Alteration of a pelagic chalk below a paleokarst surface,Oxford, South Island,New Zealand

A small isolated outlier of Lower Oligocene chalk, which grades upwards into what was originally a sandy marl, has been truncated by a paleokarst surface, which is overlain by cross-bedded, well-sorted glauconitic sands. A sandy clay horizon (probably originally tuffaceous) and a basaltic lava flow of probable Miocene age cap the local sequence. Below the paleokarst surface and roughly parallel to it, the original sediment has been intensely altered to an average depth of 1.5 m. The alteration front is sharply defined, even where it extends along the walls of glauconitic sand-filled fissures in the chalk.In the alteration zone, the chalk has been entirely replaced by silica (opal-CT, largely in the form of lepispheres). The calcareous fraction of the marl has been replaced by montmorillonite and clinoptilolite. Rounded gravel clasts (largely basaltic) in the base of the overlying glauconitic sands also have been replaced (by montmorillonite), which suggests that all alteration followed deposition of the sands. However, neither the glauconite nor any other mineral in the sands appears highly altered. Similarly, the quartz grains show no evidence of dissolution or silica precipitation. Preservation of most silica sponge spicules, the only siliceous microfossils in the chalk, indicates that the source of the silica was extraneous to the carbonate sediments.Migrating interstitial liquid, largely confined to the sands between the impervious cap of sandy clay plus basalt and the porous but less permeable chalk, is inferred to have been the causal agent for the replacement. Silica, and any other components necessary for the formation of opal-CT, montmorillonite and clinoptilolite, were probably derived by chemical alteration of the capping volcanics in a groundwater regimen. Replacement reactions in the chalk and marl presumably were dependent on the original presence of calcium carbonate, and apart from montmorillonitization of volcanic material, occurred only where this compound was present.     

Origin of a barite-sulfide ore deposit in the Mykonos intrusion,cyclades: Trace element,isotopic, fluid inclusion and raman spectroscopy evidence

The polymetallic Mykonos vein system in the Cyclades, Greece, consists of 15 tension-gashes filled with barite, quartz, pyrite, sphalerite, chalcopyrite and galena in ca. 13.5 Ma, I-type, Mykonos monzogranite. Zones of silica and chlorite–muscovite alteration are associated with the veins and overprint pervasive silicification, phyllic and argillic alteration that affected large parts of the monzogranite. The mineralization cements breccias and consists of an early barite–silica–pyrite–sphalerite–chalcopyrite assemblage followed by later argentiferous galena. A combination of fluid inclusion and stable isotope data suggests that the barite and associated mineralization were deposited from fluids containing 2 to 17 wt.% NaCl equivalent, at temperatures of ~ 225° to 370 °C, under a hydrostatic pressure of ≤ 100 bars. The mineralizing fluids boiled and were saturated in H₂S and SO₂.Calculated δ¹⁸O_H2O and δD_H2O, initial ⁸⁷Sr/⁸⁶Sr isotope compositions and the trace and REEs elements contents are consistent with a model in which the mineralizing fluids were derived during alteration of the Mykonos intrusion and subsequently mixed with Miocene seawater. Heterogeneities in the calculated δ³⁴S_SO4^− 2 and δ³⁴S_H2S compositions of the ore fluids indicate two distinct sources for sulfur, namely of magmatic and seawater origin, and precipitation due to reduction of the SO₄^− 2 during fluid mixing. The physicochemical conditions of the fluids were pH = 5.0 to 6.2, logf_S2 = − 13.8 to − 12.5, logf_O2 = − 31.9 to − 30.9, logf_H2S(g) = − 1.9 to − 1.7, logf_Te2 = − 7.9 and logα(SO₄^− 2_(aq)/H₂S_(aq)) = + 2.6 to + 5.5. We propose that retrograde mesothermal hydrothermal alteration of the Mykonos monzogranite released barium and silica from the alkali feldspars. Barite was precipitated due to mixing of SO₄^− 2-rich Miocene seawater with the ascending Ba-rich magmatic fluid venting upwards in the pluton.     

Massive sulfides of Mount Jourdanne along the super-slow spreading Southwest Indian Ridge and their genesis

Modern massive sulfide deposits are known to occur in diverse tectonic settings and it is generally expected that hydrothermal deposits of similar geological settings shall have more or less similar mineralogical and geochemical signatures. However, the Mount Jourdanne sulfide deposits along the super-slow spreading Southwest Indian Ridge deviate from this common concept. These sulfide precipitates are Zn-rich (up to 35 wt.%) and are characterized by high concentrations of Pb (≤ 3.5 wt.%), As (≤ 1.1 wt.%), Ag (≤ 0.12 wt.%), Au (≤ 11 ppm), Sb (≤ 967 ppm), and Cd (≤ 0.2 wt.%) which are unusual for a modern sediment-free mid-oceanic ridge system. Therefore, we have reinvestigated the sulfide samples collected during the INDOYO cruise in 1998, in order to explain their unusual mineralogy and geochemical composition. The sulfide samples are polymetallic and are classified as: a) chimneys, b) mounds, and c) hydrothermal breccias. The chimneys are small tube-like symmetrical bodies (30–40 cm high; ~ 10 cm diameter) and consist mainly of sphalerite and less chalcopyrite, set in a matrix of late amorphous silica. The inner wall shows a late-stage colloform sphalerite containing co-precipitates of galena and/or Pb–As sulfosalts. In contrast, the mound samples are dominated either by Fe-sulfides (pyrite) or by a mixture of pyrite and chalcopyrite with less sphalerite, pyrrhotite, amorphous silica and barite. Both, the chimney and mound samples, are characterized by layering and mineral zonation. The hydrothermal breccias are highly altered and mineralogically heterogeneous. They consist of silicified basaltic material that are impregnated with sulfides and contain cm-sized chimney fragments within a matrix of low-temperature minerals such as sphalerite and pyrite. The latter fragments mainly consist of chalcopyrite with isocubanite lamellae. In addition, these breccias contain late-stage realgar, boulangerite, galena, Pb–As sulfosalts and barite that are mostly confined to vugs or fractures. At least five mineralogical associations are distinguished that indicate different thermal episodes ranging from black smoker mineralization conditions to cessation of the hydrothermal activity. Based on the mineralogical associations and established literature in this regard, it is inferred that the mineralization at Mt. Jourdanne occurred mainly in three temperature domains. Above 300 °C, the chalcopyrite (with isocubanite)–pyrrhotite association formed whereas the sphalerite dominated assemblage with much less chalcopyrite and pyrite formed around and below 300 °C. The late-stage mineralization (below 200 °C) contains colloform sphalerite, galena, Pb–As sulfosalts, realgar and barite. The unusual mineralogy and trace element chemistry for this modern VHMS deposit could be explained assuming hydrothermal leaching of some felsic differentiates underneath the basaltic cover and subsequent zone refining processes.     

Geology,mineralogy and fluid inclusion data of the Kizilcaören fluorite–barite–REE deposit,Eskisehir, Turkey

The Kizilcaören fluorite–barite–Rare Earth Element (REE) deposit occurs as epithermal veins and breccia fillings in altered Triassic metasandstones and Oligocene–Miocene pyroclastics adjacent to alkaline porphyritic trachyte and phonolite. This deposit is the only commercial source of REE and thorium in Turkey. Most of the fluorite–barite–REE mineralisation at Kizilcaören has been formed by hydrothermal solutions, which are thought to be genetically associated with alkaline volcanism. The occurrence of the ore minerals in vuggy cavities and veins of massive and vuggy silica indicate that the ore stage postdates hydrothermal alteration. The deposit contains evidence of at least three periods of hypogene mineralisation separated by two periods of faulting. The mineral assemblage includes fluorite, barite, quartz, calcite, bastnäsite, phlogopite, pyrolusite and hematite as well as minor amounts of plagioclase feldspar, pyrite, psilomelane, braunite, monazite, fluocerite, brockite, goethite, and rutile. Fluid inclusion microthermometry indicates that the barite formed from low salinity (0.4–9.2 equiv. wt% NaCl) fluids at low temperatures, between 105 and 230 °C, but fluorite formed from slightly higher salinity (<12.4 equiv. wt% NaCl) fluids at low and moderate temperatures, between 135–354 °C. The depositional temperature of bastnäsite is between 143–286 °C. The local coexistence of liquid- and vapour-rich inclusions suggests boiling conditions. Many relatively low-salinity (<10.0 equiv. wt% NaCl), low and moderate temperature (200–300 °C) inclusions might be the result of episodic mixing of deep-saline brines with low-salinity meteoric fluids. The narrow range of δ³⁴S (pyrite and barite) values (2.89–6.92‰ CDT)suggests that the sulphur source of the hydrothermal fluids are the same and compatible with a volcanogenic sulphate field derived from a magmatic sulphur source.     

Nakhlak carbonate-hosted Pb(Ag) deposit,Isfahan province,Iran: a geological,mineralogical, geochemical,fluid inclusion,and sulfur isotope study

The Upper Cretaceous Nakhlak epigenetic vein-type Pb(Ag) deposit is located 55 km northeast of the town of Anarak in Isfahan Province, Iran. The deposit contains 7 Mt of galena-barite ore with an average grade of 8.33% Pb, 0.38% Zn, and 72 ppm Ag. The ore mineralization occurs as stratabound, epigenetic, steeply dipping, east-west–trending veins in faulted- or fracture-controlled Upper Cretaceous Sadar carbonates. Galena and barite are the primary minerals. Minor sphalerite, tennantite-tetrahedrite, pyrite, and chalcopyrite occur as inclusions in galena. Cerussite with minor amounts of anglesite and plattnerite formed in the oxidized supergene zone. The ore and ore-related minerals were deposited in the hydrothermally dolomitized carbonate host rock containing saddle-shaped dolomite. Geochemically, the dolomitized carbonate host rocks are enriched in MgO, Fe₂O₃, MnO, Pb, Zn, and Ba, but depleted in CaO. The galena concentrate contains high values of Ag (932 ppm), Sb (342 ppm), Cu (422 ppm), As (91 ppm), and Zn (296 ppm); the presence of these trace elements indicates a low-temperature type of galena mineralization. This interpretation is corroborated by fluid inclusions containing 12.98 wt.% NaCl equivalent salinity; the inclusions homogenize at the low temperature of about 152.1 °C. The similarity between δ³⁴S_(V-CDT) values in Nakhlak barite and Permian–Triassic δ³⁴S marine sulfate values indicates that the Nakhlak sulfur was probably provided from evaporates of Permian–Triassic age. The δ³⁴S_(V-CDT) values of galena and barite samples occupy the ranges of − 1.04‰ to + 8.62‰ and + 10.95‰ to + 13.71‰, respectively, and are similar to Mississippi Valley–type (MVT) deposits. The low-temperature basinal fluids, evaporate-originated sulfur, and fault- or fracture-controlled galena-rich veins in the Nakhlak deposit resemble the type of geological features documented in Pb-rich MVT deposits.     

The Mesoproterozoic Abra polymetallic sedimentary rock-hosted mineral deposit,Edmund Basin,Western Australia

Abra is a blind, sedimentary rock-hosted polymetallic Fe–Pb–Zn–Ba–Cu ± Au ± Ag ± Bi ± W deposit, discovered in 1981, located within the easterly trending Jillawarra rift sub-basin of the Mesoproterozoic Edmund Basin, Capricorn Orogen, Western Australia. The Edmund Basin contains a 4–10 km thick succession of siltstone, sandstone, dolomitic siltstone, and stromatolitic dolomite. The age of the Edmund Group is between 1.66 and 1.46 Ga. The Abra polymetallic deposit is hosted in siltstone, dolostone, sandstone and conglomerate of the Irregully and Kiangi Creek Formations, but the mineralised zones do not extend above an erosion surface marking the change from fluvial to marine facies in the lower part of the Kiangi Creek Formation. The Abra deposit is characterised by a funnel-shaped brecciated zone, interpreted as a feeder pipe, overlain by stratiform–stratabound mineralisation. The stratiform–stratabound mineralisation includes a Red Zone and an underlying Black Zone. The Red Zone is characterised by banded jaspilite, hematite, galena, pyrite, quartz, barite, and siderite. The jaspilite and hematite cause the predominant red colouration. The Black Zone consists of veins and rhythmically banded sulphides, laminated and/or brecciated hematite, magnetite, Fe-rich carbonate and scheelite. In both zones, laminations and bands of sulphide minerals, Fe oxides, barite and quartz commonly exhibit colloform textures. The feeder pipe (Stringer Zone) merges with Black Zone and consists of a stockwork of Fe-carbonate-quartz, barite, pyrite, magnetite and chalcopyrite, exhibiting fluidised and/or jigsaw textures.The Abra mineral system is characterised by several overprinting phases of hydrothermal activity, from several stages of brecciation and fluidisation, barite and sulphide veining to barren low-temperature chalcedonic (epithermal regime) veining. Hydrothermal alteration minerals include multi-stage quartz, chlorite, prehnite, Fe-rich carbonate and albite. Albite (Na metasomatism) is an early alteration phase, whereas Fe-rich carbonate is a late phase. Fluid inclusion studies indicate that the ore fluids had temperatures ranging from 162 to 250 °C, with salinities ranging from 5.8 to about 20 wt.% NaCl. In the course of our studies, microthermometric and Raman microprobe analyses were performed on fluid inclusions in carbonate, quartz and barite grains. Fluid inclusions in quartz show homogenisation temperatures ranging from 150 to 170 °C with calculated salinities of between 3.7 and 13.8 wt.% NaCl.The sulphur isotopic system shows δ³⁴S values ranging from 19.4 to 26.6‰ for sulphides and from 37.4 to 41.9‰ for barite (Vogt and Stumpfl, 1987, Austen, 2007). Sulphur isotope thermometry between sulphides and sulphide–barite pairs yields values ranging from 219 to 336 °C (Austen, 2007).Galena samples were analysed for Pb isotope ratios, which have been compared with previous Pb isotopic data. The new Pb isotope systematics show model ages of 1650–1628 Ma, consistent with the formation of the host Edmund Basin.Re–Os dating of euhedral pyrite from the Black Zone yielded an age of ~ 1255 Ma. This age corresponds to the 1320–1170 Ma Mutherbukin tectonic event in the Gascoyne Complex. This event is manifested primarily along a WNW-trending structural corridor of amphibolite facies rocks, about 250 km to the northwest of the Abra area. It is possible that the Re–Os age represents a younger re-activation event of an earlier SEDEX style system with a possible age range of 1640–1590 Ma.A genetic model for Abra is proposed based on the above data. The model involves two end-members ore-forming stages: the first is the formation of the SEDEX style mineral systems, followed by a second multi-phase stage during which there was repeated re-working of the mineral system, guided by seismic activity along major regional faults.     

Geology,geochemistry and genesis of the Qianfanling quartz-vein Mo deposit in Songxian County,Western Henan Province,China

The Qianfanling Mo deposit, located in Songxian County, western Henan province, China, is one of the newly discovered quartz-vein type Mo deposits in the East Qinling–Dabie orogenic belt. The deposit consists of molybdenite in quartz veins and disseminated molybdenite in the wall rocks. The alteration types of the wall rocks include silicification, K-feldspar alteration, pyritization, carbonatization, sericitization, epidotization and chloritization. On the basis of field evidence and petrographic analysis, three stages of hydrothermal mineralization could be distinguished: (1) pyrite–barite–quartz stage; (2) molybdenite–quartz stage; (3) quartz–calcite stage.Two types of fluid inclusions, including CO₂-bearing fluid inclusions and water-rich fluid inclusions, have been recognized in quartz. Homogenization temperatures of fluid inclusions vary from 133 °C to 397 °C. Salinity ranges from 1.57 to 31.61 wt.% NaCl eq. There are a large number of daughter mineral-CO₂-bearing inclusions, which is the result of fluid immiscibility. The ore-forming fluids are medium–high temperature, low to moderate salinity H₂O–NaCl–CO₂ system. The δ³⁴S values of pyrite, molybdenite, and barite range from − 9.3‰ to − 7.3‰, − 9.7‰ to − 7.3‰ and 5.9‰ to 6.8‰, respectively. The δ¹⁸O values of quartz range from 9.8‰ to 11.1‰, with corresponding δ¹⁸O_fluid values of 1.3‰ to 4.3‰, and δ¹⁸D values of fluid inclusions of between − 81‰ and − 64‰. The δ¹³C_V-PDB values of fluid inclusions in quartz and calcite have ranges of − 6.7‰ to − 2.9‰ and − 5.7‰ to − 1.8‰, respectively. Sulfur, hydrogen, oxygen and carbon isotope compositions show that the sulfur and ore-forming fluids derived from a deep-seated igneous source. During the peak collisional period between the North China Craton and the Yangtze Craton, the ore-forming fluids that derived from a deep igneous source extracted base and precious metals and flowed upwards through the channels that formed during tectonism. Fluid immiscibility and volatile exsolution led to the crystallization of molybdenite and other minerals, and the formation of economic orebodies in the Qianfanling Mo deposit.     

Lacustrine records of Holocene flood pulse dynamics in the Upper Paraguay River watershed (Pantanal wetlands,Brazil)

The Pantanal is the world's largest tropical wetland and a biodiversity hotspot, yet its response to Quaternary environmental change is unclear. To address this problem, sediment cores from shallow lakes connected to the Upper Paraguay River (PR) were analyzed and radiocarbon dated to track changes in sedimentary environments. Stratal relations, detrital particle size, multiple biogeochemical indicators, and sponge spicules suggest fluctuating lake-level lowstand conditions between ~ 11,000 and 5300 cal yr BP, punctuated by sporadic and in some cases erosive flood flows. A hiatus has been recorded from ~ 5300 to 2600 cal yr BP, spurred by confinement of the PR within its channel during an episode of profound regional drought. Sustained PR flooding caused a transgression after ~ 2600 cal yr BP, with lake-level highstand conditions appearing during the Little Ice Age. Holocene PR flood pulse dynamics are best explained by variability in effective precipitation, likely driven by insolation and tropical sea-surface temperature gradients. Our results provide novel support for hypotheses on: (1) stratigraphic discontinuity of floodplain sedimentary archives; (2) late Holocene methane flux from Southern Hemisphere wetlands; and (3) pre-colonial indigenous ceramics traditions in western Brazil.     

Geological setting and fluid inclusion characteristics of a lead-copper-barium occurrence hosted in a Neoproterozoic mafic sill at Kiatak,Northumberland Island,Northwestern Greenland

We describe a Pb-Cu-Ba occurrence in Northumberland Island, Northwestern Greenland. Mineralization occupies the brecciated upper contact domain of a Neoproterozoic diabase sill belonging to the Franklin-Thule dike swarm (720–716 Ma), with pyrite-bearing black shales of the Dundas Group, upper Thule Supergroup. The host tholeiitic diabase sill is of different composition (low TiO₂ and P₂O₅) than the locally crosscutting dikes (high TiO₂ and P₂O₅). Chloritization, carbonatization and silicification are intense in proximity to sulfides. Coarse grained, open space-filling galena and minor chalcopyrite are accompanied by 2 generations of calcite and 2 of barite. Galena contains significant amounts of Ag (av. 400 ppm), Sb (av. 700 ppm), Se (av. 20 ppm), traces of Bi, Cd, and Sn. Fluid inclusions in the gangue of the Kiatak occurrence indicate two fluid types. Prior to galena precipitation, a CaCl₂-NaCl-rich aqueous brine (~ 20 wt.% eq NaCl) cooled from temperatures > 300 °C and was trapped first in early calcite, and with further cooling, in barite together with solid bitumen inclusions. Following galena crystallization, secondary inclusions containing a similar brine, but of lower salinity, higher Ca:Na ratio, and lower temperature, were trapped in calcite. Corrosion of galena was followed by precipitation of lower temperature (~ 100 °C) barite from a second fluid, comprising immiscible water and CH₄. Despite its location in the contact between shale and large mafic sill, the low-temperature mineralization postdates the cooling of the sill, and may be related to basinal fluid circulation controlled by regional extensional faults parallel to diabase dikes. Although uneconomic, the Kiatak occurrence may be witness to a larger metallogenic process that could have formed significant SEDEX type metal concentrations in strata within the Thule Supergroup.     

Deposition of talc — kerolite–smectite — smectite at seafloor hydrothermal vent fields: Evidence from mineralogical,geochemical and oxygen isotope studies

Talc, kerolite–smectite, smectite, chlorite–smectite and chlorite samples from sediments, chimneys and massive sulfides from six seafloor hydrothermal areas have been analyzed for mineralogy, chemistry and oxygen isotopes. Samples are from both peridotite- and basalt-hosted hydrothermal systems, and basaltic systems include sediment-free and sediment-covered sites. Mg-phyllosilicates at seafloor hydrothermal sites have previously been described as talc, stevensite or saponite. In contrast, new data show tri-octahedral Mg-phyllosilicates ranging from pure talc and Fe-rich talc, through kerolite-rich kerolite–smectite to smectite-rich kerolite–smectite and tri-octahedral smectite. The most common occurrence is mixed-layer kerolite–smectite, which shows an almost complete interstratification series with 5 to 85% smectitic layers. The smectite interstratified with kerolite is mostly tri-octahedral. The degree of crystal perfection of the clay sequence decreases generally from talc to kerolite–smectite with lower crystalline perfection as the proportion of smectite layers in kerolite–smectite increases.Our studies do not support any dependence of the precipitated minerals on the type/subtype of hydrothermal system. Oxygen isotope geothermometry demonstrates that talc and kerolite–smectite precipitated in chimneys, massive sulfide mounds, at the sediment surface and in open cracks in the sediment near seafloor are high-temperature (> 250 °C) phases that are most probably the result of focused fluid discharge. The other end-member of this tri-octahedral Mg-phyllosilicate sequence, smectite, is a moderate-temperature (200–250 °C) phase forming deep within the sediment (～ 0.8 m). Chlorite and chlorite–smectite, which constitute the alteration sediment matrix around the hydrothermal mounds, are lower-temperature (150–200 °C) phases produced by diffuse fluid discharge through the sediment around the hydrothermal conduits. In addition to temperature, other two controls on the precipitation of this sequence are the silica activity and Mg/Al ratio (i.e. the degree of mixing of seawater with hydrothermal fluid). Higher silica activity favors the formation of talc relative to tri-octahedral smectite. Vent structures and sedimentary cover preclude complete mixing of hydrothermal fluid and ambient seawater, resulting in lower Mg/Al ratios in the interior parts of the chimneys and deeper in the sediment which leads to the precipitation of phyllosilicates with lower Mg contents. Talc and kerolite–smectite have very low trace- and rare earth element contents. Some exhibit a negative or flat Eu anomaly, which suggests Eu depletion in the original hydrothermal fluid. Such Eu depletion could be caused by precipitation of anhydrite or barite (sinks for Eu²⁺) deeper in the system. REE abundances and distribution patterns indicate that chlorite and chlorite–smectite are hydrothermal alteration products of the background turbiditic sediment.     

Mineralogical and geochemical studies of brecciated ores in the Dalucao REE deposit,Sichuan Province,southwestern China

The Dalucao deposit, located in western Sichuan Province, southwestern China, in the western part of the Yangtze Craton, is one of the largest and most extensive rare earth element (REE) deposits in the Himalayan Mianning–Dechang REE belt. Moreover, the Dalucao deposit is the only deposit identified in the southern part of the belt. The Dalucao deposit contains the No. 1, 2, and 3 orebodies; the No. 1 and 3 orebodies are both hosted in two breccia pipes, located in syenite–carbonatite host rocks. Both pipes have elliptical cross-sections at the surface, with long-axis diameters of 200–400 m and short-axis diameters of 180–200 m; the pipes extend downwards for > 450 m. No. 1 and No. 3 have total thickness varying between 55 and 175 m and 14 to 58 m respectively. The REE mineralization is associated with four brecciation events, which are recorded in each of the pipes. The ore grades in the No. 1 and 3 orebodies are similar, and consist of 1.0%–4.5% rare earth oxides (REOs). The No. 1 orebody is characterized by a Type I mineral assemblage (fluorite + barite + celestite + bastnäsite), whereas the No. 3 orebody is characterized by a Type II assemblage (fluorite + celestite + pyrite + muscovite + bastnäsite + strontianite). Argon (⁴⁰Ar/³⁹Ar) dating of hydrothermal muscovite intergrown with REE minerals in typical ores from the No. 1 and 3 orebodies yielded similar ages of 12.69 ± 0.13 and 12.23 ± 0.21 Ma, respectively, which suggest that both mineral assemblages formed coevally, rather than in paragenetic stages. Both ages are also similar to the timing of intrusion of the syenite–carbonatite complex (12.13 ± 0.19 Ma). The ore-mineral assemblages occur in breccias, veinlets, and in narrow veins. The ore veinlets, which usually show a transition to mineralized breccia or brecciated ores, are commonly enveloped by narrow veins and stringer zones with comparable mineral assemblages. The brecciated ores form 95% of the volume of the deposit, whereas brecciated ores are only a minor constituent of other deposits in the Mianning–Dechang REE belt. The carbonatite in the syenite–carbonatite complexes contains high concentrations of S (0.07–2.32 wt.%), Sr (16,500–20,700 ppm), Ba (3600–8400 ppm), and light REEs (LREE) (2848–10,768 ppm), but is depleted in high-field-strength elements (HFSE) (Nb, Ta, P, Zr, Hf, and Ti). The syenite is moderately enriched in large-ion lithophile elements (LILE), Sr (155–277 ppm), and Ba (440–755 ppm). The mineralized, altered, and fresh syenites and carbonatites exhibit similar trace element compositions and REE patterns. Brecciation events, and the Dalucao Fault and its secondary faults around the deposit, contributed to the REE mineralization by facilitating the circulation of ore-forming fluids and providing space for REE precipitation. Some hydrothermal veins composed of coarse-grained fluorite and quartz are distributed in the syenite–carbonatite complex. The oxygen isotope compositions of ore-forming fluids in equilibrium with quartz at 215 °C are − 4.95‰ to − 7.45‰, and the hydrogen isotope compositions of fluid inclusions in coarse-grained quartz are − 88.4‰ to − 105.1‰. The syenite–carbonatite complex and carbonatite are main contributors to the mineralization in the geological occurrence. Thus, the main components of the ore-forming fluids were magmatic water, meteoric water, and CO₂ derived from the decarbonation of carbonatite. According to the petrographic studies, bastnäsite mineralization developed during later stages of hydrothermal evolution and overprinted the formation of the brecciated fluorite–quartz hydrothermal veins. As low-temperature isotope exchange between carbonates of the carbonatite and water-rich magmatic fluids will lead to positive shifts in δ¹⁸O values of the carbonates, C–O isotopic compositions from the bulk primary carbonatite to hydrothermal calcite and bastnäsite changed (δ¹⁸O_V-SMOW from 8.0‰ to 11.6‰, and δ¹³C _V-PDB from − 6.1 to − 8.7‰). According to the chemical composition of syenite and carbonatite, REE chloride species are the primary complexes for the transport of the REEs in the hydrothermal fluids, and the presence of bastnäsite and parisite means the REE were precipitated as fluorocarbonates. High contents of Sr, Ba and S in the syenite–carbonatite complex led to the deposition of large amount of barite and celestite.     

Mineralogy,mineral chemistry,fluid inclusion,and stable isotope investigations of the Kabadüz ore veins,Ordu, NE-Turkey

Hydrothermal vein-type deposits of the Kabadüz region (Ordu, NE-Turkey) are located in Upper Cretaceous andesitic–basaltic rocks and were formed in fault zones along NW–SE direction lines, with thicknesses varying between a few centimetres up to 2 m. The primary mineral paragenesis of the many different ore veins consists of pyrite, chalcopyrite, sphalerite, galena and tetrahedrite–tennantite, with quartz and lesser amounts of calcite and barite as gangue minerals. Electron microprobe analyses indicate that the sphalerite and tetrahedrite–tennantite have low Fe contents, with values less than 3.37 wt.% and 1.56 wt.%, respectively. The very low Ni and Co contents of the pyrites (< 0.04 wt.%) and the Zn/Cd ratio of the sphalerite (~ avg. 100) indicate that the hydrothermal solutions were related to felsic magmatic activity. The homogenisation temperatures and calculated salinity data vary between 180–436 °C and 0.4–14.7 NaCl % eq., respectively. A well-defined negative correlation between the T_h and the salinity data suggests that meteoric water was involved in the hydrothermal solutions. Based on the measured first melting temperatures, CaCl₂, MgCl₂, NaCl and KCl were dominant in the fluid inclusions. The δ³⁴S compositions of the pyrite, chalcopyrite, sphalerite, and galena mineral separates of the investigated ore veins were measured at between 2.14 and − 1.47‰, and the oxygen and hydrogen isotope compositions varied between 7.8–8.5‰ and − 40 − 57‰, respectively. Based on the sulphur, oxygen and hydrogen isotope compositions, magmatic sources were confirmed for the hydrothermal solutions. Taking into account all of the above data and the granitic intrusions around the area, we concluded that younger granitic intrusions were responsible for the ore mineralisation around the Kabadüz region.     

Alteration mineralogy,lithochemistry and stable isotope geochemistry of the Murgul (Artvin,NE Turkey) volcanic hosted massive sulfide deposit: Implications for the alteration age and ore forming fluids

The Murgul (Artvin, NE Turkey) massive sulfide deposit is hosted dominantly by Late Cretaceous calc-alkaline to transitional felsic volcanics. The footwall rocks are represented by dacitic flows and pyroclastics, whereas the hanging wall rocks consist of epiclastic rocks, chemical exhalative rocks, gypsum-bearing vitric tuff, purple vitric tuff and dacitic flows. Multi-element variation diagrams of the hanging wall and footwall rocks exhibit similar patterns with considerable enrichment in K, Rb and Ba and depletion in Nb, Sr, Ti and P. The chondrite-normalized rare earth element (REEs) patterns of all the rocks are characterized by pronounced positive/negative Eu anomalies as a result of different degrees of hydrothermal alteration and the semi-protected effects of plagioclase fractionation.Mineralogical results suggest illite, illite/smectite + chlorite ± kaolinite and chlorite in the footwall rocks and illite ± smectite ± kaolinite and chlorite ± illite in the hanging wall rocks. Overall, the alteration pattern is represented by silica, sericite, chlorite and chlorite–carbonate–epidote–sericite and quartz/albite zones. Increments of Ishikawa alteration indexes, resulting from gains in K₂O and losses in Na₂O and the chlorite–carbonate–pyrite index towards to the center of the stringer zone, indicate the inner parts of the alteration zones. Calculations of the changes in the chemical mass imply a general volume increase in the footwall rocks. Abnormal volume increases are explained by silica and iron enrichments and a total depletion of alkalis in silica zone. Relative K increments are linked to the sericitization of plagioclase and glass shards and the formation of illite/smectite in the sericite zone. In addition, Fe enrichment is always met by pyrite formation accompanied by quartz and chlorite. Illite is favored over chlorite, smectite and kaolinite in the central part of the ore body due to the increase in the (Al + K)/(Na + Ca) ratio. Although the REEs were enriched in the silicification zone, light REEs show depletion in the silicification zone and enrichment in the other zones in contrast to the heavy REEs' behavior. Hydrothermal alteration within the hanging wall rocks, apart from the gypsum-bearing vitric tuffs, is primarily controlled by chloritization with proportional Fe and Mg enrichments and sericitization.The δ¹⁸O and δD values of clay minerals systematically change with increasing formation temperature from 6.6 to 8.7‰ and − 42 to − 50‰ for illites, and 8.6 and − 52‰ for chlorite, respectively. The O- and H-stable isotopic data imply that hydrothermal-alteration processes occurred at 253–332 °C for illites and 136 °C for chlorite with a temperature decrease outward from the center of the deposit. The positive δ³⁴S values (20.3 to 20.4‰) for gypsum suggest contributions from seawater sulfate reduced by Fe-oxide/-hydroxide phases within altered volcanic units. Thus, the hydrothermal alteration possibly formed via a dissolution–precipitation mechanism that operated under acidic conditions. The K–Ar dating (73–62 Ma) of the illites indicates an illitization process from the Maastrichtian to Early Danian period.     

Silver-base metal epithermal vein and listwanite hosted deposit Crnac,Rogozna Mts., Kosovo,part II: A link between magmatic rocks and epithermal mineralization

Crnac is an intermediate sulfidation Pb–Zn–Ag epithermal deposit located within the Vardar suture zone of the Central Balkan Peninsula. The epithermal Pb–Zn–Ag mineralization consists of (i) a series of steeply-dipping veins hosted within the Jurassic amphibolites, and (ii) overlying hydrothermal-explosive breccia with angular (level IV) or rounded fragments of listwanite (surface) cemented by epithermal mineralization. The mineralization is related to the Oligocene quartz latite dykes that crosscut the Crnac antiform. Quartz latite rocks predominantly display a shoshonitic character. The obtained ⁴⁰Ar/³⁹Ar age of fresh quartz latite is 28.9 ± 0.3 Ma. Fine-grained sericite from altered quartz latite is dated at 28.6 ± 0.5 Ma. Early, alteration related fluid inclusions within quartz latite show coexistence of high-density brine and a low-density vapor-saturated phase that homogenized at 280–405 °C. Phase separation occurs at a paleodepth of 0.6 to 0.9 km.Epithermal mineralization developed in three stages: (i) early pyrite–arsenopyrite–pyrrhotite–quartz–kaolinite; (ii) main sphalerite–galena–tetrahedrite–chalcopyrite and (iii) late carbonate–pyrite–arsenopyrite assemblage. The onset of mineral deposition within epithermal veins was initiated by boiling of Na–Cl ± K ± Ca ± Mg fluid at a paleodepth of 0.6 to 0.9 km. Coexisting vapor and liquid-rich inclusions display salinities and trapping temperatures of 4 wt.% NaCl equiv., 280–370 °C and 2–27 wt.% NaCl equiv., 230–375 °C, respectively. Boiling continued throughout the deposition of the sphalerite-galena-tetrahedrite-chalcopyrite assemblage. Late stage carbonate was deposited from diluted, non-boiling, low-temperature Na–Ca–Mg–Cl ± CO₂ fluid (0.2 to 4.8 wt.% NaCl equiv., 115–280 °C).About 100–150 m higher in the system, precipitation of listwanite breccia cement began as a result of boiling Na–Cl ± Ca ± Mg ± K fluid of medium salinities (2.6 to 12.1 wt.% NaCl equiv.) at temperatures of 245–370 °C. Boiling and dilution of fluids continue throughout the precipitation of the main sphalerite-galena-tetrahedrite and late, mainly carbonate assemblage. Surface listwanite breccia contain quartz phenocrysts deposited from a homogeneous fluid with a medium salinity (8–10 wt.% NaCl equiv.) and high temperatures (T_h = 295–315 °C), whereas the early and main stage of a surface listwanite breccia cement precipitated from a boiling fluid of decreasing salinity and temperature. Aqueous ± CO₂, high salinity (16 to 18 wt.% NaCl equiv.), low temperature (120 °C), homogeneously trapped fluid that precipitated late stage carbonates, is most likely a remnant of boiled off fluid. The epithermal assemblage of the surface listwanites precipitated at a paleodepth of 0.4 to 0.6 km.The δ¹³C values of the late stage ankerite range from − 4.2 to 4.1‰, whereas δ¹⁸O range from 9.6 to 17.5‰. The calculated δ¹⁸O of fluid that precipitated carbonates within epithermal veins, and listwanite breccia cement range from 6.3 to 11.3‰, indicating a contribution of magmatic water.Deposition of all mineralization types was initiated by neutralization of primary acidic magmatic fluid by water-rock reactions that caused widespread propylitization and sericitization. Extensive and long-lasting boiling combined with dilution by meteoric water increased the pH towards the final stage of hydrothermal activity.     

The influence of citric acid,EDTA, and fulvic acid on U(VI) sorption onto kaolinite

Uranium(VI) sorption onto kaolinite was investigated as a function of pH (3–12), sorbate/sorbent ratio (1 × 10^?6–1 × 10^?4 M U(VI) with 2 g/L kaolinite), ionic strength (0.001–0.1 M NaNO₃), and pCO₂ (0–5%) in the presence or absence of 1 × 10^?2–1 × 10^?4 M citric acid, 1 × 10^?2–1 × 10^?4 M EDTA, and 10 or 20 mg/L fulvic acid. Control experiments without-solids, containing 1 × 10^?6–1 × 10^?4 M U(VI) in 0.01 M NaNO₃ were used to evaluate sorption to the container wall and precipitation of U phases as a function of pH. Control experiments demonstrate significant loss (up to 100%) of U from solution. Although some loss, particularly in 1 × 10^?5 and 1 × 10^?4 M U experiments, is expected due to precipitation of schoepite, adsorption on the container walls is significant, particularly in 1 × 10^?6 M U experiments. In the absence of ligands, U(VI) sorption on kaolinite increases from pH ～3 to 7 and decreases from pH ～7.5 to 12. Increasing ionic strength from 0.001 to 0.1 M produces only a slight decrease in U(VI) sorption at pH < 7, whereas 10% pCO₂ greatly diminishes U(VI) sorption between pH ～5.5 and 11. Addition of fulvic acid produces a small increase in U(VI) sorption at pH < 5; in contrast, between pH 5 and 10 fulvic acid, citric acid, and EDTA all decrease U(VI) sorption. This suggests that fulvic acid enhances U(VI) sorption slightly via formation of ternary ligand bridges at low pH, whereas EDTA and citric acid do not form ternary surface complexes with the U(VI), and that all three ligands, as well as carbonate, form aqueous uranyl complexes that keep U(VI) in solution at higher pH.     

Palaeoclimatic reconstruction from Lateglacial (Younger Dryas Chronozone) cirque glaciers in Snowdonia,North Wales

The cirques of Snowdonia, North Wales were last occupied by glacier ice during the Younger Dryas Chronozone (YDC), c. 12.9–11.7 ka. New mapping presented here indicates 38 small YDC cirque glaciers formed in Snowdonia, covering a total area of 20.74 km². Equilibrium line altitudes (ELAs) for these glaciers, calculated using an area–altitude balance ratio (AABR) approach, ranged from 380 to 837 m asl. A northeastwards rise in YDC ELAs across Snowdonia is consistent with southwesterly snow-bearing winds. Regional palaeoclimate reconstructions indicate that the YDC in North Wales was colder and drier than at present. Palaeotemperature and annual temperature range estimates, derived from published palaeoecological datasets, were used to reconstruct values of annual accumulation and ‘winter balance plus summer precipitation’ using a degree-day model (DDM) and non-linear regression function, respectively. The DDM acted as the best-estimate for stadial precipitation and yielded values between 2073 and 2687 mm a^?1 (lapse rate: 0.006 °C m^?1) and 1782–2470 mm a^?1 (lapse rate: 0.007 °C m^?1). Accounting for the potential input of windblown and avalanched snow onto former glacier surfaces, accumulation values dropped to between 1791 and 2616 mm a^?1 (lapse rate: 0.006 °C m^?1) and 1473–2390 mm a^?1 (lapse rate: 0.007 °C m^?1). The spatial pattern of stadial accumulation suggests a steep precipitation gradient and provides verification of the northeastwards rise in ELAs. Glaciers nearer the coast of North Wales were most responsive to fluctuations in climate during the YDC, responding to sea-ice enforced continentality during the coldest phases of the stadial and to abrupt warming at the end of the stadial.     

Significance of trace elements in syntaxial quartz cement,Haushi Group sandstones,Sultanate of Oman

Trace element contents and distributions in authigenic quartz cement in deeply buried (2500–4000 m) Haushi Group sandstones from wells in Oman have been investigated in order to determine the factors that control trace element uptake during precipitation.Scanning electron microscope-cathodoluminescence images show well developed growth zones within the quartz cement, which correlate with chemical zonations observed in electron microprobe Al distribution maps. The most abundant trace elements are Al (50–3000 μg g^?1), Li (1–100 μg g^?1), Na (1–40 μg g^?1), and Ge (0.3–5 μg g^?1) with a strong linear correlation between Li and Al and a weaker one between Ge and Al. The molar concentration of Li (+ Na) accounts only for ~ 15% of the charge compensation for Al³⁺ substitution of Si⁴⁺. Though H was not measured in this study, these data indicate a major role of H in charge balancing Al³⁺. The samples belong to the same stratigraphic unit and have similar petrography, but show considerable variability in absolute trace element concentrations between different wells. This variability does not correlate with either sample depth or temperature and shows no regional pattern, but seems to reflect petrophysical and tectonic differences within the sedimentary basin.Petrographic observations of the cogenetic mineral assemblages and hydrochemical modelling indicate that a change from the equilibrium assemblage quartz–kaolinite (–dolomite) to quartz–illite (–dolomite) reflects a decrease in the CO₂ concentration and concurrent variations of the Al concentration. It is concluded that changes in the CO₂ concentrations are responsible for fluctuations in fluid Al concentrations and thus likely also in the investigated quartz cements.     

The Variscan Tamlalt–Menhouhou gold deposit,Eastern High-Atlas,Morocco

The Tamlalt–Menhouhou gold deposit belongs to the Neoproterozoic–Palaeozoic Tamlalt inlier located in the Eastern High-Atlas (Morocco). It occurs in altered Upper Neoproterozoic bimodal volcanic and volcano-sedimentary units outcropping in the Tamlalt–Menhouhou area. Gold mineralization has been identified in quartz veins related to shear-zones associated with a strong quartz-phyllic-argillic alteration. Visible free gold is related to goethite–malachite–barite boxworks in quartz veins. The other alteration minerals accompanying gold mineralization are mainly carbonates, chlorite, hematite, albite and pyrite whose relative proportion defines three alteration types. ⁴⁰Ar/³⁹Ar geochronology performed on phengite grains from phyllic alteration and the auriferous quartz veins, yields plateau ages ranging from 300 ± 5 Ma to 284 ± 12 Ma with a weighted mean age of 293 ± 7 Ma. This identifies a Late Variscan age for the Tamlalt–Menhouhou “shear zones-related” gold deposit and emphasizes the consequences of the Variscan orogeny for gold mineralization in the High-Atlas and Anti-Atlas Neoproterozoic inliers.     

The effect of typhoon induced rainfall on settling fluxes of particles and organic carbon in Yuanyang Lake, subtropical Taiwan

A sediment-trap monitoring program measured the fluxes of settling particles and organic carbon in Yuanyang Lake, northern Taiwan, from July 2004 to July 2006 and assessed their relations to the amounts of normal monthly and typhoon-event precipitation. The flux of settling particles varied from 0.7 mg cm^?2 month^?1 to 14.7 mg cm^?2 month^?1, and the monthly precipitation ranged from 56 mm to 1218 mm during the survey period. The contributions from typhoon-event precipitation to monthly rainfall amounts were generally larger than 70%. Higher inputs of both particulate and organic carbon into the lake were found during typhoon seasons. Of the annual settling particle loading of 14.9 tons year^?1 to the lake floor, 69% occurred during the typhoon months, and 62% of the annual organic carbon loading of 2.3 tons year^?1 happened during the typhoon months. These results show the importance of typhoon events on the fluxes of settling particles and organic carbon and their delivery to lakes.     

A combined fluid inclusion and S–Pb isotope study of the Neoproterozoic Pingshui volcanogenic massive sulfide Cu–Zn deposit,Southeast China

The Pingshui Cu–Zn deposit is located in the Jiangshan–Shaoxing fault zone, which marks the Neoproterozoic suture zone between the Yangtze block and Cathaysia block in South China. It contains 0.45 million tons of proven ore reserves with grades of 1.03 wt.% Cu and 1.83 wt.% Zn. This deposit is composed of stratiform, massive sulfide ore bodies, which contain more than 60 vol.% sulfide minerals. These ore bodies are hosted in altered mafic and felsic rocks (spilites and keratophyres) of the bimodal volcanic suite that makes up the Neoproterozoic Pingshui Formation. Metallic minerals include pyrite, chalcopyrite, sphalerite, tennantite, tetrahedrite and magnetite, with minor galena. Gangue minerals are quartz, sericite, chlorite, calcite, gypsum, barite and jasper. Three distinct mineralogical zones are recognized in these massive sulfide ore bodies: a distal zone composed of sphalerite + pyrite + barite (zone I); an intermediate zone characterized by a pyrite + sphalerite + chalcopyrite assemblages (zone II); and a proximal zone containing chalcopyrite + pyrite + magnetite (zone III). A thin, layer of exhalative jaspilite overlies the sulfide ore bodies except in the proximal zone. The volcanic rocks of the Pingshui Formation are all highly altered spilites and keratophyres, but their trace element geochemistry suggests that they were generated by partial melting of the depleted mantle in an island arc setting. Homogenization temperatures of the primary fluid inclusions in quartz from massive sulfide ores are between 217 and 328 °C, and their salinities range from 3.2 to 5.7 wt.% NaCl equivalent. Raman spectroscopy of the fluid inclusions showed that water is the dominant component, with no other volatile components. Fluid inclusion data suggest that the ore-forming fluids were derived from circulating seawater. The δ³⁴S values of pyrite from the massive sulfide ores range from − 3.6‰ to + 3.4‰, indicating that the sulfur was primarily leached from the arc volcanic rocks of the Pingshui Formation. Both pyrite from the massive sulfide ores and plagioclase from the spilites have similar lead isotope compositions, implying that the lead was also derived from the Pingshui Formation. The low lead contents of the massive sulfide ores and the geochemistry of their host rocks are similar to many VMS Cu–Zn deposits in Canada (e.g., Noranda) and thus can be classified as belonging to the bimodal-mafic subtype. The presence of magnetite and the absence of jaspilite and barite at the − 505 m level in the Pingshui deposit suggest that this level is most likely the central zone of the original lateral massive sulfide ore bodies. If this interpretation is correct, the deep part of the Pingshui Cu–Zn deposit may have significant exploration potential.