Cobar Basin / Lachlan Fold Belt Projects (NSW)
- Metal-rich Cobar Basin / Central Lachlan Fold Belt
- Hera-style target at Overflow Prospect (high grade gold and base metals)
- Overflow drill intercepts:
- 4.7m at 20.4 AuEq from 185.4m (BOBRCPC6)
- 10.0m at 7.0 AuEq from 163m (TBB001)
- 18.0m @ 4.6 AuEq from 245m (OFDD001)
In May 2016 Alchemy entered into a Farm-in and Joint Venture Agreement with Heron Resources Ltd (ASX: HRR) to earn up to an 80% interest in gold and base metal projects covering 674 sq.km in the highly prospective, under explored, central Lachlan Fold Belt (LFB) in NSW.
The LFB projects consist of the Overflow gold and base metal Project (within the Cobar Basin) including drill-ready targets at the historic Overflow mine, the Eurow copper-gold Project and the Girilambone copper Project each containing multiple gold and/or base metal targets. The projects are proximal to high profile mining centres in the Cobar Basin and central LFB, including Hera/Nymagee (Aurelia Metals Ltd), Mallee Bull (Peel Mining Ltd), Tritton (Aeris Resources Ltd) and the North Parkes mining centre (Figure 2a).
Figure 2a: Alchemy projects, major mines, Au / Cu mineral occurrences, and major structures over aeromagnetic image
Overflow Gold-Base Metal Project (378sq.km)
The Overflow Gold-Base Metal Project consists of four exploration licences located over a 50km long section of the Gilmore Suture at the intersection of the Lachlan Transverse Fault Zone within the well-endowed Cobar Basin (Figure 2a). The project is highly prospective for epithermal, porphyry Cu-Au, and Cobar-style Au and base-metal mineralisation.
Mineralisation at the Overflow Prospect is structurally-controlled high-grade Au-Ag and base metal credits, with extensive down-plunge potential, typical of Cobar-style mineralisation (Figure 4).
Figure 4: Schematic Cobar regional long section showing CSA, Nymagee, Hera and Overflow mineralisation
(Source image adapted from Aurelia Mining website)
A review of the historic drilling and 3D modelling of mineralisation at Overflow suggests the mineralisation dips steeply to the WSW, plunges to the south, is associated with distal chlorite-sericite and proximal silica alteration, and displays a significant metal zonation very similar to what is seen at the Hera deposit 30km along strike to the NW.
Metal distributions were modelled for AuEq, Au, Ag, Cu, Zn, and Pb. Combined grade x thickness grade shells for AuEq values are illustrated as a long section through the deposit and suggest that several high-grade zones remain open down plunge or open down dip (Figure 4 and 4a).
Significant drill intercepts in historic drilling by Delta Gold Limited and Triako Resources Limited at Overflow includes:
| BOBRCPC6 | 4.65m at 20.39 AuEq* from 185.4m (8.49g/t Au, 79g/t Ag, 0.22% Cu, 13.5% Zn, 7.1% Pb) | |
| TBB001 | 10m at 7.03 AuEq* from 163m (4.44g/t Au, 21g/t Ag, 0.07% Cu, 3.0% Zn, 1.3% Pb) | |
| TBB006 | 16m at 3.28 AuEq* from 162m (1.13g/t Au, 88g/t Ag, 0.09% Cu, 1.15% Zn, 0.43% Pb) | |
| TBB008 | 7m at 4.53 AuEq* from 198m (1.67g/t Au, 135g/t Ag, 0.04% Cu, 1.3% Zn, 0.5% Pb) & | |
| 7m at 7.76 AuEq* from 236m (5.46g/t Au, 19g/t Ag, 0.32% Cu, 1.9% Zn, 1.4% Pb) | ||
| TBB017 | 6m at 7.64 AuEq* from 121m (4.69g/t Au, 39g/t Ag, 0.21% Cu, 2.4% Zn, 1.9% Pb) & | |
| 6m at 10.71 AuEq* from 136m (7.55g/t Au, 29g/t Ag, 0.11% Cu, 3.6% Zn, 1.5% Pb) |
*Gold equivalent (AuEq) values were assigned to each drilling intersection using the following formula (based on metal prices at the time): AuEq (g/t) = Au (g/t) + Ag*0.014 (g/t) + Cu*1.11 (%) + Zn*0.54 (%) + Pb*0.46 (%). The AuEq calculation takes into account the following metal prices: Au US$1325/oz, Ag US$19/oz, Cu US$2.15/lb, Zn US$1.05/lb and Pb US$0.90/lb.
Figure 4: Overflow Prospect plan – left, and 3D perspective (looking down to the NW) – right
Figure 4a: Overflow Prospect long section looking east showing AuEq grade x metre shells, historic drill traces and significant intercepts, and Alchemy diamond drill hole and intercept (red).
An initial targeted drilling program has been planned to confirm the continuity of high grade gold-silver-lead-zinc mineralisation and subject to further modelling, test a VTEM conductivity anomaly at depth (350m below surface), down plunge of the high grade mineralisation. The southerly plunging grade shells, VTEM anomaly and planned drilling are illustrated in Figs. 4 & 4a.
Outside of the Overflow Mine area a number of regional targets have been delineated by multi-element anomalism identified in soil sampling analysis (Fig. 5), and positive geophysical responses. Further exploration and drill testing of these targets is warranted.
Shallow historic percussion drilling at Coopers Hill returned 30m @0.47% Pb from 30m including 6m @ 1.1% Pb (BOB-P03B). At the Parkvale target (Fig. 5), narrow high-grade intersections, including 0.7m at 6.8% Cu and 1.2% Pb from 149.4m (BO-1A) drilled in 1977, have not been followed up. Coherent Au-Zn in soil anomalism over an area of 600 x 400m at Prettyview (Fig. 5) has not been drilled tested. At Black Range Tank and Airport (Fig. 5), outcropping gossans and limited shallow drilling has returned base metal anomalism within semi-coincident EM anomalies.
Figure 5: Historic drilling over Delta Gold Exploration PL 1993-95 soil sampling images (Au, Cu, Pb, Zn).
Yellow Mountain Gold-Base Metal Project (378sq.km)
Within the Yellow Mountain exploration licence (EL8356), approximately 25km along strike to the south of Overflow (Fig. 2), previous drilling around the historic Yellow Mountain copper workings returned a number of broad Cu-Ag-Au intercepts including:
| YD13 | 32m at 1.7g/t Au, 0.36% Cu, 34g/t Ag (from 185m) incl. 7.4m at 5.7g/t Au, 0.7% Cu, 102g/t Ag, 5.1%Pb, 6.7% Zn (from 206m) |
| PYM12 | 64m at 0.40% Cu, 0.4g/t Au, 24g/t Ag (from 64m) |
| PYM11 | 56m at 0.30% Cu, 0.5g/t Au, 34g/t Ag (from 14m) |
| YP05A | 83m at 0.44% Cu (from surface) (no Au-Ag assays) |
(ref. Alchemy Resources ASX announcement dated 28 October 2016)
The prospect was last drill tested in 1986 with many of the drill holes not assayed for gold. The broad zones of mineralisation are coincident with a significant IP anomaly and the prospect represents a priority target for porphyry copper-gold mineralisation. Ground geophysics and further drill testing is warranted (Fig. 6).
Historic drill intercepts from the Rosedale and Melrose prospects to the south of the Yellow Mountain mine include:
24m @ 2.51g/t Au from 4m (PDH 2) (Rosedale)
6m @ 3.1g/t Au from 5m (PQS007) (Rosedale)
2m @ 3.09g/t gold from 56m (TYMAC069) (Melrose)
2.5m @ 3.06g/t Au, 1.54% As from 70m (TYMDD003) (Melrose)
(ref. Alchemy Resources ASX announcement dated 15 February 2017)
Figure 6: Yellow Mountain Project – Historic drilling maximum downhole copper over aeromagnetic image (left), and historic drilling maximum downhole gold over geology (right).
Eurow Copper-Gold Project (167sq.km)
The Eurow Copper-Gold Project (“Eurow”), located 30km southeast of Parkes (Fig. 2), covers meta-sediments and granite intrusives within the Lachlan Transverse Zone (Fig. 7). The Project area contains the historic Eurow-Vychan Cu-Au workings where drilling by previous companies returned high-grade intercepts including:
8m @ 2.95% Cu, 0.85g/t Au from 47m (Eu4)
5m @ 1.83% Cu,1.30g/t Au from 77m (Eu_H)
3m @ 3.99% Cu, 1.25g/t Au from 73m (Eu_D)
2.2m @ 4.65% Cu, 1.78g/t Au from 277.7m (EU027)
3m @ 5.32g/t Au, 0.21% Cu from 11m (Eu1)
3m @ 3.27g/t Au, 4.40% Cu from 89m (Eu_F)
A 3D view of the Eurow Mine drilling looking down to the NNW can be seen in Figure 8. The copper-gold mineralisation dips steeply to the west and appears to plunge to the south. Mineralisation remains open along strike to the north, south, down dip and down plunge. Further drill testing at this prospect is required.
Figure 7 Eurow Project licence (EL8192) over geology.
Figure 8 Eurow historic drilling – 3D view looking down to the NNW. Drill traces coloured by Cu (left) and Au (right).
Girilambone Copper Project (129sq.km)
The Girilambone Copper Project (“Girilambone”) is located 20km east of Aeris’ Tritton copper operation and along strike of the Murrawombie / Girilambone Copper Mine (Fig.2). The area is prospective for ‘Besshi-type’ volcanic massive sulfide (VMS) copper-gold mineralisation within mafic units of the Ordovician Girilambone Group. An historic exploration data compilation and evaluation is underway.