Hi no-idea
Why particularly does that disappoint you? Thunderbird and Coburn are different deposits, have variances in their product and thus might suit different customers.
Sheffield is an ilmenite/zircon deposit and doesn't have any rutile. It's ilmenite is upgradable to HiTi but it's sulphate ilmenite. Coburn has a broader complex with good levels of rutile which will produce a higher grade HiTi than that from Thunderbird, zircon of high enough quality for all main uses (Thunderbird's grades as premium, a bit higher) but importantly its' ilmenite is chloride grade.
It is potentially possible that some parties will prefer Coburn over Thunderbird because of the chloride vs sulphate grade ilmenite. There I speak of the Chinese whose government, in battling pollution, is actively dissuading their industry from sulphate process to chloride. Of note, Dupont uses chloride grade to make their pigment and STA has a sales agreement with them - which of course is valueless without a mine! So we wait and see but if Luke can demonstrate sufficient improvement we should not assume that Thunderbird's massive size precludes Coburn finally finding suitors.
Fungoni won't be a monster (maybe get out to 10 years with some expansion and luck) but the collective assets in Tanzania could prove to be significant. They're already looking at 20 years+ life with a lot more to learn in my opinion.
(20min delay)