There is Khumus on Rikaz

وَقَالَ مَالِكٌ وَابْنُ إِدْرِيسَ الرِّكَازُ دِفْنُ الْجَاهِلِيَّةِ، فِي قَلِيلِهِ وَكَثِيرِهِ الْخُمُسُ. وَلَيْسَ الْمَعْدِنُ بِرِكَازٍ، وَقَدْ قَالَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي الْمَعْدِنِ: «جُبَارٌ، وَفِي الرِّكَازِ الْخُمُسُ». وَأَخَذَ عُمَرُ بْنُ عَبْدِ الْعَزِيزِ مِنَ الْمَعَادِنِ مِنْ كُلِّ مِائَتَيْنِ خَمْسَةً. وَقَالَ الْحَسَنُ مَا كَانَ مِنْ رِكَازٍ فِي أَرْضِ الْحَرْبِ فَفِيهِ الْخُمُسُ، وَمَا كَانَ مِنْ أَرْضِ السِّلْمِ فَفِيهِ الزَّكَاةُ، وَإِنْ وَجَدْتَ اللُّقَطَةَ فِي أَرْضِ الْعَدُوِّ فَعَرِّفْهَا، وَإِنْ كَانَتْ مِنَ الْعَدُوِّ فَفِيهَا الْخُمُسُ. وَقَالَ بَعْضُ النَّاسِ الْمَعْدِنُ رِكَازٌ مِثْلُ دِفْنِ الْجَاهِلِيَّةِ لأَنَّهُ يُقَالُ أَرْكَزَ الْمَعْدِنُ. إِذَا خَرَجَ مِنْهُ شَيْءٌ. قِيلَ لَهُ قَدْ يُقَالُ لِمَنْ وُهِبَ لَهُ شَيْءٌ، أَوْ رَبِحَ رِبْحًا كَثِيرًا، أَوْ كَثُرَ ثَمَرُهُ أَرْكَزْتَ. ثُمَّ نَاقَضَ وَقَالَ لاَ بَأْسَ أَنْ يَكْتُمَهُ فَلاَ يُؤَدِّيَ الْخُمُسَ.And Malik and Ibn Idris said, “Rikaz is the buried treasures in the Pre-Islamic Period and Khumus is compulsory on it whether the treasure is small or large, but the mines are not considered as Rikaz.” No doubt, the Prophet ﷺ had said, “There is no Zakat on minerals. And Khumus is compulsory on Rikaz.” ‘Umar bin ‘Abdul ‘Aziz took five portions out of every two-hundred from minerals. And Al-Hasan said, “Khumus is compulsory on Rikaz found in the land owned by non-Muslims, but if found in the Muslim territory there is only Zakat on it. If one finds a Luqata (fallen property) in the territory of the enemy, he must announce it publicly. And if it belongs to the enemy, then Khumus is compulsory on it. Some people considered minerals as Rikaz similar to the buried treasures of pre-Islamic period.