Introduction

"I'm going to talk about General VMS deposits and how they form… and then I'm going to just go through a few case studies where I'm going to talk about different Metals." This article aims to present VMS deposits explained and their formation processes.

Volcanogenic Massive Sulfide (VMS) deposits develop through interaction between hydrothermal fluids and volcanic rocks, resulting in the accumulation of metals such as copper, gold, lead, zinc, and silver. This geological phenomenon has significant implications for the mining and resource industry.

Formation Environment of VMS Deposits

VMS deposits originate from underwater volcanic eruptions. These formations commonly occur at rifts or spreading centres, where extension faulting of seafloor rocks takes place. This geological action is driven by magmatic vortices within the Earth’s liquid outer core.

Rift or Spreading Centre

The extension faulting of seafloor rocks allows magma to rise, creating geological processes of VMS deposits. This ongoing process is attributed to movements within the Earth’s outer core, which impact tectonic activities on the seafloor.

Geological Processes

Magma exploits these extension faults, leading to the development of volcanic piles. Eruption cycles become a regular occurrence, triggered by the sudden influx of magma into subterranean chambers. This ongoing process has been shaping the Earth’s geological landscape since ancient times.

Eruption Cycles

With each cycle, material ejected during eruptions settles around the volcanic vent, eventually forming significant geological features. Over time, coarse materials accumulate near the volcano, while finer particles disperse further away.

Volcanic Pile Formation

This accumulation process leads to the formation of volcanic piles with varying thicknesses. The extent and composition depend on both eruption intensity and duration, with coarse materials settling closer to the epicentre.

Hydrothermal Fluid Development

Negative pressure within the volcanic pile creates a situation where seawater is drawn into the system. This interaction between seawater and magma gives rise to hydrothermal fluid dynamics.

Mineral Dissolution Process

As seawater dissolves minerals from the surrounding volcanic materials, it becomes enriched with metal-laden fluids. These fluids are rich in metals like copper, gold, lead, zinc, and silver, as well as elements like sulfur, which contribute to the composition of mineral-rich fluids.

Mineral Deposition Process

The heated hydrothermal fluids rise through the volcanic pile, interacting with it and depositing essential minerals.

Black Smoker Formation

This interaction results in black smoker formation. These are chimney-like structures that mark mineral deposits. As the fluids cool, they undergo chemical changes that precipitate valuable minerals.

Metal Zonation

There is a noticeable zonation in metal deposition. Copper and gold are often found closer to the volcanic vent, while lead, zinc, and silver are deposited further away and higher up. This zonation is attributed to varying conditions within the hydrothermal system.

Deposit Formation Timeline and Cycles

The time required for VMS deposit formation ranges from tens to hundreds of thousands of years. This extensive period involves repeated eruption cycles and the accumulation of sediment layers.

Accumulation Periods

Sediments slowly accumulate, contributing to both the volcanic pile and the eventual mineral deposits. This cyclical process ensures continuous mineral deposition through persistent interactions between magma and seawater.

Lateral and Vertical Occurrence

Deposits can occur both laterally and vertically within the geological setting, influenced by the movement of hydrothermal fluids and the underlying geology.

Post-Formation Processes

After formation, continental collision and uplift can expose these deposits, making them available for mining. Erosion and transportation also play roles in redistributing minerals, occasionally forming new economically viable deposits.

Sediment Recycling

The continuous recycling of sediments through geological processes could potentially lead to the formation of new mineral deposits.

Real-World Example: Flin Flon VMS Belt

An illustrative example is the Flin Flon VMS Belt, located in eastern Saskatchewan, Canada. Historically significant, it played an important role for the Hudson Bay Mining and Smelting Company.

Conclusion

The ongoing effort to locate VMS deposits is vital for understanding their formation processes and recognising new economic opportunities. "Understanding VMS formation processes is essential for mineral exploration and resource assessment," which remains a significant focus for the mining sector.

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