Abstract
Otago Schist orogenic mineral deposits with scheelite and gold in the Glenorchy area are mineralogically and geochemically similar to, but structurally different from, those at the active Macraes gold mine in East Otago. Glenorchy veins were mined for scheelite up to 1970s, and an abandoned processing battery site at Glenorchy is now being managed for its historical values. This <1 ha site has unevenly distributed remnants of tailings that consist principally of quartz and schist fragments. Minor pyrite and arsenopyrite are present, but tailings have pH 6-8. Bulk tailings tungsten (W) concentrations range from 500 mg/kg to 5 wt%. Scheelite particles in the tailings range from mm to micron scale, with abundant particles <100 & µm. Ore concentrates were roasted on the site to remove volatiles, resulting in essentially complete discharge of sulphur to the atmosphere, along with much of the arsenic (As). However, bulk tailings still contain As up to 4000 mg/kg. Most of this remnant As is hosted by soft particles (mm-& µm) of iron oxyhydroxide that also enclose fine silicates and scheelite. The Glenorchy tailings are broadly similar to those at the Macraes mine in having abundant fine scheelite that has resisted extraction by previous separation methods.