Occurrence, origin, and significance of melagranites in the South Mountain Batholith, Nova Scotia

2017 ◽  
Vol 54 (7) ◽  
pp. 693-713 ◽  
Author(s):  
Michael A. MacDonald ◽  
D. Barrie Clarke
Keyword(s):  
Nova Scotia ◽  
Trace Element ◽  
Alkali Feldspar ◽  
Chemical Compositions ◽  
Metasedimentary Rocks ◽  
South Mountain Batholith ◽  
Pelitic Fraction ◽  
Assimilation Process ◽  
Compositional Variations ◽  
Physical And Chemical

Melagranites (colour index > 20, with biotite > garnet > cordierite) constitute ∼0.1% of the area of the 7300 km2 peraluminous South Mountain Batholith (SMB), Nova Scotia. The melagranites occur as small bodies showing sharp to gradational contacts against the Meguma Supergroup country rocks, and coeval mingling contacts against other facies of the batholith. They also occur as elliptical or blocky metre-scale enclaves elsewhere in the SMB. Characteristic petrological features of the melagranites include high modal abundances of sulphide minerals, strongly reacted metasedimentary xenoliths, mafic mineral-rich clots, apparent porphyritic textures with highly variable proportions of alkali feldspar megacrysts, and allotriomorphic-granular textures. Chemically and isotopically, melagranite rocks have wide compositional variations. In most major-element, trace-element, and isotopic variation diagrams, the melagranites lie on mixing lines between the more abundant granodioritic and monzogranitic phases of the SMB and the metasedimentary rocks of the Meguma Supergroup. Textural evidence, supported by published experimental evidence, suggests that the garnet, cordierite, and K-feldspar are peritectic phases resulting from incongruent melting of the pelitic fraction of the Meguma metasedimentary country rocks. The field relations, mineral assemblages, textural features, and chemical compositions of the melagranites all point to the melagranites as highly concentrated contamination zones in the SMB, representing small portions of the batholith that have failed either to complete the assimilation process or to disperse their contaminants widely in the batholith. As such, these rarely preserved melagranites provide petrogenetic information disproportionate in importance to their abundance in the batholith, especially about the significant role of contamination and assimilation in determining the physical and chemical composition of the SMB. Without preservation of melagranites in the SMB, and by extension all granite bodies, the petrogenetic importance of contamination is difficult to assess, even with trace-element and isotopic data. The present study shows that high quality field observations are as important in deciphering petrogenesis as chemical data.

The petrology, geochemistry, and economic potential of the Musquodoboit batholith, Nova Scotia

1985 ◽  
Vol 22 (11) ◽  
pp. 1633-1642 ◽  
Author(s):  
M. A. MacDonald ◽  
D. B. Clarke
Keyword(s):  
Nova Scotia ◽  
Alkali Feldspar ◽  
Coarse Grained ◽  
Major Constituent ◽  
Geochemical Data ◽  
Economic Potential ◽  
Magmatic Differentiation ◽  
Metasedimentary Rocks ◽  
South Mountain Batholith ◽  
Rock Types

The Musquodoboit batholith of southwestern Nova Scotia is a massive, post-tectonic granitoid intrusion that was emplaced into the regionally deformed and metamorphosed Meguma Group metasedimentary rocks. The batholith is composed primarily of medium- to coarse-grained monzogranites into which two small (≈1 km2) porphyries and numerous dykes have been injected. All rocks contain quartz, alkali feldspar, plagioclase, muscovite, and biotite (with the exception of some leucocratic dykes). Cordierite is a major constituent in most monzogranitic rocks and also occurs in some leucocratic dykes. Andalusite and garnet 0are also present as accessory phases in some rocks.Major-element chemical analyses indicate that all rock types in the Musquodoboit batholith are peraluminous. Compositions resemble those of the eastern part South Mountain batholith; however, slightly higher concentrations of Al2O3 and P2O5 distinguish the Musquodoboit batholith from the central part of the South Mountain batholith. Major- and trace-element data indicate that magmatic differentiation has operated; however, the decrease in Σ 8 REE's, Th/U, and K/Rb from monzogranite to dyke rocks suggests that stripping by hydrothermal fluids has also occurred.Various field, petrographic, and geochemical data yield equivocal estimates of the economic potential of the Musquodoboit batholith.

scholarly journals Geochemical signatures of mineralizing events in the Juomasuo Au–Co deposit, Kuusamo belt, northeastern Finland

2021 ◽  
Author(s):  
Mikael Vasilopoulos ◽  
Ferenc Molnár ◽  
Hugh O’Brien ◽  
Yann Lahaye ◽  
Marie Lefèbvre ◽  
...  
Keyword(s):  
Trace Element ◽  
Sulfur Isotope ◽  
Mineral Chemistry ◽  
Chemical Compositions ◽  
Metasedimentary Rocks ◽  
Metavolcanic Rocks ◽  
Icp Ms ◽  
Stage 1 ◽  
Host Rocks ◽  
Relationship Of

AbstractThe Juomasuo Au–Co deposit, currently classified as an orogenic gold deposit with atypical metal association, is located in the Paleoproterozoic Kuusamo belt in northeastern Finland. The volcano-sedimentary sequence that hosts the deposit was intensely altered, deformed, and metamorphosed to greenschist facies during the 1.93–1.76 Ga Svecofennian orogeny. In this study, we investigate the temporal relationship between Co and Au deposition and the relationship of metal enrichment with protolith composition and alteration mineralogy by utilizing lithogeochemical data and petrographic observations. We also investigate the nature of fluids involved in deposit formation based on sulfide trace element and sulfur isotope LA-ICP-MS data together with tourmaline mineral chemistry and boron isotopes. Classification of original protoliths was made on the basis of geochemically immobile elements; recognized lithologies are metasedimentary rocks, mafic, intermediate-composition, and felsic metavolcanic rocks, and an ultramafic sill. The composition of the host rocks does not control the type or intensity of mineralization. Sulfur isotope values (δ34S − 2.6 to + 7.1‰) and trace element data obtained for pyrite, chalcopyrite, and pyrrhotite indicate that the two geochemically distinct Au–Co and Co ore types formed from fluids of different compositions and origins. A reduced, metamorphic fluid was responsible for deposition of the pyrrhotite-dominant, Co-rich ore, whereas a relatively oxidized fluid deposited the pyrite-dominant Au–Co ore. The main alteration and mineralization stages at Juomasuo are as follows: (1) widespread albitization that predates both types of mineralization; (2) stage 1, Co-rich mineralization associated with chlorite (± biotite ± amphibole) alteration; (3) stage 2, Au–Co mineralization related to sericitization. Crystal-chemical compositions for tourmaline suggest the involvement of evaporite-related fluids in formation of the deposit; boron isotope data also allow for this conclusion. Results of our research indicate that the metal association in the Juomasuo Au–Co deposit was formed by spatially coincident and multiple hydrothermal processes.

Major- and trace-element composition of REE-rich turkestanite from peralkaline granites of the Morro Redondo Complex, Graciosa Province, south Brazil

2010 ◽  
Vol 74 (4) ◽  
pp. 645-658 ◽  
Author(s):  
F. C. J. Vilalva ◽  
S. R. F. Vlach
Keyword(s):  
Trace Element ◽  
Inductively Coupled Plasma ◽  
Alkali Feldspar ◽  
Trace Element Composition ◽  
Inductively Coupled ◽  
Coupled Substitution ◽  
Plasma Mass Spectrometry ◽  
Compositional Variations ◽  
End Members ◽  
South Brazil

AbstractTurkestanite, a rare Th- and REE-bearing cyclosilicate in the ekanite–steacyite group was found in evolved peralkaline granitesfrom the Morro Redondo Complex, south Brazil. It occurswith quartz, alkali feldspar and an unnamed Y-bearing silicate. Electron microprobe analysis indicates relatively homogeneous compositions with maximum ThO2, Na2O and K2O contentsof 22.4%, 2.93% and 3.15 wt.%, respectively, and significant REE2O3 abundances(5.21 to 11.04 wt.%). The REE patterns show enrichment of LREE over HREE, a strong negative Eu anomaly and positive Ce anomaly, the latter in the most transformed crystals. Laser ablation inductively coupled plasma mass spectrometry trace element patterns display considerable depletions in Nb, Zr, Hf, Ti and Li relative to whole-rock sample compositions. Observed compositional variations suggest the influence of coupled substitution mechanisms involving steacyite, a Na-dominant analogue of turkestanite, iraqite, a REE-bearing end-member in the ekanite–steacyite group, ekanite and some theoretical end-members. Turkestanite crystals were interpreted as having precipitated during post-magmatic stages in the presence of residual HFSE-rich fluidscarrying Ca, the circulation of which wasenhanced by deformational events.

Oxygen isotope evidence for the genesis of Upper Paleozoic granitoids from southwestern Nova Scotia

1980 ◽  
Vol 17 (1) ◽  
pp. 132-141 ◽  
Author(s):  
F. J. Longstaffe ◽  
T. E. Smith ◽  
K. Muehlenbachs
Keyword(s):  
Nova Scotia ◽  
Oxygen Isotope ◽  
Large Scale ◽  
The South ◽  
Metasedimentary Rocks ◽  
South Mountain Batholith ◽  
Oxygen Isotope Ratios ◽  
Upper Paleozoic ◽  
Isotope Evidence ◽  
Alteration Processes

The oxygen isotope ratios for 127 rocks and coexisting minerals from Paleozoic granitoids and clastic metasedimentary rocks of southwestern Nova Scotia have been measured. The whole-rock δ18O values for samples of the South Mountain batholith range from 10.1–12.0‰.But discrete granitoid plutons, located to the south of the South Mountain batholith, have lower δ18O values (7.8–10.4‰). Coexisting minerals from the Nova Scotia granitoids are near isotopic equilibrium, indicating that the whole-rock δ18O values primarily reflect the δ18O of the magma, rather than secondary alteration processes. The Meguma Group clastic metasedimentary rocks that host the Nova Scotia granitoids range in δ18O from 10.1–12.9‰. These clastic metasedimentary rocks show no systematic geographic variation in δ18O. The greenschist facies Meguma Group rocks that host the South Mountain batholith have similar δ18O values to the amphibolite facies equivalents located about the southern discrete plutons. Large scale isotopic exchange between the Meguma Group and the South Mountain batholith, or the southern plutons, is not evident.The relatively high δ18O values of the peraluminous South Mountain batholith (10.1–12.0‰) indicate that it formed by anatexis of 18O-rich clastic metasedimentary rocks. The southern plutons were also derived by partial melting of clastic metasedimentary rocks, but their lower δ18O values reflect exchange of the source material with a low 18O reservoir (mafic magmas?) prior to, or during anatexis.The sheared Brenton pluton is much lower in δ18O (5.0‰) than any of the other rocks, probably because of exchange with low 18O fluids during shearing.

Granite-hosted mineral deposits of the New Ross area, South Mountain Batholith, Nova Scotia, Canada: P, T and X constraints of fluids using fluid inclusion thermometry and decrepitate analysis

2000 ◽  
Vol 91 (1-2) ◽  
pp. 303-319 ◽  
Author(s):  
Sarah Carruzzo ◽  
Daniel J. Kontak ◽  
D. Barrie Clarke
Keyword(s):  
Nova Scotia ◽  
Fluid Inclusion ◽  
Electron Microprobe ◽  
Meteoric Water ◽  
Mineral Deposits ◽  
Fluid Inclusion Data ◽  
Metasedimentary Rocks ◽  
Low Salinity ◽  
South Mountain Batholith ◽  
Highly Evolved

The 370 Ma peraluminous South Mountain Batholith (SMB) intrudes Meguma Supergroup metasedimentary rocks in Nova Scotia. The New Ross area of the SMB contains polymetallic mineralisation (Sn, W, U, Mo, Cu and Mn) in pegmatite, greisen and vein directly or indirectly associated with highly evolved fractions of the SMB. Eight mineral deposits from this area have several fluid inclusion types hosted by quartz: (1) monophase liquid (L); (2) monophase vapour (V); (3) aqueous, L-V (4) aqueous, L-rich + solids; (5) aqueous, L-rich + halite. Inclusions have irregular to equant shapes and are pseudo-secondary or secondary. The irregularity and variability of L:V ratios within fluid inclusion populations suggest post-entrapment modifications of inclusions (i.e. necking).Thermometric data indicate three distinct fluids in terms of salinity: (1) 19-25 wt. % equiv. NaCl (rarely 14-25 wt. % NaCl equiv.), (2) 29-43 wt. % equiv. NaCl, and (3) 0-9 wt. % equiv. NaCl. Temperatures of first melting and ice/hydrohalife melting indicate CaCl2 in solution. Proximity of the deposits to Meguma Supergroup metasedimentary rocks suggests that this Ca component may be externally derived. The majority of the low-salinity fluid population has the composition of meteoric water. Electron microprobe analyses of artificially decrepitated mounds identify Na, Ca and K as major solutes, with a continuum in terms of compositions. Other solute components in the mounds are Fe and Ba, and a variety of metals of unknown speciation also occur (Cu, Zn, Fe, Ni). Homogenisation temperatures (Th) range from c. 80°C to 370°C, but for inclusion assemblages the range is 10°C to 20°C. Given the 3 kbar depth of emplacement of the SMB, estimated entrapment temperatures are c. 200°C to 550°C. The fluid inclusion data appear to reflect: (1) trapping of mixed Na-K-Ca brines during isobaric cooling in pegmatite and greisen deposits as indicated by large ranges in Th; (2) formation of deposits at different ambient pressures (i.e. depth); and (3) mixing of fluids of different reservoirs (i.e. magmatic, metamorphic, meteoric).

Rb–Sr age and geochemical distinctions between the Carboniferous tin-bearing Davis Lake complex and the Devonian South Mountain batholith, Meguma Terrane, Nova Scotia

1989 ◽  
Vol 26 (10) ◽  
pp. 2044-2061 ◽  
Author(s):  
Jean M. Richardson ◽  
Keith Bell ◽  
John Blenkinsop ◽  
David H. Watkinson
Keyword(s):  
Nova Scotia ◽  
Trace Element ◽  
Biotite Granite ◽  
Granitic Magma ◽  
Trace Element Geochemistry ◽  
Magmatic Differentiation ◽  
Element Geochemistry ◽  
South Mountain Batholith ◽  
Granitoid Rocks ◽  
Meguma Terrane

The Davis Lake complex (DLC), composed of biotite monzogranite, leucomonzogranite, and cassiterite–topaz greisen, hosts the East Kemptville tin mine in southwestern Nova Scotia. The DLC monzogranite contains glomeroporphyritic biotite with ilmenite and many rare-earth-element (REE) bearing accessory minerals, zircon-bearing quartz phenocrysts, and xenoliths of biotite granite. Primary muscovite is rare. Major- and trace-element geochemical trends indicate well-defined, but limited, magmatic differentiation trends. REE patterns of the least-evolved granites are flat and show a Ce/Yb ratio of 10.The DLC was previously considered cogenetic with the Devonian South Mountain batholith (SMB) on the basis of its location, lithologies, and similarities in major- and trace-element geochemistry. However, new Rb–Sr whole-rock isotopic data indicate an Rb–Sr date of 330 ± 7 Ma (mean square of weighted deviates (MSWD) = 2.8) for the DLC, implying that it is at least 35 Ma younger than the SMB. The initial 87Sr/86Sr ratio of 0.727 ± 0.004 is significantly higher than those for other Meguma Terrane granites and is the highest yet reported from Appalachian granitoid rocks. Rb–Sr data from biotite indicate open-system behaviour between 260 and 240 Ma and provide more evidence for previously documented tectonothermal events after 300 Ma in the Meguma Terrane.The peraluminous nature of the DLC, its high Rb/Sr and high 87Sr/86Sr ratios, high P, F, and Sn contents, low Ca and B contents, and high differentiation indices indicate that the complex was derived from a highly evolved felsic source. Geochemical distinctions indicate that the DLC is neither derived from nor cogenetic with the SMB. A more probable source for the DLC magma is a dehydrated felsic granulite from which a previous H2O-, B-, Cl-, and Zn-rich granitic magma (perhaps the SMB) had been extracted. Such a source is analogous to that postulated for A-type granites and topaz rhyolites.The DLC shows more similarities to the "stitching" Carboniferous Appalachian volatile- and metal-rich granites than to Devonian Meguma granites. Unlike most of these Appalachian plutons, which occur marginal to terrane boundaries and were probably crystallized from locally generated, anatectic magmas, the DLC was emplaced in the centre of the most-outboard Meguma Terrane, adjacent to the Tobiatic shear zone.

The interplay of regional structure and emplacement mechanisms at the contact of the South Mountain Batholith, Nova Scotia: floor-down or wall-up?

2001 ◽  
Vol 38 (9) ◽  
pp. 1285-1299 ◽  
Author(s):  
Nicholas Culshaw ◽  
Pradeep Bhatnagar
Keyword(s):  
Mechanical Properties ◽  
Nova Scotia ◽  
Country Rock ◽  
Wall Rock ◽  
Ductile Deformation ◽  
Linear Structures ◽  
The South ◽  
Metasedimentary Rocks ◽  
South Mountain Batholith ◽  
Differential Movement

In southern Nova Scotia, the Devonian South Mountain Batholith was emplaced into metasedimentary rocks of the Cambro-Ordovician Meguma Group at ca. 370 Ma. The contact of the eastern end of the South Mountain Batholith transects at a high angle the trace of subhorizontal, upright Acadian (mid-late Devonian) folds formed in the Meguma Group. At two locations, where the contact is well exposed, there are contrasting structures in the country rocks adjacent to Acadian anticlinoria and synclinoria, respectively. Regional folds are affected by ductile deformation where anticlinoria abut the batholith but are undisturbed at the synclinoria. At the anticlinorial contacts, the metasedimentary bedding youngs towards the granite, and granite side-down shear resulted in a belt in which bedding is transposed to a new contact-parallel fabric. Deflection of linear structures that were initially horizontal in the Acadian folds (e.g., intersection lineations) illustrates the granite side-down shear. The reorientation of initially horizontal linear structures gradually diminishes as the contact is followed from the anticlinoria to the synclinoria, where the regional fold geometry is preserved right up to the contact, showing that there is no granite side-down shear in the synclinoria at the present level of erosion. Two models that potentially explain this variation in contact structure are discussed. In the first, it is explained as an artifact of emplacement of the batholith late in the growth of the Acadian folds, in which the horizontal, upright anticlinoria amplified and moved upward relative to the pluton. A shear zone was formed parallel to the contact along the thermally softened tip of the anticlinoria. The synclinoria remained fixed vertically and there was no differential movement between granite and country rock. Thus, regional structures and evidence for stoping are most widely preserved in the synclinoria, where they were not overprinted by the marginal shearing. The second model invokes floor-down emplacement of magma into folds of layered sediments with contrasting mechanical properties. The erosion surface within the synclinoria intersects slates of the Halifax Formation with mechanical properties that favour emplacement predominantly by dyking and stoping. Below the level of erosion, the stratigraphically underlying Goldenville Formation, having different mechanical properties than the Halifax, presumably is displaced downwards predominantly by ductile deformation (pure and simple shear). Within the anticlinoria, where the Goldenville Formation is exposed, the requirement of a level pluton floor necessitates that downward deflection is accompanied by relatively high ductile strains in the wall rock. A third possible model that combines features of the syntectonic and floor-down models is an obvious option.

scholarly journals Stratigraphy and depositional setting of the Silurian-Devonian Rockville Notch Group, Meguma terrane, Nova Scotia, Canada

2017 ◽  
Vol 53 ◽  
pp. 337-365 ◽  
Author(s):  
Chris E. White ◽  
Sandra M. Barr
Keyword(s):  
Nova Scotia ◽  
Volcanic Rocks ◽  
Rock Formation ◽  
Metasedimentary Rocks ◽  
South Mountain Batholith ◽  
Metavolcanic Rocks ◽  
Northwestern Margin ◽  
Meguma Terrane ◽  
Two Stages ◽  
Depositional Setting

 The Silurian–Devonian Rockville Notch Group occurs in five separate areas along the northwestern margin of the Meguma terrane of southern Nova Scotia. In each area, the lowermost unit of the group is the White Rock Formation, which unconformably overlies the Lower Ordovician Halifax Group. Early Silurian U–Pb (zircon) dates from metavolcanic rocks in the White Rock Formation indicate that the unconformity represents a depositional gap of about 25 Ma. The U–Pb ages are consistent with early Silurian (Llandovery) trace fossils and sparse shelly faunas in metasedimentary rocks interlayered with the metavolcanic rocks. The metasedimentary rocks locally contain phosphatic ironstone and Mn-rich beds, and are overlain by mainly metasiltstone with abundant quartzite and metaconglomerate lenses. Some of the latter were previously interpreted to be Ordovician tillite. The White Rock Formation is conformably overlain by the slate- and metasiltstone-dominated Kentville Formation, which contains Upper Wenlock to Pridoli graptolites and microfossils. The overlying Torbrook Formation consists of metalimestone, metasandstone and metasiltstone, interbedded with phosphatic ironstone and minor mafic metatuff, and contains Pridoli to early Emsian fossils. It is in part laterally equivalent to the New Canaan Formation in the Wolfville area, which is dominated by slate, pillowed mafic metavolcanic rocks and fossiliferous metalimestone. Volcanic rocks in the Rockville Notch Group are alkalic and formed in a within-plate setting, probably related to extension as the Meguma terrane rifted from Gondwana. This process may have occurred in two stages, Early Silurian and Early Devonian, separated by a hiatus in volcanic activity. Stratigraphic differences suggest that the Meguma terrane was not adjacent to Avalonia before emplacement of the South Mountain Batholith.

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