These transactions represent mined coin(s). These can be taxed differently on transaction and disposal based upon configured tax settings. The price recorded is indicative(estimated) based on the market value when the coin(s) was either mined or relinquished, depending on it's configuration.
On this screen it is possible to unclassify existing transactions; this will preserve the main information of the transaction and will allow you to reclassify it as a different type of transaction without needing to re-enter it. i.e. Mine -> Unclassified -> Make Sale.
You can auto use the auto-value feature for looking up historic value.
For more information on auto-value click here.