Reply to the discussion of the reply by R.L. Romer and U. Kroner on “Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian shelf” 1Appears in the Canadian Journal of Earth Sciences, 49(11): 1372–1377 [doi:10.1139/e2012-049].

2012 ◽  
Vol 49 (11) ◽  
pp. 1378-1383
Author(s):  
Rolf L. Romer ◽  
Uwe Kroner
Keyword(s):  
Earth Sciences ◽  
Canadian Journal ◽  
Sedimentary Rocks ◽  
Sedimentary Sequence ◽  
The Core ◽  
Geochemical Signature

Romer and Kroner (2012) stated “the core of the Harlech Dome (i) in part is made up of Ordovician deposits and (ii) contains tectonic repetitions”. In their comment, Schofield et al. (this issue) distort this statement and state that (i) we claim the entire sedimentary sequence of the Harlech Dome is Ordovician and (ii) we misinterpreted their zircon data. We disagree. In our reply, we demonstrate that the argumentation of Schofield et al. (this issue) is driven by circular argumentation and that their use and interpretation of U–Pb zircon data is inadequate.

Reply to the discussion by J.W.F. Waldron and C.E. White on “Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian shelf”1Appears in Canadian Journal of Earth Sciences, 2012, 49(6): 772–774 [doi: 10.1139/e2012-004].

2012 ◽  
Vol 49 (6) ◽  
pp. 775-780 ◽  
Author(s):  
Rolf L. Romer ◽  
Uwe Kroner
Keyword(s):  
Earth Sciences ◽  
Nova Scotia ◽  
Canadian Journal ◽  
Deep Water ◽  
Sedimentary Rocks ◽  
Geochronological Data ◽  
Early Ordovician ◽  
Geochemical Signature

In their comment, Waldron and White state that manganese-rich sedimentary rocks of Nova Scotia and Wales are Cambrian and were deposited in a deep-water turbidite basin called “Megumia” rather than on the Avalonian shelf. Available geochronological data are not in conflict with an Early Ordovician deposition age for manganese-rich sedimentary rocks north of the Rheic suture, including those of Nova Scotia and northern Wales. “Megumia” is part of the Avalonian plate, and the manganese-rich sediments were deposited on its shelf.

Discussion of “Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian shelf”1Appears in Canadian Journal of Earth Sciences, 2011, 48(4): 703–718 [doi: 10.1139/e10-092].

2012 ◽  
Vol 49 (6) ◽  
pp. 772-774 ◽  
Author(s):  
John W.F. Waldron ◽  
Chris E. White
Keyword(s):  
Nova Scotia ◽  
Canadian Journal ◽  
Water Depth ◽  
Deep Water ◽  
Sedimentary Environment ◽  
Sedimentary Rocks ◽  
Geochemical Data ◽  
Geochemical Signature ◽  
North Wales ◽  
Mn Concentration

The paper “Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian shelf” (Romer et al., published in 2011) describes six samples of which four are from the Meguma Supergroup of Nova Scotia. Previous work indicates that these samples are Cambrian and that they were deposited in a deep-water turbidite basin (“Megumia”), not on the Avalonian shelf. The geochemical data support models for Mn concentration, involving oxidation and reduction in a sedimentary environment but do not constrain water depth. Likely correlatives are in the Cambrian of North Wales and not in the European localities sampled by the authors.

scholarly journals Canadian Journal of Earth Sciences

Nature ◽  
1964 ◽  
Vol 203 (4951) ◽  
pp. 1227-1227 ◽  
Keyword(s):  
Earth Sciences ◽  
Canadian Journal

An Overview of the ULU Gold Deposit, High Lake Volcanic Belt, Nunavut, Canada

2004 ◽  
Vol 13 (1-4) ◽  
pp. 15-23
Author(s):  
E. FLOOD ◽  
P. KLEESPIES ◽  
M. TANSEY ◽  
H. MUNTANION ◽  
R. CARPENTER
Keyword(s):  
Mineral Assemblage ◽  
Spatial Association ◽  
Sedimentary Rocks ◽  
Volcanic Belt ◽  
Wall Rock ◽  
Potassium Feldspar ◽  
Lode Gold ◽  
The Core ◽  
Flood Zone ◽  
Alteration Minerals

Abstract BHP Minerals discovered the Archean lode gold ULU deposit on the western margin of the High Lake Volcanic Belt in 1989. The greenschist to amphibolite facies mafic volcanic and sedimentary rocks on the property are folded into a 5 km-long anticline. There is a close spatial association of Au-As zones to the trace of this F2 ULU anticline. The largest of these auriferous zones, the Flood zone, is localized at the core of the fold. The southeast-trending Flood zone consists of several anastomosing lenses that have been traced for 435 m on surface. Overall, it dips steeply (70° to 80°) to the southwest and has been intersected to depths below 600 m. The hosting high-iron tholeitic basalt displays a lower amphibolite mineral assemblage of ferrohornblende + plagioclase + ilmenite with accessory quartz and epidote. Alteration minerals include biotite, chlorite, hornblende, actinolite-tremolite, and potassium feldspar (microcline) with minor calcite, epidote, tourmaline, and titanite. The highest gold values occur where brecciated basaltic wall-rock clasts are replaced by acicular arsenopyrite + quartz + K-feldspar. BHP Minerals completed 54,783 m of both exploration and resource development drilling before selling the ULU property to Echo Bay Mines in 1995. Development of ULU as a satellite deposit to Echo Bay’s Lupin mine began in 1996. A -15% ramp was extended to the 155-meter level, and 16,011 m of underground drilling were completed before the decline in gold prices forced a suspension of activities at ULU in August 1997. The current owners, Wolfden Resources Inc., drilled 18,569 m in 2004 to increase confidence in the resource blocks. Following this drill program, a revised resource calculated by an independent consultant determined that the ULU deposit contains an inferred/indicated mineral resource of 1,130,000 t grading 11.34 g/t gold (373,748 oz) to the 360-m level. The portal was re-opened in 2005 and a prefeasibility study is underway.

Petrophysical Rocks: Electrofacies and Lithofacies

2014 ◽  
Author(s):  
John H. Doveton
Keyword(s):  
Particle Size ◽  
Physical Properties ◽  
Sedimentary Rocks ◽  
Well Control ◽  
The Core ◽  
Lateral Extent ◽  
Petrophysical Logs ◽  
Definition Of

Many years ago, the classification of sedimentary rocks was largely descriptive and relied primarily on petrographic methods for composition and granulometry for particle size. The compositional aspect broadly matches the goals of the previous chapter in estimating mineral content from petrophysical logs. With the development of sedimentology, sedimentary rocks were now considered in terms of the depositional environment in which they originated. Uniformitarianism, the doctrine that the present is the key to the past, linked the formation of sediments in the modern day to their ancient lithified equivalents. Classification was now structured in terms of genesis and formalized in the concept of “facies.” A widely quoted definition of facies was given by Reading (1978) who stated, “A facies should ideally be a distinctive rock that forms under certain conditions of sedimentation reflecting a particular process or environment.” This concept identifies facies as process products which, when lithified in the subsurface, form genetic units that can be correlated with well control to establish the geological architecture of a field. The matching of facies with modern depositional analogs means that dimensional measures, such as shape and lateral extent, can be used to condition reasonable geomodels, particularly when well control is sparse or nonuniform. Most wells are logged rather than cored, so that the identification of facies in cores usually provides only a modicum of information to characterize the architecture of an entire field. Consequently, many studies have been made to predict lithofacies from log measurements in order to augment core observations in the development of a satisfactory geomodel that describes the structure of genetic layers across a field. The term “electrofacies” was introduced by Serra and Abbott (1980) as a way to characterize collective associations of log responses that are linked with geological attributes. They defined electrofacies to be “the set of log responses which characterizes a bed and permits it to be distinguished from the others.” Electrofacies are clearly determined by geology, because physical properties of rocks. The intent of electrofacies identification is generally to match them with lithofacies identified in the core or an outcrop.

scholarly journals Amazonian Mesoproterozoic basement in the core of the Ibero-Armorican Arc: 40Ar/39Ar detrital mica ages complement the zircon's tale

Geology ◽  
2005 ◽  
Vol 33 (8) ◽  
pp. 637-640 ◽  
Author(s):  
G. Gutiérrez-Alonso ◽  
J. Fernández-Suárez ◽  
Alan S. Collins ◽  
I. Abad ◽  
F. Nieto
Keyword(s):  
Detrital Zircon ◽  
Sedimentary Rocks ◽  
Age Groups ◽  
Strike Slip ◽  
Zircon Age ◽  
Provenance Studies ◽  
The Core ◽  
Pan African ◽  
Rio Negro ◽  
Northwest Iberia

Abstract The 40Ar/39Ar age data on single detrital muscovite grains complement U-Pb zircon ages in provenance studies, as micas are mostly derived from proximal sources and record low-temperature processes. Ediacaran and Cambrian sedimentary rocks from northwest Iberia contain unmetamorphosed detrital micas whose 40Ar/39Ar age spectra suggest an Amazonian–Middle American provenance. The Ediacaran sample contained only Neoproterozoic micas (590–783 Ma), whereas the Cambrian sample contained three age groups: Neoproterozoic (550–640 Ma, Avalonian–Cadomian–Pan African), Mesoproterozoic- Neoproterozoic boundary (ca. 920–1060 Ma, Grenvillian-Sunsas), and late Paleoproterozoic (ca. 1580–1780 Ma, Rio Negro). Comparison of 40Ar/39Ar muscovite ages with published detrital zircon age data from the same formations supports the hypothesis that the Neoproterozoic basins of northwest Iberia were located in a peri-Amazonian realm, where the sedimentary input was dominated by local periarc sources. Tectonic slivering and strike-slip transport along the northern Gondwanan margin affected both the basins and fragments of basement that were transferred from Amazonian to northern African realms during the latest Neoproterozoic–earliest Cambrian. Exhumation and erosion of these basement sources caused shedding of detritus to the Cambrian basins, in addition to detritus sourced in the continental mainland. The apparent dominance of Rio Negro–aged micas in the Cambrian sandstone suggests the presence of unexposed basement of that age beneath the core of the Ibero-Armorican Arc.

U–Pb geochronology of the Moyie sills, Purcell Supergroup, southeastern British Columbia: implications for the Mesoproterozoic geological history of the Purcell (Belt) basin

1995 ◽  
Vol 32 (8) ◽  
pp. 1180-1193 ◽  
Author(s):  
H. Elizabeth Anderson ◽  
Donald W. Davis
Keyword(s):  
United States ◽  
Tectonic Setting ◽  
Sedimentary Rocks ◽  
The United States ◽  
The Other ◽  
Soft Sediment ◽  
Geological History ◽  
Sedimentary Sequence ◽  
Belt Supergroup ◽  
History Of

The Mesoproterozoic Purcell Supergroup (and its equivalent in the United States, the Belt Supergroup) is a thick sedimentary sequence formed in an extensional basin of uncertain age and tectonic setting. The voluminous tholeiitic Moyie sills intrude turbidites of the lower and middle Aldridge Formation, the lowest division of the Purcell Supergroup. Many of the sills were intruded into soft sediment and one intrudes the Sullivan sedimentary exhalative (SEDEX) orebody, so their age approximates that of the sediments and the Sullivan deposit. New U–Pb dates of zircon from four sills are older than previously published U–Pb zircon ages. One sill contained concordant zircons with an age of 1468 ± 2 Ma. Near concordant zircons from the other samples have similar 207Pb/206Pb ages, indicating that all of the sills crystallized at the same time. U–Pb dates of titanites from two of these sills yielded concordant dates ranging from 1090 to 1030 Ma, indicating that they have undergone a previously unrecognized Grenville-age metamorphism. The U–Pb systematics of abraded zircons from one sill indicate that they have also been affected by this event. The recognition of Grenville-age metamorphism in the Purcell (Belt) basin suggests that the prevalent 1.0–1.1 Ga Rb–Sr and K–Ar mineral and whole-rock dates from a wide variety of Purcell (Belt) igneous and sedimentary rocks are also metamorphic, and are not ages of sedimentation or "hybrid" dates reflecting partial resetting by the ca. 760 Ma Goat River orogeny. On this basis, all sedimentation in the Purcell (Belt) basin is constrained to be older than 1.1 Ga and is probably older than 1.25 Ga.

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