| Polaris is a 22 million tonne deposit with an average grade of 14% Zn. 4% Pb and 5% Fe, measuring 800m x 300m x 40 to 150m thick, in Upper Ordovician shelf carbonates of the Thumb Mountain Formation.;Pre-folding, late Devonian replacement-style ore was deposited from tectonically-driven bittern-derived 105;Recrystallized ("RXTL") dolomite, white dolospar, internal sediments, clay minerals and brown dolomitized limestone constitute alteration at Polaris.;Flat-lying stratigraphy during Polaris mineralization implies the existence of an intact Irene Bay and/or Cape Phillips impermeable shale "gas seal" in the late Devonian. A nearby post-Cape Phillips early Devonian basal concordant disconformity is consistent with this interpretation. Sites of Zn-Pb minor showings, elsewhere in the Cornwallis district, occur near an early Devonian basal unconformity which records erosional breaching of the Irene Bay/Cape Phillips "gas seal". Mineralized early Devonian clastics above the unconformity prove that erosion pre-dated Late Devonian mineralization.;Halokinetics in response to early Devonian compressional tectonism and faulting is proposed to explain some of the Cornwallis folding and the presence, at some localities, of concordant and, at other localities, of angular unconformable early Devonian basal contacts.;No evidence exists for post-folding unconformity-related karst or for early Devonian folding at Polaris, so previously-proposed post-folding meteoric karst is not an ore control. Host-rock dissolution was synchronous with pre-folding ore precipitation. Syn-sedimentary faults and gravity-slump breccias in the host limestones probably afforded preferential permeability. Faults and folds marking the culmination at Polaris of the late Devonian Ellesmerian orogeny ruptured the shale seal, terminating mineralization.;Areas characterized by the presence of early Devonian unconformities are probably of poor economic potential. Prospective areas are those which are horizontal now, or were so at the date of mineralization. The most prospective stratigraphy lies north of Polaris, where alteration and traces of Zn in 1974 drillcore beg follow-up. |
