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Deposit Synonyms
Eastern Lode; Elders Main Lode; Elders West Lode; Karkarilla Lode; Moonta; Moonta Eastern Belt; Taylors Lode; Treuers Lode; York Lode
Mineral District
Moonta - Wallaroo
Deposit Summary
shear-hosted Cu-Au-Ag mineralisation in host Moonta Porphyry (U-Pb age 1737Ma). Production from 1860-1923 ~4.8Mt ore for 161,100t Cu metal, significant recovery of silver & gold. Remaining resources ~86,000t @ 4.2%Cu.
Deposit Description
MOONTA EASTERN LODE, naming terminology is that adopted originally by Dr. R.L. Jack in Bulletin 6, 1917. It is the most south-eastern of 3 groupings of main lines of lode in the Moonta Lode System, and comprises 2 main lodes, Taylors and Elders trending NNE for ~1.6km from Karkarilla Mine in the south to Stuckeys Mine in the north. Moonta mine itself is located centrally on Taylors Lode.
Host rock is the Palaeoproterozoic Moonta Porphyry (U-Pb zircon age 1737 +-5Ma), a foliated, rhyolitic meta-feldspar porphyry of probable volcanic origin. Mineralisation, where unweathered, comprises chalcopyrite, pyrite, and bornite in a quartz, feldspar, tourmaline, and chlorite and hematite gangue. Mineralisation age estimate is 1599 +/-6Ma (molybdenite, Re-Os). In the weathered profile a pronounced zone of secondary sulphide (chalcocite, covellite) enrichment caps the lodes overlain by a near-surface barren zone. Hiltaba Suite granitoid in the region is considered a likely source of the hydrothermal fluids that forms the lodes.
The 'Main Lode Shears,' Taylor's and Elder's lodes have extensive ore shoots. They localise large quartz +- mica or pegmatite veins, and are recognised from decomposition of feldspar, and development of secondary mica and chlorite. Mineralised veins have dimensions up to 12m wide, and 100s m long, containing subvertical, tabular to lenticular zones enriched in sulphides. They were mined to depths of at least 650 m. Some orebodies were terminated by younger cross-cutting faults. Production figures for the eastern line of lode have not been compiled. However, production for the whole Moonta Lode System (MLS) was estimated at 4.8 million tonne (Mt) of crude ore, with eastern line of lode the main contributor. MLS estimated overall grade 3.3%Cu, best estimate for grade of dressed ore at ~17%Cu for recovery of 161,100 tonne of copper metal product. Fine gold and silver were also recovered, with best estimate of grade 0.34g/tAu, 0.56g/tAg.
Resources were virtually exhausted at close of mining in 1923. Remaining resources occurring as isolated blocks, and in extensions to Taylor's Lode are estimated at 86,000 tonne at 4.2% Cu in 1917. Bampton (2003) estimated a resource of 1.9Mtonne at 2.4%Cu, 0.2g/tAu for remnants in the underground workings (for all 3 major lode districts in the Moonta area).
Morales Ruano et al (2002), in their research on fluid inclusions at Wheal Hughes and Poona mines suggest a deposit style for the Moonta region in general of quartz-vein fill occupying fractures and shears in host Moonta Porphyry. The vein system is complex, both spatially, and in ages of emplacement, but demonstrates an association with Hiltaba Suite granite. Their work suggests a 4-staged hydrothermal event involving a complex of processes involving boiling, cooling and mixing of hydrothermal fluids. Homogenisation temperatures of >160 – 470C, and calculated oxygen isotope values from chlorite, and quartz indicate involvement of fluids of magmatic, metamorphic, and meteoric origins. The first 2 phases were dominated by iron oxides, the 3rd by iron sulphides, and the final stage by a Cu-Fe-Co-Au-Zn-Pb-S assemblage. Source of sulphur was thought to be crustal.
Cameron (2014), examining samples of ore from Moonta and Wallaroo show an abundance of pyrrhotite, with late superposed hematite inferring a shift from reducing to oxidising conditions. Replacement textures of chalcopyrite replacing bornite, and vice versa suggest multiple episodes of ore crystallisation.
Discovery Year
? 1861
Commodities
Copper, Gold, Silver
Ore Minerals
Azurite, Bismuthinite, Bornite, Chalcocite, Chalcopyrite, Gold, Malachite, Molybdenite, Silver, Uranium Minerals (Non Specific)
Gangue Minerals
Apatite, Biotite, Feldspar, Fluorite, Hematite, Magnetite, Pyrite, Pyrrhotite, Quartz, Tourmaline
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