I'm probably the resident OP1 expert, and to the best of my knowledge, fumaroles were simply never implemented. I do remember there being a blurb in the manual about them being found only on certain planet types, which I'm guessing means Venus-type planets (based on Venus being hot and geologically active, unlike all other planet types in the game [though recent evidence suggests Mercury may also be geologically active, at the time OP1 was released this was not believed to be the case]). So I suppose it's possible that fumaroles do exist, rarely, on Venus-type worlds, but considering how many other features of OP1 are broken or unimplemented, I wouldn't waste my time looking for them.