These are some of the works cited in Episode 7, in case you want to chase them down yourself for some further reading. I highly recommend Conrad and Gomez, and Wise's translation of the Tarikh al-fataash is unparalleled.
Conrad, David. Empires of Medieval West Africa: Ghana, Mali, and Songhay. Infobase Publishing, 2009.
Cooley, William Desborough. The Negroland of the Arabs Examined and Explained. London, 1966.
Gewald, Jan Bart. “Gold The True Motor Of West African History: An Overview Of The Importance Of Gold In West Africa And Its Relations With The Wider World,” in Worlds of Debt – Interdisciplinary Perspectives on Gold Mining in West Africa. Rozenberg Publishers, 2010.
Goldfarb, Richard J. et al. “West Africa: The World’s Premier Paleoproterozoic Gold Province.” Economic Geology ; 112 (1): 123–143. doi: https://doi.org/10.2113/econgeo.112.1.123
Goodwin, A. J. H. “The Medieval Empire of Ghana.” The South African Archaeological Bulletin, vol. 12, no. 47, 1957, pp. 108–112. JSTOR, jstor.org/stable/3886971.
Gomez, Michael. African Dominion: A New History of Empire in Early and Medieval West Africa. Princeton UP, 2019.
Barth, Henrich. Travels and Discoveries in North and Central Africa, 1849-1855, Vol. 5. https://biodiversitylibrary.org/page/46926800
Kemper, Steve. A Labyrinth of Kingdoms: 10,000 Miles through Islamic Africa. W. W. Norton & Company, 2012.
---------- “Timbuktu under Imperial Songhay: A Reconsideration of Autonomy.” The Journal of African History, vol. 31, no. 1, 1990, pp. 5–24. JSTOR, jstor.org/stable/182798.
Insoll, Timothy. “Timbuktu the Less Mysterious?” in Researching Africa's Past : New contributions from British Archaeologists, ed. P.J. Mitchell et al. Oxford University School of Archaeology, 2004.
McKissack, Patricia and Fredrick McKissack. The Royal Kingdoms of Ghana, Mali, and Songhay: Life in Medieval Africa. Square Fish, 2016.
Ohaegbulam, Festus Ugboaja. Towards an Understanding of the African Experience from Historical and Contemporary Perspectives. University Press of America, 1990.
Prothero, R. Mansell. “Heinrich Barth and the Western Sudan.” The Geographical Journal, vol. 124, no. 3, 1958, pp. 326–337. JSTOR, jstor.org/stable/1790783.
Wise, Christopher. Timbuktu Chronicles 1493-1599, Ta'rikh al Fattash. Africa World Press, 2011.
Wright, John. The Trans-Saharan Slave Trade. Routledge, 2007.