Caribou Dome Copper Project, Alaska

1. Location and Access

The Caribou Dome Copper Project comprises 202 mineral claims covering 26,366 acres (~106.7km2). The Project is located approximately 250km northeast of Anchorage in the Clearwater Mountains of Alaska, USA (see Figure 1). The Project is readily accessible by road. The Denali Highway passes within 20 kilometres of the Project and from there a purpose built road provides direct access to the underground workings at the Project.

Figure 1. Location of the Caribou Dome Copper Project in Alaska, USA.

The Anchorage-Fairbanks railway line is located approximately 100 kilometres west of the Project. In the event copper concentrate (or metal) is produced at the Project, it could be readily transported by road to the railway at Cantwell for shipment from the ports of Anchorage, Seaward or Port Mackenzie.

2. History

Copper mineralisation was first discovered at the Caribou Dome Copper Project in 1963. The vast majority of exploration was undertaken at the Project between 1964 and 1970. Nine lenses of outcropping mineralisation were delineated over approximately 750 metres of strike. Despite this virtually all work was focused on three of these lenses (Lenses 4, 5 and 6; see Figure 2), with a view to developing a small high-grade underground mine. Approximately 1,000 metres of underground workings were installed on two levels (an adit and a decline). 6,024 metres of diamond drilling (43 diamond core holes drilled from surface and 48 diamond core holes drilled from underground) was completed together with 3,282 metres of underground percussion drilling.

Figure 2. Location of the nine lenses of mineralisation delineated at surface at the Caribou Dome Copper Project to date, together with surface traces of diamond drill holes and underground development.

Exceptional results were returned from drilling, including:

    • 18.1m at 9.34% copper from 22.7m (DH9)
    • 18.4m at 6.25% copper from 31.4m (DH39)
    • 15.4m at 7.01% copper (DH93U)
    • 13.1m at 7.20% copper from 15.8m (DH40)
    • 11.0m at 8.20% copper from 29.0m (DH41)
    • 10.4m at 7.94% copper from 14.0m (DH37)
    • 12.8m at 5.78% copper (DH51U)
    • 13.0m at 4.94% copper (DH91U)
    • 9.1m at 6.97% copper from 28.7m (DH43)
    • 10.2m at 6.23% copper from 46.6m (DH32)
    • 12.2m at 5.04% copper from27.1m (DH32)
    • 10.7m at 4.99% copper from 18.0m (DH15)
    • 10.2m at 4.96% copper (DH70U)
    • 8.3m at 6.07% copper from 77.7m (DH44)

The cross-section in Figure 3 (through Lenses 4 and 6) and the long-section in Figure 4 (through Lenses 5 and 6) illustrate that mineralisation is predominantly comprised of sub-vertical lenses of good thickness.

Drilling is yet to constrain the extents of mineralisation at any of the known lenses.

Figure 3. Cross section through mineralised lenses 4 and 6 at the Caribou Dome Copper Project, including select drilling results.

Figure 4. Longitudinal section through mineralised lenses 5 and 6 at the Caribou Dome Copper Project, including select drilling results.

The only significant work undertaken at the Project since 1970 comprised:

  • drilling three diamond core holes from surface in 1977 (for a total of only 120 metres);
  • drilling another three surface diamond core holes in 1999 (this time for a total of 744 metres);
  • collection of a 225kg bulk sample for metallurgical testwork in 2008;
  • drilling two diamond core holes from surface in 2009 (621 metres); and
  • drilling nine shallow diamond core holes in 2011 to begin evaluation of Lenses 7 and 9, for a total of 794 metres. Copper sulphide mineralisation was intersected in six of these nine holes, with results including 4.9 metres at 3.36% copper.

A total of 112 diamond core holes have been drilled from surface and underground, for 8,360 metres (see Table 1).

 

Diamond

Percussion

 

Surface

Underground

   

Date

No. Holes

Metres

No. Holes

Metres

No. Holes

Metres

1964

7

465

       

1965

14

857

       

1966

17

877

       

1967

6

367

       

1969

2

196

7

947

   

1970

   

42

2,374

134

3,283

1977

3

120

       

1999

3

744

       

2009

2

621

       

2011

9

794

       

Totals

63

5,041

49

3,321

134

3,283

Table 1. Summary of previous drilling completed at the Caribou Dome Copper Project.

3. Geology

Copper mineralisation at the Caribou Dome Project is predominantly stratiform. Historically nine outcropping lenses of high-grade pyrite-chalcopyrite mineralisation were delineated over approximately 750 metres of strike. These are predominantly located in argillites at an interface with a sequence of volcanic rocks (see Figure 5). Interbedded limestones appear to have had an important control on the location of mineralisation.

Figure 5. Geology around the nine known lenses of mineralisation at the Caribou Dome Copper Project, together with surface traces of underground development.

Regionally the prospective contact between volcanic and sedimentary rocks has been mapped to extend over at least 15km within the Project area (see Figure 6). Considerable copper mineralisation has been mapped along this contact throughout the Project area. This is a very encouraging sign, as the known mineralisation could comprise part of a substantially larger mineralised system.

Figure 6. Regional geology at the Caribou Dome Copper Project, showing the argillite sequence that hosts the known mineralisation extends for more than 15km within the Project area.

4. Metallurgy

During 2008 a 225kg bulk sample was collected from the Project for metallurgical testwork and sent to G&T Metallurgical Services in Kamloops, Canada. The grade of this sample averaged 6.7% copper. Using flotation and GalvanoxTM leaching, recoveries of 91.7% of the copper were achieved. These results were deemed “encouraging for the project”. Further testwork was recommended.  

5. Exploration Potential

During early 2015 a technical review of historic exploration data was undertaken to characterise the surface expression of known mineralisation to:

  • Prioritise targets for follow-up; and
  • Plan suitable exploration programs to optimally delineate additional high-grade mineralisation.

5.1 Results of Technical Review

The Caribou Dome Deposit gives rise to a strong stream sediment anomaly of 2,950ppm (0.29%) copper. Despite this, and the presence of outcrops of sediment-hosted copper mineralisation over >15km of strike within the Project area, stream-sediment sampling has not been systematically undertaken across the Project area.

Systematic soil sampling has only been undertaken along approximately 3.5km of the prospective stratigraphic contact. Much of this data was collected on lines spaced approximately 500 metres apart, while a 1,000m x 400m area was sampled on lines spaced ~125 metres apart. Extensive copper anomalism is evident throughout the sampled area, with assays to 1.65% copper returned from samples taken adjacent to Lense 6 (see Figure 7).

Figure 7. Image of copper assay results in historic soil sample data together with location of known mineralisation and some of the higher priority targets at the Caribou Dome Copper Project.

Induced polarisation (IP) data were collected in 1999 on a 1,000m x 400m grid over the known mineralisation (see Figure 7). Coventry recently reprocessed these data, and despite the limited depth of penetration of this survey, distinct anomalies are evident over known mineralisation (which comprises semi-massive to massive sulphides), and, very significantly, elsewhere (see Figures 8, 9 and 10).

Figure 8. Pseudo-depth section 9800 of IP data acquired over Lenses 4 and 6 – illustrating that the known mineralisation gives rise to distinct, strong, IP responses. The location of previous drill holes is illustrated, together with histograms showing the grade of copper mineralisation intersected in drilling.

As part of the technical review, multiple high priority exploration targets were identified and prioritised (see below). These comprise a pipeline of targets, from drill-ready; to high-tenor soil anomalies that warrant further infill sampling; to corridors where reconnaissance stream and/or soil sampling and/or geophysical surveys should be undertaken for the first time. Some of these targets are described in more detail below.

5.2          Targets for Further Investigation in the Near-Term

5.2.1 Drill-Ready Targets

Multiple drill-ready targets have been identified within the 750 metre corridor where all drilling has been undertaken previously. These include:

  1. The outcropping mineralisation at Lense 2. This target has multiple favourable characteristics, including:
    • Outcropping mineralisation is up to 15 metres wide and extends for >200 metres. This compares favourably with the thickness and strike of mineralisation at Lense 6 (up to 15 metres thick and extends over ~200 metres of strike), which is the largest of the known lenses.
    • A very strong IP anomaly coincides with the outcropping mineralisation (see Figure 3). This extends over at least 350 metres of strike, including 100 metres to the northwest beyond the limits of the mapped outcrop.
    • A 600 metre long magnetic anomaly coincides with outcropping mineralisation, and may arise from extensions of the mineralisation.
    • Soil anomalism extends for several hundred metres to the NW of the outcropping mineralisation, coincident with both the IP and magnetic anomalism (see Figure 7).
    • Previously only one hole has been drilled to evaluate Lense 2. Economic mineralisation was not encountered in this hole, but it was subsequently determined that the hole was not drilled where intended.

Figure 9.  Pseudo-depth section 9000 of IP data acquired over Lense 2 showing a very strong, 350 metre long IP anomaly that coincides with outcropping mineralisation that is up to 15 metres wide that is yet to be tested with drilling. 
  1. The “Caribou South Target” – is a 400m long soil geochemistry anomaly where very high assays, up to 0.63% copper, have been returned from soil samples. It coincides with an intense IP anomaly (see Figure 10). This corridor is located immediately east of Lense 6 (see Figure 7) and has never been drilled.

Figure 10. Pseudo-depth section 10600 of IP data acquired over Lenses 3 and 8 showing a very strong, 400 metre long IP anomaly that coincides with soil anomalism up to 0.63% copper that is yet to be tested with drilling.
  1. Depth and strike extensions of mineralisation at all nine known lenses. At all nine lenses, mineralisation remains open at depth and along strike.

An example of such a target is the shallow western extension of Lense 5, where the westernmost shallow drilling intercepts are 9.1m at 7.0% copper and 10.7m at 5.0% copper (from 28.7 and 18.0 metres respectively) (see Figure 4). Mineralisation remains open to the west and will be followed up in the forthcoming field season.

Similarly the mineralisation at Lense 6 remains open at depth, with the deepest intersection comprising 15.4m at 7.0% copper (in a hole drilled from underground) approximately 250 metres below surface (see Figure 4). The extension of the thick, high-grade mineralisation within Lense 6, at depth, is another high-priority exploration target. 

5.2.2 Soil Anomaly Targets

Four high-priority and three second order targets have been identified in the broad-spaced soil data (see Figure 7):

  • The Javelin Target – This is a >600m long corridor where assay results up to 920ppm copper have been returned from previous broad-spaced soil sampling. This is the highest tenor of copper in soils outside the 750m long corridor that has been subject to drilling. Minimal additional technical information is available from this area.
  • The Menel Target – This is a >1,000m long corridor where copper-rich rock samples (with assays up to 9.1% copper), historic copper occurrences and mapped outcropping gossans coincide with a strong coherent soil anomaly (up to 370 ppm copper) that extends immediately along strike from, and to the east of the outcropping mineralisation at Lenses 7 and 9. Copper in float samples have also been identified down-slope of the target corridor (see Figure 11). Historic reports suggest that tundra in this area may cover/mask geochemical anomalies arising from mineralised bedrock. Significantly, a very strong IP anomaly on the eastern-most line of the previous survey coincides with the western end of the Menel Target area (directly below where the float sample that assayed 9.1% copper was taken). This corridor may comprise the eastern extension of the nine mineralised lenses.

Figure 11. Image of anomalous broadly-spaced soil geochemistry data (copper) over the Menel Target area, extending immediately to the ENE of the nine known lenses of mineralisation at the Caribou Dome Copper Project, together with other associated indications of mineralisation.
  • The Spartan Target is a >1,000m long, very broadly sampled, corridor of anomalous soil geochemistry (up to 0.21% copper in soils) that coincides with the western extension of mapped argillites and limestones (the rocks that host the copper mineralisation at the nine known lenses). Massive sulphides have reportedly been identified in outcrop in the upper reaches of this target area, but have never subsequently been evaluated. This corridor could comprise the western extension of the nine mineralised lenses (see Figure 7).
  • The Leon Target – Reconnaissance mapping and sampling during late 2014 resulted in the identification of extensive outcropping limestone together with copper mineralisation that coincides with regional scale geochemical anomalism in this area. Assays from recent rock samples collected there returned up to 0.35% copper.

All these targets will be followed up with infill soil sampling programs. Surface geophysical surveys will then be undertaken as appropriate, in advance of drilling.

The second order soil anomaly targets (see Figure 7) can also be readily followed up with infill soil sampling at low cost as part of a larger soil sampling program. This will be undertaken to help determine whether additional quality targets can be defined. 

5.2.3 Reconnaissance Targets

The stratigraphic horizon that hosts the sediment hosted copper mineralisation extends at least 15km within the Project area. Alaskan government mineral occurrence databases include a historic occurrence (MH035) of outcropping sediment-hosted copper mineralisation near the north eastern boundary of the Project area, where assay results up to 0.62% copper have been reported (see Figure 6). This confirms that there is potential to discover additional mineralisation across the entire Project.

Previously stream sediment sampling proved pivotal in the discovery of the deposits at Caribou Dome. Surprisingly however, there are no records of stream sampling being used systematically across the entire Project area.

Accordingly a suitable stream sampling program will be undertaken to rapidly assess the potential of delineating additional targets elsewhere on the Project along the 15 kilometres of the prospective stratigraphic horizon.  

6. Forward Work Program

A strong pipeline of exploration targets has been prioritised across the entire Project, including:

  • Extensive outcropping mineralisation at Lense 2;
  • The very strong coincident soil and IP anomalies at the Caribou South Target;
  • Strike and depth extensions of mineralisation at all nine known lenses;
  • The Javelin Target, where anomalous copper in soils results up to 920ppm copper have been returned;
  • The Menel Target where assays to 9.1% copper have been returned from rock samples; and
  • The Spartan Target where coincident soil and IP anomalies might reflect the extension of the known mineralisation to the west.  

Coventry intends advancing the highest priority targets during 2015 with a combination of reconnaissance stream sampling, infill soil sampling and ground EM and CSAMT surveys (see Figure 6). This will facilitate refinement of targets in preparation for a drilling program.

7. Analogous Deposits

The sediment-hosted copper mineralisation at the Caribou Dome Project is similar to other sediment hosted deposits around the World. Within Alaska the renowned Kennecott Copper Deposit, where approximately 4.63 million tons of ore were mined at a grade of 13% copper between 1911 and 1938, has multiple similarities, with mineralisation being of the same style, age and hosted by identical lithologies.

The White Pine Mine in Michigan is another similar deposit. Here, 198 million tons of ore were mined at a grade of 1.14% copper.

Other analogies include the Mt Isa Copper Deposit in Australia, and the deposits of the Zambian Copper Belt in Africa.

These examples demonstrate the potential for deposits of this type to be large and/or of high grade.

8. Conceptual Exploration Target

Given the grade and thickness of mineralisation delineated to date and the abundance of additional untested and/or poorly tested targets within the Project area, the Company believes there is extremely good potential to delineate a substantial economically viable high-grade copper resource at the Project. Initially the Company will target the delineation of 5-10 million tonnes of mineralisation at 2.5-4.0% copper.

Notwithstanding this initial target, the Company believes there is potential to discover a very large copper deposit within the Project area.

Based on the information disclosed, the Company considers there to be a reasonable basis for the stated exploration target. Further drilling programs will be required to delineate this target, including additional drilling to confirm historic drilling results as well as further exploration at some of the targets already delineated at the Project.

It is noted that the potential quantity and grade of these targets are conceptual in nature and there has been insufficient exploration completed to define a mineral resource (in accordance with Canadian National Instrument 43-101 or the 2012 JORC Code) and it is uncertain if further exploration will result in the target being delineated as a mineral resource.