Darlot, Centenary

Western Australia, WA, Australia

Main commodities: Au
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The Centenary orebody within the Darlot gold deposit is located some 680 km northeast of Perth and 75 km NNE of Leonora, in the Yandal greenstone belt of the Yilgarn Craton, Western Australia.

The Archaean Yandal greenstone belt comprises a lowermost banded iron formation, extensive basalt and dolerite sills, ultramafic rocks, intermediate to felsic volcanic rocks and variable clastic sedimentary rocks. It is cut dissected by early NNW trending shear zones which also form the greenstone belt margins, as well as north-south trends within the belt. Later brittle cross-faults are critical in gold localisation. Other significant gold deposits within the belt include Bronzewing, Jundee and Mount McClure.

The Centenary orebody at Darlot is hosted in a shallowly northeast-dipping sequence of tholeiitic basalt and felsic volcanic and epiclastic rocks, intruded by a differentiated, 600 m thick Archaean dolerite sill and by andesite, granodiorite, aplite and lamprophyre dykes. Displacement across major longitudinal faults resulted in repetition of the sequence and intrusives.

The host sequence has been strongly folded about open, upright, NNW plunging F2 folds, dissected by SSE-trending, transpressional, ductile D3 shear zones and east- to northeast dipping D4 brittle-ductile faults. Development of these structure which are moderately (~45°) west dipping reverse faults and steeply (>70°) dipping faults with variable strike trends, was the result of sub-horizontal east-west shortening and sub-vertical extension. This faulting was coincident with gold mineralisation. The sequence has been metamorphosed to greenschist facies to produce actinolite-albite-chlorite dominant mineral assemblages within the mafic rocks.

Gently dipping gold-related veins are localised within a 200 to 300 m wide tabular linkage zone between the three west dipping Thompson, Lords and Walters faults. These veins are subsidiary structures to the temporally, genetically and spatially related west dipping reverse and steeply dipping faults. The structurally complex mineralised linkage zone is a laterally stepping relay zone between the Thompson and Lords-Walters faults and has a pull-apart geometry.

Gold is predominantly localised within basalt and magnetite-bearing quartz dolerite, although lesser economic mineralisation occurs in felsic volcanic and intrusive rocks. The mineralisation is associated with 1 to 4 m thick quartz veins with strike and dip extents of tens to hundreds of metres within moderately-dipping reverse faults, and with sheeted arrays of thinner, shallowly southwest-dipping extensional quartz veins.

While some gold occurs within the veins, especially those in reverse faults, most is hosted in the proximal selvedge alteration zones immediately adjacent to the vein margins. This alteration is derived through the progressive destruction of metamorphic mineral assemblages by chlorite, calcite, ankerite, muscovite, pyrite, albite and quartz.

Gold mineralisation also exhibits a close spatial association with steeply-dipping, broadly northeast-striking, brittle-ductile to brittle D4 faults that crosscut, or are constrained between pairs of, moderately-dipping D4 reverse faults, and with suites of andesite, granodiorite, aplite and lamprophyre dykes that are themselves commonly emplaced along the steep faults.

At 31 Dec 2002 (Barrick website, 2008):
    The total reserve + production was 73 t (2.35 Moz) of Au
    Reserves were 8.366 Mt @ 4.92 g/t Au, for 41.2 t Au,
    Resources were 4.309 Mt @ 4.16 g/t Au for 17.9 t Au.

Resources and reserves at the end of 2007 (Barrick website, 2008) were:
    Proved + probable reserves - 5.321 Mt @ 4.0 g/t Au, for 21.3 t Au,
    Measured + indicated resources - 3.60 Mt @ 4.2 g/t Au, for 15.1 t Au.

The most recent source geological information used to prepare this summary was dated: 2007.    
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.

  References & Additional Information
   Selected References:
Kenworthy S and Hagemann S G,  2007 - Fault and vein relationships in a reverse fault system at the Centenary orebody (Darlot gold deposit), Western Australia: Implications for gold mineralisation: in    J. of Structural Geology   v29 pp 712-735
Phillips G N, Vearncombe J R, Eshuys E  1998 - Yandal Greenstone Belt, Western Australia: 12 million ounces of gold in the 1990 s: in    Mineralium Deposita   v33 pp 310-316

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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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