Question

Explain why nickel deposits are associated only with mafic magma and not with intermediate or felsic magma?

Short answer

Nickel deposits form with mafic magma because it is richer in nickel originating from the mantle, unlike intermediate or felsic magma, which has less nickel.

Step-by-step solution

- Understanding Mafic Magma

Mafic magma is rich in magnesium and iron, and has a lower silica content compared to intermediate or felsic magma. This type of magma originates from the mantle, which is also rich in these elements.

- Nickel Concentration in Mafic Magma

Nickel is often found in higher concentrations within the mantle. When mafic magma forms, it brings with it significant amounts of nickel from the mantle, leading to the potential formation of nickel deposits.

- Composition of Intermediate and Felsic Magma

Intermediate and felsic magmas have higher silica contents and are typically sourced from the crust. These magmas are lower in the magnesium, iron, and nickel that are abundant in the mantle.

- Nickel Deposit Formation

Because mafic magma originates from the mantle and is richer in nickel, the cooling and solidification of this magma can lead to the concentration and formation of nickel deposits. Intermediate and felsic magmas lack this initial nickel concentration, making the creation of nickel deposits less likely.

- Geochemical Compatibility

Nickel is geochemically compatible with the minerals found in mafic magma. During crystallization, nickel can easily incorporate into these minerals, further concentrating and forming deposits.

Key concepts

mafic magma composition

Mafic magma originates from deep within the Earth's mantle. This magma is characterized by its high magnesium (Mg) and iron (Fe) content. Compared to other types of magma, such as intermediate or felsic magma, mafic magma has significantly lower levels of silica.

The composition is critical because silica content affects the magma's viscosity and melting point. Mafic magma is less viscous due to its lower silica, allowing it to flow more readily.

When mafic magma forms, it carries substantial amounts of mantle materials, including magnesium, iron, and other heavy metals. These elements contribute to its dark color. This composition makes it a prime candidate for forming mineral deposits such as nickel.

nickel concentration in mantle

The Earth's mantle is a source-rich zone of heavy metals, including nickel. Due to its depth and high-pressure conditions, the mantle concentrates elements like nickel, magnesium, and iron.

When geological processes generate mafic magma from the mantle, this magma inherits a high concentration of nickel. As the magma migrates towards the Earth's crust, it remains enriched in these metals.

Once the mafic magma begins to cool and solidify, it creates favorable conditions for the formation of mineral deposits. The high concentration of nickel in the originating mantle makes mafic magma an ideal source for nickel ore deposits. Intermediate and felsic magmas, due to their crustal origins and higher silica content, do not share this nickel richness.

geochemical compatibility

Geochemical compatibility refers to how well certain elements or compounds can integrate into existing minerals or rocks during geological processes. In the context of mafic magma and nickel, this concept is crucial.

Nickel has a strong geochemical affinity with the minerals found in mafic magma, such as olivine and pyroxene. During the crystallization process, nickel smoothly incorporates into these minerals. This compatibility facilitates the concentration of nickel within the solidifying magma.

In contrast, intermediate and felsic magmas lack this compatibility. Their minerals, formed from higher silica content, do not favor nickel inclusion. Therefore, nickel deposits are predominantly associated with mafic magma because of this geochemical harmony.