Chapter 4 Flashcards
1
Q
Where are most diamonds mined coming from?
A
From primary deposits
2
Q
In which deposits diamonds are more concentrated?
A
In secondary deposits.
3
Q
Which deposits contain a higher percentage of gem quality diamonds?
A
Secondary deposits.
4
Q
Where geologists focus search for primary deposits?
A
They focus on cratons.
5
Q
Where geologists look for secondary deposits?
A
They look for deposits in rivers, streams, and estuaries flowing away from cratons.
6
Q
What helps geologists narrow the search areas for diamonds?
A
Various surveys.
7
Q
What kind of deposits require more bulk sampling than primary deposits to asses potential diamond content?
A
Secondary deposits.
8
Q
How open-pit mining works?
A
Open-pit mining removes diamond-bearing ore from a large opening dug at the surface of the earth.
9
Q
What is most common method of underground diamond mining.
A
Cave mining.
10
Q
What are three main steps of diamond recovery?
A
Sizing, concentrating, and recovering.
11
Q
How is sizing accomplished?
A
Through a series of crushing and scrubbing.
12
Q
What was cause of shift in emphasis from secondary to primary diamond mining?
A
Improved technology.
13
Q
Where are largest known marine deposit in the world?
A
In Namibia.
14
Q
In how many regions the majority of diamonds are produced?
A
In four main regions.
15
Q
Where are located most diverse diamond sources?
A
In Africa.
16
Q
Which country is a top diamond producer in terms of both value and volume?
A
Botswana.
17
Q
Which mine was once a major colored diamond producer?
A
Australia’s Argyle mine.
18
Q
Who is the 3rd largest diamond producer?
A
Canada in terms of both volume and value.
19
Q
From which deposits diamonds are mined in Brazil?
A
Alluvial deposits.
20
Q
How much rough diamonds Russia provides?
A
Russia provides about a third of the world’s supply.
21
Q
Definition of Alluvial deposits?
A
A deposit where gems are eroded from
their source rock and then transported away from the source and further concentrated in rivers and streams.
22
Q
What is bulk sampling?
A
Large scale character sampling of 5,000 to 10,000 tons of rock.
23
Q
What is cave mining?
A
An underground mining technique in which orebody is drilled beneath the surface, loosened, and collected as it falls.
24
Q
What is character sampling?
A
Testing the size, shape, clarity, and color of diamonds in a deposit based on 500 tons of rock.
25
What is dense media separation?
A recovery process that separates diamonds from lighter materials.
26
What is a drift?
A horizontal tunnel drilled through diamond pipe.
27
What is geochemical testing?
An analysis that determines the chemical composition of the sample
28
What is a mechanism that uses diamond's affinity for grease to separate diamonds from other minerals?
Grease belt
29
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.
30
Definition of marine deposit?
A secondary diamond deposit created by rivers or streams carrying diamonds to the shoreline or ocean floor.
31
What is micro diamond testing?
Screening for the presence of tiny diamonds in a sample.
32
Definition of ore grade?
The concentration of diamonds in a deposit, measured by the amount of diamonds in 100 tons of earth removed
33
What is overburden?
Rock or soil that covers a diamond-bearing orebody.
34
What is a parcel?
A quantity of stones, sometimes of similar size and quality, packaged together for sale or storage.
35
How do you call a deposit where gems are found in the rock that carried them to the surface?
Primary deposit.
36
Definition of recovery?
A process used to separate diamonds from host rock or sediments.
37
Definition of secondary deposit?
A deposit where gems are found away from their primary source.
38
How is called vertical tunnel drilled in stable rock near the pipe to provide access for personel, equipment, supplies and ventilation?
Shaft.
39
How is called a process to reduce diamond bearing ore to smaller, more manageable sizes?
Sizing
40
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.
41
What many mining companies do to find diamonds?
They use advanced technology to find and mine diamonds.
42
What modern mining involves?
Extensive exploration, strategic evaluation, and sophisticated construction and operation.
43
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.
44
What is first part of the mine to market journey?
Locating a diamond deposit.
45
What determines the exploration methods geologists use?
Type of deposit they are looking for.
46
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 diamonds to store.
47
How alluvial deposits form?
They form when pipes erode and their rough diamonds wash into rivers or streams.
48
Where diamonds may accumulate in alluvial deposits?
In areas of slow water, such as river bends.
49
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.
50
Are kimberlite and lamproite stable in the earths atmosphere?
No they aren't, environmental forces break them down relatively quick.
51
Where is example of onshore mining operation of diamonds?
Along the coast of Namibia.
52
What happens when diamonds are carried in river?
Diamonds are caught in small whirlpools and sink to the bottom.
53
Can alluvial deposits be found in dry places?
Yes in in places where rivers or streams once existed.
54
Where ocean currents deposit diamonds?
Offshore or wash them back onto the beach.
55
Why marine deposits contain higher percentages of high quality gem crystals then pipes do?
Because low-quality diamonds, with their inclusions and fractures, don't survive the stresses of the marine environment.
56
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.
57
What happened when De Beers researchers conducted "tumbling" experiment with gem-quality diamonds?
After 950 hours of tumbling, diamonds were still mostly whole, they had lost only 0.01 percent of their weight.
58
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.
59
How much time it takes from beginning a search to mining the first diamonds?
Usually more then 10 years.
60
What happens in first years of exploration?
## Footnote
Exploration
The deposit is located and assessed for diamond content.
61
How long time takes building the mine before operations begin?
It takes several years.
62
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.
63
Who proposed Clifford rule?
T.S. Clifford in 1966.
64
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 top of deep mantle keels.
65
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.
66
Are the exceptions to the Clifford's Rule?
Yes, like Argyle deposit in Australia and Lomonosov deposit in Russia
67
Why diamond primary deposits sometimes 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.
68
Can kimberlites be located in collision belts?
Yes, but it's more common for lamproites to occur here.
69
Where was located Argyle mine deposit?
It is located in a collision belt surrounding the Kimberley Craton.
70
What means diamondiferous?
Diamond-bearing
71
What is exception to Clifford's Rule?
Lamproites deposits.
72
What method allows geologists to locate cratons?
Geological mapping
73
How sound waves works in geological mapping?
A craton is denser than the younger surrounding rock, so when a sound wave strikes it, the wave moves faster. When rapid wave movement is detected, scientists can be fairly certain that they have found a craton.
74
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.
75
What type of diamond deposits are mostly mined in Sierra Leone?
Alluvial deposits.
76
Where alluvial diamonds are found?
In lakes, rivers, shoreline marine deposits, dried-up waterways, and offshore deposits.
77
Which deposits are easier to find?
Alluvial deposits because they're above ground and often spread over large areas.
78
What does traditional artisanal mining exploration consist of?
Sampling stream sediments or sediments of dried-up ancient riverbeds.
79
What types of sediments are sampled during traditional artisanal mining?
Stream sediments or sediments of dried-up ancient riverbeds.
80
How do prospectors use sieves in the process of artisanal mining?
Prospectors use large sieves and swirl the water around.
81
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.
82
What happens to lighter materials during the sieving process?
Lighter materials float toward the edge.
83
What do prospectors do after upturning the sieve?
To inspect the center of the sediment for any diamonds or indicator minerals.
84
Where do prospectors typically inspect the sieve for diamonds or indicator minerals?
They inspect the center of the sediment.
85
What do prospectors do if diamonds are found in a specific area? (alluvial)
If diamonds are found, they might work this area before moving to the next bend in the river.
86
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.
87
Do artisanal miners typically work alone or in groups?
These types of miners tend to work on their own or in small groups.
88
What is the typical quality of diamonds found through traditional artisanal mining?
Quality of the diamonds might be high.
89
How does the quantity of diamonds compare to their quality in artisanal mining?
The quantity tends to be low.
90
What are modern exploration methods for alluvial deposits?
There are several methods: aerial photography, satellite imaging, and radar.
91
What are more traditional exploration methods for alluvial deposits?
Field mapping, soil sampling.
92
What are exploration methods for offshore deposits?
Giant pumps dredge up sediments from the ocean bottom for testing.
93
Why in late XX century focus turned to marine deposits?
Because of the huge quantities of diamonds in offshore deposits.
94
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.
95
How much of ocean floor Mafuta will scour?
6,000 square km
96
What kind of sampling of alluvial deposit is used during exploration?
Mineral sampling.
97
How gravity surveys work?
Density variations is measured in the ground to detect kimberlite or lamproite, because they have more gravitational pull than surrounding rock.
98
What for aerial photography and digital topography are used?
To look for circular or near-circular features in the landscape that could be pipes.
99
What aerial surveys can spot that would be not obvious to geologists on the ground?
Shadows and contours.
100
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.
101
What can detect the possible presence of kimberlite pipes before ground exploration begins?
Aerial magnetic surveys.
102
How Aerial magnetic surveys work?
It maps out grid of back-and-forth passes to follow in order to cover the area thoroughly.
103
How electromagnetic surveys can be done?
It can be done on foot or from the air.
104
What happens after electromagnetic surveying a large area?
Map is generated showing various features not visible to geologists.
105
How information from surveys helps geologists?
It helps further narrow the targeted areas.
106
How modern advances helped in exploring deposits?
They have assisted in the discovery of diamond deposits in previously unexplored areas.
107
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.
108
How seismic survey works?
Seismic surveys work similarly to magnetic and electromagnetic surveys but use sound waves to detect the features of different rocks.
109
By what kind of survey unique features of kimberlite and lamproite are detected?
Their unique features are detected by seismic surveying.
110
What geologists do after finding area to test?
They focus their search more precisely and look certain minerals, called indicator minerals. Sometimes minerals are discovered prior to surveying.
111
Why indicator minerals are important?
Because they either form in kimberlite or lamproite.
112
What the presence of indicator minerals often means?
That a pipe is not far away.
113
How far were indicator minerals transported by ancient glacial deposits from their original source in some Canadian mines?
300 km away. Still their paths were traced back to the kimberlite pipes
114
Why hand sorting heavy minerals concentrate in the search for indicator minerals is best?
Because human eye can detect subtle shapes and colors that an automated process would miss.
115
Which indicator minerals collected in Canada helped locate important diamond-bearing kimberlite pipes?
Diopsides and garnets.
116
How the termite mounds can help in the search for diamonds?
Termites carry underground minerals to the surface while digging their tunnels. In termite mounds geologists have found diamond indicator minerals, and it lead to discovery of diamond pipes.
117
What is critical step in the search for diamonds?
Mineral sampling.
118
What are vital clues from mineral sampling?
Mineral's age, how far it's from source, and how it got there.
119
Why geologists try to test as wide area as possible with a few samples as possible?
To save time and money.
120
List indicator minerals found in association with kimberlite and lamproite?
Red and orange garnet, black spinel, diopside, olivine, limenite, chromite, and perovskite, tiny diamonds.
121
What is especially helpful when found in mineral sampling?
Tiny diamonds, because they indicate that source deposit is probably nearby.
122
When few or no indicators minerals found is exploration finished?
No, geologists further explore areas identified as potentially diamond bearing.
123
What was the case with Canada explorations?
The explored area had being subjected to substantial weathering and erosion by glaciers, the indicator minerals had been broken up, and the top of the kimberlite pipe was buried under the glacial deposits.
124
What is analyzed in geochemical testing to determine the presence of specific elements derived from indicator minerals in the samples?
Samples of rock, soil, or even vegetation in the targeted area.
125
What typically prompts further exploration and testing of samples in areas with alluvial diamond deposits?
The discovery of diamonds is typically what prompts more exploration and testing of samples in these areas.
126
What happens after locating a deposit, primary or secondary?
Geologists begin testing for the presence and concentration of diamonds.
127
What is required for testing for presence and concentration of diamonds?
This testing require increasingly larger samples, which are more expensive and more difficult to obtain.
128
Which stage of exploration is critical to determine whether a project is continued or abandoned?
Testing for the presence and concentration of diamonds.
129
What is order of sampling during testing deposit viability?
Microdiamond testing, Character Sampling, Bulk Sampling
130
How big parcel of diamonds requires bulk sampling to asses quality of large-scale secondary deposit?
Because secondary deposits tend to be wider and shallower than pipes, it's typically required parcel of 3,000-5,000 ct diamonds.
131
How big parcel of diamonds requires bulk sampling for accurate evaluation of primary deposit?
2,000 ct diamonds
132
How are gathered samples for microdiamond testing of primary deposits?
They are gathered from drilling cores.
133
How are gathered samples for microdiamond testing of secondary deposits?
They are gathered from river gravels or seafloor sediments.
134
How samples from microdiamond testing are sorted?
The samples are hand sorted under a microscope.
135
What equipment and mining operations are required for character sampling?
For character sampling, blasting and large excavators will be needed
136
What gives a general idea of diamond, size, shape, clarity, and color?
Character sampling.
137
What helps scientists develop indication of diamond quality and determine ore grade?
Character sampling, processing of up to 500 tons of earth.
138
How is measured concentration of diamonds (ore grade) during character sampling?
It's measured by the amount of diamonds in 100 tons of rock.
139
When testing progresses from character sampling to the last stage, bulk sampling?
If results are promising.
140
Is it usually enough to analyze one character sample?
No, usually it's necessary to analyze multiple character samples from one deposit.
141
To what bulk sampling is similar?
It's similar to character sampling, but on a much larger scale.
142
How big parcel of diamonds during bulk sampling needs to be produced for an accurate evaluation?
A diamond parcel of about 2,000 carats.
143
To what process bulk sampling on-site operations are similar?
It's the same as if a small mine were in production.
144
What about mining company must be knowledgeable about?
Company must be knowledgeable about local geology but also mindful of the local environmental and economic issues.
145
When Davik mine transitioned fully to underground mining?
In September 2012.
146
What is basic approach to mining a primary deposit?
It is to dig out and remove all the material in and around the pipe.
147
How is usually accomplished mining primary deposit?
By open pit mining followed by underground mining.
148
How digging an open-pit mine usually begins?
With the removal of layers of overburden - rock or soil - that cover the pipe.
149
What miners do with overburden?
They process it for any diamonds it main contain.
150
What is characteristic of overburden?
Overburden is highly weathered, so it's soft and easy to work on.
151
How overburden is called by miners?
Yellow ground.
152
How is called the hard rock below the overburden?
Blue ground.
153
What miners do in first in open pit mining?
They drill holes into the pipe, insert explosives into holes, and blast the ore loose.
154
What kind of explosives are used by miners?
Low-velocity charges to avoid shattering the diamonds.
155
What miners do after blasting the ore?
They remove the loosened material with hydraulic shovels and load it into large ore trucks.
156
What is true image of modern mining?
Most operations are large in scale (small towns size) and extremely expensive. Many Mines are highly mechanized. Miners use sophisticated remote-controlled devices and heavy machinery.
157
What forms as an open mine is developed?
It forms a deepening cone that follows the contours of the diamond pipe.
158
What is done to provide stability of pit so that wall doesn't collapse and cause a landslide?
Sides are terraced to provide stability.
159
What terraces in pit also provide except stability?
Terraces also provide roadways around the mine's perimeter for the ore trucks.
160
Where the trucks carry rock to?
To the processing facility, where the diamonds are recovered from the ore.
161
From what depth of an open-pit mine depends?
It depends on the characteristics of the pipe and the economics of the mining operation.
162
What happens as the pit deepens?
The quantity of diamonds decreases and it becomes much narrower and more difficult fot the giant trucks to move in.
163
Why widening of narrow pit is uneconomical?
Because rock doesn't contain diamonds.
164
What happens if the diamond-to-ore ratio is still good in the pipe, but it's to narrow?
Mining company may consider developing an underground mine.
165
What an underground mine consist of?
A series of vertical shafts and horizontal tunnels (drifts) in and around a pipe.
166
Where are shafts drilled?
They are drilled in stable rock near the pipe to provide access for personnel, equipment, supplies, and ventilation.
167
Where are drifts drilled?
Drifts - horizontal tunnels - are drilled from the shafts through the pipe to extract ore.
168
What kind of underground mining diamond method is most common nowadays?
Cave mining
169
What is cave mining?
Cave mining is the method where the orebody is drilled beneath the surface and recovered as it falls.
170
Why cave mining is most common technique today?
This technique is more mechanized, so it requires a smaller work-force.
171
Is there one category of cave mining?
There are many subcategories, but they all follow same principles.
172
How drifts are build in cave-mining method?
Concrete-lined tunnels are built directly under a large section of ore.
173
How explosives are placed in orebody in cave mining technique?
They are placed in the orebody at evenly spaced openings in the tunnel ceiling.
174
What happens when in cave mining method explosives detonate?
Low-velocity detonation loosens the ore, which falls through the openings. This leaves the a void in the rock, which causes the overlying kimberlite to fracture under its own weight.
175
(Cave mining) What happens after kimberlite falls through openings?
This eventually causes the ground at the surface to settle or collapse and some of the wall rock to fall into the pit.
176
Why cave mining is safer than traditional underground mining?
Because the orebody is collected when it falls after blasting and requires a much smaller workforce because much of the work can be automated.
177
(cave mining) What is next step of operation after broken ore falls through opening?
Miners use heavy equipment to scrape ore out of the tunnel, and load it into cars on electric trains or conveyor belts that dump it into an underground crusher.
178
(cave mining) Where ore goes from the underground crusher?
A conveyor system carries the ore to buckets that take it up a vertical shaft to the surface for further processing.
179
What happens once ore is excavated?
| Land mining
It goes through a diamond extraction process, called recovery.
180
How the sizing is accomplished?
In a series of crushing and scrubbing operations to reduce ore size to a couple of inches.
181
How strong is interface between ore and the diamonds?
It's weak, so crushing easily releases the diamonds.
182
What is the disadvantage of crushing process?
Crushing limits the size of rocks or diamonds that remain intact. Rough exceeding those limits might be destroyed.
183
What most mines do to prevent large diamonds passing through the crushers?
They use detection systems that automatically stop the conveyors.
184
Which anti-crushing detection systems are most powerful and effective?
X-ray detection system, but each mine has its own system.
185
What happens with kimberlite fragments after leaving scrubber?
They are washed with water as they flow from scrubbers. Any fragments larger then the sieve holes will go to secondary crushing.
186
How X-Ray separation process works?
A thin stream of ore passes in front of an intense X-ray beam, a diamond crystal emits light that triggers a jet of air that blows the stone away into a collection bin.
187
How dense media separation works?
The ore is mixed with liquid and fed into a cone-shaped container /cyclone/. The cyclone spins the mixture, forcing liquid to and diamond-bearing material downward.
188
What kind force is used in dens media separation?
Centrifugal force.
189
How grease belt works?
As water washes the ore over the grease belt, diamonds embed in the grease belt. The grease will be melted away, leaving the diamonds.
190
What happens after primary crushing?
Scrubbers wash and tumble the ore to remove dirt and clay. The the ore is typically passed through a screen to check the size.
191
What happens when the ore that is to large after primary crushing, washing/scrubbing and screening? (land)
Ore go again through crushing and scrubbing again, until they are small enough for the next step: concentrating.
192
How is differently called dense media separation?
Heavy media separation.
193
What happens with lighter material in dense media separation?
It floats to the top.
194
What happens with denser material in dense media separation?
It sinks to the bottom of the container.
195
How is separated material from liquid after dense media separation?
Rotating dryers evaporate the liquid.
196
How recovery process can be accomplished?
It can be accomplished by different methods, most common are grease belt and X-ray separation.
197
What kind of affinity diamond has?
For grease and oils.
198
When and by whom X-ray separation method was invented?
In 1958 by Soviet scientists.
199
On what principle X-ray separation process in based?
On the fact that diamonds almost always fluoresce when exposed to X-rays.
200
Why diamonds must be sorted by hand after grease belt or X-ray separation process of diamonds?
Recovered material contains a high proportion of diamonds, but also other minerals too.
201
Enumerate the main steps of the recovery process?
Sizing, concentrating, recovery.
202
Enumerate steps of sizing?
Crushing, scrubbing, screening
203
Recovery steps?
X-ray separation, grease belt separation, hand separation.
204
Why Letseng mine is economic viable?
Because it's ability to recover large stones intact.
205
What is largest D-flawless heart shaped diamond in the world?
The Graff-Venus 118,78-ct. Cut from 357-ct. rough recovered at Letseng mine 2015.
206
What did Gem Diamonds company did in Letseng Mine to minimize damage to large diamonds?
In mid 2013, the company replaced the crusher's large steel jaws with a cone crushing system, where ore passes over a rapidly spinning cone.
207
What is the largest diamond found at Letseng mine in 2018?
Lesotho Legend 910-ct. D-colour rough.
208
Where are still used simple equipment and methods as the first diamond rushes?
In the Kono district in eastern Sierra Leone.
209
Where marine deposits are found?
They are found in the sand on beaches (onshore) or in offshore tidal zones.
210
For how long people have recovered diamonds from alluvial deposits?
For more than 2,000 years.
211
What percentage of diamond production is attributed to alluvial mining today?
Alluvial mining accounts today for about 15% of diamond production.
212
Why alluvial deposits may be more economical for individual miners than large companies?
Many of alluvial deposits contain only small percentage of diamonds.
213
From where early alluvial diamond miners adapted their methods?
They adapted methods from gold miners.
214
Where did many veterans of the California Gold Rush of 1849 go after the word spread about the discovery of diamonds?
They went to Africa.
215
Are all alluvial mining is small scale?
No, but large-scale alluvial mining is rare.
216
What technology is used in large-scale alluvial mining?
Mechanized recovery and sieving and large earthmoving equipment, dams and dredging ships to pump diamond-bearing gravels, floating processing plant.
217
Is crushing is usual part of the recovery process for alluvial mining?
No, usually a series of sieves separates the diamonds from the surrounding waste material before they're loaded into the washing pan.
218
Where is located Lucapa's Lulo mine?
It's located approx. 630 km east of Angola's capital city, Luanda.
219
What is Lulo mine?
It's a large alluvial diamond mine with a mining lease of over 3,000 sq. km in Angola.
220
Where Lulo's diamodns are found?
Along 50km of the Caculo River in alluvial gravels.
221
What is the thickness of alluvial gravels in Caculo river?
0,2 - 1,5 m in thickness.
222
How far Lulo mine is from the largest diamond mine in the world?
It's 150 km from Catoca mine.
223
Which X-ray technology is used by Lucapa in Lulo mine?
X-ray technology that can detect diamonds up to 1,100 ct.
224
What is the largest diamond mined in Angola?
The "4 de Fevereiro" diamond 404 ct.
225
What "4 de Fevereiro" name stands for?
It's name is a reference to the Angola War of Independence.
226
What kind of diamonds is produced in in the Lulo mine?
Diamond of high clarity and colors, also pink and yellow diamonds.
227
Which alluvial mine is among of those having highest average rough price?
Lulo mine.
228
What method some onshore operations is sometimes used to dislodge diamonds trapped in small crevices?
They use large vacuums.
229
What methods are using mining companies for marine mining?
Various, these include modified alluvial large scale mining, shallow-water mining with divers, dee-sea operations with sophisticated, high-tech ships and vessels.
230
What is needed during onshore mining for dislodging and removing diamonds?
Dislodging and and removing diamonds from small cracks and crevices requires special tools and procedures.
231
onshore in Namibia: What do miners do first to expose the seabed for diamond mining?
| Near shore
First, miners build large earthen dams in the surf zone to hold back water and leave the seabed exposed, up to 20m below sea level.
232
onshore in Namibia: What do miners do second to expose the seabed for diamond mining?
Large earthmoving equipment excavates and removes sand and gravel.
233
onshore in Namibia: How do workers ensure that diamonds are not left behind in the bedrock? (Step 3)
Then workers with brooms and other tools sweep out every crevice where diamonds might be hidden in the irregular, pockmarked bedrock. Sometime they use compressed air jets to dislodge diamonds trapped in small crevices.
234
What kind of vacuums some onshore operations use?
They use giant vacuums mounted on 10-ton trailers that follow earthmoving equipment.
235
Where is one of the world's largest earthmoving projects?
In Namibia
236
What is the second type of marine mining?
Offshore diamond mining.
237
What poses an even greater recovery challenge compared to onshore diamond deposits?
Offshore diamond deposits pose even more of a recovery challenge than onshore deposits.
238
What analogy is used to describe the difficulty of offshore diamond mining?
Offshore diamond mining is a little like scattering a 900-g bag of sugar over two adjacent football fields, and then trying to to retrieve the sugar with a small vacuum on a dark night.
239
When Namibia's onshore diamond resources are expected to run out?
By approx. 2035
240
What is the trend now in marine mining?
Trend is now developing to mine more offshore marine deposits as onshore mines near the end of production.
241
How offshore deposits are divided?
They are divided into 2 zones based on the depth.
242
How are diamond deposits mined in water less than 15 meters deep compared to deeper waters?
Deposits in water less than 15 m deep can be mined by divers, in deeper water, mining operations are more complex.
243
How divers work in shallow-water mining operations?
They use a hose attached to a suction pump located on shore or in a boat.
244
How the diver vacuums work?
The vacuum vacuums gravel off the ocean floor, the gravel from the pump is sieved, and the remaining material is sent to a plant for processing.
245
Why 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.
246
What kind of vessels are used for deep-sea mining operations?
Large recovery ships, like Debmarines Debmar Atlantic.
247
How deep-sea mining operation begins?
With detailed mapping of the ocean floor.
248
What does Debmarine Namibia use to explore deep-sea ocean floor for diamonds?
Debmarine Namibia, a joint venture between De Beers and the Republic of Namibia, uses a state-of-the-art exploration vessel that scours 6,000 square km of ocean floor for diamonds.
249
What kind of equipment & methods are used for deep-sea mapping?
Mining companies use sophisticated equipment like sonar, along with data from global positioning satellites, to develop remarkably accurate maps of undersea floor.
250
How deep-sea mapping helps?
Generated maps help identify the areas most likely to contain diamond deposits, such as ravines, basins, and ridges.
251
Do divers take part in deep-see operations?
Yes
252
How work of divers look in deep-sea mining?
Divers use special heated diving suits, go down up to 40m deep, they use powerful vacuums to pick up material from the ocean floor.
253
How long diver can work deep-sea?
Diver can work for only short periods of time.
254
What some mining companies use to improve efficiency and reduce risk in offshore mining?
Some companies use automated crawlers equipped with devices that vacuum material from the ocean floor.
255
What is used for deposits at greater depths than 40m?
Large recovery ships are used.
256
What you can say about large recovery ships?
Each vessel is a self-contained unit and can operate in a variety of seafloor conditions.
257
How many ships operate in Debmarine Namibia company?
Debmarine operates a fleet of six ships, 19km off the coast of Namibia.
258
Till when Debmarine's Namibia mining license will be valid?
Until 2035.
259
Which ship is the largest in Debmarine fleet?
The SS Nujoma
260
What was a cost of building SS Nujoma?
The cost $157 million in June 2017.
261
What size and weight is SS Nujoma?
113 m long and 12,000 ton heavy.
262
How much crew can be accommodated on SS Nujoma?
80 crew members.
263
What equipment is attached to the ship on the ocean's surface during offshore diamond mining?
A horizontal crawler is attached to the ship on the ocean's surface.
264
How does the crawler operate on the sea floor, and how are the dredged sediments transported to the ship?
The crawler moves along the sea floor to the targeted area and begins to dredge. The dredged sediments are pumped up to the ship via giant pipe.
265
How much sediment deep-sea crawler can collect per hour?
Up to 60 tons of sediment.
266
What happens with sediments when they reach the ship?
Sediments are pumped to the separation facility, where it is washed and sieved into smaller and smaller sizes.
267
What you can say about operation of Debmarina Namibia fleet?
These ships operate 24h/day, in depths up to 140m, in some of the most treacherous waters on earth.
268
What is the first step in processing the dredged material during offshore diamond mining?
First rotating drums crush larger rocks.
269
What happens to the sediment and crushed rocks after passing through the sieves?
| marine mining
They pass to the next stage, and oversized sediment is returned to the ocean.
270
How is sediment processed after being washed and sieved?
| Offshore mining
It goes to a dense media separation facility and is then processed for diamonds using X-ray technology.
271
What happens to sediment that does not contain diamonds?
Any sediment not containing diamonds is returned to the ocean.
272
What happens to the diamonds after they are separated from the sediments in X-ray facility?
| Offshore mining
The diamonds are taken from the X-ray facility, sealed in an automated process, and put in small barcoded containers.
273
How are the diamonds transported after being sealed?
They are loaded into cases and flown via helicopter to the mainland three times a week.
274
What is Microdiamond Testing?
Looking for the presence of tiny diamonds in field samples under a microscope.
## Footnote
Microdiamond testing is crucial for initial assessments of diamond deposits.
275
What is Character Sampling?
Processing approximately 500 tons of rock to characterize the deposit’s diamond quality in terms of size, shape, color, and clarity.
## Footnote
Character sampling helps in understanding the overall quality of the diamond deposit.
276
What is Bulk Sampling?
Processing approximately 5,000–10,000 tons of rock to obtain a 2,000-ct. parcel of diamonds for accurate evaluation of a primary deposit.
## Footnote
Bulk sampling is essential for evaluating the economic viability of a diamond mine.
277
How many carats are typically required to assess the production quality of a large-scale secondary deposit?
Typically requires a 3,000–5,000-ct. parcel of diamonds.
## Footnote
This quantity ensures a reliable assessment of secondary deposits.
278
What is the first stage of testing after locating a diamond deposit?
Microdiamond testing
## Footnote
This stage involves looking for tiny diamonds in a sample from primary or secondary deposits.
279
What types of samples are used in microdiamond testing?
Samples from drilling cores, river gravels, or seafloor sediments
## Footnote
These samples are hand sorted under a microscope.
280
What is the second level of sampling in diamond exploration?
Diamond character sampling
## Footnote
This stage assesses diamond size, shape, clarity, and color based on processing up to 500 tons of earth.
281
What does diamond character sampling help determine?
Diamond quality and deposit's ore grade
## Footnote
Ore grade is measured by the concentration of diamonds in 100 tons of rock.
282
How much earth is processed during bulk sampling?
Between 5,000 and 10,000 tons
## Footnote
This stage produces a parcel of about 2,000 carats of diamonds for accurate evaluation.
283
What is required to evaluate the viability of a mine at a secondary deposit?
A parcel of 3,000 to 5,000 carats
## Footnote
Secondary deposits tend to be wider and shallower than primary deposits.
284
What is the purpose of concentration testing for diamonds?
To determine whether a project is continued or abandoned
## Footnote
This decision is based on the presence and concentration of diamonds found.
285
What is the third stage of sampling in diamond exploration?
Bulk sampling
## Footnote
This stage is similar to character sampling but conducted on a much larger scale.
286
What is the initial method used to detect a kimberlite?
Geochemical sampling of soil, vegetation, and other materials
## Footnote
This method helps identify the presence of indicator minerals.
287
What do indicator minerals indicate in diamond exploration?
The presence of kimberlite pipes
## Footnote
These minerals are dispersed from kimberlite pipes and aid in locating diamond deposits.
288
True or False: Bulk sampling requires less than 5,000 tons of earth to be processed.
False
## Footnote
Bulk sampling typically involves processing between 5,000 and 10,000 tons of earth.
289
How is called cone-shaped container for dense media separation?
Cyclone
