De Grey discovered the 220,000oz Wingina Well gold deposit in 2003.
Gold mineralisation at Wingina Well is hosted by steeply south dipping chert units up to 50m wide that form a prominent east-west ridge close to the northern contact of the Tabba Tabba greenstone belt with Mallina Group sediments to the north. The chert is deeply weathered to over 150m depth and is variably brecciated and gossanous. Pyrite is intersected by diamond drilling at depth. The BIF is bounded to the north by a shale unit and to the south by a zone of talc chlorite schist, as illustrated by the cross section below
Cross section across the Wingina Well Gold Deposit
A new resource model was generated for the Wingina Well gold resource in 2009 (see table below) using Multiple Indicator Kriging (MIK), a method that has been demonstrated to produce reliable estimates of tonnages and grades that would be recoverable in open pit mining using an appropriate grade control technique. As expected, the MIK resource estimates yield higher tonnages at lower estimated grades at low cut-off grades (e.g. 0.5g/t Au) and lower tonnages at higher estimated grades at high cut-off grades (e.g. 1.5g/t Au; Table 2).
WINGINA WELL 2009 RESOURCE ESTIMATES
|
Cut-off |
Measured |
Indicated |
Inferred |
Total |
|||||
|
Au g/t |
Mt |
Au g/t |
Mt |
Au g/t |
Mt |
Au g/t |
Mt |
Au g/t |
Au,.oz |
|
0.5 |
1.70 |
1.54 |
2.45 |
1.28 |
1.0 |
1.3 |
5.11 |
1.34 |
221,000 |
|
0.6 |
1.50 |
1.68 |
2.10 |
1.40 |
0.8 |
1.5 |
4.40 |
1.47 |
208,000 |
|
0.7 |
1.32 |
1.81 |
1.81 |
1.53 |
0.7 |
1.6 |
3.80 |
1.60 |
195,000 |
|
0.8 |
1.17 |
1.95 |
1.56 |
1.65 |
0.6 |
1.7 |
3.29 |
1.73 |
183,000 |
|
0.9 |
1.05 |
2.08 |
1.34 |
1.78 |
0.5 |
1.9 |
2.86 |
1.86 |
172,000 |
|
1 |
0.94 |
2.21 |
1.16 |
1.91 |
0.4 |
2.0 |
2.50 |
2.00 |
161,000 |
|
1.1 |
0.84 |
2.34 |
1.01 |
2.04 |
0.3 |
2.1 |
2.20 |
2.13 |
150,000 |
|
1.2 |
0.76 |
2.47 |
0.88 |
2.17 |
0.3 |
2.3 |
1.93 |
2.26 |
141,000 |
|
1.3 |
0.69 |
2.60 |
0.77 |
2.31 |
0.3 |
2.4 |
1.71 |
2.39 |
132,000 |
|
1.4 |
0.62 |
2.73 |
0.67 |
2.44 |
0.2 |
2.5 |
1.52 |
2.52 |
123,000 |
|
1.5 |
0.57 |
2.86 |
0.59 |
2.58 |
0.2 |
2.7 |
1.35 |
2.66 |
115,000 |
Comparisons of Wingina Well resource estimates, 2004 and 2009
|
|
2004 OK estimates |
2009 MIK estimates |
Difference |
||||||
|
Cut-off Au g/t |
Mt |
Au g/t |
Au oz |
Mt |
Au g/t |
Au oz |
Mt |
Au g/t |
Au koz |
|
0.5 |
3.44 |
1.83 |
203,000 |
5.11 |
1.34 |
220,000 |
+48% |
-27% |
+9% |
|
1.5 |
1.75 |
2.60 |
146,000 |
1.35 |
2.66 |
116,000 |
-23% |
+2% |
-21% |
The MIK resource model was subjected to Whittle pit optimisations to investigate its potential economics at gold prices up to A$1,500/oz that were prevailing early in the March 2009 Quarter. With the deposit comprising oxide material to greater than 150 metres depth, both heap leach and CIL processing scenarios were investigated using realistic assumed and estimated operating costs and metallurgical recoveries.
The work revealed that at gold prices above about A$1,400/oz, Wingina may generate attractive cash flows in an operation producing 20,000-25,000 ounces of gold per annum over a mine life of 3-4 years.
Wingina Well MIK block model and A$1,400/oz optimised pit shell
Wingina Well Resource - Metallurgical testing
- Metallurgical test results recorded a high gold recovery over 24 hours. The test results also indicated a rapid and high gold extraction rate with low reagent consumptions of cyanide (NaCN) and lime. See table below.
- The Wingina Well deposit is deeply weathered to approximately 150m. Drilling has evaluated the mineralisation to 200m vertical, where it remains open down dip.
|
Ore Type |
Number of Samples |
Gold Recovery % |
g/t NaCN |
kg/t Lime |
|
Oxide |
8 |
97.3% |
0.15 |
1.32 |
|
Transitional |
4 |
93.8% |
0.14 |
2.10 |
|
Fresh |
5 |
93.7% |
0.27 |
2.34 |
|
Deep weathering chert in diamond core |
Wingina Well |
Project value and net returns would be enhanced if capital costs were written back over a larger ore reserve. The strategy going forward therefore is to discover additional resources that will add value to the Wingina Well at low risk to De Grey through the farm-out agreement with Lansdowne Resources.