Volcanogenic Massive Sulphide (VMS) deposits are known to encrust high levels of metals such as Copper, Zinc and Lead. These materials are essential in today’s world, and are the drivers for the global clean energy revolution.
VMS deposits form on the ocean floor when the earth’s tectonic plates separate, resulting in magma heating the floor. When the magma escapes, the beginnings of a volcano start to form resulting in the magma crusting into lenses, or layers, with mineral deposits. Additionally, sea water rich in mineralization is drawn down through crevices in the ocean floor, where it becomes a mineral-rich solution called hydrothermal fluid.
The hydrothermal fluid is expelled through the ground surface in the form of black and white smokers. These smokers contain all the built up minerals, like Cu, Zn, Pb, and Ag, that were present within the hydrothermal fluid. This activity creates what will eventually become a VMS deposit, which can be found at sea level or on land.
MY VERSION OF VMS
Volcanogenic massive sulphide (‘VMS’) deposits have been explored for and been mined since ancient times. They commonly host high copper and zinc minerals with associated gold, silver and cobalt values that are needed now to support the global green energy revolution.
These deposits commonly form where the earth’s tectonic plates are spreading, such as the oceanic Mid-Atlantic ridge, or above subduction zones where there are major fault zones and tectonic movement such as around volcanic islands, often called ‘back-arcs’. They form when marine waters circulate through the fractured rocks scavenging copper, zinc and other metals from the surrounding volcanic rocks and from the hot magmas that are ascending along the fractured zones. The hot metal-rich waters are then expelled into the cold marine waters where they form mounds with dark metal-rich clouds above their volcanic vents, called ‘black smokers’. Contact and mixing with the cold marine waters cause the warm hydrothermal smokers to precipitate their metals in layers near their vents later to be covered by other mafic volcanic rocks and/or volcanically-derived sediments. There may be multiple black smoker vents associated the oceanic ridges and fault zones forming multiple VMS deposits in a favourable geologic setting.
There six different types of VMS deposits identified worldwide. In the case of the York Harbour mineralization, it is referred to as the ‘Mafic Volcanic’ type, often called the ‘Cyprus-type’ due to their similarities in host rocks, copper-zinc dominant mineralization and other structural and alteration characteristics.