***MacBook Pro mid 2014 won't connect to my LG 27UD68-W in 4k @ 60Hz

Help!

I have a mid-2014 MacBook Pro and I'm trying to get it to connect to my 27" monitor, an LG 27UD68-W at 60Hz. This laptop has 2 Thunderbolt ports and then I'm using the cable which came with the monitor for MiniDisplay Port (from the monitor) into one of the Thunderbolt ports on my MBP, it doesn't work. Via HDMI I can get the ~3800 resolution but only at 30Hz. Does anyone know why this monitor will not connect to my computer and if there is some sort of fix that I could look into?

Thanks in advance!