Question

During a geochemical exploration survey in a hilly terrain, Cu concentration of stream sediments from a third order basin outlet was measured to be 3000 ppm. Considering a catchment area of 10 km\(^2\) and a Cu background value of 200 ppm, which one of the following options is the productivity of this catchment for Cu?

• A. 1.5 × 10\(^6\) m\(^2\)
• B. 2.8 × 10\(^6\) m\(^2\)
• C. 3.0 × 10\(^6\) m\(^2\)
• D. 3.2 × 10\(^6\) m\(^2\)

Hint:

To calculate the productivity of an area for an element, subtract the background concentration from the measured concentration and multiply by the catchment area.

Answer 1

The Correct Option is B

Step 1: Understanding productivity in geochemical surveys.
The productivity of a catchment refers to the amount of a particular element (in this case, Cu) being contributed by the catchment area. It can be calculated using the formula:

    Productivity = (Cu concentration - background concentration) × Catchment area
  

Step 2: Applying the values.
We are given:
- Cu concentration = 3000 ppm
- Background Cu concentration = 200 ppm
- Catchment area = 10 km² = \(10 \times 10^6\) m²

Now, calculating the productivity:

    Productivity = (3000 - 200) × 10 × 10^6 = 2800 × 10^6 ppm·m² = 2.8 × 10^9 ppm·m²
  

Therefore, the productivity is \(2.8 \times 10^9\) ppm·m², matching option (B).