I get the Bromellite for Turner these few days...
really annoying.
I first try an ice ring about Alioth...LHS 2637 4. I spend hours and hours to get around 38 units.
For the last 13, I decided to chance my spot and I went to SANG WANA (4) ~150 LY from Alioth. There is a pristine ring close to a ice ring.
I tried the pristine ring at first but did not find any Bromellite. Then, I reached the ice ring just next the pristine.
I got my 13 remaining units in about 20 minutes. You have plenty to Broomellite around. Lot of rocks with 5 to 6%. And from time to time, rocks with around 25%.
I hope it can help other commander ^^
If a system is pristine, all rings and belts are pristine. You are thinking Metallic, which you will never find Bromellite. It only exists in
Ice rings.
Alioth doesn't have any ice rings, just metal rich and rocky, so you will never find Bromellite there. What's more, Alioth is depleted reserves, so any minerals in the rings will be in small amounts. I have mined in a couple of the rings in Alioth, but this was for materials only, so the mineral reserves don't matter.
edit - here is a system with all 4 ring types: Metallic, Metal Rich, Rocky and Icy. It's also Pristine.