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Millenbach |
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Quebec, Canada |
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Cu Zn Au Ag
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Millenbach Archaean volcanic hosted massive sulphide deposit is located 8 km north of Noranda in Quebec, Canada, and was operated by the Lake Dufault Division of Falconbridge Copper Ltd.
The deposit is hosted within a relatively undeformed sequence of Archaean andesites, dacites and rhyolites of the Blake River Group. See the main Noranda record for the setting of the Blake River Group. Mineralisation at Millenbach occurs in more than seven mushroom shaped orebodies that are distributed over and internal to these volcanics and are between 750 and 1200 m below surface.
The main orebody is associated with a sulphidic bedded tuff horizon deposited near the crest of, and on the flanks of, a porphyritic rhyolite dome. Satellite orebodies, some of which are split by younger intrusions, occur at slightly younger and slightly older stratigraphic positions. Massive sulphides at the centres of individual lenses tend to be brecciated and chalcopyrite-pyrrhotite rich, whilst pyrite-sphalerite predominates at the margins. These lenses pass downward into stringer sulphides in the underlying stem of the mushroom that are mainly chalcopyrite-pyrrhotite within a weak pyrite-sphalerite halo.
The stratigraphy in the deposit area is a follows, from the base:
Amulet Rhyolite, which is >900 m thick and composed of massive to porphyritic andesite to rhyolitic flows and flow breccias;
C Tuff, which is 0 to 0.3 m, averaging 0.2 m thick, composed of pyrite-rich tuffaceous chert;
Millenbach Andesite, which is 0 to 60 m, averaging 12 m thick and composed of massive to pillowed andesite;
Main Contact Tuff, which is 0 to 6 m, averaging 0.6 m thick and composed finely laminated tuffaceous chert, which laterally seperates a lower set of massive sulphide lenses distributed along the same unit;
Lower QFP, which is 0 to 90 m, averaging 45 m thick and composed of quartz-feldspar porphyritic rhyolite and underlies the main ore lens;
Inter QFP Tuff, which is 0 to 45 m, averaging 0.15 m thick and composed finely laminated tuffaceous chert with volcaniclastic clasts, and is at the same stratigraphic position of the main massive sulphide lens. Where the Lower QFP dome pinches out, this tuff merges with the underlying Main Contact Tuff;
Upper QFP, which is 0 to 90 m, averaging 45 m thick and is also composed of quartz-feldspar porphyritic rhyolite. It tends to be thickest over the thinnest Lower QFP and vice versa;
Top Contact Tuff, which is 0 to 12 m, averaging 0.08 m thick and composed finely laminated tuffaceous chert;
Amulet Andesite, which is >600 m thick and composed pillowed to massive andesite and is unaltered;
Post-ore rhyolite and microdiorite dykes intrude all rock types.
The host rocks and mineralisation have been metamorphosed to hornblende hornfels assemblages, whilst the alteration associated with the stockwork are only found as greenschist facies assemblages, which has significantly affected the bulk composition of the rocks. It can be shown that the alteration zones associated with the stringer mineralisation had a chlorite core which graded laterally and vertically into a sericite-rich outer zone and finally into unaltered rocks. The most characteristic features of the altered rocks are an increase in Fe and Mg, and decrease of Ca and Na, relative to fresh rocks. K and AI have generally been added at the margins and leached at the cores of these alteration zones, which crosscut all of the underlying stratigraphy, down into the Amulate Rhyolite.
The deposit originally contained around 3.56 Mt @ 3.46% Cu, 4.33% Zn, 56 g/t Ag and 0.89 g/t Au.
For detail see the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 1980.
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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Gibson H L, Watkinson D H, Comba C D 1983 - Silicification: hydrothermal alteration in an Archean geothermal system within the Amulet Ryolite Formation, Noranda, Quebec: in Econ. Geol. v78 pp 954-971
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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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Knuckey, M.J., 1975 - Geology of the Millenbach copper-zinc orebody, Noranda Distraicy, Quebec (Abstract only): in Econ. Geol. v.70, p. 247,
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Riverin G, Hodgson C J 1980 - Wall-rock alteration at the Millenbach Cu-Zn mine, Noranda, Quebec: in Econ. Geol. v75 pp 424-444
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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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