---

Typical Assay Ranges in Porphyry Copper Systems

(Cu–Au–Mo porphyry deposits)

1. Copper (Cu) Grades

Porphyry copper deposits are low-grade, high-tonnage systems.

➤ Typical Hypogene (Primary) Cu Grades

• 0.2–1.0% Cu is the most common range

• 0.3–0.6% Cu represents many operating porphyry mines

• >1.0% Cu occurs but usually only in the central high-grade core

Authoritative sources:

• USGS Porphyry Copper Deposit Model (Cox & Singer, 1992)

• Geology for Investors – Porphyry Copper Deposits

---

2. Gold (Au) Grades

Gold varies widely depending on whether it is a Cu-Au or Cu-Mo system.

➤ Typical Au Grades

• 0.1–0.7 g/t Au in Cu-Au porphyries

• 0.2–0.4 g/t Au most common

• <0.1 g/t Au in Cu-Mo porphyries (often negligible)

➤ High-Au Porphyry Examples

• Grasberg (Indonesia): 0.5–1.0+ g/t Au

• Cadia / Ridgeway (Australia): 0.5–1.5 g/t Au

References:

• Sillitoe, R.H., 2010, “Porphyry Copper Systems,” Economic Geology:

• USGS Open-File Report 2008-1155 (Deposit Model)

---

3. Molybdenum (Mo) Grades

Molybdenum occurs as molybdenite (MoS₂) and varies depending on deposit subtype.

➤ Typical Mo Grades

• 0.005–0.05% Mo in Cu-rich porphyries

• 0.02–0.1% Mo in Cu-Mo porphyries

• 0.1–0.3% Mo in Mo-rich porphyry systems (Climax-type)

Examples

• Bingham Canyon: ~0.03% Mo

• Climax (Colorado): >0.2% Mo (Mo-dominant system)

References:

• USGS Porphyry Copper and Molybdenum Deposit Models

• Singer et al. global porphyry Mo models

---

Summary Table (Typical Exploration Ranges)

Metal	Typical Range in Porphyry Systems	Notes
Cu	0.2–1.0%	Most mines run 0.3–0.6% Cu
Au	0.1–0.7 g/t	Higher in Cu-Au systems; very low in Cu-Mo porphyries
Mo	0.005–0.05%	Higher (0.1–0.3%) in Mo-dominant porphyries

---

How to Interpret These in Exploration

These numbers guide exploration teams:

Strong Indicators You’re Approaching a Porphyry Core

• Cu > 0.5%, even in short intervals

• Au > 0.3 g/t in Cu-Au systems

• Mo > 0.02% in Cu-Mo systems

• Increasing density of quartz-stockwork veining (A, B-veins)

• Potassic alteration (K-feldspar + biotite)

Peripheral/Zonal Indicators

• Cu < 0.2% usually indicates phyllic/propylitic halo

• Au often very low in outer zones

• Mo increases at depth in many systems

---

https://t.me/OreZone

https://ko-fi.com/orezone