Ann: Drilling update & Extensive Saprolite Clays at Pocos, page-59

Uhhhm; you might want to read up a bit about IACs. Just in summary, alkaline granites are the most likely to form IAC's but only under particular conditions (there are other types of granites too which essentially don't seem to respond the same way or as strongly to weathering and hydrometallurgical events). Felsic rocks are less likely but can still form IACs. Hydrometallurgical events help in this process. There's plenty of material out there if you search for formation of ionic clay deposits. Again off topic to the question I asked. I guess I give up on getting anyone who has done some depth of digging here.

edit: not held dangit, habit