Soil Cd,Cu, Pb and Zn contaminants around Mount Isa city,Queensland, Australia: Potential sources and risks to human health

This article investigates the relationship between soil Cd, Cu, Pb and Zn contaminants and the location and activities of the Pb–Zn–Ag and Cu mines at Mount Isa, Queensland, Australia. Analysis of the data focuses primarily on soil Pb distributions and concentrations because of their potential impact on children’s health. The Xstrata Mount Isa Mines lease (XMIM) is Australia’s leading emitter of numerous contaminants to the environment, including Cu and Pb, and the mining-related activities have been linked causally to the findings of a 2008 study that showed 11.3% of local children (12–60 months) have blood Pb levels >10 μg/dL. Queensland government authorities and Xstrata Mount Isa Mines Pty Ltd maintain that contaminants within environmental systems around Mount Isa are largely the result of near-surface mineralization. The evidence for whether the contamination is derived from XMIM or other possible sources, such as the natural weathering of ore-rich bedrock, is investigated using data from surface and subsurface soil chemistry, atmospheric modelling of metal contaminants from mining and smelting operations and local geological and associated geochemical studies. Sixty surface soil samples collected from sites adjacent to houses, parks and schools throughout Mount Isa city were analyzed for their total extractable Cd, Cu, Pb and Zn concentrations in the <2 mm to >180 μm (coarser) and <180 μm (finer) grain size fractions. Concentrations in the finer size fraction reveal a range of values: Cd – 0.7–12.5 ppm; Cu – 31–12,100 ppm; Pb – 8–5770 ppm; Zn – 26–11,100 ppm, with several samples exceeding Australian residential health investigation guidelines. Spatial analysis shows that surface soil metal concentrations are significantly higher within 2 km of XMIM compared to more distant samples, and that more than 1000 property lots are at risk of having detrimentally high soil Pb levels. Determination of metal concentrations in 49 samples from eight soil pits shows that surface samples (0–2 cm) are enriched significantly relative to those at depth (10–20 cm), suggesting an atmospheric depositional origin. AUSPLUME air dispersal modelling of Pb originating from the Cu and Pb smelter stacks and mine site fugitive sources confirms that Pb is deposited across the urban area, during periods of the year (∼20%/a) when the wind blows from the direction of XMIM towards the urban area and disperses dusts from the uncovered spoil and road surfaces, as well as from stack emission sources. Although there are some spatially restricted outcrops of Pb close to the surface in parts of the urban area, the Cu-ore body is ∼244 m below the surface. However, enriched and significantly correlated surface soil concentrations of Cu and Pb (Pearson correlation 0.879, p = 0.000) in and around the urban area of Mount Isa can only be explained by atmospheric transport and deposition of metals from the adjoining mining and smelting operations. The results from this study provide unequivocal evidence that both historic and ongoing emissions from XMIM are contaminating the urban environment. Given the ongoing Pb poisoning issues in Mount Isa children, it is clear that remediation, reductions in mine emissions and more stringent regulatory actions are warranted.     

Trace and rare-earth element behaviors during alteration and mineralization in the Attepe iron deposits (Feke-Adana,southern Turkey)

Hydrothermal-metasomatic iron ores consisting mainly of siderite, ankerite and hematite are located in the Lower–Middle Cambrian limestone marbles of the Eastern Taurus Belt. The siderite, ankerite, hematite and host rock samples from the deposits have been investigated for major, trace, and rare-earth elements (REE) to evaluate the element mobility and mass transfer during fluid–rock interactions.     

Origin and evolution of formation water at the Jujo–Tecominoacán oil reservoir,Gulf of Mexico. Part 1: Chemical evolution and water–rock interaction

The origin and evolution of formation water from Upper Jurassic to Upper Cretaceous mudstone–packstone–dolomite host rocks at the Jujo–Tecominoacán oil reservoir, located onshore in SE-Mexico at a depth from 5200 to 6200 m.b.s.l., have been investigated, using detailed water geochemistry from 12 producer wells and six closed wells, and related host rock mineralogy. Saline waters of Cl–Na type with total dissolved solids from 10 to 23 g/L are chemically distinct from hypersaline Cl–Ca–Na and Cl–Na–Ca type waters with TDS between 181 and 385 g/L. Bromine/Cl and Br/Na ratios suggest the subaerial evaporation of seawater beyond halite precipitation to explain the extreme hypersaline components, while less saline samples were formed by mixing of high salinity end members with surface-derived, low salinity water components. The dissolution of evaporites from adjacent salt domes has little impact on present formation water composition. Geochemical simulations with Harvie-Mφller-Weare and PHRQPITZ thermodynamic data sets suggest secondary fluid enrichment in Ca, HCO₃ and Sr by water–rock interaction. The volumetric mass balance between Ca enrichment and Mg depletion confirms dolomitization as the major alteration process. Potassium/Cl ratios below evaporation trajectory are attributed to minor precipitation of K feldspar and illitization without evidence for albitization at the Jujo–Tecominoacán reservoir. The abundance of secondary dolomite, illite and pyrite in drilling cores from reservoir host rock reconfirms the observed water–rock exchange processes. Sulfate concentrations are controlled by anhydrite solubility as indicated by positive SI-values, although anhydrite deposition is limited throughout the lithological reservoir column. The chemical variety of produced water at the Jujo–Tecominoacán oil field is related to a sequence of primary and secondary processes, including infiltration of evaporated seawater and original meteoric fluids, the subsequent mixing of different water types and the formation of secondary minerals by water–rock interaction. A best fit between measured and calculated reservoir temperatures was obtained with the Mg–Li geothermometer for high salinity formation water (TDS > 180 g/L), whereas Na–K, Na–Ka–Ca and quartz geothermometers are partially applicable for less salinite water (TDS < 23 g/L).     

The cycling of Ni,Zn, Cu in the system “mine tailings–ground water–plants”: A case study

The comparative behaviour of Ni, Cu and Zn in the system “mine tailings–ground water–plants” has been investigated at the Ni–Cu mine site operated by INCO Ltd. Thompson Operations, Thompson, Manitoba. Oxidation of sulphide minerals causes the release of metals from exposed tailings containing Ni ∼2000 ppm, Cu ∼150 ppm and Zn ∼100 ppm to the ground water, which contains 350 mg/L Ni, 0.007 mg/L Cu, and 1.6 mg/L Zn. The metal concentration in the ground water is affected by the relative proportions of sulfide minerals, the rate of oxidation of sulphide minerals (Ni-bearing pyrrhotite > sphalerite > chalcopyrite), and the affinity of the metals for secondary Fe-phases (Ni > Zn > Cu).     

Effects of long-term irrigation with treated wastewater. Part II: Role of organic carbon on Cu,Pb and Cr behaviour

The long-term impact of irrigation on a Mediterranean sandy soil irrigated with treated wastewater (TWW) since 1980 was evaluated. The main soil properties (CEC, pH, size distribution, exchangeable cations and chloride, hydraulic conductivity) as well as the organic matter and Cu, Cr and Pb speciation in an irrigated soil and a non-irrigated control soil at various soil depths were monitored and compared during a 2 year experiment. In this second part, we focused on Cu, Cr and Pb behaviour in relation with soil organic carbon (SOC). Soil samples were collected every 3 months during 2 years at the depths 0–20, 20–40 and 40–60 cm and were analysed for exchangeable and total metals, organic carbon content, metal sequential extraction and humic substances – Humic Acids (HA), Fulvic Acids (FA) and Non-Humified Fraction (NHF). Long-term irrigation with a domestic treated wastewater (TWW) may be considered safe with regard to trace metal accumulation in soil. Irrigation lowered the HA and NHF fractions of SOC and made the FA fraction more mobile. Cu bound preferentially to the SOC fraction, Cr was found mainly in the reducible fraction and Pb was bound to all fractions indiscriminately. Cu exhibited a high affinity for the HA fraction, while Pb and Cr had a high affinity for the FA fraction, which indicates a greater mobility of the organically-bound Pb and Cr than of the organically-bound Cu. Evaluation of the potential metal mobility has to take into account not only the usual speciation between labile, reducible and oxidisable fractions, but also the nature of the SOC responsible for the oxidisable fraction.     

Pyrrhotite Re–Os and SHRIMP zircon U–Pb dating of the Hongqiling Ni–Cu sulfide deposits in Northeast China

The Hongqiling (HQL) magmatic Ni–Cu sulfide deposits (Jilin Province, NE China) are located at the southern margin of the eastern Xing'an–Mongolian Orogenic Belt (XMOB) of the eastern Central Asian orogenic belt (CAOB), situated between the Siberian Craton (SC) and the North China Craton (NCC). The HQL ore-bearing mafic–ultramafic intrusions intrude into the metamorphic rocks of the lowermost Huangyingtun Formation of the Hulan Group (HLG), whose lithology is herein identified as a hornblende–zoisite gneiss. SHRIMP zircon U–Pb dating for the HLG, country rock of the HQL deposits, indicated a maximum deposition age of 272.2 ± 4.3 Ma (95% confidence level, MSWD = 2.6, n = 14).Six pyrrhotite samples separated from massive Ni–Cu sulfide ores of the Fujia (No. 7) deposit yielded a Re–Os isotopic isochron age of 208 ± 21 Ma (95% confidence level, MSWD = 2.4, n = 6), indicating that the ore-formation age was Late Triassic. Re–Os isotope analyses showed an initial ¹⁸⁷Os/¹⁸⁸Os ratio of 0.315 ± 0.050. The γ_Os values ranged from + 137 to + 161 with an average of + 151, indicating that its ore-forming materials were mainly derived from mantle with possibly < 30% crustal Os contamination. Large scale magmatic Ni–Cu mineralization in eastern Jilin occurred in post-collisional tectonic setting in the Late Triassic.Our new results suggest that the ages of the Ni–Cu sulfide deposits in the CAOB within China tended to become younger from west to east, as manifested by the Late Caledonian (~ 440 Ma), through the Late Hercynian (300–265 Ma) to the Late Indosinian (225–200 Ma). Such variation could reflect the gradual closure and post-collisional orogeny between the SC and the NCC from west to east.     

Porphyry and skarn Au–Cu deposits in the Shizishan orefield, Tongling, East China: U–Pb dating and in-situ Hf isotope analysis of zircons and petrogenesis of associated granitoids

The magnetite-series (I-type) calc-alkaline granitoid suit, ranging from pyroxene monzodiorite to granodiorite, is associated with the porphyry and skarn gold–copper deposits at the Shizishan orefield in Tongling district, Anhui Province. In-situ U–Pb dating and Hf isotope analysis of magmatic and inherited zircons are combined with whole rock Sr–Nd–Pb isotopic data and mineral thermobarometry to interpret the petrogenesis. The magmatic zircons from the quartz monzodiorites yield weighted average ²⁰⁶Pb/²³⁸U ages of ca. 139 Ma and mean ε_Hf(t) value of −19.8 ± 3.9 (1σ), while those from the pyroxene monzodiorite show a similar mean age but notably higher mean ε_Hf(t) value (−8.5 ± 1.4). The inherited zircons from the quartz monzodiorite yield ages of 0.8, 2.0 and 2.4 Ga with mean ε_Hf(t) value of −2.9 ± 1.4, while those from the pyroxene monzodiorite show younger ages (165 to 245 Ma) but similar mean ε_Hf(t) value (−5.6 ± 4.5). Whole rock Sr–Nd–Pb isotope data indicate that crustal material significantly contributed to the magma. Mineral thermobarometry results reveal that the depths of the discrete magma chambers were about 23 km, and 10 to 2 km deep.The data above combined with previous studies suggest that: 1) The magma emplacement and crystallization (typically for zircons) mainly occurred at about 139 Ma, consistent with the age of mineralization; 2) The primary pyroxene monzodioritic magma might have mixed with the magma produced by partial melting of the Yangtze lower crust, and accumulated in the magma chamber at ca. 23 km deep in the lower crust level; 3) AFC and magma mixing were the dominate processes for the magmatic evolutions at shallow level (2 to 10 km), where the circumstances were favorable for mineralization.     

The baryte-bearing beryl-phosphate pegmatite Plössberg—A missing link between pegmatitic and vein-type barium mineralization in NE Bavaria, Germany

Pegmatites and aplites enriched in P, Be, Nb, Ta and Li occur in the high-temperature metamorphic lithological units of the NE Bavarian Basement, SE Germany. They are accompanied by Ba mineralization, in vein-type deposits in the basement as well as in its foreland. Locally, Ba minerals are encountered in the late Variscan pegmatites and aplites too. The shallow discordant stock-like pegmatites (Hagendorf-type) are barren as to Ba, but in the tabular, concordant aplites and pegmatites Ba was concentrated (Plössberg-type). These concordant pegmatites and aplites are supposed to be the root zone of the intrusive pegmatites. In the rare case of low sulfur fugacity, Ba forms Ba–Zr–K–Sc phosphates/silicates in the pegmatites (transition of magmatic into the hydrothermal stages I/II). Under high sulfur fugacity, Ba is accommodated within the same stages in the structure of baryte. Barium is not accommodated in the lattice of phosphates during or in the immediate aftermaths of the emplacement of these Be–P–Nb–Ta pegmatites (stage III). This element shows up again in APS minerals during supergene alteration under acidic conditions (stage IV). Considering the host rocks of baryte mineralization, the Sr contents of baryte increased from the early Paleozoic to the Late Triassic. The Sr contents of baryte are a function of the depth below ground in the vein-type deposits and in the shear-zones bounding the tabular concordant pegmatites. Beryl is not only a marker mineral for the shear-zone-hosted pegmatites but can also be used as a tool for the geodynamic positioning of these pegmatites using its oxygen isotopes. A subdivision of the pegmatites into intrusive and shear-zone hosted may be achieved by its REE and minor elements.     

Structural features and metallogenesis of the Carlin-type Jinfeng (Lannigou) gold deposit, Guizhou Province, China

Jinfeng, previously known as Lannigou, is the largest Carlin-type gold deposit in the Yunnan–Guizhou–Guangxi region in southwestern China. Gold mineralization in the Jinfeng deposit is almost entirely fault-hosted and structurally controlled, with very little disseminated ore occurring in the adjacent host rocks. The structural elements in the Jinfeng deposit can be subdivided into 3 groups comprising NS-, NW-, and NE-striking faults and folds, with NW-striking structures controlling the overall framework of the deposit. Four tectonic stages have been recorded in the Jinfeng area, i.e., rifting, orogenic compression, lateral transpression, and lithospheric extension. A series of contemporaneous normal faults, such as the N-striking and east-dipping F1 and F7 faults developed along the edges of a carbonate platform during basin rifting (D₂–T₂). These structures provided an initial framework for subsequent basin evolution, and also represent the principal hydrothermal conduits. A gradual change of the compression direction during the orogenic stage (T₃) from E→W to NE→SW, gave rise to the NW-striking structures, including large, tight to overturned folds such as the Huangchanggou synclinorium and associated thrusts such as the F3 fault. The development of these orogenic, predominantly NE-dipping structures, as well as accompanying NE-striking dextral shear and transform faults (such as the F2 fault) along the margin of the Laizishan Dome established the structural pattern of the deposit area. The NW-striking folds were refolded by NE-striking superimposed folds during post-collisional lateral transpression (J₁) and NW–SE directed compression. Oblique stress distribution gave rise to NS-trending compression and EW-trending extension, with dilational zones developing at the intersection of the F2 and the F3 faults east of the Laizishan dome. It is these dextral- and sinistral-normal dilational zones in which gold was precipitated during the main ore-forming event at Jinfeng. Following the main ore stage lithospheric extension occurred during the Yanshan stage (J₂–K) resulting in minor reverse faults that in places cut pre-existing structures. The above four main structural deformation stages mirror the evolution of the Youjiang Basin from inception to basin inversion and post-orogenic collapse and renewed extension. Significant gold metallogenesis at Jinfeng occurred during the transition from collisional compression to extensional tectonics in the early Jurassic, and is focussed into intersections of F2 and F3 and fault splays adjacent to F3. This structurally controlled gold metallogenic model is likely to be applicable to analogous settings elsewhere in the Yunnan–Guizhou–Guangxi triangle area, and has implications for the targeting of Carlin-type gold mineralization in this region.     

Geochronological and geochemical constraints on the petrogenesis of high-K granite from the Suffi abad area, Sanandaj-Sirjan Zone, NW Iran

The Sanandaj-Sirjan Zone (SSZ) trends northwestward in western Iran on the Precambrian to Paleozoic basement and exposes abundant I-type granitoids and calc-alkaline volcanic rocks that were most active during the Late Jurassic to Upper Cretaceous. The petrogenesis of the granitoids and associated volcanic rocks has been widely related to Neotethyan subduction beneath the Iranian plate. We report a geochronological and geochemical study of the Suffi abad granite (SLG) body that crops outs southeast of Sanandaj within the SSZ and is mainly composed of K-feldspar + quartz + plagioclase ± hornblende. The SLG, which shows a high-K calc-alkaline affinity, has LA-ICPMS zircon U–Pb ages ranging between 149 ± 2 and 144 ± 3 Ma and initial ⁸⁷Sr/⁸⁶Sr of ∼0.7024–0.7069 and ¹⁴³Nd/¹⁴⁴Nd of ∼0.5125–0.5127. These value correspond to an ?_Nd (145 Ma) of +1.5 and +4.9, suggesting that the SLG originated from the juvenile crust or depleted mantle with a young T_DM (650–900 Ma) over the subduction zone beneath the SSZ. Zircon saturation temperatures suggest that crystallization of the zircons, or emplacement of the host magmas, occurred at 560–750 °C, consistent with an intergrowth texture of K-feldspar and quartz that implies crystallization around the K-feldspar-quartz eutectic at lower temperatures. Overall, geochemical data suggest that crystallization of the hornblende and plagioclase played a role in magma differentiation. These data allow us to conclude that the high-K SLG did not originate directly from the juvenile mantle source as do most I-type, calc-alkaline granitoids, but more likely was produced from the partial melting of pre-existing I-type granitoids in the upper continental crust under low pressure conditions.     

Alteration and primary geochemical dispersion associated with the Bulletin lode-gold deposit, Wiluna, Western Australia

The Bulletin lode-gold deposit is within the northernmost part of the Norseman–Wiluna greenstone belt in the Archaean Yilgarn Block, Western Australia. It is located within a brittle–ductile shear zone and hosted by tholeiitic metavolcanic rocks. Syn-metamorphic wallrock alteration envelops the gold mineralisation and is pervasive throughout the entire shear zone and extends up to 150 m into the undeformed wallrocks. Alteration is characterised by the sequence of distal chlorite–calcite, intermediate calcite–dolomite, outer proximal sericite and inner proximal dolomite–sericite zones. The thickness of the alteration envelope, and the occurrence of dolomite in the alteration sequence, can be used as a rough guide to the width, extent and grade of gold mineralisation, because a positive correlation exists between these variables. Mass transfer evaluations indicate that chemical changes related to the wallrock alteration are similar in all host rocks: in general, Ag, As, Au, Ba, CO₂, K, Rb, S, Sb, Te and W are enriched, Na and Y are depleted, and Al, Cr, Cu, Fe, Mg, Mn, Nb, Ni, P, Se, V, Zn and Zr are immobile, while Ca, Si and Sr show only minor or negligible relative changes. The degree of mobility of each component increases with proximity to gold mineralisation. The largest potential exploration targets are possibly defined by regional As (>6 ppm) and Sb (>0.6 ppm) anomalies. These anomalies, if real, extend laterally for >150 m from the mineralised shear zone into areas of apparently unaltered rocks. Anomalies defined by Te (>10 ppb), W (>0.6 ppm), carbonation indices, local enrichment of Sb (>2.0 ppm) and As (>28 ppm), and potassic alteration indices also form significant exploration targets extending beyond the HJB shear zone and the Au anomaly (>6 ppb) and, locally, into apparently unaltered rock. Gold, itself, has a restricted dispersion, with an anomaly extending for 1–35 m from ore, and being restricted to within the shear zone itself. Amongst individual geochemical parameters, only As and Sb define significant, consistent and smooth trends (vectors) when laterally approaching the ore. However, the respective dimensions of individual geochemical anomalies can be used as an extensive, though stepwise, vector towards ore.     

Relationship between CO2-dominated fluids,hydrothermal alterations and gold mineralization in the Red Lake greenstone belt,Canada

The Red Lake greenstone belt is one of the foremost Au mining camps in Canada and hosts the world-class Campbell-Red Lake Au deposit. Belt-scale hydrothermal alteration is characterized by proximal ferroan dolomite zones associated with Au mineralization surrounded by distal calcite zones, both being accompanied by potassic alterations (sericite, muscovite, and biotite). At the Campbell-Red Lake and Cochenour deposits Au mineralization (in particular high-grade ore) is associated with silica and sulfides (especially arsenopyrite) that replace carbonate ± quartz veins and the host rocks. The prevalence of carbonic fluid inclusions and rare occurrence of aqueous-bearing inclusions in carbonate–quartz–Au veins in the Campbell-Red Lake deposit, and the consistency of homogenization temperatures of carbonic inclusions within individual fluid inclusion assemblages (FIA), have been interpreted to indicate that H₂O-poor, CO₂-dominated fluids were responsible for the carbonate veining and Au mineralization. Further studies of fluid inclusions in carbonate–quartz veins within and outside the deformation zone hosting the Campbell-Red Lake deposit (the Red Lake Mine trend) including the Cochenour Au deposit, the Redcon Au prospect, and outcrops in the distal calcite zone also reveal the dominance of carbonic fluid inclusions in vein minerals. These studies indicate that CO₂-dominated fluids were flowing through fractures during carbonate vein formation and Au mineralization both within and outside major structures. The carbonic fluid may have been initially undersaturated with water, or it may have resulted from phase separation of an H₂O–CO₂–NaCl fluid. In the latter case, phase separation modeling indicates that the initial fluid likely had XCO₂${\text{X}}_{{\text{CO}}_2}$ values larger than 0.8. Calculations based on hydrothermal mineral assemblages indicate XCO₂${\text{X}}_{{\text{CO}}_2}$ values in the host rocks from 0.025 to 0.85, reflecting a change from CO₂-dominated fluids in the fractures (veins) to H₂O-dominated fluids in the host rocks away from the fractures. The CO₂-dominated fluids were likely advected from granulite facies in the deeper crust, whereas the H₂O-dominated fluids were derived from the ambient host rocks of amphibole to greenschist facies. Calculations based on CO₂ requirements and source constraints indicate that the mineralizing fluids were likely two orders of magnitude more enriched in Au than the commonly assumed values of a few μg/L, which may explain why the Campbell-Red Lake deposit has a very high-grade of Au (average 21 g/t for the whole deposit and 81 g/t for the Goldcorp High-Grade zone). Fluid inclusion data suggest that the carbonate veining and Au mineralization likely took place at depths from 7 to 14 km. The development of crustiform–colloform structures in the carbonate ± quartz veins, which was previously interpreted to indicate relatively shallow environments, may alternatively have been related to extremely high fluid pressures and the CO₂-dominated nature of the fluids, which could have enhanced the brittle properties of the rocks due to their high wetting angles.     

The Basil Cu–Co deposit,Eastern Arunta Region,Northern Territory,Australia: A metamorphosed volcanic-hosted massive sulphide deposit

The Basil Cu–Co deposit, Harts Range, central Australia, is hosted by the Riddock Amphibolite, a sequence that has been metamorphosed at upper-amphibolite- to granulite-facies conditions at 480–460 Ma (Larapinta Event), and subsequently reworked at amphibolite-facies conditions (450–300 Ma). As a result, many of the primary mineralization textures and other features that could characterise ore genesis have been obliterated. However, preserved textures and mineral relationships in the mineralized zone, allow some constraints to be placed on the genetic history of the deposit using mineralogical, petrographic and geochemical studies of host rocks and sulphides.Results of this study permit at least two genetic models to be ruled out. Firstly, whole rock geochemistry and garnet compositions suggest that the deposit is not a skarn system. Secondly, the lack of any significant Ni-signature, and the presence of abundant zircons in the host amphibolite (indicating that not all host rocks are mafic in composition and/or magmatic in character), make an orthomagmatic Ni–Cu–(PGE) system unlikely. Alternatively, Basil is assigned to a volcanic-hosted massive sulphide (VHMS)-style of mineralization, formed on the seafloor, within basaltic and sedimentary host rocks, typical of deposits occurring in such settings. The lack of a recognisable hydrothermal alteration zone is consistent with either destruction of the alteration zone during metamorphism or detachment of the ore from alteration during later deformation.The occurrence of sulphide inclusions within garnet and amphibole indicates that the sulphides must be syn-metamorphic or earlier. Partitioning of trace elements between pyrite and co-existing pyrrhotite suggests that (re)crystallization occurred under equilibrium conditions. The composition of sphalerite coexisting with pyrite and pyrrhotite indicates crystallization at pressures of at least 10 kbar, consistent with peak metamorphism during the Early Ordovician Larapinta Event. Zr-in-titanite geothermometry indicates peak temperatures of 730–745 °C.     

Mode of occurrence and environmental mobility of oil-field radioactive material at US Geological Survey research site B,Osage-Skiatook Project,northeastern Oklahoma

Two samples of produced-water collected from a storage tank at US Geological Survey research site B, near Skiatook Lake in northeastern Oklahoma, have activity concentrations of dissolved ²²⁶Ra and ²²⁸Ra that are about 1500 disintegrations/min/L (dpm/L). Produced-water also contains minor amounts of small (5–50 μm) suspended grains of Ra-bearing BaSO₄ (barite). Precipitation of radioactive barite scale in the storage tank is probably hindered by low concentrations of dissolved SO₄ (2.5 mg/L) in the produced-water. Sediments in a storage pit used to temporarily collect releases of produced-water have marginally elevated concentrations of “excess” Ra (several dpm/g), that are 15–65% above natural background values. Tank and pit waters are chemically oversaturated with barite, and some small (2–20 μm) barite grains observed in the pit sediments could be transferred from the tank or formed in place. Measurements of the concentrations of Ba and excess Ra isotopes in the pit sediments show variations with depth that are consistent with relatively uniform deposition and progressive burial of an insoluble Ra-bearing host (barite?). The short-lived ²²⁸Ra isotope (half-life = 5.76 a) shows greater reductions with depth than ²²⁶Ra (half-life = 1600 a), that are likely explained by radioactive decay. The ²²⁸Ra/²²⁶Ra activity ratio of excess Ra in uppermost pit sediments (1.13–1.17) is close to the ratio measured in the samples of produced-water (0.97, 1.14). Declines in Ra activity ratio (excess) with sediment depth can be used to estimate an average rate of burial of 4 cm/a for the Ra-bearing contaminant. Local shallow ground waters contaminated with NaCl from produced-water have low dissolved Ra (<20 dpm/L) and also are oversaturated with barite. Barite is a highly insoluble Ra host that probably limits the environmental mobility of Ra at site B.     

Delineation of mineralization zones in porphyry Cu deposits by fractal concentration–volume modeling

The purpose of this study was to identify the various mineralization zones especially supergene enrichment and hypogene in two different Iranian porphyry Cu deposits, based on subsurface data and by using the proposed concentration–volume (C–V) fractal method. The Sungun and Chah-Firuzeh porphyry Cu deposits, which are situated in NW and SE Iran, respectively, were selected for this study. Straight lines fitted through log–log plots showing C–V relations for Cu were employed to separate supergene enrichment and hypogene zones from oxidation zones and barren host rocks in the two deposits and to distinguish a skarn mineralized zone from the hypogene zone in Sungun deposit. In the proposed C–V fractal method, the identification of mineralization zones is based on power–law relationships between Cu concentrations and the volume of rocks hosting porphyry Cu mineralization. Separate subsurface data from the two deposits were analyzed by C–V fractal method and the results have been compared with geological models which included alteration and mineralogical models. The comparison shows that the interpreted zones based on the C–V fractal method are consistent with the geological models. The proposed C–V method is a new approach to defining zones in a mineral deposit and there was no commercial software available to perform the relevant calculations; therefore, a fractal concentration–volume (FCV) software was designed by the authors to achieve this goal.     

Problems of geodynamics, tectonics, and metallogeny of orogens

This is an overview of papers published in the present volume of Russian Geology and Geophysics (Geologiya i Geofizika), a special issue that covers presentations at the International Conference “Geodynamic Evolution, Tectonics, and Metallogeny of Orogens”, held on 28–30 June 2010 in Novosibirsk (http://altay2010.igm.nsc.ru). The workshop concerned the general evolution of the Central Asian orogenic system, with a special focus on continental growth, history of oceans and continental margins, and role of plumes in accretionary-collisional tectonics and metallogeny. The discussed papers are grouped in three sections: 1. General issues of geodynamics and geodynamic evolution; 2. Role of mantle plumes in tectonics, magmatism, and metallogeny; 3. Regional tectonic and geodynamic problems of Asia.The synthesis of data reported at the workshop demonstrates critical importance of mantle plumes for the evolution of the Paleoasian ocean and for orogenic processes in Central Asia.In addition to three large pulses of continental growth at about 2900–2700, 1900–1700, and 900–700 Ma, three orogenic stages have been distinguished in the geological history of Eurasia: Late Cambrian–Ordovician (510–470 Ma), Late Devonian–Early Carboniferous (380–320 Ma), and Permian–Triassic (285–230 Ma). In the evolution of the Central Asian orogen, these stages were associated with events of ultramafic-mafic and bimodal plume magmatism which promoted translithospheric strike-slip faulting. Plume magmatism was an active agent in ocean opening when the Paleotethys, Ural, Ob–Zaisan, and Turkestan basins appeared while the Late Cambrian–Ordovician orogen was forming in Central Asia (North Kazakhstan, Altai–Sayan, Tuva, and Baikal areas). Closure of the Ob–Zaisan ocean and collision of the Kazakhstan–Baikal continent with Siberia in the Late Devonian–Early Carboniferous was coeval with the maximum opening of the Turkestan ocean, possibly, as a consequence of plume activity. The Tarim (285–275 Ma) and Siberian (250–230 Ma) superplume events corresponded in time to closure of the Ural ocean and opening of the Meso- and Neotethys, as well as to major metallogenic events.     

Constraints on the source of Cu in a submarine magmatic-hydrothermal system,Brothers volcano,Kermadec island arc

Most magmatic-hydrothermal Cu deposits are genetically linked to arc magmas. However, most continental or oceanic arc magmas are barren, and hence new methods have to be developed to distinguish between barren and mineralised arc systems. Source composition, melting conditions, the timing of S saturation and an initial chalcophile element-enrichment represent important parameters that control the potential of a subduction setting to host an economically valuable deposit. Brothers volcano in the Kermadec island arc is one of the best-studied examples of arc-related submarine magmatic-hydrothermal activity. This study, for the first time, compares the chemical and mineralogical composition of the Brothers seafloor massive sulphides and the associated dacitic to rhyolitic lavas that host the hydrothermal system. Incompatible trace element ratios, such as La/Sm and Ce/Pb, indicate that the basaltic melts from L’Esperance volcano may represent a parental analogue to the more evolved Brothers lavas. Copper-rich magmatic sulphides (Cu?>?2 wt%) identified in fresh volcanic glass and phenocryst phases, such as clinopyroxene, plagioclase and Fe–Ti oxide suggest that the surrounding lavas that host the Brothers hydrothermal system represent a potential Cu source for the sulphide ores at the seafloor. Thermodynamic calculations reveal that the Brothers melts reached volatile saturation during their evolution. Melt inclusion data and the occurrence of sulphides along vesicle margins indicate that an exsolving volatile phase extracted Cu from the silicate melt and probably contributed it to the overlying hydrothermal system. Hence, the formation of the Cu-rich seafloor massive sulphides (up to 35.6 wt%) is probably due to the contribution of Cu from a bimodal source including wall rock leaching and magmatic degassing, in a mineralisation style that is hybrid between Cyprus-type volcanic-hosted massive sulphide and subaerial epithermal–porphyry deposits.     

Geochronology and tectonic setting of Pb–Zn–Mo deposits and related igneous rocks in the Yinshan region, Jinzhai, Anhui province, China

The Gaijing Pb–Zn–Mo deposit and Shapinggou Mo deposit in the Yinshan region, Jinzhai, Anhui province, China, are hosted in various granitic intrusions with ⁴⁰Ar/³⁹Ar ages obtained for biotite and hornblende of 136.8 ± 1.6 Ma (medium-grained monzogranite), 130.4 ± 1.2 Ma (fine-grained granite), and 125.4 ± 1.0 Ma (fine-grained diorite). The modes of occurrence and cross-cutting relationships among the igneous intrusions indicate that alkali quartz-syenite and quartz-syenite porphyry (cryptoexplosive breccia) formed later than the calc-alkali monzogranite, granite, and diorite. Molybdenum mineralization occurs in pipe-like bodies hosted in cryptoexplosive breccia (pipe), quartz-syenite (porphyry), monzogranite, and granite, whereas Pb–Zn mineralization occurs in veins distally from the Mo mineralization. The Re–Os isotopic model ages of molybdenite from the Gaijing Pb–Zn–Mo deposit are 112.6 ± 1.3 and 113.5 ± 1.3 Ma, consistent with the ages of other molybdenum deposits throughout the East Qinling–Dabie metallogenic belt. The geological characteristics and isotopic ages of the Gaijing Pb–Zn–Mo and Shapinggou Mo deposits indicate a genetic relationship to the emplacement of the quartz-syenite (porphyry) and to shallow-seated porphyry–cryptoexplosive breccia intrusions. The present results, combined with existing data, suggest that the Pb–Zn–Mo deposits and related igneous rocks were formed in a geodynamic setting of regional lithospheric thinning, delamination, and thermal erosion in East China. The deposits are part of the East Qinling–Dabie molybdenum belt, which in turn is part of a large-scale E–W-trending metallogenic belt in East China.     

Mineralogical and geochemical characteristics of scheelite-bearing skarns,and genetic relations between skarn mineralization and petrogenesis of the associated granitoid pluton at Sargipali,Sundergarh District,Eastern India

Skarn rocks occur at the contact between calcite-bearing dolomitic marbles and granitoids (massive varieties with pegmatites) in close spatial association with the mica schist-hosted Proterozoic Pb–Cu–Ag sulfide deposits at Sargipali, Sundergarh District, Eastern India. The exoskarn (pyroxene–garnet) of variable width (1 to 30 m) occurs in marble proximal to the granitic intrusion, and endoskarn (pyroxene–epidote) is variably developed (< 1 to 10 m). Molybdenum-free scheelite with minor pyrrhotite (0.2%) is found only in late garnet–clinopyroxene exoskarn assemblages.