Quartz-muscovite Schist Research Articles

Origin of Silurian granite in the Baiganhu field, Eastern Kulun Terrane, NW China: Implications for the tectonic setting of Sn-W mineralization

The Baiganhu area in the Eastern Kunlun Terrane on the northern margin of the Tibetan Plateau contains world-class Sn-W deposits in close association with monzogranite. However, the origin of granite and the tectonic setting for the Sn-W mineralization have not been well constrained. Here we present the petrological and geochemical data of the granite (431 Ma) associated with the Sn-W mineralization to evaluate the geological-tectonic setting for the mineralization. The monzogranite has high SiO2 contents, ranging from 65.8 to 73.5 wt%, and shows a geochemical affinity with A2-type granites. Relatively high zircon saturation temperatures, ranging between 750 °C and 921 °C, suggest that the parental magmas were hot. The whole-rock εNd (t = 431 Ma) values range from –2.7 to –3.1 with TDM ages between 1810 and 1040 Ma, and zircon εHf (t = 431 Ma) values range from + 0.7 to + 4.1 with TDM ages between 1040 and 900 Ma. The data suggest that the magmas had significant contributions of old rocks. The granitic rocks intruded into quartz-muscovite schist of the Proterozoic Xiaomiao Complex, which underlies the vast area. Zircon grains in the schist are magmatic in origin based on sharp oscillatory zoning and high Th/U ratios (>0.2). The 207Pb-206Pb zircon ages (n = 25) of the schist range from 1898 ± 2 to 1700 ± 6 Ma, suggesting that the zircon grains originate from a Paleoproterozoic magmatic belt. Such ancient rocks, either as lower crustal component or subcontinental lithospheric mantle, contributed ∼ 30 % to the parental magmas. We conclude that post-collisional extension within the Eastern Kunlun Terrane was accompanied by upwelling and adiabatic melting of the asthenospheric mantle which induced partial melting of subcontinental lithospheric mantle and lower crustal rocks and formed granitic magmas. Aqueous fluids separated from the granitic magma which preferentially incorporate W and Sn contributed to the mineralization in and around the granites.

DECCAN VOLCANIC OF MALWA, STRATIGRAPHY AND CORRELATION OF BASALTIC LAVA FLOWS USING MEGACRYST BEARING HORIZON AS TOOL, PARTS OF WESTERN M.P. INDIA

A review of earlier studies of the Deccan Trap occurrences of parts of Ratlam, Mandsaur, Jhabua, Dhar, Khargone, Indore, Ujjain and Shajapur districts of Madhya Pradesh, India was carried out of the area falling between latitudes 220 0000 to 2400000N and longitudes 7400000 to 7600000 in Survey of India Quadrangle sheet Nos. 46I, 46J, 46M and 46N.The main objectives of the study were to synthesize the data on the Deccan Trap basaltic lava flows , their types ,their diagnostic characteristics with special emphasis on delineating and identifying the various megacryst horizons , their levels with specific elevation above m.s.l. to build up the litho-stratigraphy for regional correlation. Broadly the area exhibits the Proterozoic Aravalli Supergroup, the Cretaceous, Bagh and Lameta Groups and the Deccan basaltic lava flows with intruded dykes and sills. The Aravalli Supergroup is represented by the Udaipur, Lunavada and Champaner Groups. The Udaipur Group consists mainly of hornblende gneiss, marble and calc-silicate, carbonaceous phyllites and chlorite schist. The Lunavada Group comprises dolomitic limestone (Phosphate bearing), quartzite, muscovite quartzite, quartz muscovite schist, feldspathised quartzite, gneissic feldspathic rock and biotitic gneiss. The Champaner Group is represented by dolomite, phyllite, slates and basic intrusives. The Aravalli Super group of rocks is also intruded by serpentinite, pyroxinite, granite and basic rocks. The Aravalli Supergroup of rocks is unconformably overlain by Cretaceous marine sedimentary deposits of Bagh Group. It includes Lower arenaceous and Upper calcareous units and occurs as discontinuous outcrops. These are almost horizontally to sub horizontally disposed. The Bagh Group is represented by three units / Formations i.e. Nimar sandstone overlain by nodular limestone and subsequently by coralline limestone. The Lameta Group of rocks is noticed in the area east and South East of Bagh exposures, overlying the Nimar sandstones. These rocks predominantly consist of limestone, gritty sandstone and conglomerate and generally exhibit hummocky topography and sometimes display solution channels. These are mostly horizontally to sub-horizontally disposed with an average thickness of 5- 6 m. The Deccan Trap has occupied a very long stretch of area which consists of a sequence of 121 basaltic lava flows with a cumulative thickness of about 610 m. These flows represent a sequence of cyclic lava eruptions with fine to medium grained a aphyric to sparsely / moderately / highly / mega porphyritic lava. About two third of the total flows exhibit Aa characters and the rest are compound and simple Pahoehoe. Some of these flows consist of megacryst units containing feldspar laths varying in size round two to five cm. These megacryst horizons have been identified at different elevations in Quadrangles 46I, J, M, N and on the basis of these horizons, various flows have been grouped into to six Formations which have specific nomenclatures and stratigraphic status. These formations are in the order of antiquity 1) Mandleshwar formation, 2) Choral formation,3) Dhar formations 4) Indore Formation 5) Bargonda Formation and 6) Singarchori Formation. Full sequence is exposed only in quadrangle 46N whereas the Quadrangles 46I, J, M do not exhibit Bargonda and Singarchori Formations. An attempt has been made to correlate the various Formations in degree sheets 46 I, J, M, N with the surroundings Geological Quadrangles. The Megacryst bearing lava- flows act as marker horizons for this purpose. A large number of dykes and dyke swamps of basaltic as well as doleritic compositions have been marked around the Narmada River. The intensity of the dykes is more in the oldest Mandleshwar Formations and it gradually decreases in increasing order of antiquity towards the younger Bargonda and Singarchori Formations. The general trend of these dykes varies from East North East – West South West to E-W running sub parallel to the Narmada lineament, besides a few dykes also cut across this lineament trend and oriented along NNW-SSE to N-S direction. The Length of these dykes varies from about 200 m to 20 Km with width varying from a few meters to as much as 200 m. The possibility exists that these dykes may have been actually feeders through which periodic eruptions of tholiitic basaltic lava took place resulting in formation of such a thick pile of lava flows. Besides as many as seven Intertrapean fossiliferous sedimentary horizons have been recognized within the basal part of the flows. These demonstrate episodic nature of volcanic activity, long periods of quiescence and resilience. The overall study of various lava flow s and their interrelations their relative dispositions thinning /swelling and pinching nature. Their relative elevations, occurrence of marker megacryst units, change in lava characters, overall gradient of lava flows and their relation to preexisting topography and slope elements reveals that the sources of lava eruptions of Older Formations are situated somewhere in the west and south west whereas those of Younger Formations are located in the Eastern part of Mhow of the area studied.

Provenance of Mesozoic sandstones from the northwestern Gulf of Suez, Egypt: new evidence from petrography and whole-rock geochemistry

New investigations of petrographic and geochemical characteristics of Mesozoic sandstones from the northwestern Gulf of Suez in Egypt have been undertaken, documenting dominance of quartzose sandstones containing on average ~ 5% of mostly sedimentary and subordinately metamorphic lithic fragments (siltstone, sandy siltstone, and, more rarely slate, metasiltstone, limestone, dolostone, quartz-muscovite schist, and gneiss). These sandstones are depleted in many chemical elements and display low Al2O3/SiO2 and K2O/Na2O ratios. Mineralogical and geochemical parameters point at extensive recycling from older (i.e., Paleozoic) siliciclastic strata. Relatively constant composition throughout the Mesozoic contrasts with successive palaeogeographic changes associated to the major events of rifting and dispersal, which may be explained by the widespread distribution of Paleozoic clastic wedges all across northern Gondwana.

Petrographic, geochemical and structural characteristics of gold-bearing metasedimentary rocks from the Atacora structural unit, Northwestern Bénin Republic

The metasedimentary rocks of the Atacora structural unit around Natitingou in Benin are composed of quartzites, quartz muscovite schist and mica schist. Being auriferous, the petrographic, geochemical and structural features of these rocks were investigated to ascertain the source of gold and its relation to structural deformations. Quartz, muscovite and opaque minerals constitute the dominant minerals in the quartz muscovite schist. The quartzites and mica schists are predominantly composed of quartz, plagioclase, microcline, muscovite and chlorite in varying proportions, with biotite, garnet and epidote in mica schist. The rocks have quartzose sedimentary composition and plot within the passive margin setting on major element discrimination diagrams. The Pan-African ductile and brittle deformation phases produced predominantly folds, strike-slip faults, dextral shear plane and fractures within the area. Gold-bearing veins in the host rocks occur within and near the N-S to NE-SW trending microfolds and the major brittle E-W and NE-SW faults. Gold mineralization is hosted within the NE-trending shear zones and NE-SW trending asymmetric folds which are attributed to transpressional D2 phase of the Pan-African orogeny. Pathfinder elements for gold mineralization in the Atacora are W–Cu–As–Mo ± Sn. This may suggest interaction between host rocks and mineralizing fluids, probably from deformation and metamorphic processes during the late stages of the Pan-African Orogenic event. However, fluid inclusion and stable isotopic studies are required to constrain the origin of ore fluids.

Neoproterozoic copper-gold mineralization in the Amani area, southwestern Tanzania

The Amani area in southwestern Tanzania contains several prospects where primary Cu-Au mineralization occurs at surface, the most noteworthy of these being the Amani Hills and Mpanga Hill prospects. At the Amani Hills prospect, structurally-controlled gold mineralization is hosted in quartz-muscovite schists of the Amani Group and minor high-grade gneisses belonging to the Kabelege Group. Here, quartz-carbonate veins contain pyrite-pyrrhotite-chalcopyrite, with free-milling gold occurring predominantly in quartz and along sulphide grain boundaries. These veins are associated with sericite-epidote-albite alteration of the wallrocks. At the Mpanga Hill prospect, Cu ± Au mineralization is hosted within impure micaceous marbles of the Rafiki Group. At this prospect, both the sulphidised carbonate host rocks and quartz-carbonate veins contain chalcopyrite, bornite and pyrite assemblages, with accessory phases of Au ± Pb ± Zn ± Ag ± Bi ± Se. Fluid inclusion microthermometry indicate that auriferous veins at both prospects record a bimodal occurrence of early low-temperature and low-salinity (≤23.2 wt% NaCl eq.) fluids that are overprinted by later, high temperature and hypersaline fluids (32.8 – 54 wt% NaCl eq.). These ore-forming fluids contain H2O-NaCl ± CO2 ± CH4 compositions and were trapped at near-lithostatic to supralithostatic conditions of 330 – 400 °C and 1.7 – 6.9 kbar. These hydrothermal fluids were likely variably sourced and were focussed along kilometre-scale brittle-ductile reverse shear zones in the Amani area, where fluid-rock interactions led to Cu-Au mineralization. 40Ar/39Ar dating of muscovite constrained the timing of copper – gold mineralization in the Amani area to between c. 550 – 600 Ma. Mineralization is therefore related to the Pan-African aged Kuunga orogeny, which resulted from the collision between the Tanzania Craton and Bangweulu Block during the assembly of supercontinent Gondwana. The new findings presented in this study highlight the exploration potential of copper – gold mineralization along large-scale Proterozoic shear zones in the underexplored and overlooked Upangwa terrane of southwestern Tanzania.

The Guaviare Complex: new evidence of Mesoproterozoic (ca. 1.3 Ga) crust in the Colombian Amazonian Craton

The Guaviare Complex is a new unit defined in the Colombian Amazonian Craton, which is part of the Precambrian basement located in southeastern Colombia. It is divided into three units according to their textural and compositional characteristics, termed Termales Gneiss, Unilla Amphibolite, and La Rompida Quartzite.
 Termales Gneiss rocks are petrographically classified as gneisses and quartz-feldspar granofels, with the local formation of blastomylonite-like dynamic rocks. The Unilla Amphibolite consists of only amphibolites, and La Rompida Quartzite consists of muscovite quartzites, quartz-feldspar granofels, and quartz-muscovite schists.
 The protoliths of Termales Gneiss and Unilla Amphibolite were formed in the Mesoproterozoic at 1.3 Ga due to bimodal magmatism (felsic and mafic) derived from mantle material, with some crust contamination that was probably related to the formation of extensional arcs associated with trans-arc basins in the NW section of the Amazon Craton. La Rompida Quartzite rocks originated from sediments derived from granite rocks and from other, older areas of the craton. These rocks have a maximum age of 1.28 Ga.
 The low-to-medium grade metamorphism that affected these units occurred from 1.28 to 0.6 Ga, most likely concurrently with the Putumayo orogeny of approximately 1.0 Ga, although it may have been an independent event.

Tourmalines as a Tool in Provenance Studies of Terrigenous Material in Extra-Carpathian Albian (Uppermost Lower Cretaceous) Sands of Miechów Synclinorium, Southern Poland

The mature transgressive Albian quartz sands in the Miechów Synclinorium contain a poor (<1%) heavy mineral suite consisting of tourmaline, rutile, garnet, staurolite, ilmenite, zircon, monazite, kyanite, and gahnite. The other minerals, especially those containing Fe and Ti (e.g., biotite), are subordinate. Over 512 tourmaline grains from seven outcrops in the Miechów Segment were analysed using electron probe microanalysis (EPMA). The majority of grains belong to the alkali tourmaline group in which the X-site is dominated by Na (0.4 to 0.9 apfu). Detrital tourmalines are mainly dravite with a prevalent schorl end-member with average XMg values over 0.6. Apart from Mg and Fe, the other Y-site cations rarely exceed 0.1 apfu. Fluorine content is usually below the detection limit. Their chemical composition suggests that most tourmaline grains were sourced from Al-rich and Al-poor metapelites/metapsammites. The main source rocks for the Albian sands were rocks from low- to medium-grade metamorphism, probably from Al-rich quartz-muscovite schist and/or muscovite rich gneisses. Additional minor source rocks were granites and pegmatites coexisting with them. A comparison of the examined tourmaline to tourmaline from possible source areas indicates that these areas were located in the eastern part of the Bohemian Massif and/or eastern Sudetes.

VHMS mineralisation at Erayinia in the Eastern Goldfields Superterrane: Geology and geochemistry of the metamorphosed King Zn deposit

Despite having been a target for volcanic-hosted massive sulfide (VHMS) deposits since the 1960s, few resources have been defined in the Archean Yilgarn Craton of Western Australia. Exploration challenges associated with regolith and deep cover exacerbate the already-difficult task of exploring for small, deformed deposits in stratigraphically complex, metamorphosed volcanic terranes. We present results of drill-core logging, petrography, whole-rock geochemistry and portable X-ray Fluorescence data from the King Zn deposit, to help refine mineralogical and geochemical halos associated with VHMS mineralisation in amphibolite-facies greenstone sequences of the Yilgarn Craton. The King Zn deposit (2.15 Mt at 3.47 wt% Zn) occurs as a 1–7 m-thick stratiform lens dominated by iron sulfides, in an overturned, metamorphosed volcanic rock-dominated sequence located ∼140 km east of Kalgoorlie. The local stratigraphy is characterised by garnet-amphibolite and strongly banded intermediate to felsic schists, with rare horizons of graphitic schist and talc schist. Massive sulfide mineralisation is characterised by stratiform pyrite–pyrrhotite–sphalerite at the contact between quartz–muscovite schists (‘the footwall dacite’), and banded quartz–biotite and amphibole ± garnet schists of the stratigraphic hanging-wall. A zone of pyrite–(sphalerite) and pyrrhotite–pyrite–(chalcopyrite) veining extends throughout the stratigraphic footwall. Footwall garnet-amphibolites are of sub-alkaline basaltic affinity, with a central zone dominated by chlorite ± magnetite interpreted to represent the Cu-bearing feeder zone. SiO2, CaO, Fe2O3T, MgO and Cu concentrations are highly variable, reflecting quartz–epidote ± chlorite ± magnetite ± sulfide alteration. Hydrothermal alteration in stratigraphically overlying intermediate to felsic rocks is characterised by a mineral assemblage of quartz–muscovite ± chlorite ± albite ± carbonate. Cordierite and anthophyllite are locally significant and indicative of zones of Mg-metasomatism prior to metamorphism. Increases in SiO2, Fe2O3T, pathfinder elements (e.g. As, Sb, Tl), and depletions of Na2O, CaO, Sr and MgO occur in quartz–muscovite schists approaching massive sulfide mineralisation. Within all strata (including the immediate hanging-wall), the following pathfinder elements are strongly correlated with Zn: Ag, As, Au, Bi, Cd, Eu/Eu*, Hg, In, Ni, Pb, Sb, Se and Tl. These geochemical halos resemble less metamorphosed VHMS deposits across the Yilgarn Craton and suggest that although metamorphism leads to element mobility and mineral segregation at the thin-section scale, assay samples of ∼20 cm length are sufficient to vector to mineralisation in amphibolite facies greenstone belts. Recognition of minerals such as Mg-chlorite, muscovite, cordierite, anthophyllite, biotite/phlogopite, and abundant garnet are significant, in addition to Al-rich phases (i.e. kyanite, sillimanite, andalusite and/or staurolite) not identified at King. Chemographic diagrams may be used to identify and distinguish different alteration trends, along with several alteration indices (e.g. Alteration Index, Carbonate–Chlorite–Pyrite Index, Silicification Index) and the abundance of normative corundum and quartz.

Restoration of Late Neoarchean–Early Cambrian tectonics in the Rengali orogen and its environs (eastern India): The Antarctic connection

Geological mapping and P–T path reconstructions are combined with monazite chemical age and Secondary Ion Mass Spectrometric (SIMS) U–Pb zircon age determinations to identify crustal domains with distinctive evolutionary histories in the Rengali orogen sandwiched between two Grenvillian-age metamorphic belts, i.e. the Eastern Ghats Granulite Belt (EGGB) in the south, and the amphibolite facies Gangpur Schist Belt (GSB) in the north, which in turn forms a collar along the NW/W margins of the Paleo/Mesoarchean Singhbhum Craton (SC) north of the Rengali orogen. Anatectic gneisses in the orogen core exhibit multi-phase Neoarchean/Paleoproterozoic deformation, metamorphic P–T histories and juvenile magma emplacement events. The high-grade belt is inferred to be a septum of the Bastar Craton (BC). The flanking supracrustal belt in the orogen — dominated by quartz-muscovite schists (±staurolite, kyanite, garnet pyrophyllite), inter-bedded with poorly-sorted and polymict meta-conglomerate, and meta-ultramafic/amphibolite bands — evolved along P–T paths characterized by sub-greenschist to amphibolite facies peak P–T conditions in closely-spaced samples. The supracrustal rocks and the anatectic gneisses of contrasting metamorphic P–T histories experienced D1, D2 and D3 fabric-forming events, but the high-angle obliquity between the steeply-plunging D3 folds in the anatectic gneisses and the gently-plunging D3 folds in the supracrustal unit suggests the two lithodemic units were tectonically accreted post-S2. The supracrustal belt is inferred to be a tectonic mélange formed in an accretionary wedge at the tri-junction of the Bastar Craton, the Eastern Ghats Granulite Belt and the Singhbhum Craton; the basin closure synchronous with the assembly of EGGB and the Singhbhum Craton–Gangpur Schist belt composite occurred between 510 and 610Ma. Based on the available evidence across the facing coastlines of the Greater India landmass and the Australo–Antarctic blocks at ~500Ma, it is suggested that the EGGB welded with the Greater India landmass during the Pan African along an accretion zone, of which the Rengali orogen is a part, synchronous with the final assembly of the Gondwanaland.

Geochemical and Nd isotopic constraints on provenance and depositional setting of the Shihuiding Formation in the Shilu Fe–Co–Cu ore district, Hainan Province, South China

The Shihuiding Formation, a subordinate succession hosting the Fe–Co–Cu ores, is a suite of Neoproterozoic terrigenous clastic rocks occurring in the Shilu Fe–Co–Cu ore district of the Hainan Island, South China. Integrated petrographical, geochemical, and Nd isotopic analyses have been carried out on 23 sandstone specimens of the Shihuiding Formation in order to understand their provenance and the tectonic setting of their deposition. The samples can be divided into two groups, quartzose sandstones (13 samples) and ferruginous sandstones (10 samples). The ferruginous sandstones have average SiO2 and Fetotal contents of 77.23wt.% and 18.09wt.%, respectively, and this contrasts with the higher average SiO2 (94.04wt.%) and lower Fetotal (2.67wt.%) contents of the quartzose sandstones. The bivariant Th/Sc and Zr/Sc ratios indicate a predominantly recycled sedimentary provenance, and the low to medium degrees of weathering are commonly indicated by an average chemical index of maturity (CIM) of 81 and an average chemical index of alteration (CIA) of 68. The Shihuiding Formation sandstones have REE contents of 21–249ppm, with LREE/HREE=9.18 and δEu=0.67. The εNd (970Ma) values of −5.7 to −3.4, and model (TDM) ages of 2099–1773Ma are compatible with a source mainly from the Paleo- to Mesoproterozoic Baoban Group, a suite of metamorphosed sedimentary rocks intruded by ca. 1450Ma granites. Quantitative provenance modeling indicates that the Shihuiding Formation sandstones are best modeled with a mixture of 29% plagioclase–amphibole gneiss (29 P), 38% quartz–muscovite schist (38 Q), and 33% granite (33 G) detritus. Mixing the εNd values of the sandstones, calculated at 970Ma, indicates that the sediment received 22–47% (average 34%) of its detritus from the Baoban Group quartz–muscovite schists. Components from hydrothermal fluids may also have been involved during deposition of the Shihuiding Formation sandstones, as revealed by a bivariant Al/(Al+Fe+Mn) vs. Fe/Ti plot, positive Eu anomalies, and negative Y anomalies relative to PAAS. Tectonic discrimination diagrams, such as La–Th–Sc and Th–Co–Zr/10, indicate a passive continental margin setting for the deposition of the Shihuiding Formation. In terms of its geological setting, we propose that the Shihuiding Formation was deposited in a peripheral foreland basin, supplied by detritus shed from the Grenville Orogenic Belt during the assemblage of the Rodinia Supercontinent.

Quartz-mica schist and gneiss hosted clay deposits within the Yenipazar(Yozgat, Central Anatolia) volcanogenic massive sulfide ore

The Yenipazar deposit of volcanogenic sulfide occurrence, situated approximately 9 km SW of Yenipazar, is hosted in quartz-muscovite schists and gneiss. Following the Late Cretaceous, the quartz-mica schists and gneiss have been altered to clay minerals, resulting in important kaolin deposits. The clay deposits consist mainly of halloysite, kaolinite, smectite, illite, muscovite, chlorite, and α-quartz. Biotite, alunite, jarosite, pyrite, hematite, calcite, low cristobalite, and feldspar are present in minor amounts. In places, some mixed-layer clays, such as kaolinite/smectite and smectite/illite, are also observed within the clay deposits. Barite is present in a few clay samples. α-Quartz is the dominant silica mineral in all parts of the clay bodies, though silicification becomes more intense in an upward direction. Kaolinite and halloysite are the dominant clay minerals in the upper section of the clay deposits containing up to 36.10% Al2O3. At the middle and lower parts of the clay deposits, smectite and illite/mica are predominant. The Yenipazar clays are characterized by 41.80%-66.10% SiO2, 16.80%-36.10% Al2O3, 2.10%-17.70% Fe2O3, 0.30%-6.20% MgO, 0.10%-5.70% CaO, 0.1%-0.70% Na2O, and 0.10%-3.80% K2O values. The silica gossan in the upper parts of the clay deposits and the mineral zonations reveal that hydrothermal alteration is the main cause for the development of the kaolin dominated clay deposits. Pb, Zn, Cu, Sr, Ba, and Zr enrichments and depletion of Cr, Nb, Ti, Ce, Y, and La within the clay deposits are supportive of the magmatic origin of the hydrothermal solution related to Late Cretaceous arc magmatism. Depletion of both total REEs and HREEs, as well as the enrichment of LREEs, in clay deposits refer to an altering acidic solution. The positive Eu and Ce anomalies indicate the presence of feldspar and Zr crystals in the clays, respectively. However, the data show that corrosive hot solutions, which might have arisen from magma, have played an important role in the kaolinization process together with hot meteoric waters. Scanning electron microscope investigations show that illite and smectite are the first minerals formed by the hydrothermal alteration of feldspar crystals.

S, O and Pb isotopic evidence on the origin of the İnkaya (Simav-Kütahya) Cu–Pb–Zn–(Ag) Prospect, NW Turkey

The İnkaya Cu–Pb–Zn–(Ag) prospect is a typical example of the hydrothermal mineralization occurring in the Menderes Massif, which crop out in Western Anatolia. The prospect located approximately 20km west of Simav (Kütahya-Turkey) in northern part of the Menderes Massif have been characterized through the detailed examinations involving geological, mineralogical, whole-rock geochemistry, fluid inclusion, stable isotope and lead isotope.The İnkaya Cu–Pb–Zn–(Ag) prospect is located along an E–W-trending fault in the Cambrian Simav Metamorphics, which consist of quartz–muscovite schist, quartz–biotite schist, muscovite schist, biotite schist and the Arıkayası Formation, which is composed of marbles. Galena, sphalerite, chalcopyrite, pyrite and fahlore are the main minerals, and they are accompanied by small amounts of cerussite, anglesite, digenite, enargite, chalcocite, covellite, bornite, and Fe-oxides with gangue quartz. In addition to Pb, Zn, Cu, Ag, the ore samples contain substantial quantities of As, Cd and Bi and small amount of Au. Average contents of Cu, Pb, Zn and Ag are 77,400ppm, 102,600ppm, 6843ppm and 203ppm, respectively.The δ34S values for galena, chalcopyrite and pyrite formed in the same stage vary in the range from −1.7 to −2.1‰ (average −2.0), 0.1 to 0.3‰ (average 0.2) and −1.5 to 2.6‰ (average +1.5), respectively.δ34S values for H2S, representing the composition of the fluids responsible for the sulfide mineral formations and calculated from the δ34S value are between −2.77 and 1.33‰; it is consistent with the sulfur in sulfide minerals. δ18Oquartz values range from 11.3 to 16.4‰ and estimated δ18Ofluid values range from 5.4 to 10.6‰.Pyrite–galena and pyrite–chalcopyrite pairs calculated to determine equilibrium isotope temperatures based on δ34S values are between 254.6 and 277.4°C for pyrite–galena and 274.7°C for pyrite–chalcopyrite. Sulfur and oxygen isotope values similar to the values for fluid equilibrated with an felsic magmatic source.Fluid inclusion studies on quartz of the same silicification stage coexisting with galena, sphalerite and chalcopyrite collected from the mineralized vein indicate that the temperature range of the fluids is 235°C to 340°C and that the salinities are 0.7 to 4.49wt.% NaCl equivalent. The wide range of homogenization temperatures and relatively lower salinities of the fluid inclusions indicate that at least two different fluid generations were trapped in the quartz from only one fluid type. Also, lower salinities of fluid inclusion probably indicate mixing of meteoric water and magmatic fluid.The galena has 206Pb/204Pb values of 18.862–18.865, 207Pb/204Pb values of 15.707–15.711, and 208Pb/204Pb values of 39.033–39.042. The lead isotope values show a similarity with upper crustal values.

Oxy-dravite, Na(Al2Mg)(Al5Mg)(Si6O18)(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup

Oxy-dravite, Na(Al2Mg)(Al5Mg)(Si6O18)(BO3)3(OH)3O, is a new mineral of the tourmaline supergroup. The holotype specimen originates from the locality of Osarara (Narok district, Kenya) and occurs in quartz-muscovite schist. Crystals of oxy-dravite are dark red, partially translucent with a vitreous luster, a pink streak, and conchoidal fracture. It has a Mohs hardness of approximately 7, and a calculated density of 3.073 g/cm3. In plane-polarized light, oxy-dravite is pleochroic (O = orange and E = pink) and uniaxial negative: ω = 1.650(5), ɛ = 1.620(5). Oxy-dravite is rhombohedral, space group R 3 m , with the unit-cell parameters a = 15.9273(2) and c = 7.2001(1) A, V = 1581.81(4) A3, Z = 3. Chemical characterization based on electron microprobe analysis, single-crystal structure refinement, Mossbauer, and optical spectroscopy, resulted in the empirical structural formula: ( Na 0.83 □ 0.15 K 0.02 ) X Σ 1.00 ( Al 1.34 Fe 0.58 3 + Mg 1.03 Fe 0.03 2 + Ti 0.02 ) Y Σ 3.00 ( Al 4.95 Mg 1.03 Fe 0.02 3 + ) Z Σ 6.00 ( Si 5.98 Al 0.02 O 18 ) T Σ 6.00 ( BO 3 ) B 3 ( OH ) V 3 ( O 0.76 OH 0.24 ) W Σ 1.00 . While the end-member formula of oxy-dravite may be formalized as NaY(Al3)Z(Al4Mg2)Si6O18(BO3)3(OH)3O, the most representative structural formula is NaY(Al2Mg)Z(Al5Mg)Si6O18(BO3)3(OH)3O. The difference between these two formulas is solely in Al-Mg order-disorder, i.e., there is no difference in chemical composition. Although the Mg-Al disorder over the Y and Z sites is controlled by the short-range bond-valence requirements of O2− at the O1 (≡ W) site, the amount of Mg at the Z site is a function of the degree of cation size mismatch at Z. The crystal structure of oxy-dravite was refined to statistical index R 1 of 1.17% using 1586 equivalent reflections collected with Mo K α X-radiation. Oxy-dravite is chemically related to dravite (and fluor-dravite), NaMg3Al6Si6O18(BO3)3(OH)3(OH,F), by the heterovalent substitution Al3+ + O2− → Mg2+ + (OH,F)1−.

Fluid inclusion and sulfur isotope thermometry of the Inkaya (Simav-Kütahya) Cu-Pb-Zn-(Ag) mineralization, NW TURKEY

AbstractThe Inkaya Cu-Pb-Zn-(Ag) mineralization, located about 20 km west of the Simav (Kütahya-Turkey), is situated in the northern part of the Menderes Massif Metamorphics. The mineralization is located along an E-W trending fault in the Cambrian Simav metamorphics consisting of quartz-muscovite schist, quartz-biotite schist, muscovite schist, biotite schist and the Arıkayası formation composed of marbles. Mineralized veins are 30–35 cm in width. The primary mineralization is represented by abundant galena, sphalerite, chalcopyrite, pyrite, fahlore and minor amounts of cerussite, anglesite, digenite, enargite, chalcocite, covellite, bornite, limonite, hematite and goethite with gangue quartz.Fluid inclusion studies on the quartz samples collected from the mineralized veins indicate that the temperature range of the fluids is 235°C to 340°C and the salinities are 0.7 to 4.49 wt. % NaCl equivalent. The wide range of homogenization temperatures indicates that two different fluid generations were trapped in quartz.Sulfur isotope studies of the sulfide minerals showed that all of the δ 34S values are between −2.1 and 2.6 per mil. These values are a typical range for hydrothermal sulfide minerals that have sulfur derived from a magmatic source.Pyrite-galena and pyrite-chalcopyrite sulfur isotope fractionation is consistent with an approach to isotopic equilibrium, and calculated temperatures are 254.6 and 277.4°C for pyrite-galena and 274.7°C for pyrite-chalcopyrite. The microthermometric data and sulfur isotope thermometry indicate the existence of a hydrothermal fluid that circulated along the fault crossing the Simav metamorphics and Arıkayası formation.Fluid inclusion and sulfur isotope thermometry can be used in combination with ore petrographical and geological information to provide site-specific targets for meso-hypothermal metal concentrations.

P-T conditions of the Jandagh metapelitic schists, Northeastern Isfahan Province, Iran

The metapelitic schists of Jandagh or simply Jandagh metapelites can be divided into four groups based on mineral assemblages: (1) quartz-muscovite schists, (2) quartz-muscovite-biotite schists, (3) garnet-muscovite-chlorite schists, and (4) garnet-muscovite-staurolite schists. The Jandagh garnet-muscovite-chlorite schists show the first appearance of garnets. These garnets contain 58–76% almandine, 1–18% spessartine, and 8–20% grossular. Microprobe analysing across the garnets demonstrates an increase in Mg# from core to rim. This is a feature of the prograde metamorphism of metapelites. Well-preserved garnet growth zoning is a sign that metapelites were rapidly cooled and later metamorphic phases had no effect here. The appearance of staurolite in garnet-muscovite-chlorite schists signifies a beginning of the amphibolite facies. The absence of zoning in staurolite suggests that its formation and growth during prograde metamorphism occurred at a widely spaced isograde. Thermobarometric investigations show that the Jandagh metapelites were formed within a temperature range of 400–670°C and pressures of 2.0–6.5 kbar. These results are in agreement with the mineral paragenetic evidence and show the development of greenschist and amphibolite facies in the area studied.

Petrographic and geochemical interpretation of the Late Cretaceous volcaniclastic deposits from the Hateg Basin

The present paper provides new petrographic and geochemical insights into the tectonic and depositional environment of the Late Cretaceous volcaniclastic deposits from the Hateg Basin, in the South Carpathians. These deposits are widespread in the Rachitova–Stei unit, which is tectonically delimitated from the South Carpathians' geological background by strike-slip faults. The conducted petrographic studies have revealed that the volcaniclastic rocks from the Rachitova–Stei unit are mainly pyroclastic (i.e. coarse tuffs, tuff-breccia and tuffites), with a wide variety of volcanic pyroclastic fragments, most commonly including andesites (amphibole andesites, biotite-bearing-amphibole andesites, pyroxene-bearing-amphibole andesites, pyroxene-andesites), and less frequently latite-andesites, latites, rhyolites and dacites. The rhyolites are found only in the lower sequence of the Rachitova–Stei unit. The volcaniclastic deposits were altered by diagenetic processes. The celadonite is the most common diagenetic mineral formed in these rocks, whose presence indicates that the pyroclastic fragments have interacted with sea water. The high percentage of pyroclastic fragments with mainly angular forms and the rich-hornblende content evidence a highly explosive volcanism. The poorly-sorted pyroclastic assemblages with larger blocks and with little reworked pyroclastic material indicate a very short distance of transportation and a deposition relatively close to the explosion centre. The huge quantity of pyroclastic material from the Rachitova–Stei unit suggests that the volcanic explosion had a centre of considerable dimensions, but there is no evidence of such a volcano neither in the Hateg Basin nor anywhere else in the South Carpathians. The whole-rock geochemical composition and the immobile trace element signature from the pyroclastic fragments indicate an island arc depositional environment that was placed close to an active continental margin. In addition, the andesitic nature of the pyroclasts indicates that the volcaniclastic rocks were most probably derived from a magma generated by the subduction of an oceanic plate under a thin continental plate. The presence of the non-volcanic pyroclasts (i.e. granites, quartz-muscovite schists, muscovite quartzites, graphitic phyllites etc.), detached from the continental crust by explosion, confirms that the overriding plate is of continental material. The presence of the rhyolitic magma in the first stage of eruption also supports the continental nature of the overriding plate, the magma having resulted by the partial melting of the rocks from the continental crust. The petrographic and geochemical data have evidenced that the volcanism took place on a thin continental crust. However, this crust is not characteristic to the Getic Unit from the South Carpathians, which is commonly accepted to represent the basement of the Hateg Basin. Most probably, the volcanism was generated in another geotectonic context, respectively, in a continental island arc with a thin overriding crust, most likely situated at a lower latitude. The volcaniclastic units of the Hateg Basin were displaced and moved from this tectonic context to the present location by strike-slip movements.

Yukon–Tanana terrane in the southern Campbell Range, Finlayson Lake belt, southeastern Yukon: the geological setting of retrogressed eclogite of the Klatsa metamorphic complex

Yukon–Tanana terrane in the southern Campbell Range is composed of rocks that have different metamorphic, exhumation, and structural histories, and that have formed in disparate parts of the Paleozoic Yukon–Tanana volcanic arc. The geological relationships in the southern Campbell Range reveal the tectonic and structural history of the Klatsa metamorphic complex, which represents the remnants of an Early Mississippian subduction zone beneath the Yukon–Tanana arc. The Klatsa metamorphic complex is composed of foliated to massive serpentinite, leucogabbro, amphibolite, and retrogressed eclogitic quartz–muscovite schist with lenses of metabasite. It was structurally juxtaposed on Upper Mississippian to Lower Permian metasedimentary rocks of the White Lake, King Arctic, and Money Creek formations. Regional and local structural and stratigraphic relationships suggest that the Klatsa metamorphic complex is part of the Cleaver Lake thrust sheet, the structurally highest thrust sheet in a north- to northeast-vergent thrust belt that deformed the Yukon–Tanana terrane during the Early Permian. Restoration of the displacement on the Cleaver Lake and underlying thrust faults places the Klatsa metamorphic complex on the western margin of Yukon–Tanana terrane. Late Devonian to Early Mississippian subduction is thought to have occurred along this margin based on previous paleogeographic reconstructions. Generally north- to northeast-vergent D1 to D3 folds deformed the Klatsa metamorphic complex and adjacent metasedimentary rocks. Jurassic(?) D4 imbricate thrust faulting has, in part, reactivated the Cleaver Lake thrust fault contacts and imbricated the Klatsa metamorphic complex with metasedimentary rocks in fault panels that are repeated at a scale of 10 to hundreds of metres.

A mid-Proterozoic Volcano-Sedimentary sequence in the Aggeneys Hills Duplex, Namaqua Metamorphic Complex

The western part of the Mid-Proterozoic Namaqua mobile belt consists of a series of tectonostratigraphic terranes, including the Aggeneys terrane. In the centre of the Aggeneys terrane occurs a duplex of five fold nappes, represented by the Aggeneys Hills. One of these, the Quarry fold nappe, contains sections through a distinctive volcano-sedimentary sequence correlated with the Koeris Formation that elsewhere overlies the Hotson Formation with ore-bearing assemblages. A description of the stratigraphic and petrological characteristics of the volcano-sedimentary sequence can supply guides to underlying Broken Hill type deposits in other parts of the Aggeneys terrane. The exposed portion of the Koeris Formation that was mapped in detail in the Quarry fold nappe, is 220m thick and is interpreted to be stratigraphically inverted because of large-scale thrusting and folding. The sequence starts with Mg-rich mafic lavas (now amphibolite with hornblende and cummingtonite), followed by a sedimentary sequence (now quartz-muscovite schist). The succeeding metarhyolite and felsic breccia are overlain by mafic metalava and breccia with intercalated clastic products (now quartz-muscovite schist with mafic lenses). A subsequent major clastic incursion represented by conglomerate (called the main conglomerate), is terminated by massive amygdaloidal lava flows (termed the main amphibolite). The main amphibolite is followed by sedimentary rocks (now schist and quartzite) that are in turn overlain by lava (now homogeneous amphibolite). The sequence ends with volcanoclastic conglomerate/agglomerate succeeded by fine-grained clastic deposits (now quartz-mica schist). Regional metamorphism at amphibolite grade yielded peak temperatures in the range of 400 to 700°C at ≥4 kbar. However epidote-rich parageneses (such as epidote-garnet-quartz) that locally transect the regional fabric, indicates the introduction of Ca, Si and Fe subsequent to the metamorphic peak. Vestiges of earlier alteration are represented by crystallographically zoned cordierite and anthophyllite in rocks of appropriate composition. In most of the exposed sequence, primary features such as vesicles and pillow structures have been retained in spite of the metamorphism, except in zones of high strain. The same can be said of the chemical composition of samples representing typical amphibolite and metarhyolite, matching average tholeiite and rhyolite/rhyodacite. The lavas were generated from an upper mantle source near to 1 600 Ma ago, during extensional crustal conditions subsequent to the infilling of cratonic sedimentary basins in an alluvial-fan/fluvial environment. The volcanism was followed by the Namaqua Orogeny, a long-lived compressional period that included terrane amalgamation and felsic magmatism at ~1 200 Ma ago. The orogeny was terminated during renewed extensional conditions, when easterly orientated shear zones of regional extent were formed near to 1 100 Ma ago.

Mineral-chemical studies of metamorphosed hydrothermal alteration in the Kristineberg volcanogenic massive sulfide district, Sweden

The massive sulfide deposits of the Kristineberg area, Sweden, occur within a 2- to 3-km-thick succession of felsic volcaniclastic rocks belonging to the Skellefte Group. The volcanic pile is intruded by a synvolcanic Jorn-type granitoid (Viterliden intrusive complex) and is overlain by a thick sequence of metasedimentary rocks (Vargfors Group). Mineralization occurs at two main stratigraphic levels, at the base of the felsic volcanic succession and at the contact with the metasedimentary rocks of the Vargfors Group. The Kristineberg Cu–Zn mine is the largest deposit (approximately 21 Mt) and occurs at the base of the volcanic pile, close to the contact with the Viterliden intrusive complex. Four smaller deposits (Ravliden, Ravlidmyran, Horntrask and Nyliden) occur along the upper ore horizon. These deposits are thought to be related to a late intrusive phase of the Viterliden complex which cuts the altered volcanic rocks at the Kristineberg deposit. Within an area of about 50 km2 surrounding the Kristineberg deposit, felsic volcanic rocks between the two ore horizons are affected by extensive albite-destructive alteration (sodium depletion) and development of chlorite and muscovite (strong co-enrichment in magnesium and potassium). The Kristineberg deposit is enveloped by a large and partly transposed quartz–chlorite alteration zone, approximately 2 km in diameter, and a distal but coherent pyrite–quartz–muscovite alteration zone extending as far as 4 km from the deposit. Chlorite(±talc) in the mine area is notably magnesium-rich and contains anomalous F, Ba, Zn and Mn. High fluorine is also present in coexisting muscovite and phlogopite. The magnesium-rich chlorite alteration contrasts sharply with the iron enrichment observed in many other felsic, volcanic-hosted Precambrian massive sulfide deposits. This may indicate fixation of iron by large amounts of pyrite in the section or entrainment of large amounts of seawater in the hydrothermal upflow zones. Kyanite is developed locally in the chlorite-rich pipe at Kristineberg in response to regional thermal metamorphism of highly aluminous alteration in the immediate foot-wall rocks. Spectacular, andalusite-bearing quartz–muscovite schists and quartz–biotite–cordierite schists also occur where the altered felsic volcanic rocks are intruded by the late Revsund granite. However, similar metamorphic mineral growth is not observed where the volcanic rocks at the contact are less altered. Deposits near the top of the felsic volcanic succession are characterized by magnesium-rich chlorite alteration in the foot wall and proximal calc-silicate assemblages (dolomite, calcite, tremolite, ±garnet, ±margarite) where the host sedimentary rocks are carbonate-rich. In general, the calc-silicate alteration is restricted to the immediate hanging wall and zones lateral to the deposits and does not represent a regionally extensive exploration target. The two main ore horizons in the Kristineberg area are not linked by any obvious discordant structures or alteration zones. However, mineral-chemical studies highlight several possible fluid flow pathways leading from the Kristineberg deposit to the Ravliden ore horizon, more than 2 km upsection. Overprinting regional metamorphic minerals have inherited the hydrothermal signature of the ore-related alteration. Electronic Supplementary Material is available at http://dx.doi.org/10.1007/s00126-002-0299-y. On that page (frame on the left side), a link takes you directly to the supplementary material.

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.