Placer mining in the context of "Placer deposit"

The Arkansas River is a major tributary of the Mississippi River. It generally flows to the east and southeast as it traverses the U.S. states of Colorado, Kansas, Oklahoma, and Arkansas. The river's source basin lies in Colorado, specifically the Arkansas River Valley. The headwaters derive from the snowpack in the Sawatch and Mosquito mountain ranges. It flows east into Kansas and finally through Oklahoma and Arkansas, where it meets the Mississippi River.

At 1,469 miles (2,364 km), it is the sixth-longest river in the United States, the second-longest tributary in the Mississippi–Missouri system, and the 47th longest river in the world. Its origin is in the Rocky Mountains in Lake County, Colorado, near Leadville. In 1859, placer gold discovered in the Leadville area brought thousands seeking to strike it rich, but the easily recovered placer gold was quickly exhausted. The Arkansas River's mouth is at Napoleon, Arkansas, and its drainage basin covers nearly 170,000 square miles (440,000 km). Its volume is much smaller than the Missouri and Ohio rivers, with a mean discharge of about 40,000 cubic feet per second (1,100 m/s).

A gold nugget is a naturally occurring piece of native gold. Watercourses often concentrate nuggets and finer gold in placers. Nuggets are recovered by placer mining, but they are also found in residual deposits where the gold-bearing veins or lodes are weathered. Nuggets are also found in the tailings piles of previous mining operations, especially those left by gold mining dredges.

Gold was discovered in the Yentna-Cache Creek Mining District in the U.S. state of Alaska (also known separately as the Yentna District or Cache Creek District) of the upper Susitna River Valley in 1898, soon followed by claim staking. Placer mining was reported in the Cache Creek drainage of the Dutch Hills by 1906. Quaternary glaciofluvial deposits, alluvial deposits, and Cenozoic conglomeratic white quartz-breccia units have been mined in the Dutch Hills. About 200,000 oz (12,000 lb; 5,700 kg) of gold has been produced from these placer deposits.

By 1927, a road from Talkeetna was constructed into the mining area, known today as The Petersville Road. The mining camp of Petersville, Alaska served as the area Post Office for several years in the late 1920s and early 1930s. Two areas have been set aside for recreational gold mining, the North and South units of the Petersville State Recreation Mining Areas. Many smaller one-man and family placer mining operations continue today.

In mining, tailings or tails are the materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue) of an ore. Tailings are different from overburden, which is the waste rock or other material that overlies an ore or mineral body and is displaced during mining without being processed. Waste valorization is the evaluation of waste and residues from an economic process in order to determine their value in reuse or recycling, as what was gangue at the time of separation may increase with time or more sophisticated recovery processes.

The extraction of minerals from ore can be done two ways: placer mining, which uses water and gravity to concentrate the valuable minerals, or hard rock mining, which pulverizes the rock containing the ore and then relies on chemical reactions to concentrate the sought-after material. In the latter, the extraction of minerals from ore requires comminution, i.e., grinding the ore into fine particles to facilitate extraction of the target element(s). Because of this comminution, tailings consist of a slurry of fine particles, ranging from the size of a grain of sand to a few micrometres. Mine tailings are usually produced from the mill in slurry form, which is a mixture of fine mineral particles and water.