A combined EMPA and LA-ICP-MS study of Li-bearing mica and Sn–Ti oxide minerals from the Qiguling topaz rhyolite (Qitianling District,China): The role of fluorine in origin of tin mineralization

The Sn-rich Qiguling topaz rhyolite dike intrudes the Qitianling biotite granite of the Nanling Range in southern China; the granite hosts the large Furong Sn deposit. The rhyolite dike is typically peraluminous, volatile-enriched, and highly evolved. Whole-rock F and Sn concentrations attain 1.9 wt.% and 2700 ppm, respectively. The rhyolite consists of a fine-grained matrix formed by quartz, feldspar, mica and topaz, enclosing phenocrysts of quartz, feldspar and mica; it is locally crosscut by quartz veinlets. Lithium-bearing micas in both phenocrysts and the groundmass can be classified as primary zinnwaldite, “Mus-Ann” (intermediate member between annite and muscovite), and secondary Fe-rich muscovite. Topaz is present in the groundmass only; common fluorite occurs in the groundmass and also in a specific cassiterite, rutile and fluorite (Sn–Ti–F) assemblage. Cassiterite and rutile are the only Sn and Ti minerals; both cassiterite and Nb-rich rutile are commonly included in the phenocrysts. The Sn–Ti–F assemblage is pervasive, and contains spongy cassiterite in some cases; cassiterite also occurs in quartz veinlets which cut the groundmass. Electron microprobe and LA-ICP-MS compositions were used to study the magmatic and hydrothermal processes and the role of F in Sn mineralization. The presence of zinnwaldite and “Mus-Ann”, which are respectively representative of early and late mica crystallization during magma differentiation, also suggests a significant decrease in f(HF)/f(H₂O) of the system. Cassiterite included in the zinnwaldite phenocrysts is suggested to have crystallized from the primary magma at high temperature. Within the Sn–Ti–F aggregates, rutile crystallized as the earliest mineral, followed by fluorite and cassiterite. Spongy cassiterite containing inclusions of the groundmass minerals indicate a low viscosity of the late fluid. The cassiterite in the quartz veinlets crystallized from low-temperature hydrothermal fluids, which possibly mixed with meteoric water. In general, cassiterite precipitated during both magmatic and hydrothermal stages, and over a range of temperatures. The original fluorine and tin enrichments, f(HF)/f(H₂O) change in the residual magma, formation of Ca,Sn,F-rich immiscible fluid, decrease of the f(HF) during groundmass crystallization, and mixing of magma-derived fluids with low-saline meteoric water during the late hydrothermal stage, are all factors independently or together responsible for the Sn mineralization in the Qiguling rhyolite.     

Indium in cassiterite and ores of tin deposits

The results obtained with LA-ICP-MS by less abundant lighter ¹¹³In isotope and EPMA show that in cassiterite of cassiterite–quartz veins the indium contents do not exceed 160 ppm, while cassiterite from Sn–sulfide veins is characterized by higher indium contents from 40 to 485 ppm; sulfides of Sn–sulfide veins unlike sulfides of cassiterite–quartz veins also have the highest indium contents: Fe-sphalerite (100–25,000 ppm), chalcopyrite (up to 1000 ppm), and stannite (up to 60,000 ppm). Indium contents in the Sn–sulfide ore of the Tigrinoe and Pravourmiiskoe deposits obtained using SR-XRF, ICP-MS and atomic absorption methods range from 10 to 433 ppm with average values of 56–65 ppm. Indium-rich Sn–sulfide mineralization in five large Sn–Ag ore districts of the Far East Russia (Khingansky, Badzhalsky, Komsomolsky, Arminsky, Kavalerovsky) provides the impetus for further exploration of deposits with Sn–sulfide mineralization as the most promising indium resources in Russia. Empirical observations from geology and geochronology of cassiterite–quartz and Sn–sulfide mineralization show that the combined contribution from granite and alkaline–subalkaline mafic sources and multistage ore-forming processes doubled indium resources of deposits being the main factors in the formation of high grade indium mineralization.     

Experimental Studies of the Solubility of Cassiterite and the Extraction of Tin from Granitic Melts

Experiments indicate that the solubility of cassiterite can be enhanced by increasing either acidity or alkalinity in hydrothermal solutions as a consequence of the duality of tin.The minimum solubility of cassiterite is found in neutral solutions.F-and CL-coordination compounds of Sn can alternate with hydroxyl coordination compounds with changing pH in the solutions.In this case,F^- and Cl^- and OH^- can be substituted with each other.The dissolution reaction of cassiterite is of reducing nature.High temperature and acidic reducing environment are favorable for the dissolution of cassiterite and the trans-port of Sn^2 compounds in fluids or solutions.High-temperature fluoride and chloride fluids can all dissolve,extract and enrich Sn to form F^- and /or Cl-coordination compounds,However,Fplays a more important role than Cl.F-coordination compounds are more stable and efficient than Cl-coordination compounds during the transport an enrichment of Sn in melts or solutions.The solubili-ty of cassiterite and the amount of Sn extracted from granitic melt depend not only on T,P,pH and Eh in the fluids or solutions,but also on the amounts of dissociated F^- and Cl^- in the fluids.     

Chemical and thermodynamic constraints on the hydrothermal transport and deposition of tin: I. Calculation of the solubility of cassiterite at high pressures and temperatures

Estimation of equation of state parameters for Sn⁺⁺ and calculation of the thermodynamic properties of other aqueous species and dissociation constants for various stannous and stannic complexes as a function of temperature permit prediction of the high temperature solution chemistry of tin and calculation of the solubility of cassiterite in hydrothermal solutions. The results of these calculations indicate that in the absence of appreciable chloride and fluoride concentrations, Sn(OH)₂⁰ and Sn(OH)₄⁰ are the predominant tin species in H₂O up to 350°C at ~2 $\text{\$}\text{?}$pH $\text{\$}\text{?}$7.5. The calculations also indicate that chloride complexes of Sn⁺⁺ predominate by several orders of magnitude over their fluoride and hydroxide counterparts in 1–3 molal (m) NaCl solutions, except in the presence of geologically unrealistic concentrations of fluoride or a pH greater than ~3.5 at 250°C or ~5.0 at 350°C. At higher pH values, most of the tin in solution is present as hydroxide complexes, even at concentrations of NaCl as high as 3 m. Calculated values of the solubility of cassiterite at high temperatures compare favorably with experimental data reported in the literature. Depending on the fugacity of oxygen and solution composition, the solubility of cassiterite in hydrothermal solutions may exceed 100 ppm under geologically realistic conditions.     

Evolution of mineralizing fluids of cassiterite–wolframite and fluorite deposits from Mueilha tin mine area, Eastern Desert of Egypt, evidence from fluid inclusion

Sn–W deposit of the Mueilha mine is one of many other Sn–W deposits in the Eastern desert of Egypt that associated with albite granite. Two forms of Sn–W mineralizations are known at the Mueilha Sn-mine area, namely fissure filling quartz veins and greisen. Cassiterite and/or wolframite, sheelite, and beryl are the main ore minerals in the greisen and quartz veins. Subordinate chalcopyrite and supergene malachite and limonite are also observed in the mineralized veins. To constrain the P–T conditions of the Sn–W mineralizations, fluid inclusions trapped in quartz and cassiterite, have been investigated. The following primary fluid inclusion types are observed: CO₂-rich, two-phase (L?+?V) aqueous, and immiscible three-phase (H₂O–CO₂) inclusions. Low temperature and low salinity secondary inclusions were also detected in the studied samples. Microthermometric results revealed that Sn–W deposition seem to have taken place due to immiscibility at temperature between 260°C and 340°C, and estimated pressure between 1.2 to 2.2 kb. Microthermometric results of fluid inclusions in fluorite from fluorite veins illustrated that fluorite seems to be deposited due to mixing of two fluids at minimum temperature 140°C and 180°C, and estimated minimum pressure at 800 bars.     

The partitioning of sulfur between multicomponent aqueous fluids and felsic melts

Sulfur partitioning between melt and fluid phase largely controls the environmental impact of volcanic eruptions. Fluid/melt partitioning data also provide the physical basis for interpreting changes in volcanic gas compositions that are used in eruption forecasts. To better constrain some variables that control the behavior of sulfur in felsic systems, in particular the interaction between different volatiles, we studied the partitioning of sulfur between aqueous fluids and haplogranitic melts at 200 MPa and 750–850 °C as a function of oxygen fugacity (Ni–NiO or Re–ReO₂ buffer), melt composition (Al/(Na?+?K) ratio), and fluid composition (NaCl and CO₂ content). The data confirm a first-order influence of oxygen fugacity on the partitioning of sulfur. Under “reducing conditions” (Ni–NiO buffer), D^fluid/melt is nearly one order of magnitude larger (323?±?14 for a metaluminous melt) than under “oxidizing conditions” (Re–ReO₂ buffer; 74?±?5 for a metaluminous melt). This effect is likely related to a major change in sulfur speciation in both melt and fluid. Raman spectra of the quenched fluids show the presence of H₂S and HS^? under reducing conditions and of SO₄^2? and HSO₄^? under oxidizing conditions, while SO₂ is undetectable. The latter observation suggests that already at the Re–ReO₂ buffer, sulfur in the fluid is almost completely in the S⁶⁺ state and, therefore, more oxidized than expected according to current models. CO₂ in the fluid (up to x_CO2?=?0.3) has no effect on the fluid/melt partitioning of sulfur, neither under oxidizing nor under reducing conditions. However, the effect of NaCl depends on redox state. While at oxidizing conditions, D^fluid/melt is independent of x_NaCl, the fluid/melt partition coefficient strongly decreases with NaCl content under reducing conditions, probably due to a change from H₂S to NaSH as dominant sulfur species in the fluid. A decrease of D^fluid/melt with alkali content in the melt is observed over the entire compositional range under reducing conditions, while it is prominent only between the peraluminous and metaluminous composition in oxidizing experiments. Overall, the experimental results suggest that for typical oxidized, silicic to intermediate subduction zone magmas, the degassing of sulfur is not influenced by the presence of other volatiles, while under reducing conditions, strong interactions with chlorine are observed. If the sulfur oxidation state is preserved during an explosive eruption, a large fraction of the sulfur released from oxidized magmas may be in the S⁶⁺ state and may remain undetected by conventional methods that only measure SO₂. Accordingly, the sulfur yield and the possible climatic impact of some eruptions may be severely underestimated.     

Genesis of the Xuebaoding W–Sn–Be Crystal Deposits in Southwest China: Evidence from Fluid Inclusions,Stable Isotopes and Ore Elements

The Xuebaoding crystal deposit, located in northern Longmenshan, Sichuan Province, China, is well known for producing coarse‐grained crystals of scheelite, beryl, cassiterite, fluorite and other minerals. The orebody occurs between the Pankou and Pukouling granites, and a typical ore vein is divided into three parts: muscovite and beryl within granite (Part I); beryl, cassiterite and muscovite in the host transition from granite to marble (Part II); and the main mineralization part, an assemblage of beryl, cassiterite, scheelite, fluorite, apatite and needle‐like tourmaline within marble (Part III). No evidence of crosscutting or overlapping of these ore veins by others suggests that the orebody was formed by single fluid activity. The contents of Be, W, Sn, Li, Cs, Rb, B, and F in the Pankou and Pukouling granites are similar to those of the granites that host Nanling W–Sn deposits. The calculated isotopic compositions of beryl, scheelite and cassiterite (δD, ?69.3‰ to ?107.2‰ and δ¹⁸O_H2O, 8.2‰ to 15.0‰) indicate that the ore‐forming fluids were mainly composed of magmatic water with minor meteoric water and CO₂ derived from decarbonation of marble. Primary fluid inclusions are CO₂? CH₄+ H₂O ± CO₂ (vapor), with or without clathrates and halites. We estimate the fluid trapping condition at T = 220 to 360°C and P > 0.9 kbar. Fluid inclusions are rich in H₂O, F^‐ and Cl^‐. Evidence for fluid‐phase immiscibility during mineralization includes variable L/V ratios in the inclusions and inclusions containing different phase proportions. Fluid immiscibility may have been induced by the pressure released by extension joints, thereby facilitating the mineralization found in Part III. Based on the geochemical data, geological occurrence, and fluid inclusion studies, we hypothesize that the coarse‐grained crystals were formed by: (i) the high content of ore elements and volatile elements such as F in ore‐forming fluids; (ii) occurrence of fluid immiscibility and Ca‐bearing minerals after wall rock transition from granite to marble making the ore elements deposit completely; (iii) pure host marble as host rock without impure elements such as Fe; and (iv) sufficient space in ore veins to allow growth.     

Combined zircon and cassiterite U–Pb dating of the Piaotang granite-related tungsten–tin deposit,southern Jiangxi tungsten district,China

The large low-grade Piaotang W–Sn deposit in the southern Jiangxi tungsten district of the eastern Nanling Range, South China, is related to a hidden granite pluton of Jurassic age. The magmatic-hydrothermal system displays a zonation from an inner greisen zone to quartz veins and to peripheral veinlets/stringers (Five-floor zonation model). Most mineralization is in quartz veins with wolframite > cassiterite. The hidden granite pluton in underground exposures comprises three intrusive units, i.e. biotite granite, two-mica granite and muscovite granite. The latter unit is spatially associated with the W–Sn deposit.Combined LA-MC-ICP-MS U–Pb dating of igneous zircon and LA-ICP-MS U–Pb dating of hydrothermal cassiterite are used to constrain the timing of granitic magmatism and hydrothermal mineralization. Zircon from the three granite units has a weighted average ²⁰⁶Pb/²³⁸U age of 159.8 ± 0.3 Ma (2 σ, MSWD = 0.3). The cathodoluminescence (CL) textures indicate that some of the cassiterite crystals from the wolframite-cassiterite quartz vein system have growth zonations, i.e. zone I in the core and zone II in the rim. Dating on cassiterite (zone II) yields a weighted average ²⁰⁶Pb/²³⁸U age of 159.5 ± 1.5 Ma (2 σ, MSWD = 0.4), i.e. the magmatic and hydrothermal systems are synchronous. This confirms the classical model of granite-related tin–tungsten mineralization, and is against the view of a broader time gap of >6 Myr between granite magmatism and W–Sn mineralization which has been previously proposed for the southern Jiangxi tungsten district. The elevated trace element concentrations of Zr, U, Nb, Ta, W and Ti suggest that cassiterite (zone II) formed in a high-temperature quartz vein system related to the Piaotang granite pluton.     

The giant tin polymetallic mineralization in southwest China:Integrated geochemical and isotopic constraints and implications for Cretaceous tectonomagmatic event

The Gejiu-Bozushan-Laojunshan W-Sn polymetallic metallogenic belt(GBLB) in southeast Yunnan Province is an important part of the southwestern Yangtze Block in South China.Tin polymetallic mineralization in this belt includes the Niusipo,Malage,Songshujiao,Laochang and Kafang ore fields in the Gejiu area which are spatially and temporally associated with the Kafang-Laochang and Songshujiao granite plutons.These granites are characterized by variable A/CNK values(mostly 1.1,except for two samples with 1.09),high contents of SiO_2(74.38-76.84 wt.%) and Al_2 O_3(12.46-14.05 wt.%) and variable CaO/Na_2 O ratios(0.2-0.65) as well as high zircon δ~(18)O values(7.74‰-9.86‰),indicative of S-type affinities.These rocks are depleted in Rb,Th,U,Ti,LREE[(La/Yb)N=1.4-20.51],Ba,Nb,Sr,and Ti and display strong negative Eu and Ba anomalies.The rocks possess high Rb/Sr and Rb/Ba ratios,relatively low initial ~(87)Sr/~(86)Sr ratios(0.6917-0.7101),and less radiogenic εNd(t)values(-8.0 to-9.1).The zircon grains from these rocks show negative ε_(Hf)(t) values in the range of-3.7 to-9.9 with mean T_(DM2)(Nd) and T_(DM2)(Hf) values of 1.57 Ga and 1.55 Ga.They show initial ~(207)Pb/~(204)Pb ranging from15.69 to 15.71 and ~(206)Pb/~(204)Pb from 18.36 to 18.70.Monazite from Songshujiao granites exhibits higher U and lower Th/U ratios,lower δ~(18)O values and higher ε_(Hf)(t) values than those of the zircon grains in the KafangLaochang granites.The geochemical and isotopic features indicate that the Laochang-Kafang granites originated by partial melting of Mesoproterozoic crustal components including biotite-rich metapelite and metagraywacke,whereas the Songshujiao granites were derived from Mesoproterozoic muscovite-rich metapelite crustal source.Most zircon grains from the Songshujiao,Laochang and Kafang granites have high-U concentrations and their SIMS U-Pb ages show age scatter from 81.6 Ma to 88.6 Ma,80.7 Ma to 86.1 Ma and 82.3 Ma to 87.0 Ma,suggesting formation earlier than the monazite and cassiterite.Monazite SIMS U-Pb ages and Th-Pb ages of three same granite samples are consistent and show yielded 206 Pb/~(238)U ages of 83.7 ± 0.6 Ma,83.7±0.6 Ma,and 83.4±0.6 Ma,and ~(208)Pb/~(232)Th ages of 83.2 ± 0.5 Ma,83.8 ± 0.4 Ma,and 83.5±0.9 Ma,which are within the range of the SIMS zircon U-Pb ages from these rocks.The data constrain the crystallization of the granites at ca.83 Ma.In situ U-Pb dating of two cassiterite samples from the cassiterite-sulfide ore in the Songshujiao ore field and Kafang ore field,and two from the cassiterite-oxide+cassiterite bearing dolomite in the Laochang ore field yielded weighted mean 206 Pb/~(238)U ages of 83.5±0.4 Ma(MSWD=0.6),83.5 ± 0.4 Ma(MSWD=0.5),83.6 ±0.4 Ma(MSWD=0.6) and 83.2 ±0.7 Ma(MSWD=0.6),respectively.Combined with geological characteristics,the new geochronological data indicate that the formation of the granites and Sn polymetallic deposits are coeval.We correlate the magmatic and metallogenic event with lithospheric thinning and asthenosphere upwelling in continental extension setting in relation to the eastward subduction of the Neo-Tethys beneath the Sanjiang tectonic domain during Late Cretaceous.     

滇西来利山与小龙河云英岩型锡矿成矿流体氧逸度特征对比

来利山锡矿床与小龙河锡矿床是滇西地区典型的云英岩型锡矿床。为揭示它们在成因上深层次的差异性,对来利山锡矿和小龙河锡矿的锡石进行了电子探针成分分析、镜下观察以及成矿环境对比分析。结果表明,锡石中的铁多以Fe~(3+)的形式与Sn~(4+)发生类质同象,氧逸度越高,锡石中Fe~(3+)越多,宏观上表现为锡石的颜色越深。来利山矿区锡石中Fe含量明显低于小龙河矿区,且锡石颜色明显比小龙河矿区颜色浅,反映了来利山锡矿成矿环境相对开放,成矿流体氧逸度偏低,流体中Sn络合物迁移能力较强,在花岗岩体外接触带的围岩裂隙中形成外云英岩型锡矿床;而小龙河锡矿成矿环境相对封闭,成矿流体氧逸度偏高,流体中Sn络合物迁移能力较弱,多在花岗岩体顶部的构造裂隙中形成内云英岩型锡矿床。     

Magmatic–hydrothermal rare-element mineralization in the Songshugang granite (northeastern Jiangxi,China): Insights from an electron-microprobe study of Nb–Ta–Zr minerals

The Songshugang granite, hidden in the Sinian metasedimentary stratum, is a highly evolved rare-element granite in northeastern Jiangxi province, South China. The samples were systematically taken from the CK-102 drill hole at the depth of 171–423 m. Four types of rocks were divided from the bottom upwards: topaz albite granite as the main body, greisen nodules, topaz K-feldspar granite and pegmatite layer. Electron-microprobe study reveals that the rare-element minerals of the Songshugang granite are very different from those of other rare-element granites. Mn^# [Mn/(Fe + Mn)] and Ta^# [Ta/(Nb + Ta)] of columbite-group minerals and Hf^# [Hf/(Zr + Hf)] of zircon are nearly constant within each type of rocks. However, back-scattered electron imaging revealed that Nb–Ta oxides and zircon of the Songshugang granite, especially those of topaz albite granite, topaz K-feldspar granite and greisen, are commonly characterized by a specific two-stage texture on the crystal scale. The early-stage Nb–Ta oxide is simply subhedral-shaped columbite-(Fe) (CGM-I) with low Mn^# (0.16–0.37) and Ta^# (0.05–0.29). Columbite-(Fe) is penetrated by the later-stage tantalite veinlets (CGM-II) or surrounded by complex Nb–Ta–Sn–W mineral assemblages, including tantalite-(Fe), wodginite (sl), cassiterite, and ferberite. Tantalite has wide range of Mn^# values (0.15–0.88) from Fe-dominance to Mn-dominance. Wodginite with Ta>Nb has large variable concentrations of W, Sn and Ti. Cassiterite and ferberite are all enriched in Nb and Ta (Nb₂O₅ + Ta₂O₅ up to 20.12 wt.% and 31.42 wt.%, respectively), with high Ta^# (>0.5). Similar to Nb–Ta oxides and Nb–Ta–Sn–W mineral assemblages, the early-stage zircon is commonly included by the later-stage zircon with sharply boundary. They have contrasting Hf contents, and HfO₂ of the later-stage zircon is up to 28.13 wt.%. Petrographic features indicate that the early-stage of columbite and zircon were formed in magmatic environment. However, the later-stage of rare-element minerals were influenced by fluxes-enriched fluids. Tantalite, together with wodginite, cassiterite, and ferberite implies a Ta-dominant media. An interstitial fluid-rich melt enriched in Ta and flux at the magmatic–hydrothermal transitional stage is currently a favored model for explaining the later-stage of rare-element mineralization.     

Mineralogy,geochemistry, and genesis of co-genetic granite-pegmatite-hosted rare metal and rare earth deposits of the Kawadgaon area,Bastar craton,Central India

Co-genetic pegmatites associated with the granite of the Kawadgaon area in the Bastar craton, Central India, contain a wide range of ore minerals of Nb, Ta, Be, Sn, Zr, Ti, and REE, including columbite-tantalite, ixiolite, pseudo-ixiolite, wodginite, tapiolite, microlite, fersmite, euxenite, aeschynite, beryl, cassiterite, monazite, xenotime, zircon, ilmenite, triplite, and magnetite. There is a distinct vertical zonation between the rare metal and tin pegmatites in apical parts of the host granite. Geochemically, these are LCT-S type, beryl-columbite-phosphate pegmatites that have notably high contents of SiO₂ (av. 73.80%), Rb (av. 381 ppm), and Nb (av. 132 ppm). The investigated granites probably were derived from the melting of older crustal rocks, as indicated by a high initial ⁸⁷Sr/⁸⁶Sr isotopic ratio, and the major-element geochemistry of the granites and pegmatites. Plots of mol. CaO/(MgO+FeO^t) vs. mol. Al₂O₃/(MgO+FeO^t) suggest that the source rock was pelitic metasediments. Based on the available data, it is postulated that the derivation of pegmatites from the parent granite occurred shortly after granite emplacement in the late Archaean-early Proterozoic (~2500 Ma). The K/Rb, Ba/Rb, and Rb/Sr ratios of the felsic bodies reveal that a substantial part of the granite formed from evolved melts, and further fractionation produced the co-genetic pegmatites and associated rare metal and rare earth deposits.     

The origin of tin deposits in the Mount Wells region,Pine Creek Geosyncline,Northern Territory

Tabular steeply dipping cassiterite‐bearing lodes in the Mount Wells region are hosted by lower greenschist fades metasediment of the Pine Creek Geosyncline within the contact aureole of late orogenic granitoids. The latter are predominantly I‐type, but S‐type phases are developed near the sediment‐granitoid contact.

Quartz, cassiterite, pyrite, arsenopyrite, chalcopyrite and pyrrhotite are the main minerals. Two types of lodes are present: (i) Sn‐quartz lodes containing 5–10 vol% sulphide minerals; and (ii) Sn‐sulphide lodes containing ～ 70 vol% sulphide minerals. At the surface, the former appear as normal quartz veins and the latter as hematite‐quartz breccia resulting from the collapse of original sulphide‐rich lodes as a consequence of volume reduction due to oxidation and leaching.

Two stages of quartz veining are recognized in both types of lodes. Cassiterite is present in stage I while stage II is composed of barren quartz with minor pyrite. Late stage III carbonate veinlets are present in Sn‐sulphide lodes. The lode‐wallrock contact is sharp with weak alteration effects confined to the fringe of the lodes. The alteration minerals include sericite, quartz, tourmaline, chlorite, pyrite and minor K‐feldspar.

Four types of fluid inclusions are present in vein quartz and cassiterite: Type A (CO₂ ± H₂O ± CH₄); Type B (H₂O+～ 20% vapour); Type C (H₂O+ < 15% vapour) and Type D (H₂O+ < 15% vapour + NaCl). Early ‘primary’ inclusions represented by Types A and B are present in stage I only and have a well‐defined temperature mode at ～300°C and a salinity range of 1–20 wt% eq NaCl. Types C and D inclusions are ‘secondary’ in stage I and primary in stage II and have a temperature mode at 120–160°C and salinities from about 1 to more than 26 wt% eq NaCl. Variable H₂O‐CO₂ ratios of Type A inclusions and homogenization in CO₂ or H₂O phase at near identical temperature indicate entrapment at the H₂O‐CO₂ solvus and define a pressure of ～ 100 MPa. The melting sequence of frozen inclusions suggests that the ore fluids were mainly H₂O‐CO₂‐CH₄‐Na‐Ca‐Cl brines. This is also confirmed by Raman Laser Spectrometry.

Oxygen and sulphur isotope data are consistent with a magmatic origin of the ore fluids. The δD values are up to 20%0 higher than those expected for magmatic fluids and probably resulted from interaction of the latter with the carbonaceous strata. This interpretation is supported by δ¹³C data on the fluid inclusion CO₂.

Fluid inclusions, stable isotope and mineralogical data are used to approximate the physico‐chemical parameters of the ore fluids which are as follows: T 300°C, m Cl～2, fO₂ ～ 10^‐35, mSS ～ 0.01, Sn ～ 1 ppm, Cu ～ 1 ppm and pH ～ 5.5.

It is suggested that fluids of granitic parentage interacted with the enclosing sediment and picked up CO₂, CH₄ and possibly Ca. The granitic phases became reduced due to this interaction and developed S‐type characteristics. Tin was probably partitioned into the CH₄‐bearing reduced fluids. At some stage the fluid overpressure exceeded the lithostatic lode enforcing failure of the carapace and the intruded rocks by hydraulic fracturing causing CH₄ and CO₂ loss resulting in the precipitation of the ore minerals.     

Tin-carrier minerals in metaluminous granites of the western Nanling Range (southern China): Constraints on processes of tin mineralization in oxidized granites

Huashan, Guposhan and Qitianling are three similar and representative metaluminous A-type tin granites in the western Nanling Range, China. They all have a high oxidization state with magnetite as the dominant Fe–Ti oxide. This study presents an understanding of systematic mineralogy of Sn-bearing minerals (biotite, titanite, magnetite and cassiterite) in the three granites. Biotite has an annite composition and both electron-microprobe and LA-ICP-MS analyses indicate trace amounts of tin in biotite (approximately 100–20 ppm). Chloritization of biotite is accompanied by formation of Sn-rich rutile and cassiterite. Titanite has a long history of crystallization from the early-magmatic stage through the late-magmatic stage to the hydrothermal stage. Owing to its solid-solution relationship with malayaite (CaSnSiO₅), titanite always contains tin to various extents. Early-magmatic titanite contains about 0.5 wt.% SnO₂, while the late-magmatic titanite is markedly enriched in tin (on average 14.8 and 3.4 SnO₂ in titanite from the Qitianling and Huashan granites, respectively). Magnetite grains typically display a trellis structure with ilmenite lamellae, where microinclusions of cassiterite (<1 μm in size) are present. This is likely consistent with features of the “oxy-exsolution” process of Sn-bearing titanomagnetite precursor. Cassiterite may be observed as late-magmatic phase, but most commonly appears as an alteration product of other primary minerals. All tin-bearing minerals in the three granites record a complete process of tin mineralization in granite. The features of tin in primary biotite, titanite and magnetite reflect an initial enrichment during the early stage of magmatic crystallization of the Huashan, Guposhan and Qitianling granites. Association of interstitial Sn-titanite and cassiterite suggests further tin enrichment related to fractional crystallization of granitic magmas. Fluids and alteration of primary minerals play an important role in the leaching, concentration and transportation of Sn during hydrothermal processes, which favors vein-type Sn mineralization.     

Interdiffusion of Mg–Fe in olivine at 1,400–1,600 °C and 1 atm total pressure

The interdiffusion coefficient of Mg–Fe in olivine (D _Mg–Fe) was obtained at 1,400–1,600 °C at the atmospheric pressure with the oxygen fugacity of 10^?3.5–10^?2 Pa using a diffusion couple technique. The D _Mg–Fe shows the anisotropy (largest along the [001] direction and smallest along the [100] direction), and its activation energy (280–320 kJ/mol) is ~80–120 kJ/mol higher than that estimated at lower temperatures. The D _Mg–Fe at temperatures of >1,400 °C can be explained by the cation-vacancy chemistry determined both by the Fe³⁺/Fe²⁺ equilibrium and by the intrinsic point defect formation with the formation enthalpy of 220–270 kJ/mol depending on the thermodynamical model for the Fe³⁺/Fe²⁺ equilibrium in olivine. The formation enthalpy of 220–270 kJ/mol for the point defect (cation vacancy) in olivine is consistent with that estimated from the Mg self-diffusion in Fe-free forsterite. The increase in the activation energy of D _Mg–Fe at >1,400 °C is thus interpreted as the result of the transition of diffusion mechanism from the transition metal extrinsic domain to the intrinsic domain at the atmospheric pressure.     

Oxygen isotope fractionation factors involving cassiterite (SnO2): I. calculation of reduced partition function ratios from heat capacity and X-ray resonant studies

Oxygen isotope equilibrium fractionation constants (β¹⁸O-factors) of cassiterite were evaluated on the basis of heat capacity and X-ray resonant (Mössbauer spectroscopy and X-ray inelastic scattering) data.The low-temperature heat capacity of cassiterite was measured in the range from 13 to 340 K using an adiabatic calorimeter. Results of measurements of two samples agree very closely but deviate more than 5% from previous heat capacity data used for calculation of thermodynamic functions. The temperature dependence of heat capacity was treated using the modern version of the Thirring expansion, and the appropriate temperature dependence of the vibrational kinetic energy was found.Measurements of temperature-dependent Mössbauer parameters of cassiterite were conducted in the range from 300 to 900 K. The attempt to describe Mössbauer fraction and the second order Doppler (SOD) shift on the basis of the Debye model failed. The first term of the Thirring expansion of the Mössbauer SOD shift agrees with that calculated from the Sn sublattice vibration density of states (VDOS) obtained via synchrotron X-ray scattering. Based on this agreement we calculated the kinetic energy of the cassiterite Sn sublattice from VDOS.From the kinetic energy of the total cassiterite crystalline lattice and its Sn sublattice, β¹⁸O-factors of cassiterite were computed in the temperature range 300-1500 K by the method of Polyakov and Mineev (2000). Appropriate polynomials, which are valid at temperatures above 400 K, are the following:

     

Mineralogy and chemical distribution study of placer cassiterite and some associated new recorded minerals, east Rosetta, Egypt

Highly purified picked minerals of cassiterite and associated new recorded minerals were chemically and mineralogically investigated. Most of the investigated cassiterite exhibits homogeneous grains without obvious zoning. The analyzed cassiterites have more than 98 wt.% SnO₂, which reveal clearly their considerable purity. Minor gold with traces of ferrotapiolite, cinnabar, native lead, chromite, and chevkinite are well detectable within the obtained cassiterite concentrate. The origin of the present cassiterite and the associated minerals is also discussed. The variation in color and grain size of cassiterite may be attributed to the various lithology and/or areas drained by the River Nile. The color of cassiterite is appeared to be intensified with increased Nb and Fe contents. Three categories of cassiterites are identified, (a) Ta₂O₅-rich (0.46–2.65 wt.%); (b) TiO₂-rich (0.42–1.41 wt.%), and (c) Ta₂O₅-Nb₂O₅-Fe₂O₃ rich one (Ta₂O₅:0.42–3.58 wt.%, Nb₂O₅: 0.7–1.98 wt.% and Fe₂O₃: 0.56–1.02 wt.%). Sn is usually substituted by Ta, Nb, and Fe. Minor gold with traces of new recorded ferrotapiolite, cinnabar, native lead, chromite, and chevkinite are well detectable within the obtained cassiterite concentrate. Ferrotapiolite is composed mainly of Ta, Fe, and Nb with minor Ti, Sn, and Mn, which similar to that derived from pegmatites and quartz veins. Chevkinite is generally enriched in Ti, Fe, and LREEs and depleted in P, Th, and U which analogous to that crystallized from felsic igneous rock suites.     

Sorption of Eu(III)/Cm(III) on Ca-montmorillonite and Na-illite. Part 1: Batch sorption and time-resolved laser fluorescence spectroscopy experiments

Sorption of Cm(III) and Eu(III) at trace concentrations onto Ca-montmorillonite (SWy-1) and Na-illite (Illite du Puy) has been studied under anaerobic conditions by batch sorption experiments and time-resolved laser fluorescence spectroscopy (TRLFS). Comparison of the results from spectroscopic and batch sorption experiments with Cm and Eu indicates the existence of outer-sphere complexes at pH <4 in the experiments with Na-illite (0.25 g/L solid; 2.5 × 10⁻⁷ mol/L Cm; 0.1 mol/L NaClO₄). In the case of Ca-montmorillonite, (0.25 g/L solid, 2.5 × 10⁻⁷ mol/L Cm or 10⁻⁶ mol/L Eu, 0.066 mol/L Ca(ClO₄)₂), Cm/Eu outer-sphere complexes do not form at significant levels due to the Ca²⁺ competition for the clay mineral cation-exchange sites. TRLFS spectra indicate the formation of inner-sphere surface complexes at pH >5 for both clay minerals. Five H₂O/OH⁻ molecules remain in the first metal ion coordination sphere of the sorbed Eu/Cm. Measured fluorescence lifetimes of sorbed Eu/Cm and peak deconvolution of Cm-spectra are consistent with the formation of surface complexes of the form ≡S-O-Eu/Cm(OH)_x^(2−x)(H₂O)_5−x. At pH ≥ 12 Cm becomes incorporated into a surface precipitate at the Ca-montmorillonite surface presumably composed of Ca(OH)₂ or calcium silicate hydrate. A dramatic shift of the fluorescence emission band by more than 20 nm and a clear increase in the fluorescence lifetime suggests the almost complete displacement of coordinated H₂O and OH⁻. The pH dependent Eu sorption data obtained in batch experiments are consistent with spectroscopic data on Eu and Cm within experimental uncertainties thus demonstrating the validity of Eu as a homologue for trivalent actinides. Parameterization of a two-site protolysis nonelectrostatic surface complexation and cation exchange model using the batch sorption data and spectroscopic results is discussed in Part 2 of this work.     

Effect of alkaline solutions on bentonite properties

The influence of alkaline aqueous solutions on the properties of bentonite was investigated to evaluate the performance of bentonitic engineered barriers when contacted with alkaline groundwater. Batch and hydraulic conductivity tests were conducted on Na-bentonite using six different alkaline aqueous solutions. For the batch tests, almost no change in the montmorillonite fraction of the bentonite was observed after reacting with alkaline solutions (pH = 8.4–13.1), regardless of the solution type. On the other hand, aluminosilicate minerals (e.g., albite) were dissolved and secondary minerals (e.g., anorthite) were formed in alkaline NaOH solutions (pH > 13). The cation (Ca or Na) concentration primarily affected the swelling properties of bentonite rather than the pH of the solution, which was comparable to the results of the hydraulic conductivity tests. For the Ca solutions, the hydraulic conductivity of the bentonite specimen to the 0.02 mol/L Ca(OH)₂ solution (6.5 × 10^?9 cm/s) was approximately an order of magnitude lower than that of the bentonite specimen to the 0.02 mol/L Ca(OH)₂ + 1 mol/L CaCl₂ solution (5.0 × 10^?8 cm/s), whereas the hydraulic conductivity to the 0.02 mol/L Ca(OH)₂ + 1 mol/L CaCl₂ solution (pH = 11.3) (5.0 × 10^?8 cm/s) was slightly higher than that to the 1 mol/L CaCl₂ solution (pH_i = 8.4) (4.4 × 10^?8 cm/s). For the NaOH solutions with pH > 13, the hydraulic conductivity of the bentonite specimen decreased with increasing Na concentration, suggesting that the effect of Na concentration was more dominant than that of permeant pH.     

Chromium speciation and mobility in a high level nuclear waste vadose zone plume

Radioactive core samples containing elevated concentrations of Cr from a high level nuclear waste plume in the Hanford vadose zone were studied to asses the future mobility of Cr. Cr(VI) is an important subsurface contaminant at the Hanford Site. The plume originated in 1969 by leakage of self-boiling supernate from a tank containing REDOX process waste. The supernate contained high concentrations of alkali (NaOH ≈ 5.25 mol/L), salt (NaNO₃/NaNO₂ >10 mol/L), aluminate [Al(OH)₄⁻ = 3.36 mol/L], Cr(VI) (0.413 mol/L), and ¹³⁷Cs⁺ (6.51 × 10⁻⁵ mol/L). Water and acid extraction of the oxidized subsurface sediments indicated that a significant portion of the total Cr was associated with the solid phase. Mineralogic analyses, Cr valence speciation measurements by X-ray adsorption near edge structure (XANES) spectroscopy, and small column leaching studies were performed to identify the chemical retardation mechanism and leachability of Cr. While X-ray diffraction detected little mineralogic change to the sediments from waste reaction, scanning electron microscopy (SEM) showed that mineral particles within 5 m of the point of tank failure were coated with secondary, sodium aluminosilicate precipitates. The density of these precipitates decreased with distance from the source (e.g., beyond 10 m). The XANES and column studies demonstrated the reduction of 29-75% of the total Cr to insoluble Cr(III), and the apparent precipitation of up to 43% of the Cr(VI) as an unidentified, non-leachable phase. Both Cr(VI) reduction and Cr(VI) precipitation were greater in sediments closer to the leak source where significant mineral alteration was noted by SEM. These and other observations imply that basic mineral hydrolysis driven by large concentrations of OH⁻ in the waste stream liberated Fe(II) from the otherwise oxidizing sediments that served as a reductant for CrO₄²⁻. The coarse-textured Hanford sediments contain silt-sized mineral phases (biotite, clinochlore, magnetite, and ilmenite) that are sources of Fe(II). Other dissolution products (e.g., Ba²⁺) or Al(OH)₄⁻ present in the waste stream may have induced Cr(VI) precipitation as pH moderated through mineral reaction. The results demonstrate that a minimum of 42% of the total Cr inventory in all of the samples was immobilized as Cr(III) and Cr(VI) precipitates that are unlikely to dissolve and migrate to groundwater under the low recharge conditions of the Hanford vadose zone.