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An introduction to thermodynamic modeling of fluid-rock interaction and ore-forming
processes using GEMS
ORGANIZERS: ALEXANDER GYSI [email protected], NICOLE HURTIG [email protected], DAN MIRON [email protected]
2 days Online Workshop, Geochemical Society
Tuesday Dec 8 – Wednesday Dec 9, 2020
Workshop objectives
● Give you an overview of GEMS code package for simulating fluid-rock interaction in natural magmatic-hydrothermal systems
● Overview of GEM vs. LMA code (e.g. PHREEQC) and which tool is adequate for which situation
● Get you started with the MINES thermodynamic database and possible database management in GEMS
● Get you started on modeling projects with GEMS
● Discussions and scientific exchange
Materials and handouts
● Code package, GEM-Selektor v. 3.7
http://gems.web.psi.ch → download program
● MINES thermodynamic database
https://geoinfo.nmt.edu/mines-tdb
→ download MINES19 files (DB19.default.zip)
● Handouts:
Tutorial gitbook: https://apgysi.github.io/gems-mines-tutorial/
Download the module project files on google drive...
Workshop format
● Demonstration by organizers in the Main Zoom room (15-20 min)
● Five breakout Zoom rooms for hands-on experience by the participants (30 min)
● General Q&A (5-10 min) back to the Main Zoom room
Alex breakout rooms 1-2
Nicole breakout rooms 3-4
Dan breakout room 5
Workshop program day 1
● 6-6:10am (MT)/ 14:00-14:10(CET) (Alex Gysi) Overview of the workshop and goals
● 6:10-7:00am/ 14:15-15:00 (Alex Gysi) Simulating fluid-rock interaction and ore-forming processes
● 7:00-7:50am/ 15:00-16:00 (Dan Miron) GEMSFITS, thermohub, thermodynamic databases
● Coffee break (10 min)
● 8:00-9:00am/16:00-17:00 (Alex Gysi) Module 1 Create your first project in GEM
● 9:00-10:00am/17:00-18:00 (Nicole Hurtig) Module 2 feldspar reaction path (titration model):
Workshop program day 2
● 6:00-7:00am/ 14:00-15:00 (Nicole Hurtig) Module 2 feldspar reaction path (titration model) continued...
● 7:00-8:00am/ 15:00-16:00 (Alex Gysi) Module 3 Greisen alteration, leucogranite reaction path (titration)
● Coffee break (10 min)
● 8:00-9:00am/ 16:00-17:00 (Alex Gysi) Module 4 Greisen alteration, cassiterite solubility and Sn speciation (multipass model)
● 9:00-10:00am/ 17:00-18:00 (Nicole Hurtig) Module 4 Greisen alteration, cassiterite solubility and Sn speciation (singlepass cooling model):
● Q&A? Additional Demo? Closing workshop session
●
●
Simulation of fluid-rock interaction and ore-forming processes
Alexander Gysi New Mexico Bureau of Geology and Mineral Resources
Central City, CO, USALandmannalaugar, Iceland
Blue Lagoon Iceland
Hydrothermal fluids at shallow depth
Hydrothermal fluids at shallow depth
Covellite(Cu-sulfide)
Chalcantite(Cu-sulfate)
Gypsum
Krisuvik, Iceland
Volcano, Italy
Porphyry and epithermal systems
L. Robb book “Intro Ore-forming processes” (2005)
Seedorff and Einaudi (2004b)Seedorff and Einaudi (2004a)
Hydrothermal fluids trapped at depth
Henderson Porphyry Mo system, Colorado, USA
● Mineral assemblages in ore deposits indicate specific conditions of fluid-rock reactions
● Thermodynamic phase diagrams and modeling scenarios can tell us about P-T-x conditions of crustal fluids
● x includes pH, salinity, activities of ions (Na+/K+, …), which we can’t all determine from fluid inclusion data
● The key in the modeling process is the path to understanding of these fluids rather than details and time spent on these models...
Constraining the evolution of hydrothermal fluids from a thermodynamic modeling
perspective
K-feldspar (KAlSi3O8)
quartz (SiO2) ±hematite ±fluorite
+Ca + F+ REE3+ +Fe +SiO2(aq)+H2O added by fluid
+K released by fluid
hematitefluorite
Kfs
Link mineralogical observations with alteration processes
Qtz
Dissolution texture of feldspar in peralkaline granite
Strange Lake peralkaline REE-Zr-Nb deposit, QC, Canada
● The fluid acts as the acid (HCl, H2SO4, H2S, CO2) that releases protons (H+).
● The rock acts as the base and consumes protons (H+) during rock alteration.
3KAlSi3O8 (K-feldspar)+2H+ =
KAl3Si3O10(OH)2(muscovite)+6SiO2(quartz)+2K+
Fluid-rock interaction as an acid-base titration
Rock = base
Fluid = acid
Feldspar hydrolysis model
KAlSi3O8 (Kfs)+4H++4H2O= K++Al3++3H4SiO4(aq)
+
Al(OH)3(s) (Gibbsite)Al2Si2O5(OH)4 (Kaolinite)KAl2(AlSi3)O10(OH)2 (Muscovite)
Zhu and Lu, GCA 2009. See also Helgeson et al. (1969)
Feldspar hydrolysis model
Increased reaction progress (g feldspar added)
Feldspar titration model, GEMS tutorial module 2
Greisen alteration to quartz vein formation
Halter et al. (1998)
East Kemptville Sn deposit
Leucogranite
Audétat et al. (2000)
Sn-W Mole granite, Australia
Greisen alteration
Increased reaction progress (g rock added)
Granite titration model @250 and 450 °C and 4kb, GEMS tutorial module 3 and 4
Mobility of Sn in hydrothermal solutions● Precipitation of cassiterite according to:
Sn4+O2 (cassiterite)+2H++H2(g)+3Cl- = Sn2+Cl3- + 2H2O
● SnO2 precipitation due to ligand activity, redox, pH and/or temperature change.
Single pass fluid and cooling modelGreisenization, titration
model
Numerical modeling of reaction paths in complex fluid-rock
systems
Numerical methods to solve the reaction paths of fluid-mineral systems
Aqueous geochemistry:
● Law of mass action (using logK), e.g. PHREEQC and Geochemist’s Workbench
Metamorphic/igneous petrology and hydrothermal geochemistry:
• Gibbs energy minimization (using G), e.g. Perplex, Hch, Thermocalc, Gem-Selektor, Melts.
See also: Leal et al. (2017), Pure and Applied Chemistry 89, Issue 5, 597-643Kulik (2006), Chemical Geology 225, 189-212
Law of mass action (LMA)
NaAlSi3O8 (albite) +8H2O = Na++Al(OH)4-+3H4SiO4(aq)
• Equilibrium constant:
• Activity of aqueous species:
• List of aqueous species:(Na+, Al3+,Al(OH)4
-, H+, OH-, H2O(aq))
• Mass balance equations:[Al]tot=mAl3+ + mAl(OH)4
-
[H]tot=mH++ mOH-+ mH2O(aq) …
● Charge balance:
Charge=3Al3+ + Na++ H++ Al(OH)4-+ OH- = 0
Gibbs energy minimization (GEM)
NaAlSi3O8 +8H2O = Na++Al(OH)4-+3H4SiO4(aq)
● List of components (C):Na-Al-Si-O-H
● List of phases (Φ):Albite, quartz, H2O
• Phase rule:• Schreinemakers rule for metastable/stable reaction
• Standard Gibbs energy, chemical potentials:
Law of mass action (LMA) vs. Gibbs energy minimization (GEM)
•Set of master species (Al3+, H+, OH-, H2O(aq))
•Other species built from master species (Al3+ + 4OH- = Al(OH)4
-)•Database with equilibrium constants (logKr) at T and at psat.
•LMA to solve mass balance using Newton-Raphson method (Bethke, 1996).
•Mass balance using (IC) independent components (H, O, Al, …) and electric charge (z).
•Chemical species are (DC) dependent components (aqueous species, minerals, gases…) built from IC.
•Database with standard Gibbs energy (G°) corrected at P-T.
•GEM to solve mass balance using Interior Points method (Karpov et al. 2001).
LMA GEM
•Redox (Eh, pe or redox pair Fe(II)/Fe(III)) and pH (or element charge balance) must be set at input.
•Only limited (binary) solid solution models.
•Fast convergence: kinetics rate laws and reactive transport model.
•pH and redox (pe, Eh) calculated from minimization.
•Solve equilibrium for complex non-ideal solutions.
•Slower convergence, but more output data from a single calculation: e.g. phase volumes, fugacity, etc...
LMA GEM
Law of mass action (LMA) vs. Gibbs energy minimization (GEM)
Numerical modeling using Gibbs energy minimization (GEM)
• GEM-Selektor v.3 (http://gems.web.psi.ch)
• Free geochemical modeling software written in C/C++
• Works on Windows, Mac OSX and Linux
• Tool to simulate geochemical processes based on Gibbs energy minimization
• Calculate chemical equilibria in multicomponent and -phase systems
User interface(i) Equilibria calculation mode (ii)Thermodynamic database mode
• Calculate chemical equilibrium of minerals-fluids.
• Calculate processes for rock alteration: cooling, fluid mixing, leaching etc…
• Thermodynamic properties of minerals and fluids.
• Solution models: solid solutions, non-ideal gas…
• Prepare complex rock or fluids compositions.
(i) Equilibria calculation mode
Types of simulations
Input/output buttons
Speciation results
Chemical System records (P-T-x)
Equilibria calculation mode
Types of simulations
• SysEq: compute equilibria (speciation, pH, redox, concentrations, stable minerals) of single chemical systems.
• Process simulator: compute a series of equilibria using single chemical systems subject to variations in P-T-x.
(P) P-T variable; bulk composition (b) fixed -> cooling
(S) Reaction path (titration), fluid mixing; composition (b) variable.
(G) Inverse titration.
(R) Sequential reactor (flushing and leaching of a rock by a fluid)
• GtDemo: Plot/compute selected modeling results.
• GEM2MT: Prepare files for 1-D reactive transport modeling.
• Project: Tune numerical controls.
Demonstration of chemical equilibria calculations (SysEq) = cooking a soup
Set up and calculate a chemical equilibria (SysEq)
● Define a new system (P, T).● Input of bulk chemical composition (x).● Calculate equilibrium.
What GEM-Selektor does…
Input bulk composition of
IC (b)
Output mole amounts DC (x)
Ax = b
What GEM-Selektor does…
Thermodynamic database mode
Options
Thermodynamic properties
Dependent Components (DC)
(ii) Thermodynamic database mode
Options• IComp: add an independent component (e.g. Al, H, O, Si …).
• DComp: add thermodynamic properties of a dependent component (e.g. quartz, kaolinite, Al3+, CO2(g) …)
• ReacDC: add a reaction dependent component (e.g. Al(OH)3(s)+H+= Al3++3OH-; logK = …)
• RTparm: calculate thermodynamic properties vs. P-T.
• Phase: define a phase or a mixture (e.g. mineral, mineral solid solution, gas mixtures).
• Compos: add a composition object to be used as input in the simulations (e.g. granite, fluid, acid …)
MINES thermodynamic database
Goals of the project
• Internally consistent dataset covering fluid-rock equilibria at hydrothermal conditions (≤5 kbar and ≤600 °C)
• Test experimental, theoretical, and natural datasets
• Facilitate use of GEMS and other codes to simulate fluid-rock interaction and ore-forming processes
• Community effort
• Open access and rolling-release
• Collaborations with GEMS team: Dan Miron and Dmitrii Kulik (PSI, Switzerland)
• Collaborations with students and diverse research groups and projects
Basic framework• Rock-forming minerals: 122 minerals from H&P98 database + non-silicate
minerals from R&H95
• Aqueous species from SUPCRT92 implemented in GEMS
• Some solid solution models (e.g., ternary feldspar)
Statistical/optimization method (GEMSFITS, internal consistency)
• Major cations: Na-, K-, Al-, Si-bearing species, + Ca-, Mg-, CO2-bearing
species (Miron et al. 2016, 2017)
Experimental data & Natural systems• Zeolites (14 end members) and phyllosilicates (16 end members), solid
solutions from Gysi and Stefánsson (2011)
• Experimental REE phosphate solubility experiments from our lab (Gysi et al. 2015, 2018)
• REE complexes (Migdisov et al. 2009), base and precious metals (Akinfiev and Zotov, 2001, 2010, 2014; Liu and McPhail, 2005; Brugger et al., 2007; Mei et al., 2015; Stefansson and Seward, 2003, etc...)
Current status: MINES 19
The role of hydrocarbons in Mississipi Valley-Type Zn-Pb ore formation
Ore fluid: basinal acid-sulfate brine
high Pb, Zn, Ag, and Cu contents
Mineralization: brine-hydrocarbon
interaction
Simulate controls of pH vs. redox
Hurtig et al. (2018), Ore Geol. Rev. 102
Reactive transport simulations: pH and redox
4000 steps
1000 steps
100 steps
4000 steps
100 steps
1000 steps
Hurtig et al. (2018), Ore Geol. Rev. 102
Reactive transport: ore mineralogy and metal ratios
4000 steps
Sphalerite
Galena
Chalcocite
Ag (s)
Pyrite
100 steps
Sphalerite
GalenaChalcocite
PyriteAg(s)
Calcite
FeAg
PbZn
Cu
Hurtig et al. (2018), Ore Geol. Rev. 102
Oceanic crust alteration: seawater-basalt interaction and ore formation in volcanogenic hosted sulfide
(VMS) deposits
L. Robb book “Intro Ore-forming processes” (2005)
Hydrothermal seawater-basalt interaction and hydrothermal vent fluids
Pierre et al. (2018), Geofluids
Focus on alteration mineralogy and resulting fluid-chemistry in closed system first.
Comparison between model and natural systems
Varying effects of fluid-rock ratios, temperature, and rock composition
Seawater-basalt interaction at 250 °C and 500 bar - 1D reactive transport: e.g. sequential reactors (waves) and flow-through
box-fluxes with propagation of alteration front
Live DEMO GEM2MT
1) “Closed” system models:
Cooling/heating of fluid at constant fluid/rock ratio
Titration model at varying fluid/rock ratios
Fluid mixing models at varying fluid1/fluid2 ratios
General ideas about fluid-rock interaction and numerical modeling
Variables to consider (chemical+physical parameters):
Pressure and temperature
Composition of magmatic-hydrothermal fluid: pH, salinity, redox
Composition of host rock, porosity, permeability
1) “Open” system models:
Multipass and single pass (or flow-through sequential reactor)
Reactive mass transport models (sequential reactor chain, flow-through box-flux sequences, 1-D reactive advection/diffusion)
