Note: Although this type of zakat may not be applicable to most of us; its existence is an exemplary proof of the complete nature of jurisprudence in Islam. Islam is perfect. Subhanallah.
ZAKAT ON MINES
1. A zakat of 2.5 percent is immediately due on gold and silver - that is to say - equivalent or more than the zakat minimum of gold or silver - and this excludes anything else - such as iron, lead, crystal, turquoise, cornellian, emerald, antimony, or other, on which there is no zakat;
2. The gold and silver are extracted from a mine - that is to say - a site at which Allah has created gold or silver located on land permissible for the miner to work or owned by him;
3. And that this amount of ore has been gathered by working the site one time, or several times uninterrupted by abandoning or neglecting the project;
4. The zakat is only paid after the ore is refined into metal;
5. If the person stops working on the site for a justifiable reason, such as for necessary travel (i.e. not for recreation, but for something such as an illness) or to fix equipment, then he adds the ore collected after the interruption to that collected before, in calculating the zakat minimum. Ore found on someone else's land belongs to the owner of the land.
ZAKAT ON TREASURE TROVES
6. An immediate zakat of 20 percent is due whenever one finds a treasure trove that was buried in pre-Islamic times (or by non-Muslims, ancient or modern) if it amounts to the zakat minimum and the land is not owned. If such a treasure is found on owned land, it belongs to the owner of the land. If found in a mosque or street, or if it was buried in Islamic times, it is considered as a lost and found article.
Such rulings display the unlikelihood of such zakat-due circumstances to exist today. Nevertheless, the ruling is there for Muslims to practice the commands of Allah SWT.