Cupido osiris - Osiris Blue 

Cupido-osiris-osiris-blue | PTKbutterflies
Cupido-osiris-osiris-blue | PTKbutterflies
Cupido-osiris-osiris-blue | PTKbutterflies

I seem to have encountered this species rather often in the Alps and Southern France. Initially I misidentified them as Mazarine Blues, but close inspection distinguishes fairly easily. The thin black border on the upper-side is one distinguishing feature. 

It makes for a good butterfly image.

Cupido-osiris-osiris-blue | PTKbutterflies
Cupido-osiris-osiris-blue | PTKbutterflies