SEISMIC SIGNATURE OF THE DRYBONES BAY KIMBERLITE PIPE, N.W.T

The diamondiferous Drybones Bay kimberlite pipe is the largest pipe (9 00 m by 400 m) discovered to dare in the Northwest Territories. The pi pe intrudes granodiorite of the Archean age Defeat Pluton and contains crater, reworked crater (epiclastic) and diatreme facies kimberlite. In-situ measurements of seismic p-wave velocity were recorded with in- line refraction arrays over representative areas. Refractions from fre sh kimberlite were recorded over epiclastic facies kimberlite in the e astern portion of the pipe and returned an average velocity of 4300 m/ s, Refractions from weathered kimberlite were recorded on all lines an d returned velocities ranging from 1900 m/s to 2200 m/s. Granite surro unding the pipe returned an average velocity of 5400 m/s. The results indicate that there is a definite contrast in seismic velocities betwe en kimberlite and country rocks at Drybones Bay and suggest that seism ic refraction surveys may be an effective means of screening kimberlit e targets in glaciated areas underlain by igneous or metamorphic rocks .