Yes, most likely maganese and iron oxides
see Gascoine W., 1982 - The formation of black deposits in some caves of south east Wales. Cave Science, 9 (3): 167-175 and
W.B. White, C. Vito, and B.E. Scheetz – The mineralogy and trace element chemistry of black manganese oxide deposits from caves.
Journal of Cave and Karst Studies, v. 71, no. 2, p. 136–143