Question

Which one of the following mineral associations is diagnostic of the highly-oxidized zone of a weathered primary base metal vein?

• A. Smithsonite, Malachite, Anglesite
• B. Calcite, Fluorite, Pyrite
• C. Limonite, Realgar, Chalcocite
• D. Goethite, Orpiment, Boehmite

Hint:

In the oxidized zone of base metal veins, minerals like Smithsonite (zinc), Malachite (copper), and Anglesite (lead) are commonly found as secondary products of weathering and oxidation.

Answer 1

The Correct Option is A

Step 1: Understanding the mineral association.
The highly-oxidized zone of a weathered base metal vein typically contains secondary minerals formed as a result of the oxidation of primary ore minerals. These secondary minerals are typically carbonates, sulfates, and oxides, which form under conditions of low temperature and high oxidation.
- Smithsonite is a zinc carbonate mineral that commonly forms in the oxidized zone of zinc ores.
- Malachite is a copper carbonate mineral that forms in the oxidized zone of copper ores.
- Anglesite is a lead sulfate mineral that commonly forms in the oxidized zone of lead ores.
This combination of minerals (Smithsonite, Malachite, Anglesite) is typical of the highly-oxidized zone of weathered primary base metal veins.

Step 2: Analyzing the other options.
- Option (B): Calcite, Fluorite, Pyrite. These minerals are typically associated with various geological settings, but they do not represent the highly-oxidized zone of a base metal vein.
- Option (C): Limonite, Realgar, Chalcocite. These minerals are more commonly associated with different types of mineralization or the less-oxidized zones.
- Option (D): Goethite, Orpiment, Boehmite. These minerals are often found in other geological contexts, but not specifically in the highly-oxidized zone of base metal veins.

Step 3: Conclusion.
The correct mineral association that indicates the highly-oxidized zone of a weathered base metal vein is Smithsonite, Malachite, and Anglesite, making option (A) the correct answer.
\[ \boxed{\text{Smithsonite, Malachite, Anglesite}} \]