Unit 7
The Geochemically Scarce Metals

Overview

Unit 6 introduced the metals and discussed the abundant metals—those present in concentrations greater than 0.1 per cent by weight in the Earth’s crust. Unit 7 discusses metals with concentrations less than 0.1 per cent by weight (in some cases much less): the “scarce” metals. The scarce metals fall naturally into four major groups: the ferro-alloys, the base metals, the precious metals, and the special metals. The first section of the unit introduces the scarce metals, and the next four sections discuss the geological occurrences and production of metals within each group.

Objectives

After completing this unit, you should be able to

1. describe, briefly, the process of atomic substitution and the formation of solid solutions.
2. explain the role of solid solution formation in the distribution of scarce metals in the Earth’s crust.
3. classify geochemically scarce metals into a) ferro-alloy metals, b) base metals, c) precious metals, and d) special metals.
4. describe the applications of ferro-alloy metals (nickel (Ni), chromium (Cr), Cobalt (Co), and molybdenum (Mo)) in the manufacture of special steels.
5. outline the association of Ni, Cr, and Co with large mafic and ultramafic bodies and the association of Mo with felsic intrusions.
6. outline the association of base metals, copper, lead, zinc, and tin with hydrothermal fluids, and describe the applications of the individual metals.
7. describe the occurrences and applications of precious metals (gold, silver, and the platinum group).
8. describe the occurrences of the special metals and the properties which give these metals important roles in technological applications.