In 1964, North Korea reported that it had discovered approximately 4 million tons of deposits in "Unggi-kun (웅기군)," North Hamgyŏng Province (함경북도); Hamhŭng (함흥시), South Hamgyŏng Province (함경남도); Haegŭmgang-ri (해금강리), Kosŏng-kun (고성군), Kangwŏn Province (강원도); Hamhŭng, Unggi, and Haegŭmgang. The current status of this mine is unknown. [Note: "Unggi-kun" is an old name for a section of what is now known as the "special administrative city of Nasŏn (나선직할시), which borders on Russia.]

Sources:
[1] So Yong-ha, "Capacity for Nuclear Weapons Development," Hoguk, July 1989, pp. 119-122, in "North's Nuclear Capability Assessed," FBIS-EAS-89-148, 3 August 1989, pp. 23-26.
[2] Joseph S. Bermudez, Jr., "North Korea's Nuclear Infrastructure," Jane's Intelligence Review, 1 February 1994, pp. 74-79.
[3] Osamu Eya, Kimu Jon Iru Daizukan (Tokyo: Shogakkan, 2000), pp. 64-65.
[4] Yu Min, "Pukhan Kip'okchekaebal Chipch'ak 70 Ch'arye P'okp'alshirhŏm/Russia Chŏngbu'ŭi Pukhaekp'yŏngganaeyong," Taehan Maeil, 5 January 1996, p. 6, in KINDS, www.kinds.or.kr.