Your only problem with your analysis is that you cannot have...

Your only problem with your analysis is that you cannot have cesium in the same concentrate as 6% spodumene concentrate as you contaminate the spodumene product as it has to be of a particular grade to be converted yo lithium carbonate and/or hydroxide. It will therefore require a separate process, which involves treating the tailings and that may be uneconomic unless have significant amounts of tantulum and/or tin as well.

Without blabbering further, whilst I posted this for a different stock (i.e. one where tin is a byproduct) the same arguments apply here as your first port of call in a lithium hard rock development is to get a spodumene concentrate, and then you worry about how economic it is to extract the other minerals from the tailings (unless a technological development occurs that can extract everything from the same process). Not that simple as you claim it to be. But if interested in what I have said hit my name and then read the posts I wrote in the AVZ forum on tin and the separate process required to extract it from a lithium deposit, and why it ain't easy and obviously then requires a lot of resource in the tailings and that also goes for cesium in the tailings. All IMO