The occurrences of the rare earth elements and the platinum group elements in relation to base metal zoning in the vicinity of Rote Fäule in the Kupferschiefer of Poland

The concentrations of the lanthanide rare earth elements (REE) and Pt group elements (PGE) were measured in the Kupferschiefer from the Polish Zechstein Basin at, and in proximity to, the Rote Fäule near the Lubin Mining District. The Rote Fäule is a zone of post-depositional oxidation characterized by the presence of extensive amounts of Fe(III) oxides replacing syn-sedimentary framboidal pyrite. Outward from the Rote Fäule, the remainder of the Kupferschiefer is composed of Cu- and Pb/Zn-mineralized shale surrounding the Rote Fäule and a non-mineralized pyritic black shale in the central basin.The leading hypothesis explaining the high concentrations of PGE, and REE in the Kupferschiefer states that PGE, REE and the associated base metals were mobilized by oxidizing Cl⁻ brines which migrated outward from the Rote Fäule into the reduced Kupferschiefer. According to available thermodynamic data, PGE were in all likelihood present as chloro-complexes in these oxidizing brines, as geologically realistic concentrations of Pt, Pd and Au could be transported as chloro-complexes. The Eh of these brines decreased as they migrated further from the Rote Fäule and into the Kupferschiefer. Base metals and PGE were precipitated in the order of their decreased solubility in these brines. As a result, the concentrations of least soluble PGE (Pt) are highest in the Rote Fäule and in the transition zone adjacent to the Rote Fäule (e.g. [Pt]=202–537 ppb) while the concentrations of the more soluble metals in these brines (Ag, Cu, Pb, and Re) are highest in the reduced-mineralized Kupferschiefer. The sources of the PGE and REE are enigmatic. It is likely that the metals were derived either from the underlying Rotliegendes sandstones and volcanics, the Variscan basement rocks, or the Kupferschiefer shale whose metals were mobilized by saline, oxidizing fluids released during intra-continental rifting in the Triassic period.     

Origin of the Kupferschiefer polymetallic mineralization in Poland

The Kupferschiefer ore series, between the Lower Permian (Rotliegendes) terrestrial redbeds/volcanics and the Upper Permian (Zechstein) marine sequence, is developed as dark-grey organic matter-rich and metal sulphide-containing deposits (reduced zone) and as red-stained organic matter-depleted and iron oxide-bearing sediments (oxidized zone?=?Rote Fäule). The transition zone from oxidized to reduced rocks occurs both vertically and horizontally. This zone is characterized by sparsely disseminated remnant copper sulphides within hematite-bearing sediments, replacements of copper sulphides by iron oxides and covellite, and oxide pseudomorphs after framboidal pyrite. These textural features and copper sulphide replacements after pyrite in reduced sediments imply that the main oxide/sulphide mineralization postdated formation of an early-diagenetic pyrite. Hematite-dominated sediments locally contain enrichments of gold and PGE. The Kupferschiefer mineralization resulted from upward and laterally flowing fluids which oxidized originally pyritiferous organic matter-rich sediments to form hematitic Rote Fäule areas, and which emplaced base and noble metals into reduced sediments. It is argued that long-lived and large-scale lateral fluid flow caused the cross-cutting relationships, expansion of the hematitic alteration front, redistribution of noble metals at the outer parts of oxidized areas, and the location of copper orebodies directly above and around oxidized and gold-bearing areas. The Rote Fäule may be a guide to favourable areas for both the Cu-Ag and new Au-Pt-Pd Kupferschiefer-type deposits.     

Origin of the gold deposit in the Polkowice-West Mine, Lubin-Sieroszowice Mining District, Poland

The recently discovered gold deposit in the Lubin-Sieroszowice district lies 0.0 to 1.5?m below the stratabound copper-silver orebody, mainly in the Polkowice-west mine. The deposit extends over 60?km², has a thickness of 20–80?cm and a conservative estimate of the average grade of 1.5?g/t gold, 0.3?g/t Pd and 0.2?g/t Pt. It contains gold and electrum in association with minor amounts (up to 0.4?vol%) of hematite, chalcocite, digenite, djurlite, bornite, chalcopyrite, pyrite, gersdorffite, rammelsbergite and clausthalite. The gold-bearing zone lies mainly in the Weissliegendes sandstone, but locally transgresses the stratigraphy into the overlying Kupferschiefer shale and Werra Dolomite of the Zechstein evaporite sequence. It lies within a transition zone between the oxidized, hematite-stained Rote Fäule facies and the overlying reduced organic carbon-bearing sediments. At the Polkowice-west mine, but only where gold is present, this zone is characterized by hematite-stained `patches' within grey to maroon sediment that contains little or no hematite or organic carbon. These textures were caused by downwelling reducing sulfur-rich solutions, flowing through previously oxidized sediments, and by gravitational instability between the reducing and oxidizing fluids. The oxidizing fluid originated within the Rote Fäule facies, whereas the reducing fluid originated in the overlying Zechstein sequence from which it was expelled downward during gypsum dehydration accompanying burial. Gold transport as the chloride complex in the oxidizing fluid is unlikely at the low temperature (?<100?°C) prevailing during mineralization. Some gold was probably transported as the bisulfide and, to a lesser extent, the polysulfide complexes, in the descending reducing fluid. However, the potential source rocks do not contain enough gold to account for the known deposit. Most of the gold was probably transported as the thiosulfate complex during replacement of reduced sediments by the Rote Fäule facies. Parts of the district where reduced fluids penetrated deeply into the Weissliegendes, and where the Rote Fäule facies transgressed the greatest volume of reduced sediments, should be evaluated for the presence of gold. We propose that the Polkowice-West mine represents a new class of gold deposit.     

Metal accumulation during and after deposition of the Kupferschiefer from the Sangerhausen Basin,Germany

A densely sampled profile (58 cm in thickness) composed of 13 samples of the Kupferschiefer and overlying Zechstein carbonates from the Sangerhausen Basin, Germany has been analysed by various geochemical and microscopic methods in order to clarify the mechanism of base metal accumulation. In this location, the Kupferschiefer is only slightly influenced by the hematite-bearing, oxidized fluids calledRote Fäule.The determination of facies-dependent parameters along the profile indicates that Kupferschiefer from the Sangerhausen Basin was largely deposited in a marine environment; only at the beginning of Kupferschiefer sedimentation did euxinic conditions prevail. The bottom part of the profile is significantly enriched in trace elements such as Cu, Ph, Zn, As, Co, Ag and U. The Cu concentration amounts to 19.88 wt.%. Post-depositional oxidation of the organic matter is observed only in the transition zone between the Kupferschiefer and the Zechstein conglomerate indicating the influence of ascending, oxidizing brines. Microscopic analyses show that only Fe sulfides form framboidal textures; Cu minerals are present along the total profile preferentially in fractures and as patchy structures composed of chalcocite, chalcopyrite and bornite. In the highly mineralized bottom section, Cu sulfides are associated with pyrobitumen, sparry calcite and arsenopyrite. Results from maturation studies of organic matter suggest that the maximum temperature affecting the Kupferschiefer was approximately 130°C.A 3-step-process of metal accumulation is proposed. During deposition of the sediment, framboidal pyrite and pyrite precursors were precipitated by bacterial SO₄²⁻ reduction (BSR). During diagenesis the pyrite and pyrite precursors were largely replaced by mixed Cu/Fe minerals and by chalcocite (PR). In the section with very high Cu contents (> 8%) reduced sulfur from Fe-sulfides was not sufficient for precipitation of Cu and other trace metals from ascending solutions. In this part of the profile, thermochemical SO₄²⁻ reduction (TSR) occurred after pyrite replacement as indicated by the presence of pyrobitumen and sparry calcite.     

Carbon and oxygen isotope constraints on fluid sources and fluid–wallrock interaction in regional alteration and iron-oxide–copper–gold mineralisation, eastern Mt Isa Block, Australia

The source of metasomatic fluids in iron-oxide–copper–gold districts is contentious with models for magmatic and other fluid sources having been proposed. For this study, δ ¹⁸O and δ ¹³C ratios were measured from carbonate mineral separates in the Proterozoic eastern Mt Isa Block of Northwest Queensland, Australia. Isotopic analyses are supported by petrography, mineral chemistry and cathodoluminescence imagery. Marine meta-carbonate rocks (ca. 20.5‰ δ ¹⁸O and 0.5‰ δ ¹³C calcite) and graphitic meta-sedimentary rocks (ca. 14‰ δ ¹⁸O and −18‰ δ ¹³C calcite) are the main supracrustal reservoirs of carbon and oxygen in the district. The isotopic ratios for calcite from the cores of Na–(Ca) alteration systems strongly cluster around 11‰ δ ¹⁸O and −7‰ δ ¹³C, with shifts towards higher δ ¹⁸O values and higher and lower δ ¹³C values, reflecting interaction with different hostrocks. Na–(Ca)-rich assemblages are out of isotopic equilibrium with their metamorphic hostrocks, and isotopic values are consistent with fluids derived from or equilibrated with igneous rocks. However, igneous rocks in the eastern Mt Isa Block contain negligible carbon and are incapable of buffering the δ ¹³C signatures of CO₂-rich metasomatic fluids associated with Na–(Ca) alteration. In contrast, plutons in the eastern Mt Isa Block have been documented as having exsolved saline CO₂-rich fluids and represent the most probable fluid source for Na–(Ca) alteration. Intrusion-proximal, skarn-like Cu–Au orebodies that lack significant K and Fe enrichment (e.g. Mt Elliott) display isotopic ratios that cluster around values of 11‰ δ ¹⁸O and −7‰ δ ¹³C (calcite), indicating an isotopically similar fluid source as for Na–(Ca) alteration and that significant fluid–wallrock interaction was not required in the genesis of these deposits. In contrast, K- and Fe-rich, intrusion-distal deposits (e.g. Ernest Henry) record significant shifts in δ ¹⁸O and δ ¹³C towards values characteristic of the broader hostrocks to the deposits, reflecting fluid–wallrock equilibration before mineralisation. Low temperature, low salinity, low δ ¹⁸O (<10‰ calcite) and CO₂-poor fluids are documented in retrograde metasomatic assemblages, but these fluids are paragenetically late and have not contributed significantly to the mass budgets of Cu–Au mineralisation.     

Stable isotope geochemistry and diagenetic mineralization associated with the Tono sandstone-type uranium deposit in Japan

The Tono sandstone-type uranium mine area, middle Honsyu, Japan is composed of Miocene lacustrine sedimentary rocks in the lower part (18–22 Ma) and marine facies in the upper part (15–16 Ma). Calcite and pyrite occur as dominant diagenetic alteration products in these Neogene sedimentary rocks. The characteristics of calcite and pyrite differ significantly between lacustrine and marine facies. Abundant pyrite, calcite, organic matter, and small amounts of marcasite or pyrrhotite occur in the lacustrine facies, whereas small amounts of calcite and framboidal pyrite, organic matter and no marcasite or pyrrhotite are found within the marine units. The δ¹³C values of calcite in the lacustrine deposits are low (−19 to −6‰ PDB) but those in marine formation are high (−11 to +3‰). This implies that the contribution of marine carbonate is larger in upper marine sedimentary rocks, and carbon in calcite in the lower lacustrine formation was derived both from oxidation of organic matter and from dissolved marine inorganic carbon. The δ³⁴S values of framboidal pyrite in the upper marine formation are low (−14 to −8‰ CDT), indicating a small extent of bacterial seawater sulfate reduction, whereas those of euhedral-subhedral pyrite in the lower lignite-bearing arkose sandstone are high (+10 to +43‰), implying a large extent of closed-system bacterial seawater sulfate reduction. The δ³⁴S and δ¹³C data which deviate from a negative correlation line toward higher δ¹³C values suggest methanogenic CO₂ production. During diagenesis of the lacustrine unit, large amounts of euhedral-subhedral pyrite were formed, facilitated by extensive bacterial reduction of seawater sulfate with concomitant oxidation of organic matter, and by hydrolysis reactions of organic matter, producing CH₄ and CO₂. Uranium minerals (coffinite and uraninite) were also formed at this stage by the reduction of U⁶⁺ to U⁴⁺. The conditions of diagenetic alteration within the lacustrine deposits and uranium mineralization is characterized by low Eh in which nearly equal concentrations of CH₄ and HCO₃ ⁻ existed and reduced sulfur species (H₂S, HS⁻) are predominant among aqueous sulfur species, whereas diagenetic alteration of the marine formations was characterized by a predominance of SO₄ ²⁻ among dissolved sulfur species. Modern groundwater in the lacustrine formation has a low Eh value (−335 mV). Estimated and measured low Eh values of modern and ancient interstitial waters in lacustrine environments indicate that a reducing environment in which U⁴⁺ is stable has been maintained since precipitation of uranium minerals. Received: 9 February 1996 / Accepted: 11 April 1997     

Paleomagnetism of the Cu�CZn�CPb-bearing Kupferschiefer black shale (Upper Permian) at Sangerhausen, Germany

Syngenetic, diagenetic and epigenetic models have been proposed for the Cu?CZn?CPb Kupferschiefer mineralization at Sangerhausen, Germany. Paleomagnetic and rock magnetic measurements have been made on 205 specimens from mine workings on the margin of the Sangerhausen Syncline. The mineralization is richest in the ??0.5-m-thick Upper Permian (258?±?2?Ma) Kupferschiefer black marly shale (nine sites) and dies out over ??0.2?m in the underlying Weisliegend sandstones (three sites) and overlying Zechstein carbonates (two sites). Except for one site of fault zone gypsum, characteristic remanent magnetization directions were isolated for all 14 sites using alternating field and thermal step demagnetization. These directions provide a negative fold test, indicating that the remanence postdates Jurassic fault block tilting. Rock magnetic measurements show that the Kupferschiefer shale marks a redox front between the oxidized Weissliegend sandstones and non-oxidized Zechstein carbonates. The 14 site directions give a Late Jurassic paleopole at 149?±?3?Ma. It is significantly different from the paleopole reported by E.C. Jowett and others for primary or early diagenetic Rote F?ule alteration that gives an age of 254?±?6?Ma on the current apparent polar wander path and is associated with Kupferschiefer mineralization. We suggest that the Late Jurassic extensional tectonic event that formed the nearby North German Basin also reactivated Variscan basement faults and extended them up through the overlying strata, thereby allowing hydrothermal basement fluids to ascend and epigenetically mineralize the Kupferschiefer shale. The possibility of a 53?±?3?Ma mineralization age is also considered.     

Variscan and post-Variscan lead–zinc mineralization, Rhenish Massif, Germany: evidence for sulfide precipitation via thermochemical sulfate reduction

A mechanical decrepitation device coupled with a gas chromatograph has been used to characterize the molecular composition of gaseous and liquid hydrocarbons contained in minerals. Application of this technique allows the identification of low-molecular-weight n-alkanes and some aromatic hydrocarbons in sulfides and gangue minerals from epigenetic Variscan and post-Variscan lead–zinc deposits in the Rhenish Massif, Germany. Based on the analysis of 200 samples, Variscan and post-Variscan mineralization can be distinguished by the composition of associated hydrocarbons. Variscan sulfides and gangue minerals contain high abundancies of methane. In contrast, n-alkanes in the C₂–C₉ range and aromatic hydrocarbons (benzene, toluene) are dominant in post-Variscan mineralization. The absence of high-molecular-weight hydrocarbons in ore minerals suggests highly mature gas associated with hydrothermal activity, during which hydrothermal fluids caused an increase in thermal maturation of organic matter and the generation of low-molecular-weight hydrocarbons in the adjacent organic-rich rocks. The hydrocarbon compositions contained in fluid inclusions of Variscan and post-Variscan minerals are probably governed by the maturation level of the potential source rocks. In Variscan time tectonic brines (T > 175 °C) generated predominantly methane, whereas basement brines (T < 175 °C) expelled higher-molecular-weight hydrocarbons (wet gases, condensates, aromatic hydrocarbons) from adjacent rocks during the Mesozoic event. The specific role of hydrocarbons in sulfide precipitation via thermochemical sulfate reduction is indicated by geochemical characteristics of organic matter associated with the Plombières Pb–Zn deposit, in eastern Belgium. Intense alteration phenomena were observed in near-ore kerogens, compared with unaltered kerogens far from the ore body, as well as by a very high maturity (5.40% R_o), a systematic depletion in ¹²C towards the vein-type mineralization, high atomic S/C ratios (0.49), and by low atomic H/C ratios (0.29). The data suggest that hydrothermal solutions caused a drastic increase in the thermal maturation of organic matter within the adjacent wall rock. Increased thermal maturation resulted in increased δ¹³C-values of organic carbon due to the preferential release of ¹²C. The change in the organic matter to a H-depleted and S-enriched bulk composition in association with sulfide ores strongly suggests that thermochemical sulfate reduction was responsible for organic degradation. Thus, thermochemical sulfate reduction probably triggered base metal sulfide precipitation in Variscan and post-Variscan ore deposits of the Rhenish Massif. Finally, based on data from this study and previous investigations, new genetic models are presented for both Variscan and post-Variscan mineralization in the Rhenish Massif. Received: 15 September 1999 / Accepted: 2 December 1999     

Geochemical and stable isotopic evolution of the Guarani Aquifer System in the state of São Paulo, Brazil

The purpose of this report is to explain geochemical and stable isotopes trends in the Brazilian unit of the Guarani Aquifer System (Botucatu and Piramboia aquifers) in S?o Paulo State, Brazil. Trends of dissolved species concentrations and geochemical modeling indicated a significant role of cation exchange and dissolution of carbonates in downgradient evolution of groundwater chemistry. Loss of calcium by the exchange for sodium drives dissolution of carbonates and results in Na–HCO₃ type of groundwater. The cation-exchange front moves downgradient at probably much slower rate compared to the velocity of groundwater flow and at present is located near to the cities of Sert?ozinho and águas de Santa Barbara (wells PZ-34 and PZ-148, respectively) in a shallow confined area, 50–70 km from the recharge zone. Part of the sodium probably enters the Guarani Aquifer System. together with chloride and sulfate from the underlying Piramboia Formation by diffusion related to the dissolution of evaporates like halite and gypsum. High concentrations of fluorine (up to 13.3 mg/L) can be explained by dissolution of mineral fluoride also driven by cation exchange. However, it is unclear if the dissolution takes place directly in the Guarani Aquifer System or in the overlying basaltic Serra Geral Formation. There is depletion in δ ²H and δ ¹⁸O values in groundwater downgradient. Values of δ ¹³C(DIC) are enriched downgradient, indicating dissolution of calcite under closed system conditions. Values of δ ¹³C(DIC) in deep geothermal wells are very high (>–6.0‰) and probably indicate isotopic exchange with carbonates with δ ¹³C about –3.0‰. Future work should be based on evaluation of vertical fluxes and potential for penetration of contamination to the Guarani Aquifer System. Electronic Publication     

Fluid migration through thrust faults in the Helvetic nappes (Western Swiss Alps)

The δ¹⁸O, δ¹³C and ⁸⁷Sr/⁸⁶Sr values of calcite and organic matter were measured for carbonate mylonites from numerous thrusts in the Helvetic Alps. Carbonate mylonites in most of the thrusts retain essentially unaltered protolith δ¹⁸O and δ¹³C values, consistent with there having been little to no advection of isotopically distinct fluid through these faults. Only carbonate mylonites from the basal thrusts of the largest nappes have δ¹⁸O and/or δ¹³C values that differ from those of their protoliths. The zone of isotopic alteration/exchange is confined to c. 10 to 20 meters of these fault contacts. We propose the fluids that migrated through these faults contained variable amounts of organically derived carbon and radiogenic strontium, and were probably derived from dewatering of the sedimentary rocks and prograde metamorphic reactions in the nappes' root zones. Apart from the basal thrusts of the largest nappes that behaved as narrow, laterally extensive conduits for fluids, there is little isotopic evidence that large quantities of fluids passed through most of the carbonate-hosted thrusts in the Helvetic Alps. Received: 25 August 1998 / Accepted: 26 February 1999     

Isotopic constraints on fluid evolution and precipitation mechanisms for the Boléo Cu–Co–Zn district, Mexico

Stable and radiogenic isotope composition of stratiform Cu–Co–Zn mineralization and associated sedimentary rocks within the Boléo district of the Miocene Santa Rosalía basin, Baja California Sur, constrains the evolution of seawater and hydrothermal fluids and the mechanisms responsible for sulfide and oxide deposition. Stable isotope geochemistry of limestone and evaporite units indicates a strong paleogeographic influence on the chemistry of the water column. Near-shore limestone at the base of the Boléo Formation is characterized by modified marine carbon (δ ¹³C_PDB=−6.0 to +4.4‰) and oxygen (δ ¹⁸O_SMOW=+19.5 to +26.2‰) isotope composition due to the influx of ¹³C- and ¹⁸O-depleted fluvial water. Sulfate sulfur isotope composition (δ ³⁴S_CDT=+17.21 to +22.3‰ and δ ¹⁸O_SMOW=+10.7 to +13.1‰) for basal evaporite and claystone facies are similar to Miocene seawater. Strontium isotopes are less radiogenic than expected for Miocene seawater due to interaction with volcanic rocks. Low S/C ratios, high Mn contents and sedimentological evidence indicate the basin water column was oxidizing. The oxygenated basin restricted sulfide precipitation to within the sedimentary pile by replacement of early diagenetic framboidal pyrite and pore-space filling by Cu–Co–Zn sulfides to produce disseminated sulfides. Quartz–Mn oxide oxygen isotope geothermometry constrains mineralization temperature between 18 and 118°C. Sulfur isotopes indicate the following sources of sulfide: (1) bacterial sulfate reduction within the sedimentary pile produced negative δ ³⁴S values (<−20‰) in framboidal pyrite; and (2) bacterial sulfate reduction at high temperature (80–118°C) within the sedimentary pile during the infiltration of the metal-bearing brines produced Cu–Co–Zn sulfides with negative, but close to 0‰, δ ³⁴S values. Isotope modeling of fluid-rock reaction and fluid mixing indicates: (1) sedimentary and marine carbonates (δ ¹³C=−11.6 to −3.2‰ and δ ¹⁸O=+19.0 to +21.8‰) precipitated from basin seawater/pore water that variably mixed with isotopically depleted meteoric waters; and (2) hydrothermal calcite (δ ¹³C=−7.9 to +4.3‰ and δ ¹⁸O=+22.1 to +25.8‰) formed by dissolution and replacement of authigenic marine calcite by downward-infiltrating metalliferous brine and brine-sediment exchange, that prior to reaction with calcite, had mixed with isotopically depleted pore water. The downward infiltration of metalliferous brine is inferred from lateral and stratigraphic metal distributions and from the concentration of Cu sulfides along the upper contact of pyrite-bearing laminae. The co-existence and textural relationships among framboidal pyrite, base metal sulfides, carbonate and Mn–Fe oxides (including magnetite) within mineralized units are consistent with carbonate replacement and high-temperature bacterial reduction within the sedimentary pile occurring simultaneously below a seawater column under predominantly oxygenated conditions.     

Carbonate alteration associated with talc-chlorite mineralization in the eastern Pyrenees, with emphasis on the St. Barthelemy Massif

Summary The eastern Pyrenees host a large number of talc-chlorite mineralizations of Albian age (112–97 Ma), the largest of which occur in the St. Barthelemy massif. There talc develops by hydrothermal replacement of dolostones, which were formed by alteration of calcite marbles. This alteration is progressive. Unaltered calcite marbles have oxygen isotope composition of about 25‰ (V-SMOW). The δ¹⁸O values decrease down to values of 12‰ towards the contact with dolostones. This ¹⁸O depletion is accompanied by Mg enrichment, LREE fractionation and systematic shifts in the Sr isotope compositions, which vary from ⁸⁷Sr/⁸⁶Sr = 0.7087–0.7092 in unaltered calcite marbles to slightly more radiogenic compositions with ⁸⁷Sr/⁸⁶Sr = 0.7094 near dolomitization fronts. Dolostones have δ¹⁸O values (about 9‰) lower than calcitic marbles, higher REE content and more radiogenic Sr isotope composition (⁸⁷Sr/⁸⁶Sr = 0.7109 to 0.7130). Hydrothermal calcites have δ¹⁸O values close to dolostones but substantially lower δ¹³C values, down to −6.5‰, which is indicative of the contribution of organic matter. The REE content of hydrothermal calcite is one order of magnitude higher than that of calcitic marbles. Its highly radiogenic Sr composition with ⁸⁷Sr/⁸⁶Sr = 0.7091 to 0.7132 suggests that these elements were derived from silicate rocks, which experienced intense chlorite alteration during mineralization. The chemical and isotopic compositions of the calcite marbles, the dolostones and the hydrothermal calcites are interpreted as products of successive stages of fluid-rock interaction with increasing fluid-rock ratios. The hydrothermal quartz, calcite, talc and chlorite are in global mutual isotopic equilibrium. This allows the calculation of the O isotope composition of the infiltrating water at 300 °C, which is in the δ¹⁸O = 2–4.5‰ range. Hydrogen isotope compositions of talc and chlorite indicate a δD = 0 to −20‰. This water probably derived from seawater, with minor contribution of evolved continental water.     

Origin of the Nchanga copper–cobalt deposits of the Zambian Copperbelt

The Zambian Copperbelt forms the southeastern part of the 900-km-long Neoproterozoic Lufilian Arc and contains one of the world’s largest accumulations of sediment-hosted stratiform copper mineralization. The Nchanga deposit is one of the most significant ore systems in the Zambian Copperbelt and contains two major economic concentrations of copper and cobalt, hosted within the Lower Roan Group of the Katangan Supergroup. A Lower Orebody (copper only) and Upper Orebody (copper and cobalt) occur towards the top of arkosic units and within the base of overlying shales. The sulfide mineralogy includes pyrite, bornite, chalcopyrite, and chalcocite, although in the Lower Orebody, sulfide phases are partially or completely replaced by malachite and copper oxides. Carrollite is the major cobalt-bearing phase and is restricted to fault-propagation fold zones within a feldspathic arenite. Hydrothermal alteration minerals include dolomite, phlogophite, sericite, rutile, quartz, tourmaline, and chlorite. Quartz veins from the mine sequence show halite-saturated fluid inclusions, ranging from ~31 to 38 wt% equivalent NaCl, with homogenisation temperatures (Th_TOT) ranging between 140 and 180°C. Diagenetic pyrites in the lower orebody show distinct, relatively low δ ³⁴S, ranging from −1 to −17‰ whereas arenite- and shale-hosted copper and cobalt sulfides reveal distinctly different δ ³⁴S from −1 to +12‰ for the Lower Orebody and +5 to +18‰ for the Upper Orebody. There is also a clear distinction between the δ ³⁴S mean of +12.1±3.3‰ (n=65) for the Upper Orebody compared with +5.2±3.6‰ (n=23) for the Lower Orebody. The δ ¹³C of dolomites from units above the Upper Orebody give δ ¹³C values of +1.4 to +2.5‰ consistent with marine carbon. However, dolomite from the shear-zones and the alteration assemblages within the Upper Orebody show more negative δ ¹³C values: −2.9 to −4.0‰ and −5.6 to −8.3‰, respectively. Similarly, shear zone and Upper Orebody dolomites give a δ ¹⁸O of +11.7 to +16.9‰ compared to Lower Roan Dolomites, which show δ ¹⁸O of +22.4 to +23.0‰_. Two distinct structural regimes are recognized in the Nchanga area: a weakly deformed zone consisting of basement and overlying footwall siliciclastics, and a moderate to tightly folded zone of meta-sediments of the Katangan succession. The fold geometry of the Lower Roan package is controlled by internal thrust fault-propagation folds, which detach at the top of the lowermost arkose or within the base of the overlying stratigraphy and show vergence towards the NE. Faulting and folding are considered to be synchronous, as folding predominantly occurred at the tips of propagating thrust faults, with local thrust breakthrough. The data from Nchanga suggests a strong link between ore formation and the development of structures during basin inversion as part of the Lufilian Orogeny. Sulfides tend to be concentrated within arenites or coarser-grained layers within shale units, suggesting that host-rock porosity and possibly permeability played a role in ore formation. However, sulfides are also commonly orientated along, but not deformed by, a tectonic fabric or hosted within small fractures that suggest a significant role for deformation in the development of the mineralization. The ore mineralogy, hydrothermal alteration, and stable isotope data lend support to models consistent with the thermochemical reduction of a sulfate- (and metal) enriched hydrothermal fluid, at the site of mineralization. There is no evidence at Nchanga for a contribution of bacteriogenic sulfide, produced during sedimentation or early diagenesis, to the ores.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.Editorial handling: H. Frimmel     

The Role of Organic Matter During Metal Enrichment in Permian Kupferschiefer of the Rudna Mine,Southwest Poland

The bulk composition of organic matter and saturated and aromatic hydrocarbons extracted from 16 samples collected from two Kuperschiefer profiles in the Rudna mine,Southwest Poland has been analyzed to study the role of organic matter during base metal enrichment in the Kupferschiefer shale.The results indicated that the extract yields and saturated hydrocarbon yields decreased with increasing base metal contents.GC and GC/MS analyses indicated that n -alkanes and alkylated aromatic compounds were depleted and may have served as hydrogen donators for thermochemical sulfate reduction.The enrichment of base metal is closely connected with the destruction of hydrocarbons.     

Geology,fluid inclusion and sulphur isotope characteristics of the El Cobre VHMS deposit,Southern Cuba

The El Cobre deposit is located in eastern Cuba within the volcanosedimentary sequence of the Sierra Maestra Paleogene arc. The deposit is hosted by tholeiitic basalts, andesites and tuffs and comprises thick stratiform barite and anhydrite bodies, three stratabound disseminated up to massive sulphide bodies produced by silicification and sulphidation of limestones or sulphates, an anhydrite stockwork and a siliceous stockwork, grading downwards to quartz veins. Sulphides are mainly pyrite, chalcopyrite and sphalerite; gold occurs in the stratabound ores. Fluid inclusions measured in sphalerite, quartz, anhydrite and calcite show salinities between 2.3 and 5.7 wt% NaCl eq. and homogenisation temperatures between 177 and 300°C. Sulphides from the stratabound mineralisation display δ ³⁴S values of 0‰ to +6.0‰, whilst those from the feeder zone lie between −1.4‰ and +7.3‰. Sulphides show an intra-grain sulphur isotope zonation of about 2‰; usually, δ ³⁴S values increase towards the rims. Sulphate sulphur has δ ³⁴S in the range of +17‰ to +21‰, except two samples with values of +5.9‰ and +7.7‰. Sulphur isotope data indicate that the thermochemical reduction of sulphate from a hydrothermal fluid of seawater origin was the main source of sulphide sulphur and that most of the sulphates precipitated by heating of seawater. The structure of the deposit, mineralogy, fluid inclusion and isotope data suggest that the deposit formed from seawater-derived fluids with probably minor supply of magmatic fluids.     

Stable carbon isotope characteristics of different plant species and surface soil in arid regions

The stable carbon isotope composition in surface soil organic matter (δ¹³Csoil) contains integrative information on the carbon isotope composition of the standing terrestrial plants (δ¹³Cleaf). In order to obtain valuable vegetation information from the δ¹³C of terrestrial sediment, it is necessary to understand the relationship between the δ¹³C value in modern surface soil and the standing vegetation. In this paper, we studied the δ¹³C value in modern surface soil organic matter and standing vegetation in arid areas in China, Australia and the United States. The isotopic discrepancy between δ¹³Csoil and δ¹³Cleaf of the standing dominant vegetation was examined in those different arid regions. The results show that the δ¹³Csoil values were consistently enriched compared to the δ¹³Cleaf. The δ¹³Cleaf values were positively correlated with δ¹³Csoil, which suggests that the interference of microorganisms and hydrophytes on the isotopic composition of surface soil organic matter during soil organic matter formation could be ignored in arid regions. The averaged discrepancy between δ¹³Csoil and δ¹³Cleaf is about 1.71%in Tamarix L. in the Tarim Basin in China, 1.50% in Eucalytus near Orange in Australia and 1.22% in Artemisia in Saratoga in the United States, which are different from the results of other studies. The results indicate that the discrepancies in the δ¹³C value between surface soil organic matter and standing vegetation were highly influenced by the differences in geophysical location and the dominant species of the studied ecosystems. We suggest that caution should be taken when organic matter δ¹³C in terrestrial sediment is used to extract paleovegetation information (C₃/C₄ vegetation composition), as the δ¹³C in soil organic matter is not only determined by the ratio of C₃/C₄ species, but also profoundly affected by climate change induced variation in the δ¹³C in dominant species.     

Hydrogeochemical and Stable Isotope Characteristics of the River Idrijca (Slovenia), the Boundary Watershed Between the Adriatic and Black Seas

The hydrogeochemical and isotope characteristics of the River Idrijca, Slovenia, where the world’s second largest mercury (Hg) mine is located, were investigated. The River Idrijca, a typical steep mountain river, has an HCO₃ ⁻–Ca²⁺–Mg²⁺ chemical composition. Its Ca²⁺/Mg²⁺ molar ratio indicates that dolomite weathering prevails in the watershed. The River Idrijca and its tributaries are oversaturated with respect to calcite and dolomite. The pCO₂ pressure is up to 13 times over atmospheric pressure and represents a source of CO₂ to the atmosphere. δ¹⁸O values in river water indicate primary control from precipitation and enrichment of the heavy oxygen isotope of infiltrating water recharging the River Idrijca from its slopes. The δ¹³C_DIC values range from −10.8 to −6.6‰ and are controlled by biogeochemical processes in terrestrial environments and in the stream: (1) exchange with atmospheric CO₂, (2) degradation of organic matter, (3) dissolution of carbonates, and (4) tributaries. The contributions of these inputs were calculated according to steady state equations and are estimated to be—11%:19%:30%:61% in the autumn and 0%:26%:39%:35% in the spring sampling seasons.     

Comparative studies of organic matter petrography of the late palaeozoic black shales from Southwestern Poland

There are at least two sapropelic units associated with Late Palaeozoic black shales in Central Europe. The older unit, of Late Carboniferous age, is the lower part of the Anthracosia Shales in the Intrasudetic Basin, and the younger one is the well-known Zechstein Kupferschiefer in both the Foresudetic Monocline and the Northsudetic Basin. The first unit is of lacustrine origin, while the second one represents deposition in a shallow marine depositional environment. Both units contain high amounts of organic matter, thus being typical black shales.The organic matter dispersed in these shales was studied petrographically. In general, the vitrinite reflectance of the shales studied indicates variable, but moderate organic matter maturity (0.68–1.25%), equivalent to the oil window. Detailed microscopic studies of the organic material dispersed in the lower unit of the Anthracosia Shales showed that liptinite, especially alginite is the most abundant component. Secondary altered organic matter, i.e. solid hydrocarbons, rarely occurs. Organic components together with mineral matter constitute a lacustrine sapropelic association, a humic (terrestrial) association and an intermediary association. The character and predominance of alginite and lacustrine sapropelic association are indicative of an open-lacustrine depositional environment. In general, this organic composition is typical of type I kerogen.Microscopic analysis of the Kupferschiefer revealed a mixture of liptinite, vitrinite and inertinite macerals, and other organic components such as amorphous sapropelic mass (ASM) and solid bitumens. The most common organic components are liptinite macerals. Bituminite and alginite predominate, and are diagnostic macerals of this unit. The amount of bituminite locally exceeds 85 vol.%. Other liptinite macerals such as sporinite and liptodetrinite, are present in significantly lower amounts, one exception being ASM, which may be present in higher amounts. Humic constituents (vitrinite and inertinite) are rare, present in small amounts in the Kupferschiefer beds. The organic matter composition points to type II kerogen for this unit.     

Accumulation of copper in the Permian Kupferschiefer: A result of post-depositional redox reactions

Within the Central European Zechstein Basin the Permian Kupferschiefer has been deposited under anoxic conditions. In most parts of the basin, the metal content does not exceed values commonly observed in black shales. However, in areas near to the Zechstein sea-shore which are simultaneously related to rift zones a significant base metal enrichment is observed. Organic geochemical analyses of the copper-mineralized sections in the Kupferschiefer from Southwest Poland show that significant changes in the composition of organic matter are associated with the metal enrichment processes. Porphyrins, commonly abundant constituents of the shale, have been decomposed by oxidizing fluids. Additionally, aliphatic hydrocarbons have been largely removed from the bitumen and alkylated aromatic systems were affected by side-chain degradation. This particular type of alteration is explained by ascending oxidizing solutions which transported high amounts of base metals from Lower Permian red beds into the Kupferschiefer horizon acting as a geochemical trap. The metal precipitation is suggested to be a result of thermochemical sulphide production with organic matter acting as hydrogen source. In areas such as the Lower Rhine Basin in the bottom section of the Kupferschiefer the base metals lead and zinc as well as barium have been accumulated from basinal Carboniferous formation waters. Copper enrichment is not observed because potential source rocks are missing in this area. However, the observed compositional changes of the organic matter do not point towards thermochemical redox processes.     

The origin of rhythmic sulphide bands from the Permian sandstones (Weissliegendes) in the footwall of the Fore-Sudetic “Kupferschiefer” (Poland)

Rhythmic copper sulphide bands occur in the Weissliegendes sandstones, in the footwall of the Kupferschiefer in the mining district of SW Poland. The δ ³⁴S values of sulphides vary from −39 to — 44‰ (6–7‰ lighter than Kupferschiefer sulphides). The copper sulphides are represented mainly by digenite and chalcocite. According to microprobe results their Pb, Ni, Zn and Ag contents are similar to those in the Kupferschiefer. The bands are assumed to be formed by diffusion of bacterially produced hydrogen sulphide from the Kupferschiefer into the porous volume of the white sandstones containing dissolved copper. The sulphides were precipitated in almost equidistant bands, from top to bottom, probably according to the Ostwald-Prager supersaturation theory. The increase of isotopically heavier sulphur towards the lower levels in the sandstone might be explained by closing of the bacterial sulphate reduction system. Contribution to the IGCP Project No. 254