One of the most important things to put in effect in a placer operation like the one described, is to never allow the water to go over the rag plant when the feed has been shut off. The water, by itself, with no placer material going over the ragplant, will wash much of the free gold off and it will be lost.

When starting up the operation, the same thing must be in effect. Start the feed and water at the same time so that the gold on the carpets will be protected by the placer material in the water.

In some placer operations with fine gold, where the black iron also carries free gold values, a different flow sheet has to be set up. Jigs are used to save this iron. The "hutch" product from the jig is put over concentration tables to clean the iron.

In a case like this, a rag plant ahead of the jigs and concentrating tables will scalp off 80 to 90% of the free gold recovered, with a very small amount of iron and gangue saved on the carpet.

Riffles are used on the flat bottom of the sluice to cause turbulences in the water, which drop the gold particles, and trap these particles once they are dropped. As mentioned earlier, steel punchplate riffling with indoor-outdoor carpet under it works well on fine gold (10 mesh and less). If coarser gold is present, additional riffling may have to be added to ensure that it is saved. Again, this is a case of trial and error, so make your riffling so it is easy to install and remove.

The sluice box is the most important piece of equipment, because only here can the gold be saved. The sluice should be constructed of at least one quarter inch thick steel so that the bottom is flat and smooth. Adequate bottom bracing should be used to ensure that there is no buckling or rippling of the bottom. The sluice should be suspended so that the pitch of the box can be changed. Water coming onto the sluice should be controlled so that more or less water can be used at any time.

A trommel screen is used to screen the material to the size which will be put over the sluice. A trommel is a long rotating cylinder composed of one or more different sized screens. The intake end of the screen is higher than the discharge end so that material will move through the trommel. Material is fed into the intake end of the trommel and screened by the first screen. The size of this first screen is determined by the size of the material to be put over the sluice. Material screened by the fine screen goes directly onto the sluice box.

The equipment needed at the concentrating area include a grizzle to remove large rocks from the placer material, a screen to screen the material to the size which will be put over the sluice, and the sluice box or rag plant. The most economical way to install this equipment is to have a gravity feed between each piece of equipment. The material which goes through the grizzle drops by its own gravity on to the screen intake and the screened material drops on to the sluice box by its own gravity. One disadvantage of having only gravity feed is that the unit may be too high to move easily.

The suction dredge is limited by the size of material it can pick up. Unless the deposit is mainly fine material, the suction dredge will not be as effective as a dragline. The intake hose is moved over the surface of the bottom of the pond and sucks up material. A screen is placed over the end of the intake nozzle to keep rocks from plugging it up. If there are many large rocks present very little material will be picked up and the bottom layers of the deposit will not be reached. Suction devices work well only where the deposit is composed of sand and gravel with few large rocks.

The size of the deposit will primarily determine how much money will be spent on equipment and what type of equipment will be used. Obviously, a deposit of several million tons will justify the expenditures of much more money than will an equally rich deposit of several thousand tons. Here we are concerned with the smaller operation where much of the equipment will be "used" equipment and some of the equip¬ment will be built on the site.

The results of the concentrating tests should also be studied. Was all of the gold in the samples found in the concentrate or was some of it found in the mids or tails? This lighter gold, if it is present, may be difficult to save in an actual placer operation. Laboratory equipment is designed, and can be controlled, to make a very high recovery. Production equipment will not necessarily make such a high recovery, and gold which was difficult to save in the lab very well may be lost in the field.