THE ASBESTOS HILL - IMORDENHAM STORY - Geology of the Asbestos Hill Area
CIM Bulletin, Vol. 69, No. 775, 1976
Ralph V. Stewart, Chief Geological Engineer, Asbestos Corporation Limited, Thetford Mines, Quebec
The asbestos orebody is contained within ultrabasic rocks of Precambrian age, being located in the continuous permafrost zone of the Quebec Ungava Peninsula, some 300 miles north of the tree line at approximate latitude 61°49' and longitude 73°58'.
The asbestos deposit is at the western tip of a folded ultrabasic sill complex which trends northeast and covers an elliptical area 4-5 miles wide by 15 miles long. Locally, the asbestos occurs in a completely serpentinized dunite rock. The principal rock types in the vicinity of the ore-body originally consisted of dunite, peridotite and pyrox-enite, all of which have experienced at least two periods of alteration, so that no fresh rock now remains.
The main ore zone in the open pit is approximately one quarter mile in length, 150 to 200 feet in width, and plunges at 25 to 30 degrees in a northeast direction below surface, to a vertical depth of at least 1,200 feet. Considerable tectonic activity resulted in favourable structural conditions which culminated in the formation of the ore zone in its present form.
The deposit consists principally of cross-fibre "gash type" veins which vary in length from several inches to several feet. The principal fibre vein direction is parallel to the dip of the enclosing serpentinized dunite and sill complex.
Some of the problems encountered during diamond drilling in permafrost are briefly discussed.