Porphyry copper deposits account for more than 80% of the world’s total Cu resources. However, the formation mechanism and controlling factors of porphyry copper deposits remain obscure. Previous ...studies have revealed that porphyry copper deposits are usually associated with oxidized, calc-alkalic, adakitic shallow intrusive rocks. Here we show that hematite–magnetite intergrowths are commonly found in porphyry copper deposits, suggesting high and fluctuating oxygen fugacity (fO2). Oxidation promotes the destruction of sulfides in the magma source, and thereby increases initial chalcophile element concentrations. Sulfide remains undersaturated during the evolution of oxidized sulfur-enriched magmas where sulfate is the dominant sulfur species, leading to high chalcophile element concentrations in evolved magmas. The final porphyry copper mineralization is controlled by sulfate reduction, which starts with magnetite crystallization, accompanied by decreasing pH and correspondingly increasing fO2. Hematite forms once sulfate reduction lowers the pH sufficiently and the fO2 reaches the hematite–magnetite oxygen fugacity buffer, which in turn increases the pH for a given fO2. The oxidation of ferrous iron during the crystallization of magnetite and hematite is the causal process of sulfate reduction and consequent mineralization. Therefore, the initial pH and fO2 ranges of porphyries favorable for porphyry copper mineralization are defined by the hematite–magnetite oxygen fugacity buffer and SO42−–HS−–S3− reaction lines. Adakitic rocks have higher initial contents of copper, sulfur and iron than normal arc rocks, and thus are the best candidates for porphyry copper deposits. These provide a plausible explanation for the formation of copper porphyry deposits. The hematite–magnetite intergrowth marks the upper limits of fO2 favorable for the mineralization, and thus may be a powerful tool for future prospecting of large porphyry copper deposits.
Rare Earth Elements (REE) are essential to modern society but the origins of many large REE deposits remain unclear. The U-Th-Pb ages, chemical compositions and C, O and Mg isotopic compositions of ...Bayan Obo, the world's largest REE deposit, indicate a protracted mineralisation history with unusual chemical and isotopic features. Coexisting calcite and dolomite are in O isotope disequilibrium; some calcitic carbonatite samples show highly varied δ26 Mg which increases with increasing Si and Mg; and ankerite crystals show decreases in Fe and REE from rim to centre, with highly varied REE patterns. These and many other observations are consistent with an unusual mineralisation process not previously considered; protracted fluxing of calcitic carbonatite by subduction-released high-Si fluids during the closure of the Palaeo-Asian Ocean. The fluids leached Fe and Mg from the mantle wedge and scavenged REE, Nb and Th from carbonatite, forming the deposit through metasomatism of overlying sedimentary carbonate.
Early Cretaceous A-type granites in the Lower Yangtze River belt, central eastern China, with both A1 and A2 chemical subgroups, formed at 125±2Ma, after a Cretaceous ridge subduction. Remarkably, A1 ...and A2 group granites are distributed in three zones, roughly parallel to each other and to a slightly older adakite belt. In general, A1 granites form in intraplate settings, whereas A2 granites near paleo-convergent margins. The alternate distribution of these two subgroup A-type granites is compatible with a proposed Cretaceous ridge subduction in the region. The subduction of a dry and hot spreading ridge may have only released small amount of fluids, so that metasomatism on the overriding lithosphere was undetectable, correspondingly resulted in A1 granites later on. In contrast, wetter and colder oceanic crust away from the spreading ridge was responsible for mantle metasomatism and consequently the formation of A2 granites. Further away from the ridge, the subduction angle was much steeper, and dehydration of the slab had occurred earlier during the subduction, and thus dramatically reduced mantle metasomatism, corresponding to A1 granites again. Both A1 and A2 granites formed within a short period of time due to slab window/rollback, after the ridge subduction. The distribution of the A1 and A2 granites together with the adakite belt may be taken as discrimination indice for ancient ridge subduction.
► A1 granite forms in intraplate settings, whereas A2 granite forms at convergent margins. ► A-type granites in central eastern China are classified into A1 and A2 chemical subgroups. ► Spreading ridge is a major component of the mega engine that initiates and drives plate tectonics. ► Ridge subduction may results in both A1 and A2 types of granites, together with adakitic rocks.
Mercury (Hg) enrichments in ancient sediments have been used as a proxy of volcanism, especially large igneous province (LIP) eruptions. However, considering the existence of other potential Hg ...sources besides volcanoes and the diverse factors (e.g., organic matters, clay minerals, sulfide minerals and Fe oxides) that can affect Hg sequestration, there are considerable uncertainties to simply regard sedimentary Hg anomalies as signatures of volcanic activities. Mercury stable isotopes, a promising tool for tracing the origins and transformations of Hg, have been increasingly used for determining the causes of Hg spikes and understanding the geochemical behavior of Hg in the geologic record. To date, lots of researches have applied Hg concentrations and Hg isotopes to identify LIP volcanisms linking with significant geological events such as mass extinctions, ocean anoxic events and other environmental perturbations that mainly occurred in the Phanerozoic. However, the results in previous studies clearly show that not all Hg enrichments are derived from volcanic inputs, which emphasize the need for more caution in using Hg as a fingerprint of volcanism. With a better understanding of Hg isotopes in the future, there will be important implications for Hg isotopes to reconstruct volcanic activities in the rock records and their impacts on biological evolution.
Magnesium isotopic compositions are reported for twenty‐four international geological reference materials including igneous, metamorphic and sedimentary rocks, as well as phlogopite and serpentine ...minerals. The long‐term reproducibility of Mg isotopic determination, based on 4‐year analyses of olivine and seawater samples, was ≤ 0.07‰ (2s) for δ26Mg and ≤ 0.05‰ (2s) for δ25Mg. Accuracy was tested by analysis of synthetic reference materials down to the quoted long‐term reproducibility. This comprehensive dataset, plus seawater data produced in the same laboratory, serves as a reference for quality assurance and inter‐laboratory comparison of high‐precision Mg isotopic data.
Les compositions isotopiques du magnésium sont fournies pour vingt‐quatre matériaux géologiques de référence internationaux, comprenant des roches ignées, métamorphiques et sédimentaires, ainsi qu'une phlogopite et des serpentines. La reproductibilité à long terme de la détermination isotopique du Mg, basée des analyses sur quatre ans d’échantillons d'olivine et d'eau de mer, était ≤ 0.07% (2s) pour δ26Mg et ≤ 0.05% (2s) pour δ25Mg. La précision a été testée par l'analyse de matériaux de référence synthétiques jusqu’à la reproductibilité à long terme indiquée. Cette base de données complète, ainsi que des données d'eau de mer produites dans le même laboratoire, servent de référence pour l'assurance qualité et la comparaison inter‐laboratoires de haute précision des données isotopiques du Mg.
Porphyry deposits and oxidized magmas Sun, Weidong; Huang, Rui-fang; Li, He ...
Ore geology reviews,
March 2015, 2015-03-00, Letnik:
65
Journal Article
Recenzirano
Porphyry deposits supply most of the world's Cu and Mo resources. Over 90% of the porphyry deposits are found at convergent margins, especially above active subduction zones, with much fewer ...occurrences at post-collisional or other tectonic settings. Porphyry Cu–(Mo)–(Au) deposits are essentially magmatic–hydrothermal systems, which are generally initiated by injection of oxidized magmas saturated with metal-rich aqueous fluids, i.e., the parental magmas need to be water rich and oxidized with most of the sulfur appearing as sulfate in the magma. Sulfur is the most important geosolvent that controls the behavior of Cu and other chalcophile elements, due to high partition coefficients of chalcophile elements between sulfide and silicate melts. Small amount of residual sulfides can hold a large amount of Cu. Therefore, it is essential to eliminate residual sulfides to get high Cu contents in magmas for the formation of porphyry deposits. Sulfate (SO42−) is over 10 times more soluble than sulfide (S2−), and thus the solubility of sulfur depends strongly on sulfur speciation, which in turn depends on oxygen fugacities. The magic number of oxygen fugacity is log fO2>FMQ+2 (i.e., ΔFMQ+2), where FMQ is the fayalite–magnetite–quartz oxygen buffer. Most of the sulfur in magmas is present as sulfate at oxygen fugacities higher than ΔFMQ+2. Correspondingly, the solubility of sulfur increases from ~1000ppm up to >1wt.%. Oxidation promotes the destruction of sulfides in the magma source, and thereby increases initial chalcophile element concentrations, forming sulfur-undersaturated magmas that can further assimilate sulfides during ascent. Copper, Mo and Au act as incompatible elements in sulfide undersaturated magmas, leading to high chalcophile element concentrations in evolved magmas. The final porphyry mineralization is controlled by sulfate reduction, which is usually initiated by magnetite crystallization, accompanied by decreasing pH and correspondingly increasing oxidation potential of sulfate. Hematite forms once sulfate reduction lowers the pH sufficiently, driving the oxidation potential of sulfate up to the hematite–magnetite oxygen fugacity (HM) buffer, which is ~ΔFMQ+4. Given that ferrous iron is the most important reductant that is responsible for sulfate reduction during porphyry mineralization, the highest oxygen fugacity favorable for porphyry mineralization is the HM buffer. In addition to the oxidation of ferrous iron during the crystallization of magnetite and hematite, reducing wallrock may also contribute to sulfate reduction and mineralization. Nevertheless, porphyry deposits are usually mineralized in the whole upper portion of the pluton, whereas interactions with country rocks are generally restricted at the interface, therefore assimilation of reducing sediments is not likely to be a decisive controlling process. Degassing of oxidized gases has also been proposed as a major process that is responsible for sulfate reduction. Degassing, however, is not likely to be a main process in porphyry mineralization that occurs at 2–4km depths in the upper crust. Sulfide formed during sulfate reduction is efficiently scavenged by aqueous fluids, which transports metals to shallower depths, i.e., the top of the porphyry and superjacent wallrock. According to traditional views, sulfide saturation and segregation during magma evolution is not favorable for the formation of porphyry Cu±Au±Mo deposits. This is the main difference between porphyry deposits and Ni–Cu sulfide deposits. Nevertheless, in places with thick sections of reducing sediments, e.g., the western North America, sulfide saturation and segregation may occur during evolution of the magma, forming Cu-rich cumulates at the base of plutons. These Cu-rich sulfides may evolve into porphyry mineralization or even control the ore-forming process. Their contribution depends heavily on subsequent oxidation, i.e., a major contribution can be expected only when the sulfide cumulates are oxidized to sulfate, liberating the chalcophile elements. Sulfate reduction and ferrous Fe oxidation form H+, which dramatically lowers the pH values of ore-forming fluids and causes pervasive alteration zones in porphyry Cu deposits. The amount of H+ released during mineralization and the alkali content in the porphyry together control the intensity of alterations. In principle, H2 and methane form during the final mineralization process of porphyry deposits, but are mostly oxidized by ferric Fe during subsequent processes. Some of the reduced gases, however, may survive the highly oxidizing environment to escape from the system, or even to get trapped in fluid inclusions. Therefore, small amount of reduced gases in fluid inclusions cannot argue against the oxidized feature of the magmas. Reduced magmas are not favorable for porphyry mineralization. Reduced porphyry deposits so far reported are just mineralization that has either been reduced in host rock away from the causative porphyry or through assimilation of reducing components during emplacement.
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•Raw piggery digestate was used for Desmodesmus sp. CHX1 cultivation.•Inoculation with nitrifying bacteria showed better performance.•Microalgae aggregating bacteria dominated in the ...optimized systems.
The microalgae-based system has been applied in anaerobic digestate treatment for nutrient removal and biomass production. To optimize its performance in treating piggery digestate, here, commercial bacterial agents, including organic degrading bacteria (Cb) and nitrifying bacteria (Nb), were inoculated into the microalgae-based system dominated by Desmodesmus sp. CHX1 (D). Reactor DN (inoculated with D and Nb) and DCN (inoculated with D, and Cb to Nb at a ratio of 1:2) have better performance on NH4+-N removal, with a final efficiency at 40.26% and 39.87%, respectively, and no NO3−-N or NO2−-N accumulations. The final total chlorophyll concentration, an indicator of microalgal growth, reached 4.74 and 5.47 mg/L in DN and DCN, respectively, three times more than that in D. These results suggested that high NH4+-N removal was achieved by the assimilation into high microalgal biomass after the inoculation with functional bacteria. High-throughput sequencing showed that the richness of microbial community decreased but the evenness increased by inoculating functional microorganisms. Microalgae aggregating bacteria were Cellvibrio, Sphingobacterium, Flavobacterium, Comamonas, Microbacterium, Dyadobacter, and Paenibacillus. This study revealed that the inoculation with functional bacteria reconstructed the microbial community which benefited for the microalgal growth and nutrient removal, providing a promising strategy for treating highly-concentrated digestate.
By introducing multiple molecule/intermolecular dynamic reversible hydrogen bonds into the polydimethylsiloxane elastomer system, a solid polymeric electrolyte with high ion conductivity (2.5 × 10
−4
...S cm
−1
) and a stable electrochemical window (>5 V) shows a fast self-healing speed.
By introducing multiple molecule/intermolecular hydrogen bonds into the polydimethylsiloxane elastomer system, the solid polymeric electrolyte with high ion conductivity and high electrochemical stability obtains the fast self-healing speed.
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