Usually when metallics are present(ie. not finely disseminated ore)the pulp(pulverized ore sample) is screened through a fine sieve screen(-100 to-400 mesh depending on the ore) and the  total metallics are assayed  along with usually a 29.16 gram sample of the pulp. The results are mathematically recombined leading to a more accurate final number. This helps alleviate the"nugget effect"

Sort of like dumping the whole box of raisin bran out and counting the raisins  and averaging those nuggets out to find out the probable number of raisins you would get in every scoop.