Regarding mining, there is a matching principle in accounting that suggests that income should be recognized at roughly the same time as related expenses.  So deducting expenses when incurred or paid, but capitalizing the value of mined coins and not recognizing income until the coins are sold would, in my opinion, not likely be upheld in tax audit or litigation.  By far the safest position is to recognize income at the FMV when mined.  Determining FMV is not completely clear cut, given as much as 10% spread in dollar values between exchanges.  Whatever valuation method is used should be used consistently, and it is probably worth seeking valuation advice if the mining revenues are large.  The income recognized becomes the tax basis and then additional gain or loss is recognized based on the change from basis when the coins are sold.  Several methods including LIFO and specific identification may be used to decide which coins were sold.  Whichever method is chosen should be used consistently.

I am a USA CPA licensed in CA and IL, and a certified valuation analyst, and I can be found on LinkedIn or by Google. Here is my circular 230 disclaimer.  This post is intended to provide generalized tax and valuation information that is only appropriate in certain situations. It is believed accurate at this time, but these rules, alas, are constantly changing.  It is not intended or written to be used, and it cannot be used by the recipient, for the purpose of avoiding tax penalties that may be imposed on any taxpayer. These contents should not be acted upon without specific professional guidance. Our liability, under any circumstances, is limited to the amount paid for our services.  Please contact us if you have questions.