Where does the song Sarie Marais come from?

"Sarie Marais" (also known as "My Sarie Marais", Afrikaans pronunciation: [mɛi sɑːri marɛ]) is a traditional South African folk song, created possibly during the First Anglo-Boer War (c. 1880) or (more likely) the Second Anglo-Boer War (ca. 1900).