My understanding is that the market cap is simply the current share price multiplied by the number of shares issued.
If you sell a mining tenament, the amount that it was valued at on the balance sheet is removed from the BS, and the cash received is added to the BS. If it was sold for more than its formal valuation, the balance sheet therefore improves. This has no direct effect on the market cap as such, only if the share price changes as a result of the transaction.
I am not an expert in this, but this is my understanding.
