The winzes will have been drilled mainly to measure overburden...

The winzes will have been drilled mainly to measure overburden thickness and hardness for drilling. A geologist would have previously selected the key sites to drill. The winze samples are not that important in the end as bulk sampling from them cannot be used to infer a resource size.

A simple calculation of Monday's announcements suggests they are drilling to about 30 metres (20k metres divided by 630 holes). That suggests to me they expect solid intersections close to surface and over an extensive area. This will likely allow an advantageous strip ratio keeping extraction costs low. At say 5-6 holes per day that's around 4 months drilling, maybe add 1 month for weather and technical issues. Sample testing is to be done in parallel to drilling program according to the announcement.