Authors / CoAuthors
Mernagh, T.P. | Bierlein, F.P.
Abstract
This study reports results of mass transfer calculations using chemical modelling software (HCh) to determine chemical parameters that may have a significant effect on turbidite-hosted gold deposition in Phanerozoic metamorphic terranes. The geochemical models herein consider an 18 component system (Al-As-Au-C-Ca-Cl-Cu-Fe-H-K-Mg-N-Na-O-Pb-S-Sb-Si) and thermodynamic data to simulate a number of geochemical processes including fluid-rock interaction, gas partitioning and mineral precipitation in veins. Each modelling run consists of four parts, namely (1) the minerals predicted to precipitate in the vein, (2) the composition of the fluids in the vein, (3) the predicted alteration assemblage of the host-rocks due to fluid-rock interaction and (4) the composition of the fluids during fluid-rock interaction. Results of the modelling are in good agreement with observed mineral assemblages in variably-endowed orogenic gold provinces (central Victoria and NE Tasmania, Australia; Buller Terrane, New Zealand; Meguma Terrane, Canada; Sierra de Rinconada, Argentina) and illustrate that gold can be precipitated efficiently and over a wide temperature range (350 - 200 C in this study) from low-salinity, mixed aqueous-carbonic fluids containing up to 0.1m CO2. The modelling shows that the absence of certain physicochemical processes (e.g., boiling) or fluid constituents, such as low total sulphur or lack of CO2 may inhibit gold transport and precipitation in some environments. All the modelling runs, except the one involving a low total sulphur fluid, predict the precipitation of sulphides in the host-rocks due to desulphidation processes. However, the highest gold grades are predicted to occur in the vein mainly from partitioning of H2S into the vapour phase during phase separation. This indicates that the efficiency of gold mineralisation is dependant on the concentration of CO2 and other gases in the fluid because of their effect on immiscibility (in both closed and open systems) and the efficient transport and precipitation of gold. We also investigated what effect the composition of a range of source rocks (i.e., granite, turbidites, greenstones, auriferous exhalative interflow sediments) have on gold solubility, as this relates to masses of gold that are accessible by leaching fluids and hence to ore transport and formation. Our thermodynamic calculations suggest that the chemical composition of the hypothetical source rock has only a small influence on the solubility mainly influenced by the initial concentration of gold in the rock.
Product Type
nonGeographicDataset
eCat Id
64856
Contact for the resource
Custodian
Point of contact
Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
Canberra
ACT
2601
Australia
Keywords
-
- External PublicationScientific Journal Paper
- ( Theme )
-
- economic geology
- ( Theme )
-
- geochemistry
- ( Theme )
-
- mineral deposits
- ( Theme )
-
- thermodynamics
- Australian and New Zealand Standard Research Classification (ANZSRC)
-
- Earth Sciences
-
- Published_Internal
Publication Date
2007-01-01T00:00:00
Creation Date
Security Constraints
Legal Constraints
Status
Purpose
Maintenance Information
unknown
Topic Category
geoscientificInformation
Series Information
Lineage
Unknown
Parent Information
Extents
Reference System
Spatial Resolution
Service Information
Associations
Downloads and Links
Source Information
Source data not available.