An Integrated Fluid Mineral Stable-Isotope Study of the Granite-Hosted Mineral Deposits of the New Ross Area, South Mountain Batholith, Nova Scotia, Canada: Evidence for Multiple Reservoirs

Abstract

Granitic rocks in the New Ross area, Nova Scotia, host polymetallic (Cu, Mo, Mn, Sn, U, W), aplite-pegmatite, greisen, and vein-type mineral deposits. The host granitic rocks belong to the Late Devonian (380 Ma) peraluminous South Mountain Batholith (SMB), which consists of several coalesced plutons. Among these, the New Ross Pluton, composed of monzogranite, leucomonzogranite, and leucogranite, is one of the youngest. White mica separates from aplite-pegmatite, greisen, and veins have ␦ 18 O values between +4.0 and +10.0‰, and ␦D values between-42 and-108‰. Fluid-inclusion extracts from quartz in samples from the area of the same deposits have ␦D values between-42 and-97‰. The isotopic composition of fluids in equilibrium with the white mica and isotopic data for the fluid-inclusion extracts record the transition from an early, orthomagmatic stage, in which magmatic fluid dominated (i.e., aplites, pegmatites), to a subsequent hydrothermal stage (i.e., greisens, veins) where an increasing amount of another fluid, inferred to be meteoric water, infiltrated the systems and mixed with the magmatic fluid. In addition, the low ␦D values for fluid-inclusion extracts compared with the ␦D fluid values calculated for coexisting white mica samples are considered to record infiltration of a second meteoric water much later in the evolution of the SMB. Integration of the new stable isotope data with our previous results on fluid inclusions suggests the following history of fluid evolution within the New Ross area: (1) exsolution of a magmatic fluid at ~600°C, (2) incursion of a low-␦ 18 O, high-␦D meteoric fluid at ca. 380 Ma through faults, and subsequent mixing with magmatic and metamorphic fluids through circulation by convection before cooling to ~400-500°C, and (3) incursion at a much later time of a low-␦D meteoric fluid, mostly affecting the composition of fluid-inclusion extracts.

Lithium and boron in late-orogenic granites – Isotopic fingerprints for the source of crustal melts?

“…Sano et al, 2002;Lü ders et al, 2009) and has also been inferred from numerical modeling of hydrothermal systems around intrusions (e.g., Coumou et al, 2009;Gruen et al, 2012;Weis et al, 2012). Other examples demonstrating fluid influx into granites are skarn and greisen systems and granite-internal high-temperature deposits that show stable-isotope signature suggesting the co-presence of magmatic and meteoric fluids (e.g., Sun and Eadington, 1987;Carruzzo et al, 2004;Llorens and Moro, 2010).…”

Tracing Garnet Origins in Granitoid Rocks by Oxygen Isotope Analysis: Examples From the South Mountain Batholith, Nova Scotia

“…Thus, d 18 O appears more sensitive to detecting late-stage, upper crustal contamination, whereas Sr and Nd record deeper source-related complexities. In addition, late-stage interaction of the SMB with meteoric and metamorphic waters potentially diversifies the composition of potential assimilants, complicating a simple MSG-SMB contamination scenario (Carruzzo et al 2004). …”

Geochemical variation in biotite from the Devonian South Mountain Batholith, Nova Scotia: Constraints on emplacement pressure, temperature, magma redox state and the development of a magmatic vapor phase (MVP)

“…Data sources: Musquodoboit: MacDonald (1981); Port Mouton: Douma (1988); Queensport: Ham (1988); Barren and Cu-Mo or Sn-W-Mo-mineralized Avalon-Gander Tectonic zones: Azadbakht et al (2020); Gander D'Espoir: Bennett (1990); Other northern Appalachian occurrences: Shabani et al (2003); Lands End, Cornwall: Stone et al, (1988);Stone, (2000); Müller et al, (2006). Halter et al (1995) and from the Sn-W-Cu-U-Mn deposits (19-25 wt% NaCl equivalent) associated with the New Ross and Salmon Tail Lake plutons (Carruzzo et al, 2004). The field labeled fluorite saturation corresponds to the fluorine content of the melt at fluorite saturation (8000-18,000 µg/g) measured by Icenhower and London (1997).…”

“…C) Calculated concentrations of Cl and F in melt and MVP as a function of the fraction of liquid remaining for the crystallization models presented in A) and B). The gray field corresponds to the range of Cl concentrations in fluid inclusions from the East Kemptville Sn deposit (27-41 wt% NaCl equivalent) associated with the Davis Lake Pluton reported byHalter et al (1995) and from the Sn-W-Cu-U-Mn deposits (19-25 wt% NaCl equivalent) associated with the New Ross and Salmon Tail Lake plutons(Carruzzo et al, 2004). The field labeled fluorite saturation corresponds to the fluorine content of the melt at fluorite saturation (8000-18,000 µg/g) measured byIcenhower and London (1997).…”