Mining and Stanarnaries ======================= Summary: This document consists of a few notes that I thought may be -------- of interest to other RPGers, in no particular order. Contents ======== 1. Derivation of excavation rate 2. Mining techniques 3. Ore Reduction and Metal Refining 4. Source material 5. Economics 1. Derivation of excavation rate ================================ Since I have not been able to find any records which correlate bulk tonnage of mined material with amount of labour (mines tend to record production of refined ores per year, and market cost per ton) I have used historical records of shaft/audit excavation. I will use an early record of the amount of work required to produce an audit (horizontal shaft) as an example. Since the audit was to drain a flooding mine it was done a hurry, presumably with good miners working at near maximum efficiency. To construct an 205 yd audit in softish limestone took a month, for "Eight men working in pairs, constantly and successively, night and day, six hours each sett". I presume that six hours was all that could be reasonably expected, lengthening the shift would have just reduced the overall rate of work as the miners got tired. This audit would have required the removal of about 6200 cubic ft (205 x 3 x 5 sqr ft). Which would imply about 12.5 cubic feet per man shift or just under half a cubic yard. In limestone this equates to three quarters of a tons per man shift. To work from this example requires an act of faith, but I've verified the figures against other examples and they 'seem' to correlate. I assume in the figures in table 1, that the rate of excavation is roughly proportional to the strength of the rock. Since the strength of the rock is dependant on the degree of weathering and amount of fracturing, I give figures for three idealised states; poor (well fractured and weathered), average and sound (few fractures and unweathered). Soil strength isn't as effected by weathering and fracturing as rock so only 'average' figures are given. For soft clays and peat I assume that its mass and bulk are more important than strength. 2. Mining Techniques ==================== Many metals ores where recovered in 'virgin' land through the extraction of the ore from placer (river) deposits. The placer deposits offer the highest concentration of ore, only when these where used up was underground mining economic. Placer deposits consists of the ore eroded from the parent lode which is deposited (often where the river slows down on reaching a flat wide valley) amongst gravels consisting of lighter minerals. The ores can be extracted simply with a shovel and pan. Simple panning is not a very constructive method. 'Miners' quickly moved to streaming, whereby the stream or river is diverted (and narrowed to speed up the flow, using leats) to wash over the placer deposits, washing away the lighter gravels leaving a ore concentrate. This is known as 'streaming'. When placer deposis are exhausted the normal technique was to move up river, digging trial pits as you go, until the point where the lode reaches the surface is found. The lode material can then be extracted using surface excavation, following the strike (course) of the lode across land. When the surface exposure of the lode is mined out, it is an obvious move to dig audits down through the lode, or through parent rock to the lode, which then becomes full scale underground mining. In England, at least, underground mining of non-precious metal ores did not start to be important until after the medieval period. There was three principle primitive underground mining techniques; 1) Using hand tools, mainly picks and chisels, to hack at the rock. 2) Splitting the rock using hammered in wedges (the same technique used in quarrying). This technique is good where the rock has natural cleavage (for example shale and slate). Ore vein mineralisation often occurs filling in faults in the weakened host rock where this technique is particularly valuable. 3) Heat from fires deliberately set, can be used to alter the rocks strength, making it more friable and easier to remove using hand tools. This technique was in particular used in the mediterean. 3. Ore Reduction and Metal Refining =================================== This description is based on that used in the copper, lead and tin industries in England. The first stage in ore processing is to reduce the retrieved material down to the grain size of the mineral crystals (normally sand sized). With streamed ore the materials is normally fine enough, but surface or underground mined material requires crushing. This can be done with a rotary grindstone or querns (a crazing mill) for fine fragments, or using a pestle and mortar technique for lumps of rock. The latter can be mechanised (introduced in the 14th century) to produce a knacking or knocking mill (hence being 'knackered' is to be worn down). Several shafts (stamps) where mounted in a frame, the shaft where then lifted by cams fitted to a horizontal shaft turned by a water wheel. The end of the stamps where fitted with a metal or hard stone cap which pounded the mill. The crushed material from the stamps still had to be put through the crazing mill to get a fine enough powder. This fine powder can then be washed in shallow troughs, through which water flows, removing the lighter material and leaving the ore. A later discovery was that if running water was allowed to flow over the material in the knacking mill, the rock would be reduced to a fine enough size that the crazing mill could be dispensed with. This also had the benefit of washing away much of the lighter material so that the time in the washing troughs could be reduced. Once the ores had been separated the material was smelted to produce the pure metal. The original technique was simply to build a charcoal or dried peat fire over the ore heap and then rack the metal out of the ashes. This metal would be impure and gritty and would require a second smelt to get metal of the desired standard. In about 1300 the use of furnaces was introduced. These where fuelled with charcoal, and utilised mechanically powered bellows to keep it hot enough. The metal would become totally molten and could be extracted out of the bottom of the furnace and poured in to stone moulds to produce ingots or 'pigs' of the metal. The impurities remained in the furnace where they could be disposed of later. The size of lead pigs seems to have been standardised at about 75lb (as much as a man could comfortably lift?). With lead 75lb pigs being found from the Roman period to the 17th century. Other sizes of ingot where produced of up to 200 lbs (copper in particular seems to have been made into large ingots). Ultimately smelting mills became quite mechanised workshops. Water would be brought to the mill in a leat. This water would be used to turn the mill's water wheel, with a small amount drawn off to wash the stamps in the knacking mill. After powering the mill the water would then be diverted from washing troughs and then back to the source stream or river. The water wheel would be used to drive the knacking mill and the mechanical bellows of the furnace. The whole mill would fit in to a small building much the same size as a cottage. 4. Source material ================== A few quotes from history... * A royal monopoly. "We have granted that the Chief Warden of the Staneries [...] have over the tinners plenary power to do them justice and [...] to receive them in to our prisons, if it shall happen that any of [them] ought to be siezed [...] for the tinners are of our farm and always of our demesene." King John (1201AD) Because of their royal patronage and protection ("They shall not be called from their work by any summons except that of the Chief Warden") along with a new charter of 1305AD which granted immunity from being claimed as surfs, meant that the tinners where exempt from the law of the Barons (even a Memeber of Parliment was jailed, and fined 160 pounds, in 1512 by the stannery courts for trying to evict tinners) and where freemen (even if they had run away from surfdom they could not be forced to return (a novel background for PCs?)). * A rather nice charter (from the dartmore stannaries again) you can use when PCs wish to take up minning is as follows; "They may dig tyn & tyrves for melting tin everywhere in our moors and wastes & of all other person whatsoever... and the water courses for the works of the Srannaryes to turn where & and as often as need shall be & to buy bushment for the melting of tyn as of old tyme hath bin accustined to be done." From a charter grant of King Edward I, 1305AD. NB: the 'tyrves' are of peat which was used to fuel the smelting furnaces. * A law unto themselves. "The stannary men commit trepass and assult [...] nor permit themselves to be brought to justice according to the law and custom of the realm, and when the hue and cry is heard, they take and beat the King's baliffd and [...] imprison them in the stannary gaol until randsom is paid" Complaints from the Patent Rolls of Edward II (1318AD). * About the miners holidays (subtitled: remember to give Str, End and Agl bonuses!). "Their holy-days' exercises were toilsome and violent, as wrestling, hurling, football, leaping, running, dancing with music, especially at festivals, to exhilarate their hearts and such like; which made them fit for the wars, or any other employment whatsoever, wherein hardiness, or strenth, or agility was required." Thomas Westcote, early 17th century. 5. Economics ============ To illustrate the economics of metal production, I will use the official figures from Devon Tin industry for example (NB: Official figures are likely to be less than actual production because miners would sell on the black market to avoid taxes). In the later 12th century (when stream (placer) ores where being mined production was about 340 tons per annum for the county. By the turn of the century production was down to 30 tons per annum mainly due to exhaustion of the stream ore. After lode mining began production increased again, with an average of 50 tons per annum in the first half of the 15th century, 105 tons in the second half, 200 tons in the first half of the 16th century and 95 tons by the end of that century. To give an idea of its worth, at about 1200AD it was sold at 1d per lb which rose to 4.5d per lb by 1500AD. At peak production in the 1500s approximately two million pennies worth of tin was produced. In 1200, 'by ancient custom' the king received 2s 6d per (18d) thousandweight (1200lbs) of tin on the first smelting. In 1191 this raised 80 pounds (19,200d) for the crown. A new tax of 13s 4d (160d) per thousandweight on the second smelting was introduced shortly there after and the crowns income improved to 600 pounds (144,000d). Other earners for the crown where for tolls on tin mines in royal manors, fees for export licences and customs on exported tin. Another perk was right to pre-empt or compulsorily purchase tin ("We have granted also for us & our heires that all our tynners aforesaid all this tin so wayed lawfully may sel to whom they will in the townes aforesaid ecxept we or our heires will buy the said tyn ourselves" Charter of 1305), which was then resold. In 1197AD, 352l 6s 10d was raised by this means. The right of pre-emption was often leased to wardens or merchants (who would pat a fixed fee but get to keep the profits themselves).