Nature's refineries - Metals and metalloids in arc volcanoes

Destabilization of solvated molecular metal and metalloid species in magmatic gas mixtures and changes in their redox state are triggered, as it expands to the surface by abrupt pressure drops, or throttles' in the fracture array that guides expansion to the surface. The electronically harder, low electronegativity metals, such as copper and iron, deposit rapidly in response to expansion followed more slowly by arsenic with antimony as sulfosalts. Heavy, large radius, softer elements such as bismuth, lead, and thallium along with cadmium are strongly fractionated along the way, eventually venting their excess along with SO2, CO2, and other components of the carrier gas, into the atmosphere. These elements, many of which are toxic, may also be dispersed by mixing with groundwater in the permeable crust below volcanoes and generate potential health risks due to Hg, As, and Se contamination of drinking water resources.