This term is defined in Portuguese as follows:

"Se o afastamento (distância entre o plano dos furos e a superfície livre) não é muito grande, as gretas se estendem até a superfície livre, e ocorre o desprendimento total do bloco rochoso." http://200.20.105.7/cyted-xiii/Publicaciones/Livros/Geomecan...

Here's a couple of other examples in Portuguese:

"A formação de gretas depende muito da relação entre afastamento e espaçamento entre furos." http://200.20.105.7/cyted-xiii/Publicaciones/Livros/Geomecan...

"O carregamento de explosivos segue um plano de
fogo que determina um afastamento de 2,2 m e um espaçamento de 5 m." http://www.cetem.gov.br/publicacao/CTs/CT2002-179-00.pdf

According to the "Dictionary of Mining, Mineral, and Related Terms", we have a definition very similar to the one cited in Portuguese:

"burden -- The distance from the borehole and the nearest free face or distance between boreholes measured perpendicular to the spacing (usually perpendicular to the free face.)" http://books.google.com/books?id=OV9KBUoknFIC&pg=PA74&lpg=PA...

Here's some more examples in English:


"A burden can be characterized as an infinite burden when the ratio of that to the spacing exceeds unit, and the critical size of the burden for pre-splitting is defined as a distance equal to spacing." http://books.google.com/books?id=K9U8pqwYeTQC&pg=PT229&dq=bo...

"The burden for rock fracturing without displacement of muck is called as critical burden." http://books.google.com/books?id=ZHR7Cbf8a2UC&pg=PA171&lpg=P...