Question

In porphyry copper deposits, the order of alteration zones from the intrusive body outwards is:

• A. Propylitic $\rightarrow$ Argillic $\rightarrow$ Phyllic $\rightarrow$ Potassic
• B. Argillic $\rightarrow$ Phyllic $\rightarrow$ Potassic $\rightarrow$ Propylitic
• C. Potassic $\rightarrow$ Phyllic $\rightarrow$ Argillic $\rightarrow$ Propylitic
• D. Potassic $\rightarrow$ Argillic $\rightarrow$ Phyllic $\rightarrow$ Propylitic

Hint:

Porphyry copper alteration sequence from intrusive outward: P-P-A-P = Potassic → Phyllic → Argillic → Propylitic.

Answer 1

The Correct Option is C

Step 1: Recall alteration zoning in porphyry copper systems.
- Potassic alteration (K-feldspar + biotite): core zone, highest temperature, nearest to intrusive.
- Phyllic alteration (sericite + quartz + pyrite): next outward zone, high-temperature hydrothermal fluids.
- Argillic alteration (kaolinite, montmorillonite, clay minerals): intermediate to outer zone, lower temperatures.
- Propylitic alteration (chlorite, epidote, calcite): outermost zone, peripheral alteration at lowest temperatures.

Step 2: Arrange in correct order.
From core to margin: \[ \text{Potassic} \;\rightarrow\; \text{Phyllic} \;\rightarrow\; \text{Argillic} \;\rightarrow\; \text{Propylitic}. \]

Step 3: Verify against options.
This matches option (C).

Final Answer:
\[ \boxed{\text{(C) Potassic $\rightarrow$ Phyllic $\rightarrow$ Argillic $\rightarrow$ Propylitic}} \]