Incipient Wolframite Deposition at Panasqueira (Portugal): W-Rich Rutile and Tourmaline Compositions as Proxies for the Early Fluid Composition

Abstract

The main event responsible for the deposition of tungsten at Panasqueira was closely associated with strong tourmalinization of the wall rocks. Tourmaline is coeval with a W-rich rutile (up to 8–10 wt % W), and both minerals record an early introduction of W in the system, just before the main W deposition. Uranium-Pb dating of the rutile by LA-ICP-MS yielded an age of 305.2 ± 5.7 Ma, which is 6 to 10 m.y. older than the K-Ar age of 296.3 ± 1.2 Ma obtained on muscovite, which was therefore not coeval with wolframite. Major and trace element concentration variations in tourmaline record fluid mixing between two end members, both considered to be of metamorphic derivation on the basis of rare earth element profiles. We report evidence for a fluid rich in Co, Cu, Pb, Sc, Sr, V, Cr, Nb, Ta, and Sn interpreted to be of local origin—e.g., well equilibrated with the host formations—and a fluid rich in Li, F, Fe, Mn, and W inferred to be of deep origin and related to biotite dehydration. The second fluid carried the metals (in particular Fe and Mn) that were necessary for wolframite deposition and that were not necessarily inherited from the wall rocks through fluid-rock interaction. Micrometer-scale variations in tourmaline and rutile crystal chemistry are indicative of pulsatory fluid input during tourmalinization.

Multistage development of a hydrothermal W deposit during the Variscan late-orogenic evolution: the Puy-les-Vignes breccia pipe (Massif Central, France)

“…Tungsten could be released either by magmatic fluids due to elevated fluid-melt-crystal partitioning coefficients (Hulsbosch et al, 2016;Schmidt et al, 2020) or by metamorphic fluids during high-temperature interactions with two-mica leucogranite (Vallance et al, 2001;El Korh et al, 2020;Carocci et al, 2020). The importance of fluid-rock interactions is also supported by the chemical and boron isotope compositions of tourmaline that are compatible with both a magmatic and a metamorphic fluid source (Harlaux et al, 2019) as well as by the Fe-dominated composition of wolframite (Michaud and Pichavant, 2019).…”

“…Thus, the PAU micaschists underlying the LGU gneisses may represent a distal source of metamorphic fluids produced by the HT-LP metamorphism during the late Carboniferous (320-315 Ma). Deep metamorphic fluids could be gathered into a collection zone, then focused and channelized in a mid-crustal fault zone, ascending at high rates up to a dispersion region in cooler rocks (Thompson and Connolly, 1992;Connolly, 1997;Carocci et al, 2020). The half-width of both collection and dispersion zones is typically in the 3-5 km range, and the height of the system is on the order of 10 to 15 km.…”

Rutile and Chlorite Geochemistry Constraints on the Formation of the Tuwu Porphyry Cu Deposit, Eastern Tianshan and Its Exploration Significance

“…The compiled porphyry deposits include Duobuza Cu [12], Duolong Cu [93], Zhunuo Cu-Mo [20], Dasuji Mo [94], and Northparkes Cu-Au [11]. The hydrothermal W deposit includes the Panasqueira deposit in Portugal [17]. The Au deposits include the Zhesang Carlin-type Au [6], the orogenic Au deposit in Precambrian terranes [7], and the Wulong lode Au [68].…”

“…In addition, the Zr content in the rutile lattice can be used as a geothermometer [14,15], and rutile with sufficient uranium can be used for U-Pb isotope determination [3]. To date, rutile geochemistry has been determined and applied to magmatic and metamorphic-related diagenetic systems [2,4,[16][17][18], but rarely to porphyry Cu systems [8,11,19,20].…”

Fluid Processes of Wolframite-Quartz Vein Systems: Progresses and Challenges

“…Wolframite-quartz vein-type tungsten deposits, generally related to granitic intrusions, are the source of much of the tungsten used by humans [1][2][3][4][5][6][7][8]. Mineralization of these deposits generally consists of wolframite (dominantly FeWO 4 or MnWO 4 ) in subhorizontal centimeter-to meter-scale quartz veins with lateral extents of hundreds of meters.…”