These mines, which belong to the Burma Corporation, Ltd., formerly a London company now incorporated in Rangoon, Burma, are situated in the semi-independent state of Tawng-Peng, one of the small divisions comprising the northern Shan states and erroneously known as part of Upper Burma. Bawdwin is approximately 23° 6′ N. latitude and 97° 20′ E. longitude, 450 miles north of Rangoon, 169 miles northeast of Mandalay and 50 miles south and west of the Province of Yunnan, China (see Fig. 1).
Although the mines were worked by the Chinese during the Ming Dynasty, 1412 A. D., the most extensive operations took place between 1796 and 1851, when the mines contributed largely to the silver market of China. During the reign of Tung Chik, 1868 A. D., they were abandoned partly because of the Mohammedan rebellion in Yunnan, which made life and property insecure, but largely because of the difficulty of operating the mines on account of water and poor ventilation. Since that time practically nothing was done, although the Burmese kings are said to have made several sporadic attempts to work the mines, until 1891 when Europeans were attracted by the great slag dumps (assaying about 40 per cent, lead) which the Chinese had left after extracting the silver.
After a railroad and smelter had been built and 200,000 to 300,000 tons of slag smelted for lead, exploration work was started and old workings cleaned out in order to locate the remnants of the orebody that it was supposed the Chinese had left. After two years of most discouraging work, the remains of a large orebody was discovered by the Dead Chinaman Tunnel or what is the 171-ft., or No. 2 level adit. From then on the development was rapid and today the Chinaman is considered one of the largest high-grade silver-lead-zinc orebodies in the world. The total ore reserves on Jan. 1, 1922, were:
Of this, only a little over one-tenth is designated as probable ore. No mineral with a value of less than 20 per cent, combined lead and zinc is considered commercial ore unless it is part of the 335,681 tons of copper ore that averages silver 23.2 ounces, lead 12.8 per cent., zinc 7.7 per cent., copper 11.0 per cent.
The mineral lease comprises an area 5 miles long by 2 wide and covers a period of 30 years from Jan. 1, 1920. The royalty payable to the government is 2½ per cent, of 30 per cent, of the gross value of the metal contents of the ore. The company, as reorganized in Rangoon, has a total authorized capitalization of 20,000,000 shares at Rs. 10 each, of which 13,541,682 shares have been issued. There is also a first mortgage of 8 per cent, convertible debenture stock of £1,000,000 at Rs. 10 to the pound.
Geology
The rocks at Bawdwin are of two classes: volcanics (comprising rhyolite tuffs, breccias and flows) and unfossiliferous sediments comprising quartzite, sandstone and shales, which are probably Ordovician. Rhyolite tuff (the ore-bearing formation) forms a wide band running northwest and southeast that has been exposed by the erosion of the overlying sediments. Through this band the main ore fissure passes longitudinally and forms the lode by metasomatic replacement of the rhyolite tuff by ascending ore-bearing solutions. Replacement has taken place parallel to the strike of the fissure, as shown by the laminated structure of the ore and its dimunition in value and density as it passes into low-grade ore, mineralized material, and finally barren tuff on approaching the east, or foot-wall, side.
In the Chinaman lode, there is a well-defined hanging wall, which makes a sharp demarcation between ore and waste; but there is no such foot-wall, the limit of the orebody in that direction is considered to be the limit of what is defined as commercial ore. On some levels of the Chinaman section, the solid sulfide is 50 ft. wide for over 1000 ft. along the strike and in places has reached a width of 140 ft., see Fig. 2. The faulted portion of the Chinaman lode is known as the Shan and is much narrower. This narrowing is partly accounted for by the character of the rock. In the Chinaman the fissure cuts through coarse rhyolite tuff with large feldspar crystals, which were easily dissolved by the ascending solutions making the rock more porous and favorable for the deposition of a large orebody, while in the Shan the tuff is more compact, siliceous, and fine-grained and consequently gives a clean-cut narrow fissure vein. The orebody has a tendency to finger out and become much smaller at the outcrop, as compared to the body below.
The ore is an intimate mixture of galena and sphalerite and in many places also of chalcopyrite, although the latter is often found in parallel bands alongside the former as pure unmixed chalcopyrite. The mixture of galena and sphalerite contains approximately 1 oz. of silver for every per cent, lead; it is generally considered that the silver accompanies the galena, but the ore is so complex and the crystals so intimately inter-grown that it is most difficult to make a first-class separation of the metal by mechanical means. Taken as a whole, the southern end of the Chinaman section predominates in zinc-lead ore; the middle in more equal quantities of both; and in the northern end the zinc is partly replaced by copper. In practically all sections, the ore along the hanging wall is the highest grade, with the lead predominating over the zinc, but toward the center or the foot wall the zinc contents increase until, in many sections, the zinc predominates. Still farther toward the foot wall the ore becomes lower grade and below what is classified as ore until it is only mineralized: the lead however predominates and often is found as pure crystals of galena. These conditions, together with the following, have been instrumental in determining the method of mining:
(a) The Chinese worked the mine from the surface to 50 ft. below the 171-ft. level for the silver alone and consequently did not want lead ore, high in zinc or low-grade ore; so that there is a large remnant of
the orebody on the upper levels mixed with Chinese filled stopes and workings. This remnant must be preserved for future requirements, as a considerable part of it is not commercial ore today.
(b) The banded structure of the ore; for instance, there are bands of chalcopyrite running parallel to the lead-zinc ore. These bands must be mined separately in order to save the copper.
(c) There is only one pronounced wall, the hanging wall. The ore starts from it as a solid mass high in lead and gradually passes through zinc and chalcopyrite bands into low-grade ore and, finally, into mineralized ground. That is, there is no definite stoping limit toward the foot-wall side except what is arbitrarily fixed as the limit of commercial ore (20 per cent, combined lead-zinc with whatever silver it contains). Later, this arbitrary value may be lowered and another 2,000,000 tons of low-grade ore added to the reserve. Any stoping method must take this low-grade material into consideration and not leave it in such condition that it cannot be economically mined.
General Conditions that Influence Methods of Mining
The country is very rough. There are no roads; the only means of travel are a 2-ft. gage railway with steep gradients and sharp curves, and trails along the ridges of the hills.
From November until May (the dry season), this region is healthy and enjoyable, but during the wet, or the remaining, months the climate is depressing. Many employees suffer from malaria and kindred ailments. The coolies, especially those from the high cold regions of China, suffer considerably from malaria as they do not take the necessary precautions.
The upper levels of the mines, on account of the many workings, including all the old Chinese stopes, drives, etc., in which a large surface of ore is exposed to oxidation, are quite hot. During the wet season, water percolates through and increases the oxidation and also the humidity of the air.
The rain falls in heavy showers; the fall amounting to about 70 in. in six months, making the mine quite wet and the ground heavy. It is also difficult to keep the railway free from landslides and washouts.
The mine is situated 3100 ft. above sea level, which is very favorable to the health. The air is clear and the dense fogs found 1000 to 2000 ft. lower do not prevail.
Water, Fuel, Timber, and Other Supplies
Good water, in abundance, is piped to all bungalows and to all the levels in the mine. This is a treat to one who has lived in the tropics as, in most cases, water must be boiled to insure no contamination. Partly furnished bungalows, electric lighting, and water are supplied to all Europeans and fuel to all employees. This fuel is brought in by pack mules a distance of 8 miles and costs Rs. 14 per stack (108 cu. ft.). Local timber, which is hardwood and heavier than water, is shipped in by rail from the company’s timber reserves, about 20 miles away, at the following rates:
Mine logs……………………………………………………..Rs. 41 per ton (50 cu. ft.)
Local sawn timber……………………………………Rs. 90 per ton (50 cu. ft.)
8 in. by 2 in. by 6 ft. lagging…………………………Rs. 74 per 100 pieces
8 in. by 3 in. by 7 ft. 4 in. lining boards…….Rs. 120 per 100 pieces
The laggings and lining boards are hand cut in the jungle by Chinese. Bamboo, 4-in. and 5-in., used for lining the sides of stopes preparatory to filling, cost Rs. 5 per 100 laid down in Bawdwin. High-grade ingyin
timber is shipped from Mandalay at the rate of Rs. 140 per ton (all charges). This dense, hard, local timber, which a person might think would last for years in the mine, has a short grain and breaks without any warning under no great load. Some of this timber breaks sharply across the grain and looks as though it had been sawn through. It lasts, on the average, in this humid atmosphere about three years. In all permanent workings, the timber is now creosoted, which we believe will double its life. It is difficult to frame, and a nail cannot be driven into it unless a hole is first bored.
Coke and coal are brought from India across the Bay of Bengal and then carried by rail 450 miles; coal costs at the mine, approximately, Rs. 56; coke, Rs. 79.
Fuel oil, from the Yenangyoung oil fields in Burma, is shipped from Rangoon and costs Rs. 0.3 per gallon.
Electric Power
The corporation has installed a 3000-hp. hydro-electric plant at Mansam Falls, which supplies the mine, smelter, and mill. A Diesel oil-engine plant capable of delivering 1800-hp. is available for emergencies. From the hydro-electric plant, the power is transmitted 38 miles over high-tension wires at 33,000 volts to the mine substation where it is stepped down to 550 volts for mine use. The mine uses 270,000 kw.-hr. per month and is charged Rs. 0.0106 per kw.-hr. An additional expense on the low-tension side, of motor operators, repairs, and maintenance, increases the cost to Rs. 0.0142 per kw.-hr., which is the charge applied to the mine operation. No depreciation charges are included in this cost of power, this being cared for by the head office.
Labor
Chinese from Yunnan, China, form the nucleus of the underground labor with a number of Gurkhas (from the independent state of Nepal, Upper India) and a small number of other Indians. Practically no natives of Burma work in the mine. On the surface, there are men from nearly every neighboring country. Chinamen from Shanghai, Canton, Indo-China, and neighboring Chinese provinces, many of whom cannot converse with one another; Chinese-Shans from the northern Shan states; men from all parts of India even Nepal and Afghanistan. Men of all castes, creeds, and languages. The laboring class comprises men from nearly all neighboring countries; the Burman makes a good clerk and a fair carpenter, but will not do hard labor. The other natives of the country will not work in the mine nor do manual labor on the surface under any conditions; they prefer to cultivate their small farms though they eke out a bare existence.
All technical supervision must be supplied by men from England, Australia, or the United States. It will be many years before the Anglo-Indians or Indians can be trained for this technical work and take the place of a European in the more responsible positions.
The Chinese and the Chinese-Shan coolies are the best laborers and when one makes his home in Burma, taking his family there, he makes an excellent miner. However, a large part of the labor is seasonal. The Chinaman prefers to come over at the beginning of the dry season and goes home before the wet season in order to plant his rice. It often takes 20 days for him to walk in from remote places in Yunnan. He is honest, compared to the Indian coolies, and is easy to handle if treated with reasonable justice. On an average, two Chinamen will do the work of one European, and one Chinaman that of two Indians. As a large part of the labor is seasonal, it is not efficient. The turnover is very large, averaging 11 per cent, for six months. During March, as many as 20 per cent, of the men leave for their homes. It is most discouraging to teach a coolie to run a drill or timber a stope, just to have him leave when he becomes proficient.
Pumping
The pumping problem is simple, as practically all the water is handled by a gravitysystem through three adits—No. 1 level, No. 2 level, and No. 6 level—except the development below the latter which is opened by two winzes. These require two sinking pumps (a No. 7 and a No. 9 B Cameron) to pump the water to the No. 6 level. This No. 6 level adit, known as Tiger tunnel, takes care of 40,000 gal. per hour.
Accessibility
The property is accessible from Rangoon, the main port in Burma, by the Burma Railways (a meter-gage line) that connects with the company’s private road at Nam-Yao. From this point, a 2-ft. gage line leads over the mountains to Bawdwin, a distance of 45 miles.
Exploration, Sampling, and Estimating Methods
Exploration is today chiefly done by drives, crosscuts, and winzes. In the upper part of the orebody, down to 50 ft. below the 171-ft. level, the orebody is riddled with Chinese adits and workings; but as they are small, tortuous, and filled with mud and water, new adits, drives, and crosscuts were made to explore the orebody. A small amount of diamond drilling was done; but on account of the character of the ore, the drillers were continually losing the water or the bit so that it is more satisfactory to develop by actual workings. For development purposes, drives were originally run in the ore parallel to the strike and crosscuts put out to the extremities of the ore every 100 ft. with occasional rises in ore from these crosscuts to the upper level. During the later development of the mine, the drives were made in the country rock foot wall and crosscuts run to and through the ore. These drives require no timber and being outside and parallel to the orebody become the main extraction drives for the present stoping method. Two winzes, or inside shafts, were sunk from the No. 2 adit level to open up and develop the levels below and also facilitate the driving of No. 6 adit from each end.
Sampling
Each crosscut is sampled every 5 ft. on both sides and the average of the two taken for calculations. Drives and raises are also sampled every 5 ft. but these samples are not included in the calculations of the orebody but are used to prove the continuity of the ore and grade only. As most of the ore is friable and soft, it is not difficult to cut a small trench of even width with hammer and moil. However, there are occasional patches of low-grade siliceous ore, which require the aid of a Jackhammer. Samples, when assayed, are entered in an assay ledger, one page for each crosscut, drive, etc. Using a width factor of 1 for every 5 ft. of sample and carrying a running total of width factor times ounces or per cent, facilitates the averaging of the values of any drive, crosscut, etc., for its entire length, or between any two points (see Fig. 6).
Estimating
After several levels had been opened up by crosscuts and raises every 100 ft., it was apparent from the character of the orebody—that the size and grade were fairly uniform from level to level and crosscut to crosscut and the continuity and transition of values from higher to lower grade were so gradual—that it was permissible to estimate the orebody on the crosscuts alone; that is, the width and value of the ore in the various crosscuts on any particular level (with the aid of geological evidence in faulted country) would give the area and grade of that level. For the purpose of estimating, complete assay plans are made of each level and by referring to the assay ledger the average of all 5-ft. samples (both sides) is plotted and the values marked on the map, showing location, width, and assay values. Values of samples from all crosscuts, drives, etc., are shown on this assay plan for every 5 ft., or less, notwithstanding the material is mineralized only or waste. For estimating ore and tonnage, a graphic system is employed and another plan, called the estimating plan, is made of each level (see Fig. 7).
The next question to consider, and possibly the most important, is: what is commercial ore now and what will be commercial ore during the life of the property? This question is most difficult to answer because the mine is in a state of development and no one knows its life, or only approximately so, and furthermore due consideration must be given to the possibility of new metallurgical treatment and the fluctuation in price of the products. However, the result is only an estimate based on available data. The advisers for this mine decided on 20 per cent, combined lead and zinc, in whatever combination, with its accompanying silver; or in the case of copper ore, any of the combination containing lead and zinc with 3 per cent, copper and its accompanying silver.
By referring to the assay ledger, in preference to the assay plans, the limits of commercial ore can be marked on each crosscut. Due consideration must be given to the stoping method to be applied in order to know just what samples to include. Lines are then drawn on the plan from crosscut to crosscut enclosing the body of commercial ore. The area is divided into triangles, as shown in Fig. 7 and, with the aid of a scale, the base and altitude of each triangle is measured. The areas of triangles in the adjoining half of the space between the crosscuts (that is nominally 50 ft. on either side) are multiplied by the average value of the crosscut and give as a product ounces times square feet and per cent, times square feet. The sum of all ounces times feet and per cent, times feet divided by the total of all the areas between the crosscuts, which is the area of the level, gives the average value of that level. By calculating the Pb in form of PbS, Zn in form of ZnS, and the Cu in form of CuFeS2, the total percentage of sulfides is obtained and the remainder is considered quartz. By deducting 5 per cent, for voids and using the specific gravity of the various minerals comprising the ore, the number of cubic feet per ton is obtained. The sum total of all the areas divided by this factor gives the number of ton-feet. Ton-feet multiplied by the dis¬tance up and down, which is generally half way to the next level, gives the total tonnage and value of the level; see Fig. 8. As the ratio of cubic feet to tons depends on the relative specific gravity, porosity, and moisture of the ore, the average value of the crosscuts as calculated is not exact, as they were calculated on volume and not tonnage. It is impossible and too expensive to get the specific gravity of each sample, so that this factor cuts down the metal contents per actual tons of ore 7 to 10 per cent.
Ore is classified as proved and probable. Proved is considered ore of practically no risk in estimating its value or continuity. As development work has shown the orebody to be fairly uniform from level to level with no abrupt changes in grade or size, as proved by raises every 100 ft., all ore between lines drawn from the boundaries of proved ore on one level to those above or below is considered proved; also ore 25 ft. above the
upper level and 25 ft. below the lowest. Probable ore is considered as containing some risk on account of the lagging behind of development on a level, particularly at the extremities of the orebody. From 25 to 100 ft. below the lowest level is considered probable. Probable ore would also be assumed 50 ft. ahead of the last crosscut, where geological evidence is favorable for continuity. It would be calculated on the value of the last crosscut and on an area equal to a triangle, having an altitude of 50 ft. and a base the width of the ore in the crosscut.
Accuracy of Methods of Estimation
As the mine is still in its infancy, it is not possible to check the method of estimating by actual mill yield plus tailings. In most mines, there is a loss of 10 per cent, or more in actual value. By the present method of estimating, using the algebraic average of a section, the metal contents per actual ton of ore is cut down 7 to 10 per cent, dependent on whether the high-grade or the low-grade predominates. This should take care of any mining loss, and dilution will add to the values recovered as the dilution will be low-grade non-commercial ore, instead of barren waste.
History of Mining Methods
The first method of stoping tried was the common flat-back square-set stope, which was carried very wide and long with a number of ore passes to shovel into. Fortunately, this method was stopped in time, as it is impossible to prevent such a large stope from caving and the cost of keeping so many timbered ore passes is excessive. Furthermore, the filling was laborious and expensive as all waste had to be wheeled and shoveled into position.
A narrow Gilman slice rill stope was tried in the hardest and most favorable ore, with only timber on the sides to confine the waste from the adjacent stopes. This was a failure and a death trap, as the solid sulfide ore (9 and 10 cu. ft. to the ton) would drop without any warning in large masses; and in other places the friable ore would run up in the form of a chimney and cause the stope to cave.
Present Mining Methods and Reasons for Adoption
Stoping
The upper levels of the mine have been riddled by Chinese workings; consequently the ore left is mixed with old filled stopes and gives a low-grade oxidized ore. The company does not care to mine and mill this ore at present as it plans to open-cut and quarry a large portion of it in connection with the regular waste-filling plan now being used to fill the stopes. Any method of mining the ore, must leave these upper levels undisturbed until the company is prepared to handle this ore. This eliminates several systems of stoping, for instance mill hole, top slice, and caving systems, and leaves only some form of a timbered and filled stope. The ore is so heavy and friable that it must be closely timbered to support any opening and the orebody is so wide that it requires mining in sections.
By elimination we have arrived at the square-set system of stoping with all its modifications. A flat-back square-set stope is costly and slow, on account of the laborious work in handling the ore and waste, and is not easy to ventilate. To meet these disadvantages, an efficient combination square-set rill system, of a variable width and length to meet any conditions that arise has been adopted, (see Fig. 11).
To lay out the system to the best advantage for longitudinal stoping, as required by the grades and class of ore, the development drives should be run outside and parallel to the orebody in the hard foot-wall rock and not in the ore, as were some of the earlier ones. At every 100 ft., crosscuts are driven to and through the ore to the hanging wall and continuous raises put up from level to level, and finally to the surface, so that waste may be taken directly into the stopes.
When commencing stoping operations, half way between the main crosscuts, auxiliary ones are put in with a 25-ft. radius curve to the main or extraction drive. The 50-ft. blocks on either side, with the exception of a 12-ft. pillar directly over the crosscut, comprise the stope. These rill stopes have their apexes at the main passes and slope down to the extraction crosscuts. In the early work, no pillar was left at the toe of the two stopes and one ore chute sufficed for two stopes. This toe, or section around the chute, would become very heavy, and it was difficult to prevent this from caving. A 12-ft. pillar is now left between the two stopes and individual ore chutes are carried up. The pillar is mined after the two stopes are finished.
Stopes are carried three or four sets wide, depending on the character of the ground. Four sets is the maximum width that the best ground will stand; and as the ground becomes heavier the stope is brought in to three, and sometimes two sets in exceedingly bad ground, but the length remains the same.
Where the vein is wide, a longitudinal section is first taken along the hanging wall; and when this is completed a second and third section alongside, retreating toward the foot wall. Under this arrangement, the crosscuts and drives are never in bad ground, under worked-out stopes, but in the solid ore or country rock. The part of the crosscut under the completed stope can be filled, thus doing away with all expensive repairs maintaining openings under old stoped areas. In order to get the proper rill and still not make it too steep to climb up, square sets must be of proper size and height. Those at Bawdwin mine are 5½ ft. square and 7 ft. 4 in. high.
Manways should always be on the hanging-wall side of chute and not along one side, as is the general custom. This gives access to either stope, from the manway or the chute without interfering with entance to the other. As all ore is dropped to the lowest level or adit, from which it is hauled out by electric locomotives, any system of continuous raises can be used as an ore pass, provided the raise is not being used for passing waste for a stope below. However, it has since been found cheaper to run up continuous untimbered ore passes from level to level in the foot wall when suitable hard rock can be found; this leaves the main passes for waste only. The lower repair cost of maintaining timbered chutes for the soft waste fill only and not for the heavy ore offsets the increased cost of tramming ore on the various levels to the (all rock) ore passes. Waste filling is obtained from the surface by quarrying or mill-holing around the top of these continuous mullock passes placed at intervals of 100 ft. along the strike of the orebody so that the filling can be passed directly into the stopes without any tramming.
Mine Openings, Shafts and Tunnels
The main opening to the mine, as at present developed, is the No 6. level adit, commonly known as Tiger tunnel; see Fig. 12. This is the
main haulage and drainage adit. It is nearly 2 miles long and double-tracked from the portal to the inside shaft, a distance of 7400 ft. The section is 9 ft. wide by 8 ft. high in the clear. The ditch is carried in the middle in the space between the two tracks; long sleepers pass completely over it and support both tracks. The grade of the tunnel started at 0.6 per cent, but was increased to 0.7 per cent., to accommodate the large volume of water passing through the ditch, which had a tendency to silt up on the lower grade. The average flow is 40,000 gal. per hr. but this has been exceeded many times.
The double-track part of the tunnel was run from both ends; it was begun in April, 1914, and finished Sept. 21, 1916. The length of survey was 23,300 ft., consisting of forty-nine readings of the theodolite, exclusive of those in the tunnel itself. Of these readings, three were lines less than 10 ft. in length, four between 10 and 20 ft., and six between 20 and 30 ft. The actual error of closure was 1.26 ft.; giving an error of 1 ft. in 18,500. The distance between the center lines of the two ends at right angles to their length was 0.35 ft. In elevation, the error of closure was 0.35 ft. or 1 ft. in 100,000, the distance leveled being approximately 34,000 feet.
Tiger Tunnel Construction
The work was originally started with an outfit, picked up in the country, consisting of a Class A Sargent straight-line compressor (steam cylinder 22 by 24 in., air cylinder 22¼ by 24 in., giving approximately 960 cu. ft.) and two second-hand boilers run on wood fuel; 2½-in. piston machines were used for drilling. During the first year, on account of lack of organization, poor equipment and raw coolie labor, only 2448 ft. was driven—an average of 204 ft. per month. Work was then reorganized. A new equipment was obtained and eleven trained white men were employed to supervise as follows: One foreman, three shift bosses, one mechanic, one steel sharpener, one combined track layer and pipeman, and four miners. The new equipment comprised the following, with necessary accessories:
1 new Ingersoll-Rand compressor belt-driven, Imperial type 10, 950 cu. ft.
1 Garrett semiportable boiler and engine combined.
1 No. 5 Leyner drill sharpener.
6 No. 18A Leyner drills (three machines on a bar), replacing the piston machines.
1 British Westinghouse dynamo, direct-current 9 kw.
1 Root blower.
During the following 12 months and 21 days, the outside heading advanced 3814 ft. at the rate of 300 ft. per month, the highest footage for any month being 502 ft. An average month of 300 ft. required daily 227 men, working as follows: 151 underground, 40 mechanical department, 36 surface, all working in four 6-hr. shifts; of this number eight to eleven were white men acting as supervisors. There was 3050 ft. of tunnel timbered. Many large bursts of water occurred, the flow through the tunnel being from 40,000 to 73,000 gal. per hr. The total cost of the 7400 ft. of double-track tunnel amounted to Rs. 731,000, including all charges for labor and supplies and 8 per cent, for depreciation on the capital cost of equipment. As soon as the tunnel was finished the equipment was transferred to the mine account.
All running and heavy ground was timbered, but within a year after the tunnel was completed, the rapid deterioration of the local timber made necessary a large amount of repairs and many caves and obstructions to traffic occurred. It was decided to replace the timber with masonry, as good sandstone could be had on the railway line about ½ mile from the portal. Work was started and a 15-in. wall and arch replaced the timber. Any space above the arch was filled with dry rubble. As a large proportion of the timbered sections was in spiling ground, progress was slow. Only one set of timber could be removed at a time, for the iron forms had to be put in and masonry built around them and allowed to set before the next set of timber could be taken out. Nine steel forms were used 50 ft. or more apart, and an advance of 150 to 200 ft. per month was made. The forms were so constructed and work so managed that there was no serious delay to the mine haulage, and the trolley and lighting wires were never cut. The cost of the masonry was as follows:
All ore mined is dropped to this level and hauled out by electric locomotives. Three smaller adits on the upper levels, namely Zero, No. 1 and No. 2 levels, are used for drainage and transportation of supplies. As there are only three levels that have no adits and as no ore or waste is hoisted or lowered in cages, an elaborate shaft and hoist equipment is not required until stoping operations begin below the lowest adit, or Tiger tunnel.
Two inside shafts, one of two and the other of three compartments 4 by 8 ft. and 4½ by 11 ft. in the clear, respectively, are used for hoisting and lowering men and supplies. The 8 by 8-in. timbers in the two-compartment shaft have shown considerable pressure and have been replaced by 10 by 10-in. Mandalay ingyin timber. The framing of the set has also been changed by making a bevel on the inside corners of the set; this prevents the wall plates crushing and splitting at the end plates. These shafts were sunk in the orebody as a means of develop-
ment before the lower adit was driven, consequently they are only temporary and will be replaced by a large circular shaft 14 ft. in diameter and masonry lined, Fig. 13. This will be located in the hanging wall in country rock and at some distance from the orebody.
In sinking the three-compartment shaft, one European was put in charge of the coolie labor and advanced the shaft 30 to 35 ft. per month; 5000 to 5500 gal. of water was pumped per hour. An advance of 33 ft. per month required 461 coolies divided into three shifts.
The cost per foot was:
Of the local wood in Burma, only ingyin and teak are satisfactory for shaft work and the latter is too expensive. The three-compartment shaft, which is of ingyin timber, has been completed over 6 years and the timber is still in good preservation, although a number of sets have had to be replaced on account of rock pressure. This is partly accounted for by the shaft being wet with acid water impregnated with zinc sulfate and there being a good circulation of air. Timber has been taken out of the submerged lower levels of the Chinese workings that is 50 to 100 years old and in a good state of preservation. When this old timber is brought to the surface, the absorbed water evaporates and leaves a 1/8-in. coating of zinc sulfate over the entire stick. The smaller shaft, which was sunk about the same time and timbered with local sawn timber, has been practically retimbered twice on account of the rapid decay, as this shaft is dry. The second time 10 by 10-in. Mandalay ingyin timber replaced the local timber and we expect this to remain in good shape for two or three years, but not as long as if it were wet with the acid mine water.
Underground Development
In Figs. 14 and 15 are shown longitudinal sections of the different levels.
Drilling and Blasting
The corporation has standardized on the following drills, for the following reasons:
(a) The first ones were purchased about 7 or 8 years ago and tried out with the raw coolie labor; although they are subject to much abuse they stand up well.
(b) It has taken considerable time to teach the coolies to operate and repair these particular drills efficiently.
(c) On account of the long distance Burma is from the source of supply, a large stock of repair parts is necessary; this is quite an expense when about 100 drills are operating.
(d) By using only one type that has been found satisfactory, much labor is saved that would otherwise be wasted on a new type of drill, and the stock of repairs is kept to the minimum.
(e) Burma is not the country nor the Chinaman the man to try out new machines; consequently we leave that to others.
The drills in use are: 40 I. R. B. C. 21 stopers, 40 B. C. R. 430 Jackhamers, 13 18A Leyner drifters.
For Jackhamers and stopers 7/8-in. hexagonal hollow and 1-in. cruciform solid steel are used; 1 1/8-in. round hollow steel is used for the Leyners. Ordinary cross bits are used with as few changes and as large a clearance as possible, because the coolie persists in running the steel until the machine is entirely cranked out. Drills are tempered by a separate fire by giving them a short heat not farther up than 1 in. from cutting point and then standing them on a grating, resting ½ in. below the surface of a tank of water. Sharpening is done on two Ingersoll-Rand No. 5 Leyner drill sharpeners in conjunction with oil furnaces. The average rock is not hard and requires no special bit; and as the cross bit
is the simplest and easiest to sharpen it is used on account of coolie labor. The simplest rounds are used as the placing of holes to the best advantage is the most difficult part of mining to teach the coolie.
Fifty-per cent. Nobels or Curtis & Harveys gelignite is used. This explosive is comparatively safe and only one fatal accident and two minor ones have occurred in the mine during the last 5 years and these were due to carelessness. Gelignite, a modification of blasting gelatine, resists the action of water, is safer than gelatine, and has all the plastic advantages of the latter over dynamite. It is a nitroglycerine compound to which is added nitrocotton, nitrate of potash, and wood meal. It, however, lacks the rapidity of explosion of the dynamite and does not produce the local shattering but has a larger rending action in being slower. Dynamite is more effective for bulldozing, etc., where gelignite is more effective for drill holes. Double tape fuse is used for dry work and gutta percha tripple tape for wet work. No. 7 detonators are used entirely. The coolies have very little trouble in spitting the fuse, as they roll a small piece of gelignite into a small pencil, which is quite effective especially in wet and drafty workings.
Drifting and Storing
The ordinary methods of driving and timbering are used. In going through running ground, spiling with false set and face boards is used. The latter are, however, made in two pieces. One piece has two bolts and the other a slot to accommodate them. First, room is made for the half with the two bolts and the end shoved in front of the point of the side spiling, while the other end is supported by a temporary brace. Room is then made for the other half, and the board is put in with the slot in line with the two bolts. Large washers are slipped over the bolts and the nuts tightened. This makes a rigid face board that is easy to put in and take out.
For stoping, hardwood is the only available timber. This wood is so hard that nails cannot be driven into it unless the holes have first been drilled. Wire nails are of little value, so cut iron spikes must be used. The timber is heavier than water; consequently every stope is supplied with Holman or tugger hoists. Instead of the ordinary 2-in. lagging generally used to line the inside of a stope preparatory to filling, 4-in. bamboos 11 ft. long are used, much the same as pole lagging.
Timbering
Special timber is framed by hand but all other by machine.
All framing is done on the surface and all timber, except that required for stopes, goes to the preserving plant. This consists as follows:
One creosote storage tank 5½ by 12 ft. in diameter.
Two open-treatment steel tanks, one for hot and the other for cold solution, size 5 by 5½ by 12 ft.
Three 1½-ton chain blocks and overhead crawl.
One vertical boiler, 9 hp., 100 lb. pressure.
The boiler is connected to a series of 1-in. pipe coils laid in the bottom of the hot tank, which raises the liquid to 180° or 220°.
The timber is left in this tank for 6 or 7 hr. The heat causes the wood to expand, expelling the air and moisture, and to absorb a small amount of creosote in the cellular spaces. The wood is then put in the cold tank where it is left over night. This causes contraction and a condensation of moisture, and the creosote is absorbed and forced into the wood. The wood is very hard and dense and only a ½-in. penetration is obtained. As most of the timber is thoroughly seasoned, the hot tank is not necessary except for green timber; by leaving the seasoned timber in the cold tank 12 to 24 hr. a penetration of ½ in. is obtained. The process has not been in operation more than 2 years so that we are not able to tell just how much longer life is given to the timber by the treatment. There is reason to believe from the experience of two years that the treatment will at least double the life of the timber, which will bring the chemical life of the timber close to its mechanical life, and that is as far as one is justified in going in expenditure for treatment.
The local Burmese timber is as follows:
Thitsee…………………………………….3150 lb. per 50 cu. ft.
Yindike…………………………………….3000 lb. per 50 cu. ft.
Thaukkyan………………………………3075 lb. per 50 cu. ft.
Thumalum……………………………….3037 lb. per 50 cu. ft.
Kadee………………………………………..2925 lb. per 50 cu. ft.
Yang………………………………………….3900 lb. per 50 cu. ft.
Cedar………………………………………..1500 lb. {not suitable for
Cotton wood…………………………..1440 lb. mining purposes.}
All timber is peeled in the forest, as the space between the bark and wood affords a starting place for fungi and is unsuitable for creosoting. Most of the timber is seasoned by cutting it the previous year and stacking it along the railway line; however, not more than enough for one
season should be cut as the timber decays very rapidly in the forest and is badly damaged by ants and borers.
No timber is recovered from stoping operations, as the ground is heavy and the timber takes weight very rapidly; we are satisfied if the timber will hold until the filling is completed without requiring the additional expense of putting in doubling up sets and angle braces. Timber is loaded on special timber trucks 6½ by 3 ft. wide, 2-ft. gage and is hauled into the mine in special trains, by electric locomotives, to the inside shaft and winzes, where it is loaded into cages for transportation to the various levels. In the new circular shaft, these trucks will be run onto a large cage and hoisted to the various levels without any additional handling.
Underground Sampling
Sampling has been described under exploration work. As a check, crosscuts used for estimating the ore reserve are resampled by an independent sampler and have so far closely checked the original samples.
Every set of ground mined is located by the number of the stope and the number of sets north and south of the nearest 100-ft. crosscut and east or west of the drive and with respect to the floor above the level. For example, “4-14 S. stope 6th floor 3 W. & 4 S.” locates a definite set of ground in the mine. This is interpreted as No. 4 level, 1400 S. coordinate, sixth floor, 3 west of drive, and 4 south of 1400 S. crosscut. There is great difficulty in sampling across the middle of the back of stope sets, as it is high up and, unless one is on the spot when the ground is taken out and before the lagging is placed, it is impossible to take the sample correctly. Often two or three sets fall out, leaving a dangerous hole, and the sampler thinks more of protecting his head than of getting a good sample. To avoid all trouble, danger, and careless work, samples are cut across the vein on the exposed side of the set about 4 ft. above the floor and after the timber is placed and lagged over; this arrangement gives the sampler two or three days time to cut his sample before the next set ahead is taken out.
Each level is divided into convenient sections and stope plans prepared of each floor in that section, showing all the ground taken out with its respective value. As the ore is thoroughly mixed in passing through continuous rock passes from the upper to the haulage level, ordinary hand sampling gives fairly close results. Each car is sampled as it leaves the portal of the mine. The ore then passes through the tipple, and by travelling belt, to the bins where it is discharged into 20-ton railway cars. Here it is again sampled by hand; and as it has been thoroughly mixed in going through the rock passes, cars, tipple plant, and bins, a fairly accurate result is obtained, which checks closely the sample taken at the concentrator.
Tramming and Haulage
On all levels, except Tiger tunnel or the haulage level, small ¾-ton cars of 20-in. gage are used to tram the ore from the stope chute to the nearest ore pass, which is seldom more than 200 ft. As the ore is very heavy it requires two men to a car, especially in tipping. Turntables were used at the intersection of the crosscuts and drives, as no extra ground had to be taken out for switches. As the tables used were unsatisfactory and a continual source of trouble, they were scrapped and switches put in. The mine is very heavy, and additional expense was incurred in continually replacing the long caps at the curve. However, a very satisfactory turntable was discovered at this smelter and installed in the mine, although it is more expensive than most others; it requires no repairs and is never out of order. For hand tramming, all right-angle turnings in heavy ground are provided with these turntables, which have simplified the timbering and cut down the repairs.
On the haulage level, 4-ton (56 cu. ft.) tipple cars are used. They are 6½ ft. long by 3 ft. wide by 2 ft. 11 in. deep and equipped with standard railway journals and brasses and the small size U. S. M. C. B. railway coupling. They are hauled, in trains of ten cars, by 4-ton Baldwin-Westinghouse electric locomotives of 2-ft. gage. Four of these locomotives handle the ore and supplies. Current is supplied by an overhead trolley line (one over each track), which is fed by two 42-kw. Westinghouse motor-generator sets. These sets take alternating current at 500 volts 63.3 amp., and deliver direct current at 250 volts 168 amp. The rails are 50 lb. and are bonded by General Electric twin-stud, flexible cable bonds, which have proved quite satisfactory both for safety from theft and for service. Gage of the track is 2 ft. and the grade is 0.7 per cent, in favor of the loaded train. On this grade no power is required to take out the loaded trains but considerable is necessary to take in the empties. A 4-ton locomotive will haul a train of ten empty (56 cu. ft.) cars up this grade without undue heating. A lighter grade would have been more efficient from the haulage standpoint but insufficient for drainage purposes.
Dumping
As the loaded train of ten cars (40 tons of ore) reaches the portal, it is pushed to the tipple. There are two revolving tipple drums 6 ft. 9 in. in diameter by 34 ft. long, each, geared to an Allis Chalmers, direct-current, 15-hp., 58-amp., 200-volt motor, which is fed from the trolley wire. Each drum is capable of receiving four 4-ton cars and discharging their contents in one revolution into the bin below. Four special revolving drums operated by 7.5-hp. motors are used for gates in delivering the ore from the bin to the incline belt conveyor. This belt, which conveys the ore to the storage bin, is 20 in. wide and 323 ft. long and runs on an angle of 16° 30′; it requires a 15-hp. motor and discharges on to a 20-in. distributor belt 406 ft. long equipped with an automatic tripper, which requires a 7.5-hp. motor. From the tripper, the ore is discharged into various storage bins, which supply the railway that hauls the ore to the mill at Namtu 7 miles away. As the ore passes over the end pulley of the elevator belt (just before it is discharged), it passes under a Cutler Hammer, type B, size 18, 2.75 amp. hot, 220-volt magnet, which takes out all iron.
Hoisting
As no ore is hoisted the hoisting plant, though small, is adequate and will suffice until the new 14-ft. circular shaft is sunk and equipped. Only timber supplies and coolies are hoisted at present. The hoisting is facilitated by the adits on Nos. 6, 2, 1, and 0 levels. The main inside shaft is equipped with a motor-driven double-drum electric hoist made by Allis Chalmers: one fixed and one loose drum; drum reel 4 ft. diameter by 2½ ft. inside flange, drum speed 34 r.p.m. or 408 ft. per min.; motor 50 cycles, three-phase; speed 725 r.p.m., 70 amp.; 500 volts, 60 horsepower.
The hoist is equipped with a solenoid brake on the motor and a Lilly brake (overwinding and speeding device) on the loose drum. The hoist motor is protected by an oil switch with an overload and no-volt release trip, which opens the circuit in case of a dangerous overload or stoppage of current and applies the solenoid brake on the motor. The Lilly brake controller is also connected to the no-volt release; and in case of overwinding or overspeeding, it not only applies the brakes on the hoist itself but also those on the motor. In addition, two limit switches located in the head frame open the circuit and apply all the brakes in case the Lilly brake controller does not function in an overwind. Close to the operator is a hand emergency switch for cutting off power and applying all brakes. The one fixed drum, instead of two loose ones, is a decided advantage when using coolie labor as there is just one-half the chance for an accident.
Double-cylinder 10 by 12-in. second-motion air hoists are used for operating winzes and 6 by 12-in. double-cylinder hoists for sinking. The large Holman stretcher-bar hoist is often used for the first 100 ft. in sinking. Small Holman 3 by 5-in. double-cylinder stretcher bar hoists and Little Tugger hoists are used for the stopes and rises.
Air Compressor
Compressed air is supplied by the following compressors:
1 Robey compressor, rope drive, 800 cu. ft. free air per min.; air cylinders 12 and 20½ by 30 in.
1 Ingersoll-Rand, imperial, type 10, 900 cu. ft. free air per min.; high-pressure cylinder 12 by 16 in., low-pressure 20 by 16 in.; belt driven.
1 Ingersoll-Rand, class P.R.E. 2, low-pressure cylinder 25 by 18 in., high-pressure 15¾ by 18 in., speed 214 r.p.m., motor 344 hp.; capacity of air in three stages: Full load 2370 cu. ft., 432 hp.; three-fourth load 1778 cu. ft., 321 hp.; one-half load 1185 cu. ft.; 255 hp.
The motors for the compressor plant are supplied from the low side of a substation receiving 33,000 volts and stepping it down to 550 volts; they are as follows:
On account of the large number of induction motors on the circuit of the mine, mill and smelter, this synchronous motor has been most beneficial and has brought up the power factor considerably. Another large synchronous motor has been ordered. One 350-kva. transformer at Tiger camp and two 350- and one 700-kva. at Bawdwin transform the necessary power for the mine.
Air is delivered into two air receivers (5 ft. 3 in. in diameter and 12 ft. long and 5 ft. in diameter and 13 ft. long) and then through a 10-in. steel pipe into the mine.
Ventilation
The ventilation of the mine is by natural draft assisted by mechanical means. Practically all air enters the mine through the Tiger tunnel and a shaft at the extreme north end of the Chinaman orebody, which is connected to each level. As the air enters the portal of the tunnel, it travels 7200 ft. before entering the actual mine workings. Here the current splits and passes up the various raises and winzes, spaced at least every 100 ft. along the vein, from level to level until it reaches No. 1 level, where it is accelerated by a 100-in. Sturtevant fan and discharged from the mine. This fan simply accelerates the natural draft and consequently increases the volume of air. It exhausts 70,000 cu. ft. per min. running at 579 rev. and driven by a 70-hp. motor. Although it is doing the required work, its speed is too great for efficiency and consequently consumes too much power.
As space is limited, the fan, which is a 100-in. double-inlet single-width, will be replaced by a 110-in. double-width occupying practically the same space and decreasing the power by about 50 per cent, for the same volume. At the same time it will be able to take care of a larger volume of air if required.
Lighting
Three General Electric lighting transformers, each 15 kva. 200 volts, located underground and at different parts of the plant supply the necessary electric lighting for bungalows, surface plant, main adits, haulage levels, shaft stations, and underground stores. The bulbs of all lamps are etched with the name of the corporation to prevent theft and sale in the local bazaars. Carbide lamps are used underground by the European shift bosses and candles by the coolies. These candles are of good quality and are made in the country by the Burmah Oil Co. They are colored green to prevent theft and sale but without avail. They cost Rs. 0.42 per pound.
The coolies were originally provided with three candles for an 8-hr. shift, but as they work in twos and fours it was observed that a group of four Chinamen working together would seldom have more than two candles burning at one time. The extra candles were taken home, collected, and finally sold in the bazaars of local towns. It is safe to say that the mine was furnishing light for the surrounding country. Candles have now been cut down to two for each coolie and still they have enough left to light their own homes and sell some to their neighbors. In a mine of cheap labor, the lighting account is large. In this particular mine it is the fourth largest separate account, being next to repairs and maintenance.
Telephones
A telephone system is installed at the supply stores on each level. A clerk is continually on duty and prevents meddling by the coolies. Originally, all the telephones were on the same circuit but this was found unsatisfactory for when one line became broken, which is often the case in a mine of heavy ground, all the telephones were out of commission; when defects or short circuits appeared they were more difficult to locate; the level clerks were continually using the phones for social conversation and it was difficult to get a message through. A small exchange was placed at No. 2 level store and separate lines run to each level; this system, although requiring a larger expenditure, is highly satisfactory.
Timekeeping and Store Checking
As many coolies have the same name and look alike to the new arrival (Europeans), it is necessary to give them a number; this is a round metal tag upon which the number is stamped. When he receives it, he is told in Chinese what number it bears and rarely does he forget his number or the appearance of the numerals on it. In a day or two, he can pick his number out of several disks and often will be able to call it out in English. Together with the brass disk, he is given a ticket bearing his number, rate of pay, and 15 spaces for the days of the half month. Each morning, before beginning his work, he appears at the time office and calls out his number; the disk is taken off the board and given to him. After the shift has passed through the time office, the number of tags remaining on the boards shows the timekeeper those who are absent and he can then make up his payroll sheet for subsequent checking. Checkers go underground and again check the coolies in their working places and make the required shift allocation. On coming off shift, the coolie is searched by the police (as he will steal anything no matter how small, as everything is of value to him if he gets it back to China) and presents himself again at the time office, where he hands in both his metal disk and his ticket. The former is put on the board and the latter (ticket) is punched for that day. In this way he can see at any time how many days he has worked and arguments at pay day are avoided. However, he is not paid on the ticket, that would be to his liking however, but from the actual pay roll which is kept up daily. The ticket is for his identification; if he loses it without reporting the fact, the company is not responsible if the pay envelope is delivered over to the presenter. New coolies use many ingenious schcmes for punching their own tickets when absent, thinking they will be paid according to these, but when they find out it does not work and calls forth a penalty they do not do it the second time.
Tools of all kinds, dynamite, fuse, caps, etc. are of great value to the Chinese coolie when he goes home, consequently on issuing these articles certain precautions must be taken or they will not be returned. On every level there is a supply store where the coolie can get any tool or article he requires, but he must deliver to the issuing clerk his pay ticket as security until he returns the articles at the end of the shift. If the tools are not returned, his pay ticket is turned into the office with the list of tools and he is fined, or the matter is brought to the attention of the mine foreman.
The system of timekeeping and underground store checking has been gradually developed from our experiences, and is now the simplest and most satisfactory to all concerned. The Governments of India and Burma have stringent laws concerning the use of explosives and any quantity found in the possession of coolies is investigated; and the mine management is held responsible for any that gets out of its possession. Notwithstanding the punishment (which is both corporal and imprisonment) coolies are caught every week by the police guard, attempting to take explosives out of the mine.
Records of Unit Production
An average month is taken as the basis of the following calculations (14,643 long tons per month).
Stopemen are paid on a bonus system on the number of sets of ground taken out and timbered regardless of the tonnage contained therein as the ore may be low or high grade. Development is also paid on the bonus system, but on the footage advanced and timbered; other excavations, on the sedrum (100 cu. ft.); loading ore from bins, on tonnage.
It requires the following men (8-hr. shifts) to mine and timber one set of ground and muck the contents into the chute:
17.4 miners per set One set in ordinary ground removes 270
6.6 muckers per set cu. ft. or 27 long tons of ore.
24.0 men per set.
1.55 long tons per miner in stope for 8 hr.
4.10 long tons per shoveler in stope for 8 hr.
1.10 long tons per each man in stope for 8 hr.
11.00 long tons per each man on ore and rock in development for 8 hr.
0.54 long tons per each man underground for 8 hr.
1.16 long tons per each man engaged on surface including office.
0.37 long tons per each man of total organization.
Classification of Labor
As already mentioned, a large proportion of the labor is seasonal. The Chinese in large numbers come over at the beginning of the dry and go away at the beginning of the wet season. The turnover during the 6 months, November to April, is generally over 11 per cent.
Records of Units of Supplies used per Ton of Ore Produced
The explosives used per long ton of ore produced are 0.36 lb. 50 per cent, gelignite, 3 ft. Bickfords fuse, 0.55 No. 7 detonators.
The timber required per long ton of ore produced is 0.38 cu. ft. logs, 0.33 cu. ft. sawn timber, 0.30 cu. ft. 8 by 2-in. lagging, 0.27 cu. ft. 8 by 3-in. lining boards and cribbing or a total of 1.28 cu. ft. of timber.
The power required is as follows:
Also, 10,000 cu. ft. free air compressed to 90 lb. were required per ton of ore
Safety and Welfare Work
Notwithstanding so many coolies are employed who have never handled explosives or worked underground before, the fatal accidents are very few; there has been only one fatal accident due to explosives in five years.
No safety engineer is employed; but by making each European shift boss responsible for his level and by providing him with all necessary material and instructing him that the safety of the coolies comes first, the mine has been made comparatively safe. Extreme sanitary precautions are taken to avoid epidemics, which are so prevalent in the tropics—such as plague, cholera, relapsing fever, and other contagious diseases which wipe out villages in a few days. Fresh drinking water is piped to every level and many of the working places, and at suitable places on each level latrines are provided. At first, great difficulty was encountered in getting the different types of Indians and Chinamen to use the same latrines, but by most persistent work on the part of the European staff, with the aid of heavy fines and dismissals, the mine has been brought to a stage where for safety and sanitation it will rank with the best mines employing Europeans only.
Free medical attention is given to all natives and employees on the corporation property, and hospital accommodation for those that require it. The hospital and sanitary department is one of the largest and best in Burma.
For recreation, the corporation has provided clubs with tennis courts, both for Europeans and Asiatics, and is now trying to become a member of a cinematograph circuit. A first-class race-course has been built, to which everybody migrates on the only two holidays of the year— Christmas and Boxing Day. All the employees with their families are there: from the iron mines, a day’s journey by train, from all parts of the forest, from the power plant (100 miles away), from Bawdwin (the lead mines), the mill, smelter and all the stations along the corporation’s railway. They travel by train, ox-cart, pony, and afoot. Many of the Europeans and natives own their own racing ponies.
