Hemerdon Mine
Encyclopedia
Hemerdon Mine, alternatively known as the Hemerdon Ball or Hemerdon Bal Mine, is a historic tungsten
and tin
mine. It is located 7 miles (11.3 km) 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, which has been out of operation since 1944, except for the brief operation of a trial mine in the 1980s, hosts one of the largest tungsten and tin deposits in the world.
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 in the area around the Hemerdon mine, forming. 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.
The mineralisation begins at surface and extends to depths of at least 400 metres (1,312.3 ft). 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 50 metres (164 ft) in the granitic body.
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.
Several attempts were made to establish a higher and stable price for tungsten from the government, including an application supported by Winston Churchill
for recognition of wolfram mining as a key industry. However after further price decreases, milling operations were suspended and the mill components were sold off.
In 1934 increased tungsten prices resulted in renewed prospecting of the deposit, along with metallurgical testwork. In 1939 further shortages of tungsten due to WW2 led to Hemerdon Wolfram Ltd constructing a 90,000-tonne per year mill with 55% wolfram recovery, which began operation in 1941.
The Ministry of Supply
carried out extensive evaluation of tungsten deposits in the UK, and it was concluded by 1942 that Hemerdon offered the most potential for producing tungsten on a large scale. The government took over the mine from Hemerdon Wolfram Ltd. A resource of 2.5 million tonnes of 0.14% tungsten trioxide
in addition to tin was outlined, and a new plant was hastily constructed.
The new plant took over operation from the old plant in 1943, and theoretically should have been able to treat over 1 million tonnes per year; however labour shortages and mechanical faults resulted in a much lower production. Ore output from a mixture of underground and opencast mining methods was documented as over 200,000 tonnes, with a resulting 180 tonnes of tin/tungsten concentrate during the period of government operation. Operations ceased in June 1944 due to access to overseas supplies being restored.
The plant was kept in place after the war, and the government was rumoured to have planned restarting production during the tungsten shortages associated with the Korean War
. However, nothing came of this and following the Westwood Report in 1956, the government decided to seek a private partner to move the mine’s development forwards. After further decreases in the tungsten price, resulting in the closure of the Castle-an-Dinas Mine tungsten mine in Cornwall, the government sold off all the plant in 1959.
.
The leases were transferred to Hemerdon Mining and Smelting Ltd in 1976. They initiated a drilling program shortly before they entered a joint venture to develop the project with international mining firm AMAX in 1977. An extensive exploration programme costing in excess of $10 million was completed between 1978 and 1980. By the end of 1978, deeper drilling enlarged the resource size to 20 million tonnes of ore. In 1979 this was expanded to 45 million tonnes. At the end of the exploration programme in 1980, over 14000 metres (45,931.8 ft) of diamond drilling had been undertaken, outlining a resource of 0.17% tungsten trioxide and 0.025% tin over 49.6 million tonnes.
Bulk sampling of the deposit using an underground drift for ore, and a pilot HMS and Gravity plant for processing, was undertaken in 1980. On average recoveries of around 65% were made, although in excess of 70% was achieved. The final revision of the mining feasibility study concluded in 1982 that a within a global resource of 73 million tonnes of ore, at grades of 0.143% tungsten trioxide and 0.026% tin, there was an in pit reserve of 38 million tonnes, at grades of 0.183% tungsten trioxide and 0.029% tin.
The venture was joined by Billiton Minerals Ltd, providing further finance and expertise, and forming a consortium that planned to commence production in 1986. The initial planning application was made in 1981, but a public enquiry and ‘calling in’ of the application by the Secretary of State resulting in an initial refusing of the application in 1984. This resulted in Billiton Minerals Ltd pulling out of the consortium. Hemerdon Mining and Smelting Ltd also sold their 50% stake in the project to AMAX. After making a revised application, permission was finally obtained in 1986. By then a collapse in both the tin and tungsten prices had damaged the economic feasibility of making an investment in opening the mine. Its tungsten assets were passed onto to a newly formed holding company; Canada Tungsten Ltd, in 1986.
Canada Tungsten implemented the planning permission that was obtained in 1986, and kept the project in its portfolio of prospects for many years. Before AMAX was sold to Phelps Dodge, it gradually transferred Canada Tungsten into the ownership of Aur Resources. In 1997, a new company, North American Tungsten plc, purchased all the tungsten assets from Aur Resources, and was listed with the aim of reopening the Cantung mine, and developing the Hemerdon and Mactung prospects.
However during a review of peripheral assets in 1999, it decided that with the depressed prices of tungsten, the Hemerdon prospect was not central to its future. With upkeep costs of in excess of C$150,000 per annum, almost a third of the company’s annual costs, attempts were made with the mineral rights
holders to reduce fees. The negotiations were unsuccessful and therefore during 2000, two of the three mineral rights were surrendered. To further reduce costs, it disposed the remaining assets of the Hemerdon prospect in 2003.
(an intermediate product of tungsten) price by five times, from around US$60 per STU in 2003, to in excess of US$240 per STU from 2006. This has resulted in increased tungsten mining exploration and development activities globally since 2005.
In June 2007, ASX
listed specialty metal exploration and development company, Wolf Minerals Limited, suspended trading of shares pending the acquiring of mineral leases. On December 5, 2007 trading recommenced following the public announcement of acquiring the mineral leases for the Hemerdon Mine project. The mineral leases were made for a period of 40 years, with the Hemerdon Mineral Trust and the Olver Trust. An agreement with Imerys
to purchase remaining mineral rights and freehold land was also made.
SRK Consulting were commissioned to produce a JORC-compliant resource using previous drilling data. This was released in March 2008. Subsequently it has been updated twice by SRK Consulting to incorporate new drilling data and revised geological modelling. The resource of over 300,000 tonnes of tungsten metal makes Hemerdon the fourth largest tungsten deposit in the world. In 2009, funding for a DFS (definitive feasibility study) was achieved with the support Resource Capital Funds and Traxys, completed in May 2011. It is planned that mining operations could commence in 2012, with first concentrate production scheduled for 2013. The project has planning permission dating by to 1986, which is valid till 2021. If production levels are achieved as anticipated, the mine would be the largest tungsten concentrate producer in the world.
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
and tin
Tin
Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...
mine. It is located 7 miles (11.3 km) NE of Plymouth
Plymouth
Plymouth is a city and unitary authority area on the coast of Devon, England, about south-west of London. It is built between the mouths of the rivers Plym to the east and Tamar to the west, where they join Plymouth Sound...
, near Plympton
Plympton
Plympton, or Plympton Maurice or Plympton St Maurice or Plympton St Mary or Plympton Erle, in south-western Devon, England is an ancient stannary town: an important trading centre in the past for locally mined tin, and a former seaport...
, in Devon
Devon
Devon is a large county in southwestern England. The county is sometimes referred to as Devonshire, although the term is rarely used inside the county itself as the county has never been officially "shired", it often indicates a traditional or historical context.The county shares borders with...
, 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, which has been out of operation since 1944, except for the brief operation of a trial mine in the 1980s, hosts one of the largest tungsten and tin deposits in the world.
Geology
The Hemerdon Ball graniteGranite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
is an outlying cupola intrusion surrounded by Devonian slates, known regionally as killas
Killas
Killas is a Cornish mining term for metamorphic rock strata of sedimentary origin which were altered by heat from the intruded granites in Devon and Cornwall, England. The term is used in both Devon and Cornwall.-Origin of killas:...
. Fractures in the granite and killas have been penetrated by mineralising fluids containing metallic in the area around the Hemerdon mine, forming. Two types of vein are discernible with three different orientations. Quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
and quartz-feldspar veins form a stockwork
Stockwork
In geology, a stockwork is a complex system of structurally controlled or randomly oriented veins. Stockworks are common in many ore deposit types and especially notable in greisens. They are also referred to as stringer zones....
with minor mineralisation, whilst greisen
Greisen
Greisen is a highly altered granitic rock or pegmatite. Greisen is formed by autogenic alteration of a granite and is a class of endoskarn.Greisens appear as highly altered rocks, partly coarse, crystalline granite, partly vuggy with miarolitic cavities, disseminated halide minerals such as...
bordered veins are found in a sheeted vein system with wolframite
Wolframite
Wolframite WO4, is an iron manganese tungstate mineral that is the intermediate between ferberite and huebernite . Along with scheelite, the wolframite series are the most important tungsten ore minerals. Wolframite is found in quartz veins and pegmatites associated with granitic intrusives...
and minor cassiterite
Cassiterite
Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem...
mineralisation.
The mineralisation begins at surface and extends to depths of at least 400 metres (1,312.3 ft). 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 50 metres (164 ft) in the granitic body.
The locality is renowned for its high quality scorodite
Scorodite
Scorodite is a common hydrated iron arsenate mineral, with the chemical formula FeAsO4·2H2O. It is found in hydrothermal deposits and as a secondary mineral in gossans worldwide. Scorodite weathers to limonite....
specimens, which are among the best in Europe. Pharmacosiderite
Pharmacosiderite
Pharmacosiderite is a hydrated basic ferric arsenate, with chemical formula KFe434·H2O and a molecular weight of 873.38 g/mol. It consists of the elements arsenic, iron, hydrogen, potassium, sodium and oxygen. It has a Mohs hardness of 2 to 3, about that of a finger nail...
, 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
Arsenopyrite
Arsenopyrite is an iron arsenic sulfide . It is a hard metallic, opaque, steel grey to silver white mineral with a relatively high specific gravity of 6.1. When dissolved in nitric acid, it releases elemental sulfur. When arsenopyrite is heated, it becomes magnetic and gives off toxic fumes...
, and are found in the weathered zone of the deposit. At depths beneath the existing pit it is likely they will become scarce.
1867-1959
The Hemerdon tungsten-tin deposit was discovered in 1867. In 1916, due to war associated tungsten shortages, an exploration and development program was initiated, which outlined a tin-tungsten stockwork suitable for opencast extraction. In 1917, Hemerdon Mines Ltd decided to construct a 140,00-tonne per year mill, and shortly afterwards opencast ore mining operations began. The mine was operated in 1918-1919, during which time it processed 16,000 tonnes of ore. When the British government stopped accepting tungsten ores under the war pricing scheme the mine was forced to suspend mining operations.Several attempts were made to establish a higher and stable price for tungsten from the government, including an application supported by Winston Churchill
Winston Churchill
Sir Winston Leonard Spencer-Churchill, was a predominantly Conservative British politician and statesman known for his leadership of the United Kingdom during the Second World War. He is widely regarded as one of the greatest wartime leaders of the century and served as Prime Minister twice...
for recognition of wolfram mining as a key industry. However after further price decreases, milling operations were suspended and the mill components were sold off.
In 1934 increased tungsten prices resulted in renewed prospecting of the deposit, along with metallurgical testwork. In 1939 further shortages of tungsten due to WW2 led to Hemerdon Wolfram Ltd constructing a 90,000-tonne per year mill with 55% wolfram recovery, which began operation in 1941.
The Ministry of Supply
Ministry of Supply
The Ministry of Supply was a department of the UK Government formed in 1939 to co-ordinate the supply of equipment to all three British armed forces, headed by the Minister of Supply. There was, however, a separate ministry responsible for aircraft production and the Admiralty retained...
carried out extensive evaluation of tungsten deposits in the UK, and it was concluded by 1942 that Hemerdon offered the most potential for producing tungsten on a large scale. The government took over the mine from Hemerdon Wolfram Ltd. A resource of 2.5 million tonnes of 0.14% tungsten trioxide
Tungsten trioxide
Tungsten oxide, also known as tungsten trioxide or tungstic anhydride, WO3, is a chemical compound containing oxygen and the transition metal tungsten. It is obtained as an intermediate in the recovery of tungsten from its minerals. Tungsten ores are treated with alkalis to produce WO3...
in addition to tin was outlined, and a new plant was hastily constructed.
The new plant took over operation from the old plant in 1943, and theoretically should have been able to treat over 1 million tonnes per year; however labour shortages and mechanical faults resulted in a much lower production. Ore output from a mixture of underground and opencast mining methods was documented as over 200,000 tonnes, with a resulting 180 tonnes of tin/tungsten concentrate during the period of government operation. Operations ceased in June 1944 due to access to overseas supplies being restored.
The plant was kept in place after the war, and the government was rumoured to have planned restarting production during the tungsten shortages associated with the Korean War
Korean War
The Korean War was a conventional war between South Korea, supported by the United Nations, and North Korea, supported by the People's Republic of China , with military material aid from the Soviet Union...
. However, nothing came of this and following the Westwood Report in 1956, the government decided to seek a private partner to move the mine’s development forwards. After further decreases in the tungsten price, resulting in the closure of the Castle-an-Dinas Mine tungsten mine in Cornwall, the government sold off all the plant in 1959.
1960-2006
However in the mid-1960s work on the prospect was recommenced by British Tungsten Ltd, owned by Canadian entrepreneur W.A.Richardson. In 1969 a planning application for opencast working of tin, tungsten and china clay was submitted, but it was withdrawn before a decision could be made. Further work commencing in 1970 by British Tungsten Ltd increased the resource to 5.6 million tonnes of oreOre
An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....
.
The leases were transferred to Hemerdon Mining and Smelting Ltd in 1976. They initiated a drilling program shortly before they entered a joint venture to develop the project with international mining firm AMAX in 1977. An extensive exploration programme costing in excess of $10 million was completed between 1978 and 1980. By the end of 1978, deeper drilling enlarged the resource size to 20 million tonnes of ore. In 1979 this was expanded to 45 million tonnes. At the end of the exploration programme in 1980, over 14000 metres (45,931.8 ft) of diamond drilling had been undertaken, outlining a resource of 0.17% tungsten trioxide and 0.025% tin over 49.6 million tonnes.
Bulk sampling of the deposit using an underground drift for ore, and a pilot HMS and Gravity plant for processing, was undertaken in 1980. On average recoveries of around 65% were made, although in excess of 70% was achieved. The final revision of the mining feasibility study concluded in 1982 that a within a global resource of 73 million tonnes of ore, at grades of 0.143% tungsten trioxide and 0.026% tin, there was an in pit reserve of 38 million tonnes, at grades of 0.183% tungsten trioxide and 0.029% tin.
The venture was joined by Billiton Minerals Ltd, providing further finance and expertise, and forming a consortium that planned to commence production in 1986. The initial planning application was made in 1981, but a public enquiry and ‘calling in’ of the application by the Secretary of State resulting in an initial refusing of the application in 1984. This resulted in Billiton Minerals Ltd pulling out of the consortium. Hemerdon Mining and Smelting Ltd also sold their 50% stake in the project to AMAX. After making a revised application, permission was finally obtained in 1986. By then a collapse in both the tin and tungsten prices had damaged the economic feasibility of making an investment in opening the mine. Its tungsten assets were passed onto to a newly formed holding company; Canada Tungsten Ltd, in 1986.
Canada Tungsten implemented the planning permission that was obtained in 1986, and kept the project in its portfolio of prospects for many years. Before AMAX was sold to Phelps Dodge, it gradually transferred Canada Tungsten into the ownership of Aur Resources. In 1997, a new company, North American Tungsten plc, purchased all the tungsten assets from Aur Resources, and was listed with the aim of reopening the Cantung mine, and developing the Hemerdon and Mactung prospects.
However during a review of peripheral assets in 1999, it decided that with the depressed prices of tungsten, the Hemerdon prospect was not central to its future. With upkeep costs of in excess of C$150,000 per annum, almost a third of the company’s annual costs, attempts were made with the mineral rights
Mineral rights
- Mineral estate :Ownership of mineral rights is an estate in real property. Technically it is known as a mineral estate and often referred to as mineral rights...
holders to reduce fees. The negotiations were unsuccessful and therefore during 2000, two of the three mineral rights were surrendered. To further reduce costs, it disposed the remaining assets of the Hemerdon prospect in 2003.
2007-present
Sustained tungsten metal price rises resulted in an increase of the Ammonium paratungstateAmmonium paratungstate
Ammonium paratungstate is a white crystalline salt of ammonium and tungsten, with the chemical formula 10·5H2O.Ammonium paratungstate is produced separating tungsten from its ore. Once the ammonium paratungstate is prepared, it is heated to its decomposition temperature, 600 °C. Left over is WO3,...
(an intermediate product of tungsten) price by five times, from around US$60 per STU in 2003, to in excess of US$240 per STU from 2006. This has resulted in increased tungsten mining exploration and development activities globally since 2005.
In June 2007, ASX
Australian Securities Exchange
The Australian Securities Exchange was created by the merger of the Australian Stock Exchange and the Sydney Futures Exchange in July 2006. It is the primary stock exchange group in Australia....
listed specialty metal exploration and development company, Wolf Minerals Limited, suspended trading of shares pending the acquiring of mineral leases. On December 5, 2007 trading recommenced following the public announcement of acquiring the mineral leases for the Hemerdon Mine project. The mineral leases were made for a period of 40 years, with the Hemerdon Mineral Trust and the Olver Trust. An agreement with Imerys
Imerys
Imerys is a French multinational company. It is a constituent of the CAC Mid 60 index.-History:The Company was founded in 1880 and for many years was known as Imetal....
to purchase remaining mineral rights and freehold land was also made.
SRK Consulting were commissioned to produce a JORC-compliant resource using previous drilling data. This was released in March 2008. Subsequently it has been updated twice by SRK Consulting to incorporate new drilling data and revised geological modelling. The resource of over 300,000 tonnes of tungsten metal makes Hemerdon the fourth largest tungsten deposit in the world. In 2009, funding for a DFS (definitive feasibility study) was achieved with the support Resource Capital Funds and Traxys, completed in May 2011. It is planned that mining operations could commence in 2012, with first concentrate production scheduled for 2013. The project has planning permission dating by to 1986, which is valid till 2021. If production levels are achieved as anticipated, the mine would be the largest tungsten concentrate producer in the world.
| Hemerdon Ball JORC Revised Resource estimate completed by SRK Consulting in June 2010 | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Resource Category | Ore Tonnage (Mt) | Sn grade (%) | WO3 grade (%) | Contained Sn (tonnes) | Contained W (tonnes) | ||||||||||
| Measured | 48.53 | 0.02 | 0.19 | 9700 | 72800 | ||||||||||
| Indicated | 22.39 | 0.02 | 0.18 | 4500 | 40300 | ||||||||||
| Inferred | 147.61 | 0.02 | 0.18 | 29500 | 206700 | ||||||||||
| TOTAL | 218.53 | 0.02 | 0.18 | 43700 | 318800 | Source: | |||||||||