Applied Mineral Exploration
Discussion and research relevant to mineral
exploration. The BGS model 205 decrepitometer
March, July 2017
(see also: Model 216 improved, 2019)
Because the model 105 decrepitometer operated on a
PC computer with an ISA card slot (now superseded), the model 105
decrepitometer instrument has been redesigned and the software
re-written to operate on a standard single-board Linux computer.
This system uses the same furnace, sample tube assembly and power
control unit as the model 105 instrument.
Although it operates in the same manner as the previous model 105, the software has
been completely updated to be more convenient and has a full
graphical interface, operating in the Xwindows environment. The
temperature and counts are monitored and shown on screen during
the analysis, and simultaneously plotted on screen as the
temperature rises. The data is saved to a file upon completion,
and the graphical plot can also be printed if required and easily
regenerated from the saved data file for additional review.
The system now provides the complete computer as
part of the instrument. It can be operated stand-alone with the
addition of a monitor, keyboard and mouse, or operated remotely
across a network using the included wired lan connector. The
computer and its interface electronics is in a compact 10 * 12 * 5
cm enclosure.
The computer and interface electronics unit.
The complete system includes the computer, furnace and enclosure, sample tube with detector and control electronics.
This is a screen-capture of the model 205 instrument interface including the plot of a sample in progress.
The weighed sample is added to the sample tube, which is inserted into the furnace and the door of the enclosure is closed. The sample information and control settings are entered into the control window and the "GO" button is clicked. The entire analysis is then completed automatically without further user intervention. At the end temperature, the furnace is turned off and the control window re-appears to allow analysis of additional samples. The plot remains in view, with additional plot windows being created for additional samples. It is necessary to allow the furnace to cool before analysing subsequent samples.
Samples of 0.5gm are normally used while samples as small as 0.2 gm or up to 2 gm can be analysed according to the fluid inclusion abundance in the sample. The heating rate used is almost always 20ºC per minute, but the instrument can also be operated at 10ºC or 40ºC per minute. Analyses are usually performed on quartz samples, but other minerals containing fluid inclusions can also be used, such as carbonates, feldspars and opaque minerals such as haematite and magnetite. Sulphides can also be analysed, but they can be corrosive and this reduces the life of the temperature sensor. Quartz samples are usually analysed up to 620ºC because there is no activity above the alpha to beta phase transition at 573ºC, however the instrument can be used for analyses up to 800ºC.
The system can be installed in a normal quiet laboratory location as ambient sounds are suppressed. However loud sounds or vibration can interfere and should be avoided. Because it can be operated remotely across a network the room can be unoccupied during the analysis.
All the normal Linux operating system features are available including printing and gnuplot. Data can be exchanged either by using USB memory disks or across the network and the system can be accessed from microsoft computers using the SMB protocol. Network access from Apple systems has not been tested, but should be possible.
Update 2019: Improvements have been made to this model which is superseded by model 216 which is similar but with improved sensitivity.
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