scholarly journals The Coulon deposit: quantifying alteration in volcanogenic massive sulphide systems modified by amphibolite-facies metamorphism

2016 ◽  
Vol 53 (12) ◽  
pp. 1443-1457 ◽  
Author(s):  
Lucie Mathieu ◽  
Rose-Anne Bouchard ◽  
Vital Pearson ◽  
Réal Daigneault
Keyword(s):  
Mass Balance ◽  
Massive Sulphide ◽  
Amphibolite Facies ◽  
High Grade ◽  
Bay Area ◽  
Volcanogenic Massive Sulphide ◽  
High Grade Metamorphism ◽  
And Performance ◽  
Superior Craton ◽  
Ore Zones

The Coulon deposit is a volcanogenic massive sulphide (VMS) system in the James Bay area, Superior craton, Quebec, that was metamorphosed to amphibolite-facies conditions. The chemistry and mineralogy of the VMS-related alteration halo proximal to the mineralized sulphide lenses are investigated, using samples collected in the field and 5583 chemical analyses provided by Osisko Ltd. Alteration is quantified using mass balance and normative calculations, and the application and performance of these methods in an exploration context are investigated. In VMS systems, altered rocks proximal to the ore zones are characterized by multi-element metasomatism, which is best quantified by mass balance methods that have been successfully applied in the study area. However, mass balance calculations necessitate the documentation of a precursor, which is not always possible in an exploration context; therefore, an alternative method (i.e., alteration indices) was also evaluated. In most VMS systems, proximal alteration is characterized by chlorite (chloritization), muscovite (sericitization), and quartz (silicification), while at the Coulon deposit, altered rocks contain mostly cordierite, biotite, sillimanite, and quartz. Alteration indices were calculated using observed and normative minerals, and provide satisfactory results similar to those obtained with mass balance calculations. Using these results, recommendations are made to estimate the intensity of alteration in the core shack using the proportions of observed minerals. Alteration indices are sensitive to the composition of precursors; and because of high-grade metamorphism, chloritization and sericitization are not precisely quantified. Recognizing these limitations is essential to successful quantification of alteration in areas metamorphosed to high-grade conditions.

A revised Archaean chronology for the Napier Complex, Enderby Land, from SHRIMP ion-microprobe studies

1997 ◽  
Vol 9 (1) ◽  
pp. 74-91 ◽  
Author(s):  
S.L. Harley ◽  
L.P. Black
Keyword(s):  
Time Interval ◽  
Minor Importance ◽  
High Grade ◽  
Bay Area ◽  
Igneous Activity ◽  
High Grade Metamorphism ◽  
Ancient Times ◽  
Tectonothermal Event ◽  
Very High ◽  
Napier Complex

The long and complex Archaean evolution of the Napier Complex of Enderby Land, characterized by high-grade metamorphism and several strong deformations, is reassessed in the light of new SHRIMPU–Pb zircon dating results bearing on the ages of protoliths and possible regional extents of distinct Archaean tectonothermal events. Initial felsic igneous activity occurred over a significant time interval c. 3800 Ma ago. An age of 2980±9 Ma for the emplacement of charnockite at Proclamation Island might date the oldest tectonothermal event to be recognized in the Napier Complex. An ensuing, very-high grade, previously imprecisely dated tectonothermal event occurred at 2837±15 Ma. U–Pb zircon ages ranging from 2456+8/−5 Ma to 2481±4 Ma date a subsequent, protracted high-grade tectonothermal event. Whereas the ~2840 Ma event is of regional importance in the Amundsen Bay-Casey Bay area, it is possible that the ~2980 Ma event was of only moderate grade, minor importance, or even absent, in that part of the Complex. If so, the apparent trend to very-high temperature metamorphism in the Tula and Scott mountains compared with the Napier Mountains may reflect two distinct metamorphic events rather than a simple baric and thermal gradient. The oldest crustal component in the Napier Complex appears to have been of igneous derivation. Zircon populations in paragneisses at Mount Sones are similar to those in the nearby orthogneisses, which therefore may have been basement. Another paragneiss, in the Casey Bay area, yields no zircons older than 2840 Ma, probably indicating that pre-3000 Ma crust, which is now located nearby, was not exposed at the time of sedimentation there. The isotopic data are quite complex, particularly in rocks that experienced postcrystallization metamorphic temperatures of 1000°C or more. It is postulated that this complexity, which was largely the product of migration of radiogenic Pb within the zircon grains in ancient times, and produced local excesses of this element with respect to its parent U, was caused by volume diffusion at these abnormally high regional crustal temperatures.

An application of Nd isotope mapping in structural geology: delineating an allochthonous Grenvillian terrane at North Bay, Ontario

2003 ◽  
Vol 140 (5) ◽  
pp. 539-548 ◽  
Author(s):  
A. P. DICKIN ◽  
R. H. MCNUTT
Keyword(s):  
Structural Geology ◽  
Amphibolite Facies ◽  
High Grade ◽  
Grenville Province ◽  
Nd Isotope ◽  
Bay Area ◽  
The North ◽  
Depleted Mantle ◽  
Different Types ◽  
Isotope Analyses

Fifty new Nd isotope analyses are presented from the North Bay area of the Grenville Province in Ontario. These data are used to map the extent of an allochthonous Grenvillian terrane which is an outlier of the Allochthonous Polycyclic Belt of the Grenville Province. Amphibolite facies orthogneisses from the allochthonous terrane have depleted mantle Nd model ages (TDM) below 1.8 Ga, whereas the gneisses of the structurally underlying parautochthon almost invariably have model ages above 1.8 Ga. The distribution of model ages is consistent with the distribution of distinct types of metabasic rock, used by other researchers as the criterion for recognizing rocks of the allochthonous and parautochthonous belts of the Grenville Province. The agreement between these different types of evidence demonstrates that Nd isotope mapping is a reliable and powerful tool for mapping terrane boundaries in high-grade metamorphic belts.

scholarly journals Retrograded Eclogite From Chicheng, North China Craton: New Insights Into the Fidelity of U-Pb-Hf-O Isotopes in Zircon During High-grade Metamorphism

2021 ◽  
Author(s):  
Dongya Zou ◽  
Hongfu Zhang ◽  
M. Santosh
Keyword(s):  
North China Craton ◽  
North China ◽  
Experimental Studies ◽  
Amphibolite Facies ◽  
High Grade ◽  
Grade Metamorphism ◽  
O Isotopes ◽  
Facies Metamorphism ◽  
High Grade Metamorphism ◽  
Eclogite Facies

Abstract Zircon is the most abundantly used mineral for dating igneous and metamorphic events and for tracing source characteristics. Understanding the geochemical behavior of the U-Pb-Hf-O isotope systems during high-grade metamorphism is therefore important for accurate interpretation of the isotopic information. We report zircon U-Pb-Hf-O isotopes and trace elements of retrograded eclogites and host gneisses from Chicheng, North China Craton, with the aim to obtain new insights into the fidelity of U-Pb-Hf-O isotopes in zircon as recorders of high-grade metamorphism. U-Pb dating suggested that the Chicheng mélange experienced eclogite facies metamorphism at ~1.84 Ga, and then exhumed to amphibolite facies at 320–300 Ma. Zircons with Paleoproterozoic ages formed in metamorphic melts-derived from the gneiss during the eclogite facies metamorphism. Zircons with ages of 300–320 Ma formed by recrystallization of peak metamorphic zircons during fluid-assisted amphibolite-facies retrograde metamorphism. This process led to the near-complete resetting not only of U-Pb ages but also of Hf-O isotopic compositions of the peak metamorphic zircons, while preserve REE patterns. These results contrast with the sluggish Hf diffusion rate predicted from experimental studies, and support findings that isotopic data from metamorphic zircons in retrograded high-grade metamorphic rocks need not be faithful recorders of their sources.

Characteristics of gold mineralization in volcanogenic massive sulphide deposits of the Notre Dame Bay area, central Newfoundland

1996 ◽  
Vol 33 (2) ◽  
pp. 316-334 ◽  
Author(s):  
F. Santagulda ◽  
M. D. Hannington
Keyword(s):  
Gold Mineralization ◽  
Massive Sulphide ◽  
Structural Deformation ◽  
Type I ◽  
Type Ii ◽  
Bay Area ◽  
Massive Sulphide Deposits ◽  
Volcanogenic Massive Sulphide ◽  
Free Gold ◽  
Sulphide Deposits

A reconnaissance study of 19 volcanogenic massive sulphide deposits in the Notre Dame Bay area indicates Au concentrations of up to 30 ppm (Betts Cove), and elevated gold contents (>1 ppm Au) have been found in samples from 10 additional past producers and developed prospects. Systematic trends in the occurrence of gold are observed in two principal sulphide assemblages: polymetallic, pyrite–sphalerite–chalcopyrite–galena ± arsenopyrite assemblages (type I) and pyrite–chalcopyrite ± sphalerite ± pyrrhotite assemblages (type II). Type I assemblages occur in deposits with dominantly felsic host rocks, whereas type II assemblages are restricted to deposits in mafic-dominated ophiolite sequences. Free gold grains were observed in samples from eight different deposits in both type I and type II assemblages. X-ray emission spectra and electron microprobe analyses of the gold indicate that most grains are electrum, although a Au-bearing telluride occurs at Point Leamington. Ion microprobe analyses indicate that as much as 50% of bulk gold may be present as "invisible gold" locked in pyrite or arsenopyrite (up to 140 ppm Au at Point Leamington). Well-preserved primary depositional features in gold-bearing sulphides from several deposits suggest that the gold in type I assemblages is syngenetic. A strong correlation between gold and a polymetallic suite of Zn, Ag, Pb, As, and Sb, similar to that observed in Kuroko-type massive sulphides and in modern seafloor sulphides, supports a primary origin for gold in type I assemblages. In type II assemblages primary depositional features have been largely destroyed by deformation and annealing of sulphide grains. Gold is locally enriched in Zn-rich sulphides, and sulphides containing abundant pyrrhotite have the lowest gold contents. However, consistent geochemical associations with other elements are not observed, and this may reflect the strong remobilization of gold during structural deformation. The abundant free gold in some type II assemblages is a product of recrystallization during deformation and was derived locally from primary gold originally present in the host sulphides.

scholarly journals Granitisation of basic rocks in the Bjørnesund area, near Fiskenæsset, West Greenland

1976 ◽  
Vol 73 ◽  
pp. 47-54
Author(s):  
H.R Williams
Keyword(s):  
Large Scale ◽  
Amphibolite Facies ◽  
High Grade ◽  
West Greenland ◽  
Grade Metamorphism ◽  
High Grade Metamorphism ◽  
Basic Rocks

The area studied (Fig. 22) is dominantly composed of strongly and poorly banded gneisses with intercalated supracrustal amphibolites, and was finally metamorphosed in upper-amphibolite facies about 2.7 x 10^9 y ago. Early large-scale isoclinal folds formed during high-grade metamorphism have affected the strongly banded gneisses and amphibolites, but predate the younger, poorly banded gneisses, which were subsequently deformed and metamorphosed along with the banded gneisses and amphibolites. (Williams, 1973).

U–Pb geochronologic constraints on Paleoproterozoic orogenesis in the northwestern Makkovik Province, Labrador, Canada

1997 ◽  
Vol 34 (8) ◽  
pp. 1072-1088 ◽  
Author(s):  
J. W. F. Ketchum ◽  
G. R. Dunning ◽  
N. G. Culshaw
Keyword(s):  
Sensu Stricto ◽  
Metamorphic Grade ◽  
Tectonic Activity ◽  
High Grade ◽  
Western Margin ◽  
Bay Area ◽  
Tectonic Events ◽  
High Grade Metamorphism ◽  
Tectonic Escape ◽  
High Metamorphic Grade

A 45 km wide, shear-zone-bounded segment of the northwestern Makkovik Province, Labrador, is underlain by Archean gneisses derived from the adjacent Nain craton. This lithotectonic block (Kaipokok domain) was reworked at high metamorphic grade, overthrust by supracrustal sequences (Lower Aillik and Moran Lake groups), and intruded by granitoid plutons during the Paleoproterozoic. Initial amphibolite-facies reworking of the Kaipokok domain at 1896 ± 6 Ma is indicated by U–Pb ages of metamorphic zircon from a foliated Kikkertavak metadiabase dyke. This is one of the oldest Paleoproterozoic tectonic events dated thus far in northeast Laurentia and may be linked with ca. 1890 Ma plutonism documented elsewhere in the Kaipokok domain. Intrusion of granitoid plutons at [Formula: see text], 1877 ± 5, and [Formula: see text] in the Kaipokok Bay area postdates early thick- and thin-skinned thrusting (possibly east to northeast directed) that involved Lower Aillik Group strata. U–Pb titanite ages of 1866–1847 Ma in part record a metamorphic event that followed this plutonic–tectonic activity. These early events are temporally and kinematically difficult to reconcile with accretion of juvenile Makkovikian terranes in the southeast and may instead be related to early stages of the ca. 1.91–1.72 Ga Torngat orogeny along the western margin of the Nain craton. In contrast, high-grade metamorphism, dextral shearing, and northwestward thrusting between 1841 and 1784 Ma, including crystallization of an Iggiuk granitic vein at 1811 ± 8 Ma, are in accord with accretion of Makkovikian terranes in a dextral transpressional regime (Makkovikian orogeny sensu stricto). Coeval sinistral transpression in the Torngat orogen suggests that both otogenic belts accommodated relative northward tectonic escape of the Nain craton during this interval.

Archean crustal evolution of the northwestern Superior craton margin: U-Pb zircon results from the Split Lake Block

1999 ◽  
Vol 36 (12) ◽  
pp. 1973-1987 ◽  
Author(s):  
Christian O Böhm ◽  
Larry M Heaman ◽  
M Timothy Corkery
Keyword(s):  
Superior Province ◽  
High Grade ◽  
Grade Metamorphism ◽  
Metamorphic History ◽  
Zircon Growth ◽  
Growth History ◽  
Northwestern Margin ◽  
History Of ◽  
High Grade Metamorphism ◽  
Superior Craton

The Split Lake Block forms a partly retrogressed, granulite-grade basement segment located at the northwestern margin of the Superior Province in Manitoba. Unlike other segments along the craton margin, the effects of Proterozoic tectonism are relatively minor in the Split Lake Block, making it amenable to establishing firm temporal constraints for the Archean magmatic and metamorphic history of the northwestern Superior Province margin. Consequently, samples from the main lithological units within the Split Lake Block were selected for precise single-grain U-Pb zircon geochronology. Heterogeneous zircon populations isolated from representative enderbite, tonalite, and granodiorite samples reveal a complex growth history with pre-2.8 Ga protolith ages (e.g., 2841 ± 2 Ma tonalite), possibly as old as 3.35 Ga as indicated in a granodiorite sample. The youngest Archean granitic magmatism identified in the eastern Split Lake Block is represented by the 2708 ± 3 Ma Gull Lake granite. A U-Pb zircon age of 2695+4-1 Ma obtained for leucosome in mafic granulite is interpreted to reflect the timing of granulite-grade metamorphism in the Split Lake Block, supported by polyphase zircon growth and (or) lead loss at ca. 2.7 Ga in the enderbite sample. A younger phase of metamorphic zircon growth at ca. 2.62 Ga is documented in the tonalite and granodiorite zircon populations. The 2.70-2.71 Ga crust formation, the occurrence of ca. 2695 Ma high-grade metamorphism, and broadly contemporaneous Paleoproterozoic mafic dykes in both the Split Lake Block and Pikwitonei Granulite Domain imply a common evolution of these high-grade terrains along the northwestern Superior craton margin since the late Archean.

Structure and stratigraphy of the south flank of the Kisseynew Domain in the Trans-Hudson Orogen, Manitoba: implications for 1.845-1.77 Ga collision tectonics

1999 ◽  
Vol 36 (11) ◽  
pp. 1859-1880 ◽  
Author(s):  
Herman V Zwanzig
Keyword(s):  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Continental Collision ◽  
High Grade ◽  
The South ◽  
Collision Tectonics ◽  
High Grade Metamorphism ◽  
Thrust System ◽  
Flin Flon ◽  
Superior Craton

On the south flank of the Kisseynew Domain, orthogneisses derived from 1.92-1.85 Ga volcano-plutonic rocks are overlain by paragneisses (Burntwood and Missi groups) derived from 1.855-1.84 Ga marine turbidite and 1.845-1.83 Ga terrestrial clastic and volcanic rocks. The sediments in these groups are interpreted as having been shed into the Kisseynew paleobasin from an active margin bordering the Flin Flon Belt. The sedimentation apparently followed early microcontinental collision and accompanied the last arc magmatism in the Trans-Hudson Orogen. The sedimentary rocks and their basement were deformed into a complexly refolded stack of large recumbent folds. Premetamorphic F1 structures represent a fold and thrust system initiated during the sedimentation. These structures are interpreted as transported toward the Kisseynew Domain in the northeast and the hinterland in the southwest. F2 structures (~1.82 Ga) comprise westerly transported nappes. During 1.82-1.80 Ga high-grade metamorphism, the early structures were overturned, amplified, and refolded. Basement-cored culminations and sheet-like synforms of paragneiss were horizontally attenuated and transported south and southwest. North- and northeast-trending F4 folds and F5 faults formed after 1.79 Ga. The whole cycle of deformation is related to stages of continental collision between the internal (juvenile) zone of the Trans-Hudson Orogen and the three surrounding Archean cratons (Sask, Superior, and Hearne). The F4 upright folds and steep F5 faults are interpreted as the record of intracontinental transpression, strongly controlled by the Superior Craton boundary.

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