Makhul (may Allah have mercy on him) said that Umar bin al-Khattab (may Allah be pleased with him) placed mines (ma'adin) on the same level as rikaz and said: There is khums in it as well.
This is munqati' (broken); Makhul did not reach the time of Umar (may Allah be pleased with him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7642