2.2. Investigaciones relacionadas
2.2.2. Implementación de ambientes personales de aprendizaje en donde ha mediado el uso de TIC.
Regional exploration by Wallbridge Mining Company Limited has led to several Offset dyke Ni-Cu-PGE discoveries over the past decade, including the discovery and extension of the Trill. The Trill offers unique phases and phase relationships not seen at other Offset dykes and are summarized herein:
1. Four texturally distinct varieties of Quartz Diorite (e.g., IQD, QD, QDg and SQD)
are observed at middle Trill and display minor differences in primary geochemistry.
2. Middle Trill displays two parallel splays of the Offset dyke roughly 75 m apart
(Fig. 2.4), which resembles either a large-scale en echelon dyke or there is a large granitic clast within the dyke. Regardless, the change in dyke morphology favors Ni-Cu-PGE mineralization.
3. Irregularly shaped inclusions of Metabreccia are observed within the QD (Fig.
2.5E) and the QD appears to intrude the Metabreccia groundmass (Fig. 2.5F) indicating the Metabreccia formed prior to the QD.
4. SQD and QDg are not observed as inclusions within either the QD or IQD and are
geochemically indistinguishable to the QD; therefore are interpreted to represent a rapidly quenched QD as observed and interpreted at other Offset dykes.
5. QD is observed as inclusions within the IQD (Fig. 2.5B). Both gradational (Fig.
6. For the first time, we show that the IQD dissipates along strike somewhere from 4–8 km at Trill. Interestingly, similar observations are made in flow
differentiation experiments with slower emplacement velocities.
7. There is an overall decrease in the number (Fig. 2.6B) and size (Fig. 2.6C) of
inclusions in the IQD westwards (Fig. 2.6B), along with a high abundance of diabase inclusions ~20 m west of a NW trending Matachewan diabase dyke in the host rocks (Fig. 2.6B) at middle Trill. This is interpreted to suggest the inclusions are moving more distal from their source towards the west; however, it is
important to note this does not preclude a downwards component in flow direction.
8. At Middle Trill 15% of inclusions had a measurable long-axis orientation ≤ 14°
with the local dyke orientation (Fig. 2.6A). These data are used as evidence to suggest the dyke was turbulent during emplacement and that the inclusions with a long-axis orientation were orientated near parallel with the general flow direction of the dyke (e.g. outwards).
9. Ni-Cu-PGE mineralization is most abundant to distances of at least 4 km from the
SIC and in the central IQD phase. The Co-zoned pyrite, braggite and niggliite are used as evidence to suggest the mineralization was exsolved from the MSS with some later-stage remobilization of the PGE.
2.7
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Chapter 3
3
New investigations of the Ni-Cu-PGE bearing Parkin Offset
dyke, Sudbury impact structure, Canada
3.1
Introduction
The Sudbury impact structure in Ontario, Canada is now widely accepted as the erosional remnant of a tectonized 200- to 250-km multi-ring impact basin, as originally argued by Grieve et al. (1991). Precise U-Pb zircon and baddeleyite dating of the impact lithologies place its formation at 1.85 Ga, during the Penokean Orogeny (Krogh et al., 1996), which can account for its elliptical deformation (Deutsch et al., 1995). The Sudbury structure is composed of three major geologic units, from the centre of the structure outwards they are: the Whitewater Group, the Sudbury Igneous Complex (SIC) and the shocked and brecciated host rocks of the crater floor (Fig. 3.1) (Dressler, 1984; Grieve et al., 1991). The Sudbury structure is situated between two major Precambrian terranes: the Archean granite-greenstone and gneiss terrane of the Superior Province in the north, the
Paleoproterozoic metasedimentary and metavolcanic rocks of the Huronian Supergroup of the Southern Province in the south (Dressler, 1984). The Grenville Front is situated 8 to 16 km southeast of the Sudbury structure and represents the northwestern boundary of the Grenville province (Fig. 3.1) (Brocoum and Dalziel, 1974). The Sudbury structure is host to some of the world’s largest Ni-Cu-PGE deposits and has been exploited for well over 100 years.
As initially argued in Grieve et al. (1991), the SIC is widely believed to be a differentiated impact melt sheet. In plan view, the SIC is elliptical in shape and is
approximately 27 by 60 km (Fig. 3.1), 2.5- to 3.0-km-thick and has an estimated volume
of 8,000 to 14,000 km3 (Grieve, 1994). The SIC is divided into three main geographic
regions: the North Range, which dips at about 30° to 50° to the south, the South Range and the East Range, the latter two dip steeply to near vertical northward and westward, respectively (Dressler, 1984). There are four defined lithological units of the SIC, from the top downwards they are the: Upper Contact Unit (Formerly the Onaping Intrusion), Granophyre, Quartz Gabbro and Norite (Dressler et al., 1992; Anders et al., 2015). At the
base of the SIC there are discontinuous kilometre-scale bodies of the contact sublayer situated in embayment structures (Lightfoot et al., 1997a; Lightfoot et al., 1997b; Morrison, 1984). These embayment structures are characterized by abundant xenoliths and Cu-Ni sulphide mineralization, which often extends outwards into the radial Offset dykes (Lightfoot et al., 1997a).
Emanating from some of the embayment structures are so-called Offset dykes. These structures occur as radial, concentric and discontinuous bodies around the Sudbury impact structure (Fig. 3.1) (Wood and Spray, 1998). The rocks of the Offset dykes are known as “Quartz Diorite”; however, they vary compositionally between quartz
monzodioritic, granodiorite and tonalite (Wood and Spray, 1998). Inclusion free quartz diorite (QD) and at least two variants of inclusion bearing quartz diorite (IQD) are observed within the Offset dykes. There are currently eighteen known Offset dykes surrounding the Sudbury impact structure: eleven radial dykes (Copper Cliff, Worthington, Whistle, Parkin, Ministic, Foy, Cascadian, Trill, Pele (3 dykes)), five concentric (Hess, McConnell and Kirkwood, Frood-Stobie, Vermillion, and Manchester,) and two discontinuous dykes (Creighton and Maclennan) (Fig. 3.1) (Grant and Bite, 1984; Smith et al., 2013). The focus of this investigation is on the radial Parkin Offset dyke (Parkin) located in the northeastern corner of the Sudbury impact structure (Fig. 3.1).
Figure 3.1 Simplified geological map of the Sudbury impact structure. Modified form OGS bedrock regional 1:250,000 scale maps and internal Wallbridge Mining Company Limited maps.