Systematics of Hydrothermal Alteration at the Falun Base Metal Sulfide Deposit and Implications for Ore Genesis and Exploration, Bergslagen Ore District, Fennoscandian Shield, Sweden

A detailed study of the Falun Zn-Pb-Cu-(Au-Ag) pyritic sulfide deposit reveals that hydrothermal alteration patterns and mineralization processes differ significantly from other deposits in Bergslagen. The research identifies a zonation of alteration styles, with distal sericitized and silicified volcanic rocks transitioning to intermediate sericitized and proximal chloritized rocks, enveloping the central massive sulfide bodies. This suggests a structural model where mineralization formed stratigraphically high, surrounded by footwall rocks. The study also highlights the importance of fluid-limestone interaction in trapping metals, contrasting with classic VMS models. Mass-change calculations indicate gains in Mg and Fe, losses in Ca, K, and Na, and variable Si changes, pointing to chloritization, sericitization, and silicification as dominant premetamorphic alteration processes.

Kampmann, T. C., Jansson, N. F., Stephens, M. B., Majka, J., & Lasskogen, J. (2017). Systematics of Hydrothermal Alteration at the Falun Base Metal Sulfide Deposit and Implications for Ore Genesis and Exploration, Bergslagen Ore District, Fennoscandian Shield, Sweden. Economic Geology, 112(5), 1111–1152. https://doi.org/10.5382/econgeo.2017.4504