Typical "capture the flag" mode with an SK twist: Each team has some big Mineral(should be stronger than those found on clockworks) on their base that they must protect. On center of map there should be a deposit box where you drop the minerals and gain points.
Players that grab minerals can't use abilities or attack(requires team coordination!)
The team that deposited more minerals(or took all of them from the enemy) wins.
Some problems i can think of are:
-allies (trolls or noobs) could destroy and deposit own minerals
-enemies may grab their minerals and go to their safe zone inside base(partial solution: add more chunks of minerals than amount of players so they cant grab them all).
Other random ideas: protect each team bases with monster like gun puppies wich could be upgraded with energy (or crowns).
-add diferent deposit boxes acroos the map that open/close at random.
Pretty good idea