U–Pb zircon ages from Athapuscow aulacogen, East Arm of Great Slave Lake, N.W.T., Canada

1984 ◽  
Vol 21 (11) ◽  
pp. 1315-1324 ◽  
Author(s):  
S. A. Bowring ◽  
W. R. Van Schmus ◽  
P. F. Hoffman
Keyword(s):  
Slave Craton ◽  
Great Slave Lake ◽  
Intrusive Rocks ◽  
Island Group ◽  
Minimum Age ◽  
Great Bear Magmatic Zone ◽  
Intracratonic Basin ◽  
Two Phases ◽  
Intrusive Suite ◽  
Stratigraphic Sequences

Athapuscow aulacogen is an Early Proterozoic intracratonic basin located in the East Arm of Great Slave Lake between the Slave and northwest Churchill provinces. Athapuscow aulacogen comprises three stratigraphic sequences, the Wilson Island Group, the Great Slave Supergroup, and the Et-Then Group. New U–Pb zircon ages provide constraints on the development of the aulacogen.The Blachford Lake Intrusive Suite consists of an older alkaline phase (Hearne Channel Granite) dated at 2175 ± 7 Ma and a younger peralkaline phase (Thor Lake Syenite) dated at 2094 ± 10 Ma, confirming the suggestion that the two phases may not be related. A felsite from the Wilson Island Group has an age of 1928 ± 11 Ma. The Wilson Island Group is intruded by epizonal granites (Butte Island Intrusive Suite), one of which has an age of 1895 ± 8 Ma. The Wilson Island Group and the Butte Island Instrusive Suite are entirely allochthonous with respect to the Slave craton. Rocks of the Great Slave Supergroup overlie mylonitized Wilson Island Group rocks and both were involved in northeast-directed thrusting. The Compton laccoliths intrude rocks of the Great Slave Supergroup, postdate thrusting, and are about 1865 Ma old.The Blachford Lake Intrusive Suite is significantly older than both the rift sequence in Wopmay Orogen (ca. 1900 Ma) and the Wilson Island Group; it probably is genetically unrelated. The age of the Wilson Island Group and Butte Island Intrusive Suite is considerably younger than previous estimates and is close to the minimum age of rifting in Wopmay Orogen. The Compton laccoliths are very similar to intrusive rocks in the Great Bear Magmatic Zone of Wopmay Orogen and may be related to east-dipping subduction beneath the aulacogen.The new ages strengthen the correlations between Athapuscow aulacogen and Wopmay Orogen and suggest a link with events in the Trans-Hudson Orogen to the south.

Petrochemistry of late Aphebian (~ 1.8 Ga) calc-alkaline diorites from the East Arm of Great Slave Lake, N.W.T., Canada

1981 ◽  
Vol 18 (6) ◽  
pp. 1018-1028 ◽  
Author(s):  
J. P. N. Badham
Keyword(s):  
Subduction Zone ◽  
Volcanic Rocks ◽  
Entire Length ◽  
Calc Alkaline ◽  
Slave Craton ◽  
Great Slave Lake ◽  
High Level ◽  
Chemical Trends

The East Arm of Great Slave Lake is a 2.5–1.7 Ga graben connected to the contemporaneous Wopmay Orogen on the margins of the Archean (2.5 Ga) Slave craton. It contains three major groups of sedimentary and volcanic rocks. The two earlier ones are cut by ~ 1.79 Ga diorites, which outcrop over 220 km along the graben.The diorites were preferentially emplaced as laccoliths into a horizon of megabreccia thought to be the product of evaporite solution and collapse. The diorites are similar down the entire length of the East Arm. Main phases are usually plagioclase–hornblende poryphyritic, but younger and possibly high level phases contain biotite and quartz. The diorites are calc-alkaline but show no obvious chemical trends along the graben. They cannot be related directly to the proposed easterly dipping, late Aphebian subduction zone that generated the Wopmay Orogen.

Petrology and textural classification of the Jericho kimberlite, northern Slave Province, Nunavut, Canada

2008 ◽  
Vol 45 (6) ◽  
pp. 701-723 ◽  
Author(s):  
Maya G. Kopylova ◽  
Patrick Hayman
Keyword(s):  
South African ◽  
Small Volume ◽  
Bulk Rock ◽  
Slave Craton ◽  
Slave Province ◽  
Core Logging ◽  
Kimberlite Magma ◽  
Mineral Compositions ◽  
Two Phases

The paper presents data on petrology, bulk rock and mineral compositions, and textural classification of the Middle Jurassic Jericho kimberlite (Slave craton, Canada). The kimberlite was emplaced as three steep-sided pipes in granite that was overlain by limestones and minor soft sediments. The pipes are infilled with hypabyssal and pyroclastic kimberlites and connected to a satellite pipe by a dyke. The Jericho kimberlite is classified as a Group Ia, lacking groundmass tetraferriphlogopite and containing monticellite pseudomorphs. The kimberlite formed during several consecutive emplacement events of compositionally different batches of kimberlite magma. Core-logging and thin-section observations identified at least two phases of hypabyssal kimberlites and three phases of pyroclastic kimberlites. Hypabyssal kimberlites intruded as a main dyke (HK1) and as late small-volume aphanitic and vesicular dykes. Massive pyroclastic kimberlite (MPK1) predominantly filled the northern and southern lobes of the pipe and formed from magma different from the HK1 magma. The MPK1 magma crystallized Ti-, Fe-, and Cr-rich phlogopite without rims of barian phlogopite, and clinopyroxene and spinel without atoll structures. MPK1 textures, superficially reminiscent of tuffisitic kimberlite, are caused by pervasive contamination by granite xenoliths. The next explosive events filled the central lobe with two varieties of pyroclastic kimberlite: (1) massive and (2) weakly bedded, normally graded pyroclastic kimberlite. The geology of the Jericho pipe differs from the geology of South African or the Prairie kimberlites, but may resemble Lac de Gras pipes, in which deeper erosion removed upper facies of resedimented kimberlites.

Geochronometry of the Bridge River Camp, southwestern British Columbia

1991 ◽  
Vol 28 (2) ◽  
pp. 195-208 ◽  
Author(s):  
C. H. B. Leitch ◽  
P. van der Heyden ◽  
C. I. Godwin ◽  
R. L. Armstrong ◽  
J. E. Harakal
Keyword(s):  
Volcanic Rocks ◽  
Older Age ◽  
Spreading Ridge ◽  
Early Permian ◽  
The North ◽  
Epithermal Mineralization ◽  
Minimum Age ◽  
Mineralizing Activity ◽  
Intrusive Suite ◽  
Ocean Ridge

Mineralization at the Bralorne mesothermal gold vein deposit is closely related to a suite of early Late Cretaceous to early Tertiary dykes. Premineral albitite dykes (91.4 ± 1.4 Ma by U–Pb on zircons) and postmineral lamprophyre dykes (43.5 ± 1.5 Ma by K–Ar on biotite) set definite age limits on the mineralizing event. A late intra- to post-mineral green hornblende dyke set (85.7 ± 3.0 Ma by K–Ar on hornblende) that forms a transitional series to the albitites may further restrict the age. Thus, mineralization occurred long after emplacement of the host Bralorne intrusions, dated as Early Permian (minimum age of approximately 270 ± 5 Ma by U–Pb on zircons, 284 ± 20 Ma by K–Ar on hornblende, and 40Ar/39Ar plateau at 276 ± 31 Ma). Lithologically similar intrusions 20 km to the north near Gold Bridge are also Early Permian (287 ± 20 Ma by K–Ar on hornblende and 320 ± 80 Ma by a Rb–Sr whole-rock isochron). Geochronology, radiogenic and stable isotopes, and fluid-inclusion studies suggest that there were several pulses of mineralizing activity adjacent to and east of the Coast Plutonic Complex (CPC). Decreasing temperatures and younger age of mineralization with increasing distance from the CPC imply that plutons of the CPC were the main heat source responsible for mineralization. The main pulses were about 90 Ma for mesothermal Au–Ag–As ± W,Mo mineralization at Bralorne near the CPC, ranging outwards to 65 Ma for Ag–Au–Sb–As ± Hg mineralization at the Minto and Congress deposits, to 45 Ma for Ag–Au epithermal mineralization at Blackdome, 100 km east of the CPC.The Bralorne intrusions may have been emplaced below the sea floor in a spreading-ridge oceanic environment, as suggested by the petrology of the intrusive suite, which includes serpentinized ultramafite, hornblende diorite, and soda granite (trondhjemite), typical of an ophiolite association. The chemistry of volcanic rocks mapped as Cadwallader Group, which host these intrusive bodies, is transitional from mid-ocean-ridge basalts to island-arc tholeiite, suggesting a back-arc-basin setting. Gradational contact relations between the hornblende diorite and the volcanic rocks suggest that the diorite intruded its own volcanic products. Intrusive contacts of the diorite with adjacent elongate ultramafic bodies imply that the ultramafic rocks are of Permian or older age and had been structurally emplaced into crustal levels by the time of diorite intrusion. In the Bralorne fault block the Bralorne intrusions appear to cut the adjacent Cadwallader and Bridge River groups, implying an Early Permian or older age for at least parts of these groups. Thus, rocks mapped as Cadwallader Group in the Bralorne area could be distinct from and older than lithologic equivalents exposed elsewhere, although they are similar in terms of their petrology and major- and trace-element chemistry.

Rb–Sr isochron ages, magmatic 87Sr/86Sr initial ratios, and oxygen isotope geochemistry of the Proterozoic lava flows and intrusions of the East Arm of Great Slave Lake, Northwest Territories, Canada

1982 ◽  
Vol 19 (2) ◽  
pp. 343-356 ◽  
Author(s):  
S. P. Goff ◽  
H. Baadsgaard ◽  
K. Muehlenbachs ◽  
C. M. Scarfe
Keyword(s):  
Isotope Geochemistry ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Tholeiitic Basalt ◽  
Crustal Material ◽  
Tectonic Event ◽  
Mantle Origin ◽  
Great Slave Lake ◽  
Facies Metamorphism ◽  
Island Group

Two Rb–Sr isochrons from the oldest (Wilson Island Group) and one of the youngest (Pearson Formation) Proterozoic volcanic units in the East Arm of Great Slave Lake give dates and initial ratios of 1810 ± 19 Ma, 0.7051 ± 0.0008, and 1809 ± 30 Ma, 0.7089 ± 0.0004, respectively. These dates restrict the Great Slave Supergroup entirely to the Aphebian. The Pearson Formation date is interpreted as magmatic, but it is considered to be rapidly followed by a significant metamorphic and tectonic event within the area. Both the above suites and the volcanic formations of intermediate age have undergone metamorphism up to and including epidote–amphibolite facies. A study of remnant clinopyroxene grains from these formations has indicated general increases in δ18O of whole rocks during epidote–actinolite facies metamorphism of 0.4–2.0‰. The tholeiitic volcanic rocks and intrusions all indicated δ18O values typical of modern continental tholeiites (5.9–7.0‰). The highest δ18O came from those suites that were suspected of having been contaminated by crustal material. The estimated initial 87Sr/86Sr ratios of the magmas, both from clinopyroxene separates and isochrons, indicate a mantle origin for early tholeiitic mid-Aphebian diabase (0.7016–0.7017), Union Island Group diabase (0.7021–0.7030), and Sosan Group alkali volcanics (0.7017). The later Jackson gabbro (0.7050–0.7054) and especially the Pearson Formation tholeiitic basalt (0.7089) both show the effects of significant crustal contamination. The evidence for the Wilson Island Group is less decisive but appears to indicate a mantle origin.

Geology, lithogeochemistry, and significance of porphyry intrusions associated with gold mineralization within the Timmins–Porcupine gold camp, Canada

2019 ◽  
Vol 56 (4) ◽  
pp. 399-418 ◽  
Author(s):  
Peter J. MacDonald ◽  
Stephen J. Piercey
Keyword(s):  
Partial Melting ◽  
Greenstone Belt ◽  
Deformation Zone ◽  
Gold Mineralization ◽  
Gold Deposits ◽  
Crustal Thickening ◽  
Abitibi Greenstone Belt ◽  
Crustal Structures ◽  
Intrusive Rocks ◽  
Intrusive Suite

The Timmins–Porcupine gold camp, Abitibi greenstone belt, is host >60 Moz of Au with many gold deposits spatially associated with porphyry intrusions and the Porcupine–Destor deformation zone (PDDZ). Porphyry intrusions form three suites. The Timmins porphyry suite (TIS) consists of high-Al tonalite–trondjhemite–granodiorite (TTG) with calc–alkalic affinities and high La/Yb ratios and formed during ∼2690 Ma D1-related crustal thickening and hydrous partial melting of mafic crust where garnet and hornblende were stable in the residue. The Carr Township porphyry intrusive suite (CIS) and the granodiorite intrusive suite (GIS) also have high-Al TTG, calc-alkalic affinities, but were generated 10–15 million years after the TIS; the CIS were generated at shallower depths (during postorogenic extension?) with no garnet in the crustal residue, whereas the GIS formed during D2 thrust-related crustal thickening and partial melting where garnet was stable in the residue. Gold mineralization is preferentially associated with the TIS, and to a lesser extent the GIS, proximal to the PDDZ. Intrusions near mineralization have abundant sericite, carbonate, and sulphide alteration. These intrusions exhibit low Na2O and Sr, and high Al2O3/Na2O, K2O, K2O/Na2O, Rb, and Cs, (i.e., potassic alteration); sulfide- and carbonate-altered porphyries have high (CaO + MgO + Fe2O3)/Al2O3 and LOI values. Although porphyries are not genetically related to gold mineralization, they are spatially related and are interpreted to reflect the emplacement of intrusions and subsequent Au-bearing fluids along the same crustal structures. The intrusive rocks also served as structural traps, where gold mineralization precipitated in dilatant structures along the margins of intrusions during regional (D3?) deformation.

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