The material is gypsum
I don't have the angle of repose.
No it is not a new conveyor and manufacturer is out of business and drawings are not available.
Is 200 TPH times 160fpm gives me the correct answer for lbs/ft?
JAE has described the general approach which would be conservative. I don't account for material in the sag because it should be minimal for a properly designed conveyor.
Based strictly on the OP data:
200 TPH = 400,000 Lb/Hr assuming 2000 pound Tons
400,000 Lb/Hr = 400,000/60 = 6666.67 Lb/min
Conveyors are uniformly loaded normally.
A belt speed at 160 FPM means in one minute, 6666.67 Lb of material is spread out over 160 feet
OR 6666.67/160 = 41.67 Say 42 PLF material load
This is most likely not conservative, because conveyors are run overloaded all the time in industrial operations.