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High-grade gold extensions for Alto Metals at Kohinoor reef

Updated: Mar 25

Looking west over Alto Metals’ Bull Oak open pit. Credit: File

Alto Metals has extended the mostly-unmined Kohinoor reef within its Bull Oak deposit in Western Australia’s Mid West region by 100m in both directions, with solid runs and gold grades up to a sparkling 38 grams per tonne.

The company says the 1m intercept with the highest gold grade came within an 11m hit going 4.1g/t from 34m at its Sandstone project. It was just one of several strong results from an 18-hole reverse-circulation (RC) drilling program at the granodiorite porphyry-hosted Bull Oak deposit.

At the opposite end of the known Kohinoor reef, a second hole yielded 10m running 1.5g/t gold from 19m, including 4m at 3.1g/t gold from 24m – a find which appears to extend the reef in the shallow oxide by about 100m to the north-west.

Additional results reported by the company include 7m at 4.7g/t gold from 29m, including 1m at 28.9 g/t from 32m and 3m reading 10.2g/t from 41m, including 1m at 29.5g/t from 41m.

The Bull Oak deposit is one of several in an open-ended, 20km-long, north-west/south-east belt within the Sandstone gold project.

Our drilling at Bull Oak has exceeded our expectations, with these latest results successfully demonstrating mineralisation is not just constrained within the granodiorite, but also occurs as shallow high-grade reefs outside the Bull Oak intrusive and outside the current resource. The extension of the multiple stacked lodes within the intrusive laterally and at depth is a clear indication of significant mineralisation. Alto Metals managing director Matthew Bowles

Mr Bowles said the company’s drilling focus would now include targeting the contact and the many banded-iron formation (BIF) units and cross-cutting quartz reefs it believed was driving the high-grade mineralisation.

Alto says the extensions indicated by its most recent two holes effectively stretch the total strike length of the Kohinoor reef out to about 400m and that, apart from a small high-grade section at the northern end being mined in the 1990s by Herald Resources, the rest remains unmined.

Apart from the latest shallow oxide results, the company’s deeper drilling intersected many mineralised intervals of granodiorite and BIF within an overall mafic unit. Just last month, results from two drill holes – the first of which was put into the north-east end of the Bull Oak intrusive – reported 55m at 1.5g/t within an overall intercept of 172m, running at an average grade of 0.64g/t gold from 44m. It confirmed the granodiorite-BIF contact is a favourable geological position for gold mineralisation.

A second hole put into the south-west part of the granodiorite yielded 227m at a grade 0.44g/t gold from 26m, including higher grade runs of 23m at 1.1g/t from 147m, with 8m going 2.1g/t from 157m and 1m reading 8g/t gold from 164m.

Encouragingly, drilling by previous explorers gives a bit of a guide as to the potential that may be residing not far below the surface, yielding abundant unmined runs with high gold grades beneath the Bull Oak open pit. It includes two examples – 9m at 31g/t gold, with an included 1m going a mouth-watering 275g/t from 51m, and 7m at 38.9g/t from 64m, including 1m at 154g/t from 65m.

It is almost certain that further assessment and modelling of the mineralised zones, , in addition to the multiple stacked lodes in the granodiorite, will lead to their inclusion into the current Bull Oak mineral resource.

Bull Oak is within the Hancocks Mining Centre in Sandstone. It covers an area of 3 square kilometres within Alto’s 100 per cent-owned project, about 5km south-east of the historic Sandstone township. The mine produced a total of 39,936 ounces at an average grade of 38g/t gold between 1904 and 1943.

The Bull Oak resource currently stands at 1.9 million tonnes at 1.1g/t gold for 65,000 ounces and is constrained within a $2500 per ounce gold price, optimised open-pit shell. It is within a depth of 160m from surface, effectively capturing the majority of the shallow drilling and is limited by the extent of drilling.

The project covers about 740sq km of the Sandstone greenstone belt and has a total optimised, open-pit constrained mineral resource estimate of 832,000 ounces at a grade of 1.5g/t gold. It encompasses more than 80 per cent of the total unconstrained 1.05-million-ounce resource estimate.

Significantly, Alto says that the mineral resources are shallow, with 90 per cent of them defined within 150m from surface.

The company has plenty to keep it occupied and seems to gain further encouragement with almost every drillhole as it creeps up on the magic million-ounce total resource in a unique bit of geology that will certainly keep life interesting.

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