Yanrey Uranium Project Technical Detail

The Yanrey Project

The Yanrey Project area is fully controlled by Cauldron, encompassing a total area of 1,270 km2 consisting of twelve granted exploration licences. The exploration titles cover 78 km of a highly prospective linear palaeo-foreshore which hosts much of the known uranium mineralisation in the district and is centred on the Bennet Well deposit.

The mineral endowment of the district remains to be fully tested but is considerable and exemplified by proximal uranium deposits including:

  • Manyingee Deposit held by Paladin Energy Ltd (ASX: PDN) (ASX Announcement dated 14 January 2014) an Indicated Mineral Resource (JORC 2012) of 7,127 tonnes grading 850 ppm U3O8 for an estimated 15.7 million pounds of contained U3O8 and an Inferred Mineral Resource of 4,613 tonnes grading 850 ppm U3O8 for an estimated 10.1 million pounds of contained U3O8, and
  • Carley Bore Deposit, also held by Paladin Energy Ltd (ASX:PDN) (ASX Announcement dated 17 February 2014) with an Indicated Mineral Resource (JORC 2012) of 5.4 million tonnes grading 420 ppm U3O8 for an estimated 5.0 million pounds of contained U3O8 and an Inferred Mineral Resource of 17.4 million tonnes grading 280 ppm U3O8 for an estimated 10.6 million pounds of contained U3O8.

The geography of the Yanrey project area is dominated by flat aeolian and alluvial plains. Occasional small relief is formed by sand dunes as well as ridges of granitic and gneissic basement.

Drilling completed in 2015 identified extensions to the existing Bennet Well Deposit, the channels of which along with basement topography were subsequently confirmed by the passive seismic results. Recent geological interpretations identified new high-grade uranium zones at a number of regional targets within the project area.

EXPLORATION POTENTIAL

Cauldron’s principal objective for Yanrey is to substantially increase uranium resource inventory sufficient to commence operations at Bennet Well and to explore for standalone uranium resources on the other Yanrey Project tenements. The short-term strategies are to:

  • Improve the current Mineral Resource at Bennet Well to upgrade material from Inferred to Indicated and Indicated to Measured categories, aiming for total resources containing at least 35 to 45 million pounds of U3O8 at average grades greater than 300 ppm; and
  • Explore for additional standalone uranium projects within the prospective Yanrey tenement package.

Within the current economically unstable climate, Cauldron is ensuring the ongoing advancement of exploration at Yanrey with low-cost, innovative, and non-invasive geophysical techniques such as the Tromino-based Passive Seismic system which was first trialled at Bennet Well in 2016 with great success.

BENNET WELL – Exploration Model

The most continuous and highest grade of mineralisation at Bennet Well is hosted within unconsolidated sands at the edge of, and above, the shoulder of the incised basement palaeochannel, long since buried by Mesozoic and Tertiary sand and clay sequences.

In the regional magnetics, Bennet Well is located on the northwestern margin of a circular, weakly-magnetic, dome-shaped high which is cut by a northwest-southeast, linear magnetic low.  Coincident with this linear magnetic low is an EM conductive high. This is interpreted to represent a faulted contact in basement lithologies along which the Bennet Well palaeochannel has formed, thereby acting as a conduit for uraniferous fluids.

The strong north-south oriented conductive body running through the axis of the tenement group is shown by drilling to coincide with a deepening of basement at Bennet Well marked by many channels oriented in a branching and sub-parallel array. This conductive lineament is interpreted to be an ancient coastline that flooded on the earliest marine transgression caused by the incipient separation of greater India from north-western Western Australia during the Mesozoic. This allowed the accumulation of the earliest glauconitic marine muds and sands in a deltaic environment. The muds are rich in organic material and form the present day aquicludes that act to contain the mineralisation.

In June 2016, the Company trialled the Tromino-based passive seismic system in an initial orientation survey over the Bennet Well Deposit. The passive seismic system had just been introduced to the Australian mineral exploration industry and was thus a novel and innovative exploration tool. This geophysical survey method was employed by Cauldron in an attempt to map the topographic surface of the geological basement underlying the palaeochannel – geological understanding of basement considerably increases the probability of exploration success, and the efficacy of exploration target generation.

Results of the orientation survey revealed:

  1. the topographic surface of the basement sequence (i.e., the base of the mineralised palaeochannel system) could be mapped to relatively high accuracy at a fraction of the cost of a conventional geophysical survey;
  2. an inexpensive non-drilling technique can be used to expand the exploration model and generate drilling targets in areas both proximal to Bennet Well and previously unexplored, more distal locations;
  3. an inexpensive non-drilling technique can also be used to establish an important parameter of the hydrogeological framework of the deposit;
  4. flexibility in survey specifics (station/line spacing) to delineate areas in which uranium mineralisation is currently unknown but prospectivity remains, simply based on the paucity of historical exploration work completed to date.

The results from the passive seismic allowed significant improvement of the lithological framework for the Bennet Well Deposit by incorporating basement topographic data from areas of no previous drilling. The lithological framework will provide the basis for hydrogeological modelling fundamental to understanding groundwater fluid flow, in general, and mining-fluid flow from potential in-situ recovery type mining operations, in particular. This work will help to optimise the design of Field Leach Tests (FLT) and de-risk environmental impacts of potential mining operations in the region.

Following the success of the orientation survey (Figure 1), the passive seismic technique was rolled out to exploration areas in the greater Yanrey Project.

Figure 1: Gridded topographic basement surface resulting from the 2016 passive seismic orientation survey.

YANREY – Exploration Model

Cauldron has considerably extended the exploration model for uranium mineralisation in the tenement group. The model was developed as a result of considerable expenditure in the district, through drilling and geological interpretation, collection of airborne EM and ground based gravity and passive seismic. The passive seismic data acquired in 2016 and 2017 effectively constrained dimensions of various palaeochannel targets around the greater project area, thereby vastly improving the existing exploration model. 

The geological model of the Bennet Well deposit is well advanced, now comprising three-dimensional stratigraphic, lithologic and mineralisation wireframe models based on thorough compilation and reinterpretation exercises of more than 500 drillholes, of which 445 were drilled by Cauldron.

Localisation of mineralisation at Bennet Well can be seen in the regional-scale airborne EM and is marked by complexity in the interpreted channel morphology. This occurs particularly where a northwest-southeast oriented, lower-order structure (interpreted as a channel and modelled by a linear and narrow, mildly conductive feature) intersects a major north-south trending, semi-regional scale structure.

The genetic models that can be used to explain this correlation between complex channel morphology and mineralisation may be:

  • Complex channel morphology slowed the flow of the initial sedimentation thus allowing for the accumulation of woody detritus or development of organic-rich, lignitic material in quiescent conditions formed during sedimentation. On later basin reactivation, these carbon-rich areas became the reductant required to fix uranium as grain coatings and pore-space infillings of the sediment, or
  • Complex channel morphology occurs at the intersection of faults affecting the basement, thus allowing for the inter-mixing of uraniferous groundwater with gaseous reductants (such as methane or di-hydrogen sulphide) that have migrated across the sedimentary sequences.
  • The exploration model at the Yanrey project revolves around identifying complex palaeochannel morphology which may then become targets for follow-up scout drill testing. The order of exploration work using this model is:
  • Fly new airborne EM data at regional to semi-regional scale to identify location of palaeochannels;
  • At more local scale, follow-up EM-defined areas of interest that show complex (or potential for complex) channel morphology with the acquisition of high-resolution gravity and passive seismic survey data;
  • Drill target areas of complex palaeochannel morphology with scout drill testing (if not already completed by Cauldron or some past explorer), and
  • Follow-up drill testing of anomalies identified by scout drilling.

Recent exploration work by Cauldron has used new understanding of mineralisation at the Bennet Well deposit to improve the exploration model so that it can be more predictive. The minerals / system-style exploration model presents all data (airborne magnetics, airborne EM, ground-based gravity and passive seismic, drilling and associated geochemistry) in three dimensions which aims to show inter-relationship and potential causal links between each dataset and mineralisation. The model becomes the foundation on which to plan future mineral exploration programs, with the aim of increasing the known resource at Bennet Well and also in the extensive and highly prospective tenement areas of the Yanrey project.

In 2015, Cauldron revised the Exploration Target for the Yanrey Project with a conservative estimate of between 21 million pounds to 53 million pounds at grades between 300 and 600 ppm U3O8. The potential quantity and grade of the Exploration Target is conceptual in nature and therefore is an approximation. There has been insufficient exploration to estimate a Mineral Resource and it is uncertain if further exploration will result in the estimation of a Mineral Resource. The Exploration Target has been prepared and reported in accordance with the 2012 edition of the JORC Code.

This Exploration Target does not include the Mineral Resource defined at Bennet Well. The revision of the Exploration Target resulted in a downgrade of potential size and grade relative to the previous version released in an ASX announcement on 21 February 2013. The revised Exploration Target is derived from a much more realistic set of parameters, such that any region without mineralised drilling intercepts is not accumulated in the total. These regions, once included in the previous edition of the Exploration Target, are now defined as anomalies that may or may not warrant further follow-up exploration work.

Between 2016 and 2017, additional passive seismic surveys were completed over regional exploration areas, such as the Manyingee South Channel (northeast of Bennet Well, discovered in 2015). These surveys were undertaken to help derive additional exploration targets by the identification of new palaeochannel extensions and systems, as well as assisting in the ongoing development of Project-scale geological models. Infill surveys were also completed within the Bennet Well Deposit which successfully highlighted areas of potential palaeochannel extension.

Results from the infill and more regional surveys showed:

  1. confirmation of the northwest-southeast strike of the palaeochannel hosting the Bennet Well Deposit;
  2. an area of shallow basement at Bennet Well East, correlating with previous geophysical and drilling data in which a coarse-grained pegmatitic granite was intersected at very shallow depths;
  3. apparent “jogs” in the channels likely produced as a result of intersecting fault structures;
  4. correlations between multiple datasets – passive seismic, gravity and airborne EM, drilling and currently-defined mineralisation outlines – all confirming that the uranium is not just confined to the deeper parts of the palaeochannels but is also situated within the shallower embankments of the channels;
  5. multiple, new, regional palaeochannel targets (e.g., Figure 2) with suggested strike orientations between West/Northwest and South/Southeast (similar to Bennet Well), that have consequently allowed the generation of multiple prospective drilling targets.

Additional exploration is required in order to test and progress these multiple, highly prospective targets, however the Company was forced to suspend its exploration activity after the ban on uranium mining in Western Australia following the 2017 State Election. Despite this, the Yanrey Project remains a highly valuable and globally significant uranium asset, in a part of Western Australia that is newly, and increasingly, recognised as a potentially world-class uranium province. 

Figure 2: Gridded topographic basement surface from the Manyingee South Prospect (2016 / 2017 passive seismic surveys)