Any mine or area may have already been the subject of some research and published work. However, any historian or researcher can make errors, something to remember.
There is also the British Geological Survey memoirs. South west England: Dines, northern England: Sir Kingsley Dunham etc.
The National Archives have a lot of company records, I struck gold there with my research on Talybont. You can search their database on line, plus a national database (a2a)that covers other establishments.
http://www.nationalarchives.gov.uk/ http://www.nationalarchives.gov.uk/a2a/ For individuals, you can search and download the national census records. These have been digitalised by the Mormon Church for which I praise them. The charges are reasonable and at www.ancestry.com
There is also what can be called "local knowledge" but beware of old wives tales, gross exaggerations, and wind ups. Sometimes however you can strike gold, such as turning up old photographs and documents or mine plans.
Wales has the National Library of Wales at Aberystwyth, there is quite a bit of stuff there.
Finally, and possibly the most important, is the Mining Journal. This publication started in 1835 and is still published today. It has a wealth of information on the 19th century mines and mining companies and has become the backbone of contemporary research. However, be advised that after about 1882 it mainly deals with foreign mining.
Most major libraries have it on microfilm; however the problem is finding what you want. The Northern Institute of Mining and Metallurgy have an on line index, however, I will put my head well over the parapet here and say explicitly that it is virtually useless.
The esteemed mining historian, and I am very proud to say good personal friend, Mr George W Hall compiled what may arguably be the best and most complete index to the mining journal that I personally know of. This work took a lot of his time in the 1970s and is hand written in little notebooks. There is shortly to be published, possible on disk, and index to Wales and Shropshire compiled by Mr Robert Ireland of the Welsh Mines Society. It is from Georges notes; however, I do not have a date for this.
It is also remotely possible that some time in the future a complete online version of the MJ may be available with images opening from hyperlinks or similar. I dreamt this one night after drinking too much XXXX, and I also once saw it in some tealeaves.
My avatar is a poor likeness.