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Tungsten-tin-(rare-metal) deposits are most commonly granite-related and an important source of critical metals. This study describes the fluid evolution in the Tiantangshan Rb-Sn-W deposit, Nanling Range, China, and discusses the implications for mineralizing processes. Mineralization at Tiantangshan is spatially zoned. The greisen roof hosts wolframite-cassiterite quartz veins. The surrounding volcanic rocks host biotite quartz veins (Rb mineralization) crosscut by cassiterite quartz veins and sphalerite-galena quartz veins. The earliest intermediate-density fluids are responsible for the early W-(Sn)-Rb mineralization and evolve towards decreasing homogenization temperature (Th) and ratios of W, Sn, Rb, Cs, Fe, and Mn to Na + K as the fluid migrated from the greisen to the volcanic rocks hosted veins (Th: 420 to 350 °C; salinity: 13 to 4 wt% NaCleq). The spatial distribution of mineralization and fluid paragenesis indicates that precipitation of wolframite, early cassiterite, and Rb-rich biotite was associated with a pH increase during fluid-rock interaction. Late cassiterite and intergrown quartz precipitated from a degassing fluid with lower Th (mainly 360 to 340 °C) and salinity (10 to 2 wt% NaCleq) and with distinctly lower Sn concentrations. Late cassiterite precipitation is therefore likely related with depressurization by brittle failure of the rock leading to simultaneous boiling and meteoric water input. Late Pb–Zn mineralization precipitated from low Th (< 320 °C) and salinity (0 to 2 wt% NaCleq) fluids through extensive mixing with meteoric water. The tempo-spatial development of Rb-Sn-W-Pb–Zn mineralization at Tiantangshan was controlled by a mixing fluid regime, where input of meteoric water gradually increased with time. [ABSTRACT FROM AUTHOR]

Five generations of fluorapatite in mineralized skarn and host rocks from the Mactung W (Cu-Au) deposit, Northwest Territories, Canada, are identified based on petrographic, compositional and geochronological (U–Pb) data. These data, coupled with new (in this study) and previously published data on apatite from the nearby Cantung deposit, provide constraints on the timing of skarn mineralization, as well as metal and fluid sources of the Canadian Tungsten Belt. Type-i apatite of the Mactung deposit formed from ~ 106 ± 4 to 103 ± 2 Ma through recrystallization of sedimentary apatite (type-o apatite) during regional metamorphism, pre-skarnification. Type-i apatite is W-rich (up to 47.6 ppm) and occurs with coeval scheelite and titanite, indicating a potential sedimentary source, perhaps from detrital rutile, for W. Apatite crystals in prograde (type-ii) and retrograde (type-iii and type-iv) skarns yield ages from ~ 96 ± 1 to 92 ± 1 Ma, overlapping with Mactung biotite-granite plutons and late-stage felsic dykes and confirming skarn formation during emplacement of the granites over a period of ~ 5 million years. Type-ii apatite contains high rare earth element that increases with increasingly negative Eu anomalies, suggesting prograde fluids were sourced from a felsic melt undergoing fractional crystallization. Retrograde apatite exhibits weak lanthanide tetrad effects with superchondritic Y/Ho ratios (> 38), suggesting retrograde fluids exsolved from a highly evolved magmatic source. Apatite crystals from the Cantung skarn deposit are compositionally and paragenetically similar to those from the Mactung apatite and yield ages similar to the Cantung biotite-monzogranite plutons and late-stage felsic dykes. We conclude prograde fluids were derived from biotite-granites, whereas retrograde fluids exsolved from evolved melts recorded by later felsic dykes. [ABSTRACT FROM AUTHOR]

Magmatic-hydrothermal systems, especially those causing the formation of tungsten deposits, may be enriched in boron, as is suggested by the presence of hydrothermal tourmaline. This study examines the boron and metal (including tungsten) concentrations of quartz-hosted fluid inclusions in the Lened W-(Be) deposit of the Canadian Cordillera and resolves (i) the analytical challenges involved during fluid salinity calculations of B-rich fluids and (ii) the relationship between fluid chemical composition and ore-forming processes involved at Lened. The aqueous fluid inclusions from this study have high CO2 and boron contents, indicated by the presence of a carbonic phase and sassolite crystals (H3BO3) in fluid inclusions. The boron content of the aqueous liquid phase (0.5 wt. %) was determined using microthermometric and Raman spectroscopic analyses. Boron was judged the most appropriate internal standard for quantifying the LA-ICP-MS data from these inclusions after calculation of salinity in the H2O-NaCl-H3BO3 system (3.5 to 5 wt. % NaCleq). Trace element data of the fluids show relatively high concentrations of Li (40 to 474 ppm), Al (56 to 1003 ppm), As (36 to 490 ppm) and Cs (68 to 296 ppm); and lower concentrations of Rb (3.6 to 77 ppm), Sr (0.4 to 23 ppm), Sb (1 to 32 ppm), Ba (0.6 to 163 ppm), Mg (6.9 to 7.6 ppm) and other metals, such as Be (2.4 to 10.2 ppm), W (2.4 to 27 ppm) and Cu (5.1 to 73 ppm). The high Cs and Li concentrations suggest a magmatic origin of the metals, while the moderate concentrations in Sr and Ba are indicative of fluid–rock interaction with the surrounding limestone. The presence of sassolite suggests that these fluids were highly acidic. The neutralization of this fluid through interaction with the surrounding limestone is the most probable trigger for scheelite precipitation. The presence of such high boron content in the magmatic fluid at Lened indicates the potential role in the enrichment of the source melt before fluid exsolution. [ABSTRACT FROM AUTHOR]

White mica and tourmaline are the dominant hydrothermal alteration minerals at the world-class Panasqueira W–Sn–Cu deposit in Portugal. Thus, understanding the controls on their chemical composition helps to constrain ore formation processes at this deposit and determine their usefulness as pathfinder minerals for mineralization in general. We combine whole-rock geochemistry of altered and unaltered metasedimentary host rocks with in situ LA-ICP-MS measurements of tourmaline and white mica from the alteration halo. Principal component analysis (PCA) is used to better identify geochemical patterns and trends of hydrothermal alteration in the datasets. The hydrothermally altered metasediments are enriched in As, Sn, Cs, Li, W, F, Cu, Rb, Zn, Tl, and Pb relative to unaltered samples. In situ mineral analyses show that most of these elements preferentially partition into white mica over tourmaline (Li, Rb, Cs, Tl, W, and Sn), whereas Zn is enriched in tourmaline. White mica has distinct compositions in different settings within the deposit (greisen, vein selvages, wall rock alteration zone, late fault zone), indicating a compositional evolution with time. In contrast, tourmaline from different settings overlaps in composition, which is ascribed to a stronger dependence on host rock composition and also to the effects of chemical zoning and microinclusions affecting the LA-ICP-MS analyses. Hence, in this deposit, white mica is the better recorder of the fluid composition. The calculated trace-element contents of the Panasqueira mineralizing fluid based on the mica data and estimates of mica-fluid partition coefficients are in good agreement with previous fluid-inclusion analyses. A compilation of mica and tourmaline trace-element compositions from Panasqueira and other W–Sn deposits shows that white mica has good potential as a pathfinder mineral, with characteristically high Li, Cs, Rb, Sn, and W contents. The trace-element contents of hydrothermal tourmaline are more variable. Nevertheless, the compiled data suggest that high Sn and Li contents are distinctive for tourmaline from W–Sn deposits. [ABSTRACT FROM AUTHOR]

The Roc Blanc Pb-Zn-Ag ± Au vein system in the Variscan Central Jebilet massif, Morocco, is confined within the contact metamorphic aureole of S- and I-type calc-alkaline granitic stocks (327 ± 4 to 295 ± 15 Ma) along the Marrakech Shear Zone. Host rocks consist of a succession of greenschist- to amphibolite-facies metasedimentary and metavolcaniclastic rocks of Carboniferous age. The ore mineralogy is predominantly base metal and Ag-bearing sulfides and sulfosalts, intergrown with quartz and carbonates. Late-stage gold mineralization is commonly present as electrum in intimate association with all major generations of sulfide and sulfosalt minerals. Ore-related hydrothermal alteration includes silicification, sericitization, chloritization, and carbonatization. Chlorite and arsenopyrite geothermometry suggest mean temperatures of 364 and 350 °C; respectively. Calculated δ18Ofluid values of 15 to 18‰ are consistent with metamorphic fluid sources, by which the mineralizing fluids were produced during the emplacement of granitic intrusions and subsequent devolatilization of graphitic black shale and interlayered carbonate beds. Lead and strontium isotope data constrain the source of the ore-forming components (i.e., metals and sulfur) to the enclosing host rocks. A decrease in temperature during fluid ascent and subsequent alteration-associated fluid-rock interaction resulted in the deposition of the Pb-Zn-Ag ± Au mineralization in a post-collisional extensional setting. [ABSTRACT FROM AUTHOR]

Veins and pervasive wall-rock alteration composed of coarse muscovite±quartz±pyrite are documented for the first time in a porphyritic granite at Luhr Hill in the Yerington District, Nevada. Coarse muscovite at Luhr Hill occurs at paleodepths of ~6-7 km in the roots of a porphyry copper system and crops out on the scale of tens to hundreds of meters, surrounded by rock that is unaltered or variably altered to sodic-calcic assemblages. Coarse muscovite veins exhibit a consistent orientation, subvertical and N-S striking, which structurally restores to subhorizontal at the time of formation. Along strike, coarse muscovite veins swell from distal, millimeter-thick muscovite-only veinlets to proximal, centimeter-thick quartz-sulfide-bearing muscovite veins. Crosscutting relationships between coarse muscovite veins, pegmatite dikes, and sodic-calcic veins indicate that muscovite veins are late-stage magmatic-hydrothermal features predating final solidification of the Luhr Hill porphyritic granite. Fluid inclusions in the muscovite-quartz veins are high-density aqueous inclusions of ~3-9 wt% NaCl eq. and <1 mol% CO that homogenize between ~150 and 200 °C, similar to fluid inclusions from greisen veins in Sn-W-Mo vein systems. Our results indicate that muscovite-forming fluids at Luhr Hill were mildly acidic, of low to moderate salinity and sulfur content and low CO content, and that muscovite in deep veins and alteration differs in texture, composition, and process of formation from sericite at shallower levels of the hydrothermal system. Although the definition of greisen is controversial, we suggest that coarse muscovite alteration is more similar to alteration in greisen-type Sn-W-Mo districts worldwide than to sericitic alteration at higher levels of porphyry copper systems. The fluids that form coarse muscovite veins and alteration in the roots of porphyry copper systems are distinct from fluids that formed copper ore or widespread, shallower, acidic alteration. We propose that this style of veins and alteration at Luhr Hill represents degassing of moderate volumes of overpressured hydrothermal fluid during late crystallization of deep levels of the Yerington batholith. [ABSTRACT FROM AUTHOR]

More than 50 % of the world's total reserves of tungsten are in China and most tungsten deposits are located in the Nanling range in southeast China. This study explores the potential genetic relationship between tungsten-tin (W-Sn) mineralization and shallower Ag-Pb-Zn deposits in the Nanling range based on data from the Wutong deposit, Guangxi Province. The lead, oxygen, carbon, sulfur, and strontium isotopic compositions of minerals at Wutong indicate that a single crustal-derived fluid was responsible for mineralization. Wutong likely formed at relatively low temperatures (∼200-300 °C) and low pressures, as indicated by the similarity between homogenization temperatures of fluid inclusions and those estimated from S isotopic compositions of minerals. The hübnerite age (92.3-104.4 Ma) indicates that the Wutong mineralization is likely related to nearby Late Yanshanian (Cretaceous) S-type granites derived from Proterozoic crust. This mineralization event coincides with the last W-Sn mineralization event and the Cretaceous peak of mineralization in the Nanling range. [ABSTRACT FROM AUTHOR]

- Miller Range (MIL) 03346 is the most oxidized and least equilibrated nakhlite known and displays the highest amount of intercumulus phase. The discovery of three new nakhlites, MIL 090030, MIL 090032, and MIL 090136, in the Miller Range, Antarctica, geographically close to the location of MIL 03346, suggests that they may come from the same parent meteorite. In this study, we investigate the mineralogy and texture of cumulus and intercumulus phases, in situ major and trace element compositions for the cumulus phases, as well as pyroxene crystal size distribution patterns and spatial distribution patterns of MIL 090030, 090032, and 090136. Using these combined results, we conclude that the three nakhlites studied here are paired with MIL 03346. However, modal mineral abundances of MIL 090030, 090032, 090136, and 03346 exhibit variations indicating that a single sample of a Miller Range nakhlite is not modally representative of the parent meteorite and that analyses of multiple samples for a single nakhlite may be necessary to obtain representative modal data for placement in the cumulate pile. Our calculated parental melt composition based on all the paired samples confirms a previous study suggesting that the nakhlite parent melt crystallized as a closed system. [ABSTRACT FROM AUTHOR]