How can we tell if the hot spring thermal waters are from a non volcanic or volcanic source based on the geochemistry?
Temp : 55C
pH : 4.7
Conductivity : 350 uS/cm
TDS@25C : 170
Free CO2 : 80
Bicarbonate : 81
Cl : 18
Sulphate : 7.6
F : 6.5
Sulphide : 0.4
K : 1.51
Ca : 1.54
Mg: 0.1
P : 0.06
Sulphur : 45
One another note , why do 2 hotsprings which are only 30 meters apart have different pH values one at 4.7 while another is alkaline at 7.8
The acidic waters are algae free covered but the sulphur value is high at 45 while the alkaline hot spring have algae and low sulphur values at 9 mg/L
Is this hotspring categorized as NaCl, NaHCO3 or CaHCO3 types?
Thanks
These are difficult questions, the best is to use O and H isotopes, see this publication: Giggenbach, W.F., 1992. Isotopic shifts in waters from geothermal and volcanic systems along convergent plate boundaries and thier origin. Earth and Planetary Science Letters, 113: 495-510.
Non-volcanic systems generally have a horizontal shift away from the Local Meteoric Water Line.
There are some plots which can help in differentiating the datspoints in terms of its origin and chemitsry.
You can utilize the ratio of Cl/B or Li/Cl/B triangular diagram to estimate the origin of the thermal waters. See these publications: 10.1016/j.jvolgeores.2015.12.014 . You can also use
For more advanced method, you can use isotopes of O-18 and H-2 (deuterium) to observe the contribution of magmatic fluid. Refs provided by Mr. Thomas Pichler.
As for the different water characteristic in short distance, besides the origin of the thermal fluid, it can also be explained by the different permeability at which the thermal fluid flow through, e.g. geological structures (faults), stratification, etc. More permeable path will result in less rock-water interaction, hence an acidic fluid can be neutralized (near neutral pH at discharge point). Whereas less permeable path will result in more rock-water interaction, hence less neutralized (more acid at discharge point).
In geothermal (or any geological) exploration, the combination of 3G (geology, geophysics, geochemistry) is always necessary. Geochemistry can describe the origin and rock-water interaction of thermal water along its way to the surface. But geology and geophysics is essential to define the path on which the thermal water flow through.
Volcanic or non volcanic source: I think a comparison between water and encountered volcanic rocks in the study area will give an answer. fluid inclusion analysis could help too.
Variations: this may be attributed to water rock interaction and dissolution of different rocks.
For determining the water type; you can use a hydrochemical formula such as that of Kurlov (1928) or a plot.
Hi John, I tried to work on your data and see, but there are many problems: (1) what are the units? is it mg/L?, some major elements are missing such as Sodium. The ionic balance is 88% which is too high (should be within +/-5%), so you have to go back to your data sampling and data analyses to check or re-analyze a new sample. But if I check some diagrams (even bad data) for example trinary SO4-HCO3-Cl, your water are within Peripheral waters (not volcanic origin). I highly recommend you do the analyses again from the beginning and be sure about your equipment calibration and have some expertise on how to take samples and so on. After that, we can help you to interpret the data. Regarding your second question on pH of two close waters, here I suggest you check the geology first at these two locations. Good Luck
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