Gold and platinum are recovered from valley floors and hill bases as placer deposits rather than from mines d…

Question

Gold and platinum are recovered from valley floors and hill bases as placer deposits rather than from mines dug into rock. Why are these particular minerals suited to survival as placer deposits, while many other minerals are not found this way?

Accepted Answer

## Model Answer Gold and platinum are found as placer deposits because they are **not corroded by water**. When surface rocks weather and erode, these heavy, chemically resistant minerals are transported by water and settle in valley floors and hill bases. Other minerals corrode or dissolve during this process and cannot survive as placer deposits. *Source: Chapter 5 – Mode of Occurrence of Minerals, point (iv)* --- ## Explanation The key phrase from the textbook is "minerals which are not corroded by water." Examiners expect you to: 1. State the defining property (resistance to corrosion/water). 2. Briefly explain the process (weathering → transport by water → settling). Avoid writing about veins/lodes or sedimentary beds — those are different modes of occurrence and will waste words here.

Social Science (087) — AI-generated practice question