Undeformed clastic dykes cut Archean crystalline rocks in two northeast-trending zones west of Chibougamau, Quebec. The dykes contain varying amounts of granule- to pebble-sized lithic fragments in a fine-grained matrix of angular mineral clasts, identical to material composing the nearby Lower Proterozoic Chibougamau Formation. This extends the area known to have been covered by the Chibougamau Formation more than 80 km to the west. Dyke structures suggest forceful downward intrusion of water-laden sediment, related to either syn- or postsedimentary fault movements.

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