In Fables second hand bookshop I come across the Norton edition of Heart of Darkness edited by Paul Armstrong. What a find for R92! More than 500 pages of essays of context (including Darwin and Alfred Wallace on race; the Casement report on the atrocities in the Congo) as well as Edward Said 
(“Two visions in Heart of Darkness”) and Armstrong himself (“Reading, race and representing others”).
Two very strong essays are by Chinua Achebe (must be read and very persuasive on Conrad’s own racism) and Marianna Torgovnik (“Primitivism and the African woman in HoD“). In addition to THE text itself are other writings and letters by Conrad.
Then you can start to read the heart itself, starting with its two narrators, its two rivers…
Writing Across Genres 