Abstract

We determined the concentrations of gold, silver, arsenic, antimony, and mercury in deep hydrothermal solutions (∼1 km depth, 200 to >300 °C) from six geothermal systems and calculated their fluxes for a 250-km-long segment of volcanic arc in the Taupo Volcanic Zone, New Zealand. The three orders of variation in the concentrations (<0.1–23 ppb Au; 2.7–2400 ppb Ag) and fluxes of precious metals across the arc indicate that the supply of metals in deep hydrothermal solutions is influenced by the intrusion of andesitic and basaltic magmas, which also govern the convective heat transfer and flux of metals. Two of the geothermal systems, Rotokawa and Mokai, have the highest hydrothermal fluxes of gold and/or silver known, and can supply enough metal in ∼50,000 yr or less to match the inventories of the largest hydrothermal ore deposits in the world; although, so far, no ore mineralization has been found in these systems. If the huge amounts of hydrothermal precious metals (minimum values range 80–163 kg Au/yr and 6800–13,850 kg Ag/yr) that flow through the Taupo Volcanic Zone are representative of all arcs throughout time, then focused fluid flow and efficient metal deposition are the most important processes governing the formation of gold and silver ore deposits.

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