1. The bed of ore is got at by the transverse galleries, m, n, o, q, r, s, which branch off from the extraction shaft, and terminate at the wall of the main bed;
2. Great vaults are scooped out at the level of the workings, by means of fire;
3. The roofs of these vaults are progressively propped with mounds of rubbish;
4. The ores thus detached, or by blasting with gunpowder, are then collected;
5. Lastly, they are wheeled out to the day; and washed near Z.
Comparative Table of celebrated Mines in Europe and America. By F. Burr, Esq.
(Quarterly Mining Review for July, 1835, p. 60.)
| Consolidated and United Mines. | Veta Grande Mines. | Mine of Valenciana. | Mine of Himmelsfürst. | |
|---|---|---|---|---|
| (At present the richest mines in Cornwall.) | (At present the richest mines in Mexico.) | (Richest of the Mexican mines at the beginning of the present century.) | (Richest of the Saxon mines at the beginning of the present century.) | |
| Situation | Two miles east of Redruth. | Four miles north of Zacatecas. | One mile north of Guanaxuato. | Two miles south-east of Freyberg. |
| Elevation | Elevation of the surface above the level of the sea, from 200 to 300 ft.; depth of thebottom of the mine below the level of the sea, about 1,370 feet. | Elevation of the surface above the level of the sea, supposed to be about 6000 feet.Elevation of the bottom of the mine above the level of the sea, probably near 5,000 feet. | Elevation of the surface above the level of the sea, 7,617 feet. Elevation of the bottomof the mine above the level of the sea, 5,730 feet. | Elevation of the surface above the level of the sea, 1,346 feet. Elevation of the bottomof the mine above the level of the sea, 263 feet. |
| Nature of the rock | The Veta Madre of Guanaxuato, upon which this mine is worked, traverses both clayslate and porphyry, but it is most productive in the former rock. The clay slate is considered by Humboldt to belong to the transitionclass, but situate near the limits of primary formations. This rock in depth, passes into chlorite slate, and talc slate. It containssubordinate beds of syenite, hornblende slate, and serpentine. The porphyry rests upon the clay slate, and is conformable to it, both indirection and stratification. | The rock prevailing in the neighbourhood of Freyberg, in which this and most of the othermines are situate, is a formation of primary gneiss. | Primary clay slate resting immediately on granite, a short distance westward of the mines.The clay slate is intersected by numerous channels of porphyry, which have nearly the same direction as the mineral veins, and are oftenof considerable width. The porphyry sometimes appears also to form large irregular masses in the clay slate. Both rocks are traversed byveins of quartz and clay intersecting the metalliferous veins. | Transition clay slate, alternating with dolomite, and occasionally with greywacke. Thisclay slate is sometimes decomposed; it rests on syenitic rocks, and is in some places covered with porphyry. |
| Nature of the metalliferous deposits | In the consolidated mines, the eight following lodes are extensively worked:—WhealFortune lode, Cusvea lode, Deeble’s lode, Old lode, Taylor’s lode, Tregonning’s lode, Martin’s lode, andGlover’s lode. In the united mines, the principal workings are upon the Old lode, and about five or six others are more or lessproductive. Numerous smaller lodes or “branches” occur also in both mines. The principal lodes are from 2 or 3, to 7 or 8 feetwide; the “branches” are generally 12 or 18 inches wide. The direction of the lodes varies from nearly east and west to about20 degrees north of east and south of west. The underlie of the principal lodes, is from 2 to 3 feet per fathom north, that of the smallerones about the same south. | One principal vein (the Veta Grande) which is generally separated into threebranches, and sometimes into four. When ramified, the width extends to 60 or 70 feet; when united, it varies from 8 or 10 to 20 or 30feet. The branches are generally about 10 or 12 feet wide, and the upper one is most productive. The direction of the Veta Grande, is from30 to 40 degrees south of east, and north of west, and its underlie, from two to three feet per fathom south. Other veins of less size,occur in the neighbourhood of the Veta Grande, which cross it at an acute angle. One of these appears to heave the vein for about 700feet, being the most remarkable derangement of the kind on record. | One Veta (the Veta Madre) which is often separated into three branches,extending from 130 to 160 feet in width. When not ramified, its width varies from 20 or 30 to 60 or 70 feet, but is more commonly from 40to 50 feet. The direction of the vein, is north-west and south-east; its underlie is south, and about five or six feet per fathom. Thereare five veins worked in this mine. | The principal vein (Teichflache) is from one foot six inches, to three feet inwidth, the others are from six to 12 inches wide. The direction of this vein, is nearly north and south, its underlie is west, and aboutthree feet per fathom. Some of the other veins intersect it. |
| Ores | Chiefly copper ore, occasionally native copper, blue and green carbonate of copper. Tin, oroxide of tin, also occurs, but not in very great abundance. | Chiefly red silver, native silver, sulphuret of silver, and argentiferous pyrites. | Sulphuret of silver, native silver, prismatic black silver, red silver, native gold,argentiferous galena. | Argentiferous sulphuret of lead, native silver, sulphuret of silver, red silver. |
| Produce of the ores | 91⁄4 per cent. of fine copper; average produce in 100 parts ofore. | 31⁄2 oz. per quintal. | Four ounces of silver per quintal of 100 lbs., equivalent to21⁄2parts of metal in 1,000 of ore, or 1⁄4 per cent. | Six to seven ounces of silver per quintal of 100 lbs. Equivalent to from33⁄4 to 41⁄2 parts of metal in 1,000 of ore, or from 3-8ths to nearly1⁄2 per cent. |
| Veinstone | Chiefly quartz, of which many varieties occur. | Chiefly quartz, occasionally amethyst, carbonate of lime, and sulphate of barytes. | Quartz, amethyst, carbonate of lime, pearlspar, and hornstone. | Quartz, pearlspar, and calcareous spar. |
| Mineral substances | The ores are generally accompanied by “gossan”[34] in the backs of the lodes, by blende, and by iron, andarsenical pyrites in depth. | The ores are generally accompanied by blende, sulphuret of antimony, and iron pyrites. | The ores are accompanied by blende, spathose iron, copper and iron pyrites. | The ores are accompanied by blende, spathose iron, and a little iron and arsenicalpyrites. |
| Depth of the principal shafts | Woolf’s engine-shaft, 248 fathoms; Pearce’s engine-shaft, 275fathoms. Some of the other engine shafts are scarcely inferior in depth. | Tiro General, 182 fathoms; Gallega shaft, 138 fathoms. | Tiro General, 310 fathoms. | Frankenschacht, 180 fathoms. |
| [855]Depth of aditat the principle shafts | At Woolf’s engine-shaft, 13 fathoms. The average depth of the adit at the otherengine-shafts is about 30 or 40 fathoms. | There is no adit to this mine. | There is no adit to this mine. | The adit at the shaft called Frankenschacht is 47 fathoms in depth. |
| Quantity of water | Varies from 2,000 to 3,000 gallons per minute. | About 80 gallons per minute. | The Valenciana was a dry mine from its commencement in 1760 to 1780, when it first becametroubled with water, in consequence of some of the workings being inadvertently communicated with the adjoining mine of Tepeyac; which,although upon the same vein, was extremely wet. The quantity of water raised during the late working appears to have been about 110gallons per minute, but the regular influx was much less. | 50 gallons per minute. |
| Height to which the water is raised | About 230 fathoms at the consolidated mines, at the united mines, about 110 fathoms. | On an average about 150 fathoms. | 310 fathoms. | 133 fathoms. |
| Power employed in drainage | 9 steam-engines; 3 of 90-inch cylinder, 3 of 85, 1 of 80, and 2 of 65. A water wheel, 48feet in diameter. | Usually 10 malacates.[[b]] | A steam-engine of 30-inch cylinder, and 7 malacates. | Two water-wheels, each 42 feet in diameter. |
| Probable equivalent in actual horsepower | 1,500 constantly at work, or a total number of above 4,500. | 32 horses constantly working, or a total number of about 100 horses.[[c]] | 65 horses constantly at work, or a total number of about 200. | 16 horses constantly at work or a total number of about 50.[[d]] |
| Average annual expense in drainage | 12,700l. taking the average of the last ten years.[[a]] | 20,000l. per annum.[[c]] | About 40,000l., per annum.[[d]] | Cannot be ascertained, but evidently very small.[[d]] |
| Quantity of ore annually produced | 16,400 tons of copper ore, a few tons of tin ore.[[a]] | 21,380 tons of silver ore.[[c]] | 32,500 tons of silver ore.[[d]] | 630 tons of silver ore.[[d]] |
| Produce in metal | 1,517 tons of fine copper, a little tin.[[a]] | 153,000 lbs. troy of silver.[[c]] | 221,900 lbs. troy silver.[[d]] | 6,160 lbs. troy of silver.[[d]] |
| Total returns, or value of the above | 119,800l.[[a]] | 423,400l. per annum.[[c]] | About 600,000l.[[d]] | About 18,000l.[[d]] |
| Total costs of the mine | 93,500l. exclusive of lord’s dues; 98,600l. including lord’sdues.[[a]] | 252,170l. per annum.[[c]] | 197,900l. per annum.[[d]] | 9,500l. per annum.[[d]] |
| Clear profit to the proprietors | 21,000l. per annum.[[a]] | 171,240l. per annum.[[c]] | 118,750l. per annum.[[d]] | 3,560l. per annum.[[d]] |
| Amount of capital invested | 75,000l.[[a]] | 130,000l.[[c]] | Cannot be ascertained, but known to have been very small.[[d]] | Cannot be ascertained, but probably very small.[[d]] |
| Interest on capital invested | 280 per cent. after paying back the original capital.[[a]] | Nearly 700 per cent. after paying back the original capital.[[c]] | Not known, but certainly many hundred per cent.[[d]] | Not known, but probably very high.[[d]] |
| Proportion of costs to returns | Costs exclusive of lord’s dues, 78 per cent.[[a]] | About 591⁄2 per cent. | Costs 60 per cent. In the nine years following, the proportion was 80 per cent., at theend of that time the working of the mine was stopped by the revolution, in the year 1809.[[d]] | Costs 73 per cent.[[d]] |
| Number of men employed | About 2,500 persons, of whom about 1,450 are employed under ground. | About 900, of whom nearly 600 are employed under ground. | 3,100 Indians and Mestizoes, of whom 1,800 are employed under ground. | 700 miners of whom 550 are employed under ground. |
| Wages of the mines per day | Probably about 3 shillings on an average. | About 8 or 9 shillings per day. | From 4 to 5 shillings. | About 1s. 6d. per day. |
| Quantity and expense of powder | 1,420 cwt.; value 15,830l. | 240 cwt.; value 1,070l. | ||
| Manner in which the ores are disposed of | Sold to the smelting companies, and smelted by them at Swansea, in South Wales. | Chiefly reduced by the company at the hacienda of Sanceda, by smelting and amalgamation. | Sold to the Rescatadores, and reduced by smelting and amalgamation at haciendas, in theneighbourhood of Guanaxuato. | Delivered to the government reduction works in the neighbourhood of Freyberg, where theyare partly smelted, and partly amalgamated. |
| [a] Average of the last Ten Years. [] Malacate; a horse whim. [c] Average of the last Six Years. [d] Average year at the end of the Eighteenth Century. | ||||
[34] Gossan, or Gozzan; oxide of iron and quartz.
VENTILATION OF MINES.