GCR’s Wagga Tank Exploration Licence is 100% owned and has been farmed-in to by Zinifex Australia. It is located in the southern part of the Cobar Trough in an area of intermixed volcanic and sedimentary rock intruded by later granites and porphyries. The rocks range in age from about 350 to 420 million years (Siluro-Devonian age). The licence hosts numerous mineral occurrences, old prospects and an historical gold mine, and has been the focus of modern mineral exploration activities since the early 1970s.
Zinifex have begun a detailed review process with the view to commence ground and airborne geophysical surveys in 2008.
MINERALISATION TO THE NORTH
The Cobar region to the north has produced a significant amount of metal since production commenced in 1870. (Stegman and Stegman, 1996).
This includes:
2.5 million ounces of gold
0.6 million tonnes of copper
1.5 million kilograms of silver
0.6 million tonnes of lead
1.2 million tonnes of zinc
In addition, an exploration program between 1995 and 1999 by Peak Gold Mines identified further resources of 1 million ounces of gold (Stegman 2002).
There are currently four operating mines in the district. These are CSA, Elura, Peak/New Occidental and Mt Boppy. Production from all of these mines and much of the historic production in the district has come from the Devonian rocks of the Cobar Basin. The only significant production outside of the Devonian occurred at the Girilambone Copper Mine (now closed). This and the nearby, unmined, Tritton massive sulphide deposit are hosted in Girilambone Group rocks.
In order to understand the geological setting of the various prospects within the Licence GCR undertook a comprehensive compilation and review of existing exploration data. This work suggested that known mineralisation, especially on the western side of the tenement, was preferentially located at the margins of large circular structures which where visible in aeromagnetic images. (diagram below)
GCR followed up this work with extensive geochemical sampling of soils using a Partial Leach technique. This data suggested that not only did the known mineralisation occur peripheral to these structures, but that a geochemical zonation occurred from the centre to the periphery of these. Generally soils in the centre were copper-enriched whilst on the margins they were lead-zinc enriched. This style of zonation is similar to intrusive porphyry-like geochemical halos. This led GCR to speculate that mineralisation encountered to date by previous explorers, was related to intrusive centres and/or flow-dome/cryptodome volcanic complexes perhaps associated with caldera collapse during volcanic activity.
RECENT EXPLORATION
In 1999, Pasminco farmed into the property with initial focus on the Blue Mountain Prospect where a large (3 square kilometers) lead anomaly was discovered by RAB drilling. Drill results were generally disappointing, however it was noted that lead-zinc sulphides associated with pyrrhotite occurred within an intrusive feldspar porphyry dyke. This was generally supportive of the intrusion relationship to mineralisation.
Pasminco then undertook drilling campaigns on the BMW and Siegals Prospects. It is Siegals prospect in particular which has created significant interest. In a final phase of exploration before the company withdrew from the farmin agreement, a diamond drill hole targeting a magnetic anomaly intersected two narrow zones of high grade gold and copper mineralisation. Hole PSDD1 returned 1m at 10.7 g/t gold and 1.18% copper from 79m and 1m at 7.8 g/t gold from 87m.
These intersections are regarded as highly significant because they occur within an altered, sulphide-bearing, high level, intrusion. In the past, mineralisation in this area was considered to be volcanic-hosted massive sulphide-style, occurring along depositional contacts between sedimentary and volcanic rocks. The diamond core from PSDD1 suggests that sulphide mineralisation is genetically related to and hosted in intrusive rocks.
Pasminco withdrew from the agreement in 2003 and GCR now has 100% ownership and control of the Licence. GCR has decided to focus attention on the eastern side of the tenement for the time being, in order to assess the gold potential of the Siegals and Mt Allen Gold Mine prospects.
