Just as agriculture was necessary to sustain the population of America, the products which came as a result of mining were just as necessary to the developing country. Immigrants seem to have been one of the major groups involved in mining because of the familiarity with the occupation or the need for quick employment. Many also pursued mining with a hope of "striking it rich" or simply to be able to provide for their families.
In any case, the value for the researcher is that there was a paper trail. As with other land applications, a mining claim required the claimant be twenty-one years of age and be a citizen of the United States or have made a declaration of intent to become a citizen. Along with that, after the California gold rush of 1848, the forms required by the government often included detailed questions such as a place of birth. For those with immigrant ancestors this information could break down the oceanic "brick wall."
The types of mining claims were either lode claims or placer claims. A lode claim is one which involves minerals found in rock veins such as tin, silver or gold. A placer claim is one with minerals not found in rock veins, but through means such as open pit mining or panning, for example.
When researching mineral claims, it is helpful to have know a little of when mines were formed and where they were located so that the researcher will have an idea as to whether or not the ancestor may have filed a mineral claim. It also adds to the history of ancestors as we learn more of why they moved to certain areas.
Chronology of Mining in the United States
1763 First coal mines in what is now Richmond, Virginia
1785 The government created a Land Ordinance which specified that one-third of all mineral lands were to be reserved for the United States.
1807 Legislation provided for leasing of the mineral lands held by the government.
1848 First Coal miner's union formed in Schuylkill county, Pennsylvania
1866 The government Act of 26 July 1866 provided for mining claimants to be able to obtain a patent for their mineral lands. The requirements for a patent for lode claims were that the claimant must have made a significant amount of improvement on the claim and must pay a certain amount per acre. By 1870, this included placer claims.
1872 The General Mining Law was established which defined mineral lands as those which held "any valuable minerals."
Mines in the United StatesThe largest Coal Producing States in 1889 were Pennsylvania, Illinois, Ohio, West Virginia, Iowa, Alabama, Indiana, Colorado, Kentucky, Kansas and Tennessee 
- Hone, Wade E. Land and Property Research in the United States Ancestry Incorporated, Salt Lake City, Utah, 1997
- Global InfoMine Mining in USA http://www.infomine.com/countries/SOIR/USA/ 1990-2010
- Source: Thirteenth Census of the United States, Vol. XI, Mines and Quarries, 1913, Table 4, p. 187. As quoted in Wikipedia History of Coal Mining in the United States.