Spiral concentrators are specialized pans tilted on an angle with spiraled grooves. Shaking tables are very effective and can concentrate sizeable amounts of ore at a time, providing high grade concentrates and liberated gold, but they are also relatively expensive and require some experience to operate. During this process, the table is continually shaken by a motor to agitate the material and aid in the separation of gold particles. As the material is washed down the table, specialized grooves trap gold and direct it to collection points on the side of the table as lighter minerals are washed away. The water washes the feed down the table. Mineral feed (crushed ore or sediment) and water are released at one end of the table. Shaking tables are elevated tables tilted to one side with raised ridges running horizontally down their length. The resulting concentrate must usually undergo further methods of concentration, such as panning. Sluices are good at concentrating large amounts of ore and sediment in a relatively short time but often do not yield concentrates with high amounts of gold. A constant flow will be better than a bucket-driven flow. This can be done with piping, drums, buckets, or natural flowing water bodies. Having an available and consistent water supply is necessary to have a functioning sluice operation. Simple sluices can be a single angled platform a few feet in length and others can be very elaborate. Sluices can be relatively expensive or affordable depending on the complexity of their design. The first is tilted at a steeper angle then the second, decreasing the velocity of the water as it hits the second sluice, increasing gold recovery. A zig zag sluice also achieves this by creating a drop between the first and second platform that disrupts the velocity of the water as it travels down the sluice.Ī simpler alternative to the zig zag sluice is a combination of two sluice surfaces. A series of rifles can help break the flow to improve recovery. Sluice design can lead to higher gold recovery if the force of the water traveling through the sluice is decreased. Carpets or other capturing devices on the bottom of sluices can be removed and washed in a bucket to remove the captured dense material. For this reason most gold is captured at the beginning of the sluice. As moving water travels down a sluice, it generates greater force and keeps gold particles from sinking easily. Sluices are usually inclined at 5 to 15 degree angle. As water washes sediment down a sluice, gold particles sink and are captured by material covering the bottom of the sluice, often carpets. Sluices use water to wash ore or alluvium down a series of angled platforms. Therefore, panning is often done after other methods of gravity concentration such as sluicing have completed. One of the major drawbacks to panning is that miners must pan small amounts of concentrate. Panning offers miners a low cost method of gravity concentration but it requires time and skill to be effective. Then miners can employ gold recover methods such as direct smelting (described below), although many panning operations lead to directly recoverable gold. Under right conditions, panning can produce high grade concentrates or even liberated gold. Panning works best when gold is coarse and well liberated. After a series of successful iterations have been completed, gold will be exposed on the bottom of the pan for the miner to recover. The density of gold keeps it on the bottom of the pan as lighter material is ejected along with water. The miner moves the pan in a series of motions designed to eject lighter sediments. In this process sediment or ore thought to contain gold is placed in a wide, curved pan along with water. Panning uses water to separate heavy gold particles from other lighter particles within a medium sized pan.
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