Summary:
The project is located within the Murchison Domain in the Yilgarn Craton, WA. As other parts of the Yilgarn Craton, rocks around the Weld Ragne are extensively weathered. Colluvial and alluvial sediments are extensively developed. Conglomerate derived from the erosion and transportation of banded iron formation (BIF) and bedrock iron mineralisation is locally significant.
Beebyn-W11 is a near surface, near vertically dipping Archaean BIF surrounded by mafic igneous rocks within the ENE trending Weld Range greenstone belt (Kenworthy, 2008). The lithologies in the area are multiply deformed and locally intruded by igneous rocks. The BIFs strike at approximately 070º and dip steeply (>80º) to the SE and are cut by several steeply dipping NE-SW striking faults.
The mineralised units have four types with gradations between the types: massive haematite, interbedded haematite-goethite, goethite, and well-banded magnetite. There are two categories of mineralisation: supergene - goethite-hematite mineralisation, which are the product of meteoric fluid alteration affecting BIF in the near-surface supergene environment, and hypogene - massive magnetite, specular haematite, goethite, and limonite ore bodies (During et al., 2017).
The hypogene mineralisation is a high-grade (>55 wt% Fe) iron consisting of magnetite and specular hematite BIF ore bodies that have been locally replaced by supergene goethite-hematite ore within several hundred meters of the present erosion surface.
The Beebyn-W11 deposit shows good continuity of mineralisation within well-defined geological constraints.
A total of four (BIF) are present, BIF1 to BIF 4, and the hanging wall contacts are gradational whilst the footwall contacts are sharp (SRK, 2008).
- BIF 1 is the most significant mineralised unit. It is interlayered with thin shale and mafic units. The mineralisation contains a greater proportion of magnetite and magnetic haematite with an associated higher iron-ore grade and lower Loss of Ignition (LOI). The unit is ~40 m thick. BIF 2 – 4 are thinner at between ~2 m - ~10 m. The goethite content of this lense is lower than BIF 2 – 4. BIF 1 can be subdivided into high and low Al2O3 domains.
- BIF 2 is a thin and discontinuous BIF horizon and locally merges with BIF 1. BIF 2 has on average a 2 m horizontal width.
- BIF 3 – BIF 3 has on average a 7 m horizontal width.
- The BIF 4 lense does not appear to be well mineralised
BIF 2 to 4 have Fe in the range of 55 – 60% and have higher LOI (5 – 8%) than BIF 1. The BIF is not always completely altered to goethite-hematite and in these regions the BIF occurs as the footwall, hanging wall and internal waste (SRK, 2008). The mineralogy of the BIFs includes minnesotaite, siderite, quartz, magnetite, greenalite, stilpnomelane, pyrite, and chamosite with trace amounts of pyrrhotite, arsenopyrite, chalcopyrite, apatite, and rockbridgeite (Gole, 1980). Haematite is the major iron oxide and occurs as fine (<0.02 mm), decussate micro platy crystals, as granular crystals, and as cryptocrystalline haematite (Kenworthy, 2008). The mineralogy of the interbedded high Al2O3 Fe-shale (which occurs as laminated 2 cm to 30 cm-thick bands) includes chamosite, stilpnomelane, siderite, greenalite, pyrite, magnetite, minnesotaite, and quartz with trace amounts of ilmenite, chalcopyrite, and apatite” (Gole, 1980). The SiO2 content of the BIFs relative to the iron grade is considered low (During, et al., 2012).
Dimensions
The known extent of the mineralisation modelled at W11 is:
- BIF 1: ~785 m along strike, average ~30 m horizontal width, average vertical depth of ~350 m.
- BIF 2: ~265 m along strike, average ~2 m horizontal width, average vertical depth of ~200 m.
- BIF 3: ~750 m along strike, average ~7 m horizontal width, average vertical depth of ~300 m.
- BIF 4: ~700 m along strike, average ~4 m horizontal width, average vertical depth of ~200 m.