MODULE 3: GREISEN ALTERATION (PART II)

Transcription

1 MODULE 3: GREISEN ALTERATION (PART II) Process simulation: multi-pass model (leaching) A multi-pass (leaching) model consists of consecutive batches of fresh (unreacted) greisenizing fluid (Fluid 1) reacting with a leucogranite (Rock 1) to simulate fluid-rock reactions during the formation of a hydrothermal quartz vein and alteration halo in the granite. To model this we need a PCO for the rock and fluid (already done) and a parent system equilibrium record. 1. Create the parent system records (Figure 1), by cloning the two records you already created in SysEq at 250 and 450 C and 4 kbar. Rename these system records, e.g. rock flush, and leave all the other parameters. For the input take for now 100 g of Fluid1 and 1000 g of Rock1 using the Open recipe dialog (Figure 2) and calculate the equilibrium. Save. 2. Go to the Process option (Figure 3) and clone your record built for the titration model at 450 C. Select your parent chemical system equilibria record at 450 C (i.e., rock flush), name the simulation task multi-pass and use as simulation code R this time instead of S. In the next window tick the option Leaching: Compos source, select Fluid1, then select Rock1 as illustrated in Figure 4. Click Next..., Finish. 3. Switch the tab to Sampling and select the variable J for the x-axis, which represents the number of fluid aliquots flushed through the rock. Save the record and click Re-calculate. To select other data to plot use the Remake option (Figure 5). 4. Plot the results and scale the x- and y-axis to inspect the results, which should look similar to Figure 6 and Figure 7. Note you can also modify the number of fluid aliquots by varying the number variable as indicated in Figure 4, e.g. instead of 200 use 400 aliquots. Do not forget you need to use Remake to be able 1

2 to do this, as in your Results tab the program will need to add 200 rows in the table, which cannot be done by only changing the numbers in the Controls tab window. 5. Now try to modify the initial fluid/rock ratio in your parent system record (i.e., use 200 g or 500 g initial Fluid1) and calculate the equilibria in SysEq (Figure 2), then switch back to then Process simulation and Re-calculate. 6. Try different temperatures and initial fluid/rock ratios by cloning your Process records to get the mineral sequence observed in Halter et al. (1998). Fig. 1: A parent system record needs to be created in SysEq for the process simulation. Note that the input units used for the rock and fluid in SysEq will be used in the simulated Process option. 2

3 Fig. 2: Use the Open recipe dialog in SysEq to set the initial fluid/rock ratio as preparation of a Process simulation. Fig. 3: The Process window is used for creating a multi-pass model, using R for a sequential reactor model. 3

4 (5) (6) (1) (3) (2) (4) Fig. 4: The Process dialogue for a multi-pass model (R). To set up this system select Leaching (1), then Fluid1 (2), then Rock1 (3). Check that the definitions of Rock1 and Fluid1 look similar to the script window (4). Select the number of fluid aliquots (5), i.e. 200 fluid aliquots (itm: from 1000 to 1200 in steps of 1), and set P-T conditions (6). Note if we want to increase the number of fluid aliquots flushed through the rock, we need to increase itm for e.g. from 1000 to 1400 in steps of 1 to create 400 aliquots. Also note that the fluid/rock ratio was set and can be changed in SysEq (Figure 2). (2) (1) Fig. 5: Sampling tab where x-axis (1) can be changed and the Remake option (2) to select other variables to plot on the y-axis 4

5 Fig. 6: Results of a multi-pass model at 250 C and 4 kbar showing the number of fluid aliquots (x-axis) vs. grams of minerals formed (y-axis) Fig. 7: Inset view of the results of a multi-pass model at 250 C and 4 kbar showing the number of fluid aliquots (x-axis) vs. grams of minerals formed (y-axis) 5

6 Process simulation: single-pass model (flushing and cooling) This time we simulate the evolution of a single batch of fluid reacting progressively with more granite (sequential columns of granite) upon cooling and look at the evolution of the fluid composition. Fig. 8: The Process window and selection of the system parent record for the single-pass model using the records previously created using the SysEq option 1. Clone your multi-pass simulation created in the Process option (Figure 8) and select your parent record created previously at 450 C and 4 kbar for the multipass (leaching) model. 2. Call the new record singlepass cooling and use the code R for the process simulation mode. 3. Change the parameters in the next window to cool your system from 450 down to 250 C at 4 kbar and select the Flushing: Compos source model option as shown in Figure 9. 6

7 4. Plot the log of total dissolved Sn and log activity of the aqueous Sn species as shown in Figure 10. Check the Sampling tab, if not the same use Remake to select the dissolved aqueous species to plot. Note for the x-axis we chose the temperature in C (ctc). 5. Finally, click Re-calculate. The results should look similar to Figure 11 (6) (1) (5) (2) (3) (4) Fig. 9: The Process dialogue for a single-pass cooling model (R). To set up this system select Flushing (1), then Rock1 (2), then Fluid1 (3). Check that the definitions of Fluid1 and Rock1 look similar to the script window (4). In (5) we select the temperature change between each rock column or step (i.e. from 450 to 250 C in 5 C steps), in (6) we select the number of rock columns (i.e. 40). Also note that the fluid/rock ratio was set and can be changed in SysEq (Figure 2). 7

8 Fig. 10: Selected aqueous Sn species and total dissolved Sn Fig. 11: Result of the single-pass flushing simulation showing the effect of cooling a geisen ore fluid from 450 to 250 C, simulating the alteration of a leucogranite close to a vein with a thermal gradient developing from the vein outward. Shown are the log of total dissolved Sn in the fluid and log activity of major aqueous Sn species. The fluid/rock ratio used was 100 g Fluid 1 per 1 kg Rock1, which can be changed in SysEq (Figure 2) using the parent record of your process simulation. 8