Orsu executive chairman Sergey Kurzin said he was pleased with the "spirit of cooperation and confidence" during the Sergeevskoe negotiations.
Orsu had acquired a 30% stake in the Sergeevskoe gold project in May and was going to buy the remaining 70% stake for €700 (US$811) and US$420,000 cash, provided it sold its Karchiga project in Kazakhstan before September 30 for $7.75 million.
After an initial Karchiga sale fell through in February, Orsu was able to sell its 94.75% interest for proceeds of $5.9 million last month, triggering negotiations for an amended Russian agreement.
Under the new terms, Orsu has acquired 90% of Sergeevskoe for €600 and $420,000 cash and an NSR royalty of 0.75% capped at $7.5 million.
Orsu will carry the sellers' 10% interest until completion of a definitive feasibility study, when the 10% interest will become a participating interest subject to dilution.
Kurzin said initial trenching results from Sergeevskoe in June indicated the presence of "well-mineralised high-grade gold pods," with highlights including 1m at 335g/t within 8m at 48.56g/t.
More exploration results are due within weeks.
Orsu shares rose 10% following the announcement.