Geological Investigations

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Geological Investigations (Mapping)

Geological mapping is the basis for all geological interpretations and allows for interpretations and predictions to be made. It includes identifying rock types, contacts, age relations, structural patterns, orientations, mineral assemblages etc.

What are Geological Investigations?

A geological investigation is a broad term that encompasses all stages of an exploration programme. Typically, geological investigations are divided into several sequential stages which involve increasing expenditure and decreasing risk. The overall objective is to understand the underlying geology with sufficient confidence to make accurate predictions about the geology and/or the contained mineralisation. Geological investigations normally culminate in the construction of a 3D geological model designed to make sense of all the topographical data, geological data and interpretations made during the investigations.

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Types of geological investigations performed by MINROM

GEOLOGICAL FIELD MAPPING

Geological mapping forms the foundation on which all other geological data and geological interpretations are built.

GEOCHEMICAL SAMPLING

MINROM will test the grade of a sample at a specific location for a number of elements or compounds.

GEOPHYSICAL SURVEYS

Geophysics makes use of the physical properties of the Earth in order to understand and interpret the subsurface geology without using invasive methods.

METALLURGICAL SAMPLING

Metallurgical samples are commonly extracted as a bulk sample with the aim of getting enough material to accurately represent the deposit or a lithological portion of the deposit.

DRILLING

Once target areas have been identified from the mapping data then drill holes can be planned.

TYPES OF GEOLOGICAL INVESTIGATIONS

GEOLOGICAL FIELD MAPPING

The most basic way of obtaining geological information is through geological mapping. This may sound simple enough, but this is the primary way geological data is obtained and this is especially important in the initial stages of a project. Geological mapping forms the foundation on which all other geological data and geological interpretations are built. The better the geological mapping data, the better the interpretations and the overall project understanding.

A famous quote in mining is “the orebody dictates”, meaning that we can’t tell the Earth what we want to be there, but instead, we need to listen when it tells us what is actually there. Geological mapping is one way we listen.

GEOCHEMICAL SAMPLING

This is the general term for all types of sampling. The “geo” refers to the spatial component that accompanies a sample and the “chemical” refers to the quantified numerical value of an element or compound obtained for that sample. This is a fancy way of saying we test the grade of a sample at a specific location. Any number of elements or compounds can be tested for. The most important aspect of sampling is to clearly understanding what has been sampled and what it represents. Typically, sampling can be grouped into the following types, each with different objectives:

Stream
Soil
Surface
Channel
Downhole

Stream samples

This is where samples are collected from a stream or river. Unlike other disciplines, this is not a water sample but a sample of the sediments in or around the river. The key to successful stream sampling is to understand what is being sampled and what it represents. This type of sampling is commonly used in very early stage exploration in an attempt to progressively work back up the system of streams or rivers and identify the source of the mineralisation detected downstream. This is commonly used in Au, Ag, Ta, Sn, W and diamond exploration; however, it can be applicable to many other commodities.

Soil samples

These are designed to target a specific soil horizon and test for trace element of a target commodity or indicator elements for that commodity. Soil sampling is normally performed on a grid pattern and is typically used to cover large areas in a short space of time by generating target areas within the sampled area. It is commonly used in exploration for Cu, Au, Co and diamonds, but can be applied to almost any commodity depending on the local geology.

Surface samples/Grab samples

This sampling method simply involves the selected of samples without a structured extraction method or protocol. They typically consist of outcrop chips, picked-up (grabbed) surface rocks, or other easily obtainable site rocks. They are collected with the specific intent of only providing a “snapshot” of information. These samples are generally not representative, however, depending on the method of extraction these samples can be representative of a unit within a defined degree.

Typically, these are used in the initial phases of exploration of all commodities as this method is the fastest way to test for the presence of mineralisation and obtain an indication of the degree and quality of the mineralisation.

Channel samples

Channel samples are a specific method of extracting samples in which a channel of material is carved, cut, or excavated. All the material from that channel is collected as a sample or a series of samples in regular intervals (e.g. 1 m). Typically, this is used in trench and mining face sampling. Channel samples provide a representative sample across the unit being sampled. Care should always be taken not to cross lithological boundaries with a single sample.

Downhole samples

“Downhole” refers to samples extracted from some form of drilling. The two most common types are diamond drilling (core) and reverse circulation (RC). These samples are extracted from the core or RC chips according to a predefined sampling protocol. The sampling protocol is very important as each deposit, style of mineralisation and commodity will have a different sampling protocol.

Anyone can extract a sample, but a sample needs to mean something and should be used to express or calculate something of value. MINROM has the knowledge and skills to sample properly and meaningfully.

GEOPHYSICAL SURVEYS

Geophysics makes use of the physical properties of the Earth in order to understand and interpret the subsurface geology without using invasive methods (i.e. pitting, trenching or drilling). Geophysical techniques and applications to finding all sorts of elements and commodities have grown dramatically in the last few years. It is important to match the type of geophysical survey with the mineralisation and surrounding country rock before deciding on a survey method. This is where geological expertise can really save a lot of money and help get excellent project data. Occasionally, two or three surveys might be required in tandem to identify true anomalies.

MINROM can assist you with the following types of geophysical surveys:

Seismic Surveys
Ground Penetrating Radar (GPR)
Magnetic Surveys (Mag)
Radiometric Surveys

Gravity Surveys
Induced Polarity (IP) Surveys
Electromagnetic (EM) Surveys

Once geophysical anomalies have been identified it is crucial for these targets to be verified with a ground geological survey (ground truthing).

BULK AND METALLURGICAL SAMPLING

Bulk samples are extracted with the aim of reducing the sampling bias which occurs when small samples are used to represent large entities. Bulk samples are usually anything greater 100 kg, however, the purpose and representativity of the sample are more important than the mass.

Metallurgical samples are commonly extracted as a bulk sample with the aim of getting enough material to accurately represent the deposit or a lithological portion of the deposit. The metallurgical samples are then tested for characteristics pertaining to the processing and extraction of the desired element/metal, more than to the chemical composition.

DRILLING

Drilling is probably the second most powerful tool in a geologist’s arsenal, the first being geological mapping. Once target areas have been identified from the mapping data then drill holes can be planned. The aim of drilling is to obtain material from known intersections and depths below the surface so that interpretations of the geology can be made and samples of the mineralisation can be collected.

The type of drilling performed plays a big role in what data can be collected, the method of collection and the planning of the drill holes in order to maximise the amount of data obtained. The following drilling methods are commonly used:

Diamond Drilling /Core Drilling
Reverse Circulation Drilling (RC Drilling)
Percussion Drilling
Auger Drilling

Percussion rotary air blast drilling (RAB) - widely used in Australia but not Africa
Sonic (vibratory) drilling

There are a few other types of drilling methods available, however, these are not commonly used. MINROM has experience and expertise in all these drilling methods and can advise you on which is the most appropriate for your deposit or requirements.

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