Hi Phil, This appears to be an earlier revenue stamp, Forbin #20, from 1870-71. Forbin says this has an overprint on the same basic stamp with "1870-71" and "CALLAO" although it doesn't give a picture of the surcharge. Forbin #21 has a similar overprint but for the LIMA province rather than CALLAO.
Thanks Nigel !
I believe the El Callao is the name of the port in Lima, capital of Peru and a suburb of the of it as well..