Material Distribution at the Source
A lot of people have the mistaken notion that their source gravels contain a relatively uniform distribution of gold, but savvy miners know that this isn’t so and that every bucket run will contain a significantly different amount of gold and other heavy materials.
Gold tends to be found in placers distributed in layers, streaks or pockets that all include a certain amount of float or fines that are more evenly dispersed in the beds. For this reason it is not at all unusual to be running 5-gallons of material that contains almost no gold while the next bucket might contain a lot of gold only to be followed by another bucket load that contains no gold and the cycle can go on continuously.
Under these conditions, which are very real to all of us who are moving a lot of materials at a site, the sluice gets loaded and packed with a lot of non-productive silts, sands, ultra fine gravels and black sand in between getting a load of gold bearing materials. How effective the sluice is in handling these various productive and non-productive bucket runs depends on fate more than anything else as this is simply something beyond a scientific solution at this point in our high-banker building technological curve.
You can perform tests at home that show remarkable recovery results because you are in total control of the source materials and almost always run a nice clean box with fresh unpacked mats. This is one reason you should be especially suspicious of equipment tests published by equipment manufacturers who perform tests in similar controlled conditions.
Under real life conditions in the field, you don’t have much control over anything, especially what type of materials you’re digging and feeding into your high-banker and for this reason you really need to learn how to ‘read’ your box and determine when it’s time to do a recovery cleanup or just flush it out completely.
It is this unequal distribution of gold in source gravels at any particular site that accounts for about 99% of the confusion and performance claims about various types of equipment. Two guys can buy identical boxes and be working 20-feet apart on a typical stream and one guy will end up loving his unit while his partner ends up throwing his box into the river at the end of the day. Both units perform identically but have processed very different areas in the stream bank.
Therefore, we want to build a sluice that can handle the silts, sands and other nuisance types of materials yet stay unpacked and relatively clear so that it can process and concentrate good heavy materials when they get periodically introduced. This requires creating a relatively high water velocity through the box at all times.
What may be of particular interest to others like myself, who are small-time or part-time operators, is that a two-man team can dig and prepare gravels and run and tend two to three small high-bankers that are fed from one high-pressure pump while still coming close to maintaining the 12:1 feed ratio. This type of operation can triple ones gold recovery rate very easily without much of an increase in labor.