So for those of you who, like me, are a completionist and want to clear all the missions, these things are the bane of Olympus. They start spawning once you initiate the Quarrite great Hunt campaign (necessary for some item and tech tree unlocks) and are in desparate need of rebalancing. I'll explain why my opinion is thus:
Pros- Once slain, they can be skinned like any other beast (including for vestiges) and drop meat, bones and most of all an assortment of ore that makes them a nice supplement to non-respawning nodes.
Cons- (Deep breath) They spawn in every biome despite originating in the desert and they spawn prolifically. It literally feels that for every 3-5 other animals of any combination, you're gonna get a Quarrite, roughly 1-3 per grid. This, coupled with the fact they take around as much damage to put down as a bull elephant makes them a tough opponent to tackle.
Speaking of tackling, they have an insane aggro and detection range. I had to use 3 Noise cancelling 2 armor alterations to go unnoticed and even then, just barely. Once aggroed they will literally chase you forever unlike ANY other mob which stops chasing after a grid or two. I've had one cross the arctic from teh desert and into the forest after me. Plus, their rolling attack not only lets them scale ANY obstacle and knock down trees, they can outrun you easily.
They have no weakpoint. A shot to the head literally ricochets away. If you want to take one down, go for the legs or body. I have done a lot of experimentation and here is what I have found. Assault rifle, SMG and Spear are not worth fighting them with unless you have no other option.
Use a Hunting Rifle, Sniper Scope 2, and explosive rounds. Take the sneak damage first shot on a foreleg or the body. Immediately switch to the Trench Shotgun with Narrow Spread 2 and miasmic rounds. Poison otherwise. IF you do it right, the first shot will take the armor off & a chunk of their shield-health. 2-4 shots from the shotgun will finish the job.
Otherwise, a Titanium pickaxe with poison mod to take off the armor, then a coldsteel knife with electro mod. Make sure you have a titanium tower shield on your belt or carcass slot (G by default) that you can block with right click. Shock slows them down, goves a debuff and causes damage over time. Poison does the same, and it stacks along with the freeze debuff.
Again, these things SUCK. I almost uninstalled because of them. It wouldn't be so bad if they stopped chasing after a while but as is? World bosses and sandworms are less challenging and they drop boss loot like exotics and biomass. By comparison? Quarrites are like wolves in frequency and a damned menace. Make sure to set up creature repellents around your base so they don't trash the place.
Oh and their spawning? That's just in-world. Their burrows pop up randomly and will spawn extra quarrites periodically too. They can be closed with a pickaxe but still... the fact that we are forced to play specific ways with specific builds just to "enjoy" the game rather than getting to customize to our personal tastes is crap. I hope the devs see this and take it to heart: Make them stop chasing like other critters. Lower the aggro range. At least give us the option to sneak by instead of forcing a boss fight on us every grid.
Sorry for the rant, hope the strategies help anyone else struggling with these PCP-molerats.