Hunt is an American-born singer who was the inspiration for the Stones' 1971 hit "Brown Sugar" and bore Jagger's first child.
Sotheby's says she has tasked the auction house with selling 10 letters written from the set of Jagger's film "Ned Kelly," which was shooting in Australia.
Sotheby's says the "passionate and articulate" letters sent in the summer of 1969 show a "poetic and self-aware" 25-year-old Jagger.
The auction house said Saturday that the collection, which includes song lyrics and a Rolling Stones playlist, is expected to fetch between 70,000 and 100,000 pounds ($111,300 and $159,000) and will go under the hammer on December 12.
