U-Pb geochronology of the South Mountain Batholith, Nova Scotia

Abstract

The South Mountain Batholith (SMB) is a composite peraluminous intrusion in southwestern Nova Scotia and the largest granitoid body in the Appalachian Orogen. The batholith comprises early stage biotite-granodiorite to biotite-monzogranite and a later stage of leucomonzogranite to leucogranite plutons that are associated with numerous sub-economic to economic polymetallic (Sn, W, Mo, Cu, Ta, Nb, Zn) deposits, including East Kemptville, a past-producing Sn-Zn-Cu-Ag(-In) deposit. The timing and duration of emplacement for intrusive phases that make up the SMB remain poorly constrained. The U-Pb zircon age results from Sensitive High-Resolution Ion Microprobe (SHRIMP) analyses in this study constrain the emplacement age of the early and later phases across the SMB, as well as provide insight into mineral potential in the intrusive complex. Zircons from five plutons in the batholith were analyzed; including one early phase granodiorite, to compliment previous U-Pb zircon dates from similar phases (ca. 381-373 Ma), and four late phase leucogranitic plutons. Results indicate the early granodiorite to be 380.9 ± 3.0 Ma and the later leucogranites to range between 376.0 ± 3.0 Ma and 372.8 ± 3.0 Ma. The ca. 15 Ma from oldest to youngest crystallization ages mark the beginning and end of SMB construction. Due to overlapping errors, more precise dating is necessary to determine whether the late stage polymetallic-mineralized plutons intruded as a discrete magmatic event to the early stage plutons, or as part of a protracted Late Devonian magmatism in the region.