Sampling programs can benefit from large bowl pulverizers

Although large bowl pulverizers have been used throughout the rest of the world for 10 years, acceptance of them has been slow in North America.

What are large bowl pulverizers? They can accept 500-5,000 grams of rock or drill core which have been crushed to around 10 mm in size. They homogenize the sample while pulverizing the material to a nominal 20 mesh in fewer than five minutes.

The common head sizes of 1,000-2,000 grams are detachable from the actual pulverizing machine. Larger pulverizers, such as the 5,000-gram capacity machines, have the head connected to the pulverizer itself.

Why would you use a large bowl pulverizer? The expression “bigger is better” certainly applies here. If you can pulverize and homogenize the entire rock chip or soil sample, why take the risk of riffle splitting the sample and potentially analyzing the portion without any gold?

According to Pierre Gy’s sampling theory, there are clear benefits to pulverizing a larger fraction of a bulk sample. It is theorized that if you pulverize 250-300 grams of sample, the sample should be crushed to less than 1.3 mm (or less than 14 mesh) before taking a split to be pulverized. Technically difficult and potentially expensive, this task requires additional steps, such as rolls crushing.

However, if a 2,000-gram split is pulverized, the required particle size reduction prior to splitting is 6.25 mm (or 0.25 inches), which is easily obtained using a standard jaw crusher.

The samples are homogenized while being pulverized in the large bowl pulverizers. The homogenizing action is caused by the large puck used in the bowls. The puck has an off-centre hole; as the puck agitates inside the bowl, the sample passes down the side of the bowl and back up through the hole, causing a mixing action similar to that of a food processor. Homogeneous large pulps are particularly important when analyzing samples for gold. Additional mixing is not necessary with most large bowl pulverizers. — This article by Craig Barr appeared in a recent “Newsletter” of XRAL Laboratories.