Quarry Southern Africa May 2018 - Page 13

BUSINESS design the layout correctly from the start and take the most important economic modifying factors into consideration. Detailed studies Introducing geophysical methods Geophysical methods are employed during this stage and the most common methods used are very low frequency electromagnetic / radio frequency electromagnetic (VLF-EM/ RF-EM) and the ground-penetrating radar (GPR) techniques. The VLF-EM/RF-EM method identifies major structures and the delimitation of features such as clay-filled fractures. GPR survey has a penetration depth of 10 to 25m and gives a large cross section of the subsurface fracturing and can determine zones of significant weakness, dykes and contacts. A deep drilling programme is then undertaken to describe the deposit at depth. Diamond core drilling is preferable, as the core can be evaluated for colour A dimension stone quarry, like most mining operations, starts with a desktop study, which takes into consideration the geological setting and any adjacent quarries in production. The desktop study also includes a detailed market study and a consideration of the economic drivers for dimension stone. As the deposit is the one factor that cannot be changed in a dimension stone project, it is crucial to conduct a detailed geological study. The cost of such a study is small compared to other mining endeavours, but crucial to the success of a dimension stone quarry. Identification of the target area is usually done by remote sensing for viable outcrop. Once a suitable area has been identified, the legal applications in terms of a prospecting permit and environmental management plan needs to be obtained. The conversion of the prospecting right to a mining right will generally be done quickly as the geological investigation is more high-level than for conventional exploration of minerals. The field evaluation entails establishing the general soundness and appearance of the stone, particularly the grain size and colour of the stone. Grab and drilled samples are collected to be polished and evaluated. The features that are described in the outcrop include: colour variations, textural characteristics and textural variation, structural and macro- discontinuities, micro-discontinuities, intrusions, inclusions, accessory minerals, contact zones and alterations. The initial field descriptions will also mention boulder size as that is an indication of the average size ranges that the outcrop will break into. Mapping of the outcrop is done in traverses. To be able to map discontinuities and faults, the outcrop can be cleaned by mechanical means, compressed air or pressurised water jets. The outcrop is mapped in detail on a scale of between 1:100 and 1:250 to suit the size of the deposit. Elements noted on the geological maps are rock composition, colour and structure of the stone, including fracturing. The next step is to get a 3D grasp of the physical features of the outcrop. A dimension stone block yard. QUARRY SA | MAY/JUNE 2018 _ 11 ELB THIRD