Chapter 4 Cor Flashcards
Why do geologists and mining companies invest in diamond exploration?
To maintain the world’s diamond supplies as some mines become abandoned and new mines eventually stop producing
Companies like De Beers and ALROSA invest a large amount of their revenue in exploration each year.
What are primary deposits of diamonds?
Deposits found in kimberlite or lamproite that brought them to the surface
The majority of diamonds today are mined from primary deposits.
How are alluvial deposits formed?
When pipes erode and rough diamonds wash into rivers or streams
Diamonds can accumulate in areas of slow water, such as river bends.
What happens to diamonds if river currents are strong enough?
They might be carried to the sea and form marine deposits
Ocean currents can deposit diamonds offshore or wash them back onto the beach.
What are secondary deposits of diamonds?
Deposits found outside their original pipes, often richer in diamonds
Secondary deposits result from the erosion and washing away of host rock.
What environmental factors affect kimberlite and lamproite stability?
Sunlight, heat, cold, wind, and rain
These forces break down the rocks relatively quickly once they reach the earth’s surface.
What did the De Beers experiment demonstrate about marine deposits?
Low-quality diamonds do not survive the marine environment stresses.
Marine deposits contain higher percentages of gem crystals than pipes
What percentage of weight did gem-quality diamonds lose after 950 hours of tumbling in the De Beers experiment?
0.01 percent
This shows their durability compared to industrial diamonds.
Fill in the blank: Diamonds are released from the weathered _______ or lamproite.
kimberlite
True or False: Secondary deposits are usually poorer in diamonds than primary deposits.
False
Secondary deposits are generally much richer in diamonds.
What effect does water’s rolling and tumbling action have on diamonds?
It breaks down heavily included diamonds, leaving higher-quality crystals intact
This is part of the natural sorting process in alluvial deposits.
What is the first step in exploration for diamonds?
Deciding where to focus the search.
Where do most diamond-bearing deposits form?
At the base of cratons.
What is Clifford’s Rule?
Diamonds are found in kimberlites that occur only on very old cratons.
What are lamproites in relation to Clifford’s Rule?
Exceptions that diamonds can be found near or outside cratons.
How do geologists locate cratons?
Through geological mapping and sound waves.
What characteristic of cratons allows sound waves to indicate their presence?
Cratons are denser than the surrounding rock.
What are secondary deposits?
Deposits targeted by looking for ancient or current streams, rivers, and estuaries flowing away from cratons.
What natural features do geologists look for when searching for secondary deposits?
Bends or obstacles in rivers or plunge pools below waterfalls.
What happens to diamonds in areas where water speed slows?
They drop out of suspension and accumulate.
Who proposed Clifford’s Rule and in what year?
T. S. Clifford in 1966.
What is the age of the cratons associated with diamond-bearing kimberlites according to Clifford’s Rule?
Stable for 2.5 billion years.
What are the two exceptions to Clifford’s Rule mentioned?
- Argyle deposit in Australia
- Lomonosov deposit in Russia
What geological processes affect the location of kimberlites and lamproites?
Plate tectonics and continental drift.
Where is the Argyle mine located?
In a collision belt surrounding the Kimberley Craton.
What do geologists now consider in addition to cratons when searching for diamond deposits?
Areas around cratons.
Fill in the blank: Diamonds can occur in much _______ rocks than previously proposed.
younger
True or False: Almost all diamond-bearing kimberlites are found on cratons or near their margins.
True
Why are secondary deposits easier to find than primary deposits?
They are above ground and often spread over large areas.
Where are alluvial diamonds typically found?
In lakes and rivers, shoreline marine deposits, dried-up waterways, and offshore deposits.
What does traditional artisanal mining exploration consist of?
Sampling stream sediments or sediments of dried-up ancient riverbeds.
What tools do prospectors use in traditional artisanal mining?
Large sieves to swirl water and make heavy minerals sink.
What do prospectors inspect for when using a sieve?
The center of the sediment for diamonds or indicator minerals.
What do miners do if they only find indicator minerals?
They follow these upstream in hopes of finding diamonds.
How do artisanal miners typically work?
On their own or in small groups.
What is the quality and quantity of diamonds found by artisanal miners?
Quality might be high but quantity tends to be low.
What modern methods are used for exploring alluvial deposits?
Aerial photography, satellite imaging, and radar.
What traditional methods are used in alluvial deposit exploration?
Field mapping and soil sampling.
What equipment is used for testing offshore diamond deposits?
Giant pumps to dredge up sediments from the ocean bottom.
What shift occurred in diamond exploration focus in the late 20th century?
The focus turned to marine deposits due to huge quantities of diamonds.
What is the Mafuta diamond mining vessel operated by?
Debmarine Namibia, a joint venture between De Beers and the Namibian government
What technology does the Mafuta vessel use to find diamonds?
A crawler to trawl the seabed
How much area does the Mafuta vessel scour for diamonds?
6,000 square km (2,300 square miles)
What tools do many alluvial prospectors still use?
Simple tools
What does the dark spot in sieved gravel indicate?
The presence of heavy minerals that might indicate diamonds nearby
Where is most diamond mining conducted in Sierra Leone?
Alluvial deposits
What do geologists do after locating a craton?
Narrow the search for kimberlite and lamproite pipes
What methods do scientists use to detect kimberlite or lamproite?
Gravity surveys
What do gravity surveys measure?
Density variations in the ground
What are kimberlite and lamproite rocks known for?
Having more gravitational pull than surrounding rock
What is the purpose of aerial photography and digital topography in diamond mining?
To look for circular or near-circular features in the landscape
What can aerial surveys spot that may not be obvious to geologists on the ground?
Shadows and contours
What did an aerial surveyor in Canada discover in a lake?
A round shadow that turned out to be the top of a diamond-bearing pipe
What do aerial electromagnetic surveys detect?
Possible presence of kimberlite pipes
What is the significance of mapping out a grid for UAVs?
To cover the area thoroughly for exploration
How can electromagnetic surveys be conducted?
On foot or from the air
What is generated after surveying a large area?
A map showing various features not visible to geologists
What do magnetic surveys plot?
Variations in magnetic response
How often does a person taking magnetic readings typically record data?
Every 50 meters
What technology do seismic surveys use?
Sound waves
What unique features do kimberlite and lamproite have that seismic surveys detect?
Distinct features detectable by sound waves
What are electromagnetic surveys used for?
To locate areas for diamond exploration
Electromagnetic surveys can be conducted on foot or from the air.
What are indicator minerals?
Certain minerals usually present in and around diamond deposits
Indicator minerals help in identifying the potential presence of diamond deposits.
Why are indicator minerals important in diamond exploration?
They indicate the proximity of kimberlite or lamproite pipes
Indicator minerals can form in or be brought to the surface by eruptions.
How far can indicator minerals be transported from their source?
Up to 300 km
Ancient glacial deposits can transport indicator minerals over long distances.
What role do termite mounds play in diamond exploration?
They can carry underground minerals to the surface
Geologists have discovered diamond indicator minerals in termite mounds.
What types of minerals are commonly associated with kimberlite and lamproite?
- Red and orange garnet
- Black spinel
- Diopside
- Olivine
- Ilmenite
- Chromite
- Perovskite
These minerals serve as important indicators in the search for diamonds.
What is the significance of finding tiny diamonds in samples?
It indicates that the source deposit is likely nearby
Tiny diamonds are particularly useful for tracing back to the source.
What challenges can arise in finding indicator minerals?
Weathering and erosion can break them up
For example, significant glacial activity can obscure the top of kimberlite pipes.
What is geochemical testing?
An analysis to determine the chemical composition of a sample
It helps identify the presence of elements associated with indicator minerals.
What does a large concentration of certain elements in samples indicate?
Remnants of indicator minerals and proximity to a kimberlite or lamproite
This can prompt further sampling and exploration.
What typically prompts more exploration in alluvial diamond deposits?
The discovery of diamonds
Diamonds found in such areas lead to further testing and exploration.
Fill in the blank: Indicator minerals are a good sign that a _______ is nearby.
pipe
What is the first level of sampling in diamond testing?
Microdiamond testing
Microdiamond testing looks for tiny diamonds in a sample obtained from drilling cores or river gravels.
What types of deposits are sampled for microdiamond testing?
Primary and secondary deposits
Primary deposits are from drilling cores, while secondary deposits are from river gravels or seafloor sediments.
How are samples processed during microdiamond testing?
Samples are hand sorted under a microscope.
What is the second level of sampling called in diamond testing?
Diamond character sampling
This stage assesses diamond size, shape, clarity, and color based on processing up to 500 tons of earth.
What does diamond character sampling help to determine?
Diamond quality and ore grade
Ore grade is the concentration of diamonds measured by the amount of diamonds in 100 tons of rock.
What is the typical amount of earth processed during bulk sampling?
Between 5,000 and 10,000 tons
Bulk sampling is conducted on a much larger scale than character sampling.
What is the goal of bulk sampling in diamond testing?
To produce a parcel of about 2,000 carats of diamonds for accurate evaluation.
What is typically required to evaluate the viability of a mine at a secondary deposit?
A parcel of 3,000 to 5,000 carats.
What must a company be knowledgeable about by the bulk sampling stage?
Local geology, environmental, and economic issues.
True or False: The bulk sampling stage requires the same operations as if a small mine were in production mode.
True
What influences whether a diamond project is continued or abandoned?
Results from the testing stages.
What is a characteristic of secondary deposits compared to pipes?
Secondary deposits tend to be wider and shallower than pipes.
What is often needed to determine the economic viability of a secondary deposit?
More bulk sampling is often needed.
What is the common image of diamond mining depicted in movies?
Workers covered in sweat and dirt, toiling with picks and shovels in underground tunnels.
How do modern diamond mining operations differ from traditional images?
They are large in scale, extremely expensive, and highly mechanized.
What types of devices and machinery are used in modern diamond mining?
Sophisticated remote-controlled devices and heavy machinery.
Where are diamonds found in primary deposits?
Embedded in kimberlite or lamproite.
What is the basic approach to mining a primary deposit?
Dig out and remove all material in and around the pipe.
What mining methods are typically used for primary deposits?
Open-pit mining followed by underground mining.
What is overburden in the context of diamond mining?
Rock or soil that covers the pipe.
What is yellow ground?
Highly weathered overburden that is soft and easy to work on.
What is blue ground?
The hard rock below the overburden, often having a bluish color.
What is the purpose of drilling holes and inserting explosives in the mining process?
To blast the ore loose.
What type of charges are used to avoid shattering diamonds during blasting?
Low-velocity charges.
What equipment is used to remove loosened material after blasting?
Hydraulic shovels.
How is the ore transported after being loosened?
Loaded into large ore trucks.
What shape does an open-pit mine form as it is developed?
A deepening cone that follows the contours of the diamond pipe.
Why are the sides of an open-pit mine terraced?
To provide stability and prevent landslides.
What happens to the quantity of diamonds as the pit deepens?
It decreases.
What consideration might lead mining companies to develop an underground mine?
If the diamond-to-ore ratio is still good.
What does an underground mine consist of?
A series of vertical shafts and horizontal tunnels.
What is the purpose of the shafts in an underground mine?
To provide access for personnel, equipment, supplies, and ventilation.
What are horizontal tunnels in an underground mine called?
Drifts.
What is the most common underground diamond mining method today?
Cave mining.
What is a characteristic of cave mining?
The orebody is drilled beneath the surface and recovered as it falls.
What does the removal of the orebody in cave mining create?
A large ‘cave’ where it once was.
What is a key principle followed by all subcategories of cave mining?
Blasting with low-velocity charges to loosen the ore without damaging diamonds.
What are concrete-lined tunnels used for in cave mining?
They are built directly under a large section of ore.
What is the purpose of explosive charges in cave mining?
To loosen the ore, which falls through openings in the tunnel ceiling.
What happens to the overlying kimberlite after detonating explosives?
It fractures under its own weight and falls through the openings.
What is the result of the ground settling or collapsing in cave mining?
Some of the wall rock falls into the pit.
What may happen after the uppermost block is mined out?
Cave Mining
A new block might be developed below it if there are good-quality diamonds.
Define drifts in the context of cave mining.
Horizontal tunnels used to access the orebody.
Define shafts in cave mining.
Vertical tunnels used to access the orebody and bring ore to the surface.
What equipment do miners use to scrape out broken ore from tunnels?
Heavy equipment.
How is ore transported to the surface after being scraped out?
Loaded into cars on electric trains or conveyor belts.
What is the first step in the diamond extraction process?
Sizing.
What occurs during the sizing step of diamond recovery?
Large chunks of ore are reduced in size to a couple of inches.
Why is crushing effective for releasing diamonds from ore?
The interface between the diamonds and the ore is weak.
What is a potential downside of crushing ore?
It limits the size of rocks or diamonds that remain intact.
What do most mines have to prevent large diamonds from passing through crushers?
Detection systems that automatically stop the conveyors.
Which detection system is noted as the most powerful and effective in mines?
X-ray detection systems.
Fill in the blank: The diamond recovery process includes three main steps: _______, concentrating, and recovering.
sizing
What is the primary purpose of the conveyor system in the diamond extraction process?
To carry ore to buckets that take it up a vertical shaft.
What is the main challenge of the sizing step in diamond recovery?
Preventing the destruction of rough diamonds exceeding size limits.
What is the first step in processing diamond-bearing ore?
Primary crushing
Primary crushing breaks down the ore into smaller pieces for further processing.
What is used to wash and tumble the ore after primary crushing?
Scrubbers
Scrubbers help remove dirt and clay from the ore.
What happens to the ore after it is scrubbed?
It is passed through a screen to check its size
Only materials of the target size proceed to the next step.
What is the process of separating diamond-bearing ore from lighter waste materials called?
Dense media separation
Also known as heavy media separation.
What is the purpose of the cyclone in the separation process?
To spin the mixture and separate materials based on density
The cyclone uses centrifugal force to separate lighter and heavier materials.
What happens to the lighter material during the cyclone process?
It floats to the top
The denser materials, like diamonds, sink to the bottom.
What is done to the heavy solid material after it is separated?
It is dried using rotating dryers
This process evaporates the liquid, leaving solid concentrate.
What methods can be used for the final recovery of diamonds?
Grease belt and X-ray separation
Both methods are effective in retrieving diamonds from the concentrate.
True or False: Diamonds have an affinity for grease and oils.
True
This property allows diamonds to stick to grease during separation.
Fill in the blank: The container used for dense media separation is called a _______.
Cyclone
The cyclone is designed to facilitate the separation process.
What is the role of the heavy liquid in the separation process?
To help separate diamond-bearing material from lighter waste
The heavy liquid increases the density of the separation process.
What are two common methods for diamond recovery?
Grease belt and X-ray separation
These methods utilize different physical properties of diamonds to separate them from other minerals.
How does the grease belt method work?
Diamonds stick to grease, while other minerals are washed away by water
The grease’s affinity for diamonds allows for effective separation.
What happens to the diamonds at the end of the grease belt?
The diamond-studded grease is scraped off and diamonds are removed
This process ensures that diamonds can be collected efficiently.
In what year was the X-ray separation process for recovering diamonds invented?
1958
This innovation was developed by Soviet scientists.
What is the principle behind the X-ray separation process?
Diamonds fluoresce when exposed to X-rays
This fluorescence triggers a jet of air to separate diamonds from ore.
What does the X-ray separation system use to recover diamonds?
An intense X-ray beam
The system relies on the light emitted by diamonds to facilitate their separation.
What is the primary reason for hand-sorting diamonds after recovery?
Material recovered contains other minerals
Hand-sorting ensures that only diamonds are collected for further processing.
Why is the standard diamond recovery process not used at Letšeng mine?
Letseng is economically viable due to its ability to recover large stones intact
The focus on large diamonds distinguishes Letšeng from other mines.
What significant investment did Gem Diamonds make at Letšeng mine?
Investment in new technology to minimize damage to large diamonds
This investment also aimed to reduce construction and operating costs.
What system replaced the traditional crusher at Letšeng mine?
A cone crushing system
This system was specifically configured to minimize damage to diamonds.
What is the size of ore pieces produced by the new cone crushing system?
Approximately 50 mm (about 2 inches) in diameter
This is larger than the 25 mm produced by the previous system.
What notable diamonds were produced at Letšeng mine in 2013?
Seven diamonds over 100 carats, 16 between 60 and 100 carats, and 50 between 30 and 60 carats
This production highlights the effectiveness of the new crushing system.
What is the largest diamond found at Letšeng to date?
The Lesotho Legend, a 910-ct. D-color rough
This diamond was recovered in 2018.
What type of mining still uses simple equipment and methods in Kono District, Sierra Leone?
Small-scale alluvial mining
This practice reflects the historical methods from the diamond rush era.
What are the two types of secondary deposits?
Alluvial and marine.
Where are alluvial deposits typically found?
In or near riverbeds or streams.
How long can diamonds remain in place in alluvial deposits?
For millions of years.
Where are marine deposits located?
In the sand on beaches or in offshore tidal zones.
What is required to recover diamonds from marine deposits?
Highly advanced mining methods.
What type of mining is still practiced in the Kono District of Sierra Leone?
Small-scale alluvial mining.
What equipment and methods are used in small-scale alluvial mining in Sierra Leone?
The same simple equipment and methods as the first diamond rushes.
Fill in the blank: Alluvial deposits are found in or near _______.
riverbeds or streams.
True or False: Marine deposits can be easily recovered without advanced methods.
False.
What percentage of diamond production today comes from alluvial mining?
About 15 percent
What has led to the shift from alluvial to primary deposits in diamond mining?
Improved technologies used to locate and mine primary deposits
Why are primary deposits more readily mined than alluvial deposits?
Alluvial deposits contain a small percentage of diamonds, making them less economical for large companies
What techniques did early alluvial miners adopt?
Techniques from gold miners
What tools did California gold miners use that became common in diamond mining?
Picks, shovels, sieves, and wide, shallow pans
How do miners separate diamonds from gravel in alluvial mining?
By swirling gravel in a pan with water, allowing heavier diamonds to sink
What is a common method used for washing river gravel in alluvial mining?
Using large baskets and circular sieves
True or False: Crushing is usually part of the alluvial mining recovery process.
False
What final processing techniques are used in large-scale alluvial operations?
Dense media separation and a grease belt or a carpeted table
Where is the Lulo mine located?
Approximately 630 km east of Luanda, Angola
What is significant about the diamonds found at the Lulo mine?
They are of high clarity and come in various colors, including pink and yellow
What is the largest rough diamond mined in Angola, and what is its weight?
The 404-ct. ‘4 de Fevereiro’ diamond
What are the methods used for marine diamond mining?
Modified alluvial mining, shallow-water mining, and deep-sea operations
How are onshore diamond mining operations in Namibia conducted?
By building large earthen dams to hold back water and expose the seabed
What depth can the seabed reach during Namibian onshore mining?
Up to 20 m below sea level
What special tools might be used to remove diamonds from crevices in onshore mining?
Compressed air jets
Fill in the blank: The Lulo mine has a mining lease of over _______ square km.
3,000
What kind of technology does Lucapa use for diamond detection?
X-ray technology
What kind of environmental factors influence marine diamond deposits?
Constantly changing sea levels and the weights of rough diamonds
What is the primary reason for the economic viability of individual miners in alluvial deposits?
They can operate profitably with smaller amounts of diamonds
What equipment is used in some mining operations to recover diamonds?
Giant vacuums mounted on 10-ton trailers
These vacuums follow earthmoving equipment to pick up material for transport.
How does the automated process of diamond recovery work?
Marine mining
Material picked up by vacuums goes into a pipe for direct transport to the processing plant
This makes diamond recovery secure and efficient.
What is the main challenge of offshore diamond mining compared to onshore mining?
Offshore diamond deposits pose a greater recovery challenge
It is likened to retrieving a bag of sugar scattered over two football fields with a small vacuum.
By approximately what year are Namibia’s onshore diamond resources expected to run out?
2035
This has led to a trend of mining more offshore marine deposits.
How are offshore diamond deposits categorized?
Based on the depth of the water
Deposits are divided into those in water less than 15 m deep and those in deeper water.
What method do divers use to mine diamonds in shallow water?
A hose attached to a suction pump located on shore or in a boat
Divers vacuum gravel off the ocean floor.
What happens to the gravel collected by divers during shallow-water mining?
It is sieved, and the remaining material is sent to a plant for processing
This process ensures the recovery of diamonds from the gravel.
Why do divers regularly return to explore areas that have produced diamonds in the past?
Because the surf constantly moves sand and gravel along the coast, possibly creating new diamond deposits
This makes previously mined areas potentially valuable again.
Fill in the blank: Offshore deposits are divided into two zones based on the _______.
depth of the water
This division affects the mining techniques used.
True or False: Divers in deep water use the same techniques as those in shallow water.
False
Mining operations in deeper water are more complex.
What is the first step in the search for diamonds in deeper water?
Detailed mapping of the ocean floor
This involves using advanced technologies to understand the underwater topography.
What company is involved in a joint venture with the Republic of Namibia for diamond exploration?
Debmarine Namibia
This venture is a collaboration between De Beers and the Namibian government.
How much area does Debmarine Namibia’s exploration vessel cover?
6,000 square km
This extensive area is searched for potential diamond deposits.
What types of equipment do mining companies use to map the ocean floor?
Sophisticated equipment like sonar and global positioning satellites
These tools help create accurate maps of the undersea landscape.
What features of the ocean floor are identified as likely containing diamond deposits?
Ravines, basins, and ridges
These geological features are important for locating diamonds.
To what depth do divers go to search for diamonds?
About 40 m
This depth requires special equipment for safe exploration.
What type of suits do divers wear when searching for diamonds?
Special heated diving suits
These suits are necessary for comfort and safety at depth.
What tools do divers use to collect material from the ocean floor?
Powerful vacuums
These vacuums help in efficiently collecting diamond-bearing material.
How long can divers work at depths of about 40 m?
For only short periods of time
This limitation necessitates the use of alternative methods for efficiency.
What alternative method do mining companies use to improve efficiency and reduce risk?
Automated crawlers equipped with vacuum devices
These machines can operate continuously without the limitations faced by human divers.
What type of vessels do mining companies use for deposits at great depths?
Large recovery ships
These ships are self-contained units capable of operating in various seafloor conditions.
How many ships does Debmarine Namibia operate off the coast of Namibia?
Six ships
They operate 19 km off the coast.
Until what year does Debmarine’s mining license allow operations off the coast of Africa?
2035
This license permits operations in a specific area.
What is the maximum depth at which Debmarine’s ships operate?
140 m
This depth is considered treacherous for maritime operations.
What is the name of the largest vessel in Debmarine’s fleet?
SS Nujoma
Named after Namibia’s founding president, Samuel Daniel Shafiishuna Nujoma.
What was the cost to build the SS Nujoma?
$157 million
The ship began operating in June 2017.
What is the length and weight of the SS Nujoma?
113 m long and 12,000 tons
It can accommodate 80 crew members.
How do deep sea mining operations collect sediments?
Using robotic crawlers
A horizontal crawler is attached to a ship on the ocean’s surface.
How much sediment can a crawler collect per hour?
Up to 60 tons
The crawler dredges the sediment from the sea floor.
What happens to the sediment once it reaches the ship?
It is pumped to the separation facility
The sediment is washed and sieved into smaller sizes.
What is the first step in processing the dredged sediment?
Crushing larger rocks with rotating drums
Oversized sediment is returned to the ocean.
How are diamonds processed from the sediment?
Using X-ray technology
Diamonds are separated and sealed in an automated process.
What happens to sediment that does not contain diamonds?
It is returned to the ocean
This ensures minimal waste during the process.
How are diamonds transported after being processed?
They are put in small barcoded containers and flown via helicopter
This occurs three times a week to the mainland.
What made Argyle’s mine economically viable?
High concentration of diamonds and pink/red diamonds
The main production of small brown diamonds would not have made it profitable.
What drives all mining activities?
Economics
The projected value of a mine’s diamonds must exceed the cost of mining.
What is required before making a mining commitment?
Enormous amounts of time, work, and expense
This is necessary to analyze a deposit.
