CSIR NET June 2016 Q105: Geomorphology
Placer deposits form where stream velocity abruptly decreases, allowing dense heavy minerals to be preferentially concentrated by settling while lighter material continues to be transported.
Velocity is lowest on the inner bank of a meander (point bar), where flow separates and slows, and immediately below waterfalls, where the sudden loss of kinetic energy causes rapid deposition. These are the classic sites of placer (heavy mineral) accumulation. Option 2 is correct.
1) and 4) Incorrect -- the outer bank of a meander is a zone of higher velocity and erosion (cut bank), not deposition, making it a poor placer site. 2) Correct -- inner bank (point bar) and below waterfalls are both low-velocity, high-deposition zones ideal for placer formation. 3) Incorrect -- above waterfalls, flow is typically still fast approaching the brink, not conducive to heavy mineral settling.