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.
Locating Mineral Lands and Claims
When researching mineral claims, it is helpful to know when mines were formed and where they were located in the state where an ancestor lived 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. One of the easiest ways to learn this information is to "google" a phrase such as "mining in ___(the state of interest)"
Mineral land claims and applications are found in the National Archives and are usually within the case files. To learn more about how to obtain the information for ordering these case files, see the wiki article entitled: "Obtaining the Case Files" (United States - Land and Property - The Land Acquisition Process - Federal Land)
Mineral Producing States
COAL MINING STATES: The 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
- Wikipedia History of Coal Mining in the United States Creative Commons