🎓 Lesson 8
D5
Monetizing First-Pass Yield: From % to $
First-pass yield is the percentage of ore that meets grade and size specifications right after blasting—before any sorting or processing—so you can sell it immediately instead of wasting money on extra crushing or rejection.
🎯 Learning Objectives
- ✓ Calculate first-pass yield (%) from blast fragment size distribution (FSD) and grade block model data
- ✓ Convert first-pass yield into monetary value ($) using real-time ore price, processing cost, and penalty structures
- ✓ Analyze trade-offs between burden/spacing adjustments and FPY-driven net revenue per tonne
- ✓ Explain how FPY reduces hidden costs associated with rehandling, secondary blasting, and low-grade dilution
📖 Why This Matters
In open-pit mines, up to 15–25% of blasted material is either oversize (requiring secondary breakage) or sub-economic grade (diluting mill feed). Every tonne rejected or reprocessed erodes margin—not just in energy and labor, but in opportunity cost: delayed cash flow, increased inventory carrying cost, and missed sales windows. Monetizing first-pass yield turns blast engineering from a 'cost center' activity into a direct revenue lever—where a 5% FPY improvement can lift EBITDA by $0.80–$1.20/tonne in copper or iron ore operations.
📘 Core Principles
First-pass yield rests on three intersecting domains: (1) Fragmentation quality—governed by Kuz-Ram model inputs (rock strength, explosive energy, burden/spacing), predicting the P80 and FSD; (2) Geological selectivity—defined by drill-hole grade continuity, block model cutoff grades, and muckpile mixing effects; and (3) Operational constraints—crusher feed size limits, stockpile segregation capability, and real-time assay turnaround time. FPY is not a standalone blast metric—it emerges only when all three domains are co-optimized. Critically, FPY monetization requires assigning differential value to tonnages: high-grade, correctly sized ore earns full metal price minus mining cost; oversized or low-grade material incurs penalties or zero revenue until remediated.
📐 FPY-to-$ Conversion
The monetized value of first-pass yield combines physical yield with economic weighting. It uses weighted average net revenue per tonne across FPY-qualified and non-FPY material streams, adjusted for processing penalties and recovery losses.
Monetized First-Pass Yield Value (MFV)
MFV = [FPY × (Revenue_per_t_FPY − Cost_per_t_FPY)] − [(1−FPY) × Penalty_per_t_nonFPY]Converts physical first-pass yield into net revenue contribution per tonne of blasted material.
Variables:
| Symbol | Name | Unit | Description |
|---|---|---|---|
| FPY | First-pass yield | decimal (0–1) | Fraction of blasted material meeting size and grade criteria simultaneously |
| Revenue_per_t_FPY | Net revenue per tonne of FPY material | $/t | Metal value × recovery − mining & processing cost |
| Cost_per_t_FPY | Processing cost for FPY material | $/t | Crushing, conveying, and milling cost allocated to qualified tonnage |
| Penalty_per_t_nonFPY | Average cost penalty per tonne of non-FPY material | $/t | Weighted sum of secondary blast, handling, storage, and opportunity cost |
Typical Ranges:
Copper porphyry (open pit): 60–82%
Iron ore (hard hematite): 55–75%
Coal (highwall blast): 70–88%
💡 Worked Example
Problem: A copper mine blasts 10,000 t/bench. Blast FSD shows 72% ≤ 300 mm (crusher limit). Grade block modeling indicates 85% of that 72% meets Cu ≥ 0.45% cutoff. Processing cost = $18/t; Cu price = $3.80/lb ($8,377/t Cu); recovery = 92%. Oversize (≥300 mm) requires secondary blasting at $4.20/t; low-grade (<0.45%) is stockpiled at $2.10/t handling cost and deferred revenue. Calculate MFV per blasted tonne.
1.
Step 1: Compute FPY mass = 10,000 t × 0.72 × 0.85 = 6,120 t
2.
Step 2: Revenue from FPY = 6,120 t × (0.48% Cu avg × 0.92 × $8,377/t Cu − $18/t) = 6,120 × ($187.40 − $18) = $1,036,500
3.
Step 3: Non-FPY = 3,880 t: 28% oversize (2,800 t) → $4.20/t cost = $11,760; 12% low-grade (1,080 t) → $2.10/t cost = $2,268. Total non-FPY cost = $14,028
4.
Step 4: Net revenue = $1,036,500 − $14,028 = $1,022,472 → MFV = $1,022,472 ÷ 10,000 t = $102.25/t
Answer:
The monetized first-pass yield value is $102.25 per tonne of blasted material, which exceeds the site’s breakeven threshold of $94.50/t.
🏗️ Real-World Application
At BHP’s Escondida Norte (Chile), engineers redesigned the 16-m bench blast pattern using digital twin simulation (DynaFragment + MineGrade) to increase FPY from 63% to 79% over six months. By tightening burden from 5.2 m to 4.7 m and reducing spacing from 6.8 m to 6.1 m—while holding powder factor constant at 0.28 kg/t—they improved P80 from 285 mm to 242 mm and reduced grade dilution by optimizing initiation timing across geologically distinct zones. The $10.3M annual uplift in net cash flow was attributed directly to FPY monetization—validated via reconciliation of muckpile assays, crusher feed sizing scans, and monthly financial close data.