The Library of Congress has a bilingual site, still in development, United States and Brazil: Expanding Frontiers, Comparing Cultures. Check out the Colonial Period section for more information on slavery in Brazil illustrated with engravings and old maps.
And here's a recent article about the uncovering of a mass grave exposing the bones of as many as 20,000 slaves.
A bit more in the way of historical links, lending visuals to the narrative, Joaquim Maria Machado de Assis and Euclides da Cunha have Wikipedia sites with engravings, and da Cunha has his own site. Here's an engraving of Zumbi de Palmares.