This article examines the transnational circulation of American mine engineers between the United States, southern Africa, and the Americas in the late nineteenth century. Technology and knowledge was diffused worldwide with the circulation of American engineers who styled themselves as expert race managers as they compared the labour practices of mines across the world. The article's focus is the extension of the United States’ global footprint to South Africa, where an expatriate ‘colony’ of American engineers created a resilient form of Anglo-American inter-imperial collaboration. As they worked the Rand, American engineers made transnational comparisons of South African and North and South American mines. In the process, they led a global discussion of the efficiency of mining labour that reified white management of other races. After leaving the Rand, American engineers migrated across the globe, many to Mexico, where the interwoven networks of expert knowledge, industrial capitalism, and transnational race-making that characterized late nineteenth-century global mining followed.