Hg Anomalies Research Articles

Degradation of Hg signals on incipient weathering: Core versus outcrop geochemistry of Upper Permian shales, East Greenland and Mid-Norwegian Shelf

Mercury (Hg) enrichment and elevated ratios of Hg to total organic carbon (Hg/TOC) in sedimentary rocks have often been linked to volcanism from large igneous provinces (LIPs). Primary Hg and TOC contents of sediments can be altered by secondary processes like extreme weathering. These effects must be evaluated before tying Hg anomalies in weathered rocks directly to LIP events. However, the effects of incipient weathering on Hg contents and Hg/TOC ratios are not known. In this study, we elucidate the behavior of Hg during incipient weathering by investigating visually pristine black shales from outcrops of the Ravnefjeld Formation in East Greenland (GRL) and comparing them to drill core equivalent intervals acquired from the same outcrop area and correlative shales from the mid-Norwegian shelf (MNS). By using geochemical investigations and principal component analysis, we characterize the main host phases of Hg and relate the different Hg contents of pristine samples from GRL and MNS to different Hg inputs during shale deposition. Compared with pristine drill core samples, incipiently weathered outcrop shales have up to 77% lower Hg contents and up to 64% lower Hg/TOC ratios. Incipient weathering causes the early degradation of Hg signals, which masks the primary Hg and Hg/TOC signals in sedimentary rocks. Therefore, we suggest that the presence and effects of weathering in sedimentary rock should be evaluated before discussing Hg signals.

Seawater sources of Hg enrichment in Ordovician-Silurian boundary strata, South China

The Late Ordovician mass extinction (LOME), the second-largest biodiversity crisis of the Phanerozoic, occurred in two discrete pulses, the causation of both of which has been linked to environmental stresses induced by the onset and termination of the Hirnantian Glaciation. Recent studies have inferred significant mercury (Hg) anomalies, mainly from the South China region, during the Ordovician-Silurian transition (OST) that links the LOME to massive volcanism–a hypothetical late Ordovician large igneous province (LIP). However, volcanism in South China during the OST was a dominantly regional phenomenon, even though coeval eruptions in Laurentia and Baltica were major events controlled by Caledonian tectonism. The potential linkage between regional arc or LIP volcanism and the LOME needs further investigation. Here, we examine Hg concentrations, Hg isotopes, and redox-sensitive elements in two deep-water successions (the YY2 and JY11 drillcores) of South China straddling the OST. Our analysis revealed no volcanic Hg anomalies and showed significant discordance between bentonite-bed distribution and the overall pattern of the OST redox evolution in South China. Also, Hg isotope data show relatively constant mass-independent fractionation (Δ199Hg = +0.13‰ ± 0.03‰), which implicates seawater sources of Hg enrichment during the OST. Hence, we propose that the LOME was caused not by massive volcanism, but rather by the expansion of anoxia triggered by long-term cooling and weathering P-induced marine eutrophication.

Tracing concealed gold deposits using mercury isotopes in surface soils: A study from the Shuiyindong gold deposit, Guizhou province, China

Surface soil sampling has been proved to be an effective and low-cost mineral exploration method in covered terrains. The critical question is to determine whether the surface anomalies originated from the mineralization at depth. Mercury isotope signatures have recently been employed as a tool for understanding the sources of Hg anomalies. Meanwhile, Hg is a traditional pathfinder for Au exploration. Can Hg isotopes be applied to trace the sources of Au anomalies in topsoils in covered areas? This is the first study that employed Hg isotopes as an exploration proxy for Au mineralization at depth. Surface soil samples over the concealed Shuiyindong Au deposit, China, were collected and their total Au (TAu), total Hg (THg) contents, and Hg isotope compositions were analyzed. Gold and Hg surface positive anomalies display high correlation indexes along the sampled traverse above the Shuiyindong Au deposit. Moreover, the Hg anomaly is significantly stronger than that of Au. Soils from deep ores-related areas show clearly positive δ202Hg values (−0.78‰ to −0.23‰, averaging −0.46 ± 0.19‰, n = 10, 1SD) compared with those from the background areas (−1.67‰ to −0.66‰, averaging −1.07 ± 0.28‰, n = 10, 1SD). δ202Hg and 1/THg in deep ores-related soils have been altered by the ascending geogas from the mineralized rocks of the Longtan Fm. Soil positive Au anomalies detected in the study area are sourced at depth in the Shuiyindong Au deposit. However, it is not feasible to apply Δ199Hg to trace the anomalous Au sources in topsoils, because Hg(II) photoreduction can imprint the Δ199Hg signature, leading to negative Δ199Hg values in the soils. Semi-volatile Hg and ultra-fine Au particles are mobile and could continuously migrate from the depth to the surface through macro-structures and micro-fractures with the ascending geogas, then most of them are absorbed by the surface soils. Overall, this study successfully traced the Au deposit at >650 m depth using δ202Hg, which is significant for mineral exploration of deep-seated Au deposits, especially in unknown covered areas.

Mercury enrichments of the Pyrenean foreland basins sediments support enhanced volcanism during the Paleocene-Eocene thermal maximum (PETM)

The Paleogene records the most prominent global climate change of the Cenozoic Era with a shift from a greenhouse to an icehouse world. Several transient hyperthermal events punctuated this long-term evolution. The most pronounced and the best known of these is the Paleocene-Eocene Thermal Maximum (PETM-56 Ma). This event is associated with global warming, a worldwide perturbation of the carbon cycle, and significant biotic changes. The PETM is primarily recorded by a sharp negative carbon isotope excursion (NCIE) in both carbonates and organic matter of sedimentary successions. The source of the 13C-depleted carbon for the NCIE and whether it was released in one or numerous events is still debated. Several carbon sources have been proposed to explain the PETM-NCIE and the mechanisms that triggered this abrupt climate upheaval. These include, among others, the magmatic and thermogenic release of carbon associated with the emplacement of Large Igneous Provinces (LIP). One proxy for tracking past volcanic emissions in the geological record and testing hypothetical links between volcanism and hyperthermals is the use of mercury (Hg) anomalies found in marine and continental sedimentary successions. Here, we present new high-resolution mercury and stable isotopic records from a continental-marine transect in Pyrenean peripheral basins during the PETM. Compared to deeper marine settings, the significant sedimentation rate that characterizes these high-accommodation and high sediment-supply environments allows the preservation of expanded successions, providing reliable information about the fluctuations of Hg concentration in deposits across the PETM. Our data reveal two large negative carbon excursions across the studied successions. Based on biostratigraphy and the similarity of shape and amplitude of the isotopic excursions with global records, we interpret the largest NCIE as the PETM. This main excursion is preceded by another that we interpret as the Pre-Onset Excursion (POE), found in other profiles worldwide. We find that the POE and the PETM are, in our studied sections, systematically associated with significant Hg anomalies regardless of the depositional environment. These results suggest that large pulses of volcanism, possibly related to the North Atlantic Igneous Province's emplacement, contributed to the onset and possibly also to the long duration of the PETM. Furthermore, the record of higher Hg anomalies in nearshore than offshore settings suggests a massive collapse of terrestrial ecosystems linked to volcanism-driven environmental change triggered significant Hg loading in shallow marine ecosystems. If this is correct, these findings confirm the primary role of the solid Earth in determining past terrestrial climates.

High mercury enrichments in sediments from the Baltic continent across the late Cambrian: Controls and implications

The late Cambrian witnessed significant biological and environmental changes. However, the main triggers responsible for that formidable turnover remain largely unknown. This study investigates mercury (Hg) enrichments from the late Miaolingian to Furongian section in a unique Alum Shale drilled core obtained from southeast Sweden. Our results show that the background level of Hg is relatively high because of the presence of reducing conditions and continuous Hg supply from water mass. However, our most spectacular findings are the presence of four Hg anomalies. The most pronounced Hg anomalies are characterized by the high values in total Hg (~900 ppb) and Hg/TOC ratio (~80), as well as specific signatures of mass independent fractionation of Hg (MIFs; Δ199Hg, Δ201Hg, and Δ200Hg) that we attribute to volcanic-derived Hg. This Hg loading event occurred immediately after the globally recognized Steptoean Positive Carbon Isotope Excursion (SPICE) event and could be attributed to volcanic activities during that period.

Different controls on the Hg spikes linked the two pulses of the Late Ordovician mass extinction in South China

The Late Ordovician mass extinction (LOME, ca. 445 Ma; Hirnantian stage) is the second most severe biological crisis of the entire Phanerozoic. The LOME has been subdivided into two pulses (intervals), at the beginning and the ending of the Hirnantian glaciation, the LOMEI-1 and LOMEI-2, respectively. Although most studies suggest a rapid cooling and/or oceanic euxinia as major causes for this mass extinction, the driver of these environmental changes is still debated. As other Phanerozoic’s mass extinctions, extensive volcanism may have been the potential trigger of the Hirnantian glaciation. Indirect evidence of intense volcanism comes from Hg geochemistry: peaks of Hg concentrations have been found before and during the LOME, and have all been attributed to global volcanism in origin. Here, we present high-resolution mercury (Hg) profiles in three study sections, from a shelf to slope transect, on the Yangtze Shelf Sea (South China) to address the origin of Hg anomalies across the Ordovician–Silurian (O–S) boundary. The results show Hg anomaly enrichments in the middle Katian, late Katian, the LOMEI-1 at the beginning of the Hirnantian glaciation, the LOMEI-2 in the late Hirnantian glaciation, and late Rhuddanian. The Hg anomaly enrichments during the middle–late Katian and late Rhuddanian would probably reflect a volcanic origin. We find two different controls on the recorded Hg anomalies during the extinction time: i.e., primarily volcanism for the Hg anomaly at the LOMEI-1 and euxinia for the Hg anomaly at the LOMEI-2. Expansion of euxinia at the LOMEI-1 would have been probably enhanced by volcanic fertilization via weathering of volcanic deposits during the Middle and late Katian, and combined with euxinia at the LOMEI-2 to finally be responsible for the two pulses of the LOME.

3D geochemical modeling of the Qujia gold deposit, China: Implications for ore genesis and geochemical exploration of deep concealed ore bodies

Phase separation is a crucial controlling factor of gold deposition in shallow and low-medium temperature orogenic gold systems in the Jiaodong gold province. In this study, spatial distributions by three-dimensional (3D) modeling and correlation analysis of Au, S, Cl, Hg, Fe2O3, Cu, Pb, and Bi were conducted to demonstrate the occurrence of phase separation and its significance in geochemical exploration. The modeling and analysis were based on a geochemical dataset of 1130 borehole samples from the Qujia gold deposit. The ore bodies developed in deep traps (e.g., fault intersections and dilational cracks). Gold and S are positively correlated and mainly distributed along the Jiaojia Fault (JJF). Scatter plots show little correlation between Au and Cl. However, the Au and Cl distributions presented by the ore-bearing boreholes and 3D modeling suggest that Cl escaped from the ore-forming fluid and formed enrichment zones above the ore bodies during the Au mineralization which is consistent with the salinity decrease from the early and main ore-forming stage to the late ore-forming stage of many gold deposits in the JJF and other areas of the Jiaodong gold province. The spatial distribution of Au and Hg are indicative and compelling although they have little correlation in the scatter analysis. Mercury depletion zones and subsequent funnel-like Hg anomalies are present above the ore bodies and strong Hg anomalies appear in the deep traps. The results suggest that phase separation is responsible for Au precipitation in the Qujia gold deposit. Mercury, Cl, and Pb partitioned into a gas phase forming medium-to-high anomalies along the secondary faults whereas Au, S, Fe2O3, Cu, and Bi partitioned into a liquid phase forming ore bodies and medium-to-high anomalies along the JJF during the phase separation. Specifically, the pH increase induced by the partition of CO2, HCl and minor amounts of H2S into the gas phase, and S consumption by the abundant metals (Fe2O3, Cu, Bi, etc.) in the ore-forming fluid, rather than H2S escape, are the dominant factors governing Au precipitation. Finally, potential indicators of geochemical exploration are proposed including composite anomalies of Au and Hg in the near surface medium, high Hg anomaly accompanied by no or low Au anomaly in the fault zones, and extremely high Cl or S anomalies in deep depths. Given the similarity of the ore-forming fluid and metallogenic mechanism at the shallow depths, these indicators are potentially useful for Au exploration in the Jiaodong gold province.

Mercury enrichments during the Carnian Pluvial Event (Late Triassic) in South China

Abstract The Carnian Pluvial Event (CPE) was an interval marked by global climatic and environmental change, along with biotic turnover, which occurred during the early Late Triassic. Although the causes and consequences of this event remain unclear, one possible scenario is enhanced volcanism injecting greenhouse gases into the atmosphere, perturbing the global carbon cycle, and negatively impacting the global environment. However, there is an underlying challenge in showing a true cause- and-effect relationship between volcanism and the CPE, as both the sedimentary and volcanic records are difficult to date accurately enough to demonstrate temporal correspondence. However, mercury (Hg) can be used to fingerprint catastrophic volcanism in the sedimentary record. We examined two sections that record the CPE at Laishike and Wayao in Guizhou Province, southwest China, which display high Hg contents along with spikes of Hg/total organic content (TOC), Hg/Al, Hg/total sulfur (TS), and Hg/(Mo/Al) during the CPE that indicate a shift to excess Hg loading. These Hg anomalies are correlative with the global negative excursion in δ13Ccarb values at the CPE, which suggests that increased volcanism injected both massive amounts of Hg and isotopically light carbon into the atmosphere, and these were ultimately recorded in marine sediments. This interpretation is supported by slightly negative or near-zero Δ199Hg values that are consistent with a volcanic Hg source. Our study supports the hypothesis that enhanced volcanism played a major role in the evolution of biota and the environment during the CPE.

Targeting deep-seated gold deposits: A study from the qujia gold deposit, Shandong province, China

The Jiaodong gold (Au) province is the largest gold ore cluster in China and is an important world-class Au cluster area. Due to the exploitation of shallow Au deposits, prospecting for deep-seated Au deposits (>500 m) become increasingly important. This study uses the Qujia Au deposit to illustrate how to target deep-seated Au deposits by integrating soil and borehole geochemical data into a three-dimensional (3-D) geochemical model based on nine section lines with 652 surface soil samples and 823 rock samples from 30 boreholes. The additive log-ratio (alr)-factor analysis (FA) was adopted for soil geochemical data to identify element associations, and key element associations were extracted: F5 (Au–Ag association) indicates Au mineralization, and F3 (Hg–As–Br–I–Se association) represents the mineralizing agents. Combined with Au, Ag and Hg distribution by 3-D modelling based on borehole geochemical data, Hg is extremely competent as a vector for transportation channels of Au-bearing hydrothermal fluids in shallow space and ore-hosting space in deep space. Meanwhile, Au and Ag in primary halos not only form secondary halos near the primary halos but also remobilize, migrate, and deposit to form secondary anomalies at Lower-lying areas far away from primary halos due to their high mobility, while Hg is more stable and forms anomalies near the primary halos in supergene environments. Finally, two indicators for deep-seated Au ore bodies are constructed: one is the composite anomaly of Au, Ag, and Hg derived from soil geochemical data, and the other is the Hg anomaly derived from borehole geochemical data. Overall, this study successfully constructed indicators for deep-seated Au ore bodies by integrating soil and borehole geochemical data which is significant for geochemical exploration of deep-seated Au ore bodies in the same mineralization belt of the Jiaodong district.

Flash floods controlling Cu, Pb, As and Hg variations in fluvial sediments of a river impacted by metal mining in the Atacama Desert

Solid mine wastes can be dispersed in river systems by fluvial processes contaminating distant areas. This process has been previously reported in rivers of the Atacama Desert impacted by mining. The removal of waste in these rivers is a complex environmental scenario that involves (i) mining operation plans, (ii) the spatio-temporal variability of precipitation events and, (iii) the sediment-transport pathways within the drainage network. This work presents how flash floods triggered by extreme storm events determine the redistribution and the variation of elemental concentrations of the suspended load fraction in a river with several historical and actual mine wastes situated in the Atacama Desert. The concentrations of Cu, Pb, As and Hg measured in two sampling stations of a mining segment of the Copiapó River after flash floods are lower compared to the concentrations measured in the period before these hydrometeorological events. However, the concentrations of these metals and metalloids increased in areas distant from the mine clusters, where the values observed before the flash floods were lower. The redistributions of the element concentrations can be explained by the occurrence of two major flood events triggered by the extreme storm events of March 2015 and May 2017. The combination of the element concentrations with calculated geo-accumulation indexes shows the potential source of geochemical anomalies for these elements. Cu and Hg anomalies are induced by historical mining activities in the Copiapó River while Pb and As concentrations agree with the regional background. Some Pb and As anomalies would be associated with the geology of the zone where the main cluster of mine exploitations are present. The fact that flash floods result in Cu, Pb, As and Hg concentrations in sediment load more in line with the local background, suggests that this type of hydrometeorological events probably represent the natural processes of geochemical recovery of arid river impacted by metal mining.

The mid-Tournaisian (Early Carboniferous) anoxic event in the Laurussian shelf basin (Poland): An integrative approach

A wide range of proxies (organic and inorganic geochemistry, gamma-ray spectrometry, microfacies, framboidal pyrite analysis) were applied in order to decipher changes in depositional conditions during the mid-Tournaisian anoxic event, referred to as the Lower Alum Shale Event (LASE) in the Polish part of the Laurussia basin. The LASE part of the section, unlike older Tournaisian deposits, is characterised by high concentrations of isorenieratane, palaeorenieratane, and their diagenetic derivatives, the occurrence of 2-methyl-3-iso-butyl-maleimides, and high values of the sterane-to-hopane ratio. The predominance of tiny pyrite framboids, inorganic data such as low values of the Th/U and high values of the Corg/P and V/Cr ratios, and generally higher enrichments of redox-sensitive metals such as U, V, Mo, Pb, and Zn and depletion in Mn, all suggest anoxic/euxinic conditions on the sea-bottom. The results of our investigations, especially Co, Mn, Cd, and Mo distribution patterns, demonstrate that enhanced primary productivity in the water column was responsible for a high degree of organic carbon burial rather than preservation in restricted conditions on the seafloor. This elevated productivity may have been generated by the upwelling of nutrient-rich deep water, an increase in volcanic activity and volcanogenic oceanic fertilisation, or both. Volcanically driven mid-Tournaisian climatic changes (warming), as manifested by high Zr concentrations and Hg anomalies, may have been responsible for the deglaciation of Gondwana resulting in the global crenulata transgression.The global rise in sea level and high level of organic productivity were responsible for the development of anoxic conditions and the halt of carbonate production, as reflected by drastic changes of facies not only in the sections investigated, but in many other parts of the world as well.

Major volcanic eruptions linked to the Late Ordovician mass extinction: Evidence from mercury enrichment and Hg isotopes

Abstract The Late Ordovician mass extinction (LOME) was the second most severe Phanerozoic biodiversity crisis. While environmental deterioration and oceanographic changes associated with the Hirnantian glaciation have been frequently invoked as potential extinction drivers, recent evidence for a large igneous province eruption at that time has challenged this prevailing view. As such, the triggering and killing mechanisms of the LOME remain debated. Here we report mercury (Hg) concentrations, isotopic compositions, Hg/total sulfur (Hg/TS), and Hg/total organic carbon (Hg/TOC) in Late Ordovician limestone/black shale alternations from two successions in South China and Laurentia that straddled the paleoequator. Our results, in both areas, show multiple Hg enrichments before and during the LOME, suggesting a global, or at least a widespread increase in environmental Hg loading. The initial Hg enrichments occur in the mid-upper Katian units and are followed by additional Hg anomalies in the lower Hirnantian strata that coincide temporally with the first pulse of the LOME. Extremely high levels of Hg, Hg/TS, and Hg/TOC, with maximum values of 737 ng g−1, 633 ng g−1 Hg/wt% TS, and 167 ng g−1 Hg/wt% TOC, respectively, represent ~3–13 × background values, indicating increased Hg input to the ocean. The absence of mass-independent fractionation of Hg isotopes in the Hg-enriched intervals suggests a volcanic source for the observed Hg anomalies. The temporal coincidence of Hg anomalies with the extinction horizon in both continents suggests that extensive and widespread volcanism may have had global climatic and ecological impact, and was a primary trigger for prolonged and synergetic deterioration of Late Ordovician environment such as climate changes, ocean acidification, and anoxia, causing the LOME.

Mercury linked to Deccan Traps volcanism, climate change and the end-Cretaceous mass extinction

Mercury (Hg) anomalies linked to Large Igneous Provinces (LIP) volcanism have been identified in sediments across all five major mass extinctions in Earth's history. This study tests whether Hg in marine sediments is a reliable proxy linking Deccan Traps volcanic eruptions to late Maastrichtian global climate warming and the mass extinction at the Cretaceous-Paleogene boundary (KPB). Our primary test site is the Elles section in Tunisia, the auxiliary Global Stratotype Section and Point (GSSP) to El Kef. Elles has the most complete marine sedimentary record and a high average sedimentation rate of ~4.7 cm/ky. We chose the Hor Hahar section in Israel to corroborate the geographic distribution of Hg fallout from Deccan volcanism. Reliability of the Hg proxy over the last 550 ky of the Maastrichtian to early Danian was evaluated based on high-resolution age control (orbital cyclostratigraphy), stable isotope climate record, Hg concentrations, biotic turnover and mass extinction. These results were correlated with the pulsed Deccan eruptive history constrained previously by U-Pb zircon geochronology. Our results support Hg as robust proxy for Deccan volcanism with large Hg spikes marking “extreme event” (EE) pulsed eruptions correlative with climate warming peaks separated by steady, less intense eruptions. Long-term global climate warming began near ~350 ky pre-KPB, reached maximum warming (3–4 °C) between 285 and 200 ky pre-KPB, followed by gradual cooling and rapid temperature drop between 45 and 25 ky pre-KPB. During the last 25 ky before the KPB, multiple Hg EE eruptions correlate with hyperthermal warming that culminated in the rapid mass extinction at Elles during ≤1000 years of the Cretaceous. These latest Cretaceous Hg peaks may correlate with massive, distal, Deccan-sourced lava flows (>1000 km long) that traversed the Indian subcontinent and flowed into the Bay of Bengal, bracketing the mass extinction. These results support Deccan volcanism as a primary driver of the end-Cretaceous mass extinction. • Hg anomalies in sediments are a reliable proxy for Deccan volcanism. • Deccan eruptions caused long-term climate warming in the last 350 ky of the Cretaceous. • Long-term climate warming resulted in faunal decline but no extinctions. • Paroxysmal Deccan eruptions occurred during the last 25 ky of the Cretaceous. • Deccan-induced hyperthermal and ocean acidification led to the KPB mass extinction.

Natural and anthropogenic landscapes of the gold-mining regions in Bashkortostan (Russia)

This article presents the results of laboratory and field studies of territories in the zone of influence of the gold extracting and mining enterprises of the Southern Urals. Researches were conducted on six sites of gold mining of the past years, in order to identify natural and technogenic mercury in various natural and man-made landscapes of mining Bashkortostan. A brief description of the mineralization of the study area and types of gold deposits is given. The mercury content in bedrock, in various types of ores, man-made soils (fine-grained tailings dump, tailings), soils, bed-silts, in the soil air, in water was determined. The largest technogenic anomalies are Hg dissemination flows in bed silts of watercourses and lakes. Technogenic Hg anomalies in soils are local and are formed in the areas of mining and old ores processing. The practical absence of anomalies in transit environments with intensive Hg accumulation in long-term deposition reflects the regressive residual nature of technogenic mercury anomalies.

Multi-disciplinary ore deposit exploration in Sonqor, northwest Iran

Multi-disciplinary exploration methods are used to explore for possible ore deposits in the Sonqor area, Iran, which lies within the Sanandaj-Sirjan Zone, and contains significant iron, copper and gold mineralisation. Hydrothermal alteration was mapped using field, remotely sensed, geophysical and geochemical data as well as Landsat-8 Operational Land Imager, Landsat Enhanced Thematic Mapper plus, and two Advanced Space Borne Thermal Emission and Reflection Radiometer images. Image processing techniques, viz band ratio, principal component analysis (PCA), and various spectral analysis methods were applied to map the distribution of hydrothermally altered rocks (geochemical halos) associated with porphyry (e.g. Cu–Au) mineralisation. The geochemical halos enabled vectoring to mineralised zones with mapping of advance argillic, argillic, carbonates, Fe-oxides, phyllic, propylitic and silicification using minerals such as alunite (K/Na), muscovite, kaolinite, illite, chlorite, goethite, hematite, jarosite, calcite and silica/quartz. The band ratio combination of sensors for mapping altered areas show promising results, similar to other more advanced methods. PCA exposed variations in the spatial distribution of more hydroxyl-based minerals like alunite/jarosite, whereas the geophysical magnetic survey identified the main lineaments, possible faults and magmatic intrusion boundaries. While geochemical methods show the potential occurrence of elements like Fe, Au and Fe-bearing Ti in the southeast and southern parts, and skarn-type anomalies in the northern part of Sonqor, leaking of specific geochemical elements (such as Fe, Au and Fe-bearing Ti) produce false anomalies. Copper, Pb and Zn anomalies in the central part show the possibility of sulfide-based mineralisation. KEY POINTS Space-based satellite technologies were used to identify mineral prospects in the Sonqor area, within the iron, copper and gold-rich Sanandaj-Sirjan Zone, Iran. The Sonqor area, part of the Zagros Orogen, is within the extensive Alpine–Himalayan orogenic belt formed by collision of the Arabian continent with the Iranian microcontinent in the Late Cretaceous to Cenozoic. The western part of the Sonqor area has first rank Hg, Au, Ag, Ta and Sb anomalies with abundant detachment faults. Dacite domes with surrounding alteration have potential for Au epithermal mineralisation (Dashkasan type); the central part may yield Cu, Zn and Pb sulfide mineralisation. The Sonqor geological map suggests good potential for Au, Fe and Fe–Ti mineralisation at the contact between limestones in the eastern and southeastern parts, but greenschist and amphibolite facies metamorphism necessitates caution in interpretation of geochemical anomalies.

Volcanic related methylmercury poisoning as the possible driver of the end-Devonian Mass Extinction

The end-Devonian global Hangenberg event (359 Ma) is among the most devastating mass extinction events in Earth’s history, albeit not one of the “Big Five”. This extinction is linked to worldwide anoxia caused by global climatic changes. These changes could have been driven by astronomical forcing and volcanic cataclysm, but ultimate causes of the extinction still remain unclear. Here we report anomalously high mercury (Hg) concentration in marine deposits encompassing the Hangenberg event from Italy and Austria (Carnic Alps). The Hangenberg event recorded in the sections investigated can be here interpreted as caused by extensive volcanic activity of large igneous provinces (LIPs), arc volcanism and/or hydrothermal activity. Our results (very large Hg anomalies) imply volcanism as a most possible cause of the Hangenberg event, similar to other first order mass extinctions during the Phanerozoic. For the first time we show that apart from anoxia, proximate kill mechanism of aquatic life during the event could have been methylmercury formed by biomethylation of a volcanically derived, huge concentration of inorganic Hg supplied to the ocean. Methylmercury as a much more toxic Hg form, potentially could have had a devastating impact on end-Devonian biodiversity, causing the extinction of many pelagic species.

Ecological disturbance in tropical peatlands prior to marine Permian-Triassic mass extinction

AbstractThe Permian-Triassic mass extinction is widely attributed to the global environmental changes caused by the eruption of the Siberian Traps. However, the precise temporal link between marine and terrestrial crises and volcanism is unclear. Here, we report anomalously high mercury (Hg) concentrations in terrestrial strata from southwestern China, synchronous with Hg anomalies in the marine Permian-Triassic type section. The terrestrial sediments also record increased abundance of fossil charcoal coincident with the onset of a negative carbon isotope excursion and the loss of tropical rainforest vegetation, both of which occurred immediately before the peak of Hg concentrations. The organic carbon isotope data show an ∼5‰–6‰ negative excursion in terrestrial organic matter (bulk organic, cuticles, and charcoal), reflecting change in atmospheric CO2 carbon-isotope composition coincident with enhanced wildfire indicated by increased charcoal. Hg spikes provide a correlative tool between terrestrial and marine records along with carbon isotope trends. These data demonstrate that ecological deterioration occurred in tropical peatlands prior to the main marine mass extinction.

Mercury spikes at the Devonian-Carboniferous boundary in the eastern part of the Rhenohercynian Zone (central Europe) and in the South China Block

Mercury (Hg) chemostratigraphy is an efficient tool for tracing distal volcanism, as suggested in many recent studies. In our research, we focused on Hg and other trace element contents in two Devonian-Carboniferous boundary sections from two different and spatially distant areas. The Lesní lom section (Czech Republic) was located in the south-eastern part of the Laurussia plate and the Duli (Guangxi, China) section in the South China Plate. In both studied sections, the highest Hg, Hg/Fexs or Hg/Al values occurred at the Devonian-Carboniferous boundary. In Lesní lom, organic matter remineralization was connected with origin of pyrite which sequestered a part of the Hg content. The decoupling of Hg and TOC within the Duli section strata and the significant correlation with Al and Fe may suggest that Hg is hosted primarily by clay particles, derived from the landmass into the marine realm. Mercury was also incorporated into pyrites but the poor correlation between Hg and TS (total sulfur) indicates a possible loss of S during oxygenation events. In the Lesní lom section, and partly in the Duli section, Fe and Mn redox cycling may have played an important role in sediment Hg content. Both sections were influenced by widespread hydrothermal and volcanic activity, indicated by positive Eu anomalies, MSI, Fe/Ti, Zr/Al2O3 and Ti/Al2O3 values. It remains to be clarified whether, besides the interplay of local magmatic activity and redox oscillations, there may have been some additional influence of the multi-phase Viluy Large Igneous Province, although its younger phase (364.4 ± 1.7 Ma) slightly precedes the Hg anomalies obtained.

Marine anoxia and sedimentary mercury enrichments during the Late Cambrian SPICE event in northern Scotland

Elevated mercury concentrations in ancient sedimentary rocks are used as a fingerprint for large igneous province (LIP) volcanism because there is a tight association between known LIPs and coeval sedimentary Hg anomalies. While nonvolcanic processes of sedimentary Hg enrichment, including redox variations, have been demonstrated in modern settings, interpretations of ancient sedimentary Hg records have focused on LIP volcanism. Here, we document a link between sedimentary Hg enrichment and marine redox changes during the late Cambrian Steptoean positive isotopic carbon excursion (SPICE) event, a time with no known LIP. We report a new occurrence of the SPICE event from the Eilean Dubh Formation of northern Scotland, which preserves a series of coeval Hg enrichments. Abundant glauconite, a redox-sensitive iron-bearing mineral, co-occurs stratigraphically with the SPICE and Hg enrichments but is rare to absent from the rest of the section, and bioturbation is low in strata spanning the SPICE. We suggest that local Hg enrichments were driven by changing marine redox conditions during the SPICE event, rather than emplacement of a LIP. Redox oscillations should be considered as an additional control on Hg enrichments in the geologic record.

Mercury anomalies across the Palaeocene–Eocene Thermal Maximum

Abstract. Large-scale magmatic events like the emplacement of the North Atlantic Igneous Province (NAIP) are often coincident with periods of extreme climate change such as the Palaeocene–Eocene Thermal Maximum (PETM). One proxy for volcanism in the geological record that is receiving increased attention is the use of mercury (Hg) anomalies. Volcanic eruptions are among the dominant natural sources of Hg to the environment; thus, elevated Hg∕TOC values in the sedimentary rock record may reflect an increase in volcanic activity at the time of deposition. Here we focus on five continental shelf sections located around the NAIP in the Palaeogene. We measured Hg concentrations, total organic carbon (TOC) contents, and δ13C values to assess how Hg deposition fluctuated across the PETM carbon isotope excursion (CIE). We find a huge variation in Hg anomalies between sites. The Grane field in the North Sea, the most proximal locality to the NAIP analysed, shows Hg concentrations up to 90 100 ppb (Hg∕TOC = 95 700 ppb wt %−1) in the early Eocene. Significant Hg∕TOC anomalies are also present in Danish (up to 324 ppb wt %−1) and Svalbard (up to 257 ppb wt %−1) sections prior to the onset of the PETM and during the recovery period, while the Svalbard section also shows a continuous Hg∕TOC anomaly during the body of the CIE. The combination with other tracers of volcanism, such as tephra layers and unradiogenic Os isotopes, at these localities suggests that the Hg∕TOC anomalies reflect pulses of magmatic activity. In contrast, we do not observe clear Hg anomalies on the New Jersey shelf (Bass River) or the Arctic Ocean (Lomonosov Ridge). This large spatial variance could be due to more regional Hg deposition. One possibility is that phreatomagmatic eruptions and hydrothermal vent complexes formed during the emplacement of sills led to submarine Hg release, which is observed to result in limited distribution in the modern era. The Hg∕TOC anomalies in strata deposited prior to the CIE may suggest that magmatism linked to the emplacement of the NAIP contributed to the initiation of the PETM. However, evidence for considerable volcanism in the form of numerous tephra layers and Hg∕TOC anomalies post-PETM indicates a complicated relationship between LIP volcanism and climate. Factors such as climate system feedbacks, changes to the NAIP emplacement style, and/or varying magma production rates may be key to both the onset and cessation of hyperthermal conditions during the PETM. However, processes such as diagenesis and organic matter sourcing can have a marked impact on Hg∕TOC ratios and need to be better constrained before the relationship between Hg anomalies and volcanic activity can be considered irrefutable.