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Marvel Loch - Southern Cross Belt |
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Western Australia, WA, Australia |
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Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Marvel Loch mine lies within the Archaean Southern Cross Greenstone Belt, Southern Cross Domain, in the Youanmi Terrane of the Yilgarn Craton, some 235 km WSW of Kalgoorlie, 375 km east of Perth and 32 km SE of the town of Southern Cross, Western Australia (#Location: 31° 27' 56"S, 119° 29' 42"E).
Over the period from the late 1990s to at least 2019, Marvel Loch has been the core of the main gold mining operation in the Southern Cross Greenstone Belt where ore has been trucked from a series of open pits and underground mines to a central procession plant for treatment.
Gold production at Marvel Loch began in 1905 and continued until 1914, before resuming in 1933 until 1938 and closing again. Cumulative production over that period was 0.785 Mt of ore @ 5.4 g/t Au recovered to yield 4.317 t of gold. The mine at Marvel Loch was reopened and refurbished in 1973, the shaft deepened and from 1979 commenced underground operations. A new decline was excavated in 1986. Open pit mining in the oxide zone commenced at the main Marvel Loch deposit in 1984, and in 1986 and 1987 expanded northward to incorporate the Exhibition-Firelight and then the Undaunted mines respectively into a single 1500 m long pit. Operations at the open pit were suspended in July 2009, while underground mining continued. Gold mineralisation in the underground workings, at that stage was known to extend over a 1.3 km strike length, and had been identified to depths of >800 m below surface and remained open at depth. In 2009, the underground mining rate was increased to >1 mtpa. From the early 1990s and to the mid 2000s many of the mines in the Southern Cross Belt were amalgamated into the same operation, and a >2 mtpa mill at Marvel Loch has been fed since then by ore from a series of open pits, including Marvel Loch itself, Yilgarn Star, Mary Lena, Hercules, Achilles, Nevoria, Cornishman, Treasury, the GVG cluster and by the Golden Pig, Transvaal, Marvel Loch and Ruapehu underground operation. These mines are distributed over a strike length of ~35 km. Between 1973 and 2019 Marvel Loch and the other deposits have changed ownership on a number of occasions and in 2009 was purchased by a Chinese entity which does not appear to publicly report geological, production and resource/reserve information.
For regional information on the Southern Cross Belt and its deposits see also the Transvaal, Fraser, Yilgarn Star, Bounty, Nevoria and Copperhead records
The Marvel Loch deposit lies within a sequence of mafic to ultramafic volcanics on the western fringe of a younger ovoid gneissic granite, the Ghooli Dome. The greenstone belt sequence commences with psammitic sedimentary rocks, and ultramafic intrusives, overlain by a 3 to 5 km thick succession of mafic to ultramafic and interlayered sedimentary rocks. These are followed in turn by a felsic volcanic sequence and then a 3 to 5 km thick package of pelitic sedimentary rocks. The sequence is cut by east-west Proterozoic dolerite dykes and has been metamorphosed to amphibolite facies, and locally to granulites.
The ore lenses at Marvel Loch are a series of steeply-plunging flattened shoots that are found within a regional, multi-phase shear system in a meta-pelite unit, sandwiched between an Mg-rich amphibolite/fine grained komatiitic basalt in the hanging wall, which includes banded iron formation (BIF) units, and a 200 m wide footwall meta-gabbro. All of these units belong to the thick mafic to ultramafic package described above. The host meta-pelite Mine Sequence comprises interlayered fine grained basalt and medium grained pelite, carbonaceous pelite and turbidite. The shear within the Mine Sequence that hosts the mineralisation is recognisable over a length of 5 km, is 80 to 100 m wide and 1 km to the west of the Ghooli Granite contact.
Mineralisation is present within the shears in two forms, namely:
i). Disseminated sulphide lode systems occurring as steeply dipping, south plunging pods within the meta-pelite, with associated biotite-carbonate-pyrite alteration; and
ii). Quartz-sulphide veins along the upper contact of the meta-pelite associated with carbonate-diopside alteration. The principal ore mineral association is arsenopyrite-pyrite-gold. Other sulphides and metallic minerals include scheelite, pyrrhotite, lesser galena, sphalerite and argentite.
Lodes are developed along the NW trending greenstone belt on the western margin of the Ghooli Dome.
The total Mineral Resource in June 2000 was 24 Mt @ 2.54 g/t Au, including the Ore Reserve of 11.52 Mt @ 2.8 g/t Au.
The total remaining Mineral Resource in June 31 2009 was 4.88 Mt @ 4.3 g/t Au, including the Ore Reserve of 2.28 Mt @ 3.8 g/t Au.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2009.
Record last updated: 28/8/2019
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Marvel Loch
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Selected References:
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Bloem E J M, Dalstra H J, Groves D I and Ridley J R 1994 - Metamorphic and structural setting of Archaean amphibolite hosted gold deposits near Southern Cross, Southern Cross province, Yilgarn Block, Western Australia: in Ore Geology Reviews v9 pp 183-208
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Doublier, M.P., Thebaud, N., Wingate, M.T.D., Romano, S.S., Kirkland, C.L., Gessnar, K., Mole, D.R. and Evans, N., 2014 - Structure and timing of Neoarchean gold mineralization in the Southern Cross district (Yilgarn Craton, Western Australia) suggest leading role of late Low-Ca I-type granite intrusions: in J. of Structural Geology v.67, pp. 205-221.
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Mueller A G, McNaughton N J 2000 - U-Pb ages constraining batholith emplacement, contact metamorphism, and the formation of Gold and W-Mo Skarns in the Southern Cross Area, Yilgarn Craton, Western Australia: in Econ. Geol. v95 pp 1231-1257
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Rolley P J, Baxter J L 1990 - Marvel Loch Gold deposit: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne Mono 14, v1 pp 297-300
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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