“In digging a mine,” says Dr. Maton, “the three material points to be considered, are the removal of the barren rocks or rubbish, the discharge of water, (which abounds more or less in every mine,) and the rising of the ore. Difficulties of course increase with depth, and the utmost aid of all the mechanical powers is sometimes ineffectual, when the workings are deep and numerous. Mountains and hills are the most convenient for working, because drains and adits are then easily cut to convey the water away into the neighbouring valleys. These adits are sometimes driven (as the miners term it) to the distance of one, or even two miles; and though the expense is enormous, these are found a cheaper mode of getting rid of the water than by raising it to the top, especially when there is a great influx, and the mine very deep. It seldom happens, however, that a level can be found near enough for an adit to be made to it from the bottom of a mine; recourse must be had then to a steam engine, by which the water is brought up to the adit, be the weight of it what it may. As soon as a shaft is sunk to some depth, a machine, called a whim, is erected, to bring up either rubbish or ore, which is previously broken into convenient fragments, by pickaxes and other instruments. The whim is composed of a perpendicular axis, on which turns a large hollow cylinder of timber, (called the cage) and round this a rope winds horizontally, being directed down the shaft by a pulley fixed perpendicularly over the mouth of it. In the axis a transverse beam is fixed, at the end of which two horses or oxen are fastened; and go their rounds, hauling up a bucket or kibbul, full of ore or rubbish, while an empty one is descending. The ore is blown out of the rock by means of gunpowder, and when raised from the mine, is divided into as many shares or doles as there are lords and adventurers, and these are measured out by barrows, an account of which is kept by a person who notches a stick for that purpose. Every mine enjoys the privilege of having the ore distributed on the adjacent fields. It is generally pounded or stamped on the spot, in the stamping mill. If full of slime, it is thrown into a pit called the buddle, to render the stamping more free, without choaking the grates, (thin plates of iron full of small holes.) If free from slime, the ore is shovelled into a kind of sloping canal of timber, called the pass, whence it slides, by its own weight, and the assistance of a small stream of water, into the box, where the lifters work. The lifters are raised by a water wheel, and are armed at the bottom with large masses of iron, about one hundred and a half in weight, which pound or stamp the ore small enough for its passage through the holes of an iron grate, fixed in one end of the box. To assist its attrition, a rill of water keeps it constantly wet, and it is carried by a small gutter into the fore pit, where it makes its first settlement, the lighter particles running forwards with the water into the middle pit, and thence into the third, where what is called the slime, settles. From these pits the ore is carried into a large vat, called the keeve, where it is washed and rendered clean enough for the smelting house. Most of the tin mines now working have steam engines, the advantages of which have proved a great benefit to the proprietors of them.”
The famous Wood Tin, as it is called, has frequently been found in the stream works. It nearly resembles the colour of Hæmatites, with fine streaks, or Striæ, converging to the different centres like the radiated zeolite. From the experiments of the celebrated Klaproth, wood tin was found to yield 63 parts in a hundred of tin. The most general state in which the tin of Cornwall is found, is the calciform, the greater quantity of ore being indurated, or glass-like; and its most prevalent matrix is either an argillaceous or a silicious substance, or a stone composed of both, and called by the miners caple: none of the calcareous genus ever appear contiguous to the ore, except the fluors.”
The discovery of the Copper Mines in Cornwall is of a much later date than those of tin, being about the year 1690. Although the propriety of searching was strongly recommended by Norden to King James, many years expired before the real value of the copper mines was discovered. Subsequent improvements and perseverance have rendered the copper mines one of the most important branches of commerce in this county; and the quantity of that valuable ore, now annually raised, is said to be worth, upon a moderate calculation, the sum of £350,000, or £90,000 greater than the value of tin. Copper ores are found in Cornwall, in great abundance and variety. Native copper is sometimes found on the sides of fissures in thin films, deposited by the impregnated water that runs from the lodes. Veins of copper are also frequently discovered in cliffs that are left bare by the sea, but the most certain sign of a rich ore is an earthy ocherous stone, called Gossan, of a ruddy colour, and crumbles like the rust of iron. Another sign of the presence of copper is, when the ground is inclinable to an easy free working blue Killas, intermixed with white clay. A white crystaline stone is also found to contain a great quantity of yellow copper. The lodes of copper ore generally lie deeper than those of tin, and its ores are mostly of the pyritous and sulphurated kinds, with more or less arsenic. “The lodes, both of tin and copper, appear most frequently to have granite for their country, and to make an angle from 60° to 76° with the horizon.” The matrices of copper ore are very numerous. Among the blue ores, there is one of an extremely fine blue earth. The grey ore is frequently spotted with yellow and purple, but is deemed richest when of an uniform colour throughout.
The copper ore is cleansed and dressed by the same process as that adopted for tin, but as it generally rises in large masses, requires less washing. Owing to the expense of importing coal, the ore is disposed of after it is prepared for the smelting houses, and owing to the expense of importing coal, the Smelting Houses at Hayle have ceased working for a considerable time past. “Nothing,” says Dr. Maton, “were so deleterious as the fumes of arsenic constantly impregnating the air of these places, and so profuse is the perspiration occasioned by the heat of the furnaces, that those who have been employed at them a few months, became most emaciated figures, and in the course of a few years are generally laid in their graves.”
The principal copper mines now working, are mostly in the neighbourhood of Redruth, of which the Gwennass, United, Poldice, Huel Unity, Cook’s Kitchen, and Dolcooth Mines, have yielded an abundant source of gain to their numerous adventurers.
A very accurate and well executed geological map of the mining districts, by Mr. Richard Thomas, was published in the year 1819.
Lead is found in several parts of Cornwall, but not in any great abundance. The ores are very dissimilar, but the sort most frequently discovered is galena, or pure sulphuret of lead, which is found both crystallized and in masses. Its colour is most of a bluish grey, and the form of its crystals is generally the cube. The most common varieties are the cube, truncated at the angles and corners, and the octahedron of two four-sided pyramids, applied base to base. The principal mines are Huel Pool and Huel Rooe, near Helston. There are also a few others on the north coast, in the neighbourhood of Endellion and St. Minver, but of little consequence. The oxides of lead are valuable for painting and dying, and also for medicinal uses.
Among the numerous mineral productions of Cornwall, Gold and Silver ought not to be omitted; the former has been frequently found in extremely small granules, generally intermixed with the tin ore, in the stream works. The largest piece ever found, is mentioned by Borlase to have weighed 15 pennyweights and 16 grains. The latter has been found at different periods in considerable quantities, particularly in a mine called Huel Mexico, some years ago, near St. Agnes; also in the Herland Copper Mine, in the parish of Gwinear.—A particular account of the discovery of silver in the Herland Mine, was furnished by the Rev. Malachy Hitchins, and printed in the transactions of the Royal Society for 1801. But it appears that after the mine was sunk to a considerable depth, the works were abandoned, the expenses of the mine having considerably exceeded the receipts.
Within the last three years, a considerable quantity of silver has been discovered in a mine belonging to Sir Christopher Hawkins.
Iron, in rich lodes of red and brown ore, has been found in great abundance, in many parts of the county, but there are not any iron mines which have been much worked.—Iron Pyrites, or sulphuret of iron, occur in most of the veins of copper, as well as some magnetical iron ore at Penzance, and specular iron ore at Tin Croft Mine, in Illogan, Botallack Mine, near the Land’s End, and other places.