Not a single sect of Islam confines the meaning of ghanimah to the 'spoils of war'.
In addition to the 'spoils of war' the following items are subject to khums:
(a) Minerals: eligible for khums in Shi`ah and Hanafi sects.
(b) Buried treasure: eligible for khums in all Muslim sects (that is, Shiah, Hanafi, Maliki, Hanbali and Shafiiy).
What has been quoted above can also be substantiated from the practice of the Prophet of Islam himself.
For example, when the Prophet sent `Amr bin Hazm to Yemen, he wrote instructions for him in which, among other things, he says, "...to gather the khums of Allah from the gains [of Yemenis]."
(Ibn Khaldun, Ta'rikh, vol. 2, part II (Beirut: al-Alami, 1971) p. 54; Ibn Kathir, al-Bidayah wa 'n-Nihayah, vol. 5 (Beirut: al-Maarif, 1966) pp. 76-77; Ibn Hisham, Sirah, vol. 4 (Beirut: Daru 'l-Jayl, 1975) p. 179.)
And when the tribe of Bani Kilal of Yemen sent its khums to the Prophet, the latter acknowledges it by saying, "Your messenger has returned and you have paid the khums of Allah from the gains (al-ghana'im)."
(Abu Ubayd, al-Amwal (Beirut: Mu'assah Nasir, 1981) p. 13; al-Hakim, Mustadrak, vol. 1 (Hyderabad:Uthmaniyyya Press, 1340 AH) p. 395. For more references, see Jafar Murtada al-Amili, al-Sah¡h fi Sirati 'n-Nabi, vol. 3 (Qum: n.p, 1983) p. 309.)
It is interesting to note that the Bani Kilal obeyed the Prophet's order and sent the khums of its gains to him while no war had taken place between the Muslims of Yemen and the unbelievers. This is a clear indication that khums was not restricted by the Prophet to the spoils of war.