Metallogenesis at the Carris W–Mo–Sn deposit (Gerês, Portugal): Constraints from fluid inclusions, mineral geochemistry, Re–Os and He–Ar isotopes

Abstract

The Carris orebody consists of two partially exploited W-Mo-Sn quartz veins formed during successive shear stages and multipulse fluid fillings. They cut the Variscan post-D3 Gerês Itype granite. The most important ore minerals are wolframite, scheelite, molybdenite and cassiterite. There are two generations of wolframite. The earlier generation of wolframite is rare and has the highest WO 4 Mn content (91 mol%) and the most common wolframite contains 26-57 mol% WO 4 Mn. Re-Os dating of molybdenite from the ore quartz veins and surrounding granite yield ages of 279 ±1.2 Ma and 280.3±1.2 Ma, respectively which are in very good agreement with the previous ID-TIMS U-Pb zircon age for the Carris granite (280±5 Ma). The fluid inclusion studies on quartz intergrown with wolframite and scheelite, beryl and fluorite reveal that two distinct fluid types were involved in the genesis of this deposit. The first was a low to medium salinity aqueous carbonic fluid (CO 2 between 4-14 mol%) with less than 1.95 mol% N 2 , which was only found in quartz associated with wolframite. The other was a low salinity aqueous fluid found in all the four minerals. The homogenization temperatures indicate minimum entrapment temperatures of 226-310ºC (average 280ºC) for the H 2 O-CO 2 -N 2 -NaCl fluid and averages temperatures of 266ºC for scheelite and 242ºC, 190ºC and 160ºC for the last generations of beryl, fluorite and quartz, respectively. It was estimated that wolframite was deposited ~7 km depth, assuming a lithostatic pressure, probably due to strong pressure fluctuation caused by seismic events triggered by brittle tectonics during the exhumation event. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTPrecipitation of scheelite and sulphides took place later, at the same depth, but under an hydrostatic or suprahydrostatic pressure regime, and probably caused by mixing between the magmatic-hydrothermal fluid and meteoric waters that deeply penetrated the basement during post-Variscan decompression.

Contrasting fluid behavior during two styles of greisen alteration leading to distinct wolframite mineralizations: The Echassières district (Massif Central, France)

“…Several studies, particularly in recent years, suggest that FI in gangue minerals may not provide the same data as those investigated in Sn-W ore minerals, particularly for quartz which shows systematically lower FI T h (e.g., Campbell and Panter 1990;Moura et al, 2014;Ni et al, 2015a;Legros et al, 2019). Nevertheless, in most of these studies, petrographic textures clearly show that the gangue minerals postdate the ore.…”

Geochronology and Genesis of the Xitian W-Sn Polymetallic Deposit in Eastern Hunan Province, South China: Evidence from Zircon U-Pb and Muscovite Ar-Ar Dating, Petrochemistry, and Wolframite Sr-Nd-Pb Isotopes

“…Deng et al [43] obtained a molybdenite Re-Os age of 225.5 ± 3. 6 Ma from altered granites in the Indosinian granitic batholith, indicating a possibility for the Indosinian mineralization event in the Xitian ore field; however, this age may not represent the age of the large-scale skarn-type W-Sn mineralization in the Xitian ore field. It was proposed that the skarn occurred in the contact zone between the Yanshanian granites and the Devonian dolomitic limestone [19].…”

“…Accompanied by the greater demand for W-Sn, the study and exploitation of W-Sn deposits have long been a hot topic [1][2][3][4][5][6][7][8][9][10][11][12][13]. China holds the largest resources of W and Sn in terms of production and reserves, and their reserves have accounted for ca.…”

Late-Variscan multistage hydrothermal processes unveiled by chemical ages coupled with compositiona.

“…In Cornwall, high-temperature Sn-W mineralization related to granite yields ages of 293.3±1.2Ma, whereas hydrothermal mineralization is younger (Late Jurassic/Early Cretaceous; Chen et al, 1996). In the Iberian Massif, W-Mo-Sn quartz veins of the Carris deposit, north Portugal, yield a Re-Os molybdenite age of 279.4±1.2Ma, indicating that circulation of mineralizing fluids took place up to 1-4Ma after the emplacement of the Carris granite (Moura et al, 2014). Thus, although late-Variscan mineralization in part is related to intrusions, in part to hydrothermal veins, it is controlled by the same extensional processes that acted on the large scale.…”