It looks like a George I copper! Very rare to find any coin from the early 1700's, George I halfpennies are from 1717-1724. If it is 25mm-27mm it is from 1717-1718, these ones are also slightly thicker. If it is 27mm-29mm, it is from 1719-1724. The most common ones are the 1719-1724 ones. Congrats on a very early piece.
I think you have a period George counterfeit, looks like typical tin/pewter/lead alloy used with most examples.
And I have several showing the raised lines like yours.
Easy to gather another clue w your detector, place this and similar size copper coin (modern us quarter) on ground and sweep w your detector, if they both sound copper you'll know it ain't likely a fake.
No olive oil, please never ever use olive oil on any coin. It has shown to lead to further damage down the road. Safest for anything is distilled water soak. Change water daily and lightly tooth brush or detail gently with tooth pick when changing water. Can sometimes take weeks to get as much as you can.