Transactions of the Geological Society, 1st series, vol. 4/Account of the Veins in the Mine of Huel Peever
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By JOHN WILLIAMS, Junr. Esq.
HONORARY MEMBER OF THE GEOLOGICAL SOCIETY.
[Read 2d June, 1815.]
THE county of Cornwall, in whatever part it has been explored in the working of its numerous mines, has been found so devoid of perfect regularity and agreement, either as regards the course, dimension, or contents of its veins, or the uniformity of the country they traverse, that the history of any one mine can by no means be considered as exhibiting a portrait of them in general. Each mine, not to say each vein, will be found to have some peculiar claim to attention. It is not perhaps hazarding too much, to presume that a knowledge of what occurs, even to the limited depth to which the Cornish veins are followed, may be found to throw some light on a branch of science which is yet involved in considerable obscurity, but it is to be lamented that facts have not hitherto been sufficiently attended to with a view to their preservation. The object of the miner is the most expeditious manner of arriving at gain; his knowledge is derived from the book of his own experience: but so greatly do the circumstances attending veins differ, that they sometimes set at defiance his experience, however great or general it may be. Some of the most interesting phenomena attending the veins of Cornwall are the interruptions they meet with from each other; these are of various descriptions. In the mine of Huel Peever, which is the object of this memoir, almost every species of interruption occurred to which the veins of Cornwall are liable; and so completely was the skill and experience of the miner baffled in the progress of its workings, that its tin vein having been heaved (to use a technical phrase) by other veins, it was not discovered again by the exertion of much labour and expense during a lapse of nearly forty years. It may perhaps serve to render more intelligible the following description of the remarkable circumstances attending the veins of Huel Peever, if we notice on the subject of veins in general that those of which the direction is north and south are rarely metalliferous; that the veins containing copper and tin run, with little exception, about east and west. Their downward direction is seldom quite vertical; there is however a species of vein having also an east and west direction which is never metalliferous, but consists generally of clay; this vein is for the most part found to take a course under-ground much less approaching the perpendicular than the metalliferous veins. This variation from the perpendicular in an east and west vein, whether it be towards the north or south, is called the underlie, and when its direction or dip is opposed to that of the metalliferous vein, it mostly, disturbs the direction of the latter. The east and west non-metalliferous veins either from their customary effect in respect to other veins, or from their generally quick underlie, or from both, have obtained the name of slides.
The mine called Huel Peever is situate in the parish of Redruth, about one mile and a half north-east of the town of the same name. Its veins, to the extent of their workings both in length and depth, were found to pass only through schist, occasionally of a micaceous appearance, but in many parts the mica not being perceptible, it assumed the character of argillaceous schist.
By a reference to the accompanying ground plan of the mine, Pl. 7, fig. 1, it will be seen that it consisted of one tin vein a and one copper vein b; the latter called John's Gossan, running in the direction of east and west, and forty fathoms south of the former; two other veins c and d not metalliferous, took the same direction, one 25 fathoms south of the copper vein, and the other 28 fathoms still further south. Many fathoms north of the tin vein, but at what exact distance is not precisely known, a channel of porphyry; or in the language of the miner, of elvan, also ran in the direction of east and west, and a copper vein c near it. It will also be seen that there were three cross veins, not metalliferous, technically called cross courses, the easternmost of which x runs from 10 degrees west of north to 10 degrees east of south, that next to it y, about 9 fathoms to the west, runs a little more to the west of north, and east of south. The precise direction of the westernmost z, which was 145 fathoms distant from that next to it on the east, is not known; nor is that essential to the present object, since as it formed the utmost limits of the workings of the mine on the west, and was situate in the poorest part, it was not found to contribute any thing towards the strange circumstances which have rendered the history of this mine so well deserving of detail and preservation.
The tin vein a is from three to thirty feet wide, but its general average may be estimated at about eight feet. The copper vein b is about three feet wide. It is almost needless to observe that these veins were not equally productive in every part; in some places, they were very rich, in others quite poor; but it is worthy of notice, that where the tin vein was thirty feet wide, its substance consisted of a mass of rich tin ore extending several fathoms in every direction. The substances enclosed in the copper vein, consisted, near the surface, of quartz and iron ochre, or gossan, amongst which was interspersed a little yellow copper ore, accompanied by quartz, chlorite and iron pyrites to a considerable depth. Both the tin and copper veins have been traced for about a mile in length.
The two slides which run parallel with the metalliferous veins afforded no trace of either copper or tin. The northernmost of the two is from 4 to 12 inches wide; the southernmost from 2 to 3 inches. They were found to consist wholly of an argillaceous 3 clay, called by the miner flucan. These veins, as will hereafters seen, notwithstanding their poverty, were one principal cause of the remarkable incidents attending this mine.
It will be seen by the ground plan that the eastern cross course x, (which was about 4 feet wide, consisting of 3 feet of quartz on the western side, and 6 inches of flucan on the eastern,) traversed the channel of porphyry, the tin and copper veins, as well as the two slides, heaving them all 54 fathoms to the north on its western side, where they maintain the same distance from one another as on the eastern side. The cross vein y next on the west, which consisted of the same substances as the cross vein x, and on the surface where it cut the tin vein at P was distant from it only about 26 fathoms, had precisely the same effect on all the east and west veins, except that the distance of the heave north was only 18 fathoms, so that the tin vein, at its place of contact with the west side of the cross vein y at P was exactly 72 fathoms north of that part of it in contact with the eastern side of the cross vein x at Q. Of the cross vein at the western extremity of the mine, (as has before been noticed) little is known. But the two former have been traced nearly five miles in length intersecting every tin and copper vein, and from every observation, it seems probable that they extend from the Bristol to St. George's Channel, and are very distinctly seen in the digs near Porthtowan on the northern coast.
The intersection and heave of the east and west veins by the north and south veins in Huel Peever, form an interesting part in the detail of its history; although such occurrences are by no means rare, as they are found to exist in a greater or lesser degree in almost every mine traversed by north and south, or non-metalliferous veins. But some remarkable and almost peculiar circumstances belonging to the downward direction or underlie of the several veins in Huel Peever remained to be noticed: these are of so complex a nature, as to render a verbal description difficult; but they are of great interest in a geological point of view.
The channel of porphyry, and copper vein near it, being in no degree connected with the ensuing detail, are wholly omitted in the accompanying transverse section, which represents the underlie of the tin, copper and flucan veins on the west side of the cross vein y.
The underlie of the tin vein is towards the south, 2 feet in every fathom, that of the copper vein is towards the north, 4 feet in a fathom, so that the horizontal distance between them at the surface being 31 fathoms, they would have come in contact at the depth of about 31 fathoms, but for the intervention of the flucan vein on the south of the copper vein. The underlie of this flucan is towards the north, and much quicker than that of the copper vein, being about 14 feet in every fathom; and by the transverse section it will be seen that the flucan overtook the copper vein at A, and cut it short at the distance of about 22 fathoms, measured along its inclination, from the surface; whence pursuing its direction in a strait line about 14 fathoms, it met with, and in like manner, interrupted the course of the tin vein at B at about 26 fathoms measured along its underlie, or 24 fathoms perpendicular from the surface; after which the flucan or slide proceeded regularly.
It next became the object of the miner to discover the parts of the copper and tin veins, which had been severed and carried away by the flucan. This after much labour and expence was effected. On pursuing the downward direction of the flucan vein, after it had quitted the tin vein at B, it was found that the copper vein had been carried down about 18 fathoms from A to C, and the tin vein as much from B to D.
The working of the tin vein being the object of the miner, he found it proceeding in its underlie from D in the same direction as it had assumed between the surface and its place of intersection with the vein of flucan at B; but after sinking upon it about 9 fathoms, it was found (to use his phrase) cut out by the copper vein at E, whence a new and unlocked for delay and expense were incurred. It was at length discovered that the effect of this intersection was immediately opposed to that occasioned by the flucan vein, for the tin vein was as it were, heaved up by the copper vein 8 fathoms to F, whence it resumed its customary underlie and direction, and was followed for about 42 fathoms in depth to G, where it was intersected by the south slide d, by which it was heaved up about nine feet; it afterwards continued its course downwards as before, and was worked about 38 fathoms below to H. The south slide underlies towards the north about six feet in a fathom.
The accompanying longitudinal section of Huel Peever is along the run of the tin vein, and supposes its south side or wall taken away in order to exhibit the workings of the mine; and for the same reason also supposes a perfect continuation of the tin vein from the eastern side of the western cross vein z to the western side of the eastern cross vein x, although the fact was, as has been already noticed, that the tin vein was separated by the slide at 26 fathoms on its underlie from the surface, and carried away 18 fathoms towards the north, and also that the tin vein was 18 fathoms further north between the western and the middle cross vein than between the latter and the eastern cross vein. The workings to the east of the latter are not exhibited in the longitudinal section, in consequence of its being another mine called Old Huel Peever.
By the longitudinal section it will be seen that the downward direction of the eastern cross vein x, towards the west, was 4 inches in a fathom, the underlie of that 17 fathoms on the west of it at the surface at y, was towards the west one foot and a half in a fathom. The underlie of the cross course at the western extremity of the mine z, was in opposition to the latter, being very little towards the east, though nearly perpendicular.
c c, d d, Represent the north and south slides intersecting the tin vein, the former at 25 fathoms perpendicular from the surface at the engine shaft, and the latter about 50 fathoms below. 9, shews the situation of the shallow adit or water course, and 10, the deep adit; all the other horizontal lines represent the passages or levels made by the miner in the search after tin, or for the convenience of his occupation. The dark parts of the longitudinal section shew the places in which tin was found.
- Pl. 7, fig. 2.