Do not mount your TV above the fireplace!
Mounting a TV above a fireplace may seem like a good idea and often the most convenient place to instal, however it’s really not a good idea at all unless just to watch TV occasionally, but if it’s your main TV and watching for hours it’s just not acceptable. It can be a problem getting Power and HDMI cables to it if mounting to a brick wall. Another problem is height and viewing at such an angle can result in a sore neck after an hour or more. The heat from a fireplace is not good for a TV either.
Though it my look stylish mounting a TV above a fireplace isn’t the best for your TV. So think before this type of instal. The best viewing for any TV is that you are looking at one third of bottom of the TV screen from your seating position.