Since you have had one before I'm sure you know about the floating chamber and/or ejector pin sticking over time. If not there is plenty of info on YouTube to help you out. I've worked on a few over the years for friends who have had one. I'm not a gunsmith but am more of a tinkerer when it comes to gun problems. Great gun when taken care of. Have fun with it.
Welcome Vladimir ... CTX 3030 can find gold but better at coins/relics etc. Don't know anything about gold in Bulgaria but I bet an investment in a GM1000 would serve you better with finding gold! Just my opinion though!
I would break a piece off and crush it in my mortar and pestle and then pan it to see if there's gold. When I first got the mortar and pestle, I would have crushed the whole rock, but that would be hours of work to get the entire sample to -50 mesh. Now I just crush a piece that would fit inside a closed fist, not the size of the closed fist, but inside the closed fist. Saul's trick is much easier, but there's no workout involved. If you press the gold with the knife and it crumbles, it's pyrite. If it leaves a malleable indentation, probably gold.
I don't see any gold. It is Thursday morning and I've got not much else to do, so why not crush some rocks!