Prox-Mine: The Prox-Mine is a proximity detonated anti-personnel mine composed of a thermite charge. Once fired, the Prox-Mine will stick to a surface. If any enemies are detected near the Prox-Mine it will detonate. The Prox-Mine is not too effective against Xenomorph targets, usually taking multiple mines to kill a "standard" caste such as a Lurker, Warrior or Spitter.
Unlike every other Armat-manufactured underbarrel attachment in Aliens: Colonial Marines, the Prox-Mine Launcher does not have a "U-" designation as part of its name (e.g. U4 Firebomb Launcher). It is not clear if this is intentional or an oversight on the part of the developers.
The Prox-Mine Launcher in Aliens: Colonial Marines is visually identical to the U1 Grenade Launcher unit fitted to Pulse Rifles as standard. Given that the Colonial Marines Technical Manual states the U1 is capable of using a variety of ammunition types, it seems possible the name "Prox-Mine Launcher" is simply a gameplay designation, and that the weapon is in fact a U1 loaded with a different ammo type. The fact the Prox-Mine Launcher is named after ammunition it fires rather than having a specific designation (unlike the U1) further supports this theory.