Technogenic hydrogeochemical anomalies of tungsten deposits in Kykylbey ore region

Peculiarities of the tungsten deposits drainage flow chemical composition formation, the development of which was ceased almost 40 years ago, have been considered. Migration peculiarities of ore components have been covered, and forms of their migration have been calculated. Inertial characteristics of the surface flow contamination are shown.

A Preliminary Review of Metallogenic Regularity of Tungsten Deposits in China

Tungsten ore resources are abundant in China with relatively complete types of deposits. Skarn type and quartz vein type deposits are dominated in the tungsten resources, whereas quartz vein type wolframite deposits are most important in terms of exploitation and utilization. Skarn type tungsten deposits are concentratedly distributed in the central Nanling region, such as South Hunan, South Anhui and the eastern Qinling region, while quartz vein type tungsten deposits occur mainly in South China, such as West Fujian, South Jiangxi, North Guangdong and South Hunan. The most important metallogenic epoch of tungsten is the Mesozoic, while the metallogenic tectonic setting is featured by an intracontinental environment after orogeny with sever tectonic movements, deep-seated faults and frequent magmatic activities, especially Mesozoic granitoids closely related to tungsten-tin mineralization. 22 metallogenic series of ore deposits characterized by or significantly related to tungsten were defined based on precise statistic information of 1199 tungsten mining areas and thorough the summary of metallogenic regularities. Based on studies of the metallogenic regularity of tungsten deposits, skarn type （or greisen type）, quartz vein type and massif-type of tungsten deposits are thought to be the key prediction types. 65 tungsten-forming belts and 22 key ore concentration areas were ascertained and a distribution map of tungsten-forming belts of China was compiled, which provided a theoretical basis for evaluation and prediction of potential tungsten resources.

Oxygen Isotope Studies of Wolframite in Tungsten Ore Deposits of South China

Based on the oxygen isotopic compositions of 133 wolframite samples and 110 quartz sampleseollected from 30 tungsten ore deposits in south China,in conjunction with δD values and other data,thesc deposits can be divided into four types. （l）Reequilibrated magmatic water-hydrothermal tungsten ore deposits. The δ18O values ofwolframite and quartz samples from this type of tungsten ore deposits are about +5-+12‰,respectively.The calculated δ（18）OH2O values of ore fluids in equilibrium with quartz are about+65‰,and the δDH2O values of fluid inclusions in quartz range from -40 to-70‰. （2）Meteoric water-hydrothermal tungsten ore deposits.Theδ18O values of wolframite in this type oftungsten dePosits are around-1‰. （3）Stratiform tungsten ore deposits.In these deposits,theδ18O values of quartz and wolframite areabout+17 and+3‰,respectively.It is considered that these stratiform tungsten ore deposits aregenetically related to submarine hot—spring activities。 （4）Complex mid-hydrothermal tungsten ore deposits.These tungsten ore deposits arecharacterized by multi-staged mineralization.The δ18O values of early wolframite are around+5‰,butof later wolframite are lower than+4‰,indicating that the early wolframite was precipitated fromreequilibrated magmatic water-hydrothermal solutions and the late one from the mixture ofhvdrothermal solutions with meteoric waters or mainly from meteoric waters, Based on the δ18O values of the coexisting quartz and wolframite and temperature data,twocalibration equilibrium curves have been constructed,and the corresponding equations have beenObtained: 1000 lnaQ-Wf=2.565×107T-2—7.28×l04T-1+57.27 1000 In aWf-H20=-2.285×107T-2+7.49×104T-1-61.79.

Trace elements in magmatic and hydrothermal quartz:Implications on the genesis of the Xingluokeng Tungsten Deposit,South China

The Xingluokeng deposit is the largest gran-ite-related tungsten deposit within the Wuyi metallogenic belt in South China.The Xingluokeng intrusion primarily consists of porphyritic biotite granite,biotite granite,andfine-grained granite.The deposit is represented by veinlet-disseminated mineralization with K-feldspathization and biotitization,alongside quartz-vein mineralization with gre-isenization and sericitization.This study investigates in-situ analyses of quartz compositions from both the intrusion and hydrothermal veinlets and veins.Trace element correlations indicate that trivalent Al^(3+)and Fe^(3+)replace Si^(4+)within the quartz lattice,with monovalent cations(such as Li^(+),Na^(+),and K^(+))primarily serving as charge compensators.Low Ge/Al ratios(<0.013)of quartz from granites suggest a mag-matic origin.The low Al/Ti and Ge/Ti ratios,accompanied by high Ti contents in quartz,suggest that the porphyritic biotite granite and biotite granite are characterized by rela-tively low levels of differentiation and high crystallization temperatures.In contrast,thefine-grained granite exhibits a higher degree of fractionation,lower crystallization tem-peratures,and a closer association with tungsten miner-alization.Ti contents in quartz from quartz veins indicate Qz-Ⅰformed at temperatures above 400°C,while Qz-Ⅱto Qz-Ⅴformed at temperatures below 350°C.Variations in different generations of quartz,as indicated by Al content and(Al+Fe)/(Li+Na+K)ratio,suggest that Qz-Ⅰprecipi-tated from a less acidicfluid with a stable pH,whereas Qz-Ⅱto Qz-Ⅴoriginated from a more acidicfluid with notable pH variations.Consequently,alkaline alteration and acidic alteration supplied the essential Ca and Fe for the precipita-tion of scheelite and wolframite,respectively,highlighting a critical mechanism in tungsten mineralization at the Xin-gluokeng deposit.

Comparative stability analyses of traditional and selective room-and-pillar mining techniques for sub-horizontal tungsten veins

The stability and productivity concerning a modification on the traditional room and pillar for a new selective technique at the Portuguese Panasqueira Mine have been described.The traditional room-and-pillar stoping uses 5.0-m wide rooms with 3.0 m×3.0 m pillars,while the selective room-and-pillar mining technique consists in stoping with rooms of 4.0 m wide and pillars of 4 m×4 m with a subsequent selective cutting of the quartz veins at the mid pillar of approximately 0.5 m high,to obtain a pillar section with an area of 3.0 m×3.0 m.The stability and productivity analyses indicate that the selective technique obtains smaller average pillar safety factor,more rock mass displacement,more extraction and selectivity ratios,and ore grade improvement,compared with the traditional technique.These results show that the selective technique is also more convenient.This proposed selective room-and-pillar mining technique is applicable to any sub-horizontal narrow quartz veins with wolfram,gold,etc.such as the famous La Rinconada gold mine in the Peruvian Andes.

Characteristics of Tungsten,Titanium,Rare-Earths and Antimony Mineral Resources of China

Large areas of old basements of metamorphic volcanic series, and magmatic and sedimentary rocks of different ages existing in China. China is rich in Mesozoic granite rocks which are closely related to nonferrous metals ore deposits, and favourable for the formation of tungsten, titanium, rare earths and antimony ore deposits. The article identifies the major types and locations of these mineral resources from a geological point of view.

Isotopic Chronological Study of the Huangsha-Tieshanlong Quartz Vein-Type Tungsten Deposit and Timescale of Molybdenum Mineralization in Southern Jiangxi Province,China

The Huangsha-Tieshanlong quartz-vein tungsten polymetallic ore deposit, located in the northern Pangushan-Tieshanlong tungsten ore field in eastern Ganxian-Yudu prospecting areas of the Yushan metallogenic belt, is a well-known tungsten deposit in southern Jiangxi province, China. SHRIMP-determined dating of zircons from the Tieshanlong granite yields ages of 168.1±2.1 Ma （n=11, MSWD-1.3）. Rhenium and osmium isotopic dating of molybdenite from the Huangsha quartz-vein tungsten deposit determined by ICP-MS yields a weighted average ages of 153-3 Ma and model ages of 150.22.1 Ma - 155.4-2.3 Ma. The age of the Huangsha tungsten deposit is 10 to 15 Ma later than the Tieshanlong granite, which shows that there might have been another early Late Jurassic magmatic activity between 150 and 160 Ma, a process which is closely related with tungsten mineralization in this area. The Tieshanlong granite, the Hnangsha tungsten deposit and the Pangushan-Tieshanlong ore field were all formed around 150-170 Ma, belonging to products of a Mesozoic second large-scale mineralization. According to the collected molybdenite Re-Os dating results in southern Jiangxi province, the timescale of the associated molybdenum mineralization is 2-6 Ma in the tungsten deposit and the timescale of independent molybdenum mineralization is 1-4 Ma, implying the complexity of tungsten mineralization. Times of molybdenum mineralization are mainly concentrated in the Yanshanian, which includes three stages of 133-135 Ma, 150-162 Ma, and 166-170 Ma, respectively. The 150-162 Ma-stage is in accordance with ages of large-scale WoSn mineralization, which is mainly molybdenum mineralization characterized by associated molybdenum mineralization with development of an even greater-intensity independent molybdenum mineralization. Independent molybdenum mineralization occurred before and after large-scale W-Sn mineralization, which indicates that favorable prospecting period for molybdenum may be in Cretaceous and early late Jurassic.

Re-Os Dating of Molybdenite from the Yaogangxian Tungsten Deposit,South China,and Its Geological Significance

The Yaogangxian tungsten deposit is located in the central part of the Nanling polymetailic metallogenic province. The orebodies occur as veins. Wolframite and molybdenite are the dominant ore minerals. Two samples were selected for molybdenite Re-Os dating in order to elucidate the timing of mineralization. Re-Os datings of molybdenite from quartz-woiframite veins and disseminated in granite yield ages of 153±7 Ma and 163.2±4.2 Ma respectively. The results indicate that the Yaogangxian tungsten deposit is the product of large-scale metallogenesis in the middle Yanshanian period in South China, and that the evolution from late magmatic to postmagmatic hypothermal mineralization occurred at about 10 Ma. The rhenium content of molybdenite in the Yaogangxian tungsten deposit suggests that the ore materials originated from the crust.

Hydrothermal alteration processes in the giant Dahutang tungsten deposit, South China: Implications from litho-geochemistry and mass balance calculation

The giant Dahutang tungsten(W)deposit has a total reserve of more than 1.31 Mt WO3.Veinlet-disseminated scheelite and vein type wolframite mineralization are developed in this deposit,which are related to Late Mesozoic biotite granite.Four major types of alterations,which include albitization,potassic-alteration,and greisenization,and overprinted silicification developed in contact zone.The mass balance calculate of the four alteration types were used to further understanding of the mineralization process.The fresh porphyritic biotite granite has high Nb,Ta,and W,but low Ca and Sr while the Jiuling granodiorite has high Ca and Sr,but low Nb,Ta,and W concentrations.The altered porphyritic biotite granite indicated that the Nb,Ta,and W were leached out from the fresh porphyritic biotite granite,especially by sodic alteration.The low Ca and Sr contents of the altered Neoproterozoic Jiuling granodiorite indicate that Ca and Sr had been leached out from the fresh granodiorite by the fluid from Mesozoic porphyritic biotite granites.The metal W of the Dahutang deposit was mainly derived from the fluid exsolution from the melt and alteration of W-bearing granites.This study of alteration presents a new hydrothermal circulation model to understand tungsten mineralization in the Dahutang deposit.

A Megaton Tungsten Deposit Discovered in Dahutang, Jiangxi Province

Jiangxi Province, China＇s largest base tbr tungsten production and export is known as the world capital of tungsten. By the end of 2002, there were 72 primary tungsten deposits tbund, with accumulated reserves and a proven resource of reserves of 1.9 Mt and 1.12 Mt, respectively, accounting for 20 percent of China＇s total reserves.

Microstructure and Deuterium Retention of Tungsten Deposited by Hollow Cathode Discharge in Deuterium Plasma

Tungsten has been chosen as one of the most promising candidates as the plasma-facing material in future fusion reactors. Although tungsten has numerous advantages compared with other materials, issues including dust are rather difficult to deal with. Dust is produced in fusion devices by energetic plasma-surface interaction. The re-deposition of dust particles could cause the retention of fuel atoms. In this work, tungsten is deposited with deuterium plasma by hollow cathode discharge to simulate the dust production in a tokamak. The morphology of the deposited tungsten can be described as a film with spherical particles on it. Thermal desorption spectra of the deposited tungsten show extremely high desorption of the peak positions. It is also found that there is a maximum retention of deuterium in the deposited tungsten samples due to the dynamic equilibrium of the deposition and sputtering process on the substrates.

U-Pb Zircon Dating of the Yeniutan Granitic Intrusion in the Western Sector of the North Qilian Mountains

Zircons from granodiorite and biotite granite in the Yeniutan granitic intrusion in the western North Qilian Mountains yielded a weighted mean 206Pb/238U apparent age of 460±3 Ma, suggesting that the intrusion originated during the late stage of plate subduction. Its related Ta'ergou and Xiaoliugou deposits are two of the few large tungsten deposits formed in the plate subduction environment in the world. The U-Pb dating of the zircons from the biotite granite gave a discordant lower intercept age of 183±4 Ma, which implies that the Yanshanian event was probably superimposed on the North Qilian region.

Geology and mineralization of the supergiant Shimensi granitic-type W-Cu-Mo deposit(1.168 Mt)in northern Jiangxi,South China:A Review

The Shimensi deposit is a recently discovered W-Cu-Mo polymetallic deposit located in the Jiangnan porphyry-skarn W belt in South China.The deposit has a resource of 0.74×10^(6)t of WO_(3)accompanied by 0.4×10^(6)t Cu and 28000 t Mo and other useful components like Ga,making it one of the largest W deposits in the world.This paper is aimed to reveal the ore-controlling mechanisms of the Shimensi deposit,involving the role of the ore-related granites,the tectonic background for its formation,and the metallogenesis model.The systematic geological survey suggests multi-types of alteration are developed in the deposit,mainly including greisenization,potassic-alteration,sericitization,chloritization,and silicification.Drilling engineering data and mining works indicate that the Shimensi deposit consists of two main orebodies of I and II.Therein,the W resource has reached a supergiant scale,and the accompanied Cu,Mo,Au,Bi,Ga,and some other useful components are also of economic significance.The main ore-minerals consist of scheelite,wolframite and chalcopyrite.Disseminated mineralization is the dominant type of the W-Cu-Mo polymetallic orebodies,and mainly distributes in the inner and external contact zone that between the Neoproterozoic biotite granodiorite and the Yanshanian granites.The main orebody occurs at the external contact zone,and the pegmatoid crust near the inner contact zone is an important prospecting marker of the W mineralization.Of them,the disseminated W ores within the wall rock of the Neoproterozoic biotite granodiorite is a new mineralization type identified in this paper.Combining previous geochronological and isotopic data,we propose that the mineralization of the Shimensi deposit is closely related to the intruding of the Yanshanian porphyritic biotite granite and granite porphyry.Geochemical data suggest that the biotite granodiorite is rich in Ca and had provided a large amount of Ca for the precipitation of scheelite in this area.Thus,it is a favorable wall rock type for W mineralization.The Shimensi deposit belongs to granitic-type W polymetallic deposit related to post-magmatic hydrothermal,and the ore-forming fluid was initially derived from the Yanshanian magmas.

Timing and Tectonic Setting of the Gaoaobei TungstenMolybdenum Deposit in Nanling Range, South China

The Gaoaobei tungsten-molybdenum deposit is a newly discovered large-scale quartzvein-type deposit in the Nanling metallogenic belt in South China.The ore bodies are hosted in the Indosinian granites and the Cambrian Xiangnan Group slates and are controlled by NWW-oriented faults,which are obviously different from the“five-story building”model in southern Jiangxi Province.The magmatic rocks in the study area are dominated by medium-to coarse-grained biotite monzogranite,with a few NW-oriented fine-grained granite dykes.The medium-to coarse-grained biotite monzogranite and fine-grained granite dykes have zircon U-Pb ages of 229.4±1.9 Ma(MSWD=1.5)and 164.9±3.3 Ma(MSWD=0.75),respectively,corresponding to the Indosinian and Yanshanian magmatism.The monzogranites have higher contents of FeO,CaO,K2O,P2O5,and TiO2,while the granite dykes have slightly higher contents of SiO2,Al2O3,MnO,and Na2O.Their A/CNK values are 1.11-1.75 and 1.19-2.25,and the contents of CIPW normative corundum are 1.71%-6.66%and 2.41%-9.50%,suggesting both the monzogranites and granite dykes are S-type granite.The total amount of rare earth elements in the monzogranites(from 84.7 ppm to 129 ppm)is slightly lower than that in the granite dykes(from 128 ppm to 133 ppm).The Eu/Eu*values range from 0.12 to 0.30 in monzogranites and from 0.0011 to 0.0013 in granite dykes,indicating the fine-grained granites underwent more intense fractional crystallization.The monzogranite and granite dykes have high 87Sr/86Sri values of 0.7169-0.7193 and 0.72825-0.72880,lowεNd(t)values ranging from-10.2 to-9.6 and from-11.5 to-11.4,and TDM2 ages of 1835-1785 and 1957-1946 Ma,respectively.These isotope data indicate their origin from the remelting of the Paleoproterozoic crustal materials.Combined with regional geology,it is concluded that the medium-to coarse-grained biotite monzogranite was formed in a post-collisional extensional environment.In addition,40Ar-39Ar dating of the greisen type tungsten-molybdenum ore gave consistent plateau age of 164.0±1.2 Ma,isochronal age of 162.0±2.4 Ma and anti-isochronal age of 161.4±1.8 Ma.Combined with the published molybdenite Re-Os age,the Gaoaobei tungsten-molybdenum deposit was formed at~164 Ma,which is inferred to be genetically related to the contemporaneous finegrained granite dykes(165 Ma).The deposit was likely formed during the large-scale magmatism and mineralization event in the early Yanshanian of the Nanling Range in an intra-continental extensional environment caused by the subduction of the paleo-Pacific plate.The late and small granite dykes within the large granite plutons thus require further attention during mineral prospecting in the regions.

Skarn-type tungsten mineralization associated with the Caledonian(Silurian) Niutangjie granite, northern Guangxi, China

The Niutangjie tungsten deposit is a bedded skarn-type scheelite deposit and is located at the junction between Ziyuan and Xingan counties in the north of Guangxi,China.The deposit is genetically related to a fine-grained two-mica granite within the orefield.Zircon LA-ICP-MS U-Pb dating of the granite yielded a Silurian(Caledonian)age of 421.8±2.4 Ma,which is contemporaneous with the adjacent Yuechengling batholith.Mineralization within the skarn is associated with a quartz,garnet,and diopside gangue,and scheelite is present in a number of different mineral assemblages,such as quartz-scheelite and quartz-sulfide-scheelite;these assemblages correspond to oxide and sulfide stages of mineralization.Sm-Nd isotope analysis of scheelite yielded an isochron age of 421±24 Ma.Although the uncertainty on this date is high,this age suggests that the scheelite mineralization formed during the Late Caledonian,at a similar time to the emplacement of the Niutangjie granite.Zircons within the granite have?Hf(t)values and Hf two-stage model ages of?6.5 to?11.6,and 1.79 to 2.11 Ga,respectively.These data suggest that the magma that formed the granite was derived from Mesoproterozoic crustal materials.Scheelite?Nd(t)values range from?13.06 to?13.26,also indicative of derivation from ancient crustal materials.Recent research has identified Caledonian magmatism in the western Nanling Range,indicating that this magmatism may be the source of contemporaneous tungsten mineralization.

Origin and Geodynamic Implications of Concealed Granite in Shadong Tungsten Deposit, Xinjiang, China： Zircon U-Pb Chronology, Geochemistry, and Sr-Nd-Hf Isotope Constraint

Shadong deposit is the first large-scale tungsten deposit found in the East Tianshan orogenic belt, and the geologic characteristics of the deposit indicate that the deeply concealed granite body is ge- netically related with the mineralization. The LA-ICPMS U-Pb age of zircons from the Shadong concealed granite obtained in this research is 239±2.0 Ma, belonging to the Middle Triassic. The whole rock samples are metaiuminous to slightly peraluminous （A/CNK=0.95-1.02） with low contents of SiO2 （64.0 wt.%-68.5 wt.%） and low K2O/Na2O ratios （0.73-0.96）. The samples reveal enrichment of K, Rb, Th and depletion of Nb, Ta, P, Ti and have a negative slope from La to Lu （LaN/YbN=16.29-36.8） with weak negative Eu anom- aly （Eu/Eu＊= 0.71-0.82）. Initial ^87Sr/^86Sr ratios of whole rock range of 0.706 59-0.707 75, eNd（t） values range from -1.77 to -2.53 and εnf（t） values of zircon are between 2.54 and 4.90. The lithogeochemistry and Sr-Nd-Hf isotopic characteristics revealed that the concealed granite in Shadong tungsten deposit is I-type granite, and occurs in an intraplate tectonic setting. The magma mixing during intraplating of mantle de- rived magma intruding into the crust in Indosinian Period is the major formation mechanism of the granite. Of which, the proportion of mantle derived magma ranges from 58% to 60%, and the crustal materials are mainly the metamorphic basement of Xingxingxia Group of Mesoproterozoic Changcheng System, which may orovide the main source of ore forming metals of Shadong tungsten deposit.

Geological characteristics and mineralization setting of the Zhuxi tungsten(copper) polymetallic deposit in the Eastern Jiangnan Orogen

The Zhuxi ore deposit is a super-large scheelite(copper) polymetallic deposit discovered in recent years. It grew above copper/tungsten-rich Neoproterozoic argilloarenaceous basement rocks and was formed in the contact zone between Yanshanian granites and Carboniferous-Permian limestone. Granites related to this mineralization mainly include equigranular, middle- to coarse-grained granites and granitic porphyries. There are two mineralization types: skarn scheelite(copper) and granite scheelite mineralization. The former is large scale and has a high content of scheelite, whereas the latter is small scale and has a low content of scheelite. In the Taqian-Fuchun Basin, its NW boundary is a thrust fault, and the SE boundary is an angular unconformity with Proterozoic basement. In Carboniferous-Permian rock assemblages, the tungsten and copper contents in the limestone are both very high. The contents of major elements in granitoids do not differ largely between the periphery and the inside of the Zhuxi ore deposit. In both areas, the values of the aluminum saturation index are A/CNK>1.1, and the rocks are classified as potassium-rich strongly peraluminous granites. In terms of trace elements, compared to granites on the periphery of the Zhuxi ore deposit, the granites inside the Zhuxi ore deposit have smaller d Eu values, exhibit a significantly more negative Eu anomaly, are richer in Rb, U, Ta, Pb and Hf, and are more depleted in Ba, Ce, Sr, La and Ti, which indicates that they are highly differentiated S-type granites with a high degree of evolution. Under the influence of fluids, mineralization of sulfides is evident within massive rock formations inside the Zhuxi ore deposit, and the mean SO_3 content is 0.2%. Compared to peripheral rocks, the d Eu and total rare earth element(REE) content of granites inside the Zhuxi ore deposit are both lower, indicating a certain evolutionary inheritance relationship between the granites on the periphery and the granites inside the Zhuxi ore deposit. For peripheral and ore district plutons, U-Pb zircon dating shows an age range of 152–148 Ma. In situ Lu-Hf isotope analysis of zircon in the granites reveals that the calculated e_(Hf)(t) values are all negative, and the majority range from -6 to -9. The T_(DM2) values are concentrated in the range of 1.50–1.88 Ga(peak at 1.75 Ga), suggesting that the granitic magmas are derived from partial melting of ancient crust. This paper also discusses the metallogenic conditions and ore-controlling conditions of the ore district from the perspectives of mineral contents, hydrothermal alteration, and ore-controlling structures in the strata and the ore-bearing rocks. It is proposed that the Zhuxi ore deposit went through a multistage evolution, including oblique intrusion of granitic magmas, skarn mineralization, cooling and alteration, and precipitation of metal sulfides. The mineralization pattern can be summarized as "copper in the east and tungsten in the west, copper at shallow-middle depths and tungsten at deep depths, tungsten in the early stage and copper in the late stage".

Deuterium retention in chemically vapor deposited tungsten carbide coatings and hot-rolled tungsten exposed to low-energy deuterium plasma

Samples of chemically vapor deposited(CVD)coatings of tungsten carbides W_(45)C_(55)and W_(60)C_(40)and samples of hot-rolled tungsten were exposed to deuterium(D)plasma at sample temperatures ranging from 323 to 813 K,as a result of which the samples were irradiated with D ions with an energy of about 200 eV per D particle at a flux of D particles of about1.1×10^(21)D·m^(-2)·s^(-1)to a fluence of about 2×10^(24)D·m^(-2).The concentration of deuterium in these samples was examined by the D(3 He,p)4 He nuclear reaction.Based on the measured deuterium depth profiles and assuming that these profiles are determined by diffusing D atoms,the diffusion coefficients of deuterium in the CVD tungsten carbide coatings were determined.Using these diffusion coefficients,an estimate of the Arrhenius relation for the diffusion coefficients of deuterium in CVD tungsten carbide coatings was obtained:D=2.5×10^(-3)exp(-1.12 eV/kT)m~2·s^(-1),where T is temperature expressed in Kelvin,and k is the Boltzmann constant.The concentration of trapped deuterium in the bulk of CVD tungsten carbide coatings is practically independent of the stoichiometry of the coatings.It decreases from about 5×10^(-2)to about 7×10^(-4)D/(W+C)with an increase in the deuterium plasma exposure temperature from 373 to 813 K.The concentration of trapped deuterium in hot-rolled tungsten,expressed in units of the D/W atomic ratio,is more than an order of magnitude lower than the concentration of deuterium in tungsten carbides,and also decreases with increasing plasma exposure temperature.