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Forest Reefs Volcanics

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Silurian conodonts from the uppermost parts of the Forest Reefs Volcanics (from drill hole CC003 at 362.4 m). A. Unidentified coniform element. B, C. Distomodus sp., M element, lateral and oblique basal views. D. Panderodus unicostatus. E. Panderodus unicostatus. F. Distomodus? sp., fragmentary element in oblique basal view. G. Oulodus cf. O. planus, fragmentary Pa element. H. Oulodus cf. O. planus, Pa element. J. Oulodus sp., M element. K, L. Distomodus sp., Pb? element, lateral and oblique basal views. Features of these conodonts are consistent with those considered Early Silurian (Llandovery-Wenlock) in age.

Silurian conodonts from the uppermost parts of the Forest Reefs Volcanics (...

Published: 01 June 2014
Fig. 8 Silurian conodonts from the uppermost parts of the Forest Reefs Volcanics (from drill hole CC003 at 362.4 m). A. Unidentified coniform element. B, C. Distomodus sp., M element, lateral and oblique basal views. D. Panderodus unicostatus . E. Panderodus unicostatus . F. Distomodus ? sp
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Siltstone and sandstone of the Weemalla Formation and Forest Reefs Volcanics. A. Laminar interbeds of feldspathic sandstone and siltstone of the Weemalla Formation. B. Feldspathic sandstone, siltstone, and siliceous siltstone replaced by epidote-garnet-feldspar alteration, Weemalla Formation. C. Erosive base to a thin succession of feldspathic sandstone and siliceous siltstone intercalated within the Forest Reefs Volcanics.

Siltstone and sandstone of the Weemalla Formation and Forest Reefs Volcanic...

Published: 01 June 2014
Fig. 5 Siltstone and sandstone of the Weemalla Formation and Forest Reefs Volcanics. A. Laminar interbeds of feldspathic sandstone and siltstone of the Weemalla Formation. B. Feldspathic sandstone, siltstone, and siliceous siltstone replaced by epidote-garnet-feldspar alteration, Weemalla
Journal Article

Marine Volcanosedimentary Basins Hosting Porphyry Au-Cu Deposits, Cadia Valley, New South Wales, Australia

Anthony C. Harris, Ian G. Percival, David R. Cooke, Richard M. Tosdal, Nathan Fox, Charlotte M. Allen, Ian Tedder, Colin McMillan, Paul Dunham, Dean Collett
Journal: Economic Geology
Published: 01 June 2014
Economic Geology (2014) 109 (4): 1117–1135.
DOI: https://doi.org/10.2113/econgeo.109.4.1117
...Fig. 8 Silurian conodonts from the uppermost parts of the Forest Reefs Volcanics (from drill hole CC003 at 362.4 m). A. Unidentified coniform element. B, C. Distomodus sp., M element, lateral and oblique basal views. D. Panderodus unicostatus . E. Panderodus unicostatus . F. Distomodus ? sp...
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View PDF for article title, Marine Volcanosedimentary Basins Hosting Porphyry Au-Cu Deposits, Cadia Valley, New South Wales, Australia
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Fig. 3. Interpreted geology and structure of section 11050E through the Ridgeway deposit. Mineralization is intimately associated with monzonite intrusions of the Ridgeway Intrusive Complex. Minor dislocation of mineralization is associated with the North and Purple faults. In addition, variation in the stratigraphic thickness of the andesite-clast volcanic conglomerate unit that overlies the transitional unit is interpreted to suggest that the North fault was in extension during deposition of at least part of the Forest Reefs Volcanics and may have influenced localization of the Ridgeway Intrusive Complex. Abbreviations: cpx = clinopyroxene, FRV = Forest Reefs Volcanics, Om = Weemalla Formation, pl = plagioclase. Numbers after the Forest Reefs Volcanics lithology in the key refer to the lithofacies association discussed in the text.

F ig . 3. Interpreted geology and structure of section 11050E through the R...

Published: 01 December 2003
in the stratigraphic thickness of the andesite-clast volcanic conglomerate unit that overlies the transitional unit is interpreted to suggest that the North fault was in extension during deposition of at least part of the Forest Reefs Volcanics and may have influenced localization of the Ridgeway Intrusive Complex
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Method for correlating volcanic stratigraphy through the Forest Reefs Volcanics. Shown here are correlative volcanic and volcaniclastic rocks that show identical phenocryst proportions (type, size, and abundance), irrespective of their mode of formation. This method can show that coherent facies (with same proportion of phenocrysts and, therefore, similar whole-rock geochemistry) intercalate lateral reworked equivalents that comprise dominant clasts of similar lava compositions. The same scale applies to all photographs. Ferromagnesian minerals are colored yellow. Feldspars are colored red.

Method for correlating volcanic stratigraphy through the Forest Reefs Volca...

Published: 01 June 2014
Fig. 2 Method for correlating volcanic stratigraphy through the Forest Reefs Volcanics. Shown here are correlative volcanic and volcaniclastic rocks that show identical phenocryst proportions (type, size, and abundance), irrespective of their mode of formation. This method can show that coherent
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Regional geologic map of the Cadia Valley and surrounding district (compiled from geologic maps produced during the 1990s; Homestake Mining and Newcrest Mining Ltd). Regionally, the Late Ordovician volcanic and volcaniclastic rocks interfinger with arc-derived feldspathic turbidite succession; Ea3 graptolites in turbidites (of the Weemalla Formation) are time equivalent to the Ea3 calcareous units of the Forest Reefs Volcanics.

Regional geologic map of the Cadia Valley and surrounding district (compile...

Published: 01 June 2014
succession; Ea3 graptolites in turbidites (of the Weemalla Formation) are time equivalent to the Ea3 calcareous units of the Forest Reefs Volcanics. Continuity of sedimentation between underlying deep marine basin deposits of the Weemalla Formation and Forest Reefs Volcanics, coupled with the predominance
Image
Regional geologic map of the Cadia Valley and surrounding district (compiled from geologic maps produced during the 1990s; Homestake Mining and Newcrest Mining Ltd). Regionally, the Late Ordovician volcanic and volcaniclastic rocks interfinger with arc-derived feldspathic turbidite succession; Ea3 graptolites in turbidites (of the Weemalla Formation) are time equivalent to the Ea3 calcareous units of the Forest Reefs Volcanics.

Regional geologic map of the Cadia Valley and surrounding district (compile...

Published: 01 June 2014
succession; Ea3 graptolites in turbidites (of the Weemalla Formation) are time equivalent to the Ea3 calcareous units of the Forest Reefs Volcanics. Continuity of sedimentation between underlying deep marine basin deposits of the Weemalla Formation and Forest Reefs Volcanics, coupled with the predominance
Book Chapter

Chapter 30: Geologic Evolution of Late Ordovician to Early Silurian Alkalic Porphyry Au-Cu Deposits at Cadia, New South Wales, Australia

Author(s)
Anthony C. Harris, David R. Cooke, Ana Liza Garcia Cuison, Malissa Groome, Alan J. Wilson, Nathan Fox, John Holliday, Richard Tosdal
Book: Geology of the World’s Major Gold Deposits and Provinces
Series: Special Publications of the Society of Economic Geologists
Publisher: Society of Economic Geologists
Published: 01 January 2020
DOI: 10.5382/SP.23.30
EISBN: 9781629496429
...). The ore deposits are hosted by volcaniclastic rocks of the Weemalla Formation and Forest Reefs Volcanics, which were deposited in a submarine basin on the flanks of the Macquarie Arc during the Middle to Late Ordovician. Alkalic magmatism occurred during the Benambran orogeny in the Late Ordovician...
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Abstract The Cadia district of New South Wales contains four alkalic porphyry Au-Cu deposits (Cadia East, Ridgeway, Cadia Hill, and Cadia Quarry) and two Cu-Au-Fe skarn prospects (Big Cadia and Little Cadia), with a total of ~50 Moz Au and ~9.5 Mt Cu (reserves, resources, and past production). The ore deposits are hosted by volcaniclastic rocks of the Weemalla Formation and Forest Reefs Volcanics, which were deposited in a submarine basin on the flanks of the Macquarie Arc during the Middle to Late Ordovician. Alkalic magmatism occurred during the Benambran orogeny in the Late Ordovician to early Silurian, resulting in the emplacement of monzonite intrusive complexes and the formation of porphyry Au-Cu mineralization. Ridgeway formed synchronous with the first compressive peak of deformation and is characterized by an intrusion-centered quartz-magnetite-bornite-chalcopyrite-Au vein stockwork associated with calc-potassic alteration localized around the apex of the pencil-like Ridgeway intrusive complex. The volcanic-hosted giant Cadia East deposit and the intrusion-hosted Cadia Hill and Cadia Quarry deposits formed during a period of relaxation after the first compressive peak of the Benambran orogeny and are characterized by sheeted quartz-sulfide-carbonate vein arrays associated with subtle potassic, calc-potassic, and propylitic alteration halos.

Journal Article

Automated Core Logging Technology for Geotechnical Assessment: A Study on Core from the Cadia East Porphyry Deposit

Cassady L. Harraden, Matthew J. Cracknell, James Lett, Ron F. Berry, Ronell Carey, Anthony C. Harris
Journal: Economic Geology
Published: 01 December 2019
Economic Geology (2019) 114 (8): 1495–1511.
DOI: https://doi.org/10.5382/econgeo.4649
... the Forest Reefs Volcanics and is spatially and temporally associated with the Cadia Intrusive Complex. To extract ore, the underground mine currently uses the block cave mining method. The Cadia East geotechnical model provides data inputs into a range of numerical and empirical analysis methods that make...
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The Silurian Waugoola Group. A. Unconformity between the fossiliferous limestone of the Late Silurian Waugoola Group and the altered volcaniclastic rocks of the Early Silurian-Late Ordovician Forest Reefs Volcanics. B. Polymictic sedimentary breccia comprising contrasting intrusive rocks, including aphanitic basalts and feldspar-phyric basaltic andesite. Epidote-altered clasts also occur. The sedimentary matrix in this breccia is altered by hematite-chlorite. C. Clasts of hydrothermal quartz veins and skarn occur in sedimentary breccias. Extracted fossils from these breccias are diagnostically Early Silurian. Limestones found at the top of the Forest Reefs Volcanics imply that accumulation of the volcanic-derived detritus occurred till the Early Silurian. A considerable thickness of volcanic and sedimentary overburden was removed (over 1 km) prior to the Early Silurian; exhumation resulted in the exposure of the Cadia Intrusive Complex, resulting in basin-fill material rich in monzonite clasts. Subsequent exhumation occurred prior to the deposition of the Silurian Waugoola Group (Wenlock to Ludlow, to Pridoli; Rickards et al., 2001; Rickards and Wright, 2004).

The Silurian Waugoola Group. A. Unconformity between the fossiliferous lime...

Published: 01 June 2014
Fig. 7 The Silurian Waugoola Group. A. Unconformity between the fossiliferous limestone of the Late Silurian Waugoola Group and the altered volcaniclastic rocks of the Early Silurian-Late Ordovician Forest Reefs Volcanics. B. Polymictic sedimentary breccia comprising contrasting intrusive rocks
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Graphic log showing lithology variation in the basal parts of the Forest Reefs Volcanics. Hyaloclastites overlap and intercalate fine-grained feldspathic turbidites. Lava compositions change upsequence.

Graphic log showing lithology variation in the basal parts of the Forest Re...

Published: 01 June 2014
Fig. 14 Graphic log showing lithology variation in the basal parts of the Forest Reefs Volcanics. Hyaloclastites overlap and intercalate fine-grained feldspathic turbidites. Lava compositions change upsequence.
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Graphic log showing lithology variation through largely coherent facies in the uppermost parts of the Forest Reefs Volcanics. Lateral equivalents to the lavas occurring at the top of this section include air-fall deposits that record sustained phreatomagmatic eruptions (drill hole NC582, east of Cadia East).

Graphic log showing lithology variation through largely coherent facies in ...

Published: 01 June 2014
Fig. 15 Graphic log showing lithology variation through largely coherent facies in the uppermost parts of the Forest Reefs Volcanics. Lateral equivalents to the lavas occurring at the top of this section include air-fall deposits that record sustained phreatomagmatic eruptions (drill hole NC582
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Schematic representation of the volcanic facies architecture of the Cadia district showing the position of several key geographic locations, including the Ridgeway and Cadia East ore deposits. The paleogeography shown is that inferred for the Late Ordovician, immediately prior to the emplacement of the ore-forming intrusions. The preserved stratigraphy records an evolution from effusive to explosive volcanism. Available chronologic data suggests the Forest Reefs Volcanics were deposited from the Ordovician through to the Early Silurian.

Schematic representation of the volcanic facies architecture of the Cadia d...

Published: 01 June 2014
to the emplacement of the ore-forming intrusions. The preserved stratigraphy records an evolution from effusive to explosive volcanism. Available chronologic data suggests the Forest Reefs Volcanics were deposited from the Ordovician through to the Early Silurian.
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Heat map showing the distribution of poles to fracture surfaces on a lower hemisphere equal area stereographic projection. Measured (A) and calculated (B) fracture orientations for detected fractures in the Forest Reefs Volcanics. Measured (C) and calculated (D) fracture orientations for fractures in the Cadia Intrusive Complex. In general, the trends observed in the calculated and measured stereographic projections are similar.

Heat map showing the distribution of poles to fracture surfaces on a lower ...

Published: 01 December 2019
Fig. 9. Heat map showing the distribution of poles to fracture surfaces on a lower hemisphere equal area stereographic projection. Measured (A) and calculated (B) fracture orientations for detected fractures in the Forest Reefs Volcanics. Measured (C) and calculated (D) fracture orientations
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Lithology variations across the transition from the Weemalla Formation (including the Mt. Pleasant Basalt) to the Forest Reefs Volcanics (drill hole NC570, located west of Ridgeway). New zircon U-Pb ages have been determined from volcaniclastic rocks of the Mt. Pleasant Basalt and yield a mean age of ca. 452 Ma (App. 1A). Intercalated fossiliferous carbonates imply that shallow marine conditions existed during effusive volcanism. Plag. = plagioclase. Rock unit legend used here applies to all graphical logs presented in this paper.

Lithology variations across the transition from the Weemalla Formation (inc...

Published: 01 June 2014
Fig. 6 Lithology variations across the transition from the Weemalla Formation (including the Mt. Pleasant Basalt) to the Forest Reefs Volcanics (drill hole NC570, located west of Ridgeway). New zircon U-Pb ages have been determined from volcaniclastic rocks of the Mt. Pleasant Basalt and yield
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Fig. 2. Geology of the Cadia district and location of the principal zones of porphyry- and skarn-related gold-copper mineralization. The Ridgeway deposit is concealed by Miocene basaltic lava flows. The location of sections 11050E and 22750N at Ridgeway (Figs. 3 and 4, respectively) are also shown. Based on unpublished mapping of Newcrest Mining Limited (reproduced with permission), and modified from Holliday et al. (2002). Abbreviations: CIC = Cadia Intrusive Complex, FRV = Forest Reefs Volcanics.

F ig . 2. Geology of the Cadia district and location of the principal zones...

Published: 01 December 2003
shown. Based on unpublished mapping of Newcrest Mining Limited (reproduced with permission), and modified from Holliday et al. (2002) . Abbreviations: CIC = Cadia Intrusive Complex, FRV = Forest Reefs Volcanics.
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Deposit characteristics of coherent lava and in situ monomictic lava breccia (Forest Reefs Volcanics). A. Clast-rich unit of finely vesicular juvenile clasts exhibiting distinct polygonal clast shapes. This clast-supported, tightly packed autoclastic breccia exhibits jigsaw-fit textures. B. Juvenile clasts can show irregular curviplanar and cuspate margins. In fine detail, the clast margins are distinctly ragged. Rare lobate (pillow-like) structures occur in more coherent domains. Pencil is 15 cm long (GR. 684468, 6298826).

Deposit characteristics of coherent lava and in situ monomictic lava brecci...

Published: 01 June 2014
Fig. 9 Deposit characteristics of coherent lava and in situ monomictic lava breccia (Forest Reefs Volcanics). A. Clast-rich unit of finely vesicular juvenile clasts exhibiting distinct polygonal clast shapes. This clast-supported, tightly packed autoclastic breccia exhibits jigsaw-fit textures. B
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Geology of the Late Ordovician Macquarie Arc of New South Wales. The Ordovician Molong volcanic belt (MVB) is one of the four segments of the dismembered oceanic arc. These volcanic belts formed together as part of one arc and were disrupted during rifting of the Hill End and Cowra trough. Middle to Late Ordovician rocks of the Junee-Narromine volcanic belt (JNVB) preserve the center of the volcanic arc, where basaltic andesitic and andesitic stratovolcanoes are the expression of suprasubduction zone magmatism (e.g., Simpson et al., 2007). The Molong volcanic belt comprises multiple packages of volcanic and volcaniclastic rocks, including the Forest Reefs Volcanics, host to the Cadia Valley porphyry Au-Cu deposits. The arc-related andesitic succession is dominated by thick sequences of volcanosedimentary breccias with volumetrically minor lavas (Squire, 2001). The volcaniclastic rocks conformably overlie and interfinger with fine-grained turbidites deposited in a restricted sedimentary basin east-southeast of an arc-like volcanic succession. A thicker apron of deep marine turbidites and fine-grained volcaniclastic rocks filled a more extensive basin that developed to the east of the Cadia district, occurring as the arc volcanic rocks of the Rockley-Gulgong volcanic belt (RGVB). KVB = Kiandra volcanic belt.

Geology of the Late Ordovician Macquarie Arc of New South Wales. The Ordovi...

Published: 01 June 2014
packages of volcanic and volcaniclastic rocks, including the Forest Reefs Volcanics, host to the Cadia Valley porphyry Au-Cu deposits. The arc-related andesitic succession is dominated by thick sequences of volcanosedimentary breccias with volumetrically minor lavas ( Squire, 2001 ). The volcaniclastic
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District geology map of the Cadia Valley based on surface mapping by Newcrest Mining Ltd between 1997 and 2002. Geologic boundaries were further constrained using top-of-collar drill hole information (unpub. data, Newcrest Mining Ltd). Washburn (2008) mapped the Silurian cover rocks. Felsic intrusions and most of known ore deposits form a broad northwest trend that parallels the broader district trends evident in the previous map. Systematic logging of the drill holes across the Cadia Valley helps constrain the volcanic architecture. As has been shown elsewhere (Holliday et al., 2002; Wilson et al., 2003), the outcropping stratigraphy becomes younger to the east. The Forest Reefs Volcanics vary laterally and vertically in terms of eruptive style and composition of volcanism. At Ridgeway, a narrow zone (300 m) of porphyry-style alteration and mineralization occurs in and around multiphase monzonitic stocks. By contrast, the Cadia East deposit occupies a mineralized zone 2 km long, 600 m wide, and >1,500 m in vertical extent. Here, hydrothermal alteration and mineralization is lithologically controlled at surface, becoming more structurally controlled (as stockwork and sheeted vein arrays) at depth.

District geology map of the Cadia Valley based on surface mapping by Newcre...

Published: 01 June 2014
., 2002 ; Wilson et al., 2003 ), the outcropping stratigraphy becomes younger to the east. The Forest Reefs Volcanics vary laterally and vertically in terms of eruptive style and composition of volcanism. At Ridgeway, a narrow zone (300 m) of porphyry-style alteration and mineralization occurs
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Fig. 6. Plan view of the 5280 R.L. of the Ridgeway underground mine (based on unpublished underground mapping and sampling data of Newcrest Mining Limited). A. Geology of the 5280 R.L., showing the location of the principal pyroxene porphyry dikes, the monzodiorite intrusion (pre- to early-mineral) and the monzonite porphyry complex (early- to late-mineral). Individual phases of the monzonite body have not been differentiated during mapping. The pyroxene porphyry dikes occupy important east-northeast– and west-northwest–trending fault zones, the latter set possibly controlling the localization of the monzodiorite and monzonite intrusions. B. Gold grade (contour intervals are 85th, 90th, 95th, and 98th percentile values). The monzodiorite intrusion (thick dashed line) is marginal to the main body of mineralization, but the monzonite intrusive complex (gray polygon at the center of the mineralization) is partially coincident with the high-grade portion of the deposit. C. Copper grade (contour intervals are 75th, 90th, 95th, and 98th percentile values). D. Gold/copper ratio (* Au/Cu = Au (ppm) × 10,000/Cu (ppm); contour intervals represent 50th, 75th, 85th, and 90th percentile values). A close spatial association between gold, copper, and the monzonite intrusions is evident. The highest Au/Cu ratios occur along the southern flank of the monzonite intrusion, in an area where early-mineral monzonite intrusions have been logged on section 11050E, as part of this study (Fig. 3). Abbreviations: FRV = Forest Reefs Volcanics.

F ig . 6. Plan view of the 5280 R.L. of the Ridgeway underground mine (base...

Published: 01 December 2003
: FRV = Forest Reefs Volcanics.