Dartmoor tin-mining
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The '''Dartmoor tin mining''' industry is thought to have originated in pre-[[Roman Empire|Roman]] times,{{Fact|date=April 2008}} and continued right through to the 20th century. From the 12th century onwards tin mining was regulated by a [[Stannary Courts and Parliaments|Stannary Parliament]] which had its own laws.
[[Tin]] is [[smelting|smelted]] from [[cassiterite]], a [[mineral]] found in [[hydrothermal]] veins in [[granite]], and the uplands of [[Dartmoor]], in [[Devon]], [[England]], were a particularly productive area. The techniques used for the extraction of tin from Dartmoor followed a progression from streaming through open cast mining to underground mining.
Many of the older sites carry the prefix ''Wheal'' from a [[Celtic languages|Celtic]] word meaning ''mine'' or ''works''.{{Fact|date=April 2008}}
==Stannary laws==
{{Main|Stannary Courts and Parliaments}}
[[Image:Crockern Tor, Dartmoor.jpg|thumb|left|Crockern Tor – Parliament Rock as seen from the "floor" of the Great Court.]]
[[Mining]] became such an important part of life in the region that as early as the 12th century, tin miners developed their own set of laws ([[stannary]] laws) and, ultimately, their own parliaments ([[Stannary Parliament]]s). These laws applied to anyone involved in the industry.
Stannaries were established in [[Tavistock, Devon|Tavistock]], [[Ashburton, England|Ashburton]] and [[Chagford]] by King [[Edward I of England|Edward I]] in 1305. [[Plympton]] followed soon after. The Devon stannary parliament met in an open air forum at [[Crockern Tor]] from 1494.<ref>Finberg 1950, p.296.</ref>
Anyone who broke a stannary law could find himself imprisoned in the gaol at [[Lydford]]. The stannary courts were abolished in 1836.
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==Mining methods==
===Streaming===
[[Image:Open tinners workings Fox tor 2.jpg|thumb|right|An example of the characteristic pattern of parallel ridges and scarp left by tin-streaming, east of [[Fox Tor]].]]
The earliest means of recovery, known as streaming or streamworking, involved the collection of [[alluvial]] deposits from river and stream beds where they had accumulated after being eroded from the ore-bearing [[lode]]s. The geological processes that resulted in the deposition of the cassiterite in the stream beds often resulted in very pure tin gravel which was mixed with gravels of other, unwanted, minerals such as quartz, mica and feldspar, collectively known an "gangue".<ref name ="Newman11">Newman 1998, p.11.</ref> It was relatively easy to separate these minerals on the basis of their very different [[specific gravity|specific gravities]] – cassiterite about 7 and gangue 3 or less.<ref name ="Newman11"/> The separation was performed by passing a stream of water over the gravels: the gangue would be washed away faster than the wanted tin gravel.<ref>Newman 1998, p.12.</ref>
Once a tin-bearing valley had been identified, the stream-workers would arrange a stream of water, probably carried by a [[leat]] from higher up the valley, and starting at the lowest end of the deposit they would dig a trench (known as the "tye") as deep as possible to allow the finer gangue to be washed away.<ref name ="Newman13">Newman 1998, p.13. (Quoting Hitchens' & Drew's ''History of Cornwall'' 1824.)</ref> From there they would start working up the valley, using the stream of water to wash over the debris they had loosened from the bed with picks.<ref name ="Newman13"/> This method of working leaves characteristic evidence in the valleys - a series of ridges of the larger gangue material, sometimes roughly perpendicular to, sometimes coaxial with the line of the valley, sometimes apparently haphazard, all bounded by a scarp which marked the edge of the worked ground and whose height relates to the depth of the deposits.<ref>Newman 1998, p.13-16.</ref>
[[Eluvium|Eluvial deposits]]—those that had weathered from the lode in the usual way, but had not then been transported by flowing water—were also worked; these tended to be poorer deposits due to the lack of sorting that a stream provides, and they usually did not have such a ready supply of water available to work them. They are found on gently-sloping hillsides. Where possible the water needed to work these deposits was carried by a leat from the nearest available river, or if the site was above such supplies, reservoirs were constructed to collect rainwater and runoff from hillsides.<ref>Newman 1998, p.20.</ref>
A study has shown that a phase of [[aggradation]] occurred in the [[River Erme|Erme valley]] between the 4th century and 7th century, providing evidence of late [[Roman Empire|Roman]] or early post-Roman tin mining activity in this valley.<ref>Geoarchaeology, 2004, Vol 19, Issue 3, pp 219-236, Wiley InterScience. [http://www3.interscience.wiley.com/cgi-bin/abstract/107614460/ABSTRACT Abstract]</ref> The same study confirmed what documentary evidence also relates: that there was a boom in tin production in the 13th century. The first written record of tin streaming dates back to the 12th century.<ref name="npa_tin">{{cite web
|url=http://www.dartmoor-npa.gov.uk/lab-tinindustry
|title=Dartmoor's Tin Industry Factsheet
|publisher=www.dartmoor-npa.gov.uk
|accessdate=2008-04-19}}</ref>
===Open cast===
[[Image:Tinners gullies near Warren House Inn.jpg|thumb|left|Openworks near the [[Warren House Inn]]. Looking down one gully towards a group of them in the middle distance, and more on the left side of the ridge beyond.]]
By the 15th century, the sources of stream tin were becoming scarce and since the demand for tin was as strong as ever, the direct working of lodes was considered viable despite the greater effort needed in both extraction and refining.<ref>Newman 1998, p.20-21.</ref> "Beamworks" was the name given by the tinners to workings where the lode was followed by digging down from the surface, and the massive gullies that resulted remain prominent features of the moor today. Several of these gullies retain names that include the word ''beam'': Gibby Beam, Willabeam and Scudley Beam, for example. They are also known as "openworks" or "gerts".<ref name ="Newman22">Newman 1998, p.22.</ref>
Another method of surface mining involved digging pits at intervals along the lode – this was known as "lodeback-work". At times these pits were dug in pairs along the back of the lode and the lode followed underground between them.<ref name ="Newman26">Newman 1998, p.26.</ref> This may have been the precursor to beamworks in a number of locations, but enough lodeback pits survive to indicate that it was a separate technique.<ref name ="Newman22"/> The issue that mine managers had to decide was whether it was worth removing the extra overburden to form a gulley in order to be able to mine deeper into the lode.<ref name ="Newman26"/>
In a similar fashion to streamworking, much use was made of water for the removal of the overburden and gangue. When digging large gullies the overburden, which consisted at least partly of decomposed granite ("growan"), was loosened with picks, and then water was used to wash away the unwanted material instead of manhandling it.<ref name ="Newman26"/> Means of collecting, diverting and storing water were always associated with openworks. In some cases when only poor sources of water were available complex systems of reservoirs were built.<ref name="Newman26"/>
===Underground===
{{Seealso|Underground mining (hard rock)}}
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The Dartmoor tin industry declined in importance during the early 18th century and had fallen to nothing by 1730.<ref>Worth 1967, p.287</ref> This was due to a number of factors, but the most important was likely to be the exhaustion of the easily-accessible deposits.<ref name="Newman55">Newman 1998, p.55.</ref> It was not until the [[Industrial Revolution]] fuelled demand for all metals and also provided the technology to mine them that mining resumed on the moor on any scale.<ref name="Newman55"/>
Although underground mining technology had been available for many centuries, it is likely that the joint problems of the hardness of the granite rock and the preponderance of underground water together with the relatively easy pickings from near the surface made deep mining not viable until the late 18th century.<ref name="newman56">Newman 1998, p.56.</ref>
Many small mining enterprises started up on Dartmoor in the late 18th and 19th centuries – 48 mines are known to have produced some tin during this period.<ref name="Harris45">Harris 1972, p.45.</ref> Many of these ventures were unsuccessful, despite being given optimistic names like Wheal Fortune, Wheal Lucky and Wheal Prosper. Some larger mines, however, such as [[Drizzlecombe#Eylesbarrow tin mine|Eylesbarrow]] and the Vitifer – Birch Tor complex were productive for many years.<ref name="Newman55"/>
Virtually all of the underground mines re-worked lodes that had been already been mined from the surface.<ref name="newman56"/> Because of the great quantity of underground water, it was necessary to dig horizontal adits into the hillsides to de-water the mines. Dartmoor's topography, cut with deep valleys, helped here and in many cases it was possible to dig to a reasonable depth without the need to pump out water.<ref>Harris 1972, p.38.</ref> These adits connected with shafts that were either sunk vertically downwards or followed the line of the steeply dipping lode. Working the lode then took place by [[Stoping#Mining method|stoping]] from the horizontal levels in the usual manner.<ref>Harris 1972, p.40-41.</ref>
When it became necessary to go deeper than the lowest adit, it was essential to pump out the water. Large waterwheels were used for this and where the shaft was higher than a good water supply, the waterwheel was located lower down the hillside and the power transferred up to the shaft by a "flatrod" system. Evidence for these systems survive as double rows of stones with grooves on their tops – these held the pulleys that guided the metal rods. Such stone rows are still visible at Eylesbarrow and at Hexworthy.<ref>Newman 1998, p.59.</ref>
The discovery of extensive tin deposits in Malaya in the later 19th century had a major impact on the Dartmoor industry, and many miners emigrated.<ref>{{cite web
|url=http://www.poldark-mine.co.uk/geology%203.htm
|title=The Geology of the Poldark Mine and its surrounding area: Part 3 – Mineralisation Overview.
|publisher=www.poldark-mine.co.uk
|author=N. G. LeBoutillier
|accessdate=2008-04-21}}</ref> The last tin mine on Dartmoor finally closed just before the [[Second World War]].<!-- more to follow -->
==Processing==
After collection the tin ore had to be crushed, concentrated and then smelted. Over time a series of ever more sophisticated processes were used for these operations.
===Crushing===
Early streamworkers operating on a small scale used a block of hard stone as a mortar and perhaps a metalbound piece of wood or a ball of stone as a pestle to break up the ore when necessary,<ref>Harris 1972, p.28.</ref> but the rich gravels would have required little or no crushing before concentration.<ref name="Newman40">Newman 1998, p.40.</ref> A later technique called "crazing" employed a pair of circular stones used like millstones, the top one rotating on the fixed lower stone. The coarse gravel or crushed ore was introduced into a hole in the centre of the top stone and was rendered to a fine sand. Only three examples of such crazing mills have been found; at Gobbet mine both stones are still visible.<ref>Newman 1998, p.44-45.</ref>
As it became necessary to regularly process pieces of ore-bearing rock that were too large to be directly ground in a crazing mill, stamping was introduced. This involved vertical hammers powered by a waterwheel in a stamping mill, of which at least 60 are known to have existed on Dartmoor.<ref name="Newman40"/> The first documentary evidence for a stamping mill on Dartmoor is dated 1504, though they would almost certainly have been in use earlier than this (the first reference for Cornwall is from 1400, for instance).<ref name="Newman42">Newman 1998, p.42.</ref> Stamping mills were also known as "knacking" or "knocking" mills; Knacking Mill Gulf, a shallow side valley in the upper reaches of the [[River Erme]], attests to the existence of such a mill there at one time.<ref>Worth 1967, p.321.</ref>
[[Image:Mortarstones and mouldstone on Dartmoor.jpg|thumb|right|Discarded mortarstones and a broken mouldstone at the Walkham Valley higher tin mill.]]
The hammers or "stamps" in a stamping mill consisted of vertical balks of timber, iron-shod at the bottom, which were lifted by cams attached to the waterwheel drive shaft, and repeatedly dropped onto the ore which lay on a block of granite known as a mortarstone. There were usually two or three of these stamps in a row, powered by the same drive and operating in sequence.<ref name="Newman42"/> At first this process operated on the dry ore, which was shovelled in and removed by hand. However in a 16th century innovation from Europe, the stamp heads were surrounded by a wooden box with a finely perforated grill at one end and the ore was washed into the box by a stream of water which also washed out the crushed ore once it was just fine enough to pass through the grill. This was a vast improvement over dry stamping because it was a continuous process that also stopped the production of unwanted very fine dust.<ref name="Newman42"/>
The characteristic indicator of a former stamping mill is the mortarstone. These are blocks of granite up to a metre long with flat faces bearing two, three or (rarely) four circular or elliptical hollows usually around 17cm in diameter and up to about 10cm deep. Many of these mortarstones have hollows on more than one face, showing that they were turned and reused once the hollows became too deep for effective stamping.<ref>Newman 1998, p.42-44.</ref>
Improvements to the technology in the 18th and 19th centuries involved increasing the number of stamping heads and replacing the granite mortarstone with a thick bed of crushed quartz contained in a masonry or iron box.<ref name="Newman62">Newman 1998, p.62.</ref> By the 1900s there were several different types of stamps in use: Cornish, Californian, Holman's Pneumatic, etc.<ref>Richardson 1992, p.154.</ref>
===Concentration===
Although individual grains or pebbles of alluvial tin collected by streaming were often of high purity it was usually still necessary to remove the unwanted "gangue" material before the ore could be smelted. The need for this process, which was known as dressing the ore, increased as the poorer sources of lode tin were exploited. The principle of concentration was a refined version of that used by the early tin-streamers: it depended on the large difference in [[specific gravity]] between the wanted tin ore and the gangue. Many different mechanical methods were used, including rectangular and circular buddles, Wilfley tables and revolving slime tables, kieves, trommels, and even magnetic separation.
An early separation method was the rectangular buddle which was simply a slightly inclined plane over which the crushed material was washed by a gentle stream of water.<ref name="Newman62"/> The heavier ore would settle near the top of the incline while the lighter material would settle lower down or be washed off the buddle altogether. As there was a gradation in quality from the top to the bottom, the mineworker's skill lay in deciding where to make the dividing line between the wanted material and the waste. The division was often made in three parts: the "heads", which represented the best quality ore; the "middles", which was often reprocessed; and the "tailings", which was dumped.
[[Image:View Hooten Wheels2.jpg|thumb|left|The dressing floor at Hooten Wheals, showing the remains of two early 20th century circular buddles.]]
From about 1848 a circular form of the buddle was introduced.<ref>{{Cite book
| last = Stanier
| first = Peter
| title = Mines of Cornwall and Devon - an Historic Photographic Record
| publisher = Twelveheads Press
| location = Truro
| date = 1998
| pages = 43
| isbn = 0-906294-401
}}</ref> The crushed ore, suspended in water was introduced onto a central cone and spread outwards over a slightly inclined conical surface. The "heads" would settle near the centre and the "tailings" at the outer edge. The main innovation of the circular buddle was a set of sweep arms, powered by a waterwheel, which rotated above the buddle and carried brushes or pieces of fabric that dragged across the surface of the settling deposits. By continuously disturbing the surface of the deposit, these stopped the formation of rivulets and allowed better separation to be obtained. The buddle would be run until the deposit built up to between 6 and 12 inches (15 and 30 cm.) deep. The deposits would then be dug out in three portions, the "middles" often being reprocessed in another buddle of a slightly different specification.<ref name="Newman62"/><!-- to expand -->
===Smelting===
{{Main|Blowing house}}
[[Image:Blowing House near Black Tor.jpg|right|thumb|The ruins of a blowing house near Black Tor.]]
The earliest method of liberating the metal from the tin ore necessitated two smeltings: the first was done at or near the streamworks and involved no more than a fire used to roast the ore; the second smelting was done at one of the [[Stannary|Stannary towns]].<ref name="Newman35">Newman 1998, p.35.</ref> Little is known of the details of these practices, but their existence is confirmed by early documents that mention taxation of first and second smeltings.<ref>Worth 1967, p.289-290.</ref> The introduction of the efficient [[blowing house]] process in around 1300 allowed the use of just one smelting.<ref name="Newman35"/> Later still [[reverberatory furnace]]s were used. Both types were in use at Eylesbarrow in the first half of the 19th century—the last place on Dartmoor where smelting was done.<ref name="Harris45"/>
==Consequences==
The effects of the large scale of early tin streaming were felt on the coast, as several harbours silted up due to the amount of fine material that was washed down the rivers. Because of this, in 1532 a Stannary Court decree ordained that all rubbish should be deposited in "old Hatches, Tipittes, miry Places, or other convenient Places" away from the main streams.<ref>Finberg 1949, p.169.</ref>
The impact of mining on the Dartmoor landscape is still clear to see. Walkers on the moor will often stumble upon ruined blowing houses and mortar stones, featuring rows of semi-circular depressions, in which the ore was crushed. Many of the later mine shafts have now been filled in, but a few do still remain, fenced off to prevent walkers or animals from falling in.
==See also==
*[[Hydraulic mining]]
*[[Hushing]]
==Notes==
{{Reflist|2}}
==References==
*{{cite journal
| last = Finberg
| first = H. P. R.
| title=The Stannary of Tavistock
| journal = Rep. Trans. Devon. Ass. Advmt Sci.
| volume=81
| year=1949}}
*{{cite journal
| last = Finberg
| first = H. P. R.
| title = An Unrecorded Stannary Parliament
| journal = Rep. Trans. Devon. Ass. Advmt Sci.
| volume = 82
| date = 1950}}
*{{cite book
| title=Industrial Archaeology of Dartmoor
| last=Harris
| first=Helen
| date=1972
| publisher=David & Charles
| location=Newton Abbot
| isbn=0 7153 4302 5}}
*{{cite book
| last = Newman
| first = Phil
| title = The Dartmoor Tin Industry - A Field Guide
| publisher = Chercombe Press
| location = Newton Abbot
| date = 1998
| isbn = 0-9532708-0-7}}
*{{Cite book
| last = Richardson
| first = P. H. G.
| title = Mines of Dartmoor and the Tamar Valley after 1913
| publisher = The Northern Mine Research Society
| location = Sheffield
| date = 1992
| isbn = 0-901450-38-3}}
*{{cite book
| title=Worth's Dartmoor
| last = Worth
| first = R.N., edited by G.M. Spooner & F.S. Russell
| date=1967
| publisher=David & Charles
| location=Newton Abbot}}
[[Category:Dartmoor]]
[[Category:Tin mining]]
[[Category:Mining in England]]
[[Category:History of mining]]