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Concluded: 30th June 2000

North Pilbara project (1995-2000)

      

Objectives

The objectives of the North Pilbara project were to provide the resources sector with timely and relevant new-generation geoscientific information to reduce investment risk. The objectives were met by an integrated geoscientific mapping program, supported by a craton-scale synthesis and advanced GIS by utilising

  1. regional airborne magnetic, gamma ray spectrometric and gravity data,
  2. remotely sensed multispectral images,
  3. regional (1:100 000) and detailed geological and structural mapping, and
  4. compilation of the geological characteristics of mineral deposits, combined with isotopic age data, mineral deposit descriptions, and geochemical data for igneous rocks.

The data were used to generate metallogenic and tectonic syntheses, and to develop empirical models of exploration for the North Pilbara. These programs enhanced exploration activity in the North Pilbara and so, increase the probability of significant mineral discoveries.


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Background

Results from the conclusion of this NGMA project highlighted fundamental tectonic and metallogenic differences between the mid Archaean Pilbara craton (3.65-2.8 Ga) and the late Archaean cratons (2.75-2.5 Ga), viz:

  1. Presence of common mineral deposit types such as Sn-Ta pegmatites, porphyry Mo-Cu deposits and adularia-sericite epithermal Au deposits that are better known in Proterozoic or younger rocks, and are absent in the late Archaean cratons.
  2. Multiple mineralising events over a period of 800 Ma (eg. 4VHMS events and 5 orogenic gold events) as opposed to the single, global events in the Neoarchaean (eg. 2710±20 Ma for VHMS and 2630±10 Ma for orogenic gold in the Eastern Goldfields, the Superior & Slave Provinces).
  3. Phanerozoic-like characteristics for some deposit types in the Pilbara (eg significant Pb and baryte with calc-alkaline volcanic rocks in VHMS deposits).
  4. Different regional controls on mineralisation (eg general lack of craton-scale shear zones which are first-order controls on orogenic gold deposits in the Eastern Goldfields and Superior Provinces).
  5. Different crustal architecture of the Pilbara relative to late Archaean Provinces (eg the greenstone belts and the domal granitoids that they envelop both extend to greater depths (~14 km) in the Pilbara).

Exploration models and genetic interpretations of Archaean mineral deposits are largely based on late Archaean examples and therefore somewhat limited in application in the Pilbara. The aim of the Pilbara project has been to document these differences by providing regional thematic synthesis datasets so that more robust models can be developed to encompass the entire Archaean era. These datasets, together with our research into new exploration tools, will assist exploration in the Pilbara, and have applications to other terranes.


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Overview

The project began in 1995 and was completed in June 2000. Geoscience Australia's role focussed on developing a multidisciplinary understanding of the entire North Pilbara craton. Our activities included:

  • Characterisation of North Pilbara's mineral deposits (especially Gold) and definition of ore vectors;
  • Investigation of new exploration techniques;
  • Acquisition, interpretation and presentation of geophysical data;
  • Review and capture of existing data/information into a North Pilbara GIS and 1:1.5M scale atlas;
  • Advanced Landsat-5-TM processing, interpretation and presentation;
  • Specialist problem-solving fieldwork;
  • Petrological and geochemical studies;
  • Sm-Nd geochronology;
  • Development of stratigraphic framework and tectonic models of crustal evolution;
  • 1:100 000 geological mapping of the Wodgina and Wallaringa sheets;
  • 3D modelling of the Pilbara.

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Major achievements

  1. New Potential–Old Province
    Extensive areas of the Pilbara are presently exposed close to the c. 2765 Ma Hamersley Basin unconformity surface. This exceptional preservation significantly improves younger mineralising events of gold and possibly diamonds in the mostly older mid Archaean Pilbara granite-greenstone terrane. Newly documented areas of high-level (epithermal) systems preserved in west and far east Pilbara are related to NNW dextral faults and associated relay movements during early Fortescue extension (NW-SE). Epithermal veins cut 2765 Ma Opaline Well Granite, and similarly aged Gregory Range Granite. Epithermal veins are incorporated in NNW-trending Gidley Granophyre breccia dykes (2765 Ma).
  2. New Exploration Tools
    The Pilbara project had significant success with alteration mapping using the HYMAP multispectral scanner, gamma ray spectrometrics, oxygen isotopes, and whole rock geochemistry. These tools were successful over the poorly exposed and calcretised Mallina-Indee gold prospects and over the well exposed Panorama VHMS district. The HYMAP data successfully mapped alteration minerals such as pyrophyllite, sericite, successfully separated Fe-chlorite from Mg-chlorite, and separated dolomite from calcite in calcrete. Several of the targets generated from the HYMAP image maps produced anomalous gold on subsequent analysis. Oxygen isotope mapping and conversion to palaeotemperatures in VHMS terrains can be used as an exploration tool. The temperatures define fluid pathways as vectors to ore and are predictors of metal deposition (Zn vs Cu). District-scale depletion of Zn and Cu was mapped with whole-rock geochemistry, and these depletion zones map the fluid pathways related to VHMS deposits. Regional Geoscience Australia gamma ray spectrometric data were used to map K-depletion anomalies associated with the Panorama alteration system.
  3. Regional synthesis and GIS
    The project brought together a comprehensive set of digital themes for the entire Pilbara craton. These are stored in a project GIS, from which a set of derivative products were produced. These include a 1:1 500 000 scale colour atlas with 36 A3 pages, as well as a thematic series of 1:500 000 scale maps and images (print-on-demand or postscript files). A subset teaching GIS was produced. These datasets provide explorers with a suitable baseline and regional context for their exploration and target generation. The project documented the variety of mineral deposits – especially gold, VHMS, Sn-Ta, and high-level deposits, and produced databases (GIS) and Geoscience Australia Records. The diversity of the Pilbara gold was documented. A successful industry (June–July 1999) field trip was run to examine key deposits and relationships. A regional structural synthesis was conducted and a new deformation chronology and kinematics of some of the major shear zones produced. The advances include a better understanding of shear zone timing and movement senses, an improved understanding of the complexity of the polyphase deformation, recognition of the importance of horizontal compression as a tectonic driving force, and a clearer link between regional tectonics and mineral deposits (especially gold).
  4. 3D geometry of the Pilbara
    3D mapping the entire Pilbara craton using gravity, magnetics and seismic refraction data resulted in the following new observations of the Pilbara Craton. Applications of the 3D knowledge include constraints on tectonic models, ideas on which are the important shear zones that transect the crust, estimates of depth and volumes of metal reservoirs and fluid pathways.
    • the craton is ovoid with dimensions of 600 × 550 km diameter, only 25% is exposed
    • the average crust depth is 30-32 km (thickening to the south), the mid crust is at 14 km
    • the greenstones are highly magnetic and extend to the base of the mid crust (14 km) and most granitoids have steep (vertical) contacts to the base of the mid crust (14 km)
    • more dense and faster lower crust, more dense and less magnetic crust in the northeast vs the northwest
    • major shear zones present in the northwest and the east, circular patterns of granitoids are everywhere except the far northwest.

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Publications

2002


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2001


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2000


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1999


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1998


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1997

  • Glikson, A.Y. 1997. Mineral mapping in the North Pilbara craton: A directed principal components of band ratios method for correlating Landsat-5 Thematic Mapper spectral data with geology. Australian Geological Survey Organisation, Research Newsletter, 26, 1-4.

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Products

Geological maps - 1:100 000 scale.


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Landsat-TM-5


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Layered mafic-ultramafic complexes

  • Hoatson, D.M., Wallace, D.A., Sun, S-s., Simpson, C.J. and Keays, R.R. 1993. Layered intrusions of the Pilbara Block. Geoscience Australia Bulletin 242. Not available.

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Geophysics


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Regional maps 1:500 000 scale

The following 1:500 000 scale maps are available as print-on-demand maps. Please contact the sales centre if you require this service.

  • Mackey, T.E. and Richardson, L.M., 1997. Total magnetic intensity (reduced to the pole) with northeast illumination colour pixel-image map of the Pilbara Region, WA, scale 1:500 000, Australian Geological Survey Organisation.
  • Milligan, P.R. Minty, B.R.S., Franklin, R. and Mackey, T.E. 1999. Airborne gamma ray spectrometric colour composite pixel image map of the Pilbara region WA, scale 1:500 000, Australian Geological Survey Organisation.
  • Blewett, R.S., Wellman, P. Ratajkoski, M. 2001. North Pilbara synthesis series. Solid geology map. Scale 1:500 000. Australian Geological Survey Organisation.
  • Huston, D.L., Blewett, R.S., Ratajkoski, M. 2001. North Pilbara synthesis series. Gold distribution map. Scale 1:500 000. Australian Geological Survey Organisation.
  • Huston, D.L., Blewett, R.S., Ratajkoski, M. 2001. North Pilbara synthesis series. Other metals and minerals distribution map. Scale 1:500 000. Australian Geological Survey Organisation.
  • Wellman, P., Blewett, R.S., Ratajkoski, M. 2001. North Pilbara synthesis series. First vertical derivative of total magnetic intensity (reduced to the pole) greyscale pixel-image map. Scale 1:500 000. Australian Geological Survey Organisation.
  • Wellman, P., Blewett, R.S., Ratajkoski, M. 2001. North Pilbara synthesis series. Geophysical interpretation of near surface features map. Scale 1:500 000. Australian Geological Survey Organisation.
  • Wellman, P., Ratajkoski, M. 2001. North Pilbara synthesis series. Residual gravity anomaly image map. Scale 1:500 000. Australian Geological Survey Organisation.
  • Wellman, P., Ratajkoski, M. 2001. North Pilbara synthesis series. Short wavelength magnetic relief image map. Scale 1:500 000. Australian Geological Survey Organisation.
  • Wellman, P.,  Ratajkoski, M. 2001. North Pilbara synthesis series. First vertical derivative of total magnetic intensity (reduced to the pole) greyscale pixel-image map with gravity colour. Scale 1:500 000. Australian Geological Survey Organisation.
  • Wellman, P.,  Ratajkoski, M. 2001. North Pilbara synthesis series. Gradient enhanced pseudocolour topography image map. Scale 1:500 000. Australian Geological Survey Organisation.
  • Wellman, P.,  Ratajkoski, M. 2001. North Pilbara synthesis series. First vertical derivative topography image. Scale 1:500 000. Australian Geological Survey Organisation.
  • Wellman, P.,  Ratajkoski, M. 2001. North Pilbara synthesis series. 3D shape of Granitoid complexes thematic map. Scale 1:500 000. Australian Geological Survey Organisation.
  • Wellman, P.,  Ratajkoski, M. 2001. North Pilbara synthesis series. Gamma ray spectrometric red-green-blue image showing low concentrations of K-Th-U. Scale 1:500 000. Australian Geological Survey Organisation.
  • Wellman, P.,  Ratajkoski, M. 2001. North Pilbara synthesis series. Gamma ray spectrometric data - chemical map.  Scale 1:500 000. Australian Geological Survey Organisation.
  • Wellman, P.,  Ratajkoski, M. 2001. North Pilbara synthesis series. Gamma ray spectrometric data - felsic igneous rocks - C1. Scale 1:500 000. Australian Geological Survey Organisation.
  • Wellman, P.,  Ratajkoski, M. 2001. North Pilbara synthesis series. Gamma ray spectrometric data - felsic igneous rocks - C2. Scale 1:500 000. Australian Geological Survey Organisation.
  • Wellman, P.,  Ratajkoski, M. 2001. North Pilbara synthesis series. Gamma ray spectrometric data - felsic igneous rocks - types. Scale 1:500 000. Australian Geological Survey Organisation.
  • Wellman, P.,  Ratajkoski, M. 2001. North Pilbara synthesis series. Gamma ray spectrometric data - intermediate rocks and sediments - C1. Scale 1:500 000. Australian Geological Survey Organisation.
  • Wellman, P.,  Ratajkoski, M. 2001. North Pilbara synthesis series. Gamma ray spectrometric data - intermediate rocks and sediments - C2. Scale 1:500 000. Australian Geological Survey Organisation.
  • Wellman, P.,  Ratajkoski, M. 2001. North Pilbara synthesis series. Gamma ray spectrometric data - intermediate rocks and sediments - C3. Scale 1:500 000. Australian Geological Survey Organisation.
  • Wellman, P.,  Ratajkoski, M. 2001. North Pilbara synthesis series. Gamma ray spectrometric data - mafic igneous rocks - C1.
  • Wellman, P.,  Ratajkoski, M. 2001. North Pilbara synthesis series. Gamma ray spectrometric data - mafic igneous rocks - C2.
  • Wellman, P.,  Ratajkoski, M. 2001. North Pilbara synthesis series. Gamma ray spectrometric data - mafic igneous rocks - C3.

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1:250 000 Magnetic maps

  • Mackey, T.E., 1997. Total magnetic intensity (reduced to the pole) with northeast illumination colour pixel-image map of Nullagine/Yarrie, WA, scale 1:250 000, Australian Geological Survey Organisation. Not available.
  • Mackey, T.E., 1997. First vertical derivative of total magnetic intensity (reduced to the pole) greyscale pixel-image map of Nullagine/Yarrie, WA, scale 1:250 000, Australian Geological Survey Organisation. Not available.
  • Mackey, T.E. and Richardson, L.M., 1997. Total magnetic intensity (reduced to the pole) with westerly illumination colour pixel-image map of Marble Bar, WA, scale 1:250 000, Australian Geological Survey Organisation. Not available.
  • Mackey, T.E. and Richardson L.M., 1997. East-west gradient of first vertical derivative of total magnetic intensity (reduced to the pole) greyscale pixel-image map of Marble Bar, WA, scale 1:250 000, Australian Geological Survey Organisation. Not available.
  • Mackey, T.E. and Richardson, L.M., 1997. Total magnetic intensity (reduced to the pole) with northwest illumination colour pixel-image map of Port Hedland, WA, scale 1:250 000, Australian Geological Survey Organisation. Not available.
  • Mackey, T.E. and Richardson L.M., 1997. Fractional vertical derivative of total magnetic intensity (reduced to the pole) greyscale pixel-image map of Port Hedland, WA, scale 1:250 000, Australian Geological Survey Organisation. Not available.
  • Mackey, T.E. and Richardson, L.M., 1997. Total magnetic intensity (reduced to the pole) with northwest illumination colour pixel-image map of Roebourne/Pyramid, WA, scale 1:250 000, Australian Geological Survey Organisation. Not available.
  • Mackey, T.E. and Richardson L.M., 1997. Fractional vertical derivative of total magnetic intensity (reduced to the pole) greyscale pixel-image of Roebourne/Pyramid, WA, scale 1:250 000, Australian Geological Survey Organisation. Not available.

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1:250 000 scale gamma ray maps

  • Mackey, T.E., 1997. Airborne gamma ray spectrometry colour composite pixel-image map of Nullagine/Yarrie, WA, scale 1:250 000, Australian Geological Survey Organisation. Not available.
  • Mackey, T.E. and Richardson L.M., 1997. Airborne gamma ray spectrometry colour composite pixel-image map of Marble Bar, WA, scale 1:250 000, Australian Geological Survey Organisation. Not available.

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Economic geology


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Structural geology


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Geochemistry

  • Wyborn, L.A.I. 1995. ROCKCHEM - Pilbara Block digital dataset and Record. Geoscience Australia Record 1995/026. Not available.

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Atlas


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GIS


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