Elucidation of time-space relationships between a given wolframite deposit and the associated granites, the nature of the latter, and their alterations, is a prerequisite to establishing a genetic model. In the case of the world-class Panasqueira deposit, the problem is complicated because the associated granites are concealed and until now poorly known. The study of samples from a recent drill hole and a new gallery allowed a new approach of the Panasqueira granite system. Detailed petrographic, mineralogical, and geochemical studies were conducted, involving bulk major and trace analyses, BSE and CL imaging, EPMA, and SEM-EDS analyses of minerals. The apical part of the Pansqueira pluton consisted of a layered sequence of separate granite pulses, strongly affected by polyphase alteration. The use of pertinent geochemical diagrams (major and trace elements) facilitated the discrimination of magmatic and alteration trends. The studied samples were representative of a magmatic suite of the high-phosphorus peraluminous rare-metal granite type. The less fractionated members were porphyritic protolithionite granites (G1), the more evolved member was an albite-Li-muscovite rare metal granite (G4). Granites showed three types of alteration processes. Early muscovitisation (Ms0) affected the protolithionite in G1. Intense silicification affected the upper G4 cupola. Late muscovitisation (Fe–Li–Ms1) was pervasive in all facies, more intense in the G4 cupola, where quartz replacement yielded quartz-muscovite (pseudo-greisen) and muscovite only (episyenite) rocks. These alterations were prone to yield rare metals to the coeval quartz-wolframite veins.

Palaeoproterozoic (ca. 1.8 Ga) mafic and ultramafic dykes are widely distributed within the whole Sarmatian segment of the East-European craton. This paper focuses on new geochronological, geochemical and isotope data obtained for mafic and ultramafic dykes of the Ingul terrain. Geochronological data available for these dykes indicate ages around 1800 Ma. We provide a new U–Pb zircon age of 1810 ± 15 Ma obtained for a dolerite dyke in the Kirovograd area. Geochemical and petrographical data allow identification of three groups of dykes: (1) kimberlites, (2) high-Mg# subalkaline rocks (picrite, camptonite, subalkaline dolerite etc.) and (3) tholeiite dolerite. Rocks of these groups were probably derived from different sources. εNd₁₈₀₀ values of studied rocks vary from 0.7 to 2.8. The highest values were obtained for mantle xenoliths and their kimberlite host (εNd₁₈₀₀ = 2.5–2.8). Rb–Sr data yield a regression age of 1729 ± 20 Ma with an initial ⁸⁷Sr/⁸⁶Sr = 0.70366 ± 41 (MSWD = 10.8). The whole-rock lead isotope data scatter, but data for sub-groups of samples can tentatively be fitted to parallel 1.8 Ga isochrons. The geochemical data indicate rocks to have formed by partial melting and the degree of melting is thought to be a function of formation depth, the latter ranging from sub-lithospheric to lower-crustal levels; we assume that melting was caused by a mantle plume. Dyking in the Ingul terrain was closely associated in time and space with metasomatic albitites that host numerous economic U deposits.

Spectacular alteration of monazite by diagenetic/hydrothermal brines is well documented in some Proterozoic sedimentary basins in close relationship with high-grade uranium (U) deposits. Hence, monazite has been proposed as a viable source for some U deposits. However, monazite alteration remains enigmatic with regard to its high stability in relatively low temperature hydrothermal conditions. Here, the results of batch experiments in which 10 mg of natural monazite grains were reacted with 15 mL of Na-Ca-Cl (6 molal Cl) solutions as well as in pure water at 150 ºC and saturated vapor pressure (psat) for one and six months are reported. The influence of pH (pH = 1, 3, 7) and relative molar proportions of Na and Ca (Na/(Na + Ca) = 0, 0.5, 1), were tested. Discrete alteration features (etch pits and roughened surfaces) appear in a minority of the one month experiments and are more developed in the six months experiments, especially at pH = 1 and 3. Although spectacular alteration of monazite, as seen around U deposits, could not be reproduced here, this study shows that monazite is unstable in the presence of fluids analogous to acidic deep basinal brines.

The Longshoushan Metallogenic Belt (northwestern China) is known for its word-class Jinchuan Ni-Cu sulfide (Pt) deposit and is also an important uranium metallogenic belt. The Jiling uranium deposit in this belt is a typical Na-metasomatic uranium deposit, which rarely occurs in China. Mineralization in the Jiling uranium deposit is hosted in granitoids that have suffered a Na-metasomatic alteration. There are three kinds of uranium minerals, including uraninite, pitchblende, and coffinite in the Jiling uranium deposit. Pitchblende is the predominant uranium mineral. Integrating the mineralogy and geochemistry of uranium minerals, and in situ electron microprobe analyzer (EMPA) U-Th-Pb chemical dating, we aimed to unravel the age and nature of the mineralization, to decipher the characteristics of the hydrothermal alteration and the U mineralization process. Based on the microtextural features and compositional variations, primary uraninite was altered to uraninite A and B, and fresh pitchblende was altered to pitchblende A and B. The best-preserved uraninite crystals displayed a euhedral-shape with high Pb and low SiO₂, CaO, FeO, and Al₂O₃ contents, and was interpreted as primary uraninite. The EMPA U-Th-Pb chemical ages revealed that uraninite may have formed at 435.9 ± 3.3 Ma. High ThO₂ + ΣREE₂O₃ + Y₂O₃ contents illustrated that the best preserved uraninite crystallized at a high temperature. Altered pitchblende A showed a relatively brighter gray color in backscattered electron (BSE) images and with a lower SiO₂ content than B. Three analysis spots of the fresh pitchblende showed low contents of ΣSiO₂ + CaO, indicating no obvious alteration. EMPA U-Th-Pb chemical dating gave a mean chemical age of 361 Ma. The low Th + ΣREE₂O₃ contents indicated that this pitchblende formed at a relatively low temperature. According to the different characteristics of occurrence and chemical composition, the coffinite in the Jiling uranium deposit can be divided into coffinite A and B, respectively. The compositional variation of the fresh and altered uraninite and pitchblende indicated that both uraninite and pitchblende underwent at least two discrete hydrothermal fluid alterations. The U mineralization was divided into two stages; uraninite was formed at a high temperature and possibly from a magmatic-hydrothermal fluid during ore stage I. Then, pitchblende was formed at a low temperature, during ore stage II. According to the petrographic observations and their chemical compositions, coffinite A and B resulted from the alterations of uraninite and pitchblende, respectively.