scholarly journals Fluid-saturation textures and Rb-Sr isotopic data from the East Kemptville tin deposit, southwestern Nova Scotia

1988 ◽  
Author(s):  
J M Richardson ◽  
K Bell ◽  
J Blenkinsop ◽  
D H Watkinson
Keyword(s):  
Nova Scotia ◽  
Isotopic Data ◽  
Fluid Saturation ◽  
Tin Deposit

Geochemistry of the Namurian Lismore Formation, northern mainland Nova Scotia: sedimentation and tectonic activity along the southern flank of the Maritimes Basin

1999 ◽  
Vol 36 (10) ◽  
pp. 1655-1669 ◽  
Author(s):  
Jacquelyn E Stevens ◽  
J Brendan Murphy ◽  
Fred W Chandler
Keyword(s):  
Nova Scotia ◽  
Tectonic Activity ◽  
Isotopic Data ◽  
Rock Fragments ◽  
Metasedimentary Rocks ◽  
Clastic Rocks ◽  
Granitoid Rocks ◽  
Maritimes Basin ◽  
Group B ◽  
Southern Flank

Geochemical and isotopic data from the clastic rocks of the Namurian Lismore Formation in mainland Nova Scotia identify key episodes of tectonic activity during the development of the Maritimes Basin in Atlantic Canada. The Lismore Formation forms part of the Mabou Group and is an upward-coarsening 2500 m thick fluvial sequence deposited in the Merigomish sub-basin along the southern flank of the Maritimes Basin. Based on stratigraphic evidence, the Lismore Formation can be divided into upper and lower members which reflect variations in depositional environment and paleoclimate. The geochemical and isotopic data may also be subdivided into two groupings that primarily reflect varying contributions from accessory phases, clay minerals, or rock fragments. This subdivision occurs 115 m above the base of the upper member. The data from the lower grouping (group A) show an important contribution from underlying Silurian rocks, with a relatively minor contribution from Late Devonian granitoid rocks from the adjacent Cobequid Highlands and possibly metasedimentary rocks from the Meguma Terrane to the south. The data from the upper grouping (group B) reveal a more important contribution from the Cobequid Highlands granitoid rocks. This variation in geochemistry is thought to constrain the age of renewed motion and uplift along the faults along the southern flank of the Maritimes Basin and, more generally, suggests that geochemical and isotopic data of continental clastic rocks may help constrain the age of tectonic events that influence deposition of basin-fill rocks.

40Ar/39Ar dating of micas from the East Kemptville tin deposit, Yarmouth County, Nova Scotia

1985 ◽  
Vol 22 (10) ◽  
pp. 1546-1548 ◽  
Author(s):  
M. Zentilli ◽  
P. H. Reynolds
Keyword(s):  
Nova Scotia ◽  
North America ◽  
Iberian Peninsula ◽  
South Mountain Batholith ◽  
Northwest Africa ◽  
Acadian Orogeny ◽  
Tin Deposit

The East Kemptville tin deposit in Nova Scotia, the largest known tin deposit in North America, lies in a greisen zone within the Davis Lake Pluton, generally considered to be part of the Devonian South Mountain Batholith. Our dating of micas from within the deposit suggests that the greisenization process that accompanied mineralization took place about 295 ± 5 Ma ago, that is, ca. 60 Ma after the emplacement of the batholith.Hydrothermal alteration–mineralization activity in southern Nova Scotia coincided with extensive shearing and tectonism throughout the Hercynian orogen. The East Kemptville deposit appears to be approximately coeval with similar mineralization in southwest England, the Iberian peninsula, and northwest Africa and much younger than the Devonian Acadian orogeny.

Nature and longevity of hydrothermal fluid flow and mineralisation in granites of the Bushveld Complex, South Africa

2000 ◽  
Vol 91 (1-2) ◽  
pp. 269-281 ◽  
Author(s):  
L. J. Robb ◽  
L. A. Freeman ◽  
R. A. Armstrong
Keyword(s):  
Fluid Flow ◽  
Bushveld Complex ◽  
Hydrothermal Activity ◽  
Incompatible Trace Element ◽  
Ore Deposits ◽  
Fluid Saturation ◽  
Fracture Systems ◽  
Sulphide Ores ◽  
Tin Deposit ◽  
Granite Suite

The Lebowa Granite Suite of the Bushveld Complex is a large, 2054 Ma old, A-type batholith, characterised by numerous relatively small magmato-hydrothermal, polymetallic ore deposits. The mineralisation is represented by a three-stage paragenetic sequence: early magmatic Sn-W-Mo-F ores (600°C > T > 400°C), followed by a Cu-Pb-Zn-As-Ag-Au paragenesis (400°C > T > 200°C) and then late-stage Fe-F-U mineralisation (< 200°C). The first stage of mineralisation (typified by the endogranitic Zaaiplaats tin deposit) is related to incompatible trace element concentration during crystal fractionation and subsequent fluid saturation of the magma. Evolution of the late magmatic fluids as they were channelled along fractures, as well as mingling with externally derived connate or meteoric fluids, resulted in the deposition of the second stage of mineralisation (typified by the fracture-related, endogranitic Spoedwel and Albert deposits and the exogranitic, sediment-hosted Rooiberg mine) which is dominated by polymetallic sulphide ores. As the externally derived fluid component became progressively more dominant, oxidation of the polymetallic sulphide assemblage and precipitation of hematite, pitchblende and fluorite occurred generally along the same fracture systems that hosted the earlier sulphide paragenesis.Small hydrothermal zircons trapped along quartz growth zones from the Spoedwel deposit yield a U-Pb concordia age of 1957 ± 15 Ma. Whole-rock Rb-Sr age determinations from the Lebowa Granite Suite fall in the range 1790 ± 114 Ma to 1604 ± 70 Ma and are interpreted to reflect alkali element mobility and isotopic resetting during exhumation of the Bushveld granite. In contrast to thermal modelling which indicates that hydrothermal activity should have ceased within 4 my of emplacement, isotopic evidence suggests that mineralisation was long-lived, but episodic, and that fluid flow events were linked to major periods of Palaeo- and Mesoproterozoic orogenic activity along the margins of the Kaapvaal Craton. During these orogenic episodes, fluid flow was enhanced by tectonically induced fluid over-pressuring and/or exhumation of the Bushveld Complex.

The East Kemptville tin deposit, Yarmouth County, Nova Scotia: a Pb-isotope study of the leucogranite and mineralized greisens—evidence for a 366 Ma metallogenic event

1992 ◽  
Vol 29 (6) ◽  
pp. 1180-1196 ◽  
Author(s):  
D. J. Kontak ◽  
A. K. Chatterjee
Keyword(s):  
Nova Scotia ◽  
Isotopic Composition ◽  
Regression Line ◽  
Data Set ◽  
Rock Samples ◽  
Best Estimate ◽  
Magmatic Reservoir ◽  
Pb Isotopic Composition ◽  
Isotope Study ◽  
Tin Deposit

Pb isotopic data for whole-rock leucogranite and mineral separates, variably mineralized greisen, and galena from the East Kemptville Sn(–Cu–Zn–Ag) deposit, Yarmouth County, southwestern Nova Scotia, Canada, are presented. In contrast with ca. 300–340 Ma ages (40Ar/39Ar, Rb–Sr) previously published, an age of 366 Ma is indicated from (i) a 207Pb/206Pb slope age for whole-rock samples (leucogranite and greisen) and galena; (ii) 207Pb/206Pb slope age for leachate analyses of whole-rock and mineral separates (muscovite, K-feldspar) for a leucogranite sample (EK-161); (iii) 207Pb/206Pb slope age for all samples (leucogranite, greisen, galena) combined; and (iv) a concordia plot for 12 whole-rock samples of leucogranite and greisen. The best estimate for the time of magmatic and hydrothermal events at East Kemptville, derived by using the entire Pb–Pb data set for both mineralized and barren samples, is 366 ± 4 Ma (2σ, N = 34, mean square of weighted deviates (MSWD) = 2.63), comparable to the concordia age of 367 ± 10 Ma (2σ, N = 10, MSWD = 4.62). Isochron plots for the U–Th–Pb data may suggest mild overprinting at ca. 300 Ma, but the data are not as conclusive as results from previous Rb/Sr and 40Ar/39Ar geochronological studies.Leachate analyses of mineral separates indicate that less radiogenic compositions are obtained with each progressive leach; however, initial lead compositions are not provided by the analyses for the residues of either K-feldspar or muscovite separates. This suggests, possibly, that these minerals have reequilibrated (i.e., exchanged lead) during the subsolidus stage with fluids enriched in radiogenic Pb. Instead, the best estimate of the initial lead compositon at East Kemptville (207Pb/204Pb = 15.601, 206Pb/204Pb = 18.141) is provided by the intersection of the 366 Ma Pb–Pb regression line for a leucogranite sample (EK-161) with a second-stage growth curve having μ = 9.75; this value is less radiogenic than the average measured isotopic composition of galena (207Pb/204Pb = 15.629 ± 0.004, 206Pb/204Pb = 18.627 ± 0.005, N = 4). The calculated μ value (9.75) for the source is consistent with an evolved upper crustal reservoir. Using the calculated initial Pb composition, it is calculated that 3–5 Ma would be required to generate the measured Pb isotopic composition of the galena assuming μ values of 980 and 590, respectively. The measured day average μ value for the leucogranite and greisen is 674 (N = 12, 1σ), which is consistent with the aforementioned calculations.The coincidence of independently derived ages for both leucogranite and mineralized greisens indicates that the host muscovite–topaz leucogranite and mineralizing fluids had a common magmatic reservoir, a conclusion supported by δ18O analyses for whole-rock leucogranite (8.2–10.5‰) and greisen (7.9–10.9‰) and previously published δ34S data. The data also indicate that magmatic and hydrothermal processes at East Kemptville are coeval with emplacement of the adjacent Davis Lake pluton. In addition, the results reaffirm the 365–370 Ma period to be a significant time for Sn(–W–Mo) metallogeny within the Meguma Zone of the Canadian Appalachians.

U–Pb and Rb–Sr geochronology of the Wedgeport granitoid pluton, southwestern Nova Scotia

1988 ◽  
Vol 25 (2) ◽  
pp. 255-261 ◽  
Author(s):  
R. F. Cormier ◽  
J. D. Keppie ◽  
A. L. Odom
Keyword(s):  
Nova Scotia ◽  
Shear Zone ◽  
Large Scale ◽  
Shear Zones ◽  
Potassium Feldspar ◽  
Slow Cooling ◽  
Northwestern Margin ◽  
Meguma Terrane ◽  
Tin Deposit ◽  
Straight Lines

Zircons from biotite monzogranite of the Wedgeport Pluton, intrusive into deformed metasediments of the Cambrian(?) Goldenville Formation in the southwestern Meguma Terrane of Nova Scotia, yield concordant U–Pb ages of 316 ± 5 Ma. This is interpreted as the time of intrusion and crystallization. Within the error limits, the 323 ± 12 Ma Rb–Sr whole-rock isochron age is identical and gives an initial 87Sr/86Sr ratio of 0.7137 ± 0.0056. Rb–Sr analyses of mineral separates of biotite, potassium feldspar, and quartz–plagioclase from several samples yield subparallel, internal isochrons with an average age of 257 ± 8 Ma. Initial ratios of the internal isochrons range from 0.716 to 0.759. A slow-cooling model for these latter data is discarded because the mineral data fall on straight lines. Instead, a reheating event related to plutonism ca. 257 Ma ago, which was sufficient to cause local grain-to-grain migration and reequilibration of strontium and rubidium but not large-scale redistribution, is invoked. This reheating is also inferred to be responsible for the hydrothermal alteration and Sn–U mineralization concentrated along the northwestern margin of the pluton. A dextral northeast–southeast shear zone cutting the pluton is also inferred to be ca. 257 Ma old. It may be related to the last stages of westward obduction of the Meguma Terrane.These results provide a clear example of Permo-Carboniferous plutonism in the southwestern Meguma Terrane and suggest a similar interpretation may apply to other anomalously young ages recorded in this area. In light of these results, the Permo-Carboniferous age of the large East Kemptville tin deposit and its location in a dextral shear zone suggest that the association of younger plutonism and shear zones may be a significant factor for economic mineralization.

Sm/Nd isotopic investigation of the age and origin of the Meguma Zone metasedimentary rocks

1985 ◽  
Vol 22 (1) ◽  
pp. 102-107 ◽  
Author(s):  
D. B. Clarke ◽  
A. N. Halliday
Keyword(s):  
Nova Scotia ◽  
Residence Times ◽  
Isotopic Data ◽  
Metasedimentary Rocks ◽  
Depositional Age ◽  
Isotopic Investigation

The Meguma Zone of southern Nova Scotia is a suspect terrane in the eastern Appalachians. Sm/Nd isotopic data on six samples from the thick sequence of flyschoid metasediments of the Meguma Group show that these rocks have a mean crustal residence age of TDM = 1773 ± 95 Ma, considerably older than their Cambro-Ordovician depositional age. This information should be useful in locating the matching terrane for the Meguma and ultimately in determining whether it was derived from one or more Precambrian sources with different crustal residence times.

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