Hemerdon Ball Project, United Kingdom

The Hemerdon Ball mine is one of the world's largest tungsten and tin resource located in Devon, approximately seven miles north east of Plymouth in south-west England. The historic mine was discovered in 1867 and was mined briefly twice in the 1900s and 1940s before going out of operation in 1944.

A comprehensive feasibility study for further development of the mine was completed in 1981 by joint venture partners AMAX and Hemerdon Mining and Smelting (HMSL) who acquired the property in 1976. Planning permission, valid until 2021, to develop the mine was obtained in 1986. The mine was sold to Wolf minerals in December 2007.

Wolf Minerals is advancing the project towards development having announced a positive result from a Definitive Feasibility Study (DFS) on 16 May 2011.

The project, valued at $105m (£74m), will involve developing a two-phase open pit and a 3Mtpa concentrator with the related infrastructure.

The mine will begin production by the end of 2013 and produce 3Mtpa over an estimated 10 year life.

Reserves

The mine contains 23.5Mt of proven reserves grading at 0.19% WO3 (Tungstic oxide) and 0.03% Sn (Tin). Probable reserves total 3.2Mt graded at 0.19% WO3 and 0.03% Sn. Resources in the measured category amount to 76.8Mt graded at 0.02% Sn, 0.15% W (Tungsten) and 0.19%WO3.

Indicated resources have been estimated to be 40.3Mt graded at 0.02% Sn, 0.14% W and 0.18% WO3. Inferred resources are 284.2Mt graded at 0.02% Sn, 0.14% W and 0.18% WO3.

Geology

The deposit is a remote cupola intrusion bordered by Devonian aged slates that are locally referred to as killas.

Mineralisation begins near surface and continues till a depth of 400m. The mineralisation remains open at depth and along strike. Two vein types are distinguished by three different orientations.

The first type includes a stockwork of quartz and quartz-feldspar veins that host minor mineralisation. Veins bordered by greisens are hosted in a sheeted vein system with wolframite and minor cassiterite mineralisation. The veins system occurs within a steeply dipping dyke like granite structure that is flanked by killas formed due to contact metamorphism.

The killas also host veins of low wolframite and cassiterite content. Kaolinisation up to a depth of 50m is observed in the granite structure.

Secondary arsenate minerals include Scorodite and Pharmacosiderite, hosted in the upper oxidation zones of the ore structures. The minerals have been formed due to arsenopyrite alteration and occur within the weathered regions of the deposit.

Mining

The mining will involve a standard hydraulic excavator and truck operation. The proposed pit will measure 800m in length, 450m in width and 200m in depth.

The waste to ore strip ratio will be 0.7:1 in the first stage of open pit development. It will be 1.5:1 for the life of mine.

The mine will operate on three shifts for six days weekly. The ore will be sent to the Run of Mine (ROM) over the three shifts while waste will be delivered to the waste dump over two shifts. Mine waste will be used to construct the Tailings Management Facility embankment.

Ore processing

Processing will be a three stage operation including comminution, pre-concentration and final concentrate production.

Wolframite (tungsten) and the cassiterite (tin) will be separated from the gangue in a 3Mt processing plant. The plant's operations will involve crushing, screening, scrubbing, dense media separation, de-slime and gravity separation, concentrate processing, tailings thickening and disposal.

Production

A saleable concentrate grade of 65% WO3 will be produced from approximately 58% of tungsten that will be recovered from the soft granite and 66% that will be recovered from the hard granite. Wolf Minerals will produce approximately 345,000t of WO3 per year.