Superior Lake Zn-Cu Project
The Superior Lake Zinc and Copper Project is located approximately 200km’s east of Thunder Bay in the province of Ontario, Canada.
The Project covers 175km² and consists of two deposits – Winston Lake and Pick Lake. The Project is a high-grade Zinc and Copper deposit with a 43-101 Indicated resource of 2.35 Mt at 17.9% Zn, 0.8% Cu, 0.4g/t Au and 33.6 g/t Ag. (Pick Lake 43-101 published Jan 2021).
The Project is close to production, with most Capex-heavy infrastructure in place. The Project is currently in the Advanced Exploration phase with the permitting process to de-water underground workings underway
Step 1 : Pick Claims to Mining Lease
Q3 / 2022
Step 2 : Obtain Advanced Exploration and Dewatering Permit
H2 / 2022
Step 3 : Sign the IBA with FN
Q4 / 2022
Step 4 : Commence Dewatering
Step 5 : Construction and Advance Development
H2 / 2023 - H2 / 2024
Step 6 : Start Production
Q4 / 2024
The Winston Deposit was mined between 1988 and 1998, and produced approximately 3.3 Mt at 14% Zn, 1% Cu, 1g/t Au and 30g/t Ag. The mine closed in 1998 due to low Zinc prices. Winston Lake Mine has produced 900 Mlbs of Zn, 54 Mlbs of Cu, 1,172 kHz of Ag and 51 coz Au over the course of its 9-year production.
The Zn recovery rates varied from 93-97% with 50-52% Concentrate Grades. Pick Lake recoveries were 97% Zn and 54% concentrate in the test stope that was mined during Inmet.
The Pick and Winston Lake deposits are defined as VMS deposits. Modern analogues include “black smoker” polymetallic base-precious metal sulphide deposits seen on the ocean floor.
Within this family of deposits, the common denominator is that they are associated with sub-marine volcanism.
Copper-rich deposits are generally associated with more mafic, deeper, “hotter” systems, while zinc-rich deposits are associated with more felsic, shallower and “cooler” systems.
VMS deposits differ in terms of size, metal ratios, metal grades, metal zonation, morphology, and style of mineralization. An idealized VMS deposit is shown in Image 1.
The Pick and Winston Lake deposits are characterised as being very rich in zinc and deficient in other metals, aside from minor copper and gold. They are also associated with pyrrhotite, not commonly seen with sphalerite but fortuitous in this case as it has a very pronounced geophysical signature which led to the discovery of both deposits. VMS deposits are never as simple as depicted in Image 1 above.
Hydrothermal fluids circulating through the volcanic sequence alter the mineralogy of the host rocks, often in a recognizable, zoned fashion, but not always, and subsequent structural events can deform the sequence to an almost unrecognizable extent.
This is the case at the Pick Lake deposit where typical “footwall alteration” was documented stratigraphically above, not below, the deposit; this is less the case at Winston Lake where alteration was documented in its normal position.
Later metamorphism can exacerbate this effect even further by changing the already altered original mineral assemblages for a second time. A simplified series of sections across the Project area depicting the respective locations of the various known deposits and the associated hydrothermal alteration is highlighted below.
As neither the Pick nor Winston Lake deposits were exposed at surface, direct observation of the features summarised above was not possible. Identification of these deposits and potential new deposits must therefore rely upon indirect methods that are based upon recognising the geochemical and geophysical expression of these features.
The Project has the substantial infrastructure in place which allows it to fast track the Restart Pick Lake Mine at a substantially reduced cost and development timeline compared to the development of a greenfield.
The current infrastructure in place at the Project is set out below:
- 20km all-weather access road
- 20km 115kV transmission line
- ~2km transmission line from the Winston to Pick Lake
- Electrical Substations including a 115kV to 44kV transformer
- 650m Winston Shaft
- 650m Pick Internal Shaft
- 2.5km development drive between Winston and Pick Lake deposits
- The tailings dam with design capacity to incorporate the Pick
- Lake resources
- Fresh water dam
- Four ventilation shafts
- Backfill raises
- Underground ramps and development on multiple levels in both Pick and Winston deposits
- Over 180,000m of surface and underground drilling
- 16km underground development to the remaining ore deposit
Stoping of the ore at Winston Lake initially planned to use a mechanized cut and fill method, however this was changed to the more productive methods of mechanized AVOCA stoping and where no development existed, Alimak stopping. Access on ore was achieved through a series of sublevels developed at 20m vertical intervals connected via a hanging wall ramp (gradient of 1 in 7) at a 4m x 4m profile. Once the ore was extracted from the stope, unconsolidated rock-fill material was then placed into the mined-out stope.
Ore mined from Pick Lake Deposit was transported via a rail system on the 615-access drive where it along with ore from Winston was hoisted to the surface via the Winston Shaft.
Dilution from past mining was caused through a number of factors:
- In Winston Lake dilution was impacted by the size of ore drives, a chert intrusion along certain parts of the hanging wall, and the use of the AVOCA mining method.
- Development of new ground support techniques, such as the use of cable bolting to minimize the hanging wall failures occurring. The research and development work completed at Winston on cable bolting was leading edge at the time and is now standard procedure in many underground mining methods to minimize dilution.
- The Alimak mining method used at both Pick and Winston, where there was minimal access development resulted in dilution occurring due to no backfill being used. This lack of access prevented Inmet from backfilling the mined out areas as a result hanging wall dilution occurred. It was in this context that Inmet recognized these impacts on stoping and performed a test stope in Lower Pick.
In 1998, Inmet carried out extensive studies on alternative mining methods to limit the effect of dilution and costs in the prevailing low-price zinc environment at the time.
As part of this strategy, Inmet completed a successful test using the longhole stoping method on the 1045 level of Pick Lake (Figure 8 & 9). The 1045 test stope had a strike length of 25m, an average width of 2.5m and a height of 15.5m.
On completion of the stope, a cavity monitoring survey measured the void to calculate dilution from the hanging wall and footwall. As part of this test, ground monitoring was installed prior to mining to measure hanging wall movement. After 20 days no measured movement of the hanging wall was recorded (no fill was placed in the stope). At the successful completion of the test stope, dilution was calculated at 18% however, prevailing zinc prices at the time meant that the Project was not viable until there was a substantial and sustained increase in the zinc price and the decision was made to permanently close the operation.
Uses for Zinc (Zn)
Zinc is a naturally occurring metal found in nature in conjunction with lead in sulfide ores and the fourth most used metal after iron, aluminium and copper. Zinc is usually separated from other metals during the refining process. Zinc is widely used in industry due to its corrosion resistant properties and easy application.
Zinc is popularly used as a protective coating for iron and steel – effective in protecting them from corroding in the water, soil and atmosphere. This is made possible because zinc reacts preferentially to iron in most environments to form what is known as protective layers of carbonate, oxides or other similar zinc reaction to products that are resistant to atmospheric corrosion. Furthermore, in the event that the coating of zinc is scratched, it will still corrode before the iron – Zinc can be thought to be a sacrificial metal.
There are several methods of coating iron and steel with zinc. One of which is hot dip galvanising – where the material is soaked in a bath of molten zinc. Also, steel is commonly galvanised by uncoiling rolled steel sheet and passing them through a bath of molten zinc. This process is very useful in the production of several white goods (washing machines, refrigerators) and car frames.
Similarly, Zinc alloy anodes are crucial in both ship and marine applications as it is commonly applied to steel where they are allowed to corrode in preference to the steel – they are subsequently replaced when it must have completely corroded.
Zinc is also a constituent of ordinary dry cell battery which is the preferred battery option for devices that consume minimal power like remote controls. Brass, an alloy consisting of zinc and copper is also used to make both functional and decorative products like marine fittings, door handles, screw fixings and plumbing components.
Owing to heavy demand and dwindling reserves, there is said to be a supply imbalance that is approaching an all-time low. The price of Zinc has surged by more than 90% since January 2016, and it even reached a ten-year peak in August 2017. This zinc supply imbalance is predicted to still continue as some very key mines in China and Ireland have announced their closure.
The high demand for Zinc is said to be primarily driven by huge investment and demand for infrastructure across the globe. Demand for electronics, automobiles, consumer goods and raw materials for construction are soaring. One metal that is common to them all is Zinc.
The Demand for zinc has never been as high as it is today. High demand for consumer goods and infrastructure are some of the major forces driving demand for the fourth most used metal.
2021 October Feasibility Study