Question

Which of the following statements regarding ore deposits is/are CORRECT ?

• A. Both replacement and exhalative ores are possible in SEDEX type deposits
• B. Rampura-Agucha Pb-Zn deposit is a Mississippi Valley Type deposit
• C. Orogenic gold deposit is an epigenetic type deposit
• D. Fluid boiling in the early stage of magmatic crystallization is responsible for Cu- (Mo) deposits

Hint:

- SEDEX → Both exhalative + replacement ores.
- Rampura–Agucha → SEDEX type (not MVT).
- Orogenic gold → Epigenetic.
- Porphyry Cu–Mo → Fluid boiling is crucial.

Answer 1

The Correct Option is A, C, D

Step 1: SEDEX deposits.
- SEDEX (Sedimentary Exhalative) deposits form from hydrothermal fluids venting onto the seafloor.
- These can produce both exhalative ores (deposited on the seafloor) and replacement ores (formed by replacement of host sediments).
- Therefore, statement (A) is correct.
Step 2: Rampura–Agucha deposit.
- Rampura–Agucha Pb–Zn deposit (Rajasthan) is the world’s largest SEDEX-type deposit, not a Mississippi Valley Type (MVT) deposit.
- Hence, statement (B) is incorrect.
Step 3: Orogenic gold deposits.
- Orogenic gold deposits form from hydrothermal fluids migrating along shear zones and faults, typically after host rock formation.
- They are epigenetic deposits (formed later than their host rocks).
- Thus, statement (C) is correct.
Step 4: Fluid boiling and Cu–Mo deposits.
- Porphyry Cu–Mo systems form in magmatic arcs.
- Early-stage fluid boiling during magmatic crystallization plays a key role in ore deposition.
- Therefore, statement (D) is correct.
Step 5: Final Answer.
Thus, the correct set of statements is: \[ \boxed{\text{A, C, and D are correct.}} \]