Geological characteristics of high-level subvolcanic porphyritic intrusions associated with the Wolverine Zn-Pb-Cu volcanic-hosted massive sulphide deposit, Finlayson Lake District, Yukon, Canada (original) (raw)
Related papers
Economic Geology, 2008
Porphyritic rhyolite sills form an important component of the footwall of the Wolverine volcanogenic massive sulfide (VMS) deposit, Yukon, Canada, and occur proximal to mineralization in the immediate deposit area (Wolverine/Lynx zone) and at similar stratigraphic levels along strike (Fisher, Puck, and Sable zones). Porphyritic rhyolites are of two types: an older quartz-feldspar porphyritic (QFP) rhyolite suite; and a younger feldspar porphyritic (FP) suite. Both the QFP and FP suites of intrusions are semiconcordant, suggesting a silllike morphology, and are altered and crosscut by veinlet mineralization, suggesting that they are pre-to synmineralization. The margins of QFP suite of intrusions contain minor xenoliths of surrounding shales and poorly developed chilled margins suggesting emplacement into partially consolidated sedimentary rocks, whereas the FP suite of intrusions shows well-developed chilled margins indicative of emplacement into fully solidified sedimentary rock. These features suggest that the QFP suite of intrusions represents an older phase of rhyolitic magmatism, whereas the FP suite represents a younger event. This is supported by U-Pb zircon ages, which indicate a 352.4 ± 1.5 Ma emplacement age for the FP suite and a ~347 to 346 Ma emplacement for the FP suite (two ages at 347.8 ± 1.3 and 346.0 ± 2.2 Ma). Both suites of porphyries have inherited Proterozoic zircon and have ratios of La/SmUCN~1 and Nb/ThUCN~1 (UCN -upper continental crust normalized), indicating derivation from and/or extensive interaction with ancient upper continental crustal materials. The FP suite, however, has elevated high field strength element (HFSE) and rare earth element (REE) contents, high zircon saturation temperatures, and higher Nb/Ta ratios and lower Ti/Sc ratios than the QFP suite. These features are interpreted to reflect that the FP suite of magmas was hotter (>900°C) melts with a greater mantle component in their genesis. Both suites, however, are interpreted to have formed due to basaltic upwelling, crustal melting, and crust-mantle mixing during ensialic back-arc basin activity. The presence of mantle heat within the Wolverine basin from ~352 to ~347 to 346 Ma, a minimum of 5 m.y., suggests that sustained mantle heat flow was critical to the genesis of the Wolverine porphyries. It is also suggested that this sustained mantle heat was responsible for the Wolverine hydrothermal system and that upwelling mantle may be essential in providing the heat to drive hydrothermal systems even in continental margin-type VMS environments (e.g., Bathurst, Iberian pyrite belt).
2001
The Wolverine polymetallic volcanic-hosted massive sulphide deposit occurs in a highly deformed but coherent stratigraphic succession of early Mississippian to early Permian metavolcanic and metasedimentary rocks of the Yukon-Tanana Terrane. The deposit is part of the emerging Finlayson Lake volcanic-hosted massive sulphide district and contains a geological resource of 6,237,000 tonnes grading 12.66% zinc, 1.33% copper, 1.55% lead, 370.9 g/t silver and 1.76 g/t gold. Local stratigraphy consists of four major units including (from oldest to youngest): (1) quartz-and feldspar-phyric volcaniclastic, carbonaceous sedimentary and porphyritic intrusive rocks; (2) interbedded argillite, aphyric rhyolite and magnetite-carbonate-pyrite exhalite; (3) fragmental rhyolite; and (4) interbedded carbonaceous argillite, greywacke, basalt and rhyolite. The mineralization consists of pyrite and sphalerite, with lesser pyrrhotite, chalcopyrite, galena, tetrahedrite-tennantite and arsenopyrite. Mineralization occurs as massive stratiform, massive replacement and sulphide stringer veins. Sulphides are typically massive, fine-grained, layered and locally brecciated. Styles of hydrothermal alteration identified in the host rocks include proximal silicification and more distal chloritization, sericitization and, in places, carbonatization. Future research will be focussed on identifying the salient physico-chemical controls on the mineralization process and their implications for volcanic-hosted massive sulphide exploration in the district and elsewhere. RÉSUMÉ Le gisement de sulfure massif volcanogène polymétallique de Wolverine est logé dans une succession stratigraphique fortement déformée mais concordante, composée de roches méta-volcaniques et méta-sédimentaires du terrane de Yukon-Tanana, d'âge Mississippien précoce à Permien précoce. Ce gisement est situé dans le district minier émergent de Finlayson Lake; il contient une ressource géologique de 6 237 000 tonnes de minerai ayant une teneur de 12,66% de zinc, 1,33% de cuivre, 1,55% de plomb, 370,9 g/t d'argent et 1,76 g/t d'or. La stratigraphie locale comprend quatre unités majeures (en ordre d'âge décroissant) : (1) roches volcaniclastiques à porphyres de quartz et feldspaths, roches sédimentaires carbonées et intrusions porphyritiques; (2) interstratifications d'argilite, de rhyolite aphanitique et de roches exhalatives à magnétite, carbonate et pyrite; (3) rhyolite bréchique; et (4) interstratifications d'argilite carboné, de grauwacke, de basalte et de rhyolite. Le minerai se compose de pyrite et de sphalérite, et de quantités moindres de pyrrhotite, chalcopyrite, galène, tetrahédrite-tennantite, et arsénopyrite. La minéralisation est présente sous forme de veines massives stratiformes, de remplacements massifs, et de veinules de sulfures. Les sulfures sont généralement massifs, à grains fins, laminés et, localement, bréchiques. Les types d'altération hydrothermale reconnus dans les roches encaissantes comprennent une silicification proximale, une chloritisation et sericitisation plus distales, et une carbonatisation localisée. Les études à venir seront concentrées sur l'identification des principaux facteurs physicochimiques contrôllant les processus de minéralisation et leurs influence sur l'exploration pour des sulfures massifs volcanogènes dans cette région et ailleurs.
Yukon Exploration and Geology 2000, 2000
The Wolverine polymetallic volcanic-hosted massive sulphide deposit occurs in a highly deformed but coherent stratigraphic succession of early Mississippian to early Permian metavolcanic and metasedimentary rocks of the Yukon-Tanana Terrane. The deposit is part of the emerging Finlayson Lake volcanic-hosted massive sulphide district and contains a geological resource of 6,237,000 tonnes grading 12.66% zinc, 1.33% copper, 1.55% lead, 370.9 g/t silver and 1.76 g/t gold. Local stratigraphy consists of four major units including (from oldest to youngest): (1) quartz- and feldspar-phyric volcaniclastic, carbonaceous sedimentary and porphyritic intrusive rocks; (2) interbedded argillite, aphyric rhyolite and magnetite-carbonate-pyrite exhalite; (3) fragmental rhyolite; and (4) interbedded carbonaceous argillite, greywacke, basalt and rhyolite. The mineralization consists of pyrite and sphalerite, with lesser pyrrhotite, chalcopyrite, galena, tetrahedrite-tennantite and arsenopyrite. Mineralization occurs as massive stratiform, massive replacement and sulphide stringer veins. Sulphides are typically massive, fine-grained, layered and locally brecciated. Styles of hydrothermal alteration identified in the host rocks include proximal silicification and more distal chloritization, sericitization and, in places, carbonatization. Future research will be focussed on identifying the salient physico-chemical controls on the mineralization process and their implications for volcanic-hosted massive sulphide exploration in the district and elsewhere.
Mineralium Deposita, 2000
Magnetite-rich calc-silicate alteration in relation to synvolcanic intrusion at the Ansil volcanogenic massive sul®de deposit, Abstract The Ansil Cu±Au volcanogenic massive sul-®de deposit is located within an Archean-age cauldron in®ll sequence that contains the well-known Noranda base metal mining district. The deposit is unusual in that 17% of the massive pyrrhotite±chalcopyrite orebody is replaced by semi-massive to massive magnetite. Temporally associated with the magnetite formation are several calc-silicate mineral assemblages within the massive sul®de lens and the underlying sul®de stockwork vein system. Coarse-grained andradite±hedenbergite and ferroactinolite±ilvaite alteration facies formed in the immediate footwall to the massive mag-netite±sul®de lens, whereas an epidote±albite±pyrite-rich mineral assemblage overprints the margins of the chlorite-rich stockwork zone. The epidote-rich facies is in turn overprinted by a retrograde chlorite±magnetite± calcite mineral assemblage, and the andradite±hedenbergite is overprinted ®rst by ferroactinolite±ilvaite, followed by semi-massive to massive magnetite. The footwall sul®de-and magnetite-rich alteration facies are truncated by a late phase of the Flavrian synvolcanic tonalite±trondhjemite complex. Early phases of this intrusive complex are aected to varying degrees by calcsilicate-rich mineral assemblages that are commonly con®ned to miarolitic cavities, pipe vesicles and veins. The vein trends parallel the orientation of synvolcanic faults that controlled volcanism and hydrothermal¯uid migration in the overlying cauldron succession. The magnetite-rich calc-silicate alteration facies are compositionally similar to those of volcanic-hosted Ca±Fe-rich skarn systems typical of oceanic arc terranes. Tonalite± trondhjemite phases of the Flavrian complex intruded to within 400 m of the base of the earlier-formed Ansil deposit. The low-Al trondhjemites generated relatively oxidized, acidic, Ca±Fe-rich magmatic±hydrothermal uids either through interaction with convecting seawater, or by assimilation of previously altered rocks. These¯uids migrated upsection along synvolcanic faults that controlled the formation of the original volcanogenic massive sul®de deposit. This is one of the few documented examples of intense metasomatism of a VMS orebody by magmatic±hydrothermal¯uids exsolved from a relatively primitive composite sub-sea¯oor intrusion.
Volcanic-hosted massive sulphide deposits of the Finlayson Lake District, Yukon
Mineral Deposits of Canada, 2007
The Finlayson Lake District (FLD) is a crescent-shaped 300 km long, and 50 km wide area within southeastern Yukon Territory. It comprises part of the Yukon-Tanana Terrane, one of the innermost terranes of the Canadian Cordillera that underlies much of the central Yukon and parts of Alaska and British Columbia, and part of the Slide Mountain Terrane. The FLD is consists of several fault- and unconformity-bound groups and formations of early Mississippian to early Permian metamorphosed plutonic, volcanic, and sedimentary rocks. The rocks were formed in a variety of tectonic settings, including rifted frontal arc, continental back-arc, and oceanic back-arc that range in age from 365 to 275 Ma.The FLD hosts numerous base metal sulphide deposits that collectively contain in excess of 30 Mt. The Fyre Lake Cu-Co is a Besshi-type deposit containing 15.4 Mt grading 1.2% Cu, 0.8% Co, and 0.46 g/t Au that occurs at the transition from mafic volcanic rocks to overlying turbiditic sedimentary rocks in a fore-arc setting. The Kudz Ze Kayah Zn-Pb-Cu and GP4F Zn-Pb Kuroko-type deposits are hosted by felsic volcanic and volcaniclastic rocks in the immediate footwall whereas the Wolverine Zn-Pb-Cu deposit is hosted by graphitic shales and felsic volcanic and volcaniclastic rocks and is best classified as a volcanic-sediment-hosted massive sulphide (VSHMS) deposit. These latter three deposits are thought to have formed in ensialic back-arc rift or back-arc basin environments. The deposits have strongly hydrothermally altered rocks in the stratigraphic footwalls, with alteration styles varying from chlorite (Fyre Lake, Kudz Ze Kayah, Wolverine, Ice), sericite (Kudz Ze Kayah, GP4F, Wolverine), silica/quartz (Kudz Ze Kayah, Wolverine), carbonate (Wolverine) and albite (Kudz Ze Kayah). Feeder zones/stringer veins are present at the Fyre Lake, Kudz Ze Kayah, Wolverine and Ice deposits. Hanging-wall alteration is present at Fyre Lake (weak chlorite) and Wolverine (weak sericite). Wolverine has a laterally extensive (>10 km strike length) chemical exhalative sedimentary iron formation horizon in the hanging wall that is not present at Kudz Ze Kayah or GP4F. Much of the Kudz Ze Kayah deposit likely formed as a mound on the seafloor, as did at least some of the Wolverine deposit. However, subsurface replacement was important at Wolverine, and likely was entirely responsible for the formation of GP4F. The Kudz Ze Kayah deposit contains an inferred geological resource of 13 Mt at 5.55% Zn, 1.00% Cu, 1.30% Pb, 125 g/t Ag, and 1.2 g/t Au. GP4F contains an inferred resource of 1.5 Mt grading 6.4% Zn, 3.10% Pb, 0.10% Cu, 89.7 g/t Ag, and 2.0 g/t Au. Wolverine has measured and indicated reserves of 4.51 Mt grading 12.04% Zn, 1.15% Cu, 1.57% Pb, 351.5 g/t Ag, and 1.68 g/t Au; with an additional inferred resource of 1.69 Mt grading 12.16% Zn, 1.23% Cu, 1.74% Pb, 385.1 g/t Ag, and 1.71 g/t Au. The Ice Cyprus-type deposit is hosted by mafic volcanic rocks at the transition from underlying brecciated pillow basalt to overlying massive basalt and is thought to have formed in a back-arc basin/ocean basin setting. The geological resource at Ice is 4.56 Mt grading 1.48% Cu; some intervals contain about 1% Zn, but a Zn resource has not been calculated. There are numerous other showings and prospects that require additional exploration work. The relatively nascent level of exploration in the FLD suggests that prospecting, coupled with traditionally successful exploration methods, such as surficial geochemistry, and airborne and ground geophysics (magnetics, EM) focused on the prospective rock units, are likely to result in new discoveries in the coming years.
Economic Geology, 2001
The Finlayson Lake volcanic-hosted massive sulfide (VHMS) district represents one of Canada's most recent VHMS discovery regions with ~34 million metric tons (Mt) of massive sulfide mineralization found since the mid 1990s. Felsic volcanic rocks are associated with three units: the Fire Lake unit, the Kudz Ze Kayah unit, and the Wolverine succession. Significant accumulations of polymetallic felsic VHMS deposits (Kudz Ze Kayah, GP4F, and Wolverine) have only been discovered in the Kudz Ze Kayah unit and Wolverine succession to date. In the hanging wall of the Money Creek thrust, felsic volcanic and high-level intrusive rocks in the Fire Lake unit have calc-alkalic and tholeiitic affinities with low high field strength element (HFSE) contents and intermediate Zr/Sc (9.4-43.4) and Zr/TiO 2 (254-864) ratios. These rocks are interlayered with mafic rocks with arc geochemical signatures, to date devoid of significant VHMS mineralization, and represent bimodal magmatism within an evolving Devonian-Mississippian continental-arc system. The Kudz Ze Kayah unit in the footwall of the Money Creek thrust stratigraphically overlies the Fire Lake unit and consists of felsic volcanic rocks with high HFSE contents, within-plate (A-type) signatures, and high Zr/Sc (15.3-190.3) and Zr/TiO 2 (630-2,185) ratios. The Kudz Ze Kayah unit felsic rocks are crosscut and overlain by alkalic mafic rocks, are associated with abundant carbonaceous sedimentary rocks, and represent magmatism within a Devonian-Mississippian ensialic back-arc rift-basin environment. The Wolverine succession unconformably overlies the Kudz Ze Kayah unit. Felsic rocks below the Wolverine deposit have geochemical attributes similar to the Kudz Ze Kayah unit with high HFSE contents, within-plate (A-type) signatures, and high Zr/Sc (29.9-84.2) and Zr/TiO 2 (391-1,220) ratios. In contrast, aphyric rhyolite flows in the hanging wall of the deposit have much lower HFSE contents and the lowest Zr/Sc (3.5-27.7) and Zr/TiO 2 (181-591) ratios in the district. All the felsic rocks of the Wolverine succession are interlayered with abundant carbonaceous sedimentary rocks and are overlain by midocean ridge basalt (MORB)-like basaltic rocks. The Wolverine succession is interpreted to have formed within an Early Mississippian ensialic back-arc basin environment that eventually evolved to sea-floor spreading. The variation in the HFSE budgets of the felsic rocks of the Finlayson Lake district likely reflects variations in the source and/or temperature of crustal melting. In particular, felsic rocks of the Fire Lake unit have higher Nb/Ta and lower Ti/Sc ratios than other volcanic rocks in the district, suggesting possible derivation from mafic crustal sources and/or lower crustal fusion temperatures. The Kudz Ze Kayah unit and footwall rocks to the Wolverine deposit are inferred to have formed from high-temperature partial melting of continental crust. The hanging-wall aphyric rhyolites from the Wolverine deposit may have formed from either lower temperature continental crustal melting or may have been derived from the mixing of HFSE-depleted N-MORB mafic magmas and evolved continental crust. Polymetallic felsic volcanic-associated, VHMS deposits within the Finlayson Lake district are preferentially associated with HFSE-enriched felsic rocks with high Zr/Sc (15.3-190.3) and Zr/TiO 2 (391-2,105) ratios. The HFSE and rare earth element (REE) systematics of VHMS-associated felsic rocks of the Finlayson Lake district are different from prospective felsic rocks from Archean VHMS environments in the Superior province and are displaced toward higher Zr/Y and La/Yb n ratios. Their HFSE and REE systematics are similar to many Phanerozoic VHMS environments, in particular those at least partially to fully underlain by evolved continental crust. The geochemical differences between the felsic rocks of the Finlayson Lake district and those from Archean VHMS environments most likely reflect differences in the substrates from which the felsic rocks were derived (e.g., evolved versus juvenile).
Canadian Journal of Earth Sciences, 2016
The Boundary volcanogenic massive sulphide deposit (0.50 Mt at 3.5% Cu, 4.0% Zn, and 1.0% Pb, 34 g/t Ag) is hosted by the Tally Pond group (ϳ510 Ma), Victoria Lake supergroup, central Newfoundland, Canada, and represents a subseafloor replacement-style massive sulphide deposit. The deposit is hosted by rhyolitic lapilli tuff of the Bindons Pond formation. The rhyolites have immobile element signatures consistent with the formation of felsic rocks through the melting of juvenile-weakly evolved crust within an extensional rift environment (rifted peri-continental arc). The host rocks of the Boundary deposit contain elevated alteration indices, including high Ba/Sr, Hg/Na 2 O, chlorite-carbonate-pyrite index, and Ishikawa alteration index values. The mobile element geochemistry effectively differentiates between three distinct hydrothermal alteration styles: intense chlorite, chlorite-sericite, and quartz-sericite. Intense chlorite alteration exhibits mass gains in MgO and Cu and depletions in K 2 O and Ba. Chlorite-sericite alteration contains variable gains and losses of SiO 2 , K 2 O, Ba, MgO, and Fe 2 O 3 depending on the dominant matrix mineral phase (i.e., chlorite vs. sericite). The quartz-sericite assemblage has mass gains in SiO 2 , K 2 O, Ba, and Fe 2 O 3. Shortwave infrared spectroscopic data, particularly AlOH and FeOH absorption hulls, differentiate alteration styles and correlate with lithogeochemical results: AlOH absorption features increase in length (>2208 nm) proximal to Zn mineralization and wavelength variations correspond to relative abundances of sericite and chlorite. Electron probe microanalyses indicate that increasing shortwave infrared wavelengths correlate with increasing Mg-Fe and Fe contents in sericite and chlorite, respectively. Collectively, these data have been used to develop a three-dimensional alteration model of the Boundary deposit. Résumé : Le gisement de sulfures massifs volcanogènes Boundray (0,50 Mt contenant 3,5 % Cu, 4,0 % Zn, 1,0 % Pb, 34 g/t Ag) est encaissé dans le Groupe de Tally Pond (ϳ510 Ma) du Supergroupe de Victoria Lake dans le centre de Terre-Neuve, Canada; il s'agit d'un gisement de sulfures massifs de style remplacement sous le plancher océanique. Le gisement est encaissé dans un tuf rhyolitique à lapilli de la Formation de Bindons Pond. Les rhyolites ont des signatures d'éléments immobiles qui concordent avec la formation de roches felsiques par la fusion d'une croûte juvénile peu évoluée dans un environnement de rift d'extension (un arc péricontinental distendu). Les roches encaissant le gisement Boundary ont des indices d'altération élevés, incluant des rapports Ba/Sr, Hg/Na 2 O élevés, un indice chlorite-carbonate-pyrite élevé et des valeurs élevées de l'indice d'altération d'Ishikawa. La géochimie des éléments mobiles permet de distinguer trois styles distincts d'altération hydrothermale : une altération intense en chlorite, en chlorite-séricite et en quartz-séricite. L'altération intense en chlorite montre des gains massiques en MgO et en Cu et des pertes en K 2 O et Ba. L'altération en chlorite-séricite montre des gains et des pertes variables en SiO 2 , K 2 O, Ba, MgO et Fe 2 O 3 selon la phase minérale dominante de la matrice (c.-à-d. chlorite par rapport à séricite). L'assemblage quartz-séricite a accru sa masse en SiO 2 , K 2 O, Ba et Fe 2 O 3. Les données spectrométriques d'infrarouge de courte longueur d'onde (SWIR), surtout les enveloppes d'absorption d'AlOH et de FeOH, différencient les styles d'altération et concordent avec les résultats lithogéochimiques : les caractéristiques d'absorption d'AlOH augmentent de longueur (>2208 nm) à proximité de la minéralisation en zinc et les variations de longueur d'onde correspondent à des abondances relatives de séricite et de chlorite. Des microanalyses électroniques indiquent qu'une augmentation de la longueur d'onde des SWIR correspond à une augmentation respective du contenu en Mg-Fe et Fe dans la séricite et la chlorite. Prises ensemble, ces données ont été utilisées pour développer un modèle tridimensionnel d'altération du gisement Boundray. [Traduit par la Rédaction]