Hol Kol Mine (Holgol; Suan; Namjong), Suan-gun, North Hwanghae Province, North Korea

A gold-copper mine in contact metasomatosed ore in dolomitic marble around a granite intrusion, 75km SE of Pyongyang. Worked in the mid-19th century by the Korean royal family, then in the early 20th century by a succession of different British-Korean-American-Japanese interests. The ores are hosted in boron-rich skarn and marble. The first boron mineral found was ludwigite, by Shannon, an American. Later, two new boron species, kotoite and suanite, were found by a Japanese mineralogist. Kotoite was first found in the wall rock of the "New Ore Body".

Ref.: Palache, C., Berman, H., & Frondel, C. (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II: 370.