Case Study - 3D mineral mapping of the Channel Iron Ore deposit of Rocklea Dome, Western Australia
Aim | Geological Setting | Potential for Mineralisation | Project | People | References | Links
The Rocklea Dome Channel Iron Deposit (CID) is one of the case studies that have been established to evaluate and showcase the geoscience products created by the Centre of Excellence for 3D Mineral Mapping at CSIRO (Cudahy et al. 2008).
These geoscience products have been applied to airborne hyperspectral data and to hyperspectral drill core data (Haest et al. in prep. b), acquired using one of CSIRO’s commercially available HyLoggingTM systems. Integration of both surface and subsurface spectroscopic mineral data will assist in targeting of CIDs in various regolith and geomorphic environments.
The Rocklea Dome is located in the Hamersley Province of Western Australia (Fig. 1A), 40km West of Tom Price. The Rocklea Dome has a core of Achaean granites, surrounded by metavolcanics and metasediments of Archaean to Proterozoic age. A Tertiary palaeochannel meanders from northeast to southwest over the Rocklea Dome. Large areas are covered by Quaternary transported cover (Fig. 1B).
Fig. 1 (A) Location of the Rocklea Dome in the Hamersley Province of Western Australia; (B) Geological map of the Rocklea Dome, with the tenements of Murchison Metals Ltd (MML) and AusQuest Ltd. outlined in red and black respectively; 1 outlines the CID resource identified by MML; position of B indicated in A; geological map of the Rocklea Dome after Thorne and Tyler 1996; figure from Haest et al. (in prep. a)
The Pilbara iron ore province hosts most of Australia’s iron ore resources, totalling > 32000 Mt. Most of the iron ore is contained in bedded iron ore deposits (BIDs) (~25000 Mt) that are essentially the product of upgraded bedded iron formations (Morris 1980). Erosion of BIDs formed detrital iron deposits, but with a resource of only 500 Mt and negligible production, they are less significant (Morris and Ramanaidou 2007). Concentration of the BID erosion products along channels of tertiary age resulted in CIDs, which form an estimated resource of > 7000 Mt. As they constituted about 40 % of all iron ore mined from this area in 2005, CIDs have received large economic significance (Morris and Ramanaidou, 2007).
The Tertiary palaeochannel meandering through the Rocklea Dome hosts the Rio Tinto Ltd Beasley River 400Mt CID (Fig. 1B). The Rocklea Project of Murchison Metals Limited covers over 400 km2 downstream of the Beasley River CID. This part of the Rocklea Dome is therefore considered to be highly prospective for more CID style mineralisation. Satellite imagery and geological mapping helped to identify up to 40 strike kilometres of prospective palaeochannels on the tenements
Latest studies on the relationship between parent rock type and the development of CIDs suggest that carbonates and granites are unattractive parent rocks, due to potential effects on pH and silica content of the groundwater (Morris and Ramanaidou 2007). Metasediments and mafic/ultramafic rocks on the other side promote the development of reduced neutral fluids that would preferentially remove ferrous iron in solution. Good quality CID ores develop, when iron rich (Si-poor) fluids move up into still water surface environments, where ferrous iron is oxidised into insoluble ferric iron. Drilling results from the Hamersley Basin have confirmed that metasediments are associated with higher quality iron ores in contrast to CID developed over granite rocks, which are characterised by high opaline silica contents (Morris and Ramanaidou 2007).
Hyperspectral sensing techniques are being applied to accurately map mineral compositions of the parent rocks, which allow inferring redox and pH conditions (Cudahy et al. 2008, www.em.csiro.au/NGMM) and therefore possibly help to target higher quality iron ores in the Hamersley Basin. In a first step drill cores made available by MML have been analysed with one of CSIRO’s commercially available HyLoggingTM systems. Hyperspectral drill core data are interpreted using the dedicated software package The Spectral Geologist (TSGTM). A multiple feature extraction method is applied to extract relative abundance and composition of VNIR and SWIR active minerals from the infrared reflectance spectra, resulting in a suite of public available geoscience products. To validate C3DMM’s public geoscience products these reflectance spectroscopic mineral results were compared with geochemical analyses (e.g. multi-element geochemistry, X-ray diffraction) (Fig. 2; Haest et al. in prep. b).
Fig. 2 Validation of Fe-oxide abundance derived from hyperspectral data by comparison with wt% Fe results from XRF analyses (after Haest et al. in prep. b).
The validated mineral abundance and composition products derived from hyperspectral data have been used in 2D sections (Fig. 3) and 3D LeapfrogTM-based models (Fig. 4) to delineate the major ore zones and compositional variations within these zones (i.e. more vitreous and ochreous goethite zones in Fig. 4). Spectral derived mineral data along drill cores also allowed mapping the different contaminants to the iron ore, like clays and carbonates (e.g. kaolinite horizons in Fig. 3).
Fig. 3 Compilation of hyperspectral data from 5 diamond drill cores at a 1 cm spatial resolution, revealing 5 mineralogical zones (1-Calcrete; 2-Kaolin; 3-Fe ore; 4-med. Fe/med. clay; 5-Bottom of channel, low Fe & high clay)
Fig. 4 3D distribution of ochreous and vitreous goethite zones in the MML defined Rocklea Dome CID (position of model corresponds to zone 1 in Fig. 1B)
Prime contact: Tom Cudahy (Spectral Geologist, CSIRO and CoE C3DMM Director, email)
Erick Ramanaidou (Geologist, CSIRO)
Maarten Haest (Research Geoscientist, CSIRO)
Andrew Rodger (Physicist, calibration and algorithm development CSIRO)
Michael Caccetta (Software Engineer, CSIRO)
Carsten Laukamp (Research Geoscientist, CSIRO)
Klaus Gessner (3D Engineer, Geologist, UWA)
Andrew Hacket (Spectral Technician, CSIRO)
Michelle Cardy (Spectral Technician, CSIRO)
Lena Hancock (Mineralogist, GSWA)
Sean Greogory (Chief Geologist, Murchison Metals Limited)
Cudahy T, Jones M, Thomas M, Laukamp C, Caccetta M, Hewson R, Rodger A, Verrall M (2008) Next Generation Mineral Mapping: Queensland Airborne HyMap and Satellite ASTER surveys 2006-2008. CSIRO Exploration & Mining, Perth, Publicly available report: P2007 / 364 (http://www.em.csiro.au/NGMM/), pp 152
Haest M., Cudahy T., Laukamp C., Gregory S. (in prep. a) Quantitative mineralogy from visible to shortwave infrared spectroscopic data: (II) 3D mineralogical characterisation of the Rocklea Dome channel iron deposit in Western Australia.
Haest M, Cudahy T, Laukamp C, Verall M, Gregory S (in prep. b) Quantitative mineralogy from visible to shortwave infrared spectroscopic data: (I) Validation of mineral abundance and composition algorithms at the Rocklea Dome channel iron deposit in Western Australia.
Morris RC (1980) A textural and mineralogical study of the relationship of iron-ore to banded iron-formation in the Hamersley Iron Province of Western Australia. Economic Geology 75:184-209.
Morris RC, Ramanaidou ER (2007) Genesis of the channel iron deposits (CID) of the Pilbara region, Western Australia. Australian Journal of Earth Sciences 54:733-756.
Thorne AM, Tyler IM (1996) Geology of the Rocklea 1:100000 sheet. Western Australia Geological Survey, Perth
Rocklea - http://www.mmi.net.au/