Messenger of Allah ﷺ said, "There is no Diya for persons killed by animals or for the one who has been killed accidentally by falling into a well or for the one killed in a mine. And one-fifth of Rikaz (treasures buried before the Islamic era) is to be given to the state." (Using translation from Bukhārī 6912)  

عَنِ النَّبِيِّ ﷺ قَالَ «جُرْحُ الْعَجْمَاءِ جُبَارٌ وَالْبِئْرُ جُبَارٌ وَالْمَعْدِنُ جُبَارٌ وَفِي الرِّكَازِ الْخُمُسُ»