The near total absence of sulphide mineralization in the Eagle’s Nest dyke in the more
southerly intersections, coupled with the presence of extensive magmatic breccias with clear
evidence for stoping of the host rocks along the south-eastern margin of the dyke, tends to
confirm that the bottom of the Eagle’s Nest dyke was the north-western tip at the time of
emplacement. If the roughly flat surface of the south-eastern limit of net - textured sulphide is
taken as a paleo -horizontal plane then the entire system can be considered to have been
subject ed to a right -handed rotation of about 100º (i.e. slightly overturned) about a horizontal
axis oriented at N030º. In this interpretation, the dyke originally was a flat blade-shaped
intrusion ascending along a shallowly inclined fracture towards the base of the overlying sill
containing the Blackbird deposit. The abundant presence in the dyke of autobrecciated
textures, stoping, and repeated re -intrusion along the same axis, suggests that the conduit
followed a brittle fault which would have simultaneousl y guided the intrusion and facilitated
assimilation of the previously fractured wallrocks.
The present plunge of the keel of the dyke at the level of the deposit is about 70º along an
azimuth of N180º from surface to a depth of 300 m. If the dyke system has been slightly
overturned, then future efforts to locate more pods of sulphide down plunge should be done
on the assumption that the original base of the dyke, and any sulphide-hosting embayment
along it, might be at lower paleo-levels than the current Eagle’s Nest pod; this would place
them beneath Eagle’s Nest and, possibly, slightly to the southwest.
