PGC Logo Learning from Rocks & Mines
IOCG 2013
Australian Iron Oxide Cu-Au Deposits
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[Ernest Henry pit]
[E1 pit]
Ernest Henry and E1 North open pits. The group transferred from Cloncurry to the Ernest Henry mine on the morning of Monday 25, arriving by 9:00 am. After a safety induction at the mine gate, they were taken to the mine office for an introduction to the geology of the Ernest Henry deposit and the E1 and Monakoff deposits of the Mount Margaret project. They were then divided into two teams, one visiting the Ernest Henry (top) and E1 North (bottom) pits pictured above, while the remainder were taken to a core layout area to study drill holes through the Ernest Henry, E1 North and Monakoff deposits, guided by Xstrata geological staff. When the first team returned, the second then also visited the pits, and on their return, both further studied the core.
    In the top image (which looks south), note that open pit mining has been completed at Ernest Henry, which is now an underground operation, serviced by a shaft (see the headframe to the east, on the far left) and decline (portal on the right of the image, at the far end of the wide bench half way down the pit wall). The >1% Cu ore-shell of the deposit, which is hosted by magnetite-altered brecciated intermediate volcanic rocks, has a generally cylindrical shape, with 350 x 250 m plan dimensions, plunging at 45°S, to depths in excess of 1000 m vertically, with an unclosed down-plunge length of >1400 m. In this image, the deposit is exposed on the far lower benches, where yellow-green staining after sulphides is evident, passing up into structures on the far wall.
    Mining at E1 North, 8 km east of Ernest Henry, commenced in July, 2012. Within the E1 deposit, mineralisation is generally stratabound, predominantly hosted by thin (a few to a few tens of metres thick) magnetite altered metasedimentary rocks over an interval of several kilometres, sandwiched between more competent basaltic and trachytic volcanic units. The three main ore concentrations at E1 North, South and East, are localised in more structurally complex fold hinges and zones of cross-faulting.   Photographs by Mike Porter.

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