Mining Valuation Handbook Flashcards
What inventory ratio is a good predictor of metals prices on the LME?
The stock to demand ratio. In other words, the number of weeks of demand that current inventory levels (stocks) could meet if all production ceased.
What is a typical sequence of steps in which Exploration is undertaken?
1 regional studies and area selection
2 airborne and ground reconnaissance
3 detailed ground (surface) evaluation
4 sub-surface evaluation — exploration drilling.
what is laterite
a reddish clayey material, hard when dry, forming a topsoil in some tropical or subtropical regions and sometimes used for building.
what is alluvium?
a deposit of clay, silt, and sand left by flowing floodwater in a river valley or delta, typically producing fertile soil.
What is done during regional studies and area selection?
Regional geological maps, either existing or compiled from available data, are studied and interpreted to identify the rock types in the area; certain rock type assemblages are favourable for specific types of mineral occurrences. Exploration tenements are then acquired (by application, joint venture or purchase) over selected areas of favourable rock types.
what is an outcrop?
a rock formation that is visible on the surface: dramatic limestone outcrops.
What is meant by ‘blind deposits’?
No outcrops. (ie. not visible from the surface)
How are magnetic surveys used to identify deposits?
he Earth’s natural magnetic field interacts with magnetic mineral contained in a rock, inducing magnetism. The strength of the rock’s magnetism is related to the amount of magnetic minerals (predominately magnetite—Fe3O4) present, often associated with igneous and metamorphic rocks. The position and size of the anomaly obviously depends on the depth, position and size of the magnetic body. Most magnetic surveying is now done by aircraft for both reconnaissance and detailed surveys.
How are Gravimetric surveys used?
These measure variations in the Earth’s gravity field. Variations are due to the density of underlying rock, with the least dense being sedimentary and the most dense extrusive igneous (basalt). Very dense and heavy minerals will also cause local variations. The effectiveness of this method can be up to 10 kilometres in depth.
How are Radioactive Surveys used?
These measure the decay of radioactive elements, particularly gamma rays, which are emitted from three radioactive elements: uranium, thorium and potassium. Those areas where geological processes have concentrated minerals may concentrate radioactive elements that emit an anomalous gamma-ray reading where up to 90 per cent of measured gamma rays are received from the top 30 centimetres of the ground. Measurements can be done both from the air and on the ground.
What surface evaluation methods are used in exploration?
Most of the aerial reconnaissance exploration methods are also used on the ground to increase resolution. Others include:
1) Electrical and Electromagentic methods
2) Geochemsitry and
3) Seismic Survey
What are Electrical and electromagnetic methods?
hese are used to map variations in the polarisation (induced polarisation or IP) and the conductivity (electromagnetics or EM) of the sub-surface. For induced polarisation methods, a current is applied directly to the ground on the surface, while in electromagnetic methods, electromagnetic fields are generated in wire loops (either on the ground or suspended from a helicopter), which induce an electric current in the ground. Fresh rock (unexposed) is generally a poor conductor, but metallic minerals are good conductors so the electromagnetic techniques are often applied in the search of the smaller copper, lead and zinc massive sulphide deposits, with effectiveness ranging to a depth of several hundreds metres.
Are fresh rocks good electrical conductors? What about metallic minerals?
Fresh Rocks - No!
Metallic Minerals - Yes,
What typices of minerals are typically searched using electromagnetic techniques?
he search of the smaller copper, lead and zinc massive sulphide deposits.
What is the range of electromagnetic methods
several hundred metres
How is Geochemistry (a surface evaluation method) used in exploration?
ampling and specialised chemical analysis of soils, some superficial deposits and stream sediments can be applied to map the chemical make-up of the soils and rocks on the ground in order to determine abnormal chemical patterns on the basis that metal ions have been dispersed from mineral deposits by erosion, or have migrated to the surface (by weathering processes or ground water circulation) from the buried mineral deposit, producing a surface geochemical anomaly.
How are Seismic Surveys (a surface evaluation method) used in exploration?
For oil and gas deposits in sedimentary basins, seismic surveys are most commonly employed. The process involves firing an explosive charge or pneumatic pulse that sends a signal into the ground. The time for the reflections, from different density layers,
to reach the surface is measured and translated into depth using estimates of the relative density of the sedimentary sequences to provide an image of the underground layers and structures
What is meant by the ‘oxide zone’?
that portion of the orebody that is above the water table (weathered). The oxide zone that has been in contact with oxygen for a long time differs in mineralogy, is generally lower in specific gravity and may be softer than the minerals of the deeper primary zone, which is below the water table and not affected by weathering.
What are the most common base metal oxides?
» copper — malachite, azurite » iron — goethite, hematite » lead — anglesite, cerussite » nickel — gaspeite, garnierite » zinc — smithsonite.
What are the methods used to drill down and recover samples from the orebody?
1) Rotary Air Blast ;
2) Reverce Circulation; and
3) Diamond Core Drilling
How does Rotary Air Blast Drilling work?
This is not unlike the way a home handyman’s hammer drill is used to drill a hole into masonry or brickwork. A tungsten bit drills down towards the target and drill cuttings are blown back up the hole and collected as they reach the surface. This method is the cheapest, but the accuracy is the lowest. Drill cuttings arrive intermittently at the surface, providing a low level of confidence about their true location down the drill hole, and because they travel up the hole in contact with the rocks already drilled through, they are almost always contaminated by the up-hole rocks.
How does Reverse Circulation drilling work?
the drill bit is similar to the RAB drill but the drill cuttings are forced up the hollow centre of the drill bit by compressed air or fluid. This is more expensive than RAB, but the accuracy is markedly increased.
How does Diamond Core Drilling work?
Narrow, thin-walled drill tubes are used to support and rotate a diamond impregnated bit which cuts an annulus (the space between the drill pipe and the open hole formed by the drill bit) in the rock. This results in the cutting of a solid core of rock which passes through the hollow centre of the diamond bit and is collected in a special tube immediately behind the dill bit. When the tube (usually 2 metres in length) is full, it is withdrawn up the inside of the drill tubes using a wire cable winched by the drill rig. At the surface, the tube is opened and the rock core is placed in a special core tray. This is the most expensive drilling technique, but the most accurat
How are RAB and RC drill cuttings used once collected?
ypically taken over one-metre intervals, are mixed to ensure representivity and passed through a splitting device to provide a sample of the cuttings (say, 5 to 10 per cent of the original weight) and then placed in labelled bags. If the mixing has been done correctly, then duplicate bagged samples for a particular one-metre interval should have the same grade and characteristics. The duplicate bagged samples are often sent to a separate assay lab for analysis to check for bias between labs.
How are diamond core drillings used?
the core is photographed, geologically logged and sections marked for sampling. The samples are obtained by cutting (splitting) the core along the long axis, generally using a diamond impregnated circular saw system. One half is placed in labelled bags and dispatched for assaying and the remaining core is kept in storage (usually at the project site) as a record
Why are drilling samples for oil tested under ultraviolet light?
as oil is very fluorescent; the company might report the occurrence of strong fluorescence, which may be an encouraging sign.
How are steel casings used for oil drilling?
steel casing will be placed in the hole and cement forced between the casing and the sides of the well. A smaller diameter bit will then be lowered down through the narrower casing to recommence the drilling operations. These operations may be repeated a number of times before the total depth of the well is reached.
Are drill holes typically drilled vertically or at an angle?
at an angle, with the objective of intersecting the orebody at right angles, so that the intercept is close to the true width of the mineralisation
What is typically the first step when evaluating drilling results?
Determining the tonnage of the orebody by multiplying the volume by the ore’s specific gravity (SG). Note:Water has an SG of 1, coal seams have an SG of around 1 and lead-zinc ore bodies have an SG of around 3.
What is the area of influence of a drill hole?
The area of influence is the area for which the exploration hole’s thickness and grade will be applied. An area of influence is is a square centred around the drill hole.
How do you calculate the volume of the block.
= Area of Influence x thickness of the drill intercept
How is the tonnage of a block calculated?
Tonnage of block = Volume of bloxk x Specific Gravity of Ore
How is the mineral content of a block determined?
Grade Per Tonne x Tonnes in the block
What is the risk of estimating mineral content of a block?
Grade has been obtained from a drill hole only several centimetres in diamater over areas of influces covering thousands of square metres.
