Bulk density is the measure of the mass of a solid substance (particularly powder, granules or divided solids), with the total volume they occupy. The volume includes the volume of the particle, the volume of the spaces between the particles and the pores present in any solid object.
There are reasons why we need to get the bulk density of ores. First is to compare it with the density of pure substance that the manufacturers are interested with.
Second, during the delivery of the ore, tapping may occur. Tapping can increase the bulk density thus can be a source of confusion if not recorded properly.
Third, when an ore is broken, air will now have spaces for them to occupy. This will decrease the bulk density.