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Bits ‘n Pieces – The Driller’s Blog

Geology 101 for Diamond Drillers: Basic Information

Posted by Rod McCoremick on May 9, 2016 10:30:00 AM

Rock and ground play an important role in drilling as nearly every decision a driller makes is based to some degree, on the type of ground conditions he will be drilling. The rocks and minerals found in that ground become important and knowing basic geology can help drillers understand how decisions are made regarding location of the drill.

The following are basic geology terms you should be familiar with:

Igneous rock

Igneous rock is formed when magma (lava) cools and solidifies, it may do this above or below the Earth's surface. The upper section of the Earth's crust is made up of around 95% igneous rock. There are over 700 different types of igneous rocks and common examples include basalt, granite, pumice, obsidian, tuff, diorite, gabbro and andesite.



Sedimentary rock

Sedimentary rocks are formed by sediment that includes minerals, small pieces of plants and other organic matter, and is deposited over time, usually as layers at the bottom of lakes and oceans. The sediment is compressed over a long period of time before consolidating into solid layers of rock. Sedimentary rocks forms layers called strata which can often be seen in exposed cliffs and mountains. Common types of sedimentary rocks include limestone, sandstone, mudstone, greywacke, chalk, coal, claystone and flint.


Metamorphic rock

Metamorphic rocks can be formed by pressure deep under the Earth's surface, from the extreme heat caused by lava or by the intense collisions and friction of tectonic plates.

Uplift and erosion help bring metamorphic rock to the Earth's surface. Examples of metamorphic rocks include anthracite, quartzite, marble, slate, granulite, gneiss and schist.




The shield is a large are of exposed igneous rock and high-grade metamorphic rock. Together they form stable areas that can be billions of years old. Due to this stability, erosion has flattened out most of the continental shields.



The platform is a continental shield area that is covered in sediment. In the mineral exploration industry, this is commonly referred to as “overburden”.



Ore body

An accumulation of ore minerals, sufficient in quantity and of adequate quality so that it can be recovered profitably.


MOH scale

The hardness of the ground is measured according to Mohs Hardness scale, a chart of relative hardness of various minerals. The scale consists of numbers one through ten; 1 being the softest and 10 being the hardest. It is named after geologist Friedrich Mohs.


Geological log

Geologists working onsite will create a geological log of the downhole core which is the record of the depths and rock type from the surface to the end of the borehole.



Additionally, it can help drillers to know about the rules and regulations on geological reporting. These may vary according to country.

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Topics: Basic drilling information

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