Different Types Of Deposits Research Articles

Copper isotopes as monitors of redox processes in hydrothermal mineralization

The stable copper isotope composition of 79 samples of primary and secondary copper minerals from hydrothermal veins in the Schwarzwald mining district, South Germany, shows a wide variation in δ 65Cu ranging from −2.92 to 2.41‰. We investigated primary chalcopyrite, various kinds of fahlores and emplectite, as well as supergene native copper, malachite, azurite, cuprite, tenorite, olivenite, pseudomalachite and chrysocolla. Fresh primary Cu(I) ores have at most localities copper isotope ratios ( δ 65Cu values) of 0 ± 0.5‰ despite the fact that the samples come from mineralogically different types of deposits covering an area of about 100 by 50 km and that they formed during three different mineralization events spanning the last 300 Ma. Relics of the primary ores in oxidized samples (i.e., chalcopyrite relics in an iron oxide matrix with an outer malachite coating) display low isotope ratios down to −2.92‰. Secondary Cu(I) minerals such as cuprite have high δ 65Cu values between 0.4 and 1.65‰, whereas secondary Cu(II) minerals such as malachite show a range of values between −1.55 and 2.41‰, but typically have values above +0.5‰. Within single samples, supergene oxidation of fresh chalcopyrite with a δ value of 0‰ causes significant fractionation on the scale of a centimetre between malachite (up to 1.49‰) and relict chalcopyrite (down to −2.92‰). The results show that—with only two notable exceptions—high-temperature hydrothermal processes did not lead to significant and correlatable variations in copper isotope ratios within a large mining district mineralized over a long period of time. Conversely, low-temperature redox processes seriously affect the copper isotope compositions of hydrothermal copper ores. While details of the redox processes are not yet understood, we interpret the range in compositions found in both primary Cu(I) and secondary Cu(II) minerals as a result of two competing controls on the isotope fractionation process: within–fluid control, i.e., the fractionation during the redox process among dissolved species, and fluid–solid control, i.e., fractionation during precipitation involving reactions between dissolved Cu species and minerals. Additionally, Rayleigh fractionation in a closed system may be responsible for some of the spread in isotope compositions. Our study indicates that copper isotope variations may be used to decipher details of natural redox processes and therefore may have some bearing on exploration, evaluation and exploitation of copper deposits. On the other hand, copper isotope analyses of single archeological artefacts or geological or biological objects cannot be easily used as reliable fingerprint for the source of copper, because the variation caused by redox processes within a single deposit is usually much larger than the inter-deposit variation.

Some aspects of the interrelations between magmatism and ore formation: Evidence from oxygen isotope data on ore-magmatic systems, Armenia

The results of oxygen-isotope study of the Kokhb-Shnokh (J3) and Vokhci (N1) intrusive complexes and the related Tekhut and Kadzharan Cu-Mo porphyry deposits of different types, Armenia, were used to discuss the relevant problems of rock and ore genesis and their relationships. It was established that the assimilation of parental mantle basaltic melts by crustal, mainly feldspathic material is a decisive factor in the formation of multiple gabbro-granite complexes. Specifics in the composition and crystallization of the hybrid melt causes the enrichment of the residual melt and hydrothermal fluids in Fe and other elements, in particular, Cu and Mo. The ore-bearing solutions are generated over the solidification time of the melt. They are removed by the hydrothermal system of directionally moving solutions, a process that gives way to a convective-circulation hydrothermal system. A change in the spatial position of the hydrothermal solutions during the formation of the deposit supplies them to different sites, creating a seeming discontinuity in ore deposition, which is observed at many deposits. In fact, the supply of the ore-bearing solutions is continuous process. The ore stage is not a time interval with particular ore-bearing solutions but rather a certain physicochemical state of the solutions attained during their interaction with the environment. This process resulted in the simultaneous precipitation of different mineral assemblages and the asynchronous precipitation of the same assemblages. The formation of deposits of various metals related to a common intrusive complex, as changes in the composition of mineral assemblages, is caused by the influence of various geochemical barriers rather than by compositional variations in the initial hydrothermal solutions.

Reply to comment by F. Molz et al. on “Investigating the Macrodispersion Experiment (MADE) site in Columbus, Mississippi, using a three‐dimensional inverse flow and transport model”

Reply to comment by F. Molz et al. on “Investigating the Macrodispersion Experiment (MADE) site in Columbus, Mississippi, using a three‐dimensional inverse flow and transport model”

Gold in Turkey—a missing link in Tethyan metallogeny

The gold metallogeny of Turkey constitutes a sector of the Tethyan Eurasian Metallogenic Belt (TEMB) within the Alpine–Himalayan orogenic system that formed from Jurassic–Cretaceous to the present. This orogenic system produced many different types of deposits related to subduction, collision, post-collision and rifting processes. Gold deposits, as well as other mineral deposits of Turkey, are mainly concentrated in Late Mesozoic and Tertiary rocks. Evaluation of the gold metallogeny of Turkey is based on a GIS database compilation of known gold deposits and prospects. Currently available data show that Turkey has a gold endowment, including reserves and resources, of approximately 31.5 M oz [979 tonnes] in 51 deposits, 21 of which contain more than 0.2 M oz gold. The other 30 deposits contain a total of approximately 1 M oz [31 tonnes] gold resources. Two recent discoveries, Kisladag and Copler, currently contain total resources of 17.6 M oz Au [549 tonnes], more than 50% of the total Turkish gold endowment. Turkey possesses a wide spectrum of gold deposits related to Mesozoic and Cenozoic volcanoplutonic arcs. However, porphyry gold (copper), epithermal gold (including both high- and low-sulfidation styles), and gold-rich volcanic-associated massive sulfide (including both Kuroko- and Cyprus-types) are the most economically important to date. Orogenic gold, including listwanite-hosted, placer gold and skarn-hosted gold are relatively less important or abundant deposit types. Other potential gold systems for exploration include Carlin-type gold, detachment-fault-related gold, iron oxide–copper–gold, and gold in carbonate-replacement and manganese deposits.

The Bond Market and Fiscal Institutions: Have Budget Stabilization Funds Reduced State Borrowing Costs?

Since budget stabilization funds have the potential to aid states in mitigating periods of fiscal stress , they may reduce the default risk associated with state-issued debt. This paper explores how budget stabilization funds affect state borrowing costs. While the empirical results reveal that the typical state experiences a modest reduction in bond yields following the adoption of a bud- get stabilization fund, stabilization funds with different types of deposit and withdrawal rules are found to affect borrowing costs differently. The largest reduction in yields occurs in states that have budget stabilization funds governed by strict deposit and withdrawal rules.

As–(Ag) sulphide veins in the Spanish Central System: further evidence for a hydrothermal event of Permian age

The Spanish Central System (SCS) has been subjected to repeated deformation and fluid flow events which have produced both sulphide-bearing and barren vein systems. Although several hydrothermal episodes took place between 300 and 100 Ma, fluid circulation during the Permian was especially important, giving rise to a range of different types of deposits. This study presents a multidisciplinary approach leading to the characterisation of the chemistry and age of the hydrothermal fluids that produced the As–(Ag) mineralised stockwork of Mónica mine (Bustaviejo, Madrid). Fluid inclusion data indicate the presence of two different fluids. An initial ore stage (I) formed from a low- to moderate salinity (3–8 wt.% eq. NaCl) H 2O–NaCl–CO 2–CH 4 fluid, at minimum trapping temperature of 350±15 °C and 0.3 kbar. A second H 2O–NaCl fluid is found in three types of fluid inclusions: a high temperature and low salinity type (340±20 °C; 0.8–3.1 wt.% eq. NaCl) also associated to ore stage I, a moderate temperature and very low salinity type (160–255 °C; 0–1.5 wt.% eq. NaCl) represented in ore stage III, and a very low temperature and hypersaline type (60–70 °C; 30–35 wt.% NaCl), unrelated to the mineralising stages and clearly postdating the previous types. 40Ar– 39Ar dating on muscovite from the early As–Fe stage (I) has provided an age of 286±4 Ma, synchronous with the late emplacement phases of La Cabrera plutonic massif (288±5 Ma) and with other Permian hydrothermal events like Sn–W skarns and W–(Sn) sulphide veins. δ 18O of water in equilibrium with stage I quartz (5.3–7.7‰), δD of water in equilibrium with coexisting muscovite (−16.0‰ to −2.0‰), and sulphide δ 34S (1.5–3.6‰) values are compatible with waters that leached metamorphic rocks. The dominant mechanism of the As–(Ag) deposition was mixing and dilution processes between aqueous–carbonic and aqueous fluids for stage I (As–Fe), and nearly isobaric cooling processes for stages II (Zn–Cu–Sn) and III (Pb–Ag). The origin and hydrothermal evolution of As–(Ag) veins is comparable to other hydrothermal Permian events in the Spanish Central System.

Relationships between the Concentrations of Phyto-Pigments, Nitrogen, and Phosphorus in Bottom Deposits of Water Reservoirs

Samples characterizing the horizontal distribution of bottom deposits of different types in the Upper Volga reservoirs were used to study the statistical relationship between the indicators of the potential and actual trophy of water bodies. These indicators are the amount of biogenic elements (the total nitrogen and phosphorus) and phyto-pigments (in the dry and wet masses of soil and in its organic fraction). The relationship between the above indicators for the channel deposits from the Upper Volga reservoirs and for the deposits in the lake hollows is found to he linear.

An Assessment of Osmium Isotope Ratios as a New Tool to Determine the Provenance of Gold with Platinum‐Group Metal Inclusions*

The sudden increase in the amount of Celtic gold coins circulating in central Europe during the second century bc coincides with the appearance of platinum‐group mineral (PGM) inclusions in the Celtic gold. It has been proposed that large amounts of gold were introduced from the eastern Mediterranean by mercenaries following the conquest by Alexander the Great, but another hypothesis might be the discovery of entirely new gold sources in central Europe during this time. The presence of PGM inclusions in gold objects is usually taken as an indication for an origin from placer deposits (Hartmann 1970; Park 1986). Initially, it was hoped that those inclusions could be characteristic for a certain deposit, but Meeks and Tite (1980) have shown that the compositional variation within a single gold object can be as large as the total variation observed in all investigated gold artefacts. Therefore, the elemental composition of the PGMs in gold artefacts does not provide any reliable information on the provenance of the gold.An alternative to chemical analysis of the inclusions is the determination of their osmium isotope ratios. Similarly to lead, osmium exhibits a variable isotopic composition due to the radioactive decay of 187Re and 190Pt. In order to investigate the potential of this new geochemical tool to determine the provenance of ancient gold, a quasi‐non‐destructive method for the determination of Os isotope ratios with LA–MC–ICP–MS has been developed.The results show that different types of deposits can be distinguished by Os isotope patterns and their distributions when applying a simple descriptive statistical method. In contrast to lead isotope ratios, the variations of Os isotope abundances are rather large in many ore deposits. But, also contrary to lead, the heterogeneity of the Os isotope ratios of the deposits is preserved in the artefacts, because the analysed PGMs are not dissolved during melting of the gold. Therefore, it is feasible to distinguish between different types of gold sources and to define specific deposits provided that the artefact contains several PGMs. The application of this new technique to Celtic gold coins from southern Germany and coins from western Anatolia has been demonstrated in this study.

Lithogeochemistry of Carlin-type gold mineralization in the Gold Bar district, Battle Mountain-Eureka trend, Nevada

The Gold Bar district contains five Carlin-type gold deposits and four resources for a combined gold endowment of 1.6 M oz [50 t]. The gold deposits are hosted in Devonian carbonate rocks below parautochthonous and allochthonous Paleozoic siliciclastic rocks emplaced during the Early Mississippian Antler orogeny. The district is in the Battle Mountain-Eureka trend, a long-lived structural feature that localized intrusions and ore deposits of different types and ages. The whole-rock geochemistry of four different mineralized and unmineralized Devonian carbonate rock units (two favorable and two unfavorable) were determined and interpreted in the context of the regional geology. A combination of basic statistics, R-mode factor analysis, isocon plots, and alteration diagrams were utilized to (1) identify favorable geochemical attributes of the host rocks, (2) characterize alteration and associated element enrichments and depletions, and (3) identify the mechanism of gold precipitation. This approach also led to the recognition of other types of alteration and mineralization in host rocks previously thought to be solely affected by Carlin-type mineralization. Unit 2 of the Upper Member of the Denay Formation, with the highest Al 2O 3, Fe 2O 3 and SiO 2 contents and the lowest CaO content, is the most favorable host rock. Based on the high regression coefficients of data arrays on X– Y plots that project toward the origin, Al 2O 3 and TiO 2 were immobile and K 2O and Fe 2O 3 were relatively immobile during alteration and mineralization. Specific element associations identified by factor analysis are also prominent on isocon diagrams that compare the composition of fresh and altered equivalents of the same rock units. The most prominent associations are: Au, As, Sb, SiO 2, Tl, –CaO and –LOI, the main gold mineralizing event and related silicification and decalcification; Cd, Zn, Ag, P, Ni and Tl, an early base metal event; and MgO, early dolomitization. Alteration diagrams, consisting of X– Y plots of SiO 2/Al 2O 3, K 2O/Al 2O 3, CO 2/Al 2O 3, [S/Al 2O 3]/[Fe 2O 3/Al 2O 3], provide evidence for progressive silicification, decarbonation (decalcification and dedolomitization), argillization (illite), and sulfidation as a function of gold mineralization. The latter process is identified as the principal mechanism of gold precipitation. The lithogeochemistry of the ores in the Gold Bar district is typical of that documented in classic Carlin-type gold deposits in the region, but the size of the deposits and the intensity of alteration and mineralization are less. The presence of other types of mineralization in the Gold Bar district is also common to most of the other Carlin-type districts located in major mineral belts. The approach used in this study is well suited to the interpretation of multi-element geochemical data from other study areas with superimposed alteration and mineralization.

Chronology and origin of Au-Cu deposits related to paleozoic intracontinental rifting in West Tianshan Mountains, NW China

Located between the Tarim platform and Junggar massif, the West Tianshan intracontinental rift abuts against the China-Kazakhstan boundary in the west part, borders on the Yilianha-bierga late Paleozoic relic ocean basin and the South Tianshan late Paleozoic ocean basin respectively in the northeast separated by the Aibi Lake fault and in the southeast by the fault along the southern margin of the Yili massif. During the development and after the close of the West Tianshan intracontinental rifting in the Carboniferous-Permian period, a series of nonferrous and precious metal mineralizations occurred with the Au-Cu deposits being the most important. Isotopic chronologic study of representative deposits of different types shows that gold-copper mineralization in the West Tianshan intracontinental rift zone mainly happened during the middle-late Her-cynian Period, among which the Axi volcanic hydrothermal type gold deposit was formed during the Carboniferous with a fluid inclusion Rb-Sr isochron age of (339 ± 28) Ma; the Qiabukanzhuota quartzolite type gold deposit has a Rb-Sr isochron age of (312 ± 46) Ma; the Tawuerbieke porphyry type gold deposit has a Rb-Sr isochron age of (295 ± 16) Ma; the Jingbulak magmatic liquation Cu-Ni deposit and the Musizaote porphyry type Cu deposit have the forming ages of 300 Ma± and 250 Ma±, respectively. Analyses of crustal evolution and metallogenetic geological backgrounds of Au-Cu mineralizations in the studied area shows a close correlation with the rifting.

Reworked calcretes: their significance in the reconstruction of alluvial sequences (Permian and Triassic, Minorca, Balearic Islands, Spain)

The Permian and Triassic of Minorca (Balearic Islands) consists of a 670-m-thick, red, alluvial succession that includes in situ calcrete profiles and reworked calcrete material. In the Permian succession, the calcretes vary from laminar forms developed on the Carboniferous basement to weakly developed nodular calcretes in fluvial sediments. The palaeosols in the Triassic are mostly dolomitic, and the profiles reach up to Stage III of soil development (Spec. Pap.-Geol. Surv. Am. 203, (1995) 1). The clasts, formed through reworking of the palaeosol profiles, are about 0.5–10 cm across and include mosaics of calcite/dolomite crystals, brecciated clasts, rhizolith fragments, and aggregates of clay and/or silt. These clasts appear in three different types of deposits. Type 1 corresponds to lenticular bodies that fill small scour surfaces, and consists only of intraformational conglomerates. These deposits are interpreted as ephemeral channels and sheet-floods that represent the interfluvial drainage systems that captured only the precipitation falling on the alluvial plain. Type 2 includes sand dune 3-D bodies with flat bottoms and convex tops. These bodies are about 20 cm high and 2 m wide, and were formed by floodwaters that flowed down the levees of the major streams. Type 3 channel deposits contain reworked calcretes and extrabasinal clasts, which overlie erosive surfaces and are found in layers within cross-bedded sandstones and conglomerates. These are interpreted as channel-floor lag deposits of major channels that entered from distant uplands and drained the alluvial plain. Variations in the aggradation rates of the floodplain resulted in five different infill stages. In the lowstand to early transgressive interval, as in stages I (P1) and IV (B1), the fluvial deposits filled palaeovalleys; calcretes and reworked calcrete deposits were of difficult formation (apart from terraces) and preservation. Accommodation space was at its greatest in the transgressive, stages II (P2) and V (B2). This caused the greatest aggradation of the floodplains, which are formed of thick sequences of fine-grained sediments, isolated meandering channels, weakly developed calcretes (compound) and reworked calcrete deposits, mostly of types 1 and 2. The density of channels notably increased in stage III (P3), highstand interval, because of the reduction of accommodation space, this could favour the formation of composite or even cumulative palaeosols, but of difficult preservation. Reworked calcrete deposits are mostly of type 3, but types 1 and 2 are also recognised. The reworked calcrete deposits are an important part of the Permian and Triassic fluvial sediments and their occurrence and characteristics are important in order to interpret the infill of terrestrial basins and the construction of floodplains.

Holocene evolution on Galician coast (NW Spain): an example of paraglacial dynamics

The recent evolution and the present coastal dynamic in middle Atlantic latitudes, as the coast of Galicia, can be considered in a paraglacial context. The fossilization of Eemian coastal landforms by deposits developed under cold conditions, followed by a paraglacial environment during the Holocene transgression. The characteristics of the different types of deposits and the rising sea-level curve controlled the evolution of the coastline, showing the co-existence of bluff-retreat and continental sedimentation.

Tin-cobalt electrodeposition from sulfate-gluconate baths

The electrodeposition of tin + cobalt alloys from a slightly acidic sulfate‐gluconate bath on both vitreous carbon and copper substrates has been studied for diAerent [Sn(II)]/[Co(II)] ratios in the bath, varying between 1/10 and 1/2. A relationship between the electrochemical stripping analysis and the morphology of the deposits has been found. Two different types of deposit were obtained. At low [Sn(II)]/[Co(II)] ratios and relatively high deposition rates a nodular, cobalt-rich, nanocrystalline coating was obtained, while at high [Sn(II)]/[Co(II)] ratios and low deposition

Arsenic content and groundwater geochemistry of the San Antonio-El Triunfo, Carrizal and Los Planes aquifers in southernmost Baja California, Mexico

The San Antonio-El Triunfo mining district, located at a mountainous region 45 km south-east of La Paz, Baja California, has been worked since the late 1700s. Mine waste material produced during 200 years of mineral extraction area poses a risk of local groundwater pollution and eventually, regional pollution to the Carrizal (west basin) and the Los Planes (east basin) aquifers. There are different types of deposits in the mining area. These are dominated by epithermal veins, in which arsenopyrite is an important component. Carrillo and Drever (1998a) concluded that, even though the amount of mine waste is relatively small in comparison to the large scale area, significant As in groundwater derived from the mine waste piles is found locally in the groundwater. This paper shows the results of geochemical analyses of groundwater samples from the San Antonio-El Triunfo area and the Carrizal and Los Planes aquifers during several years of monitoring (1993–1997). The highest values of total dissolved solids (TDS) and As are in the mineralized area where the mining operations occurred (∼1500 ppm TDS and 0.41 ppm As). The lowest concentrations of TDS and As are, in general, away from the mineralized area (∼500 ppm TDS and 0.01 ppm As). Sulfate and bicarbonate (alkalinity) are, in general, high near the mineralized area and low away from it. The arsenic concentrations vary seasonally, especially after the heavy summer thunderstorms. Geochemical modeling (MINTEQA2 and NETPATH) and analysis of the regional geochemical evolution of the groundwater from the mining area towards the aquifer of Los Planes shows that the most likely hydrochemical processes include: dilution, precipitation of calcite, and adsorption of As onto surfaces of iron oxyhydroxides (ferrihydrite). These processes act as natural controls to the extent and amount of As pollution in the Carrizal and Los Planes aquifers.

Observation of deposits on disposable contactlenses by bio-, light and scanning electron microscopy

There has been little published on the presence of deposits on disposable hydrogel contact lenses. The purpose of the present study was to determine the possible existence of such deposits. Seventy-two disposable lenses (polymacon; FDA group 1; non-ionic, low water contact lenses) were fitted to six patients and replaced weekly in the course of a total follow-up period of six weeks. By means of biomicroscopy, light microscopy and scanning electron microscopy, different types of deposits were observed on all the lenses studied. Our results also indicate that the accumulation rate of these deposits expressed as a percentage of the total area of the lens which they covered increased after the third replacement of the lenses over the 4th, 5th and 6th weeks. Finally, we observed that the amount of deposits varies in the different patients studied in the course of a 6 week follow-up period.

Methanogenesis in sediments from deep lakes at different temperatures (2–70°C)

Methanogenic degradation of organic matter occurs in a wide temperature range from psychrophilic to extreme thermophilic conditions. Mesophilic and thermophilic methanogenesis is relatively well investigated, but little is known about low temperature methanogenesis and psychrophilic methanogenic communities. The aim of the present work was to study methanogenesis in a wide range of temperatures with samples from sediments of deep lakes. These sediments may be considered deposits of different types of microorganisms, which are constantly exposed to low temperatures. The main question was how psychrophilic methanogenic microbial communities compare to mesophilic and thermophilic ones. Methanogenesis in a temperature range of 2–70°C was investigated using sediment samples from Baldegger lake (65 m) and Soppen lake (25 m), Switzerland. Methane production from organic matter of sediments occurred at all temperatures tested. An exponential dependence of methane production rate was found between 2 and 30°C. Methanogenesis occurred even at 70°C. At the same time stable methane production from organic matter of sediments was observed at temperatures below 10°C. Methanogenic microbial communities were enriched at different temperatures. The communities enriched at 4–8°C had the highest activity at low temperatures indicating that a specific psychrophilic community exists. Addition of substrates such as cellulose, volatile fatty acids (butyrate, propionate, acetate), methanol and H2/CO2 stimulated methane production at all temperatures. H2/CO2 as well as methanol were directly converted to methane under thermophilic conditions. At low temperatures these substrates were converted to methane by a two-step process. First acetate was formed, followed by methane production from acetate. When acetate concentrations were high, acetoclastic methanogenesis was inhibited at low temperatures. This reaction appears to be one of the “bottle neck” in psychrophilic methanogenesis.

The Hf isotopic composition of ferromanganese nodules and crusts and hydrothermal manganese deposits: Implications for seawater Hf

We present Hf and Pb isotopic data, and chemical compositions of the outermost layers of marine ferromanganese deposits of different types (hydrogenous and hydrothermal) with a worldwide distribution. The Hf isotopic compositions display a broad range and refine previously reported regional differences as follows: Atlantic Ocean ɛ Hf = −4to+2, Indian Ocean ɛ Hf = +2to+4, Pacific Ocean ɛ Hf = +3to+10. The most radiogenic Hf isotopic compositions in the Pacific samples are for hydrothermal manganese deposits that also have low 207Pb 204Pb, demonstrating that this signature reflects a contribution from hydrothermal venting of Hf leached from oceanic volcanic rocks rather than from riverine inputs, volcanic ash, or eolian dust. Hafnium concentrations in the deposits increase from 20 ppb to 20 ppm with decreasing ɛ Hf, The Hf and Pb isotopic compositions for ferromanganese crusts define an apparent mixing trend between literature values of average continental crust and MORB. The range in ɛ Hf for ferromanganese crusts is narrower than it is for 206Pb 204Pb compared to the differences in isotopic composition of the sources of Hf and Pb. This is consistent with Hf having a longer residence time than Pb. The concentration of Hf in ferromanganese crusts has been found to co-vary with growth rate, and inversely correlates with Hf isotopic compositions. Hf isotope ratios may be used to determine not only the source of Hf, but possibly the source of Fe and Mn. Measurements of ɛ Hf and Hf concentrations in nodule tops, bottoms and associated sediments show that the ɛ Hf of nodules is sensitive to sedimentary oxic and sub-oxic diagenetic processes and thus most nodules may not reliably reflect the isotopic composition of Hf in seawater.

A kinetic study of the cementation of gold from cyanide solutions onto copper

The kinetics of cementation of gold onto copper was evaluated using a copper rotating disc and suspended particles systems. It was found that the cementation of gold onto copper is controlled by a kinetic step. For both rotating disc and suspended particles systems, the effects of temperature, cyanide and gold concentration on the rate of cementation are more significant than those of rotation speed and solution pH. The kinetic rate constant of cementation of gold onto copper is comparatively smaller than those found for the gold-zinc-cyanide or silver-copper-chloride systems. The activation energy was found to be 53.4 and 54.1 kJ/mol for copper rotating disc and suspended particles, respectively, which values are close to the measured value of 56.9 kJ/mol found in the electrochemical study. The morphology of the deposits, determined by Field Emission Scanning Electron Microscope, confirmed observations from experimental measurements, showing the passivation or acceleration of cementation due to the different types of deposit formed.

Methanogenesis in sediments from deep lakes at different temperatures (2–70°C)

Methanogenic degradation of organic matter occurs in a wide temperature range from psychrophilic to extreme thermophilic conditions. Mesophilic and thermophilic methanogenesis is relatively well investigated, but little is known about low temperature methanogenesis and psychrophilic methanogenic communities. The aim of the present work was to study methanogenesis in a wide range of temperatures with samples from sediments of deep lakes. These sediments may be considered deposits of different types of microorganisms, which are constantly exposed to low temperatures. The main question was how psychrophilic methanogenic microbial communities compare to mesophilic and thermophilic ones. Methanogenesis in a temperature range of 2–70°C was investigated using sediment samples from Baldegger lake (65 m) and Soppen lake (25 m), Switzerland. Methane production from organic matter of sediments occurred at all temperatures tested. An exponential dependence of methane production rate was found between 2 and 30°C. Methanogenesis occurred even at 70°C. At the same time stable methane production from organic matter of sediments was observed at temperatures below 10°C. Methanogenic microbial communities were enriched at different temperatures. The communities enriched at 4–8°C had the highest activity at low temperatures indicating that a specific psychrophilic community exists. Addition of substrates such as cellulose, volatile fatty acids (butyrate, propionate, acetate), methanol and H2/CO2 stimulated methane production at all temperatures. H2/CO2 as well as methanol were directly converted to methane under thermophilic conditions. At low temperatures these substrates were converted to methane by a two-step process. First acetate was formed, followed by methane production from acetate. When acetate concentrations were high, acetoclastic methanogenesis was inhibited at low temperatures. This reaction appears to be one of the “bottle neck” in psychrophilic methanogenesis.

Re-Os Isotope ages of molybdenum deposits in East Qinling and their significance

Dating of metallic ore deposits has been one of the problems concerned with by ore geologists for many years. The establishment of the Re-Os Isotope Laboratory at the Institute of Rock and Mineral Analysis, Chinese Academy of Geological Sciences, has provided us with a new technique to carry out geochronological studies of molybdenum ores. As one of the most important Re-bearing minerals, molybdenite contains almost no common osmium, but187Os was derived completely from decay of187Re, with187Os content as the function of Re content in the mineral. An ID-ICP-MS technique has been used in this study, and Re-Os isotopic ages of several large molybdenum deposits of different types from the East Qinling molybdenum belt have been determined. It is indicated that the Huanglongpu carbonatite vein-type molybdenum-(lead) deposit has a Re-Os age corresponding to Indosinian, while the rest porphyry-type molybdenum deposits and porphyry-skarn-type molybdenum-(tungsten) deposits have Re-Os ages corresponding to Yenshanian.