Monazite sand (rare-earth phosphate placer mineral): the typical uranium content by mass is approximately what percentage?

Introduction / Context:Monazite is a phosphate mineral rich in rare-earth elements and thorium, and it can contain trace uranium. Understanding typical assay values helps in resource evaluation and in distinguishing thorium-bearing sands from uranium ores.

Given Data / Assumptions:

• Coastal placer monazite sands.
• Typical global averages; local deposits vary.
• Question seeks an order-of-magnitude estimate, not an exact assay.

Concept / Approach:Monazite commonly contains significant thorium (often a few percent up to 7–10%), while uranium is much lower—generally a few tenths of a percent or less. Therefore, an estimate near 0.25% aligns with standard references and is widely used in exam keys to represent “trace-but-nonzero” uranium content.

Step-by-Step Solution:Recall monazite composition: rare-earth phosphate with Th and minor U.Compare typical Th content (percent level) to U content (sub-percent).Select the closest sub-percent value among options.Hence, 0.25% is the accepted typical figure.

Verification / Alternative check:Mining and mineral-processing texts list uranium in monazite on the order of several thousand ppm (i.e., a few tenths of a percent), corroborating the 0.25% choice, while thorium is notably higher.

Why Other Options Are Wrong:0.01%: too low for many monazite placers.1.2% and above (7%, 12%): characteristic of thorium, not uranium, in monazite.

Common Pitfalls:Confusing uranium and thorium assay levels in monazite.Assuming a single deposit’s value is universal.

Final Answer:0.25%