Gold in Ellicott City Granodiorite. The Ellicott City granodiorite (ECG) is famous as an example of an epidote-bearing granite. Magmatic epidote forms only at high pressures, indicating that this magma intruded and cooled deep within the Earth's crust. The ECG also contains magmatic sulfides. Gold and other water-soluble metals partition into the magmatic vapor phase, which typically exsolves from granites at low pressures after sulfide saturation. Because the ECG crystallized at high pressures, it is possible that Au was incorporated into the magmatic sulfides before it was lost to the vapor phase. This project will entail understanding the field relations of the ECG, detailed petrography of the sulfides in the ECG , characterization with by electron microprobe and measurement of their Au concentrations by laser ablation ICP-MS in order to determine whether the sulfides incorporated significant Au, hence crystallized before saturation of a vapor phase.

Supervisors: Roberta Rudnick, Philip Piccoli, Bill McDonough, Philip Candela