you can add animations to interface buttons in the same way that you can add animations to scene objects or characters...
just use a static image of the open chest as background & then add a button at the top which contains 2 animations. have the initial animation containing the static closed chest image set to loop infinite & then the next animation containing the chest opening animation set to loop amount 1; the animation will automatically hide/unload after it has done playing.
next when you want to open chest just hide/stop initial closed chest animation & start the open chest animation playing & voila - I think