Through placement, Newmont bought 29.2 million commons shares at a price of C9.1c (US6.9c) each, with the total US$2 million including an initial advance of $250,000 announced in June.
At the time, Orosur had not named Newmont, only describing the investor that had acquired a 2.97% stake in the company for $250,000 as a "sophisticated international mining company".
The two companies have also signed an exploration agreement with venture option for the Anzá project in Antioquia, Colombia.
The three-phase earn-in agreement will allow Newmont to earn up to 75% interest in the project by spending at least $30 million over 12 years, completing a feasibility study and making cash payments to Orosur of $4 million over the first two phases.
The first phase allows Newmont to earn a 51% interest by spending $10 million over four years and paying Orosur $2 million.
In the second four-year phase, it will earn another 14% interest in Anzá by funding $20 million, completing a compliant pre-feasibility study and paying Orosur $2 million.
Newmont can elect to earn an additional 10% ownership during the third and final four year period by finishing a feasibility study.
If, after the 12 years, Orosur elects for Newmont to solely fund all expenditure until commercial production starts, Newmont's ownership will increase to 80%.
Then, once Anzá starts production, Orosur will begin contributing funds for adopted programs and budgets in proportion to its ownership interest or face penalties.
Orosur had a disappointing first half of 2018, with its production and finances down and it having to place its San Gregorio mine in Uruguay on care and maintenance and the operating subsidiary into voluntary creditor protection.
Orosur CEO Ignacio Salazar said the company was pleased to be partnering with Newmont, which was known for its "exploration track record, proprietary technology, financial strength, and its focus on leading in safety, social and environmental responsibility".
He said the placement and earn-in agreement strengthened Orosur's cash position and providing a well-structured deal to advance the Anzá project.
Neither companies had opened for trading Monday morning on their main listings, although on AIM, Orosur shares were up a whopping 212.9% to 5.63p (US7.3c).