If both nuggets have the same mass and different densities then it can be concluded that the volume with the highest density is smaller.
For, so to speak, density is a relation of how much mass is there in a given volume. So the more the mass and the smaller the volume, the greater the density.
To verify this, let us calculate the volumes of iron pyrite and gold pyrite.
For the iron pyrite nugget:
density = mass / volume
volume = mass / density
volume = 50/5
volume = 10cm3
For the gold nugget:
volume = mass / density
volume = 50 / 19.3
volume = 2.59cm3
Therefore it is found that the nugget with the highest density (gold) is the one with the lowest volume.