Rockfire Resources PLC (LSE:ROCK) shares fell on Wednesday, after the explorer temporarily suspended drilling in one hole at its Molaoi zinc deposit in Greece after encountering extensive faulting and poor ground conditions.
The small-cap said it stopped drilling hole HMO-009, which is expected to be re-drilled later in the programme.
Chief executive David Price described it as "extremely difficult to drill" and said a rapid decision was made to move on "for the sake of increased drilling productivity".
Rockfire subsequently moved the drill rig to another hole, HMO-010, where it said it had already intersected sulphide mineralisation at 44.20m.
Better ground conditions are aiding drilling progress, Rockfire said, noting that a second rig is expected to be mobilised in January.
"Early signs of massive sulphide mineralisation in hole HMO-010 is pleasing ... Drilling is progressing well in this hole, and we anticipate better ground conditions."
In London, Rockfire shares fell 17% to change hands at 0.13p each.