Globally accepted standard, created by GIA, for describing diamonds in terms of their colour, clarity, cut and carat weight, thereby assessing their quality. The 4Cs enables us to communicate diamond quality in a universal language and allows diamond customers to know what they are purchasing.
A process to clean a rough diamond pre-sale, which serves to thoroughly remove any dirt or impurities from the diamond’s natural surface.
Aeromagnetic refers to a geophysical magnetic survey carried out above the ground commonly using a helicopter or a fixed wing aircraft.
Annual General Meeting
deposits of diamonds which have been removed from the primary source by natural erosive action over millions of years, and eventually deposited in a new environment such as a river bed, an ocean floor or a shoreline. It tends to be harder to calculated resources and reserves in Aalluvial deposits than in kimberlite deposits, due to variations in grade, distribution, stone size and diamond value.
- Autogenous mill
so-called due to the self-grinding of the ore: a rotating drum throws larger rocks of ore in a cascading motion which causes impact breakage of larger rocks and compressive grinding of finer particles
Broad based black economic empowerment is a policy of the South African government aimed at addressing past economic imbalances, stimulating further growth and creating employment. This policy is applied to the mining industry through the Minerals and Petroleum Resources Development Act (MPRDA) and the Mining Charter.
In the context of the diamond industry, this refers to the process of adding value along the diamond pipeline, from mining through to the final fabrication of a consumer product.
- Block caving
Cave mining, which is currently used at our underground operations in South Africa, is a well-established and safe mechanised mining method that was first introduced at Kimberley, South Africa in 1951. It is now used extensively as an underground mining method as it allows for the bulk mining of large orebodies and can provide access to a higher extraction percentage of ore than other underground mining methods. It can be applied to mine massive orebodies which have large, regular “footprints” and either dip steeply or are of large vertical extent. Read more about block caving in 'How are diamonds mined?'
- Bottom cut-off
alterations the bottom cut-off in a diamond processing plant enable the Company to change the size of the smallest diamond that can be recovered
- brecciated volcaniclastic Kimberlite
esedimented volcaniclastic kimberlite with 40% to 75% granite clasts
- Bulk sample
a large sample for the purpose of estimating the grade of a diamond deposit and to produce a large enough quantity of diamonds to enable an evaluation of diamond quality
The ‘Centenary Cut’, a major resource of 133 million carats located beneath the B block of the Cullinan orebody.
Compound Annual Growth Rate
hardened deposits of calcium carbonate formed in the near surface environment in arid or semi-arid environments
- Carat or ct
a measure of weight used for diamonds, equivalent to 0.2 grams
carats per hundred tonnes
a part of the Earth’s crust which has been relatively stable for a very long period
Corporate Social Investment
carats per annum
- Cut-off grade
The lowest grade of mineralised material considered economic to extract; used in the calculation of the ore reserves in a given deposit.
- Deflation soil sampling
sampling the topmost soil layer to obtain heavy mineral grains that have been concentrated by wind action in arid or semi-arid environments
- Dense Media Separation or DMS
a gravity separation process using a solid/liquid suspension
- Diamond grade
the content of diamonds, measured in carats, within a volume or mass of rock
Diamond Producers Association
openings on the sides of the drift going up into the block cave
a near-horizontal passageway in a mine, often connecting shafts
DTR rule 4 Periodic Financial Reporting
earnings before interest, tax, depreciation and amortisation
mine effluent is a regulated discharge from a point source like a treatment plant or dam spillway
a mass of sand, silt, etc: a product of the erosion of rocks that has remained in its place of origin; derived by in-situ weathering only, or in-situ weathering with gravitational movement
earnings per share
environmental, social and governance
- Exceptional diamonds
Petra classifies 'exceptional' diamonds as stones that sell for US$5 million or more each
prospecting, sampling, mapping, diamond drilling and other work involved in the search for mineralisation
- Feasibility study
A definitive engineering estimate of all costs, revenues, equipment requirements and production levels likely to be achieved if a mine is developed; the study is used to define the economic viability of a project and to support the search for project financing.
informal term for a narrow, vertical, vein-like kimberlite dyke
General and Administration Costs, or ‘corporate overhead’.
- Geophysical prospecting
the prospecting of an area in which physical properties (e.g. resistivity, gravity, conductivity, magnetic properties) unique to the rocks in the area are quantitatively measured by one or more geophysical methods.
mineral exploration techniques which measure the changes in various physical properties of the Earth’s crust and which may be ground-based or airborne; measures electrical, magnetic, gravity or other properties.
Gravity – a technique which measures variations in the local gravity field.
Magnetic – an airborne or ground-based technique which measures variations in the Earth’s magnetic field.
Electromagnetic – any of a large number of geophysical techniques which measure the electrical properties of the Earth and are very applicable to mineral exploration.
the content of diamonds, measured in carats, within a volume or mass of rock.
a medium to coarse-grained felsic intrusive rock that contains 10-50 per cent. quartz.
- Grease table
machinery used in diamond processing for further recovery after the x-ray system (or as an audit of the x-ray machine’s efficiency). Due to a diamond’s hydrophobic and lipophilic nature, it will stick to grease whereas other minerals will wash off.
iron bars (over an ore pass or a hopper) spaced to control the size of broken rock going into the ore pass, or crushing plant.
- Group II kimberlite
otherwise known as orangeites or micaceous kimberlites, Group II kimberlites do not contain ilmenite as an accessory mineral. The absence of ilmenite indicates that a Group II kimberlite has different sources of magma and perhaps intrusion history to Group I and it is thought to have been formed by contamination of kimberlitic magma during its passage through the Earth’s crust. Group II kimberlites have an approximate age of 120 million years old. The Fissure mines and Finsch are examples of Group II kimberlites.
- H1 or H2
first half, or second half, of the financial year
hectare, equal to 10,000 square metres
with reference to the deposition of diamonds, these deposits include kimberlite pipes, dykes, blows and fissures as well as lamproites
health, safety, environment and quality
Physical property having little or no affinity for water – diamonds are hydrophobic and therefore a drop of water placed on a diamond will form a coherent droplet, whereas in most other minerals the water would spread out to cover the surface.
- In situ
in its original place; most often used to refer to the location of the mineral resources
- Indicated Resource
that part of a diamond resource for which tonnage, densities, shape, physical characteristics, grade and average diamond value can be estimated with a reasonable level of confidence. It is based on exploration sampling and testing information gathered through appropriate techniques from locations such as outcrops, trenches, pits, workings and drill holes. The locations are too widely or inappropriately spaced to confirm geological and/or grade continuity but are spaced closely enough for continuity to be assumed and sufficient diamonds have been recovered to allow a confident estimate of average diamond value (SAMREC Code).
- Indicator minerals
minerals that can help locate the presence and establish the diamond-bearing potential of kimberlite; these minerals do not weather easily and are preserved in soils and gravels
- Inferred Resource
that part of a diamond resource for which tonnage, grade and average diamond value can be estimated with a low level of confidence. It is inferred from geological evidence and assumed but not verified by geological and/or grade continuity and a sufficiently large diamond parcel is not available to ensure reasonable representation of the diamond assortment. It is based on information gathered through appropriate techniques from locations such as outcrops, trenches, pits, workings and drill holes that may be limited or of uncertain quality and reliability (SAMREC Code).
- Jig Plant
small plant that concentrates diamonds and other relatively dense minerals
- Karoo time
approximately 300 Ma to 80 Ma ago
A brecciated ultrabasic igneous rock containing phlogopite mica, bronzite pyroxene and ilmenite; kimberlites may or may not contain diamonds.
- kimberlite indicator minerals
diamonds, garnets, and several other minerals, the presence of which are used to identify kimberlitic rocks
thousand tonnes per annum
large diameter drilling
load haul dumper
in the case of diamonds this means that grease and oil readily collect on their surface, while on other minerals oil would for coherent drops
Life of Mine
lost time injury; a work-related injury resulting in the employee/contractor being unable to attend work on the day following the injury
lost time injury frequency rate; the number of LTIs multiplied by 200,000 and divided by the number of hours worked
one million years
diamonds too large to pass through a 0.5mm screen
a rock texture that has no layering or regular structure
million carats per annum
- Measured Resource
that part of a diamond resource for which tonnage, densities, shape, physical characteristics, grade and average diamond value can be estimated with a high level of confidence. It is based on detailed and reliable exploration sampling and testing information gathered through appropriate techniques from locations such as outcrops, trenches, pits, workings and drill holes. The locations are spaced closely enough to confirm geological and grade continuity and sufficient diamonds have been recovered to allow a confident estimate of average diamond value.
diamonds small enough to pass through a 0.5mm screen
- Milling plant
crushing plant; milling implies finer grinding
- Mini bulk sample
a large sample, commonly in the order of 50 tonnes to 100 tonnes, for the purpose of determining the exploration potential of a diamond prospect
million tonnes per annum
Net asset value
narrow diameter drilling
Net present value
National Union of Mine Workers in South Africa
- Opencast or open pit
mining in which ore that occurs close to the Earth’s surface is extracted from a pit or quarry
- Optical sort plant
a plant designed to capture diamonds that don’t fluoresce well under X-ray (i.e. Type II diamonds)
a continuous well-defined mass of material of sufficient ore content to make extraction feasible
material of little or no value, which overlies rock formations of economic interest
a highly sophisticated software package commonly used by companies involved in block caving for mine planning purposes
a highly sophisticated software package commonly used by companies involved in sub level caving for mine planning purposes
referring to the detailed description of rocks, usually under the microscope
- Primary deposit
with reference to the deposition of diamonds, these deposits include kimberlite pipes, dykes, blows and fissures as well as lamproites; contrasted with alluvial
- Primary gravel
potentially diamondiferous alluvial gravels derived from primary deposits
- Probable reserves
the economically mineable material derived from a measured and/or indicated diamond resource. It is estimated with a lower level of confidence than a proven reserve. It is inclusive of diluting materials and allows for losses that may occur when the material is mined. Appropriate assessments, which may include feasibility studies, have been carried out, including consideration of, and modification by, realistically assumed mining, metallurgical, economic, marketing, legal, environmental, social and governmental factors. These assessments demonstrate at the time of reporting that extraction is reasonably justified
- Proven reserves
the economically mineable material derived from a measured diamond resource. It is estimated with a high level of confidence. It is inclusive of diluting materials and allows for losses that may occur when the material is mined. Appropriate assessments, which may include feasibility studies, have been carried out, including consideration of, and modification by, realistically assumed mining, metallurgical, economic, marketing, legal, environmental, social and governmental factors. These assessments demonstrate at the time of reporting that extraction is reasonably justified.
a method of developing vertical or inclined excavations by drilling a pilot hole, then reaming the pilot hole to the required dimensions
reverse circulation (drilling)
- Re-crush system
processes oversized material from the primary crushers, further reducing its size
- Recovery tailings
Dense Media Separation (“DMS”) concentrate material which has been rejected by final recover and is retreated
the process of restoring mined land to a condition approximating to a greater or lesser degree its original state
- Reverse circulation
a method of percussion drilling used to provide large samples of the subsurface rocks
Republic of South Africa
South African Code for Reporting of Exploration Results, Mineral Resources and Mineral Reserves
an underground vertical or inclined passageway
safety, health and environment
high density material in which diamonds are concentrated
sub level cave
the fine fraction of tailings discharged from a processing plant without being treated; in the case of diamonds, usually that fraction which is less than 1mm in size
- Slimes dam
a storage facility for all fine waste products from the processing plant
a thick suspension of solids in a liquid
- Slusher drift block cave
a block cave where drawpoints are not loaded individually, but are allowed to empty into a drift that is cleaned by a slusher (or a scraper winch)
a store of unprocessed ore
the strike line of a bed, fault, or other planar feature is a line representing the intersection of that feature with a horizontal plane.
- Stripping ratio
refers to the ratio of waste material to ore
- Sub level caving
This method owes the first part of its name to the fact that work is carried out on intermediate levels (that is, sub-levels) between the main production levels. It follows the same basic principles as the Block Caving mining method, but the caves are smaller in size and not as long lasting. This method of mining is quicker to bring into production than block caving, as the related infrastructure does not require the level of permanence needed for a long-term block cave. However, the operating costs are slightly higher, as more drilling and blasting is required.
Petra utilises this mining method to supplement Block Caving, in order to provide production flexibility. For example, at the Finsch mine sub-level caving will be used as part of the mine’s expansion programme to maintain underground production levels during the transition from the Block 4 cave to the Block 5 cave.
- Synthetic diamond
a laboratory-grown reproduction of a diamond, created by an artificial process as opposed to a geological process.
material left over after processing ore
- Tailings dump
dumps created of waste material from processed ore after the economically recoverable metal or mineral has been extracted
quantities where the tonne is an appropriate unit of measure; typically used to measure reserves of target commodity bearing material or quantities of ore and waste material mined, transported or milled
tonnes per annum
tonnes per day
tonnes per hour
tonnes per month
- Trackless equipment
equipment that does not operate on tracks (rails)
- Transvaal Supergroup
a sequence of sedimentary rocks in Southern Africa deposited between 2.65 and 2.05 Ga
- Type II diamonds
Type II diamonds have no measurable nitrogen impurities, meaning they are often of top quality in terms of colour and clarity.
Type IIa diamonds make up 1-2% of all natural diamonds. These diamonds are almost or entirely devoid of impurities, and consequently are usually colourless. Many large famous diamonds, such as the Cullinan and the Koh-i-Noor, are Type IIa.
Type IIb make up about 0.1% of all natural diamonds. In addition to having very low levels of nitrogen impurities comparable to Type IIa diamonds, Type IIb diamonds contain significant boron impurities which is what imparts their blue/grey colour. All blue diamonds are Type IIb, making them one of the rarest natural diamonds and very valuable.
- Underground pipe mines
Petra's underground kimberlite pipe mines, being Finsch, Cullinan, Koffiefontein and Kimberley Underground
describes a sedimentary rock composed of fragments of volcanic rocks
a form of electromagnetic radiation
- Yield / Recovered grade
the actual grade of ore realised after the mining and treatment process