After some hours it became clear that I had searched through the whole fireplace. I dug a hole for all the rubbish and placed back all the tufts of grass. I had seen a few meter away a little dump in the ground and went over to investigate it. The detector screamed as I swept it across the dump, but unfortunately it was a rubbish pit from the 1970s. After a little while I found another such dump and it was a wartime one. I spent a couple of hours searching it but it was all rusted food tins and animal bones.
I called it quits and headed back home to clean some finds and enjoy some sun on the porch. Tomorrow I might go back here as Im sure there are some more bits of rust to be found.