Create custom rock (Rock1) and fluid (Fluid1) compositions. 1. Copy the folder Module3 to your project folder located in Library\Gems3\projects.

Transcription

1 MODULE 3: GREISEN ALTERATION In this tutorial we will use the GEMS project file Module3 in the examples to model the reaction path of a leucogranite during greisenization and evaluate the solubility of Sn. We will learn how to: a) create Predefined Composition Objects (a rock or fluid composition), b) add new minerals and aqueous species to your thermodynamic database and c) model more complex fluid-rock interaction processes (titration, multi-pass and leaching models). Create custom rock (Rock1) and fluid (Fluid1) compositions 1. Copy the folder Module3 to your project folder located in Library\Gems3\projects. 2. Open GEMS, choose the project and switch to the Thermodynamic Database Mode and select in Panel 2 the option Compos for creating a a predefined composition object (PCO). The user interface is shown in Figure Select any record and click on Clone a new record in Panel 1. Fill the parameters as shown in Figure 2. On the dialog select Use formulae of Dependent Components (Figure 3). In the next dialog choose first IComp (i.e., K, Al, Si, O, H, Na) then the DComp microcline, muscovite, albite and quartz (Figure 4). 4. Select the Settings tab and fill out the amounts of Dependent Components (Figure 5). Select the Page 1 tab, add informations for this PCO and normalize it to 1 kg (Figure 6). Press Re-calculate in Panel 1 and save. 5. To create the composition of the fluid, select the Rock1 record and click on Clone a new record in Panel 1. Call the fluid Fluid1 and in the next dialogue only tick the Independent Components option (Figure 3). Click next. 6. Select the Page 1 tab, add informations for this PCO using the fluid composition shown in Figure 7. Press Re-calculate in Panel 1 and save. 7. Switch to the Equilibria Calculation Mode, choose Open recipe dialog in Panel 1 (Figure 8) and add 200 g of Rock1 and 1000 g of Fluid1. Calculate the equilibrium at 250 and 450 C and 4000 bar and explore the detailed results (Figure 9). (a) What is the ph of this system? (b) How much Sn (molality) can you dissolve in this solution? (c) What is the major Sn aqueous species? Following the paper by Halter et al. (1998), which Sn species is missing? 1

2 Fig. 1: GEMS user interface in Thermodynamic Database Mode Fig. 2: Parameters for creating a rock as PCO Fig. 3: Options for adding chemical components for a PCO. These include Independent Components (e.g. Al, K, Na), Dependent Components (e.g. microcline, quartz, H 2 O) or user-defined formulae. 2

3 Fig. 4: Dialog to select Dependent Components. Fig. 5: Dialog to add amounts of Dependent Components. Note the units are here in wt. percent 3

4 Fig. 6: Dialogue to add informations on the PCO and add its normalization value (i.e., 1 kg) Fig. 7: Input parameters for the fluid composition PCO (Fluid1) 4

5 Fig. 8: Calculation in Equilibria Calculation Mode using the newly created PCO 5

6 Fig. 9: The Eq Demo window (1) can be selected to have a detailed results view of the total dissolved Independent Components (2), activity and concentrations of Dependent Components (3) and general properties of the system including ph, pressure, temperature and gas fugacitites (4) Create a new thermodynamic record for Topaz-F 1. Switch to the Thermodynamic Database Mode and select in Panel 2 the option DComp for adding a new mineral phase. Select the record Topaz-OH (Tpz-OH) and Clone a new record in Panel 1 (Figure 1). Fill the input dialogue (Figure 10) and click next and accept all subsequent options. 2. Add the mineral formula and standard thermodynamic properties for Topaz-F (Figure 11). Switch to the Page 2 tab and fill the coefficients for the heat capacity (Cp) function (Figure 12). Press Re-calculate in Panel 1 and save. 3. To have the new phase appear in our project we need to add it. Switch to the option Phase in Panel 2, Clone a new record in Panel 1 and fill the parameters listed in Figure 13. Then fill the parameters listed in Figure 14. Click next and select the mineral (phase) for which you want to create a new phase, i.e. Topaz- OH and -F for a binary solid solution (Figure 15). Note that if we would like to only add a pure phase we select only one mineral in this menu. The resulting phase record should be similar to Figure Switch to the Equilibria Calculation Mode, accept addition of the newly created phase and recalculate the equilibrium at 250 and 450 C and 4000 bar. Now expand the Topaz solid solution. (a) What is the mole fraction of Tpz-F vs. Tpz-OH? 6

7 Fig. 10: Input for creating a record for Topaz-F Fig. 11: Input for the standard thermodynamic properties (1), mineral formula (2) and literature references (3) of Topaz-F 7

8 Fig. 12: Input for the heat capacity (Cp) of Topaz-F Fig. 13: Input parameters for adding a new phase, i.e. an ideal solid solution between Topaz-OH and -F 8

9 Fig. 14: Input parameters for adding a new phase, i.e. an ideal solid solution between Topaz-OH and -F Fig. 15: Input parameters for adding a new phase, i.e. an ideal solid solution between Topaz-OH and -F 9

10 (1) (3) (2) Fig. 16: Input parameters for the created new ideal solid solution between Topaz-OH and -F with (1) name of phase, (2) selected mineral end members of the solid solution and (3) code for defining junior and major mineral (reserved for non-ideal solid solution) Create new thermodynamic records for Sn chloride species Now it is time to add the missing aqueous Sn species to our thermodynamic database. Use the data for chlorotin(ii) species given in Figure 17 and the relations: Sn 2+ + Cl = SnCl + (reaction 1) SnCl + + Cl = SnCl 0 2 (reaction 2) SnCl Cl = SnCl 3 (reaction 3) 1. Switch to the Thermodynamic Database Mode and select in Panel 2 the option ReacDC for adding a new reaction dependent species. 2. Clone a new record (Panel 1). Fill the input dialogue (Figure 18) and click next following Figure 19 and accept all subsequent options. Then select the aqueous species that will appear in the reaction, i.e. for SnCl + the species to select are Sn 2+ and Cl (Figure 20) following reaction 1 corresponding to β 1 in Figure The resulting record should look like in Figure 21. On Page 1 only add (1) the species name and its formula (note the oxidation state II needs to be added for this species), (2) the stoichiometric coefficient of the species in the reaction 10

11 (positive for products and negative for reactants) and (3) the logk at 25 C. Other value fields need to be replaced by three dashes (- - -). 4. Then switch to Page 2 and fill the logk function for A, B and C parameters ( Figure 22) using the values given in Figure 17. Then click on Re-calculate in Panel 1 and save the record. 5. To add the two remaining chlorotin(ii) species SnCl 0 2 and SnCl 3, simply clone the newly created SnCl + species and use the values given in Figure 17 and reactions 2 and 3. Fig. 17: Thermodynamic properties for chlorotin(ii) species SnCl +, SnCl 0 2 and SnCl 3 Fig. 18: Input parameter for SnCl + 11

12 Fig. 19: Input parameter a reaction dependent component Fig. 20: Select aqueous species, i.e. Sn 2+ and Cl, for defining your new chlorotin(ii) species (i.e., SnCl + ) 12

13 (1) (2) (3) Fig. 21: Input parameters for the reaction dependent component SnCl + using the logk from Figure 17. Note that only the logk at 25 C needs to be entered here, and the parameters on Page 2 for its T dependence (see Figure 22). Fig. 22: Input parameters for the reaction dependent component SnCl + using the logk equation shown in Figure 17. Once the values have been entered, click Re-calculate and compare the results on Page 1 with Figure

14 Fig. 23: Input parameter for the reaction dependent component SnCl 0 2 Fig. 24: Input parameter for the reaction dependent component SnCl

15 Fig. 25: Input parameter for the reaction dependent component SnCl 3 Fig. 26: Input parameter for the reaction dependent component SnCl 3 15

16 Process simulation: titration of leucogranite to a greisenizing fluid 1. Switch to the Equilibria Calculation Mode and since we have already computed a single system chemical equilibrium we can go ahead and select in Panel 2 the option Process. Create a titration model following Module 2 for K-feldspar, except this time we will choose Rock1 as the titrant, conditions will be 450 C and 4000 bar and we will add 0.1 g to 2000 g of Rock1 to Fluid1 as shown in Figure 27, with the data to be plotted shown in Figure 28. Don t forget to un-tick the box Save generated SysEq records (Figure 29) to avoid saving too many equilibria. Click Next, and Finish. 2. Check Controls (P-T-x and calculation script), then switch to the Sampling window, for xp[j] choose cnu (extent of reaction, i.e. amount of rock added), then click Re-calculate (Figure 30). 3. Now plot the results using g for the x-axis and for the y-axis in the Customize menu. The results should look similar to Figure Clone a new record using the previous one as template and change the temperature to 250 C. The results should look similar to Figure 32. Customize the inset view of your graph (Fragment option) to see what happens to cassiterite and topaz. The result should look similar to Figure 33. (a) Note what happens to cassiterite, pyrrhotite and topaz from 450 to 250 C? (b) Do you recognize the two different alteration types we described in Module 1 in class? (c) Compare your simulations to Figs. 2 and 4 in the paper from Halter et al. (1998). What is the difference for the mineralogy vs. reaction progress? (d) Why is cassiterite precipitating together with K-feldspar in our model but not in natural systems? (e) Give three factors you think affect cassiterite (SnO 2 ) precipitation in a hydrothermal fluid. 16

17 (1) (4) (3) (2) Fig. 27: Input parameter for a titration model of a leucogranite (Rock1) reacting with a greisenizing fluid (Fluid1). (1) Select tiration mode, (2) titrant, (3) amount of rock to add, (4) P-T conditions. Fig. 28: Data to be plotted (i.e. grams of minerals formed) in the titration model of a leucogranite (Rock1) reacting with a greisenizing fluid (Fluid1). 17

18 Fig. 29: Additional options menu to avoid saving too many equilibrium records in larger simulations (1) (2) (4) (5) (3) Fig. 30: Before plotting your results, (1) check you calculation control (P-T-x) script under Controls, then (2) switch the tab to Sampling and choose (3) cnu for extent of reaction (amount of rock added) for the x-axis, (4) Re-calculate (numerical results can be viewed in the Results tab), then click (5) Plot to visualize the results. 18

19 Fig. 31: Graph for the reaction path of leucogranite (Rock1) reacting with fluid (Fluid1) at 450 and 4 kbar. Fig. 32: Graph for the reaction path of leucogranite (Rock1) reacting with fluid (Fluid1) at 250 C and 4 kbar. Comparison with the Halter et al. (1998) paper (Fig. 2 in paper), indicates that the overall simulated mineralogy is similar to what we see in natural greisen from a fluid buffered ph (quartz vein), to qtz-greisen, qtz-topaz-greisen, qtz-sericite greisen, to leucogranite. 19

20 Fig. 33: Graph inset view for the reaction path of leucogranite (Rock1) reacting with greisenizing fluid (Fluid1) at 250 C and 4 kbar. Note that other minerals included in the calculations (e.g., magnetite and annite) are not displayed in this and previous graphs. Comparison with the Halter et al. (1998) paper (Fig. 2 in paper), indicates that the overall simulated mineralogy is similar to what we see in natural greisen from a fluid buffered ph (quartz vein), to qtz-greisen, qtz-topaz-greisen, qtz-sericite greisen, to a leucogranite. Note also that we need to dissolve more rock in our simulations to achieve a certain reaction progress in comparison to their simulated mineralogy (Fig. 4 in paper), because some Fe-bearing minerals have not been considered in their calculations. You could try to switch off magnetite, hematite and annite in SysEq (panel 2) and re-calculate the reaction progress for comparison. 20