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[OLD] Any developments on plotting siderite in Act2?


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From: Garry Davidson

Subject: any developments on plotting siderite in Act2?

Reading the manuals, Act2 can only plot phases for diagrams speciated over X-Y relative to one set of species, e.g., SO4--, whereas siderite requires speciation for C in X-Y as well.Is that still the case for GWB3.2? How can I modify the following text for Fe-S-O to best include siderite?


swap O2(g) for O2(aq)

diagram Fe++ on O2(g) vs pH

T = 250

x = 2 to 10

y = -50 to -30

suppress FeO©

suppress Troilite

suppress Hercynite

add SO4--

log a SO4-- =-3

log a Fe++ =2

speciate SO4-- over X-Y


From: Paul Barton

Subject: Re: any developments on plotting siderite in Act2?

I, too, am interested in siderite; and I write to call attention to the question of the quality of the compiled thermo data on siderite. When we model an epithermal ore deposit having the siderite + hematite assemblage, the data base proposes a PCO2 that is far too high for the probable temperature and depth (250 C and 500m). To the extent that the assembled data for siderite utilize "equilibrium" studies involving reduction of siderite to magnetite and graphite, BEWARE. Graphite is very slow to react, and those experiments need to be evaluated in that light. I my view, superior data (unfortunately not reversed, and for that reason not published properly) are available from the oxidative reaction to hematite and magnetite studied by Chou and Williams (1978), EOS, 59, 402. Chou and I mentioned this briefly in Econ. Geol. (1993), 88, 873-884. If someone else has discovered better data, please share them.


From: Craig Bethke

Subject: Re: any developments on plotting siderite in Act2?

There is nothing magic about a mosaic diagram: you can assemble one simply by calculating diagrams for the various ligand species you wish to consider, trimming each diagram to the limits for its ligand species, and assembling the “tiles�. You could you this with scissors and tape, but more likely you'd just use an Illustration program. For the example you cite, calculate a diagram for iron, speciating sulfur over x-y and carbonate over x. Calculate a second diagram as before, but replace the carbonate with methane (no need to speciate). Clip off the portion of the second diagram above the methane-carbonate bounds and paste what's left over the first diagram.

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