The Torrington Project comprises EL 8258 and adjoining EL 8355 held by Torrington Minerals Pty Ltd (TMPL) a wholly owned subsidiary of Chase Mining Corporation Limited (the Company or CML). The Project is located in northern New South Wales, 240km south-west of Brisbane, Queensland in proximity to the Torrington Township approximately 65km by road south-west of the local Shire town of Tenterfield (see Figure below). The Project area encompasses ~51km2and covers most of the numerous historic shallow tungsten mines and workings located within the State Forest Reserve and on private land holdings.
The Torrington region and particularly the area of the Torrington Pendant, within which the Torrington Project is located, contains potential economic concentrations of tungsten and topaz mineralisation. The area has been mined since the early 1880’s, initially for tungsten and tin, and more recently (1970s) within the EL areas for its topaz content (for refractory feedstock and abrasive purposes). Numerous small rich tungsten lodes were exploited into the 1980s until prices fell below sustainable levels.
The Company is targeting silexite bodies associated with the Torrington Pendant which lies within the Mole Granite. The Torrington Pendant is a remnant elliptical metasediment cap and covers ~20km2, most of which lies within the Project tenements. Silexite consists predominantly of quartz (~80%) and topaz (~20%) and other minor minerals. Target minerals are tungsten and topaz, but also include (but are not limited to) bismuth and REE.
Since acquiring the Torrington tenements, the Company has conducted extensive exploration on the tenements culminating in a RC percussion and diamond drill programme totaling 400 holes for 11,217m in 2017. In addition, a robust plant flowsheet for the recovery of tungsten and topaz based upon a metallurgical testwork programme on a one tonne sample split from a representative bulk three tonne sample was developed.
In parallel with the exploration programme, TopFibre Pty Ltd (a 100% owned subsidiary of CML) entered into an agreement with the University of New South Wales (UNSW) in 2015 to conduct research at theirSchool of Materials Science and Engineering into developing high-value products from the topaz found at Torrington. Topaz is an aluminosilicate and the specific goal was to explore the potential for developing fibres of mullite from the topaz.
In 2016 a submission was lodged with the Federal Government by the Grants Management Office of the UNSW through their Research Management System with TopFibre as the industry partner. The application was accepted by the Federal Government as 2016 Australian Research Council (ARC) Linkage Project (LP160101569). The three-year co-funded Federal Government research was approved in August 2017. The outcome if successful is aimed at proving the commercial viability of producing single-crystal mullite fibres from topaz, which are high-value products (expected value ~US$1,000/kg).
Given the importance to have access to mined product for the supply of topaz concentrate in the event the topaz research at UNSW is successful in the short-term, TMPL lodged an application for a Mining Lease (MLA547) as shown in theFigure below.
Geology and Mineralisation
Geology: The Project area is underlain by the Mole Granite and metasediments of the Torrington Pendant. The majority of the Torrington Pendant lies within ELs 8258 and 8355. The Torrington Pendant has been intruded by the Mole Granite and contains numerous silexite bodies. The silexite is described as a quartz-topaz greisen and was formed as a late stage intrusion. It forms dykes and sills within metasediments and contacts of the Mole Granite. Some silexite bodies grade into the adjacent Mole Granite and display metasomatic characteristics. In appearance, the Torrington Pendant silexite looks like white sandstone / quartzite and varies from sugary texture to massive.
Mineralisation: The mineralisation of the Mole Granite covers an area of ~50 x 60km2with over 2,000 known mineral occurrences. The mineralisation is extensive and isn’t limited to the Mole Granite and has been identified in the surrounding rocks.
The Mole Granite contains significant metal mineralisation and includes polymetallic tin, gold, tungsten, arsenic and base metals, while common non-metallic minerals include beryl, topaz, and emerald and fluorine compounds. Mineral zonation is evident in the Mole Granite, with a tin rich heart, gold, and tungsten rich zones near the granite contacts. The surrounding country rocks have common base metal mineralisation.
The silexite of the Torrington Pendant signifies one of the world’s largest topaz (Al2SiO4(FOH)2) resources (Kmetoni, NSW Government Report 1984). Silexite in the Torrington Pendant is a topaz-quartz greisen of the late intrusive phase of the Mole Granite. Topaz within the silexite has an average grain size of 2mm and has been seen to be evenly distributed throughout. Overall topaz content of the silexite is between 15-20%.
Tungsten mineralisation occurs mainly as ferberite, the Fe rich wolframite end member. It appears as either disseminated euhedral-anhedral (fine to coarse grained) crystals in silexite bodies and quartz veins or euhedral crystals <5cm in length and in bungs within silexite bodies or quartz veins. The Torrington Pendant has produced many multi-tonne wolframite deposits. The single largest wolframite lode was recorded at 12.5 tonnes.
Resource Estimation: In March 2018 the Company received an updated resource estimate document from H&S Consultants Pty Ltd (H&SC) for the Wild Kate and Mt Everard projects where the Company’s comprehensive drilling programme was completed in 2017. The data from this drilling programme completely replaced the previous (historical) drilling.
While the silexite host rock to the tungsten mineralisation at the Wild Kate Prospect is a continuous semi-flat lying sheet or sill as previously modelled, the tungsten mineralisation is not evenly distributed throughout the silexite body as interpreted in the two previous resource reports. Details of the 2018 JORC Resource estimation are given in ASX announcements of 22 and 23 March 2018.
What is also now evident is the presence of small, high-grade tungsten mineralised pipes, such as at the Mt Everard Project where the angled drillholes have allowed for the geological interpretation of such a pipe (see Figure below). Similarly, the carrot-shape zones at the base of the Wild Kate silexite body in places may indicate depth extensions to the high-grade mineralisation. The small footprint of these almost vertical pipes would make their (blind) discovery a difficult and costly task based on drilling alone. The Company plans to investigate geophysical methods to locate these highgrade tungsten bearing pipe-like features.
The Company will not evaluate the tungsten potential of the large number of old workings and outcropping silexite occurrences within its tenements in the immediate future, as it focusses its efforts to increase the topaz purity for bulk market (abrasive) applications and the high value oriented mullite fibre from topaz research at the UNSW.
The extensive topaz bearing silexite body centred on the Wild Kate Prospect is shown in plan and section below. It covers an area of 500 by 200m and varies in thickness from 20m to 40m.
In the Mineral Resource estimation (ASX 22 March 2018) a Silexite Exploration Target of 2 to 4Mt at 15 to 20% topaz has been interpreted at Wild Kate based on the geological logging of the silexite from the drillholes by assuming a density of 2.7t/m3with previously reported studies on the silexite used to provide an expected topaz grade. The potential quantity and grade of the Exploration Target is conceptual in nature and there is insufficient exploration to estimate a Mineral Resource and that it is uncertain if further exploration will result in the estimation of a Mineral Resource.
The Company will revisit the drilling samples (laboratory pulps) to obtain a better measure of the topaz grade and distribution for both Wild Kate and Mt Everard by undertaking systematic chemical and XRD analyses of the topaz content to allow this to be done. It is anticipated that simple modelling of the data would allow for the generation of resource estimates for topaz at both areas.
Development Programme: Work on the Environmental Impact Study (EIS) has recommenced whilst water supply issues were resolved.
In 2016 a submission was lodged with the Federal Government by the Grants Management Office of the UNSW through their Research Management System with TopFibre as the industry partner. The application was accepted by the Federal Government as 2016 Australian Research Council (ARC) Linkage Project (LP160101569). The three-year co-funded Federal Government research was approved in August 2017 to which TopFibre will contribute approximately $460,000 (approximately 40% of which is cash and the rest in kind) over the three-year period.
The outcome if successful is aimed at proving the commercial viability of producing single-crystal mullite fibres from topaz, which are high-value products (expected value ~US$1,000/kg).
Recent studies (ASX 15thJanuary 2019) have produced quantifiable results and a major processing breakthrough in the production of mullite fibre from Torrington sourced topaz concentrate, namely:
- Separable mullite fibre is being produced (Ultimate aim of the research programme)
- Topaz being fed into the furnace no longer requires grinding or pelletising (Cost saving)
- Lower furnace operating temperatures are now possible (Cost saving)
Previous reports have suggested that mullite whisker formation is possible at only specific calcination conditions: (1) at elevated temperatures (≥1600°C), (2) following milling of topaz, and (3) pressing topaz into pellets. These conditions were considered to facilitate vapour-solid interactions during the conversion from topaz to mullite. It also was concluded that retention of the vapour (SiF4) at elevated temperatures assists the formation of mullite whiskers. Milling was assumed to enhance gas formation and uniaxial pressing was assumed to enhance the vapour retention.
The present work reports studies of calcination of as-received (minus 1mm) topaz without milling or pressing while enclosed as an alternative approach. The later (successful) experimental arrangement reported on and being used is shown in the Figure below. This has the advantage of facilitating vapour (SiF4) retention within the topaz sample being calcined.
The present results suggest that pure, separable, mullite whiskers can be produced from as-received minus 1mm topaz concentrate from Torrington packed as a loose, but enclosed bed at temperatures lower than 1600°C in ≤2 hours.
Experimental Procedure – Mullite Whisker Fabrication
Compared to previous experimentation, the present work reports data for the conversion of as-received topaz (not milled) in a loosely packed bed using an enclosed crucible arrangement. The calcination was done at 1400°-1600°C for 1-3 hours using relatively rapid feed rates (70-120 sec over a 54 cm transit distance). The samples were examined by field emission scanning electron microscopy (FE-SEM). The images below are examples of the whiskers / fibre products produced in the current studies.
Morphology of product sample S1600-2 (fibre powder).
- Uniaxial pressing was found to enhance the formation of mullite whisker intergrowths, thus reducing the potential to separate them.
- The use of a loose bed of unmilled topaz and enclosure within nested crucibles appeared to have enhanced retention of the vapour phase and resulted in the growth of well-formed and separable whiskers.
- Longer heating times resulted in longer and thicker whiskers but these were at the expense of increased interfibre bonding strength, which made separation by grinding with mortar and pestle more difficult. However, there remains no direct observation of intergrowths, which would be impossible to separate.
- The locations of the whiskers within the bed affected the extent of calcination and whisker size, where the upper two-thirds of the volume exhibited greater extent of reaction and longer and thinner whiskers while the bottom one-third exhibited the converse.
- The results confirm the importance of the retention of the vapour phase in order to allow the availability of sufficient material for continuous mullite whisker growth.
- Investigation of topaz conversion at lower temperatures in closed crucibles.
- Investigation of conditions conducive to growth of fibres.
- Development of means of separation and classification of mullite whiskers.