Evidence suggest halogens (F, Cl, Br, and I) play an important role in hydrothermal ore deposit formation and therefore have the potential to be useful elements for mineral exploration. With advances in analytical methodologies, halogens are now able to be routinely measured, providing another geochemical tool for explorers. Soil, vegetation and water can be routinely analyzed for halogens.
Halogens in ore deposit formation & fluid inclusions
Halogens are found in fluid inclusions from many deposit types. Fluid inclusions are preserved bubbles of the mineralising hydrothermal fluids and show that high concentrations of halogens were present to support the transportation of metals in fluids (Yardley et. al. 1993; Trofimov, and Rychkov, 2004). Halogens are also commonly found in the crystal structure of alteration facies minerals that develop during hydrothermal alteration. An example from the Kristineberg volcanogenic massive sulfide district, Sweden, shows high fluorine in muscovite and phlogopite associated with mineralisation (Hannington et al., 2003). Halides are known to be important complexing agents for metals, enhancing their concentration and transport in hydrothermal solutions prior to eventual deposition (Wilkinson, J.J., 2001; Trofimov, and Rychkov, 2004). Evidence from contemporary active hydrothermal systems clearly show the association between elevated halogens and metals (Trofimov, and Rychkov, 2004).
Historically, published investigations into halogens in ore deposits were dominated by Russian research described by Trofimov and Rychkov (2004, translated from Russian version published in 1994) on I and Br associations with mineral deposits. More recent work on the use of F, Cl, Br, and I, has investigated till soils (Dunn et al., 2007), and vegetation (Dunn et al., 2007; Dunn and Heberlein, 2020). These workers have identified a clear relationship between mineralization and halogen concentrations.
Halogen solubility & mobility in water
This can produce a dispersion halo both larger than that visible in alteration minerals, and with the ability to form in post-mineralization cover sequences that overlay target lithologies. Direct detection by geochemical methods through transported cover requires that elements can move through the cover sequences to form surface anomalies. The high solubility also permits uptake and concentration in organic phases by vegetation (Dunn et al., 2007). Dunn et al., (2007) noted that the halogen element associated with each deposit is variable and therefore the analyses of all four non-radiogenic halogens is recommended.
Cost-effective halogen analysis
The analysis of halogens by ALS method ME-HAL01™ represents an extractable component rather than the total concentration. These data are considered most applicable as an exploration tool in soils and vegetation where the comparison of relative concentrations is useful. Where analysis of the total concentration of Cl, Br and I are required in solid media, alternative neutron activation analysis (NAA) methods are offered. Please contact ALS for more information about halogen analysis.
Halogen testing methods & packages
De-ionized water leach with ICP-MS & ion chromatograph analysis.
|Analytes & Detection Limits (ppm)|
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Vegetation sample is ashed at 475°C for 24 hours. Pre- and post-ashing weights are reported. Average ash yields are 2-4% for species commonly used in exploration surveys.
Minimum sample weight required 100g.
|Price per sample|
Sample pre-treatment for super trace halogens analysis. Required for soils and un-ashed vegetation.
Minimum sample weight required varies, contact your local lab to discuss your project.
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Dunn, C.E. and Heberlein, D.R., 2020. Geochemical investigation of halogens in spruce treetops and integration with existing multi-element data from the Blackwater region and TREK project area, central British Columbia (NTS 093C, F); in Geoscience BC Summary of Activities 2019: Minerals, Geoscience BC, Report 2020-01, pp. 101–108.
Dunn, C.E., Cook, S.J., and Hall, G.E.M., 2007. Halogens in surface exploration geochemistry: evaluation and development of methods for detecting buried mineral deposits. Geoscience BC, Report 2007-10, 62 pages.
Hannington, M.D., Kjarsgaard, I.M., Galley, A.G., and Taylor, B., 2003. Mineral-chemical studies of metamorphosed hydrothermal alteration in the Kristineberg volcanogenic massive sulfide district, Sweden. Mineralium Deposita, issue 38, pp. 423-442.
Trofimov, N.N., and Rychkov, A.I., 2004. Iodine and bromine: Geochemical indicators of deep ore deposits. Colorado Mountain Publishing House. Originally published 1994 in Russian.
Wilkinson, J.J., 2001. Fluid inclusions in hydrothermal ore deposits. Lithos. Vol. 55. pp. 229-272.
Yardley, B.W.D., Banks, D.A., and Bottrell, S.H., 1993. Post-Metamorphic Gold-Quartz Veins from N.W. Italy: The Composition and Origin of the Ore Fluid. Mineralogical Magazine. Vol. 57, pp. 407-422.