Mining, Quarrying and Excavation using hand tools. ================================================== Summary: A skilled labourer could excavate (mine/quarry) about 0.75 tons per working day in moderately strong rock (though this may vary from 0.25 tons/day in strong rock, to 1.75 tons in very weak rock, or 3.75 tons of 'soil'). The material presented here is based on records from the 16th to 18th century and modern rock mechanics. However, this material is not considered to be historically or practically acurate, but is rather a set of guidelines I would be happy to use in role playing games. The range given above (0.25 to 1.75 tons per day) compares with 2 to 6 tons quoted in a popular RPG. Contents: --------- 1 Rocks and Soil: types and distribution 2 Excavation facts and figures Table 1: Rate of Excavation Table 2: Density and spoil volume Table 3: Density, volume and yeild of ores 3 Examples of use of the figures Construction Tunneling Transport of materials Mining. 1: Rocks and Soil: types and distribution ----------------------------------------- Not wishing to write a treatise on geology I will be brief. The follwing materials are used in this document. GABBRO: Igneous (volcanic) rock found in large intrusions SLATE: Metamorphic rock formed from heating clay at high temperatures and pressures - good roofing material MARBLE: Metamorphic rock formed from limestone - a good building material. GNEISS/SCHIST: Metamorphic rocks which have been heated to near molten BASALT/DOLERITE: Fine grained igneous rock which is produced in volcanic regions (as lava or underground) GRANITE: Mountain forming igneous rock - often a source of rich minerals in rurrounding rocks. LIMESTONE: A sedimentary rock - a good building material SANDSTONE: A sedimentary rock - a good building material CHALK: A soft pure limestone - practically worthless SHALE: A metamorphic rock like slate but no good for roofing, but may contain economic ore veins STIFF CLAY: A sedimentary rock - used for bricks and pottery SANDY GRAVEL: Formed on beaches and river beds SAND: Uncememted sand often formed from the weathering of igneous rocks or sandstone. SOFT CLAY: Typically 'soil', PEAT: Wet organic matter. Good fuel when dry. Location: Generally speaking the Igneous and metamorphic rocks will be found in mountains andrough terrains; the hard sedimentary rocks (limestone, sandstone and chalk) will be forming the hilly terrain; whilst the softer materials (clays, sands, gravels) will be found in the valley bottoms or flatter areas. Peat is normally found in marshy areas or in moors. Uses: All the harder rocks are quarried as building material. Clays are used to make bricks, tiles and pottery. Sands and gravels are extracted for use in cements and concrete. Peat is dug for fuel, but is normally only used locally. Granite, Gabbro, schist and gneiss can all contain valuable gemstones. Granite and Gabbro instrusions metamorphose the local rocks (turning them in to shales, slates, quartzites, marble etc.) and generally lead to the formation of valuable ore veins within these rocks (generally the heaviest metals (gold lead) are deposited nearest the igneous rock, whilst the lightest metals (copper, lithium etc) are deposited furthest from the intrusion. 2: Excavation Facts and Figures =============================== Given here are three tables. The first is a table of the rate of rock and soil excavation that can be expected per man each working day, the second gives rock and soil densities and 'bulked up' volumes, and the last gives the density, loose volume and yeild of a few principle mineral ores. Table 1 ------- In the first table, the rates of excavation assume that the worker is skilled, whether a miner, quarryman or construction worker. Unskilled workers can be expected to work at 50% to 75% of the efficiency of a skilled worker. Note these figures are for the rate of excavation from a working face, transportation to the spoil dump would require additional (less skilled) labour. The derivation of this table is given in the accompaning document. The rate of excavation of rock types will vary dramatically dependant on the ammount and severity of weathering and fracturing of the rock in-situ. I give figures for three idealised states; poor - frequent fractures and well weathered average - occasional fractures and moderately weathered sound - few fractures and unweathered Soil strength isn't as effected by weathering and fracturing as rock so only 'average' figures are given. The figures given are the volume of material excavate (in terms of the size of the hole, not the size of the spoil heap) quoted in cubic feet per day. The second is the tonnage of the rock removed. Table 1: Rate of Excavation (per skilled man shift) --------------------------------------------------- Rock Poor Average Sound ---- ---- ------- ----- Gabbro 17.5 (1.39) 8.0 (0.64) 5.0 (0.40) Slate 22.5 (1.69) 10.0 (0.75) 6.5 (0.49) Marble 20.0 (1.47) 10.0 (0.74) 6.0 (0.44) Gneiss/Schist 17.5 (1.26) 8.0 (0.58) 5.0 (0.36) Basalt/Dolerite 12.5 (0.89) 6.0 (0.42) 3.5 (0.25) Granite 17.5 (1.25) 8.0 (0.57) 5.0 (0.36) Limestone 25.0 (1.56) 12.5 (0.78) 7.5 (0.47) Sandstone 22.5 (1.38) 12.5 (0.76) 6.0 (0.36) Chalk 32.5 (1.80) 17.5 (0.96) 9.0 (0.50) Shale 22.5 (1.24) 10.0 (0.55) 6.5 (0.35) Stiff clay 25.0 (1.32) Sandy gravel 37.5 (1.88) Sand 42.5 (1.87) Soft clay 30.0 (1.31) Peat 50.0 (1.28) Figures are: bulk volume in cubic feet (weight in tons). Table 2 ------- Table 2 gives the density of different types of rock and soil (these figures are used to derive table 1) and the Spoil volume. The spoil volume is given in cubic feet per ton, this is not the same as the bulk density of the rock, but subsumes the air space within a loose pile of material (the amount of void space is dependant on the materials size and texture, and varies from 12% for sand, to 70% for fresh blocky rock). The spoil volume can be used to calculate the size of the spoil heap or, more usefully, the transport requirements to bring the material to its pount of use. Table 2: Rock and Soil volume and density data ---------------------------------------------- Rock/soil type density Spoil volume -------------- ------- ------------ Gabbro 2.14 21 Slate 2.03 18 Marble 1.98 22 Gneiss/Schist 1.94 23 Basalt/Dolerite 1.92 21 Granite 1.92 21 Limestone 1.69 26 Sandstone 1.66 25 Chalk/Shale 1.49 25 Stiff clay 1.42 24 Sandy gravel 1.35 23 Sand 1.19 25 Soft clay (soil) 1.18 30 Peat 0.69 43 Where, denisty is in tons per cubic yd loose volume is in cubic ft per ton Table 3 ------- Table three gives the same figures as table 2 for PURE mineral ores, along with the metal yeild given as a percentage of the mineral by weight. To convert from tons per cubic yard to pounds per cubic feet multiply by 83. The bulking factor for crushed mineral ore is assumed to be 1.35 (ie loose ore contains 26% void space). Mineral (ore of...) denisty Yeild ------------------- ------- ----- Azurite (copper) 2.77 45% Cassiterite (tin) 5.07 79% Chalcopyrite (copper) 3.13 42% Cinnabar (mercury) 5.91 86% Cuprite (copper) 4.37 89% Galena (lead) 5.40 87% Haematite (iron) 3.83 70% Limonite (iron) 2.66 63% Magnetite (iron) 3.86 72% Malachite (copper) 2.92 57% Pyrite (iron) 3.72 47% Sphalerite (zinc) 2.95 67% Where, denisty is in tons per cubic yd Yeild is % of metal by weight of the mineral 3: Examples of Use ================== The figures given here can be used in a variety of ways, given here are examples for construction, tunneling, transport of materials and mining. Construction ------------ To calculate the time to dig foundations, cellars etc you need to decide the ground type. Then simply calculate the volume of the hole in cubic feet, and divide this by the number of cubic feet a skilled worker could excavate in a day (table 1) to give the number of man days of work. Example 1: a cellar needs to be dug which is twelve feet by seventeen feet and eight feet deep. The cellar situated in a valley which is assumed to be stiff clay. The volume of the cellar is 1632 cubic feet and a skilled workman can excavate 25 cubic feet per day. The cellar will take 67 man days to dig (1632 / 25 cubic feet). Tunneling --------- Typically in mining small audits and vertical shafts are dug to reach the ore deposit, and in the case of veins, to follow them. Generally, the size of an audit is only just big enough for the miners to work in, about fourty inches high by eighteen inches wide. After allowing for the uneven sides and rounded roof an audit can be assumed to have a cross sectional area of five square feet. Historically audits (and shafts) are quoted in terms of fathoms of length. Example 2: Ten fathoms of audit would take the following times to excavate; 38 man days in ave. chalk (600 cubic feet / 17.5 c.ft per man day) 60 man days in ave. slate (600 cubic feet / 10.0 c.ft per man day) 80 man dayt in strong limestone (600 c.ft / 7.5 c.ft per man day) Note: for softer material time and wood must also be allowed to shore up the sides of the audit. Transport of materials ---------------------- To calculate the carrying capacity of vessels requires knowledge of the 'Spoil volume' given in table 2. Basically divide the cubic volume of the vessel by the spoil volume givem to generate the capacity in tons. Example 3: If a lurry (a heavy goods carrying wagon, which gives rise to 'lorry' in modern usage) has a cargo area of five feet by with three foot side walls it could carry, seven tons of granite (135 c.ft / 21 c.ft per ton) five tons of clayey soil (135 c.ft / 30 c.ft per ton) or three and a half tons of peat (135 c.ft / 43 c.ft per ton) Example 4: If a glassworker transports pure sand in barrels (a quite common practice for ores) of a internal volume of ten cubic feet, then each barrel will contain 896 lbs of sand (10 c.ft / 25 c.ft per ton, times 2240 lbs per ton). The same barrel filled with galena would contain 1 3/4 tons of the ore (10 c.ft / 5.75 c.ft per ton). Mining ------ This last section is an example of how the amount of ore produced from a mine could be calculated. Firstly the 'geology' of the mine, must be decided. The example mine is a very large lead mine in a limestone district. The limestone is of average strenth. I assume that the lead is in the form of ore, galena. This galena is in veins (along the joints in the limestone) with an average of one inch thick. The galena vien isn't pure but is mixed with unwanted (gangue) minerals such as calcite and barytes - only 30% by volume is galena. This mine is being mined by ten miners, and six labourers to cart the ore and waste rock about, and a mule handler. They ship the ore (by mule) in wooden crates which measure 2 ft 6 inches by 1 ft by 6 inches. What the GM wants to know is a) how much ore is produced per day, and b) what is this worth to the refiner? A) Mine production. In average limestone each miner can shift 12.5 cubic feet per day, so between them they mine 122 cubic feet of productive raw rock per day (12.5 c.ft per day x 10 miners). They have to mine using audits. Within each audit, a four and a half foot long by one inch wide ore vien is exposed; this vein represents 3.75% of the total raw rock volume (4.5 x 1/12 ft divided by 10 ft cross sectional area of the audit). This means that 4.57 cubic feet of ore bearing vein rock is mined per day. Since 70% of the vien is wasted, this leaves 1.37 cubic feet of pure galena ore. Galena has a denisty of 5.40 tons per cubic yard which is 449 lbs per cubic feet (5.40 tons divided 27 cubic feet per cubic yard and multiplied by 2240 lbs per ton). So 1.37 cubic feet of ore weighs about 615 lbs. B) What will the miners get. Since the refining process requires quite a lot of investment in equipment and fuel, I presume that the cost of the refined metal is divided equally between the miner and refiner (most miners will do both, running a remote mine and a refinery near the point of sale, eg village). The mine is producing 615lbs of ore per day. The yeild of galena is a relatively high 87% (table 3), which means the ore can be refined to produce 535 lbs of pure lead (615 lbs times .87). Lead sells for one ha'penny per pound, so the lead is worth 267.5d and the refiner (in this example) is prepared to buy it from the miner for 132d (11 shillings). NB: the refiner won't be producing pure lead, rather 563 lbs of 95% pure lead in the form of seven and a half 75lb ingots. This represents a good profit for the Master of the mine. His daily accounts can be set out as follows; Income from lead 132d Tithe to lanowner (*) 8d 3f Title to miners guild (@ 5%) 6d 2f Labour costs; 10 miners @ 3.5d / day 35d 6 laborers @ 1.75d / day 10d 2f 1 mule driver @ 2d / day 2d Food, Feed and fuel 39d Tools, mules, buildings etc. 9d ---- Total costs: 110.75d NET PROFIT: ~21d per day. (*)Most land owners (the local lord) require a tithe, one early english agreement is one 'pigg' in every fifteen; this equates to a tax of 6 2/3 %. Though 21d per day (52.5s per month) seems a fair ammount it must be remembered that there is likely to be only one mine of this size per harnic kingdom. Most mines would be around a fifth of this size (with a profit of about 10s a month, hardly enough to live on). No account has been taken of efficiency overall: taking in to account illness, accident, time 'wasted' sinking access audits, the time digging through barren rock when the ore vein disappears etc.; the profits will quickly vanish. Long term profitability depends on the rare occasions when a wide vein is found. J M Davidson, 1996