Rare earth elements (REEs) have become increasingly important to our modern society due to their strategic significance and numerous high technological applications. Regolith-hosted heavy rare earth ...element (HREE) deposits in South China are currently the main source of the HREEs, but the ore-forming processes are poorly understood. In these deposits, the REEs are postulated to accumulate in regolith through adsorption on clay minerals. In the Zudong deposit, the world's largest regolith-hosted HREE deposit, clay minerals are dominated by short, stubby, nanometer-scale halloysite tubes (either 10 or 7 Å) and microcrystalline kaolinite in the saprolite and lower pedolith and micrometer-sized vermicular kaolinite in the humic layer and upper pedolith. A critical transformation of the clay minerals in the upper pedolith is coalescence and unrolling of halloysite to form vermicular kaolinite. Microcrystalline kaolinite also transformed to large, well-crystalline vermicular kaolinite. This transformation could result in significant changes in different physicochemical properties of the clay assemblages. Halloysite-abundant clay assemblages in the deep regolith have specific surface area and porosity significantly higher than the kaolinite-dominant clay assemblages in the shallow soils. The crystallinity of clay minerals also increased, exemplified by decrease in Fe contents of the kaolinite group minerals (from ∼1.2 wt% in the lower saprolite to ∼0.35 wt% in the upper pedolith), thereby indicative of less availability of various types of adsorption sites. Hence, halloysite-abundant clay minerals of high adsorption capacity in deep regolith could efficiently retain the REEs released from weathering of the parent granite. Reduction in adsorption capacity during the clay transformation in shallow depth partially leads to REE desorption, and the released REEs would be subsequently transported to and adsorbed at deeper part of the soil profile. Hence, the clay-adsorbed REE concentration in the lower pedolith and saprolite (∼2500 ppm on average) is much higher than the uppermost soils (∼400 ppm on average). Therefore, weathering environments that favor the release of the REEs in the shallow soils but preservation of halloysite in the deep regolith can continuously adsorb REEs in the clay minerals to form economically valuable deposits.
Zircons from granitic gneisses in North Vietnam have magmatic cores dated at 2.28–2.19 Ga, and constitute the first reported evidence of continental crust with these ages in the Yangtze Block of the ...South China Craton. Overgrowths on zircon rims indicate two periods of metamorphism at 1.97–1.95 Ga and ∼1.83 Ga. These events, along with a previously reported ∼2.36 Ga metamorphic overgrowth on ∼2.9 Ga crystallized zircons from the same region, suggest a sequence of events similar to that recorded for the northwestern region of Laurentia and possibly Siberia, which are associated with assembly of the Nuna supercontinent. These include the 2.4–2.3 Ga Arrowsmith Orogen and a range of events in the interval 2.32–1.80 Ga, including accretionary magmatism in northwestern Laurentia and Siberia (2.32–2.07 Ga), the Thelon orogeny (2.02–1.96 Ga) and the 1.85–1.80 Ga collision between the Superior and Hearne–Rae cratons during the Trans-Hudson Orogen in Laurentia, and the Akitkan Orogen in Siberia (2.03–1.86 Ga). Subsequent attempted breakup of Nuna may be represented by ca. 1.80 to 1.59 Ga consanguineous extension related sedimentation and magmatism in the southwestern Yangtze Block and northwestern Laurentia. These correlations favor location of the Yangtze Block adjacent to northwest Laurentia, and possibly Siberia, within the Nuna supercontinent.
•The first reported 2.28–2.19 magmatic event in southwestern Yangtze Block.•Two periods of metamorphism, 1.97–1.95 Ga and ∼1.83 Ga, occurred on the 2.28–2.19 rocks.•The Yangtze Block was an exotic terrene accreted to Laurentia at ∼2.4–2.3 Ga.•The Yangtze Block was linked to northwestern Laurentia, and possibly Siberia, in the Nuna supercontinent.
Organophosphate esters (OPs) are substitutes for polybrominated diphenyl ether (PBDE) flame retardants. China is the largest producer of OPs globally, with the production rate increasing at 15% ...annually. Since some OPs are neurodevelopmental and/or carcinogenic toxicants, human exposure is a concern. In this study, concentrations of eight OP metabolites (mOPs) were measured in human urine samples collected from 13 cities located in Northern, Eastern, Southern, and Southwestern China. All target mOPs were frequently detected with detection rates of 50% to 100%, indicating widespread human exposure to OPs. Bis(2-chloroethyl) phosphate (BCEP; median: 0.68 ng/mL), bis(1-chloro-2-propyl) phosphate (BCIPP; 0.30 ng/mL), diphenyl phosphate (DPHP; 0.30 ng/mL), and dibutyl phosphate (DBP; 0.29 ng/mL) were the dominant mOPs across all participants. Regional differences in concentrations (ΣmOPs varied from 0.86 to 3.7 ng/mL) and composition profiles (contribution of chlorinated mOPs to ΣmOPs varied from 35% to 95%) of mOPs were observed within China. In comparison to the concentrations reported worldwide, urinary DPHP and bis(1,3-dichloro-2-propyl) phosphate (BDCIPP) levels in China were lower, whereas BCEP and DBP levels were comparable or higher. The total daily intake (TDI) of tris(2-chloroethyl) phosphate (TCEP), tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) and triphenyl phosphate (TPHP) were estimated from daily urine excretion rate and the fraction of OP metabolized in human liver microsomes (TDIHLM) or S9 fraction (TDIS9). The intake estimates showed that Chinese residents were exposed to TCEP from 96.9 to 46,700 (or 52.2 to 25,200) ng/kg bw/day. Depending on the reference dose, we found that approximately 5% of the individuals exceeded the limit (i.e., 2200 ng/kg bw/day) for TCEP intake. To our knowledge, this is the first nationwide baseline survey to determine urinary levels of mOPs in Chinese residents.
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•First nationwide baseline survey of urinary mOPs levels in China•Chinese residents are widely exposed to OPs, regardless of sampling locations.•BCEP, BCIPP, DPHP and DBP were the dominated mOPs.•BCEP and DBP levels in China were comparable or higher than those in various countries.•Potential health risk of human TCEP exposure was identified.
Oxidative stress is recognized as free radical dyshomeostasis, which has damaging effects on proteins, lipids and DNA. However, during cell differentiation and proliferation and other normal ...physiological processes, free radicals play a pivotal role in message transmission and are considered important messengers. Organisms maintain free radical homeostasis through a sophisticated regulatory system in which these “2‐faced” molecules play appropriate roles under physiological and pathological conditions. Reactive oxygen species (ROS), including a large number of free radicals, act as redox signalling molecules in essential cellular signalling pathways, including cell differentiation and proliferation. However, excessive ROS levels can induce oxidative stress, which is an important risk factor for diabetes, cancer and cardiovascular disease. An overall comprehensive understanding of ROS is beneficial for understanding the pathogenesis of certain diseases and finding new therapeutic treatments. This review primarily focuses on ROS cellular localization, sources, chemistry and molecular targets to determine how to distinguish between the roles of ROS as messengers and in oxidative stress.
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•A descriptive nomenclature of “regolith-hosted REE deposits” is recommended.•Hydrothermal alteration was essential for the formation of HREE-rich granites and magmatic ...differentiation for LREE-enriched granites.•Combination of mass removal of major elements and eluviation-illuviation dynamics of REEs forms this type of deposit.•Both ion adsorption and secondary REE minerals contribute to the REE budget in regolith.•Favorable exogeneric conditions are required for forming this type of deposits.
Regolith-hosted rare earth element (REE) deposits, also called ion-adsorption or weathered crust elution-deposited REE deposits are distributed over Jiangxi, Guangdong, Fujian, Hunan, Guangxi and Yunnan provinces in South China. In general, these deposits can be categorized into the HREE-dominated type, for example the famous Zudong deposit in southern Jiangxi province and the LREE-dominated type, such as the Heling and Dingnan deposits in southern Jiangxi province. Most of these deposits form from weathering of biotite and muscovite granites, syenites, monzogranites, granodiorites, granite porphyries, and rhyolitic tuffs. The parent rocks are generally peraluminous, siliceous, alkaline and contain a variety of REE-bearing minerals. Mostly, REE patterns of regolith are inherited from the parent rocks, and therefore, characteristics of the parent rocks impose a significant control on the ore formation. Data compilation shows that autometasomatism during the latest stage of granite crystallization is likely essential in forming the HREE-enriched granites, whereas LREE-enriched granites could form through magmatic differentiation. These deposits are normally two- to three-fold, but could be up to ten-fold enrichment in REE compared to the parent granites, where the maximum enrichment usually occurs from the lower B to the upper C horizon. Ce shows different behavior with the other REEs. Strongly positive Ce anomalies commonly occur at the upper part of weathering profiles, likely due to oxidation of Ce3+ to Ce4+ and removal of Ce from soil solutions through precipitation of cerianite. Vertical pH and redox gradients in weathering crusts facilitate dissolution of REE-bearing minerals at shallow level and fixation of REE at depth through either adsorption on clay minerals or precipitation of secondary minerals. At the same time, mass removal of major elements plays an important role in concentrating REE in regolith. Combination of mass removal and eluviation-illuviation dynamics is the main mechanism for REE accumulation in weathering crusts. Favorable exogenetic factors facilitate the accumulation of REE in regolith and preservation of the ore bodies. These include quasi-equilibrium between denudation and exhumation at regional scales, local geomorphology dominated by low-lying gentle slopes, adequate rainfall, and favorable groundwater conditions. Continuous operation of such a dynamic weathering system is essential in the formation of regolith-hosted REE deposits.
Mesozoic mineral deposits in South China include world-class deposits of W, Sn and Sb and those that provide the major sources of Ta, Cu, Hg, As, Tl, Pb, Zn, Au and Ag for the entire country. These ...deposits can be classified into polymetallic hydrothermal systems closely related to felsic intrusive rocks (Sn–W –Mo granites, Cu porphyries, polymetallic and Fe skarns, and polymetallic vein deposits) and low-temperature hydrothermal systems with no direct connection to igneous activities (MVT deposits, epithermal Au and Sb deposits). Recent studies have shown that they formed in the Triassic (Indosinian), Jurassic–Cretaceous (Early Yanshanian), and Cretaceous (Late Yanshanian) stages. Indosinian deposits include major MVT (Pb–Zn–Ag) deposits and granite-related W–Sn deposits. Early Yanshanian deposits are low-temperature Sb–Au and high-temperature W–Sn and Cu porphyry types. Many Late Yanshanian deposits are low-temperature Au–As–Sb–Hg and U deposits, and also include high-temperature W–Sn polymetallic deposits. The formation of these deposits is linked with a specific tectonothermal evolution and igneous activities. This special issue brings together some of the latest information in eight papers that deal with the origins and tectonic environments of mineral deposits formed in these stages. We anticipate that this issue will stimulate more interests in these ore deposits in South China.
The Paleoproterozoic to Mesoproterozoic (1742–1503Ma) Dongchuan Group in the southwestern Yangtze Block is a rift-related sedimentary sequence that was associated with the breakup of the ...supercontinent Columbia and is particularly important for the possible linkage between the Yangtze Block and other continents in Columbia. The Dongchuan Group consists of the Yinmin, Luoxue, Etouchang and Luzhijiang formations from the base upward. Sandstones from the Yinmin Formation are mainly arkose containing dominant K-feldspar with subordinate plagioclase and quartz. Abundant feldspar and high Qm/Q ratios (0.94–1) are indicative of plutonic sources. These sandstones have high La/Sc (3.06 to 4.32), low Sc/Th (0.74 to 1.15) and Co/Th (0.85 to 1.52) and highly evolved Nd isotopes (εNd(t)=−6.2 to −8.2), consistent with an old, felsic igneous source. Detrital zircons of this formation have two major age groups at 2602–2887Ma and 2224–2392Ma. Siltstones of the Etouchang Formation have detrital zircons with a prominent age peak at ~2560Ma and several subordinate peaks at ~2180Ma, ~2100Ma and ~1900Ma. They have high Sc/Th (1.00–7.08), Co/Th (0.13 to 6.31) and εNd(t) (−2.1 to −6.7), significantly different from the Yinmin Formation. The Yinmin Formation is interpreted to deposit during the initial stage of extensional rifting receiving detritus of granites and TTG mainly from uplifted shoulder. The Etouchang Formation more likely formed in a passive margin with sedimentary material largely from cratonic sources. Paleoproterozoic to Mesoproterozoic rift basins in the southwestern Yangtze Block, north Australia and northwestern Laurentia have remarkably similar provenance and tectonic setting in their lower part (1742–1596Ma), but significantly different since the onset of the Etouchang Formation (ca. 1596Ma). Therefore, the southwestern Yangtze Block was likely connected with the north Australia and northwestern Laurentia in Columbia and drifted away from these continents on or before ca. 1596Ma.
•The Dongchuan (DC) Group in SW Yangtze Block formed between 1742Ma and 1503Ma.•Remarkably different provenance for the lower and upper DC groups.•Sedimentation of the DC Group was associated with rifting setting to passive margin.•The SW Yangtze Block was connected with N Australia and NW Laurentia in Columbia.•The Yangtze Block drifted away from adjacent continents on or before ca. 1590Ma.
Metastasis is a major cause of death in patients with breast cancer. In the process of cancer development, epithelial-mesenchymal transition (EMT) is crucial to promoting the invasion and migration ...of tumor cells. In a previous study, the role of resveratrol in migration and metastasis was investigated in MDA-MB-231 (MDA231) human breast cancer cells and a xenograft-bearing mouse model. Additionally, the related mechanism was explored. In the present study, in vitro Transwell assays showed that resveratrol can inhibit the migration of transforming growth factor (TGF)-β1-induced MDA231 cells in a concentration-dependent manner. An enzyme-linked immunosorbent assay (ELISA) showed that resveratrol can reduce the secretion of matrix metalloproteinase (MMP)-2 and MMP-9. Immunofluorescence was performed to confirm the expression of EMT-related markers. Immunofluorescence assays confirmed that resveratrol changed the expression of the EMT-related markers E-cadherin and vimentin. Western blot analysis demonstrated that resveratrol decreased the expression levels of MMP-2, MMP-9, Fibronectin, α-SMA, P-PI3K, P-AKT, Smad2, Smad3, P-Smad2, P-Smad3, vimentin, Snail1, and Slug, as well as increased the expression levels of E-cadherin in MDA231 cells. In vivo, resveratrol inhibited lung metastasis in a mouse model bearing MDA231 human breast cancer xenografts without marked changes in body weight or liver and kidney function. These results indicate that resveratrol inhibits the migration of MDA231 cells by reversing TGF-β1-induced EMT and inhibits the lung metastasis of MDA231 human breast cancer in a xenograft-bearing mouse model.
The Yinachang deposit in the Kangdian region, Southwest China, contains large amounts of Fe, Cu and REE, and formed at ∼1700Ma. In this deposit, there are three stages of alteration and ...mineralization, including pre-ore Na–(Fe) alteration, Fe–(REE) mineralization, and Cu–(REE) mineralization. In the Fe–(REE) mineralization stage, REE-rich fluorapatite, with total REE concentrations ranging from 10,700 to 34,000ppm, formed together with magnetite. In the following Cu–(REE) mineralization stage, large amounts of REE, especially LREE, were leached out of the REE-rich fluorapatite due to the interaction between fluorapatite and Cl-, F-, CO2-, and Ca-rich, but REE-unsaturated fluids. The leaching of REE was associated with the removal of Si, Na, Th, U, Pb, and Ba, and modification of the oxygen isotope signature in the fluorapatite.
During a ∼840Ma tectonothermal event, REE-rich fluorapatite underwent the second interaction with oxidized, F-, CO2-, and possibly Cl-rich, but Na- and Ca-deficient fluids. Due to fluid–fluorapatite interaction, REE were removed from the fluorapatite, but were immediately reincorporated into new phases within the fluorapatite. Thus, the altered fluorapatite contains abundant REE mineral inclusions, including bastnäsite-(Ce), monazite-(Ce), and minor xenotime-(Y). A very small portion of the LREE were transported out of the fluorapatite, and formed bastnäsite-(Ce) and monazite-(Ce) grains in the vicinity of the altered fluorapatite.
In addition to the metasomatism of fluorapatite, allanite and “primary” synchysite-(Ce) from the Cu–(REE) mineralization stage were also altered with variable replacement of allanite by an assemblage of synchysite-(Ce)+chlorite±bastnäsite-(Ce) and “primary” synchysite-(Ce) by bastnäsite-(Ce). These styles of alteration were possibly synchronous with the second alteration phase of the fluorapatite.
This study demonstrates that REE can be mobilized during multiple stages of hydrothermal activities and highlights the significant controls fluid compositions have on REE transportation and deposition in hydrothermal system.
With the integration of information technology and foreign language education, it has exerted a profound influence on foreign language learning, and has formed a new open, free and personalized ...foreign language learning system. In order to give full play to the advantages of computer network-assisted English teaching, it is necessary to take students' learning demands as the core and interpret correctly the multiple advantages of computer network-assisted English teaching, actively constructing a new model of computer network-assisted English teaching. Based on the analysis of the background of the development of computer network-assisted English teaching and the innovation of English teaching, this paper puts forward some strategies for constructing a new model of computer network-assisted English teaching.
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