The Alphachron

Alphachron – Automated Helium Thermochronology

Exceptionally accurate turn-key helium measurement solution for (U-Th)/He thermochronology.

The Alphachron is the first commercially available, automated, integrated and compact turnkey system designed for the extraction and measurement of gases from mineral samples. The Alphachron was developed by the CSIRO Division of Exploration and Mining (DEM), and Patterson Instruments, and is now manufactured and marketed by Thermochron Systems.

During the course of research on the 4D evolution of ore systems, the CSIRO DEM found the need to develop instrumentation for rapid and automated analysis of mineral samples, which became the Alphachron. The Alphachron technology, based on an innovative helium extraction/measurement instrument, is being adopted by the market as a standard analytical platform allowing an accurate determination of the thermal history of the Earth’s crust.

Up to 25 mineral samples can be loaded into the laser chamber of the Alphachron and heated (approximately 1000°C for apatite, and approximately 1250°C for zircon) under vacuum for five to fifteen minutes with a 980 nm diode laser. The extracted gas samples are analyzed to determine their radiogenic helium-4 content. The gas extraction process is repeated to ensure all the gas has been removed from the sample. Parent mineral concentration is subsequently determined by ICP-MS analysis of the sample.

Specifications

The Alphachron is a turnkey system for the automated extraction and measurement of radiogenic helium from mineral samples. The instrument integrates a laser-heating module with a gas-handling module and an optional quartz-halogen heating system. The system is delivered prefabricated and is ready to use for measurement after installation and minimal commissioning. After extraction of the helium by diode laser or quartz-haologen heating (with the optional Diffusion Cell add-on), mineral grains are digested and analyzed using standard ICP-MS techniques.

System features include:

• High vacuum system consisting of oil-free diaphragm fore pump, hybrid turbomolecular pump with controller, and ion pump with controller

• Two pressure gauges, one Pirani gauge at the fore pump and one Full Range gauge (<5e-9 torr) at the turbo pump

• Quadropole mass spectrometer (QMS):

  • Range of mass magnitude: 1-100 amu

  • Detector: Faraday/secondary electron multiplier

  • Detection limit: < 2×10-11 mbar

  • Sensitivity of Ar: > 5×10-4/200 A/mbar

• Two SAES getters with getter control and activation power supply

• Stainless steel high-vacuum line with automatic and manual valves

• Automated X-Y laser stage with machine vision

• 915 nm diode laser, lens system, power supply and safety shield

• 3 x 3.3 litre stainless steel tanks with 3He spike, an analytical 4He standard, and a 4He reference standard

• 25 sample capacity laser chamber with sapphire window

• He diffusion cell option, (maximum operating T = 600°C) and integrated automation software;

• Dedicated computer system with a Windows computer interfaced to the Alphachron digital I/O system, quadrupole, laser controller, diffusion cell controller (option), CCD camera and X-Y stage controller

• Solenoid system and control panel for automatic valve control

• Alphachron system software/drivers for laser automation, gas handling and measurement of radiogenic helium

• Installation and training

• Data reduction software

• Instrument manuals

A powerful visual software package based on LabVIEW allows users to create and adjust the operational sequence of the system experiments without any previous programming knowledge. An intuitive interface is included to help users manage experiments using simple textual files. These ‘scripts’ are able to control tightly all aspects of the system’s automated operation. Users can define separate scripts for each of the samples present on the sample disk, allowing multiple tests on varying samples during one automated run, without the need for user intervention, or loading/reloading of samples between tests.

Application Notes

An increase in the number of research institutions around the globe utilizing (U-Th)/He thermochronometry for applications including mineral and petroleum exploration, geohazards assessment, and continental evolution studies, has prompted demand for a world-first technology developed by CSIRO Exploration & Mining and manufactured by Thermochron Systems.

Uranium-thorium-helium thermochronometry is a highly sensitive and cost-effective method of radiometric age dating that can be used to determine the thermal history of the Earth’s crust. The major benefit of this technology to the mineral resources industry lies in the ability to quantitatively determine the low temperature thermal histories of mineral belts (see references below) and petroleum basins. Helium thermochronometry also has applications in several fields of geological research such as landscape evolution, plate tectonics, sedimentary provenance studies, and more.

References

Recent publications demonstrating the application of this technology in ore deposit research include:

McInnes, B.I.A., Evans, N..J., Fu, F.Q. and Garwin, S., 2005. Application of thermochronometry to hydrothermal ore deposits, in Reiners, P. and Ehlers, T. (Eds.), Thermochronology, Reviews in Mineralogy & Geochemistry, Vol. 58, p. 467-498 (ISSN 1529-6466).

McInnes, B.I.A., Evans, N.J., Fu, F.Q., Garwin, S., Belousova, E., Griffin, W.L., Bertens, A., Sukarna, D., Permanadewi, S., Andrew, R.L. and Deckart, K., 2005. Thermal history analysis of selected Chilean, Indonesian and Iranian porphyry Cu-Mo-Au deposits; in Porter, T.M. (Ed.), Super Porphyry Copper & Gold Deposits: A Global Perspective, Vol. 1; PGC Publishing, Adelaide, pp. 27-42.

McInnes, B.I.A., Farley, K.A., Sillitoe, R.H and Kohn, B. 1999. Application of (U-Th)/He dating to the estimation of the sense and amount of vertical fault displacement at the Chuquicamata Mine, Chile, Economic Geology 94, 937-948.