Contrasting geochemistry of orogenic gold deposits in Yukon, Canada and Otago, New Zealand

Geochemistry: Exploration, Environment, Analysis

Published Online First doi:10.1144/geochem2013-262

© 2015 AAG/The Geological Society of London. For permissions: http://www.geolsoc.org.uk/permissions. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics

Orogenic deposits are an important source of gold on a global scale, and a major target for ongoing mineral exploration efforts (Bierlein & Crowe 2000; Goldfarb et al. 2005; Hronsky et al. 2012). Geochemical exploration programmes for these deposits can target Au itself, in rocks, soils, and stream sediments, and this approach has some success (Boyle 1979; Bowell et al. 1993; Townley et al. 2003; Crawford & Mortensen 2009; Chapman et al. 2010, 2011). However, analysis for Au in these settings is com-monly confounded by the nugget effect during sampling, and the common presence of detrital Au from other deposits (Boyle 1979; Dominy et al. 2010; Chapman et al. 2010, 2011). Hence, geo-chemical exploration programmes generally employ additional pathfinder elements, which commonly occur at higher concentra-tions and over broader areas than Au (Boyle 1979; Bierlein & Crowe 2000; Eilu & Groves 2001; Goldfarb et al. 2005; McClena-ghan & Cabri 2011). Choice of appropriate pathfinder elements depends on the local geology and the geochemical processes that were involved in formation of the orogenic gold deposits, and pre-diction of these pathfinder elements is an important stage in design of an exploration programme.

The Yukon-Tanana Terrane (YTT) of northern Canada and the Otago Schist belt (OSB) of New Zealand are two regions which have a long history of mining and exploration of orogenic gold deposits and the placer gold derived from those deposits. The two regions developed in similar ways at essentially the same time in

convergent orogens on opposite sides of the Pacific Plate, and the regions have many strong similarities in tectonic, structural, and mineralization histories (Fig. 1). Despite these many temporal and geological parallels, the geochemical signatures of orogenic gold deposits in these regions are distinctly different, and as a conse-quence, geochemical exploration strategies in these regions must rely on entirely different approaches. In this paper, we outline the key features of the parallel geological evolution of the orogenic gold deposits of the two regions, and relate the geochemistry of the orogenic deposits to the local geological characteristics. From these observations, we show how differences in local geology have led to differences in geochemical signatures during formation of the orogenic gold deposits. We focus in particular on As, which is the most common pathfinder for orogenic gold worldwide (Boyle 1979; Bierlein & Crowe 2000; Eilu & Groves 2001), and on Mo, which is otherwise generally associated with high temperature magmatic-hydrothermal systems (Redmond et al. 2010).

General Geology

The YTT and OSB both formed and were mineralized during con-vergent tectonism that spanned Palaeozoic, Mesozoic and Cenozoic (Fig. 1). Initial Palaeozoic accretion and construction of the basement of both regions were followed by distinct collisional events that produced the main orogenic gold deposits in the

Contrasting geochemistry of orogenic gold deposits in Yukon, Canada and Otago, New Zealand

Dave Craw1*, Jim Mortensen2, Doug Mackenzie1 & Iain Pitcairn3

1 Geology Department, University of Otago, Dunedin, New Zealand2 Mineral Deposits Research Unit, University of British Columbia, Vancouver, Canada3 Department of Geological Sciences, Stockholm University, Stockholm, 10691 Sweden* Correspondence: [email protected]

Abstract: 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 metasedi-ments, 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 back-ground 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 trans-formed 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.

Keywords: gold, arsenic, antimony, molybdenum, metamorphism, hydrothermal, graphite, orogenic

Received 3 January 2014; revised 17 October 2014; accepted 17 October 2014

2013-262research-articleThematic set: IAGS Rotorua 2013XXX10.1144/geochem2013-262D. Craw et al.Contrasting orogenic geochemistry2015

Thematic set: IAGS Rotorua 2013

by guest on March 14, 2015http://geea.lyellcollection.org/Downloaded from

http://www.geolsoc.org.uk/permissions

mailto:[email protected]

http://geea.lyellcollection.org/

D. Craw et al.2

Fig. 1. Summary comparison of the parallel geological histories of the YTT and OSB, with particular reference to formation of orogenic Au deposits (grey shading). See text for references.

Jurassic (Fig. 1). Additional Au mineralization occurred during post-orogenic extensional processes in the middle to Late Cretaceous in both regions (Fig. 1). Then both regions were dis-membered by hundreds of kilometres of oblique dextral strike-slip offset, starting in the middle Cenozoic (Fig. 1). The Cenozoic deformation also caused topographic rejuvenation, leading to con-centration of placer gold that was exploited during major gold rushes in the 19th century (Fig. 1; Williams 1974; Lowey 2006).

Yukon

The basement rocks of the YTT consist of Palaeozoic schists and gneisses that underwent late Palaeozoic deformation, metamor-phism, and pervasive recrystallization during the convergent Klondike Orogeny (Fig. 1; Mortensen 1990, 1992, 1996; Beranek

& Mortensen 2011). Metamorphic grade ranges from greenschist facies in the north, to amphibolite facies in the south (Fig. 2). The basement schists and gneisses are metamorphosed clastic sedimen-tary rocks, mafic and felsic volcanic rocks, and felsic (granitoid) intrusives (Mortensen 1990). Metasedimentary rocks include quartzite, marble, and micaceous schists and gneisses.

This paper focuses on the northern part of the YTT, where numer-ous orogenic deposits occur, although with only minor historic min-ing (Lowey 2006; MacKenzie et al. 2008a). Past mining has focussed on placer Au derived from the orogenic deposits, and included the spectacular Klondike goldfield (Fig. 2; Lowey 2006; MacKenzie et al. 2008a; Chapman et al. 2010, 2011). The main period of oro-genic Au mineralization was during Jurassic convergence, in the lat-ter stages of what is herein called the Bonanza event (Fig. 1).



Contrasting orogenic geochemistry 3

Fig. 2. Geological map of the YTT, showing the principal basement slices and intervening ultramafic rocks. Principal areas with known orogenic Au deposits are indicated, with cross-section line shown in Figure 3.

During the Bonanza event, slices of rocks from 0.1–1 km thick with differing degrees of metamorphic reconstitution were tectoni-cally stacked by Jurassic thrust faults subparallel to the pervasive foliation (Mortensen 1990, 1996). This thrust stacking also incor-porated some Triassic sedimentary rocks, and mafic and ultramafic rocks of the Palaeozoic Slide Mountain Terrane (Figs 2 and 3; Mortensen 1990, 1996). Tabular foliation-parallel bodies of ser-pentinite, up to 50 m thick, were emplaced during the Bonanza event, with a new greenschist facies cleavage, as the slices of schists and gneisses were stacked (Mortensen 1990; MacKenzie et al. 2008a,b). These shallow-dipping rocks were then locally deformed by upright folds and cut by steep faults as the rocks were uplifted from greenschist facies conditions to near-surface brittle conditions (MacKenzie et al. 2008a,b; 2010). Gold-bearing quartz veins fill localised extensional sites, especially in fold hinges in the Klondike goldfield (Fig. 2; MacKenzie et al. 2008a,b), and faults

have controlled hydrothermal alteration and disseminated gold mineralization (MacKenzie et al. 2010).

Regional compression gave way to regional extension during middle Cretaceous exhumation, accompanied by minor normal fault-controlled mafic and felsic magmatism (Gabrielse & Yorath 1991; Mortensen 1996). Cretaceous Au-bearing veins and dissem-inations were controlled by extensional structures (Fig. 1; Wainwright et al. 2011). Extension persisted with Eocene initia-tion of the major transcurrent Tintina Fault (Figs 1 and 2; Gabrielse & Yorath 1991; Gabrielse et al. 2006).

Otago Schist

The basement rocks of the OSB are lithologically monotonous compared to the Yukon-Tanana Terrane, and consist primarily of metamorphosed turbidites dominated by metagreywacke,



D. Craw et al.4

serpentinite

Fig. 3. Representative geological cross-section through a portion of the YTT (see Fig. 2), showing the principal rock types and their structure.

with subordinate metamorphosed argillites (Mortimer 1993). Metamorphic grade ranges from sub-greenschist facies rocks on the margins of the belt, to a core of upper greenschist facies schists with rare biotite and garnet (Fig. 4; Craw 1998; Mortimer 2000). The schist belt consists of three different terranes that were amal-gamated during a Jurassic collision event, the Rangitata Orogeny (Fig. 1; Mortimer 1993; Craw 1998). These terranes can be broadly subdivided internally into structurally and/or metamorphically dis-tinct domains, but with the same general lithological variations (MacKenzie & Craw 2005; Fig. 4). Most of the exposed belt is a schistose part of the Torlesse Terrane, which consists of Carboniferous–Jurassic quartzofeldspathic metasediments and minor metabasites that formed an accretionary complex before the Jurassic metamorphism (Fig. 1). The Caples Terrane, on the SW side of the schist belt, consists of an accretionary complex of largely volcanogenic metasediments that was metamorphosed dur-ing Jurassic terrane amalgamation (Figs 1 and 4). The intervening Aspiring Terrane (Fig. 4) occurs only as upper greenschist facies schists that include relatively large amounts (c. 5%) of metabasite horizons, with minor associated ultramafic rocks (Figs 1, 4 and 5).

The main orogenic Au mineralization occurred during the Rangitata Orogeny, in the Late Jurassic and Early Cretaceous, and was associated with thrust structures (Figs 1, 5A and B; Mortensen et al. 2010). Mineralization was controlled by ductile-brittle shear zones, and was dominated by Au disseminations in host schist, with minor quartz veins (Fig. 5B; Mitchell et al. 2006; Cox et al. 2006). The Macraes mine is the only actively mined deposit, and this has a total resource of c. 9 million ounces of gold in a region-ally-continuous structure, the Hyde-Macraes Shear Zone (Figs 4, 5A and B; Teagle et al. 1990; Mitchell et al. 2006).

Faulting during regional extension in the middle Cretaceous, combined with the metamorphosed terrane boundaries, has broken the schist belt into several domains with contrasting structure, lithologic constitution, and metamorphic grade (Fig. 4). The min-eralized Hyde-Macraes Shear Zone has been truncated by a Cretaceous normal fault at the boundary between two such domains (Figs 5A and B). The extensional tectonics also facilitated shallow-level formation of swarms of vein-hosted Au deposits in normal faults (Figs 5A and C; Mortensen et al. 2010). These veins have been mined historically, but production was small (Williams 1974). Renewal of compressional tectonics during the initiation of the major transcurrent Alpine Fault in the Miocene facilitated a later stage of Au mineralization (Fig. 1; Kaikoura Orogeny), hosted by normal faults that cut across Miocene folds and faults (Fig. 5D; Campbell et al. 2004; Craw et al. 2009). This style of mineralization still continues in the active mountain belt to the NW of the OSB (Fig. 1).

Methods

This paper is a synthesis of results from numerous exploration pro-grammes in both the OSB and YTT, combined with production

data from the Macraes mine in Otago. More than 20 000 rock anal-yses have been obtained during this work, and we have summa-rized the relevant parts of these data sets in order to extract the most prominent geochemical signals. Consequently, the data pre-sented herein are only a small fraction of the data available, and the set of elements considered is only a small subset with the most significant variations. Some representative selections of the data have been published previously, as referenced herein, and details of relevant sample sizes, analytical techniques, detection limits, and uncertainties are described in those publications.

Exploration drill-hole samples were typically splits of 1-m intervals, and Macraes mine production data were obtained on splits of 2.5-m drill-hole samples. Gold analyses for all studies were obtained by fire assay from a variety of commercial laborato-ries, with internal and external standards. Arsenic concentrations from OSB deposits were mainly determined by X-ray fluorescence (XRF) on pressed powder pellets in a range of laboratories, where detection limits are c. 1 ppm. These data were augmented by hand-held XRF results that were calibrated with laboratory XRF analy-ses, but with a practical detection limit of c. 50 ppm. Arsenic contents of YTT rocks were mainly determined via inductively coupled plasma mass spectrometry (ICP-MS) after four-acid digestion. Antimony and metals relevant to this study in both OSB and YTT were mainly determined by ICP-MS after four-acid digestion. Practical detection limits for most of these data sets are apparent in the data plots presented herein, as the lower cutoff of reported analyses, or in the lower compositional range in which continuous variation breaks up to discrete values quoted by the laboratory.

Geochemical Features of Otago Schist Au Mineralization

Arsenic and antimony

The basement metaturbidites that make up most of the OSB typi-cally contain 2–20 ppm As (Fig. 6A; Campbell et al. 2004; Pitcairn et al. 2006). This As is strongly partitioned into pyrite in low-grade rocks, where pyrite As contents can exceed 1000 ppm (Fig. 6A). The background As content of the metaturbidites is broadly consistent up to greenschist facies, and then drops to below 1 ppm in amphibolite facies metaturbidites (Fig. 6A; Campbell et al. 2004; Pitcairn et al. 2006). This drop in background As content of the metaturbidites has been attributed to bulk synmetamorphic As mobilization into a metamorphic fluid, with subsequent expulsion from the rocks (Pitcairn et al. 2006; Large et al. 2012).

All orogenic Au deposits in the OSB contain abundant As, mainly in arsenopyrite which almost invariably either accompa-nies, or encloses, the Au. Arsenopyrite occurs with Au in quartz veins and breccias, and both elements are commonly disseminated through immediate host rock. Arsenic contents of mineralized rocks can exceed 3 wt % at the hand specimen scale, and bulk




Fig. 4. Geological map of the OSB, with principal structural/metamorphic domains (after MacKenzie & Craw 2005), showing the principal orogenic Au deposits (white lines), and locations of cross-sections (black dotted lines) in Figure 5. HMSZ, Hyde-Macraes Shear Zone (hosting Macraes mine); R&S, Rise & Shine Shear Zone. Inset shows the distribution of Mesozoic schistose rocks (shaded) including the OSB, and the box shows the location of the main map.

analytical data from Macraes mine (2.5-m scale; Fig. 6B) show that As contents typically range from c. 100–10 000 ppm (1 wt%). Macraes ore-grade rock, with > 0.5 ppm Au, generally has > 500 ppm As, and an overall As/Au ratio of c. 1000 is implied by the large data set (Fig. 6B). This ratio is typical of many of the OSB

orogenic deposits, irrespective of age of formation, and even higher As/Au ratios (2000–10 000) occur in some mineralized rocks on the metre scale (MacKenzie et al. 2007).

Antimony concentrations in most metaturbidite host rocks (0.1–1 ppm) are at least an order of magnitude lower than As, and



D. Craw et al.6

Fig. 5. Cross-sections through the OSB, showing the basement structure in relation to orogenic Au deposits. (a) Section across the Hyde-Macraes Shear Zone and neighbouring structures (see Fig. 4 for location). (b) Enlarged section through the Hyde-Macraes Shear Zone (see A for location) which hosts the Macraes mine.(c) Sketch section across a mineralized normal fault (see A for location). (d) Section across the NW OSB (location in Fig. 4), showing the geological relationships between Early Cretaceous W-rich orogenic vein systems at Glenorchy, and Miocene Au-bearing orogenic veins.

are approximately constant through to the greenschist facies (Fig. 7A). Amphibolite facies metaturbidites have distinctly lower Sb contents than their lower grade equivalents, implying metamor-phic mobilization in a similar manner to As (Fig. 7A; Pitcairn et al. 2006). Orogenic Au deposits all have some degree of Sb enrich-ment compared to their immediate host rocks, but at levels consid-erably lower than As (Figs 7A and B). The Sb in the Macraes mineralized rocks is hosted largely in arsenopyrite, which can have >2000 ppm Sb in solid solution (Fig. 7A; Petrie et al. 2005). Some accessory boulangerite (Pb5Sb4S11) occurs in Macraes rocks as well. The As/Sb ratio of Macraes mineralized rocks is typically c. 100 (Figs 7A and B). Solid solution Sb in arsenopyrite is the prin-cipal occurrence of Sb in most other OSB orogenic Au deposits. Localized accumulations of massive stibnite occur within Au-bearing veins or in structurally related veins nearby. Stibnite is particularly common in the Tertiary orogenic vein systems (Fig. 5D). However, typical As/Sb ratios for Au-bearing rocks in these Tertiary deposits, on the hand specimen and metre scale, are

c. 1000, distinctly higher than for the Macraes mineralized rocks. The Rise & Shine Shear Zone, a middle Cretaceous deposit (Fig. 4; Cox et al. 2006), also has relatively high As/Sb ratios of c. 1000 (Fig. 7B).

Tungsten and molybdenum

Tungsten was mobilized during metamorphism of the host metat-urbidites at greenschist facies in a similar manner to As and Sb (Pitcairn et al. 2006). Some of this mobilization was localized only, and scheelite occurs scattered through syn-metamorphic veins in low-grade rocks (Craw & Norris 1991). The Macraes Au deposit also contains abundant scheelite, and auriferous pyrite por-phyroblasts contain up to 100 ppm W (Large et al. 2012). Approximately coeval vein-hosted scheelite mineralization, with only minor Au, was emplaced at Glenorchy on the western side of the OSB (Fig. 5D; Paterson 1986; Mortensen et al. 2010). Quartz veins at both Macraes and Glenorchy were mined for scheelite at




Fig. 6. Summary of As concentrations in the OSB. (a) Arsenic concentrations in host rocks of differing metamorphic grade (after Pitcairn et al. 2006), and As contents of diagenetic pyrite in low grade precursor turbidites, and As contents of pyrites in Macraes orogenic Au mine (after Large et al. 2012). (b) Relationship between Au and As in ore at the Macraes mine. Inset shows histogram distribution of As concentrations for Au >0.5 ppm.

times in the early 20th century (Williams 1974). Scheelite occurs as an accessory mineral in some of the middle Cretaceous Au deposits as well, and minor scheelite production occurred in the Barewood normal fault system (Fig. 4). The Barewood fault sys-tem also hosts several deposits that contain stibnite, although the stibnite and scheelite appear to be mutually exclusive (MacKenzie et al. 2006).

Molybdenum contents of low-grade metaturbidites are typi-cally c. 1 ppm and this Mo is apparently partitioned into diage-netic pyrite, which can contain up to 100 ppm Mo (Fig. 8A; Pitcairn et al. 2006; Large et al. 2012). There is no consistent change in Mo contents of metaturbidites with increasing meta-morphic grade, although some mobilization of Mo has apparently occurred in the greenschist facies (Figs 8A and B; Pitcairn et al. 2006). There has been weak Mo enrichment of mineralized rocks in the Macraes Au deposit, although this Mo is not enriched in either pyrite or scheelite (Fig. 8A; Craw 2002; Large et al. 2012), and no molybdenite has been observed in the mine. Likewise, Mo

is not enriched in scheelite from other Otago localities and no molybdenite has been observed in the other Au-bearing systems (Williams 1974).

Graphitic carbon

Fine-grained (micrometre scale) detrital organic carbonaceous material occurs scattered through the lowest grade metaturbidites, and this material became progressively graphitized with increasing metamorphic grade (Landis 1971; Henne & Craw 2012). The pri-mary detrital textures were overprinted and the graphite was remo-bilized into various schist foliations as the metaturbidites were structurally deformed and recrystallized (Fig. 9). Localised graph-ite enrichment occurred in crosscutting structures as well, yielding some graphitic veins on the millimetre to centimetre scales in greenschist facies and lower grades (Fig. 9; Henne & Craw 2012). Graphite remobilization and concentration into late metamorphic shears and veins accompanied Au mineralization at the Macraes mine, where non-carbonate carbon concentrations reach 3 wt% in



D. Craw et al.8

Fig. 7. Summary of Sb concentrations in the OSB. (a) Antimony concentrations in host rocks of differing metamorphic grade (after Pitcairn et al. 2006), and Sb contents of Macraes arsenopyrite (Petrie et al. 2005), Macraes mineralized rock (Craw 2002), and Sb contents of mineralized rocks in the Rise & Shine Shear Zone (Cox et al. 2006). (b) Relationships between As and Sb in host metaturbidites (after Pitcairn et al. 2006), variably mineralized rocks at Macraes (Craw 2002), Rise & Shine Shear Zone (Cox et al. 2006), and the Miocene orogenic veins (Fig. 5D; MacKenzie et al. 2007).

some ore-grade rocks (Craw 2002; Pitcairn et al. 2005; Henne & Craw 2012). Graphitic enrichment at this locality facilitated devel-opment of the mineralized shear zone, and may have prompted some deposition of hydrothermal minerals (Upton & Craw 2008; Henne & Craw 2012).

Yukon Au Mineralization

Klondike Au-bearing veins

Klondike Schist (Fig. 2) consists of pervasively-foliated green-schist facies rocks with a wide range of compositions that are inter-layered on the 1–100 m scale. Some of the schists were derived from clastic and exhalative sedimentary rocks, and these are inter-leaved with mafic and felsic volcanic rocks (Mortensen 1990, 1996). There also some km-scale metamorphosed felsic intrusions within the schist complex (Mortensen 1990). Most rocks have been fully recrystallised, although some primary igneous feldspars are locally preserved as augen. Syn-metamorphic and late meta-morphic quartz veins, commonly with associated chlorite selvages, are locally abundant parallel and sub-parallel to the pervasive foli-ation.

Gold-bearing veins in the Klondike Schist are dominated by quartz, some of which is prismatic and has grown into open cavities (Rushton et al. 1993). Vein formation occurred during

uplift of the rock mass in the latter stages of the Bonanza event (Fig. 1). There has been only minor wall rock alteration adjacent to veins, predominantly as ankeritic carbonate impregnation of more mafic rock-types. The most notable geochemical feature of the Au-bearing veins of the Klondike area is their relatively low As contents (Fig. 10A). Arsenopyrite is relatively rare, only few occurrences are responsible for enrichment of As to > 1000 ppm, and those few do not generally have strongly elevated Au contents (Fig. 10A). There is a broad correlation between As and Au in some vein systems, but any As enrichment is localised and incon-sistent (MacKenzie et al. 2008c; Liverton 2007). In general, there is a distinct lack of As enrichment with elevated Au contents com-pared to the OSB (Fig. 10A; Table 1). The only historic mine in Klondike veins, at Lone Star, has generally low As contents that are poorly correlated with Au (Table 1), and many of the host rocks have low As backgrounds as well, down to c. 1 ppm or less (Fig. 11A).

Background Cu and Mo concentrations are highly variable in the Klondike Schist (Figs 10B and C) because of the presence of sedimentary exhalative protoliths and possible pre-metamorphic hydrothermal alteration associated with volcanism and plutonism (Mortensen 1990, 1996). However, there has been little or no enrichment of these metals during subsequent Au-bearing vein for-mation (Figs 10B and C). Minor chalcopyrite, sphalerite and




Fig. 8. Summary of Mo concentrations in the OSB. (a) Molybdenum concentrations in host rocks of differing metamorphic grade (after Pitcairn et al. 2006), and Mo contents of diagenetic pyrite and Macraes mine Au-bearing pyrite (shown in (b)and (c) respectively, after Large et al. 2012). (d) Photograph of metamorphic molybdenite in an epidote-altered greenschist facies rock unrelated to Au mineralization (sample collected by AF Cooper).

galena occur in some Au-bearing veins, typically in central zones that apparently post-date the Au mineralization stage (Rushton et al. 1993; MacKenzie et al. 2008a). Scheelite is conspicuously absent from Klondike Au-bearing orogenic vein systems.

There is some evidence for au mobility and concentration in the latter stages of host rock metamorphism, linked to formation of Palaeozoic late metamorphic veins but not confined to those veins (Figs. 11A and B; MacKenzie et al. 2008c). This generation of Au mineralization clearly predates the widespread Jurassic vein for-mation in the Bonanza event, and probably occurred towards the end of the Palaeozoic Klondike Orogeny (Fig. 1). Arsenic contents of the rocks are low (typically near 1 ppm), and there has been little As enrichment associated with the localized Au enrichment (Figs 11A and C). Visible Au grains in late metamorphic veins are gen-erally not accompanied by sulphides, although some metamorphic

pyrite occurs in close proximity (MacKenzie et al. 2008c). The host rocks are weakly and variably enriched in Cu and Mo (Fig. 11D), reflecting primary (pre-metamorphic) enrichment processes (above). However, neither of these metals was concentrated during Au enrichment (Fig. 11D).

Some micaceous metasedimentary schists in the Klondike gold-field contain elevated non-carbonate carbon contents (typically 0.5–2 wt%; MacKenzie et al. 2008b) that show up as graphite along metamorphic foliations. This graphite has been locally enriched (up to c. 4 wt%; MacKenzie et al. 2008b) in lower green-schist facies shears associated with Bonanza event thrusting (Fig. 9). No direct links between graphite-bearing shears and Au miner-alization have been determined as yet, although the graphitic schists are commonly in close proximity to Au-bearing vein swarms.



D. Craw et al.10

Other Jurassic orogenic Au deposits

Recent exploration activity to the south of the famous Klondike goldfield has identified some new Au-bearing hydrothermal sys-tems that were apparently emplaced during the Bonanza event (MacKenzie et al. 2010, 2013). These deposits are hosted by amphibolite facies gneisses derived from metasedimentary and meta-igneous rocks of the YTT (Fig. 2). Thrust slices of these amphibolite facies host rocks were stacked under greenschist facies conditions during the Bonanza event, and mineralization occurred after this stacking, under lowering temperatures during uplift.

The principal host rocks for Au deposits are quartzites, grani-toid gneisses, and mafic gneisses. Gold-bearing quartz veins are rare, especially in the White River area (Fig. 2), where Au is dis-seminated with sulphides through variably altered host gneisses. Quartzites at White River are enriched in graphite, and some of these contain porphyroblasts of arsenopyrite, disseminated pyrrho-tite and chalcopyrite along the foliation (MacKenzie et al. 2010). Consequently, these host rocks have relatively high As back-grounds (up to 100 ppm; Fig. 12A, and Au-bearing hydrothermal zones in these quartzites are also strongly enriched in As (up to 1 wt%; Fig. 12A; Table 1). In contrast, hydrothermally altered granitoid gneisses, in close proximity to the quartzites (tens of metres away) have only minor As enrichment during Au minerali-zation, and the most Au-rich of these rocks have low As contents (c. 10 ppm; Fig. 12A) above backgrounds of c. 1–5 ppm. Antimony contents of mineralized rocks reflect the associated As contents, with only minor Sb enrichment of altered granitoid gneisses and Sb enrichment up to 100 ppm in mineralized quartzites (Fig. 12B). The As/Sb ratios of the latter mineralized rocks are typically c. 100 (Fig. 12B).

Hydrothermal alteration and minor vein formation in mafic gneisses and associated quartzites and granitoid gneisses in the Stewart River area (Fig. 2) has only minor As enrichment (Fig. 13A; MacKenzie et al. 2013), partly reflecting locally elevated background values especially in quartzites, as in the White River area. There is no positive correlation between As contents and Au contents in these rocks (Fig. 13A). In particular, Au-bearing quartz veins contain minor pyrite, but arsenopyrite is absent, even though nearby graphitic quartzites contains minor metamorphic arsenopy-rite. Antimony contents are positively but crudely correlated with As contents, and this reflects primary rock compositions, rather than mineralization. The As/Sb ratio in all the Stewart River rocks is c. 10 (Fig. 13B), much lower than the mineralized quartzites at White River (Fig. 12B).

Most unaltered and incipiently altered granitoid gneisses in both White River and Stewart River areas have weakly elevated Mo

contents, typically c. 10 ppm but up to several hundred ppm (Table 1). Mo is also enriched in more mineralized zones as well (Figs 12C and 13C). Molybdenite is a common, though minor, accessory mineral in the mineralized zones in the White River area, and molybdenite occurs in Bonanza event quartz veins in the Stewart River area, although no molybdenite has been found in Au-bearing veins at Stewart River. Elevated Cu in mineralized quartzites at White River (Fig. 12C) reflects remobilization of metamorphic, and probably primary, chalcopyrite (MacKenzie et al. 2010). There has been minor Cu enrichment in alteration zones and veins in the Stewart River area also (Fig. 13C). Scheelite has not been detected in any of the White River or Stewart River hydrothermal systems.

Graphite has been remobilized and locally strongly enriched in shears, veinlets, and breccia cements in amphibolite facies quartz-ites during Bonanza event deformation and mineralization in both White River and Stewart River areas. The White River quartzite hosts have up to 5 wt% non-carbonate carbon, and mineralized rocks can contain >15 wt% non-carbonate carbon (MacKenzie et al. 2010). In both areas, graphite remobilization was accompa-nied by recrystallization of metamorphic pyrrhotite to hydrother-mal pyrite (±coexisting hydrothermal pyrrhotite). There is a close relationship between Au mineralization and graphitic rocks in the White River area, but the relationship is less clear in the Stewart River area (MacKenzie et al. 2010; 2013).

Cretaceous Au deposits

Orogenic Au deposits cut Cretaceous granites and immediate host rocks in the Coffee deposit and other similar prospects to the SW of White River (Fig. 2; Wainwright et al. 2011; McKenzie et al. 2013; MacKenzie et al. 2014). These deposits contain ele-vated As and Mo and also contain stibnite, which is rare in YTT orogenic systems. Because of locally elevated As backgrounds in some host rocks, especially quartzites (up to 100 ppm; cf Fig. 12A), the Sb enrichment can be a more significant indicator of Au mineralization than As in these deposits (MacKenzie et al. 2014).

Epithermal Au deposits have formed in hydrothermal systems associated with late Cretaceous magmatism in several parts of the YTT (Chapman et al. 2011). These deposits contain electrum with high Ag content (up to 70%) and locally elevated Hg (Chapman et al. 2011). In addition, some of the Au contains inclusions of sulpharsenides and tetrahedrite (Chapman et al. 2011), attesting to elevated As, Sb and Cu in association with the Au mineralization process. Hence, this epithermal style of mineralization is distinctly different from the orogenic deposits formed earlier in the geologi-cal history of the YTT (above).

Table 1. Representative metal contents of mineralised and unmineralised rocks from the Yukon-Tanana terrane; see text for information on localities and references

ppm

KlondikeSchist

Lone Star

KlondikeSchist

Lone Star

KlondikeSchist

Lone Star

White RiverQuartzite

WhiteRiver

Quartzite

WhiteRiver

Granitoid gneiss

WhiteRiver

Granitoid gneiss

Stewart RiverGranitoid

gneiss

Stewart River

Granitoid gneiss

Au 39 33 0.1 0.18 3.1 4.9 13 <0.003 <0.003Ag 0.7 4.5 0.7 3 3 16.2 3 <0.02 0.4As 5 4 67 801 8830 11 16 3 16Co 8 11 11 46 7 1 4 2 1Cu 20 18 50 165 181 46 6 6 35Mo 5 1 11 5 9 15 53 4 271Ni 15 17 43 153 56 <1 <1 3 3Pb 21 9 35 19 24 59 11 5 11Sb 0.3 0.3 3.4 23 97 19 3 1 0.3Zn 56 56 113 881 352 <2 30 20 9




Discussion

Host rock metal enrichment

One of the most prominent differences between OSB and YTT as hosts for orogenic Au deposits lies in the variable but locally dis-tinct host rock enrichment of metals in the YTT. This metal enrich-ment of the YTT is shown up mostly by elevated Mo and Cu that are related to pre-metamorphic exhalative sediments and hydro-thermal alteration associated with volcanic rocks and intrusions (Table 1; Mortensen 1990; 1996). These primary enrichment signa-tures can be seen in both the Klondike Schist complex, and the higher metamorphic grade rocks to the south (Figs 10–13; Table 1). Metamorphic arsenopyrite in some of the YTT quartzites attests to pre-metamorphic enrichment of As in these units. Syn-metamorphic to late metamorphic Au mobilization and enrichment in the YTT (Figs 11A and B) may have been linked to primary Au enrichment in these rocks as well. Variations in primary metal enrichment in the YTT occur on a scale of tens of metres, and are broadly predictable from lithologic observations. In particular, most felsic intrusives have some degree of enrichment in Mo, at least locally, and some distinctive units in the YTT are enriched in Cu, as are some gra-phitic quartzites (MacKenzie et al. 2010; 2013).

In contrast to the YTT, the OSB host rocks are broadly uniform in composition over the whole region, with no distinct bulk metal enrichment in any of the rocks. There has been minor enrichment of As, Au and Mo, among other metals, in diagenetic pyrite, but this enrichment is broadly uniform across the principal rock types, sandstones and argillites, in the primary turbidites (Large et al. 2012). These primary rock types vary little in composition over hundreds of cubic kilometres of low grade rocks (Pitcairn et al. 2006). The initial weak enrichment of Mo in these rocks remained dispersed through the metamorphic rocks at higher metamorphic grade, as the diagenetic pyrite transformed to pyrrhotite. There has

been only minor local Mo enrichment in some greenschist facies rocks (Fig. 8D), and negligible enrichment in orogenic Au depos-its. Conversely, initial low and uniform W contents of the rocks were mobilized during metamorphism into orogenic Au deposits, particularly during the Jurassic (Pitcairn et al. 2014).

Arsenic and antimony

The OSB has broadly uniform background As contents of 2–20 ppm and Sb contents of 0.1–1 ppm (Fig. 7; Pitcairn et al. 2006), but these metalloids have been strongly enriched in the oro-genic Au deposits formed in the belt at all stages in the geological history (Figs 6–7). This enrichment came about because of regional scale metamorphic mobilisation of the metalloids from rocks as they passed through the upper greenschist facies towards amphibo-lite facies (Figs 6A and 7A; Pitcairn et al. 2006). This was fol-lowed by incorporation of the metalloids into arsenopyrite, with minor associated stibnite, in orogenic hydrothermal systems at several stages in the geological history (Fig. 1). The As/Sb ratio varies across the various deposits between 100 and 1000, with the highest ratios in the younger deposits (Fig. 7B), although many of these younger deposits have associated stibnite-rich zones as well.

Despite the primary metal enrichment in the YTT, there is rela-tively low As in most host rocks (1–2 ppm), and in associated orogenic deposits, compared to the OSB (Figs 10–13). Klondike Schist hosted veins have a weak, or even locally negative, correla-tion between As and Au, compared to the strong positive relation-ship evident in the OSB (Fig. 10A; Table 1). The principal exceptions in the YTT are As-bearing graphitic quartzites, which host As-bearing Au-rich zones at White River. Even in these quartzites, only small volumes of rock (< 1 m scale) have As con-centrations approaching the bulk As levels observed in the OSB (Figs 6B and 12A). The As/Sb ratio in the YTT hydrothermal zones, between 10 and 100, is distinctly lower than in the OSB,

Fig. 9. Sketch of pathways of graphite remobilization and recrystallization with progressive metamorphism of the YTT and OSB, and the temporal and spatial relationships between graphite and Au. S1 and S2 refer to foliations formed during progressive metamorphism. Suggested equations which may govern carbon mobility are indicated (after Craw 2002; Henne & Craw 2012; MacKenzie et al. 2013).



D. Craw et al.12

Fig. 10. Metal and metalloid contents of Klondike Schist in the YTT, from exploration databases. Samples are variably mineralized, as indicated by Au contents. (a) Arsenic concentrations; with some data from Liverton (2007). (b) Copper concentrations. (c) Molybdenum concentrations.




and this reflects the low As of the YTT, as Sb levels in the YTT are comparable to those in the OSB (e.g. Figs 7B vs 12B).

One explanation for the generally low As in the YTT rocks and hydrothermal zones may lie in the geological history of the YTT compared to that of the OSB. YTT rocks were metamorphosed in the Klondike Orogeny to upper greenschist facies or higher grades, and it may have been this metamorphism that initially mobilized original As, so that As was lost from the rocks. Consequently, oro-genic hydrothermal processes that occurred in the later Bonanza event had little or no available As to mobilize. Apparently Au and Sb were less affected than As in this earlier (Palaeozoic) stage of element mobilization, although reasons for this difference are not understood. The Palaeozoic metamorphic event must also have partially dehydrated the host rocks, leaving less potential dehydra-tion fluid available for the Bonanza event. It is possible that Palaeozoic orogenic Au deposits did form in the YTT, but that these have since been eroded. In contrast, most of the rocks of the OSB had undergone negligible or only low-grade (sub- greenschist facies) metamorphism prior to the principal orogenic processes that led to the Jurassic and younger Au deposits. Hence, OSB retained its metals and metalloids through the late

Palaeozoic–Triassic (Fig. 1) stages of terrane accretion, to be vari-ably mobilised as the rocks reached upper greenschist facies (Pitcairn et al. 2006).

Scales of element mobility

The metal and metalloid enrichment processes inferred for the OSB require mobilisation of these elements by metamorphic fluids and redistribution in the metamorphic belt on a scale of kilometres (Pitcairn et al. 2006, 2010, 2014). Bulk removal of c. 90% of As and Sb, for example, and nearly half of the Au has occurred on the scale of hundreds of cubic kilometres of rock. Associated concen-tration of these metalloids requires transport in solution from the ductile middle crust, through the brittle-ductile transition, and up to brittle depositional sites, some of which were near-surface (Mortensen et al. 2010). Similar processes are currently occurring in the active Kaikoura Orogeny in the mountains to the NW of the OSB, where a hydrothermal fluid system at least 10 km deep, 20 km wide, and >100 km long is actively forming small orogenic Au deposits (Fig. 1; Upton & Craw 2009; Craw et al. 2009; Pitcairn et al. 2014).

Fig. 11. Metal and metalloid contents of Klondike Schist in the YTT. Samples are from two drill-holes at the Lone Star historic mine, through rocks that contain no veins emplaced in the Bonanza event, and Au is disseminated through the host rocks (after MacKenzie et al. 2008c). (a) Gold and As contents plotted with depth down one drill-hole. (b) Gold contents of a c. 1-m interval of the drill-hole in A, in samples taken 2.5 cm apart, showing the elevated Au levels of schist in this interval, particularly associated with late metamorphic quartz veins (indicated). (c) Gold and As contents of schist from the full length of the drill-hole in A and B, and another nearby drill-hole. (d) Comparison of Cu and Mo contents of schist from the drill-holes in C.



D. Craw et al.14

Fig. 12. Metal and metalloid contents of variably mineralized rocks from orogenic Au deposits in the White River area of the YTT (after MacKenzie et al. 2010), comparing granitoid gneisses with quartzites. (a) Arsenic concentrations in relation to disseminated Au content. (b) Antimony concentrations in relation to As concentrations. (c) Copper and Mo concentrations.




Fig. 13. Metal and metalloid contents of variably mineralized rocks, some containing small orogenic quartz veins, in the Stewart River area of the YTT (after MacKenzie et al. 2013), comparing granitoid gneisses with quartzites. (a) Arsenic concentrations in relation to Au content. (b) Antimony concentrations in relation to As concentrations. (c) Copper and Mo concentrations.



D. Craw et al.16

The YTT is lithologically much more diverse than the OSB, and some of those lithologies apparently had pre-mineralization ele-mental enrichment (Mortensen 1990; 1996). Consequently, only smaller scale metal and metalloid mobility was required to form orogenic deposits in the YTT, and hydrothermal water-rock inter-action reactions may have been much more localized by lithologi-cal variations. These water-rock interactions initially involved mobilization of metals from rocks that have enriched primary compositions. Much of that metal and metalloid mobility occurred within the original rock types and the immediately adjacent rocks, so that mobility has been mainly on the scale of metres to hundreds of metres only. The close association between elevated hydrother-mal As and Sb and the anomalous As-Sb-bearing quartzite layers attests to this small scale of metalloid mobility in a terrane in which As is otherwise generally low. Pre-metamorphic Mo enrich-ment is widespread in the YTT (Figs 10C and 13C; Table 1), but this Mo has been hydrothermally mobilized locally (metres to hun-dreds of metres) into small veins within the Mo-enriched rocks, some of which are now Au-bearing. The scale of Au mobility in the YTT is less clear. The late metamorphic Au enrichment zones in some Klondike Schist lithologies (Fig. 11) appear to have been remobilized into Bonanza event veins only on a scale of metres or tens of metres (MacKenzie et al. 2008b, 2008c). Conversely, Au mineralization at White River resulted from passage of fault-con-trolled hydrothermal fluids on the kilometre scale (MacKenzie et al. 2010). Regional scale mobility and concentration of W apparently has not happened in the YTT, in contrast to the OSB (above). The orogenic Au deposits of the YTT are therefore dis-tinct from the W-rich intrusion-related deposits elsewhere in the region (Thompson et al. 1999; MacKenzie et al. 2010).

There is commonly a spatial, and possibly genetic, relationship between orogenic Au and graphitic rocks around the world (Bierlein & Crowe 2000; Bierlein et al. 2001; Vial et al. 2007). Some OSB and YTT orogenic Au deposits also display this spatial relationship, especially at the Macraes Au mine in the OSB, and in some of the White River mineralized rocks (YTT). Graphite has been remobilized in both OSB and YTT during progressive meta-morphism, and also during subsequent shearing that occurred in the deformation stages that accompanied Au mineralization (Fig. 9). The graphite mobility in the YTT has occurred primarily on the centimetre to metre scale, in reactivated cleavages in the Klondike Schist (MacKenzie et al. 2008b) and in faults, veins and breccias in the White River and Stewart River areas (MacKenzie et al. 2010, 2013). Widespread graphite mobility, on a scale of metres or tens of metres, has occurred in low grade OSB rocks (Henne & Craw 2012) and in sheared Macraes mine rocks (Craw 2002; Pitcairn et al. 2005). None of these examples of graphite mobility have defined genetic links to Au precipitation, although graphite concentration may have facilitated structural evolution of Au-bearing structures (Upton & Craw 2008) or may have facili-tated deposition of sulphides that host the Au (Craw 2002).

Conclusions

The YTT and OSB have similar geological histories as convergent tectonic belts and both host orogenic Au deposits, mainly Jurassic-Cretaceous in age, that formed without associated magmatism. The YTT host rocks are lithologically diverse, whereas the OSB host rocks are lithologically monotonous. The OSB orogenic Au deposits are all As-rich (commonly up to c. 1 wt%), and As/Sb ratios range from 100– 1000. The Au, As and Sb for these deposits was mobilized during Mesozoic metamorphism of host rocks (c. 10 ppm As) as they passed through the upper greenschist facies. The YTT was initially constructed in the Palaeozoic, and the rocks were metamorphosed to upper greenschist facies and amphibolite facies. This early metamorphic event may have mobilized As from

the YTT rock mass, as the rocks are now generally As-poor (1 ppm or less), and the Jurassic orogenic Au deposits have As of <100 ppm with little or no arsenopyrite. Graphitic quartzites are an exception, and most contain elevated As concentrations, including some arse-nopyrite porphyroblasts, and associated orogenic Au deposits are As-rich (up to 1 wt%). The As/Sb ratio for YTT orogenic Au deposits is <100 and Sb contents of these deposits are similar to those in the OSB.

Some YTT host rocks were enriched in Au, Mo and/or Cu before Palaeozoic metamorphism, and these enriched rocks have provided local sources for these elements during Mesozoic oro-genic mineralization, including some molybdenite in veins. Low metamorphic grade OSB rocks had minor diagenetic enrichment of Mo in pyrite, but this Mo remained largely dispersed through the metamorphic pile during prograde metamorphism, with little accumulation in orogenic Au deposits. In contrast, low-grade OSB rocks have low W contents, but this W was mobilised during pro-grade metamorphism and strongly concentrated into some oro-genic Au deposits as scheelite. Scheelite does not occur in the YTT orogenic Au deposits.

From a genetic perspective, the key difference in orogenic Au deposit formation processes between YTT and OSB was the scale of element mobility. The OSB mineralization involved pervasive leaching of elements from large volumes (hundreds of cubic kilo-metres) of homogeneous rocks, followed by transport of fluids on the 10-km scale to sites of deposition and concentration. In con-trast, the YTT orogenic mineralization involved relatively local elemental transport (metre to kilometre scale), commonly focussed around particular rock types with elevated metal or metalloid con-tents. This has led to greater diversity of geochemical signatures of mineralization in the YTT than in OSB, particularly with respect to As. This geochemical diversity may have been enhanced by an early (Palaeozoic?) As extraction process prior to the main Mesozoic mineralization period in the YTT. These observations regarding differing scales of metal mobility, and differing degrees of geochemical diversity, for the OSB and YTT, identify two pos-sible end-members in a spectrum of orogenic Au deposit types, and associated genetic processes, that undoubtedly spreads between these end-members.

Acknowledgements and FundingPreparation of this paper was funded by the NZ Ministry for Business, Innovation and Employment, University of Otago, and MDRU, University of British Columbia. Data from Macraes mine were kindly provided by Matthew Grant and Jonathan Moore. The project would have been impossible without the input of the many different exploration teams involved in both Otago and Yukon, particularly those of CanAlaska, Glass Earth, Klondike Star, Klondike Gold, Underworld, Smash, and Kaminak. Discussions with Adrian Fleming, Tim Liverton, Murray Allan, Damon Teagle, Richard Norris, Alan Cooper, and Simon Cox were helpful in developing our ideas. A constructive review by Rich Goldfarb improved the presentation.

ReferencesBierlein, F.P. & Crowe, D. 2000. Phanerozoic orogenic lode gold deposits. In:

Gold in 2000. Reviews in Economic Geology, 13, 103–140.Bierlein, F.P., Cartwright, I. & McKnight, S. 2001. The role of carbonaceous

“indicator” slates in the genesis of lode gold mineralization in the western Lachlan Orogen, Victoria, southestern Australia. Economic Geology, 96, 431–451.

Beranek, L.P. & Mortensen, J.K. 2011. The timing and provenance record of the Late Permian Klondike orogeny in northwestern Canada and arc-continent collision along western North America. Tectonics, 30, TC5017, http://dx.doi.org/10.1029/2010TC002849

Bowell, R.J., Foster, R.P. & Gize, A.P. 1993. The mobility of gold in tropical rain forest soils. Economic Geology, 88, 999–1016.

Boyle, R.W. 1979. The geochemistry of gold and its deposits.Geological Survey of Canada Bulletin, 280, 579 pp.

Campbell, J.R., Craw, D., Frew, R., Horton, T. & Chamberlain, C.P. 2004. Geochemical signature of orogenic hydrothermal activity in an active tec-tonic intersection zone, Alpine Fault, New Zealand. Mineralium Deposita, 39, 437–451.

Chapman, R.J., Mortensen, J.K., Crawford, E.C. & Lebarge, W.P. 2010. Microchemical Studies of Placer and Lode Gold in the Klondike District,


http://dx.doi.org/10.1029/2010TC002849

http://dx.doi.org/10.1029/2010TC002849



Yukon, Canada: 2. Constraints on the Nature and Location of Regional Lode Sources. Economic Geology, 105, 1393–1410.

Chapman, R.J., Mortensen, J.K. & Lebarge, W.P. 2011. Styles of lode gold mineralization contributing to the placers of the Indian River and Black Hills Creek, Yukon Territory, Canada as deduced from microchemical characteri-zation of placer gold grains. Mineralium Deposita, 46, 881–903.

Cox, L., MacKenzie, D.J., Craw, D., Norris, R.J. & Frew, R. 2006. Structure and geochemistry of the Rise & Shine Shear Zone mesothermal gold sys-tem, Otago Schist, New Zealand. New Zealand Journal of Geology and Geophysics, 49, 429–442.

Craw, D. 1998. Structural boundaries and biotite and garnet ‘isograds’ in the Otago and Alpine Schists, New Zealand. Journal of Metamorphic Geology, 16, 395–402.

Craw, D. 2002. Geochemistry of late metamorphic hydrothermal alteration and graphitisation of host rock, Macraes gold mine, Otago Schist, New Zealand. Chemical Geology, 191, 257–275.

Craw, D. & Norris, R.J. 1991. Metamorphogenic Au-W veins and regional tec-tonics: Mineralisation throughout the uplift history of the Haast Schist, New Zealand. New Zealand Journal of Geology and Geophysics, 34, 373–383.

Craw, D., Upton, P. & MacKenzie, D.J. 2009. Hydrothermal alteration styles in ancient and modern orogenic gold deposits, New Zealand. New Zealand Journal of Geology and Geophysics, 52, 11–26.

Crawford, E.C. & Mortensen, J.K. 2009. An ImageJ plugin for the rapid mor-phological characterization of separated particles and an initial application to placer gold analysis. Computers and Geoscience, 35, 347–359.

Dominy, S.C., Platten, I.M. & Nugus, M.J. 2010. Application of geol-ogy to alleviate sampling bias during the evaluation of high-nugget gold systems. Australasian Institute of Mining and Metallurgy Publication Series 3, 75–85.

Eilu, P. & Groves, D.I. 2001. Primary alteration and geochemical dispersion haloes of Archaean orogenic gold deposits in the Yilgarn Craton; the pre-weathering scenario. Geochemistry: Exploration, Environment, Analysis, 1, 183–200.

Gabrielse, H. & Yorath, C.J. 1991. Tectonic synthesis, Chapter 18. In: Gabrielse, H. & Yorath, C.J. (eds) Geology of the Cordilleran Orogen in Canada. Geology of Canada, 4, 677–705.

Gabrielse, H., Murphy, D.C. & Mortensen, J.K. 2006. Cretaceous and Cenozoic dextral orogen-parallel displacements, magmatism, and paleogeography, north-central Canadian Cordillera. In: Haggart, J.W., Enkin, R.J. & Monger, J.W.H. (eds) Paleogeography of the North American Cordillera: Evidence For and Against Large-Scale Displacements. Geological Association of Canada Special Paper, 46, 255–276.

Goldfarb, R.J., Baker, T., Dube, B., Groves, D.I., Hart, C.J. & Gosselin, P. 2005. Distribution, character and genesis of gold deposits in metamorphic terranes. In: Economic Geology 100th Anniversary Volume. 407–450.

Henne, A. & Craw, D. 2012. Synmetamorphic carbon mobility and graphite enrichment in metaturbidites as a precursor to orogenic gold mineralization, Otago Schist, New Zealand. Mineralium Deposita, 47, 781–797.

Hronsky, J.M.A., Groves, D.I., Loucks, R.R. & Begg, G.C. 2012. A unified model for gold mineralisation in accretionary orogens and implications for regional scale exploration targeting methods. Mineralium Deposita, 47, 339–358.

Large, R., Thomas, H., Craw, D., Henne, A. & Henderson, S. 2012. Diagenetic pyrite as a source for metals in orogenic gold deposits, Otago Schist, New Zealand. New Zealand Journal of Geology and Geophysics, 55, 137–149.

Liverton, T. 2007. Geological mapping, trenching, rock sampling, bulk sam-pling and grid preparation on the JAE Property. Klondike Star Mineral Corp. Yukon mining assessment report. Curated by Yukon Geological Survey; yma.gov.yk.ca/094882.pdf.

Lowey, G.W. 2006. The origin and evolution of the Klondike goldfields, Yukon, Canada. Ore Geology Reviews, 28, 431–450.

MacKenzie, D.J. & Craw, D. 2005. Structural and lithological continuity and discontinuity in the Otago Schist, Central Otago, New Zealand. New Zealand Journal of Geology and Geophysics, 48, 279–293.

MacKenzie, D.J., Youngson, J.H. & Craw, D. 2006. Taieri River mineral-ized vein swarm, east Otago. In: Geology and Exploration of New Zealand Mineral Deposits. Australasian Institute of Mining & Metallurgy Monograph, 25, 305–312.

MacKenzie, D.J., Craw, D. & Begbie, M. 2007. 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, 93, 160–176.

MacKenzie, D., Craw, D. & Mortensen, J.K. 2008a. Structural controls on oro-genic gold mineralisation in the Klondike goldfield, Canada. Mineralium Deposita, 43, 435–448.

MacKenzie, D., Craw, D. & Mortensen, J.K. 2008b. Thrust slices and associ-ated deformation in the Klondike goldfield, Yukon. Yukon Exploration and Geology 2007, Yukon Geological Survey, 199–213.

MacKenzie, D., Craw, D., Mortensen, J.K. & Liverton, T. 2008c. Disseminated gold mineralisation associated with orogenic veins in the Klondike Schist, Yukon. Yukon Exploration and Geology 2006, Yukon Geological Survey, 215–224.

MacKenzie, D., Craw, D., Cooley, M. & Fleming, A. 2010. Lithogeochemical localisation of disseminated gold in the White River area, Yukon, Canada. Mineralium Deposita, 45, 683–705.

MacKenzie, D., Craw, D., Brodie, C. & Fleming, A. 2013. Foliation develop-ment and hydrothermal gold emplacement in metagabbroic rocks, central Yukon, Canada. Yukon Exploration and Geology 2012, Yukon Geological Survey, 47–64.

MacKenzie, D., Craw, D. & Finnigan, C. 2014. Lithologically controlled invis-ible gold, Yukon, Canada. Mineralium Deposita. http://dx.doi.org/10.1007/s00126-014-0532-5

McKenzie, G.G., Allan, M.M., Mortensen, J.K., Hart, C.J.R., Sánchez, M. & Creaser, R.A. 2013. Mid-Cretaceous orogenic gold and molybdenite min-eralization in the Independence Creek area, Dawson Range, parts of NTS 115J/13 and 14. Yukon Exploration and Geology 2012, Yukon Geological Survey, 73–97.

McClenaghan, M.B. & Cabri, L.J. 2011. Review of gold and platinum group element (PGE) indicator minerals methods for surficial sediment sampling. Geochemistry: Exploration, Environment, Analysis, 11, 251–263.

Mitchell, M., Maw, L., Angus, P.V. & Craw, D. 2006. The Macraes gold deposit in east Otago. In: Geology and Exploration of New Zealand Mineral Deposits, Australasian Institute of Mining & Metallurgy Monograph, 25, 313–318.

Mortensen, J.K. 1990. Geology and U-Pb chronology of the Klondike District, west-central Yukon. Canadian Journal of Earth Science, 27, 903–914.

Mortensen, J.K. 1992. Pre-mid-Mesozoic tectonic evolution of the Yukon-Tanana Terrane, Yukon and Alaska. Tectonics, 11, 836–853.

Mortensen, J.K. 1996. Geological compilation maps of the northern Stewart River map area, Klondike and Sixtymile Districts (115N/15, 16; 1150/13, 14; and parts of 1150/15, 16). Exploration and Geological Services Division, Yukon Region, Indian and Northern Affairs Canada. Open File 1996-1, 43 pp.

Mortensen, J.K., Craw, D., MacKenzie, D.J., Gabites, J.E. & Ullrich, T. 2010. Age and origin of orogenic gold mineralisation in the Otago Schist belt, South Island, New Zealand: Constraints from lead isotope and 40Ar/39Ar dat-ing studies. Economic Geology, 105, 777–793.

Mortimer, N. 1993. Jurassic tectonic history of the Otago Schist, New Zealand. Tectonics, 12, 237–244.

Mortimer, N. 2000. Metamorphic discontinuities in orogenic belts: Example of the garnet-biotite-albite zone in the Otago Schist, New Zealand. International Journal of Earth Science, 89, 295–306.

Petrie, B.S., Craw, D. & Ryan, C.G. 2005. Geological controls on refractory ore in an orogenic gold deposit, Macraes mine, New Zealand. Mineralium Deposita, 40, 45–58.

Pitcairn, I.K., Roberts, S., Teagle, D.A.H. & Craw, D. 2005. Detecting hydro-thermal graphite deposition during metamorphism and gold mineralisation. Journal of the Geological Society, London, 162, 429–432.

Pitcairn, I.K., Teagle, D.A.H., Craw, D., Olivo, G.R., Kerrich, R. & Brewer, T.S. 2006. Sources of metals and fluids in orogenic gold deposits: Insights from the Otago and Alpine Schists, New Zealand. Economic Geology, 101, 1525–1546.

Pitcairn, I.K., Olivo, G.R., Teagle, D.A.H. & Craw, D. 2010. Sulfide evolu-tion during prograde metamorphism of the Otago and Alpine Schists, New Zealand. Canadian Mineralogist, 48, 1267–1295.

Pitcairn, I.K., Craw, D. & Teagle, D.A.H. 2014. The gold conveyor belt: Large-scale gold mobility in an active orogen. Ore Geology Reviews, 62, 129–142.

Redmond, P.B., Einaudi, M.T. & Meinert, L.D. 2010. The Bingham Canyon porphyry Cu-Mo-Au deposit; I, Sequence of intrusions, vein formation, and sulfide deposition. Economic Geology, 105, 43–68.

Rushton, R.W., Nesbitt, B.E., Muehlenbachs, K. & Mortensen, J.K. 1993. A fluid inclusion and stable isotope study of Au quartz veins in the Klondike district, Yukon Territory, Canada: A section through a mesothermal vein sys-tem. Economic Geology, 38, 647–678.

Teagle, D.A.H., Norris, R.J. & Craw, D. 1990. Structural controls on gold-bearing quartz mineralisation in a duplex thrust system, Hyde Macraes shear zone, Otago Schist, New Zealand. Economic Geolog, 85, 1711–1719.

Thompson, J.F.H., Sillitoe, R.H., Baker, T., Land, J.R. & Mortensen, J.K. 1999. Intrusion-related gold deposits associated with tungsten-tin provinces. Mineralium Deposita, 34, 323–334.

Townley, B.K., Herail, G., Maksaev, V., et al. 2003. Gold grain morphology and composition as an exploration tool: Application to gold exploration in covered areas. Geochemistry: Exploration, Environment, Analysis, 3, 29–38.

Upton, P. & Craw, D. 2008. Modelling the role of graphite in development of a mineralised mid-crustal shear zone, Macraes mine, New Zealand. Earth & Planetary Science Letters, 266, 245–255.

Upton, P. & Craw, D. 2009. Mechanisms of strain rate and reaction dependent permeability in the mid crust of the Southern Alps: Insight from 3D mechani-cal models. Geofluids, 9, 287–302.

Vial, D.S., Duarte, B.P., Fuzikawa, K. & Vieira, M.B.H. 2007. An epigenetic origin for the Passagem de Mariana gold deposit, Quadrilatero Ferrifero, Minas Gerais, Brazil. Ore Geology Reviews, 32, 596–613.

Wainwright, A.J., Simmons, A.T., Finnigan, C.S., Smith, T.R. & Carpenter, R.L. 2011. Geology of new gold discoveries in the Coffee Creek area, White Gold district, west-central Yukon. Yukon Exploration and Geology 2010, Yukon Geological Survey, 233–247.

Williams, G.J. 1974. Economic Geology of New Zealand. Australasian Institute of Mining & Metallurgy Monograph, 4, 1–490.


http://dx.doi.org/10.1007/s00126-014-0532-5

http://dx.doi.org/10.1007/s00126-014-0532-5


Documents

Contrasting geochemistry of orogenic gold deposits in Yukon, Canada and Otago, New Zealand