Summary:
The white smoker deposit model is proposed for the Nash Creek deposit, in contract to a traditional black smoker deposit. These deposits types are described below.
Sulphide mineralization at Nash Creek includes pyrite, sphalerite, galena and minor chalcopyrite. Silver consistently accompanies the sulphides, possibly the result of argentiferous galena or presence of a silver rich sulphosalt. Sulphide concentrations of potential economic interest occur as: 1) stratabound and/or laterally continuous zones of matrix filling or replacement style mineralization within coarse to fine grained pyroclastic deposits of both mafic and felsic affinity; 2) fracture filling, stringer or vein arrays mainly within competent flow units or flow breccia; and 3) discrete breccia zones (e.g., flow breccia, autobrecciation, etc.). Strong intraclast chlorite mineralization is associated with concentrations of zinc and lead in the brecciated mafic rocks.
Moderate to intense clay alteration and silicification are common in the mineralized zones and broader zones of strong carbonate, hematite and potassium alteration occur in footwall, and occasionally hangingwall, to mineralized host rocks. Mineralization occurs as multiple stacked zones of laterally extensive pyroclastic units and flow top rubble zones which are cross cut locally by north, northeast and northwest trending structures that may have acted as pathways for mineralized hydrothermal fluids (Cullen and Barr, 2005).
Four zones hosting stratabound mineralization have been identified on the Nash Creek Property by previous workers. These four zones are, roughly from north to south, the MacMillan, Hickey and Hayes zones and to the east, the Central Zone. Drilling completed by Callinex in 2017 has extended the Hickey Zone to the north.
Mineral resource estimates have been stated for the Hickey and Hayes zones. Walker, 2006 describes the Superjack A Zone as two subparallel, easterly thickening, massive sulphide lenses that strike approximately east-northeast and dip about 80°N. The larger, northern lens has a strike length of approximately 380 m and extends downdip for about 280 m, where intersections of 8.93% Zn over 9.75 m have been reported (McAllister 1960; Mitton 1994). Sulphide intersections in the western end of the deposit are between 0.3 m and 3 m in thickness. Massive sulphides in the deposit are dominated by pyrite but include subordinate pyrrhotite, sphalerite, galena, and chalcopyrite. In the western part of the Superjack A Zone, massive sulphides are immediately overlain by basalt and are underlain by an approximate 20 m thick sericite- or chlorite-altered zone of tuffaceous sedimentary rocks cute by quartz-sulphide veins.
In drill logs, the massive sulphides at the A Zone are described as fine-grained, containing predominantly pyrite with intermittent bands of sphalerite and galena throughout, as well as intermittent disseminated sphalerite and galena throughout. The massive zones occasionally contain quartz-chloritic flooding (<1%). Medium-grained blebby chalcopyrite can frequently be observed at both the upper and lower contacts of the massive zones. The sulphides are locally magnetic due to disseminated pyrrhotite. Stringer sulphides, interpreted as stockwork zones, occur mainly on the footwall, but occasionally on the hanging wall as well; this repeating is likely due to local fold patterns. They are hosted by banded argillite and/or sericite schist. Mineralization at the B and C zones is described very similarly to that in the A Zone. Both contain pyrite-dominated massive sulphides with intermittent sphalerite-galena banding/disseminations. The B Zone contains fewer and thinner stringer sulphide zones than both the A and C zones.