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MAX (Trout Lake) |
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British Columbia, Canada |
| Main commodities:
Mo
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Super Porphyry Cu and Au
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The MAX (previously Trout Lake) porphyry molybdenum deposit is located near the town of Trout Lake, 60 km southeast of Revelstoke, in southeastern British Columbia.
The MAX deposit is associated with the 79±3 Ma (K-Ar on biotite) Late Cretaceous Trout Lake stock, within the Omineca magmatic belt of the Canadian Cordillera. The cordillera is a collisional orogen that resulted from the accretion onto the western margin of the North American continent of at least two allochthonous terranes, the Intermontane and Insular terranes during the Middle Jurassic to mid-Cretaceous, and Early Cretaceous to Early Cenozoic, respectively. The Omineca magmatic belt is interpreted to have formed as a result of these collisions. Granitic batholiths representing three magmatic epochs occur within a 100 km radius around the MAX deposit: (i) The 173±5 Ma Middle Jurassic Kuskanax batholith, a clinopyroxene-amphibole-bearing alkaline quartz monzonite of volcanic arc affinity, is located ~5 km south of the Trout Lake stock, while the smaller 161.60±5 Ma Galena Bay stock, at the northern end of the Kuskanax batholith, has a similar volcanic arc chemical signature; (ii) Postkinematic mid-Cretaceous batholiths of the Bayone Plutonic Suite form a southeast-trending belt which passes ~25 km to the northeast of Trout Lake, and includes the dominantly biotite-hornblende granite of the Battle Range, Bugaboo and Horsethief Creek plutons, and the strongly peraluminous biotite and two-mica granites of the Fry Creek batholith, ~90 km southeast of MAX. The geochemistry of these granites is typical of within-plate or syn-collisional granites, which may have formed by crustal anatexis during collision-related crustal thickening; (iii) The Trout Lake stock and 79±2 Ma Whatshan batholith are the only known Late Cretaceous intrusion in the area. Their chemistry is typical of volcanic arc granitoids, implying a return to active subduction following mid-Cretaceous collisional tectonics and likely related to renewed convergence between Quesnellia and the North American continent (Lawley et al., 2010 and sources quoted therein).
The mineralised Trout Lake stock intrudes phyllite, siliceous phyllite, quartz metagrit, carbonate and mafic volcanic rocks of the Palaeozoic Lardeau Group, which have been subjected to several phases of metamorphism, faulting and northwesterly trending coaxial folding. The immediate host rocks belong to the Broadview Formation and comprise phyllite, schist and marble. The initial Middle Palaeozoic phase of folding and metamorphism is overprinted or obliterated by an intense second Middle Jurassic deformation and subsequent regional metamorphism. Regional metamorphic assemblages are in turn overprinted by contact metamorphic hornfels and diopside zones related to intrusion of the Trout Lake stocks that define the extent of the known molybdenite mineralisation.
Northwest-trending faulting cuts rocks of the Lardeau Group into ~600 m wide slices in the vicinity of the MAX deposit. The curvilinear, down-dip displaced Z fault between two of these northwest-trending structures appears to bound but also crosscuts the host pluton.
The Trout Lake stock at the MAX deposit consists of at least five distinct intrusive phases, although some may not be primary, but be the result of the influence of hydrothermal alteration. All of these intrusive phases crosscut or are crosscut by mineralised quartz veins, indicating coeval development of the magmatic and mineralis ing hydrothermal systems.
An elliptical zone (~1.2 x 2.0 km at surface) of strongly developed biotite hornfels envelopes the Trout Lake stock. This hornfels is characterised by its strong to massive biotite content, accompanied by secondary quartz, garnet and rare andalusite porphyroblasts. The biotite hornfels overprints regional metamorphism and is in turn overprinted by potassic, phyllic and propylitic alteration associated with the MAX hydrothermal system. Clinopyroxene±garnet±pyrrhotite±calcite±wollastonite±scheelite skarn is strongly developed along fault zones extending away from the Trout Lake stock and along granodiorite-marble contacts, and appears to be coeval with stock emplacement.
Both potassic and silicic alteration are most strongly developed within the high-grade molybdenite zone, and are characterised by biotite + K feldspar flooding, and by quartz flooding and increased quartz vein density respectively. Intense quartz veining commonly crosscuts potassically altered rocks, although, narrow potassic-altered dykes crosscut intense silicic alteration. The close relationship between silicic and potassic alteration and Mo mineralisation suggests all three events were coeval. However, while potassic alteration continues to depth, silicic alteration is limited to the apex of the high-grade ore zone.
Phyllic alteration assemblages of muscovite±pyrite±calcite are wide-spread and locally pervasive, and are typically most intensely developed in areas peripheral to the high-grade ore zone where coarse-grained muscovite replacement of biotite is accompanied by fine-grained muscovite replacement of feldspars. Zones of pervasive phyllic alteration are commonly accompanied by muscovite-molybdenite intergrowths. Similarly, phyllic alteration halos around mineralised quartz veins overprint potassic and silicic alteration assemblages.
Late propylitic alteration is widely distributed, characterised by chlorite±epidote±muscovite±calcite±titanite±pyrite.
Molybdenite is the only mineral of economic interest at MAX and is largely hosted within a well-developed quartz vein stockwork and several granodiorite dykes where it commonly occurs as fine- to coarse-grained disseminations and rosettes deposited along quartz±feldspar vein margins. A high-grade Mo zone is intimately associated with one of several lenticular granodiorite dykes extending from the much larger biotite granodiorite body at depth. Within this zone, molybdenite is present as coarse-grained disseminations within granodiorite, molybdenite-pyrrhotite intergrowths, and irregular stringers that are oriented parallel to the strike of the dykes and the regional foliation. High-grade Mo mineralisation is restricted to the upper portions of the host dyke with grade decreasing with depth. Rare chalcopyrite is locally observed associated with pyrrhotite in high-grade zones. Molybdenite is associated with each of the alteration assemblages except hornfels, occurring as biotite-molybdenite and muscovite-molybdenite intergrowths in the potassic and phyllic zones respectively. Minor molybdenite disseminations are also associated with late propylitic alteration halos along quartz vein margins, and rarely in peripheral W skarn and Pb-Zn-Ag veins. The highest Mo grades positively correlate with the intensity of silicic and potassic alteration. Sheeted quartz±K feldspar veins crosscut granodiorite-hosted Mo stringers, and are in turn crosscut by variably oriented mineralised quartz±K feldspar veins within the stockwork.
At a 0.1% MoS2 cutoff, the total NI 43-101 compliant mineral resources in 2010 (Roca Mines Inc. website, 2012) were:
Measured + indicated - 42.94 Mt @ 0.20% MoS2
Inferred - 8.9 Mt 0.16% MoS2.
The most recent source geological information used to prepare this decription was dated: 2010.
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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Lawley C J M, Richards J P, Anderson R G, Creaser R A and Heaman L M, 2010 - Geochronology and Geochemistry of the MAX Porphyry Mo Deposit and its Relationship to Pb-Zn-Ag Mineralization, Kootenay Arc, Southeastern British Columbia, Canada: in Econ. Geol. v.105 pp. 1113-1142
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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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