Chapter 4 Flashcards
Where are most diamonds mined coming from?
From primary deposits
In which deposits diamonds are more concentrated?
In secondary deposits.
Which deposits contain a higher percentage of gem quality diamonds?
Secondary deposits.
Where geologists focus search for primary deposits?
They focus on cratons.
Where geologists look for secondary deposits?
They look for deposits in rivers, streams, and estuaries flowing away from cratons.
What helps geologists narrow the search areas for diamonds?
Various surveys.
What kind of deposits require more bulk sampling than primary deposits to asses potential diamond content?
Secondary deposits.
How open-pit mining works?
Open-pit mining removes diamond-bearing ore from a large opening dug at the surface of the earth.
What is most common method of underground diamond mining.
Cave mining.
What are three main steps of diamond recovery?
Sizing, concentrating, and recovering.
How is sizing accomplished?
Through a series of crushing and scrubbing.
What was cause of shift in emphasis from secondary to primary diamond mining?
Improved technology.
Where are largest known marine deposit in the world?
In Namibia.
Where are the majority of diamonds are produced?
In four main regions.
Where are located most diverse diamond sources?
In Africa.
Which country is a top diamond producer in terms of both value and volume?
Botswana.
Which mine was once a major colored diamond producer?
Australia’s Argyle mine.
Who is the 3rd largest diamond producer?
Canada in terms of both volume and value.
From which deposits diamonds are mined in Brazil?
Alluvial deposits.
How much rough diamonds Russia provides?
Russia provides about a third of the world’s supply.
Definition of Alluvial deposits?
A deposit where gems are eroded from
their source rock and then transported away from the
source and further concentrated in rivers and streams.
What is bulk sampling?
Large scale character sampling of 5,000 to 10,000 tons.
What is cave mining?
An underground mining technique in which orebody is drilled beneath the surface, loosened, and collected as it falls.
What is character sampling?
Testing the size, shape, clarity, and color of diamonds in a deposit based on 500 tons of rock.
What is dense media separation?
A recovery process that separates diamonds from lighter materials.
What is a drift?
A horizontal tunnel drilled through diamond pipe.
What is geochemical testing?
An analysis that determines the chemical composition of the sample
What is a mechanism that uses diamond’s affinity for grease to separate diamonds from other minerals?
Grease belt
What are indicator minerals?
Minerals that form along with diamonds at great depths and are brought to the surface by the same kimberlite or lamproite.
Definition of marine deposit?
A secondary diamond deposit created by rivers or streams carrying diamonds to the shoreline or ocean floor.
What is micro diamond testing?
Screening for the presence of tiny diamonds in a sample.
Definition of ore grade?
The concentration of diamonds in a deposit, measured by the amount of diamonds in 100 tons of earth removed
What is overburden?
Rock or soil that covers a diamond-bearing orebody.
What is a parcel?
A quantity of stones, sometimes of similar size and quality, packaged together for sale or storage.
How do you cal a deposit where gems are found in the rock that carried them to the surface?
Primary deposit.
Definition of recovery?
A process used to separate diamonds from host rock or sediments.
Definition of secondary deposit?
A deposit where gems are found away from their primary source.
How is called vertical tunnel drilled in stable rock near the pipe to provide access for personel, equipment, supplies and ventilation?
Shaft.
How is called a process to reduce diamond bearing ore to smaller, more manageable sizes?
Sizing
What is X-ray separation?
A rough recovery method that uses X-rays to detect diamonds and an air jet to remove them from ore.
What many mining companies do to find diamonds?
They use advanced technology to find and mine diamonds.
What modern mining involves?
Extensive exploration, strategic evaluation, and sophisticated construction and operation.
Why large mining companies such De Beers and ALROSA invest a large amount of their revenue in exploration each year?
Even newer mines will eventually stop producing and need to be replaced in order to maintain the world’s diamond supplies.
What is first part of the mine to market journey?
Locating a diamond deposit.
What determines the exploration methods geologists use?
Type of deposit they are looking for.
What most people don’t realize about bringing diamonds to retail?
They don’t realize the time and money that was invested and the many tons of rock excavated to bring to store.
How alluvial deposits form?
They form when pipes erode and their rough diamonds wash into rivers or streams.
Where diamonds may accumulate in alluvial deposits?
In areas of slow water, such as river bends.
What happens if the speed of water in the rivers/streams is high enough?
Diamonds might be carried all the way to the ocean and form marine deposits.
Are kimberlite and lamproite stable in the earths atmosphere?
No they aren’t, environmental forces break them down relatively quick.
Where is example of onshore mining operation of diamonds?
Along the coast of Namibia.
What happens when diamonds are carried in river?
Diamonds are caught in small whirlpools and sink to the bottom.
Can alluvial deposits be found in dry places?
Yes in in places where rivers or streams once existed.
Where ocean currents deposit diamonds?
Offshore or wash them back onto the beach.
Why marine deposits contain higher percentages of gem crystals then pipes do?
Because low-quality diamonds, with their inclusions and fractures, don’t survive the stresses of the marine environment.
Who and what kind of experiment conducted to show why marine deposits contain higher percentages of gem quality diamond crystals?
De Beers researchers conducted experiment in which they filled large cylinder with 265 pounds of steel balls, some gravel, water, and natural industrial diamonds. Then they rotated cylinder to simulate the tumbling similar to one that takes place in an onshore or tidal environment. After 7 hours the industrial diamonds were reduced to a fine powder.
What happened when De Beers researchers conducted “tumbling” experiment with gem-quality diamonds?
After 950 hours of tumbling, diamonds were still mostly whole, they gad lost only 0.01 percent of their weight.
What you can say about exploration for diamonds?
Exploring for diamonds is a long, difficult, and expensive process. Mining companies spend millions of dollars each year.
How much time it takes from beginning a search to mining the first diamonds?
Usually more then 10 years.
What happens in first years?
The deposit is located and assessed for diamond content.
How long time takes building the mine before operations begin?
It takes several years.
What is Clifford’s Rule based on?
Its based on the observation that diamond-bearing kimberlites are associated with old cratons that have been stable for 2,5 billion years.
Who proposed Clifford rule?
T.S. Clifford in 1966.
What Clifford Rule states?
The rule states that although not all kimberlites contain diamonds, those that do occur only on these very old cratons on to of deep mantle keels.
Is Cliffords Rule holds true?
Largely yes, nearly all diamond-bearing kimberlites have been found on cratons or their margins, and most occur in the oldest cratonic areas.
Are the exceptions to the Clifford’s Rule?
Yes, like Argyle deposit in Australia and Lomonosov deposit in Russia
Why diamond deposits occur outside of cratons and away from their margin?
Plate tectonics and continental drift push younger rocks up to the much older cratons in collision belts.
Can kimberlites be located in collision belts?
Yes, but it’s more common for lamproites to occur here.
Where was located Argyle mine deposit?
It is located in a collision belt surrounding the Kimberley Craton.
What means diamondiferous?
Diamond-bearing
What is exception to Clifford’s Rule?
Lamproites deposits.
What method allows geologists to locate cratons?
Geological mapping
How sound waves works in geological mapping?
Craton is denser than the younger surrounding rock, so when a sound wave strikes it, the wave move faster? When rapid wave movement is detected, scientists could be fairly certain they had found a craton.
How are targeted secondary deposits by geologists?
Geologists look for ancient or current streams, rivers, and estuaries (tidal mouths of rivers) flowing away from cratons, or those that are located on direct paths from or near known kimberlite or lamproite pipes.
What type of diamond deposits are mostly mined in Sierra Leone?
Alluvial deposits.
Where alluvial diamonds are found?
In lakes, rivers, shoreline marine deposits, dried-up waterways, and offshore deposits.
Which deposits are easier to find?
Alluvial deposits because they’re above ground and often spread over large areas.
What does traditional artisanal mining exploration consist of?
Traditional artisanal mining exploration consists of sampling stream sediments or sediments of dried-up ancient riverbeds.
What types of sediments are sampled during traditional artisanal mining?
Stream sediments or sediments of dried-up ancient riverbeds.
How do prospectors use sieves in the process of artisanal mining?
Prospectors use large sieves and swirl the water around.
Why do prospectors swirl water around when using sieves?
Prospectors use large sieves and swirl the water around to make diamond and other heavy minerals sink to the bottom of the pan, while lighter materials float toward the edge.
What happens to lighter materials during the sieving process?
Lighter materials float toward the edge.
What do prospectors do after upturning the sieve?
To inspect the center of the sediment for any diamonds or indicator minerals.
Where do prospectors typically inspect for diamonds or indicator minerals?
They inspect the center of the sediment.
What do prospectors do if diamonds are found in a specific area?
If diamonds are found, they might work this area before moving to the next bend in the river.
What actions do prospectors take if only indicator minerals are found?
If only indicator minerals are found, they follow these upstream in hopes of finding diamonds.
Do artisanal miners typically work alone or in groups?
These types of miners tend to work on their own or in small groups.
What is the typical quality of diamonds found through traditional artisanal mining?
Quality of the diamonds might be high.
How does the quantity of diamonds compare to their quality in artisanal mining?
The quantity tends to be low.
What are modern exploration methods for alluvial deposits?
There are several methods: aerial photography, satellite imaging, and radar.
What are more traditional exploration methods for alluvial deposits?
Field mapping, soil sampling.
What are exploration methods for offshore deposits?
Giant pumps dredge up sediments from the ocean bottom for testing.
Why in late XX century focus turned to marine deposits?
Because of the huge quantities of diamonds in offshore deposits.
What is an example of diamond mining vessel ship operated in Namibia?
The Mafuta operated by Debmarine Namibia, a joint venture between DeBeers and the Namibian government.
How much of ocean floor Mafuta will scour?
6,000 square km
What alluvial deposit exploration often uses?
Mineral sampling.
How gravity surveys work?
They measure density variations in the ground to detect kimberlite or lamproite, because they have more gravitational pull than surrounding rock.
What for aerial photography and digital topography are used?
To look for circular or near-circular features in the landscape that could be pipes.
What aerial surveys can spot that would be not obvious to geologists on the ground?
Shadows and contours.
What have seeing an aerial surveyor in Canada for example?
Round shadow at the bottom of a lake that turned turned to be the top of a diamond-bearing pipe.
What can detect the possible presence of kimberlite pipes before ground exploration begins?
Aerial magnetic surveys.
How Aerial magnetic surveys work?
It maps out grid of back-and-forth passes to follow in order to cover the area thoroughly.
How electromagnetic surveys can be done?
It can be done on foot or from the air.
What happens after electromagnetic surveying a large area?
Map is generated showing various features not visible to geologists.
How information from surveys helps geologists?
It helps further narrow the targeted areas.
How modern advances helped in exploring deposits?
They have assisted in the discovery of diamond deposits in previously unexplored areas.
How magnetic surveys on foot are taken?
Typically, a person holding a handheld GPS moves along a predetermined path and takes a reading every 50 meters. The data is saved and carefully studied for signs of magnetic variations.
How seismic survey works?
Seismic surveys work similarly to magnetic and electromagnetic surveys but use sound waves to detect the features of different rocks.
Why kimberlite and lamproite have unique features?
They posses unique features that are detected by seismic surveying.
