Premier said it had accepted Arc's offer of 6.13 million Arc shares, or about 1.9% of Arc's enlarged share capital.
When the offer closes May 10, the company, formerly known as Ortac Resources, will own 95.9% of Casa, which holds a 71.25% stake in the 1.57 million ounce inferred resource Akyanga gold deposit in the Democratic Republic of Congo.
Arc started a comprehensive soil sampling programme at Akyanga in February, which is testing the potential mineralised zones between the Akyanga deposit and the Akyanga East prospect.
The company's nomad and broker SP Angel said the move to increase its Casa stake highlighted Arc's new African focus.