Hanging 60 lb beveled glass frame in courtyard on a brick wall
I would suggest using Z clips, unless you want the chain as ornamental.

These are attached to the wall and to the mirror's new frame.

To attach to the wall, I'd set anchors into the mortar (It's as strong as the brick and easier to patch if you move the mirror later.) Then use screws to attach the clips.

You have some fussy alignment to do to get the clips to match when using more than 2 pairs.

If you don't want to put a frame on the mirror, look at buying a single sheet of pressure treated plywood, cut it to match the size of the mirror, and glue to mirror to the plywood.  I don't recommend this for an exterior application.  Glass has a fairly high coefficient of thermal expansion.  I think the usual is to leave 1/8" per foot of glass dimension.  So a 4 foot high window has 1/2" of header space in the frame for it to wiggle in.  Might be 1/16" per foot.  Have to look.

A compromise is to use a plywood back, and then a lighter weight frame.  Frame elements only need to be big enough to hide the expansion room.  If you go this route, be sure to put drain holes in the channel at the bottom.  Otherwise water getting into that channel will rot the wood.