The Driftpile Creek developed prospect is based on stratiform barite-lead-zinc mineralization, and is situated near the headwaters of Driftpile Creek near the western edge of the Muskwa Ranges, about 22 kilometres northeast of the Northern Rocky Mountain Trench (Assessment Report 7658).
The deposit is in the Gataga mineral district, in a belt of Paleozoic basinal-facies sedimentary strata known as the Kechika Trough, the southeastern arm of the Selwyn Basin (Exploration and Mining Geology, Volume 1, page 1). These rocks belong to Ancestral North America (Geological Survey of Canada Map 1713A). The Gataga mineral deposits are characterized by stratiform sedimentary exhalative barite-sulphide mineralization, which occurs at certain Ordovician, Silurian and Devonian stratigraphic horizons. The last, represented by the Driftpile Creek deposit among others, are the most economically significant. They are believed to have formed during sedimentation, from metal-enriched brines released into fault-controlled, starved sub-basins which developed during rifting of the ancient continental margin.
The Driftpile mineralization was discovered in 1973 following a regional geochemical reconnaissance survey done in 1970 (Assessment Report 5359). A number of limonitic gossans, ferricrete and 'kill zones' are present on the property but unaltered mineralization is uncommon on the surface, so subsequent exploration has concentrated on detailed geological mapping and soil sampling, and close to twenty thousand metres of diamond drilling.
The area around the Driftpile Creek deposit is underlain mainly by the Middle to Upper Devonian Gunsteel Formation (informal name) of the Devono-Mississippian Earn Group (Geological Survey of Canada Memoir 373, Map 1343A). This unit is preserved in a broad, northwest-trending, tightly-folded synclinorium disrupted by moderately-dipping, northeast-verging thrust faults. Fold axes plunge 10 to 20 degrees to the northwest. Bedding, cleavage and fold axial planes generally strike about 325 degrees and dip moderately to steeply southwest, though there may be northeastward dips due to the folding. To the southwest of the immediate area, rocks of the underlying Ordovician to Lower Devonian Road River Group are exposed in the hanging-wall of the Mount Waldemar thrust fault (informal name).
Mineralization is restricted to the Gunsteel Formation (the same unit that hosts lead-zinc-silver mineralization at the Stronsay or Cirque deposit, 80 kilometres to the southeast). Conodonts extracted from carbonate rocks at Driftpile Creek indicate that the age of the mineralization is mid-Fammenian (Late Devonian) (Insley 1990).
The Gunsteel Formation mostly comprises blue-grey weathering, carbonaceous black shale and silty mudstone, cherty argillite and radiolarian chert. Within this dominantly mudstone-shale stratigraphy are a number of horizons of siliceous shale or cherty argillite which are enriched with barite and/or pyrite. Barite is in the form of nodules, disseminations, intercalated thin laminae, or massive, centimetre-scale beds. Pyrite is generally present as laminations in mudstone, or may be associated with barite, or with carbonate concretions.
Although their stratigraphic relationships are uncertain because of the structural complexity, at least two different sulphide-rich zones have been distinguished by detailed mapping and diamond drilling (Assessment Report 23109; Insley (1990); Fieldwork 1994). The lower or 'main' zone is primarily a sulphide-carbonate facies; visible barite is uncommon. The zone consists of 35 to 80 per cent sulphide in a carbonate matrix, separated or 'diluted' by intervals of black graphitic shale or mudstone. Most of the sulphide is fine-grained, finely laminated or framboidal pyrite, associated with irregular bands and concretions of calcite. The pyrite grains may be graded, or show soft-sediment deformation. Sphalerite and galena may be present with the pyrite, but they are particularly well-developed in some places in a layer of fine-grained massive sulphide near the base of the zone, as irregular masses or discrete bands. The estimated true thickness of the 'main' zone is between 20 and 70 metres (Fieldwork 1994); Insley (1990) expressed the thickness in terms of two 3- to 36-metre thick subunits. Overall, it carries 1 to 2 per cent zinc (Assessment Report 23109).
The 'upper' zone, 100 to 200 metres higher in the formation, comprises barite-sulphide mineralization, in siliceous or non-siliceous mudstone with pyritic laminations. Barite occurs in massive beds or laminations, or in nodules. Pyrite is subordinate to barite, but may form massive layers, locally accompanied by strong sphalerite and galena. There are few carbonate concretions here. According to Insley (1990), this 'upper' zone occurs in four 2- to 20-metre thick units.
The best mineralization exposed on the surface on the property is that in trenches 1400 metres north of Driftpile Creek (Assessment Report 7658, Figure 4a). Thin parallel bands of discrete, irregular galena and sphalerite occur in dark grey bedded barite; this is probably the 'upper' zone. The best drill intersection from here (hole 78-07) was 11.7 metres grading 7.45 per cent combined lead-zinc
Drilling in 1993 confirmed that high grade mineralization in the 'main' zone extends down dip for at least 100 metres, although farther south along strike, drilling failed to intersect mineralization, indicating that it weakens in that direction. Previous work has demonstrated that mineralization in the Driftpile Creek area has a strike length of between 2 and 3 kilometres and a surface width of 1.5 kilometres (Assessment Report 7658; Fieldwork 1994). Other favourable zones in the area are known as the Camp, East, North Trench, South, and Canyon zones (Fieldwork 1994). Past diamond drilling assay results are given in Assessment Reports 7149, 7658, 23109 and 23561, among others. In 1993 drilling, the best result came from hole 93-56 which intersected a 12-metre zone grading 10 per cent zinc and 1 per cent lead, including a zone of 6.02 metres grading 12.26 per cent zinc and 1.36 per cent lead (Assessment Report 23109).
In 1980 it was reported that shallow drilling in 11 areas indicate reserves of approximately 18,145,000 tonnes averaging 2.38 per cent combined lead-zinc (Canadian Mines Handbook 1980-81, pages 280-281). A more recent, qualitative and preliminary estimate of the geological resource in the lower mineralized subunit of the 'main zone' is 2.44 million tonnes averaging 11.9 per cent zinc and 3.1 per cent lead, with a cutoff grade of 8 per cent zinc (Fieldwork 1994, page 263).
Twenty-six diamond-drill holes totalling 4817 metres were drilled on the Driftpile Creek property during 1994. The program was undertaken to test areas of known mineralization on the property, other than the Main zone, tested in 1993. A total of five target areas, termed the Camp, South, Ridge, East and Canyon zones, were tested during the 1994 program (Assessment Report 24609).
Drilling on the Camp zone has determined that mineralization is present in the keel of a syncline, trending across a ridge top. The mineralized horizon has been largely eroded, limiting tonnage potential.
Complex, tight to isoclinal folding was intersected in the South zone area. Although thick intercepts of high sulphide (pyrite) mineralization were initially intersected, continued drilling demonstrated that the mineralization thinned and weakened along strike and downdip.
Strong pyritic mineralization with discrete sphalerite/galena laminations was intersected on the Ridge zone. Thrust faulting has displaced the mineralized horizon such that it has been subsequently eroded along strike.
Geological mapping in the Canyon zone indicated potential for a second mineralized horizon at depth. Subsequent drilling confirmed the presence of a single horizon, repeated by thrusting. All mineralization is baritic and distal.
Drilling on the East zone identified a mineralized horizon consisting of barite and sulphide. The horizon was tested in three places over a one kilometre strike length. Several narrow intercepts of high grade were obtained, including; 17.5 per cent zinc over 1 metre and 7.93 per cent zinc over 2 metres from hole 94-88, and 10.4 per cent zinc over 1 metre from hole 94-89, 800 metres to the south. Locally, tight to isoclinal folding has thickened the mineralized horizon by up to five times. The horizon has not been tested for 800 metres between sections drilled in 1994, and has not been tested north of the northernmost section drilled in 1994.