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4.1 Finding a Mineral Deposit
Before a mine can be built or operated, a mineral deposit must be located and evaluated. The process of finding and evaluating mineral deposits is the business of mineral exploration.
Mineral exploration is the search for mineral or rock occurrences that have the potential of being a mineral deposit. Exploration also includes the evaluation of such occurrences for their shape, size, grade and economic potential.
Prospecting is also part of exploration. It is generally considered to be the first stage of exploration wherein a prospector covers large amounts of ground looking for signs of mineralization.
Mineral deposits are rare and economic mineral deposits are even rarer. Exploring
for these deposits is often likened to finding a needle in a haystack. In fact, mineral deposits are geological anomalies. In other words, they represent a unique
situation where geological processes have concentrated a mineral commodity in a specific location within the rocks of the earth (see Table 1). As such, a mineral deposit is defined as an anomalous concentration of a mineral or rock that has the potential of being extracted (mined) at a profit.
Metal enrichment factors
Metal
Crustal Abundance (%)
Minimum Grade (%) for mining
Enrichment Factor
Mercury
0.0000089
0.2
22,500
Lead
0.0013
4.0
3,100
Tin
0.00017
0.5
2,900
Tungsten
0.00011
0.2
1,800
Gold
0.00000035
0.0003
900
Molybdenum
0.00013
0.1
800
Uranium
0.00017
0.1
600
Zinc
0.0094
3.0
300
Copper
0.0063
0.3
50
Nickel
0.0089
0.3
35
Iron
5.80
30.0
5
Aluminum
8.30
30.0
4
The chances of finding a mineral deposit
Since mineral deposits are rare, finding one of these deposits is challenging and the odds of any exploration program succeeding are relatively low. Once a mineral
deposit is discovered, the odds of the deposit eventually becoming an operating mine are one in a thousand. However, if an economic mineral deposit is discovered, the financial and professional rewards are significant for the companies and people involved. To maximize the chances of success, exploration companies and geologists use a wide range of skills and tools in the search and evaluation of mineral deposits. Nevertheless, there is always an element of luck -- more than one deposit has been found by pure chance
A summary of distribution of global exploration expenditures in 2010
Exploration involves many steps ranging from prospecting for new deposits with simple hand-held tools to aggressive drilling programs aimed at defining the size, shape and grade of a known deposit. Exploration expenditures range from a few thousand dollars for small prospecting programs to several million dollars for aggressive drill programs. The total cost involved in moving a deposit from discovery to the point at which a mining decision can be made is $10-$50 million.
Exploration is undertaken by a wide range of companies and individuals and occurs throughout the world. In recent years, annual global exploration expenditures have been in the $2-$5 billion range with 20-30% of this in North America, 25-30% in Latin America, 15-20% in Australia, 15% in Africa, and about 15% in other parts of the world.
4.2 The Who and What of Exploration
Commodities in exploration
The commodities that are sought after in exploration are diverse and vary with time depending on current prices and industry demand. The main groups of commodities are:
Precious metals
: gold, silver, platinum group elements (PGEs) which include platinum, palladium, osmium, iridium, ruthenium and rhenium.
Base metals
o
Ferrous metals
: iron, nickel, molybdenum, chromium, cobalt, manganese, and tungsten.
o
Non-ferrous metals
: copper, zinc, lead, tin, aluminium.
Fushionable metals and fuels
: uranium, coal, oil sands
Gems and gemstones
: diamonds, rubies, etc
Industrial minerals and rocks
: a wide assortment of minerals and rocks with industrial uses. An industrial mineral is
defined as: any rock, mineral, or other naturally occurring substance of economic value, exclusive of metallic ore, mineral fuels and gemstones; one of the non-metallics.
The science of exploration
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Geology and the related fields of geochemistry and geophysics are the foundations
of exploration. Knowledge of geology and geological processes and geological, geochemical and geophysical techniques are used extensively in the search and evaluation of mineral deposits.
Participants in exploration
A number of different individuals and companies are involved in mineral exploration.
Companies
Exploration is undertaken by any of the following types of companies:
junior exploration companies
metal mining companies
industrial mineral companies (to a lesser degree)
(Refer back to Module 3 for detailed information on these types of companies.)
Individuals
Prospectors, technologists and geologists undertake or supervise much of the on-
the-ground technical work with the help of students, labourers, and contractors. They are supported by a team of individuals back at the office with managerial, business, accounting and legal expertise.
Prospector
"An individual engaged in prospecting for valuable mineral deposits, generally working alone or in a small group, and on foot with simple tools or portable detectors. The term implies an individual searching on his own behalf, rather than an employee of a mining company." (Dictionary of Geological Terms).
In many jurisdictions, prospectors are a vital component of the exploration industry. They are the people who spend long days in the field, examining rocks and land forms for the presence of mineralization. It is argued that the majority of new mineral discoveries are made by prospectors.
T
echnologist
An individual with training in geology or mining that was attained from a post-
secondary college or technical institute. These individuals have the range of knowledge and skills needed to undertake and/or design exploration programs.
Technologists are familiar with field exploration techniques and with the interpretation of exploration data. They may be involved in managing, organizing and conducting field exploration programs.
Geologist
An individual with a university degree in geology, earth sciences or geological engineering. These individuals are highly trained in the geological sciences and typically design, manage, interpret and report on the results of exploration programs. In Canada most geologists are registered with professional associations,
such as the Association of Professional Engineers and Geoscientists of British Columbia, and hold the designation of P.Geo., P.Geol., or P.Eng.
Geologists supervise and manage exploration programs and as carry out activities such as mapping, core logging, and interpretation of data. Most major technical decisions in exploration are made by experienced and highly trained geologists.
4.3 Funding Exploration
Sources of funding for exploration
Exploration is, in a sense, a form of research and development. Funds must be put into exploration (research) before a deposit can be discovered and developed into an operating mine that provides a financial return on the research dollars spent. During the 1990s, annual global exploration expenditures were around $4-$5 billion per year. Where does most of this money come from? There are two main sources of funding for exploration:
1.
Equity financing on stock markets (primarily from stock markets located in Canada, the US, Australia, Britain, and South Africa)
2.
Revenue from mining operations
Stock markets
Equity financing on stock markets is one of the most important sources of funding
for exploration. Almost all of the money raised by junior exploration companies is
on the stock market. In addition, a significant portion of the exploration dollars spent by major companies comes from the stock market. In Canada, exploration companies raise money through the TSX Venture Exchange and the Toronto Stock
Exchange. Information on the stock market and how Juniors obtain funding through the stock market is provided in Module 3.
Mine revenue
Mine revenue is the dominant source of exploration funds and is the primary way in which metal mining companies fund their exploration. Mine revenue is generally directed in two ways:
1.
Exploration within and around existing mine sites. These dollars are aimed at
finding new mineralization to replace the mineralization that has been mined.
2.
Global exploration in areas outside of the company's mine sites. A portion of
a company's total revenue or profit for the year from all operations is directed
towards global exploration.
Requirements for exploration
What makes a jurisdiction attractive for exploration?
Mineral exploration is a global business. A company based in Vancouver and listed on the Toronto Stock Exchange may undertake exploration just about anywhere in the world. Many regions have recognized this and provide incentives for exploration companies to work in their country or region. However, in order for exploration to succeed in a given region or jurisdiction, an exploration company needs to consider a number of factors, including the following:
1. Good geological potential
There must be good geological potential for the deposit(s) of interest. For example, Alberta has low potential for gold deposits, but high potential for coal deposits. The geological potential is usually assessed by a geologist or mineral technologist.
A recent discovery in an area clearly indicates good geological potential. This will lead many investors and companies to invest heavily in the same area.
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2. Access to a large land mass
The more land that is available, the greater the chance of finding a deposit. Mineral deposits are rare and can't be moved. If a region has a patchwork of unavailable land, then exploration is less favourable.
3. Good geological data base (generated by governments and/or companies)
Good geological, geochemical and geophysical maps and maps at a relatively detailed scale must be available.
Records of past exploration work (assessment reports) must be
organized and detailed.
Information needs to be readily available and easy to navigate.
Today, that means available for free on the World Wide Web.
4. Secure land tenure (a mineral property owner must have secure legal rights to explore and ultimately develop mineral deposits)
Land tenure laws must be strong and clear. A claim holder must have clear legal rights.
There should be no record of property expropriation or government intervention in property rights.
If a deposit is discovered, a company should have a reasonable ability to develop the deposit into a mine as long as it follows all laws and environmental regulations.
5. Fair and streamlined regulations
Permitting laws must be transparent and the region must show
a record of fair treatment and consistent application of the laws. If there is a record of lengthy permitting delays or court challenges to development, then companies may avoid that region.
If a company follows the regulations then it should receive development permits in a reasonable time.
6. Good land access
The physical lay of the landscape and access to the land, particularly road access, are important considerations in exploration.
Properties that can only be accessed by air, or by the construction of a long road are not as attractive as those with road access.
Land with high populations or extensive agricultural development are less attractive.
7. Access to a talented workforce
The region should have a good pool of talented people including trades people, technologists, geologists, engineers, and lawyers.
The region should also offer good access to exploration contractors such as drill companies and geophysical contracts.
Regions that require the use of expatriates and contractors brought in from overseas make exploration more expensive.
8. Access to investment capital (venture capital and speculative investors)
A company must be able to raise funds to explore. Investors are unwilling to fund exploration in some regions because of war, unsure land tenure, high cost of exploration, low potential, etc.
9. Favourable tax regime
The region should have favourable tax incentives for exploration, development, and mining. Such incentives include
tax write-offs for people investing in exploration (e.g., flow-
through shares in Canada).
10. Social acceptance of mining
Regions with a high level of opposition to mining are not attractive for exploration. In these areas, permitting will be difficult or impossible and long delays will ensue.
11. Good commodity prices
It is an advantage if the price of the specific mineral commodities that the country produces are strong. For example, Chile is known for Cu mining, so exploration in Chile will be driven by high Cu prices.
Investors tend to fund exploration for commodities when prices are strong.
However, it takes many years to develop a mine so some companies will use low commodity prices to help them pick up projects at much lower prices. By the time the company has developed the project into a mine the commodity prices may be high again.
4.4 Acquiring Exploration
Properties
Exploration is undertaken on an
exploration property. An exploration
property is an area of ground in which
the mineral rights have been acquired by
a person or company. To acquire the
mineral rights, the ground must be
staked.
In Canada, the mineral rights for most of the country are owned and regulated by provincial or territorial governments. These governments have a system in place whereby a person or company can
acquire these rights by staking a claim.
Staking ground (claims)
Staking ground in Canada is currently
undertaken in one of two ways:
1. Ground staking
This is the traditional method that has
been used for more than a century.
Ground staking requires that an
individual physically go into the field and
stake the area of interest. It involves
erecting wooden claim posts at the
corners of a claim and attaching claim
tags to the posts that contain information
about the person who staked the claim
and when it was staked. It also requires
that the boundaries of the claim are walked and clearly marked out by blazing trees, cutting underbrush, or by using other clearly visible markers.
After the claim has been staked an application must be filed with the appropriate government agency in order to validate ownership of the claim.
Claim post for a claim in northern BC
Diagram of a hypothetical 4-post claim in
British Columbia
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2. Map staking or internet staking
This is a relatively new system that has been adopted in many provinces. Map or internet staking involves submitting an application for a claim on a "map" from your office rather than physically staking a claim on the ground.
More details about staking a claim in British Columbia can be found at the Mineral Titles Online
.
For another Canadian example see the regulations from the Newfoundland provincial government
.
In Canada, the size of a single claim is typically 500m by 500m (25 hectares), and a person or company can own an unlimited number of claims. The size of a typical
exploration property varies considerably depending on the stage of exploration and
the type of mineral deposit being sought. Properties can range from a single claim to an area covering 10 km2 (1600 claims) or more.
Keeping a claim
Once a claim is acquired or staked, the person or company then owns the mineral rights for a defined period of time (usually one or two years). They can renew their ownership of the mineral rights beyond the initial period of time by undertaking a certain dollar amount of exploration work on the property and filing
a report (assessment report) that details the amount of expenditures that were incurred and the type of exploration work that was completed.
Examples of Claims
Claim map for Thorn Property located in northern BC
Staked claims in Newfoundland
Click on the thumbnails of these claim maps to see the larger scale maps.
The dollar value is in the range of $100 to $300 of work per claim per year. The assessment report is a technical report -- commonly written by a geologist or prospector-- that outlines the type of work that was done (e.g. geological, geochemical, geophysical, drilling), the results of the work, and the cost of the work.
The principle aim of the mineral rights system in Canada is to encourage exploration work. As such, the relevant person or company can only keep the mineral rights if they continue to undertake work.
4.5 Types of Exploration Properties and Stages of Exploration
Exploration properties vary considerably in size, mineral deposit type, amount of geological information that is known, and amount of amount of exploration work previously completed. In general we can identify three classes of properties: grassroots, advanced, and pre-feasibility.
Grassroots
Grassroots properties are early stage properties that have had a limited to moderate amount of past exploration work. No significant mineral deposits are identified. However, the properties have potential and contain one or more features that make them of interest to exploration companies. For example, they may host mineral showings or prospects, or they may contain geochemical or geophysical anomalies that suggest a mineral deposit is present. Exploration work on grassroots properties is directed at finding new mineral showings or testing showings or deposits that are poorly known. A variety of exploration techniques are used on these properties including geological mapping and sampling, trenching, soil and stream geochemistry, airborne and ground geophysics, and drilling. Annual budgets on these properties typically range from $50K to $500K.
Advanced
Advanced-stage properties are those that contain a known mineral deposit that requires further exploration to enlarge or better define the mineralization. At this stage, the mineral deposit shows potential to be economic, but more work is required to assess this potential. As well, most of the work involves drilling to expand and define the mineral deposit. However, more grassroots style exploration
may take place on other parts of the property. Annual budgets on these properties typically range from $300K to several million dollars.
Pre-feasibility
Mining expenditure chart
(
Click to see the full view version
.)
Pre-feasibility stage properties are those that contain a well-defined mineral deposit and a calculated mineral resource. The primary aim of exploration at this stage is to better define the known mineralization by drilling in anticipation of mine development. In addition to drilling, a variety of engineering, metallurgical, environmental, and economic studies are undertaken in preparation for a full feasibility study and mine development. Annual budgets are usually several million dollars for these properties.
Advancing Cost, Decreasing Risk
Exploration occurs in stages, starting with the initial discovery of a mineral showing and continuing through to mine development. At each stage along the way, there is a gradual reduction in risk. In other words, the risk that the property will or will not contain an economic and mineable mineral deposit is reduced. However, as risk is reduced, the cost of exploration increases. Along the path from
discovery to development there are several key decision points at which the exploration geologist and company must decide if they should continue to work on a property or mineral deposit. Since the cost of exploration increases as exploration proceeds, it is important that the potential of the property or deposit warrants the expenditures that are required at the next stage. This is not an easy decision to make and requires a combination of good science, skill, intuition, and luck.
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4.6 Exploration Techniques
A wide variety of techniques are used in mineral exploration. These methods can be broadly grouped into the following categories:
Research:
Examination of all known data for a target area
Remote sensing techniques:
Analysis of air photographs and satellite images.
Geological techniques:
Includes geological mapping, trenching and drilling.
Geochemical techniques:
includes analysis of rock, soil, and
stream sediment material
Geophysical techniques:
includes evaluating the electrical, electromagnetic, magnetic, and density properties of rocks and minerals.
An exploration program employs techniques that vary depending on the stage of exploration, the location of the property, the type of mineral deposit under investigation, and the budget. However, in all cases the aim is to build a database of information and study the data for the presence of anomalies. In mineral exploration, an anomaly is a geological, geochemical or geophysical feature that is
different from the general surroundings and which potentially indicates the presence of economic mineralization. For example, a high level of copper in a rock sample relative to other samples is anomalous and may indicate the presence of a mineral deposit.
Various exploration techniques complement each other in that each technique provides different information about the geology and mineral potential of an area. Ideally, explorationists hope to locate areas that contain coincident geological, geochemical and geophysical anomalies. Areas with coincident anomalies are strong exploration targets with good potential for the presence of mineralization.
Areas that are anomalous in only one parameter are weaker targets with lower potential for the presence of mineralization.
Research
Background research on a property or region of interest is a vital first step in any exploration program. In countries like Canada, which has a long history of exploration and mining as well as established government geological surveys, there is extensive information available on past exploration work (assessment reports) and on the geology of mineral areas. Consulting the scientific literature also helps to ensure that the best and most effective exploration techniques are selected for a region of interest and mineral deposit of interest.
Why would you want to do research prior to exploration?
It’s an inexpensive exploration method
It provides a strong understanding of the property setting (Location, infrastructure, adjacent properties and mineral deposits, possible environmental or permitting difficulties)
It provides a geological background to the work
It helps you to avoid duplicating work that was previously completed
There is the potential to re-interpret the data using different perspective or new methods
Remote sensing
Remote sensing is the collection of information about an area without being in physical contact with it. There are two principle types of remote sensing techniques used in mineral exploration
Aerial photographs
Electronic scanners that record information in a digital form.
During exploration, many important terrain questions are answered by air and satellite photo analysis. Examples include:
Which areas of a property will be easy to access on foot?
Where are the nearest roads?
Are the rivers too deep or wide to cross?
Are any lakes large enough to land a float plane?
Are some sections covered in swamp or have no outcrop?
If you are interested in learning more about satellite based remote sensing, take the tutorial at the Canada Centre for Remote Sensing (link to http://ccrs.nrcan.gc.ca/resource/tutor/fundam/chapter1/01_e.php
)
(click images to see larger image)
Grids
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Most of the work on an exploration
program is carried out through surveys
(e.g., mapping surveys, soil surveys,
geophysical surveys). This work is
typically conducted on an exploration
grid, which is a set of reference lines
marked out on the ground. Grids are
used for location purposes, so that the
position of all work, samples and zones
of mineralization are well known. In tree
or bush covered areas, the grid consists of cut lines, where the vegetation is cleared
along the length of the grid line. In
barren regions, pickets, posts or rock
cairns may be used to mark out the grid
lines. Grids consists of one or more
baselines and a series of perpendicular
grid lines spaced 20-100 metres apart.
Ideally the grid lines are oriented
perpendicular to the trend of
mineralization, so as many grid lines as
possible cross the mineralization. If the
grid lines are oriented parallel to the mineralization, the mineralized zone might lie between grid lines, and thus could be missed when undertaking surveys.
Grids are established using a variety of survey equipment but most predominantly GPS (global positioning system) units. Prospectors, technologists, and geologists in the field also use hand-held GPS units to establish the location of showings or samples.
Geological mapping and trenching
Exploration grid
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Establishing a grid
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Geology is the keystone of exploration.
Mineral deposits are part of the rock
record.
Knowledge of the rocks and their structures (e.g., faults) is essential to analyze the often complicated nature of mineral deposits.
In many regions, good, detailed geology maps are available from government sources and can be used for exploration. However, these maps often lack enough detail so that exploration companies need to produce their own maps.
If a geology map is unavailable or is not suitable, the exploration company must produce one. Geological mapping is a systematic process whereby a geologist spends many days or weeks in the field observing, recording, and interpreting the characteristics of the rocks (and mineral showings) in an area. The information is then plotted onto a base map (often a topographic map or an air photograph). As field mapping progresses, a geology map of the area emerges.
Stripping and trenching
Geological mapping
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A geological map
(click thumbnail to see larger image)
In most parts of the world, and certainly
throughout Canada, much of the ground
surface is covered in overburden
(sand,
gravel, dirt, earth). This makes the
underlying rocks not directly visible.
Rock exposure may be limited to 20-
30% of the ground surface or less. This
presents challenges in the preparation of
a geological map and requires that the
geologist interpret between rock
exposures. A knowledgeable and skilled
geologist can do this effectively and
produce a reliable geology map.
However, if mineralization is discovered,
the geologist will want to examine it in
detail and expose as much of the
mineralized zone as possible. This is where exploration companies use stripping and trenching.
Stripping involves removing the overburden to expose the underlying mineralized zone. Trenching involves digging or blasting down into the rock to expose a vertical face of mineralization that can be examined. Both these techniques provide
a clean and continuous exposure of the mineralization that can then be mapped and sampled.
Geochemical sampling
Geochemical sampling is the process of collecting and analyzing samples of rock, soil, stream sediments, and, to a lesser extent, vegetation and water to determine if
it contains anomalous concentrations of desirable chemical elements (e.g. copper, gold, silver). Analysis takes place at an assay
lab where the collected material is analyzed for a wide range of chemical elements such as gold, silver, copper, zinc, lead, platinum, and nickel.
Rock sampling
Trenching
(click thumbnail to see larger image)
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Samples of rock are collected during all phases of exploration. These samples are used for geochemical analysis and for future reference. A geologist in the field can
recognize a mineralized rock -- for example, a rock containing the copper-bearing mineral chalcopyrite
-- and can estimate the amount (percentage) of the rock that is chalcopyrite. However, for an accurate estimation of the amount of copper in the rock, an assay lab needs to do an analysis on a rock sample. The assay lab crushes and pulverizes the rock and uses a series of laboratory techniques to determine the amount of copper present.
Types of samples
Rock sampling is a very important part of exploration and must be undertaken carefully since the results of rock analysis guide many exploration decisions. Three main types of rock samples are
taken at the surface: grab, chip, and
channel.
Grab sample
A grab sample is a rock that is collected
at a location where mineralization is
seen or suspected. A grab sample may be
taken at random or it may be a sample of
the "best" mineralization that could be
found. Grab samples are used in the early
stages of exploration to test for the
presence of economic minerals. These
samples are not considered to be representative of an outcrop or area, and they give
no information about the size of a mineral showing or deposit.
Grab samples are usually a sample of bedrock
(i.e. rock that was collected from its
place of origin). However, in some cases, grab samples of float are collected. Float is a rock that has moved from its place of origin by weathering or glacial movement. Samples of float can indicate the presence of nearby mineralization, but
the exact origin of the float may be unknown. The type of material collected should be clearly identified for all samples.
Grab sample
(click thumbnail to see larger image)
Chip sample
This is a composite sample collected by
chipping rock fragments continuously
along a width of rock exposure. The
intent is to collect an equal volume of
material along the length of the sample.
Chip samples are used to determine the
average grade of mineralization across
the width of a mineralized zone. If collected carefully they can provide information about the potential economic significance of a mineral zone (grade times width information).
Channel sample
This is a continuous sample of rock
collected by cutting into a rock face and
removing an equal volume of rock along
the length of the sample. It is usually
done with a rock saw that has two blades
spaced several centimeters apart. If collected properly, these samples can provide accurate information about the grade of mineralization that can be used in resource estimates.
Soil sampling
Although it is best to sample mineralized rock directly, in many places there is little or no rock exposed and explorationists must test for mineralization by other means. One method is to collect a sample of soil material that is the weathered product of the underlying rock. Rocks at the earth's surface are subjected to a variety of weathering forces such as rain, heat, and freeze-thaw action that break down and convert the rock to soil material. The broken down rock combines with organic material from plants and trees to produce soil. If a mineral deposit on the earth's surface is subjected to weathering and breaks down into soil material, collecting and analyzing a sample of that soil material indirectly serve to detect the mineral deposit.
Chip sample
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Channel sample
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Cuting a channel sample
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Soil sampling is used extensively in
exploration programs around the world.
However, there are many different types
of soils and not all types are effective at
detecting a nearby mineral deposit. For
example, soil material derived from
glaciers may have had its origin many
tens of kilometers from its current
location. Good knowledge of the origin
of the soil material must be known before undertaking a soil survey.
Soil samples are typically collected on an exploration grid with samples collected every 10-50 metres along the grid lines. A sample usually consists of a small shovelfull of soil taken from a depth of 10-50 cm below the surface. In some cases,
a hand or mechanical auger is used to sample soil at depths below 1 metre.
Interpreting soil analysis involves plotting the results on a map in such a way as to indicate the location of anomalous samples (e.g. samples with higher than normal gold values).
Stream sediment sampling
Geochemical sampling
(click thumbnail to see larger image)
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Another indirect way of sampling for the
presence of a mineral deposit is to
collect a stream sediment sample.
The aim is to collect a sample of
sediments (i.e., weathered rock) that is
representative of the drainage area above
the sample. If a mineral deposit is near
the surface, material eroded from it may
eventually make its way down into a
stream. Such a deposit can be detected in
a stream sediment sample. Stream
sediment sampling is an effective early
stage reconnaissance exploration method that is used to evaluate large areas for mineral potential.
Drilling
Drilling is the most widely used, and
probably the most important exploration
method. In this method a drill bit
penetrates the ground so that rock can be
brought to the surface. This rock
material can then be sampled and
analyzed.
Drilling is the only technique that can directly sample rocks and mineral deposits that lie below the Earth’s surface. This is very important, since mineral deposits are three-dimensional bodies whose depth, extent, shape, and grade must be known to properly evaluate their economic potential.
Drilling typically follows up on anomalies that were detected by mapping, geochemical sampling, or geophysics. On advanced properties, drilling is generally the dominant exploration method and may account for 80-90% of the exploration budget.
There are two main drilling techniques that are currently used:
reverse circulation drills (RC)
diamond drills.
Stream sediment sampling
(click thumbnail to see larger image)
Drilling as an exploration technique
(click thumbnail to see larger image)
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Reverse circulation drilling
RC drills are a type of percussion drill
wherein a hammer force is transmitted
down a length of steel drill rods to a
rotating bit that breaks the rock into
chips. The method involves forcing air or
water down the outer chamber of twin-
walled drill rods to the drill bit. The
cuttings are picked up by the air or water
and driven back to the surface via the
inner chamber of the rods. On the
surface, the cuttings enter a cyclone that removes most of the air or water and then drops the chips into a splitter which divides the sample into several fractions for analysis (assaying), geological examination and future reference. Samples are commonly collected in five-foot intervals as drilling progresses down the hole.
RC drills are cost-effective, fast, and can drill to depths of 100-300 metres. The disadvantage is that rock material is returned as chips, thereby limiting the subsurface geological information that can be obtained. Most of these drills are truck or skid mounted which requires land access to the drill site. RC drills are not effective for hard crystalline rocks and are not used in northern Canada.
Diamond drilling
Diamond drills are the Remote diamond drilling
Diamond drill
RC drill
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most common type of exploration drill used in Canada. In this method a hollow drill bit impregnated with diamonds is attached to the end of a series of drill rods. The rods and bit are rotated rapidly and forced downward into the rock. The result is a cylinder of rock (called core
) that is recovered from inside the drill rods.
Diamond drilling is relatively expensive but can drill to depths in excess of 1000 metres. Drills are often portable
and can be transported by helicopter to remote or difficult to access areas. The biggest advantage of a diamond drill is that core is returned. This core can be logged or mapped geologically and it can be sampled accurately over any interval that is required. (click thumbnail to see larger image)
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Diamond drilling
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Diamond drill core
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Logging of core
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A geological cross-section
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4.7 Exploration Techniques - Geophysics
Geophysical anomalies 1
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Geophysics is the process of measuring and interpreting the physical properties of the rocks that underlie the surface of the earth (e.g., magnetic or density properties). In exploration, geophysics is used for a few main purposes:
To identify anomalies in the physical properties of rocks that may indicate the presence of a mineral deposit
To better define a deposit beneath the ground or in areas of heavy overburden cover
As a mapping technique where the rocks' physical properties are mapped instead of their geology
Many mineral deposits have physical properties that are different and distinct from
the rocks that surround them. This allows the deposits to be detected by geophysics. Geophysics is also useful in that it can penetrate into the rock to detect physical characteristics that occur below the surface. In some methods, geophysical anomalies can be detected at depths of 200-300 metres below the surface. This is an important complement to the geological and geochemical methods described above that are confined to the surface.
Geophysical anomalies 2
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Geophysical measurements can be taken on the ground surface, in the air, or down
a drill hole. Airborne surveys are able to cover a large area and are useful in remote areas, or areas with difficult access. Airborne surveys are usually followed up with ground surveys to better locate and more accurately define any airborne anomalies that were detected. Bore-hole geophysics is used to located anomalies that are located around drill holes.
Commonly used geophysical methods
There are many different types of geophysical methods, but the most commonly used methods in exploration are:
magnetic
electromagnetic
electrical
Magnetic methods
Magnetic methods are used to detect the magnetic properties of rocks. All rocks contain a minor amount of magnetic minerals (primarily magnetite). The amount of these minerals varies from rock type to rock type. A magnetic survey results in a magnetic map of an area that can be used to indicate which way the rock units are trending and where there are changes in rock types. Since many mineral deposits are associated with specific rock types or geological features, a magnetic map can help located mineral deposits by detecting these rock types or features. Some mineral deposits are strongly magnetic and thus can be detected directly using a magnetic survey.
Magnometer (aka mag bird)
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A helicopter-based airborne magnetic survey typically involves flying the mag bird
100 - 200 metres above the ground in a grid pattern. The spacing between the grid lines will be combined to produce a single magnetic map of the area (see Thorn Property).
Electromagnetic methods
Ground Electromagnetics
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Electromagnetic surveys are used to locate conductive materials below the surface
of the Earth. This method is typically used to detect mineral deposits rich in sulphide minerals such as those hosting copper and zinc.
Electric methods
Electric methods are used to detect for materials that produced a weak natural electric current or for materials that can temporarily hold an electrical charge. The
minerals associated with some mineral deposits are characterized by an ability to hold an electric charge (electrical conductors), whereas others lack the ability to hold a charge (resistors).
Airborne magnetometer
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