Petrochemistry and U–Pb (zircon) age of porphyry dykes at the McKenzie Gulch porphyry–skarn Cu–Ag–Au deposit, north-central New Brunswick, Canada: implications for emplacement age, tectonic setting, and mineralization potential (original) (raw)
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Atlantic Geology, 2006
A steeply west-dipping, north-northwest-trending, biotite-bearing quartz-feldspar porphyry dyke is associated with the Lake George granodiorite, a cupola of the Pokiok Batholith. These Early Devonian intrusions are spatially and temporally related to W-Mo-Au and Sb-Au mineralization in the area. The porphyry dyke yielded an age of 420.8 +5.9/-4.0 Ma (U-Pb zircon) and is inferred to be coeval with or slightly older than the Lake George granodiorite (412 +5/-4 Ma, U-Pb zircon). The variably altered dyke contains subhedral to anhedral (rounded) quartz, plagioclase, and orthoclase phenocrysts (0.5 to 30 mm; 30 to 60 vol. %), and numerous angular to subrounded xenoliths of altered intrusion carapace and quenched dyke rocks, as well as local Kingsclear Formation metasedimentary rocks. The dyke is similar to the Lake George granodiorite in phenocryst population, volcanic arc (I-type) affi nity, average Zr (157 ppm), TiO 2 (0.54 %), La/Yb ratio (13), and REE (129 ppm). The average Au content is lower in the dyke (20 ppb) than in the granodiorite (32 ppb), the abundance of gold is related to minor magmatic hydrothermal chalcopyrite and pyrrhotite (< 2 %). Based on textural evidence, including autobrecciation, coupled with rheological and thermal modeling calculations for the 5 m-wide dyke, it is suggested that fl uidization (vapour exsolution) of the magma was key to its rapid emplacement as a quenched glass-gas mixture (tuffi site). The S abundance and S isotopic signature of the dyke, relative to Au and Cu abundance, support reduced I-type magmatic volatiles involved in dyke emplacement and cogenetic autometasomatic alteration.
Atlantic Geology, 2000
The Cheverie Zn-Pb occurrence, within the Windsor Basin of southern Nova Scotia, is associated with intense carbonate alteration of a mafic dyke and surrounding deformed dark grey siltstone and shale of the Carboniferous Horton Bluff Formation. The mafic dyke, consisting of euhedral plagioclase (Afl45-60), augitic pyroxene, and ilmenite with late-stage mesostasis and granophyre, is subalkaline, has within-plate affinities and is similar to E-MORB; clinopyroxcne chemistry indicates a transitional subalkaline-alkaline chemistry. Dating (40Ar/39Ar whole rock) of the mafic dyke indicates emplacement at 315 Ma, thus providing a minimum age for ductile deformation of the sedimentary rocks and a maximum age for the mineralization. The occurrence of pyrite, marcasite, sphalerite (Fe-poor and Fe-rich), and galena with bitumen is similar to the metal association at the nearby Walton harite-ba.se metal deposit and suggests a metallogenic affinity. Two phase (I-H20-V) fluid inclusions in vein c...
Geology and age of the Morrison porphyry Cu-Au-Mo deposit, Babine Lake area, British Columbia
Canadian Journal of Earth Sciences, 2016
The Morrison porphyry Cu–Au–Mo deposit is genetically and spatially related to Eocene plagioclase–hornblende–biotite porphyry intrusions. One porphyry intrusion yielded a U–Pb age of 52.54 ± 1.05 Ma. Mineralization occurs in three stages: (1) vein-type and disseminated chalcopyrite and minor bornite (associated with potassic alteration and gold mineralization); (2) vein-type molybdenite (associated with weak phyllic alteration); and (3) polymetallic sulfide–carbonate veins (dolomite ± quartz–sphalerite–galena–arsenopyrite–chalcopyrite, associated with weak sericite–carbonate alteration). Re–Os dating of molybdenite yielded ages of 52.54 ± 0.22 and 53.06 ± 0.22 Ma, similar to the age of the host porphyry intrusion. Stage 1 vein fluids were predominantly of magmatic origin: Th = 400–526 °C; salinity = 39.8–47.8 wt.% NaCl equiv.; δ18Ofluid = 3.7‰–6.3‰; disseminated chalcopyrite–pyrite δ34SCDT = 0.2‰ and −0.8‰ (CDT, Canyon Diablo Troilite). Stage 2 fluids were a mixture of magmatic and ...
Precambrian Research, 2005
In the Grenville Province of western Quebec, Archean gneisses and Paleo-to Mesoproterozoic dykes have been reworked during a short-lived high-pressure metamorphic event at about 1.0 Ga. To the SE of the Grenville Front, a SE-dipping 30 kmthick slab of quartzofeldspathic granulites and biotite-garnet (±opx) gneisses overrides, along the McLaurin thrust, a 4 km-thick zone of steeply dipping muscovite-sillimanite micaschists that abuts on the Grenville Front. The granulitic slab in turn dips under amphibolite-grade migmatites, along the Dorval detachment. The micaschists, the granulites, the biotite-garnet gneisses, and the migmatites are of Archean provenance (Sm-Nd model ages) and correspond to the Grenvillian parautochthon. Metamorphosed mafic dykes are found to intersect at several localities the gneissic foliation of these rocks. Pods of coronitic metagabbros are also found in the same area. New U-Th-Pb chemical ages on monazite from the host rocks support previous estimations of ca. 2.7 Ga for the Archean metamorphism and 1.0 Ga for the Grenvillian reworking. As these determinations failed to recognize intermediate ages, it is likely that Proterozoic mafic dykes and pods are truly monocyclic, i.e. they only went through the Grenvillian metamorphic event. Metamorphic dykes have preserved fine-grained chilled margins, igneous fabrics, magmatic layering and Fe-Ti-rich, Si-poor chemistry in spite of a strong overprint attested by various types of reaction rims (coronitic structures). The coronitic gabbros lack magmatic fabrics and have a more primitive composition with higher Mg-number and normative quartz. In metamorphosed mafic dykes of the granulite slab, large pyroxenes are rimmed by garnet coronas with minute quartz inclusions, suggesting the reaction pl+opx = grt+qtz. Garnet coronas, in turn, are locally replaced by symplectites of opx, hbl, pl and qtz, probably formed through back reactions grt+cpx+qtz = pl+opx and grt+cpx = hbl+qtz. Thermobarometric calculations using the above assemblages indicate peak equilibration at 2 3 about 1.2-1.4 GPa at temperatures of about 800°C followed by a quasi-isothermal decompression in the vicinity of 0.9 MPa at temperatures around 700°C. Cross-cutting relationships and the persistence of magmatic fabrics within the dykes of the granulitic slab suggest emplacement in a brittle extensional setting whereas garnet coronas attest to subsequent burial under high-pressure (HP) granulite facies at relatively high temperature. As it is likely that some of the metamorphosed dykes belong to the 1.14 Gaold Abitibi swarm, Grenvillian HP granulite metamorphism would corresponds to burial of upper crustal levels down to sub-Moho depths with concomitant heating, followed by rapid exhumation. This situation is reminiscent of the emplacement-deformation-exhumation history of the SE-striking 1240 Ma-old Sudbury dyke swarm in Ontario (Bethune, 1997) and may be a characteristic of the Grenville Front Tectonic Zone.
Within the Avalon composite terrane exposed in southern New Brunswick, late Precambrian, low-grade volcanicsedimentary sequences are juxtaposed against late Precambrian gneisses (Brookville Gneiss) and older platformal metasedimentary rocks (Green Head Group) along the Caledonia Fault. Both assemblages host petrographically similar suites of calc-alkalic dioritic and granodioritic plutons. Those intruding volcanic-sedimentary sequences (Caledonia terrane) record ca. 615 -625 Ma crystallization ages typical of arc-related magmatism throughout the Avalon composite terrane. However, 40Ar/3yAr age data from stocks intruding gneisses and platformal metasedimentary rocks (Brookville terrane) suggest significantly younger crystallization ages. 36Ar/40Ar versus 39Ar/40Ar isotope correlation ages recorded by hornblende are interpreted to closely date postmagmatic cooling within six plutons: Fairville Granite (547 + 1 Ma); French Village Quartz Diorite (539 f 2 and 537 + 1 Ma); Rockwood Park Granodiorite (529 f 2 and 523 f 3.5 Ma); Musquash Granite (526 f 2 Ma); Milkish Head Granite (Red Bridge pluton, 520 f 1.5 Ma); Lepreau Diorite (Talbot Road pluton, 519 + 2 Ma and Hansen Stream pluton, 518 f 1.5 Ma. A hornblende isotope correlation age of 530 f 2 Ma from penetratively foliated amphibolite within the French Village Quartz Diorite suggests that the magmatic activity was locally accompanied by ductile shear. Muscovite within granitic pegmatite in the Brookville Gneiss records a 40Ar/3yAr plateau age of 510 f 1 Ma interpreted to date final phases of associated magmatic activity. Arc-related magmatism extending into the Cambrian contrasts with the characteristic tectono-stratigraphic record in the Avalon composite terrane where late Precambrian igneous rocks are overstepped by Cambrian-Ordovician shallow-marine strata with only a local and minor record of rift-related volcanic activity. Although the Brookville terrane shows affinities with the Avalon composite terrane during the late Precambrian, the 40Ar/3yAr age data suggest that it was isolated as a distinct tectono-stratigraphic element by the Early Cambrian. Le secteur du terrane d'Avalon composite qui affleure dans le Nouveau-Brunswick meridional montre des sequences volcano-skdimentaires faiblement mCtamorphistes, d'Lge prtcambrien tardif, qui sont juxtaposCes B des gneiss Cgalement d'Lge prCcambrien tardif (Gneiss de Brookville) et des roches mktasedimentaires d'une ancienne plate-forme (Groupe de Green Head) le long de la faille Caledonia. Les deux assemblages sont les hBtes de suites ~Ctrographiquement analogues de plutons calco-alcalin dioritique et granodioritique. Ces intrusifs qui recoupent les sCquences volcano-~Cdimentaires (terrane de Caledonia) fournissent des Bges de cristallisation de 615 -625 Ma, caractCristiques de I'activitC magmatique d'arc associCe i tout le terrane dlAvalon composite. Cependant, les rCsultats des analyses de 40Ar/39Ar fournis par les petits massifs qui recoupent les gneiss et les roches metastdimentaires de I'ancienne plate-forme (terrane de Brookville) suggbrent des Bges de cristallisation significativement plus jeunes. Les Lges dCduits du diagramme de corrtlation des isotopes 36Ar/40Ar versus 39Ar/40Ar sur la hornblende sont interprCtts comme la date reprksentative du refroidissement postmagmatique dans les six plutons : Granite de Fairville (547 + 1 Ma); Diorite quartzique de French Village (539 f 2 et 537 f 1 Ma); Granodiorite de Rockwood Park (529 2 et 523 + 3,5 Ma); Granite de Musquash (526 + 2 Ma); Granite de Milkish Head (pluton de Red Bridge, 520 f 1,5 Ma); Diorite de Lepreau (pluton de Talbot Road, 519 + 2 Ma et pluton de Hansen Stream, 518 f 1,5 Ma). Un Lge de 530 f 2 Ma deduit d'une corrtlation isotopique sur la hornblende d'une amphibolite, affectCe par une foliation ptnttrative, localiste au sein de la Diorite quartzique de French Village, suggkre que cette activitC magmatique fut accompagnke localement d'un cisaillement ductile. La muscovite d'une pegmatite granitique incluse dans le Gneiss de Brookville fournit un Bge plateau 40Ar/39Ar de 510 f 1 Ma, interprttt comme la date des phases finales de I'activitC magmatique associke. Le magmatisme relit I'arc dont I'activitC s'est poursuivie jusque dans le Cambrien contraste avec les donnCes tectonostratigraphiques caractkristiques du terrane d'Avalon composite, oii les roches igntes prkcambriennes sont trangresstes et par des strates discordantes d'Bge cambrien-ordovicien, dCposCes en milieu marin peu profond, et qui ne prksentent qu'un seul indice local et mineur plaidant en faveur d'une activitt volcanique associCe a un rift. Bien le terrane de Brookville ait eu durant le PrCcambrien tardif certaines affinitks avec le terrane d' Avalon composite, les Lges 40Ar139Ar obtenus suggbent qu'il Ctait isolt, et qu'au dCbut du Cambrien il reprCsentait un ClCment tectono-stratigraphique distinct. [Traduit par la rkdaction]
Extensive exploration, west of Glenwood in the Mount Peyton intrusive suite (MPIS), has outlined a 13.5-km, north-northwest -trending corridor termed the Mount Peyton trend, which is anomalous in gold, silver, arsenic and antimony. In the south-southeast part of the trend, mineralization occurs at the Corsair, Hurricane and Peyton prospects and the Sabre and Com-manche showings; in the north-northwest, mineralization occurs at the Slip and associated showings. Mineralization at Cor-sair and Hurricane consists of narrow (typically <2 cm), sulphide-poor quartz veins that have broad (cm-to 13 m-scale) pyrite–arsenopyrite–sericite–siderite–silica alteration envelopes in fine-grained quartz diorite, locally intruded by monzo-granite. The alteration zones and mineralized veins are northeast trending and moderately southeast dipping, and veins at surface correlate with one set of conjugate regional joint surfaces. Mineralization at Hurricane‒Corsair has elevated concentrations of As, Au, Sb, Ag and locally Cd. At the Slip showing, granophyric monzogranite cupolas exhibit classic magma-mingling relationships with gabbro–diorite. The latter is also cut by straight margined, miarolitic monzogranitic dykes containing pyrite–muscovite–calcite–chalcopyrite ± galena ± arsenopyrite-filled miarolitic cavities that have anomalous Au, As, Sb, and Ag, and minor enrichment in Cu, Pb, Zn, Mo and Bi. The data show that the mineralized monzogranite at the Slip showing is a late-stage, deuteric fluid-enriched and metal-bearing residual magma that intruded a slightly older gabbro‒dior-ite. A CA-TIMS U–Pb zircon crystallization age of 418 ± 1.6 Ma constrains the age of the miarolitic monzogranite and 'intru-sion-related'gold mineralization and places a minimum age on the gabbro‒diorite and granophyric monzogranite. Petrolog-ically similar gabbro at Norris Arm yielded a TIMS U–Pb zircon crystallization age of 422 ± 1.2 Ma, overlapping, within error, with an age of 423.6 ± 1.8 Ma for a layered gabbro near Rolling Pond. These ages constrain magmatism in the MPIS to the interval 425‒418 Ma. Similar metal enrichments along the length of the Mount Peyton trend suggest that the metal endowment of this mineralized corridor may be, at least, in part, a result of contributions from such, 'intrusion-related' fluids. Mineralization at Hurricane‒Corsair may represent more distal, vein-related, disseminated mineralization structurally above miarolitic granite dykes and cupolas.
Mineralium Deposita, 2009
Kemess South is the only Cu-Au-Mo mine in the Toodoggone district and a major Cu and Au producer in British Columbia. Porphyry-style Cu-Au-Mo mineralization is mainly hosted by the tabular, SW-plunging, 199.6±0.6-Ma Maple Leaf granodiorite, which intrudes tightly folded, SWdipping, Permian Asitka Group siltstone and limestone and homogeneous Triassic Takla Group basalt. Southwest-dipping 194.0±0.4-Ma Toodoggone Formation conglomerate, volcaniclastic, and epiclastic rocks overlie the granodiorite and Asitka Group rocks. Minor Cu-Au-Mo mineralization is hosted by the immediate Takla Group basalt country rock, whereas low-tonnage high-grade Cu zones occur beneath a 30-m-thick leached capping in supergene-altered granodiorite and in exotic positions in overlying Toodoggone Formation conglomerate. Granodiorite has an intrusive contact with mineralized and altered Takla Group basalt but displays a sheared contact with unmineralized and less altered Asitka Group siltstone. The North Block fault is a deposit-scale, E-striking, steeply S-dipping normal fault that juxtaposes the granodiorite/basalt ore body against unmineralized Asitka Group rocks. Younger NW-and NE-striking normal-dextral faults cut all rock types, orebodies, and the North Block fault with displacements of up to 100 m and result in the grabenand-horst-style block faulting of the stratigraphy and ore body. Both basalt and granodiorite host comparable vein sequence and alteration histories, with minor variations in hydrothermal mineral assemblages caused by differing protolith chemistry. Early potassic alteration (and associated early-stage Cu ± Au ± Mo mineralization) is partly replaced by phyllic and intermediate argillic alteration associated with main-stage Cu-Au-Mo mineralization. Two main-stage veins have Re-Os molybdenite ages of 201.3±1.2 and 201.1±1.2 Ma. These mineralization ages overlap the 199.6±0.6-Ma U-Pb zircon crystallization age for the Maple Leaf granodiorite. Late-stage pyrite-rich stringer veins and related phyllic alteration assemblages are cut by anhydrite-rich, carbonaterich, and chlorite veins. Fluids and metals associated with early-, main-, and late-stage veins were probably derived principally from the same deep magma chamber as the Maple Leaf granodiorite. These magmatic-derived fluids interacted with Asitka and Takla Group country rocks and possibly with meteoric and metamorphic fluids prior to mineralization.
The Central Hearne supracrustal belt (CHSB), Hearne domain, Western Churchill Province forms a large (ca. 30,000 km2), greenschist grade Neoarchaean (2711–2660 Ma) terrane of predominant metavolcanic and less common metasedimentary rocks intruded by three groups of plutonic rocks. Pre-tectonic group 1 plutons (>2690 Ma) include rare gabbro, dominant diorite to tonalite and rare granodiorite and granite. These intrude and incorporate angular inclusions of cogenetic volcanic rocks and have variably developed foliations. Syn-tectonic group 2 plutons (2690–2679 Ma) comprise rare gabbro and diorite, predominant tonalite and granodiorite and rare granite, and exhibit N–S-trending, ductiley deformed supracrustal schlieren-rich intrusive margins. Post-tectonic group 3 plutons are rare, and comprise either potassic, biotite monzogranite or alkalic nepheline syenite and rare carbonatite. Abundant tonalite to granodiorite, biotite ± hornblende – bearing mineralogies and metaluminous and generally low-medium K2O compositions, indicate that most rocks are I- or M-type granitoids. Molecular Na–Ca–K variations and AFM indices indicate transitional calc-alkaline – trondjhemitic trends with both tholeitic and calc-alkaline affinities. Rare earth and incompatible element variations suggest that most granitoids exhibit volcanic arc- or tonalite–trondhjemite–granodiorite (TTG)-like abundances with multi-element patterns varying gradationally from La-poor (LaN/YbN <12) to La-rich compositions (LaN/YbN > 12). Nd isotopic values overlap with contemporaneous depleted mantle indicating that the granitoids represent melts derived from predominantly juvenile mantle or crust. La-poor rocks likely formed through low-P anatexis of amphibolitic crust with plagioclase + amphibole ± clinopyroxene present, whereas high-La rocks were generated via high-P partial melting of a garnet+ clinopyroxene-bearing protolith (plausibly a subducted slab). Granitoid evolution from early dominant low-P, tholeiitic and calc-alkaline melts, to later, predominant high-P, high-Al2O3 TTG melts, reflects a change in the tectonomagmatic setting at ca. 2690 Ma. Construction of proto-arc crust from ca. 2711–2690 Ma, and extension of the leading edge of normal (ca. 40 km) Archaean oceanic crust, in response to lithospheric processes analogous to those of the Eocene SW Pacific Ocean, resulted in asthenospheric upwelling, intrusion of mantle-derived melts into the lower crust, and their subsequent ascent and fractionation. Partial melting at the base of the extended, thick oceanic crust likely yielded sparse high-La melts at this time. At ca. 2690 Ma, a change from an extensional to a shortening regime resulted in initiation of subduction of adjacent oceanic lithosphere, partial melting of the eclogitic downgoing slab and generation of voluminous, high-P, La-rich granitoid magmas. This yielded less abundant low-P, La-poor melts emplaced into the “infant-arc” crust during and following tectonism. The complete sequence was intruded by late potassic granites derived from tonalitic lower crust and alkalic magmas that originated in the lithospheric mantle.
Precambrian Research, 2002
Porphyry gold deposits constitute a new challenge for mineral exploration in Archean greenstone belts, yet the relationships between intrusive rocks and mineralisation remain poorly understood. The Messegay gold occurrence is situated in the Taschereau-Launay plutonic complex of the Northern Volcanic Zone of the Abitibi greenstone belt. The Taschereau intrusion (2718 92 Ma) represents a complex network of sills composed of tonalite with minor amounts of diorite, monzonite and gabbro. The Launay granite, which intrudes the Taschereau pluton, is late-orogenic and its emplacement was controlled by an early reverse ductile N -S shear zone. Intrusive rocks have been subjected to four episodes of alteration: epidote-chlorite-carbonate, magnetite-hematite-microcline, albite-pyrite, and sericite-quartz. Shear zone hosted and metasomatic Au-Mo mineralisation is mainly associated with albitepyrite assemblages, but also occurs within zones of intense magnetite-hematite-microcline and sericite-quartz alteration. The Messegay gold occurrence is interpreted as a new type of disseminated gold-molybdenum porphyry deposit associated with a zone of magmatic differentiation in a magnetite-series pluton.