Sulphur Bank Mine, California: An Example of a Magmatic Rather Than Metamorphic Hydrothermal System

Abstract

Sulphur Bank mine hydrothermal system (218?C) is surrounded by the youngest eruptions in the Clear Lake volcanic field, and nearby conductive thermal gradients exceed 1 at 1-3 km depth. values for He in Sulphur Bank gases are 7.5. Hydrothermal fluids are highly enriched in deuterium as well as oxygen-1 8 relative to local meteoric waters and resemble magmatic waters discharged from many arc volcanoes. However, we show herein that magmatic, connate, and metamorphic fluids are indistinguishable based on and plots. Sulphur Bank waters have and ratios of metamorphic fluids and Sulphur Bank gases are strongly influenced by marine, organic-rich source rocks. We believe that Sulphur Bank fluids originate during metamorphism of Franciscan Complex rocks after shallow intrusion km) by magmas of the Clear Lake volcanic field.