The Stavely Project is located in western Victoria on the Stavely tablelands approximately 250 km to the west of Melbourne. The Project comprises exploration licence 4556, over which a retention licence (RL2017) has been applied for.
At the Thursday’s Gossan prospect, a near surface secondary chalcocite-enriched blanket has an estimated Mineral Resource of (using a 0.2% Cu grade lower cut-off) –28Mt at 0.4% copper for 110kt of contained copper.
The Company is targeting a Cadia-style gold-copper porphyry and Lake Cowal-style gold mineralisation in the Stavely Project.
The Stavely Project is located within the Mount Stavely Volcanic Complex considered a northern extension of the Mt Read Volcanic in Tasmania, which is host to-
- Mount Lyell (1.8 Mt Copper /2 M oz Gold)
- Rosebery (1.1 Mt Lead / 820 kt Zinc/ 115 kt Copper/ 110 M oz silver / 2 M oz Gold)
- Henty (1.2 M oz Gold)
The Mount Stavely Volcanic Complex (MSVC) is classified into the Grampians-Stavely Zone in western Victoria. The Moyston Fault separates the Delamerian Fold Belt, in which the Stavely Project is located, to the west from the Lachlan Fold Belt to the east. West of the Moyston Fault are fault-bounded belts of submarine calc-alkaline volcanics (Mount Stavely Volcanics) within a sequence of quartz-rich turbidites (Glenthompson Sandstone) deforming during the Late Cambrian to form the basement of the Grampians-Stavely Zone. The Dalamerian Fold Belt rocks are unconformably overlain by an Ordovician-Silurian shallow marine to fluvial sequence of the Grampians Group. The Mount Stavely Volcanics consists of a basal ultramafic unit and then a suite of andesitic lavas at the base of the pile, conformably overlain by felsic volcanics/tuffs, shales and sandstones, with plugs of tonalite and rare slices of ultramafic rocks of the Dimboola Igneous Complex. The Mount Stavely Volcanics are either interbedded with, or faulted against, the arenites of the Glenthompson Sandstone.
Thursday’s Gossan Copper – Gold Porphyry Prospect
Recent RC and diamond drilling at the Thursday’s Gossan Copper-Gold Porphyry target has not only produced impressive copper-gold assays but the additional technical work has provided strong independent support for the ongoing search for a world-class porphyry copper-gold deposit.
The initial RC drilling in mid- 2017 returned high-grade porphyry copper-gold mineralised intervals including:
- 24 metres at 0.64% copper and 1.2 g/t gold
- 29 metres at 0.53% copper and 0.30 g/t gold to end-of-hole (EoH)
- 25 metres at 0.52% copper and 0.37 g/t gold to EoH
- 25 metres at 0.30% copper and 0.29 g/t gold
- 43 metres at 0.55% copper and 0.11 g/t gold, and
- 28 metres at 0.59% copper and 0.19 g/t gold
In the follow-up diamond drill ‘tails’ to the shallow RC holes, additional strong porphyry-style copper-gold mineralisation was intersected in multiple holes with broad moderate-grade intervals including:
- 124 metres at 0.31% copper, 0.12 g/t gold and 13 g/t silver, including
- 13 metres at 0.31% copper 0.35 g/t gold and 18 g/t silver, and including
- 6 metres at 2.35% copper, 1.05 g/t gold and 48 g/t silver
- 36 metres at 0.43% copper, 0.20 g/t gold and 7 g/t silver, including
- 20 metres at 0.65% copper, 0.30 g/t gold and 12 g/t silver, including
- 1 metre at 5.17% copper, 1.26 g/t gold and 24 g/t silver
- 85 metres at 0.35% copper, 0.18 g/t gold and 3 g/t silver, including
- 35 metres at 0.44% copper, 0.28 g/t gold and 4 g/t silver
- 53 metres at 0.37% copper, 0.15 g/t gold and 8 g/t silver, including
- 23 metres at 0.57% copper, 0.20 g/t gold and 12 g/t silver
- 48 metres at 0.47% copper, 0.15 g/t gold and 2 g/t silver, including
- 5 metres at 1.89% copper, 0.24 g/t gold and 7 g/t silver
- 27 metres at 0.39% copper, 0.16 g/t gold and 10 g/t silver, including
- 3 metres at 2.65% copper and 1.17 g/t gold and 68 g/t silver
All of these assay results support Stavely Minerals’ conceptual model that the fluids responsible for the copper-gold mineralisation seen in drilling to date at Thursday’s Gossan have migrated up structures from a late-stage alkalic copper-gold porphyry source at depth.
Evidence from a number of independent datasets indicate that a significant copper-gold porphyry target zone is located beneath the recent drilling. Technical indicators include:-
- Short-wavelength absorption features for white micas highlight the shortest wavelengths in the hanging wall to the ‘leakage’ structure, indicating proximity to a porphyry source; and
- The occurrence of ‘acid-sulphate’ alteration minerals including pyrophyllite and alunite together with observed vuggy silica textures are characteristic of a high-level position in the mineralised system for the drilling to date.
- Sulphur isotope data with strongly negative values to -21.6‰ δ34 sulphur and with many -3‰ to -6‰ results clustering around the target zone are comparable to those documented from many alkalic copper-gold porphyry systems from British Columbia, the Yukon, Alaska and Australia – including the Cadia Valley and North Parkes copper-gold deposits.
- D-vein occurrences in all drilling have been characterised, and the spatial distribution of the critical copper-gold D-veins coincides with the target zone.
In September 2017, Greg Corbett of Corbett Geological Services visited Stavely’s core facility in western Victoria to review recently drilled drill core (and RC drill chips). Mr Corbett was tasked to review Stavely Minerals’ exploration model for the Thursday’s Gossan and nearby prospects.
Mr Corbett reviewed a number of geologic features commonly used as a vector to porphyry mineralisation including:
- Pebble dykes
- Overprinting evolved porphyry-related ore fluids
- Zoned prograde and overprinting retrograde alteration
- Metal zonation
- Structural control to porphyry localisation
Mr Corbett found that the features noted in drill core support Stavely Minerals’ interpretation of an ‘above porphyry’ environment and that drilling of deeper holes below recent results be progressed as a priority. Mr Corbett’s full report is available under the Technical Data tab on this website.
The target zone has now been relatively well defined and drilling is in-progress in a step-wise progression that will materially advance what has been identified as a significant discovery opportunity.
Thursday’s Gossan Resource – Conceptual Study
The Company’s conceptual study on the potential for copper concentrate production from the chalcocite-enriched supergene ‘blanket’ at the Thursday’s Gossan copper deposit demonstrated sufficient positive outcomes with respect to net revenue and Net Present Value, as well as an attractive Internal Rate of Return, to proceed to a scoping study.
There are as not yet reasonable grounds to support the discussion of these projected economic outcomes in detail.
The key elements of the conceptual study include:
- An average feed grade of 0.5% copper;
- A sulphide flotation recovery of 87% (based on metallurgical testwork); and
- A sulphide concentrate grade of 27% copper (based on metallurgical testwork) producing a very ‘clean’ concentrate with low deleterious elements.
Financial assumptions included:
- World Bank forecast copper prices;
- A range of A$/ US$ exchange rates of A$1 = US$0.60 to US$0.75
The conceptual study identified a number of opportunities to enhance project economics including:
- Increasing the size of the resource –recent drilling has identified chalcocite copper mineralisation outside the current Mineral Resource. Stavely Minerals’ drill hole SMD004 intersected 52m at 0.23% copper from 39m downhole depth. This intercept is located approximately 400m to the west of the existing Mineral Resource and illustrates the potential for material increases;
- Reducing the assumed mining and milling costs by investigating the suitability of using continuous surface mining equipment. The attraction of the mining method is that it is well suited to long and wide, flat-lying, mineralisation; the oxidised nature of the mineralisation is well suited to this mining method; the product is already partially comminuted and reduces the need for primary crushing; and this mining method can be very selective in the vertical dimension.
- Reducing the processing costs through lowering reagent usage and by streamlining the processing flowsheet – the Scoping Study will investigate the potential to beneficiate the mineralised from un-mineralised clays prior to flotation of the sulphide concentrate amongst other processing enhancements.
Mount Stavely Copper-Gold Porphyry Prospect
The exploration target at Mount Stavely is porphyry related copper-gold mineralisation associated with the Mount Stavely Volcanic Complex (MSVC) in the Mount Stavely Belt.
The Mt Stavely porphyry target is reflected as a ‘low’ in gravity data and as a ‘low’ in the airborne magnetic data which is interpreted to reflect magnetite destructive hydrothermal fluid alteration. A porphyry is inferred to exist at depth and is in proximity to marginal gold mineralisation at the Fairview gold prospect, which itself is interpreted to be a low-sulphidation epithermal style mineralisation. An IP survey in the Mt Stavely area returned a chargeability feature which was slightly offset from the gravity low. Geochemical soil sampling over the Mount Stavely prospect returned anomalous arsenic, molybdenum and gold values.
Two diamond holes, one which was co-funded by the Victorian Government TARGET minerals exploration initiative, where drilled to test the co-incident geophysical and geochemical anomalism, which together with the prospective host rocks define an excellent porphyry copper-gold target. Many porphyry deposits are emplaced into dilatant structural settings such as splay faults at depth which may pass upwards to flexures within the negative flower structure model. A possible flexure apparent on the magnetic data is consistent with a sinistral sense of movement of the NNW structures during mineralisation, a trend which is recognised throughout the Lachlan Orogen.
Diamond drilling at Mount Stavely has provided valuable geological information in a highly prospective belt, which has effectively been unexplored. The drill hole did encounter the ultramafics which were expected from the aeromagnetic signature in the area. While no mineralisation or porphyry alteration signatures were observed in the drill core, a pebble dyke characterised by rounded milled clasts in a pyrite altered rock flour matrix has been identified. Pebble dykes are commonly used to vector towards porphyry mineralisation and its’ presence is considered to be extremely encouraging that there is a copper-gold porphyry in the Mount Stavely area.
Fairview Gold Prospect
The 4.8 kilometre long Fairview North and Fairview South mesothermal to epithermal gold anomalies was originally identified in soil sampling and followed-up with shallow reconnaissance aircore, RC and limited diamond drilling. The previous drilling returned numerous anomalous gold intercepts, including:
- 5 metres at 17.44 g/t gold from 28 metres drill depth to end of hole,
- 2 metres at 16.06 g/t gold from 23 metres drill depth,
- 4 metres at 6.69 g/t gold from 10 metres drill depth,
- 17 metres at 1.70 g/t gold including 5 metres at 3.1 g/t gold from 12 metres drill depth,
- 12 metres at 2.16 g/t gold from 18 metres drill depth to end of hole including 3 metres at 5.1 g/t gold from 27 metres drill depth to end of hole.
The Fairview gold anomaly is associated with sericite albite and K-spar (adularia) alteration and quartz sulphide veins with chalcopyrite, sphalerite, galena and gold. The sphalerite is of a pale yellow colour and in conjunction with the adularia suggest a low-temperature possibly low-sulphidation epithermal affinity. The target at Fairview is a Lake Cowal-style gold deposit.
Previous drilling failed to provide a focus for further drilling and the IP programme conducted in late 2016 was also not successful in identifying any definitive drill targets.
Following a new interpretation of the structural controls for gold mineralisation at the prospect by Stavely Minerals a single diamond hole was drilled at Fairview North in early 2017. The hole returned an encouraging intercept of:
- 30 metres at 1.4 g/t gold including
- 11 metres at 2.4 g/t gold
Follow-up drilling in mid -2017, comprising four RC drill holes around this previous intercept, has returned good widths of moderate grade gold mineralisation within large widths of low-grade gold mineralisation including:
- 17 metres at 1.23 g/t gold from 23 metres drill depth within a larger low-grade interval of
- 57 metres at 0.57 g/t gold from surface
- 16 metres at 1.04 g/t gold from 6 metres drill depth within a larger low-grade interval of
- 68 metres at 0.42 g/t gold from surface.
Additional intercepts included:
- 6 metres at 1.65 g/t gold from 53 metres drill depth;
- 4 metres at 1.70 g/t gold from 5 metres drill depth; and
- 1 metre at 6.70 g/t gold from 76 metres drill depth.
Independently, Geoscience Australia drilled a diamond hole (STAVELY-17) in the immediate vicinity of the Fairview South prospect in 2014 as part of a series of holes drilled in the Stavely region as pre-competitive stratigraphic drilling.
A geochemical study of the pyrites recovered from STAVELY-17 was released in 2017 and concluded that there was two-stage pyrite growth – a high temperature early stage which was likely to be related to porphyry-style mineralisation at depth and a low-temperature later stage which is likely an epithermal overprint.
This was compared by Geoscience Australia to the pyrite in the Wafi-Golpu and Lihir porphyry / epithermal copper-gold and gold deposits. Jeff Steadman and Ross Large (ARC Centre of Excellence in Ore Deposits, University of Tasmania) went on to conclude that the estimated distance to the target porphyry would be 0.5 – 1 km.