It follows last month's latest resource update for Windfall, which CEO John Burzynski had said placed it among the best high-grade development projects globally.
The well-funded company said yesterday it had placed an order with leading technology and equipment supply company FLSmidth for a SAG mill and ball mill and ancillaries.
It said the grinding mills had a capacity of processing up to 3,900 tonnes per day based on 92% availability.
"Securing these critical long lead time components of the grinding circuit is an important first step in solidifying detailed engineering for the Windfall plant," Burzynski said.
"We continue to advance all aspects of work on Windfall including our environmental assessment and consultation with our host communities and look forward to additional near-term announcements regarding our infrastructure plans."
The company expected the equipment to be delivered in the second half of 2022.
Installation would follow pending successful receipt of all permits and authorisations.
Windfall has a measured and indicated 6 million tonne resource averaging 9.6g/t gold and 5.9g/t silver, for 1.86 million ounces of gold and 1.15Moz silver. It has an inferred 16.4Mt at 8g/t gold for 4.24Moz and 2.7g/t silver for 1.45Moz.
Osisko closed a C$70 million placement in February at $5.35 per flow-through share for exploration as it aims to complete a further 200,000m of drilling by the third quarter.
This would be followed by another resource update, for a feasibility study.
Its shares (TSX: OSK) have spanned C$1.67-$4.85 over the past year.
They closed up 5.3% yesterday to $2.98, capitalising it at $1.06 billion (US$0.8 billion).