research program 2
mineral explortion through areas of cover
Metal migration: Tracing, tiIming and Modelling (TRIMM)
Project Leader : Robert Hough, CSIRO Exploration and Mining
Start date and duration: I July 2006, 2 years (June 2008)
Participants : CSIRO Exploration and Mining, Australian National University, Primary Industries and Resources SA
Brief project description :
Step changes in exploration geochemistry will only occur if we can truly define where geochemical anomalies reside and how and when they got there. To achieve this we need to understand the fundamental dispersion processes. This has been the aim of the LEME initiative in Mineral Hosts and Mechanisms of Metal transfer and through this project we now focus on the DELIVERY of key components from these studies and plana how to further capitalise on the progress made to date for future projects.
Hydromorphic dispersion is an important mechanism for the transport of metals to the near surface environment during deep weathering of ore deposits, and plays a key role in the final residence of metals in regolith minerals and hence anomaly formation.
This project is a fundamental mineralogical and geochemical study of this dispersion into deeply weathered (both in-situ and transported) regolith environments together with developing a new understanding of solid gold grain provenance in these environments (supergene or primary).
In summary, we are providing outputs through peer reviewed publications from: 1. A study of phreatic mineral deposits such as alunite acting as a mineral host including a detailed description of how such minerals incorporate or adsorb metals. 2. Dating element dispersion by combining in-situ geochronological and geochemical analyses of the same samples. 3. Utilising gold crystallography to decipher supergene and primary origins and combined with chemistry to determine the effects of weathering on native gold occurring at or near the surface and how this modifies bulk gold chemistry. 4. Advanced study of gold anomaly formation in calcrete. 5. Exploration methodology in interpreting anomaly formation and anomaly significance.
Aim : To deliver key products on the timing and role of hydromorphic dispersion in metal transport (including supergene gold) and the mineralogy of anomaly formation with a focus on peer-reviewed literature.
Deliverables (outputs)
Priority Outputs
Peer Reviewed Papers
- Stanley and Noble , 2007, Quantitative assessment of the accuracy and precision of exploration techniques using minimum probability methods. In review, GEEA.
- Hough, Butt, Reddy, Verrall, 2007, Gold nuggets: Hypogene or Supergene, in press, AJES. The internal crystallography and composition of gold nuggets are described and a hypogene origin is proposed. Internal depletion of silver within the gold is crystallographically controlled and proposed to occur by a process akin to depletion gilding.
- Hough, Reddy, Hitchen, Vaughan , Anand, Saunders, Clode, Hart, Verrall, Noble, Gray, Natural ultra thin gold nanoplates. Nature. Gold occurs as ultra thin nanoplates in saprock at this site, a nanoparticulate gold population has also been discovered here and probably represents the ‘invisible' gold detected in clays as a the ppm level enrichment. An inorganic mode of formation is proposed through the evaporation of gold and chloride rich groundwater.
- Lintern, M.J., 2007. Vegetation controls on the formation of gold anomalies in calcrete and other materials at the Barns Gold Prospect, Eyre Peninsula , South Australia . In review. GEEA. The role of vegetation in the formation of gold anomalism at the Barns prospect is described.
- Noble and Stanley , 2007. A comparison of novel and traditional extractions over a Copper Zinc soil anomaly, NW Victoria. GEEA. Much has been made of selective extractions in exploration geochemistry, this study assesses their efficacy.
- Keeling, Pillans.Timing and mechanism of Cu transfer into cover sediments at Moonta, SA, in prep for submission to GEEA. A study of Cu dispersion at the Moonta Site and how Cu is found associated with Alunite.
- McQueen and Pillans , History of element dispersion at the McKinnons gold deposit, Cobar, NSW. GEEA. Dating element dispersion within individual mineral hosts.
- M.J. Lintern, J. Watling, M. Verrall and A.N. Other (TEM) The nature of the gold associated with calcrete anomalies. Australian Journal of Earth Science. Calcretes containing Au from three Au prospects/mines will be examined using various techniques including LA ICPMS, SEM and TEM to investigate the distribution of Au at the micron to sub-micron scale, leading to a better understanding of how geochemical anomalies form.
- M.J. Lintern and M.J. Sheard, Dispersion of gold and other elements at Edoldeh Tank Gold Prospect, western Gawler Craton , South Australia . Journal of Geochemical Exploration. The dispersion of Au and other elements in vegetation, calcrete and other regolith materials at the Edoldeh Tank Gold Prospect will serve as a model to understand how surficial geochemical anomalies form at the landscape scale; Edoldeh Tank is one of the largest Au in calcrete anomalies in South Australia.
CONFERENCE ABSTRACTS
IAGS (June 07)
Frontiers in Mineral Science , Joint meeting of the Mineralogical Societies of GB, Ire , France , America and Canada . 2007. (Hough funded by PCB scholarship).
1. Hough, Butt, Verrall, Saunders and Reddy; Gold nuggets: Hypogene or supergene?
2. Hough, Reddy, Saunders, Hart, Anand, Clode, Vaughan , Hitchen, Noble and Verrall; Natural ultra-thin nanoplates of gold.
3. Scott, Radford and Hough; Rutile geochemistry at the Super pit, Kalgoorlie .
Kalgoorlie 07 , Recent advances in understanding of the geology and mineral deposits of the Yilgarn Craton and its margins.
Invited talks
1. Hough, Gold grains as an exploration tool.
2. Anand, advances in understanding of regolith processes and metals mobility
3. Gray, Hydrogeochemical exploration
American Soil Science Society, 2007.
1. Noble; Geochemical dispersion in soils at Stawell, NW Victoria.
Outputs
REPORTS:
- Hough, Butt, Verrall and Reddy : The primary origin of gold nuggets. Report of research into the internal crystallography of gold nuggets that displays their primary origin and not supergene secondary growth.
- Hough, Anand, McQueen, Keeling, Phang, Norman , Ryan, Etschmann, Belton : Mineral Hosts for trace element residence in the regolith. Report on the insitu microanalyses of metal residence in regolith materials encompassing laser ablation ICPMS, Proton induced X-ray emission element mapping and Synchrotron X-ray fluorescence together with results of SEM and EMP analyses.
OTHER PRESENTATIONS
Preliminary CRCLEME Mineral Exploration Seminar - Aug 07 and Mar 08. CSIRO Exploration and Mining Innovation series lectures.
Outcomes
- Identification and analyses of minerals related to phreatic processes (e.g. sulfates) as a vector for exploration. Be able to determine the timing of metal dispersion which is pivotal to understanding the origin and formation of anomalies and palaeoenvironments
- A new understanding of alluvial/lateritic gold grain provenance based on combined crystallography and chemistry.
- Build a chemical (reactive transport) numerical modelling tool which will enable prediction of the location and relative tenor of geochemical anomalism in different regolith units depending on such factors as the:
- Size, grade, sulphide content and attitude of the target orebody.
- Chemical characteristics of the rock units that might host the target orebody.
Thickness and nature the regolith overlying the ore.
- An ability to date metal dispersion through combined insitu microchemical and geochronological analyses.
- International recognition and call for collaboration with gold grain studies worldwide.
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