When you scope a new open pit, constrain the first phase with an economic shell aimed at a 10–12 year LOM, then back-calc fleet, power, and water balances before sketching haul roads or pads. If anyone wants a quick review, I can show how we turn block model cashflows into phased pushbacks and a consumables plan that holds capex steady in year one.
I always “back-calc fleet, power, and water balances” with a stress test before sketching ramps: on the 10–12 yr shell I model +15% diesel, -5% price, and 1-in-5 wet-season inflows to size pumps and tyres so Phase 1 doesn’t wobble. @OP small caveat — if you need capex steady in year one, seed the first pushback from an 8–9 yr shell with a slightly higher cutoff to shorten early hauls without overcapitalizing.
I force one constraint: the starter ramp must hit ore by bench 2 and the longest initial haul stays under about 2.2 km; that keeps the fleet you ‘back‑calc’ from drifting and holds year‑one capex even in a wet start, @mark39. Only caveat — if the ore plunges, I’ll allow a short spur ramp.
Quick example: on a copper start-up we right-sized by freezing the first crusher pad and demanding a ‘12‑week ore exposure’ in the micro‑schedule before any permanent haul alignment, then let the pushback geometry follow. That gate kept prestrip and rehandle flat without inflating the truck count, but in saprolite we swap to a small mobile sizer so the pad can drift if groundwater surprises. If you post a shell, @OP, I’m happy to sanity-check that exposure window.