While floating it pumps water from the stream picking up rocks, brown and black sand, as well as gravel and of course gold from the
stream bed. When gold is deposited in a stream, it works its way down through the sands and gravel until it hits bedrock, or some other
material that it can’t penetrate. This happens when the cascading run off water churns the stream bed. This churning keeps the objects
in a state of partial suspension in the water. The objects with the highest specific gravity, which is the gold, then have the opportunity to
settle to the very bottom.
Often I have been asked how a pump can pick up rocks without being damaged. Those who are familiar with many types of equipment
and machinery probably already know, but for those who don’t I will explain. The pump draws water from the stream and with a
tremendous velocity pushes it through what is known as a venturi in the pick-up hose. The venturi pushes the water in the direction
of the sluice, which creates a suction in the pick-up hose. The rocks picked up simply by-pass the pump going directly into the sluice.
The equipment size indicates the diameter of the intake hose, and they come in many sizes, starting at 2”, which is usually a very
portable “back pack” type. The size of the intake hose determines the size of rocky material that can be moved. Larger sizes, up to
10” with diesel engines are readily available. Often very large holes, going clear down to bedrock must be made to find the gold.
Obviously the bigger the dredge, the faster the hole can be opened up, but should be done only by experienced professionals.
If you haven’t already seen the sluice box information, please link to that page. The sluice on this equipment
is modified from that one by removing the up-stream flared end. Otherwise, the sluice operates the same way.
