Lewis Ponds consists of one tenement (EL5583) which covers approximately 148 km² located around 15 km east of Orange. Access to the tenement is via the sealed White Rocks-Dry Creek-Lower Lewis Ponds roads.
This project is one of the highest priority targets for Godolphin due to the extensive historical workings and infrastructure (including the presence of historic on-site smelting), outcropping mineralisation, a current Mineral Resource Estimate and free-hold title held by TriAusMin (a subsidiary of Godolphin). Another tenement (ELA5794) centred around historic workings at Mt Bulga is currently under application.
The project area contains sediments and volcanoclastic sediments, which have been structurally deformed.
The project hosts massive sulphide and shear hosted copper mineralisation with a potential later stage gold overprint.
An updated Mineral Resource was disclosed in the Godolphin Prospectus, 29 October 2019.
The Lewis Ponds area was an active mining centre from around 1884 till the 1920s. The workings were centred around two major areas; Main Zone (also called Spicers Mine) and Tom’s Zone. Main Zone was actually the site of a smelter and an adjacent limestone quarry – postulated to be a flux source. Spicers Mine was reported to have produced around 6000 t of ore at 6.7% lead and 187 g/t silver (Rowe, 1999). Tom’s Zone was reportedly a pyrite mine and was in operation from 1913 to 1921.
Historical workings are extensive, consisting of numerous shafts (mostly collapsed and shallow) and shallow surface workings. These locations were mapped by Ardea to assist in identifying the surface expression of mineralisation and hence assist in the creation of a geological\mineralisation model.
Around two to three kilometres south of the Main Zone workings, there is another group of workings including; Mt Nicholas, Brittania, Icely and Ophir Copper Mine.
In the western part of the tenement, around Mt Bulga, there is a line of workings and mineral occurrences running over a distance of approximately 6 km. The Mt Bulga Mine was reported to have a copper grade of 6.5% and also has a historical resource from 1970.
In the far northern part of the tenement, west of Summer Hill Creek, there are numerous workings and occurrences around the historical Mt Lindsay copper mine.
The Lewis Ponds deposit lies on the east limb of the Mullions Range Anticline and is hosted within the Late Silurian Mumbil Group. The actual mineralisation is hosted within the Anson Formation, a fining up sequence from a conglomeritic base to siltstones at the top. The stratigraphic sequence has been metamorphosed to lower greenschist facies. Other deposits in the region with similar mineralisation styles include; Daydawn, Calula, Mt Lindsay, Icely and Mt Bulga.
Within the sulphide lenses at Lewis Ponds, alteration varies in intensity, mineralogy and distribution. Dip of the mineralised zones is generally steep to the northeast, however they can range from vertical to more steeply westerly dipping.
The most prominent regional structure is the Lewis Ponds Fault, located less than one kilometre to the west of Lewis Ponds, which is interpreted as a splay off the Godolphin Fault.
Two series of faults have been noted at Lewis Ponds, one regular set strikes southwest-northeast and dips to the northwest and a second dipping steeply and striking east-west.
The Lewis Ponds polymetallic deposit is a stratabound and disseminated sulphide system and is historically considered to be of a VHMS type. Godolphin has documented a later stage deformation and an orogenic overprint that has introduced a component of remobilisation and the introduction of silica respectively into the system, as well as flexuring of the stratigraphy.
Agnew (2002) concluded that Tom’s Zone was a sheet style VHMS deposit formed at or near the sea floor, which has later been deformed, remobilised and fluids introduced by the Lewis Ponds Fault. The Main Zone however has similarities with carbonate-hosted replacement deposits, where sulphides have infiltrated into the pore spaces of poorly sorted breccias. Textures within the sulphides indicate rapid sea water quenching.
Drilling has been conducted at the Lewis Ponds Project since the late 1960s, with various minor programs carried out from 1970-1990 before more intensive drilling being carried out from 1991 through to the present by Tri Origin\TriAusMin.
Over 200 hundred holes have been drilled in and around Lewis Ponds with around 75% of the holes being diamond. The latest program, drilled in February-March 2017 by Ardea, consisted of four holes, mainly drilled to obtain samples for metallurgical test work, but were also assayed. To assist in updating the geological model, these holes and other older holes on the same section (where suitable quality core still existed) were logged in a geological, mineralogical and structural context.
Mineral Resource Estimates have previously been reported in 2005 and 2016. No additional drilling was included in the 2016 update, however the Mineral Resource was reviewed and updated to comply with JORC (2012).
The revised 2019 Mineral Resource Estimate is based on and assisted by further work that was completed after the 2016 estimate. This included:
- Four equally spaced (200 m apart) diamond drill holes drilled along the strike length of the Lewis Ponds deposit
- A re-logging campaign of selected diamond core
- Modification and standardisation of historical geological logging
- Drill database validation
- Field mapping and spatial location of underground and surface workings
The above points assisted in refining the geological model in preparation for an updated Mineral Resource Estimate.
The 2019 Mineral Resource Estimate was divided into an open pit Resource and an underground Resource. Table 1 and Table 2 tabulate the open pit and underground Resource respectively:
|Category||Tonnes (Mt)||Au (g/t)||Ag (g/t)||Cu (%)||Zn (%)||Pb (%)|
|Category||Tonnes (Mt)||Au (g/t)||Ag (g/t)||Cu (%)||Zn (%)||Pb (%)|
Metallurgical test work
Material obtained from four PQ\HQ diamond drillholes that were drilled in February-March 2017 at 200 m spacings through the deposit, was submitted to SGS (Perth) for metallurgical testwork. This was completed and reported in late 2018.
The test work showed that with an initial dense media separation (DMS) at a relatively large crushed particle size (-12.5 mm), over 90% of the sulphide and precious metals are recovered, on top of 25% of the material being rejected. DMS is a method that could be applied to ore feed that rejects lower grade or gangue material and hence allowing for higher grade process plan feed material or a lower mine cut-off.
Test work indicated that two concentrates could be produced via gravity and flotation methods. The zinc concentrate contained 66% zinc and 64 g/t silver for 80% zinc recovery, while the second Cu-Pb concentrate contained 30.3 % lead, 4.78% copper, 1,619 g/t silver and 17.6 g/t gold for 70.3% lead recovery and 61.8% Cu recovery.
The metallurgical testwork concluded that:
- The flotation process is expected to be relatively simple
- The test work material contained low talc
- A fine re-grind size (20-35 µm) may be required to liberate acceptable levels of galena (lead)
- A moderate grind size (40-60 µm) would be required for sphalerite (zinc) liberation
- Gold preferentially deports to copper-lead concentrate
- Intervals within ALD0001 (75-93 m and 110-122 m) showed poor zinc and lead recoveries respectively
More historical test work was carried out by Amdel (1994 and 1995) and Metcon (1995) on two diamond holes. However, a different process route was being tested at that time (cyanide leach for gold, followed by flotation), so comparisons between the two series of test work is not possible. The test work did indicate that only approximately 54-74% of the gold could be extracted by gravity followed by cyanide leach, indicating a proportion of the gold is locked up in sulphides.
The potential to increase the Lewis Ponds Mineral Resource is considered to be high. Further infill drilling and drilling along strike not only has the potential to increase, but also to improve confidence in the Mineral Resource. A more thorough investigation of the block model in relation to existing drilling will have a high chance of identifying potential drill targets that may lead to increasing the Resource.
Although Ardea has completed a re-logging campaign on four drill sections, further benefit could be gained from further re-logging, as a large amount of historic diamond core is still stored on site. This become apparent during the 2019 Mineral Resource update and as a result hindered the creation of a new geological model and subsequent estimate.
Diamond drilling at Lewis Ponds is planned to increase confidence in the Mineral Resource model and update the geological model. It has been suggested to drill horizontal or near horizontal holes through the whole sequence as previous drilling has not really achieved a complete cross section through the complete mineralised sequence.
Depending upon land access negotiations, mapping, rock chip sampling and general reconnaissance is planned for the Mt Lindsay and Mt Nicholas/Icely/Ophir/Williams Lode areas.
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