The role of granites in volcanic-hosted massive sulphide ore-forming systems: an assessment of magmatic�Chydrothermal contributions

Assessment of geological, geochemical and isotopic data indicates that a significant subgroup of volcanic-hosted massive sulphide (VHMS) deposits has a major or dominant magmatic?Chydrothermal source of ore fluids and metals. This group, which is typically characterised by high Cu and Au grades, includes deposits such as those in the Neoarchean Doyon-Bousquet-LaRonde and Cambrian Mount Lyell districts. These deposits are distinguished by aluminous advanced argillic alteration assemblages or metamorphosed equivalents intimately associated with ore zones. In many of these deposits, ??³⁴S_sulphide is low, with a major population below ?3??; ??³⁴S_sulphate differs from coexisting seawater and ??³⁴S_{sulphate?Csulphide}????20?C30??. These characteristics are interpreted as the consequence of disproportionation of magmatic SO₂ as magmatic?Chydrothermal fluids ascended and cooled and as a definitive evidence for a significant magmatic?Chydrothermal contribution. Other characteristics that we consider diagnostic of significant magmatic?Chydrothermal input into VHMS ore fluids include uniformly high (>3 times modern seawater values) salinities or very ¹⁸O-enriched (??¹⁸O?>?5??) ore fluids. We do not consider other criteria [e.g. variable salinity, moderately high ??¹⁸O_fluid (2?C5??), ??³⁴S_sulphide near 0??, metal assemblages or a spatial association with porphyry Cu or other clearly magmatic-hydrothermal deposits] that have been used previously to advocate significant magmatic?Chydrothermal contributions to be diagnostic as they can be produced by non-magmatic processes known to occur in VHMS mineral systems. However, in general, a small magmatic?Chydrothermal contribution cannot be excluded in most VHMS systems considered. Conclusive data that imply minimal magmatic?Chydrothermal contributions are only available in the Paleoarchean Panorama district where coeval seawater-dominated and magmatic?Chydrothermal systems appear to have been physically separated. This district, which is characterised by chloritic and sericitic alteration assemblages and lacks aluminous advanced argillic alteration assemblages, is typical of many VHMS deposits around the world, suggesting that for ??garden variety?? VHMS deposits, a significant magmatic?Chydrothermal contribution is not required. Other than deposits associated with advanced argillic alteration assemblages, the only deposit for which we ascribe a major magmatic?Chydrothermal contribution is the Devonian Neves Corvo deposit. This deposit differs from other deposits in the Iberian Pyrite Belt and around the world in being extremely Sn-rich, with the Sn closely associated with Cu and in having formed from high ¹⁸O-rich fluids (??¹⁸O_fluid ??8.5??). We consider these characteristics, particularly the last, as diagnostic of a significant magmatic hydrothermal contribution. Our analysis indicates that two subgroups of VHMS deposits have a major magmatic?Chydrothermal contribution: Cu/Au-rich deposits with aluminous alteration assemblages and reduced, very Sn-rich deposits in which Sn was introduced in a high-temperature ore assemblage. Comparison with ??normal?? VHMS deposits suggests that these subgroups of VHMS deposits may form in specialised tectonic environments. The Cu/Au-rich deposits appear to form adjacent to magmatic arcs, an environment conducive to the generation of hydrous, oxidised melts by melting metasomatised mantle in the wedge above the subducting slab. This contrasts with the back-arc setting of ??normal?? VHMS deposits in which relatively dry granites (In this contribution, we use the term granite sensu latto) formed by decompression melting drive seawater-dominated hydrothermal circulation. The tectonic setting of highly Sn-rich VHMS deposits such as Neves Corvo is less clear; however, thick continental crust below the ore-hosting basin may be critical, as it is in other Sn deposits.     

The genesis of Pb‐Zn sulphide occurrences in the Lower Devonian Buchan Group,Victoria

Six minor sulphide occurrences hosted by the Lower Devonian Buchan Group have been investigated. Sulphide minerals and associated phases are hosted by both dolostone and limestone lithologies along stylolitized bedding planes, cross‐cutting fractures, low angle minor faults and in cavities. Mineralization was closely associated with minor structures of inferred Tabberabberan age (Middle Devonian), which it appears to have post‐dated, but was largely strata‐bound in nature. The mineralogy of the occurrences is simple and characterized by the following generalized paragenesis which reflects the increasing oxidation state and pH of the mineralizing fluids: pyrite (pseudomorphous after marcasite)‐galena ± sphalerite ± pyrite‐dolomite ± barite‐calcite ± fluorite ± dolomite.

The sulphur isotope composition of sulphide minerals varies from ‐32.1 to +4.1‰, with iron and base metal sulphide minerals forming two distinct populations around ‐25‰ and 0‰, respectively. A single barite sample gives a sulphur isotope composition of +22.4‰, which is similar to that estimated for Early Devonian seawater. Fluid inclusions in fluorite and calcite homogenize at temperatures in the range 160 to 212° C and have average salinities of approximately 10 wt% NaCI eq. Sphalerite contains up to 1.81 wt% iron which correlates with colour, and up to 1.43 wt% cadmium. The Pb isotopic pattern of galena suggests a source region with U/Pb(= μ) lower than the crustal average, and a high Th/U.

A genetic hypothesis is proposed which involves the circulation of saline fluids through the Snowy River Volcanics, which directly underlie the Buchan Group, during or at some time after the Tabberabberan Orogeny. Although the Buchan occurrences show features characteristic of both Mississippi Valley‐type and stratiform ore deposits, they are most directly comparable to the epigenetic zones of Irish carbonate‐hosted base‐metal deposits. However, Pb‐Zn sulphide mineralization at Buchan appears to have been associated with minor compressional structures, suggesting that a simple correlation with the Irish deposits is not directly applicable.     

An investigation of crack formation in surface paste disposal method for pyritic Pb–Zn tailings

Surface paste disposal method can be used to minimize environmental risks during storage of mine process tailings. There are some researches and industrial applications which prove success of the method. The surface paste disposal of mineral process tailings obtained from a Pb–Zn underground mine was simulated considering mine site conditions at laboratory scale in the study. The paste material was stored in the cabin/container layer by layer, and then, the cracks occurred after the paste formation of each layer were analyzed by image process. Meanwhile, leachate water collected from the bottom of the cabin was subjected to electrical conductivity (EC) analysis. Furthermore, the wetting–drying process was conducted to simulate the climatic conditions of the region. Additionally, some physical and geochemical parameters such as matric suction, volumetric water content, and oxygen consumption of the paste material were obtained using sensors displaced into different layers. The results of the crack analysis for each layer showed that the cracks intensity increased at lower layers. Moreover, the crack intensity and EC values of each layer showed a similar trend, and the crack intensity increased almost five times during the wetting–drying tests. The measured values of the parameters obtained from the tests indicated that the deposited paste material can be stabile during the deposition over the years under the climatic conditions of the region.     

Mobility of heavy metals from tailings to stream waters in local zinc smelting activities contaminated site

It has been found that stream waters were severely contaminated with wastes from a long-time smelting factory in Hezhang, Guizhou, China. The main sources of contamination are the smelting wastes stored in the open air and abandoned in the vicinity of stream. A method of lead isotope was adopted in order to identify relations between tailings and water contamination. Representative samples of tailings and stream sediments were collected. Mineralogical characterizations were conducted using XRD and TEM/SEM, while acid digestion was carried out for determining metal contents. BCR sequential leaching tests were performed in order to assess metal mobility. The tremendous ‘actual＇ and ‘potential＇ mobility of heavy metals indicates that the smelting waste and stream sediments present a considerable threat to the environment. Besides the chemical remobilization of heavy metals from the sediments and the reworking of riverbed sediments act as a secondary source of pollution. Also groundwater and stream water were sampled in specific locations and were measured.     

Effect of plant growth on Pb and Zn geoaccumulation in 300-year-old mine tailings of Zacatecas,México

Concentrations of Pb and Zn, plant uptake of these metals, the influence of the plants’ growth on the physicochemical properties and metal concentrations in the tailings of an abandoned 300-year-old mine tailing dam in Zacatecas, Mexico were investigated. Tailings were found to be heavily contaminated, with average levels of 2621 ± 53 and 3827 ± 83 mg/kg for Pb and Zn, respectively (maximum concentrations of 8466 ± 116 and 12,475 ± 324 mg/kg, respectively), exceeding international standards. Though physico-chemical conditions (pH, conductivity, redox potential, moisture, organic matter, nitrate, nitrite, ammonium nitrogen, total nitrogen, phosphorus and sulfates) do not favor the development of vegetation, some plants have adapted to these adverse conditions. Moreover, there was a significant reduction of Pb and Zn concentration in the rhizosphere (between 10–78% for Pb and 18–62% for Zn, depending on plant species). Sporobolus airoides showed average biomass concentrations of 173 ± 2 and 313 ± 6 mg/kg, for Pb and Zn, respectively; which implies a risk for mobility and possible incorporation into the food chain. Barcleyanthus salicifolius, Asclepsias linaria and Cortaderia selloana on the other hand, showed average biomass concentrations of 28 ± 3 and 121 ± 5 mg/kg of Pb and Zn, respectively, thus representing a lower biomagnification risk. The effect of these plants to reduce metal concentrations in the rhizosphere, improve physico-chemical conditions in metal polluted substrates, but with limited metal accumulation in biomass, suggests that they can be evaluated for use in stabilizing metal polluted tailings.     

Geological and geochemical characteristics of the Baimazhai Ni-Cu-（PGE） sulphide deposit in Yunnan, China

The sulphide ores of the Baimazhai deposit, although typically orthomagmatic, locally exhibit peculiar textural features and are intimately associated with hydrothermal minerals, such as biotite, amphibole and chlorite. This association suggests that the magmatic sulphide ores were subjected to hydrothermal alteration and subsequent redistribution, resulting in the observed textural features. Geochemically, the Baimazhai sulphide ores are enriched in Cu, Pd and Au, which,according to previous studies, reflects the action of hydrothermal fluids. Interestingly, Ar-Ar dating yielded the plateau ages of about 160–170 Ma, which are at odds with the established Permian age of the Emeishan large igneous province. We interpreted these younger ages as due to thermal resetting during post-Permian tectonothermal events. We have proposed a model in which tectonic movements and hydrothermal fluids related to these events modified the pre-existing magmatic sulphides. Given the degree of overprint, we suggested two possible scenarios: 1) the sulphide disseminations that surround the massive magmatic ores are the result of deformation and hydrothermal alteration; and 2) there were both magmatic massive and disseminated sulphides, in which case the scale and relocation of remobilization would have been smaller, but still detectable.     

Oxide–sulphide relationships in sodalite-bearing metasomatites of the Epembe–Swartbooisdrif Alkaline Province, north-west Namibia

The south-eastern part of Kunene Intrusive Complex (KIC), Namibia/Angola, is host to volumetrically significant, and economically important, concentrations of sodalite in the area around Swartbooisdrif, north-west Namibia. The mineralisation was formed by metasomatic exchange with carbonatites of the Epembe–Swartbooisdrif Alkaline Province. This process led to the breakdown of ore minerals initially present in various rock types of the KIC and caused the formation of new opaque phases in the sodalite-bearing metasomatites. A detailed investigation of textures and chemical compositions of the Fe–Ti oxides and sulphides has allowed evaluation of the complex ore-forming processes related to the polyphase magmatic and metasomatic history of the sodalite deposit. The predominant opaque phases in the various rock types of the KIC are ilmenite and (titano)magnetite, which are highly concentrated in the so-called magnetite plugs. It is clear from the textural evidence that most of the ilmenite and (titano)magnetite, although of orthomagmatic origin, recrystallised under subsolidus conditions. Conformably, their respective chemical compositions and phase relations represented in the system FeO–1/2Fe₂O₃–TiO₂ point to re-equilibration at temperatures below 600 °C. Ilmenite and (titano)magnetite were affected by later deformation and decomposed by various reactions, related to, or outlasting, the metasomatic process. Oxidation of ilmenite led to the formation of symplectitic aggregates of rutile and secondary magnetite. Carbonatisation of the Fe–Ti oxides produced rutile and the siderite and rhodochrosite components in ankerite. Pyrite, in part together with rutile and secondary magnetite, was formed by sulphidation of the Fe–Ti oxides. Conspicuous aggregates of granular or lamellar intergrowths of pyrite with hematite and/or magnetite are interpreted as products of contemporaneous sulphidation and oxidation of former igneous pyrrhotite. Rarely observed pyrrhotite with pentlandite lamellae is probably not an igneous relic, but was formed during the metasomatic event. Smaller amounts of chalcopyrite, bornite, digenite–chalcocite, galena, ferroan siegenite, millerite and polydymite testify to different cooling stages during or after metasomatism. Applying the phase relations in the simplified system Fe–Co–Ni–S–O, we were able to reconstruct a semi-quantitative T–f(S₂)–f(O₂) path for the ore-forming processes. Received: 22 October 1998 / Accepted: 27 October 1999     

Phosphate amendment of metalliferous tailings, Cannington Ag–Pb–Zn mine, Australia: implications for the capping of tailings storage facilities

This study appraised the use of phosphate fertilisers in immobilising metals in mine tailings to prevent their uptake into Curly Mitchell grass (Astrebla lappacea), when grown on capped, phosphate-amended tailings. Leaching experiments showed that Pb mobility was reduced by both bone meal and superphosphate amendment. Bone meal amendment also reduced Cd mobility. By contrast, Cd, Mn and Zn mobility increased in superphosphate-amended tailings due to increased acid production and, Cu was mobilised in bone meal-amended tailings possibly through the formation of soluble metal-complexing organic compounds. Arsenic and Sb were mobilised in both treatments due to phosphate ligand exchange. Greenhouse trials used Curly Mitchell grass grown on 1-m-high columns stacked with waste materials and different amendments overlain by clean topsoil. Curly Mitchell grass showed substantial uptake of Cd, Mn, Pb and Zn from unamended tailings and waste rock, where these were penetrated by the plant’s root system. Addition of phosphate fertilisers to the surface of tailings did not result in reduced metal uptake by Curly Mitchell grass. In tailings capped with limestone, the limestone layer formed an effective physical barrier preventing root penetration into the tailings and led to substantially reduced metal uptake in grass. The study demonstrates that thorough mixing of waste materials and fertilisers as well as irrigation may be required for successful phosphate immobilisation of metals in base metal tailings. Alternatively, the placement of a thin layer of crushed limestone on top of the tailings pile prior to capping may lead to the formation of a chemical and physical barrier and prevent the transfer of environmentally significant elements into the above-ground biomass of Mitchell grasses.     

Modeling and predicting of drainage quality for sulfide mine tailings impoundments

Effluent from tailings impoundments of sulfide mine is an important environmental problem. The oxidation of sulfide minerals in tailings impoundments and consequent release of acid and contaminants, including heavy metals and arsenic, to tailings pore-water can last for decades to centuries. Pollution of water bodies including surface water and groundwater occurs when infiltration of precipitation is unhindered, bottom liners are absent and no drainage collection is installed. So there is a great need to develop reliable modeling techniques for characterizing geochemical interactions taking place within the tailings and predicting potential future environmental hazard which favor further prevention and remediation of the acidic mine drainage （AMD）. In this paper, a comprehensive dynamic model for tailings-water interaction was established on the basis of considering the coupling and feedback among many factors and processes such as sulfide oxidation, gangue dissolution, oxygen diffusion, water flow and mass transport,     

Rapid development of negative Ce anomalies in surface waters and contrasting REE patterns in groundwaters associated with Zn–Pb massive sulphide deposits

Ground and surface waters collected from two undisturbed Zn–Pb massive sulphide deposits (the Halfmile Lake and Restigouche deposits) and active mines in the Bathurst Mining Camp (BMC), NB, Canada were analysed for the rare earth elements (REE). REE contents are highly variable in waters of the BMC, with higher contents typical of waters with higher Fe and lower pH. There are significant differences between ground- and surface waters and between groundwaters from different deposits. The REE contents of surface waters are broadly similar within and between deposit areas, although there are spatial variations reflecting differences in pH and redox conditions. Surface waters are characterised by strong negative Ce anomalies ([Ce/Ce*]_NASC as low as 0.08), produced by oxidation of Ce³⁺ to Ce⁴⁺ and preferential removal of Ce⁴⁺ from solution upon leaving the shallow groundwater environment. Groundwaters and seeps typically lack significant Ce anomalies reflecting generally more reducing conditions in the subsurface environment and indicating that Ce oxidation is a rapid process in the surface waters. Deeper groundwaters at the Halfmile Lake deposit are characterised by REE patterns that are similar to the host lithologies, whereas most groundwaters at the Restigouche deposit have LREE-depleted patterns compared to NASC. Halfmile Lake deposit groundwaters have generally lower pH values, whereas Restigouche deposit groundwaters show greater heavy REE-complexation by carbonate ions. Shallow waters at the Halfmile Lake and Stratmat Main Zone deposits have unusual patterns which reflect either the adsorption of light REE onto colloids and fracture-zone minerals and/or precipitation of REE–phosphate minerals. Middle REE-enrichment is typical for ground- and surface waters and is highest for neutral pH waters. The labile portion of stream sediments are generally more middle REE-enriched than total sediment and surface waters indicating that the REE are removed from solution by adsorption to Fe- and Mn-oxyhydroxides in the order middle REE≥light REE>heavy REE.     

The nature and genesis of marginal Cu–PGE–Au sulphide mineralisation in Paleogene Macrodykes of the Kangerlussuaq region, East Greenland

The Kangerlussuaq region of East Greenland hosts a variety of early Tertiary extrusive and intrusive igneous rocks related to continental break up and the passage of the ancestral Iceland plume. These intrusive bodies include a number of gabbroic macrodykes, two of which—the Miki Fjord Macrodyke, and the newly discovered Togeda Macrodyke—contain Cu–PGE–Au sulphide mineralisation along their margins. Sulphides occur as disseminated interstitial blebs and rounded globules of chalcopyrite and pyrrhotite with some Fe–Ti oxides and platinum-group minerals, comprising largely Pd bismuthides and tellurides. The globules are interpreted to have formed from fractionation of trapped droplets of an immiscible Cu- and Pd-rich sulphide melt and show geopetal indicators. Sulphur isotopes imply a local crustal source of S in these from pyritic sediments of the Kangerlussuaq Basin. Thus, generation of these sulphide occurrences was controlled by local country rock type. Low Ni/Cu and Pt/Pd ratios, also present in the Platinova reefs in the Skaergaard Intrusion, indicate that early fractionation of olivine may have depleted the magma of Ni and suggest the likely presence of a large magma chamber at depth. Xenoliths of Ni-rich olivine cumulates in the Miki Fjord Macrodyke may have been sourced from such a body. The location of thus far unidentified conduit or feeder zones to the macrodykes beneath the present day surface may represent potential targets for more massive sulphide orebodies.     

Chemical speciation of heavy metals and arsenic in tailings and soils contaminated by mining activities （Northern Portugal）

A chemical sequential speciation of heavy metals （Fe, Mn, Cu, Zn, Pb, Cd, Sn, W, Bi, Ni, Cr, Mo, Co） Al, Ti and As in tailings and soils around five W/Sn mines （Adoria Mine, Ervedosa Mine, Regoufe Mine, Rio de Frades Mine and Tarouca Mine-Northern Portugal） was realized using a 7-steps fractionation procedure. Each of the chemical fractions was operationally defined as （Dold and Fontbote 2001）： （1） water-soluble; （2） exchangeable; （3） bound to Fe oxyhydroxides （or easily reducible）; （4） bound to Fe oxides （or moderately reducible）; （5） bound to organic matter and secondary Cu-sulfides; （6） bound to primary sulfides; and （7） residual. The extracted element contents at each step were measured by ICP-MS. Samples were also analyzed for pH, electrical conductivity and organic matter. The results allowed us to notice that： （1） the pH was the main factor controlling the geochemical distribution of the studied elements. The tailing and soil samples were very acid, with an average pH of approximately 4.37. Some metal cations （Mn, Cd, Cu, Zn, Pb, Co, Cr, Ni） behave in a similar way, revealing important enrichments in the most bioavailable fractions （water-soluble and exchangeable fractions）. In contrast, oxyanions such as Mo and As show low mobility through adsorption to Fe（Ⅲ） oxyhydroxides dissolved in the two reducible fractions. These results reflect the pH dependent adsorption on the clay minerals, Fe and Mn oxyhydroxides and the co-precipitation with these secondary minerals; （2） residual fraction was the most important fraction for Sn, Ti, Al, Mn, V, Cr and Zn. These results suggest that in these soils these elements are in a detrital, non-available form; （3） large amounts of Fe, Mn, Cu, Zn, Pb, Cd, Bi, Cr, Ni, Co and As were present in the most bioavailable fractions in all sampling sites as consequence of the oxidation and acidification processes in sulfidic mine wastes;     

Arsenic in iron cements developed within tailings of a former metalliferous mine—Enguialès,Aveyron, France

Arsenopyrite-rich waste from a former metalliferous mine were spread out over the sloping side of a deep valley after processing. Over the past 30 a, they have been subjected to rainfall and acid water originating from the abandoned mine galleries. This intensive leaching has led to the formation of thin layers of As–Fe crusts on the tailings surface acting as a cement. X-ray diffraction and SEM coupled with EDS determined that jarosite was present in all mineral samples and could contain a small amount of As (∼5.7 wt.%). In addition EMPA and Raman microspectroscopy characterised the presence of amorphous As(V) Fe hydrates as well as rare arsenate minerals (e.g. scorodite). Raman microspectroscopy in particular identified a preponderance of goethite or hematite within the mineral framework of the tailings materials that is likely to sorb recalcitrant As species. The characterisation of the components of the tailings enable the identification of their evolution, shows the progressive decrease of their As-content and emphasises the consequences of the temporary trapping of As in the very acidic and oxidising conditions prevailing in such environments. Resinous amorphous material was identified as the richest in As with As ∼17.1 wt.%. This material evolved toward more crystallised phases (e.g. goethite, jarosite) which contained less As (3.2 wt.%<As <5.7 wt.%). Paragenesis showed the progressive release of As with the crystallisation evolution of the As-trapping material.     

Aquatic chemistry of the Rudnaja River affected by mine tailings and processing plants

In the bed of the Rudnaja River( Primorye, Russia) the influents of the polymetallic mine tailings and processing factories affected the river water chemistry, especially heavy metal concentrations. Decreasing of production in the last 10–15 years was re…     

Sulphur source and genesis of polymetallic sulphide occurrences of the Ofoten district in the Central–North Norwegian Caledonides: evidence from sulphur isotopic studies

Fourteen stratiform, stratabound and vein-type sulphide occurrences in the Upper Allochthon of the Central–North Norwegian Caledonides have been studied for their sulphur, oxygen and hydrogen isotope composition. Depositional ages of host rocks to the stratabound and stratiform sulphide occurrences range from 590 to 640?Ma. The sulphides and their host rocks have been affected by polyphase deformation and metamorphism with a peak temperature of 650?°C dated to 432?Ma. A total of 104 sulphide and 2 barite samples were analysed for δ³⁴S, 16 whole-rock and quartz samples for δ¹⁸O and 12 samples of muscovite for δD. The overall δ³⁴S values range from ?14 to +31‰ with the majority of sampled sulphides lying within a range of +4 to +15‰. In most cases δ³⁴S within each hand specimen behaves in accordance with the equilibrium fractionation sequence, δ³⁴S_gn<δ³⁴S_cp<δ³⁴S_sph<δ³⁴S_py. A systematic increase in δ³⁴S from the vein sulphides (?8‰) through schist/amphibolite-hosted (+6‰) and schist-hosted (+7 to +12‰) to dolomite-hosted (+12 to +31‰) occurrences is documented. The δ³⁴S averages of the stratiform schist-hosted sulphides are 17 to 22‰ lower than in the penecontemporaneous seawater sulphate. The Bjørkåsen (+4 to +6‰) occurrence is a volcanogenic massive sulphide (VMS) transitional to sedimentary massive sulphide (SMS), exhalative, massive, pyritic deposit of Cu–Zn–Pb sulphides formed by fluids which obtained H₂S via high-temperature reduction of seawater sulphate by oxidation of Fe²⁺ during the convective circulation of seawater through underlying rock sequences. The Raudvatn, volcanic-hosted, disseminated Cu sulphides (+6 to +8‰) obtained sulphur via a similar process. The Balsnes, stratiform, ‘black schist’-hosted, pyrite–pyrrhotite occurrence (?6 to ?14‰) is represented by typical diagenetic sulphides precipitated via bacteriogenic reduction of coeval (ca. 600?Ma) seawater sulphate (+25 to +35‰) in a system open to sulphate supply. The δ³⁴S values of the Djupvik–Skårnesdalen (+7 to +12‰), Hammerfjell (+5 to 11‰), Kaldådalen (+10 to +12‰) and Njallavarre (+7 to +8‰) stratiform, schist-hosted, massive and disseminated Zn–Pb (±Cu) sulphide occurrences, as well as the stratabound, quartzite-hosted, Au-bearing arsenopyrite occurrence at Langvatnet (+7 to +11‰), suggest that thermochemically reduced connate seawater sulphate was a principal sulphur source. The Sinklien and Tårstad, stratabound, dolomite- and dolomite collapse breccia-hosted, Zn (±Cu–Pb) sulphides are marked by the highest enrichment in ³⁴S (+20 to +31‰). The occurrences ?are?assigned to the Mississippi-Valley-type deposits.?High δ³⁴S values require reduction/replacement of contemporaneous (ca. 590?Ma) evaporitic sulphate (+23 to +34‰) with C_org-rich fluids in a closed system. The Melkedalen (+12 to +15‰), stratabound, fault-controlled, Cu–Zn sulphide deposit is hosted by the ca. 595?Ma dolomitised Melkedalen marble. The deposit is composed of several generations of ore minerals which formed by replacement of host dolomite. Polyphase hydrothermal fluids were introduced during several reactivation episodes of the fault zone. The positive δ³⁴S values with a very limited fractionation (<3‰) are indicative of the sulphide-sulphur generated through abiological, thermochemical reduction of seawater sulphate by organic material. The vein-type Cu (±Au–W) occurrences at Baugefjell, Bugtedalen and Baugevatn (?8 to ?4‰) are of hydrothermal origin and obtained their sulphur from igneous sources with a possible incorporation of sedimentary/diagenetic sulphides. In a broad sense, all the stratiform/stratabound, sediment-hosted, sulphide occurrences studied formed by epigenetic fluids within two probable scenarios which may be applicable separately or interactively: (1) expulsion of hot metal-bearing connate waters from deeper parts of sedimentary basins prior to nappe translation (late diagenetic/catagenetic/epigenetic fluids) or (2) tectonically driven expulsion in the course of nappe translation (early metamorphic fluids). A combination of (1) and (2) is favoured for the stratabound, fault-controlled, Melkedalen and Langvatnet occurrences, whereas the rest are considered to have formed within option (1). The sulphides and their host rocks were transported from unknown distances and thrust on to the Fennoscandian Shield during the course of the Caledonian orogeny. The displaced/allochthonous nature of the Ofoten Cu–Pb–Zn ‘metallogenetic province’ would explain the enigmatically high concentration of small-scale Cu–Pb–Zn deposits that occur only in this particular area of the Norwegian Caledonides.     

Estimation of potential pollution from mine tailings in the San Pedro River (1993–2005), Mexico–US border

The San Pedro River (SPR) is located in northern Sonora (Mexico) and southeastern Arizona (USA). SPR is a transboundary river that develops along the Sonora (Mexico) and Arizona (USA) border, and is considered the main source of water for a variety of users (human settlements, agriculture, livestock, and industry). The SPR originates in the historic Cananea mining area, which hosts some of the most important copper mineralizations in Mexico. Acid mine drainage derived from mine tailings is currently reaching a tributary of the SPR near Cananea City, resulting in the contamination of the SPR with heavy metals and sulfates in water and sediments. This study documents the accumulation and distribution of heavy metals in surface water along a segment of the SPR from 1993 to 2005. Total concentrations of Cd, Cu, Fe, Mn, Pb, and Zn in surface waters are above maximum permissible levels in sampling sites near mine tailing deposits. Nevertheless, a significant decrease in the Fe and SO₄ ²⁻ in surface water (SO₄ ²⁻: 7,180–460.39 mg/L; Fe: 1,600–9.51 mg/L) as well as a gradual decrease in the heavy and transition metal content were observed during the period from 1994 to 2005. Approximately 2.3 km downstream of the mine tailings, the heavy metal content of the water drops quickly following an increase in pH values due to the discharging of wastewater into the river. The attenuation of the heavy metal content in surface waters is related to stream sediment precipitation (accompanied by metal coprecipitation and sorption) and water dilution. Determining the heavy metal concentration led to the conclusion that the Cananea mining area and the San Pedro River are ecosystems that are impacted by the mining industry and by untreated wastewater discharges arising from the city of Cananea (Sonora, Mexico).