Highlights

• Vertex Minerals (ASX:VTX) plans to follow up Nickel Sulphide latitude at Taylor Rock project on back of drilling and geophysics results obtained by former explorer Norilsk Nickel.
• Vertex geologists intend to understand the nickel potential at shallower depths, because as per the mineralisation, it is likely to continue up dip.
• The drill hole 10NLJC0132 is the ‘most interesting intersection of greenstone stratigraphy so far’ at the Taylor Rock project, as per the company.

Vertex Minerals Limited (ASX:VTX) intends to undertake follow up work at the Taylor Rock project, which sits in the very poorly explored far south-eastern margin of the Archaean Lake Johnston greenstone belt.

The work will focus on the Nickel Sulphide latitude, given outcomes from drilling and geophysics work undertaken by former explorer Norilsk Nickel. As per 3D modelling of geochemical data, fertile lava channels have been intersected at Taylor Rock and a huge untested open target is present below and north of the existing drilling*.

*source, Poseidon Nickel Limited 2015 Annual Report

Also, the nickel potential at shallower depths will be targeted by Vertex geologists for better understanding, because the mineralisation hints that it may continue up dip. However, Norilsk had no follow up on this.

Source: Company update

Understanding the regional geology

As per the recent work, the emphasis has been laid on the importance of early thrust faulting due to which the age relationships between rock units have been complicated.

There is a possibility that it may imitate the presence of desirable contacts and thus strengthen the prospects of exploration. At some locations, the BIF may have been a suitable surface for thrusting. Post thrusting, the belt got impacted due to folding and faulting at a high angle to the strike of the belt.

The exhaustive details relating geology of the greenstone belt has been obtained from the Emily Ann – Maggie Hays. Three ultramafic units have been identified in the region –

• Western Ultramafic: WUU is thicker and more persistent than the EUU and typical nickel sulphide host rock types have been identified.
• Central Ultramafic: CUU is the thickest and contains a succession of ultramafic differentiates with basal olivine peridotite which is a typical host for nickel sulphide mineralisation.
• Eastern Ultramafic: EUU consists of thin discontinuous volcanic flows and may also host minor nickel sulphide mineralisation.

The stratigraphic relationships between the three ultramafics are not certain because of the early thrust faulting.

 
Image source: Company update
Location of Taylor Rock 

Features of the project geology

The Taylor Rock area was targeted on the basis of a distinct magnetic high, present next to the interpreted Koolyanobbing Shear Zone on the eastern limb of the Mt Gordon Anticline. Amphibolite had been mapped in this area. The presence of chert/BIF and silica cap-rock developed over an ultramafic substrate was confirmed with further mapping and rock chip sampling.

Mafic amphibolites have dominated the bedrock geology. Two distinct ultramafic units have been detected - a western ultramafic dominated by tremolite-chlorite assemblages and an eastern, high-MgO ultramafic marked by near-surface siliceous caprock.

A thin sedimentary chert/BIF unit spans over the three northernmost lines and divides the two ultramafic units. Limited outcrop of the BIF suggests the sequence dips moderately to the west. To the south, where the greenstone sequence thins, only amphibolites were intersected in drilling.

At the Polly Jean prospect situated at the northern end of the tenement, a feature indicating a greenstone sequence in both limbs of a plunging fold can be observed in the regional magnetic image.

Image source: Company update
Taylor Rock showing a number of EM plate targets

An overview of mineralisation

There are two styles of mineralisation –  (i) Sulphide nickel mineralisation in Western Australia, usually occurs on basal contacts in ultramafic rocks, often in embayments and often in massive style. (ii) Disseminated sulphides also occur in the ultramafics. Within the Lake Johnston area, both the styles have been identified.

Further, massive nickel sulphide has been found in areas without any related ultramafic rocks or in areas having narrow discontinuous ultramafic units. It is believed that such nickel mineralisation is related to deformation by remobilisation of sulphides during movement on the thrusts.

In the Lake Johnston area, nickel mineralisation is typically pentlandite (nickel iron sulphide) related with other sulphides like pyrite (iron sulphide), pyrrhotite (iron sulphide) and chalcopyrite (copper-iron sulphide). In the supergene zone, violarite (a secondary nickel iron sulphide) is present as replacement to pyrrhotite and pentlandite.

Small showings of gold mineralization are also known from across the Lake Johnston area although no historical production has been observed.

The prime focus of the historical nickel exploration remained on the western margin of the greenstone belt around and along strike from the Maggie Hays and Emily Ann nickel sulphide deposits.

As per exploration work done so far, it has been observed that geology includes a west facing succession of mafic and felsic volcanics, some sediment horizons, including BIF, and two, potentially three, ultramafic units.

The volcanics and sediments are flanked and intruded by granitic rocks which disturb the flow of the greenstone belt. Pegmatitic and doleritic dykes are common. The sequence is extensively faulted, and inclined north- and south-plunging folds have been recognised. The boundaries of the greenstone belt are thought to be defined by strike parallel shears and faults.

VTX shares were spotted trading at AU$0.090 on 13 March 2023.