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Here's how the mineralisation is described at Olympic Dam:

"RD1 drilled through 335m of flat-lying Proterozoic and Cambrian sediments before passing through an unconformity into haematite altered basement rocks. In theory the copper mineralisation was supposed to be in the overlying sediments but assays revealed fine-grained hypogene chalcocite in the basement. RD1 returned 38m @ 1.05%Cu, which was considered uneconomic at these depths at this time, but RD10 changed that with an intersection of 170m @ 2.12%Cu and 0.58kg/t U3O8 and is considered the “Discovery Hole”."

From http://odx.bhpbilliton.com/expansion/geology.asp

It was assays that confirmed the mineralisation at Olympic.