Remobilization Processes Research Articles

Multi-stage Cu remobilization of the Huping metamorphic-hydrothermal deposit in the southern North China Craton

The Zhongtiao region is a well-endowed Cu metallogenic province in the southern North China Craton and contains a large number of early Precambrian Cu deposits of different styles, most of which have been subjected to the ca. 1.85 Ga regional metamorphism. However, whether there was any role for the Proterozoic metamorphism on the extensive Cu mineralization is yet to be well understood. This paper presents an integrated investigation on the field geology, mineral chemistry, fluid inclusion and C–H–O–S isotopes of the Huping metamorphic-hydrothermal deposit in the Neoarchean–Paleoproterozoic Zhongtiao metamorphic terranes, and reveals multi-stage Cu remobilization that formed and upgraded the Cu deposits in the region. We identified three stages of syn- to post-metamorphic Cu remobilization/transportation in the Huping Cu deposit, including (I) early mechanical transport, (II) intermediate metamorphic-hydrothermal remobilization and (III) late meteoric fluid incursion. In stage I, sulfides were remobilized and transported internally under lower-greenschist facies metamorphism, forming the veinlet–disseminated ores and chalcopyrite (avg. δ34S = 2.1‰, similar to the chlorite-amphibole schist wall rocks). In stage II, the immiscibility of metamorphic fluids (avg. δ18O = 4.6‰ and δD = −56.6‰) from the metamorphic terranes triggered the precipitation of higher δ34S chalcopyrite (avg. 8.0‰), led by the incorporation of extra sulfur during the fluid migration. In stage III, incursion of meteoric fluids into the waning metamorphic-hydrothermal system formed the barren quartz-calcite veins (avg. δ18O = 0.09‰ and δ13C = −0.88‰). During these Cu remobilization processes, the earlier-formed sulfides were chemically stable during the mechanical transfer by regional metamorphism and deformation. Subsequently, the immiscibility of metamorphic fluids induced significant Cu remobilization and precipitation in the metamorphic-hydrothermal system. We thus propose a model of multi-stage mechanical and chemical Cu remobilization for the Huping Cu deposit, which highlights the crucial impacts of metamorphic-remobilization processes on the regional Cu mineralization in the Zhongtiao region.

Combined ToF-SIMS and XPS characterization of 304L surface after interaction with caesium iodide under PWR severe accident conditions

In case of a severe accident (SA) occurring in a pressurized water reactor (PWR) fission products (Cs, I) are released from the degraded fuel and transported through the reactor coolant system (RCS). A part is deposited onto surfaces of the RCS and can be subsequently chemically re-mobilized, in case the atmosphere composition changes. In order to improve our understanding on the re-mobilization processes, it is important to describe the interactions between deposited fission products and surfaces representative of RCS in SA conditions (mainly oxidized SS 304L) and to identify the species formed after remobilization. In this study CsI aerosols were deposited on the surface of 304L coupons, which have been previously oxidized. The deposits were afterwards re-heated (up to 750 °C) in either air or steam. At every step, the 304L coupons were analysed by a combination of surface analysis techniques (XPS, ToF-SIMS), Raman spectroscopy and SEM. It has been established that the initial surface state of the 304L coupons (i.e. oxidation in air or steam) has no effect on the release of caesium or iodine. However, the composition of the carrier gas during the re-heating phase influences significantly the release of caesium. Specifically, in air a significant amount of Cs remains on the coupon and forms mixed oxides with chromium, such as Cs2CrO4 and Cs2Cr2O7. The results are then discussed and compared with literature data.

REY and Trace Element Chemistry of Fluorite from Post-Variscan Hydrothermal Veins in Paleozoic Units of the North German Basin

Hydrothermal fluorites from Paleozoic sedimentary rocks and volcanic units in the North German Basin (NGB) have been investigated to create a petrographic and geochemical inventory—with particular focus on strategic elements such as rare earth elements (REE)—and to uncover possible links between the post-Variscan hydrothermal mineralization in the NGB and bordering areas such as the Harz Mountains and Flechtingen Calvörde Block (FCB). Fluorites from ten localities underwent a detailed petrographic examination, including SEM-BSE/CL imagery, and were compositionally analysed using LA-ICP-MS. Overall, REY concentrations are comparatively low in fluorite from all investigated areas—the median sum of REY ranges from 0.3 to 176 ppm. EuropiumCN anomalies are slightly negative or absent, indicating that either the formation fluid experienced temperatures above 250 °C or that fluid-rock interactions and REE enrichment was likely controlled by the source rock (i.e., volcanic) composition and complexation processes. Fluorites from the Altmark-Brandenburg Basin (ABB) and the Lower Saxony Basin (LSB) display distinctly different REYCN signatures, suggesting that fluid compositions and genetic processes such as fluid-rock interaction differed significantly between the two areas. Complex growth zones and REYCN signatures in fluorite from the ABB and the FCB reflect geochemical variability due to adsorption processes and intrinsic crystallographic controls and imply that they are genetically related. Two petrographically and geochemically distinct generations are observed: Fluorite I—light SEM shades, relatively enriched in LREE; Fluorite II—darker SEM shades, comparatively depleted LREE, slightly higher HREE concentrations. These fluorite generations represent zoned (or cyclical) growth within a single progressive hydrothermal event and do not reflect a secondary remobilization process. We demonstrate that increasing Tb/La ratios and decreasing La/Ho ratios can be the result of continuous zoned growth during a single mineralizing event, with significant compositional variations on a micron-scale. This has implications for the interpretation of such trends and hence the inferred genetic evolution of fluorite that displays such geochemical patterns. The complex micro-scale intergrowth of these generations stresses the need for detailed petrographic investigations when geochemical data are collected and interpreted for mineral exploration.

Insights into Extinct Seafloor Massive Sulfide Mounds at the TAG, Mid-Atlantic Ridge

Over the last decade there has been an increasing interest in deep-sea mineral resources that may contribute to future raw metal supply. However, before seafloor massive sulfides (SMS) can be considered as a resource, alteration and weathering processes that may affect their metal tenor have to be fully understood. This knowledge cannot be obtained by assessing the surface exposures alone. Seafloor drilling is required to gain information about the third dimension. In 2016, three extinct seafloor massive sulfide mounds, located in the Trans-Atlantic Geotraverse (TAG) hydrothermal area of the Mid-Atlantic Ridge were drilled. A mineralogical and textural comparison of drill core and surface-grab samples revealed that in recent ceased mounds high-temperature copper assemblages typical for black smoker chimneys are still present whereas in longer extinct mounds the mineralogy is pre-dominated by an iron mineral assemblage. Zinc becomes remobilized early in the mound evolution and forms either a layer in the upper part of the mound or has been totally leached from its interior. Precipitation temperatures of sphalerite calculated using the Fe/Zn ratio can help to identify these remobilization processes. While the Fe/Zn ratios of primary sphalerites yield temperatures that are in very good agreement with fluid temperatures measured in white smokers, calculated temperatures for sphalerites affected by remobilization are too high for SMS. Overall drilling of SMS provides valuable information on the internal structure and mineralogy of the shallow sub-surface, however, additional drilling of SMS, at a greater depth, is required to fully understand the processes affecting SMS and their economic potential.

Retention and remobilization mechanisms of environmentally aged silver nanoparticles in an artificial riverbank filtration system

Riverbank filtration systems are important structures that ensure the cleaning of infiltrating surface water for drinking water production. In our study, we investigated the potential risk for a breakthrough of environmentally aged silver nanoparticles (Ag NP) through these systems. Additionally, we identified factors leading to the remobilization of Ag NP accumulated in surficial sediment layers in order to gain insights into remobilization mechanisms.We conducted column experiments with Ag NP in an outdoor pilot plant consisting of water-saturated sediment columns mimicking a riverbank filtration system. The NP had previously been aged in river water, soil extract, and ultrapure water, respectively. We investigated the depth-dependent breakthrough and retention of NP. In subsequent batch experiments, we studied the processes responsible for a remobilization of Ag NP retained in the upper 10 cm of the sediments, induced by ionic strength reduction, natural organic matter (NOM), and mechanical forces. We determined the amount of remobilized Ag by ICP-MS and differentiated between particulate and ionic Ag after remobilization using GFAAS. The presence of Ag-containing heteroaggregates was investigated by combining filtration with single-particle ICP-MS.Single and erratic Ag breakthrough events were mainly found in 30 cm depth and Ag NP were accumulated in the upper 20 cm of the columns. Soil-aged Ag NP showed the lowest retention of only 54%. Remobilization was induced by the reduction of ionic strength and the presence of NOM in combination with mechanical forces. The presence of calcium in the aging- as well as the remobilizing media reduced the remobilization potential. Silver NP were mainly remobilized as heteroaggregates with natural colloids, while dissolution played a minor role.Our study indicates that the breakthrough potential of Ag NP in riverbank filtration systems is generally low, but the aging in soil increases their mobility. Remobilization processes are associated to co-mobilization with natural colloids.

The Zhaxikang Vein‐type Pb‐Zn‐Ag‐Sb Deposit in Himalayan Orogen, Tibet: Product by Overprinting and Remobilization Processes during Post‐collisional Period

AbstractThe Zhaxikang Pb‐Zn‐Ag‐Sb deposit, the largest polymetallic deposit known in the Himalayan Orogen of southern Tibet, is characterized by vein‐type mineralization that hosts multiple mineral assemblages and complicated metal associations. The deposit consists of at least six steeply dipping vein‐type orebodies that are hosted by Early Jurassic black carbonaceous slates and are controlled by a Cenozoic N–S‐striking normal fault system. This deposit records multiple stages of mineralization that include an early period (A) of massive coarse‐grained galena–sphalerite deposition and a later period (B) of Sb‐bearing vein‐type mineralization. Period A is only associated with galena–sphalerite mineralization, whereas period B can be subdivided into ferrous rhodochrosite–sphalerite–pyrite, quartz–sulfosalt–sphalerite, calcite–pyrite, quartz–stibnite, and quartz‐only stages of mineralization. The formation of brecciated galena and sphalerite ores during period A implies reworking of pre‐existing Pb–Zn sulfides by Cenozoic tectonic deformation, whereas period B mineralization records extensive open‐space filling during ore formation. Fluid inclusion microthermometric data indicate that both periods A and B were associated with low–medium temperature (187–267°C) and low salinity (4.00–10.18% wt. NaCl equivalent) ore‐forming fluids, although variations in the physical–chemical nature of the period B fluids suggest that this phase of mineralization was characterized by variable water/rock ratios. Microprobe analyses indicate that Fe concentrations in sphalerite decrease from period A to period B, and can be divided into three groups with FeS concentrations of 8.999–9.577, 7.125–9.109, 5.438–1.460 mol.%. The concentrations of Zn, Sb, Pb, and Ag within orebodies in the study area are normally distributed in both lateral and vertical directions, and Pb, Sb, and/or Ag concentrations are positive correlation within the central part of these orebodies, but negatively correlate in the margins. Sulfide S isotope compositions are highly variable (4‰–13‰), varying from 4‰ to 11‰ in period A and 10‰ to 13‰ in period B. The Pb isotope within these samples is highly radiogenic and defines linear trends in 206Pb/204Pb vs. 207Pb/204Pb and 206Pb/204Pb vs. 208Pb/204Pb diagrams, respectively. The S and Pb isotopic characteristics indicate that the period B orebodies formed by mixing of Pb–Zn sulfides and regional Sb‐bearing fluids. These features are indicative of overprinting and remobilization of pre‐existing Pb–Zn sulfides by Sb‐bearing ore‐forming fluids during a post‐collisional period of the Himalayan Orogeny. The presence of similar ore types in the north Rhenish Massif that formed after the Variscan Orogeny suggests that Zhaxikang‐style mineralization may be present in other orogenic belts, suggesting that this deposit may guide Pb–Zn exploration in these areas.

Crystallization and partial melting of rhyolite and felsite rocks at Krafla volcano: A comparative approach based on mineral and glass chemistry of natural and experimental products

Rhyolite and felsite cuttings were collected at Krafla volcano during the perforation of the Iceland Deep Drilling Project Well 1 (IDDP-1). The perforation was stopped at a depth of 2100 m due to intersection with a rhyolite magma that intruded the felsite host rock. Rhyolite cuttings are vitrophiric (glass ~95%, RHL) and exhibit a mineral assemblage made of plagioclase + augite + pigeonite + titanomagnetite. Felsite cuttings display evidences of partial melting, responding to variable degrees of quartz + plagioclase + alkali feldspar + augite + titanomagnetite dissolution. The interstitial glass analyzed close to (i.e., FLS1) and far from (i.e., FLS2) the reaction surface of pyroxene from felsite cuttings shows continuous changes between the two end-members. FLS1 is compositionally similar to RHL, showing Na2O + K2O + REE depletions, counterbalanced by MgO + CaO enrichments. Conversely, FLS2 exhibits opposite chemical features. REE-exchange thermobarometric calculations reveal that plagioclase and augite cores from rhyolite and felsite formed under identical conditions, along a thermal path of 940–960 °C. However, in terms of major and trace element concentrations, plagioclase and augite crystal cores are not in equilibrium with the rhyolite magma, suggesting the incorporation of these minerals directly from the host felsite. To better understand the petrogenetic relationship between rhyolite and felsite, two sets of crystallization and partial melting experiments have been carried out at P = 150 MPa and T = 700–950 °C. Rhyolite crystallization experiments (RCE) reproduce the two-pyroxene assemblage of IDDP-1 rhyolite cuttings only at T ≤ 800 °C, when the crystal content (≥19%) is higher than that observed in the natural rhyolite (~5%). Under such conditions, the RCE glass is much more differentiated (i.e., marked CaO depletion and Eu anomaly) than RHL. On the other hand, felsite partial melting (FPM) experiments show interstitial glass with a bimodal composition (i.e., FPM1 and FPM2) comparable to FLS1 (≈RHL) and to FLS2, only at T = 950 °C. This effect has been quantified by fractional crystallization and batch melting modeling, denoting that FLS1 (≈RHL) and FLS2 reflect high (≥70%) and low (≤8%) degrees of felsite partial melting, respectively. In contrast, modeling RHL by crystal fractionation requires the removal of an amount (~22%) of solid material that is inconsistent with the low crystal content of the natural IDDP-1 rhyolite. It is therefore concluded that natural rhyolite and felsite represent, respectively, the near-liquidus and sub-solidus states of a virtually identical silicic magma, either feeding aphyric to subaphiric rhyolitic eruptions, or solidifying at depth as phaneritic quartzofeldspathic rocks. Felsite lenses from the Krafla substrate may explore variable degrees of remelting and remobilization processes. The intrusion into felsite of a fresh silicic magma from depth may lead to low degrees of partial melting, whereas the persistent heat release from intense basaltic intrusive events at Krafla may be the source of high degrees of felsite partial melting and consequent rejuvenation of the previously solidified silicic magma.

Macro and Micronutrient Storage in Plants and Their Remobilization When Facing Scarcity: The Case of Drought

Human mineral malnutrition or hidden hunger is considered a global challenge, affecting a large proportion of the world’s population. The reduction in the mineral content of edible plant products is frequently found in cultivars bred for higher yields, and is probably increased by intensive agricultural practices. The filling of grain with macro and micronutrients is partly the result of a direct allocation from root uptake and remobilization from vegetative tissues. The aim of this bibliographic review is to focus on recent knowledge obtained from ionomic analysis of plant tissues in order to build a global appraisal of the potential remobilization of all macro and micronutrients, and especially those from leaves. Nitrogen is always remobilized from leaves of all plant species, although with different efficiencies, while nutrients such as K, S, P, Mg, Cu, Mo, Fe and Zn can be mobilized to a certain extent when plants are facing deficiencies. On the opposite, there is few evidence for leaf mobilization of Ca, Mn, Ni and B. Mechanisms related to the remobilization process (remobilization of mineral forms from vacuolar and organic compounds associated with senescence, respectively) are also discussed in the context of drought, an abiotic stress that is thought to increase and known to modulate the ionic composition of grain in crops.

Results of LA-ICP-MS sulfide mapping from Algoma-type BIF gold systems with implications for the nature of mineralizing fluids, metal sources, and deposit models

Quantitative laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) element distribution maps combined with traverse mode analyses have been acquired on various sulfides (pyrite, pyrrhotite, arsenopyrite) from three Canadian Algoma-type BIF-hosted gold deposits (~ 4 Moz Au Meadowbank, ≥ 2.8 Moz Au Meliadine district, ~ 6 Moz Au Musselwhite). These data, in conjunction with detailed petrographic and SEM-EDS observations, provide insight into the nature and relative timing of gold events, the presence and implication of trace element zoning regarding crystallization processes, and elemental associations that fingerprint gold events. Furthermore, the use of an innovative method of processing the LA-ICP-MS data in map and traverse modes, whereby the results are fragmented into time-slice data, to generate various binary plots (Ag versus Ni) provides a means to identify elemental associations (Te, Bi) not otherwise apparent. This integrated means of treating geochemical data, along with petrography, allows multiple gold events and remobilization processes to be recognized and their elemental associations determined. The main gold event in each of these deposits is characterized by the coupling of an As-Se-Te-Ag element association coincident with intense stratabound sulfide-replacement of the Fe-rich host rock. Additionally, the data indicate presence of a later remobilization event, which upgraded the Au tenor, as either non-refractory or refractory type, along fracture networks due to the ingress of subsequent base metal-bearing metamorphic fluids (mainly a Pb-Bi association). Furthermore, the data reveal a stratigraphic influence, as reflected in the elemental associations and the elemental enrichments observed and the nature of the sulfide phase hosting the gold mineralization (arsenopyrite versus pyrite).

Environmental fate and ecotoxicological risk of the antibiotic sulfamethoxazole across the Katari catchment (Bolivian Altiplano): Application of the GREAT-ER model

Antibiotics are emergent contaminants that can induce adverse effects in terrestrial and aquatic organisms. The surface water compartment is of particular concern as it receives direct waste water discharge. Modeling is highlighted as an essential tool to understand the fate and behavior of these compounds and to assess their ecotoxicological risk. This study aims at testing the ability of the GREAT-ER model in simulating sulfamethoxazole (SMX) concentrations in the surface waters of the arid high-altitude Katari catchment (Bolivian Altiplano), assessing the sensitivity of the parameters considered, and evaluating the ecotoxicological risk posed. The model predicted the general spatial pattern of SMX concentrations. No contaminant abatement was observed during the wet season, supporting the idea that non-point sources, such as runoff and remobilization processes, play an important role during that season. During the dry season, the abatement capacity was 91%, suggesting that natural attenuation, particularly photodegradation, is high during low flow. Pharmaceutical consumption was the parameter that influenced the environmental concentrations the most. The ratio of Predicted Environmental Concentrations to predicted no-effect concentrations varied between 0.14 and 26.6 for the wet season and between 0.14 and 7.6 for the dry season depending on the river stretch.

The genesis of Mo-Cu deposits and mafic igneous rocks in the Senj area, Alborz magmatic belt, Iran

The geochemical and isotopic investigations were provided on the Upper Eocene Senj mafic intrusion and Mo-Cu mineralization to better understand the tectono-magmatic evolution and metallogeny of the central part of the Alborz magmatic belt. The Senj mafic intrusion is composed of gabbro to monzodiorite and monzonite in lithology, and intruded as a sill into volcano-sedimentary rocks of the Eocene Karaj Formation. The Karaj Formation consists of volcano-sedimentary rocks, such as altered crystalline to shaly tuffs. The Senj intrusion (39.7 ± 0.4 Ma) shows LILE and LREE enrichment and negative anomaly of Nb, Ta and Ti, the geochemical signatures similar to those from subduction-related mafic magmas. The Hf-O zircon analyses yield eHf(t) values of + 4.1 to + 11.1 and δ18O values of + 4.8 to + 6.2‰. The zircon isotopic signatures together with shoshonitic affinity in the Senj mafic samples suggest partial melting of an enriched lithospheric mantle that had already been metasomatized by slab-derived melts and fluids. The Mo-Cu mineralization mainly occurs as veins and veinlets in the volcano-sedimentary rocks of the Karaj Formation and is dominated by molybdenite with minor amounts of chalcopyrite, bornite, pyrite and tetrahedrite-tennantite. The associated gangue minerals are tremolite, actinolite, quartz, calcite, chlorite and epidote. The Senj Mo-Cu deposit formed in volcano-sedimentary rocks following the emplacement of the Late Eocene Senj sill. The source of molybdenite in the Senj deposit is dominantly from crustal materials as it is revealed by Re contents in the molybdenite minerals (0.5 to 0.7 ppm). In fact, the molybdenite occurrence may be a remobilization process related to the emplacement of the Senj mafic magma.

Reframing housing struggles

After Augusto Pinochet’s dictatorship (1973–1990), Chile’s post-dictatorial governments drew on market-based policies to develop large-scale subsidised housing projects and, accordingly, avoid the reappearance of mass housing movements. However, the considerable building of subsidised social housing in the 1990s did not lead to better living conditions for pobladores (the urban poor). To become homeowners, they began to be systematically expelled from their neighbourhoods of origin and relocated to segregated peripheries. This phenomenon has resulted in the re-emergence of housing protests in the last decade, which are mostly organised around pobladores’ demands for staying in their neighbourhoods. This paper analyses such a remobilisation process by scrutinising ethnographically the case of a state-regulated housing assembly in La Florida, a district of Santiago undergoing a housing affordability problem due to the generalised increase in land prices in Santiago’s Metropolitan Area. It focuses on how pobladores’ demands for the right to stay put in La Florida account for a broader reframing of right-to-housing struggles, expressed in the growing incorporation of right-to-the-city claims in their political language. In doing so, I show that current urban struggles allow for the rise of a type of urban citizenship through which the urban poor, by conceiving of themselves as city-makers, generate particular understandings of themselves as rights-bearers. This process of citizen formation, however, is paradoxical: although it is the result of mobilisations aimed at contesting market-based policies, it is permeated by a neo-liberal ethics through which the urban poor legitimate themselves as urban citizens.

Decoding magma plumbing and geochemical evolution beneath the Lastarria volcanic complex (Northern Chile)—Evidence for multiple magma storage regions

The petrology of quaternary andesites and dacites from Lastarria volcano was investigated to reconstruct the magma plumbing and storage conditions beneath the volcano. The mineral phase compositions and whole-rock major and trace element compositions were used to constrain temperature, pressure and possible mechanisms for magma differentiation. The applied thermobarometric models include two-pyroxene thermobarometry, plagioclase-melt thermometry, amphibole composition thermobarometry, and Fe-Ti oxide thermo-oxybarometry. The overall temperature estimation is in the range 840°C to 1060°C. Calculated oxygen fugacity ranges between NNO to NNO+1. Results of the geo-barometric calculations reveal multiple magma storage regions, with a distinct storage level in the uppermost crust (~6.5–8km depth), a broad zone at mid-crustal levels (~10–18km depth), and a likely deeper zone at intermediate to lower crustal levels (>20km depth). The highest temperatures in the range 940–1040°C are recorded in minerals stored in the mid-crustal levels (~10–18km depth). The whole-rock compositions clearly indicate that magma mixing is the main parameter controlling the general differentiation trends. Complex zoning patterns and textures in the plagioclase phenocrysts confirm reheating and remobilization processes due to magma replenishment.

Analysis of source and sink dynamics involved in oil and protein accumulation in sunflower achenes using a bi-linear model

Most recent mechanistic crop models are based on source-sink relationships. To build a conceptual framework for achene quality traits in sunflower (Helianthus annuus L.), source-sink relationships were investigated in contrasting environments. Two experiments were performed under field conditions in 2011 and 2012. Oil, protein, hull (sink), leaves, receptacles and stems (source) were measured weekly under contrasting nitrogen (N−: no fertilization; N+: 150kgNperha), plant density (3 and 4.5plantsperm2) and genotype (cv. Kerbel, cv. LG5451 HO and cv. Olledy) treatments. A bi-linear model was fitted to source and sink component dry weight (DW) dynamics perm2. Nitrogen and plant density influenced rates and duration of all source and sink dynamics, while genotype had a significant influence on timing parameters. More significant factor interactions were found in 2011 than in 2012, probably because of other factors that occurred or interacted during grain filling (water stress and/or thermal stress). We constructed a robust source-sink framework for oil and protein accumulation in relation to remobilization processes. The observed “source” chronology was receptacles, stems and green leaves, and we confirmed the “sink” chronology of receptacles, hulls, protein and oil. Chronologies were influenced mostly by genotype. Such a framework is highly useful for dynamic modeling of sunflower. We also discuss the relevance and adaptability of the bi-linear model.

Geochemistry, Nd-Pb Isotopes, and Pb-Pb Ages of the Mesoproterozoic Pea Ridge Iron Oxide-Apatite–Rare Earth Element Deposit, Southeast Missouri

Iron oxide-apatite and iron oxide-copper-gold deposits occur within ~1.48 to 1.47 Ga volcanic rocks of the St. Francois Mountains terrane near a regional boundary separating crustal blocks having contrasting depleted-mantle Sm-Nd model ages (TDM). Major and trace element analyses and Nd and Pb isotope data were obtained to characterize the Pea Ridge deposit, improve identification of exploration targets, and better understand the regional distribution of mineralization with respect to crustal blocks. The Pea Ridge deposit is spatially associated with felsic volcanic rocks and plutons. Mafic to intermediate-composition rocks are volumetrically minor. Data for major element variations are commonly scattered and strongly suggest element mobility. Ratios of relatively immobile elements indicate that the felsic rocks are evolved subalkaline dacite and rhyolite; the mafic rocks are basalt to basaltic andesite. Granites and rhyolites display geochemical features typical of rocks produced by subduction. Rare earth element (REE) variations for the rhyolites are diagnostic of rocks affected by hydrothermal alteration and associated REE mineralization. The magnetite-rich rocks and REE-rich breccias show similar REE and mantle-normalized trace element patterns. Nd isotope compositions (age corrected) show that: (1) host rhyolites have ɛ Nd from 3.44 to 4.25 and TDM from 1.51 to 1.59 Ga; (2) magnetite ore and specular hematite rocks display ɛ Nd from 3.04 to 4.21 and TDM from 1.6 to 1.51 Ga, and ɛ Nd from 2.23 to 2.81, respectively; (3) REE-rich breccias have ɛ Nd from 3.04 to 4.11 and TDM from 1.6 to 1.51 Ga; and (4) mafic to intermediate-composition rocks range in ɛ Nd from 2.35 to 3.66 and in TDM from 1.66 to 1.56. The ɛ Nd values of the magnetite and specular hematite samples show that the REE mineralization is magmatic; no evidence exists for major overprinting by younger, crustal meteoric fluids, or by externally derived Nd. Host rocks, breccias, and magnetite ore shared a common origin from a similar source. Lead isotope ratios are diverse: (1) host rhyolite has 206Pb/204Pb from 24.261 to 50.091; (2) Pea Ridge and regional galenas have 206Pb/204Pb from 16.030 to 33.548; (3) REE-rich breccia, magnetite ore, and specular hematite rock are more radiogenic than galena; (4) REE-rich breccias have high 206Pb/204Pb (38.122–1277.61) compared to host rhyolites; and (5) REE-rich breccias are more radiogenic than magnetite ore and specular-hematite rock, having 206Pb/204Pb up to 230.65. Radiogenic 207Pb/206Pb age estimates suggest the following: (1) rhyolitic host rocks have ages of ~1.50 Ga, (2) magnetite ore is ~1.44 Ga, and (3) REE-rich breccias are ~1.48 Ga. These estimates are broadly consistent and genetically link the host rhyolite, REE-rich breccia, and magnetite ore as being contemporaneous. Alteration style and mineralogical or textural distinctions among the magnetite-rich rocks and REE-rich breccias do not correlate with different isotopic sources. In our model, magmatic fluids leached metals from the coeval felsic rocks (rhyolites), which provided the metal source reflected in the compositions of the REE-rich breccias and mineralized rocks. This model allows for the likelihood of contributions from other genetically related felsic and intermediate to more mafic rocks stored deeper in the crust. The deposit thus records an origin as a magmatic-hydrothermal system that was not affected by Nd and Pb remobilization processes, particularly if these processes also triggered mixing with externally sourced metal-bearing fluids. The Pea Ridge deposit was part of a single, widespread, homogeneous mixing system that produced a uniform isotopic composition, thus representing an excellent example of an igneous-dominated system that generated coeval magmatism and REE mineralization. Geochemical features suggest that components in the Pea Ridge deposit originated from sources in an orogenic margin. Basaltic magmatism produced by mantle decompression melting provided heat for extracting melts from the middle or lower crust. Continual addition of mafic magmas to the base of the subcontinental lithosphere, in a back-arc setting, remelted calc-alkaline rocks enriched in metals that were stored in the crust. The St. Francois Mountains terrane is adjacent to the regional TDM line (defined at a value of 1.55 Ga) that separates ~1600 Ma basement to the west, from younger basements to the east. Data for Pea Ridge straddle the TDM values proposed for the line. The Sm-Nd isotope system has been closed since formation of the deposit and the original igneous signatures have not been affected by cycles of alteration or superimposed mineralizing events. No evidence exists for externally derived Nd or Sm. The source region for metals within the Pea Ridge deposit had a moderate compositional variation and the REE-rich breccias and mineralized rocks are generally isotopically homogeneous. The Pea Ridge deposit thus constitutes a distinctive isotopic target for use as a model in identifying other mineralized systems that may share the same metal source in the St. Francois Mountains terrane and elsewhere in the eastern Granite-Rhyolite province.

Involvement of Arginase in Methyl Jasmonate–induced Tomato Fruit Chilling Tolerance

The physiological role of arginase in nitrogen remobilization processes from protein degradation during seed germination has well been described in several species. However, very little is known about its possible roles in plant stress responses. Treatment of tomato fruit (Solanum lycopersicum L.) with 0.05 mm methyl jasmonate (MeJA) enhanced transcription levels of arginase genes, especially LeARG2. Chilling injury (CI) of fruit treated with 0.05 mm MeJA for 12 hours was also effectively alleviated, as manifested by decreases in CI index, electrolyte leakage, and malondialdehyde (MDA) content. To investigate the potential role of arginase in MeJA-induced chilling tolerance, fruit were treated with MeJA or the arginase inhibitor Nω-hydroxy-nor-l-arginine (nor-NOHA) combined with MeJA and then stored at 2 °C for 28 days. MeJA-induced arginase activity was strongly inhibited and the reduction of CI by MeJA was nearly abolished by the inhibitor. In addition, MeJA treatment increased the activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX); inhibited peroxidase (POD) activities; and promoted proline and polyamines accumulation. These effects were partially counteracted by nor-NOHA; putrescine accumulation, however, was unaffected by the inhibitor. Our results indicate that arginase may be involved in MeJA-induced chilling tolerance, possibly by ameliorating the antioxidant enzyme system of fruit and increasing proline levels.

Gold remobilisation and formation of high grade ore shoots driven by dissolution-reprecipitation replacement and Ni substitution into auriferous arsenopyrite

Both gold-rich sulphides and ultra-high grade native gold oreshoots are common but poorly understood phenomenon in orogenic-type mineral systems, partly because fluids in these systems are considered to have relatively low gold solubilities and are unlikely to generate high gold concentrations. The world-class Obuasi gold deposit, Ghana, has gold-rich arsenopyrite spatially associated with quartz veins, which have extremely high, localised concentrations of native gold, contained in microcrack networks within the quartz veins where they are folded. Here, we examine selected samples from Obuasi using a novel combination of quantitative electron backscatter diffraction analysis, ion microprobe imaging, synchrotron XFM mapping and geochemical modelling to investigate the origin of the unusually high gold concentrations. The auriferous arsenopyrites are shown to have undergone partial replacement (∼15%) by Au-poor, nickeliferous arsenopyrite, during localised crystal-plastic deformation, intragranular microfracture and metamorphism (340–460°C, 2kbars). Our results show the dominant replacement mechanism was pseudomorphic dissolution-reprecipitation, driven by small volumes of an infiltrating fluid that had relatively low ƒS2 and carried aqueous NiCl2. We find that arsenopyrite replacement produced strong chemical gradients at crystal-fluid interfaces due to an increase in ƒS2 during reaction, which enabled efficient removal of gold to the fluid phase and development of anomalously gold-rich fluid (potentially 10ppm or more depending on sulphur concentration). This process was facilitated by precipitation of ankerite, which removed CO2 from the fluid, increasing the relative proportion of sulphur for gold complexation and inhibited additional quartz precipitation. Gold re-precipitation occurred over distances of 10μm to several tens of metres and was likely a result of sulphur activity reduction through precipitation of pyrite and other sulphides. We suggest this late remobilisation process may be relatively common in orogenic belts containing abundant mafic/ultramafic rocks, which act as a source of Ni and Co scavenged by chloride-bearing fluids. Both the preference of the arsenopyrite crystal structure for Ni and Co, rather than gold, and the release of sulphur during reaction, can drive gold remobilisation in many deposits across broad regions.

The multistage genesis of the giant Dongshengmiao Zn-Pb-Cu deposit in western Inner Mongolia, China: Syngenetic stratabound mineralization and metamorphic remobilization

The genesis of the giant Dongshengmiao in the northern margin of the North China Block has been debated since its discovery in the 1950s, because it shows geological and geochemical characteristics with both syngenetic and epigenetic signatures. It has geological settings and sulfur and lead isotopic compositions that are similar with typical SEDEX (sedimentary exhalative) deposit, while the Zn-Pb-Cu mineralization was controlled by shear deformation and metamorphism, showing similarities with orogenic-type deposits. In this contribution, both the syngenetic and epigenetic features of the Dongshengmiao are envisaged, and accounted for in the context of a genetic model with two metallogenic periods. Massive pyrite at the Dongshengmiao was mostly recrystallized during metamorphism, but fine-grained texture was locally preserved, indicating its syngenetic origin. On the contrary, all the Zn-Pb-Cu ores observed in this study show characteristics of epigenetic hydrothermal mineralization that controlled by metamorphism and accompanying shear deformation. The sulfur and lead isotopic compositions of sphalerite and galena indicate that they were in situ remobilized from a syngenetic stratabound source, and the oxygen and hydrogen isotopic ratios of ore-fluid indicate that the large-scale remobilization was assisted by metamorphic fluid. The thermodynamic modeling indicates that the ore-fluid during remobilization has a great potential of transporting Cu. This may account for the abnormally enriched Cu in the remobilized SEDEX deposit. The metamorphic fluid might strip Cu from the fluid source during devolatilization, and overprint it on the Zn-Pb orebodies during remobilization. A secondary flow-through modeling reveals that Zn- and Cu-sulfides would be preferentially redistributed in Fe-rich carbonates during remobilization, as a result of fluid-rock interaction. Conclusively, a multistage genetic model is proposed. During the development of the Proterozoic rift, stratabound Zn-Pb mineralization took place in a SEDEX ore-forming system. The syngenetic sulfides subsequently underwent a large-scale fluid-assisted remobilization during the early Cretaceous metamorphism and thrusting, forming the shear zone-controlled epigenetic orebodies. During the remobilization process, Cu was scavenged from the source of metamorphic fluid, and deposited accompanying remobilized Zn-Pb sulfides. Shear structures and Fe-rich carbonates are ideal sites for redistribution and re-deposition of remobilized sulfide.

Lacustrine turbidites produced by surficial slope sediment remobilization: A mechanism for continuous and sensitive turbidite paleoseismic records

Turbidite records along ocean margins and in lake basins are increasingly used as paleoseismic proxies. However, the slope remobilization processes that formed the earthquake-related turbidity currents are poorly understood and, therefore, it is difficult to assess the consistency of turbidite paleoseismic records. We analyzed the sedimentary imprint of the giant AD 1960 (Mw 9.5) Chile earthquake in four South-Central Chilean lakes. Mass-transport deposits and turbidites were compared by interpreting reflection-seismic profiles, sedimentary facies, volume balances and proxies for turbidite composition (i.e. grain size, radionuclides, sediment color, organic matter). Sediment lightness was used as a proxy for organic matter content. Comparison of lightness of turbidites and the underlying sediments shows that earthquake-triggered turbidites in the four lakes result from remobilization of a thin veneer (on average about 5cm) of slope sediments and do not result from disintegration of subaquatic landslides. Statistical analysis of 34 turbidites in a new 5200year sedimentary record does not show any correlation between inter-event time and turbidite thickness (and thus volume). This means that inter-event slope recharging is not a dominant factor governing turbidite recurrence and that initiation of turbidity currents by remobilization of surficial sediments is different to slope failure related to subaquatic landslides. We conclude that surficial slope sediment remobilization forms a valid mechanism that explains why turbidite paleoseismic records can be of excellent continuity and high sensitivity. Moreover, based on correlations between seismic intensity, turbidite volume and stratigraphic remobilization depth, we propose that surficial slope sediment remobilization allows for turbidite records containing information about paleo-earthquake intensity.

Regeneration dynamics of iron and nutrients from bay sediment into bottom water of Funka Bay, Japan

We studied iron remobilization and nutrient regeneration in bottom water of Funka Bay, Japan, bimonthly from August 2010 to December 2011. The bay basin (bottom depth, 92–96 m) is separated from the northwest Pacific Ocean at its mouth by a sill with a depth of 60 m. After a spring phytoplankton bloom during early March–early April, nutrients in bay bottom water tended to accumulate with time until August–September, and to increase gradually with depth during April–October, by the oxidative decomposition of settling particulate organic matter on the bay bottom. In contrast, the process of iron remobilization into bottom water of the bay is remarkably different from nutrient regeneration. The much higher concentrations of dissolved and total dissolvable iron near the bottom and the seasonally variable relationship between dissolved iron concentration and apparent oxygen utilization in bay bottom water likely reflect a balance between dissolved iron input and removal processes within the bay bottom water. The release of soluble Fe(II) from reducing bay sediments might induce the high concentrations of dissolved and total dissolvable iron in deep–bottom waters of Funka Bay and might be one of the most important sources of iron in Funka Bay. The upward transport of iron from the bay bottom to the surface water during the winter vertical mixing may play an important role in the supply of bioavailable iron for phytoplankton growth in the coastal waters.