Low Sulfide Research Articles

Geochemistry of zinc and cadmium in coal waste rock, Elk Valley, British Columbia, Canada

Weathering of mine waste rock can result in high concentrations of zinc (Zn) and cadmium (Cd) in surface and ground water. Design and implementation of mitigation measures requires an understanding of the mineralogical occurrence of Zn and Cd within the waste rock as well as the subsequent weathering and leaching processes. Recent geochemical studies have focused on the characterization of selenium and arsenic leaching from sphalerite and pyrite in waste rock from coal mines in the Elk Valley, British Columbia, Canada. Data collected from these studies provide an opportunity to evaluate the distribution and behavior of Zn and Cd. The abundance and mineralogical association of Zn and Cd were determined in waste rock placed at different times in the dump and leaching of Zn and Cd at the dump-scale was estimated by analyzing porewater and effluent water samples in a rock drain. Mean contents of Zn and Cd in the waste rock samples (n = 260) were 152 mg/kg (range: 48.4–591 mg/kg) and 3.02 mg/kg (range: 0.97–7.56 mg/kg), respectively. Electron microprobe analysis showed Zn and Cd are present in rock samples as primary sphalerite and sorbed onto secondary Fe oxides. The mean concentrations of Zn and Cd in porewater in the dump (n = 121) were 231 μg/L (range: 4.27–1046 μg/L) and 0.61 μg/L (range: <0.01–6.85 μg/L), respectively. The sorption onto secondary Fe oxides is identified as the sink for aqueous Zn and Cd in the dump. Under the oxidizing conditions that exist throughout much of the dump, Fe oxides will likely be a long-term sink for aqueous Zn and Cd. Mean concentrations of Zn and Cd in the rock drain water were 56.4 μg/L (range: 1.2–523 μg/L, n = 213) and 1.53 μg/L (range: 0.004–3.92 μg/L, n = 209), respectively. As such, these low concentrations are attributed to dilution by drain waters sourced upstream of the dump and sorption of Zn and Cd onto secondary Fe oxides and calcite precipitated in the drain within 200 m after discharge from the dump. The relative increase of Cd concentration in rock drain water compared to porewater can be because of its lower affinity for the sorption onto secondary Fe oxides and calcite. This study suggests that the mobility of Zn and Cd from the weathering of any low sulfide – high carbonate waste rocks will be limited because the precipitation of secondary Fe oxides and calcite provide a strong internal geochemical control on Zn and Cd mobilization.

The Gold Mineralization of the Baranyevskoe Au-Ag Epithermal Deposit in Central Kamchatka

The Baranyevskoe Au-Ag epithermal deposit of low-sulfidation (LS) type is located on the Kamchatka Peninsula in the Neogene-Quaternary Central Kamchatka Volcanic Belt, where Au-bearing quartz veins are usually accompanied by veinlet stockworks. Two economic associations are typical of the Baranyevskoe deposit. The first corresponds to gold-pyrite-quartz association with low-grade native gold (521–738‱) intergrown with pyrite. Some accessory Au-Ag minerals within the early association were also identified: acanthite AgS2, hessite AgTe2, lenaite Ag(Fe,Cu)S2, petzite Ag3AuTe2, utenbogardite Ag3AuS2 and unnamed Ag-Sb-As sulfosalts. The former Au-Ag minerals were most likely formed in the temperature range of 320–330 °C based on the study of arsenopyrite thermometers and fluid inclusions. The second, a gold-sulfosalt-quartz association, includes high-grade native gold (883-941‱) in intergrowth with chalcopyrite. Cuprous phases (bornite, chalcocite, heerite, native copper, Cu-Zn solid solutions), Bi-rich sulfosalts (aikinite PbCuBiS3, emplectite CuBiS2, witticenite Cu3BiS3), stannoidite Cu8Fe3Sn2S12, mawsonite Cu6Fe2SnS8), Au-bearing galena, Te-free and Bi-rich tetrahedrite-tennantite represent this association. Fluid inclusions in gold-sulfosalt-quartz association are characterized by homogenization temperature ranging from 226 to 298 °C, and salinity from 0.4 to 1.2 wt. % NaCl eq.

Preliminary Study of Geology, Alteration and Ore Mineralisation at East Motoling Area, South Minahasa District, North Sulawesi, Indonesia

The East Motoling area is one of the prospect areas in the Minahasa region of North Sulawesi, which has indications of low sulfidation epithermal-type mineralization. The research was conducted as a preliminary study to determine the characteristics of geological conditions, alteration, and ore mineralization in the epithermal system. The research method is divided into two main parts, such as fieldwork including surface geological mapping (lithology, stratigraphy, geomorphology, structural geology, alteration and mineralization) and laboratory analysis methods including petrographic analysis. The stratigraphy of the study area consists of altered volcaniclastic breccia, altered lapilli tuff, altered tuff, limestone, welded lapilli tuff, and andesitic breccia. Volcaniclastic breccia, altered lapilli tuff, and altered tuff, member of the Volcanic Rock Formation which is Late – Middle Miocene age, are the host rock for ore mineralization and hydrotermal alteration process. There are 3 types of alterations that have developed, namely argillic (illite + quartz ± kaolinite), sericitic (sericite + illite ± chlorite), and propylitic (chlorite + epidote ± illite). The dextral slip fault with NW – SE trend present as a main control structure to formation of extention fracture/vein. The epithermal veins are relatively north-northeast – south-southwest, north-northwest – south-southeast, and northwest – southeast. The textures of the veins divided into 7 main groups, namely that is bladed-quartz, breccia, calcedony, colloform, comb, mold, and massive quartz. Ore mineralization is forms in the veins as pyrite and banded sulfide. Apart from that, the disseminated pyrite also limitedly found around the veins.

Reversible Metal Sulfide Transition in a Two-Step Thermochemical H2S Splitting

Two-step thermochemical H2S splitting process is a promising method to recover both H2 and S from a toxic waste H2S gas via low/high metal sulfide conversion. Several studies have examined the potential of the process experimentally. Still, there is a lack of comprehensive research into such as to provide a guideline for selecting the appropriate metal for the process. The most common metals in the periodic Table (28 metals) have been examined to find stable low/high metal sulfide couples. A list consisting of 17 metals that can form thermodynamically stable couples has been shortlisted, in which six metals: K, Zr, Hf, Nb, Fe, and Ni, were found to be promising candidates with a high H2S splitting efficiency, high H2 yield and good reversible transition between low and high sulfides. The transition between sulfide crystals has been experimentally demonstrated with the Ni3S2/Ni3S2+x couple. This couple can decompose up to 90 mg H2S/g-Ni3S2 at 500 °C to produce H2 and high sulfides Ni3S2+x that was successfully regenerated at 700 °C for multiple cycles. The thermodynamic calculations revealed that the sulfides of Zr, Hf, and Nb are favorable for the two-step H2S splitting process, but have not been explored experimentally. The sulfide of Zr was examined in this work, but they got oxidized by residual oxygen in the test gas before the crystalline transition was detected and remained as a challenge in the future works.

Research Progress of Hydrogen Sulfide Adsorption Based on MOFs

AbstractAdsorption method is one of the main technologies for hydrogen sulfide treatment. Developing an adsorbent with good selectivity, large adsorption capacity, stability and good regeneration is the key to the removal of hydrogen sulfide by adsorption method. Compared with the traditional adsorbents, Metal‐organic frameworks (MOFs) have a large specific surface area, a variety of framework structures, adjustable pore sizes and functionality, showing significant advantages in the adsorption of hydrogen sulfide. In this paper, the research progress of hydrogen sulfide adsorption based on MOFs in recent years was summarized. The influences of pore structure and unsaturated metal sites on the hydrogen sulfide adsorption performance of MOFs were discussed, and the strategies of functionalized groups and preparation of composites were proposed to improve the hydrogen sulfide adsorption performance of MOFs. Finally, the problems and challenges in the future industrial application of MOFs as low concentration hydrogen sulfide adsorbents were pointed out.

Analysis of Geomagnetic and Geoelectric Data to Identify the Potential of Gold Deposits (Case Study: Randu Kuning, Wonogiri, Central Java)

The gold deposit of the low sulfidation epithermal system at the Randu Kuning prospect, Wonogiri, Central Java is the effect of magmatism during the Oligocene due to microdiorite intrusion. The magmatism causes a mineralization process that fills the fractures in the rock. The mineralized of ores that formed in the study area are pyrite, chalcopyrite, sphalerite, galena, electrum and native gold, magnetite and hematite. The appropriate geophysical method to this case study is using the geomagnetic and geoelectric Induced Polarization method. The application of the geomagnetic method aims to delineate mineralized zones and geological structures as channel way for hydrothermal fluids. The results of the geomagnetic method are in the form of a map of Total Magnetic Intensity carried out by filters such as Reduce to Pole (RTP) - High pass (HP) and Horizontal Gradient (HG). The west side of RTP - HP anomaly shows a low response of -4.9 to -0.8 nT due to intensely mineralized rock and the presence of fractures. The comparison between RTP - HP anomaly and HG anomaly shows the suitability due to intense mineralization which reduces the fault anomaly. A high HG value area of 0.001-0.0017 nT/m is interpreted as a mineralized fault. This can be seen from the alteration map which shows the continuity of veins from measurements in the field. The application of the geoelectric Induced Polarization method aims to identify associated mineral of gold vertically subsurface. Based on the results of geoelectric Induced Polarization data shows that there are chalcopyrite minerals at a depth of 20-30 m with a chargeability of 4-9 msec which is located in intrusion of igneous rock with a resistivity >200 Ωm. Based on geomagnetic geoelectric data, it can identify potential gold deposits in the Randu Kuning area, Wonogiri, Central Java.

Assessing the impacts of differential depositional settings and/or anthropogenic perturbations on sulfur and iron diagenesis in sediments of the Bohai Sea and North Yellow Sea

Natural processes and human activities exert important impacts on elemental cycling in coastal sediments, which has not been well documented. Sediments in the Bohai Sea and North Yellow Sea were investigated to assess the impacts of the Yellow River inputs and/or anthropogenic perturbations on diagenesis of iron and sulfur. Labile iron (0.5 M HCl-extractable iron) in the sediments is low due to iron-poor nature of source materials. Dynamic regimes and low availability of labile organic carbon (OC) result in relatively low sulfide contents in deltaic sediments. However, low but continuous supply of labile OC exported from an anthropogenically impacted bay could substantially elevate sulfide burial in sediments near the bay. Neither offshore oil exploitations nor frequent algal blooms in the seas have detectable influences on iron and sulfur diagenesis in the sediments. The sediments are capable of quickly consuming porewater sulfide by reaction with reactive iron under the current conditions.

Effect of hydration on failure surface evolution of low sulfide content cemented paste backfill

Backfill in deep and high-stress mining controls stress redistributions and provides rock mass support on the mine-wide scale. The advantages of Cemented Paste Backfill (CPB) include fastest filling rate (including the potential for continuous backfilling), uniform as-placed properties, and tight filling of the mined voids. Numerically analyzing CPB response during filling, curing, and subsequent mining must account for evolving strength properties arising from ongoing hydration processes, particularly in the first 3–28 days. This work uses Brazilian tensile strengths, a specially designed zero-effective stress Unconfined Compressive Strength (UCS) test, and drained confined triaxial test results to characterize the non-linear failure envelope for a typical low sulfide content CPB with binder contents from 3.0% to 7.5%, and strength evolution from 3 to 28 days. Power functions in terms of Cement Content (CC) and Cure Time (CT) are calibrated using the entire data range and then used to determine UCS (ranging approximately from 55 kPa at 3%/3-day to 460 kPa at 7.5%/28-day) and tensile strength (ranging approximately from 8 kPa at 3%/3-day to 60 kPa at 7.5%/28-day). Other power functions are then used for the failure envelopes and show that confining stress dependency becomes increasingly nonlinear with increasing CC, with the exponents ranging from 0.874 at 3% CC to 0.789 at 7.5% CC. The formulated strength envelopes with hydration time dependency are an improvement on existing models for CPB strength (typically based on Mohr-Coulomb with time-dependent parameters) and can be conveniently incorporated into numerical analysis codes.

T-P-fO2 conditions of sulfide saturation in magmatic enclaves and their host lavas

Physicochemical conditions under which early sulfide saturation occurs and the role of this process in the mineralising potential of magmas in different geodynamic settings have been the subject of interest in many recent studies. Here we present new temperature-pressure-fO2 data on sulfide-saturated magmatic enclaves and host lavas from volcanic systems in subduction, post-subduction and intraplate geodynamic settings, some of which are associated with porphyry and epithermal deposits. Petrographic investigations coupled with mineral chemistry of sulfide inclusions and their host minerals and with bulk chemistry of amphibole, plagioclase and pyroxene-rich enclaves and their host lavas indicate that sulfide occurrence, abundance, and composition depend on magma evolution. Sulfides are more abundant and have higher Ni/Cu bulk ratios when found in mafic enclaves compared to sulfide inclusions occurring in more evolved lavas. Thermo-oxibarometry estimates indicate that mafic hornblende-rich cumulates (SiO2 < 45 wt%) occurring at the studied intraplate setting evolve and reach sulfide saturation already in the mantle (61 ± 7 km) at high temperature and pressure conditions (17 kbar and 1135 ± 28 °C) and low ΔNNO (< −1). These cumulates are associated with a greater sulfide abundance (up to 0.23 area %) compared to other types of enclaves and have Cu-poor sulfides (mostly pyrrhotite, with Cu median = 0.16 wt%) with high Ni/Cu values (up to 65). In contrast, more evolved (SiO2 > 50 wt%) gabbroic plutonic enclaves found in arc settings saturate sulfides at shallower crustal levels (~26 ± 10 km, i.e. ≤ 7 kbar) and at lower temperature (1014 ± 28 °C) and higher ΔNNO (> +1), and are characterised by a lower sulfide abundance (down to 0.01 area %), dominated by Cu-rich sulfides (mostly chalcopyrite and bornite with Cu median = 50 wt%). By accounting for the sulfide volume, our results suggest that sulfides can retain significantly higher amounts of metals in the enclaves (Cu = 32–113 ppm) compared to sulfides in the host lavas (Cu < 8 ppm). Considered altogether, our results indicate that alkaline mafic, less oxidised, and barren magmas corresponding to intraplate and back-arc settings saturated in sulfides in the upper mantle. In contrast, calc-alkaline-felsic, oxidised and ore-related magmas corresponding to convergent margins started to be saturated in sulfides at the expected depth of the MASH zone and at shallower crustal levels. This seems to be a consequence of the investigated alkaline systems not forming shallow crustal magma chambers allowing magma differentiation, rather than the fact that late and shallow sulfide saturation is necessary for porphyry formation.

Surficial geochemical and mineralogical signatures of Ni-Cu-PGE deposits in glaciated terrain: Examples from the South Range of the Sudbury Igneous Complex, Ontario, Canada

A till geochemistry and indicator mineral (IM) study was carried out in the South Range of the Sudbury Igneous Complex (SIC) to develop surficial mineral exploration techniques that are suitable for low sulfide, high precious metal (LSHPM) and massive sulfide Ni-Cu-PGE mineralization. Surficial exploration in this region is problematic because of heterogeneous till deposits overlain by glaciolacustrine sediments, a naturally high surficial geochemical background, and a paucity of undisturbed till for geochemical sampling due to mining-related operations. The Vermilion and Crean Hill deposits were selected for this case study because their geology and mineralogy have been extensively studied. Pathfinder elements that show a strong, positive (r2 > 0.6, n = 120) correlation with ore elements Ni, Cu, Au and PGEs (Pt, Pd, Ru, Rh, and Ir), which are derived from mineralization and present in elevated concentrations in till samples overlying mineralization are As, Bi, Co, Cr, Pb, Sb and Te. Ore minerals that survive glacial transport and post-glacial weathering and are the best indicators of Ni-Cu-PGE-Au mineralization are grains of gold, chalcopyrite, and sperrylite, predominantly recovered from the < 0.25 mm pan concentrate fraction of till. Despite challenges, this study has identified new exploration targets that warrant further investigation and demonstrates that till geochemistry and IM methods can be used to explore for Ni-Cu-PGE mineralization in established mining camps.

Intermediate sulfidation epithermal Pb - Zn (± Ag ± Cu ± In) and low sulfidation Au (± Pb ± Ag ± Zn) mineralization styles in the Gonzalito polymetallic mining district, North Patagonian Massif

The Gonzalito polymetallic mining district is located within the northeast tip of the 600 km-long NE-trending polymetallic belt of the North Patagonian Massif, in Patagonia, Argentina. It comprises Paleozoic igneous-metamorphic rocks of the Mina Gonzalito complex, which are intruded by Middle Triassic trachytic-andesitic dykes of the Monasa Fm. through a complex system of high-angle fractures. Rhyolitic dykes crosscut the pre-Jurassic rocks. Numerous semi-parallel vein-like mineral deposits, whose classification and age have been subject of debate, sharply crosscut the igneous-metamorphic, trachytic-andesitic and rhyolitic units. Mineralization shows a strong structural control through a complex system of semi-parallel NW-N-NE oriented fracture-hosted mineral deposits. Extensional jogs and open dilational fractures allow multiband vein infills, vein-like hydrothermal and fault-tectonic breccias, stockwork veins and veinlets with primary growth open-space and boiling-derived textures, indicating a brittle geological setting that is proper of the epithermal environment. Based on the structural setting, sulfide-gangue-alteration mineral assemblages and textures, sulfide mineral chemistry and whole-rock geochemical analyses, two different styles of hydrothermal deposits can be distinguished: massive-sulfide intermediate sulfidation epithermal Pb – Zn ± Ag ± Cu ± In and disseminated-sulfide low sulfidation Au ± Pb ± Ag ± Zn. The first has a main-stage pyrite – In-rich sphalerite – chalcopyrite – galena ore assemblage in scarce quartz - carbonates gangue. The second shows disseminated pyrite ± sphalerite ± chalcopyrite ± galena with economic grades of Au in abundant quartz – adularia ± fluorite gangue. SHRIMP U–Pb zircon data of rhyolites reveal Early Jurassic ages of 193 ± 2 and 191 ± 2 Ma and, along with their bulk-rock geochemical features, they can be included within the Chon Aike magmatic province, locally known as Marifil volcanic complex. Crosscutting relationships between the Lower Jurassic rhyolites and the epithermal veins in the Gonzalito district, and the presence of Oligocene basalts partially covering the epithermal deposits towards the western area, constrain the mineralization event between the Lower Jurassic and the Oligocene. However, the crosscutting relationships of this district along with the already proven genetic, temporal and spatial links between epithermal ore and fluorite-rich deposits and the Jurassic magmatism-rifting of Patagonia suggest that the studied epithermal deposits might be yielded closer or during the Lower Jurassic.

Rapid sulfur cycling in sediments from the Peruvian oxygen minimum zone featuring simultaneous sulfate reduction and sulfide oxidation

AbstractBacterial sulfate reduction (SR) is often determined by radiotracer techniques using 35S‐labeled sulfate. In environments featuring simultaneous sulfide oxidation, SR can be underestimated due to re‐oxidation of 35S‐sulfide. Recycling of 35S‐tracer is expected to be high in sediment with low concentrations of pore‐water sulfide and high abundance of giant filamentous sulfur‐oxidizing bacteria (GFSOB). Here, we applied a sulfide‐spiking method, originally developed for water samples, to sediments along a shelf‐slope transect (72, 128, 243, 752 m water depth) traversing the Peruvian oxygen minimum zone. Sediment spiked with unlabeled sulfide prior to 35S‐sulfate injection to prevent radiotracer recycling was compared to unspiked sediment. At stations characterized by low natural sulfide and abundant GFSOB (128 and 243 m), the method revealed 1–3 times higher SR rates in spiked sediment. Spiking had no effect on SR in sediment with high natural sulfide despite presence of GFSOB (72 m). Bioturbated sediment devoid of GFSOB (752 m) showed elevated SR in spiked samples, likely from artificial introduction of sulfidic conditions. Sulfide oxidation rates at the 128 and 243 m station, derived from the difference in SR between spiked and unspiked sediment, approximated rates of dissimilatory nitrate reduction to ammonium by GFSOB. Gross SR contributed considerably to benthic dissolved inorganic carbon fluxes at the three shallowest station, confirming that SR is an important process for benthic carbon respirations within the oxygen minimum zone. We recommend to further explore the spiking method to capture SR in sediment featuring low sulfide concentrations and high sulfur cycling by GFSOB.

Reactivity of inorganic sulfide species towards a pentacoordinated heme model system

The reactivity of inorganic sulfide towards ferric bis(N-acetyl)- microperoxidase 11 in sodium dodecyl sulfate has been explored by means of visible absorption and resonance Raman spectroscopies. The reaction has been previously studied in buffered solutions at neutral pH and in the presence of excess sulfide, revealing the formation of a moderately stable hexacoordinated low spin ferric sulfide complex that yields the ferrous form in the hour's timescale. In the surfactant solution, instead, the ferrous form is rapidly formed. The spectroscopic characterization of the heme structure in the surfactant milieu revealed the stabilization of a major ferric mono-histidyl high spin heme, which may be ascribed to out of plane distortions prompting the detachment of the axially ligated water molecule, thus leading to a differential reactivity. The ferric bis(N-acetyl)- microperoxidase 11 in sodium dodecyl sulfate provides a model for pentacoordinated heme platforms with an imidazole-based ligand.

Modeling of Thermal-Hydrological-Chemical (THC) Processes During Waste Rock Weathering Under Permafrost Conditions

The oxidation of sulfide minerals such as pyrite present in waste rock results in elevated sulfate, enhanced metal loadings and in many cases low pH conditions. Recently, many mines have opened in remote areas, including regions subject to permafrost conditions. In these regions, freeze-thaw cycles and the possible development of permafrost in mine waste add to the complexity of weathering processes, drainage volumes and mass loadings. To assess weathering in these waste rock piles, the reactive transport code MIN3P-HPC has been enhanced by implementing constitutive relationships related to freeze-thaw cycles that control flow patterns, solute transport, generation and transport of heat, as well as geochemical reactions and their rates. Simulations of a hypothetical pyrite-rich waste rock pile placed onto natural permafrost were conducted under reference climate conditions. Additionally, the effect of a warming climate was also studied through a sensitivity analysis. The simulation results indicate a potentially strong coupled effect of sulfide mineral weathering rates and a warming climate on the evolution and persistence of permafrost within waste rock piles and the release of acidic drainage. For relatively low sulfide mineral oxidation rates, the simulations indicate that permafrost can develop within waste rock piles, even under warming climate conditions. However, the results for low reactivity also show that mass loadings can increase by &amp;gt;50% in response to a slight warming of climate (3°C), relative to reference climate conditions. For the chosen reference reaction rates, permafrost develops under reference climate conditions in the simulated waste rock pile; however, permafrost cannot be maintained for a marginally warmer climate, leading to internal heating of the pile and substantially increased production of acidic drainage (&amp;gt;550%). For high reaction rates, the simulations suggest that internal heating takes place irrespective of climate conditions. Evaluation of thermal covers indicates that significant reductions of mass loadings can be achieved for piles with low and reference reactivity (91–99% in comparison to uncovered piles), but also suggest that thermal covers can be ineffective for piles with high sulfide content and reactivity. Together, these simulations provide insights into the complex interactions controlling waste rock weathering in cold-region climates.

The Effect of Hydrodynamic Conditions on the Selective Flotation of Fully Liberated Low Grade Copper-Nickel Ore

Low grade sulfide ores are difficult to process due to their composite mineralogy and their fine grained dissemination with gangue minerals. Therefore, fine grinding of such ores becomes essential to liberate valuable minerals. In this research, selective flotation was carried out using two pitched blade turbine impellers with diameters of 6 cm and 7 cm to float copper and nickel. The main focus of this research was to generate optimum hydrodynamic conditions that can effectively separate nickel and copper from gangue minerals. In addition, we investigated the effects of superficial gas velocity, impeller speed, bubble size distribution, and bubble surface area flux on the flotation recovery and rate constant. The results demonstrated that a 7 cm impeller comparatively produced optimum hydrodynamic conditions that improved Cu-Ni recovery and the rate constant. The maximum copper and nickel recoveries in the 7 cm impeller tests were observed at 93.1% and 72.5%, respectively. However, a significant decrease in the flotation rate of nickel was observed, due to entrainment of nickel in copper concentrate and the slime coating of gangue minerals on the nickel particle surfaces.

Constraints of magmatic differentiation on epithermal mineralization at Dongan, NE China: Insights from zircon geochronology, elements and Sr–Hf–Nd isotope geochemistry

Low-sulfidation (LS) epithermal deposits formed under relatively low temperature and pressure conditions are generally associated with volcanic activity. To better understand magmatic processes prior to epithermal mineralization, field geology, petrology, UPb zircon geochronology, whole-rock major, and trace element geochemistry along with HfNd isotopic geochemistry of the cogenetic volcanic rocks at Dongan were assessed. The Early Cretaceous (109.8 to 107.0 Ma) volcanic suite consists of high-K calc-alkaline andesitic-rhyolitic tuff and granite porphyry dikes or/and stocks. Arc magma affinity characterizes the suite with enrichments in large-ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depletions in high field intensity elements (HFSEs) and heavy REEs (HREEs). The extrusive andesitic rocks showing enriched mantle features (εNd(t) = + 0.76 to +1.83, εHf = − 3.4 to +3.7, TDM2 = 933 to 1124 Ma) are the result of the hybridization between the mantle and lower crust melts with the contamination of upper crustal materials during eruption or ascending of melts. The intrusive granite porphyry (εNd(t) = +3.81 to +3.9, εHf = −0.3 to +3.7, TDM2 = 901 to 1187 Ma) is geochemically comparable with andesitic rocks and was likely formed by the fractional crystallization of plagioclase and amphibole minerals from cooling andesitic melts at middle–upper crustal levels. Note that the rhyolitic magmas show distinct features of lower εNd(t) (−3.05 to – 2.78), εHf (−0.6 to +1.6) and total REE values (54.78 to 70.09 ppm), older TDM2 (1464 to 1662 Ma) and obvious negative europium anomalies (0.34 to 0.37), suggesting an origin of upper crustal remelting (compositionally equivalent to water-poor felsic granulite or tonalite) that results from the heating of the underlying andesitic magmas. In summary, the sequential emplacement of the ore-related andesitic and granitic melts is attributed to the magmatic processes of the active magma chamber in a continental extensional setting, and the metal-rich bubbles focused at the tops of this chamber due to prolonged differentiation are released to produce epithermal veins at shallower levels (< 1.5 km).

Geochemical behaviour of benign desulphurised waste rocks for mine drainage control and sustainable management

Large volumes of waste rock (WR) are generated in open-pit mines. WR is characterised by high anisotropy in its physical, chemical, mineralogical, and hydrogeological properties. WR is often deposited in unsaturated piles on the mine surface. Mineralogical investigations defined the diameter of physical locking of sulphides (DPLS) allowing the WR to be separated into two fractions: i) a reactive fine fraction (<2.4 mm), and ii) an inert coarse fraction (>2.4 mm). Environmental desulphurisation carried out on the reactive fine fraction decreased the risk of contamination caused by WR oxidation. The geochemical behaviour of three benign desulphurised lithologies (altered greywacke (AGR), carbonated greywacke (CGR) and carbonated porphyry (CPO)) and their corresponding fine fractions (<2.4 mm) were assessed using kinetic weathering cells (WCs). These tests confirmed the effectiveness of environmental desulphurisation to prevent acid mine drainage formation. In fact, geochemical analyses of the leachates from WCs showed that pH values ranged between 7.4 and 8.9. Moreover, instantaneous concentrations of iron and zinc were below 0.5 mg/L and 3 mg/L, respectively. Pyrite oxidation rates, which represent sample reactivity, were higher for head samples (3.01, 4.86, and 2.54 μmol/kg/day for AGR, CGR, and CPO lithologies, respectively) in comparison to the benign desulphurised materials (2.32, 2.4, and 2.25 μmol/kg/day for AGR, CGR, and CPO lithologies, respectively). Pyrite in the dismantled material was only partially liberated or almost encapsulated, making it mineralogically unavailable for oxidation. The benign desulphurised material with low initial sulphide content was potentially non-acid generating at the long-term scale. Upstream environmental desulphurisation has been confirmed as an effective strategy for WR management and valorisation.

In situ detection of the fine scale heterogeneity of active cold seep environment of the Formosa Ridge, the South China Sea

The active cold seep at Formosa Ridge (Site F) sustains the most flourishing ecosystem on the continental slope of the northern South China Sea. However, the physicochemical environment around the cold seep has scarcely been investigated. The knowledge about the variability of the seafloor habitat around the cold seep was poor and the key processes within the associated chemosynthetic ecosystem remain unclear. Here, we used an in situ integrated sensors detection approach combined with geochemical measurements to investigate the environmental condition around the chemosynthetic ecosystems fueled by the hydrocarbon seepage. Methane, hydrogen sulfide, dissolved oxygen and other biogenic elements in the bottom water were detected on a fine scale. The mixed gas composition and carbon isotope value of methane from the vent fluids suggested its origin was predominantly biogenic with slight thermogenic incorporation. Both horizontal and vertical variations in methane and oxygen concentrations were observed, which showed contrasting trends in fields from the center of flourishing communities to the margin of sediments. The concentration of methane decreased from 31,200 ppm at the flourishing center to 381 ppm at the margin on a horizontal gradient. The low concentration of hydrogen sulfide indicated that sulfide could be an energy-limiting factor for chemoautotrophic symbionts. The in situ oxygen levels were variable near the flourishing community but homogeneous at the margins. The results suggested that the availability of oxygen and methane played a substantial role in structuring the seep communities. Overall, from the flourishing center to the periphery, the chemical gradients drive the spatial distribution of chemosynthetic community at site F. The observations of the fine scale survey highlight the heterogeneity of microenvironments and provide novel information on the environmental dynamics within site F for the first time. • In situ detection of the fine scale environment in the cold seep were conducted. • Variations of methane and oxygen were observed from the center to the periphery. • The low sulfide level could be a limiting factor for the chemosynthetic community.

In situ monitoring of an inclined cover made with mine waste materials to control water infiltration on a reactive waste rock dyke

The development of a cover for inclined acid-generating areas, such as the external face of dykes and the slope of waste rock piles, is undoubtedly one of the biggest technical reclamation challenges at several mine sites. The LaRonde mine site, owned and operated by Agnico Eagle Mines (Quebec, Canada) is currently engaged to identify an optimal reclamation scenario for the Dyke 1 of its acid-generating tailings storage facilities. One of the promising reclamation options for controlling water infiltration in the acid-generating waste rock on the Dyke 1 is the use of an inclined cover built with available mine waste materials. An instrumented inclined cell with an inclination angle of 18.3 degrees was built on a slope of this dyke to validate if low sulfide tailings and non potentially acid-generating waste rock can be used as cover material to reclaim the Dyke 1. The instrumented inclined cell was monitored for 3 years (2017 to 2019) using volumetric lysimeters, suction sensors, and volumetric water content sensors. The monitoring was done under natural climatic conditions and artificial wetting events. Under natural conditions, less than 1% (5 mm) of incident rainfall percolated in the volumetric lysimeters installed along the slope of the inclined cell. Under controlled conditions associated with artificial wetting events of 6.4 mm/h over a period of 12 h, net percolation values between 1 and 9% (4 to 60 mm) of the sum of incident precipitation were measured. The distance between the top of the cell and the Down Dip Limit (DDL) point was greater than the slope length of the cover under natural conditions and the DDL point moved from the bottom toward the top to reach values between 12 and 20 m from the top of the slope when the wetting events were applied on the cover. These results confirmed the suitability of mining materials as an inclined cover material to control water infiltration in reactive mine waste rocks.

Natural and anthropogenic factors influencing hydrochemical characteristics and heavy metals in groundwater surrounding a gold mine, Thailand

This study focused on groundwater quality around a gold mine at the border between the Phichit and Phetchabun provinces by investigating hydrogeological and hydrochemical characteristics and performing a multivariate analysis to determine the impact of natural and anthropogenic processes on groundwater quality. Groundwater samples were collected from 47 wells in the summer and rainy seasons, and hydrochemical parameters were measured on-site and analyzed in a laboratory. The hydrogeologic characteristics of the study area can be categorized into Quaternary floodplain deposits (Qfd), terrace deposits (Qt), weathered fractures volcanic rocks (Vw), volcanic rocks (Vf), and massive volcanic rocks (Vm). According to the Piper Diagram, water types in the summer season are Ca-Na-HCO3 (34.29%), Ca-HCO3 (22.86%), and Na-HCO3 (22.86%), whereas the rainy season primarily features Na-HCO3 (44.74%), and Ca-Na-HCO3 (39.47%). The principal component analysis (PCA) produced seven significant components that explained 71.50% of the cumulative variance. We divide primary contributors to groundwater into two groups. PC1–PC5 (from natural processes) include Na+, K+, Ca2+, and Al (mineral components of potassium feldspar and plagioclase feldspar), Fe, Zn2+, Pb2+, Cu2+, Co2+, and Mn2+ (associated minerals, such as sphalerite (ZnS), galena (PbS), chalcopyrite (CuFeS2), and pyrite (FeS2)), and inclusions in gold ore (low sulfidation epithermal gold deposits). The second source, PC6 and PC7 (mainly from human activities), includes NO3−, and, PO43− from fertilizers in agricultural areas and wastewater discharge from residential areas. This study revealed that natural and anthropogenic processes affected the hydrochemistry of groundwater, but natural processes played a greater role.