Once polishing and floor sweeps have been received and weighed, they are loaded into a tray to be incinerated.

Here the burning tray loaded with the sweeps is ready to be loaded into the incinerator.

The tray is loaded into the incinerator.

The door is closed and the incinerator turned on.

The tray with the completely burnt sweeps is ready to be removed from the incinerator.

The tray as it is being removed for the incinerator.

A good look at the burnt sweeps

The sweeps are transferred to a ball mill.

An array of balls are added to enhance the grinding and crushing action.

The mill is sealed.  Once it is sealed to keep all powder and dust inside, it is turned on and left to rotate with the balls moving around banging into each other and the side of the mill crushing the sweeps to a fine powder.

After a sufficient time has elapsed – usually a few hours  or more– the mill is opened and the crushed powder is scooped out and transferred to an extremely fine sieve in a vibratory sieving machine.

The sieve shown here is “80 mesh”.  This means for every linear inch there are 80 holes.  The resulting sieved powder is extremely fine, as fine as talcum or baby powder.  As a result once this sieved powder is blended well, it becomes homogeneous.  This means that a sample taken and analyzed will give an extremely accurate per cent of what is in the entire amount.

As the sweeps are sieved, there is material that does not got through the sieve.  Such things as drill bits, centers of polishing brushes, saw blades, little clips of solder, broken spring rings, etc.  As the sieving progresses, this “oversize” is periodically removed and placed aside in a tub.  This material can contain a substantial amount of precious metals.  As a result it is retained, the magnetic non-precious metals removed and all the remaining melted (usually requiring a smelt with added copper) to obtain a homogeneous result from which a sample can be taken and an accurate assay gotten so the client can receive credit for all the precious metals in the oversize as well as the powder.

Once the sieving of the sweeps is complete, the sieved sweeps are usually put back in the mill and blended for a period of time to ensure that they are well mixed.  At this point they are “prepared” and are transferred to a container for sampling

A hollow pipe or “thief” is used to remove samples from top to bottom and from several locations.

The samples thus taken are put on a piece of paper or other clean surface.

Once all the samples have been added to the sampling surface, they are thoroughly mixed together.

After it is mixed well, it is spread out to form a thin layer on the sampling surface.  Then small amounts are taken from several different places and put in the sample bag.