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Mines Gaspe - Copper Mountain, Needle Mountain |
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Quebec, Canada |
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Cu Mo
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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 Mines Gaspé - Copper Mountain porphyry-skarn and Needle Mountain skarn/manto copper-molybdenum deposits are located within the Chick Chock Mountains in the north central part of the Gaspé Peninsula, Quebec, Canada, within the municipality of Murdochville and 75 km WNW of the coastal town of Gaspé (#Location: 48° 58' 0"N, 65° 31' 8"W).
Forty-five years of exploration in the Gaspé area to 1952 led to the outlining of a reserve in excess of 66.0 Mt of ore, of which almost 50 Mt was in the nearby Needle Mountain zones at an estimated average grade of 1.44% Cu. Other significant discoveries between 1961 and 1971 resulted in the delineation of an additional 209 Mt of resources @ 0.40% Cu and 0.02% Mo at Copper Mountain. Mining began on the Needle Mountain skarns in 1955, and at Copper Mountain in 1968, with a short break from 1982 to 1984, and then continued until 1999, with the smelter ceasing operations until 2002. The mine was operated by Mines Gaspé, which was progressively owned by Noranda Inc., Xstrata Copper Canada and Glencore. When production ended, more than 141 Mt @ 0.9% Cu had been extracted from the Needle and Copper Mountain deposits from two open pits and eight underground mining areas.
The Gaspé Peninsula is part of the Canadian Appalachians that resulted from terrane accretion to the North American Craton during the Palaeozoic (e.g., Bourque et al., 1995). Broadly, the peninsular is bounded to the north, by the Mesoproterozoic Grenville Province, which is separated from the Taconian, peri-Laurentian Humber Terrane by a NE-SW trending structural contact below the St Lawrence River. The Humber Terrane is, in turn, structurally bounded to the SE by post-Taconian sedimentary rocks of the Gaspé Belt, correlated with the widespread Late Ordovician to Early Silurian (to Devonian) Matapedia-Badger forearc marine basin which overlies the Notre Dame Subzone of the Dunnage Terrane. The Gaspé area has been subjected to Taconian orogenesis, overprinted by both Salinic and late Acadian deformations. For detail of the regional tectonic framework and geologic setting, see the Northern Appalachian - Overview record (available soon).
The Peninsula is largely made up of Siluro-Devonian rocks that are divided into three major structural zones, from north to south of the: i). Connecticut Valley-Gaspé Synclinorium, ii). Aroostook-Percé Anticlinorium, and iii). Chaleurs Bay Synclinorium (Malo and Bourque 1993). The Connecticut Valley-Gaspé Synclinorium, in which the deposits are located, lies between the allochtonous Cambro-Ordovician rocks of the Taconian Orogen Humber Terrane to the NW and the Aroostook-Percé Anticlinorium to the SE. Its northern margin is defined by the Shick Shock-South fault, a dextral strike-slip structure (Malo and Bourque 1993), and by the Restigouche Fault to the south. The stratigraphic succession within the synclinorium comprises shallow marine clastic, carbonate and minor volcanic rocks assigned to the Chaleur Group. This group is overlain by the Upper Gaspé Limestone Group that is composed of shallow to deep-water shelf carbonates deposited on a stable platform (Bourque et al., 1995). This group is, in turn, overlain by the Gaspé Sandstones Group, representing a gradually shallowing basin in an intra-arc extensional setting, and is accompanied by increasing bimodal volcanic activity (Bellehumeur and Valiquette 1993). All of these rocks within the synclinorium are intruded by dykes and plutons spatially associated with Acadian faults.
The Gaspé skarn and porphyry deposits are located along the northern limb of the Connecticut Valley-Gaspé Synclinorium where east-trending and moderately dipping Lower Devonian calcareous sedimentary rocks are intruded by numerous multiphase syn- to post-orogenic Acadian porphyry sills, dykes and plugs of Devonian age (Allcock, 1982; Marcelissen, 2020). Both porphyry and skarn type mineralisation occurs within the zoned overlapping alteration aureoles of two of these, the Copper Brook and Porphyry Mountain intrusions. The deposits of the Gaspé Peninsula, i.e., Mines Gaspé, Sullipek, Mines Madeleine, Reboul, Patapédia and Ste-Marguerite, are all related to hydrothermal systems generated by these intrusions. Abundant felsic dykes and quartz-feldspar-porphyry intrusions are also found throughout the area, and the sedimentary country rocks have been subjected to extensive alteration/skarn halos. Re-activation of the Shick Shock South Fault resulted in a dense and complex network of faults, particularly N to NW Reidel structures, which were a major control on the mineralisation.
The stratigraphy of the immediate Mines Gaspé deposit area, spanning the Gaspé Limestone and lower Gaspé Sandstone groups, is as follows, from the base:
• Indian Point Formation, which is >600 m thick and comprises a sequence of very fine calcareous siltstones.
• Forillon Formation that is >550 m thick, which includes a lower 335 m of black calcareous mudstone, overlain by an ~50 m thick interval that includes a 6 m thick tuffaceous mudstone (Unit T3), another 30 m of black calcareous mudstone (Unit P5) and 10 m of limestone (Unit L2). These are followed by 165 m of black calcareous mudstone and tuff.
• Shiphead Formation which is ~175 m thick and comprises, 40 m of argillaceous limestone (Unit L1); 5 m of calcareous mudstone (Unit P3); 48 m of brown mudstone and tuff with limestone nodules (Unit T2); 6 m of calcareous mudstone (Unit P2); 42 m of mudstone with siliceous limestone concretions (Unit W1); 8 m of calcareous mudstone (Unit P1); 23 m of brown mudstone and tuff (Unit T1). The T1, T2 and T3 tuff units, which are generally unaltered, fairly homogenous, and beige brown in colour, are non-reactive to hydrochloric acid, distinctly hard, and often strongly magnetic. Unit W1 is generally unaltered with distinct 5 to 10 cm patches of whitish grey calcite which show a coarser effervescence reaction to HCl compared to the surrounding rock.
• Indian Cove Formation composed of a lower 120 m of calcareous/siliceous mudstone with limestone nodules (Unit Q1), overlain by 520 m of calcareous mudstone with limestone nodules. The mudstones/siltstones of the Indian Cove Formation are medium grey to black in colour with calcareous concretions that give it a distinctly less well-bedded appearance. Concretions occur as nodules which define a crackled and irregular bedding texture.
• York River Formation, which is >900 m thick and comprises well bedded siltstones with inter-bedded sandstones. The sandstone beds can range from well bedded to distorted, with a lensoid shaped. Thickness and frequency of lighter coloured sandstone varies significantly. Sediments are generally unaltered, and highly reactive to HCl.
Altered rocks in the sequence include: porcelanites (calc-silicates), skarns, hornfels and unaltered sedimentary rocks as well as porphyritic quartz-feldspar intrusive rocks, both altered and unaltered.
The altered sedimentary rocks surrounding the Mines Gaspé deposits include porcelanites that are grouped into three categories, in increasing order of alteration and/or metasomatism, as porcelanites, bleached porcelanites and diopsidic porcelanites (sometimes classified as a skarn). Porcelanites are intersected in almost all drill holes surrounding the deposits, with bleached porcelanites appearing to be increasing with depth. Some bleached porcellanite have a spotty diopsidic texture, generally found closer to the intrusions. Mineralisation is not widely associated with this type of rock.
Skarns contain the highest grades, but only represent a small volume of the total deposit. They are mostly encountered within the L1 and L2 units (marbles) but also occur within P3, P4 and P5 units. The most common skarns contain 40 to 60% garnet with lesser amounts of clinopyroxene (diopside). The L units are generally heavily altered and mineralised.
The Copper Mountain porphyry Cu-Mo deposit comprised a 700 m diameter hollow cylinder of mineralisation in the metasomatised Indian Cove sediments that surrounded a low grade intrusive porphyry core of the Copper Brook rhyodacite porphyry plug. The Porphyry Mountain intrusion and a sill in the Copper Mountain pit have been dated at 378.80 ±0.57 Ma and 377.60 ±0.62 Ma. Epidote U-Pb ages at Mines Gaspé overlap within error from 367 to 352 Ma, but is ~10 m.y. younger than the Porphyry Mountain intrusion (Marcelissen 2020). The Copper Mountain porphyry deposit is surrounded by a concentric, annular, 100 to 150 metres wide Cu skarn rich zone in carbonate hosts that contains >1% Cu. Within the main porphyry deposit, chalcopyrite is the major hypogene sulphide, occurring as fracture fill in veins where it is associated with calcite and/or quartz, and as a replacement or disseminated sulphides in skarn and quartz-feldspar porphyry. It occurs as sub-hedral to anhedral crystals or as interlocking irregular blebs. Chalcopyrite grain can be generalised into two size fractions: i). coarse, 0.5 to 10.0 mm, which is characteristic of the vein materiel; and ii). fine, 0.1 to 0.9 mm, where disseminated. Fine grains of chalcopyrite also occur as inclusions in other minerals. Other copper minerals present in the hypogene sulphide zone are bornite and tetrahedrite.
Molybdenite is sparsely distributed throughout the entire Copper Mountain Deposit, generally occurring as subsidiary vein material or as a disseminated sulphide. Concentrations of molybdenite were more abundant in the centre of the deposit, mostly in quartz veins. There appears to be a spatial relationship between molybdenite mineralisation, and the density of quartz veining and kaolinization of the quartz-feldspar porphyry. The molybdenite is generally tabular or occurs as rosettes, and is also found as inclusions in chalcopyrite and sphalerite. Pyrite is the most abundant sulphide, widely distributed, and extends south almost to the needle Mountain Deposits. Within the orebody, the pyrite is always associated with the copper sulphides and the pyrite-chalcopyrite ratio is approximately 1:3. Pyrrhotite is found in the eastern portion of the Copper Mountain orebody, usually mixed with pyrite. Other minerals that occur within the deposit are galena, sphalerite, magnetite, arsenopyrite and scheelite, all in minor amounts and with a fairly even distribution.
An up to 150 m thick leached cap overlies much of the sulphide orebody. The extent and shape of the zone of oxidation was dependent upon the pyrite and chalcopyrite content, intensity of fracturing and a varying water table. The oxidation phase produced a varying assemblage of limonite, malachite, chrysocolla, azurite, brochantite and copper hydroxide. The contact between the oxide and sulphides zones is generally well defined, although a mixed sulphide-oxide zone does occur in some areas. In the western part of the deposit, a thin, poorly defined zone of secondary enrichment between the oxide and sulphide zones contains chalcocite, digenite and covellite.
The concordant, manto-like Needle Mountain skarns were hosted by altered lower Devonian calcareous sediments within the zoned aureole of the Upper Devonian to Carboniferous Copper Brook rhyodacite porphyry plug. The orebodies in the metamorphosed sediments at Needle Mountain occur at distinct stratigraphic levels, and are named from the top down, the A, B, C and E zones. These correspond to Unit Q1 of the Indian Cove Formation; Unit W1 and L1 of the Shiphead Formation; and Units T3 to L2 of the Forillon Formation.
Deposit sizes estimated in 1974 were:
Copper Mountain - 242 Mt @ 0.4% Cu + 32 Mt of oxidised ore @ 0.45% Cu,
Needle Mountain & Needle East - 47 Mt @ 1.35% Cu (underground),
Needle East Pit - 14.5 Mt @ 0.7% Cu.
Production 1955-1999 - 141 Mt @ 0.9% Cu (Banville, R., 2017).
This summary is largely drawn from: Banville, R., 2017 - Needle and Copper Mountains, Mines Gaspé Stockpiles and Surficial Rock Sampling; Prepared for Glencore Canada, 241p.
The most recent source geological information used to prepare this decription was dated: 2017.
Record last updated: 21/6/2020
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.
Gaspe
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Allcock J B 1982 - Skarn and porphyry copper mineralisation at Mines Gaspe, Murdochville, Quebec: in Econ. Geol. v77 pp 971-999
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Shelton K L 1983 - Composition and origin of ore-forming fluids in a carbonate-hosted porphyry copper and skarn deposit: a fluid inclusion and stable isotope study of Mines Gaspe, Quebec: in Econ. Geol. v78 pp 387-421
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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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