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Hemerdon Mine
Hemerdon Mine – now officially known as the Drakelands Mine, and alternatively known as the Hemerdon Ball or Hemerdon Bal Mine〔(Mindat online database )〕 – is a historic tungsten and tin mine. It is located NE of Plymouth, near Plympton, in Devon, England. It lies to the north of the villages of Sparkwell and Hemerdon and adjacent to the large china clay pits near Lee Moor. The mine was out of operation since 1944, except for the brief operation of a trial mine in the 1980s, but work started to re-open it in 2014. It hosts the fourth largest tin-tungsten deposit in the world.〔(Mineweb Article )〕〔(''Tungsten and tin mine to reopen'' ), BBC news, Tuesday, 4 December 2007, 09:12 GMT〕
==Geology==
The Hemerdon Ball granite is an outlying cupola intrusion surrounded by Devonian slates, known regionally as killas. Fractures in the granite and killas have been penetrated by mineralising fluids containing metallic ores in the area around the Hemerdon mine.〔(Devon County Council Register of Geological Sites )〕 Two types of vein are discernible with three different orientations. Quartz and quartz-feldspar veins form a stockwork with minor mineralisation, whilst greisen bordered veins are found in a sheeted vein system with wolframite and minor cassiterite mineralisation.〔(CSM Virtual Museum Field Excursion )〕
The mineralisation begins at surface and extends to depths of at least . The vein system is hosted in a dyke like granite body, extending from the Hemerdon Ball towards the Crownhill Down granite. It is flanked by killas, formed by contact metamorphism, which also contains veins although wolframite and cassiterite is found as a lower percentage of the rock bulk. Kaolinisation occurs to depths of up to in the granitic body.〔(Wolf Minerals )〕
The locality is renowned for its high quality scorodite specimens, which are among the best in Europe. Pharmacosiderite, Cassiterite and Wolframite of specimen quality have also been recovered from the mine. Scorodite and Pharmacosiderite are secondary arsenate minerals, that form in the upper oxidation zones of ore bodies. They are formed from alteration of arsenopyrite, and are found in the weathered zone of the deposit. At depths beneath the existing pit it is likely they will become scarce.〔(Crystal Classics Article )〕
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