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Fraser - Southern Cross Belt
Western Australia, WA, Australia
Main commodities: Au

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The Fraser gold deposit is located 1 km south of Southern Cross and 380 km east of Perth in the Southern Cross Domain, Youanmi Terrane of the Archaean Yilgarn Craton in Western Australia.

The deposit was discovered in 1888, and was the first underground gold mine in Western Australia. The leases were worked by various companies and syndicates, until declining returns forced closure in 1909. Like some of the other deposits of the Southern Cross Belt it was relatively large and relatively low grade affairs with little alluvial or bonanza style gold. The leases became the subject of much litigation and a number of failed attempts at mining until the gold price rose in the mid 1930s. Operations ceased again in 1939 and did not reopen until the early 1950s. Ore was mined from a newly discovered hanging wall lode, from a deeper part of the main deposit and from an open cut. However, by 1963, rising costs and the pegged gold price resulted in closure of the mine again. Limited tribute mining occurred in the 1970s, followed by a deep diamond drilling program which showed the lodes to persist to at least 700 m depth, which was then, in turn followed by extensive underground drilling. This resulted in a Proved + Probable Reserve of 0.942 Mt @ 4.28 g/t Au. In 1988 the three mines at Fraser, namely Central, Fraser's and Fraser's South were combined into one larger open pit and operations continued until being suspended in 1997. Subsequent testing to 2011 outlined an Indicated + Inferred Mineral Resource of 2.122 Mt @ 5.2 g/t Au containing 11 t of gold at a 2.5 g/t Au cut-off grade. This resource is located in the down-plunge and southern strike extensions to the mineralisation. It is uncertain if additional resources are available in the deeper extensions below the old underground workings tested in the program prior to 1988. Historic production to 1992 was 0.85 Mt @ 11.5 g/t Au for 9.8 t of gold from underground, and 2.2 Mt @ 3.2 g/t Au, for 16.5 t of gold from open pit mining.

For background information on the Southern Cross Belt, its geological setting and deposits see also the Transvaal, Yilgarn Star, Marvel Loch, Nevoria, Bounty and Copperhead records.

The host sequence of the Southern Cross greenstone belt comprises an Archaean mafic-ultramafic sequence of volcanic and volcaniclastic rocks metamorphosed to amphibolites with extensive banded iron formations (BIFs).   The base of the sequence is intruded by syntectonic granitoids and late stage pegmatite dykes, locally cutting the lodes. The sequence observed at Fraser comprises (after Dale and Thomas, 1990), from the base: i). younger granitic intrusion; ii). banded amphibolite; iii). ultramafic amphibolite; iv). banded amphibolite; v). banded iron formation or jaspilite; v). ultramafic amphibolite; vi). banded amphibolite.

Individual units within this sequence are lenticular and vary from a few to several hundred metres in thickness. The ultramafic amphibolite appears to be a metamorphosed pyroxenite which is generally without compositional banding, but locally contains a fine magnetic layering. Chemical analysis suggest these rocks have a komatiitic origin (Hallberg, 1976). The mafic amphibolite is banded, with layers of varying thickness composed of hornblende, plagioclase, some biotite, diopside and coarse hornblende. A massive variety is also present locally (Gee, 1982). Both are classified as tholeiitic (Hallberg, 1976). The BIF occurs as thin beds within the amphibolite and is composed of alternating bands of quartz, grunerite and minor magnetite (Dale and Thomas, 1990).

For more detail of the broader greenstone belt, see the Yilgarn Star record.

The ore at Fraser is present as quartz- and sulphide-rich lodes.   The quartz lodes (including 'Frasers', 'Sholls' and 'Battery') are developed in tremolite-hornblende-biotite schist with diopside, anthophyllite or cummingtonite and plagioclase on the selvages of the veins and minor carbonates (calcite dolomite and ankerite).   Gold is associated with sulphides, usually pyrrhotite, occassional pyrite, galena and sphalerite.   Frasers, with an average width of 6 m and length of 1000 m was the main producer with 0.4 Mt of underground ore @ 16 g/t Au. Sholls lode has a strike length of ~500 m and average width of 6 m, and is not known in the northern section of the mine

The sulphide-rich 'Greenstone' lodes are a brown foliated schist with layering defined by bands of alternating brown to bronze biotite, quartz, plagioclase and carbonate, with finely disseminated gold associated with sulphide (largely in the quartz bands).   Alteration includes diopside and carbonate. The sulphide lodes represent BIFs with magnetite almost totally altered to pyrrhotite. Scheelite is apparently present but mostly relatively minor, but is mentioned by Gibb-Maitland in 1919 stating scheelite is often associated with the ore where gold is richest. Some coarse gold is found, typically in these scheelite rich zones.

The lodes follow the Southern Cross trend of 325° and dip 60° W.

For Ore Reserve, Mineral Resource and production figures see the second paragraph that outlines the history of mining and exploration.

For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this decription was dated: 1990.    
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.

    Selected References
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
Dale G R, Thomas B D  1990 - Fraser Gold deposit, Southern Cross: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v1 pp 287-288
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.

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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