PDB Values Research Articles

AGE OF THE KINTEREP FORMATION OF THE NORTHWESTERN SALAIR: CHEMOSTRATIGRAPHY AND U-Pb ZIRCON DATING

A comprehensive study of the stratotype section of the Kinterep formation of the North-Western Salair was carried out, including geochemical and isotope (Sr, C, O) studies of carbonate rocks, and U-Pb dating (LA-ICP-MS) of igneous zircon crystals from tuffites. The studied carbonate rocks are pure limestones with Mg/Ca less than 0.007 and a low proportion of insoluble residue (average 5 %). Kinterep limestones are characterized by δ 18 O SMOW values from 19.8 to 23.8 ‰ and δ 13 С PDB values from –0.7 to +0.9. The Sr isotope composition in limestones of the Kinterep formation varies in a narrow range of 87 Sr/ 86 Sr values between 0.70851 and 0.70859. Comparison of the obtained isotopic characteristics ( 87 Sr/ 86 Sr and δ 13 С PDB ) of Kinterep formation limestones with the generalized global 87 Sr/ 86 Sr variation curve and δ 13 С PDB values in the pale-ocean suggests two equally probable interpretations of the time of accumulation of Kinterep formation limestones: 550–540 and 525–510 Ma. U-Pb dating of magmatic zircon crystals from tuffite, which forms an interlayer among limestones of the Kinterep formation, showed the age at the boundary of ~515 Ma. Thus, using a combination of isotope (Sr, C) chemostratigraphy of carbonate rocks and U-Pb dating of igneous zircon crystals from tuffites syngenetic to limestones, the age limit of 525–510 Ma was established for the time of the formation of the Kinterep formation of the Salair basin. Carbonate rocks of similar age and similar features of the isotopic composition are known in neighbouring areas (for example, the Kuznetsk Alatau) and in regions of the Siberian Platform and microcontinents of Central Asia (Tuva-Mongolian and Dzabkhan) spatially distant from the Salair basin.

Temperature and depth distribution of Japanese eel eggs estimated using otolith oxygen stable isotopes

Oxygen isotope ratios of the core region of otoliths were examined in Anguilla japonica glass eels collected from two rivers in Japan to verify the possible temperature and depth layer experienced by these eels when they were at the egg stage in their spawning area. To determine the relationship between otolith δ18O values and water temperature, the otoliths of glass eels reared under four different temperatures (15, 20, 25 and 30 °C) were analyzed. The otolith δ18O values showed an inverse relationship to ambient water temperature. Linear regression of the fractionation between otolith oxygen isotopic ratio from the δ18O of seawater and water temperature produced a precisely determined relationship from 15 to 30 °C: δ18Ootolith,PDB − δ18Oseawater,SMOW = −0.153 × T (°C) + 1.418. The δ18O core,PDB values of the otolith core region of the glass eels from the two locations were −2.53 ± 0.12 and −2.59 ± 0.07 respectively, and could be converted to water temperatures of 26.3 ± 0.8 °C and 26.7 ± 0.4 °C, respectively, using the equation and assuming a seawater δ18Oseawater,SMOW = 0.06‰. The water depth corresponding to these temperatures is ∼150 m in the water column in the spawning area of Japanese eels, which corresponds to the upper-most part of the thermocline and chlorophyll maximum in the vertical hydrographic profile. These results were consistent with the field studies that egg development after the beginning of otolith formation and hatching occurs around the upper-most part of thermocline, suggesting that stable isotope micro-analysis is a powerful method to extrapolate unknown spawning ecology of fishes.

Fluid inclusion and O–H–C isotopic constraints on the origin and evolution of ore-forming fluids of the Cenozoic volcanic-hosted Kuh-Pang copper deposit, Central Iran

The Kuh-Pang copper deposit (2.8 Mt @ 1.65% Cu, 0.52 g/t Au, 34 g/t Ag) is a volcanic-hosted epithermal deposit in the central part of the Late Eocene-Oligocene Urmia-Dokhtar Magmatic Arc of Iran. Three stages of fluid evolution are identified at the Kuh-Pang deposit: (i) early pre-ore stage: with homogenization temperature of 205–372 °C (298 ± 45 °C), salinity of 11.3 ± 2.9 wt% NaCl equiv., fluid trapped at ∼200 bars, (ii) main-ore stage: with homogenization temperature of 175–310 °C (253 ± 43 °C), salinity of 2.1–12.5 wt% NaCl equiv. at ∼150 bars, and (iii) late post-ore stage: with homogenization temperatures of 148 to 231 °C (199 ± 24 °C), and salinity of 1.1–9.8 wt% NaCl equiv. These data record an evolution of mineral precipitation from deeper (>2 km) to shallower environments (<500 m). Fluids trapped in the early (quartz I) and main-ore stages (quartz II) yielded δ18Ofluid values of +5.7 to +5.9‰ and +3.2 to +3.8‰, and δDfluid values of −77 to −41‰ and −84 to −60‰, respectively. These data indicate a major magmatic fluid source, with slightly increasing mixing of meteoric waters. Calcite in the late post-ore stage has δ13CV–PDB values of −5.8 to −5.6‰ and δ18OV–SMOW values of 8.2–8.6‰, with calculated δ18Ofluid and δ13Cfluid values of −1.0 to −1.4‰ and −5.4 to −5.2‰ respectively, that are also consistent with a predominantly magmatic carbon source and a significant fluid mixing by meteoric waters.

The Characteristics of the Hydrothermal Exhalative Dolostone of Lucaogou Formation in Santanghu basin and its Geology Setting Indication

The NW‐SE trending Santanghu basin is located in Xinjiang, NW China, between Tianshan Mountains and Altai Mountains. The tectonic evolution history of north Xinjiang has long been debated, especially the question when did that area began its intraplate rift evolution stage. This abstract discusses the features and possible origin of the hydrothermal exhalative dolostone of Lucaogou Formation in Santanghu basin, aiming to provide relevant information about this question.The target dolostone are characterized by extreme thin lamina of 0.3cm – 1 cm thick. Dolomite, ankerite, potassium feldspar and analcite are dominant composition. Most dolomite is poor crystallized and is in anhedral or subhedral shapes. Ankerite is generally porphyritic, few is in irregular shapes. It has to be noted that the porphyritic ankerite commonly develop zonal textures characterized by rings with various FeO content. Potassium feldspar and analcite (&lt;50%) are commonly observed in dolostones. Thin sections show some analcite is tetragonal trisoctahedron with harbour – like corrosion rims. Besides, few fragments of carbonatite rocks are observed in Lucaogou Formation and they perform intermittent or scattered distribution in rock layers.Previous work done by our study team shows δ 13C PDB values are 4.8 ± ∼11.4±, 6.93± on average. The δ18 O PDB values are between −5± ∼ −21.1±, −10.94 ± on average. Paleosalinity calculated by δ 13C and δ 18 O is between 128.35 and 136.81, 134.42 on average. Sr content of dolostones in study area reaches to 164 × 10−6∼537 × 10−6 (379.1 × 10−6 on average), most Sr/Ba &gt; 1 (4.05 on average). 87Sr/86Sr of iron–rich dolostone in target area are between 0.70457∼0.706194, average at 0.705360.Considering either accompanying residual tuff or residual leucite is found via electron probe, this indicates the analcite may derive form analcime phonolite. Furthermore, fragments of carbonatite rocks proves mantle‐derived magmatism exist. The rapid variation of δ18 O indicates multiple interactions of hydrothermal fluids with lake water during Lucaogou sedimentary period. 87Sr/86Sr values are much lower than that of crustal silica rocks while are more close to mantle derived rocks, which indicates diagenetic hydrothermal fluid is mantle‐origin.It has been reported that dolostone does not intergrow with iron‐rich dolostone in study area. According to the latest X diffraction results of cores, iron‐rich dolostone distributes rather locally. Given that ankerite commonly develop zonal textures characterized by various FeO content, we confirm it is due to multiple hydrothermal fluids activities in different hydrothermal vents.There should be abundant hydrothermal vents during Lucaogou period. Deep faults and its relevant fractures built plenty paths for mantle‐origin hydrothermal fluids to run up. Different vents owned various fluid properties, so did relevant sedimentation products.Hence we inclined to believe Santanghu basin was at intraplate rift evolution stage, under regional extension condition in late Carboniferous. During early‐mid Permian the basin was a starved, deep lacustrine intracontinental rift basin. Accordingly, in northern Xinjiang, ocean basin may close in late Carboniferous and started continental sedimentary development in early Permian.

Geochemistry of a large impoundment – Part II: Fe and Mn cycling and metal transport

Depletion of oxygen in lakes and reservoirs due to summer stratification has significant effects on many aspects of water chemistry, including lake productivity, elemental cycling and water quality. We have studied the redox conditions of Lake Texoma, a large impoundment lake on the border of Texas and Oklahoma, USA, formed from the confluence of the Red and Washita rivers, in order to understand the impact of summer anoxia on metal distribution. In summer, dissolved oxygen decreases with depth (from c. 7.0 to 0.1 mg/L), whereas dissolved (&lt;0.45 µm) Fe (and Fe 2+ ), Mn and HS − concentrations show complementary increases in the hypolimnion. Summer anoxia is, to a large degree, responsible for vertical variations in Fe and Mn concentrations, and Fe speciation is controlled by Fe-oxyhydroxide reduction and subsequent pyrite precipitation in sulphide-rich bottom waters. Summer anoxia is also responsible for vertical variations in the concentration of other metals including Ba, Pb and Ni in the deepest portion (main lake) of the lake. Lake Texoma and its two river arms show relatively minor variation in δ 34 S CDT (from +11.5 to +13.4‰), mirroring variation in Permian/Cretaceous marine gypsum and anhydrite deposits (δ 34 S CDT +10 to +15‰) in the headwater regions of the catchment. Increasing δ 34 S CDT with depth (&gt;16 m) in the main lake is consistent with fractionation associated with sulphate reduction in anoxic bottom waters. δ 13 C PDB values of dissolved inorganic carbon (DIC) become more negative (from –2.5 to –8.2 ‰) with depth in summer, due to bacterial oxidation of organic matter linked to sulphate reduction. Summer anoxia may induce temporal degradation of water quality in the central three zones of the lake with elevated Fe and Mn concentrations owing to breakdown of oxyhydroxides and release of adsorbed heavy metals, such as Pb and Ni. However, complete turnover of the water column in the autumn lowers dissolved Fe, Mn and heavy metal concentrations by oxidation and formation of oxyhydroxides . The characterization of anoxia in Lake Texoma provides the background for further water quality research and management for the rapidly increasing population of North Texas and improves our understanding of redox cycling and metal mobility in reservoirs.

Fluid Inclusion and Isotopic Constraints on the Origin of the Paleoproterozoic Yinachang Fe-Cu-(REE) Deposit, Southwest China

The Yinachang deposit in the Kangdian Fe-Cu metallogenic province, Southwest China, contains approximately 20 Mt ore @ 41.9 to 44.5 wt % Fe and 15 Mt ore @ 0.85 to 0.97 wt % Cu, with potentially significant REEs. Orebodies are hosted in the late Paleoproterozoic Dongchuan Group, and consist mainly of massive and banded replacement ores. The paragenetic sequence of this deposit includes pre-ore Na-(Fe) alteration (stage I), Fe-(REE) mineralization dominated by magnetite and siderite with subsidiary apatite and fluorite (stage II), and Cu-(REE) mineralization with chalcopyrite, ankerite, biotite, and subordinate apatite, fluorite, allanite, and synchysite (stage III). This sequence is similar to those of many iron oxide copper-gold (IOCG) deposits elsewhere. There are two distinct types of fluid inclusions within apatite of both stages II and III. Type 1 fluid inclusions with liquid and vapor phases have relatively low homogenization temperatures (98°–345°C) and salinities (4.7–16.2 wt % NaCl equiv), whereas type 2 fluid inclusions with one or more solid phases, a liquid phase, and a vapor phase have higher homogenization temperatures (273°–>500°C) and salinities (36.2–>59.8 wt % NaCl equiv). Fluids in sulfur isotope equilibrium with chalcopyrite of stages III have δ 34 S CDT values ranging from −2.8 to +2.7‰, consistent with a magmatic origin for the sulfur. Thus, sulfur isotopie compositions imply that magmatic-hydrothermal fluids, probably represented by the hot and saline type 2 fluid inclusions, were involved in the ore-forming process, although δ 34 S close to 0 might also mean that sulfur was leached from igneous rocks by nonmagmatic fluids. Siderite of stage II and ankerite of stage III have δ 13 C PDB values ranging from −12.4 to −7.5‰ and from −8.5 to −4.4‰, respectively. The large variation of δ 13 C PDB values reveals a strong interaction between the magmatic-hydrothermal fluids and the dolostone in the ore-hosting sequence. Calculated δ 18 O SMOW values of the fluids in stages II and III are broadly similar, and vary from 11.1 to 17.1‰ (avg = 13.5‰). Such values are higher than that of magmatic-hydrothermal fluids and thus, may indicate extensive fluid–wall-rock interaction and/or mixing of magmatic-hydrothermal fluids with shallow-level nonmagmatic fluids. This interpretation is consistent with the radiogenic Sr isotope compositions of bulk ores (( 87 Sr/ 86 Sr) i = 0.710404–0.734034) and fluorite separated from ores (( 87 Sr/ 86 Sr) i = 0.709851–0.723658). These nonmagmatic fluids are probably representative of the type 1 fluid inclusions. Bulk ores and mineral separates have ɛ Nd(t) values ranging from −8.1 to +0.4 (mostly −0.9 to +0.4), similar to the coeval mafic intrusions in the region (+2.0 to +2.8). This similarity suggests that REEs in the Yinachang deposit might have been derived dominantly from mantle-derived magmas. On the other hand, relatively low ɛ Nd(t) values (−5.5 and −8.1) of some samples indicate insignificant REE contributions from wall rocks. The Yinachang deposit is temporally associated with regional mantle-derived mafic magmatism, and may have a genetic relationship with it. Fluids derived from deep-seated magmas may have supplied abundant sulfur and carbon as well as some of the ore metals in this deposit. The mafic magmatism could also have provided heat to induce the shallow level nonmagmatic fluids to interact with the sedimentary-volcanic sequence, thus leaching additional ore metals into the ore-forming system. Fluid mixing can effectively trigger saturation and deposition of ore minerals. Our work highlights that nonmagmatic fluids are not a prerequisite for Cu-(Au-REE) mineralization, but may facilitate metal deposition in magmatic-hydrothermal IOCG systems.

Mass and isotopic concentrations of water-insoluble refractory carbon in total suspended particulates at Mt. Waliguan Observatory (China)

Mass concentration and isotopic values δ13C and 14C are presented for the water-insoluble refractory carbon (WIRC) component of total suspended particulates (TSP), collected weekly during 2003, as well as from October 2005 to May 2006 at the WMO-GAW Mt. Waliguan (WLG) site. The overall average WIRC mass concentration was (1183±120)ng/m3 (n=79), while seasonal averages were 2081±1707 (spring), 454±205 (summer), 650±411 (autumn), and 1019±703 (winter) ng/m3. Seasonal variations in WIRC mass concentrations were consistent with black carbon measurements from an aethalometer, although WIRC concentrations were typically higher, especially in winter and spring. The δ13C PDB value (−25.3±0.8)‰ determined for WIRC suggests that its sources are C3 biomass or fossil fuel combustion. No seasonal change in δ13C PDB was evident. The average percent Modern Carbon (pMC) for 14C in WIRC for winter and spring was (67.2±7.7)% (n=29). Lower pMC values were associated with air masses transported from the area east of WLG, while higher pMC values were associated with air masses from the Tibetan Plateau, southwest of WLG. Elevated pMC values with abnormally high mass concentrations of TSP and WIRC were measured during a dust storm event.

Isotope geochemistry and its implications in the origin of Yangla copper deposit, western Yunnan, China

The Yangla copper deposit is located in western Yunnan Province, China, with an estimated Cu reserve of approximately 1.2 million tons. It is a typical giant copper deposit, and its mining started only recently. The δ13CV–PDB values of the calcites studied vary from −5.1‰ to 1.0‰, implying that the hydrothermal fluids from which the calcites precipitated were derived from the granitic magma. The δ18OSMOW(H2O) and δDSMOW values of quartz fluid inclusions range from 0.11‰ to 2.50‰ and from −120‰ to −100‰, respectively. These data may suggest the following: (1) mixing between meteoric and magmatic fluids, or (2) the evolution of meteoric fluid by its interaction with igneous or metamorphic rocks. The δ34S values of sulfides range from −4.20‰ to 1.85‰ (average: −0.85‰), which is consistent with the magmatic origin. Based on the 3He/4He ratios of fluid inclusions trapped in sulfides of the deposit (0.14–0.17 Ra) and 40Ar/36Ar ratios of 301–1053, it can be inferred that the ore-forming fluids of the deposit were derived primarily from the crust with a minor mantle component during the metallogenic processes. Based on C, H, O, and S isotopic compositions, and the Yangla copper deposit is bordered primarily by gently dipping thrust faults near the Linong granodiorite. Moreover, the 187Re–187Os isochron age of molybdenite puts the time of metallogenesis at 233.3 ± 3 Ma, which is virtually coeval with the emplacement of the Linong granodiorite (235.6–234.1 Ma) and highlights the genetic link between the Yangla copper deposit and the Linong granodiorite. It is likely that the ore-forming fluids exsolved from the Linong granodiorite, which was formed by crustal melting induced by the intrusion of mantle-derived magma. During the late Early Permian, the Jinshajiang oceanic plate was subducted to the west, resulting in the formation of a series of gently dipping thrust faults in the Jinshajiang tectonic belt. Subsequently, the thrust faults was tensional during the early Late Triassic, which was a time of transition from collision-related compression to extension in the Jinshajiang tectonic belt; such conditions produced an environment favorable for the formation of ore fluids. This extension, in turn, induced the upwelling of hot asthenosphere, triggering intense melting in the lithospheric mantle and producing voluminous basaltic magma. Subsequently, the mantle-derived magma likely ascended along the fractures and faults to underplate the lower crust, which underwent partial melting to generate voluminous granitic magma. After the magma reached the base of the early-stage Yangla granodiorite, the platy granodiorite at the base of the Yangla body shielded the late-stage magma. Then, this magma cooled slowly, releasing some of its ore-forming fluids into the gently dipping thrust faults near the Yangla granodiorite and producing mineralization.

Contexto geológico, estudos isotópicos (C, O e Pb) e associação metálica do depósito aurífero Tocantinzinho, domínio Tapajós, Província Tapajós-Parima

The Tocantinzinho ore deposit is located along a NW-SE-trending lineament, southwestern of Itaituba (Para, Brazil), and is the largest known gold deposit of the Tapajos Province. The host Tocantinzinho granite is essentially isotropic and dominated by syenogranites and monzogranites that have been weakly to moderately altered by hydrothermal fluids. Microclinization (earliest), chloritization, sericitization, silicification and carbonatization (latest) are the main types of alteration. Most mineralization was contemporaneous with the sericitization/silicification and is represented by sulfide- and gold-bearing veinlets which locally occur as stockwork. Pyrite, chalcopyrite, sphalerite and galena are the most common sulfides. Among the ore metals, Cu, Pb and Zn present the highest contents, but Mo, As and Bi locally show anomalous concentrations. The relationship of Au with Cu, Pb or Zn is at random and the Au/Ag ratios range from 0.05 to 0.5. The higher the sulfide contents, the higher the Au concentrations, though it occurs mainly included in pyrite. Zircon monocrystals from the Tocantinzinho granite yielded an average Pb-Pb age of 1982 ± 8 Ma and may represent an earlier event of the Creporizao magmatic arc. δ13C PDB values for calcite from the carbonatization stage fall dominantly between -3.45 and -2.29‰, being compatible with a deep crustal source that may include carbonatite reservoirs. In turn, δ18O SMOW values vary from +5.97 to +14.10‰, being indicative of magmatic derivation, although the less positive values suggest contribution from surficial waters. Unpublished fluid inclusion study reveals the presence of aquo-carbonic fluids, whose CO2 could have been dissolved in the granitic magma rather than being related to the shear zone. The available data allow the Tocantinzinho deposit to be classified as a granite-hosted, intrusion-related gold deposit.

Carbonate veins trace seawater circulation during exhumation and uplift of mantle rock: Results from ODP Leg 209

Carbonate veins hosted in ultramafic basement drilled at two sites in the Mid Atlantic Ridge 15°N area record two different stages of fluid-basement interaction. A first generation of carbonate veins consists of calcite and dolomite that formed syn- to postkinematically in tremolite–chlorite schists and serpentine schists that represent gently dipping large-offset faults. These veins formed at temperatures between 90 and 170 °C (oxygen isotope thermometry) and from fluids that show intense exchange of Sr and Li with the basement ( 87Sr/ 86Sr = 0.70387 to 0.70641, δ 7Li L-SVEC = + 3.3 to + 8.6‰). Carbon isotopic compositions range to high δ 13C PDB values (+ 8.7‰), indicating that methanogenesis took place at depth. The Sr–Li–C isotopic composition suggests temperatures of fluid-rock interaction that are much higher (T > 350–400 °C) than the temperatures of vein mineral precipitation inferred from oxygen isotopes. A possible explanation for this discrepancy is that fluids cooled conductively during upflow within the presumed detachment fault. Aragonite veins were formed during the last 130 kyrs at low-temperatures within the uplifted serpentinized peridotites. Chemical and isotopic data suggest that the aragonites precipitated from cold seawater, which underwent overall little exchange with the basement. Oxygen isotope compositions indicate an increase in formation temperature of the veins by 8–12 °C within the uppermost ~ 80 m of the subseafloor. This increase corresponds to a high regional geothermal gradient of 100–150 °C/km, characteristic of young lithosphere undergoing rapid uplift.

The role of biomineralization in the origin of sepiolite and dolomite

Sepiolite is an important industrial mineral whose mechanism of formation and detailed origin are still not clear. Sepiolite is frequently found with dolomite, Mg-smectites or palygorskite in the Intermediate Unit of Miocene sediments of the Madrid basin. Herein, we describe mineralogy, texture and mineral chemistry of sepiolite-rich layers (up to 90% concentration) in marl-clay sediments, either with gypsum, chert (micro-crystalline quartz), or dolomite, that are up to 2 to 3 m thick. The materials studied were formed in shallow lake environments or mudflats. These sediments contain dolomite aggregates resembling mineralized microorganisms (biomorphs) with ovoid morphologies and spherical to tubular internal voids. The regular size and relatively uniform shape of the aggregates are likely controlled by the shape and size of the microorganisms. The paper describes the presence of organic debris, silicification processes and potassium silicate depletion related to the basal sediments that preceded sepiolite rich layers. Potassium depletion, as a nutrient, in detrital components and the occurrence of organic and reduced sediment (U and sulfide concentration) at the interface with sepiolite also can be linked to biosignatures related to the origin of sepiolite. In addition, the occurrence of dolomite with carbon that has δ¹³C PDB values of &lt; −7.5 permil confirms the possibility of an organic carbon source. High concentrations of sepiolite are observed where the amount of dolomite is small. The remaining dolomite in virtually pure sepiolite layers is present as partially dissolved biomorphs or fully recrystallized isolated crystals. Thus, a general process for dolomite dissolution and recrystallization is associated with sepiolite differentiation. In addition, the formation of sepiolite related to the biomineralization of dolomite is likely. The potential role of biomineralization in the formation of these high-grade sepiolite deposits depends on two factors: (1) specific organic-inorganic interactions and (2) the highly porous nature of the sepiolite precursor dolomite during the diagenetic evolution of these sediments. The confirmation of these processes awaits the future development of sepiolite synthesis strategies that incorporate the appropriate biogeochemical reactions.

Mesogenetic dissolution of the middle Ordovician limestone in the Tahe oilfield of Tarim basin, NW China

The mesogenetic dissolution is well developed in the middle Ordovician Yijianfang formation (O 2yj) limestone, and the dissolution pores are very important for petroleum accumulation in the south slope area of the Tahe oilfield which lies in the north of the Tarim basin, northwestern China. Mottled, dotted or laminar dissolution can be observed in the O 2yj limestone. Under microscope, the grains, lime matrix and all stages of calcite cements (including oil-inclusion-bearing blocky calcite cements) can all be found dissolved ubiquitously. The stylolites in the limestone were enlarged and rounded because of dissolution. Some dolomite rhombs, precipitated along stylolites in burial environment, were found dissolved as well. The dissolution of the blocky calcite cements and dolomite rhombs and the enlarging of stylolites demonstrate that the dissolution took place in the mesogenetic environment. Concentration of trace elements, including REEs, of the eroded part of the O 2yj limestone is intermediate between that of the uneroded part and that of the underlying lower Ordovician limestone hydrocarbon source rocks. Both δ 13C PDB and δ 18O PDB values of the eroded part are less than those of the uneroded part, respectively. The geochemical characteristics indicate that the eroding fluids are hydrocarbon-bearing fluids coming from the underlying hydrocarbon source rocks.

The possible contribution of a mantle-derived fluid to the Ningwu porphyry iron deposits – Evidence from carbon and strontium isotopes of apatites

Apatite is a characteristic mineral for the iron deposits in the Ningwu region. Apatite shows a range of δ 13C PDB values from −9.6‰ to −0.6‰, and most of them with the δ 13C PDB values distributed in a range of mantle carbon (i.e., −2‰ to −9‰), except for samples T-06-1 and J-06-3. Apatites in the Ningwu porphyry iron deposits yield a narrow variation range of 87Sr/ 86Sr values from 0.706326 to 0.707577, similar to those of the volcanic and subvolcanic rocks and higher than that of a typical mantle-derived magmatic apatite (i.e., about 0.7040), indicating that formation of the apatites was involved with crust material contamination. δ 13C PDB and 87Sr/ 86Sr values of the apatite indicate a possible contribution of mantle-derived fluid and material to formation of the Ningwu porphyry iron deposits, supported by regional geology, regional gravities and geochemistry of the volcanic and subvolcanic rocks in the Ningwu region.

Variações dos isótopos de C e Sr em carbonatos pré e pós-glaciação Jequitaí (Esturtiano) na região de Bezerra-Formosa, Goiás

Carbonate rocks of the upper Paranoá Group and lower Bambuí Group (Sete Lagoas Formation) have been founded at the occidental border of the São Francisco craton. These units have been separated by the Sturtian glaciation, identified by Jequitaí Formation, but in some localities the glacial record is absent and is difficult to separate these two carbonates units. In this paper two sections with a good stratigraphic control have been chosen to find C, O and Sr isotopic values to have tools for the correlations. Carbonates of the Paranoá Group present a trend of positive δ 13 C PDB varying between +0.8 e +2.7‰, of δ 18 O PDB varying between -9.0 e -4.7‰ and 87 Sr/ 86 Sr ranging from 0.7063 to 0.7068. The diamictite sample of Jequitaí Formation has δ 13 C PDB values of -1.8‰ and δ 18 O PDB values of -5.1‰. The cap dolomites of the Sete Lagoas Formation are associated with an extremely negative δ 13 C PDB values between -6.0 e -3.2‰, δ 18 O PDB values between -9.1 e -5.3‰ and high 87 Sr/ 86 Sr ratios suggesting a radiogenic Sr isotope anomaly. Limestone and muddy-limestone above the cap dolomite still starts with extremely negative δ 13 C PDB values (-6.0‰) and are followed by an upward trend of increasing carbon isotope values up to +9.2‰. In the same interval the δ 18 O PDB values ranging from -10.1‰ at the base to -5.5‰ in direction to the top of formation and primary 87 Sr/ 86 Sr ratios between 0.70745 and 0.70758. The Carbon and Sr isotope data presented here reveal significant differences between carbonates from the Paranoá Group and the Bambuí Group. These data developed here provides the framework for a new regional isotopic correlation model to the carbonates units of the Paranoá and Bambuí groups.

Variações dos isótopos de C e Sr em carbonatos pré e pós-glaciação Jequitaí (Esturtiano) na região de Bezerra-Formosa, Goiás

Carbonate rocks of the upper Paranoa Group and lower Bambui Group (Sete Lagoas Formation) have been founded at the occidental border of the Sao Francisco craton. These units have been separated by the Sturtian glaciation, identified by Jequitai Formation, but in some localities the glacial record is absent and is difficult to separate these two carbonates units. In this paper two sections with a good stratigraphic control have been chosen to find C, O and Sr isotopic values to have tools for the correlations. Carbonates of the Paranoa Group present a trend of positive δ 13 C PDB varying between +0.8 e +2.7‰, of δ 18 O PDB varying between -9.0 e -4.7‰ and 87 Sr/ 86 Sr ranging from 0.7063 to 0.7068. The diamictite sample of Jequitai Formation has δ 13 C PDB values of -1.8‰ and δ 18 O PDB values of -5.1‰. The cap dolomites of the Sete Lagoas Formation are associated with an extremely negative δ 13 C PDB values between -6.0 e -3.2‰, δ 18 O PDB values between -9.1 e -5.3‰ and high 87 Sr/ 86 Sr ratios suggesting a radiogenic Sr isotope anomaly. Limestone and muddy-limestone above the cap dolomite still starts with extremely negative δ 13 C PDB values (-6.0‰) and are followed by an upward trend of increasing carbon isotope values up to +9.2‰. In the same interval the δ 18 O PDB values ranging from -10.1‰ at the base to -5.5‰ in direction to the top of formation and primary 87 Sr/ 86 Sr ratios between 0.70745 and 0.70758. The Carbon and Sr isotope data presented here reveal signific ant differences between carbonates from the Paranoa Group and the Bambui Group. These data developed here provides the framework for a new regional isotopic correlation model to the carbonates units of the Paranoa and Bambui groups.

Determination of δ13 CV−PDB and δ15NAIR values of cocaine from a big seizure in Germany by stable isotope ratio mass spectrometry†

In this study, δ13CV− PDB and δ15NAIR values of 132 cocaine samples from a big seizure in Germany in 2002 were determined using elemental analyser isotope ratio mass spectrometry. The 1.2 tons of cocaine were packed in 1 kg packages and the cocaine bricks inside these packages showed certain logos. Twenty different logos could be identified. Results show a large variability among some samples, for δ15NAIR values ranging from−17 to −2 ‰. Furthermore, the possibility of linking samples with the same logo was checked. The results show that, in general, there is no relationship between the determined isotope ratio and a certain logo. †Extended version of a paper presented at the 26th Annual Meeting of the German Association for Stable Isotope Research (GASIR), 10–12, October, 2005, Jena, Germany.

Carbon and oxygen isotope geochemistry of Ediacaran outer platform carbonates, Paraguay Belt, central Brazil

After the late Cryogenian glaciation the central region of Brazil was the site of extensive deposition of platformal carbonates of the Araras Group. This group includes a basal cap carbonate sequence succeeded by transgressive, deep platform deposits of bituminous lime mudstone and shale. Facies and stratigraphic data combined with carbon and oxygen isotopic analyses of the most complete section of the transgressive deposits, exposed in the Guia syncline, were used to evaluate the depositional paleoenvironment and to test the correlation of these deposits along the belt and with other units worldwide. The studied succession consists of 150 m thick tabular beds of black to grey lime mudstone and shale with predominantly negative delta13C PDB values around -2.5 to -1‰ . The delta13C PDB profile of Guia syncline shows a clear correlation with the upper portion of Guia Formation in the Cáceres region, about 200 km to the southwest. The delta13C PDB profile of the Araras Group is comparable with delta13C PDB profiles of Ediacaran units of the southern Paraguay Belt, western Canada, and the Congo and Kalahari cratons. Moreover, facies distribution, stratigraphy and the carbon isotopic profile of the Araras Group match the middle Tsumeb Subgroup in Namibia, which reinforces the Ediacaran age assigned to the Araras Group.

Geochemistry of Late Cretaceous phosphorites in Egypt: Implication for their genesis and diagenesis

Phosphorite deposits in Egypt, known as the Duwi Formation, are a part of the Middle East to North Africa phosphogenic province of Late Cretaceous to Paleogene age. Phosphatic grains in these deposites are classified into phosphatic mudclasts and phosphatic bioclasts. Phosphatic bioclasts are subdivided into fish bone fragments and shark tooth fragments. All phosphatic grains are composed of francolite. Chemical mapping of the phosphatic grains using Electron Probe Microanalysis (EPMA) indicated that the phosphatic mudclasts are homogeneous in their chemical composition and no concentric texture nor chemical zoning are observed. Some of the bone fragments show Fe and S zoning. No significant difference in chemical composition is observed between the phosphatic mudclasts and bioclasts. Acid-insoluble residues of the phosphorites show lower values of the Chemical Index of Alteration (CIA) compared to the associated rocks. Structural CO 2 contents in the francolites range from 3.32% to 7.21% with an average of 5.3%. The δ 13C PDB values range from −4.04‰ to −8.7‰, while the δ 18O PDB values range from −4.3‰ to −10.3‰. The compositional homogeneity of the mudclasts, Fe and S zoning in some of the bone fragments and the difference in the Chemical Index of Alteration between the acid-insoluble residues of the phosphorites and the associated rocks suggest that the phosphatic grains in the Duwi Formation are derived from pre-existing authigenic phosphorites, which reworked and concentrated afterward. Negative δ 13C values of structural CO 2 suggest that the CO 2 was derived from degradation of organic matter. Low δ 18O values of structural CO 2 can be attributed to the influence of meteoric water. Higher CO 2, SO 3 and F contents compared to the recent authigenic phosphorites and negative δ 13C and δ 18O values of structural CO 2 indicate that diagenesis plays an important role in the modification of the chemical composition of phosphatic grains and that the studied apatite was francolitized during diagenesis.

Isotope geochemistry of the Huize Zn-Pb ore field, Yunnan Province, Southwestern China: Implication for the sources of ore fluid and metals

The Huize ore field, which is the most famous high-grade Zn-Pb ore field in China, comprises the Kuangshanchang and Qilinchang deposits. The Zn and Pb reserves of these two deposits are more than 5 Mt with ore grades ranging from 25% to 35% in weight. Lead, sulfur, carbon, oxygen, hydrogen and strontium isotope geochemistry is reported to help understand the sources of the ore fluid and metals. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of the ores range from 18.251–18.530, 15.663–15.855 and 38.487–39.433, respectively. These values are similar to those of the wall rocks. The pyrites disseminated in the wall rocks have indistinguishable Pb isotope composition with the ores. These data indicate that the wall rocks provided metals to the ore fluid. Most δ34S values of the ores range from 13 to 17 per mil. The sulfur of the ores originated by in situ reduction of sulfate. Three kinds of gangue calcite from the ores have similar isotope compositions, which have δ13C values in the range of −2.1 to −3.5 per mil with respect to PDB and δ18O values in the range of 16.8 to 18.6 per mil with respect to SMOW. The δDFI values of fluid inclusions in the three kinds of gangue calcites have a narrow range of −50 to −60 per mil and the δ18OH2O values calculated from δ18O values of calcite range from 7.0 to 8.8 per mil at 200°C. These data suggest that the ore fluid was a basinal brine that passed through shale, clastic rocks and mudstone underlying the host rock. Initial 87Sr/86Sr values of the pyrite, sphalerite and calcite from the ores range from 0.714 to 0.717. The initial 87Sr/86Sr values of unaltered host rock (0.7083–0.7093) are lower than that of the altered host rock (0.7106). It suggests that the ore fluids have higher initial 87Sr/86Sr values than the wall rocks. These high initial 87Sr/86Sr values may be due to the reaction between the ore fluid and the shale, clastic rocks and mudstone underlying the host rock or the fluid might have originated from these rocks.

The source of pedogenic carbonate associated with gold-calcrete anomalies in the western Gawler Craton, South Australia

Elevated Au concentrations above bedrock mineralization are commonly closely associated with calcrete in arid residual and semi-residual soils in Australia. The origin of Australian calcrete has been argued for many years but there have been very few published studies. Calcrete from Au deposits and prospects, and elsewhere in the Gawler Craton (South Australia) were studied for their geochemical composition, and Sr and C isotope ratios. By comparing carbonate 87Sr/ 86Sr ratios with underlying weathered rock and bedrock, it is demonstrated that many samples have overwhelmingly atmospheric Sr (> 94%) and, by inference, Ca (> 98%) rather than a local bedrock or soil mineral origin. The isotopic composition of calcretes at the Challenger Gold Deposit lie on a mixing trend of decreasingly marine Sr from the Nullarbor Plain to Tarcoola, 300 km to the east. The δ 13C PDB values (− 7.5‰ to + 0.1‰) suggest that the carbonate C in calcrete has a mixed origin derived from C3 and C4 plants. A model is presented to explain how the Au–Ca association may form in calcrete at Challenger based on these new Sr and C isotope data and in which the role of plants and atmospherically deposited Sr and Ca combine with pre-existing Au in the soil. The implication for mineral exploration is that, since most of the Ca is derived from marine sources, it is not a pre-requisite that autochthonous soil minerals (derived from underlying weathered bedrock) supply Ca for calcrete to form and for the Au–Ca association to occur. Thus, the independence of the Ca with respect to underlying lithology reaffirms the usefulness of calcrete as a sampling medium for Au exploration.