Extending beyond the Near-Mine targets, Heron holds several regional exploration prospects described below.
Woodlawn Regional Prospects
Heron continues to maintain and explore a strategic 1,372km² tenement package which covers the prospective Silurian volcanic rocks which host the Woodlawn VMS deposit. Heron’s exploration strategy is to focus on historically known mineralisation zones with prospective geology and comparable grade and metallurgy to Woodlawn, and within potential trucking distance of the Woodlawn processing facility.
Exploration Joint Venture Projects
Heron retains interests in tenement holdings within the Lachlan Fold Belt of NSW and the Eastern Goldfields of Western Australia. This tenure is held through farm-in and joint venture interests which include a number of other free-carried residual or royalty interests which results in minimal costs to Heron.
Alchemy Farm-In and JV (Overflow, Girilambone, Eurow And Yellow Mountain)
Heron entered into a Farm-In Agreement with Alchemy Resources Limited (Alchemy) (ASX: ALY) covering a portfolio of Heron’s NSW exploration tenements in May 2016. The Farm-In Agreement covers 674km² of the central Lachlan Orogen in NSW. During the period Alchemy had earnt a 51% interest in the JV tenements after spending $1 million and has the option to earn 80% by spending an additional $1 million by 30 May 2021. Current expenditure for this second phase is estimated by Alchemy to $0.6M.
Farm-out Agreement with Sky Metals Ltd
As reported to the ASX on the 9 October 2019, a farm-out agreement has been signed with Sky Metals Ltd (“Sky”) relating to three tenements at Cullarin and Kangiara, targeting initially McPhillamy’s style gold mineralisation. Key terms are $400k minimum expenditure in first year; a further $1.6M over next 2 years to earn 80% with Heron free carried to DFS or $10M of expenditure; 10M Sky options at a strike price of 15¢.
During the period Sky completed its first exploration programme at Heron’s Cullarin Project. (Refer to Sky ASX announcement 10 February 2020). Sky completed a soil geochemistry programme (360 samples) and two diamond drill holes totalling 755.3 metres at the Hume gold prospect (previously known as Wet Lagoon). Drilling was designed to validate historical results and test the geometry and depth extensions of previously identified mineralisation. This is the first drilling at this prospect since 2008.
Cullarin (EL 7954) is located 35km NNW of the Woodlawn Mine and contains a variety of significant mineralisation including VMS, intrusion-related porphyry (Cu) and skarn (magnetite-Cu)/replacement, and epithermal base metal/gold mineralisation.
Heron’s immediate focus is to evaluate a possible Cu-Au porphyry system in the south of the tenement that shows characteristic epidote-rich and iron-rich skarns (Hannan’s Flat/Breadalbane) proximal to a more dominant gold/base metals system at Wet Lagoon, see Figure 1.
In 2014, an airborne electromagnetic (AEM) survey was undertaken across the tenement. A number of electromagnetic (EM) anomalies were identified and coincide with elevated base metal geochemistry, IP chargeability zones and phyllic alteration.
Kangiara (EL 8400) is located 90km NW of Woodlawn and covers felsic volcanic and related sedimentary rocks of the Silurian Douro Group. The Kangiara Mine operated during the early 1900s to produce ~40,000 tonnes at 16% Pb, 3% Cu, 5% Zn, 280g/t Ag and 2g/t Au from narrow N-S trending sulphide veins up to 120m depth.
An Indicated and Inferred Mineral Resource at Kangiara was defined in 2010 by the previous owners, Paradigm Metals Ltd. Heron has not yet verified this estimate and is reported here as an Exploration Target of approximately 2.0 to 3.0 million tonnes at grades of approximately 1.3% Zn, 1.0% Pb, 0.18% Cu, 0.5g/t Au and 24g/t Ag. This includes a higher-grade component of 1.25 million tonnes to 1.9 million tonnes at grades of approximately 1.9% Zn, 1.6% Pb, 0.28% Cu, 0.75g/t Au and 36g/t Ag. A gold-silver oxide cap has also been defined which grades 2g/t Au equivalent, averages 10m in thickness, is 260m long and up to 40m wide.
Heron is examining the potential to build on these positions, see Figure 2.
The Crosby Prospect is a potential Cu/Au porphyry system located 5km to the NE of Kangiara. The strong gold anomaly (2.3g/t Au in rock chips and 0.17g/t Au) was rotary air blast (RAB) drilled in 2016 and 2017 and a NW-trending zone of anomalous geochemistry was defined (Au, As, Zn, Pb, Cu) that includes 42m at 0.20g/t Au and 0.26% Cu from 4m to end of hole (CRRB027).
The Crosby anomaly and geological setting has similarities in terms of age, rock-types and metal association to the McPhillamy’s gold deposit (2.2Moz @1.4g/t Au, discovered 2012) that lies 130km to the NNE. The gold in soil anomaly at Crosby Main is approximately 250m long and 120m wide (at the 70ppb Au level) and hence smaller than McPhillamy’s but may have a small surface footprint and expand significantly at the source depth.
Peelwood – 100% Heron
Heron’s Peelwood Project (EL 8712) is located 90km north of Woodlawn and is contiguous with the Black Springs Project (EL 8623) to the south (Figure 3). Historic mining occurred at Peelwood, Cordillera and Mt Costigan during the late 1800s. Production consisted of mixed copper, silver and lead oxidized ores with some gold. Primary ore occurred as lenses of massive sulphides with abundant sphalerite, pyrite and lesser galena and chalcopyrite.
In 2008 Peelwood had a Mineral Resource estimate completed for the John Fardy and Peelwood deposits by the previous owners Sultan Corporation Ltd. As with Kangiara, Heron has not yet verified these estimates to a JORC standard but can report an Exploration Target at John Fardy of approximately 0.6Mt to 0.65 million tonnes at grades of approximately 4.4% Zn, 1.0% Cu, 0.5% Pb, 15g/t Ag, for a ZnEq of 9.0%. Within this mineralisation are higher grade components at relatively shallow depths and below the base of oxidation (approx. 50m below surface).
Exploration aims to test for additions to the current mineralisation focussing initially on a number of EM targets directly north of John Fardy. If high-grade resources can be defined, there is potential to develop a mining operation trucking low volumes of high-grade ore to Woodlawn.
The historic Cordillera underground mine is located 4km north-west of Peelwood, Figure 4. It operated in the late 1800s and treated some 9,000 tonnes of ore to produce copper, lead, silver and gold. Evidence of the historical mining activity is still present at the site. The Cordillera Mine and other mines in the district were generally worked to a depth where fresh sulphides were encountered.
The mined lode at Cordillera was reported as being 1.2m wide and 107m in strike. However, DDH coring in 1971 by A1 Consolidated Gold Pty Ltd intercepted 2.2g/t Au, 11.6g/t Ag, 0.78% Zn. 0.1% Cu and 0.44% Pb over 17m from 111.6m downhole depth. A core intercept to the south returned a similar broad zone 24m wide with a better portion of 2.9g/t Au, 10.2g/t Ag, 0.3% Zn, 0.24% Cu and 0.83% Pb over 2.7m from 89m downhole depth. The intercepts indicate a broad zone of alteration associated with the mineralisation at Cordillera.
Mineralisation is considered to be of a Volcanogenic Massive Sulphide (VMS) type consisting of lenses contained within shales close to the contact with the overlying felsic volcanics. A recent grab sample of such massive base metal sulphides from the Cordillera dumps returned assays of 16% Zn, 25% Pb and 497g/t Ag providing support for the presence of high-grade mineralisation.
A 2014 Airborne Electro-Magnetic (AEM) survey undertaken by previous owners has been reviewed by Heron’s geophysical consultant who has identified several bedrock conductors potentially related to mineralisation. In particular, these EM conductors occur along the line of the historically mined mineralisation and have not been tested at depth. The conductors north of the old mine are modelled starting at some 50m below the surface in an area of known workings (shafts and costeans) with moderate pyrite alteration seen in the surface felsic volcanic and shale rocks. A program of drilling is being planned to test these conductors. The Company is working through land owner access arrangements and statutory approvals.
Burra Project - 100% Heron
The Burra Project (EL8797) is located over the Queanbeyan Thrust on the eastern side of the Cowra-Yass Trough within the eastern Lachlan Fold Belt and approximately 65km southwest of Woodlawn. It covers the historic London Bridge and Burra Pb-Ag deposits that were worked in the early 1900’s with London Bridge having a reported average production grade of 15% Pb and 765 g/t Ag. The area contains Siluro-Devonian sequences of felsic flows, marine sediments, carbonates and intermediate intrusions known as the Colinton Volcanics, Cappanana Formation and Bransby Beds. Mineralisation at London Bridge and Burra is hosted within limestone lenses of the Cappanana Formation which is overlain by the Colinton Volcanics, a time equivalent to the Woodlawn Volcanics to the north.
London Bridge Mine
Initial drilling by Conwest returned high grade zinc 2.8m @ 15.6% Zn (DDH4) hosted within Silurian limestone and conglomerate. Drilling by Universal at London Bridge and London Bridge south has upgraded the mineral resources potential at London Bridge with significant high grade Zn intersections including (Figure 5):
- 3m @ 19.20% Zn, 0.98% Pb from 39m
- 4m @ 18.04% Zn, 1.23% Pb from 43m
- 2m @ 14.20% Zn, 1.21% Pb from 48m
- 6m @ 4.92% (Pb+Zn) from 9m
- 25m @ 5.49% (Pb+Zn) from 33m (including 1m @ 13.45%Zn & 1m @ 18.25% Zn)
- 14m @ 4.11% (Pb+Zn) from 82m
- 22m @ 3.55% (Pb+Zn) from 42m
- 6m @ 7.73% (Pb+Zn) from 56m
An estimate of the resource is 500,000 tonnes @ 4.7% Zinc (cut off 1% Zinc, SG 3.5). This is open to the south and the upper and lower zones remain open. Alderan Resources (2015) undertook 3D modeling of the Universal drill holes at London Bridge and defined a potential exploration target of 450,000 tonnes at 5.16% zinc.
Exploration potential is targeted at the Cappanana Formation and its basement contact that extends for approximately 1500m south of the London Bridge Mine to the Burra Mine. Drilling has only tested to a maximum depth of 120m vertical depth and so the deposit remains open both along strike and at depth. Drilling at London Bridge South (RCB015 – RCB019) intersected several narrow low-grade zinc sections within broad zones of anomalous lead-zinc and scattered pathfinder elements arsenic, cadmium and antimony. These are postulated to be an aureole to a deposit at depth and is supported by two discrete magnetic anomalies (Figure 6).
The Burra Mine gossan has a discontinuous strike length of 750m. Rock chip sampling returned values up to 2.3% Zn and 2.5% Pb and 6 g/t Ag. Three short holes were drilled into the Burra Mine (Figure 7) and returned:
- 67.1m @ 0.41% Zn, including 36.6m @ 0.48% Zn and 0.45% Pb (DDH1).
- 17m at 1.27% Zn (twinned DDH1 with RCB026).
Difficult drilling and poor core recovery led to holes prematurely terminated and drilling failed to adequately test targets. The shallow, low-grade oxidised mineralisation (to >200m downhole depth) suggests that the ‘plumbing’ system for oxidising fluids along this portion of the Queanbeyan Fault is of a significant size. Mineralisation at Burra has not been adequately tested and the broad, oxide intersections indicate the potential for a sizeable system at depth.
The Burra project has significant potential for the discovery of a massive, high grade deposit. The Silurian lithostratigraphy of the Burra Project area is similar to that of the Woodlawn Deposit. Most recently Alderan Resources highlighted a donut-shaped magnetic anomaly west of the Burra-London Bridge mineralised trend and appears to be very similar to the classical bullseye anomaly with surrounding magnetic low which typifies VMS-style massive sulphide deposits (Figure 8).