Language:

Gold from Surface to Great Depth

120601 drilling_diagram_joinedIndependent academic research and a 2,000 metre deep core hole has provided sound evidence that our Charters Towers gold mineralisation could reasonably persist to over three kilometres deep.

Citigold's 11 million ounce gold mineral resource has been estimated to 1200 metres deep based on the limit of our resource drilling. However, our consultant geologist, Mr Chris Towsey, states that a James Cook University PhD thesis presented important evidence for him to conclude that the goldfield's mineralisation was reasonably considered to persist to a depth of at least 3000 metres.

Subsequent to the resource drilling used by Citigold, with the financial support of Queensland State Government Department of Mines and Energy of a very deep hole 2,000 meters long has proved that the mineralised fractures containing gold extend to this depth. This is a huge positive step towards eventually increasing the gold deposits size.
Findings of the study by James Cook University were based on a detailed geological analysis of the goldfield's mineralisation which relied upon mineral and entrained fluid compositions to estimate underground pressures and temperatures of formation.
Several researchers examined the 'bubbles' of fluid inclusions within the mineral grains by accessing new drill core samples, vein samples from a number of deposits, and underground openings and pits that have only been accessible since 1997.
Fluid inclusion samples, taken from the company's Charters Towers Brilliant, Queen and Day Dawn Reefs, were subjected to various tests, including heating and cooling, to work out their composition.
Knowing the composition of the mineral fluid inclusions told the researchers the 'chemistry of the melt' and allowed them to estimate the underground temperature and pressure that was present during mineral formation.
Researchers used this temperature and pressure data to indicate the depth at which each sample was formed at. The depths were equivalent to between five and fifteen thousand metres.
Other studies have supported this finding and after allowing for erosion, the preferred depth range interpreted by research for the remaining mineralisation was between 3000 and 5000 metres.
Further research, done by Citigold and others, into the 400 million year old North Queensland resource, indicates to Citigold that the gold mined historically at Charters Towers is the structural top of the resource, the 'tip of the iceberg' so to speak.


Deep Hole Drilling

Of the 1,559 significant drill intersections used in the 2012 Inferred Mineral Resource estimate, there are 22 drill intersections deeper than 1,000 metres, of which 19 are deeper than 1,100 metres and 10 deeper than 1,200 metres, with a maximum gold grade of 20.54 g/t Au. The deepest intersection prior to 2008 was 1,300.1 metres which returned 2.3 metre-grams per tonne.

In 2008, a 2,000 metre deep hole was drilled. This hole produced the following highlights:

Gold mineralisation extended a further 700 metres vertically to 1,900 metres.
• 
Continuity of mineralisation confirmed.
Potential to significantly increase total gold resource.
• 
Geological model of deep gold structures proven.
• 
Record depth for Atlas Copco Diamac U8 APC drill.


This is believed to be a world record depth hole drilled with the Atlas Copco U8 APC diamond core drill and the deepest diamond drill hole in northeast Queensland. The 2 kilometres of BQ drill rods in the ground weighed nearly 13 tonnes with this powerful 'mighty midget' drill rig completed the hole and pulled the rods successfully.

120601 deep_holeThe final piece of drill core retrieved by the rig was from 2001.1 metres. The hole was drilled at a steep angle from surface of 78 degrees and stayed remarkably straight.

Citigold Corporation's Chariman Mr Mark Lynch said "The results from the deep hole are awesome and prove beyond doubt that the Charters Towers mineralised system extends to great depths, way beyond the limits previously mined and remains open at depth and to the east"

The hole intersected additional separate mineralised structures of 0.50 metres length at 1,615 and 1,778 metres plus a smaller 0.02 metres at 1,982 metre depth. The results confirm the presence of gold related alteration and mineralisation and demonstrate that the mineralised structures persist to at least 1,900 m depth on the eastern side of the gold field.

Citigold currently has defined a 11 million ounce gold resource, with total Inferred Mineral Resources of 25 million tonnes, at 14 grams of gold per tonne*. The Mineral Resource report was prepared in accordance with the Australasian ore reserve, mineral resource and exploration JORC Reporting Code, after an extensive evaluation period.

The huge area below the deepest drill holes have great potential. Future deep drilling of the structural extensions of the gold mineralisation, below the existing 1200 metre deep holes, would be expected to increase the size of Citigold's current gold resource. The current focus is on moving back into and growing gold production.

The majority of past mining at Charters Towers was mainly about 700 metres depth with many reefs left unexplored and unmined. 

pdf Click HERE for the full 173 page technical report "Mineral Resources and Reserves 2012 Charters Towers Gold Project" 

(Updated September 2016)