Monakoff Mine, Cloncurry, Cloncurry Shire, Queensland, Australiai

Regional Level Types
Monakoff Mine	Mine
Cloncurry	Town
Cloncurry Shire	Shire
Queensland	State
Australia	Country

The Mount Margaret mining operation exploits the Monakoff and E1 group of IOCG-style copper-gold deposits in the Cloncurry District of NW Queensland, Australia. Monakoff is located ~15 km ENE of Cloncurry, and is 20 km south of the Ernest Henry deposit. The E1 group of deposits are 22.5 km to the NNE of Monakoff and 8 km east of Ernest Henry.

The Mount Margaret ore is treated at the Ernest Henry mine (#Location: E1 20° 26' 36"S, 140° 47' 10"E; Monakoff 20° 37' 30"S, 140° 41' 20"E).

All of these deposits are hosted within the Eastern Succession of the Mount Isa Inlier, which consists of poly-deformed Palaeo- and Mesoproterozoic volcano-sedimentary Cover Sequences 2 and 3 (CS2 and 3), deposited between 1790 and 1690 Ma and from 1680 to 1610 Ma respectively.

For details of the regional setting and geology of the northeastern Cloncurry district, see the Ernest Henry record.

The upper 100 m of footwall lithologies comprise thinly (1 to 3 mm) intercalated magnetite-bearing muscovite pelites, psammopelites, and meta-dolerites of the uppermost Mount Norna Quartzite, overlain by massive porphyroblastic garnet-biotite schist (mostly of intrusive andesitic igneous origin, although the upper 3 to 5 m are vesicular), then a regionally persistent magnetite iron formation, and finally by strongly sheared metasediments immediately hosting the Monakoff West ore. The continuous, 1 to 2 m thick, prominently banded, quartz-magnetite±hematite iron formation can be traced through the whole prospect, occurring ~5 to 10 m above the top of the porphyroblastic garnet-biotite schist, hosted by pelitic metasediment. Banding varies from 1 to 2 mm 'wrinkly' lamination (possibly crenulations), to 0.5 cm interbands of quartz-barite, and spessartine-magnetite. The metadolerites are present as continuous sills, locally with angular contacts and variable epidote alteration, particularly adjacent to sediment contacts.

The hanging wall above the thin strip of sheared metasediment that hosts ore, commences with a 20 to 30 m thick interval of short strike-length metabasalts, minor iron formation, volcanic conglomerate, and breccia bearing clasts of limestone and meta-dolerites. A local pillow breccia outcrops close to the ore package near the centre of the deposit, while black carbonaceous limestone and stromatolitic cherts are also reported. More common rocks of the Toole Creek Volcanics occur above this complex, comprising massive medium- to coarse-grained meta-dolerite to gabbro in the west, and mixed meta-dolerite, meta-basalt, siliceous siltstone and minor iron formations in the east (Davidson et al., 2002).

The "ore package" is defined as the altered rocks adjacent to the ore, the ores themselves, and the overlying altered sediments and basaltic tuff, all of which young and dip to the south. Near-ore alteration in the footwall commences with porphyroblastic spessartine-biotite-quartz-plagioclase-chloritoid-tourmaline-biotite development within the meta-andesite, with idioblastic garnet occuring as disseminations or irregular bands localised on peperite zones. Locally, pink spessartine is overgrown by coarse-grained almandine + quartz, indicating peak metamorphism exceeded the almandine isograd. The timing of almandine stability is uncertain (Davidson et al., 2002).

The major enriched components of the ore compared to the country rocks are: S (>20% S), Ba (>25% BaO), F (~2 to 10% F), Fe (>10% FeO) and Ca (~10% CaO), with significant enrichments of minor element including economic Co, Cu, Au and Ag, plus, Pb, Sb, As, W, U, La, Ce and Zn. P2O5 abundances are low, with most ores containing only 0.2 to 0.4 wt.% P2O5. The highest values are systematically found in the iron formation, although no strong Fe-P correlation exists when all of the data is considered. La and Ce abundances are also very high, with values typically of >1000 ppm. Rather than apatite, the host phase for REE, U, and possibly P2O5, is monazite, which is common in ore intersections, and concentrates the LREE (Davidson et al., 2002).

The western Monakoff ore zone is enclosed by, and replaces, magnetite-bearing meta-siltstones, occurring at surface as a friable, but resistant, massive unit with variable black pyrolusite and malachite staining. At depth it occurs as a massive unit composed of barite, ponite (Fe-rhodochrosite), magnetite, chalcopyrite, pyrite, spessartine, fluorite ±K-feldspar, sphalerite, galena, arsenopyrite, mackinawite, molybdenite, brannerite/davidite, pentlandite and linnaeite (Ashley, 1983).

The eastern Monakoff ore zone appears to mainly comprise replacement of a medium- to coarse-grained amphibolite, within a tight D2 fold adjacent to an unexposed east-west fault, represented at surface by buff-coloured silica, studded with randomly oriented crystals of coarse magnetite, magnetite-hematite, and hematite, that are consistent with faithful pseudomorphing of meta-gabbro. The silica is most likely a surficial regolith replacement product of carbonate. At depth this rock-type is a package of comparatively thin massive meta-dolerites and intercalated peperitised sediments, with the contact between the two lithologies more completely silicified, and an alteration zonation into the sediment of i). siderite-magnetite-pyrrhotite-chalcopyrite; ii). magnetite-siderite-quartz, to iii). biotite-quartz-magnetite over 1 m or less, while the adjacent dolerite contains incipient siderite alteration. It is interpreted that in the core of the fold, severe alteration affected the interior of the folded metadolerite as well as the sediment margins. The fluids, which were tightly focussed by the fold structure, produced wholesale replacement of dolerite, and a narrow west-plunging pipe with grades of 1.4 to 3.0% Cu, consisting of siderite-barite-magnetite-chalcopyrite, which is likely to have considerable depth extent (Davidson et al., 2002 and sources quoted therein).

Resource and reserve figures for the Mount Margaret Operation deposits were:
Monakoff + Monakoff East deposits (Xstrata, 2012):
Indicated resource - 2 Mt @ 1.4% Cu, 0.4 g/t Au
Inferred resource - 1 Mt @ 1.2% Cu, 0.4 g/t Au
Total resource - 3 Mt @ 1.33% Cu, 0.4 g/t Au
Nearly 3500 t of U3O8 is contained within these deposits. The average in-situ recoverable grade is ~112 ppm U3O8.


This Precambrian iron oxide - copper - gold deposit is located in the Mt Isa Inlier, northeast of Cloncurry.it formed in dilational zones in a shear zone in metasediments and metavolcanics. It is enriched in F, Ba, Co, Ag, Mn, REE, U, Pb, Sr and Zn.

Other Regions, Features and Areas containing this locality

References