Early exploration

Early exploration was the result of placer working of cassiterite. As the workings extended up shallow valley systems the miners would eventually arrive at the primary source of the heavy mineral. Later, costeaning (digging of pits) near the source would delineate the lode. Adits were subsequently driven in from cliffs or hillsides to explore for metals. Divining, using wooden or metal rods, was recommended in the 1700s as a tool for finding ores. As a result of advances in scientific knowledge and improvements in engineering technology in the 1800s, new methods for exploration were developed.

Certain minerals fluoresce under ultraviolet light or are radioactive and can be detected by a Geiger counter or scintillometer. Both these properties can be used a field tool for mineral prospecting.

Geiger Counter

 

Geochemical reconnaisance is often followed up by trenching, mapping, sampling and analysis, prior to diamond drilling. Diamond drilling, either from surface or underground, has proved very successful in the orefield for testing mineralization in depth. Cores of rock can be physically examined, mapped, sampled and analysed for elements of interest.

A exploration case study for a part of SW England can be downloaded as a PDF file (1.36MB) here.

Geophysical investigation has been used for exploration to test for physical contrast between the host rocks and mineralization. One of the early uses of geophysics as an exploration tool was tested in the St Agnes district at Lambriggan for zinc and lead sulphides in the 1930s. Satellite and remote sensing has also been tested to produce lineament maps. The British Geological Survey has published technical information using a variety of exploration techniques in the Cornubian Orefield in their Mineral Reconnaissance Reports - see www.bgs.ac.uk

Photomicrograph of cassiterite

New laboratory techniques have been invaluable in understanding the genesis and composition of the ore. Microscopy, using thin and polished sections of the host rocks and ores, has given a greater understanding of the ore deposits, and fluid inclusion studies have indicated temperatures of deposition. The scanning electron microscope, with inbuilt analytical facilities, produces high-resolution images of minerals and element composition of ore samples and X-ray diffraction can determine mineral species.

X-ray diffraction