From the parking lot at the Granisle marina we have a good view north up Babine Lake toward Bear Island with Old Fort Mountain in the distance. This part of Babine lake is underlain by the Eocene Newman volcanics which are preserved within the core of a north-trending graben. This graben extends from just south of Ganisle to Old Fort Mountain where it is truncated by a northeast trending fault. Old Fort Mountain is an uplifted block of early and middle Jurassic Hazelton Group rocks.
The Newman volcanics, which are flat-lying to southeast dipping are exposed on the west and east shores of the lake and on Bear Island. These rocks sit unconformably on folded early Cretaceous strata of the Skeena Group. The ridges east and west of the lake are tilted fault blocks comprised of volcanic and sedimentary rocks of the early to middle Jurassic Hazelton Group. These fault blocks are tilted inward towards the central part of the Granisle graben. The Newman volcanics are also found further to the west, outside of the Granisle graben where they form a broad plateau called Turkey Mountain.
The Newman volcanics are the last magmatic episode in the evolution of a continental volcanic arc that extended from Babine Lake to the Coast Mountains. This arc was active from Late Cretaceous to Eocene time and was built on uplifted Early Cretaceous and older rocks. Formation of this arc and its associated porphyry copper mineralization occurred during a period of transpression related to oblique subduction along the North American continental margin.
The plutonic and volcanic remnants of this arc are exposed at different structural levels by Eocene or younger extension and block faulting, a key factor that must be considered when exploring for associated mineral deposits such as porphyry copper deposits and epithermal vein systems.
The characteristic rock of the Newman volcanics is a hornblende+/-biotite+feldspar andesite with a crowded porphyritic texture. The Babine intrusions, which are lithologically and compositionally identical, are coeval with the volcanic rocks and have important porphyry copper mineralization associated with them. Mike Villeneuve of the GSC has done Ar-Ar isotopic dating of the Newman volcanics as part of the Nechako NATMAP project (Struik and MacIntyre, 1999). Ages range from 53 to 50 Ma.
The town of Granisle was created in 1966 when the Granisle (Granby) mine opened on MacDonald-Sterritt island due east from our vantage point (mine site not visible from here). The Bell mine, located at the north end of the Newman peninsula (mine site not visible from here), opened in 1972. Granisle closed in 1982 and Bell in 1992.
Quaternary geology note: Like much of the northern Nechako Plateau, the Babine Lake area was extensively sculpted by multiple glacial cycles throughout the Pleistocene. During the late Wisconsinan Fraser Glaciation (29 – 11 Ka), ice accumulated in montane areas including the Skeena Arch and the Babine Mountains. Early ice flow was focused along the structurally-controlled pre-glacial Fulton, Babine and Hautête valleys. Around 19 Ka, the area was completely inundated by southeast flowing ice streams, forming part of the Cordilleran Ice Sheet. Evidence of late Wisconsinan iceflow is preserved at a variety of scales. Glacial striae and grooves are commonly preserved on bedrock surfaces throughout the area, and indicate regional palaeoice-flow directions ranging from 130o to 180o. This dispersal pattern is reflected in larger scale glacial streamlined landforms; including drumlins, flutes and crag-and-tail features. Regional iceflow has in part accentuated the local structural grain.