The mines operated by the South American Development Co. are located in the Zaruma mining district of southwestern Ecuador. They are near the old mining town of Zaruma, which is the only important city in the canton of the same name. The district is situated in the upper end of a valley lying between two spurs of the Cordillera, one of which may be considered the Coast Range and the other an intermediate range. The mining camp proper, known as Portovelo, and the plant are 2.4 km. south of Zaruma, on the north bank of the Amarillo River, a tributary of the Tumbes River, which flows southwestward through Peru to the Pacific.
Portovelo is difficult of access; it is reached from Guayaquil by means of river steamers and muleback. Embarking at Guayaquil, the route is down the Guayas River, across the Jambeli Canal, and up the Santa Rosa River to Santa Rosa, a distance of 177 km. From Santa Rosa, the road or trail follows the Santa Rosa River, then across the summit of the Coast Range into Portovelo, a distance of 74 km.—a two-day trip on muleback.
The mining property of the South American Development Co. comprises 297 lode claims and 142 placer claims. The combined lode claims cover an area, roughly rectangular in shape, 9000 m. long from north to south by 4000 m. wide; the northern edge of the rectangle is about 3000 m. north of the central plaza of Zaruma. Mineral lands in Ecuador are held by virtue of an annual tax per claim paid to the central government, no surface rights being included.
The Zaruma mine has been worked by white men since 1549, probably before that it was worked by Indians. The followers of Pizarro, led by traces of gold in the sands of the Tumbes River, followed that stream to its source, worked the gold veins that they found and established the city of Zaruma. Among the mines worked by them were the Sesmo, Leonora, Viscaya, and Mina Grande. Only the soft ores at the outcrop were mined, making many shallow openings, none being of any considerable vertical extent. Traces of these old superficial workings have been important in outlining recent development.
Foreign capital became interested in the district in 1875, when a Chilean company was formed to work several of the old mines. Its efforts met with little success, as did the attempts of a few small, contemporary, native companies; in 1880, an English company, the Great Zaruma Mining Co., was organized to take over the properties. Later this was reorganized as the Zaruma Gold Mining Co. and carried on operations for several years; it spent considerable money on road construction and the building of a 20-stamp mill. Sporadic efforts to open up the Fortovelo mine were made, some stoping was done, and some bullion shipped. Later, the South American Development Co. acquired the rights and property of the English company, together with those of other smaller companies; it has since increased, its holdings through purchases and denouncements. Since 1900, there has been continuous exploitation of the mines of the Zaruma mining district by practical modern methods.
At present, the mines are operated in three units, known as the Portovelo or shaft mine, the Soroche, and the Jorupe. In addition, considerable work has been done in opening and prospecting other old mines of the district.
The mines are located 610-914 m. above sea level. The district is rugged, being cut by many small ridges and streams. The climate is tropical to subtropical, the temperature ranging between 82° F., at mid-day, to 62° F., at night. The dry season extends from about the first of June to the last of December, with occasional showers, and the wet season from December to June, with late afternoon showers; the average annual precipitation is about 70 inches.
Power is obtained from the Amarillo River through two canals, the water being used on turbines or Pelton wheels and the power used directly or converted into electricity to be transmitted and used in various operations.
For timber, the mine is dependent on native supplies; that within a radius of 5 miles has already been used. Native contractors supply all timber, dragging it in with mules during the dry season. The maximum size of round timber is 12 in.; and of squared 9 in. in lengths up to 10 ft. Timber is not seasoned, for it appears to last better when placed underground in a green condition. The hard, heavy woods, sanon and amarillo, are used extensively for timbering and tarapo in 4-in. poles for lagging. While the woods are very hard, they are short- fibered and do not withstand blasting well.
The mine freight from the coast, averaging about 750 tons yearly, is brought in on muleback during the dry season, by contract. The cargoes are arranged in loads of about 200 lb. per mule. Some heavy pieces are slung between two mules while a string of mules is used to carry cables, each carrying sufficient coils to make a load of 200 lb.; exceptionally heavy pieces are lashed to bamboo poles and carried by relays of men. The company has improved the trail in many places, cutting out fords and paving muddy places. The movement of freight from the coast costs about $35 per ton, hence high-grade material is used throughout the operations— high-strength dynamite, high-strength cyanide, special alloy steels, etc. Supplies are ordered through the New York office and purchases are made to the best advantage either in the United States or Europe. Delivery is made at Puerto Bolivar, where it is placed in river steamers that carry it to Santa Rosa, the lower terminal of the mule trail. The long time between ordering and delivery at mine necessitates placing the orders nearly a year in advance.
The mine labor is nearly all native Ecuadorian (a mixture of Spanish, negro and Indian); a few Columbians, Peruvians, and negroes also are on the pay roll. Bonuses are paid to men working 20 shifts or more per month, but the many religious holidays interfere materially with steady work. Nearly all work is done by contract. There is one pay day per month, but the men may draw from day to day the greater part of what is due them.
The Ecuadorian unit of currency is the sucre, with a par value of $0.4878. Recently it has fluctuated through wide ranges, therefore it is practically impossible to give the operating costs in dollars.
Granites and syenites, connected with gneisses and crystalline schists of Archean age, are the dominant rocks of the eastern range or main Cordillera, while in the Coast Range and inter-Andean country greenstones and porphyries are found in connection with Cretaceous formations.
The gold-quartz veins worked by the South American Development Co. occur in a belt of greenstone. The dominating structural feature (shown in Fig. 1 by the heavy line) is a major fault zone, known locally as the Abundancia fault, that has been traced several kilometers on the surface. Its general strike is N. 3° W., with an average dip of 65 to 68° to the east. Underground workings have opened up this fault for about 2000 m. along the strike. It is always strong and well defined, with a heavy gouge indicating a great deal of movement, and contains more orebodies than any of the other known fissures. Several lesser fractures making away from this fault at small angles are ore carriers; these are known as Cantabria, Portovelo, Soroche, Twenty-six, Nudo, and Quebrada veins. Tamayo and Jorupe veins are outlying fractures; their relation to the Abundancia fault has not been proved but they are commercially valuable. The San Guillermo vein, worked in the Soroche mine, is without doubt a development on the Abundancia fault proper and should not have a separate name. The Agua Dulce vein, which is in the development stage and on which some ore has already been found, may . be an extension of the Cantabria system of mineralization. What is known as the Portovelo vein, in the southern part of the property, is really an Abundancia fault, and should be known as such.
The rock in either wall of the fault is dacite. Near the veins it is considerably altered. The width of the altered dacite at the southern end is about 15 m., while at the northern end where there are more branch veins, the zone is 200 m. wide.
About 2.7 km, from the Soroche mine is a sharp conical peak of rhyolite; it is quite possible that the veins of the Zaruma district are genetically related to this intrusion of rhyolite.
The veins as developed along the Abundancia and Portovelo faults are composed of an intergrowth of quartz and massive calcite, with subordinate amounts of iron and copper sulfides, sphalerite, and galena. Considerable gouge is present on the foot wall, indicating much movement; and in some of the stopes, pronounced brecciation and recementing of the breccia is distinctly evident, showing at least two stages of mineralization. Some of the branch veins have different characteristics, indicating different periods of mineralization. The Twenty-six vein, in the upper levels, is practically pure quartz; but, with depth, it approaches the Abundancia type. Soroche and Tamayo veins consist of ribs of hard quartz, alternating with soft sugary quartz and without calcite. Cantabria, Nudo, and Agua Dulce veins, while having quartz and calcite in normal quantity, carry an excess of sulfides. Jorupe vein carries little calcite but large amounts of sulfides. It appears as though the gold-bearing solutions were introduced into the various fissures through the Abundancia fault, but penetrated only a certain distance from it. In all veins where high-grade ore is found, tetrahedrite is present.
The major fault, the Abundancia, represents the oldest of a series of faults; all others are of minor importance. The other veins never break through the Abundancia fault, but have a tendency to flatten against it and parallel it before they pinch out.
The veins as opened by underground workings on A level, or projected on to that level from others where they have been opened up, are shown in Fig, 1. Abundancia fault, while easily traceable throughout the lateral extent of the underground workings, is not always marked by the pres-
ence of vein material. The sheets of quartz and calcite, some minable and others almost barren of precious metals, occur in large lenticular masses. They have the strike of the fault plane, in general N. 3° W., and its dip of 65°-68° to the east. These lenses may extend vertically 200 m., while the greatest length opened up on any one level is about 80 m. Stoping widths of 1 to 6 m. are found. The lenses have a rake to the north with dip of 65°-70°, and may be found anywhere along the fault; seemingly, there is no rule as to the position where one may be expected, although large orebodies have been found near the junctions of Abundancia vein with the Portovelo and Cantabria veins. As a rule, the extent of the orebody is less than that of the quartz lens; or in other words, the lens is not all ore. Some lenses have more than one oreshoot, and others are entirely barren of ore. They apex at different altitudes, not all of them cropping at the surface, and pinch out at variable depths. The valuable portion of the vein may lie on the foot wall at one elevation, and on the hanging wall at another, the oreshoot proper consisting of overlapping lenses within the main lens. The difference between ore and waste is not discernible to the eye, hence the necessity for close sampling. True walls are present, with considerable gouge, especially on the foot wall. A false foot wall, characterized by a strong slip, is often found. Between it and the true foot wall, there is commonly from 0.30 to 0.75 m. of low-grade quartz. The walls will not stand after mining the vein, but break well back on both sides to parallel slips within the fault zone. Many tongues of quartz follow minor fractures out into the hanging wall away from the main body, but never beyond the hanging wall of the fault zone proper.
Twenty-six vein is short, only 100 m. long on the longest level. It has only one oreshoot with a depth of 150 m. In the upper part, it is a hard white quartz averaging 1 m. wide. Calcite appears in depth, where it grows wider and is of low grade.
Cantabria vein is a fracture making away from Abundancia fault to the northeast. It holds many orebodies, generally lenticular in form. The ore extends from 150 to 180 m. below the surface. The most intense mineralization is near the fault; here the company worked to a depth of 200 m., the length of the oreshoot being 85 m. and its width 4.5 m. Cantabria is the most base of all veins worked, galena, sphalerite, chalcopyrite and pyrite being present. Its walls are not well defined except at the junction with Abundancia fault.
Soroche vein makes into the Abundancia fault from the foot wall side; it has made several good sized orebodies. It has a banded structure of alternate ribs of hard and soft quartz with little calcite or sulfides. There are no walls. Stringers of quartz lead out from the main body into the foot and hanging walls and many overlapping kidneys of ore are found. The vein itself is badly broken and has numerous pockets of high-grade ore. The average stoping width has been 2.74 meters.
Tamayo vein has not been connected with Abundancia fault so far. Its ore lies in overlapping, slightly offset lenses of quartz that strongly resemble those of the Soroche vein. Some sulfides are present and it is strongly oxidized in the upper levels.
The Jorupe vein is composed of very hard massive quartz and the base sulfides. Several oreshoots have been developed, on one of which stoping has been started.
The ore deposits of fault planes and fissures of the Zaruma district have a dip of 50° from the vertical, usually to the east. The oreshoots vary in length and width and may apex or bottom at any elevation. They rake usually toward the north. There is no secondary enrichment and values bear no relation to topography. On account of thick soil and undergrowth, outcrops of ore are found with difficulty, except upon the sharp ridges and in the deep ravines, where the surface is worn to bed rock.
Preliminary exploration is generally carried on through adits. Depressions resulting from the cavings of old workings, dumps, etc., have often guided exploration. The abandoned workings are seldom found to contain ore; they were quite thoroughly mined to the water level, but they indicate where ore may be found at greater depths.
Prospect tunnels are driven on the vein or in the walls, depending on the character of the formation. Where the vein is wide, frequent crosscuts are made to the wall; and where it pinches, crosscuts are extended into foot and hanging walls in search of overlapping veins. Following the development of ore on one level, additional levels are opened 30 m. above or below the first, depending on the surface contour, and raises are put up at intervals of 30 meters.
Close sampling is the practice wherever a vein is exposed. Channel samples are moiled from the face and back 1 m. from each other, about 15 lb. being cut per meter. The samples may represent the whole width of the vein, or may be split as the character of the vein changes. The usual records and sample maps are preserved.
In the stopes, the faces are frequently sampled under the direction of the mine superintendent for the purpose of directing the daily work. Once every 6 months, the entire stope surface is sampled and mapped just as the drifts are sampled, and tonnage estimates are made, using 2.9 tons per cubic meter. Because of the indefinite walls at many places, the tonnage recovered is usually larger and the values lower than estimated from moil sampling.
In the early Spanish days, mining was conducted in the customary crude manner. The ore was followed in depth to water level, usually about 100 ft., leaving low-grade ore for pillars. The ore was carried out, the men using chicken ladders, steps cut in the walls, or built of masonry. The Spaniards left no ore that can now be mined at a profit.
The first work done by the South American Development Co. was through adits, the principal working adit being known as A level. Many large oreshoots were found above this level and worked out with filled stopes on the rilling system. The usual procedure was as follows: After the development of an orebody by drifting, a lateral was driven parallel to it about 6 m. in the foot wall, and crosscuts were broken through from the lateral to the drift at 20-m. intervals. Raises were then driven through to the surface from alternate crosscuts. The orebody was next silled off from wall to wall, as high as the ground would stand without timbering. Rills were then started from the raises, and the ore stoped above the fill which was introduced from mill holes on the surface. The broken ore was shoveled from the toe of each rill and later was handled through chutes built in the crosscuts. Costs were low by this method.
Some time later, the shrinkage system was adopted. This change was hastened by the fact that the stopes were located farther and farther away from the surface, making it increasingly difficult to get the cheap surface fill. Moreover, this fill was not altogether satisfactory. It was composed of surface wash, badly weathered, mostly very fine and not possessed of sufficient body for good fill. As it was worked into the stopes in quantities, a mill hole was formed around the top of each filling raise or chimney. During the rainy seasons, these mill holes had to be bulkheaded off to hold back the accumulated mixture of surface wash and water.
In order to work the deposits on the Abundancia and Portovelo veins lying below A level, the American shaft was sunk; it is collared in the hanging wall a short distance south of the intersection. This location was advantageous because it was close to many large, high-grade stopes on both leads, but disadvantageous because of the temporary loss of good ore left in the shaft pillars. At this time, stoping by shrinkage reached its maximum development. Shrinkage stoping of the narrower oreshoots on the northern end of Cantabria vein was a success. The walls were firm, standing very well, and the ore suffered but very little dilution through the admixture of waste. On the wide orebodies of the Cantabria vein near its intersection with the Abundancia fault, and on the ore-bodies of the Abundancia and Portovelo veins, shrinkage stoping was not so successful. After drifting and opening the veins to their full width, the stopes were either cut out for a height of about 4.57 m. above the rail, timbered, and breaking carried up on the timber; or box-hole raises were driven for chutes, the raises being lengthened both ways on the strike of the vein, connected a short distance above the level, and the stope carried up from them. This system was efficient as far as low breaking costs were concerned, but a large percentage of the ore in any orebody was lost. In the first place, it was impossible to delineate clearly the outlines of an orebody as irregular as these; and, in the second place, much ore was lost through caving of the walls in great slabs so that the ore was hung up and left behind in the stopes. Even when the walls did not cave, there was a loss in the ore that clung to the foot wall when drawing the stopes. There was also dilution of the ore through admixture of waste from the walls.
In late years the shrinkage system of stoping has been abandoned almost entirely, there being a reversion to filled stopes of the horizontal cut with back-fill type, or the modified rill with waste obtained from development on the upper levels or broken in waste raises at the head of the rill. Costs are higher, because of the extra cost of breaking and handling fill and the extra handling of ore in the stopes, but a close examination of the records shows that up to 40 per cent, more ore is obtained from a given orebody. The ore is also kept much cleaner, as considerable waste is sorted out and left in the stopes for fill. In high-grade stopes, however, there is a chance for loss through the mixture of fines with the fill. After blasting rich ore, it has paid, in some instances, to remove the upper layer of fill, to a depth of 0.61 m. (2 ft.) and send it as ore to the mill. The development of the Soroche mine, or that part of the property lying adjacent to the northern end of A level and extending about 152 m. to the surface above, which has taken place during the last four years, is chiefly responsible for the change in practice. The ore-bodies in this mine are characterized by the lack of definite walls, the overlapping lenticular structure being decidedly pronounced, and the walls extremely shattered and heavy. Many of the stopes must be closely timbered and then filled tightly as soon as possible to prevent caving. The finding of so much ore in the walls led to the adoption of this method on the other veins with similar results.
Previous to the installation of the modern cyanide plant, which began operations in April, 1919, the milling practice was straight amalgamation, followed by a rough classification and cyanide leaching of the sands. The extraction was low, as well as the tonnage. For some years, selective mining was carried on and the mill heads kept at $18 or better, so that operations might be carried on at a profit. This resulted in taking the cream of an orebody, with much lower grade material left unbroken as pillars and on the ends of the old stopes. A considerable part of the present tonnage is derived from working the edges of these old stopes; the cut-and-fill system is admirably adapted to the extraction of this ore. The operation, on the whole, is similar to that of any cut-and-fill stope, except that the old adjacent stope must be filled as well as the actual working stope; see Fig. 6.
The combined Portovelo and Soroche mines are now worked through a shaft and two adits. The collar of the American shaft and A level are at the same elevation. The levels above A level, known as B, C, D, etc., are driven 30 m. apart. Mining is being done on D and E levels, while A, B, and C are on development work. Ore from above A level is passed through rock chutes to that level and transferred to the mill by mule train. Waste is used in filling stopes either above or below A level.
Eight levels are turned off from the American shaft at intervals of 30 m. each. The shaft has two compartments down to the seventh level, then three to the ninth, and two below to the depth of 320 m. Sinking will continue to a depth 343 meters.
The greatest lateral development is on the third level, which has been opened up for 420 m. to the south of the American shaft and for 920 m. to the north. The levels of the Soroche mine overlap those of the Portovelo mine (American shaft) on the south and extend 360 m. beyond the north face of the third level. Increased depth is gained by following the Abundancia fault to the north, the country rising in that direction. The combined length of the lateral openings of the Portovelo, Soroche, and Jorupe mines, including the outlying prospects, is over 35 kilometers.
The usual method of development is to drive a crosscut, to the vein to be developed, from the American shaft, in the case of the Portovelo mine, or from the working raise in the Soroche, perpendicular to the Abundancia fault, then turn off drifts both north and south. Drifts are run on the foot wall with crosscuts to the hanging wall at frequent intervals, in high-grade ore; and at greater intervals in low-grade ore or waste. When the faulted area is barren, laterals are often run paralleling it, with occasional crosscuts to the fault for exploration. This avoids the necessity of timbering, which must always be done when following the faulted area.
When an orebody is outlined, a raise is generally driven to the level above, for the purpose of further developing the block, for ventilation, and to serve as a working raise for stoping. The method of stoping to be used is then decided. If the orebody is to be stoped through a lateral, this is driven in the foot or hanging wall, and chute raises are broken through; otherwise the stope is cut out or box-holed over the drift for stoping by shrinkage or by the cut-and-fill method. During the last ten years, about 25 tons of ore have been developed for each meter of development.
Nearly all development is done by contract. The contractor pays for all supplies, including timber, but excepting tools, drill steel, oil and air. Track and pipes are laid by the company; it also pays for the timbering in headings.
Sinking, Stations, Pockets, Etc.
Native labor is extremely inefficient on sinking, 10 m. per month being about the maximum attainable. For drilling No. 55 Clipper, No. 95 Waugh drills, and B.C.R. Jackhamers are used. Blasting is done with 1 in., 60 per cent, gelatine, using ordinary fuse and caps. Local timber will not withstand the shock of electric blasting and delay-action primers are too complicated for the native workmen.
Ordinary shaft sets are used; 7-in. timbers being placed on 6-ft. centers. Formerly bearers were of squared timbers hitched into the walls. At present, bearers are made of concrete, poured in place, and reenforced with old rails and twisted rods. The hoisting compartment is lagged throughout on all sides with 3-in. plank; the other compartments are lagged only where the ground requires it. The guides are of 4 by 6 in. timbers, with notched lap joints, and are lag-screwed to the end plates and centers. Two small auxiliary hoists have been used for sinking, the dirt being raised in buckets to a pocket at a level above. A No. 6 Cameron sinking pump handles the water during sinking operations.
The stations at the levels are small, no car capacity being required. Ore pockets up to 175 tons capacity and waste pockets of 10 to 15 tons capacity are provided at each level. Grizzlies, made of 30-lb. rails and having 1-ft. square openings, cover each pocket.
The drilling machines used in the headings are the No. 21 Turbro with 1¼-in. round hollow steel and the No. 50 Clipper and No. 93 Waugh with 7/8-in. hollow hexagonal steel. The Turbro is too heavy for the average native and is only used in very hard ground. Average advance is about 20 m. per month. There is nothing peculiar in the method of advancing the faces, except that in the hard veins, consisting of quartz and massive calcite, a larger number of holes is necessary; the calcite makes the ground tough and hard to break. Headings are driven 5 by 7 ft. in the clear and the average round pulls 1.1 to 1.2 meters.
In addition to the machine work, over one-half of the total advance is made by hand, chiefly because a great saving on compressed air is made, the compressor capacity not being sufficient to do all of the necessary development by machine. Hand work is also cheaper from all other angles. Single-jackers are paid lower wages than machine-men, explosives are used more efficiently, and there are savings on oil, piping, drill steel, drill repairs, etc.
Most of the raises driven are stoping raises for blocking out the ore and for ventilation; later these serve as stope manways. Other raises are driven solely for ventilation and for permanent manways or safety exits, or for transfer raises for ore or waste. All raises in waste are driven as two-compartment raises; those in ore may have two or three compartments.
Drilling is done with No. 16V Waugh stoperor No. 71 Waugh stoper; 50 to 35 per cent, gelatine is used for blasting. An advance of 50 ft. per month is considered good work. A Little Tugger hoist is part of the equipment for all raises. Two-compartment raises are carried in the country rock, 11 by 5½ ft. over all. These are timbered as raised and lagged with polls or planks. Manway platforms are placed at intervals of 30 ft. The ends of the timber, as a rule, are not notched, cleats being used instead of notches. Centers are placed every 5 ft., and the rearing, or chute lining, is of 3-in. plank as before. Bulkheads are carried over the manway in all cases.
The shrinkage method of stoping was formerly used extensively, but as the walls are unsuited to its use, it has now been abandoned almost
entirely and will not be considered here, except as to the first steps which are practically the same for the cut-and-fill method that is now commonly used. The stopes are either cut out for timber, or box-holed for chute raises and manways; see Fig. 2. With the first method, two cuts are taken out of the back of the drift from wall to wall, leaving the back of the cutting-out stope about 16.4 ft. above the rail. The muck from this first operation is then cleaned up and timbering started. When the veins are narrow, sets of caps and posts are placed, the caps reaching from wall to wall. On the wider veins, timber cannot be obtained long enough for this purpose. The sets are placed and blocked temporarily, then pole lagging is placed back of the posts of all sets, and the space between the lagging and the walls filled with waste to the level of the caps. Sets are placed 4½ ft. center to center.
Chute mouths of double 3-in. plank are built at every third set. Two manways are generally carried up with the stopes, either timbered in the usual manner or cribbed. When a stope is started by box-holing, the raises are spaced at intervals of 16.4 ft. They are opened 5 ft. long on the level, this length being increased in both directions with each succeeding round, until they are connected about 16.4 ft. above the back of the level, leaving triangular shaped pillars between the chutes.
Practically all of the present stopes are worked by the cut-and-fill method. They are either carried on timber or worked through stoping laterals. In the first case (see Fig. 3) the stope is cut out and timbered in the same manner as a shrinkage stope, except that chutes are built in every fifth set. Cribbed chutes and manways are carried up through
the stopes. With soft ores, cribs of round timbers, unlined, are sufficient; with hard ores, the unlined cribs wear rapidly and are a constant source of trouble. Cribs of squared timbers lined with 3-in. plank are better for this class of muck. The round, unlined cribs are carried with the dip of the vein, no offsets being necessary. Cribs of square timber, plank lined, are carried up vertically with offsets, to facilitate the nailing of the lining in a secure manner. When stoping from a lateral, the lateral is driven parallel to the orebody at a distance of 5 m. in the wall; see Fig. 5. The foot wall is the preferable location, but in the case of parallel veins separated by a small width of country rock, one of the laterals must be driven in the hanging wall. The chutes are raised from the laterals to the stopes each 8 m., and are carried up with cribbed timbers. When working stopes in heavy ground, timber as well as filling must be used; see Fig. 3. Stope timbering is done after the manner of drift sets, with caps from wall to wall. The posts are stood on footboards placed on the fill, and the sets are 8 ft. high; they are spaced from 5 to 8 ft. center to center. Stringers of 6-in. round sticks are laid from cap to cap, about 1 ft. apart, and blocked down from the back. Filling closely follows breaking in these timbered stopes, the fill being kept close to the back. The posts are lost in the fill, but the caps and
stringers are recovered to be used on the next cut. Breaking of ore and waste in the cut-and-fill stopes is done with stoping machines of the No. 16V or No. 71 Waugh type, or with jackhammers of the Waugh No. 95 or Ingersoll-Rand BCR-430 types. As a rule, one or more horizontal banks are carried across the stope followed by filling, which is obtained by driving raises and crosscuts into the foot and hanging walls. A small
amount of fill is also obtained by sorting the ore in the stopes. In some of the stopes, part of the fill is obtained from development waste on the level above, this waste being dumped through the stoping raise. When waste is obtained in the latter manner, the stope may be rilled to this raise; see Fig. 4. Other rills are made by breaking waste in the end of the stope by raising on the barren vein, and then rilling to the waste raise; see Fig. 4. These raises serve the double purpose of providing waste and developing the vein. It is important that a part, at least, of the fill should be broken in crosscuts or raises in the walls, as these workings have the added value of being good prospects. They need not be long, as the overlapping lenses are always found within a few meters; often they are separated by only a shell of waste. The advantages of the cut-and-fill system are 100 per cent, recovery of the ore in any oreshoot; the ore is kept cleaner, as sorting can be carried on in the stope; and there is no admixture of wall rock, as when pulling a shrinkage stope.
The drilling in all stopes is done on a contract basis, the machine men receiving a fixed rate per meter of hole drilled. All holes are spotted by native stope bosses, and measured by them before blasting. Bonuses are paid to those machine men that work steadily and drill more than a
given meterage per month; the bonus takes the form of a higher rate for all meters drilled. Loading and blasting is done by the drillers under the supervision of the stope bosses.
An analysis of the cost sheets will show that, for the period from 1902 to 1908-9, the direct mining costs, including development, amounted to S/9.40 — S/9.50 per ton milled. During this time, the average yearly development amounted to 925 m. at a cost of S/57 per m. This period represents that in which the large surface stopes were mined by the rilled cut-and-fill method. The ores near the surface were softer, much more easily and cheaply mined, and the surface fill was cheap. Moreover, many of the stopes were above A level, so that pumping and hoisting costs were low.
During the period 1909-19, the direct mine costs were S/8.00-S/8.10 per ton milled; this includes an average yearly development of 1530 m. at an average cost of S/49 per meter. During this time, when shrinkage stoping was at its height, therefore, the mine costs were much lower in spite of increased development. A great part of the tonnage came from the American shaft, so that hoisting and pumping charges were inevitably higher. The cost of supplies during the latter years of the period, the years of the war, also was high. The bulk of the tonnage, however, came from the enormously large bodies of ore lying within a short distance of the shaft. A few stopes were sufficient to give the desired tonnage, and close supervision was possible; this fact accounts for cheap breaking, tramming, and total mining costs. The great disadvantage of this cheap mining lies in the high loss of broken and unbroken ore left behind in the caves that resulted when the stopes were pulled, or overlooked in the walls during actual mining.
From 1920-22, inclusive, the average direct mining costs were S/12.40-S/12.50 per ton milled. This seems to be a large increase, but can be accounted for in several ways. Shrinkage stoping had been almost entirely discontinued, the cut-and-fill method, by back filling or with the modified rill, having been adopted once more. This method undoubtedly requires more labor, resulting in increased costs. A minimum increase of 20 per cent, in the wages of all mine labor also went into effect at the beginning of this period. The costs of all supplies have continued to be high. Moreover, there has been a big increase in the quantity of development work done. In this period, an average yearly development of 3796 m. at a cost of S/51 per m. was done. While the cost per meter compares favorably with the costs of the preceding periods, the greatly increased meterage shows its effects in the total mine costs. Most of the big orebodies near the shaft had been worked out before this time. The tonnage came from smaller bodies at long tramming distances, or from the edges of worked-out and caved stopes. A great deal of filling had to be put into these old stopes before the remaining ore could be mined. Mining of the orebodies in the heavy ground of the Soroche mine has necessitated the use of a great quantity of timber, the first cost of which, together with its maintenance, constitutes a big percentage of the increase in total costs. More bosses were needed to cover the scattered workings and even then the supervision was not as close. The big advantage of this method of mining lies in the greatly increased tonnage gained from an orebody. All things considered, the cut-and-fill method of mining, with the stopes worked through stoping laterals, seems best adapted to the orebodies of the district. A tabulation of costs is as follows:
Records of Unit Production
The following figures have been obtained from one year of normal operation (1922).
Tons per man per hour for all underground and surface labor exclusive of office………………………………………………………………………0.0534
Man-hours per ton for all underground and surface labor exclusive of office …………………………………………………………………………………18.73
Tons per man per hour for all underground labor………………………………..0.0614
Man-hours per ton for all underground labor………………………………………..16.28
Tons per man per hour for all surface labor…………………………………………..0.4087
Man-hours per ton for all surface labor…………………………………………………..2.45
Classification of Labor, Expressed in Percentage of Total
The percentage labor turnover is unknown, but it is very high.
Records of Unit Supplies
Pounds of dynamite per ton of ore mined………………………………………..2.24
Pounds of dynamite per meter of development………………………….15.45
Pounds of dynamite per foot of development………………………………..4.71
Safety and Welfare Work
No safety organization of any kind is maintained, this work being left in the hands of the mine bosses. Due to the inability of the natives to take care of themselves, close attention must be paid to all working places. Obviously, the accident rate with this class of labor is high; the only surprising feature of it being that serious accidents are not more common. All serious accidents are reported to the local authorities in compliance with a compensation law passed in 1922. The company, however, has had an agreement with its employees for several years which is much more favorable to them than the compensation law.
The company hospital is the most modern and best equipped in the Republic. An American surgeon and trained nurse, together with an Ecuadorian doctor, are in attendance. All employees and dependent members of their families are given free treatment and medicines for all classes of cases without restriction. Many outside cases are also treated at the company hospital, this work being done for a nominal fee or free of cost. All prospective employees are subjected to a hospital examina¬tion, as a result of which they are passed for work or rejected as unfit. Those qualifying for employment are treated for hookworm, and classified as to their fitness for surface or underground employment. Many sanitary measures have been instituted, and strict enforcement of sanitary regulations is maintained.
A large boarding house is operated by the company for the benefit of the Ecuadorian employees, they having the option of boarding with the company or receiving an allowance of 50 centavos per day above wages. This boarding house is operated at a loss, using the amount of 50 centavos per day per man as a basis to figure from. Dwelling quarters at a very low rent are also provided for all employees who wish them.
The members of the staff are quartered in frame and concrete houses; married men being furnished with houses, and bachelors with single rooms. A boarding house is also operated for the benefit of the single men on the staff. House rent, lights, fuel, water, etc., are furnished free, as well as ice and distilled drinking water. Recreation is provided for in the shape of a clubhouse, tennis courts, baseball field, and swimming tanks. There is also a company stable, where staff employees horses and mules are cared for at a very small charge.
Rudolph Emmel, Quayaquil, Ecuador.—All the labor is very inefficient and the bonus system is the only way we can get anything at all. Drilling is done by paying so much per meter of holes. Drifting is done by contract on the basis of so much per meter.
George A. Packard, Boston, Mass.—That accounts for the apparently very low efficiency in man-hours per ton. At Cornucopia and at Jarbidge, the drillers in stopes practically average 2 tons per man per hour, or 1½ hour per man per ton; whereas at Zaruma the average is 0.05 ton per man-hour or practically 19 hours labor. Later the author shows that machine men and helpers on developing and stoping make about 32 per cent, of the labor, which would mean 60 man-hours per ton of ore or twelve times the requirement at Cornucopia and Jarbidge. This figure includes both the tons per man per hour in the shrinkage stoping and in the other; what is the production on shrinkage stoping alone?
Rudolph Emmel.—I have no figures on shrinkage stoping here; the figures given include all of the developments and we are doing an abnormal amount of development work. For a mine producing 225 tons, 4 km. a year is a large amount and tends to bring down that figure. However, the labor is very inefficient; it is incredible the small amount of work that one of those men can do in a day.
Fred Hellmann, New York, N. Y.—My experience in the mines of South America has been entirely different from that. The Chileans would compare favorably with drill men in any part of the world. I consider the Chilean one of the best drill men in the world.
R. M. Raymond, New York, N. Y.—It is largely a matter of the make-up of the men. Mexicans are rather fond of mechanical work. They make excellent men for running drills, do not mind dust, and work fairly steadily. They are good at any kind of machinery, even running hoisting machines. They are showing themselves adapted to such work in a surprising manner. How do the Bolivians compare with the Chileans?
Fred Hellmann.—The Bolivians cannot compare with the Chileans. They are not nearly as intelligent. The Inca race, as you know, was conquered by the Spaniards, and their present conditions testify to the inaptitude of the race and its weakness.
R. M. Raymond—How do the Chileans compare with the Kaffirs as to man power?
Fred Hellmann.—The Kaffir must be taught everything when he enters the mine, while the Chilean is much more intelligent. The Chileans are essentially a mining people. You can induce the Kaffir to do things, and under certain conditions he is a wonderful worker. The Kaffir can be taught to run a machine but it will take him much longer than the Chilean. I do not know how you could state it in percentage, but you would get possibly twice as much work out of the Chilean miner as out of the Kaffir.
In Bolivia, there are large mines but the results obtained could never be had by our methods of mining. If an American should go there with the intention of lowering the cost of getting out the ore by using more modern methods, he would soon find his mistake. They mine about as cheaply as is possible, though their methods are somewhat primitive. Access to the mine is usually given by a spiral stairway—the so-called Boca Mina—up which the ore is carried on the backs of the workers. It is hard to believe that you cannot improve on that, but the supply of labor is so great and the comparative cost of it so small that when you figure the cost of installing and operating machinery in a country that is not mechanically inclined, you find that the present is the better method. Of course mining 50,000 tons of ore a day is another kind of mining; that is done with steam shovels.
Arthur Notman, New York, N. Y.—The report of the Union Miniere du Haut Katanga for 1923 indicates roughly the number of men employed by the company for that year. There was no classification of labor or segregation as to operation and construction given in the report, but taking the whole number of employees as given, an output of 35 lb. of copper per man per day is indicated. Somewhat similar figures for the Chile Copper Co. indicate, for 1923, an output of 115 lb. per man per day. The output of the porphyry copper mines in this country runs from 150 to 190 lb. per man per day. Even after making due allowance for perhaps an extraordinary proportion of the labor on construction work in the Congo, it does seem as though the much higher grade ore and lower wages were pretty well offset by the low labor efficiency.
Fred Hellmann.—You have an entirely different type of labor in the Congo. The northern tribes and the tribes of central Africa are not nearly as husky and strong physically as the natives of the more southern parts. They are much weaker and much more subject to disease and death when they do work, especially under changing climatic conditions.
C. F. Jackson, Skouriotissa, Cyprus.—Labor is our chief problem; the technical problems would not be so bad if our labor did not keep undoing our work. For example, the other day coming out the main intake airway of the mine, we found a canvas had been stretched across the portal by some workmen employed nearby who wanted to shut off the chill air; sometime ago we sealed off a small fire but not long after some native opened a 9-in. hole in the wall with a pick. These people tear out ventilating doors, remove brattices, close doors that are supposed to be kept open and leave open doors that should be kept closed, and pick into pillars that are necessary to the maintenance of important airways and roadways. With good labor the work would be comparatively easy, but the Cypriot is the worst workman in the world to deal with; there is no punishment that he cares anything about so that it is next to impossible to discipline him.
Rudolph Emmel (Author’s reply to discussion).—The figures of 2 tons per man per hour at Jarbidge compared with 0.05 ton per man per hour at Zaruma is a comparison of the output of men directly engaged in stope drilling at Jarbidge with the output of all men connected with the work of the mine, underground and surface, at Zaruma. The figures used for comparison should be 0.4 ton per man per hour at Jarbidge (mining by shrinkage) against 0.05 ton per man per hour at Zaruma (mining by cut-and-fill methods). The mines at Zaruma also are undoubtedly carrying a much heavier burden in the nature of development work necessary than those at Jarbidge.
As to the efficiency of the Chilean miner, one must bear in mind that the Chilean is working under entirely different conditions from those that prevail in Ecuador. The Chilean is the product of the temperate zone, is physically and intellectually much superior to the Ecuadorean miner, and has had the benefit of a much closer contact with American and European labor and methods. We all know that the Mexican, when in competition with American labor, has developed to the point where he works side by side with miners of all nationalities in the United States, and has supplanted the higher priced labor to a great extent throughout the West. Chile is a very cosmopolitan country, is one of the most advanced of the Latin-American nations, and the Chilean workman has undoubtedly benefited therefrom. The Ecuadorean workman physically is a poor specimen, he has generations of hookworm and malaria and other diseases back of him, is working in hot, poorly ventilated mines in a tropical country, and has come into no competition or association with the outside world.