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Location

The Mt Gibson Gold Project (MGGP) is located approximately 280 kilometres northeast of Perth and less than 10 kilometres from the main arterial Great Northern Highway, in the Murchison region of Western Australia. It is 150 kilometres SSE of Yalgoo (Golden Grove VHMS base metal deposits) and 240 kilometres SSW of Cue and the Big Bell and other lode gold mines.

Mt Gibson project location
Background

Gold production commenced at the MGGP in 1986 on a modest laterite resource. By 1999, when the mine was placed on care and maintenance, the MGGP had mined several shallow laterite pits, 14 open pits with a maximum depth of approximately 100 metres, mining oxide, transitional and primary ore zones and an underground mine.

The CIL plant (decommissioned and removed) processed 12.5 million tonnes of ore at an average grade of 1.99g/t gold for production of 799,600 ounces. A further 68,868 ounces of gold was recovered from a 4 million tonne heap leach operation, taking total historic gold production at the MGGP to 868,468 ounces. Historical gold recoveries through the CIL plant of >90% were indicative of the ores treated at that time being free milling.

Deposit Geology

The MGGP tenements are located at the southern extremity of the Retaliation Greenstone Belt, in the SW portion of the Yalgoo-Singleton Greenstone Belt in the Murchison Province of the Yilgarn Craton.

The tenements are mostly covered by a veneer of alluvial quartz sands and laterite gravels, with sporadic greenstone subcrop and outcrop, increasingly exposed in the north of the project area. The mineralised laterite gravels are situated slightly down-slope from the lode deposits on the Gibson trend.

Regionally, the greenstone belt has been metamorphosed to middle amphibolite facies and hosts a number of Au-Cu deposits and prospects, including Golden Grove, 90km to the northwest of Mount Gibson.

The deposit has been defined by drilling over an 8km strike length and as deep as 950m down-dip where it is still mineralised and open down-dip.

The mineralised shoots are present in drilling as broad zones up to 50m wide and are continuous down plunge. It is thought the shoots are developed in dilation zones along the main structures.

A large laterite and oxide weathering zone is developed over the primary geology and this is mineralised in the near surface, up-dip position of the main shoots of primary mineralisation.

A thin veneer of transported sand and colluvium soil covers the deposit and is typically less than 6m thick, the transition/fresh rock boundary is about 40 to 60m below surface.

Mineralisation – The Gibson Trend

The lode style mineralisation at Mount Gibson is predominantly hosted by three main trends of which the majority of the known and mined mineralisation is hosted by the Gibson Trend.

It is believed to have originally been a gold-copper-zinc rich Volcanogenic Hosted Massive Sulphide (VHMS) deposit that has been overprinted by a later hydrothermal gold mineralising event. This mineralised shear zone has an arcuate north-south to north-easterly strike (trending more north-easterly in the north) and extends for more than seven kilometres from the southern granite contact to beyond the Hornet ore body.

The so-called “Mine Sequence” is around 400 metres wide and consists of a parcel of sheared, metamorphosed and chlorite-biotite-muscovite altered mafic volcanics. Numerous felsic porphyries intrude the Mine Sequence. Mineralisation is hosted within multiple sets of elongate lodes with strong strike continuity, which anastomose and pinch-swell along strike and to depth. The main lode systems include the historical Hornet, Enterprise, Orion and S2 open pits.

Unique MGGP Opportunity

The combined area of the tenure covers approximately 139 square kilometres and in excess of 15 kilometres of strike on the gold bearing Retaliation Greenstone Belt, in the SW portion of the Yalgoo-Singleton Greenstone Belt.

The MGGP has been the subject of approximately 660,000 metres of exploration and operations drilling, of which less than 5% is deeper than 150 metres below surface. Further, as noted above, the deepest open pit at the MGGP finished only approximately 100 metres below surface while the average depth of mining is between 60 – 80 metres below surface. The gold price in 1999 when the mining operations ceased was in the order of A$450 per ounce (compared to current price of circa A$2,400 per ounce).

Acquisition

In July 2021 Capricorn announced the acquisition of the MGGP which the Company estimated had a JORC 2012 compliant Inferred MRE of 79Mt @ 0.8g/t Au for 2,083,000 ounces of gold at MGGP.

In December 2021 all key mining tenure was granted over the project area allowing Capricorn to expedite work to grow the gold resource and advance the project towards a maiden reserve estimate and feasibility study.

In January 2022 an extensive infill and extensional RC drilling programme commenced at MGGP to form the basis of an updated MRE and maiden ORE (refer to exploration section below for more details). In conjunction with the commencement of drilling, technical work and studies across numerous disciplines commenced at MGGP as required for reserve estimation, feasibility studies, permitting applications and ultimately project development.

In June 2022 Capricorn’s application for a mining lease was granted covering all of the areas required to develop the mining project.

Mineral Resource Estimate

Capricorn announced an updated MGGP Mineral Resource Estimate (MRE) on 7 Nov 2022 as follows:

Notes on the Mineral Resource estimate:

  1. Mineral Resources are estimated using a gold price of A$2,200/ounce.
  2. Mineral Resources are estimated using a cut-off grade over 0.4g/t Au.
  3. The above data has been rounded to the nearest 100,000 tonnes, 0.1 g/t gold grade and 1,000 ounces. Errors of summation may occur due to rounding.

Maiden Ore Reserve Estimate

Capricorn announced in April 2023 a maiden Ore Reserve Estimate (ORE) at the wholly owned Mt Gibson Gold Project (MGGP) in Western Australia.

The maiden MGGP JORC 2012 compliant ORE is 48.7 million tonnes @ 0.9g/t Au for 1.45 million ounces.  This ORE is based on a Mineral Resource Estimate (MRE) of 104.9 million tonnes @ 0.8g/t Au for 2.76 million ounces(refer ASX announcement 7 November 2022). 

Ore Reserve:

Notes on the Ore Reserve estimate:

  1. Ore Reserves are a subset of Mineral Resources.
  2. Ore Reserves are estimated using a gold price of A$1,900/ounce.
  3. Ore Reserves are estimated using a cut-off grade over 0.4g/t Au.
  4. The above data has been rounded to the nearest 100,000 tonnes, 0.1 g/t gold grade and 1,000 ounces. Errors of summation may occur due to rounding.