Magmatic Sulphide Deposits

Summary

This video explores mafic and ultramafic magmatic deposits, focusing on their formation, metal content, and global significance. It explains how mantle-derived magmas rise through thinning continental crust, assimilate sulfur from surrounding rocks, and concentrate metals like nickel, copper, cobalt, and platinum group elements into sulfide ore layers. Real-world examples include giant deposits in Russia and South Africa, as well as smaller, yet economically important, deposits in Scotland. The video also highlights modern exploration techniques and emphasizes the importance of environmentally responsible mining, particularly as demand grows for metals essential to energy transition and electric vehicle batteries.

Takeaways

• 🌋 Mafic and ultramafic magmas, rich in dark minerals and low in quartz, are major sources of nickel, chromium, platinum group elements, copper, and cobalt.
• 🔥 These magmas form primarily in areas where continental crust is rifting and new oceanic crust is forming due to upwelling of hot mantle material.
• 🪨 Mafic magmas crystallize into mafic rocks, which are common but only under certain conditions lead to significant metal mineralization.
• 💧 Sulfur assimilation from the continental crust is crucial for forming magmatic sulfide ores, as metals like nickel and copper bind with sulfur to form ore minerals.
• ⚫ Sulfide droplets in magma act as collectors, sinking due to higher density and concentrating metals at the base of magma chambers, forming cumulate layers.
• 🔁 Repeated injections of magma and incorporation of sulfur-rich liquids enhance ore layer formation, sometimes concentrating metals at least 10 times compared to mantle levels.
• 🏭 Notable large magmatic sulfide deposits include the Norilsk district in Russia and the Bushveld Complex in South Africa, which are both massive and rich in metals.
• 🇬🇧 Northeast Scotland hosts smaller mafic intrusions where AB Minerals has discovered significant nickel, copper, and cobalt mineralization through deep drilling and geophysical surveys.
• 🧪 Modern exploration uses drilling, core analysis, and geophysical techniques (like electromagnetic surveys) to accurately map sulfide ore zones.
• ⚡ The global demand for metals like nickel and copper is rising due to the energy transition and electric vehicle production, making responsible sourcing increasingly important.
• 🌱 Environmental and societal considerations are critical; jurisdictions with strong regulations and responsible mining practices are becoming more significant sources of metals.
• 🗺️ Initial discoveries of mafic sulfide deposits often rely on soil sampling since many deposits are buried beneath soil and poorly exposed at the surface.

Q & A

What are mafic and ultramafic magmas, and why are they important for metal deposits?

Mafic and ultramafic magmas are types of molten rock rich in dark minerals and low in quartz. They are important because they are primary sources of metals like nickel, chromium, cobalt, copper, and platinum group elements.

How do mafic magmas form beneath the Earth's crust?

Mafic magmas form when hotter-than-average mantle material wells up beneath the continental lithosphere, causing the crust to thin and fracture. This melting at the base of the lithosphere produces mafic magmas that rise through fractures and faults.

Why is sulfur essential for the formation of magmatic sulfide deposits?

Sulfur is needed for metals in the magma, such as nickel and copper, to react and form sulfide minerals. Without sulfur assimilation from crustal rocks, the metals cannot concentrate into economically viable ore bodies.

What role do sulfide droplets play in metal enrichment within magmas?

Sulfide droplets act as collectors for metals. Metals migrate into these droplets because they preferentially react with sulfur. Being denser than the surrounding magma, the droplets sink to the bottom of the magma chamber, forming cumulate layers enriched in metal ores.

What are the two main types of ore deposits in mafic and ultramafic intrusions?

The two main types are: 1) Magmatic sulfide ores, where metals like nickel and cobalt combine with sulfur; 2) Chromite ores, where chromium combines with oxygen rather than sulfur.

Why are giant deposits like Norilsk and Bushveld important examples of magmatic sulfide ores?

These deposits are massive, with extensive horizontal and vertical ore zones. They have high metal concentrations and illustrate how large-scale accumulation of sulfide-rich magma can produce economically valuable metal deposits.

What makes the Northeast Scotland mafic intrusions a noteworthy case study?

The intrusions formed 400 million years ago above a subduction zone and intersected sulfur-rich crustal rocks. Recent drilling by AB Minerals has confirmed continuous sulfide zones with elevated nickel, copper, and cobalt, highlighting their potential as responsible, smaller-scale sources of metals.

How has modern technology improved the exploration of magmatic sulfide deposits?

Modern exploration uses deep drilling, geophysical surveys (like electromagnetic data), and high-resolution core analysis to accurately map sulfide zones, determine metal concentrations, and assess the economic potential of deposits that are otherwise buried or poorly exposed.

Why is nickel particularly important in the context of energy transition?

Nickel is a key component in electric vehicle batteries and other low-carbon energy technologies. Growing demand for nickel has increased the strategic importance of exploring both large and smaller deposits in environmentally responsible regions.

How do environmental and geopolitical factors affect metal sourcing today?

Global nickel production is concentrated in regions like Russia and Indonesia, which may have geopolitical risks or environmentally damaging mining practices. Deposits in regions with strict environmental and societal regulations, like Scotland, are increasingly valuable for responsible metal sourcing.

What are pentlandite and pyrite, and why are they significant in sulfide deposits?

Pentlandite is a nickel sulfide mineral, and pyrite is an iron sulfide mineral. Pentlandite is especially important because nickel is easier to extract from it than from iron sulfides. Both contribute to the overall metal content of magmatic sulfide deposits.

Why are metal concentrations in magmatic sulfide ores typically much higher than in the mantle?

Although the mantle contains metals like nickel and copper in low concentrations, the process of sulfur assimilation and sulfide droplet formation concentrates these metals into cumulate layers, increasing their concentration at least tenfold in ore deposits.