What you say about S32 is correct. S32 is generating huge profits from producing manganese ore. Mn ore is currently best commodity profit wise/tonne. Currently around US$7/dmtu.
There are only two x manganese ore miners on the ASX, that being S32 and OMH. These are the only two companies enjoying the huge profits on manganese ore. Likes of EPM and GMC are not in the race and never will be.
S32 has as you say have two huge projects "Australia (Groote Eylandt Mining Co) and South Africa ( Samancor Holdings)" both hugely profitable.
OMH has its own Mn mine at Bootu Ck in the Northern Territory (currently 800,000 tonnes pa) and a joint operation with Ntsimbinle and JMS in the Tshipi the worlds largest manganese ore mine (this year will likely produce near 4 millions tonnes).
Next week OMH will report an even greater Net profit than Santos STO did today. STO is a $13 billion MC company.
You can be sure of one thing, S32 wouldn't be interested in GMC, infact they'll stay well clear of Indonesia PERIOD.