The Company’s Elizabeth Hill Silver Project is located approximately 40km south of Karratha in Western Australia. Silver was historically mined from underground operations between 1998 and 2000 producing 1.17 Moz. More recent exploration was expanded to investigate the potential for base metal and nickel sulphide deposits associated with the highly prospective Archean Munni Munni Complex that intrudes the Archean granitic and gneissic basement rocks of the Pilbara Craton. Exploration activities at Elizabeth Hill were put on hold during 2017.
In 2001 the Company and its former JV partner (since withdrawn) sold certain assets relating to Elizabeth Hill, including Elizabeth Hill Plant, equipment and associated infrastructure (including tailings) (known as the Sub-Lease Assets) to a third party. Those assets were assigned and are currently owned by Artemis Resources. Artemis is yet to advise of its intentions with respect to the Sub-Lease Assets.
The Munni Munni Complex
The Munni Munni Complex (MMC) is a platinum group element (PGE) bearing Archaean layered mafic-ultramafic complex within the Pilbara Craton, 45 km south of Karratha. The complex intrudes older granites and is unconformably overlain by the late Archaean to Palaeoproterozoic Mount Bruce Supergroup of the Hamersley Basin.
The MMC covers an area of 225 sq. km (9×25 km) and is at least 5.5 km thick. It is composed of a lower, 1850 m thick ultramafic series overlain by a >3630 m gabbroic series. The ultramafic series is layered, dipping at 20 to 40°S and comprises a sequence of cyclically layered olivine cumulates and clinopyroxene cumulates. Orthopyroxene and chromite are only significant in the upper 100 m of this series, the Websterite Zone.
The PGE mineralisation is hosted by the porphyritic websterite of the Websterite Zone and is associated with an interval of copper-nickel sulphide accumulation some 0 to 15 m below the sharp ultramafic-gabbro contact. The PGE layer has been defined over a strike length of more than 7.5 km and to a depth of 600 m and remained open along strike and down dip.
Elizabeth Hill Silver Deposit
The deposit is hosted by veins adjacent to the northerly trending Munni Munni Fault, lies at the basal contact (northern edge) of the ultramafic zone of the Munni Munni Intrusion with an underlying granitoid body. Mineralization may be similar to deposits of silver (and cobalt) associated with gabbroic intrusions in the Cobalt district of Ontario, Canada.
High-grade silver was discovered during nickel-copper exploration by AGIP in 1987. Further exploration of the prospect since 1994 by East Coast Minerals NL – Legend Mining NL has revealed a very rich, but small, silver deposit. Mineralization is in a series of rich pods formed in a shear structure that links to the Munni Munni Fault lying immediately to the west. Native silver and lesser amounts of silver sulfide minerals occur as both fine and coarse grains within a coarse-grained calcite vein stockwork considered that the mineralization is primary and could be related either to differentiation in the layered-mafic intrusion or to assimilation of country rock by mafic magma.
Elizabeth Hill Scoping Study 2011
The currently known mineralisation is finite and is from surface to a depth of 60 metres. At 60 metres a small shaft underground mine extracted a high-grade zone of mineralization.
Silver was mined by East Coast Mining and Legend Mining from the Elizabeth Hill underground mine between 1998 and 2000. 16,800 tonnes of ore grading 2,100 g/t silver (70 oz/t) were mined to produce 1,170,000 ounces of silver. A shallow high-grade pod of similar material was reported to remain in place (East Coast Minerals* March 2012 Quarterly Activities Report).
Exploration potential exists along the granite and ultramafic contact for repetitions of silver pods to the east and west of Elizabeth Hill and also at depths below known mineralisation.
A scoping study was compiled in 2011 at a silver price of A$50/ounce. Following the scoping study, the silver price retreated and no further work was undertaken. Until further mineralisation was identified or the silver price increases the Company resolved that it was not beneficial to spend further money on this part of the project.
*Karratha Metals Group Ltd was previously known as East Coast Minerals Ltd.