Geological data summary for boreholes drilled for he 384-m instrument array at the Underground Research Laboratory. Volume 1

Twenty-one boreholes were drilled for the 384-m instrument array in the circular shaft at the Underground Research Laboratory (URL) between 1988 March 29 and 1988 April 25; two additional boreholes were drilled between 1989 March 17 and 1989 April 10. Preliminary geological results from detailed core logging, summarizing drilling, rock substance, rock mass and discontinuity, and testing data, are presented. These results suggest lithologic units intersected in the boreholes can be correlated to those identified in the URL shaft. The rock in the vicinity of the array comprises mainly homogeneous grey granite intersected by leucocratic segregations, xenolithic zones, and later granodiorite and pegmatite dykes. No fractures were intersected in the boreholes, and none are suspected in the area of the investigation. (author)