Excelsior Gold’s 100%-owned Kalgoorlie North Gold Project is located 30 to 55 kilometres north of Kalgoorlie in Western Australia in close proximity to existing gold treatment facilities and associated infrastructure to facilitate low capital cost developments.
The Project covers 96 square kilometres of granted mining leases and prospecting licences over the intersection of the well mineralised Bardoc Tectonic Zone greenstone sequence with the cross cutting Black Flag Fault system. The convergence of these major gold mineralising structural systems has resulted in widespread gold mineralisation throughout the Project area.
Over 90 gold occurrences have been recorded to date within the Project with the mineralisation mostly localised in favourable rock units at the interaction of the north-northwest trending Bardoc Tectonic Zone and the northeast trending Black Flag Fault structures.
Historic gold production of 56,700 ounces is recorded from the Bardoc Mining Centre located in the central part of the Project. This production occurred largely from the underground Zoroastrian mine in the late 1890s to early 1900s. Recent production from the Zoroastrian and Excelsior open pits by Aberfoyle Gold from 1987 to 1991 totalled 2,220,000 tonnes at 1.6g/t Au for 113,000 ounces of gold.
Exploration work completed to date by Excelsior Gold has delineated a number of priority areas including 22 defined resource areas and over 60 advanced prospects or zones with significant drill intercepts, which present further resource expansion opportunities.
Current Measured, Indicated and Inferred Resources for the Project total 17.1 million tonnes at 1.6g/t Au for 887,000 ounces of contained gold.
The Project hosts multiple deposit styles and an extensive distribution of gold mineralisation hosted in a series of strike parallel shear zones and lithological units which extend the length of the tenements.
Gold mineralisation is localised by the interaction of northeast and northwest cross-cutting faulting with at least five main north-northwest trending zones identified within the Bardoc Tectonic Zone mafic and metasedimentary sequence.
Resource definition drilling to date has been focused on two of these north-northwest trending zones leading to the definition of substantial gold resources in the central part of the Project associated with mineralisation hosted within the Zoroastrian Dolerite and the Excelsior shear zone. Numerous smaller gold resources and priority resource targets remain to be tested on these and other favourable parallel structural and lithological zones throughout the Project.
During 2016/17 open pit mining by Excelsior Gold concentrated on the Zoroastrian system where gold mineralisation is hosted in quartz veins and stockwork zones within the differentiated Zoroastrian Dolerite. The quartz veining has been defined over a strike length of 1.4 kilometres and remains open below a vertical depth of 380 metres . The high gold grades associated with the stockwork and narrower vein style mineralisation demonstrates excellent potential for the delineation of further open pit and underground resources.
Mining of the Zoroastrian open pit by the Company to a depth of about 110 metres below surface produced approximately 55,000 ounces from 810,000 tonnes of ore grading 2g/t Au treated at the Paddington plant and Golden Mile Milling’s Lakewood plant.
The deeper mineralisation at Zoroastrian was modelled at a cut-off grade of greater than 1.0g/t Au and is quoted at a 3.0g/t Au cut-off to reflect underground mining economic parameters. The current Indicated and Inferred Resource of 0.955 million tonnes at 4.80g/t Au for 147,500 ounces of contained gold will be updated with knowledge gained from mining of now completed open pit. An updated resource model for the greater Zoroastrian area is currently being generated.
The new interpretation of the distribution of mineralisation within the Zoroastrian Dolerite and the adjacent sediment contact provides a template for the assessment of other prospects along the 13 kilometres of strike of the dolerite unit within the Project tenements to the south of the open pit and in other parallel dolerite horizons.
The Excelsior deposit located to the northeast of Zoroastrian represents a different mineralisation style, hosted within a sequence of tightly folded and sheared ultramafic/sedimentary schists within the Excelsior shear zone. Gold mineralisation occurs in a broad 20 to 50 metres wide zone of altered quartz-sericite-carbonate schists.
The Excelsior shear is a major north-northwest trending structure up to 80 metres wide and extending for over 6 kilometres to the north and potentially 15 kilometres to the south of the Excelsior deposit within the Project tenements. Satellite resources at Lochinvar, Three Star and Ellen Pearce to the north and at Castlereagh, Parkerville and Snibbo to the south demonstrate the potential for additional gold resources along the shear.
The current Measured, Indicated and Inferred Resources at the Excelsior deposit, based on gold mineralisation interpreted and wireframed at a nominal 0.6g/t Au lower cut-off with high grade cut to 40.0g/t Au total 11.06 million tonnes at 1.28g/t Au for 456,100 ounces of contained gold. This again will be remodelled with the knowledge gained from recent mining.
Conceptual mining studies have confirmed that the broad zones of gold mineralisation host potential for a large-scale, low strip ratio open pit mine development.
The Bulletin South area in the southwestern portion of the Project tenements hosts gold mineralisation more closely related to the Black Flag Fault system than the Bardoc Tectonic Zone shear structures.
Gold mineralisation at Bulletin South is associated with stockwork zones within a felsic porphyry unit proximal to the regionally significant Black Flag Fault structure, which is interpreted to be close to the southern end of the former open pit. Primary gold mineralisation in the quartz stockwork system within the felsic porphyry may represent mineralisation along splay structures emanating from the Black Flag Fault. The stockwork mineralisation in the porphyry averages 15 metres true width.
The Indicated and Inferred Resource for Bulletin South currently stands at 645,000 tonnes at 2.3g/t Au for 47,000 ounces of contained gold a 0.6g/t Au lower cut-off. The resource extends over 250 metres of strike and down to 150 metres below surface and remains open down dip and down plunge to the south.