UNPATENTED MINING CLAIM: An Unpatented mining claim is a particular parcel of Federal Land, valuable for a specific mineral deposit or deposits. It is a parcel for which an individual has asserted a right of possession. The right is restricted to the extraction and development of a mineral deposit. The rights granted by a mining claim are valid against a challenge by the United States and other claimants only after the discovery of a valuable mineral deposit.  

This means: You are leasing, from the government, the right to extract minerals. No land ownership is conveyed.
 

There are two types of mining claims, lode and placer.

Lode Claims: Deposits subject to lode claims include classic veins or lodes having well-defined boundaries. They also include other rock in-place bearing valuable minerals and may be broad zones of mineralized rock. Examples include quartz or other veins bearing gold or other metallic minerals and large volume but low-grade disseminated metallic deposits. Lode claims are usually described as parallelograms with the longer side lines parallel to the vein or lode . Descriptions are by metes and bounds surveys (giving length and direction of each boundary line). Federal statute limits their size to a maximum of 1,500 feet in length along the vein or lodge. Their width is a maximum of 600 feet, 300 feet on either side of the centerline of the vein or lode. The end lines of the lode claim must be parallel to qualify for underground extra lateral rights. Extra lateral rights involve the rights to minerals that extend at depth beyond the vertical boundaries of the claim.

Placer Claims: Mineral deposits subject to placer claims include all those deposits not subject to lode claims. Originally, these included only deposits of unconsolidated materials, such as sand and gravel, containing free gold or other minerals. By Congressional acts and judicial interpretations, many nonmetallic bedded or layered deposits, such as gypsum and high calcium limestone, are also considered placer deposits.
Placer claims, where practicable, are located by legal subdivision of land (for example: the E 1/2 NE 1/3 NE 1/4, Section 2, Township 10 South, Range 21 East, Mount Diablo Meridian). The maximum size of a placer claim is 20 acres per locator .
 

There are two  types of mineral entries, mill sites and tunnel sites.

Mill Sites: A mill site must be located on nonmineral land. Its purpose is to either (1) support a lode or placer mining claim operation or (2) support itself independent of any particular claim. A mill site must include the erection of a mill or reduction works and/or may include other uses reasonably incident to the support of a mining operation. Descriptions of mill sites are by metes and bounds surveys or legal subdivision. The maximum size of a mill site is 5 acres.

Tunnel Sites: A tunnel site is where a tunnel is run to develop a vein or lode. It may also be used for the discovery of unknown veins or lodes. To stake a tunnel site, two stakes are placed up to 3,000 feet apart on the line of the proposed tunnel. Recordation is the same as a lode claim. Some States require additional centerline stakes (for example, in Nevada centerline stakes must be placed at 300-foot intervals).