The Emperor mine is situated in the village of Vatukoula, 8 km south of Tavua in the northern island of Viti Levu, Fiji. It is a giant deposit (~310 t Au content @ 9.3 g/t) that exploits a system of Au-Te bearing veins, breccias and disseminated orebodies. The mineralised complex, dated at 3.9 Ma, straddles the SW rim of the Tavua Caldera. The Caldera is the final product of an evolving late Miocene-Pliocene shoshonitic palaeovolcano in the presently inactive Vitiaz island arc (compare LT plates 2860, 2861).
The host rocks in the mine area are mainly near-horizontal olivine flow basalts, trachybasalt pyroclastics and steep trachyandesite dykes. Most of the gold won from the mine has come from 3 types of veins, namely: (1) steeply dipping low-sulphidation north-west shears containing epithermal quartz, calcite, dolomite, pyrite, Cu-Zn-Pb-Sb-As sulphide fracture veins enveloped by adularia, sericite, roscoelite and ankerite alteration; (2) gently dipping 'flat makes', and (3) shatter structures.
Veins are dominantly composed of quartz with minor pyrite, tellurides, gold, sphalerite, arsenopyrite, chalcopyrite, tetrahedrite, galena, dolomite, calcite and mica and are both pre and post faulting, contain vugs and show evidence of repeated opening. The vein selvages are composed of an inner K feldspar and an outer chlorite-carbonate rim.
“Invisible” gold is bound in arsenian pyrite and visible gold comes as electrum and in Au-Ag tellurides, especially sylvanite. The most common host is absarokite (=shoshonitic basalt). Low-grade porphyry style Cu-Au mineralisation has been discovered under the epithermal system along steep caldera margin faults.
Between 1934 and 1987 the mine produced 112 tonnes of gold and 40 tonnes of silver. The overall average grade of the lodes mined from underground had been 7.5 g/t Au.
(Source: Modified after Peter Laznicka, 2003)