Abstract The New Mine Sapphire Syndicate was a British-owned company which operated the Yogo sapphire mines in Judith Basin County, Montana. Records consist of incoming (1914-1934) and outgoing (1904-1931) correspondence between mine manager Charles T. Gadsden and syndicate offices in London; directors' minutes (1914-1930); stockholders reports (1915-1933); financial records; organizational materials; and miscellany. Also included are two letterpress books of outgoing correspondence (1924-1931)...