LITHOLOGICAL AND STRUCTURAL CONTROLS ON NON-SULFIDE ZINC ORES AT KUH-E-SURMEH, ZAGROS FOLD BELT, SW-IRAN

The Kuh-e-Surmeh Zn-Pb sulfide/non-sulfide mine is situated within the Zagros fold belt in SW Iran. The ores are hosted by dolomite and limestone of the Lower Dalan Fm., Permian. The mine produces some 4.000 t of sulphide ore p.a. (15% Zn, 15% Pb). Three ore bodies are separated by faults, the Choobandak, Dasht-e-Bahran, and Cheshmeh Sormeh ore bodies, all of which follow the trend of a major NW-SE-anticline. The succession is truncated some 5 km to the NW by a salt diapir, which has produced an aureole of pronounced brecciation in the adjacent country rocks.

The mineralisation comprises some stratiform sulfides (e.g. framboidal pyrite with sphalerite) and vein and breccia-hosted sulfide/non-sulfide (mainly carbonate) ores. The non-sulfide ores form a cap to the underlying sulfide ores. The former show a zonation from a Zn-rich top (14% Zn; 2-3% Pb) to a Pb-rich base (no precise data available). The latter, in contrast, feature a Pb-rich top (40% Pb, 10% Zn) and a more Zn-rich deeper part (15% Zn; 20% Pb). The vein and breccia-hosted ores are restricted to the massive dolomitic Lower Dalan Fm., overlain by well-bedded limestone and gypsum of the Middle Dalan Fm.

The massive dolomite is extremely brittle-fractured on all scales and has thus provided excellent geochemically reactive fluid conduits/traps for epigenetic ore fluids. The overlying laminated gypsum-limestone unit, in contrast, has reacted more ductile and with abundant translations planes, acting as a relatively impermeable and less reactive fluid barrier. The siting of the ores, although stratabound on a regional scale is thus both structurally/rheologically and lithologically/geochemically controlled. The pronounced supergene metal zonation patterns will be the focus of our forthcoming investigations.