For the US, there are several sources:
Mineral Resources Data System (MRDS)
MRDS is a collection of reports describing metallic and nonmetallic mineral resources throughout the world. Included are deposit name, location, commodity, deposit description, geologic characteristics, production, reserves, resources, and references. It subsumes the original MRDS and MAS/MILS. As of 2011, USGS has ceased systematic updates to MRDS, and is working to create a new database, focused primarily on the conterminous US.
This record is maintained in the National Geologic Map Database (NGMDB). The NGMDB is a Congressionally mandated national archive of geoscience maps, reports, and stratigraphic information, developed according to standards defined by the cooperators, i.e., the USGS and the Association of American State Geologists (AASG). Included in this system is a comprehensive set of publication citations, stratigraphic nomenclature, downloadable content, unpublished source information, and guidance on standards development. The NGMDB contains information on more than 90,000 maps and related geoscience reports published from the early 1800s to the present day, by more than 630 agencies, universities, associations, and private companies. For more information, please see http://ngmdb.usgs.gov/.
Data.Gov Mining related data set.
Digital Rockhound's companion
(Shameless plug for my software, not free though).
I created a new user interface to search MRDS and MAS/MILS databases.
Natural Resources Canada
This map depicts the location of Canada's principal producing mines for the given reference year. It includes locations for significant metallic, nonmetallic and industrial mineral mines (except clay products, peat, and most construction materials [most stone, sand and gravel]), coal mines, oil sands mines, and oil and gas fields across the country. Also depicted are the locations of significant metallurgical facilities across Canada. The data in this map are based on Natural Resources Canada's annual Map 900A – Principal mineral areas, producing mines, and oil and gas fields in Canada.
Australia's mineral resources and their global status
Australia's known resources of a wide range of mineral commodities are considerable in comparison with rates of production. Australia has the worlds largest economic demonstrated resources of bauxite, lead, zinc, silver, ilmenite, rutile, zircon, tantalum, and uranium. In addition, Australia is ranked in the top three countries in the world for economic demonstrated resources of brown coal, copper, cobalt, gold, iron ore, manganese ore, nickel , gem/near-gem and industrial diamond. Despite a high rate of discovery of significant new mineral deposits, particularly since the 1950s, there is considerable potential for discovery of further mineral deposits in Australia.
OZMin database (from site)
These data represent the OZMIN Oracle relational database containing geological and resource information for Australian mineral deposits. OZMIN has been compiled from published references and has been designed so that attribute information can be retrieved and analysed in relation to spatial data contained in geographic information systems. The national mineral deposits dataset contains data on over one thousand major and historically significant mineral deposits for 60 mineral commodities (including coal).
For United Kingdom:
MineralsUK is the British Geological Survey (BGS) Centre for Sustainable Mineral Development. Facilitated by the BGS Minerals and Waste science programme, the Centre is a global leader in the compilation, provision and analysis of mineral statistics and the major UK national provider of spatial and statistical minerals information. We also carry out research in areas directly relevant to our user community, such as metallogenesis, land-use impacts of mineral extraction and geomaterials.