RECURSOS MINERAIS aula 02

Summary

This lesson delves into the geological formation of diamond deposits, differentiating between primary and secondary deposits. Primary deposits, associated with kimberlites and lamproites, are formed under extreme conditions deep within the Earth's crust. Secondary deposits result from weathering and transportation by water, concentrating diamonds due to their density and hardness. The script highlights key diamond-rich regions in Brazil, such as Minas Gerais and Goiás, and touches on the role of carbonatites in diamond formation. The video provides valuable insights into the complex processes involved in diamond genesis and their distribution in the Earth's geological environments.

Takeaways

• 😀 Primary diamond deposits are found in kimberlite and lamproite rocks, formed by magmatic processes deep in the Earth's mantle.
• 😀 Kimberlites are magmatic rocks formed at depths of 150-200 km with temperatures ranging from 1,100 to 1,500°C and contain minerals like olivine and serpentine.
• 😀 Lamproites are chemically similar to kimberlites but have distinct morphology and mineral composition, being rich in magnesium and fluorine.
• 😀 Secondary diamond deposits are the result of erosion and weathering of primary deposits, with diamonds being transported by water to areas of higher concentration.
• 😀 In Brazil, the first diamond deposits were found in the 18th century in Minas Gerais, with kimberlite deposits discovered later in the 1960s.
• 😀 The Jequitinhonha and Paranaíba River Basins are the main regions in Brazil where diamonds are concentrated.
• 😀 The provinces of Serra do Espinhaço, Alto Paranaíba, and Oeste São Francisco are key diamond-producing areas in Brazil.
• 😀 Carbonatites, rich in carbonate minerals, play a significant role in the geology of diamonds, with the only active carbonatite volcano being located in Tanzania.
• 😀 Diamonds are formed under extreme pressure and temperature conditions about 160 km below the Earth's surface and are brought to the surface by volcanic eruptions.
• 😀 The age of diamonds ranges from 1 to 3 billion years, making them almost as old as the Earth itself (4.5 billion years).

Q & A

What are primary and secondary diamond deposits?

Primary diamond deposits are those formed deep within the Earth's mantle at depths of 150 to 200 km and temperatures ranging from 1,100 to 1,500 degrees Celsius. These deposits are typically found in kimberlites and lamproites, which are magmatic rocks. Secondary deposits, on the other hand, are formed through weathering and erosion of primary deposits, with diamonds being transported by water and concentrated in areas based on their density and hardness.

What are kimberlites and lamproites, and how do they differ?

Kimberlites and lamproites are both magmatic rocks associated with diamond deposits. Kimberlites are typically rich in olivine and occur as intrusions in the Earth's crust, forming diamond-bearing chimneys. Lamproites, which were once thought to be kimberlites, are also ultrapotassic rocks, rich in magnesium and poor in carbon dioxide. They share a similar appearance with kimberlites but have a different chemical composition.

What minerals are commonly found with diamonds in primary deposits?

In primary diamond deposits, diamonds are often accompanied by minerals such as olivine, calcite, serpentine, phlogopite, diopside, and granate. These minerals form the matrix or may appear as xenoliths, fragments of other rocks that the magmatic intrusion passed through.

How are secondary diamond deposits formed?

Secondary diamond deposits are created through weathering and erosion of primary deposits. As diamonds and other minerals are transported by water, they undergo natural classification due to their varying densities, hardness, and granulometry. The diamonds, being denser and harder, accumulate in certain areas where conditions favor their concentration.

Where in Brazil are significant diamond deposits found?

In Brazil, significant diamond deposits are found in regions such as the Jequitinhonha and Paranaíba river basins in Minas Gerais. Other notable areas include the Serra do Espinhaço, Alto Paranaíba, and Oeste São Francisco provinces, along with smaller deposits in regions like Goiás, Mato Grosso, Rondônia, and Piauí.

What are carbonatites, and how are they related to diamonds?

Carbonatites are rare igneous rocks primarily composed of carbonates, such as calcite. These rocks are associated with environments like continental rift zones and hotspots. While not directly linked to diamond formation, carbonatites can occur in areas where diamonds are found, as they are sometimes intruded by magmatic fluids that could facilitate diamond crystallization.

Why are diamonds considered so old?

Diamonds are incredibly old because they form deep within the Earth's mantle, at depths of around 150 to 200 km, and are brought to the surface through volcanic eruptions. Most natural diamonds are between 1 to 3 billion years old, making them nearly as old as the Earth itself, which is approximately 4.5 billion years old.

How do diamonds reach the Earth's surface?

Diamonds are transported to the Earth's surface through volcanic eruptions, which occur when magma from deep within the Earth forces its way up to the surface. This magma, rich in carbon, brings diamonds along with it as part of the eruption process.

What factors influence the concentration of diamonds in secondary deposits?

The concentration of diamonds in secondary deposits is influenced by factors such as the density, hardness, and granulometry of the diamond compared to other minerals in the sediment. The natural sorting of materials during transport by water allows the heavier and harder diamonds to accumulate in specific locations.

What are the main geological environments where carbonatites form?

Carbonatites primarily form in continental intraplate environments, associated with hotspots, continental rifts, and fault zones. They can also occur in areas of continental separation or during tectonic events such as those related to the break-up of supercontinents.