Volcanogenic Massive Sulfide (VMS) Deposits

Volcanogenic massive sulfide (VMS) deposits are a type of mineral deposit that forms on or below the seafloor as a result of volcanic and hydrothermal activity. They are typically composed of metal sulfide minerals such as copper, zinc, lead, gold, and silver, and can also contain significant amounts of iron, sulfur, and other elements. VMS deposits are typically small- to medium-sized and occur in clusters or belts, often in association with submarine volcanic rocks and hydrothermal vents.

VMS deposits are important sources of base and precious metals, and have been mined for thousands of years. They are found in both modern and ancient seafloor settings, and are typically associated with mid-ocean ridges, island arcs, and back-arc basins. Some of the most significant VMS deposits are found in Canada, Australia, Scandinavia, and the Iberian Peninsula.

Geologic setting

Volcanogenic massive sulfide (VMS) deposits are formed in association with submarine volcanic activity, typically located along the margins of tectonic plates in areas of volcanic and/or seismic activity. The deposits are commonly associated with ancient island arcs or back-arc basins, where the seafloor has been modified by subduction-related volcanism.

VMS deposits are generally hosted by volcanic and sedimentary rocks, including basaltic to andesitic volcanic rocks, rhyolitic volcanic rocks, and marine sedimentary rocks. They are commonly found in greenstone belts, which are geological terranes that contain a variety of volcanic and sedimentary rocks, and are associated with ancient volcanic arcs.

The geologic setting of VMS deposits is characterized by the presence of hydrothermal vents or “black smokers” on the seafloor, which release hot, metal-rich fluids into the ocean. These fluids react with seawater and with the surrounding rocks, depositing minerals in and around the vents. The deposits may occur in clusters or “fields” along submarine volcanic chains, and may be associated with other types of mineral deposits, such as seafloor massive sulfides (SMS) and submarine exhalative deposits.

Historical significance

VMS deposits have been an important source of base and precious metals throughout history. They have been mined since ancient times, particularly for copper and silver, and were a major source of copper during the Bronze Age. The Rio Tinto mine in Spain, for example, has been in use for over 5,000 years, with mining operations dating back to the 3rd century BCE.

In the modern era, VMS deposits were a major target of mineral exploration during the 20th century, particularly in the 1960s and 1970s. Many of the world’s largest VMS deposits were discovered during this period, and they continue to be important sources of base and precious metals today.

Types of VMS Deposits

There are several types of VMS (volcanogenic massive sulfide) deposits, which are classified based on their geologic setting and mineralogy. Here are some of the common types:

1. Bimodal VMS Deposits: These deposits are formed in volcanic environments that are characterized by the presence of both mafic and felsic rocks. The mafic rocks are usually basaltic and the felsic rocks are usually rhyolitic or dacitic.
2. Felsic VMS Deposits: These deposits are formed in volcanic environments that are dominated by felsic rocks, such as rhyolite and dacite.
3. Mafic VMS Deposits: These deposits are formed in volcanic environments that are dominated by mafic rocks, such as basalt.
4. Sedimentary Exhalative (SEDEX) VMS Deposits: These deposits are formed in sedimentary basins and are associated with the discharge of hydrothermal fluids through sedimentary rocks.
5. Cyprus Type VMS Deposits: These deposits are named after the massive sulfide deposits in Cyprus, which are formed in submarine volcanic environments and are associated with ophiolites (segments of oceanic crust).
6. Kuroko Type VMS Deposits: These deposits are named after the massive sulfide deposits in Japan’s Kuroko mine, which are formed in submarine volcanic environments and are characterized by their high content of zinc, lead, and copper.
7. Algoma Type VMS Deposits: These deposits are named after the massive sulfide deposits in Canada’s Algoma district, which are formed in submarine volcanic environments and are characterized by their high content of copper.

Each type of VMS deposit has its own unique characteristics in terms of geologic setting, mineralogy, and economic significance.

Formation Processes and Mineralogy

Volcanogenic massive sulfide (VMS) deposits form from hydrothermal fluids that originate from volcanic activity. The fluids are rich in sulfur and metals, and they are often expelled from volcanic vents on the seafloor. When the hot fluids encounter cold seawater, they cool rapidly, causing the metals and sulfur to precipitate and form mineral deposits.

The mineralogy of VMS deposits is complex, with many different minerals present. The deposits typically consist of layers of metal sulfides, such as chalcopyrite, sphalerite, and galena, intermixed with gangue minerals such as pyrite, quartz, and feldspar. The deposits may also contain significant amounts of gold and silver, as well as minor amounts of other metals such as cobalt, nickel, and tin. The mineralogy of VMS deposits can vary depending on the specific geologic setting in which they form.

Economic Significance and Uses

VMS deposits are important sources of base metals such as copper, lead, and zinc, as well as precious metals like gold and silver. They are also a source of other critical metals like cobalt and tellurium, which are used in various industries, including electronics, renewable energy, and aerospace.

VMS deposits can be highly profitable for mining companies due to their high metal content and relatively low extraction costs compared to other deposit types. However, the economic viability of a VMS deposit depends on a variety of factors, including the grade and tonnage of the deposit, the accessibility and infrastructure of the site, and the prevailing market conditions for the metals produced.

In addition to their economic significance, VMS deposits are also valuable for scientific research, as they provide important clues about the geological processes that formed them and the evolution of the Earth’s crust.

Environmental Issues

Mining of VMS deposits can have environmental impacts, as with any mining activity. VMS deposits are often found in areas of natural beauty and ecological sensitivity, which can exacerbate the environmental effects of mining.

The mining process can involve the removal of large amounts of soil and rock, which can lead to soil erosion, altered drainage patterns, and changes in water quality. In addition, the waste products from mining can contain toxic chemicals, which can contaminate soils and waterways.

To mitigate these environmental impacts, mining companies are required to follow environmental regulations and best practices, such as minimizing the amount of waste produced and properly treating any waste that is generated. In addition, some mining companies work to rehabilitate the land after mining activities have ceased, such as by replanting vegetation or restoring habitats for wildlife.

Examples of Notable VMS Deposits

Some notable VMS deposits around the world include:

1. Kidd Creek Mine, Canada: This is one of the world’s largest and highest-grade VMS deposits, located in the Timmins district of Ontario. The deposit was discovered in 1963 and has been in production since 1966.
2. Myra Falls Mine, Canada: Located on Vancouver Island in British Columbia, this VMS deposit is a significant source of zinc, copper, gold, and silver.
3. Laisvall Mine, Sweden: This VMS deposit is located in the northern part of Sweden and has been in production since the early 1950s. It is a significant source of zinc, lead, and copper.
4. Skorpion Zinc Mine, Namibia: This is one of the largest known VMS deposits in the world and is located in southern Namibia. It is a major source of zinc, and also produces some lead and silver.
5. Hellyer Mine, Australia: This VMS deposit is located in Tasmania and has been in production since the 1980s. It is a significant source of zinc, lead, and silver.
6. Neves-Corvo Mine, Portugal: This VMS deposit is located in southern Portugal and is a major source of copper, zinc, and lead.
7. Boliden Mine, Sweden: This VMS deposit is located in northern Sweden and has been in production since the early 1920s. It is a significant source of copper, zinc, lead, gold, and silver.
8. Kuroko Mine, Japan: This VMS deposit is located in northern Japan and was one of the most important mines in the country until its closure in 1981. It was a significant source of copper, lead, zinc, and silver.
9. Golden Grove Mine, Australia: This VMS deposit is located in Western Australia and has been in production since the early 1990s. It is a significant source of copper, lead, zinc, gold, and silver.
10. Navan Mine, Ireland: This VMS deposit is located in County Meath, Ireland and was in production from the late 1970s until 2006. It was a significant source of zinc, lead, and copper.

Summary of Key Points

VMS (volcanogenic massive sulfide) deposits are a type of mineral deposit that form on the seafloor in submarine environments. Key points about VMS deposits include:

• VMS deposits form through the interaction of seawater and hot, metal-rich fluids that are expelled from the seafloor.
• VMS deposits are typically composed of sulfide minerals that contain copper, zinc, lead, and other valuable metals.
• VMS deposits can be economically significant and have been mined around the world for their metal content.
• Examples of notable VMS deposits include the Kidd Creek deposit in Canada, the Iberian Pyrite Belt in Spain and Portugal, and the Kuroko deposit in Japan.
• Environmental issues associated with VMS mining can include acid mine drainage and the release of heavy metals into the environment.

Overall, VMS deposits are an important type of mineral deposit that have played a significant role in human history and continue to be a target of mineral exploration and mining today.