A set of sheeted quartz veins cutting 380 Ma monzogranite at Sandwich Point, Nova Scotia, Canada, provide an opportunity to address issues regarding fluid reservoirs and genesis of intrusion-related gold deposits. The quartz veins, locally with arsenopyrite (<= 5%) and elevated Au-(Bi-Sb-Cu-Zn), occur within the reduced South Mountain Batholith, which also has other zones of anomalous gold enrichment. The host granite intruded (P = 3.5 kbars) Lower Paleozoic metaturbiditic rocks of the Meguma Supergroup, well known for orogenic vein gold mineralization. Relevant field observations include the following: (1) the granite contains pegmatite segregations and is cut by aplitic dykes and zones (<= 1-2 m) of spaced fracture cleavage; (2) sheeted veins containing coarse, comb-textured quartz extend into a pegmatite zone; (3) arsenopyrite-bearing greisens dominated by F-rich muscovite occur adjacent the quartz veins; and (4) vein and greisen formation is consistent with Riedel shear geometry. Although these features suggest a magmatic origin for the vein-forming fluids, geochemical studies indicate a more complex origin. Vein quartz contains two types of aqueous fluid inclusion assemblages (FIA). Type 1 is a low-salinity (<= 3 wt.% equivalent NaCl) with minor CO(2) (<= 2 mol%) and has T (h) = 280-340 degrees C. In contrast, type 2 is a high-salinity (20-25 wt.% equivalent NaCl), Ca-rich fluid with T (h) = 160-200 degrees C. Pressure-corrected fluid inclusion data reflect expulsion of a magmatic fluid near the granite solidus (650 degrees C) that cooled and mixed with a lower temperature (400 degrees C), wall rock equilibrated, Ca-rich fluid. Evidence for fluid unmixing, an important process in some intrusion-related gold deposit settings, is lacking. Stable isotopic (O, D, S) analyses for quartz, muscovite and arsenopyrite samples from vein and greisens indicate the following: (1) delta(18)O(qtz) = +11.7aEuro degrees to 17.8aEuro degrees and delta(18)O(musc) = +10.7aEuro degrees to +11.2aEuro degrees; (2) delta D(musc) = -44aEuro degrees to-54aEuro degrees; and (3) delta(34)S(aspy) = +7.8aEuro degrees to +10.3aEuro degrees. These data are interpreted, in conjunction with fluid inclusion data, to reflect contamination of a magmatic-derived fluid (delta(18) O(H2o) <=+10%) by an external fluid (delta(18) O(H2o) >= +15%), the latter having equilibrated with the surrounding metasedimentary rocks. The delta(34)S data are inconsistent with a direct igneous source based on other studies for the host intrusion (delta(18)O(H2o) = +5%) and are, instead, consistent with an external reservoir for sulphur based on delta(34)S(H2S) data for the surrounding metasedimentary rocks. Divergent fluid reservoirs are also supported by analyses of Pb isotopes for pegmatitic K-feldspar and vein arsenopyrite. Collectively the data indicate that the vein- and greisen-forming fluids had a complex origin and reflect both magmatic and non-magmatic reservoirs. Thus, although the geological setting suggests a magmatic origin, the geochemical data indicate involvement of multiple reservoirs. These results suggest multiple reservoirs for this intrusion-related gold deposit setting and caution against interpreting the genesis of intrusion-related gold deposit mineralization in somewhat analogous settings based on a limited geochemical data set.
