Marymia - Keillor 1, 2

Western Australia, WA, Australia

Main commodities: Au
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The Marymia Archaean gold deposit is located within the Plutonic greenstone belt of the Marymia Inlier, a discrete, fault bounded gneiss-greenstone-granitoid domain north of the Yilgarn Craton, surrounded by the sediments of the southern Capricorn Orogen, ~175 km NNW of Wiluna, ~40 km NE of the Plutonic deposit and >1000 km NNE of Perth in Western Australia (#Location: 25° 6' 38"S, 119° 44' 35"E).

The Marymia operation comprised a cluster of at least 8 small pits within a couple of square kilometres, e.g., the K1 pit is 170 x 150 m and 50 m deep. The K2 is of similar dimensions, but also has a 700 m underground decline. The K1 mine is the most northeastly of this group. The K2 mine is about 500 m to the SW. Resolute Resources Ltd and Titan Resources NL began exploration in the Marymia area in June 1988 with gold mineralisation first discovered in the Keillor Shear Zone, leading to the delineation of the Keillor 1 (K1) deposit in 1989. Resolute commenced mining at the K1 and K2 pits in 1992 which progressively closed between 1998 and 2002. Originally these deposits were mined as a separate operation, with its own processing plant, until the leases were taken over by companies controlling the much larger Plutonic mine.

The Marymia Inlier is a generally NE-SW elongated 200 x 50 km block that is more than 150 km northwest of the northern extremity of the Norseman-Wiluna greenstone belt, the most prolific gold producing zone within the Yilgarn Craton.   It differs from the greenstone belts of the Yilgarn in that it has been subjected to additional Palaeoproterozoic periods of deformation and metamorphism.   Late Archaean deformation (D1 & D2) was ductile to brittle-ductile, while the Palaeoproterozoic deformations (D3 to D7) were predominantly brittle, resulting in faulting, thrusting and shearing.

The Inlier comprises two meta-sediment and meta-volcanic dominated greenstone belts embraced by granitoids, some of which have been dated ay 2.72 Ga, and by gneiss complexes.   The western of the two is the 60x10 km Plutonic Well greenstone belt which hosts both the major Plutonic and the Marymia deposits, is deeply weathered (to 100 m), comprises interdigitated, deformed, metamorphosed and altered ultramafic, mafic and felsic igneous and sedimentary rocks which have been folded and faulted and intruded by at least two phases of felsic intermediate porphyries (2.69 to 2.60 Ga).   Within the Plutonic Well greenstone belt gold is preferentially hosted by meta-volcanics and meta-sediments, including banded iron formations.

The hosts at Marymia comprise rheologically and geochemically heterogenous and metamorphosed komattiitic, tholeiitic and sedimentary rocks, with lithological contacts invariably being structural.   The two orebodies that constitute the Marymia deposit (Keillor 1 and 2) are on the western limb of a NE plunging tight D2 antiform that is truncated by granite.   The deformation is complex.   The metamorphism is also complex, involving an early (2.66 to 2.63 Ga, D1-D2) amphibolite facies grade phase, followed by a later (1.72 Ma) pervasive retrograde event.

Mineralisation is associated with intense silicification and narrow, variably deformed, quartz-dominant, carbonate bearing veins parallel to the D1-D2 foliation.   Lodes are generally located within structurally favourable D2 sites in shear zones and folds, while individual veins are 1 to 3 cm thick, locally up to 50 cm, and are discontinuous both along strike and down dip (eg in the Keillor 1 pit, gold was extracted from a series of NE plunging, irregular, high grade shoots that were up to 2 m thick and only 10 to 20 m in strike length within highly boudinaged and folded amphibolite and BIF at the contact with ultramafic schist which is basically barren.   The ore shoots plunge subparallel to D2 fold axes, boudin elongation directions and D2 mineral lineations and in plan form two elongated, discontinuous ore zones, which in section are stratabound and closely follow fold geometry.   In Keillor 2 gold was mined from two main planar lodes within amphibolite.

Production from the mine opening in 1992 to 2002 was 1.4 Mt @ 4 g/t Au for 5.6 t Au.
Remaining reserves and resources in 2002 were of the order of: 15 tonnes of Au.

Re-assessed Mineral Resources in 2011 were (Dampier Gold Limited, ASX Release, 19 April, 2011):
  K1 open pit Measured + Indicated + Inferred Mineral Resource - 0.752 Mt @ 2.4 g/t Au for 1.80 t of gold;
  K2-K3 open pit Measured + Indicated + Inferred Mineral Resource - 0.489 Mt @ 3.2 g/t Au for 1.56 t of gold;   K2-K3 underground Measured + Indicated + Inferred Mineral Resource - 0.245 Mt @ 6.1 g/t Au for 1.49 t of gold.

For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 2002.    
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:
Vielreicher N M, Ridley J R, Groves D I  2002 - Marymia: an Archean, Amphibolite facies-hosted, orogenic lode-Gold deposit overprinted by Palaeoproterozoic orogenesis and base metal mineralisation, Western Australia: in    Mineralium Deposita   v37 pp 737-764

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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