Macraes Flat Research Articles

Empidadelpha pokekeao (Diptera: Empididae): a new species from New Zealand

ABSTRACT Empidadelpha pokekeao sp. nov. (Empididae: Empidinae) is described from male specimens collected in native forest at Sullivan’s Dam, Dunedin, New Zealand and in snow tussock at Macraes Flat, New Zealand. The species is distinguished from other species of Empidadelpha by the colouration of the body and legs, the remarkable length of the male antenna, and the distinctively darkened wings with a large dark cloud anteroapically. The two only other New Zealand species of this genus, E. propria Collin, 1928 and E. torrentalis Miller, 1923, were also examined and are discussed here.

Placer gold and associated supergene mineralogy at Macraes Flat, East Otago, New Zealand

ABSTRACTMacraes Flat occupies a shallow upland tectonic basin that contains only Late Pleistocene sediments. The gold-bearing Hyde–Macraes Shear Zone is hosted by schist basement that underlies the basin. Supergene alteration of the mineralised shear zone has been occurring periodically since the Eocene, with both oxidised and unoxidised alteration of gold-bearing sulphides and associated silicates. This alteration led to liberation of gold from encapsulation in sulphides and enhancement of gold particle size into millimetre-scale irregular particles by supergene processes. Erosion of the supergene zone during faulting and tilting of basin margins in the Pleistocene has transferred gold particles into proximal placers on the basin floor. Nanoparticulate and microparticulate authigenic gold has formed on the surface of the supergene gold particles, intergrown with secondary minerals that include arsenolite, Fe sulphates and Fe oxyhydroxide. Chemical gold mobilisation and reprecipitation was facilitated by fluctuating redox conditions and pH variations near to the sulphide–sulphate redox boundary over the last 40 Ma.

Comparison of camera traps and kill traps for detecting mammalian predators: a field trial

Currently there are few robust techniques being used in New Zealand to assess the results of pest control targeting predatory mammals such as stoats (Mustela erminea), feral cats (Felis catus) and hedgehogs (Erinaceus europaeus), with most operations using capture rates from kill traps as a measure of success. We conducted field trials of camera traps to detect these species at two sites—Macraes Flat and Tasman Valley—where intensive predator trapping is conducted by the New Zealand Department of Conservation. We compared camera traps with kill traps in terms of capture rate per 100 trap nights. Camera traps detected all three target species, as well as various non-target animals. Capture rates of cats and hedgehogs were higher with cameras than with kill traps. Comparisons for stoats were inconclusive due to a low number of detections. We suggest that camera traps are suitable for monitoring relative abundance of cats and hedgehogs, and recommend further testing in areas of higher stoat abundance.

Phylogeography of the Endangered Otago Skink, Oligosoma otagense: Population Structure, Hybridisation and Genetic Diversity in Captive Populations

Climatic cooling and substantial tectonic activity since the late Miocene have had a pronounced influence on the evolutionary history of the fauna of New Zealand's South Island. However, many species have recently experienced dramatic range reductions due to habitat fragmentation and the introduction of mammalian predators and competitors. These anthropogenic impacts have been particularly severe in the tussock grasslands of the Otago region. The Otago skink (Oligosoma otagense), endemic to the region, is one of the most critically endangered vertebrates in New Zealand. We use mitochondrial DNA sequence data to investigate the evolutionary history of the Otago skink, examine its population genetic structure, and assess the level of genetic diversity in the individuals in the captive breeding program. Our data indicate that the Otago skink diverged from its closest relatives in the Miocene, consistent with the commencement of tectonic uplift of the Southern Alps. However, there is evidence for past introgression with the scree skink (O. waimatense) in the northern Otago-southern Canterbury region. The remnant populations in eastern Otago and western Otago are estimated to have diverged in the mid-Pliocene, with no haplotypes shared between these two regions. This divergence accounts for 95% of the genetic diversity in the species. Within both regions there is strong genetic structure among populations, although shared haplotypes are generally evident between adjacent localities. Although substantial genetic diversity is present in the captive population, all individuals originate from the eastern region and the majority had haplotypes that were not evident in the intensively managed populations at Macraes Flat. Our data indicate that eastern and western populations should continue to be regarded as separate management units. Knowledge of the genetic diversity of the breeding stock will act to inform the captive management of the Otago skink and contribute to a key recovery action for the species.

Movements, Home Ranges, and Capture Effect of the Endangered Otago Skink (Oligosoma Otagense)

Otago Skinks (Oligosoma otagense) are some of New Zealand's largest and most rare lizards. The movements and home ranges of these skinks were investigated using radio-telemetry at the Redbank Reserve near Macraes Flat, Central Otago, New Zealand. Thirteen Otago Skinks were tracked from December 2003 through April 2004 for 26–111 days. There was no significant difference in the distance or frequency of movements between sexes. Home ranges estimated for all individuals using the 100% Minimum Convex Polygon method varied from 200–5,400 m2. Male home ranges were significantly larger than female home ranges, and nongravid females had significantly larger home ranges than gravid females. There was a considerable amount of home-range overlap and interaction between individuals. Human capture of skinks, the most common method for the monitoring this species, increased the frequency of movements. Capture-induced disturbance caused skinks to increase the frequency of movements in the days immediately following the event. The results of this study will be used in the future conservation management of the Otago Skinks.

In situ 14C depth profile of subsurface vein quartz samples from Macraes Flat New Zealand

We present results of measurements of cosmogenic in situ 14C produced in a quartz vein from Macraes Flat, East Otago, New Zealand, where concentrations of in situ produced 10Be and 26Al were previously studied by Kim and Englert [Earth Planet. Sci. Lett. 223 (2004) 113]. 14C was extracted from the quartz samples up to depths of 400gcm−2 using a low temperature wet extraction method [D. Lal, A.J.T. Jull, Nucl. Instr. and Meth. B 92 (1994) 291]. Based on the results for 10Be and 26Al, we expected that the 14C activity in the samples would be at saturation levels, in equilibrium with erosion. The surface exposure age of this site was found to be about 25000 years using 10Be and 26Al at the surface, with a surface erosion rate of at least 10−3cm/y [K.J. Kim, P.A.J. Englert, Earth Planet. Sci. Lett. 223 (2004) 113]. The measured 14C activities were compared with those expected from spallation of Si and O in quartz by energetic neutrons and fast muons, and from capture of negative muons in O in quartz [B. Heisinger, A.J.T. Jull, D. Lal, P. Kubik, S. Ivy-Ochs, K. Knie, E. Nolte, Earth Planet. Sci. Lett. 200 (2002) 357; B. Heisinger, D. Lal, A.J.T. Jull, P. Kubik, S. Ivy-Ochs, S. Neumaier, K. Knie, V. Lazarev, E. Nolte, Earth Planet. Sci. Lett. 200 (2002) 345]. Surprisingly, we found that the 14C activities were significantly greater than those expected, by factors of 2–3, especially in samples of depths <200gcm−2. We suspect that the excess 14C probably resulted from capture of thermal neutrons in nitrogen present in the fluid inclusions in quartz. This study shows that great care has to be taken in measurements of in situ 14C in quartz, especially in samples exposed near sea level and greater depths, where rates of spallation produced 14C are low.

Annual Reproduction in Females of a Viviparous Skink (Oligosoma maccanni) in a Subalpine Environment

Females of most of New Zealand's endemic reptiles show low rates of annual reproductive output, involving extended gestation and small clutch size. The main purpose of the present study was to investigate the female reproductive cycle and patterns of clutch size in McCann's Skink (Oligosoma maccanni) from a subalpine site in southern New Zealand (Macraes Flat). The results were then compared with those available for the Common Gecko (Hoplodactylus maculatus) from the same site, where females have biennial reproduction with a gestation of up to 14 months. Palpation was used to assess reproductive condition of O. maccanni noninvasively. A subset of females was then dissected to confirm reproductive condition, determine patterns of change in yolk and embryo mass with pregnancy, and determine plasma progesterone profiles. Both species are lecithotrophic with autumn-spring vitellogenesis; however, in contrast to H. maculatus, female O. maccanni are annual breeders with a spring-summer gestation of 4–5 months. Clutch size in O. maccanni decreases (relative to snout–vent length, SVL) between vitellogenesis (mean 3.33, range 2–5) and pregnancy/birth (mean 2.83, range 1–6). Plasma progesterone concentration is elevated during mid-pregnancy, and lowest during early vitellogenesis. More frequent reproduction at Macraes Flat in the diurnal skink O. maccanni than in the primarily nocturnal gecko H. maculatus in part may be a consequence of different thermoregulatory behavior.

The behavior of nitrogen and nitrogen isotopes during metamorphism and mineralization: Evidence from the Otago and Alpine Schists, New Zealand

Metamorphism is a major mechanism for the re-distribution of fluids and mass in the Earth's crust, with these processes most prominently highlighted by the occurrence of major gold resources within these terranes. However, although orogenic gold deposits have contributed over 20% of the global gold production, their origins remain controversial. The nitrogen concentration and isotopic composition of rocks and minerals are potentially powerful tracers of crustal metamorphism and mineralization, but there have been few detailed applications of this approach to date. Although nitrogen isotopes have recently been used to elucidate the source of fluids in some Neoarchean orogenic gold deposits and Proterozoic to Paleozoic mountain belts, due to their age and geological complexity of these terranes, major uncertainties as to the behavior of nitrogen remain. The Otago and Alpine Schists in the South Island of New Zealand comprise a large, comparatively young (< 190 Ma), metasedimentary belt with multiple generations of quartz ± carbonate veins, some of which are mineralized with gold. A range of rocks, with little primary compositional variation, is exposed from unmetamorphosed protolith to high-grade amphibolites and as such they present an ideal laboratory to investigate the mobility of nitrogen and potential nitrogen isotopic fractionations during metamorphism and mineralization. Here we present nitrogen concentrations and isotopic analyses of whole rock samples and mica separates from a number of crustal transects through the Otago crust. The range of δ 15N values for mica and whole rock samples from the schists spans 0.2 to 7.0‰, and the nitrogen concentration from 23 to 3483 ppm. Sample provenance and rock type have minimal influence on the nitrogen concentration and isotopic value, which appears to have been inherited from the original sedimentary kerogen. There is no systematic variation between metamorphic temperature and δ 15N or N concentration in micas, suggesting that there has been little discernible loss of 15N-depleted fluids from silicates with increasing metamorphic temperature. Comparison of fluid mobile alkali element (K, Rb and Cs), carbon and nitrogen whole rock concentrations, indicates that for the Otago and Alpine Schists, in rocks up to upper greenschist facies significant nitrogen remains hosted in phases other than micas, most likely poorly matured carbonaceous material. Samples from Macraes Flat, a major gold producer, have a similar range of δ 15N values to the host terrane, but show distinctly higher nitrogen concentrations relative to unmineralized samples, due to the incorporation of nitrogen from the mineralizing hydrothermal fluid. This suggests that there is only a subtle metamorphic re-distribution of nitrogen during mineralization, albeit with minimal isotopic fractionation. In the case of nitrogen at least, the isotopic signatures of mineralized rocks support a metamorphic fluid source, and are inconsistent with mantle or meteoric fluid reservoirs. However, due to the high relative abundance of nitrogen in sedimentary rocks compared to other potential reservoirs, unless fluid fluxes are very large and well channeled, nitrogen signatures are not sensitive recorders of fluid inputs from mantle, magmatic or meteoric reservoirs. Conversely, the absence of a “sedimentary”-source nitrogen isotope signature similar to the host rock in an orogenic deposit would be a very strong indicator of an external, exotic source for the mineralizing fluids.

ECTOPARASITE AND HEMOPARASITE INFECTION IN A DIVERSE TEMPERATE LIZARD ASSEMBLAGE AT MACRAES FLAT, SOUTH ISLAND, NEW ZEALAND

A lizard assemblage at Macraes Flat, New Zealand, comprising the common skinks Oligosoma maccanni and Oligosoma nigriplantare polychroma, the endangered species Oligosoma grande and Oligosoma otagense, and the common gecko Hoplodactylus maculatus, was studied to determine the prevalence of ectoparasites and hemoparasites. The mites Odontacarus lygosomae and Ophionyssus scincorum infected all Oligosoma spp. only, and the mite Neotrombicula naultini infected only H. maculatus. The hemoparasite Hepatozoon lygosomarum infected all Oligosoma skinks, except O. n. polychroma. Oligosoma otagense had the highest infection levels of all parasites by several orders of magnitude. For all lizard species, there was no difference in mite prevalence between adult males and adult females, but juveniles were less often infected. For all skink species, there was a significant relationship between presence of the hemoparasite He. lygosomarum and infection intensity of the supposed vector, O. scincorum. It is unclear if patterns of parasite infection reflect species-specific susceptibility, host-parasite species-specific spatial ecology, or environmentally induced host physiological impairment. Considering the threatened nature of O. otagense, evidence of high parasitemia should stimulate further investigation.

Profiles of in situ 10Be and 26Al at great depths at the Macraes Flat, East Otago, New Zealand

The production of cosmic ray-produced 10Be and 26Al in vein quartz was investigated from near the surface to 49,300 g cm −2 depth at three locations in Macraes gold mine, East Otago, New Zealand. The measured 26Al/ 10Be ratios are dependent on depth, which indicates that the production mechanisms of these nuclides change with depth. The transition from neutron-induced production to muon-induced production was observed at about 1000 g cm −2. The measured attenuation lengths of 10Be and 26Al from the surface down to 400 g cm −2 of this study are much larger than steady state apparent neutron attenuation length at near surface. The large measured attenuation lengths at shallow depths could be caused by deep erosion, which results in a large muon contribution to the production of the isotopes at all depths. Using revised production rates, the average model surface exposure age of the Macraes Flat was determined to be 25.0±3.3 kyr. The erosion rate of the sampling site was estimated to be at least 12 m Myr −1 using the depth profiles of 10Be and 26Al of this study. Production systematics below ∼5000 g cm −2 are poorly known, and a model is proposed for those depths. We emphasize the importance of using depth profiles of cosmogenic nuclides in understanding surface processes and past geological histories.

The diet of grand skinks (Oligosoma grande) and Otago skinks (O. otagense) in Otago seral tussock grasslands

The threatened grand skink (Oligosoma grande) and Otago skink (O. otagense) live sympatrically in seral tussock grassland habitat of Otago, New Zealand. The diets of juvenile, male, and female grand and Otago skinks were investigated at five sites (grand skinks) and two sites (Otago skinks) in the vicinity of Macraes Flat, Otago. No differences were found in the diet of Otago skinks in relation to site, age, and sex class. For grand skinks, there was some evidence that site influenced diet, but the data were not convincing. No sex or age‐based diets were found in grand skinks. In general, grand skinks consumed large quantities of small‐bodied dipterans, as well as substantial amounts of the fruit Leucopogon fraseri and Melicytus alpinus. In contrast, Otago skinks consumed large amounts of the fruit Coprosma taylorae and Leucopogonfraseri, small‐bodied coleopterans, and large bodied dipterans (Calliphoridae). Diet overlap between grand skinks and Otago skinks was greatest in midsummer, and at this time 78% of food items detected were ingested by both species. Pronounced diet separation was evident only in late summer, when both species ate only a small range of food items, and some “specialisation” in fruit dietary items was evident. Although both species appear to consume substantial amounts of fruit, Otago skinks rely on fruit for most of summer. For grand skinks fruit is also important, especially in May. Neither species are likely to survive long‐term any habitat modification that destroys fruiting plants. Habitat restoration initiatives should target plant species favoured by both species, in particular C. taylorae, L. fraseri, and Melicytus alpinus.

Round Hill Shear Zone-Hosted Gold Deposit, Macraes Flat, Otago,New Zealand: Evidence of a Magmatic Ore Fluid

The 0.8-Moz Round Hill shear zone-hosted gold deposit is one of several located on, or near, the Hyde-Macraes shear zone, Macraes Flat, New Zealand. Field relationships show stockwork veins are the oldest part of the hydrothermal system, followed by flat and ramp veins. Hanging-wall shear veins formed early but have been modified by late deformation. Fluid inclusion microthermometric results for dominant type I inclusions show that flat and ramp veins have the same average wt percent NaCl equiv values (2.2± 0.6%) and were precipitated from the same fluid. Salinity data for these veins overlap with those from hanging-wall veins (average 1.3 ± 0.3%) and stockwork veins (1.6 ± 0.6% for vein margins; 0.9 ± 0.3% for vein centers), although both of the latter trend toward lower overall wt percent NaCl equiv values, suggesting mixing between relatively dilute and more saline end members. All of the above veins have similar temperatures of homogenization (T h ), ranging between 110° and 188°C. Fluid inclusion trapping temperatures are considered to be ~300°C, equating to a ~10-km depth of formation. Carbon dioxide dissolved in the hydrothermal fluid is responsible for up to one third of fluid inclusion apparent salinities. Stockwork and hanging-wall veins thus have true salinities of <1 wt percent NaCl equiv (<0.17 molal) and flat and ramp veins have true salinities of Fluid inclusion volatiles from Round Hill and other Macraes deposits are dominated by H 2 O (99.02–99.69 mol %), with lesser CO 2 (0.14–0.76 mol %), N 2 (0.03–0.32 mol %), and CH 4 (0.06–0.17 mol %). Noticeable concentrations of hydrocarbons occur in many of the samples. Fluid inclusion cation and anion data show few components of relatively low concentration are dissolved in the hydrothermal fluid, consistent with CO 2 -corrected microthermometric measurements. A range in fluid inclusion δ D H 2 O values obtained for the Round Hill deposit is coincident with the different vein types and also indicates mixing between two fluids. One fluid is considered to be O isotope shifted meteoric water, as trapped by the early stockwork veins, and has the lowest δ D H 2 O values of –80 per mil. The other fluid is represented by flat and/or ramp and hanging-wall veins that have δ D H 2 O values up to –40 per mil. The Macraes δ D H 2 O data show a trend toward the magmatic water end member for geothermal systems associated with convergent plate boundaries and are consistent with a 25 to 50 percent magmatic component in the Macraes hydrothermal system.

Round Hill Shear Zone-Hosted Gold Deposit, Macraes Flat, Otago, New Zealand: Evidence of a Magmatic Ore Fluid

Round Hill Shear Zone-Hosted Gold Deposit, Macraes Flat, Otago, New Zealand: Evidence of a Magmatic Ore Fluid

Evolution and sulphide mineral occurrences of an incipient nonmarine sedimentary basin, New Zealand

Abstract River sediments at Macraes Flat, east Otago have formed in a tectonically active depression in the Otago Schist basement adjacent to an active northeast striking fault. The depression is the most juvenile of a series of nonmarine basins currently forming during tectonic convergence. The sediments were derived from rapid erosion of the rising fault scarp, with long-term average sedimentation rates between 0.15 and 0.18 mm/year. The Hyde–Macraes Shear Zone crosses the depression, and this shear zone hosts the Macraes gold mine. The shear zone contains sulphide minerals, mainly pyrite and arsenopyrite. Sulphide minerals were eroded and deposited in the Macraes Flat river sediments at least 28,000 years ago. The sulphide minerals have not suffered any detectable decomposition in the sediments, even though some oxygenated water incursion has occurred. This sulphide longevity is due to general water saturation in the basin floor, despite possible occasional drying. Some sands have remained unaffected by oxygenated waters, and authigenic pyrite deposition has occurred. The pore waters in recently-exposed outcrops of organic sands with authigenic pyrite are too oxidised to be in equilibrium with pyrite. The Macraes Flat example demonstrates that sulphide minerals can remain stable for tens of thousands of years, and authigenic sulphides can form locally, within only 5 metres of the surface in an oxygenated atmosphere and only sporadic water saturation in a tectonically active nonmarine environment.

Preliminary observations on the biology of a manuka chafer,Pyronotasp. (Coleoptera: Scarabaeidae) in Otago

In oversown tussock grassland 540 m in altitude at Macraes Flat, Otago, Pyronota sp. aff. laeta followed a 2 year life cycle, spending the first winter as 1st or 2nd instar larvae and the second winter as 3rd instar larvae. Pupation occurred from early November to early December, and adults were present from late November to mid January. Larvae made some movement downwards in the soil during winter but more than 70% of larvae and pupae were always situated in the top 4 cm, many larvae feeding immediately below the turf mat.