Refiners and mining companies deal in larger gold bars that are mixed with gold and other metals. These bars weigh around 400 Troy ounces / 12.4 kg / 27 pounds. A dore bar is a semi-pure alloy of gold and silver and is weighed and melted to ensure the contents are homogenous. This also guarantees the bar has no pockets of high or low purity within the bar. A sample is taken from this melted dore and assayed to determine the exact amount of gold and silver present.
The refinery will then take the pure silver and gold and melt into their own gold and silver bars, or sell the pure precious metal in whatever form it is in. To fully own a bar, the refiner must complete a loco swap with the miner to acquire the bar.