Geological Survey of Finland

Mineralogical classifications of rocks and other minerals

Our main research methods consist of light and electron optics and X-ray diffraction, including preparation and processing of samples. These methods together allow research of the structure, phase structure and concentration of the samples and identification of minerals. The research laboratory is also specialised in jewels and gemstones, including gold nuggets. New technologies, such as high voltage pulses, are used in processing samples. At the moment, we can provide accurate information for particles the size of micrometres, but in the near future we will be able to study particles on the nano scale.

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Pyrochlore anomaly in Ilomantsi

GTK sampled moraine in Northern Karelia to find possible diamond indicators. Microscopic studies of a sample, taken from the bottom of the moraine layer, revealed promising heavy mineral grains that were collected as kimberlitic ilmenites. Electron optical studies revealed, however, that it was the high-tech indicator yttropyrochlore-(Y), (Y,Na,Ca,U)1-2(Nb,Ta,Ti)2(O,OH)7. The second sample showed that the number of pyrochlore grains in the moraine profile increases rapidly towards the bottom of the profile while the disintegration of the grains increases towards the top of the profile. The reason for this is that pyrochlore is an easily soluble mineral that disintegrates easily.

Element analysis conducted with a microanalyser indicated that the source of pyrochlore in the bedrock was an unidentified alkaline rock deposit.

Based on this information, we can conclude that the use of heavy mineral concentrations in identifying different types of ore indicators is of limited value. The use of this method can be optimised by concentrating on the bottom parts of the moraine bed, where oxidisation after the ice age has not been as strong as on the surface layers. Another important factor involves mapping the mineral concentrations of heavy mineral concentrations with electron optical methods to identify important minerals.

. Tyypillinen muuttunut pyrokloorirae moreenin pohjaosasta, jossa primääriä pyroklooria esiintyy vain vaalealla alueella rakeen ytimessä.

Figure 1. A typical transformed pyrochlore grain from the bottom layer of moraine, in which primary pyrochlore occurs only on the light area in the centre of the grain. The light grey colour indicates partial disintegration of the crystal grating, and a belt of goethite has developed around the grain. According to the element mapping of the grain, yttrium concentration is highest on the light areas and yttrium has started to dissolve from the other areas.

 

 

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Page created: 2017/07/22