If you have dowsed a signal, red X is probably what you were picking up on, about 23-25 feet in the direction of your red arrow. I think it is a very valuable artifact, rather than a buried treasure, but could be wrong. Red circle is for an artifact might be worth recovering, probably less than 6 feet away. If you are tunneling in, looks like you could be down a little far. Don't recommend digging into the roof of that tunnel, looks too dangerous for that type of recovery. Green circles for other archaeological signals.
I get at 11-14 feet deep, where the red circles and the X a treasure like signal, but the kind from valuable artifacts. Green circles for other archaeological type signals.
Red X and circles, again could be some artifacts, valuable enough to give a treasure type signal, rather than a buried treasure about 11-16 feet deep. Green Xs for archaeological type signals.
"i think this place is a old tomb, what is your opinion? " If the site contains a buried treasure, it will be where marked by the red X/circles. If you are right about it being a tomb, which contains a treasure, the red X/circle will be the location. But if there is no tomb or buried treasure, the red X/circle should be the most important or significant artifacts.