Papers by Doug J MacKenzie
Geological setting of the Bigorne gold deposit, Iberian Variscan belt (Northern Portugal) and Au-Bi-Te mineral assemblages as indicators of the ore-forming conditions
Ore Geology Reviews, 2022
Contrasting geochemistry of orogenic gold deposits in Yukon, Canada and Otago, New Zealand
Geochemistry: Exploration, Environment, Analysis, 2015
The Yukon-Tanana Terrane (YTT) of western Yukon Territory in NW Canada and Otago Schist belt (OSB... more The Yukon-Tanana Terrane (YTT) of western Yukon Territory in NW Canada and Otago Schist belt (OSB) of South Island, New Zealand share similar geological evolutionary histories as convergent orogenic belts. Both belts host orogenic gold deposits of mainly Jurassic to Early Cretaceous age. Jurassic mineralization in the YTT occurred during convergent orogenesis and stacking of previously-metamorphosed (Palaeozoic) greenschist-amphibolite facies metasediments, metavolcanic rocks, and metagranitoids. Early Cretaceous OSB mineralization occurred in the latter stages of terrane accretion of un-metamorphosed turbidites with minor basaltic rocks. Metamorphism of the OSB turbidites mobilised background levels of Au (0.6–1.3 ppb), As (2–20 ppm), Sb (0.1–1 ppm), and W (< 10 ppm), primarily under greenschist to lower amphibolite facies conditions when diagenetic pyrite (Au c. 0.5–2 ppm; As c. 500–10 000 ppm) transformed to pyrrhotite on a regional scale. In contrast, the previously-metamorphosed YTT rocks had generally low background As contents (1–2 ppm) apart from some As-rich quartzites (up to 100 ppm As). Consequently, there was less As available for orogenic mobilisation, and YTT Au deposits generally have lower concentrations of this pathfinder element compared to the OSB. YTT host rocks, especially metagranitoids, have anomalous levels of Mo (10–300 ppm), and many orogenic deposits contain elevated Mo, locally including molybdenite. OSB turbidites have elevated Mo (2–200 ppm), along with elevated Au and As, in diagenetic pyrite, but this Mo became largely dispersed through the metamorphic pile as metamorphic grade increased and pyrite transformed to pyrrhotite. OSB orogenic deposits have only marginally elevated Mo (c. 1 ppm), no molybdenite, and accessory scheelite in these deposits is distinctly Mo-poor. Only minor mobilisation of base metals occurred in these orogenic belts, and orogenic Au deposits contain sparse base metal sulphides. Orogenic deposits in the YTT and OSB differ in that Au (and other associated elements) in many of the orogenic deposits in the YTT was remobilised from relatively local sources (e.g. pre-existing Cu-Mo-Au porphyry or volcanogenic sulphide mineralization) whereas Au in the OSB was mobilised from larger volumes of homogeneous rock at depth.
This paper provides a regional-scale background for understanding gold-mineralising processes in ... more This paper provides a regional-scale background for understanding gold-mineralising processes in the Otago Schist during the Cretaceous. At this time the schist belt was in the latter stages of formation as an accretionary complex with 2000 km strike length on the Pacific margin of Gondwana. The Otago Schist is interpreted as an exhumed accretionary wedge of structurally stacked clastic metasedimentary rocks with minor metabasic rocks. Metamorphic grade reached upper greenschist facies. Gold and other related elements were mobilised from the metasedimentary rocks during metamorphism, and these elements contributed to the high levels of orogenic gold endowment (>18 million ounces in the schist belt. Mesozoic Gold deposits were emplaced in two distinct pulses, one at the beginning of the Early Cretaceous (~140-135 Ma) and the other at the end of the Early Cretaceous (~112-100 Ma). These mineralising pulses were driven by regional tectonic events that may have involved episodic unde...
Hydrothermal footprint of the Birthday Reef, Reefton goldfield, New Zealand
New Zealand Journal of Geology and Geophysics, 2017
ABSTRACT The Birthday Reef was the most productive gold producer during historic mining of the Re... more ABSTRACT The Birthday Reef was the most productive gold producer during historic mining of the Reefton goldfield on the west coast of the South Island of New Zealand. Deep exploration drill holes (up to 1.6 km long) intersected the mineralised quartz vein zone and adjacent hydrothermal alteration halo beneath the historic mine workings. The Paleozoic metasedimentary host rocks contain between 0.5 and 8 ppb Au and between 4 and 30 ppm As, and metamorphic pyrite typically contains 0.1 to 1 ppm Au in solid solution. The Au and As halo, above these background values, extends <20 m from the Birthday Reef, and other petrographic indicators of alteration are also confined to this narrow envelope. Porphyroblasts of pyrite and arsenopyrite, with minor Au enrichment, grew across the metamorphic cleavage in the alteration halo before emplacement of the Birthday Reef and associated shearing, and reflect an earlier, late metamorphic precursor to the main gold mineralisation phase.
SpringerBriefs in World Mineral Deposits, 2016
The SpringerBriefs in World Mineral Deposits book series seeks to publish monographs or case stud... more The SpringerBriefs in World Mineral Deposits book series seeks to publish monographs or case studies focused on a single mineral deposit or a limited group of deposits (sub-regional level), with regard to their mineralogy, structure, geochemistry, fluid geochemistry, and any other aspect that contributes to explaining their formation. This series is aimed at academic and company researchers, students, and other readers interested in the characteristics and creation of a certain deposit or mineralized area. The series presents peer-reviewed monographs. The Springer Briefs in World Mineral Deposits series includes both single and multi-authored books. The Series Editors, Prof.
Taieri River Mineralised Vein Swarm, East Otago
The Taieri River mineralised vein swarm is a set of mineralised normal faults exposed in the Taie... more The Taieri River mineralised vein swarm is a set of mineralised normal faults exposed in the Taieri River gorge of east Otago. On a regional scale the Taieri River gorge is structurally controlled, and some of these same structures controlled mineralisation during Cretaceous extension, to form a 25 km long variably mineralised corridor. The Barewood system is the best known portion of the vein swarm and this was the main focus of exploration in the 1980s, but many other veins have similar structural and mineralogical characteristics and are thought to be genetically related. The Hindon vein swarm, in particular, has had similar structural and mineralisation history to that at Barewood. Early anhedral white quartz with little gold has been overprinted by later clear and prismatic quartz with breccias and gold-bearing arsenopyrite. The later mineralisation stage occurred at shallower structural levels than the early stage, and localised fluid immiscibility implies near-surface mineralisation. Stibnite mineralisation in and near the vein swarm is associated with a more saline fluid than the gold mineralisation and may represent an even later stage. The Taieri River vein swarm is one of the most laterally persistent sets of genetically related mineralised structures in the Otago Schist. Keywords: gold, antimony, quartz vein, fluid inclusions, structure, normal faults, mesothermal, Otago Schist, Taieri River.
Rise and Shine Shear Zone, Central Otago
The Rise and Shine shear zone is a mineralised low-angle deformation zone in biotite zone schist ... more The Rise and Shine shear zone is a mineralised low-angle deformation zone in biotite zone schist of the Dunstan Range of central Otago. The shear zone and associated mineralised rocks are traceable for at least 7 km along a northwest strike, with mineralised rocks best developed in three separate areas. The shear zone occurs in the immediate footwall of the Thomsons Gorge Fault, a regional scale Cretaceous normal fault that juxtaposes lower greenschist facies rocks against biotite zone schist. This fault may have faulted-out sections of the shear zone, including its southeastern extensions. The Rise and Shine shear zone is distinctly different from the nearby Bendigo gold-bearing quartz reefs in having large volumes of mineralised rocks that lack well defined quartz veins. Most mineralised rocks are deformed and hydrothermally altered schist, with variable silicification and chloritisation, and widespread carbonate alteration. Gold is associated with pyrite and arsenopyrite disseminated through the altered schist. Mineralised rocks extend for tens of metres below the hanging wall shear, with overall gold concentrations generally in the 0.2 - 1.0 g/t range. Within this zone there are many localised sections assaying 1 - &gt;10 g/t Au. The Rise and Shine shear zone marks a major structural discontinuity and bears some similarities to the Hyde-Macraes Shear Zone. Thus, it has potential for the occurrence of a bulk-mineable, disseminated orogenic gold deposit. Keywords: gold, quartz vein, mineralisation, shear zone, faults, structure, mesothermal, Otago Schist, Rise and Shine.
40Ar/39Ar geochronology and Pb isotopic evidence for the role of ridge subduction in generating orogenic gold mineralization in the Otago Schist Belt, New Zealand
Geochimica et Cosmochimica Acta
Orogenic gold mineralization in the Otago Schist Belt (OSB) of South Island, New Zealand, occurs ... more Orogenic gold mineralization in the Otago Schist Belt (OSB) of South Island, New Zealand, occurs as synto late tectonic veins and disseminations in brittle-ductile shear zones (e.g., Hyde-Macraes, Rise&Shine), as well as in late and posttectonic fissure veins. Gold is hosted within lower to upper greenschist facies metaclastic rocks of the Otago Schist that comprise part of a long-lived (Triassic to mid-Cretaceous) accretionary complex that developed along the active margin of Gondwana. Orogenic gold mineralization in the OSB is thought to have formed from fluids produced during prograde dehydration reactions within the Otago Schist at depth that also liberated and mobilized S and metals (including Au). Ar/Ar dating of muscovite within veins at the Macraes Mine (Hyde-Macraes shear zone) and the Glenorchy District yield ages in the range of 135-141 Ma, and are interpreted to represent the age of veining. Previous Ar/Ar dating of muscovite from the Rise&Shine shear zone and several late gold-bearing fissure veins elsewhere in the OSB suggest ages for that mineralization of ~101-106 Ma. Pb isotopic analyses of 48 sulphide separates from all of the various styles of gold mineralization within the OSB define two distinct clusters: a less radiogenic cluster of analyses that includes samples from Macraes and Glenorchy, and a more radiogenic cluster that includes samples from the Rise&Shine shear zone and other veins that have yielded younger Ar/Ar ages. Together the age and Pb isotopic data suggests that gold mineralization in the OSB formed during two discrete and relatively short-lived pulses, at ~135-141 Ma and ~101-106 Ma. The highly episodic nature of the gold mineralization argues that hydrothermal activity that produced orogenic gold mineralization in the OSB was not simply part of a steadystate process related to the normal development of an accretionary complex, but rather was related to specific tectonic events that affected the wedge. Age and geochemical studies of the associated arc complex suggest that a ridge subduction event occurred under the OSB at ~135-140 Ma, and reconstructions of probable plate motions in the region appear to require a younger ridge subduction event at ~100 Ma. We suggest that gold mineralization in the OSB was related to two discrete ridge subduction events, analogous to gold mineralization in the Chugach accretionary complex in southern Alaska. Zircon U-Pb age discordance and trace element alteration due to deep, post-impact flow: Implications for planetary chronology D.E. MOSER, W.J. DAVIS, S. REDDY, R.L. FLEMMING AND R.J. HART Dept. of Earth Sciences, Univ. of Western Ontario, London, Ontario, Canada N6A 5B7 (desmond.moser@uwo.ca) Geological Survey of Canada, 601 Booth St., Ottawa, Canada, K1A 0E8 (bidavis@NRCan.gc.ca) Dept. of Applied Geology, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia (s.reddy@curtin.edu.au) iThemba labs, Johannesburg, South Africa (hart@tlabs.ac.za)
Lithologically controlled invisible gold, Yukon, Canada
Mineralium Deposita, 2014
ABSTRACT The newly discovered Cretaceous Coffee orogenic gold deposit (&amp;gt;4 Moz resource... more ABSTRACT The newly discovered Cretaceous Coffee orogenic gold deposit (&amp;gt;4 Moz resource) consists of an extensive oxidised zone developed on primary sulphidic rock. The primary mineralised rock is characterised by invisible gold in arsenian pyrite that has replaced biotite in selected host rocks. The deposit has a cryptic surface expression and is an example of an extremely subtle exploration target. Hydrothermal emplacement was controlled by extensional fractures, with breccias, but most mineralisation was focused on biotite-bearing granitic gneiss, metasedimentary gneisses, and younger biotite granite. Fine-grained (
New Zealand Journal of Geology and Geophysics, 2005
A regional study of gold from Otago Schist vein deposits from both Caples and Torlesse Terranes h... more A regional study of gold from Otago Schist vein deposits from both Caples and Torlesse Terranes has revealed the presence of both Au-Ag and Au-Ag-Hg alloys in both terranes. Almost all Hg-bearing gold occurs in east Otago vein systems, and Hg-free gold occurs in central and northwest Otago vein systems, irrespective of host terrane. One Central Otago mineralised zone has up to 1.7 wt% Hg in the gold. Au-Ag alloy (3-8 wt% Ag) is typical for gold found in most Torlesse-hosted vein deposits, and Au-Ag-Hg alloys with 1-4 wt% Hg are found in vein material from the Torlesse-hosted Hyde-Macraes Shear Zone. Au-Ag-Hg alloy (3-8 wt% Ag, 2-8 wt% Hg) is found in many Caples-hosted vein deposits. There is no relationship between depth of vein emplacement and Hg content of gold, as both high and low Hg gold are found in shallow-formed (<2 km) and deep-formed (>6 km) deposits. There is no spatial relationship between Hg-bearing gold and cinnabar-bearing veins that occur in Caples Terrane rocks on the southern edge of the schist belt. Mercury-bearing placer gold in eastern Southland may have been derived from erosion of east Otago veins. The source of Hg-bearing placer gold in northern Southland is unknown as yet.
New Zealand Journal of Geology and Geophysics, 2005
The Otago Schist in Central Otago has undergone complex late metamorphic and post-metamorphic def... more The Otago Schist in Central Otago has undergone complex late metamorphic and post-metamorphic deformation during uplift and exhumation. Two late metamorphic structural generations can be recognised and these may be genetically related. The earlier Manorburn Generation has been widely recognised and described previously. This generation has fold axes subparallel to a prominent syn-metamorphic quartz rodding lineation. A later generation, herein named Poolburn Generation, has folds which superficially resemble Manorburn Generation, but has fold axes that are at a high angle to the quartz rodding lineation. Both generations occur in mappable fold zones (kilometre-scale) that are generally not vergence boundaries, and some minor relative displacement may occur across fold zones. Fold zones occur within structurally and lithologically uniform schist domains. Abrupt changes in lithological sequences and orientations of structural elements such as Manorburn and Poolburn Generation fold axes and quartz rodding lineations occur at post-metamorphic faults which separate different schist domains. Central Otago schist can be subdivided on the regional scale (tens of kilometres) into at least nine schist domains whose structural and lithologic continuity is disrupted by fault discontinuities. The domains and bounding discontinuities developed during Late Jurassic and Early Cretaceous uplift. Syn-metamorphic compressive ductile deformation evolved to localised fold zones in the early stages of this uplift. Subsequently, regional extension caused juxtaposition of domains with different textural zones, and schists from slightly different structural levels. The Caples/Torlesse Terrane boundary is a composite feature, and different segments formed at different stages through the transition from ductile compression to brittle extensional deformation.
Structure and geochemistry of the Rise & Shine Shear Zone mesothermal gold system, Otago Schist, New Zealand
New Zealand Journal of Geology and Geophysics, 2006
... L. COX DJ MACKENZIE D. CRAW* RJ NORRIS R. FREW† Geology Department University of Otago PO Box... more ... L. COX DJ MACKENZIE D. CRAW* RJ NORRIS R. FREW† Geology Department University of Otago PO Box 56 Dunedin, New Zealand *Author for ... The Rise &amp;amp; Shine Shear Zone has some structural and geochemical features in common with the Hyde-Macraes Shear Zone, but ...
Lead isotope constraints on the origin of Cenozoic orogenic gold systems in the Southern Alps and northwestern Otago, South Island, New Zealand
New Zealand Journal of Geology and Geophysics, 2010
Lead isotopic compositions were determined for sulphides from Pliocene-Pleistocene gold-bearing v... more Lead isotopic compositions were determined for sulphides from Pliocene-Pleistocene gold-bearing veins in the Alpine Schist and from Miocene gold-bearing veins and vein breccias from the Shotover-Macetown area in the northwest Otago Schist belt. The lead isotopic signatures are consistent with derivation of Pb in the vein minerals predominantly from metasedimentary rocks that underlie the region. Differences in Pb isotopic signatures
New Zealand Journal of Geology and Geophysics, 2010
Darran Suite dioritic, tonalitic and granodioritic plutonic rocks and schistose Loch Burn Formati... more Darran Suite dioritic, tonalitic and granodioritic plutonic rocks and schistose Loch Burn Formation volcaniclastic rocks in the central Murchison Mountains at the Dana Peaks have been affected by widespread biotite-sericite-chlorite-albite-quartz-pyrite9carbonate9epidote/clinozoisite9titanite/rutile9actinolite alteration. More intense, paler coloured sericite-albitequartz-pyrite9carbonate alteration is concentrated along orange weathered shear zones. Alteration assemblages are transitional between those commonly referred to as propylitic, potassic and phyllic. Altered rocks contain anomalous concentrations of copper, lead, zinc and silver over an area of c. 2.5 )6 km. Metal concentrations 2Á5 times those typical of Darran Suite plutonic rocks and the Loch Burn Formation are commonly associated with more extensive weak to moderate intensity alteration. Higher metal grades up to c. 0.5% copper, 1% zinc, 1.3% lead and 30 ppm silver are concentrated in or adjacent to the 1Á5 m wide, more intensely altered shear zones which contain entrained lenses of pyritised country rock, breccias and quartz 9K-feldspar9chlorite9carbonate9hematite9tourmaline veins. Some mineralised rocks also contain traces of tungsten (2Á7 ppm), arsenic (B5Á35 ppm) and tellurium (0.2Á5.4 ppm). Most samples lack detectable molybdenum (B3 ppm), gold (B0.004 ppm) or bismuth (B0.2 ppm), with atypical higher values (40, 0.03 and 50 ppm, respectively) generally restricted to the most intensely altered and/or deformed rocks. The mineralised rocks show a close spatial and temporal relationship with several narrow ductile shear zones that probably developed in the Early Cretaceous between c. 128 and 110 Ma. Mineralised shear zones form minor splays off larger shear zones that are part of a major intra-arc fault system, active along or near the boundary between inboard and outboard parts of the Median Batholith at this time. Traces of similar lead mineralisation are present at the head of the Mid Burn c. 8 km to the northeast along strike on the same regional-scale fault system as the Dana Peaks locality. Fluids and metals are likely to have been derived from metamorphism of the Loch Burn Formation and/or adjacent plutonic rocks. A magmatic hydrothermal origin is considered unlikely as the metal assemblage lacks Mo, Bi, Au, Sn and W and the adjacent plutonic rocks probably crystallised several million years or more before alteration and mineralisation.
Hydrothermal alteration styles in ancient and modern orogenic gold deposits, New Zealand
New Zealand Journal of Geology and Geophysics, 2009
... Page 4. 14 New Zealand Journal of Geology and Geophysics, 2009, Vol. 52 ... Margins Table 1 S... more ... Page 4. 14 New Zealand Journal of Geology and Geophysics, 2009, Vol. 52 ... Margins Table 1 Summary comparison of the three orogenic gold alteration styles. Veins Carbonate Chlorite Metallic minerals ... Structural setting Depth Temperature Fluid Fluid sources Tectonic setting ...
Lithogeochemical localisation of disseminated gold in the White River area, Yukon, Canada
Mineralium Deposita, 2010
Abstract Gold mineralisation in the White River area, 80 km south of the highly productive Klondi... more Abstract Gold mineralisation in the White River area, 80 km south of the highly productive Klondike alluvial goldfield, is hosted in amphibolite facies gneisses in the same Permian metamorphic pile as the basement for the Klondike goldfield. Hydrothermal fluid which ...
Structural controls on Tertiary orogenic gold mineralization during initiation of a mountain belt, New Zealand
Mineralium Deposita, 2006
... 2005). Lamprophyre dykes are commonly found closely associated, both temporally and spatially... more ... 2005). Lamprophyre dykes are commonly found closely associated, both temporally and spatially, with orogenic gold deposits (Taylor et al. 1994; Kerrich and Wyman 1994; Ashley et al. 1994). ... 1994; Kerrich and Wyman 1994; Ashley et al. 1994). ...
Mineralogy, geochemistry, and structural controls of a disseminated gold-bearing alteration halo around the schist-hosted Bullendale orogenic gold deposit, New Zealand
Journal of Geochemical Exploration, 2007
... metamorphism (Craw, 1985). Associated development of pervasive foliations was accompanied by ... more ... metamorphism (Craw, 1985). Associated development of pervasive foliations was accompanied by progressive recrystallisation of coarse grained (> 100 μm) muscovite and chlorite (Turnbull et al., 2001). This penetrative fabric ...
Mineralisation and structural setting of the Rise and Shine Shear Zone, Otago Schist: Comparisons to the Macraes deposit
Proceedings of the New …, 2005
... Mineralium Deposita 40: 45-58 Teagle, DAH, Norris, RJ and Craw, D. 1990. Structural controls ... more ... Mineralium Deposita 40: 45-58 Teagle, DAH, Norris, RJ and Craw, D. 1990. Structural controls on gold-bearing quartz mineralization in a duplex thrust system, Hyde-Macraes Shear Zone, Otago Schist, New Zealand, Economic Geology 85: 1711-1719.
Late metamorphic structural zones in the Otago Schist: Prospective hosts for gold mineralisation
Proceedings of the …, 2005
... (eds) 2003 Millpress, Rotterdam. Teagle, DAH, Norris, RJ and Craw, D., 1990. Structural contr... more ... (eds) 2003 Millpress, Rotterdam. Teagle, DAH, Norris, RJ and Craw, D., 1990. Structural controls on gold-bearing quartz mineralisation in a duplex thrust system, Hyde-Macraes Shear Zone, Otago Schist, New Zealand. Economic Geology 85: 1711-1719. Turnbull, IM comp. ...
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Papers by Doug J MacKenzie