Bong Mining Co. in Liberia had a highly structured organization, not unlike many large mining operations in less developed countries. In many ways it resembled the organization of the old Braden Copper Co. in Chile as observed by one of the authors (JVT) in 1965. Basically, under a resident general manager, there were three groups. While the titles of the managers of the groups might be called by different names in an American-managed company, they were essentially, general manager of production, controller (or manager of administartion) and general manager of services.

Under the production manager (called technical manager at Bong), there was the geology and engineering group, mine, concentrator, pellet plant (a later addition not in the original facilities), mechanical department and electrical department. The mechanical department contained the central shops, railroad, port, power plant, water system and several smaller groups such as the motor pool. The controller´s department consisted of supply, accounting and data processing (computer center). The services department, which in an American company might have a title such as human resources or employee welfare, consisted of personnel including safety, and administration including housing, security, health, education and vocational training. The fore´going mentions only major groups. The only comment one might be tempted to make is that it would seem that the port rated a higher status such as being directly under the resident general manager or the manager of production rather than under the mechanical department.

Overall view in 1971. Mine across top. Primary crushed ore blending system, middle right. Concentrator, center, showing primary crusher and eight grinding line concentrator. No 1 pellet plant, lower right

The Expansions

Beginning in 1966, Bong started to expand, producing both sinter feed and pellets and ultimately reaching a combined production of 7,000,000 mtpy. The first expansion phase at the end of 1967 had increased production production capacity by a theoretical 16.66% with the additionn of a seventh grinding line. The daily capacity of concentrates was now 11,000 mtpd. The expansion of Bong over the years can best be illustrated in tabular and graphic form. The following table tabulates the production data through 1990. The figures for 1990 are estimates inasmuch as the operation was shut down in May 1990.

Mine Expansion

170-ton truck in 1975, gone are the original 45-ton trucks Mine expansion is illustrated on Table 7. Note that the mining machinery always got bigger and this was tracking developments in the rest of the open pit mining world. Note that Bong always bought American designed mining machinery until near the end when they bought a German-made DEMAG hydraulic shovel. (DEMAG was a pioneer in hydraulic shovels.) They also acquired frontend loaders when these machines became more rugged and dependable. Like most open pit mines of the period, machines did not wear out; they became obsolete and no longer cost effective. Most machinery can be maintained in perpetuity but they are retired because larger machines are more economical.

Concentrator Expansion

The concentrator in 1988 at maximum. Note the silos are not all the same size. Early on it was determined that even without expansion, there would have to be two primary crushers and they lasted, after redesigning, for the life of the operation. The expansion did not follow the symmetry of the original six grinding lines. By 1967, the seventh autogenous mill was somewhat larger than the original 22-ft. by 7-ft. mills. See table 8. By 1973, there were two 22-ft. by 8-ft. mills and two 24-ft. by 8-ft. mills, and by 1987 there were four of the 24- ft. mills for a total of 12 autogenous mills. As the ore became less weathered and hence harder, some mills were charged with large balls and became semi-autogenous or SAG mills.

Humphreys Spirals in concentrator 1976. The Humphreys spiral sections were always 1:1:1 ratio, roughers, cleaners and recleaners. Spirals were added to meet increasing throughput. The same abandonment of symmetry followed in the regrind ball mills grinding cobber concentrates from the spiral tailing. They were not in a ratio of one to one with the autogenous mills. By 1978, there were 10 ball mills, eight were 10.5-ft. by 14-ft., one was 12.5-ft. by 25.5-ft., and one was 14.5-ft. by 29-ft. As the ratio of hematite to magnetite changed to produce more magnetite hard ore, more ball mill capacity was needed. There were many changes in size and use configurations of magnetic separators over the years as the various flowsheets indicate. They were always permanent magnet type drums. At one time screw type classifiers were used on the spiral concentrate in attempt to classify out theminus 150 mesh in order to bypass it to the pellet plant feed. This effort failed and the spiral concentrate was later scalped with magnetic separators which achieved the same purpose.

One of the outstanding additions to the concentrator was the primary coarse ore blending systems. This was completed in 1970. This was quite simply a remarkable installation. Few people would attempt to distribute, blend and reclayim minus 12in.x 0 raw ore. It was known from the beginning that it would be difficult to maintain a uniform feed to the concentrator in terms of soft/hard ore mix and iron grade. There was a limit to shovel blending in the pit; however the blending system did not totally eliminate shovel blending. Blending prevented wide swings between hard and soft ore. This would affect performance throughout the concentrator. With the blending system it became more practical to go to larger shovels in the pit. The facility had a capacity of 2650 mtph input into two parallel blending piles vovering a total area of 2625-in. x 330-ft. holding 250,000 mt. Reclaiming wass done by two bucketwheel bridge type machines at a rate of 2000 mtph, which was later replaced by a larger reclaimer having a capacity of 3000 mtph.

The First Pellet Plant

Close up view of the pellet plant. One of the kilns is shown at center of photo A pellet plant of 2,000,000 mpty employing the Allis-Chalmers grate-kiln system was to be ready at the end of 1970 for start up in late 1970 or early 1971. The Bong operation would then have a name plate capacity of 2,000,000 mtpy of pellets and 3,000,000 mtpy of sinter feed by early 1971. The major items in the pellet plant started with a 3,000 ton capacity feed bin. (The feed was almost all megnetite from the magnetic section of the concentrator.) There were two ball mills 29ft. by 14ft.4in. of 4,000hp each. They discharged open circuit into an 800mt slurry mixer. The slurry was filtered on eight Eimco disc filters. Balling was accomplished with six drums 10ft. by 30ft. in closed circuit with 6ft. by 14ft. screens. The grate was 17ft.5in. width by 95ft.long (effective length). The kiln was 20ft.x144ft. There was a rotary cooler 56ft. in diameter with a bed depth of 8ft. The pellet storage area held 50,000 mt with a reclaiming system to load cars at a rate of 1000 mtph.

The Second Pellet Plant

Ultimate Pellet Plant Folwsheet The second pellet plant came on stream in November 1977 and the two plants had a combined capacity of 4.8 million mpty (the second pland was essentially the same as the first). Additional feed blending capacity was provided ahead of the plants involving two blending piles of 100,000mt each with a reclaiming capacity with bucketwheels at the rate of 1200mtph. The initial 1971 plant did not have reverse flotation for silica removal but it was added in the 1974 pellet systems. The following figure shows the flowsheet of the pellet plants as of 1978. Pellets assayed 64.5% Fe and 7.5 SiO2

In 1980 the original pellet plant was shut down due to high energy cost and market decline in pellets. Production from the number two plant was increased to 3,000,000 mpty of pellets. When the second pellet plant was in the planning stage it was justified but the high cost of energy and the unexpected decline in demand for pellets resulted in the shutting down of the number one plant. German steel mills, given their choice, preferred sinter to pellets and a cutback in production of steel would encourage them to use their sinter plant capacity in preferrence to Bong pellets. The first pellet plant was not as efficient as the second and it was never restarted. An effort was made to sell it to the Chinese but nothing came of it.

Industrial and Social Infrastructure Expansion

The following table shows the expansion additions of infrastructure.

Year 1967 1973 1978 1980 1984 1989
Production mtpy 3,408,000 6,208,000 7,151,000 6,898,000 7,068,000 7,100,000
Power Plant 4-8000kW Sulzer diesel electric units 4-8000kW 4-9000kWSulzer diesel electric units 4-8000kW 9-9000kWSulzer diesel electric units No additional units No additional units No additional units
Railroad major items only 129 ore cars 65 ton; 2-diesel hydraulic switch engines 176 ore cars 65 ton; 3-diesel hydraulic switch engines; 2-225hp 1-500hp No additional ore cars; 2-diesel hydraulic switch engines; 2-225hp 1switch engine 274hp 186 ore cars 65 ton; No change in switch engine; 1-rail bus No change, One switch engine; 275hp retired No changes, except added 1-1600hp diesel hydraulic locomotive
Family Staff Houses 200 337 610 615 525 398
Bachelor staff qtrs. 235 172 274 185 174 153
Family labor houses 550 609 767 785 802 801
Bachelor labor qtrs. 104 not listed 27 28 10 not listed
Hospital beds 65 70 115 115 97 91

Early on the power plant was expanded with larger Sulzer diesel electric units. The four diesel road locomotives lasted for the life of the operation though they were at times high maintenance, low available units. Near the end a diesel hydraulic 1600hp locomotive was acquired. This type of locomotive is widely used in Europe but the US railroads have seldom used them except experimentally. Rolling stock and maintenance of way equipment was increased as needed.

The port was expanded by the addition of storage and handling equipment. The harbour was deepened to 45-ft. so that 90,000 dwt ships could be loaded.

The above table tabulates the townsite expansion and in some respects contraction. Fewer expartiate houses were required as the expatriate staff was decreased. A table showing the number of employees over the years of operation is added below. The number of Liberian trainees over the years numbered 50 to 100.

Bong Mining Co. was totally dedicated to education of employees´ children through high school. As time went on these students were candidates for trainees for higher skilled and better paying jobs. The objective was always to reduce the number of expatriates and to increase the number of Liberians in supervisory and skilled operator jobs. The table below indicates that this indeed was being accomplished.

Empl. %

Empl. %
1965 318 54 372 1,625 1,679 1,997 18.6 81.4 15.9 84.1
1966 315 67 382 1,457 1,524 1,839 20.8 79.2 17.1 82.9
1967 351 78 429 1,607 1,685 2,036 21.1 78.9 17.2 82.8
1968 320 93 413 1,668 1,761 2,081 19.8 80.2 15.4 84.6
1969 310 102 412 1,752 1,854 2,164 19.0 81.0 14.3 85.7
1970 347 111 458 1,923 2,034 2,381 19.2 80.8 14.6 85.4
1971 356 126 482 2,008 2,134 2,490 19.4 80.6 14.3 85.7
1972 355 130 485 2,015 2,145 2,500 19.4 80.6 14.2 85.8
1973 350 142 492 2,180 2,322 2,672 18.4 81.6 13.1 86.9
1974 334 193 527 2,267 2,460 2,794 18.9 81.1 12.0 88.0
1975 352 230 582 2,455 2,685 3,037 19.2 80.8 11.6 88.4
1976 360 289 649 2,456 2,745 3,105 20.9 79.1 11.6 88.4
1977 380 331 711 2,524 2,855 3,235 22.0 78.0 11.7 88.3
1978 355 350 705 2,518 2,868 3,223 21.9 78.1 11.0 89.0
1979 307 396 703 2,455 2,851 3,158 22.3 77.7 9.7 90.3
1980 280 414 694 2,361 2,775 3,055 22.7 77.3 9.2 90.8
1981 258 398 656 2,224 2,622 2,880 22.8 77.2 9.0 91.0
1982 259 411 670 2,201 2,612 2,871 23.3 76.7 9.0 91.0
1983 231 388 619 1,940 2,328 2,559 24.2 75.8 9.0 91.0
1984 208 339 547 1,716 2,055 2,263 24.2 75.8 9.2 90.8
1985 198 336 534 1,683 2,019 2,217 24.1 75.9 8.9 91.1
1986 198 336 534 1,659 1,995 2,193 24.4 75.6 9.0 91.0
1987 187 316 503 1,527 1,843 2,030 24.8 75.2 9.2 90.8
1988 182 315 497 1,515 1,830 2,012 24.7 75.3 9.0 91.0
1989 179 313 492 1,493 1,806 1,985 24.8 75.2 9.0 91.0

© James V. Thomson and Wolfgang Jacobs