Geological and geochemical signature of sea-floor alteration rocks of the highly metamorphosed Hongtoushan massive sulfide deposit, Liaoning

The Hongtoushan Archean Cu-Zn Massive Sulphide Deposit (MSD), which has been metamorphosed (3.0 similar to 2. 8 Ga) to upper amphibolite facies, occurs in the Hunbei granite-greenstone terrane, Liaoning Province of NE China. Cordierite-orthoamphibole gneiss (COG) is widespread at Hongtoushan. The COG that occurs hundreds of meters below the ore horizon corresponds to the metamorphosed simiconformable alteration zone of MSD hydrothermal system, whereas the COG immediately below the main ore layer represents the metamorphosed pipe.-like alteration zone. Geochemical analyses indicate that the stratiform COG was derived ultimately from five lithologies (basalts, basaltic andesites, andesites, dacites, and rhyolites), whereas the pipe-like COG from a single lithology (rhyolites). Amphibolite and biotite gneiss are identified as metamorphosed unaltered parent rocks. In comparison to unaltered rocks, stratiform COG is enriched in Fe and Mg, and depleted in Na, K, Ca, while pipe-like COG is enriched in Fe, Mg, Si and Na, and depleted in K.