The Kootenay Arc located in SE B.C. has experienced more than one episode of tectonism, metamorphism and plutonism. The Mid-Jurassic to Eocene thermal history of the area has been investigated using K-Ar and 40/39 dating methods of biotite and muscovite; however there are no reliable hornblende dates from this area. This study will investigate two easterly stocks of the Nelson Plutonic Suite, the Mine and Wall stocks. Both of these have U-Pb zircon ages between 171 and 168 Ma but record a wide range of mica cooling and overprinting dates between 166 Ma in the west and 67 Ma in the east. 40Ar/39Ar age spectra for hornblende from 11 rocks in these stocks comprising a transect of the area, will aid in defining the higher temperature part of the thermal history. Previous attempts to prepare bulk hornblende separates were unsuccessful due to overgrowths and intergrowths of biotite, chlorite, plagioclase and K-feldspar. Part of this study involves testing the efficiency of SELFRAG disaggregation, which uses pulses of electrostatic power to break apart the biotite-hornblende-epidote granodiorite along mineral cleavage planes and grain boundaries. This should lead to higher purity mineral separates and better dates. Scanning Electron Microscopy (SEM) and Microprobe analysis analyse the separates looking for K-rich inclusions and the hornblendes variation in chemistry. Ca/K ratios are typical of igneous amphibole. Combined with previous K-Ar and 40/39 results for micas these hornblende dates should provide some insight into the history of the Next Creek fault and the thermotectonic history of the area.