The Carolin mine is located on the west fork of Ladner Creek, approximately 18 kilometres northeast of Hope. The portal of the Idaho decline is situated approximately 300 metres north of the No. 1 adit of the Aurum mine (MINFILE 092HNW003), which operated intermittently between 1928 and 1942. At least three saddle-shaped ore bodies have been outlined to date at the Idaho zone and deep drilling has shown that several additional auriferous zones are present below the No. 3 ore body.
Geology in the mine area is characterized by sediments assigned to the Lower and Middle Jurassic Ladner Group and greenstone of the Lower Triassic Spider Peak Formation, in contact with ultramafic rocks of the Coquihalla serpentine belt along a variably dipping, northwest- trending segment of the East Hozameen fault. Rocks of the Permian to Jurassic Hozameen Group lie west of the West Hozameen fault, which also bounds the serpentine belt to the west.
The Ladner Group succession at the mine has been divided into three units. The heterogeneous and coarsely clastic lower unit comprises wacke, siltstone and minor conglomerate and is approximately 200 metres thick. These rocks are overlain by a 200- metre thick succession of dark coloured, well-bedded siltstone with minor wacke and an upper, organic-rich, slaty argillite unit more than 1000 metres thick. These rocks have a weak to intense slaty cleavage and were subjected to at least three periods of regional folding. Despite this, Ladner Group sediments give an overall impression of being less deformed than the Hozameen Complex rocks to the west, and a wide variety of sedimentary structures are commonly preserved. Regional folding has resulted in widespread structural repetition; graded bedding suggests that the Ladner Group succession adjacent to the Coquihalla serpentine belt is structurally overturned.
Ladner Group sediments stratigraphically overlie massive to pillowed, spilitized greenstone of the Lower Triassic Spider Peak Formation. The Spider Peak/Ladner contact is commonly marked by faulting and shearing, but in places the sedimentary members rest directly on the volcanic rocks with either an unconformable or a disconformable relationship. Two elongate, fault-bound masses of gabbro and massive to brecciated greenstone outcrop north and south of the surface exposure of the Idaho zone. These rocks are enriched in sodium and are believed to be thrust slices of Spider Peak Formation.
The Hozameen Complex consists largely of cherts, pelites and altered spilitic basalts that, west of the Carolin mine area, have been subjected to lower greenschist facies metamorphism and strong deformation. Some parts are also overprinted by either a schistosity or an intense, subhorizontal mullion structure. Close to the serpentine belt, Hozameen Complex rocks commonly show signs of increased deformation and crushing, minor silicification, late brittle faulting and pronounced slickensiding.
The Coquihalla serpentine belt forms an elongate, north- northwest –trending, steeply dipping, ultramafic unit separating supracrustal Ladner Group sediments to the east from rocks of the Hozameen Complex to the west. The belt lies within a major crustal fracture, the Hozameen fault, and exceeds 50 kilometres in discontinuous strike length. The serpentine belt reaches its maximum development in the Carolin mine-Coquihalla River area, where it is greater than 2 kilometres in width. It gradually narrows to the south and north until, in the Boston Bar and Manning Park areas, the Hozameen and Ladner rocks are in direct fault contact. Dark, highly sheared to massive serpentinite of probable peridotite and dunite parentage characterizes the belt, but it also contains substantial amounts of highly altered gabbro-diabase rocks as well as minor listwanite. The eastern margin of the serpentine belt is sharply delineated by the East Hozameen fault, which comprises several generations of oblique, intersecting fractures. The fault generally dips to the east, but locally exhibits an undulating character and may dip westward. The subvertical West Hozameen fault marks the western margin of the belt and, like its eastern counterpart, has had a long and complex history of both vertical and horizontal movements. With the gradual disappearance of the belt to the north and south, these boundary fractures merge into a single tectonic feature.
The Carolin orebodies are turbidite-hosted, mesothermal, epigenetic deposits characterized by the introduction of sulphides, albite, quartz and precious metals. This mineralization is hosted in the lower clastic unit of the Ladner Group succession, approximately 150 to 200 metres above the unconformable contact with the Spider Peak Formation. Here, this unit includes discontinuous wedges of interbedded greywacke, lithic wacke, sedimentary breccia and conglomerate, together with intercalated sequences of siltstone and minor argillite. The basal portion also includes rare, thin horizons of clastic, impure limestone. Surface mapping in the mine area indicates that both the Ladner Group and the stratigraphically underlying Spider Peak Formation were tectonically inverted, and subsequently deformed into large scale, upright to asymmetric folds.
Underground mapping has demonstrated that the gold mineralization is both lithologically and structurally controlled. It is preferentially concentrated in the more competent and permeable coarser-grained wacke, lithic wacke and conglomerate layers in the tectonically thickened hinge regions of a disrupted, asymmetric antiform. As a result, the orebodies exhibit a saddle reef-like morphology and the deposit plunges gently northwest, subparallel to the antiformal axis. Polished section studies indicate that pyrite predominates in the upper parts of the deposit, while pyrrhotite predominates at depth. Similar zoning has been noted in other gold deposits, such as the Mount Charlotte deposit in Western Australia (Phillips et al., 1983). The pyrite-pyrrhotite zoning suggests that the deposit is upright and younger than the tectonic overturning that affected the host rocks. However, the presence of folded, post-ore quartz veins suggest that mineralization either predated or accompanied the episode of upright to asymmetric folding (Fieldwork 1985).
The surface expression of the deposit is a strongly faulted and altered zone up to 40 metres in exposed width. It is characterized by secondary manganese and iron oxides, intense albitic alteration, disseminated sulphides and a dense network of irregular, variably deformed, multiphase, quartz-carbonate veins. Not all areas containing these features are, however, enriched in gold. The ore largely consists of quartz and albite with variable amounts of carbonate, chlorite, very fine sericite and opaque minerals. Opaque minerals make up between 1 and 15 per cent of the ore and comprise, in decreasing order of abundance, pyrrhotite, arsenopyrite, pyrite, magnetite, chalcopyrite, bornite and gold. Minor sphalerite and, in rare instances, small flakes of pyrobitumen have also been observed.
Gold generally forms small grains, up to 0.02 millimetre in size, that generally occur as inclusions in pyrite and arsenopyrite, or as rims around pyrite, pyrrhotite and chalcopyrite crystals. Gold is also found independent of the sulphides as minute grains within or along the grain boundaries of some quartz, carbonate or albite crystals. Visible gold, although uncommon, is present as thin plates and smears on fault surfaces and as rare leaf-like masses, small scales and rods.
Several theories of paragenesis of the opaque minerals have been put forward. Earlier reports suggest the following: (1) magnetite, (2) arsenopyrite, (3) pyrite, (4) gold, (5) pyrrhotite, (6) sphalerite and (7) chalcopyrite, with a partial overlap in the deposition of arsenopyrite, pyrite and pyrrhotite (Kayira, 1975). Shearer (1982), however, determined the order to be: (1) magnetite; (2) arsenopyrite and some gold; (3) contemporaneous deposition of pyrite, pyrrhotite and some gold; (4) minor magnetite and finally, (5) traces of chalcopyrite and gold. In any case, magnetite appears to be the oldest opaque ore mineral and is probably unrelated to the mineralization since it shows no spatial relationship to either gold or sulphides.
Weak silicification and intense, pervasive, albitic and carbonate alteration are evident throughout the Idaho zone and adjacent wallrocks. Exceedingly fine-grained chloritic and sericitic alteration related to the mineralizing event is also well developed in the surrounding wallrocks, but is not so abundant in the ore. This alteration is believed to have occurred according to the following sequence of events: (1) chloritization together with some sericitization and weak kaolinization; (2) the introduction of quartz, albite, sulphides and gold; (3) continuing introduction of quartz and albite; (4) emplacement of multiple phases of quartz with or without carbonate veins with local envelopes of disseminated carbonate followed by (5) the late emplacement of veins and disseminations of calcite and ankerite. Weak sericitization and chloritization probably took place throughout the entire sequence.
There are at least three generations of albitization, the earliest and finest grained being coeval with the sulphide-gold mineralization. The subsequent two generations produced veins and masses containing coarse-grained, well-twinned albite crystals. Locally, angular fragments of sulphide-rich ore are engulfed by the youngest albitic phase. The deposit is surrounded by an albitic envelope, which extends at least 60 metres beyond the mineralization. The gold mineralization is marked by distinct zones of barium and potassium depletion that are generally twice as thick as their associated gold-bearing horizons.
The deposit is cut by numerous north-trending faults, some of which contain carbonaceous material. It is also truncated to the north by the younger, east striking, north dipping "hangingwall shear", which may be the downward continuation of the Richardson fault, a normal fault mapped on the surface.
In 1973, Carolin Mines completed a program of seven diamond drill holes, totalling 538 metres, soil sampling, a 37.0 line-kilometre ground magnetic survey, geological mapping and trenching on the area. In 1974, the McMaster zone (MINFILE 092HNW018) was discovered approximately 1.5 kilometres northwest of the Carolin orebodies. Mineralization similar to that developed at the mine was encountered in trenches and preliminary drill holes. In 1977 and 1978, Carolin Mines conducted an extensive underground exploration program including the construction of a new access road and sampling plant, the driving of a main decline and crosscut, geological mapping and sixty-eight diamond drill holes, totalling 3204 metres. In 1981, work began on a northerly extension of the main haulage level (800 metre level) at the Carolin mine towards the McMaster zone. The status of this extension is not known.
In 1989, a program of underground diamond drilling, totalling 610.5 metres in 13 holes, was completed to continue the No.1 zone northward and to investigate the No.3 zone below the 79 and 73 stopes. This work outlined five separate mineralized zones with similar grade and tonnage potential to the Idaho zone orebodies. Drilling on the No.1 zone (NEX 9) yielded intercepts of 3.25 grams per tonne gold over 36.48 metres. Drilling on the No.3 zone (DH 89-776-1) yielded 4.28 grams per tonne gold over 10.34 metres, including 6.84 grams per tonne gold over 3.94 metres (Assessment Report 20048).
When the milling of ore began in late 1981 at the Carolin mine, measured geological reserves were 1.5 million tonnes grading 4.83 grams per tonne gold using a cut-off grade of 2.74 grams per tonne gold and a 20 per cent dilution factor (Fieldwork 1985). The mine closed at the end of 1984 due to poor gold recoveries, environmental concerns and low gold prices. During the three years, 1, 018, 425 tonnes of ore were mined (901,567 tonnes milled), from which approximately 1450 kilograms of gold and 109 kilograms of silver were recovered. An additional 12 kilograms of gold and 3 kilograms of silver were recovered from custom ore milled in 1988. In 1990, indicated (probable) reserves were stated as 898,000 tonnes grading 4.3 grams per tonne gold (George Cross News Letter No.25, February 5, 1990).
Athabaska Gold Resources Ltd. continued underground exploration drilling and development. Preliminary resource estimates from the underground workings are 900,000 tonnes grading 4.4 grams per tonne gold. A further resource of approximately 800,000 tonnes of tailings grading 1.7 grams per tonne gold is also viewed as potential mill feed. The 1995 program included 110 metres of new drifting to extend the workings on the 875 level, 1630 metres of underground drilling in 19 holes and 564 metres of surface drilling in six holes (T. Schroeter, personal communication, 1995).
In 1995, drill testing and assaying of the tailings pond reserve was completed, validating proven reserves of 799, 155 tonnes grading 1.74 grams per tonne gold (George Cross News Letter No.37 (February 21), 1996).
In 1995, with partial support from the Explore B.C. Program, Athabaska Gold Resources Ltd. undertook an aggressive exploration program consisting of 7010 metres of underground diamond drilling in 92 holes, 50 metres of trenching and 280 metres of tunnelling. This work demonstrated that mineralization continues at least to 11,100N on the 875 level. It also discovered a new type of higher grade mineralization hosted by altered Spider Peak Formation volcanics, west of old workings and alongside the Hozameen fault (Explore B.C. Program 95/96 - M130).
Drilling, in 1996, increased the underground resource by 272,100 tonnes for a total underground resource estimate of 1,621,715 tonnes grading 4.42 grams per tonne gold plus an additional tailings resource of 598,620 tonnes grading 1.75 grams per tonne gold (Information Circular 1997-1, page 22).
In 2008, Module Resources prospected the area. In 2012, New Carolin Gold completed a program of airborne magnetic and radiometric surveys, totalling 759 line-kilometres, and 12 diamond drill holes, totalling 1400 metres. Also, at this time, the 900-level portal was re-built and the underground workings were inspected.
At this time, an NI 43-101 compliant inferred mineral resource estimate of 12,352,124 tonnes grading 1.5 grams per tonne with a cut-off grade of 0.5 gram per tonne was released (Assessment Report 34111).