The company closed the placement, priced at $2.45 per share and $3.10 per flow-through share, last week.
"The offering was subscribed to by, among others, a single institutional investor, Mr Pierre Lassonde and Trinity Capital Partners Corporation and Affiliates," Marathon said.
Highlights from a feasibility study in March had outlined a 13-year mine at Valentine with peak average annual production of 173,000 ounces, targeting first gold in October 2023.
Initial capex was put at US$229 million, after-tax NPV5 at $651 million and IRR at 42% using a $1,750/oz gold price.
The study did not incorporate the Berry zone, where drilling results earlier this month included 101m at 1.96g/t gold.
Marathon has expanded the Berry drilling programme to 120,000m by mid-2022, to establish the resource potential "over its full 1.5km-long extent".
The company is working to de-risk construction at Valentine and is planning to finance the project through a mix of debt and equity.
Marathon Gold (TSX: MOZ) shares have ranged from C$1.50-$3.35 over the past year and closed down about 1% on Friday to $2.98, capitalising it about $639 million (US$529 million).
