Rather than trot out the usual fundamentals of rock slope stability which is well documented in books, we encourage you to go to the fascinating site where you will find a beautifully presented story of regional-scale rock slope stability currently being investigated by the various Geo-technical Institutes, worldwide.
We are pretty sure that there is more to the site than we know, but go there and you can download free e-books.
In order to know more on slope stability and rock mechanics, we would suggest to go through the papers–
STABILITY ASSESSMENT OF A CRITICAL SLOPE
It is very important to conduct a stability assessment of a critical slope and takes necessary measures to avoid any accidental slope failures. Stability assessment through a probabilistic and risk analysis approach brings in light all the factors which can cause these failures. Risks are identified, remedial measures are suggested and a cost study is done covering both long-term and short term stability of the rock slope.
Many remedial measures (reduction of slope height, reduction of slope angle, reinforcement and drainage) need to be considered for improving the long-term stability of the slope; short-term stability is not considered an issue under a modeled conditions. Costs is estimated for each of the remedial measures. Reducing the slope angle is selected as the preferred alternative due to a technical and economic point of view.
- World’s Largest O/C mine: Bingham Canyon Mine (details are as mentioned below)
- India’s Largest O/C Mine: Rampura Agucha Open Cast mine (details are as mentioned below)
Rampura Agucha Open Cast Mine:
Hindustan Zinc Limited today is part of one of the top global companies Vedanta Limited. Hindustan Zinc Limited (HZL) is the only integrated Lead & Zinc manufacturer in India which owns captive Lead and Zinc Mines that supply complete requirement of Lead and Zinc concentrate for its smelters. Rampura Agucha is
presently having mining and beneficiation capacity of 6.15 and 6.50 million ton ore production and beneficiation. It is an ISO 9001, ISO 14001 & OHSAS 18001 and SA-8000 certified Mines.
Rampura-Agucha Open Cast Mines once reached the capacity of 6.15 Mtpa ore production and beatification plant to produce zinc and lead concentrates. But currently it has been reduced to 1.7 Mtpa. Rampura-Agucha Open Cast and Underground Mines is one of the largest & richest Lead-Zinc deposits in the world. The Mines were commissioned in the year 1991 with capacity of 0.90 Mtpa. Further, the capacity of the Mines was increased from 0.90 Mtpa to 1.35 Mtpa. Furthermore the production was enhanced to 3.75 Mtpa in 2004-05. The production capacity was once again expanded to 5.00 Mtpa in 2007-08 and 6.15Mtpa Mines production and 6.50 Mtpa ore beneficiation plant in Dec.2009.
Rampura Agucha deposit is 5th largest deposit with a total of 75.03 Mt of reserves & resources with an
situ grade of 1.86 % Pb and 12.65% Zn and 3rd largest in terms of production of contained Zinc metal
in the world. Besides being a world-class deposit it also boasts of high complexity in terms of its geometallurgical
characteristics i.e. textural characters, which makes it challenging for a metallurgist to
achieve optimum recoveries and grade. The various mineralogical characteristics that directly impact
the process parameters are described in the paper.
Location: 225 km north of Udaipur (Rajasthan)
Mining Lease Area: 1,200 Ha
Reserves: 69.3 million tonnes
Resources: 41.1 million tonnes
Avg. reserves grade: 13.7% Zn, 1.9% Pb
Ore Production capacity: 6.15mtpa
Mining Method: Open Cast up to 372m,underground beyond
Waste Management: Waste dump (20m x 7 lifts)
GEOLOGY AND MINERALIZATION
Graphite mica sillimanite schist /Gneiss but as in several portions of the ore body ore mineral
concentration is more than 50 % it would be more appropriate to call the ore bearing rock as
Sphalerite — pyrrhotite silliminite graphite gneiss
Shape and Extent of Ore Body
The ore body is lens shaped with a maximum width of 100m in the central portion and an average
width of 58 m and extends for about 1550 m from S725 to N825. In the depth extent it is extending for
more than 750 m below surface level.
Sphalerite, Galena, Pyrite, Pyrrhotite, Arsenopyrite & other Sulpho salts
Quartz, Feldspar, Graphite, Sillimanite, Mica, Gypsum & Calcite
Modal Percentage Ranges
Sphalerite :15-20%, Galena: 1-2%, Pyrite:15-18%, Pyrrhotite : 12-14%, Graphite: 4-7-%,
Gangue : 45-50%.
Mineralogy of the Ore
The sphalerite is of two types; Coarse grained granular variety with abundance of more than 60 % (>74 microns) (Fig No 2) having inclusions of submicroscopic size pyrrhotite ( 5-10 microns) and fine grained, cataclastic variety (Fig No 3)containing fine grained< 50 microns inclusions of gangue minerals which are thoroughly intermixed with sphalerite and other sulfides leading to poor liberation. Fine grained sphalerite is noted wherever it has been involved in cataclasis The rounded fragments of quartz — felspar occur in a fine grained ground mass of sphalerite, pyrrhotite, pyrite and silicates. The rounded porphyroclasts of quatzo-felspathic materials are coarse grained while the sphalerite rich matrix is fine grained having inclusions of pyrrhotite, pyrite, quartz, plagioclase and potash felspar. Pyrrhotite inclusions are common in both coarse and fine grained sphalerite. Minor amounts of gangue minerals are also present in sphalerite ex graphite, silliminite and biotite.
Occurs as medium to fine grained intergrowths with sphalerite, pyrite, pyrrhotite also as inclusion in
other sulphides and entrapped in grains within graphite and micaceous minerals (10 — 20 microns) due
to which recovery may not exceed 65 % (Fig No 3). Coarse-grained Galena is found in hanging wall
area. Normally galena does not contain inclusions of other minerals but graphite occurs as inclusion in
galena. Besides occurring as granular aggregates galena is found as infilling along cleavages of mica and graphite. Galena displays deformation in the form of flowage, shearing out, emplacement along cleavage, fractures and as fine thin lamellar form.
Pyrite occurs as coarse grained aggregates intergrown with pyrrhotite and represents about 15-18 %
by volume. Large porphyroblasts of pyrite show brittle fractures filled with other sulfides.
Pyrrhotite occurs as granular medium grained aggregates associated with sphalerite and pyrite and
galena and represents about 12-14 % by volume. It also occurs commonly as 5- 10 micron inclusions
It is the commonest gangue mineral in association with ore minerals. It occurs as coarse 150 microns
by 50 microns long grains showing bent and kinked flakes and fine grained fracture fillings encircling
other gangue and ore minerals and represents about 7- 10 % by volume and is interlocked with
Sphalerite and galena to form a sandwich like texture.
Major Focus Areas:
−Focused exploration to enhancethe reserves & resources base
−Operational efficiencyimprovement through continuousimprovement initiatives
−Continuous technological up-gradation
−Utilization of HEMM at par withglobal benchmark
Mine planning and designing:
- Pit designing and optmization with best in class software
- Ramp gradient changed to 1:16 to 1:12 and finally to 1:10, resulting into 10% reduction of waste and improvement OEE of HEMMDrilling & Blasting:
- ANFO to SME (Site mix emulsion) and from D Chord to electronic detonator.
- Established (in consultation with CIMFR) and carrying out pre-splitting at the perimeter of every cut back –
enabled mining upto a depth of 400m.Loading & Hauling:
- Bigger fleet from 50 T to 100 T and to 221 T class trucks and excavators from 4.3 Cub M to 34 Cub M
- Real TIME management through Truck Dispatch System (TDS) improved truck utilization from 70% to
Slope Stability Management:
- Established three layers slope monitoring system i.e. SSR, Prisms, & Inclinometers; First mine in India
to use SSR.
- Depressurization of pit walls through vertical and sub horizontal holes
- Slope Stability Radar (SSR): Slope Stability Radar Ultimate Solution for Monitoring Slopes And Managing Slope Instability Hazards:Assessing and managing instability hazard in open pit mines is an essential activity when working with the natural and engineering slopes, due to its potentiality for loss of life and property. The slope stability radar (SSR) is an all-weather system that remotely scans wall of the slopes to measure the slope surface movement with sub-millimeter precision. It allows user to detect and alert personnel of rock movements that result in instability. It allows greater productivity without compromising safety.The standard methods for dealing with slope instability are:–
- Development of a monitoring system
- Adopting acceptable deformation criteria
- Warning and alert systems
- Design of stabilization works
- Risk/hazard mitigation strategies.
- Truck mounted mobile equipment
- RAPS(Remote area power supply)
- CEB (Computer electronics box) :operation of SSR & displaying of data
- REB(radar electronics box): Radio wave generation & data analysis
- Tripod: Positioning of SSR
- Repeater: Collects data from SSR & transfer these to PMP system
- PMP: Primary monitoring point
- High precision measurement (±0.2 mm)
- Broad area coverage (1000’s points/scan)
- Continuous monitoring (2 – 8 min/scan, 24 hrs/day)
- 100m – 1700 m range
- All weather operation (including dust, rain, fog, smoke)
- Mobile & easy to set up
- Self-powered System scans 270° horizontally and 100 ° vertically
Inclinometer is also used to determine subsurface movement around the pit peripheri–
The Vertical Digital Inclinometer System comprises a biaxial probe, cable reel and a rugged field PC supplied with ‘Inport’ data logging software. The Digital Inclinometer System takes highly accurate readings of lateral deflections.
A Bluetooth connection between the instrument and the field PC makes taking readings fast, simple and allows for winding of the cable reel as you take readings without having to disconnect datalogging equipment. The Kevlar reinforced cable provides strength but yields significant weight reductions.
This method is the oldest slope monitoring technique but very much effective compared to other monitoring techniques.
Bingham Canyon Copper
Chalcopyrite, or copper iron sulfide, is among the best-known copper minerals. Chalcopyrite crystals have unevenly faced tetrahedrons that are striated in different directions, a metallic luster and a brassy-gold color somewhat less yellow than pyrite. Crystals usually tarnish to iridescence or even to deep blues, purples or blacks. Among all metal sulfide minerals, only pyrite exceeds chalcopyrite’s crustal abundance. Chalcopyrite, however, is the most abundant copper mineral.Chalcopyrite is a popular mineral among collectors. Fine specimens, such as those from Arizona, Missouri and Mexico, may have well-formed tetrahedrons measuring as many as four or five inches across. Chalcopyrite’s true claim to fame, however, is not its visual appeal but that it is the major ore of copper. When it comes to sheer size in chalcopyrite deposits, nothing approaches the deposit at Bingham Canyon, Utah.For 90 years, Kennecott Utah Corporation’s Bingham Canyon Mine has been the granddaddy of all copper mines. Just how big is Bingham Canyon? Whether you’re talking about metal production or the actual size of the mine, Bingham Canyon is simply the largest copper mine in the world.To begin with a few production statistics, the Bingham Canyon Mine has produced more copper than any other mine in history–about 14.5 million tons of the metal. Bingham Canyon is primarily a copper mine, but it has also yielded a bonanza in byproduct metals. These include 18.5 million troy ounces (about 620 tons) of gold, 157 million troy ounces (nearly 5,000 tons) of silver, 610 million pounds of molybdenum and significant amounts of platinum and palladium. The cumulative value of Bingham Canyon metals far exceeds the total worth of the Comstock Lode and the California and Klondike gold rushes combined. With production statistics like that, it’s no wonder that the Bingham Canyon Mine has been nicknamed “the Richest Hole on Earth.” The Bingham Canyon open pit stretches for 2.5 miles across the rim and is the largest manmade excavation on Earth
Bingham Canyon is also the biggest hole on earth. As the largest of all man-made excavations, Bingham Canyon is more than a half-mile deep. If the world’s tallest building, the 1,454-foot-high Sears Tower, were placed at the bottom of the pit, it would reach only halfway to the mine’s rim. The Bingham Canyon open pit stretches more than 2.5 miles across at the rim and covers 2,000 acres. Its immensity makes it the only manmade feature visible to the naked eye from the orbiting space shuttle.
Nestled in the Oquirrh Mountains 20 miles southwest of Salt Lake City, Bingham Canyon sits atop what may be the greatest single metal deposit ever discovered. The Bingham Canyon story, which combines geology, history, technological innovation and modernization, is a classic in American mining.
The oldest rocks at Bingham Canyon–sandstones, quartzites and limestones–were originally deposited as sediment by the shallow seas that covered the region 300 million years ago (in the late Paleozoic Era). Much later, between 60 and 135 million years ago, extensive folding and faulting of the sediments created the Oquirrh Mountains.
Just 30 to 40 million years ago, massive igneous intrusions initiated the process of mineralization. Extreme pressure forced superheated, mineral-rich solutions into fractured intrusive and adjacent sedimentary rock. Upon cooling, the mineralized solutions deposited enormous quantities of metals throughout a broad section of igneous and sedimentary rock that is now known as the Bingham Stock.
Bingham Canyon is not presently a source of notable mineral specimens. The Bingham Stock is a porphyry deposit, meaning that copper minerals–primarily chalcopyrite–are present in very low grades and disseminated throughout the granite-like host rock as tiny grains, seams and fracture coatings. Other metals associated (in smaller quantities) with the chalcopyrite include the following: gold, silver, lead, molybdenum, platinum and palladium.
In relatively recent geologic time, erosion exposed the upper part of the Bingham Stock, permitting surface and near-surface oxidation to enrich many outcrops. In the 1860s, prospectors searching the rugged Bingham Canyon area discovered outcrops of high-grade lead carbonate, or cerussite. In 1873, the persistent prospectors found gold and silver in the outcrops, triggering a mining boom. Underground mining continued for 20 years as miners pursued rich, oxidized pockets and veins of gold- and silver-bearing cerussite and two copper carbonates, azurite and malachite.
If Bingham Canyon ever produced notable mineral specimens, it was during the early underground mining period. The oxidized ores mined during the 1870s and 1880s were so rich that they could be smelted immediately, with no need for prior concentration.
By the early 1890s, underground mining had exhausted the high-grade, oxidized ores. An enormous amount of mineralization remained, but it consisted only of deep, unoxidized sulfides so low in grade that mining them was not economical. The problem of low-grade ores was not unique to Bingham Canyon. Miners across the West were rapidly running out of high-grade, direct-smelting ores, and many mines and entire districts were closing. The subsequent drop in metal production had national implications, for American industry, embarking on broad programs of industrialization, mechanization and electrification, now needed huge quantities of base metals, especially copper. But if low-grade, porphyry copper deposits, such as that at Bingham Canyon, were to supply the national demand for copper, a great technological advancement was necessary.
The breakthrough began in 1898 when Daniel Jackling, a metallurgical engineer, and Robert Gemmell, a mining engineer, proposed new mining and milling methods that would revolutionize metal mining. Jackling and Gemmell believed that low-grade, porphyry copper ores could be mined profitably. They figured the key was to combine massive surface-mining methods with a then unproved milling process: flotation separation.
In 1903, Jackling formed the Utah Copper Company and built a 300-ton-per-day mill at Bingham Canyon. Three years later, he began using steam shovels in the nation’s first mechanized open pit mine. Jackling then constructed another mill to provide the first large-scale demonstration of the flotation separation process.
Flotation separation uses the tendency of oil-covered mineral particles, particularly those of metal sulfides, to adhere to oil bubbles. In the process, finely ground ore slurry is mixed with an oily reagent, then vigorously agitated and aerated in tanks. Mineral particles adhere to the rising bubbles and float off as an oily froth, while particles of nonmineralized rock, called gangue, fall to the bottom and are discarded as tailings.
At Bingham Canyon, the effectiveness of large-scale flotation separation exceeded Jackling’s hopes. Although Bingham Canyon ore contained a mere 0.6-percent copper–a ton yielded only 12 pounds of the metal–inexpensive flotation separation produced a smelter-ready concentrate containing 23 percent copper and byproduct metals.
Mining engineers throughout the West widely copied the combination of mechanized, large-scale open-pit mining and flotation separation, enabling a new generation of large surface mines to supply ample amounts of copper for national industrialization. Even so, no other mine grew as rapidly as Bingham Canyon. Kennecott Utah Copper Corporation acquired the mine property in the 1930s and stepped up expansion. During World War II, Bingham Canyon alone provided more than one-third of the prodigious amount of copper used by the Allies in the war effort.
By 1980, the huge Bingham Canyon Mine had 2,500 miners who drilled and blasted 370,000 tons of ore and overburden every day. An additional 5,200 employees worked in haulage, concentrating, smelting and refining to produce 300,000 tons of pure copper each year. By then, Bingham Canyon had become an antiquated, labor-intensive, inefficient mine. Saddled by high costs of production and environmental compliance, Bingham Canyon could longer compete with producers of cheap, foreign copper. When copper prices plummeted in 1982, Bingham Canyon incurred huge annual operating losses. Soon afterwards, Bingham Canyon shut down for the first time in eighty years. The old mine still had one big asset, though. That was its world-class copper deposit, with enough reserves for 30 more years of mining–if the mine could regain market competitiveness.
Over the next decade, in testimony to its confidence in the size and quality of the remaining chalcopyrite ore body, Kennecott Utah Copper poured $1.5 billion into upgrading its mining, concentrating, smelting and refining operations. Today, the rejuvenated Bingham Canyon Mine is among the most safe, clean and efficient major mining operations anywhere.
At Bingham Canyon, the process of recovering copper from chalcopyrite begins when miners drill and blast the in situ ore and overburden. Detonation of large patterns of 55-foot-deep, 12-inch-diameter drill holes, each loaded with a half-ton of explosive, breaks the solid rock. Electric shovels, some lifting nearly 100 tons of material in a single bucket “bite,” fill 240-ton-capacity haulage trucks that move the broken rock to the crusher.
After crushing, a five-mile-long conveyor belt moves the ore to the concentrator, where huge grinding mills reduce it to the consistency of face powder. Flotation then separates the gangue from the metalliferous particles, which float off as a 28-percent concentrate of copper along with lesser amounts of silver, gold, lead, molybdenum, platinum and palladium. A selective flotation step separates the molybdenite (molybdenum disulfide) from the chalcopyrite.
The filtered concentrate slurry is piped 17 miles to the smelter, where it is dried, and then injected along with oxygen into a flash smelting furnace to oxidize the iron and sulfur. The oxidized iron is skimmed off, while the sulfur dioxide gas is captured and sent to an on-site acid plant for conversion to valuable sulfuric acid–a million tons of it each year.
Left behind is a molten copper sulfide called matte. The 70-percent-copper matte is water-quenched to form a sand-like solid, then injected, with oxygen, into a flash-converting furnace that produces molten, 98.6-percent-pure copper. This copper is then cast into 700-pound anode plates and shipped by rail to the refinery.
At the refinery, the anode plates are pressed flat and interleaved with stainless steel cathode blanks. Automated robotic vehicles place the prepared anodes in cells containing an acidic electrolyte. When the cells are electrified, the anodes slowly dissolve, freeing copper ions that are deposited on the cathode as 99.9-percent-pure copper.
Impurities and precious metals settle to the bottom of the electrolytic cells as “slimes.” A chlorination leaching process recovers the gold and silver, which is melted in induction furnaces and poured into 400-troy-ounce gold bars and 1,000-troy-ounce silver bars. Each year, the precious metals refining plant pours 500,000 troy ounces of gold and 4 million troy ounces of silver–surpassing the production of many large primary gold mines.
Bingham Canyon is a half-hour drive southwest of Salt Lake City. If you’re ever in the area, it’s certainly worth a visit. The Kennecott Utah Copper Corporation maintains an overlook with an unforgettable view of the vast open pit, and distributes publications explaining the mine’s history and operations. An hour or two at Bingham Canyon will leave visitors with a good idea of the effort behind American copper mining. The huge open pit illustrates just what lengths some people will go to for a little chalcopyrite.
Mining equipment and operations
• There are 11 giant electric shovels and one hydraulic shovel operating in the mine.
• The largest electric shovel has a 56-cubic-yard dipper that scoops up approximately
98 tons of material in a single bite, a weight equivalent to about 50 automobiles.
• The newest electric shovel costs more than $20 million and weighs 3.2 million
• There are about 70 gigantic haulage trucks operating in the mine. These trucks
carry from 255 to 320 tons of material in a single trip.
• A new haul truck costs about $3.5 million.
• The fleet of haul trucks will travel a total of more than 10,000 miles a day at an
average speed of 13 miles per hour.
• The mine has eight large drills that stand between 75 and 100 feet tall and drill
blast holes 55 feet deep. On average, 200 holes are drilled in a typical day and
packed with 1,200 pounds of special blasting agents.
• The in-pit crusher reduces ore to less than 10 inches in diameter or about the size
of a basketball. Very fine dust particles are captured in an air pollution control
device called a bag house— similar to a very large vacuum cleaner.