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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.

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The 370 Ma peraluminous South Mountain Batholith (SMB) intrudes Meguma Supergroup metasedimentary rocks in Nova Scotia. The New Ross area of the SMB contains polymetallic mineralisation (Sn, W, U, Mo, Cu and Mn) in pegmatite, greisen and vein directly or indirectly associated with highly evolved fractions of the SMB. Eight mineral deposits from this area have several fluid inclusion types hosted by quartz: (1) monophase liquid (L); (2) monophase vapour (V); (3) aqueous, L-V (4) aqueous, L-rich + solids; (5) aqueous, L-rich + halite. Inclusions have irregular to equant shapes and are pseudo-secondary or secondary. The irregularity and variability of L:V ratios within fluid inclusion populations suggest post-entrapment modifications of inclusions (i.e. necking).Thermometric data indicate three distinct fluids in terms of salinity: (1) 19-25 wt. % equiv. NaCl (rarely 14-25 wt. % NaCl equiv.), (2) 29-43 wt. % equiv. NaCl, and (3) 0-9 wt. % equiv. NaCl. Temperatures of first melting and ice/hydrohalife melting indicate CaCl2 in solution. Proximity of the deposits to Meguma Supergroup metasedimentary rocks suggests that this Ca component may be externally derived. The majority of the low-salinity fluid population has the composition of meteoric water. Electron microprobe analyses of artificially decrepitated mounds identify Na, Ca and K as major solutes, with a continuum in terms of compositions. Other solute components in the mounds are Fe and Ba, and a variety of metals of unknown speciation also occur (Cu, Zn, Fe, Ni). Homogenisation temperatures (Th) range from c. 80°C to 370°C, but for inclusion assemblages the range is 10°C to 20°C. Given the 3 kbar depth of emplacement of the SMB, estimated entrapment temperatures are c. 200°C to 550°C. The fluid inclusion data appear to reflect: (1) trapping of mixed Na-K-Ca brines during isobaric cooling in pegmatite and greisen deposits as indicated by large ranges in Th; (2) formation of deposits at different ambient pressures (i.e. depth); and (3) mixing of fluids of different reservoirs (i.e. magmatic, metamorphic, meteoric).