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

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.

 

Cheers,

Sebastian

 

 

 

Pyrite Stab.ac2

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

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,

Sebastian