Mineralogical controls on mine drainage of the abandoned Ervedosa tin mine in north-eastern Portugal

The Ervedosa Mine, in north-eastern Portugal, has Sn-bearing quartz veins containing cassiterite and sulphides that cut Silurian schists and a Sn-bearing muscovite granite. These veins were mined for Sn and As₂O₃ until 1969. Cassiterite, the main Sn ore, has alternate lighter and darker growth-zones. The darker zones are richer in Fe, Nb, Ta and Ti, but poorer in Sn than the adjoining lighter zones. Exsolution blebs of ferrocolumbite, manganocolumbite, Ti ixiolite, rutile, ilmenite and rare wolframite were found in the darker zones. Arsenopyrite is the most abundant sulphide and contains inclusions of pyrrhotite, bismuth, bismuthinite and matildite. Other sulphides are pyrite, sphalerite, chalcopyrite and stannite. Secondary solid phases consisting mainly of hydrate sulphate complexes of Al, Fe, Ca and Mg (aluminocopiapite, copiapite, halotrichite, pickeringite, gypsum and alunogen, meta-alunogen) occur at the surface of the Sn-bearing quartz veins and their wall rocks (granite and schist), while oxides, hydroxides, arsenates and residual mineral phases (albite, muscovite and quartz) occur in mining tailings. Toxic acid mine waters (acid mine drainage AMD), which have high conductivity and significant concentrations of As, SO₄ and metal (Cu, Zn, Pb, Fe, Mn, Cd, Ni and Co), occur in an area directly affected by the mine. Surface stream waters outside this area have low conductivity and a pH that is almost neutral. Metal and As concentrations are also lower. Stream waters within the impact area have an intermediate composition, falling between that of the AMD and the natural stream waters outside impact area. Waters associated directly with mineralised veins must not be used for human consumption or agriculture.     

Contrasting evolution of low-P rare metal granites from two different terranes in the Hoggar area, Algeria

Two mineralogically different rare metal granites located in two distinct terranes from the Tuareg area are compared: the Tin-Amzi granite in the north of the Laouni Terrane and the Ebelekan granite in the Assodé–Issalane Terrane.The Tin-Amzi granite is enclosed within Eburnean granulitic gneisses, and consists of albite, quartz, protolithionite, K-feldspar and topaz granite (PG). The accessory minerals include columbite tantalite, U- and Hf-rich zircon, Th-uraninite, wolframoixiolite and wolframite. This facies is characterised by a mineralogical evolution from the bottom to the top underlined by a strong resorption of K-feldspar and albite and the crystalliK-feldspar of more abundant topaz and protolithionite II which is further altered in muscovite and Mn-siderite. It is underlain by an albite, K-feldspar, F-rich topaz, quartz and muscovite granite (MG), with W–Nb–Ta oxides, wolframite, Nb-rutile, zircon and scarce uranothorite as accessories.The Ebelekan granite intrudes into a coarse-grained biotite granite enclosed within upper amphibolite-facies metasediments. It comprises a zinnwaldite, albite, topaz porphyritic granite (ZG) with “snow ball” quartz and K-feldspar. The accessories are zircon, monazite, uranothorite, Ta bearing cassiterite, columbite tantalite and wodginite. It is capped by a banded aplite-pegmatite (AP).The geochemistry of Tin-Amzi and Ebelekan granites is nearly comparable. Both are peraluminous (A/CNK=1.10–1.29; ASI=1.17–1.31), sodolithic and fluorine rich with high SiO₂, Al₂O₃, Na₂O+K₂O, Rb, Ga, Li, Ta, Nb, Sn and low FeO, MgO, TiO₂, Ba, Sr, Y, Zr and REE contents. These rare metal Ta bearing granites belong to the P-poor subclass, relating to their P₂O₅ content ( 0.03–0.15 wt.%). Nevertheless, they are distinguished by their concentration of W, Sn and Ta. The Tin-Amzi granite is W–Ta bearing with high W/Sn ratio whereas the Ebelekan granite is Ta–Sn bearing with insignificant W content.At Tin-Amzi the W–Nb–Ta minerals define a sequence formed by W-columbite tantalite followed by wolframoixiolite and finally wolframite showing the effect of hydrothermal overprinting with an extreme W enrichment of the fluids. At Ebelekan, the Sn–Nb–Ta oxides follow a Mn sequence: manganocolumbite→manganotantalite→wodginite+titanowodginite→cassiterite that represents a trend of primary crystallisation resulting from progressive substitution Fe→Mn and Nb→Ta during the magmatic fractionation.     

Mineralogical and Geochemical Characterization of Beryl-Bearing Granitoids, Eastern Desert, Egypt: Metallogenic and Exploration Constraints

Mineral chemistry and geochemical characteristics of beryl-bearing granitoids in Eastern Desert of Egypt, were examined in order to identify the metallogenetic processes of the host granitoids. The investigated Be-bearing granitoids and type occurrences are classified into two groups: (i) peraluminous, Ta ≥ Nb + Sn + Be ± W-enriched, Li-albite granite (e.g. Nuweibi and Abu Dabbab); and (ii) metasomatized, Nb >> Ta + Sn + Be ± W ± Mo-enriched alkali feldspar granite (i.e. apogranite; e.g. Homr Akarem, Homr Mikpid and Qash Amir). In these two groups, beryl occurs as stockwork greisen veins, greisen bodies, beryl-bearing cassiterite ± wolframite quartz veins, dissemination, and miarolitic pegmatites. Beryl of the Be-granitoids, particularly those of miarolitic pegmatites, contains appreciable contents of Fe, Na, and H₂O. An important feature of the Be-apogranites is the occurrence of white mica as the sole mafic mineral in the unaltered alkali feldspar granite in lower zones. Presence of white mica as volatile-rich pockets suggests that the melt underwent disequilibrium crystallization, rapid nucleation rates, and exsolving and expulsion of volatiles.     

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.     

Geological setting,mineralogy and genesis of tungsten mineralization in Dayu district,JiangXi (People's Republic of China): An outline

The city of Dayu is the center of the most important tungsten district of PRC. Valuable quantities of Sn, Mo, Bi, Nb, Ta, REE, Cu, Pb, Zn, Ag, Be and Li are also recovered. At the Xihuashan and Dangping mines, hundreds of the typical Jiangxi wolframite-quarz veins, located at the top and marginal parts of a Jurassic biotite granite intrusion, are mined. At Piaotang the mined ore bodies consist of a stockwork-type of mineralization which cuts the roof-rocks (Cambrian metasediments: phyllite, quartz sandstone, hornfels) of the biotite granite. Around the mineralizations, the country rocks display extensive alteration: namely K-feldspar alteration and greisenization in granite; tourmalinization, muscovitization, silicification, pyrophillitization in the metasediments. The main mineralogy and parageneses of the veins and veinlets can be summarized as follows: I stage — oxide — (wolframite, cassiterite, molybdenite, quartz, K-feldspar, beryl, fluorite, topaz), the best represented; II stage — sulphide — (chalcopyrite, galena, sphalerite, pyrite, pyrrhotite, bismuthinite, cassiterite, wolframite, quartz) well represented at Piaotang; III stage — carbonate — (pyrite, scheelite, chlorite, sericite, fluorite, quartz, calcite). The fracture-controlled mineralizations of Dayu appear to be the product of a continous multistage process related to the late phases of the jurassic Yenshanian magmatism.

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Nel Distretto di Dayu, in cui operano tre miniere principale e sei centri estrattivi minori, viene prodotto poco meno di un quarto (2300 ton/anno) del l'intera produzione in tungsteno della RPC. Oltre al W vengono prodotte apprezzabili quantità di una ventina di altri elementi, fra i quali: Sn, Mo, Bi, Nb, Ta, Terre Rare, Cu, Pb, Zn, Ag, Be, Li, etc.. I corpi minerari sono costituiti, sia da alcune centinaia di vene a quarzo-wolframite, che con una potenza media di 40 cm, tagliano le parti marginali di una intrusione di granito biotitico del Giura, sia da mineralizzazioni tipo stockworks che si espandono nelle metamorfiti (filladi, arenarie quarzose parzialmente cornubianitiche) cambriane poste a tetto della cupola granitica. Il granito biotitico, all' intorno delle vene, presenta zone simmetriche di alterazione, a K-feldspato e greisen; nei metasedimenti i principali minerali di alterazione sono: tormalina, muscovite, quarzo, pirofillite e topazio. Le principali caratteristiche mineralogiche e paragenetiche dei corpi minerari possono essere come di seguito schematizzate: I stadio — a prevalenti ossidi (wolframite, cassiterite, molibdenite, quarzo, K-feldspato, berillo, fluorite, topazio), il meglio rappresentato; II stadio — a prevalenti solfuri (calcopirite, galena, sfalerite, pirite, pirrotina, bismutinite, cassiterite, wolframite, quarzo), particolarmente ben rappresentato nella miniera di Piaotang; III stadio — a prevalenti carbonati (pirite, scheelite, clorite, sericite, fluorite, quarzo, calcite). La metallogenesi di Dayu, sviluppatasi in un sistema tettonicamente attivo é geneticamente associabile alle fasi tardive del magmatismo Yenshanide giurassico.

     

Geochemical signatures and mechanisms of trace elements dispersion in the area of the Vale das Gatas mine (Northern Portugal)

A geochemical survey involving the collection and analysis of 170 stream sediment samples was carried out in Vale das Gatas area in order to delineate geochemical signatures and to detect pollution hazards due to mining.Factor analysis applied to the data showed that the most important variables accounting for the first factor are Ag, Pb, Bi, As, W, Cd, Zn and Cu. These variables represent the most significant metalliferous elements of the original paragenesis, which still maintain a close relationship in the secondary geological environment. The spatial distribution of the factor scores referred to factor 1 indicates that positive scores occur predominantly in the Vale das Gatas and Sabrosa streams and in the main Pinhão river. The results also show that the Vale das Gatas mine is the most important contamination source in the Vale das Gatas district.In order to study the dispersion, transfer and uptake mechanisms of trace elements from the Vale das Gatas mine, additional sample media were collected, i.e., stream sediments, tailings, coatings, waters (surficial and mine waters) and specific biological species. Four sample stations were selected, namely two in connection with abandoned adits of the Vale das Gatas mine, one located in the Vale das Gatas stream and one located in the Pinhão River. The results show that chemical reactions of leaching and precipitation took place controlling the heavy metals in areas near the Vale das Gatas mine.At the same time, positive anomalous patterns are visible along the Pinhão river for about 20 km. The mineralogical composition of the stream sediments suggests that processes of mechanical dispersion also interfere in the secondary distribution of the metalliferous elements in that media.     

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.     

江西盘古山石英脉型钨矿床钨铋矿物特征及矿物的垂直分带

南岭石英脉型钨矿存在形态分带(五层楼格式)已有不少报道,但像江西盘古山钨铋石英脉型矿床这样垂直延深大、矿物成分复杂、矿物分带清楚的矿床实例并不多见。参照矿床的矿物空间分带、确定矿体露头的空间部位和矿床所受的剥蚀程度,是评价矿床的一个重要参考因素。矿物空间分带对寻找盲矿体也具有实际意义。     

Compositional characteristics of wolframite in tin deposits,Dupangling, Guangxi

Statistical data on major, trace and rare-earth elements in wolframite from the quartz vein-and greisen-type tin deposits in the Dupangling orefield reveal: (1) The components in wolframite can be divided into two relatively independent groups: the WO₃-Nb-Ta-Sc-REE group, in which WO₃ is negatively correlated with the others and the FeO-MnO-Sn group, in which MnO is negatively correlated with the other two; (2) In general, REE fractionation is not significant, reflected mainly by the separation of Eu from other REE’s. LREE and HREE increase or decrease simultaneously, with HREE being more variable; (3) Nb, Ta, Sc, REE substitute for W, and Sn may enter into wolframite lattice accompanied by Fe-Mn substitution; (4) In contrast to wolframite in quartz veins, which is poor in REE, Nb, Ta and Sc and has highδ Eu values and LREE / HREE and Nb/Ta ratios, wolframite in greisen is rich in REE, Nb, Ta, Sc and has lowδ Eu values and LREE/HREE and Nb/Ta ratios; and (5) The contents and ratios of trace elements and REE partitioning parameters of wolframite can be used as guide for prospecting.     

Characterization and timing of the different types of fluids present in the barren and ore-veins of the W-Sn deposit of Panasqueira,Central Portugal

The Panasqueira W-Sn deposit is the largest quartz-vein type deposit of the Iberian Peninsula and the most important wolframite deposit in Western Europe. The ore-veins are almost exclusively sub-horizontal. Besides ore-bearing sub-horizontal veins, the Panasqueira mine also contains barren quartz veins. There are essentially two generations of barren quartz: quartz, contemporaneous with the earliest regional metamorphism (QI), and recrystallized quartz, contemporaneous with the thermal metamorphism related to the granite intrusion (QII). Fluid inclusion studies (microthermometry and Raman) were undertaken in order to distinguish fluids contemporaneous with the barren quartz from those contemporaneous with the ore-bearing quartz (QIII). Fluid inclusion data indicate that the barren and ore-bearing quartz fluids are dominantly aqueous (93 to 98 mol% H₂O), with a nearly constant bulk salinity (8 to 12 wt% eq. NaCl), with the quantity of volatile component (determined by Raman spectrometry) higher in QIII, but never greater than 5 mol%. However, the CO₂/CH₄ + N₂ ratio is different for each type of quartz. Volatiles are dominated by CH₄ (10 to 96 mol% ZCH₄ and/or N₂ (3 to 87 mol% ZN₂) in the barren quartz and by CO₂ (60 to 73 mol% ZCO₂) in ore-bearing quartz. The bulk chemical composition of the fluids in QIII is comparable to that found commonly in hydrothermal fluids associated with wolframite mineralization, where Na>K>Ca and HCO₃>Cl>SO₄. A dispersion in TH (226 to 350 °C) found in QIII, together with a variation in the degree of filling (0.5 to 0.7) and with the consequent variation of fluid densities (0.70 to 0.79), may result from changes in the fluid pressure regime below lithostatic pressure, suggesting vein filling related to tectonic events.     

江西省武功山地区浒坑钨矿床的Re-Os年龄及其地质意义

浒坑钨矿床是位于江西省中部武功山成矿带的大型石英脉型黑钨矿床。为了确定该矿床的成矿时代,笔者选取了浒坑含钨石英脉中与黑钨矿共生的辉钼矿进行了高精度Re-Os同位素定年,并获得5个辉钼矿样品的Re-Os等时线年龄和模式加权平均年龄分别为150.2±2.2Ma和149.82±0.92Ma。测年数据表明浒坑钨矿床的成矿时代为150Ma左右,是华南地区中生代大规模成岩成矿作用高峰期的产物。辉钼矿含铼较低,表明成矿物质可能来自壳源,与形成浒坑花岗岩体的燕山期重熔S型花岗岩岩浆活动有关。该矿床形成于燕山期岩石圈伸展减薄环境。     

La cassitérite zonée du gisement de Sokhret Allal (Granite des Zaër; Maroc Central): Composition chimique et phases fluides associées

Résumé La composition chimique d'une cassitérite zonée provenant du gisement de tungstène-étain de Sokhret Allal (Granite des Zaër; Maroc Central) a été analysée par microsonde électronique. La zonation optique du minéral correspond à des variations en éléments mineurs (Fe, Ti, Nb): les bandes sombres apparaissent corrélées à une augmentation en titane et fer tandis que les bandes claires sont plus pures. Les inclusions fluides contemporaines du dépôt de la cassitérite sont primaires et constituées de fluides typiquement aqueux de composition (97 a 99 moles % H₂O, 3 à 1 moles % équivalent NaCl, température=270–330 °C) et sont piégées en phase liquide. La contribution de ces nouvelles données à la métallogenèse W-Sn du Maroc Central est discutée.

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The chemical composition of a zoned cassiterite from the tungsten-tin deposit of Sokhret Allal (Zaër granite, Central Morocco) has been analyzed with an electron microprobe. The mineral zoning is related to variable Fe, Ti, and Nb contents: the darker zones are enriched in titanium and iron whereas lighter zones are purer. Fluid inclusions contemporaneous with cassiterite deposition are primary, and the fluids are aqueous with a composition of 97–99 mol% H₂O and 3–1 mol% eq. NaCl (temperature=270–330 °C) and were trapped in the liquid-stability field. The contribution of these data to the central Morocco W-Sn metallogenesis is discussed.

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Adresse permanente     

Fluid Inclusion Studies of Ore and Gangue Minerals from the Piaotang Tungsten Deposit, Southern Jiangxi Province, China

The Piaotang deposit is one of the largest vein-type W-polymetallic deposits in southern Jiangxi Province, South China. The coexistence of wolframite and cassiterite is an important feature of the deposit. Based on detailed petrographic observations, microthermometry of fluid inclusions in wolframite, cassiterite and intergrown quartz was undertaken. The inclusions in wolframite were observed by infrared microscope, while those in cassiterite and quartz were observed in visible light. The fluid inclusions in wolframite can be divided into two types: aqueous inclusions with a large vapor-phase proportion and aqueous inclusions with a small vapor-phase ratio. The homogenization temperature (Th) of inclusions in wolframite with large vapor-phase ratios ranged from 280°C to 390°C, with salinity ranging from 3.1 to 7.2 wt% NaCl eq. In contrast, the Th values of inclusions with small vapor-phase ratios ranged from 216°C to 264°C, with salinity values ranging from 3.5 to 9.3 wt% NaCl eq. Th values of primary inclusions in cassiterite ranged from 316°C to 380°C, with salinity ranging from 5.4 to 9.3 wt% NaCl eq. Th values for primary fluid inclusions in quartz ranged from 162°C to 309°C, with salinity values ranging from 1.2 to 6.7 wt% NaCl eq. The results show that the formation conditions of wolframite, cassiterite and intergrown quartz are not uniform. The evolutionary processes of fluids related to these three kinds of minerals are also significantly different. Intergrown quartz cannot provide the depositional conditions of wolframite and cassiterite. The fluids related to tungsten mineralization for the NaCl-H2O system had a medium-to-high temperature and low salinity, while the fluids related to tin mineralization for the NaCl-H2O system had a high temperature and medium-to-low salinity. The results of this study suggest that fluid cooling is the main mechanism for the precipitation of tungsten and tin.     

Geology and geothermometry of vein-type W-Sn deposits at Pennaichaung and Yetkanzintaung Prospects,Tavoy Township,Tennasserim Division,southern Burma

The Pennaichaung and Yetkanzintaung W-Sn Prospects are located in Tavoy Township, Tennasserim Division, southern Burma. The W-Sn mineralization at the Pennaichaung is closely related with a small, satellitic granitoid pluton of presumably Late Mesozoic age, which intruded the metaclastic rocks of Mergui Group (mostly Carboniferous). The mineralized quartz veins at the Pennaichaung penetrated the granitoid-metasedimentary rocks contact. In contrary to the Pennaichaung deposit, the W-Sn veins at the Yetkanzintaung are exclusively in the metasedimentary rocks of slates and quartzites of Margui Group. Mineralized quartz veins in the Pennaichaung area trend NNE-SSW, NW-SE and NE-SW with a maximum thickness of 30 cm, but only quartz veins trending NNE-SSW are found to be productive and contained economically workable wolframite and cassiterite. Majority of the mineralized quartz veins in the Yetkanzintaung area trend approximately N-S with easterly dip of 50°–70°. The thickness of the ore veins in the Yetkanzintaung area are thinner than those of the Pennaichaung and range from 1 cm to 20 cm with an average width of 5 cm. Fluid inclusion studies of the quartz from the ore veins cutting the granitoid in the Pennaichaung area have yielded a filling temperature range of 170°–270°C with a maximum mode of 220°C, while quartz crystals from the ore veins in the nearby metasedimentary rocks gave a filling temperature range of 140°–220°C with a maximum mode of 160°C. Hence, the Pennaichaung deposit was thought to have emplaced under a filling temperature range of 140°–270°C. A similar low filling temperature range was recorded for the Yetkanzintaung deposit. Quartz from the Yetkanzintaung ore veins have yielded filling temperatures of 200°–240°C, whereas the fluorites associated with the mineralized quartz veins gave a temperature range of 140°–160°C. Limited freezing runs indicate a salinity of less than 5 NaCl equivalent weight percent for inclusions in quartz from both orebodies. No fluid inclusion evidence of boiling of ore fluids nor presence of liquid CO₂ was observed in this study. Thus, the ore fluids responsible for the W-Sn mineralization at the Pennaichaung and Yetkanzintaung areas were of low temperature, diluted, CO₂-deficient, NaCl brines.     

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.     

松树岗钽铌钨锡矿床石英脉的矿物学研究——云母和黑钨矿成分对热液成矿过程的制约

矿石矿物和脉石矿物的成分演化蕴含了热液成矿过程的详细信息。本文基于岩相学观察,从云母和黑钨矿着手,利用电子探针和LA-ICP-MS分析技术,对赣东北松树岗Ta-Nb-W-Sn矿床的浅部热液成矿过程开展了研究。结果表明,松树岗矿床浅部的钨锡矿体的石英脉,从早到晚,由深至浅,可以划分为黑钨矿石英脉、锡石石英脉、硫化物石英脉和贫矿石英脉。4类石英脉中都含有早期的铁锂云母和晚期的白云母与铁的氧化物集合体,深部早期脉中的云母以铁锂云母为主,而浅部晚期脉中的云母以白云母为主。与早期铁锂云母相比,晚期白云母具有明显较低的Ti、Na、Rb、Cs、W、Nb、Zn、Li_2O含量和明显较高的Pb、Cu、B含量。从深部早期脉到浅部晚期脉,云母成分存在如下演化趋势:Ti、Na、W、Nb含量降低,Pb、Zn、Cu、Li_2O、B含量增高。不同深度的黑钨矿石英脉中含有两种不同成分的黑钨矿,属同一期演化早晚形成。相对于热液流体早期沉淀的黑钨矿,晚期黑钨矿具有明显较低的Nb、Ta、Zr、Hf、Ti、Sn、U、In、Sc含量和明显较高的Mo含量和Fe O/MnO值。云母和黑钨矿主微量元素成分的演化揭示了在松树岗矿床浅部的热液成矿早期以岩浆热液为主,晚期由于水岩反应的加强有较多围岩物质贡献。     

Tracking magmatic and hydrothermal Nb–Ta–W–Sn fractionation using mineral textures and composition: A case study from the late Cretaceous Jiepailing ore district in the Nanling Range in South China

The Jiepailing mining district in the Nanling range in South China is well-known for its granite-related Sn–Be–F-mineralization. Recently, drill holes have exposed an Nb–Ta–W–Sn mineralized granitic porphyry and topaz-bearing granite–greisen at depth, which we have studied here, using mineral (columbite, rutile, wolframite, cassiterite, zircon, and mica) major- and trace-element compositional data, mineral textures, and zircon and columbite U–Pb geochronology. Our age data shows that the porphyry and the granite and their mineralization formed at ~ 91–89 ± 1 Ma in the late-Cretaceous, and thus subsequent to the main ore-forming events of the region. Continuous mineral compositional trends indicate that the studied granitoids are related by progressive fractionation. We propose that: (1) subhedral–euhedral, low-Ta columbite crystallized from melt; (2) euhedral–subhedral rutile and wolframite and subhedral and subhedral cassiterite up to ~ 30 μm in size formed at the magmatic–hydrothermal transition of the system; and (3) high-Ta columbite and subhedral cassiterite up to ~ 10 μm in size formed from subsolidus hydrothermal fluids. In combination with the Nb, Ta, W, and Sn compositions of zircon and mica, their textures and compositional variation allow us to track the magmatic to hydrothermal rare-metal fractionation (concentration, mobilization, and deposition) of the system in detail, despite our limited access to it through only two exploration drill cores. Using the Nb, Ta, W, and Sn concentrations in zircon (refractory, early-crystallized) and in micas (late equilibrated), respectively, was particularly useful for tracing the partial loss of Sn and W ore components from the intrusion, and to constrain the information which is crucial for any rigorous ore exploration.     

The mineralized veins and the impact of old mine workings on the environment at Segura, central Portugal

At Segura, granitic pegmatite veins with cassiterite and lepidolite, hydrothermal Sn–W quartz veins and Ba–Pb–Zn quartz veins intruded the Cambrian schist–metagraywacke complex and Hercynian granites. Cassiterite from Sn–W quartz veins is richer in Ti and poorer in Nb and Nb+Ta than cassiterite from granitic pegmatite. Wolframite from Sn–W quartz veins is enriched in ferberite component. The Sn–W quartz veins contain pyrrhotite, arsenopyrite, sphalerite, chalcopyrite, stannite, matildite and schapbachite and the Ba–Pb–Zn quartz veins have cobaltite, pyrite, sphalerite, chalcopyrite, galena and barite, which were analyzed by electron microprobe. The presently abandoned mining area was exploited for Sn, W, Ba and Pb until 1953. Stream sediments and soils have higher concentrations of metals than parent granites and schists. Sn, W, B, As and Cu anomalies found in stream sediments and soils are associated with Sn–W quartz veins, while Ba, Pb and Zn anomalies in stream sediments and soils are related to Ba–Pb–Zn quartz veins. Sn, W, B, As, Cu, Ba, Pb and Zn anomalies in stream sediments and soils are also related to the respective old mining activities, which increased the mobility of trace metals from mineralized veins to soils, stream sediments and waters. Stream sediments and soils are sinks of trace elements, which depend on their contents in mineralized veins and weathering processes, but Sn, W and B depend mainly on a mechanic process. Soils must not be used for agriculture and human residence due to their Sn, B, As and Ba contents. Waters associated with mineralized veins were analyzed by flame atomic absorption spectroscopy (FAAS) and ICP-AES have high As, Fe and Mn and should not be used for human consumption and agriculture activities. The highest As values in waters were all related to Sn–W quartz veins and the highest Fe and Mn values were associated with the Ba–Pb–Zn quartz veins. No significant acid drainage was found associated with the old mine workings.     

Infrared microthermometric and stable isotopic study of fluid inclusions in wolframite at the Xihuashan tungsten deposit,Jiangxi province,China

The Xihuashan tungsten deposit, Jiangxi province, China, is a world-class vein-type ore deposit hosted in Cambrian strata and Mesozoic granitic intrusions. There are two major sets of subparallel ore-bearing quartz veins. The ore mineral assemblage includes wolframite and molybdenite, with minor amounts of arsenopyrite, chalcopyrite, and pyrite. There are only two-phase aqueous-rich inclusions in wolframite but at least three major types of inclusions in quartz: two- or three-phase CO₂-rich inclusions, two-phase pure CO₂ inclusions and two-phase aqueous inclusions, indicating boiling. Fluid inclusions in wolframite have relatively higher homogenization temperatures and salinities (239–380°C, 3.8–13.7 wt.% NaCl equiv) compared with those in quartz (177–329°C, 0.9–8.1 wt.% NaCl equiv). These distinct differences suggest that those conventional microthermometric data from quartz are not adequate to explain the ore formation process. Enthalpy–salinity plot shows a linear relationship, implying mixing of different sources of fluids. Although boiling occurred during vein-type mineralization, it seems negligible for wolframite deposition. Mixing is the dominant mechanism of wolframite precipitation in Xihuashan. δ³⁴S values of the sulfides range from −1.6 to +0.1‰, indicative of a magmatic source of sulfur. δ¹⁸O values of wolframite are relatively homogeneous, ranging from +4.8‰ to +6.3‰. Oxygen isotope modeling of boiling and mixing processes also indicates that mixing of two different fluids was an important mechanism in the precipitation of wolframite.     

Hydrothermal processes and shifting element association patterns in the W—Sn enriched granite of Regoufe, Portugal

Combined research in geochemistry and mineral chemistry of the hydrothermally altered W-Sn specialized granite of Regoufe and its derivatives in Portugal was undertaken to gain insight in the mineralogical changes associated with hydrothermal processes within a single granite cupola. Over 1000 unpolished rock sections were analyzed by automated X-ray fluorescence spectrometry (XRF). On the basis of the XRF data, a small number of these same sections was selected for investigation by electron probe microanalysis. The study focuses on fourteen elements of interest that are measurable with the chosen techniques. Major pervasive alteration within the Regoufe granite is virtually contemporaneous with mineralization in the form of Sn- or W-bearing quartz veins. Two phases of hydrothermal activity are discerned, characterized by different element associations. Fluids of the first phase were especially rich in Sn, Cs and F, whereas the second phase was marked by a W-Ta-Nb-Rb association and presumably carried less F. Phosphorus probably was an important fluid component in both phases. The fluids are inferred to have fractionated from a related granitic magma at depth.Tin, W, Nb and Ta are mainly found as substitutions or inclusions in biotite in the least altered part of the Regoufe granite. Tantalo-niobian rutile is an important control for the distribution of Nb. Tin occurs in rutile and rarely as cassiterite. Muscovitization caused leaching of Ti and Zr from the granite. Tin, supplied or mobilized by the hydrothermal fluids, behaves differently from W, Nb and Ta. In the most altered rocks, muscovite hosts significant amounts of Sn. Whereas Sn is still related to Cs and Ti, elements that probably represent altered biotite, W, Ta and Nb are related to newly formed Rb-rich muscovite. Columbitetantalite was detected embedded in late muscovite. In contrast to Sn, the fluid-supplied W was predominantly deposited as wolframite in quartz veins and the altered granite is not enriched in W compared to the relatively unaltered rocks. Strontium is preferentially hosted by K-feldspar in the least altered granite; Ca in this rock is still partly contained in albite. With increasing albitization and muscovitization, Sr and Ca were released and are partly bound in newly formed apatite. The primary magmatic apatites have near-ideal formula compositions, but mobilization of P during hydrothermal activity resulted in the formation of Mn-rich apatite in all parts of the granite, and Sr- and probably Li-rich varieties in the most altered rocks. Eosphorite, and scorodite as the oxidation product of arsenopyrite, were also formed as a result of P mobilization. In the least altered rocks, Cs is mainly contained in biotite. In the most altered granite and aplitic rocks, enrichment of Cs and Rb is evenly distributed over K-feldspar and micas. The processes that lead to increased Rb are partly independent of Cs enrichment, and apparently related to the W-Nb-Ta mineralization event, separate from the preceding Sn mineralization.