The mill building was designed and built for function rather than style. Important considerations in establishing and constructing the mill were selection of the site, cost of labour, security precautions, and lighting possibilities.
During the entire period of gold mining in 19th century Nova Scotia, water power was not exploited to the extent it could have been. Although water may have been available as a power source most stamp mills used steam.(1) In Goldenville, mills were built on the main brook of the North West Arm, or what Faribault called "Crusher Brook", as well as close to the actual diggings.(2) In selecting the site, water had to be available to facilitate the stamp mill operation, but not as a source of power. The presence of rock for the stamp mill mortar foundations was of utmost importance. Since the mills were operated on a gravity feed system, there was an attempt to use the landscape to that advatage.(3) However, in an area like Goldenville, where the topography did not lend itself to such use, the design of the building would have to compensate.
… it is always advisable, when possible, to choose the side of a hill having a fairly rapid slope, and consisting of rock sufficiently solid to form a good foundation for the battery. The average height of a mill of the "high" type, with a rock-breaker floor above ore bins of normal capacity, may be taken as 50 to 55 feet from the level of the car track to that of the concentrator floor, the length over all of the profile of the mill being rather over a 100 feet. Hence, a slope of 1 in two is most suitable for a mill site.(4)
As discussed in section 3.2 mills built during the 1860 period were not always located close to the mine shaft (s). Labour was relatively cheap, so it was simple to haul the ore with horse and cart or in wheelbarrows.(5) During this later period, there was general attempt to reduce the amount of handling of the ore both above and below ground. The site of the mill was considered with this factor in mind. The mills were located close by and usually connected by means of a tramway system.(6) ILLUS. 21, 22, & 23.
Throughout the gold mining districts of the province, and virtually wherever they existed, there was a perpetual concern about security. Miners were forever suspected of pilfering nuggets.(7) There was considerable precaution exercised in the appointments of millmen:
In conversation with Mr. W. L. Libbey, he told me that Howard Martin and Rufus Mosher were good amalgamators, and if you wish me to engage one for you I will do it. Mr. Libbey thinks that Mr. Mosher would be the man for you. I certainly think it is a good idea for you to have a man from North Brookfield with you, particularly one who you know is perfectly honest, and one who would look after affairs so there would be no danger of the amalgam being stolen.(8)
This same type of concern would be reflected in the design of most mills:
A mill should always be enclosed in a substantial building, admission to which should only be obtained at one or two points.(9)
Similar concern was expressed about the ability of the building to withstand the elements and also, potential fire damage:
In America, these structures are mostly of all wood but this material, though possessing some advantages, presents great risk on account of fire… The system prevalent in America of building all the roof in one plane is also not to be recommended, as such a roof is liable to damage from storms. It is better built in three or four bays, which moreover give excellent opportunities for lighting and ventilation.(10)
The problem of adequate light and working space was also an important matter in mills of the later period.(11) Prior to the turn of the century, most Nova Scotian mills were lit by natural light and kerosene lamps. ILLUS. 51. Some mills, such as Lake Lode Gold Mine mill at Caribou were designed to take advantage of whatever natural light there may be during the day. This mill had a system of skylights installed to provide light to two levels within the building. ILLUS. 52. The use of windows to provide additional light is evident in the Royal Oak Mill and the Harrigan Gold Mine Mill. ILLUS. 50, 53-55.
Mill structures would be at least three stories in height, to accommodate all the necessary mill equipment as well as to use a gravity-feed system. ILLUS. 49, 52, 55. The Blue Nose Mill appears to have been a three and one half-story building; the Royal Oak was a substantial four-story building.
The mill flooring was usually a substantial material that did not allow the leakage of either water or cement. It would appear from ILLUS. 51 and ILLUS. 52 that plank flooring was installed. In his 1897 edition of A Handbook on Stamp Milling, Henry Louis recommended "a good cement floor, or failing this, a floor of stout 3-inch plank having the joints carefully caulked like the deck of a ship." (12)
Hardman's Oldham Mill floor was "laid in hard pine with a pitch of half an inch to the foot, and a sluice was arranged to carry all washing from this floor to a mercury trap below."(13)
The arrangement of milling equipment with a mill followed Louis' rule of thumb, that the ore was not to be lifted once it had entered into a mill building. An examination of the Oldham Mill Plan, 1891, and Louis' prototype mill plan demonstrated amount of hoisting power.(14) ILLUS. 49, 57, & 58.
The ore was hoisted to the top of the mil building either by tramway or skip. If the crusher was not located in the shaft building or in its own separate structure, it would be found at the top level of the mill building. From the crusher, the ore fell into ore bins which were located directly below the crusher. From the ore bin, the ore fed either automatically or by hand into the stamp battery. Following pulverization and amalgamation tables. If the mill had any concentrating equipment, frue vanners or wilfely tables, they were located on the next level, below the amalgamating tables.
The power source, the engine, and the boilers were usually located on the ground floor of the mill. In the North Brookfield Mill, the plant engine and two 60 horse power boilers were installed.(15) The engines and boilers were generally not placed close to the stamp battery, because of the problem of dirt and grease in the mill operations. ILLUS. 23, 50, 54, 55, & 59. Both the Royal Oak and the Blue Nose appear to have had a power house annexed to the mill building. The Blue Nose equipment included two boilers of 80 horse power and 100 horse power to supply the engines of 40 and 30 horse power respectively which provided motive power for the mill, pumps, hoist and rock breaker.(16) An examination of the terrain surrounding the Blue Nose and the Royal Oak shows that the boilers and engines were installed on a floor faced with fire bricks.
Following is a look at some of the pieces of equipment within the mill, as well as the different parts of the stamp mill itself.
Rock crushers had become fairly common within larger operations by the end of the 19th century. Independent miners may have continued to rely on sledgehammers to crush the quartz ore, but larger groups preferred the efficiency of the crusher. Some operations moved to a system using two crushers to increase the amalgamating potential of the stamp mill.(17)
The rock crushers weighed from two to twelve tons and the amount of power required for operation varied directly to the weight.(18) Hardman's mill used a "Forster rock breaker" in lieu of either the "old Blake" or the newer "Gates". The choice made was based on the following reasons:
Hardman argued that weight and amount of vibratory motion were of equal importance to the questions of power and cost for a small mill.
The Blue Nose used all three types of crushers in its operations between 1896 and 1904: A Dodge Breaker was added in 1898; a Forster breaker was in use according to the report, and 1901 and 1903 reports refer to 1 Gates ore breaker. A 7' x 9' Dodge ore breaker was installed in the Royal Oak plant circa 1899 - 1900.(20) ILLUS. 60.
In the larger, more modern plants a grizzly was essentially "an inclined plane ore iron bars leading down to the mouth of the rock-breaker, the bars set at a distance apart equal to the space between the bottom ends of the rock-breaker".(21)
The function of the grizzly was to sort the chunks of ore so that the small pieces would bypass the crusher and be fed directly into the battery ore bin. The usual arrangement was for the ore to be dumped from the tramcar or onto the rock-breaker floor set level with the top of the mouth of the machine and covered with iron plates. The man in charge of the breaker was equipped with "a stout iron hook or scraper to enable him to drag the ore into the month of the steel shovel for the small stuff".(22)
From the rock-crusher the crushed ore was fed into the ore bins located directly blow. A general rule for the capacity of the bins was that they should hold at least a 24-hour supply to guarantee continuous mill operation.(23) The ore bins in the Blue Nose in 1901 had a 125-ton capacity.(24)
To improve the efficiency of the stamp mill, each battery was often fitted with an automatic feeder which maintained a regular flow of crushed quartz into the mill. The 60 stamp mill at Salmon River had 12 "Challenge Ore Feeders" that were manufactured by Fraser and Chalmers in Chicago.(25) The Blue Nose Mill had 6 Hammand ore-feeders to regulate ore to each battery of its 30 stamp mill.(26) ILLUS. 61 & 62.
Mortar Box Foundations:
The Stamp mills of the 1890s were designed so that the stamp mill was independent of the mill buildings:
In designing the structure, care was given to make each component of the mill independent, i.e. the building, the battery frames, and ore bins are each entirely separate from the others, so that the building is simply a cover with no strains upon it other than those due to the wind and weather.(27)
Traditionally the foundation of the mortar boxes of the stamp mill had consisted of heavy timbers set upon bedrock:
The mortar blocks are built of selected two-inch spruce plank, twelve inches and six inches wide, planed on both sides and joined on both edges. The blocks are built thirty inches wide, and are Therefore made up of two twelve inch planks and one six inch in each layer; joints in one layer are broken in the next, and each layer is spiked to the previous one with 40 dy. nails (five inches long), so that each nail holds in three layers. Each plank is fitted on the bottom to the surface of the bedrock, as it was found impracticable to dress off the whin rock to a smooth and level surface, and concrete is valueless unless put down in a large mass.(28)
eventually the wooden timber foundations were supplemented and then replaced by concrete:
The mortar block was built of concrete set on bedrock. The rock used was a hard, fine quartzite, locally known as "whip", … The quartzite, broke in sharp angular fragments and was most excellent product for concrete. At the bottom the proportions were-The proportion of cement was increased toward the top. The top was composed of - (29)
Broken stone (2"-0) 5 ¼ parts Sharp sea sand 1 ¾ parts Porltland cement 1 part
Broken stone (3/8" - 1/8") 1 part Shape sand ½ part Portland cement 1 part
Millmen who had worked with the wood foundations preferred them to concrete because of their resilience.(30) So, in mills with concrete foundations there was an attempt to provide that quality by adding an additional layer of wood, as well as a sheet of rubber or blanking.
On top of the concrete block was placed a piece of five inch unbled hard pine thoroughly covered with tar. In regular modern installations it seems a general practice to place a piece of ¼ inch pure rubber between the concrete and the anvil block [mortar block].(31)
Not only was it desirable to have a resilience of a mortar foundation, it was necessary to have stable foundation as well. To fully exploit the strength of the bedrock, the following practice was recommended at the end to the 1890s:
Too much and attention cannot possibly be bestowed upon the foundations of the mortar block. It is set in a trench especially excavated for it, which should always be carried down into the solid rock, all decomposed or broken up parts of the rock being cut away and the bottom of the trench being then made as level as possible. If the sides of the trench are not wholly in hard rock they should be protected by massive retaining walls, built of stone or brick laid in cement or else concrete. At least 6 inches of good concrete should next be rammed into the bottom of the trench, being leveled off as carefully as possible… Upon this foundation the mortar blocks are then set, great care being bestowed upon their alignment and their leveling. The space between them and the sides of the trench should then be rammed with concrete, or else, as is sometimes done in America, some barren quartz may be crushed in the mill and the tailings allowed to run into and fill the trench. These tailings will pack in quite solid, aided no doubt in their settlings down tihgt by the vibration of the mortar blocks in the partly filled trench; in either case the packing should be as tight as possible.(32)
Once the foundations for the mortar blocks were complete, the next phase of construction was the mill framing.(33)
There were two systems of battery frames in use - the 'A' frame and the 'knee frame'. E. Gilpin's 1882 article about stamp mils in Nova Scotia was illustrated by an 'A' frame mill, which was suitable for light mills with stamps of up to 750 lb.(34)
However, with the development of the heavier mills, the knee frame, developed in Grass Valley, was preferred.(35) ILLUS. 63 & 64.
Its essential point is the removal of the line shaft from its usual position behind the mortar and beneath the feeder floor to the front of the batteries and on a level with the cam shaft.
Hardman preferred the knee frame construction for the following reasons:
A further variation on the knee frame was the back-knee or reverse-knee Pattern in which the battery posts were bolted to the ore bin timbers. The advantage of this pattern was that it gave an uninterrupted view over the entire mill floor and presented no obstacle to mill men working on either side. However, this style could not be employed unless there were automatic feeders in place since it obstructed easy access to the back of the mortars to provide crushed quartz manually.(37)
The ten-stamp mill frame could be constructed using a plan of three or four posts.(38) The two batteries of the Dufferin mines ILLUS. 51 (following p. 76, this report) appear to have been arranged using the three-post system, as does the Royal Oak Mill ten-stamp mill. ILLUS. 50. In the three-post system the bull wheel was located at either side of the battery, while in the four-post it was situated between the center posts. ILLUS. 65 & 66.
Some of the foundries that had produced stamp mills during the 1860 period continued to cast mortar boxes, stamps, dies, cams, and lifters in this later period - the Truro Foundry,(39) I. Matheson,(40) and the Windsor Foundry.(41) ILLUS. 67 & 68. An addition to the list would be Fraser Brothers in New Glasgow, which began production in 1883. (42) (ILLUS. 69). Mills were bought as well in the United States, as were other pieces of milling equipment.
However, the Nova Scotian mill had gained a place in Canadian industrial history. In an 1899 letter to Edwin Gilpin about an upcoming exhibit of Nova Scotian gold specimens, George Dawson, CGS, argued against a separate display of Canadian mining machinery because:
nearly everything made here is made on foreign pattern and by branch establishments. There may be one or two exceptions - … and it occurs to me that one such case might be the stamp mills made at Truro which appear to have gained such an excellent reputation.(43)
The mortar boxes for stamp mills were made of cast iron and were cast in one piece. The weight of the boxes was proportioned to that of the stamps:(44)
| Number of Stamps in Each Mortar | Weight of Stamp lbs. | Weight of Mortars | |
| Tons | cwt. | ||
| 5 | 1250 | 4 | 0 |
| " | 1050 | 3 | 5 |
| " | 950 | 2 | 17 |
| " | 900 | 2 | 10 |
| " | 850 | 2 | 5 |
| " | 750 | 2 | 0 |
| " | 700 | 1 | 16 |
The five-stamp battery mortar box measured between 45 inches and 60 inches long, 18 inches to 24 inches wide at the base, and 39 inches to 56 inches high. At the back of the box there is an opening to facilitate the feeding of the quartz either by hand or automatic feeders.(45)
There were modifications in the mortar box according to whether the stamp mill would be a custom mill, crushing and amalgamating quartz from a number of different operations, or a company mill. Hardman's mill was a custom mill and he had made the following changes to the mortar box:
The mortar are modified from the Homestake pattern only in the fronts which are cut down to within two inches of the bottom, the height of the front being regulated by wooden chuck blocks faced with thin steel plates. Also the lip has been extended three and a half inches.The essential character of the mortar is not at all affected by these modifications which have been made only for minor points of convenience. The cutting down of the iron was done for two reasons: …it was desirable that the whole mortar should be readily accessible for a though clean-up; and secondly, because of the very diverse character of the quartz coming to a custom mill, necessitating perhaps a high discharge for one lot and a low discharge for another.(46)
Another factor affecting the design of the mortar box was whether inside copper plates were used to maximize the amalgamation process. In Gilpin's 1882 article about stamp mills, he remarked that only a few Nova Soctian had made use of inside plates.(47) Hardman's old mill employed just one inside plate, at the front of the battery:
The first plate lies inches inside the mortar just at the lower edge of the screen, and about ten inches above the dies. It is made from a strip of copper one - eight of an inch thick and three - quarter inches wide; the length being the full length of the screen; about 48 inches.(48)
Hardman found the inside plate worked quite well; it did not choke or fill with the sands, "the splash form the screen being sufficient to dislodge the sands but not the amalgam".
There appears to have been some controversy about the effectiveness of using inside plates. Through its use, the mill lost mill lost efficiency in pulverizing the crushed ore, but gained in the amalgamating process.(49)
The front of the mortar box was covered by perforated metal plates or woven wire screens set inside a removable wooden frame. The Blue Nose Mining Company made use of a 40-mesh wire screen in its stamp mill; the Dufferin Stamp Mill at Salmon River used a 30-mesh wire screen.(50) The advantage of the perforated steel plate over the wire screen was its durability. However, the latter provided a larger discharge area, and was to be recommended for the milling of low-grade ores.(51)
The frames were most often made of wood, although some companies made the move to iron. J.G. McNulty recommended the use of a "two inch seasoned hard wood" for the screen frame. The screen was attached to the frame by means of "ten ¼ inch stud bolts, four along the upper and four along the lower sides of the opening, with one on either end."(52)
The screen frame did not entirely cover the mortar box opening, but left a space of at least six inches at the tops, to permit access to the interior of the mortar box during operations. This space was often filled with either canvas or a piece of thin board. ILLUS. 70 & 71.
The screen frames were usually set at a small angle , 9 to 15 degrees inclined outward to increases the discharge area, to provide more room between the upper part of the screen and the stamp, and to increases the potential longevity of the screen. However the angle was an important issue, for if the screen inclined at too great an angle, it would not facilitate the discharge of the pulp at all.(53)
The mortar box was also fitted with a splash board "to keep the pulp, which issues from the screen with considerable violence, from being thrown in all directions". Canvas or a thin board was used in Nova Scotia mills for this purpose.(54) 4 ILLUS. 70 & 71.
The die forms were the working face of the anvil upon which the ore was crushed. In the older mills the die was made in one piece occupying the full length of the mortar box, but in the later mills there was one die per head. The dies were made either of cast iron or forged cast steel. Shapes include cylindrical, hexagonal and octagonal. The most common shape of the die used in the later part of the century is illustrated in ILLUS. 72.
The dies were placed inside the mortar box so that they virtually filled it, fitting snugly against the back and front liner plates. The bases of the dies were set from 1/8 to ¼ of an inch apart. The upper levels of the die had to be at the same level to make the most efficient use of the stamp mill.(55)
The stamp head, ILLUS. 73, was usually a cylindrical piece of iron, one end of which was bored out to receive the tapered end of the stem, and the other end recessed to receive the shank of the shoe. The latter end was cast rather than bored. The Stamp heads were also known as 'bosses'.
The stamp shoe, like the die was made of either cast iron or forged or cast steel. ILLUS. 74 shows the shape universally used and that of the ten-stamp Truro mill. The shank of the shoe was generally circular, rather than hexagonal or octagonal, and usually measured between 4 and 6 inches. The diameter of the butt of the shoe was the same as the stamp head and the die, although some dies were slightly larger.(56)
The stamp stem formed the main portion of the entire stamp. It usually measured between 9 and 16 feet in length and 2 ¼ to 3 inches in diameter. Wrought iron or mild steel was the material used in its construction.(57)
The two - armed cast - iron cam was the pattern adopted in the mills of the '90s. Cams were either right - handed: "one that runs on the right side of the stamp when the observer is looking in the direction in which the upper arm of the cam is revolving, hence the boss or hub of the cam is also on the right hand side", or left handed: one that runs on the left hand side of the stamp, etc.
Cam shafts were designated as left - handed and right - handed according to which end carried the bull wheel. A right - handed or left - handed cam shaft could have either right or left handed cams.(58)
The stamp mill was used for two different functions: 1) to thoroughly pulverize the crushed quartz, and 2) to facilitate the amalgamation process. The weight and movement of the stamps sufficiently accomplished the first aim; the height and rate of drop of the stamps, the mesh and angle of the screen and the addition of water and inside amalgam plates assisted amalgamation.
A variety of means had been tried to improve the pulverization process, only to hinder amalgamation:
High front and fine screens have been used to prevent the gold escaping from the mortar. High fronts and fine screens are conducive to fine grinding, and no doubt liberate a large percentage of gold that would otherwise escape in low fronts and coarse screens. When, however, you increase the height of your Fronts and use closer screens, you also increase the difficulty of having a sufficient supply of water reach the crushing surface of the dies to thoroughly wash out the disintegrated particles of pulp after each thrust of the stamp, and also to keep the base below the crushing surface of the dies, so essential to the protection of the coarse particles of gold so so common in our ores … Do we, by raising fronts, and using finer screens and subjecting all the gold values to the pulverization action of the stamp during the period of the run before the clean - up is made, lose in float gold (or what I term the wear and tear of gold) an equivalent in values equal to what we liberate by fine grinding?(59)
Water had always played an essential part in the amalgam process, but it was not until the later '90s that it was recommended that the water be introduced into the mortar box below the crushing surface of the dies:
… the water usually dropped or directed into the mortar by means of a series of small jets or nozzles at any desired point below the crushing level of the dies would bring about the desired agitating result…(60)
O'shaughnessv concluded that the addition of water below the stamp dies would retain a large percentage of the coarse gold within the battery between the stamp dies "in particles still having their sharp angles, and as free from wear as when first liberated from the ore".
Inside amalgamation was carried out by the addition of mercury to the mortar Boxes. The quantity of mercury used was about three times the amount of gold thought to be held by the crushed quartz. The mercury globules were broken down by both the stamp action and the wash of the pulp to become thoroughly mixed with the pulp. When the mixture comes in contact with the gold particles, it forms an amalgam. The amalgam either settles down between the dies or is projected through the screen to be caught either on the amalgam tables outside or to adhere to the inside plates, if used.
Few millmen used automatic mercury feeders, preferring to regulate the feed themselves. The mercury was kept in the mill in closely stoppered bottles of very thick glass". As discussed in section 3.3, a sodium amalgam was sometimes added to the mercury to prevent it from flouring or sicking.(61)
Outside amalgamation was done by means of copper - plated amalgam tables.(62)
These consist of a sheet of copper, the upper surface of which has been thoroughly amalgamated, to the scopper amalgam so formed, a thin film of mercury will always adhere, and this film of mercury immediately amalgamates any gold that may come in contact with it, the gold amalgam so produced adhering to the surface of the copper plate unless there is a great excess of mercury present… The theory of table - amalgamation, therefore demands a clean surface of copper amalgam, carrying a small excess of mercury with which every particle of the escaping pulp shall be brought into contact.
The arrangement of amalgam tables varied from mill to mill. ILLUS. 51 and 70, 71 and 75. Ideally the tables were independent from the stamp mill, arranged in such a manner that their levels could be easily adjusted. The length of the tables depended upon the nature of the gold:
If the gold is coarse a short table will suffice, but if fine a proportionately longer one must be used. The length varies accordingly between five and twenty feet. A good average length is fifteen feet, or say five plates three feet long, with a drop of about two inches in depth between each one.(63)
The quantity of water necessary to keep the pulp travelling slowly down the amalgam plate depended on the fineness of the crushing as well as the nature of the gold, coarse of fine. Finely - crushed ore required more water and less grade than coarsely crushed. Louis recommended that the grade of tables should range between ½ inch and two inches to the foot.(64)
Generally, when there was inside amalgamation there was no need to add mercury to the outside plates, although some millmen followed this procedure. For a discussion of arrangement of tables see Del Mar, p. 118 - 123, a copy of which is in the research files at Sherbrooke.
The tools used in cleaning up the amalgam plate included:
ILLUS. 51 (p. 76) and 75 depict men cleaning up the amalgam from the tables. Using scrubbing brushes or "the india-rubbers", the millmen started at the base of the tables and rubbed all the collected amalgam upwards. Any amalgam that adhered too firmly to the table was loosened carefully with the scraper or wooden chisel. Once the amalgam knife into the amalgam plate, In ILLUS. 51, the plate is at the feet of the men on the left hand side of the photo. The tables were then rubbed down with a small amount of mercury and the mill was again ready for operation.
This level of clean-up of the plates was a fairly procedure. It should have only taken about 10 minutes. It was also a time to re-adjust screens, blocks and to make any necessary small repairs while the stamps were hung up(65)
To thoroughly clean the amalgam plates a more - involved process was required. It was easier if the plates were heated up. In some mills, they were removed and heated; in others the steam power in the plant was used to heat up the plate "by turning a jet of steam onto it" and then cleaning thoroughly as before.(66)
In addition to cleaning up the tables, the batteries were cleaned weekly, fortnightly or monthly. Following is Louis' description of a thorough clean - up:
It need hardly be said that a clean-up offers specially favorable opportunities for theft, so that constant vigilance is demanded on the part of the mill - manager, who should really never leave the mill from the commencement to the end of the operation. The contents of all the boxes have now been collected and are ready for treatment. Here again, if a large staff is available, the treatment of box is emptied out, and may proceed simultaneously with the cleaning out of the remaining boxes. There are various ways of treating these sands, each of which has its advocates. In a small mill they are sometimes simply panned up; the first panning is done in large prospecting pans in a tub >or tank of convenient height filled with water, in which the tailings collect. The final panning of the amalgam is performed in pans, the bottom of which consists of a sheet of amalgamated copper, a little mercury being poured into the pan. This greatly facilitates the cleaning - up and collecting of the P>amalgam, which, being softened by the mercury added in the pan, adheres to the bottom. Any pieces of iron met with in panning are put on one side for treatment as described further on.(67)
The amalgam collected from the regular cleaning - up of the tables and the battery was stored in a safe place by the manager of the mining operation. Usually there was a mercury room off the mill in which a safe was installed to hold the amalgam collected in the clean - ups. The work space for the millman or assayer - manger consisted of as strong work table with a surface of stone or a hard - wood plank. In addition there would have been a supply of cups and pails of enameled iron, amalgam knives, a supply of chamois cloth or canvas for squeezing the amalgam.(68)
If the amalgam contained too much mercury and was "too soft", it had to be squeezed. This was done by pouring the amalgam into the chamois which had already been well soaked:
The free ends of the leather or canvas are then grasped in the left hand just above the point occupied by the amalgam and twisted round so as to prevent the latter from escaping; the whole is then immersed in water contained in a mercury pail or pan, and the gobular lump so formed twisted strongly with the right hand; by this means considerable pressure is put upon the amalgam contained in the skin or canvas, and the fluid free mercury is squeezed through the pores of the latter, until only a ball of hard amalgam remains behind, all the superfluous mercury having been squeezed out of it.(69)
Following this operation the amalgam was retorted to separate the gold from the mercury. ILLUS. 76. Before the amalgam was placed in the retort, its inside was coated with a material to prevent the gold sponge from sticking to it. Following is Louis' description of the preparation of the retort and the retorting process:
The principle of this operation consists of heating the amalgam to a temperature above the volatilization point of mercury, when this metal distills over, leaving the gold in a loose cellular state, in which it is known as gold sponge, the mercury being condensed by appropriate coiling apparatus. Practically, there are only two forms of retort in use in gold mills, the pot retort for small quantities, say up to 1,000 ounces of amalgam, and the cylindrical retort for larger amounts. Pot retorts are made in various sizes to hold from 250 to 1,000 ounces; the former are about 6 inches deep inside, and the latter 9 inches, the diameter being about 2/3 of the depth. The usual shape is shown in Fig. [22]. It will be seen that the retort consists essentially of two parts, namely the body and the cover, the delivery - pipe being screwed into the latter. These retorts are made of cast - iron and carefully turned inside. It is advisable to have the inside of the cover turned as well as the body; the joints between these two should be very accurately turned and be as true as possible. It is advisable to have a v - shaped projection on the face of the flange of the body which fits into a corresponding annular groove in the flange of the cover. A piece of good wrought iron piping is screwed onto the cover, its other end screwing into a stout Liebig condenser. This condenser consists of a pipe (of the same diameter as the retort outlet pipe) which passes axially through a short piece, 2 to 3 feet long, of a wider pipe so that an annular space, closed at both ends, is left all round the central pipe. An old mercury bottle answers capitally for the outer pipe. Two smaller pipes communicate with the top and bottom respectively of the annular space, water being supplied through the lower and escaping through the upper one. In its passage up it completely cools the heated vapors that are passing down through the small central pipe. The retort is usually supported on a strong iron tripod, and may have a special furnace for heating it, although this is not necessary. Often a fire is built on the ground under and round the retort, the heat being concentrated upon the retort by laying a few bricks, or supporting some pieces of sheet - iron round it. The assay furnace does admirably for heating the retort; sometimes a smith's hearth is used, but this practice is not to be recommended. There are several methods by which the cover is secured to the retort body. The flanges may be clamped together, or they may be bolted together by three bolts passing through them, cotter bolts being better than screwed ones. Sometimes a semi - circular bale is used catching under the flange of the body, whilst a strong set - screw or sedge presses on the top of the cover. Of al these plans the last, illustrated in the above figure, is the best, as it is the least apt to be injured by the action of the fire. Before charging the amalgam into the retort, its inside should be coated with some substance to prevent the gold sponge from sticking to it. It may be well rubbed in with chalk or whitening, but the best coating consists of equal parts of finely ground fire clay and graphite made up into a thin paste. The retort should be washed out with this, and then put in a warm place so as to dry the coating. The same mixture worked up with water to the consistency of cream may be used for luting between the flanges of the body and cover. It is also advisable to coat the outside of the entire retort with a similar mixture, to which a little fine asbestos has been added, as this preserves the retort from burning out rapidly. The balls of amalgam should be broken into two or three pieces each, and piled loosely upon each other in the retort, which should never be more than two-thirds full. A disc of stout asbestos millboard, just about 1/8 inch smaller in diameter than the top of the retort, should then be dropped in, a thin layer of lute spread on the flange, the cover put on, turned backwards and forwards a few times to ensure a tight fit, and then secured in its place. The retort is next placed on its tripod ready for heating and the condenser attached. The end of the condenser pipe should be a few inches above the surface of water contained in a mercury pail, and should on no account dip below it. A strip of canvas should then be tied round the end of the discharge pipe so as to form a kind of loose tube dripping into the water, but care must be taken that this tube is not air tight. Sometimes a canvas or India - rubber bag is attached to the end of the pipe, but the above arrangements is preferably so arranged as to burn from above downwards, and the temperature very gradually raised until mercury begins to distill over. The heat of the fire must then be moderated so as just to keep the mercury distilling over in a gentle stream, but no more. The temperature of the retort should never approach redness as long as any mercury at all distills over. When no more comes over, the heat must be raised to redness, and kept at this point for a few minutes. The fire can then be removed, and the retort allowed to cool. The entire operation takes two to four hours as a general rule. It must not be forgotten that, as the mercury distills over and collects in the pail, the level of the water in it will rise, so that a little must be dipped out from time to time to prevent its rising above the mouth of the pipe. When the retort is cool enough to handle, the cover is taken off, the luting scraped off the flange, and the disc of asbestos borad lifted stout paper or a prospecting pan, when the sponge will drop out in one coherent retort piece, if the operations has been badly coated, or the heat too great, the sponge may adhere in places to the retort. It may then mostly be dislodged by a few taps of a hammer on the bottom of the retort, or, in extreme cases, a light hammer and chisel may have to be used. The object of the disc of asbestos borad is to prevent spiriting, and the mechanical carrying off of any of the amalgam in the vapors of mercury. The sponge, when perfectly cold, is weighed and cut up with a hammer and chisel preparatory to melting.(70)
The next step in the procedure would be to melt the remaining mass in a crucible. In a small mine operation the crucible could be heated on the black smith's hearth. The best material for heating the crucible was coke, but hard wood charcoal was also suitable to insure a sufficient melting temperature.
When the heating was complete, the substance in the crucible was a bright yellow colour. The fluid, if no further treatment was required, was then poured into an ingot.(71)
During the later period of mining in Nova Scotia most mining companies installed shaking tables, frue vanners or Wilfley tables to treat the tailing that escaped from the amalgamation process. Although the gold in the province was largely "free mining" a portion of it was tied up with sulphides and other chemical combinations that prohibited recovery through amalgamation alone. Concentration was the means by which the auriferous portions of the tailings were collected in small portions for further treatment.
ILLUS. 56 interior of the Royal Oak Mill, provides an illustration of the arrangement of the Wilfely table below the amalgam tables; ILLUS. 51 Dufferin Mill, Salmon River, depicts the shaking tables installed below the amalgam table to catch and treat the tailings; ILLUS. 49 plan of Oldham Mill, shows the arrangement of the concentrator within this mill vis a'-vis the stamp battery and tables. The concentrator installed in the Oldham Mill, 1891, was a Golden Gate apparatus.(72) The Bluenose Mill at Goldenville installed two Wilfley tables to handle the tailings from its operation in 1900.(73)
Following is Louis' description of the apparatus available for concentration.
Shaking tables - Nearly all the modern concentrating machinery used in gold mils belongs to this class, which includes the various forms of shaking - tables, of which there are endless modifications. Generally speaking, the shaking - table consists of a suspended inclined table upon which the tailings are delivered in a very thin stream. This table receives a rapid oscillating motion, the effect of which is to propel the lighter particles along one path, and the heavier ones along another, so that each may flow off into receptacles provided for the purpose. These machines are very effective and produce clean concentrates, whilst the loss in the tailings can be kept within very low limits. The original form of shaking - table is that divised by Rittinger, which has not been much improved on since, in which the direction of the shake is at right angles to the flow of the pulp. These tables are usually built in Paris, their general constructed being shown in [ILLUS. 77 and 78], which represent Rittinger's original design, the first figure giving a section, the next a plan and the third a front elevation of the machine. The table "is strongly made of hardwood, carefully planed and made as smooth as possible. It is suspended by four rods which allow its grade to altered at will. The framing of the table is very substantial, and it carries a stout transverse piece near the middle, which receives a series of thrusts from cam which pushes it against a strong wooden spring. The action of this spring throws it back sharply against a bumping block, which gives the shake to the table, the shake thus consisting of a series of sharp shocks. Each table is usually 8 feet long by 4 feet wide, and has an inclination of from 3 degrees to 6 degrees to the horizontal. The average number of blows is about 100 per minute, but in working very fine sands as many as 150 per minute are sometimes given, the length of each stroke being about 1 ¼ inches. Above the upper and of the table is fixed a head - board with the usual distributing pins. The pulp to be concentrated is delivered to one - fourth only of the head - board, the remainder being supplied with clear water. If the table were at rest all the particles achieving the journey more rapidly than the lighter ones. The impulse due to the shaking action acts in a direction at right angles to the line of flow, and hence the particles move down in a line, which is the resultant of these two motions; the heavier particles, however, moving more slowly, are exposed for a longer time to the action of the transverse impulses than the lighter ones, and hence are thrown further from the straight line of flow. It is thus possible to obtain a very complete separation of the pulp into concentrates and barren sands, the action being quite continuous. This machine answers well, except in the case of very fine slimes. Each double table requires about ¼ indicated H.P.; one man can attend to two double table without any difficulty. The capacity of a double table is about 3 ½ to tons per 24 hours; the consumption of water is considerable, being altogether about 0.5 to 0.8 cubic foot per minute, three - fourths of which amount constitutes the stream of clear water. In more modern forms the tables have been made of planished sheet iron, of slate, and of plate glass, whilst metal has been substituted for wood in nearly every part, the supporting frame being light castings, the spring, etc.""The Wilfley Table: This concentrator is one of the most recent of this class of appliances, but has already met with a certain amount of success. Its general appearance is shown in [ILLUS. 79] it consists of a flat wooden table 16 feet long and 7 feet wide covered with linoleum, upon which are nailed a series of strips of wood gradually increasing in length from the back to the front of the machine and gradually tapering to nothing from a depth of about 3/8 inch at the motion end. The table slopes upwards about ½ inch from the motion, end and also slopes forward from the back; the amount of this latter inclination can be altered at will, according to the nature of the material that is undergoing treatment. The table is moved by an eccentric combined with a link and toggle, so as to have a quick forward and a slow backward motion; a spring keeps the table close against the motion the whole time, so that there is no shock or bump properly speaking. The pulp to be concentrated is fed on to the table form a head - borad near the motion end for a width of some three feet; the rest of the table receives clear water only. When the table is in operation, quartz and other minerals of low specific gravity are carried by the stream of water down the table in practically straight line; heavier bodies sink below the edge of the riffles, are thus unable to escape straight down the table, and are hence gradually moved along it by the series of impulses to which they are subjected; they are only capable of being carried by the water current when they have moved clear of the riffles, hence a particle of mineral on this table moves in a direction that varies from nearly parallel with the length of the table to nearly transversely across it, according to its size and specific gravity, or, if particles of practically uniform size are alone considered, they move according to their respective specific gravities. Clean tailings run at once to waste, middlings are returned by small raff wheel to the head - board, and the heavier minerals are discharged at different points of the table in accordance with the principle already stated. The great advantage of this table is that it makes a very clear and distinct separation upon various species of minerals; it does not however do equally good work upon un sized pulp, hence it should be preceded by spitz - lutten or some other form of automatic classifier. A table is put in to 50 tons; in some American mills one table is put in to every ten head of stamps. The supply of clear water required varies greatly with the character of the ore to be" "concentrated; it may be said to range from 5 to 20 gallons per minute. The weight of the table is about 22 cwt,"(74)
Chemical milling processes were not used in the Goldenville area during the 19th century, although there were attempts in other parts of the province, most notably, North Brookfield Mines.(75)
1 A. Heatherington, MINS, Annual Summary, Gold Yield of Nova Scotia, 1862 - '73. There were 53 mills in the province, 19 of which were water - powered. In Goldenville there were 9 steam mills and 3 water - powered mill operations.
2 Map 4, GSC Sherbrooke Gold District, 1893. H. Y. Hind, Report on the Sherbrooke Gold District, Map of Sherbrooke Gold District, PAC 45, v.145, Notebook XLVII, 1884, August 30, 1884, p.30.
3 H. Louis, op. cit., p.491: "… the great principle must always be remembered that, for economic workings the ore should never be lifted from the time it enters the battery until it escapes after the final treatment, in the form of exhausted tailing, but should continuously descend from stage to stage moved by gravity alone." Many of the mills constructed during both periods of gold mining in Nova Scotia failed to follow this rule of thumb. See H. Y. Hind, Report on the Waverley Gold District, Halifax 1869, p.57. Hind criticized the location of the Waverley crushing mill as being too low, "the tailings as they leave the mill, are now required to be hoisted by a revolving wheel, furnished with buckets, to a sluice" so that they could escape over the accumulated tailing dump situated by the mill. PANS MG 1, Cantley Letterbook, Blue Nose Gold Mining Company, 3 February 1900 and 10 January, 1900 correspondence re: the need for a pump to lift the tailings as they come from the stamp mill.
4 H. Louis, op. cit., p. 490.
5 See Endnotes, Section 5.3.3 of this report.
6 J. C. Murry, op. cit., p.3; Woodhouse, op. cit., p. 21; F. H. Mason, p. 5. N. S. RDM, 1899. The Royal Oak Mill was constructed within 600 feet of the shaft.
7 E. Gilpin, "The Gold Fields of Nova Scotia", p.2: "… in every district a very considerable quantity of gold is stolen by the miners".
8 Neily Correspondence, J. B. Neily, Goldenville, to R. V. Neily, Goldenville, 8 August 1914.
9 H. Louis, op. cit., p.491.
10 H. Louis, op. cit., p.491.
11 J. G. McNulty, "Observation on Gold Mining", Transactions of the Mining Society of Nova Scotia, … 1903, p.100: "The provision for ample room and light are too often neglected in the average mill structure." See discussion re: battery frame arrangement to maximize to maximize working space and available light. "Twentieth Century Mine", Industrial Advocate, February 1903 - '04, p.40.
12 H. Louis, op. cit., p.261.
13 J. E. Hardman, op. cit.
14 J. E. Hardman, op. cit., H. Louis, op. cit., p.263 - figure 67 and 69.
15 B. T. A. Bell, ed., op. cit., 1899, p. 77-78.
16 N. S. RDM, 1901, p. 49 - 50.
17 H. Louis, op. cit., p. 114 - 115.
18 Ibid. p. 103 - 107.
19 J. E. Hardman, op. cit., p. 35 - 36.
20 N. S. RDM, 1899; B. T. A. Bell, ed., op. cit., 1899. N. S. RDM, 1902.
Nova Scotia Mining Number, (Halifax), 1903.
21 H. Louis, op. cit., p. 109 - 112.
22 Ibid. p. 110 - 111.
23 See Hardman's Mill Plan for location of ore-bins. H. Louis, op. cit., p. 112.
24 The rock breaker at the Blue Nose was located at the deckhead of the main shaft along with a 40-ton ore bin. From the shaft the ore was transported in a skip up an incline to the mill ore bins, which had a 125-ton capacity.
25 PAC RG 45 Notebook 4451 (1899) Dufferin Mines, Salmon River, September 13, 1899. The stamp mill illustrated in Gilpin's 1882 "Gold Fields of Nova Scotia" was also manufactured by Fraser and Chalmers. Not all mines used automatic feeders, even though they were recommended. The five-stamp battery mill operated by Edgar Horne at Renfrew, 1978 has an automatic feeder made from a carriage spring.
26 Nova Scotia Mining Number, (Halifax), 1903.
27 J. E. Hardman, op. cit., p. 35.
28 Ibid. p. 37. The mortar blocks for the Oldham 10-stamp mill were built in one solid piece"… one solid piece of timber 30 inches wide, 14 feet deep and 12 feet 2 inches long".
29 Prof. H. Sexton, "A Gold Stamp Mill for Laboratory Testing", Journal of the Mining Society of Nova Scotia, V. X, 1905 -06, p. 126.
30 William Neily, Interview, Tape 1, side A: "A lot of millmen didn't like it [the concrete] unless they had a thickness of rubber belting or something underneath it [the mortar] to pick up the shock. The cement was too much of a shock and it would split the battery. I think most of them were wooden foundations".
31 Prof. H. H. Sexton, op. cit., p. 126.
32 H. Louis, op. cit., p. 125 - 26. Hardman makes no reference to this procedure in the construction of the mortar blocks for the Oldham mill. It was unlikely that he used concrete to shore up the foundation but more likely a combination of quartz, slate and tailings.
33 H. Louis, op. cit., p. 126 - 27. Del Mar discusses mortar foundations in Stamp Milling, op. cit., p. 79 - 92.
34 E. Gilpin, op. cit., Illustration of 10-stamp mill, 750 lb. Stamps in research file Sherbrooke Village, op. cit., p. 232: "These A frames do very well for small and light mills, but are not recommended for stamps over 750 lbs. They have been almost entirely replaced of late years by the so called knee-frame…"
35 J. E. Hardman, op. cit., p. 36.
36 Ibid.
37 H. Louis, op. cit., p. 235 - 238. algernon del Mar, op. cit., p. 73. Mar disliked the front knee pattern style because it "had the disadvantages of cutting out light from the battery plates and [had] proven weak with heavy stamps requiring a back-knee brace to give stability. The only point in its favor [was] that the tight side of the driving belt is uppermost…" According to del Mar by 1912 the "A" frame style was seldom seen.
38 Ibid. p. 74, p. 77 -78, p. 92 - 95.
39 McAlpine's Directory, Nova Scotia 1890 - '97, p. 462. Truro Foundry and Machine Company. This industry was intricately involved in gold mining operations in the province. The director of the Dufferin Gold Mine at Salmon River was G. Clish (Truro) and all the members of the Board of Directors were from Truro. Clish was also President of the Truro Foundry. Canadian Mining Manual, 1893, p. 129.
40 McAlpine's Directory, Nova Scotia 1890 -97, p. 966. Matheson's Foundry, New Glasgow.
41 Industrial Advocate, June 1897, p. 1, Windsor Foundry.
42 Ibid, November 1896, "Goldenville at the Present Day", p. 15. Our Dominion, 1887, p. 133.
43 PANS, RG 21, Series "A", v.20. Correspondence - George Dawson, G. S. C., to E. Gilpin, 28 April 1899.
44 H. Louis, op. cit., p. 128 -132.
45 Ibid. p. 131 - 132.
46 J. E. Hardman, op. cit., p. 38 - 39.
47 E. Gilpin, op. cit., p. 17. Gilpin's 10-stamp mill employed both front and back inside copper plates. Henry Louis argued against the use of rear plates inside the mortar box because they seriously reduced the crushing efficiency of the stamps. op. cit., p. 152 - 53.
48 J. E. Hardman, op. cit., p. 38 - 39; "This copper strip is placed on a bar of square iron, and from ¼ to 3/8th of an inch in width, is bent over at right angles for the whole of its length. It is then fastened to the rounded screws, the longer side sloping upwards towards the screen at an angle of about 45 degrees with the horizon, while the shorter side inclines towards the stamp at an equal angle, forming a narrow V-shaped trough.
49 H. Louis, op. cit., p. 149 - 153.
50 B. T. A. Bell, ed., op. cit., 1897. PAC 45 v. 146, Notebook 4451,
51 J. G. McNulty, "Observations on Gold Mining" in Transactions of the Mining Society of Nova Scotia, p. 97. H. Louis, op. cit., p. 132 - 135. Louis recommended the frames "be made of strips of wood 1 ½ inch thick and 3 inches broad, the screens tacked to the inside of the frame, and a strip of blanket the exact width of the screen frame tacked over it."
52 H. Louis, op. cit., p. 132 - 135. The longevity of the screen was related to the material of which it consisted, steel perforated plate or woven wire mesh. The perforated screens lasted considerably longer, but were much more expensive. Thus a number of the woven mesh screens would equal the same cost as one perforated plate. Because of the possibility of screen damage, Louis recommended that each mill maintain a duplicate set of screens, so that if there was a breakage, etc., the mill would not have to be shut down while it was repaired and replaced. The screens were held in place by means of "two long steel (or oak) keys at either end, and one or two shorter wedges at the bottom".
53 Ibid. p. 135 - 36.
54 A. L. Carr, "Treatment of Low-Grade Ores of Nova Scotia", Industrial Advocate, January 1903, p. 13.
55 H. Louis, op. cit., p. 163 - 66.
56 Ibid. p. 175 - 183.
57 Ibid. p. 173 -174.
58 Ibid. p. 191 - 200.
59 M. R. O'Shaughnessy, op. cit., p. 118. In research files, Sherbrooke Village.
60 Ibid. p. 120 - 121.
61 H. Louis, op. cit., p. 302 - 307.
62 Ibid. p. 307.
63 Ibid. p. 310.
64 Ibid. p. 310 - 311.
65 Ibid. p. 3318.
66 Ibid. p. 319.
67 Ibid. p. 421 - 426.
68 Ibid. p. 433 - 34.
69 Ibid. p. 435 - 436.
70 Ibid. p. 435 - 436.
71 Ibid. p. 447 - 448; p. 452.
72 J. E. Hardman, op. cit., p. 39.
73 N. S. RDM, 1900, p. 38 -39; PANS, MG1, Cantley Papers, Correspondence, 24 April 1900. Letter to Truro Foundry requesting price list of Wilfley tables, delivered either to New Glasgow or Halifax.
74 H. Louis, op. cit., p. 350 - 355; p. 360 -362.
75 B. T. A. Bell, op. cit., 1899, p. 77 - 80; W. Malcolm, op. cit., p. 112 -117.