The original Savannah sulphide rich nickel, copper and cobalt orebody is hosted by the layered mafic-ultramafic Savannah Intrusion which is enveloped by aluminous metasediments and para-gneisses of the Tickalara Metamorphics. The Savannah Orebody is mostly confined to a marginal norite unit up to 40 metres thick developed above the base of the intrusion. Areas of massive, matrix and disseminated sulphide mineralisation, dominated by pyrrhotite, chalcopyrite, pentlandite and minor pyrite occur throughout the marginal norite unit.
Prior to the development of the Savannah Open Pit, the marginal norite unit outcropped as a prominent 250 metre long limonite-goethite gossan with fresh sulphide mineralisation developing approximately 20 metres below surface. At approximately 500 metres below the surface, a significant sub-horizontal fault, the 500 Fault, cuts the orebody and offsets it 200 metres to the northwest. Mineralisation above the 500 Fault is referred to as the “Upper Zone” and below the 500 Fault as the “Lower Zone”.
The orebody was mined continuously between 2003 and 2016 initially via open pit and then underground with the majority of the ore mined via long-hole open stoping, a highly mechanised and low cost method. Access to the top and bottom of the ore block was established with tunnels, a slot raise created, and holes then drilled to blast vertical slabs off the ore block. Once the ore block was blasted and extracted, the stopes were filled with paste (tailings and cement mix) to stabilise the void and allow extraction of adjoining ore blocks. The minimal waste material mined was either stockpiled underground or trucked to surface.
Operations restarted at Savannah in December 2018 with the first shipment of Savannah concentrate departing Wyndham port in February 2019. The Company is currently focussing on the ramp up to full production from the Savannah orebody and the development drive to access the higher grade Savannah North orebody.
The process plant at Savannah was commissioned in August 2014 and comprises a single stage crusher, SAG mill, flotation, thickening and filtering stages to produce a bulk nickel, copper, cobalt concentrate. Over the 2004 to 2016 initial operating period, metallurgical recoveries averaged 86-89% for nickel, 94-97% for copper and 89-92% for cobalt. The plant was originally designed for a throughput of 750,000 tonnes per annum, but consistently outperformed the design specifications. The plant operated at significantly higher throughput rates immediately prior to being placed on care and maintenance in May 2016 with rates exceeding 1 million tonnes on an annualised basis.
The Savannah concentrate was contracted for sale to Sino Nickel (a JV between the Jinchuan Group of China and Sino Mining International Limited) until April 2020. A new Concentrate Offtake Agreement was executed in June 2018 covering 100% of production for a four year period from recommencement of production. The terms of the new Concentrate Sales Agreement are considered by Panoramic to be very competitive in global terms.
In 2009/10, Panoramic reported on the Lower Zone Ore Reserve below the 500 Fault and that the Lower Zone orebody was truncated by a fault structure (the 900 Fault) at approximately 900 metres below surface. Resource definition drilling extended the mineralisation significantly to the north and west above the 900 Fault.
Below the 900 Fault & Western Splay
Ongoing exploration around the Savannah ore body above and below the 900 Fault have led to an upgrade in the Savannah Resource. A maiden Resource of 905kt @ 1.65% Ni for 14,900t Ni was announced by the Company in August 2015.
In early 2014, the Company announced it had intersected 89.3m @ 1.6% Ni and followed it up with another significant intersection of 33.7m @ 1.56% nickel at Savannah North approximately 600 metres north of the original Savannah orebody. A successful resource drilling program undertaken during 2015 provided an interim Resource estimate of 3.15Mt @ 1.75% Ni for 55,200t Ni for Savannah North.
A major upgrade in Resource increased to 175,100t Ni was announced in August 2016. Combined Resources at Savannah now 218,300t Ni, 99,100t Cu and 14,900t Co metal contained.
Potential 2km strike at Savannah North
Resource Open – Savannah North Resource drilling programs have not closed off the mineralisation. Potential strike length of the Upper Zone is ~2km based on the large, highly conducting on-hole EM responses identified in surface drills holes SMD164, Section 5400mE and SMD167 SMD 167A, Section 5100mE. Only half of the potential Upper Zone mineralisation has been tested by resource drilling. The Upper Zone Resource remains open to east and west and the Lower Zone Resource remains open down dip to the northwest.
The Company resumed exploration activities in 2018 to drill test four under-explored layered mafic-ultramafic intrusions located near Savannah. The impetus and focus of the 2018 exploration program was driven by the results of a series of Panoramic / Minerals Research Institute of WA (MRIWA) funded research projects with CSIRO Mineral Resources. The aim of the research projects, which commenced in 2015, was to improve the Company’s understanding of the petrography, mineralogy, geochemistry and geochronology of the Savannah Style layered mafic intrusions and the origin and emplacement mechanisms of their parental melts.
A number of other mafic/ultramafic intrusive bodies occur at the Savannah Project
- Dave Hill
- Subchamber D
- Frog Hollow
Little or no modern exploration has been conducted on these intrusions. Previous drilling by Panoramic has demonstrated that both Dave Hill and Wilsons host disseminated/blebby magmatic nickel-copper sulphide mineralisation. Past drilling has been minimal and has not tested the most prospective basal parts of these intrusives.
- Dave Hill – one 700m deep and five shallow core holes
- Wilsons – one core and seven shallow RC holes
- Subchamber D – one core hole
- Frog Hollow – never been drilled
The research conducted by CSIRO Mineral Resources on Subchamber D, Dave Hill and Wilsons concluded that all three intrusions were emplaced at the same time and by the same magmatic event that was responsible for the emplacement of the mineralised Savannah and Savannah North intrusions. Consequently, the CSIRO considers all three intrusions to be highly prospective for Savannah Style magmatic nickel-copper sulphide mineralisation. The Frog Hollow intrusion, which has never been drill tested, was not part of the CSIRO research project but is included in the Company’s 2018 exploration program based on its many geological similarities with the other Savannah Style intrusions.