Element mobility in high-sulfidation epithermal alteration systems: insights from mass transfer, and pyrophyllite and chlorite mineral chemistry at the pueblo viejo Au-Ag(-Cu) deposit, dominican republic
Author(s)
Tonks, Ethan
Type
Thesis
Abstract
The spatial footprint of alteration associated with magmatic-hydrothermal mineral deposits is typically significantly larger than corresponding ore mineralisation. Advancements to the understanding of the genesis of this style of alteration can help to considerably improve exploration targeting. A detailed geochemical study of magmatic-hydrothermal alteration at the Pueblo Viejo high-sulfidation (HS) epithermal Au-Ag(-Cu) deposit, Dominican Republic, is presented in this thesis. The zonation of alteration facies and the minerals within them were determined and variations in whole-rock and mineral chemistry (pyrophyllite and chlorite) investigated.
Chemical changes that occurred during development of each alteration facies—quartz-alunite (proximal), quartz-pyrophyllite, and chlorite-carbonate-illite (distal)—were quantified using a Gresens-Grant geochemical mass balance approach. Elemental components were separated into nine groups based on their behaviour both within and between alteration facies. For several groups, the lateral trends are spatially systematic, which has important implications for geochemical exploration. The mineralogical deportment of elements was estimated to infer the key mineral breakdown-precipitation reactions that controlled their bulk rock and mineralogical behaviour, which were linked to systematic changes in fluid physico-chemical properties and provide insight into the genesis of HS epithermal alteration.
For both pyrophyllite (Li, Na, Mg, V, Mn, Cu, Zn, Ga, Ge, As, Rb, Sr, Sb and Cs) and chlorite (Si, [iv]Al, [vi]Al, Mg, Li, K, V, Mn, Ni, and Zn), concentrations of multiple elements were determined to be spatially systematic. The primary controls on these trends are thought to be spatial changes in fluid temperature, pH, and metal and ligand concentrations, although the behaviour of some elements (e.g. V) may be related to fO2.
Overall, these results illustrate that detailed study of magmatic-hydrothermal alteration can not only enhance our understanding of HS epithermal deposit genesis, but potentially also be utilised to aid the exploration for undiscovered systems.
Chemical changes that occurred during development of each alteration facies—quartz-alunite (proximal), quartz-pyrophyllite, and chlorite-carbonate-illite (distal)—were quantified using a Gresens-Grant geochemical mass balance approach. Elemental components were separated into nine groups based on their behaviour both within and between alteration facies. For several groups, the lateral trends are spatially systematic, which has important implications for geochemical exploration. The mineralogical deportment of elements was estimated to infer the key mineral breakdown-precipitation reactions that controlled their bulk rock and mineralogical behaviour, which were linked to systematic changes in fluid physico-chemical properties and provide insight into the genesis of HS epithermal alteration.
For both pyrophyllite (Li, Na, Mg, V, Mn, Cu, Zn, Ga, Ge, As, Rb, Sr, Sb and Cs) and chlorite (Si, [iv]Al, [vi]Al, Mg, Li, K, V, Mn, Ni, and Zn), concentrations of multiple elements were determined to be spatially systematic. The primary controls on these trends are thought to be spatial changes in fluid temperature, pH, and metal and ligand concentrations, although the behaviour of some elements (e.g. V) may be related to fO2.
Overall, these results illustrate that detailed study of magmatic-hydrothermal alteration can not only enhance our understanding of HS epithermal deposit genesis, but potentially also be utilised to aid the exploration for undiscovered systems.
Version
Open Access
Date Issued
2024-03-01
Date Awarded
01/06/2024
License URL
Advisor
Wilkinson, Jamie
Armstrong, Robin
Sponsor
Barrick Gold Corporation (Firm)
Publisher Department
Earth Science & Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)
Rights Embargo Date
2025-05-31