Metallogenic characteristics and genesis of granite type uranium ore bodies in South China

South China is the key producing area of granite-type uranium deposits in China. After decades of exploration, many important progress has been made in the study of metallogenic regularity of granite type uranium deposits in this area. On the basis of previous studies, this paper attempts to sort out the geological conditions and characteristics of diagenesis and mineralization of granite type uranium deposits in South China, and discuss their metallogenic models, so as to better summarize the metallogenic regularity and serve the prospecting and prediction.

Tourmaline as a Recorder of Ore-Forming Processes in the Xuebaoding W-Sn-Be Deposit, Sichuan Province, China: Evidence from the Chemical Composition of Tourmaline

The Xuebaoding W-Sn-Be deposit located in the Songpan-Ganze Orogenic Belt (Sichuan Province, China) is a hydrothermal deposit with less developed pegmatite stage. The deposit is famous for the coarse-grained crystals of beryl, scheelite, cassiterite, apatite, fluorite, muscovite, and others. The orebody is spatially associated with the Pankou and Pukouling granites hosted in Triassic marbles and schists. The highly fractionated granites are peraluminous, Li-Rb-Cs-rich, and related to W-Sn-Be mineralization. The mineralization can chiefly be classified based on the wallrock and mineral assemblages as muscovite and beryl in granite (Zone I), then beryl, cassiterite and muscovite at the transition from granite to triassic strata (Zone II), and the main mineralized veins composed of an assemblage of beryl, cassiterite, scheelite, fluorite, and apatite hosted in metasedimentary rock units of marble and schist (Zone III). Due to the stability of tourmaline over a wide range of temperature and pressure conditions, its compositional variability can reflect the evolution of the ore-forming fluids. Tourmaline is an important gangue mineral in the Xuebaoding deposit and occurs in the late-magmatic to early-hydrothermal stage, and can thus be used as a proxy for the fluid evolution. Three types of tourmalines can be distinguished: tourmaline disseminations within the granite (type I), tourmaline clusters at the margin of the granite (type II), and tourmalines occurring in the mineralized veins (type III). Based on their chemical composition, both type I and II tourmalines belong to the alkali group and to the dravite-schorl solid solution. Type III tourmaline which is higher in X-site vacancy corresponds to foitite and schorl. It is proposed that the weakly zoned type I tourmalines result from an immiscible boron-rich aqueous fluid in the latest stage of granite crystallization, that the type II tourmalines showing skeletal texture directly formed from the undercooled melts, and that type III tourmalines occurring in the mineralized veins formed directly from the magmatic hydrothermal fluids. Both type I and type II tourmalines show similar compositional variations reflecting the highly fractionated Pankou and Pukouling granites. The higher Ca, Mg, and Fe contents of type III tourmaline are buffered by the composition of the metasedimentary host rocks. The decreasing Na content (<0.8 atoms per formula unit (apfu)) and increasing Fe3+/Fe2+ ratios of all tourmaline samples suggest that they precipitated from oxidized, low-salinity fluids. The decreasing trend of Al content from type I (5.60–6.36 apfu) and type II (6.01–6.43 apfu) to type III (5.58–5.87 apfu) tourmalines, and associated decrease in Na, may be caused by the crystallization of albite and muscovite. The combined petrographic, mineralogical, and chemical characteristics of the three types of tourmalines thus reflect the late-magmatic to early-hydrothermal evolution of the ore-forming fluids, and could be used as a geochemical fingerprint for prospecting W-Sn-Be mineralization in the Xuebaoding district.

Two genetic types of pseudotachylytes

The study of two varieties of pseudotachylytes (PST) in granitoids of the Riphean complex on the Barents Sea coast of the Kola Peninsula (Rybachii and Srednii peninsulas) and in metapsammite of the Paleoproterozoic complex in the Northern Ladoga region by a few independent analytical methods has made it possible to establish that they belong to different genetic forms, such as mechanically crushed rocks and melting products, respectively. As for the melting differences, we have given a detailed description of the mineral and material transformations of the original rock into the PST glass matrix and obtained evidence for the initial melting out of the micaceous eutectics with its subsequent shift to the granite type. The conclusion has been made on the most likely formation of molten PST due to frictional rock melting under rapid rise of its blocks from a depth of 12–15 km to the crustal surface (less than 3 km) along the faults of presumably seismogenic nature. It is suggested that crushing and frictional melting can be complementary, rather than mutually exclusive processes, and the formation of molten PST is commonly preceded by the mechanical rock crushing stage.

Comparison of different approaches for bioleaching of a granite-type uranium ore

Uranium bioleaching has been rapidly developed in China during recent years. However, some problems during bioleaching, such as low uranium leaching efficiency for rocks lacking pyrite, remain to be solved. A granite type uranium deposit from southern China was selected for the study of U bioleaching with addition of pyrite. Experiments using four approaches, including (i) pyrite ores mixing with culture, (ii) pyrite tiled on the surface of ores with culture, (iii) no pyrite ores with culture, and (iv) pyrite ores without culture were examined in this study. Results showed that bacteria can improve U leaching efficiency, particularly by adding pyrite into ore. Approach (i) pyrite ores mixing with culture had the highest U concentration and the highest recovery rate of the four approaches. No significant difference was observed between approaches (ii) pyrite tiled on the surface of ores with culture and (iii) no pyrite ores with culture.

Taxonomic and conservation status of Dockrillia striolata (Rchb.f.) Rauschert (Orchidaceae) in Tasmania'

Dockrillia striolata (Rchb.f.) Rauschert, known as the yellow rock-orchid, occurs in New South Wales, Victoria and along the east coast of Tasmania. Within Tasmania, populations occur on the islands of the Furneaux Group and on mainland Tasmania (Kelvedon Hills south of Swansea through to wukalina/Mount William in the northeast). The taxonomy of the species is revised, with subsp. chrysantha no longer recognised as distinct based on a morphological examination of flower size and other characters. The species is restricted to Devonian granite-type rocks and Jurassic dolerite, usually in near-coastal areas and in various vegetation types. A review of the conservation status indicates that the species does not qualify as threatened under the Tasmanian Threatened Species Protection Act 1995, with it being well reserved throughout its range, an extent of occurrence of ca. 7500 km2, represented by at least 30 well-defined subpopulations, no apparent historical or contemporary declines in any population parameters, nor any identifiable risks.

Source areas of the Grybów sub-basin: micropaleontological, mineralogical and geochemical provenance analysis (Outer Western Carpathians, Poland)

The Grybów Unit occurring in the Ropa tectonic window was the subject of micropaleontological and geochemical investigation. Studies, based on calcareous nannofossils, proved that the level of reworked microfossil is not higher than 22 % and it varies between two sections. Quantitative analyses of the reworked assemblages confirmed the domination of Cretaceous and Middle Eocene species. The Sub-Grybów Beds, Grybów Marl Formation and Krosno Beds were assigned to the Late Oligocene and represent the terminal flysch facies. Detrital material accumulated in the Oligocene sediments originated from the Marmarosh Massif, which is the eastern prolongation of the Fore-Magura Ridge. The microscopically obtained petrological features agree with the chemical composition of the samples. Mica flakes, rounded grains of glauconite, heavy mineral assemblage, including abraded grains of zircon, rutile and tourmaline as well as charred pieces of plant tissues are reworked components. Enrichment in zircon and rutile is confirmed geochemically by positive correlation between Zr and SiO2. Zr addition is illustrated on 10×Al2O3–Zr–200×TiO2 and Zr/Sc vs. Th/Sc diagrams. Interpretation of the A–CN–K diagram and variety of CIA and CPA values indicate that the source rocks were intensely weathered granite-type rocks.