From the Wikipedia page 
The Brazilian National Archives (in Portuguese: Arquivo Nacional) were created in 1838 under the name of "Imperial Public Archives". They took their present name in 1911.
The building housed from 1868, the old Brazilian Mint, which operated in it until 1983. It is a jewel built in Neoclassical style with gneiss stone by the engineers Antonio Pinheiro Guimarães Francisco and Teodoro Antonio de Oliveira. Access is given through a portal of classical composition with three pediments on the same facade, a solution which gives a palatial grandeur to the building.
The Portuguese-language website is .