Whether that's good or not really does depend on how much gold was found though, could be that 10kg was kept for all we know!

>could be that 10kg was kept for all we know!

Doubtful. Finding such a hoard and reporting it to the authorities for formal examination by default means showing where you found it so the site itself can be examined by archaeologists. They'd likely be able to tell if you'd found more than you reported in the cache site. It's like forensics, but for ancient artefacts and ruins, pretty sophisticated at times.