I remember reading that Rio Tinto looks at prospective...

I remember reading that Rio Tinto looks at prospective acquisitions on a risk basis and would rather pay overs for a relatively derisked project than look for a bargain in a project still loaded up with risk. I reckon that would especially be the case now as they would still be smarting from the Serbian lithium project that fell over due to lack of permitting and social license. So, yes, Rio say they are keen to get into lithium and they already have a finger to the breeze near to Adina but my guess is that any big move by them is a long way ahead.

I think your threshold of 100mt for Adina is not too ambitious. A key issue will be how much of those resources can be converted into reserves. In any case it is not as if Adina is all by itself. For starters Azimut Exploration and SOQUEM have the block immediately south of Adina's Jamar deposit and they also have reported impressive assay results (source: here). Also Loyal Lithium have reported drill hits and Midland and Rio have been kicking rocks along that trend. And last month Comet Lithium reported gravity surveying of their Liberty block indicated a pegmatite targets just over the boundary from Adina (source: here).

The development model for that area around the Trieste Formation could be that several operators all run their own races eg both Adina and Azimut's block, Galinee, both get mines and concentrators, or they work cooperatively eg both Adina and Galinee each get mines but the two companies share a processing plant, or the area undergoes consolidation eg Rio buys out everything. It makes sense for permitting and infrastructure aspects for the various players to work as a cluster rather than as insular entities. That SOQUEM is sitting at the table probably adds extra oomph for there to be cooperation.

Here is a schematic of the area around Adina: they are all as snug as a bug in a rug.