[Boatanchors] Repeater antenna on a cold mountain top

[HL1FB]

We are installing a 70cm repeater on the summit of a 1600meter mountain.

Temperature there goes down to -20 degree centigrade and everything will

frozen covered with ice in winter. Antenna there is also expected to be covered with 

thick ice. So antenna performance will be poor, I guess. 

How poor will the antenna performance be?

My question is what kind of antenna will be suitable for this kind of environment.

Any body has experience??