Brochure Bethlehem in Marmora

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BETHLEHEM IN

MARMORA

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This map, compiled by the Geophysics Division, Geological Survey of Canada (Department of Mines and Technical Surveys) indicated the possibility of iron ore southeast of the town of Marmora, and aroused Bethlehem's interest in the area. The photograph shows the same general area.

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BETHLEHEM IN

MA RM0 RA The Marmora orebody is located in Hastings County, Province of Ontario, about 120 miles east of Toronto, in a locality where small occurrences of magnetic iron ore were mined as early as 1820. Failure of earlier steel plants to utilize this ore economically resulted in the abandonment of iron ore mining in this district about 1873.

In January of 1949 the Ontario Department of Mines in conjunction with the GeologicalSurvey of Canada, conducted an aeromagnetic survey of the region.

An anomaly, or strong magnetic high on the geo-magnetic maps, about one mile east of the town of Marmora, indicated the possibility of a deposit of magnetite. Bethlehem geologists became interested in the area and in May, 1950, the company obtained options on a 290-acre tract on the Roger's and Saliner's farms. Additional property later acquired has increased Bethlehem's holdings at Marmora to about 1900 acres.

Diamond drilling was started the following month and completed in August, 1951. The survey-fortyd rill holes in all, ranging from 460to 1800 feet in depthoutlined sufficient quantities of ore to warrant open-pit mining operations.

The orebody, an oblong mass roughly 2100 feet long and up to 400 feet wide, occurs as a replacement of Pre-Cambrian limestone which was overlaid by about 130 feet of flat-lying Paleozoiclimestone. The ore occurs as stringers and. irregular massesof magnetite mixed with Pre-Cambrian limestone and intrusion dikes. The average grade of the ore is about 35 per cent iron.

With exploration completed, development work began with clearing of landabout 100 acres of scrub timber-in September, 1951. The land which lies close to the southern fringe of the Pre-Cambrian shield was quite rugged and rocky, and unsuited for either farming or lumbering. The standing timber had little commercial value.

Bethlehem engineers were first confronted with the problem of exposing the orebody in as short a period as possible. With the ore horizon located at a depth of 130 feet it was necessary to remove over 20,000,000 tons of rock.

This task, along with the construction of a beneficiation plant at Marmora and dock facilities at Picton, was accomplished in less than three years.

By mining at an annual rate of 3.1 million tons (ore and waste), the Marmora operation is capable of producing 500,000 net tons of high grade pellets. This product is transported by rail over Canadian National Railway'S tracks to the Lake Port of Picton, on the Bay of Quinte, 64 miles away. During the shipping season, pellets are loaded into Lake ore carriers for shipment, through the Welland Canal, to Bethlehem Steel Company's large steel plant at Lackawanna, N.V., a distance of 211 miles.

The Marmora pit is roughly half a mile long, a quarter of a mile wide, and about 250 feet deep.

Electric shovel with 4\12 cubic yard bucket loads blasted material into 22路ton truck. Percussion drill on upper bench prepares for the next blast.

Thousands of tons of rock and ore are loosened in a single blast.

Delayed-actton blasting is used, with the holes fired in sequence at a few thousandths of a second intervals.

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OVER TWENTY-TWO MILLION TONS OF LIMESTONE CAP STRIPPED Actual stripping operations were started in March, 1952. Due to the extensive rock-moving program planned, extra heavy equipment was required. Two electrically powered rotary drills, equipped with 6%·inch bits, were used to drill the blast holes which were driven to a depth of 45 feet and spaced up to 20 feet apart. Drilling proceeded at a rate of 22-30 feet per hour, including the time required for moving the rigs.

The blasted overburden was loaded into trucks with three 6-cubic yard electric shovels. Twenty-one rear-dump, 275-hp Diesel trucks of 22-ton capacity were used in hauling the stripped rock to the adjacent waste dump.

As much of the waste rock as was needed was broken in a jaw crusher used as aggregate and fill in plant construction which included

several

and in a road building

and

program

sidings. Stripping operations were carried out on a 24-hour a day basis. Approximately 22,000,000 tons of rock were removed, to create a pit roughly half a mile long and a quarter of a mile wide, and about 130 feet deep. The pit will ultimately

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miles of access roads to the pit, dump, and railway

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be carried down to a depth of over 700 feet. }

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MINING OPERATIONS

TO YIELD

OVER 4000 TONS OF ORE A DAY Except for the rotary drills all equipment shifted

to ore production

additional

equipment

pneumatic After electric

required

rock drills capable

blasting,

used in the stripping

as soon as the stripping for the actual of drilling

7-inch

operations

was completed.

mining

operations

was three

holes in hard rock and ore.

the broken ore and waste are loaded into pit trucks

shovels now equipped

was

The only

with 4V2-cubic yard dippers,

by the

and hauled to a

skip-loading pocket located below the pit floor.

The ore is hoisted from the pit over an incline with 45° slope and an initial length of about 240 feet. The incline is lengthened as the mine gets deeper. Two counterbalanced skips, each large enough to carry an entire 22-ton truck load of ore, are used. With normal operation

about 4250 tons will be hoisted every

day. In addition foot wall and hanging wall rock within the pit limits will be mined and trucked to the dumps. Approximately 50,000,000 tons of this waste must be removed along with the ore over the life of the pit. Operations in the pit are carried out on two shifts only, while the mill operations The skips discharge primary

crusher,

directly

into a stone

located at the head frame.

are around the clock.

box above the 48-inch Crushing

gyratory

is done in three steps;

the primary crusher reduces the ore to minus 5V2 inches; the secondary crusher takes it down to minus 1% inches; while the tertiary cone-type crusher discharges the ore at about %-inch size.

A stockpile with a conveyor stocking

arrangement

and a tunnel

reclaiming

system follow the primary crusher. From the stockpile the ore is conveyed to the secondary

crushing

plant where it passes over several magnetic

ahead of and three following the secondary

crusher.

pulleys, four

These magnets separate

waste rock from the crude ore. The barren rock is screened and placed in a bin for use as ballast or construction through

the tertiary

crusher,

aggregate, while the crude ore, after passing

is delivered to the mill for further

treatment.

Three percussion rock drills, one of which is shown below, drill the ore on 45-foot benches.

They are equipped with seven-inch tungstencarbide bits and will drill at a rate of more than 11 feet per hour.

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MINE

elECTRIC

SHOVel

WITH 4Y2~CU. YD. BUCKET

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_,rr;f1. ',_il:.

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22·TON TRUCKS HAUL THE ORE TO THE SKIPS

SKIP INCLINE

DRILLING

BLASTING

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HAULING

CONE CLASSIFIER

MILL

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~ COAL

ROD MILL (Coarse Grind) BALL Mill

(Fine Grind)

TAILINGS

BENTONITE TAILING

BALLING

DRUM CONVEYOR FEEDER ON SHUTTLE CAR

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l----FINES

PELLET PLANT

UNDERSIZED TO ACT AS

THICKENER

PELLETS ARE FeD BACK SEED PELLETS

FINES

PEllET

FURNACI

(Oil. Fired}

CRUSHING

PLANT

CONVEYOR

'RIMARY CRUSHING

PLANT

RECLAIMING

TUNNEL SECONDARY CRUSHER

2-DECK SCREEN WATER

MAGNETIC PULLEYS

TERTIARY CRUSHER

CLARIFIED WATER FOR RE-USE

TO TAILING

DISPOSAL

SIMPLIFIED FLOWSHEET FOR

TO

PICTON VIA RAil

PORT

MARMORA MINE

FINE GRINDING PRECEDES

MAGNETIC

OF ORE CONCENTRATION

Because the iron-bearing mineral is present as very fine particles, it is necessary to reduce the crushed ore to fine sizes, so that all of it will pass through a screen with about 100 mesh per lineal inch, before it can be concentrated to the desired iron content. This is done by wet grinding in two rod mills and two ball mills.

First the ore passes through a rod mill, a revolving cylinder partly filled with steel rods between which the ore particles are ground to small size. The rod mill discharges into a ball mill, which is of similar construction, but shorter and of larger diameter, and partly filled with steel balls instead of rods. This mill grinds the ore to final size.

A cone-type classifier removes oversize particles from the discharge of the ball mill and returns them to the feed end of the same mill for regrinding, thus increasing the grinding efficiency and assuring good magnetic separation.

The finely ground ore, mixed with a suitable amount of water, is passed through magnetic separators. A separator consists of a cylindrical drum revolving around a fixed magnet and suspended in a box through which the ore slurry is passed. The fine particles of magnetic iron ore are picked up by the revolving drum and carried over a bridge, out of the magnetic field. Here they drop off the drum, and are collected and pumped to four dewatering filters or to storage pits in the pelletizing plant.

The non-magnetic waste material, or tailings, flow out of the separator box and go to a large thickener. The thickened slurry is pumped to a tailing pond, while the water overflowing from the thickener is returned to the grinding circuit.

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The trucks are dumped into the loading pocket at the base of the hoist incline. Two counterbalanced skips, each holding a truck load, take the ore to the top of the pit and discharge it into the primary crusher.

FINE CONCENTRATE

AGGLOMERATED

IN PELLETIZING

PLANT

In the pelletizing operation the magnetic iron concentrate is filtered and then fed to a revolving balling device where it is rolled into small balls, or pellets, approximately %-inch maximum diameter. To improve the quality of the pellets a small amount of bentonite is mixed with the concentrate before balling. Fine hard fuel is added to the concentrate before filtering to assist in the subsequent heating of the pellets.

The pellets which contain about 10 per cent moisture are fed into an oil-fired vertical shaft-type furnace, by means of an oscillating belt conveyor. Passing slowly through the furnace they are first dried and preheated, followed by baking at about 1250째 C, which makes them hard enough to withstand breakage in transit and the crushing pressure in the blast furnace. During the burning period considerable heat is evolved by oxidation of the magnetic constituent to form hematite. The plant can produce 1750 tons of pellets every 24 hours.

After cooling and screening to remove undersize material, the pellets are conveyed to a bin from which they are loaded into bottom dump cars for rail shipment to Picton, 64 miles away. One train is run daily, made up of 25 to 30 cars, depending upon the capacity of the cars.

In full operation about 300 men are employed at Marmora, in the mine, mill, and shops.

All main buildings at Marmora, including the mill, pelletizing plant, and crusher, are steel construction with insulated asbestos roofs and sidings. The main shop is a U-shaped single-story structure, 260 x 50 feet, with two 120 x 40-foot wings. It houses the machine shop, carpenter shop, and truck service

The incline. at the left, has a slope of 45 degrees and a length of about 240 feet. It will be lengthened as the depth of the mine increases.

shop and garage. The general office building also houses engineering offices and a dispensary. A modern change room with showers, washroom facilities, and lockers has also been provided.

LOADING FACILITIES AT LAKE PORT

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At Picton, the cars are run out over an 800·foot trestle and the pellets are dumped into a storage pit 30 feet deep, excavated from the solid rock. The pit has live storage space for 25,000 tons of pellets. Space is also available for storing 330,000 tons of pellets on the ground during the winter months when Lake shipping is discontinued. Crane service is provided for transferring pellets from pit to ground storage, and vice versa.

The pellets are drawn from the pit through any of 25 chute gates in the roof of a recovery tunnel running underneath the pit, for its full length. The gates are operated manually and discharge on a 42·inch belt conveyor under the chutes.

The conveyor which operates at approximately 500 feet per minute has a capacity of 2000 tons per hour. It discharges to a second conveyor of the same size and speed, running at 90° to it, out toward the water. This conveyor in turn discharges the pellets to a third conveyor mounted on a retractable loading tower, the boom of which can be raised or lowered for loading the pellets into ships.

The retractable loading tower is designed for a shuttle travel of 54 feet perpendicular to the dock fender, to permit loading and trimming of vessels of different beams. The boom can be raised or lowered in order to minimize the free drop of the pellets into the vessel. A 16,000-ton ore carrier can be loaded in about 10 hours.

A 1200-foot dock supported on steel piling, with a 240·foot loading section, has been constructed to accommodate the largest Lake carriers. The bay outside the dock has been dredged to a depth of 26 feet below mean low water .

Shipping is carried on about eight months of the year. During the winter months incoming pellets are stock- piled.

A brick service building houses general office, welfare facilities, a shop and customs house.

Interior of concentrator, showing rod mills on the right, ball mills at each end, and magnetic separators at the left center.

Each worker is assigned a locker for his street clothes, and a basket for work clothes. Excellent shower and toilet facilities are provided.

About 300 men are employed at Marmora, in mine, mill, and shops.

Harbor at Picton with BOO路 foot trestle spanning the storage pit. Pellets are withdrawn enabling an ore carrier to be loaded in about 10 hours.

from below by a system of conveyors,

AIR VIEW OF MARMORA MINE

a. Mine b. Incline skip and primary crushing plant c. Crushing plant d. Mill e. Pellet plant f. Tailings disposal area g. Waste dump area 路h. General office

i. Shops and warehouse facilities.

Booklet

1998

639. Printed in U.S.A.