Without even looking at the record of historical development for this project, I'd say that they started with an open pit, mined that out, and from the access provided from the depths of the pit, they poked drill holes into the surrounding rock until they found more ore. They decided that underground mining was then the way to go, and off they went.
Mine development decisions are made incrementally. Your first step is not to drop a shaft down 2500 metres. You put in a shaft that goes deep enough to reach ore, and you mine that out. While you're doing that, you employ drills designed for use underground, and you build up your knowledge of the cheapest and most efficient way to exploit the yet deeper but adjacent parts of the deposit predicted by your 43-101 resource estimate many moons ago. You might extend your shaft another 30 metres or whatever, put in your stopes and ventilation and all that, and repeat. (I'm sure that major changes such as shaft extensions are not done exactly as I've described here, but I'm trying to illustrate the incremental growth of a mine.) It's a process, not an event.
Just from looking at the pretty picture, I see at least four major phases of mine development, and many times that many episodes of incremental expansion of the internal infrastructure.
The original Eagle 1 technical report demonstrated the economic viability of mining just that ore. Once they're down at the 225 metre level, for example, do you think they might consider it worthwhile to drop down another 75 metres and take out whatever is accessible from there? Pencil shaped though it may be? (Aside: I don't believe it's a pencil.)
Lar
