The Duncan mine is located on a small island in Duncan Lake in the Slocan Mining Division.

Regionally, the area is underlain by strongly deformed Late Proterozoic to early Paleozoic metasedimentary and metavolcanic rocks and by numerous plutonic bodies (Paper 1992-1).

The oldest rocks exposed in the area belong to the middle and upper portions of the Upper Proterozoic Horsethief Creek Group which has been divided in five mappable units. In ascending order these are: (Ht1) a dark limestone and calcareous argillite; (Ht2) a light green-grey argillite and muscovite quartz schist; (Ht3) a coarser grained, dark grey-green, micaceous quartzite and quartzose schist; (Ht4) a sequence of interbedded light grey to white grits, quartzite and thin carbonates; and (Ht5) a sequence of interbedded grits and dolostone-clast conglomerate. The lower units are laterally continuous, but the upper units are not. The total thickness of these units is estimated at 2.0 to 2.5 kilometres (Paper 1992-1). The contact between the Horsethief Creek Group and the overlying Hamill Group is marked by a distinctive transitional unit, which is included in the base of the Hamill Group. The transitional unit is characterized by quartz and feldspar grit and pebble conglomerate in a quartz sand matrix. The remainder of the Hamill Group, overlying the transitional unit, is divided into four map units, including the Mohican Formation. The lowermost unit (Hm1) is a clean, crossbedded quartzite, with minor quartz grit and pebble conglomerate. It lies conformably on the transitional unit. The middle Hamill Group (Hm2) contains pelitic schist, impure quartzite, minor carbonate and volcanic rocks. The upper part of the Hamill Group (Hm3) consists of clean, white quartzite at the base, and interbedded light and dark quartzite and pelite near the top. It is overlain by the Mohican Formation, a calcareous schist which is transitional between the Hm3 unit and the Badshot Formation (Paper 1993-1).

The Badshot Formation overlies the Hamill Group and is characterized by cliff-forming, white to medium grey, commonly laminated marble or dolomitic marble. The marble horizons are tens of metres thick and usually separated by grey, locally calcareous schist. The marble is overlain by a thick succession of fine grained, dark grey and green schists of the Index Formation (Lardeau Group).

The Index Formation is overlain by dark grey argillite and argillaceous quartzite of the Triune Formation. Grey blocky quartzite, the Ajax Formation quartzite, overlies the Triune Formation, and dark grey to black argillite of the Sharon Creek Formation overlies the Ajax. Schist grading into blocky greenstone of the Jowett Formation overlies the Sharon Creek Formation. Green and locally grey micaceous quartzites, greywackes, grits and fine grained mica schists of the Broadview Formation overlie the Jowett. All formations (Index to Broadview) form the Lardeau Group (Bulletin 49).

Structurally, the area is divided into three domains. From east to west, these are the western Purcell anticlinorium; a transitional domain; and the western Kootenay Arc. The Purcell anticlinorium is dominated by open to locally tight, upright folds, which deform an upward-facing stratigraphic sequence (Phase I folds). The dominant regional schistosity is axial planar to the folds and locally developed shear zones are parallel to the foliation. Rock of the Purcell anticlinorium have undergone regional metamorphism to lower greenschist facies.

The transitional domain is characterized by a belt of subvertical rocks. The stratigraphic sequence is deformed by upright isoclinal folds and ductile high-strain zones (Phase II folds). These structures deform earlier outcrop-scale isoclinal folds. The deformation was accompanied by upper greenschist to amphibolite facies metamorphism.

The Kootenay Arc is dominated by more intense and complex deformation and by amphibolite facies metamorphism. Large-amplitude (10 kilometre scale) west-verging recumbent folds were deformed by two phases of upright, tight to isoclinal folds which overturned much of the stratigraphic sequence. The boundary between the transitional and Kootenay Arc terranes is marked by a subvertical, locally mylonitic fault, which separates the Purcell anticlinorium from the Kootenay Arc (Paper 1993-1). The Duncan Lake area contains complex folds which plunge to the north at low angles. In general, the areas in which rocks of the Hamill Group are exposed are anticlinal and those in which the Lardeau Group are exposed are synclinal - the trace of the Badshot and Mohican formations outlines the folds.

The oldest folds recognized are isoclinal and plunge at low angles to the north (Phase I folds). The limbs and axial planes of these folds are curved and have been folded by Phase II structures. The principal Phase I folds in the area are the Howser syncline, the Duncan anticline, the St. Patrick syncline and the Meadow Creek anticline. No well-defined faults clearly related to Phase I folds are recognized.

Phase II folds are more open than Phase I folds. They are clearly visible in many outcrops. The folds plunge mainly to the north and northwest at angles as great as 30 degrees, but most plunge between 335 to 345 degrees at 5 to 10 degrees. The largest Phase II folds include the Lavina synform, the Comb Mountain antiform, the Glacier Creek synform, the Lake Creek antiform and the Kootenay Lake antiform. Several large faults are known, some of which may be related to the Phase II deformation. They strike north or north-northwest and dip steeply; commonly the apparent dip-slip is west-side-down and the strike-slip is thought to be small (Bulletin 49).

Rocks on the Duncan property belong mainly to the Mohican and Badshot formations but include the upper part of the Hamill Group and lowermost rocks of the Index Formation (Lardeau Group). These formations are on the eastern limb of the Duncan anticline, a major Phase I isoclinal fold. The Hamill Group is a succession of grey to brown micaceous quartzites with minor schist and platy white quartzite. It is overlain by the Mohican Formation of interlayered carbonates, mica schist and very fine grained micaceous quartzite. The Badshot is a succession of limestone and dolomite with siliceous dolomite at the top. The lowermost part of the Index Formation which overlies the Badshot is dark grey to black siliceous argillite and fine grained mica schist.

Virtually all structures seen on the property are Phase II folds. These are relatively tight asymmetric or overturned folds, well displayed in the Mohican Formation in crosscuts in the Duncan underground workings. Most of the folds are a metre across, but some are larger. On the peninsula, an anticline with Hamill Group quartzite in the core lies east of a shallow syncline with Mohican Formation in the trough. The anticline, somewhat modified by steep westerly dipping strike faults, probably passes just west of the portal leading to the underground workings. It is not the Duncan anticline, but a Phase II fold on the eastern limb of the Duncan anticline. In cross-section, the exposed folds have steeply dipping axial planes and have the shape of a reversed "N", rising more or less step-like to the west. The axial planes, defined by a well-marked cleavage in micaceous rocks of the Mohican Formation, dip steeply to the east near Glacier Creek and dip steeply to the west on the peninsula. The axes of the folds plunge 340 degrees at 5 to 10 degrees. The folds are important in determining the average dip of the formations and in controlling at least part of the mineralization.

Two important westerly dipping strike faults and several smaller ones are recognized in the underground workings. The faults exposed strike 340 degrees and dip steeply to the west. The apparent dip-slip is a couple of hundred metres down on the west.

Mineralized zones comprise the Duncan No. 1 zone (082KSE019) on the north side of Glacier Creek, the Duncan No. 2 zone (082KSE020) on the crest and western side of the ridge between Glacier Creek and Duncan Lake, the Duncan No. 3 zone (082KSE021) on the south side of the entrance to the Lower Arm of Duncan Lake, the Duncan No. 4 zone (082KSE022) on the peninsula (now an island due to the Duncan Dam and subsequent flooding of the valley) on the north side of the entrance to the Lower Arm, and the main Duncan zone (No. 5 - 8 zones), midway up the peninsula and the subject of this report.

Underground development at the Duncan property began in June 1959 with the driving of a crosscut adit at the 565 metre elevation, 12 metres above Duncan Lake. The crosscut passed through No. 6 zone and drifts followed No. 7 and 8 zones. No. 5 zone is beneath the level. In 1966, the crosscut adit above the lake level was sealed. The Duncan Dam, completed in 1967, raised the level of the lake approximately 27 metres, flooding a portion of the property.

Mineralized zones consist of pyrite, sphalerite, galena and minor pyrrhotite disseminated in dolomite and siliceous dolomite of the Badshot Formation. They are lenticular zones with gradational but in general well-defined margins. The attitude of the zones is essentially parallel to that of the enclosing formations with steep dips. Drilling has shown that the longest axes of the mineralized zones plunge at a low angle to the north - an average plunge of 7 degrees at 340 degrees. This plunge is parallel to the most prominent lineation and to the axes of Phase II folds in the surrounding rocks.

The mineralized zones are in dolomite and siliceous dolomite of the Badshot Formation. The lithologic succession consists of a lower and an upper dolomite separated by a thin layer of crystalline limestone. The uppermost part of the upper dolomite is siliceous. Mineralized zones are found in both the lower and the upper dolomites and along the contact between the upper dolomite and the siliceous dolomite.

In general, pyrite is the most abundant sulphide, and sphalerite is more abundant than galena. Pyrrhotite in minor amounts is present in one zone and minute amounts of chalcopyrite, marcasite, pyrargyrite and meneghinite are reported by Muraro (1962). The sulphides in general are very fine grained. They form disseminated grains, lenticular clusters, or fairly massive layers in dolomite.

The No. 7 zone is a steeply dipping tabular body averaging 4.5 to 6 metres thick along the western contact of the siliceous dolomite. The zone as indicated by drilling plunges about 7 degrees to the north and is approximately 122 metres high. It has been followed for 914 metres in the drift and found in drilling beyond. The zone is layered, with a western layer in which dolomite, pyrite and sphalerite are found in fairly well-marked bands; a central layer with lenticular masses of pyrite, galena and sphalerite in carbonate layers associated with fine-grained quartz; and an eastern siliceous layer in which pyrite and sphalerite are the dominant sulphides. Some bands of sulphides within the layers follow small discontinuous, nearly isoclinal folds which plunge to the north at low angles. Bands of sulphides are a fraction of a centimetre to a couple of centimetres thick, and the grains of sulphides within them are generally less than 1 millimetre across.

No. 5 zone is below and to the south of No. 7 zone along the same western contact of siliceous dolomite. It has the same plunge as No. 7 zone and is separated from it by a zone along the contact approximately 61 metres high in which there is only scattered sulphide mineralization.

No. 8 zone is a relatively small lens in the upper dolomite approximately 30 metres west of No. 7 zone. It dips at moderate angles to the east and, although not fully outlined, is 91 to 122 metres high parallel to the dip. It plunges to the north and appears to be offset on a steeply dipping strike fault above the main crosscut. Pyrite and sphalerite are the main sulphides, and galena has been found only in polished sections.

No. 6 zone is 91 to 122 metres west of No. 7 zone and is the most westerly and the largest zone found. The dominant sulphide is pyrite, with minor amounts of sphalerite and galena. Pyrrhotite is present locally in bands two to several centimetres wide. The zone is lenticular in cross-section, approximately 91 metres high and 6 to 30 metres thick. The zone has been found in drilling for 914 metres along the plunge which is at low angles to the north, parallel to that of the other zones. The zone in the main crosscut is bounded on the east and probably offset by a westerly dipping fault. Most of the mineralization is uniformly fine-grained pyrite with varying small amounts of galena and sphalerite disseminated in closely-spaced thin lenses or bands in siliceous dolomite. The siliceous dolomite appears to form a tight syncline. Pyrite near the fault on the eastern side locally forms rounded clusters resembling a sheared breccia. In the trough of the syncline it occurs in massive layers associated with limestone and siliceous dolomite.

Studies by Muraro (1962) of the textures of the sulphides have shown that the pyrite is older than the galena and sphalerite, and that the pyrite is crushed and deformed, whereas the galena and sphalerite are not. The pyrrhotite in No. 6 zone is not obviously deformed and at least is partly formed by replacement of pyrite (Bulletin 49).

Indicated reserves for the property are 9 million tonnes grading 2.7 per cent lead and 2.9 per cent zinc (CIM Bulletin April 1982, page 125). The crosscut adit was sealed prior to the completion of the Duncan Dam, which raised the lake level about 27 metres, flooding a portion of the property.

Cominco Ltd. drilled about 4000 metres in six holes in 1997. At this time, Cominco geologists reported that north of the Duncan mine that an additional 900 metres of strike length of the mineralized structure has the potential to host 5 million tonnes grading 11.5 per cent zinc and 1 per cent lead in the No. 7 zone and 2 million tonnes grading 7 per cent zinc and 0.3 per cent lead in the No. 8 zone and if the known mineralization is projected 2100 metres north to Jubilee Point there could be 16 million tonnes grading 10 per cent zinc (Lane, R.A. (2018-07-20): Technical Report on the Duncan Lake Zinc-Lead Project).

In 2016 and 2017, Jack and Robert Denny commenced a recovery and re-sampling program of old drill cores and general site clean-up work. In 2018, Rokmaster Resources Corp. examined the area.