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Niobium (Nb) and tantalum (Ta) are quoted as “strategic” or “critical” elements for contemporaneous society. The main sources of Nb and Ta are minerals of the pyrochlore supergroup (PSGM) and the columbite group (CGM) mined from different magmatic lithologies. Textures and chemical compositions of PSGM and CGM often provide key information about the origin of NbTa mineralization. Therefore, we decided to carry out a detailed study of the relations between the PSGM and CGM and their post-magmatic transformations, and the Madeira peralkaline pluton (Brazil) is an ideal object for such a study. Textures of the PSGM and CGM were studied using BSE imaging and SEM mapping, and their chemical compositions were determined using 325 electron microprobe analyses. Pyrochlore from the Madeira granite can be chemically characterized as Na, Ca-poor, U- and Pb-dominant, and Sn- and Zn-enriched; REE are enriched only during alteration. Two stages of alteration are present: (i) introduction of Fe + Mn, with the majority of them consumed by columbitization; (ii) introduction of Si and Fe, and in lesser amounts also Pb and U: Si, Pb, and U incorporated into pyrochlore, iron forming Fe-oxide halos around pyrochlore. During both stages, F and Na decreased. In the case of a (nearly) complete pyrochlore columbitization, U and Th were exsolved to form inclusions of a thorite/coffinite-like phase. In contrast to altered pyrochlores from other localities, pyrochlore from Madeira shows a relatively high occupancy of the A-site. Although Madeira melt was Na-, F-rich, contemporaneous crystallization of cryolite consumed both elements and pyrochlore was, from the beginning, relatively Na-, F-poor.

Zircon is one of the most common accessory minerals in all types of granitoids. Due to its resistance to secondary processes, it preserves information about the composition of magma and conditions at the time of crystallization. Madeira albite granite, Brazil, offers optimum conditions for the study of chemistry and shape of zircon and the relation between the contents of particular trace elements in magma vs. in crystallizing zircon. Textural and chemical zircon data obtained using scanning electron microscopy (BSE) and cathodoluminescence (CL) imaging, automated mineralogy by TESCAN Integrated Mineral Analyzer (TIMA), and electron probe microanalyses (EPMA) enabled us to define four albite granite facies containing zircons of specific structures and chemistry. Zircon in the Madeira albite granite was formed during several, largely temporally and spatially independent episodes. During the crystallization of the common facies, occupying most of the intrusion volume, Zr/Hf value in zircon decreased from 40 to 20. This zircon, in some episodes, incorporated a higher amount of Th, which was later unmixed in the form of thorite inclusions. The pegmatoidal facies, representing crystallization of residual magma, contains zircon without thorite inclusions with a Zr/Hf value from 35 to 5. The Th/U and Y/Yb values during this evolution scattered but generally evolved to Th, Yb-enriched compositions (Th/U up to >10, Y/Yb down to 0.1). The Li-poor facies, located in the center of the stock near the cryolite deposit, contains zircon with comparatively high Zr/Hf = 45–70 and higher U and Y contents. Later, part of the common facies was hydrothermally altered to border facies, but zircon did not change noticeably during this process. The contents of minor elements in all zircon varieties are generally low (U + Th + Y + REE ˂ 0.05 apfu); Y and REE are incorporated exclusively in the xenotime component. Many crystals have low analytical totals, down to 95 wt%, and are enriched in Al, Fe, Mn, Ca, and F but this process does not influence the primary Zr/Hf, Th/U, and Y/Yb ratios. Zircons from other Madeira granite facies, including the neighboring Europa pluton, differ mainly in much higher Y/Yb values and in having (Y + REE) >> P, indicating a different than xenotime substitution mechanism. Zircon from the Madeira albite granite differs from zircons from many metaluminous rare-metal granites in low contents of minor elements and a common assemblage with thorite, instead of forming Zrn–Thr–Xnt solid solutions.

Zircon from four plutons of peralkaline granites and quartz-bearing syenites, differing in geotectonic positions, petrological and mineralogical compositions, and contents of volatile and trace elements, was studied using SEM, CL, and EPMA with the intention to define typical textural and chemical features of zircon from peralkaline rocks. In strongly peralkaline Na-pyroxene-bearing rocks represented by the Khan Bogd and Khalzan Buregte plutons (Mongolia), the primary zircon is scarce or missing. Most zircon grains are secondary, originating in hydrothermal stage from primary Zr silicates. They often form globular or radial aggregates. Chemical compositions of zircon in these rocks typically show high contents of Y, moderate contents of REE (thus high Y/Yb values) together with low contents of U and Th and low analytical totals. In mildly peralkaline mica-bearing rocks represented by Ivigtut stock (Groenland) and Madeira pluton (Brazil), the exclusive primary Zr mineral is zircon, mostly of orthomagmatic origin. Its analytical totals approach 100 wt%, enrichment in HREE, resulting in low Y/Yb values, is typical. Zircon populations from two types of peralkaline granitoids can be distinguished from each other and from zircon from S-type granites based on combination of the Zr/Hf, Y/Yb, and U/Th values, or on the Y-Hf-P ternary diagram.

Micas are the most common hosts of lithium in granitoid igneous rocks. Unfortunately, their Li contents cannot be determined by electron-probe microanalysis (EPMA) which is the most common method of mineral analysis. In an effort to avoid the use of other, technically more complex and expensive methods, several empirical schemes for the estimation of Li-contents from EPMA data have been developed. The methods proposed by Tischendorf (Mineralogical Magazine, 1997) have found the widest application. After 25 years of common usage, we have evaluated these methods by direct Li determination using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Approximately 3000 spot analyses of Li in micas from eight areas worldwide obtained by LA-ICP-MS were compared with the values yielded by the methods of Tischendorf. We conclude that none of the lithium estimation methods can compensate fully for a real local analysis by LA-ICP-MS or secondary-ion mass spectrometry (SIMS). Generally, SiO2-based estimation for trioctahedral micas provides a better match to the analysed values than F-based estimation for dioctahedral micas. The Rb-based estimation for dioctahedral micas does not provide acceptable results. The usage of averaged Si- and F-based estimations can be accepted in common petrological studies for a general characterisation of mica species. Large errors of individual spot estimations preclude their usage in detailed mineralogical studies.

Representative samples of high-Mg (picritic) rocks of Eocene to Oligocene age (38 to 21 Ma) from the České středohoří Mts. (CSM) in the Ohře/Eger Rift were studied and compared with Cenozoic high-Mg rocks from the Bohemian Massif. The picritic rocks of the CSM correspond to picrite, meimechite and basanite to tephrite. Individual petrographic types are characterised by the association of mafic minerals: magnesian olivine (Fo86–80) + clinopyroxene (aluminian diopside) ± amphibole (pargasite/kaersutite) ± dark mica (ferroan phlogopite). The contents of incompatible elements, such as Nb, Ta, U, Th, the LaN/YbN ratios, and the overall Sr–Nd–Pb isotope signatures of the high-Mg rocks partly overlap the basanites of the Ústí Formation, also showing a similar age (44–21 Ma). The Pb isotope signature for all recognised high-Mg rock types is compatible with a variable contribution from an inherited (Variscan) orogenic Pb component preserved in their lithospheric mantle source. Both the high-Mg volcanic rocks from the CSM and from other areas of the Bohemian Massif require the involvement of a heterogenous lithospheric source. Their parental melts were generated by variable degree of melting of an olivine-rich peridotitic mantle, containing clinopyroxene–amphibole (± phlogopite) vein assemblages with highly radiogenic Sr and Pb signatures.

A rare and unusual Ni-Sb-Ag-Au association of ullmannite, NiSbS, associated with allargentum, Ag6Sb, Au-rich silver, Au9 7Ag85 0Sb2 9, and Au-bearing dyscrasite was found in medieval mine dump material of the Oselské pásmo \"silver\" lode of the historic Kutná Hora Pb-Zn-Ag ore district. Ullmannite is the first and only Ni sulphide found in the base-metal paragenesis of otherwise exclusively Ag-(Cu)-(Pb)-Sb sulphosalts. No other nickel mineral is known from this base-metal ore district. The mineral was identified in two polished sections of one sample as anhedral grains up to 50 gm across enclosed in allargentum. The average chemical composition of ullmannite Ni 26.76-27.17, Sb 57.80-59.17, S 15.14-15.28 wt. % corresponds to the empirical formula Ni0 98Sb101As001S100 on the basis of Ni + Sb + S = 3 apfu, i.e. it is close to the ideal formula with only trace contents of As. Au-rich silver with 15.52-16.34 wt. % of gold was found in association with freibergite and pyrargyrite as anhedral inclusions up to c. 5 gm across. The chemical composition corresponds to Au9 7Ag85 0Sb2 9 on the basis of 100 apfu. One more gold-containing phase was determined: Au-bearing dyscrasite with ~0.7 wt. % of Au. The sample also produced an example ofAg-rich \"bonanza\" with stephanite, acanthite, pyrargyrite and miargyrite. The likely source of nickel and gold were the serpentinized ultrabasic bodies, cut by the \"silver\" lodes in the South of the ore district. The serpentinites contain 2000 ppm ofNi and low but stable contents ofAu. Penetration of hydrothermal fluids could have caused the mobilization of nickel and gold in serpentinites and in earlier ore mineralization (arsenopyrite). This process resulted in the breakdown of earlier silver minerals while allargentum, dyscrasite and stephanite crystallized. The discovery of Ni-Sb-Ag-Au association in Kutná Hora ore district sheds new light on the elemental variability of this hydrothermal vein-type deposit of Variscan age.

Core samples recovered from exploration boreholes and granite/greisen outcrops at the Panasqueira world-class tungsten deposit in central Portugal were subjected to chemical analyses and petrographic studies. We present a geochemical dataset and the trace element compositions of quartz and micas from a large part of the unexposed Panasqueira granitic pluton. Our data suggest that the hidden granite body is more complicated than previously believed. It consists of a flat cupola of porphyritic granite with only traces of mineralization at Rio and a steep stock of greisenized leucogranite surrounded by a swarm of flat quartz–muscovite veins rich in wolframite between Barroca Grande and Panasqueira. The contents of W (Sn, Nb, Ta) in muscovite markedly drop at a transition from the unmineralized greisen body to quartz veins. The W deposit was formed in three principal stages: (1) intrusion of porphyritic two-mica granite accompanied with local near-contact greisenization and uncommon quartz–wolframite veinlets; (2) intrusion of a more strongly fractionated leucogranite and formation of the cupola and apophyses; (3) circulation of hydrothermal fluids from deeper parts of the granite body into the cupola, greisenization, hydraulic fracturing and opening of flat structures in and outside the cupola and formation of ore veins.

Micas are the most common hosts of lithium in granitoid igneous rocks. Unfortunately, their Li contents cannot be determined by electron-probe microanalysis (EPMA) which is the most common method of mineral analysis. In an effort to avoid the use of other, technically more complex and expensive methods, several empirical schemes for the estimation of Li-contents from EPMA data have been developed. The methods proposed by Tischendorf ( Mineralogical Magazine , 1997) have found the widest application. After 25 years of common usage, we have evaluated these methods by direct Li determination using laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS). Approximately 3000 spot analyses of Li in micas from eight areas worldwide obtained by LA–ICP–MS were compared with the values yielded by the methods of Tischendorf. We conclude that none of the lithium estimation methods can compensate fully for a real local analysis by LA–ICP–MS or secondary-ion mass spectrometry (SIMS). Generally, SiO 2 -based estimation for trioctahedral micas provides a better match to the analysed values than F-based estimation for dioctahedral micas. The Rb-based estimation for dioctahedral micas does not provide acceptable results. The usage of averaged Si- and F-based estimations can be accepted in common petrological studies for a general characterisation of mica species. Large errors of individual spot estimations preclude their usage in detailed mineralogical studies.