Yes, it is very important to say where you are, because no two countries/states have the same tax laws 100%. There's always something different between them. 
For example, in the USA on the federal tax return you would have to report the mined bitcoin as of the day you received it as income. So if it was $450 when you received it, you report $450 income and pay regular income tax on that amount. Then if you sell it at $490, since you already paid taxes on the $450 you don't pay taxes on that part but pay cap gains taxes on the profit of $40.
For example, in the USA on the federal tax return you would have to report the mined bitcoin as of the day you received it as income. So if it was $450 when you received it, you report $450 income and pay regular income tax on that amount. Then if you sell it at $490, since you already paid taxes on the $450 you don't pay taxes on that part but pay cap gains taxes on the profit of $40.
I shouldve said where i live earlier but it is in the USA, so then i would have to pay double tax on my bitcoins and i continously mine daily with a pool, but what about if i mined a bitcoin worth $500 one day and then sell it at $450 another day would i have to pay income taxes on the $500 or $450?
P.S. I am trying to look for a tax advisor who knows everything about the bitcoin tax but to no avail.
In that scenario you have $500 of ordinary income you pay taxes on, and a $50 short term capital loss. You can deduct up to $3,000 per year of losses from your other income. So effectively you would only have to pay taxes on the $450 that you realized.