Name of the Project
Windfall gold project.

Location
Abitibi greenstone belt, Québec, Canada.

Project Owner/s
Osisko Mining.

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 three principal areas – Lynx, Main and Underdog.

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 comprise primary crushing, followed by a grinding circuit consisting of a semiautogenous grinding mill (in close circuit with a pebble crusher) and ball mill (in close 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 project has an estimated 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 2 years from the start of production.

Capital Expenditure
The project will require capital expenditure of $607-million.

Planned Start/End Date
Process plant construction is planned for the second quarter of 2024, with ramp-up beginning in the third quarter of 2025.

Latest Developments
Gold Fields has partnered with Osisko Mining to develop and mine the Windfall project.

The agreement between the companies, with the joint venture (JV) to be called the Windfall Mining Group, involves Gold Fields’ acquiring a 50% interest in Windfall through a wholly owned Canadian subsidiary.

Gold Fields has paid a $220-million, or C$300-million, cash consideration on signing, and will pay another $220-million on the issuance of key permits by the Canadian authorities for the project to be built and operated.

Osisko and Gold Fields will each incur 50% of the interim and construction capital expenditures on the project, and jointly undertake management and operatorship of the project.

Having conducted extensive due diligence, management interaction and site visits for more than a year, Gold Fields believes that the Windfall project is on track to become a high-quality, low-cost underground gold mine with a relatively small surface footprint and considerable growth prospects along strike and down plunge, well beyond delineated mineral reserves and the current ten year projected mine life.

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, 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 and 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.