Question

The given figure shows the self-potential anomaly observed over a two-dimensional thin sheet-type ore body whose strike is perpendicular to the plane of the paper. Which one of the following directions of polarization of the ore body leads to the given anomaly? \includegraphics[width=0.5\linewidth]{11.png}

• A. \includegraphics[width=0.2\linewidth]{12.png}
  (B) \includegraphics[width=0.2\linewidth]{13.png}
  (C) \includegraphics[width=0.2\linewidth]{14.png}
  (D) \includegraphics[width=0.2\linewidth]{15.png}
• B.
• C.
• D.

Hint:

In self-potential anomalies, the anomaly sign order (negative-to-positive or positive-to-negative) directly indicates the sequence of poles along the survey line. Negative pole first gives a negative lobe first.

Answer 1

The Correct Option is A

Step 1: Understanding the anomaly.
The graph shows a negative potential anomaly (trough) first, followed by a positive anomaly (peak). This means as we move along the profile, the self-potential decreases (negative lobe) and then increases (positive lobe). Step 2: Relation to dipole orientation.
A polarized ore body can be approximated as an electric dipole. The direction of the dipole determines the order of the anomalies. - If the negative pole is encountered first along the profile, the anomaly begins with a negative trough. - If the positive pole is encountered first, the anomaly begins with a positive peak. Step 3: Matching with the figure.
From the figure: - At around 50 m distance, the anomaly is negative (–20 mV to –40 mV). - After about 150 m, the anomaly turns positive (up to +20 mV). This sequence (negative → positive) implies the left side is a negative pole and the right side is a positive pole. \[ \boxed{\text{Thus, the polarization is Negative pole (left) → Positive pole (right), i.e., Option (A).}} \]