FINALLY!!! Last night, just before I planned to call it quits for the night, a stroke of luck. Came out of a search glide over a trench, made a visual recon of the surroundings (abusing the external camera for this, much better view than from the cockpit), gave up, found a really cool looking camping spot on a hill in the middle of a trench, headed towards it to land and go to sleep when a small blue dot appeared on the scanner. My heart missed a beat, my life rushed through my mind (a fraction of drama added here) and with trembling hands I steered the ship towards the position of the dot (no drama added here).
Anyway, it turned out to be one of the volcanics (silicate geysers) with almost no plumes. I expected to see silicate plumes from far away but this place appeared in front of me with no visual clues before the fumaroles became visible. Also it was pretty dark, I hope the next time I get to play it will be daytime so I can post a nice pic.
I was really really glad to find this place, finding a site of volcanic activity on an untagged planet/moon in an untagged system was on my to-do list for a looong time but I lack the time and dedication to do proper search as described in the OP. This time too I started by taking a long look at the planetary surface in the system map, selecting the features that looked promising and went for gliding. The damn tick is at only 18km on this moon so I had little room for the glide.