The Early Jurassic (190 ±1 million years ago (Scheel, 2007)) Turnagain complex comprises a central core of dunite with bounding units of wehrlite, olivine clinopyroxenite, clinopyroxenite, representing crystal cumulate sequences, hornblende clinopyroxenite and hornblendite.The complex is elongate and broadly conformable to the northwesterly trending regional structural grain.

The ultramafic rocks are generally fresh to mildly serpentinised; however, more intense serpentinisation and talc-carbonate alteration occur along faults and restricted zones within the complex. The central part of the ultramafic body is intruded by granodiorite to diorite, and hornblende–plagioclase porphyry dikes and sills.

Showings of semi-massive and massive sulphides have been identified by work to date. These semi-massive and massive zones, plus broad zones of disseminated sulphides, are generally hosted by dunite and wehrlite near the southern and eastern margins of the ultramafic body. The central and northern dunite is largely devoid of sulphide minerals although their highly magnesian olivine is more enriched in nickel (up to 0.20 to 0.30 weight percentage) than the olivine in the peridotites and pyroxenites of the Horsetrail and Northwest zones, which may be nickel-depleted in areas of sulphide mineralisation. Nixon (1998) suggests that these features are further evidence of fractional crystallisation of the ultramafic magma.

Primary sulphide minerals consist o ........

The Turnagain deposit will be mined using an open pit mining method, employing high volume trucks and shovels. The use of large mining equipment will achieve high mining rates and ensure the lowest possible mine operations unit costs. The waste and mineralized rockwill require blasting and typical grade control methods using blast-hole sampling.

The mine will feed the crusher at an average rate of 45,000 t/d during the first five years and increase to an average of 90,000 t/d thereafter. The resource will be mined for 37 years at these rates based on a 365-day production year.

To access the most economic mineralisation in the early years and provide a smooth strip ratio throughout the life of mine, mineralisation production from the Horsetrail pit is scheduled from five mining phases. Stage 1 will commence at the centre of the pit, where the highest grade and lowest strip ratio will be encountered.

An elevated cut-off grade will be employed in the initial production years to enhance the economics of the project. Mineralisation that is below the mine high-grade (HG) direct feed cutoff, but of sufficient grade to cover the cost of milling and rehandling once it is hauled out of the pit, will be classified and stockpiled by categorised value for subsequent rehandling. Stockpile reclaim will occur at the end of the mine life or it will be blended with the ROM feed as the appropriate opportunity arises. Low-grade (LG) stockpiles will be placed in ........

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