verglichen werden mit den Bauxiteinschaltungen in klastische Coastal-plain-Serien von Guiana und Queensland und schließlich mit Sidérolitique- und Wealdenfazies.Als ähnliche klastische Serie ist die Tambo Group der Cape York-Halbinsel in Queensland, die nach Evens (1959) ins Tertiär gestellt wird, zu betrachten. Durch Lateritisierung und Bauxitisierung der kaolinitischen Sandsteine (Loughnan u. Bayliss, 1961) bildeten sich hier die wichtigsten derartigen Verwitterungslagerstätten der Welt.Zahlreiche ähnliche Sedimentserien — vorwiegend aus dem Tertiär (Sidérolitique), aber auch aus der Unterkreide (Wealden) und dem Karbon (Millstone grit. Schottlands) werden von Millot (1964, p. 170–183) in dem Kapitel Faciès sidérolitique sehr anschaulich geschildert.

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Middle miocene deltaic sediments forming kaolinitic quartz sands with intercalations of kaolinitic clay layers, lignite lenses and lateritoid horizons are interpreted as reworked detritus of premiocene lateritic soils on the cristallin basement. On top of this series a lateritic horizon of post middle miocene age is developped. The neoformation of iron concretions, kaolinite and traces of Al- hydroxides and -oxidhydrates is accompanied by solution of quartz and destruction of heavy minerals and clay minerals.This deltaic facies — demonstrating a combination of reworked lateritic detritus with autochthonous lateritic soil formation is compared with bauxite intercalations in clastic coastal plain series of Guiana and Queensland and last not least with Sidérolithique and Wealden facies.

     

Evolution of mineralizing fluids of cassiterite–wolframite and fluorite deposits from Mueilha tin mine area, Eastern Desert of Egypt, evidence from fluid inclusion

Sn–W deposit of the Mueilha mine is one of many other Sn–W deposits in the Eastern desert of Egypt that associated with albite granite. Two forms of Sn–W mineralizations are known at the Mueilha Sn-mine area, namely fissure filling quartz veins and greisen. Cassiterite and/or wolframite, sheelite, and beryl are the main ore minerals in the greisen and quartz veins. Subordinate chalcopyrite and supergene malachite and limonite are also observed in the mineralized veins. To constrain the P–T conditions of the Sn–W mineralizations, fluid inclusions trapped in quartz and cassiterite, have been investigated. The following primary fluid inclusion types are observed: CO₂-rich, two-phase (L?+?V) aqueous, and immiscible three-phase (H₂O–CO₂) inclusions. Low temperature and low salinity secondary inclusions were also detected in the studied samples. Microthermometric results revealed that Sn–W deposition seem to have taken place due to immiscibility at temperature between 260°C and 340°C, and estimated pressure between 1.2 to 2.2 kb. Microthermometric results of fluid inclusions in fluorite from fluorite veins illustrated that fluorite seems to be deposited due to mixing of two fluids at minimum temperature 140°C and 180°C, and estimated minimum pressure at 800 bars.     

Combined zircon and cassiterite U–Pb dating of the Piaotang granite-related tungsten–tin deposit,southern Jiangxi tungsten district,China

The large low-grade Piaotang W–Sn deposit in the southern Jiangxi tungsten district of the eastern Nanling Range, South China, is related to a hidden granite pluton of Jurassic age. The magmatic-hydrothermal system displays a zonation from an inner greisen zone to quartz veins and to peripheral veinlets/stringers (Five-floor zonation model). Most mineralization is in quartz veins with wolframite > cassiterite. The hidden granite pluton in underground exposures comprises three intrusive units, i.e. biotite granite, two-mica granite and muscovite granite. The latter unit is spatially associated with the W–Sn deposit.Combined LA-MC-ICP-MS U–Pb dating of igneous zircon and LA-ICP-MS U–Pb dating of hydrothermal cassiterite are used to constrain the timing of granitic magmatism and hydrothermal mineralization. Zircon from the three granite units has a weighted average ²⁰⁶Pb/²³⁸U age of 159.8 ± 0.3 Ma (2 σ, MSWD = 0.3). The cathodoluminescence (CL) textures indicate that some of the cassiterite crystals from the wolframite-cassiterite quartz vein system have growth zonations, i.e. zone I in the core and zone II in the rim. Dating on cassiterite (zone II) yields a weighted average ²⁰⁶Pb/²³⁸U age of 159.5 ± 1.5 Ma (2 σ, MSWD = 0.4), i.e. the magmatic and hydrothermal systems are synchronous. This confirms the classical model of granite-related tin–tungsten mineralization, and is against the view of a broader time gap of >6 Myr between granite magmatism and W–Sn mineralization which has been previously proposed for the southern Jiangxi tungsten district. The elevated trace element concentrations of Zr, U, Nb, Ta, W and Ti suggest that cassiterite (zone II) formed in a high-temperature quartz vein system related to the Piaotang granite pluton.     

Lead isotope studies of strata-bound,vein-type,and unconformity-related Pb,Sb, and Bi ore mineralizations from the western edge of the Bohemian Massif (F.R. Germany)

Specimens from strata-bound/stratiform Kieslager, lineament-bound, and unconformity-related Pb occurrences from the NE Bavarian Saxothuringian and Moldanubian belts and samples from stibnite and polymetallic Sb-Au quartz veins were analyzed for their lead isotope composition.The strata-bound Pb at Bodenmais yielded an Upper Proterozoic ²⁰⁷Pb/²⁰⁶Pb model age which correlates with the assumed stratigraphic age of the host rock. Late Precambrian rift activity may have triggered the formation of this ore mineralization. This type of Pb was also found in the Kieslager at Waldsassen hosted by Early Paleozoic country rocks and in the fluorite veins at Kittenrain.The vein-type lineament-bound, and unconformity-related Pb occurrences show a similar isotopic pattern which suggests that this type of Pb originated from the same source. The ²⁰⁷Pb/²⁰⁶Pb model ages which are too old compared to the assumed age of formation and the accelerated ²⁰⁸Pb evolution indicate that the detritus of the source rock underwent a high-grade metamorphism in the Precambrian.The formation of the unconformity-related Pb concentrated in galena of fluorite-barite veins is correlated with late Variscan magmatic intrusions. The older model ages of about 100–150 Ma from the lineament-bound lead, located along deep-seated lineamentary fault zones, suggest an earlier separation of this type of Pb possibly triggered by the Caledonian A-subduction-related metamorphism.     

Lewis Ponds, a hybrid carbonate and volcanic-hosted polymetallic massive sulphide deposit, New South Wales, Australia

The Lewis Ponds Zn–Pb–Cu–Ag–Au deposit, located in the eastern Lachlan Fold Belt, central western New South Wales, exhibits the characteristics of both volcanic-hosted massive sulphide and carbonate-hosted replacement deposits. Two stratabound massive to disseminated sulphide zones, Main and Toms, occur in a tightly folded Upper Silurian sequence of marine felsic volcanic and sedimentary rocks. They have a combined indicated resource of 5.7 Mt grading 3.5% Zn, 2.0% Pb, 0.19% Cu, 97 g/t Ag and 1.9 g/t Au. Main Zone is hosted by a thick unit of poorly sorted mixed provenance breccia, limestone-clast breccia and quartz crystal-rich sandstone, whereas Toms Zone occurs in the overlying siltstone. Pretectonic carbonate–chalcopyrite–pyrite and quartz–pyrite stringer veins occur in the footwall porphyritic dacite, south of Toms Zone. Strongly sheared dolomite–chalcopyrite–pyrrhotite veins directly underlie the Toms massive sulphide lens. The mineralized zones consist predominantly of pyrite, sphalerite and galena. Paragenetically early framboidal, dendritic and botryoidal pyrite aggregates and tabular pyrrhotite pseudomorphs of sulphate occur throughout the breccia and sandstone beds that host Main Zone, but are rarely preserved in the annealed massive sulphide in Toms Zone. Main and Toms zones are associated with a semi-conformable hydrothermal alteration envelope, characterized by texturally destructive chlorite-, dolomite- and quartz-rich assemblages. Dolomite, chlorite, quartz, calcite and sulphides have selectively replaced breccia and sandstone beds in the Main Zone host sequence, whereas the underlying porphyritic dacite is weakly sericite altered. Vuggy and botryoidal textures resulted from partial dissolution of the dolomite-altered sedimentary rocks and unimpeded growth of base metal sulphides, carbonate and quartz into open cavities. The intense chlorite-rich alteration assemblage, underlying Toms Zone, grades outward into a weak pervasive sericite–quartz assemblage with distance from the massive sulphide lens. Limestone clasts and hydrothermal dolomite at Lewis Ponds are enriched in light carbon and oxygen isotopes. The dolomite yielded ¹³C_VPDB values of –11 to +1 and ¹⁸O_VSMOW values of 6 to 16. Liquid–vapour fluid inclusions in the dolomite have low salinities (1.4–7.7 equiv. wt% NaCl) and homogenization temperatures (166–232°C for 1,000 m water depth). Dolomitization probably involved fluid mixing or fluid–rock interactions between evolved heated seawater and the limestone-bearing facies, prior to and during mineralization. ³⁴S_VCDT values range from 2.0 to 5.0 in the massive sulphide and 3.9 to 7.4 in the footwall carbonate–chalcopyrite–pyrite stringer veins, indicating that the hydrothermal fluid may have contained mamgatic sulphur and a component of partially reduced seawater. The sulphide mineral assemblages at Lewis Ponds are consistent with moderate to strongly reduced conditions during diagenesis and mineralization. Low temperature dolomitization of limestone-bearing facies in the Main Zone host sequence created secondary porosity and provided a reactive host for fluid-rock interactions. Main Zone formed by lateral fluid flow and sub-seafloor replacement of the poorly sorted breccia and sandstone beds. Base metal sulphide deposition probably resulted from dissolution of dolomite, fluid mixing and increased fluid pH. Pyrite, sphalerite and galena precipitated from a relatively low temperature, 150–250°C hydrothermal fluid. In contrast, Toms Zone was emplaced into fine-grained sediment at or near the seafloor, above a zone of focused up-flowing hydrothermal fluids. Copper-rich assemblages were deposited in the Toms Zone footwall and massive sulphide lenses in Main and Toms zones as the hydrothermal system intensified. During the D₁ deformation, fracture-controlled fluids within the Lewis Ponds fault zone and adjacent footwall volcanic succession remobilized sulphides into syntectonic quartz veins. Lewis Ponds is a rare example of a synvolcanic sub-seafloor hydrothermal system developed within fossiliferous limestone-bearing facies. The close spatial association between limestone, hydrothermal dolomite, massive sulphide and dacite provides a basis for new exploration targets elsewhere in New South Wales.Editorial handling: D. Lentz     

Jurassic kimberlites from Picton and Varty Lake,Ontario: Geochemical and stable isotopic characteristics

Micaceous ultramafic dikes of Jurassic age from Picton and Varty Lake, Ontario, consist mineralogically of olivine — phlogopite — serpentine — calcite-spinel. The rocks are characterized by abundant Ba-rich phlogopite (up to 6.5 wt.% BaO) and spinels with a diagnostic kimberlite trend-1. Compositionally the dikes are characterized by extreme silica-undersaturation (21–30 wt.% SiO₂), primitive Mg/(Mg + Fe^T) ratios (0.75–0.83), large enrichments of volatile components (CO₂ and H₂O), and relatively high abundances of both incompatible and compatible trace elements. The dikes exhibit pronounced enrichments of light rare earth elements (LREE) (La_N=320–1330) combined with strongly fractionated patterns (La_N/Yb_N=45–108). Calcite in the dikes is a primary magmatic phase, from textural relations and C-isotopic compositions ( ¹³C= –4.0 to –8.3). A calcite-rich aphanitic phase of the Picton dike is interpreted to be a late stage magmatic differentiate, which possibly involved olivine fractionation. Although the dikes lack most of the macrocrysts generally considered to be important diagnostic minerals of kimberlite magmatism, the geochemical, mineralogical and C- and O-isotopic characteristics collectively indicate that the dikes are evolved varieties of hypabyssal facies kimerlite.     

Oxygen isotope studies of wolframite in tungsten ore deposits of south China

Based on the oxygen isotopic compositions of 133 wolframite samples and 110 quartz samples collected from 30 tungsten ore deposits in south China, in conjunction withδD values and other data, these deposits can be divided into four types.

Stable isotope study of antimony deposits in the Muratdagi region,western Turkey

The Muratdagi region is rich in antimony deposits having the following common characteristics: post Miocene age, location on the down-thrown blocks next to normal faults, in the vicinity of active or fossil thermal springs, and in contact with carbonate rocks. The isotopic composition of — 7. SMOW of the mineralizing fluid calculated from the measured ° ¹⁸O of quartz and the fluid inclusion microthermometry, is indicative of meteoric water origin. The ° ¹³C of the inclusion CO₂ of — 19.1 to — 25.4 PDB is indicative of interaction with organic material-graphite. The ° ³⁴S of stibnite — 3.6 to — 0.7 is, in view of the mineral assemblage, indicative of magmatic origin of the sulphur. A tightly confined set of structural, lithological, hydrological and geochemical features define a sequence of geochemical processes; formation of acid and reducing fluid, leaching and transport of antimony complexes and precipitation of stibnite within defined lithological units. The set of processes seems to have taken place within a space of 5000 m lateral and 1000 m vertical extension.     

Sedimente und Mikrofaunen im Bereich der Grenzschwelle Zweier Ozeanischer Räume,Dargestellt an Einem Schnitt Über den Island-Färöer-Rücken (Nordatlantischer Ozean Rosengarten — Europäisches Nordmeer)

Zusammenfassung Der Begriff der Grenzschwellen ozeanischer Räume wird definiert und zunächst ihre Bedeutung für die Ausbildung der Beckenfazies dargelegt. Anschließend wird an Hand eines Schnittes über die Färöer-Island-Schwelle gezeigt, daß unter bestimmten hydrographischen Bedingungen auch die Faziesverhältnisse in Schwellenbereichen durch den durch die Dichteunterschiede bedingten Wasseraustausch zwischen zwei ozeanischen Räumen nachhaltig beeinflußt werden können. Es ergibt sich, daß sogar in Wassertiefen von 2000 m und mehr — lediglich als Folge von Überströmungsvorgängen — die Möglichkeit zur Bildung von sandigen Ablagerungen gegeben ist. Nicht jeder Sand des tiefen Wassers braucht demnach durch turbidity currents zu seinem Absatzort verfrachtet zu sein.Der mikrofaunistische Inhalt der Sedimente wird angegeben und in Verbindung mit den hydrographischen Verhältnissen — insbesondere den Temperatur-schwankungen im Grenzbereich zwischen dem kalten subarktischen und dem warmen nordatlantischen Wasser — betrachtet.