Jump to content
Geochemist's Workbench Support Forum

T-P range, total sulphur content, coexisting mineral phases

Recommended Posts

First of all, I'm using the student version of GWB since a while and must say that great piece of software, especially for research in hydrothermal mineralizing systems.

I am trying to convince my research group to buy a full version for a workstation, however, while I am working with GWB I encountered a few questions that I like to ask:


1) Range of T-P in activity diagrams:

The maximum temperatures to create activity diagrams (e.g., pH vs. fO2) are at 300 °C.

In natural hydrothermal systems temperatures and pressure can be significantly higher, e.g. in lode gold deposits typical temperatures are ~ 400-450 °C and pressures 2-3 kbar.

How is it possible to work with higher T-P in ACT2?


2) Total activity of an element as independent variable (e.g., total sulphur)

Assuming the speciation of Fe in a pH-fO2 diagram at ~ 300 °C and 1 kbar.

Now I want speciate Fe in presence of S.

When I am adding sulphur as independent variable (in the "in the presence of" field) and select "speciate x over y" it is only possible to do this using either HSO2-, H2S, HS-, etc species.

Since the present minerals, pyrite for example, are stable over more than one predominance fields (at 300°C and 1kbar, pyrite is stable in the HSO2- and H2S fields) it would be better to use the total S content as independent variable.

How can I realize this?


3) Co-existing mineral phases

In some cases it is helpful to show the stability fields of co-existing minerals phases in activity diagrams.

A good example using the above described system is: pyrite, bornite and chalcopyrite.

The co-existance of these minerals can expressed by:

4 Pyrite + Bornite + 2 H2O = 5 Chalcopyrite + 2 H2S + O2

How is possible to show such stability fields in Act2?


Many greets,


Link to comment
Share on other sites

Hello Sebastian,


1) The GWB programs operate within the temperature range of the thermo dataset currently loaded. The default thermodynamic dataset (thermo.dat) contains log K entries compiled at 1 bar up to 100 C, and along the vapor pressure of water above that temperature. If you’d like, you can compile a thermo dataset at higher temperature and/or pressure. See the K2GWB and DBCreate references on our thermo data page for more information.


2) Can you please clarify what you would like the diagram to display? Are you interested in creating a mosaic diagram or are you wanting to display sulfur on the y-axis? Please attach your Act2 script so I can take a better look at what you’re trying to do.


3) A stability diagram will plot the most predominant mineral form under the conditions you have defined. In any activity diagram, you can suppress a mineral to allow the next most stable species to form in its place (Confing à Suppress..). Make sure your Basis pane includes all the necessary components to form the minerals you are interested, and then suppress species as needed.


Kind regards,



Aqueous Solutions LLC

Link to comment
Share on other sites

Hi Katelyn,


many thanks for your answer.


1) I got it.


2) I attached the Act2 script for you. As you can see I speciated pyrite in a pH-fO2 diagram in presence of H2S.

If you have a look on the plot, you will see that pyrite is stable in the H2S field, but also in the HSO4-, SO4-- and the HS- fields.

In HS- field pyrite is stable at ~ pH of 9 and fO2 of about -33.


In the Basis pane, however, it's only possible to select ONE sulphur species (in the act2 file I used H2S).

So how can I add the log activity for the other sulphur species, in which pyrite is also predominant?

Would it be possible to add a value for the total sulphur that accounts for the the entire system?


3) I understand that the most predominant mineral will be plotted in the stablility diagram. I was just wondering if it is possible to select a group of minerals that are predominant under the given conditions. In some cases it is the good show the predominance of two minerals in same field. A good example that is often used in phase diagrams is: pyrite + bornite vs chalcopyrite.







Pyrite Stab.ac2

Link to comment
Share on other sites

Hello Sebastian,


Thank you for sharing your Act2 file. When constructing a mosaic diagram you don’t need to set a total sulfur activity, instead you set the activity for one sulfur species and the program assumes its equal for any species with the same number of sulfurs (ie. SO4--, HS-, H2S(aq), HSO4-). To understand this better, set up another activity diagram with your sulfur species as your diagram species (swap H2S(aq) for SO4--). Suppress S-- as you did in your example and set the same axes, temperature and pressure conditions. Move to the Plot pane and select view results to see the text output for your diagram, including information on the activity for the species and minerals in the main system. You can read more on mosaic diagrams in section 5.3 of the GWB Essentials Guide.


I’m not familiar with the phase diagram you mention, pyrite + bornite vs chalcopyrite. Do you have an example image file you could attach?


Kind regards,



Aqueous Solutions LLC

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...