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New Broken Hill Consolidated Shaft and Core Yard
New Broken Hill Consolidated Shaft and Core Yard

From Exploration to Opening a Mine

A sizeable amount of time and money go into a property from the exploration process to the ideal outcome of a mine site. This summary article will serve as a good starting point to anyone interested in investing in the mineral exploration and mining industries.

Staking Your Claim

The first step for any exploration company, once an area is selected, is to stake a claim.  Traditionally, this required the literal hammering in of stakes around the area of land claimed.  Some jurisdictions these days operate an on-line system for registering claims, but many still require manual staking. Some areas may require contact with local or national governments in order to obtain mineral rights. In some case landowners may hold mineral rights and direct negotiation is required. Regardless, obtaining the mineral rights to a property is essential before any exploration expenses are incurred.

An anticline structure controls the gold-bearing mineralisation in Bendigo

An anticline structure controls the gold-bearing mineralisation in Bendigo

Finding Your Exploration Target

Once a company is allowed to conduct work on the property, their first goal is to find prospective ‘targets’ of mineralization. The preliminary work on a property can take many different forms. This often depends on the size and budget of the company involved, as well, what, if any, geology data is available.

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seismic survey

Layout of a seismic survey. An old rugged landscape overlain by recently deposited volcanic ash layers is detected by this method. A topographic high is the result of differential weathering and erosion of the ancient land surface.

Geophysical Methods

A large range of geophysical methods is used in exploration, including seismic, gravity, magnetic, electrical and electromagnetic techniques. Geophysical surveys conducted by flying over an area (airborne geophysics) are by far the most common in the early stages of exploration. This is because they typically cover a much larger area and therefore have a higher probability of finding prospective targets.

Airborne surveys include magnetometers that measure magnetic anomalies in Earth’s magnetic field (metal exploration) and Geiger counters that determine the amount of radioactivity (uranium exploration). In the later stages of exploration, ground-based surveys may be used to investigate smaller areas. An example of a ground-based geophysical survey is electromagnetic geophysics. This technique detects materials that are more conductive than the surround rock, e.g. metals, at much more detail than an airborne survey.

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Geologist's hammer or pick

Geologist’s hammer or pick

Geologic Mapping

During geologic mapping, a geologist will systematically map an area looking for rock outcrops. The geologist will analyze each outcrop recording data including rock type and structural geology as well as taking samples for geochemical analysis.

A geology mapping program may be conducted at the same time as a soil sampling program.  More detailed mapping of smaller areas, i.e. individual outcrops or a few hundreds of meters square may be undertaken if an area of interest is found.

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QC Geochemistry Analysis

Scatter-plot of chromium assays against copper assays for previously analysed blanks. Most of the assays plot in a cluster which is the “Normal Population”. Two “Outliers” plot away from this cluster, which indicate possible contamination during sample preparation at the laboratory.

Geochemical Methods

Geochemical analysis is important in most exploration programs. Sampling aims to discover either anomalies the commodity of interest directly e.g. gold, or elements that are known to be associated with that commodity e.g. arsenic is often associated with gold. A program of any or all of soil, rock chip and stream sediment sampling may be undertaken. Soil and stream sediment sampling is particularly useful in areas where there are a few outcrops of the underlying rocks.

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coal-rig

Australian coring drill rig with a rod visible on the stands to the right.

Drilling  The Target

Once a prospective target has been identified, the next step is to try to better define the size of the mineralization found.

The first stage of drilling is to assist in the further definition of an exploration target.  Drilling not only confirms and extends the understanding of the geology of the deposit, it also allows a sampling program which established the grade of the resource. The ultimate goal of a drilling program is for resource evaluation, i.e. quantify the grade and tonnage of the mineral occurrence. A successful drilling program is the first step towards the confirmation of an economic  ore reserve.

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mine-delays-weather

Evacuating a mine site after torrential rains have turned the main access road into a waterway.

Feasibility Studies

Determining the economics of a potential ore reserve definition involves far more than the size and grade of the resource. A feasibility study must also consider many other aspects including:

  • mining techniques,
  • logistics of getting the resource to markets, and getting staff to site,
  • metallurgical requirements to process the ore,
  • likely future demand for the commodity which may affect its price,
  • staff availability and housing  issues,
  • legal issues,
  • environmental issues and cost ,
  • governmental factors including legislative risk and governmental stability in some countries.

The economics, or otherwise, of a given deposit is a complex decision with many variable factors involved.

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New Broken Hill Consolidated Shaft and Core Yard

New Broken Hill Consolidated Shaft and Core Yard

Opening A Mine

Ultimately, the process of opening a new mine can take years and sometimes even a deposit that may seem economical at first can prove to be uneconomical due to any number of the factors mentioned.  To evaluate this one of three formal mining feasibility studies (order of magnitude, prefeasibility and detailed feasibility) is carried out. These studies determine whether the commodity can be mined economically or not. If the site is still economically viable after the detailed feasibility study, the company will begin the process of generating a mine site.

Read more about the difficulties of developing and operating a mine:

About Staff @ Geology for Investors

Geology for Investors seeks to demystify mineral exploration and mining projects for mining company investors. All of our writers and contributors are experienced and educated in geology and the geosciences.