There is no markings so at best it"s worth bullion, the store with the XRF if you make up some story of this being owned by your grand mother and you are trying to find it"s value. Ask nicely if you can photo the XRF reading or if store offers reasonable buy price
You could make up a story or even better just tell the truth and ask them for their assessment. I would consider it part of your costs of acquisition. I agree best case is something like 999 purity, but if it really was poured by some dude in his garage, then it might be more like 95% or 99%. Knowing the purity will be important to setting an accurate price when you are ready to sell.
"If you climb a good tree, you get a push." -----Ghanaian proverb
"The danger we all now face is distinguishing between what is authentic and what is performed." -----King Adz