Name of the Project
Windfall gold project.

Location
Abitibi greenstone belt, Québec, Canada.

Project Owner/s
Osisko Mining and Gold Fields.

Gold Fields reported on August 12, 2024, that it will buy Canadian firm Osisko Mining for C$2.16-billion in an all-cash deal that will consolidate Gold Fields’ 50% partnership stake in the Windfall project into full ownership and control.

The acquisition is consistent with Gold Fields’ strategy to improve the quality of its portfolio through investment in high-quality, long-life assets with a low carbon footprint.

Full ownership of Windfall enables Gold Fields to streamline decision-making and increase flexibility with respect to the development and subsequent operation of Windfall.

Gold Fields has said that the transaction could be "rapidly implemented" and is expected to close in the fourth quarter. The deal is subject to the approval of at least two‐thirds of the votes cast by Osisko shareholders, as well as a simple majority of the votes cast by Osisko shareholders, excluding certain related parties, at a shareholder meeting that will be held in October.

Both companies’ boards of directors have approved and are supportive of the transaction, with Osisko directors recommending that shareholders vote in favour of the transaction.

Osisko CEO John Burzynski has said the company is pleased to be handing over the reins to Gold Fields.

Project Description
The Windfall deposit is currently one of the highest-grade resource-stage gold projects in Canada and has world-class scale. Mineralisation occurs in the Lynx, Main and Underdog areas.

The project is expected to produce 306 000 oz/y of gold, with peak production of 374 000 oz of gold expected in year two.

The process flowsheet comprises primary crushing, followed by a grinding circuit consisting of a semiautogenous grinding mill (in closed circuit with a pebble crusher) and ball mill (in closed circuit with cyclones – semiautogenous ball mill crusher circuit). A gravity circuit followed by intensive leaching recovers coarse gold from the cyclone underflow, while the cyclone overflow is treated in a carbon-in-pulp circuit.

Gold is recovered in an adsorption-desorption-reactivation circuit, followed by electrowinning  cells. The tailings filtration plant is located less than 1 km south-east from the Windfall process plant building.

The plant consists of pressure filters and their ancillaries, paste mixers, paste pumps, a clarifier, a binder storage and dosing system, as well as a dry-stack storage facility. The totality of the process tailings is filtered. Based on the mine plan, about 39% of the tailings are transformed in paste backfill. The remaining tailings are disposed of as dry stack.

Potential Job Creation
The project is expected to create more than 1 100 direct and indirect jobs during construction and more than 670 direct permanent jobs during operation.

Net Present Value/Internal Rate of Return
The 2022 feasibility estimates an after-tax net present value of C$1.17-billion and an internal rate of return of 33.8%, with an after-tax payback of two years from the start of production.

Capital Expenditure
Total investment in the project to date is more than C$1-billion.

Planned Start/End Date
Gold Fields is expected to have the environmental-impact assessment approved in the first quarter of 2025, with a final investment decision by midyear. With an 18-month build programme, first gold could be delivered by the end of the fourth quarter of 2026 or early 2027.

Latest Developments
Development of Windfall is well advanced. 

Gold Fields has indicated that the life extension upside – through expected resource conversion and on-site exploration, together with significant regional exploration potential in the highly prospective Urban Barry and Quévillon district exploration camps – will provide a range of additional opportunities for the group’s pipeline. 

The near-mine, exploration upside is further enhanced by Osisko’s joint venture with Bonterra Resources, which secures a 70% interest over an additional 225 km2 of prospective exploration ground adjacent to the Windfall deposit.

Key Contracts, Suppliers and Consultants
A2GC (rock mass characterisation and rock engineering, in support of the underground mine design); BBA Inc (historical data review; current and historical geology, exploration and drilling; sample preparation, quality assurance and control, and data verification; geological modelling and mineral resource estimate; metallurgical testwork management and analysis, crusher and process plant mass and water balance; crusher and process plant design, capital costs and operating costs; electrical infrastructure design and costs; information technology and communications infrastructure design and costs; integrated remote operations centre design and costs; general and administration operating costs; financial analysis and overall NI 43-101 integration); Entech Mining (underground mine design, underground infrastructure, ventilation, production scheduling, underground capital costs and operating costs); Golder Associates (waste rock, tailings and ore geochemical characterisation; surface tailings management facility designs and costs; site-wide water balance; hydrogeology and groundwater quality input into environmental studies; hydrogeology input for underground mine design); WSP Canada (design and costs of surface infrastructure for Windfall site, site utilities, on-site roads and pads, site infrastructure electrical distribution, surface mineralised material, waste rock, overburden and topsoil management facility, surface water management infrastructure, tailings filtration plant and dry tailings storage/handling, as well as underground paste backfill distribution, infrastructure design and costs); GCM Consultants (water treatment design, capital and operating costs).

Contact Details for Project Information
Osisko Mining, tel +1 416 363 8653 or emailinfo@osiskomining.com.