VEIN AND SKARN FORMATION AT THE CANNINGTON Ag-Pb-Zn DEPOSIT, NORTHEASTERN AUSTRALIA

摘要

Synchronous deformation and metamorphism at the Cannington Ag-Pb-Zn deposit, in northeastern Australia, involved a phase of Ca and Mn mobilization that accounts for the distribution of pyroxene-and garnet-bearing rocks, which were preferentially overprinted by sulfide mineralization. Garnet composition and its textural association in relation to three generations of planar fabric (S_1 to S_3) show that skarn-related grossular-rich garnet formed in the last garnet-stable event, D_3. The D_3 Cl-rich biotite in the gneiss is intergrown with garnet in veins, and within skarn rocks is continuous along strike with veins of garnet + - pyroxmangite, hedenbergite or amphibole, which indicates a period of anhydrous through to hydrous metasomatism. Compositional maps show that infiltration extended from alteration fronts through fractures, which indicates the high permeability of S_3; these maps and X_(Grt) profiles across skarn-gneiss contacts show that there was large-scale transport of mass by infiltration and varying degrees of hydrodynamic dispersion. Precipitation of oscillatory Ca-and Mn-zoned grossular-rich garnet in veins parallel to veins filled with Cl-rich biotite, in conjunction with the distribution of biotite-filled veins across the deposit, suggest that the mass transfer during D_3 may be responsible for deposit-scale Ca-Mn skarn-like zoning.