How often should an open pit be resurveyed for reserve reconciliation?

The standard answer: monthly, tied to your reporting cycle

Most operations resurvey the pit monthly because that's the cadence everything else runs on: mine plan updates, grade control reconciliation, and if there's a loan in the picture, the covenant reporting the project agreed to. A monthly end-of-month survey gives you a volume figure that lines up cleanly with the period you're reconciling: scheduled tonnes against mined tonnes in the plan, or a draw against a borrowing base.

Weekly surveys show up on some operations, usually where grade control needs tighter feedback inside a single bench or where ore and waste boundaries are moving fast enough that a month is too coarse to catch problems early. But a weekly cadence is expensive to sustain with a full survey crew, and most of what a lender or a corporate planning group needs shows up fine at monthly resolution.

Quarterly is the other end you'll see, mostly at smaller or lower-activity sites where the cost of mobilizing a survey crew doesn't pencil out against a modest monthly move. The tradeoff is real: a bad month hides inside a quarter, and if you're holding a covenant tied to extraction pace, three months is a long time to find out the number came in short.

Why the interval matters more once a lender's attached

If you're the mine's own survey and engineering team, you can set cadence around operational needs and not think about it much beyond that. Once a financier or an outside reserve reconciliation requirement enters the picture, the interval itself becomes something that gets scrutinized. A covenant that says "monthly extraction volume" is only as good as having a real monthly number, and if that number comes from the same team whose draw depends on hitting it, the interval doesn't solve the independence problem. You can resurvey every week and still be relying on the operator's own instrument, crew, and reporting chain.

That's the gap that comes up most often in site visits and loan reviews. It's rarely a disagreement about how often to survey. It's a question of who did the surveying, and whether the resulting number was produced independently of the people whose numbers it's checking.

Picking a cadence that fits your mine plan

A few things to weigh when you're setting, or questioning, a survey interval:

• Plan granularity. If your mine plan schedules tonnes by month, survey monthly. Matching your reconciliation interval to your planning interval is the point. A finer survey cadence than your plan resolution adds cost without adding usable signal.
• Covenant language. If a loan agreement specifies a reporting period, that period sets your floor. Don't let survey cadence drift looser than what the agreement requires.
• Pit activity level. A pit moving a lot of material fast benefits from tighter intervals, simply because more can go wrong, and go unnoticed, in a bigger window.
• Cost of the survey itself. Drone or terrestrial LiDAR crews aren't free to mobilize repeatedly. That cost is a big part of why monthly has become the practical floor at most operations rather than the ideal one.

For reserve reconciliation tied to a mine plan or a financing agreement, monthly is the answer for most projects. It also happens to suit how satellite and aerial stereo coverage works in practice: enough time between passes to register real change on the ground, short enough that a shortfall doesn't sit undetected for a full quarter.

If what's missing isn't a cadence decision but a volume number nobody on site produced themselves, that's the gap Pit Progression is built to close: a monthly elevation difference across the pit turned into a moved-material figure you can set against the plan or the covenant, without waiting on the operator's own reported numbers.

See what a monthly, independent read would look like next to your current plan or covenant number.