mining Flashcards
In mining, what is the cut-off grade?
the grade at which the gross value of the mined ore
is equal to the cost of mining
In mining, what is cost?
Cost = cutoff grade x price x recovery
What affects whether mineral resources can become reserves or ores?
Mineral resources can become reserves or ores and vice versa depending on technological advances and market price.
Legal, environmental and economic constraints must be considered for a resource to become a reserve.
What % wt in the Earth’s crust are abundant metals?
greater than 0.1% wt
What % wt in the Earth’s crust are scarce metals?
less than 0.1% wt
These are more difficult to find and therefore more expensive to extract
Metals can be classified as abundant or scarce. How are the scarce metals further classified?
Ferro-Alloy metals (Nickel, Chromium) Base metals (Copper, Lead, Zinc, Tin) Precious metals (Gold, Silver, Platinum) Special metals (Gallium, Rare Earths, Lithium)
Why is pyrite not mined for iron?
Because there are severe environmental issues associated with it
why aren’t all minerals in which the abundant metals (e.g. iron, aluminium) are present considered ore minerals?
not all minerals are able to be economically extracted
e.g. aluminium is present in many silicate minerals but extraction is prohibitively expensive
most ore minerals of the abundant metals are simple oxides, hydroxides or carbonates
From prospecting, to metal production what are the stages in project development?
1) Prospecting and exploration (Find potential mineral resource)
2) Resource estimation (how big is it?)
3) Feasibility studies (is it worth mining?)
4) Mine development (how is it going to be mined?)
5) Processing (what else do we need to do to produce the final product?)
All factors must be considered to determine whether a project will proceed
Most copper ore minerals are what?
Sulphides:
Chalcopyrite (CuFeS2)
Bornite (Cu5FeS4)
Chalcocite (Cu2S)
What is Recovery?
The fraction of the metal in the feed to the process that is recovered to the concentrate stream
Recovery = Flowrate of metal in concentrate/flowrate of metal in feed
What is grade?
The mass fraction of metal in the feed, concentrate or tailings
Grade = mass in stream/total mass of solids in stream
What factors affect grade and recovery?
Particle size (huge production costs) Mineral liberation Operating parameters (chemicals used etc) Feed grade Tonnage
What is a smelter or NSR (Net Smelter Return)?
A smelter will pay for metal but charge for treatment; this sets desired grade of the final concentrate from the separation
A simple smelter contract might be:
Revenue = mass metal x price - mass concentrate x treatment charge
How are oxide minerals produced?
Oxide minerals are a result of weathering of a sulphide ore
In an ore body, what is found beneath the oxidised zone?
There is sometimes a very high-grade sulphide ore zone of secondary enrichment beneath the oxidised zone and therefore beneath the water table
What are the primary Cu sulphide deposits?
Magmatic segregation deposits
Hydrothermal deposits
Sediment-hosted stratiform deposits
What make up the Hydrothermal Cu deposits?
Small veins - most have been exhausted because they were easy to mine (e.g. Cornwall)
Porphyry copper deposits -major source of copper ore (60%)
Skarns - associated with porphyry-type ores (e.g Antamina)
Volcanogenic massive sulphide (12%) (e.g. black smokers)
*remainder as bi-product of Ni and Pb-Zn ores and reprocessing of dumps
What are the main characteristics of porphyry copper deposits?
tend to be very large, contain small fractures
low grade but profitable due to size
What make up Sediment-hosted stratiform deposits and what percentage of Cu comes from these types of deposits?
Marine sedimentary rocks (shales)
20%*
*remainder as bi-product of Ni and Pb-Zn ores and reprocessing of dumps
What stages are involved in the methodology of Prospecting and Exploration?
Before mining can occur, a strategy consisting of the following steps is carried out:
- Target Generation
- Target Identification
- Target definition
- Evaluation (pre-feasibility/feasibility)
- Target Generation during Prospecting and Exploration consists of what strategic decisions?
Do we have the right to the land holdings?
What risks are there (political, climate etc.)?
What are the mineral types and their associated challenges?
- Target Identification during Prospecting and Exploration is done how?
Using key exploration techniques such as:
Geology: interpretation of mineral environments origins and variations
Geochemistry: Detection of mineralization in vegetation, soil, sediments and rocks
Remote sensing: Satellite/airborne analysis of earth data
Geophysics: Detection of mineral deposits physical properties
When using geophysics as a key exploration technique during Target Identification (Prospecting and Exploration), what data can be used?
EM, magnetic, density (gravity), seismic, electrical, radiometric; surface, over and in water and down borehole
Why are so many techniques used during Target Identification (Prospecting and Exploration)?
Because the deposits can either be exposed, hidden or buried
When trying to identify a deposit, in what ways can a deposit be hidden?
- Lithocap - Host rock exposed but mineralization hidden
- Deposit hidden under residual soil cover
- Deposit hidden under non-residual soil cover
What is the term used for a buried deposit?
‘Blind’ deposit
Hidden at depth below non-residual overburden and/or post mineral cover
- Target Definition during Prospecting and Exploration aims to achieve what and how?
It aims to determine how big the deposit is and what is the mineralization by DRILLING
During mine planning and development, what are the important considerations that will determine whether the deposit will be mined?
Size, shape and location of the ore body
The physical characteristics of the ore
The physical characteristics of the overburden
The physical characteristics of the country rock
The grade of the ore
The distribution of the ore grades
Mineralogy (essential for process design)
During the (4.) Target Evaluation: Pre-feasibility and Feasibility stage of Prospecting and Exploration, what is the aim and how long does it take to get there?
Pre-feasibility addresses the question “Is this an orebody?”
It can take 15-25 years to get here depending on size, investment
What are the risks associated with the (4.) Target Evaluation: Pre-feasibility and Feasibility stage of Prospecting and Exploration?
Huge risks are based upon (in)adequate amount of data and understanding of the geology of the deposit:
The 3D shape, V, tonnage, grade, grade variation etc. are all based on very thin cores through a much larger deposit - this data is extrapolated to represent the whole
Define ‘ore’
Natural accumulation of minerals from which a metal or metals can be extracted profitably
Define ‘ore body’
A fairly continuous mass of ore that is contained within the surrounding country rock
Define ‘gangue’
Worthless minerals that a mixed with the valuable minerals in an ore
Define ‘waste’
Material associated with the ore deposit that must be mined to get to the ore, and is discarded
Mining operations can be divided into what two types?
Surface and Underground mining
Surface mining is split into what two methods?
Mechanical and Aqueous
What mining techniques are considered as Mechanical Surface Mining?
Quarrying, open pit and strip/open cast mining
What mining techniques are considered as Aqueous surface mining?
Placer (dredging and hydraulicking) and solution (leaching)
Underground mining consists of what methods?
Supported, unsupported and caving
During supported underground mining, what methods are used?
Cut-and-fill stoping, stull stoping, square set stoping
During unsupported underground mining, what methods are used?
Room-and-pillar mining, stope-and-pillar mining and sublevel stoping
During caving underground mining, what methods are used?
Longwall mining, block caving and sublevel caving
What are the considerations when surface mining?
Surface operations are often large scale
Tonnage of waste and ore is higher than underground methods (ave. 2.6 vs 0.07)
Lower cost of mining, allowing extraction of lower grade ores
What are the advantages of an Open Pit mine?
High productivity (t/employee-shift) and production rate Low operating cost Low labour requirement Low rock breakage cost Simple development and access Little support required (benches provide stability) Good recovery No underground hazards
What are the disadvantages of an Open Pit mine?
Limited by depth (300m) Limited by stripping ratio (4m^3/t) High capital investment Extensive reclamation required* Requires large deposit and large equipment Slope stability is critical Waste disposal required Pit may fill with water afterwards (pollution risk)
What are the considerations when underground mining?
- Surface mining allows larger equipment and automation, and lower operating costs
- However as near-surface deposits are depleted, underground mining will become more viable
- Poorer safety record than surface mining
Sublevel stoping is used in what method of mining? What is it used for? And give an example
Underground: Unsupported
Used for vertical deposits
Mt Isa (Aus)
Block caving is used in what method of mining? Give an example
Underground mining: Caving
El Teniente
What are the advantages of Caving as an extraction method?
High productivity and production rate Suitable for mechanisation Relatively low operating cost Reasonably high recovery No drilling and blasting during production (block caving)
What are the disadvantages of Caving as an extraction method?
Caving and subsidence of surface possible
Selectively low
High capital cost and long development time
Draw control is critical to success (sublevel and block caving)
What is the grade of the average copper ore? What must happen after the ore has been mined?
Average copper ore 0.5% Cu
Further processing is required to get product
Processing comprises of what?
Different UNIT OPERATIONS
and the actual process depends on type or ore, mineral and metal
What does the summarised Metal Extraction Flowsheet look like?
Extract or from ground ->
Extract mineral from ore ->
Extract metal from mineral
What are the two key routes for Copper Extraction?
Pyrometallurgy (flotation and smelting) and Hydrometallurgy (leaching)
What is the flowsheet for the production of Cu using pyrometallurgy, from ore to metal?
COPPER SULPHATE (80%) -> Comminution -> Flotation -> Dewatering -> Smelting -> Converting -> Casting Anodes -> Electrorefining -> COPPER
What is the flowsheet for the production of Cu using hydrometallurgy, from ore to metal?
COPPER OXIDES (20%) -> Crushing -> Heap leaching -> Solvent extraction -> Electrowinning -> COPPER
What does the general mineral processing flowsheet look like?
LIBERATE ->
SEPARATE ->
METAL(S) OR DISPOSE
What is the objective of Comminution, and how is it achieved?
Breaking the rock and liberating the valuable mineral
Break ore (e.g. using Jaw Crusher or Gyratory Crusher) so that each particle comprises entirely one mineral, either only value or gangue
What are the drawbacks of Comminution?
Hugely power intensive
Highly inefficient
Thus, very expensive
How are minerals separated from Gangue?
Using their physical properties:
Density, magnetic properties, optical properties, surface properties
How are minerals separated from Gangue using their density (1)?
Process: Gravity concentration
Shaking tables, jigs and spirals all used
Simple and used in addition to other methods
Size control is key; feed deslimed using cyclones
E.g. tin, coal and iron ores
How are minerals separated from Gangue using their density (2)?
Process: Dense medium separation (sink-and-float)
Used to preconcentrate minerals before final liberation
Used for coal, diamonds
Heavy liquids (or suspension of fines to increase p) used of specific p so that lighter particles float
Better at coarse sized fractions; fine particles (i.e.
How are minerals separated from Gangue using their magnetic properties?
Magnetic separation: used to separate magnetite from qtz, or cassiterite (tin) from wolframite
Magnetic seraration can be low-intensity (coarse sands that are strongly magnetic; magnetite) or high intensity (e.g. beach sands), with wet or dry feed but is HIGH COST
Low-intensity wet-feed magnetic separation is used for what ore?
Low grade iron ore (haematite)
How are minerals separated from Gangue using their optical properties?
Photometric sorting is based on optical differences
Low throughput
Used for industrial minerals (magnesite, talc, marble etc)
Used for diamonds (diamonds fluoresce under x-ray beam)
How are minerals separated from Gangue using their surface properties?
FROTH FLOTATION
Make one mineral hydrophobic using surface chemistry
Bubble air through the mineral-water mixture
Hydrophobic particles stick to the bubbles, float to the surface and form a froth, overflow and are collected
The gangue stays in the pulp and is disposed
(conceptually simple, chemically and physically complex)
What kinds of ores is Froth Flotation used for?
Used extensively for LOW GRADE and COMPLEX ores;
Predominantly SULPHIDES but also non-metallic ores including PHOSPHATES, COAL and IRON ORE
What is the problem with mineral processing regarding the Grade-Recovery balance?
Mineral processing is a physical separation, and is not perfect, so we recover gangue in the concentrate stream, and lose valuable mineral in the tailings
What is recovery?
The fraction of the metal in the feed, to the process that is recovered to the concentrate stream:
Recovery = Flowrate o’ metal in concentrate / Flowrate o’ metal in stream
What is grade?
The mass fraction of metal in the feed, concentrate or tailings:
Grade = Mass metal in stream / Total mass solids in stream
What factors affect grade and recovery?
Particle size (huge production costs) Mineral liberation Operating parameters (chemicals used etc.) Feed grade Tonnage
What is a typical smelter contract?
NSR (Net Smelter Return)
A smelter will pay for metal but charge for treatment; this sets the desired grade of the final concentrate from the separation
What might a simple Smelter Contract be?
Revenue = (mass metal x price) - (mass concentrate x treatment charge)
During pyrometallurgy, after flotation and dewatering, what happens next?
Smelting, converting and electrorefining
Used for concentrated copper sulphide ores (i.e. those concentrated by froth flotation) to CHEMICALLY separate metal from mineral
What does smelting (pyrometallurgy) do?
CuFeS2 -> CuS (Matte) + FeO (slag) + SO2 gas
What does converting (pyrometallurgy) do?
CuS (matte) -> Cu (blister copper) + SO2 gas
How are minerals separated from Gangue using their surface properties?
FROTH FLOTATION
Make one mineral hydrophobic using surface chemistry
(Sulphides naturally hydrophobic)
Bubble air through the mineral-water mixture
Hydrophobic particles stick to the bubbles, float to the surface and form a froth, overflow and are collected
The gangue stays in the pulp and is disposed
(conceptually simple, chemically and physically complex)
What are the pros and cons of using hydrometallurgy over pyrometallurgy?
Leaching is typically slower and has poorer recoveries than flotation
However it can be used to recover oxidised ores and low grade ores
It is cheap, which makes it an attractive option
Chalcopyrite, however, leaches very slowly
What is the current price of Gold?
$38.5 per g (April 2015)
$41.8 per g (January 2015)
What is the current price of Copper?
$6000 per tonne (April 2015)
$5700 per tonne (January 2015)
What is the current price of oil?
$50.25 per barrel (April 2015)
$45.07 per barrel (January 2015)
What are the objectives and challenges with developing a drill programme?
Objectives: • To determine extent of mineralisation • Presence of additional mineralisation • Mineralogy of deposit • Maximum information for minimum drillholes
Challenges:
• Cost
• Time
• Location – e.g. depth, licensing area
Many common rocks contain significant quantities of abundant metals and some scarce metals, but few can be feasibly and profitably extracted. What are the most important factors for rocks to become ores?
- Mineralogy
- Grade
- Grain size and texture
- Deposit size
- Deposit depth
- Geographic location
- Market value
- By-products
Why can’t Copper oxides be extracted by pyrometallurgical process routes?
- it would produce unwanted chemicals
- Oxide minerals are not responsive to the froth flotation chemicals or process (i.e. they do not bind to the kerosene-based chemicals)
What is hydrometallurgy?
- Hydrometallurgy (leaching) is the extraction and recovery of copper from ores using aqueous (water-based) solutions. Hydrometallurgical processes are applied mainly to oxide ores and to low-grade oxide and sulphide mine wastes
- About 25 percent of domestic copper production is now through the use of solution mining techniques
Outline how copper is extracted from Copper oxides using hydrometallurgy.
•Once the ore has been leached, the copper is recovered from the pregnant Ieachate through precipitation or solvent extraction.
Outline the solvent extraction process.
- Pregnant Leach Solution (PLS) has a concentrate of 1-6kg Cu/m³ solution
- An immiscible organic solvent is used to extract the Cu from the PLS
- And then strip the Cu from the loaded organic into an electrolyte stream that feeds the electrowinning plant
- The barren organic phase is recycled back to the extraction stage
Hydrometallurgical processes have several advantages over pyrometallurgical copper recovery methods. What are they?
The ability to treat lower grade ores (even waste dumps) economically, flexibility in scale of operations, simplified materials handling, and good operational and environmental control
•Copper can be produced from dump leaching plus solvent extraction and electrowinning for around 30 cents per pound. This is a clear cost advantage over pyrometallurgical production.
The electrolyte has almost no impurities and few environmental problems. Solvent extraction also makes relatively efficient use of the various solutions used: the spent Ieachate is returned to the leaching operation, the barren solvent is recycled to the pregnant Ieachate, and the spent electrolyte to the loaded solvent
What are the limitations of hydrometallurgy?
- Solvent extraction is still largely confined to copper oxides
- It should be made clear that dump/heap leaching is primarily a means of lowering average production costs. It is not a substitute for conventional copper production by pyrometallurgical or other leaching methods
What is pyrometallurgy used for?
•Pyrometallurgy (smelting, coverting and electrorefining) is used for concentrated copper sulphide ores (i.e. those concentrated by froth flotation) to chemically separate metal from mineral
You have used drillhole data to generate a grade-tonnage report using Micromine. Discuss briefly the sources of error in the calculated values and state what must be considered when deciding whether to carry out further drilling.
The volume, tonnage and grade produced from the geological interpretation are estimates because they have been determined from a non-definitive vein interpretation. The interpretation itself is also based upon the assumption that the initial drillhole data is valid.
There is a huge risk based on a perhaps inadequate amount of data and understanding of the geology of the deposit. The 3D shape, volume, tonnage, grade, grade variation etc are based upon very thin cores through a much larger mineral deposit and this data is extrapolated to represent the whole.
The estimated shape and direction of mineralization both down dip and along strike must be considered when deciding whether to carry out further drilling in order to know where to place the boreholes and to what depth. Perhaps more importantly, the price of the extracted materials and whether the project actually has the potential to be economic needs to be considered to see whether it is worth investing more money.
What is block caving?
Block caving consists of having an underground tunnel leading to draw points where the overlying rock, broken by gravity more or less flows to the draw point, to be gathered and taken away for processing.
What are the advantages of block caving?
High productivity and production rate because the ore is being gathered and taken away for processing right away
Suitable for mechanisation
Relatively low operating cost
Reasonably high recovery
No drilling and blasting during production
What are the disadvantages of block caving?
Caving and subsidence of surface possible due to caving and extraction of a massive volume of rock
Selectively low – it only can be used on an ore body that is sufficiently massive and fractured
High capital cost and long development time
Draw control is critical to success
You have been given some drillhole data that must be interpreted using Micromine. First, it must be validated. Give two errors that may be found during data validation.
- Incorrect codes in the lithology data. For example a record may shown that within the LITH column a cell for a hole is blank and by referring to the original data it is possible to correct this error to contain the correct code. This process is repeated for the remaining errors.
- Depth errors in the lithology and assay files. E.g. there may be overlapping fields in the lithology data and this can be corrected by referring to the original data and changing it to the correct depth interval.
A large porphyry-type copper deposit has been discovered in Chile. What factors will determine whether it will be mined?
- Size, shape and location of the ore body
- The physical characteristics of the ore
- The physical characteristics of the overburden
- The physical characteristics of the country rock
- The grade of the ore (must be greater than the cut-off grade – the grade at which the gross value of the mined ore is equal to the cost of mining)
- The distribution of the ore grades
- Mineralogy (essential for process design)
briefly discuss how the grade and recovery affect the revenue based on a simple smelter contract
- The recovery factor of the metal at the mill is important to know what proportion of the metal sent to the mill is actually old
- Concentrate grade is important to establish how much metal is contained in a tonne of concentrate
There are different methods for separating minerals from gangue based on their physical properties. Why is this required? Give three different methods of separation used industrially and an example of mineral(s) that are separated using each method
To remove the valuable mineral resource from the worthless minerals
- Gravity concentration uses the minerals densities, by use of shaking table, jigs and spirals. Tin, coal and iron ores
- Dense medium separation (sink-and-float method) is used to pre-concentrate minerals before final liberation. Coal, diamonds
- Magnetic separation is used to separate magnetite from qtz, but feed is high cost
- Photometric sorting is based on the optical differences of minerals. Used for industrial minerals magnesite, talc, diamonds
- Froth Flotation. Copper from copper suphides
What is room-and-pillar mining?
Room and pillar mining is commonly done in flat or gently dipping bedded ore bodies. Pillars are left in place in a regular pattern while the rooms are mined out. In many room and pillar mines, the pillars are taken out starting at the farthest point from the stope access, allowing the roof to collapse and fill in the stope. This allows for greater recovery as less ore is left behind in pillars
