Overview
Stage | Preliminary Economic Assessment |
Mine Type | Open Pit |
Commodities |
|
Mining Method |
|
Processing |
- Gravity separation
- Calcining
- Flotation
- Concentrate leach
- Carbon in leach (CIL)
- Elution
- Solvent Extraction & Electrowinning
- Cyanide (reagent)
|
Mine Life | 25 years (as of Jan 1, 2017) |
Latest News | Skeena Completes Sale of GJ to Newcrest for C$7.5M May 1, 2020 |
Source:
p. 4
Skeena Resources Limited holds a 100% interest in the Spectrum property and an option to acquire a 100% interest in the adjoining GJ property.
Deposit Type
- Porphyry
- Vein / narrow vein
Summary:
The Project Area hosts two principal styles of mineralization that have been the target of past and current exploration. The first and older style is porphyry Cu-Au mineralization related to intrusion and alteration by Late Triassic alkalic to sub-alkalic diorite to monzonite dykes and stocks exemplified by the Central Zone and Donnelly Deposit. The second comprises later, structurallyhosted and high-grade gold zones associated with shearing, fracture zones and quartz-carbonate vein/fault controlled pyrite, arsenopyrite, sphalerite, galena and chalcopyrite hosted by altered volcanic units and monzonite dykes.
Porphyry-Style Mineralization - Central Zone
Porphyry-style Cu-Au mineralization occurs within a north-south trending, moderately west dipping and fault-bounded structural panel of Triassic Stuhini volcaniclastic lithologies intruded by syn- to late-mineral monzonite dykes. Porphyry- style mineralization has been defined over a strike length of 1,000 m, with widths of 70 m to 200 m, it has been tested to 400 m downdip and it remains open along strike and downdip.
Mineralization occurs as quartz-pyrite-chalcopyrite with or without magnetite veinlets, stockworks, fracture fills and fine grained disseminations of pyrite and chalcopyrite. Metal grades appear to be directly related to the abundance of quartz-sulphide-magnetite vein development.
Porphyry-Style Mineralization - Donnelly Deposit
Of the many porphyry Cu-Au prospects located on the GJ claims block, the most advanced is an area measuring 3.5 km east-west and north-south where disseminated, fracture, quartz vein and quartz stockwork-controlled pyrite with variable chalcopyrite, rare bornite and trace molybdenite mineralization containing elevated gold values occurs. This area contains the Donnelly Deposit, the North Donnelly deposit and the GJ and North zones.
Typically, the best chalcopyrite mineralization occurs where pyrite is weaker and IP chargeability responses are moderate, which generally occurs on the flanks of more intense chargeability anomalies. Secondary magnetite, generally associated with chalcopyrite, is found as disseminations, irregular clots, in veins with K- feldspar with or without chlorite and/or epidote and/or as fillings in single or sheeted fractures that are one to three millimetres thick and millimetres to 10 cm apart. Exceptions to this association (the Donnelly Deposit and portions of the North zone) appear to be where magnetite has been altered to hematite.
Porphyry-Related, Vein-Hosted Mineralization
The second style of mineralization found on the Project Area comprises higher grade gold mineralization that post-dates the porphyry Cu-Au mineralization described above. It is structurally controlled in that it occurs in veins, fracture zones and stockwork crackle zones and as gold- bearing quartz-carbonate-sulphide veinlets and stockworks proximal to faults and shear zones. Petrographic work by Oliver (2016) indicates gold is associated with late fractures/microveinlets in high sulphide veinlets cutting arsenopyrite, which is one of the younger veining events. Gold also occurs as free gold within strongly fractured and strongly chlorite-sericite-calcite-pyrite altered zones with no associated sulphide veining but close associations to coarse grained laths of chlorite and sericite, and only a weak linkage to secondary K-feldspar or quartz. Gold mineralization often shows additional enrichment of Ag, Cu, Pb, Zn, As and Sb.
Summary:
Conventional truck and shovel open pit mining was selected because, overall, it represents the least risk, most sustainable option from both economic and environmental perspectives.
Processing
- Gravity separation
- Calcining
- Flotation
- Concentrate leach
- Carbon in leach (CIL)
- Elution
- Solvent Extraction & Electrowinning
- Cyanide (reagent)
Flow Sheet:
Summary:
During Stage 1, plant feed comprises 100% feed from Donnelly Pit, at a rate of 10,000 tpd, from which gold gravity concentrates are produced for sale in the market. Phase 3 starts in Production Year 12 when plant feed once again comprises 100% feed from Donnelly Pit, but at a rate of 30,000 tpd.
Stage 1 (10,000 tpd)
Processing during Stage 1 will be by a conventional copper/gold porphyry flowsheet, incorporating two stages of crushing and ball milling, followed by rougher flotation, concentrate regrinding and cleaner flotation to produce a pulp containing the final concentrate. A gravity circuit will be incorporated into the grinding circuit. The concentrate will be dewatered by thickening and filtration and loaded into trucks for delivery to Port of Stewart from where it will be shipped to smelters located in the Far East.
The ROM material from Donnelly Pit will be tipped onto a production grizzley that reports direct to a rasebored muckpass. The tipped mat ........

Recoveries & Grades:
Commodity | Parameter | Avg. LOM |
Copper
|
Head Grade, %
| 0.27 |
Gold
|
Head Grade, g/t
| 0.35 |
Silver
|
Head Grade, g/t
| 2.04 |
Projected Production:
Commodity | Units | LOM |
Copper
|
B lbs
| 1 |
Gold
|
M oz
| ......  |
Silver
|
M oz
| ......  |
All production numbers are expressed as payable metal.
Operational Metrics:
Metrics | |
Stripping / waste ratio
| ......  |
Daily milling capacity
| ......  |
Waste tonnes, LOM
| ......  |
Ore tonnes mined, LOM
| ......  |
Total tonnes mined, LOM
| ......  |
Tonnes milled, LOM
| ......  |
* According to 2017 study.
Reserves at January 6, 2017:
Category | Tonnage | Commodity | Contained Metal |
Indicated
|
246.4 Mt
|
Copper
|
1,303 M lbs
|
Indicated
|
246.4 Mt
|
Gold
|
3.08 M oz
|
Indicated
|
246.4 Mt
|
Silver
|
15.67 M oz
|
Inferred
|
58.1 Mt
|
Copper
|
161.5 M lbs
|
Inferred
|
58.1 Mt
|
Gold
|
0.73 M oz
|
Inferred
|
58.1 Mt
|
Silver
|
2.98 M oz
|
Commodity Production Costs:
| Commodity | Units | Average |
Cash costs
|
Copper
|
USD
|
1.37 / lb *†
|
Cash costs
|
Gold
|
USD
|
461.56 / oz *†
|
All-in costs
|
Copper
|
USD
|
1.81 / lb *†
|
All-in costs
|
Gold
|
USD
|
730.97 / oz *†
|
Assumed price
|
Copper
|
USD
|
2.75 / lb *
|
Assumed price
|
Silver
|
USD
|
17.8 / oz *
|
Assumed price
|
Gold
|
USD
|
1.25 / oz *
|
* According to 2017 study / presentation.
† Net of By-Product.
Operating Costs:
| Units | 2017 |
Total operating costs ($/t milled)
|
CAD
| 14.3 * |
* According to 2017 study.
2017 Study Costs and Valuation Metrics :
Metrics | Units | LOM Total |
Pre-Production capital costs
|
$M CAD
|
......
|
Sustaining CapEx
|
$M CAD
|
......
|
Total CapEx
|
$M CAD
|
......
|
After-tax Cash Flow (LOM)
|
$M CAD
|
......
|
Pre-tax NPV @ 8%
|
$M CAD
|
......
|
After-tax NPV @ 8%
|
$M CAD
|
......
|
Pre-tax IRR, %
|
|
......
|
After-tax IRR, %
|
|
......
|
Pre-tax payback period, years
|
|
......
|
After-tax payback period, years
|
|
......
|
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