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Copper Point on Virgin Gorda, British Virgin Islands, is a national park containing the ruins of an abandoned 19th century copper mine, the only copper mine in the West Indies.
History
Columbus is said to have first noticed the outcrop of the copper lode, which is clearly visible in the white granodiorite cliffs. Copper was first discovered on Virgin Gorda in the 17th century by the Dutch, but they were never able to successfully exploit it. Local legends suggest the shafts were originally dug by Spanish adventurers to mine silver in the late 15th century, but no documented evidence can be found to support this claim, and no firm evidence of Spanish occupation of the islands prior to the Dutch settlement exists, much less the size of settlement which would be needed to sink shafts.
The first serious mining operation began in 1835 when the Virgin Gorda Mining Company was formed. The first shaft was sunk in 1838. An 1842 report stated that in sinking, lining and excavating, 210 tons of ore had been raised yielding 20% copper. The mine ceased operation at that time due to finances, but reopened as the Virgin Gorda Mine Adventure in 1859, continuing until 1862 (or 1867). Ore production peaked at 721 tons (valued at 10,000 British pounds) during 1861. During its heyday, the mine’s workforce totaled 174.
According to reports, “the mine …was reached by two vertical shafts, one for entrance and egress and the other for pumping and ventilation. Ladders led down 10 fathoms at a time, and at each 10 fathoms level a horizontal stope was driven, in which ore was won.” The total depth of the mine was reported to be 240 to 360 feet, and levels extended under the sea. During both periods of working, copper ore was taken by sailing ship to Swansea, South Wales.
The mine’s engine beam is the oldest surviving Cornish engine beam in the world. Manufactured by the Perran Foundry, Cornwall, in 1836 and brought to the site in 1840, it was the workhorse of the mine. It was used to pump water from the mine, raise the copper ore up the shafts and to power the ore dressing machinery. A Cornish boiler produced steam to drive the engine. Invented in 1815, these boilers were the first to use high-pressure steam. (The beam is presently on the beach in Handsome Bay).
Caution:
Exploring the ruins can be dangerous, and visitors are urged to be cautious. The boiler house and chimney have badly deteriorated, and there are many loose rocks around entrances to timbered-up shafts that lie several feet below ground level. There are also 5 abandoned prospecting shafts, each about 60 feet deep, at the top of the hill, above the stack.
Rich veins of copper are still visible on the point today, although not remotely in the quantities which would make modern commercial mining economical. Rummaging among stones near the boiling house, you may find rock specimens containing malachite (a greenish-colored carbonate of copper); quartz (containing metallic-brown crystals of copper-iron sulfide); and a soft grayish metal called molybdenite.
Mining Metals: Copper
Metals are often found as compounds in ores. An ore is a mixture of minerals and rock (called gangue) that has enough metal in it to make it worth extracting. Approximately 80% of all copper extracted comes from sulfide ores. The most common copper minerals are:
Cuprite (Cu2O); red, earthy; 89% copper when pure
Chalcocite (Cu2S); dark grey, metallic; 80% copper
Bornite (Cu5FeS4); golden brown, metallic; 63% copper
Malachite (CuCO3Cu(OH)4; bright green, earthy; 58% copper
Azurite (2CuCO3Cu(OH)4; blue, glassy; 55% copper
Chalcopyrite (CuFeS2); golden yellow, metallic; 35% copper
Copper minerals and ore are found throughout the Earth’s crust. They occur in both sedimentary and igneous rocks. The outer 10 km of the crust contains 33 gm of copper for every ton of rock. The amount of copper believed to be accessible for mining on the Earth’s land is 1.6 billion tons, with an additional 0.7 billion tons available in deep-sea nodules. Copper mines are only set up when there is >5 kg of copper per ton of rock (0.5% by mass). Ideally, the figure should be closer to 2%.
Concentrating the Ore
The copper ore is crushed, ground and then enriched (concentrated) by froth flotation. The powdered ore is mixed with a special paraffin oil which makes the copper mineral particles water repellent. It’s then fed into a water bath containing a foaming agent which produces a kind of bubble bath. When jets of air are forced up through the bath, the water repellent copper mineral particles are picked up by the bubbles of foam, which float to the surface making a froth. The unwanted gangue falls to the bottom and is removed. The froth is skimmed off the surface and the enriched ore (mainly the copper mineral) is taken away for roasting. At this stage the enriched ore now contains ~25% copper by mass.
Roasting, Smelting & Conversion
At this stage of the process, the chemical reactions begin, converting the copper minerals into copper metal.
In roasting, the enriched ore is heated between 500 to 700C in air. The product from the roaster is called calcine, a solid mixture of copper oxides, sulfides, sulfates, etc. The calcine is now smelted, being further heated >1200C with fluxes such as silica and limestone. Some impurities form a slag, which floats on the surface of the liquid and is easily removed. This is very similar to the removal of impurities in the blast furnace. The liquid left is a mixture of copper salts called a matte (~60% copper by mass). The liquid matte is oxidized with air to form blister copper in a converter, yielding 99+% pure copper by mass. The name “blister” copper comes from the fact that this step produces bubbles (e.g., sulfur dioxide) on the surface of the copper. Finally, the blister copper is cast into anodes ready for electrolytic refining.
The blister copper anodes are immersed in an electrolyte containing copper sulfate and sulfuric acid. Pure copper cathodes are arranged between the blister copper anodes and current is passed through the solution. Under these conditions, copper ions dissolve from the “impure” anode to form copper ions. These migrate towards the cathodes where they are deposited back as pure copper atoms. Gradually, the anode is eroded and the cathode grows, yielding 99.99% pure copper metal by mass.
**NOTE**:
REMEMBER -- THIS IS A BVI NATIONAL PARK. HELP MAINTAIN THE SAFETY & INTEGRITY OF THE ENVIRONMENT & THIS HISTORICAL SITE BY TAKING NOTHING & LEAVING NOTHING, AND BY NOT ENTERING ANY OF THE RUINS OR MINE SHIFTS. THIS WILL HELP ENSURE THAT THIS EC REMAINS IN PLAY FOR THE ENJOYMENT OF CACHERS WHO FOLLOW!
To claim this EarthCache you must
1. Take and post a picture of you and your GPSr at the mine’s boiler house or chimney and email me the answers to the following questions:
2. Why does copper turn green over time? What is an approximate time period for the formation of the patina?
3. What two compounds make up bronze?
Do NOT post your answers, encrypted or otherwise, on the log.
DO NOT LOG AS A FIND UNTIL YOU HAVE A PICTURE READY TO POST AT THE TIME OF LOGGING A FIND FOR THIS EC. Logs with no photo of the actual cacher logging the find or failure to answer required questions through e-mail will result in a log deletion without notice. Exceptions will be considered if you contact me first.
Additional Hints
(Decrypt)
Qb ABG ragre gur ratvar ubhfr be bgure ehvaf, be gur zvar funsgf!