Quebec, Canada

Main commodities: Au Cu
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The Troilus gold deposit is located some 150 km north of the town of Chibougamau and 520 km NE of Val d'Or in central Quebec, Canada (#Location: 51° 0' 41"N, 74° 27' 59"W).

The deposit is hosted by the Frotet-Troilus greenstone belt, to the north of the main Abitibi Greenstone Belt in the Superior Province, and has been interpreted to represent an approximately 2714 Ma porphyry Au-Cu system in relatively low-strain tectonic domain.

The succession within the Frotet-Troilus greenstone belt. comprises, from the base:
Odon Formation - variolitic and pillowed basaltic komatiites to high Mg tholeiitic basalts;
Lac Allonge Formation (to the NW) - a series of ferro-tholeiitic lavas, comprising lower basalts, overlain by a discontinuous band of calc-alkaline intermediate to felsic tuffs, followed by an upper unit of ferro-tholeiitic mafic to intermediate tuffs and flows - Frotet Formation (to the SE) - a thick sequence of fine to coarse intermediate pyroclastics, mainly lapilli and crystal tuffs, with minor fine sediments near the top;
Crochet Formation above an angular unconformity - a thin but laterally extensive unit of komatiitic pillowed basalts and massive flows;
Testard Formation- calc-alkaline felsic ash and lapilli tuffs with fine sediments towards the top;
Mesiere Formation - a thick sequence of tholeiitic pillow basalts with narrow interbedded intermediate to felsic volcaniclastics and common gabbroic sills;
Habitation Formation - a complex mix of fine and well laminated calc-alkaline tuffs, crystal tuffs, cherts and epiclastics with minor sulphides.

The Troilus deposit is localised in the upper sections of the Lac Allonge Formation on the NW limb of the regional synform in which the greenstone belt is preserved. In the vicinity of the deposit, the host ferro-tholeiitic mafic to intermediate tuffs and flows have been intruded by post tilting, syn to late tectonic felsite and feldspar porphyry dykes and sills. The bulk of the Au-Cu mineralisation is hosted within a zone of in situ breccia along the contact between the intermediate and mafic volcanics. Mineralisation consists of 2 to 3% sulphides, locally up to 7%, as disseminations, tiny veinlets and narrow semi-massive seams of chalcopyrite, pyrite and pyrrhotite with rare sphalerite. Gold is present as electrum, with minor native metal.

The deposit exhibits a distinct zonation, from a core of intense biotite alteration, centred on a large felsic dyke in the immediate footwall of the deposit, grading outwards with a decrease in biotite and an increase in plagioclase, epidote and calcite. Vertically the alteration is asymmetric, with potassic alteration in the footwall, grading up into sodic in the hangingwall. The potassic core is characterised by a chalcopyrite-pyrrhotite rich assemblage, grading up into a pyrite rich shell with more gold in the sodic sections of the system. The zone of brecciation, which has both Na and K enrichment, is both Au and Cu rich. The mineralisation occurs as a series of NE trending anastomosing lenses from 10 to 100 m thick over a combined strike length of 1 km, and continues to a depth of at least 500 m. With increasing depth, the individual lenses coalesce to form a single zone some 40 m thick, with a 55°NW dip.

Construction of the pit and plant commenced in 1994 and was in full production by early 1997. The Troilus open pit mine and mill had an annual throughput of 5.4 Mt. In 2000 it produced 3.8 t (0.1225 Moz) Au.

The initial geological resource was 60 Mt of ore, later more accurately determined to be 49.6 Mt @ 1.38 g/t Au, 0.12% Cu, 1.23 g/t Ag.
In 2000 the proven + probable ore reserves were stated at 30.5 Mt @ 1.04 g/t Au, 0.1% Cu.

Mining in the main open pit was completed in April 2009, with processing of ore from the low-grade stockpile continuing into 2010.

The most recent source geological information used to prepare this summary was dated: 2005.    
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:
Fraser R J  1993 - The Lac Troilus Gold-Copper deposit, northwestern Quebec: a possible Archean Porphyry system: in    Econ. Geol.   v88 pp 1685-1699
Goodman S, Williams-Jones A E and Carles P  2005 - Structural Controls on the Archean Troilus Gold-Copper Deposit, Quebec, Canada: in    Econ. Geol.   v100 pp 577-582

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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