Supergene

Geological process of mineral enrichment

Overview

Example of a plant with supergene characteristics.

The term supergene refers to a set of geological processes that occur near the Earth's surface, resulting in the alteration and enrichment of mineral deposits. These processes are primarily driven by the interaction of meteoric waters with existing mineral deposits, leading to the formation of secondary minerals. Supergene processes are significant in the field of economic geology as they can enhance the concentration of valuable metals, making them more economically viable to mine.

Formation Processes

Supergene processes typically involve the weathering of primary minerals and the subsequent transport and redeposition of metals. This occurs in the vadose zone, where oxygen-rich waters percolate through the soil and rock, oxidizing sulfide minerals and leaching metals. The metals are then redeposited at lower levels, often forming enriched zones known as "supergene enrichment zones."

Oxidation

The initial stage of supergene processes is the oxidation of primary sulfide minerals. This involves the conversion of sulfides such as pyrite (FeS₂) into oxides, sulfates, or other secondary minerals. For example, pyrite can oxidize to form goethite (FeO(OH)) and sulfuric acid, which further contributes to the leaching of metals.

Leaching

Leaching is the process by which metals are dissolved and transported by percolating waters. Acidic conditions, often resulting from the oxidation of sulfides, enhance the solubility of metals such as copper, zinc, and lead. These metals are carried downward through the soil and rock profile.

Precipitation

As the leachate moves downward, it encounters reducing conditions or neutral pH environments, leading to the precipitation of secondary minerals. This can result in the formation of enriched zones of minerals such as chalcocite (Cu₂S) or covellite (CuS), which are more concentrated than the original ore.

Economic Importance

Supergene enrichment is a critical factor in the economic viability of many ore deposits. The process can significantly increase the concentration of metals, making low-grade deposits profitable to mine. Notable examples include the enrichment of copper in the porphyry copper deposits of Chile and the United States.

Environmental Considerations

While supergene processes can enhance mineral deposits, they can also pose environmental challenges. The oxidation of sulfide minerals can lead to the generation of acid mine drainage, which can have detrimental effects on local ecosystems. Effective management and remediation strategies are essential to mitigate these impacts.

Related Pages

• Ore genesis
• Weathering
• Economic geology
• Mineral deposit