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Ansil |
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Quebec, Canada |
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Cu Au Zn Ag
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Super Porphyry Cu and Au
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The Ansil volcanogenic massive sulphide deposit was located 15 km NNW of Rouyn-Noranda, in western Quebec, Canada.
The Ansil deposit is one of more than 20 VHMS deposits contained within the Central Volcanic Complex of the Blake River Group, part of the Archaean Abitibi Sub-province. The Central Volcanic Complex has been interpreted to represent a large shield volcano made up of five volcanic cycles. Of these, cycles three and four you are taken to the five a cauldron infill succession that is up to 3 km thick and 20 km wide and is known as the Noranda Cauldron. The VHMS deposits are either contained within this cauldron, or located near its margins. All five volcanic cycles our composed of bimodal volcanic successions. The first two of these, which are pre-cauldron, are tholeiitic, whilst the two cauldron cycles are transitional tholeiitic to calc-alkaline andesite to rhyolite. The cauldron cycles are intruded at their base by the sub-volcanic FLavrian intrusion, which is comagmatic with the overlying volcanic rocks. The early trondhjemitic phase of the intrusion has been dated at 2700.8 ±2.6 Ma while the post-cauldron rhyolites return ages of 2697.9 ±1.3 Ma (U-Pb zircon; Mortensen, 1993).
The Ansil deposit occurs on the contact of weakly metamorphosed footwall lobe-hyaloclasite rhyolite flows of the North-west Formation and hangingwall massive to pillowed andesites of the Rusty Ridge Formation. The deposit, which comprises a single, 350 m long x 150 m wide averaging ~6 m thick lens of massive pyrrhotite-chalcopyrite-sphalerite, that is concealed and strikes north-south, dipping at 50° east. The dominantly chlorite-quartz-pyrrhotite-chalcopyrite footwall zone extends for ~400 m below the massive sulphide lense, to where it is truncated by the FLavrian intrusion. In detail, it is composed of two Cu rich massive sulphide lenses up to 40 m thick connected by a thinner (<15 m thick) Cu-rich zone. Each lens is underlain by a distinct stringer zone, which merge below a lower lens. Zinc rich zones are peripheral to the copper bodies. A 0.3 Mt magnetite mass has been mapped in the immediate hanging wall and footwall of the Cu-Zn orebody and in a distinct stringer zone below the ore zone. Directly above the magnetite and within 50 m of the contact Cu grades generally exceed 20%.
The deposit is unusual, in that this late massive to semi-massive magnetite mass replaces ~17% of the massive pyrrhotite-chalcopyrite sulphide body. The magnetite is temporally associated with several calc-silicate mineral assemblages. These include coarse-grained andradite-hedenbergite and ferroactinolite-ilvaite within the massive sulphides in the immediate foot wall of the magnetite, while epidote-albite-pyrite assemablges overprint the stringer zone. Early phases of the Flavrian Pluton are also affected by cal-silicate alteraton.
Prior to mining, proved reserves for the deposit were: 1.58 Mt @ 7.2% Cu, 0.9% Zn, 26 g/t Ag, 1.6 g/t Au.
The deposit lies between 1180 and 1460 metres below surface.
See the main Noranda record for more background.
For more detail see 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.
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Selected References:
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Galley A G, Watkinson D H, Jonasson I R, Riverin G 1995 - The subsea-floor formation of volcanic-hosted massive Sulfide: evidence from the Ansil deposit, Rouyn-Noranda, Canada: in Econ. Geol. v 90 pp 2006-2017
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Galley, A.G., Jonasson, I.R. and Watkinson, D.H., 2000 - Magnetite-rich calc-silicate alteration in relation to synvolcanic intrusion at the Ansil volcanogenic massive sulfide deposit, Rouyn-Noranda, Quebec, Canada: in Mineralium Deposita v.35, pp. 619-637.
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Kerr D J, Gibson H L 1993 - A comparison of the Horne volcanogenic massive Sulfide deposit and intracauldron deposits of the mine sequence, Noranda, Quebec: in Econ. Geol. v88 pp 1419-1442
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Westendorp R W, Watkinson D H 1991 - Silicon-bearing zoned magnetite crystals and the evolution of hydrothermal fluids at the Ansil Cu-Zn mine, Rouyn-Noranda, Quebec: in Econ. Geol. v86 pp 1110-1114
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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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