I just made 100M today in about an hour, only found two Opal asteroids. the rest was like grandidierite and alexandrite.
Not rare to do 140 - 150 when RNG stops throwing bromellite my way. Maybe you'd need a faster ship to cover more ground for deep core mining?
I tend to boost constantly while spamming the scanner and only stopping for the core mining asteroids. A T9 is very slow and it just takes longer to find ore