Vassilios Carellas, on Thursday, bought 2,644,017 Ortac shares at an average price of 0.2531p a share, the firm said, taking his interest to 1.53%.
Shares in the firm were lifted 3.92% to 0.265p.
Last month, a pre-feasibility study (PFS) of the firm's Šturec gold and silver project in Slovakia revealed it has “good economic viability”.
It said the project has a net present value (NPV) of US$195mln (post-tax NPV of US$145mln) and an internal rate of return (IRR) of 30% at US$1,343 per ounce of gold equivalent.
The project has a projected lifespan of 11 years with average annual production tipped to hit 71,000 ounces of gold equivalent.