Re: HEG-HARGRAVES POTENTIAL
plenty of info about hargraves,comments appreciated derty...tb
http://austexploration.com.au/region.html
HARGRAVES REGIONAL SETTING and ECONOMIC POTENTIAL
The north-south, parallel, doubly plunging folds of the Hargraves Gold Field comprise slates, siltstones and litharenites of the Middle Devonian Cunningham Formation, the Early Devonian Merrions "tuff" Formation of rhyolitic and dacitic lavas, tuffs and basal conglomerate and the earlier Devonian Crudine Group which comprises feldspathic and lithic greywackes, slate, tuff and conglomerate. The Merrions Formation is a regional marker for the overall structure of the area. (Refer figures 26 & 27)
The earliest sediments, the Crudine Group sediments outcrop centrally within the Hargraves Gold Field and at their core host the Tuckers Hill greywacke as gold mineralised quartz saddle reefs. To the west and east of Tuckers Hill, respectively, lie the Hampden Hill - Great Western line of gold mineralisation and the Reef Hill, Oakey Creek, Blue Spec line. Both of these gold mineralised anticlinal structures are hosted by the Merrions Tuff Formation and are also associated with the volcanogenic and volcanic rhyolitic and dacitic tuffs and flows of the Merrions Tuff Formation. The Cunningham Formation that is exposed as the anticlinal fold zone of the Big Nugget Hill beds and its hosted mineralisation, Big Nugget Hill, at its most eastern side, extends westwards towards the Stuart Town Gold Field.
Hence the Big Nugget Hill line of gold mineralisation is underlain by the Hampden Hill - Great Western Merrions Tuff Formation and then the Tuckers Hill greywacke of the Crudine Group.
South of Exploration Licence No 5952 the south plunging Big Nugget Hill anticlinal zone continues in outcrop as the Crudine Group sediments flanked by the Merrions Formation and then the Chesleigh Formation appears further south. All of these stratigraphic units contain gold mineralisation which extends to the Hill End Gold Field. To the east of Hargraves the Crudine Group hosts the Windeyer Gold Field mineralisation and to the west the Stuart Town Gold Field is hosted within the younger Cunningham Formation beds, as at Hargraves, (Refer figure 27)
Each of the above three stratigraphic units within Exploration Licence No 5952 is known to host rich gold mineralisation. Accordingly, beneath the main domal structure at Big Nugget Hill, where ore-fluid flows, focus and gold deposition appears to have been maximised, the underlying Merrions Formation and Crudine Group sediments are also highly likely to host gold mineralisation. It is also reasonable to expect that the Crudine Group sediments underlying the Hampden Hill - Great Western anticlinal zone would be mineralised.
In two places within the Big Nugget Hill fold complex, inverse quartz saddles, (the synclinal legs of the quartz reefs) have been found to be economic by early miners. No drilling of the synclinal quartz has been conducted, but it is known that within such fold structures more gold tends to be deposited within the lower pressure saddles of the anticlines and inverse saddles of the synclines rather than in the legs. If this is the case in the Hargraves Gold Field then the following resource deliberations may be as much as doubled.
There is no way to quantify the likely gold resources at depth beneath the currently defined Big Nugget Hill resource. The total currently defined resource plus that reported and unreported as mined previously within the 550 metre zone drilled to date appears to be in the order of 78,300 to 135,000 oz. Assuming extension of the 70 metre thick Big Nugget Hill resource down the north and south plunges for a distance of as little as 200 metres beyond that determined as shown in (Figure 27) an additional 150,000 to 225,000oz. could be expected to lie within 180 to 200 metres of the surface. The Alma Zone, Triamble Road Zone and BNH North Zone would probably add another 75,000 to 125,000oz. to this figure.
As at Bendigo there is likely to be replication of this mineralisation at depth within the Cunningham - Big Nugget Hill beds and, as above, one would expect gold mineralisation within the deeper underlying Merrions Formation and Crudine Group sediments. Geoservices models that even excluding the Hampden Hill - Great Western and Tuckers Hill mineralised zones an at depth gold resource beneath the Big Nugget Hill anticlinal zone of 1,000,000 to 1,500,000 oz. is possible within 800 to 1000 metres of the surface. This postulated resource figure is based on 4,500 metres of the Big Nugget Hill anticlinal complex.
The total known outcropping, gold rich, anticlinal quartz reef configurations determined to date is in excess of 12,000 metres. Only 550 metres at Big Nugget Hill and one vein at Tuckers Hill have been investigated to date.
The Hargraves gold field must be considered to have similar potential to the Bendigo gold field prior to the major mining that has been carried out to a depth of 1,000 metres on that gold field.