Blackwood Goldfield Project Technical Detail
Blackwood Gold Project
The Blackwood Gold Project comprises Exploration Licence (EL 5479) covering an area of 24 km2 located in central Victoria, 40 km east-northeast of Ballarat.
The Project is centred on the Sultan Mine which historically produced a little over 73,000 ounces of gold at an average grade of 28 g/t. In addition, the project contains in excess of 250 underground workings; with the largest known producers shown in Table 1, which follows.
Most mining activity on reef structures in the goldfield halted at shallow depths. Cessation of mining in many cases was not due to depletion of mineralisation but to other factors such as inability to cope with high ground water flows in the underground workings or inability to raise the capital for development work.
GEOLOGY AND MINERALISATION
The Blackwood Gold Project is located in the highly prospective “Golden Triangle”, which is a colloquial term for the highly productive central portion the Victorian gold province. The Golden Triangle contains the Bendigo (>22.4 million ounces, or Moz, of gold production), Ballarat (>13.1 Moz of gold production), Castlemaine (>4.2 Moz of gold production) and Stawell goldfields (>2.6 million ounces of gold production).
The central portion of the Victorian gold province, one of the world’s most productive and until recently, largely forgotten gold producing areas, accounting for more than 2% of world gold production and 30% of Australian gold production since 1850.
The geology of Victoria is split into twelve distinct zones, each having a distinct stratigraphic, structural and lithological style. Of these zones, the Ballarat (mustard colours), Melbourne (blue colours) and Stawell zones (mauve colours) are historically the most productive for gold (Figure 1).
Gold mineralisation is associated with quartz hosted by tightly folded monotonous fine-grained sedimentary rock sequences (interbedded sandstone and siltstone becoming slate). The folds have upright geometry with trends that are oriented north-south. As folding developed the sequence ‘locked-up’ causing differential tension in the deforming and shortening rock sequence. Faulting released the built-up stresses leading the development of zones of weakness having some specific geometry relative to the north-south trending folds. Of the range of fault sets that develop on this ‘locking up’ folded geometry, the high angle reverse fault has a major influence on the development of mineralisation.
The combination of folding and faulting of certain geometry allowed dilational openings which localised the deposition of quartz, gold and minor sulphide mineralisation (Figure 2). This process occurred over the regional area causing much of the lode-style mineralisation now known in the Victoria gold province.
Three-dimensional modelling of the Barrys Reef workings (Turner 2019) including the eastern reefs of Annie Laurie and Grace Egerton, as well as the Sultana-Mounters group leads to the following conclusions:
- Gold-quartz structures are formed by interaction of faults that are sub-parallel to bedding, but when encountering a change in bedding orientation will refract with possible dilation.
- Mineralised shoots may be controlled by the intersection of faults with bedding, some high-angle reverse faults refract as they pass through changes in competency of host rocks.
- Reef structures are not always associated with anticlines or synclines.
- Gold shoots plunge towards the south and dip towards the west; the vertical historic shafts markedly diverged from the shoots with increasing depth and quickly undershot the lode.
These conclusions will form part of the drill targeting process of the lode structures after the compilation of the underground mapping data and assays has been completed.
Historical Exploration and Mining Activities
The discovery of gold at Red Hill (near Blackwood) in 1855, led to a rush of prospectors to the goldfields. It is reported that at the peak of mining activity, there were about 13,000 miners along the Lerderberg River and its tributaries.
Alluvial mining quickly gave way to underground hard-rock mining of gold-rich quartz reef structures. More than 90% of the gold produced from the Blackwood goldfields came from the hard rock source. The largely forgotten Blackwood Goldfield produced significant gold (220,000 ounces pre-1890 from near surface historic mining, with great potential for large tonnage high grade gold, down-plunge and along strike of workings, most less than 100 m below surface.
There is a cluster of mines along parallel but stepped reef structures around the Sultan Mine, including
Central, Mounters, Intermediate, Pioneer, Homeward Bound, Western, Edgerton, and Annie Laurie (Figure 3). Often each of these lodes were owned and operated by different companies. The well-capitalised Sultan mine having the deepest workings effectively dewatered the workings of the adjacent mines. When pumping halted at Sultan the adjacent mines lacked the ability to keep their workings dry and ceased operations when their mines flooded. The operations ceased because of flooding as distinct to depletion of ore reserve.
Historical exploration work in the area of the exploration licences includes mineral resource definition drilling, completion of mineral resource estimates (not compliant with JORC 2012 reporting standards), mapping and soil sampling, costeaning and drilling.
Cauldron and independent researchers associated with the vendor has completed a desktop study with preliminary fieldwork and has identified highly prospective target areas for gold mineralisation in the Project area. There is potential for near-term production of gold ore from the mining lease at Nuggety. In addition, there is strong potential for down-dip extensions to mineralisation at Sultan, Barrys Reef East and Yankee, with ability to expand the Target Range and define a Mineral Resource (JORC 2012) of considerable size.