Changes in hydrocarbon maturity indices with coal rank and type,Buller Coalfield,New Zealand

The Buller Coalfield (South Island, New Zealand) is an inverted late Paleogene Basin that contains middle Eocene bituminous coals which exhibit considerable variation in both coal rank (across-basin), and coal type (in-seam). Twenty-two fractionated bitumen extracts of Brunner Coal Measures coal samples from 12 drillholes were analyzed by GC and GC–MS to characterize the effect of coal rank and type on conventional hydrocarbon maturity indices at the beginning and end of the oil window (0.56–1.26% Ro_max).The Carbon Preference Index, pristane/phytane and isoprenoid/n-alkane ratios evolve throughout the high volatile bituminous B rank stage, while other biomarker ratios [18α(H)-22,29,30-trisnorneohopane/17α(H)-22,29,30-trisnorhopane (Ts/Tm), 18α(H),21β(H)-30-norneohopane (C₂₉ Ts)/17α(H),21β(H)-30-norhopane and C₃₀ diahopane/hopane] do not show appreciable change in value until medium volatile bituminous rank. Various aromatic based ratios appear to be more effective in delineating rank throughout the entire oil window; in particular the Methylphenanthrene Index and vitrinite reflectance are positively correlated over the entire bituminous rank range. However, subtle changes in depositional conditions (variable coal type) complicate these rank estimates. Within a given coal seam, variation in CPI, isoprenoid/n-alkane and hopane/sterane ratios appear to be related to the hydrogen content of the coal, while the homohopane index and the oleanane/hopane ratio covary with sulfur content. As with depressed vitrinite reflectance values, MPI is similarly lowered in the perhydrous samples. The mechanisms that control these hydrocarbon parameters during deposition and diagenesis are complex and convoluted, however, changes in bacterial activity and community (with marine incursion) appear to play an important role. Due to these anomalies, none of the hydrocarbon maturity indices calculated can be singularly used to constrain coal rank.     

Leaching of inorganics in the Cretaceous Greymouth coal beds, South Island, New Zealand

Leaching processes are believed to be responsible for the unusually low-ash content (sometimes less than 1%) of the thick (up to 35 m) Cretaceous coals located in the Greymouth coalfield, South Island, New Zealand. Although leaching of inorganics in peat is a generally accepted process, little is known about leaching after burial. The “Main” and “E” seams in the Greymouth coalfield show good correlation between low ash and bed thickness. The ash content, however, is often less than 1%, which is lower than most known modern analogues (i.e. peat). There are several lines of evidence that suggest that mineral matter may have been removed from the coal not only in the peat stage but also after burial. For example, etching features found in quartz grains and clay aggregates indicate that some leaching processes have taken place. In addition, liptinitic material (e.g., bitumen) in the cleat networks supports the conclusion that there has been some movement of solutions through the coal after burial. These solutions may have helped to remove some of the inorganics originally within the Greymouth coals.     

Palaeoenvironmental control on coal formation, distribution and quality in the Permian Vryheid Formation, East Witbank Coalfield, South Africa

The No. 1 and No. 2 coal seams from the Permian Vryheid Formation in the east Witbank Coalfield, South Africa are described with respect to their distribution, thickness and quality. These two coal seams accumulated in a postglacial climatic environment and peat accumulation was closely associated with and influenced by deposition in a braided river system. The fluvial channels that were syndepositional with peat accumulation have resulted in thinning of coal below and above channel axes and pinch-out of coal adjacent to channel margins. Low-ash coal originated from peat which accumulated in areas away from the influence of clastic sedimentation. In contrast, higher-ash coals are situated adjacent and parallel to channel margins where interbedded channel sand and silt contaminated the peat.The lower No. 1 seam peat originated under near-optimum conditions in a lacustrine swamp which blanketed an underlying platform of glaciofluvial braided river sediment. This peat swamp was not subjected to syndepositional clastic contamination and as a result is of superior quality (lower ash/higher calorific value and volatile matter) than the overlying No. 2 coal seam. The No. 2 seam is split by a clastic parting produced by a braided fluvial channel which transected the swamp midway through peat accumulation. This fluvial clastic parting deleteriously affected coal thickness and quality.A comparison of the Gondwanan Permian peat-forming conditions with those from Carboniferous northern hemisphere counterparts suggests that the differences in coal characteristics between these two regions are probably related to different palaeoclimatic conditions and basin tectonics. Cool-temperate climatic conditions which prevailed over the Permian peat swamps resulted in less species diversification of vegetation at these high-latitude settings than the diverse floral assemblages of the Carboniferous swamps. A stable intracronic basin platform caused lateral dispersion of sedimentary facies rather than the stacking of vertical facies which occurred in rapidly subsiding depositories. Partial exposure of the Permian peat swamps during peat accumulation may account for the relatively higher inertinite content of the coals.     

Cyclic characteristics of sediments in the Moon Island Beach Subgroup, Newcastle Coal Measures, New South Wales

Cyclic characteristics of a sequence of Permian coal-measure sediments have been studied using Markov chain analysis on borehole data. Fining-upwards and oscillating sequences can be distinguished, and depositional regimes are proposed to explain the observed sequences. However, there is no clearly defined relationship of sequence type to tectonosedimentary environment. The relationship of the number of coal-defined and fining-upwards cycles to total thickness and mean cycle thickness is examined using linear regression. The relationships for coal-defined and fining-upwards cycles are essentially the same. Significant positive correlations are present between the number of cycles and total thickness and significant inverse relationships are present for the number of cycles and the mean cycle thickness.     

Phonolitic Diatremes within the Dunedin Volcano, South Island, New Zealand

The Port Chalmers Breccia is a vent-filling, clastic volcanicunit exposed within the Miocene Dunedin Volcano of South Island,New Zealand. Clasts (up to in excess of 1 m but generally <20cm) are supported in ash and fine lapilli of phonolitic (ne-benmoreiteor tephro-phonolite) composition and the dominant clast type(55 to almost 100%) is also phonolitic. Less abundant lithologiesinclude ne-normative basalt (basanite), hawaiite, mugeariteand trachyandesite, syenites and microsyenites, coarse-grainedmafic (gabbros) and ultramafic rocks (pyroxenites, hornblendites),schists and sediments. The breccias were emplaced as diatremesassociated with localized, but highly explosive, eruptive eventsin which mantle-derived CO₂ was an important component. Thesyenitic and ultramafic clasts could represent intrusive suitesproduced by crystal fractionation acting on parental ne-benmoreitemagmas that may themselves have been derived by crystal fractionationfrom basanitic precursors. An alternative variation on thismodel is that the parental ne-benmoreites were generated throughpartial melting of an alkalic igneous underplate. Sr, Nd andPb isotopic compositions are strikingly similar to those ofintraplate igneous rocks, ranging in age from 100 to less than10 Ma, from elsewhere in the South Island, and New Zealand'ssub-Antarctic islands, the south Tasman Sea and the Ross Searegion. This regional, HIMU-influenced, isotopic signature isbelieved to be derived from within the lithospheric mantle. KEY WORDS: phonolite; diatreme; nepheline syenite; Dunedin Volcano; alkalic rocks; fractional crystallization     

Glacial forest refugium in Howard Valley,South Island,New Zealand

Fossils of forest habitat beetles and leaves of Nothofagus menziesii provide evidence of a forest refugium at times between ca. 34 000 and ca. 18 500 cal. a BP at an upland site in Howard Valley, located adjacent to glaciated valleys in South Island, New Zealand. The stratigraphy of the glacial‐aged terrace sequence of organic‐rich silts and fluvial sand/gravels indicates that soil development occurred episodically for around 15 000 a. Fifty‐four beetle taxa represent seven habitat types: forest, forest or scrub, riparian and aquatic, litter, grass/tussock, marshland and moss habitats. Leaf and beetle fossils indicate that forest dominated by N. menziesii persisted at the site for most of the time period represented, and tree line taxa such as Taenarthrus sp. 1 (Carabidae) and Podocarpus sp. (Podocarpaceae) indicate that the site may represent the upper tree limit for full‐glacial time. The finding of forest at this elevated site adds to the growing fossil evidence for multiple forest refugia in New Zealand during the last glaciation and is consistent with the pollen records, which have consistently indicated the presence of forest species during the last glaciations. Copyright © 2009 John Wiley & Sons, Ltd.     

Petrology and geochemistry of the Banks Peninsula volcanoes,South Island,New Zealand

Within the volcanic sequence of the twin volcanoes of Lyttelton and Akaroa, Banks Peninsula, New Zealand a number of different magma series have been distinguished.An early series of hawaiites (McQueens Valley Formation) was erupted about 32 m.y. ago and is of transitional or mildly tholeiitic chemistry. Stratigraphically above the McQueens Valley Formation, but unconformably overlain by the main volcanic dome sequence, is a unit of rhyolite (Gebbies Pass Rhyolites) which is not directly related to the earlier or later basaltic volcanism. The rhyolite was probably formed during intracrustal melting which was related to the rise of basaltic magma into the crust.Between 12 and 9.7 m.y. a large volcanic dome, composed mainly of hawaiite, was built at Lyttelton. Dykes, which intrude the Lyttelton volcanic sequence, range in composition from basalt to trachyte. Late, mildly alkalic, basaltic flank flows (7.5–5.8 m.y.) occur in several areas and they, and the differentiated rocks of the dyke swarm can be related by a crystal fractionation model which has been quantitatively tested.Following construction of the Lyttelton dome a second larger dome was built at Akaroa between 9 and 7.5 m.y. The rocks of the Akaroa Volcano are principally hawaiites but rocks ranging in composition through to trachyte also occur. The differentiated rocks of the Akaroa volcano have derived from the basaltic rocks by a crystal fractionation controlled process, operating during ascent through the crust.None of the Banks Peninsula basalts appear to have derived from primitive (pyrolitic) mantle material, but progressive changes in the chemistry of the basalts with time implies that the mantle source regions were evolving geochemically as partial melting proceeded. Later lavas tend to be more alkalic and to have lower MgO/FeO ratios than earlier lavas. The volcanic rocks of the Banks Peninsula volcanoes were derived by fractional removal of olivine, plagioclase, clinopyroxene, magnetite and apatite from ascending basaltic magma batches. Variations between the suites reflect differences between the parental magma batches.     

Depositional Record of Tidal-Flat Sedimentation in the Permian Coal Measures of Central India: Barakar Formation, Mohpani Coalfield, Satpura Gondwana Basin

The Permian Barakar Formation in the Mohpani coalfield, Satpura Gondwana basin, is composed of three broad lithologies that occur repetitively and are iterdigitated: (1) several metres thick coarse- to medium-grained sandstone bodies with scoured bases, (2) 5-20 m thick medium- to fine-grained sandstone bodies and (3) 5-20 m thick mudstone-dominated packages with variable proportions of centimetre- to decimetre-scale, fine- to medium-grained sandstone, carbonaceous shale and coal. The Barakar strata were previously interpreted as deposits of braided rivers and associated inter-channel flood basin in a continental setting. However, this study recognizes signatures of tidal current from the mudstone-dominated packages implying marine influence during Barakar sedimentation.

The mudstone-dominated sediment bodies are the focus of this paper and comprise of three lithofacies that bear imprints of tidal processes during Barakar sedimentation: (1) heterolith, (2) sandstone, and (3) coal-carbonaceous shale, which alternate with one another within individual bodies. The heterolithic facies show interlayering of sandstone and claystone resembling flaser, wavy and lenticular bedding, as well as pinstripe stratification. Successive sandstone-mudstone couplets indicate periodic waxing and waning of flows. Within individual heterolithic packages, the sandstone:claystone ratio along with the bedding style, varies cyclically upwards giving rise to alternate sandstone-dominated and claystone-dominated intervals suggesting tidal velocity fluctuation reflective of spring-neap lunar cycle. Thickness plots of successive sand-mud couplets also reveal cyclic variation with a conspicuous periodicity of around 12 couplets per cycle, which corroborates the spring-neap-spring (or neap-spring-neap) lunar cycle. Presence of abundant desiccation cracks indicates periodic emergence and points towards an intertidal setting. The sandstone facies is characterized by a variety of wave-generated features such as bundled and chevron upbuilding of lamina, bi-directional foreset orientations, offshooting and draping laminae, scour-and-drape feature, swollen lens-like geometries suggesting their emplacement under storm-induced combined-flow on the tidal-flat. The coal-carbonaceous shale facies represent supratidal marsh environment.     

Evaluation of coseismic landslide hazard on the proposed Haast-Hollyford Highway,South Island,New Zealand

Coseismic landsliding presents a major hazard to infrastructure in mountains during large earthquakes. This is particularly true for road networks, as historically coseismic landsliding has resulted in road losses larger than those due to ground shaking. Assessing the exposure of current and planned highway links to coseismic landsliding for future earthquake scenarios is therefore vital for disaster risk reduction. This study presents a method to evaluate the exposure of critical infrastructure to landsliding from scenario earthquakes from an underlying quantitative landslide hazard assessment. The method is applied to a proposed new highway link in South Island, New Zealand, for a scenario Alpine Fault earthquake and compared to the current network. Exposure (the likelihood of a network being affected by one or more landslides) is evaluated from a regional-scale coseismic landslide hazard model and assessed on a relative basis from 0 to 1. The results show that the proposed Haast-Hollyford Highway (HHH) would be highly exposed to coseismic landsliding with at least 30–40?km likely to be badly affected (the Simonin Pass route being the worse affected of the two routes). In the current South Island State Highway network, the HHH would be the link most exposed to landsliding and would increase the total network exposure by 50–70% despite increasing the total road length by just 3%. The present work is intended to provide an effective method to assess coseismic landslide hazard of infrastructure in mountains with seismic hazard, and potentially identify mitigation options and critical network segments.     

Greta Coal Measures in the Muswellbrook Anticline area,New South Wales

The Greta Coal Measures are the lower of two main coal‐bearing intervals in the Permian northern Sydney Basin. High quality outcrop and continuous core data are available from the Muswellbrook Anticline area in the Hunter Valley, enabling a sequence‐stratigraphic interpretation of the Greta Coal Measures to be presented for the first time. Age and core relationships indicate an unconformity at the base and the top of the Greta Coal Measures. A correlation between dated tuffs in the upper Greta Coal Measures in the Muswellbrook area and the Maitland Group in the Cessnock area establishes a clear diachronous upper boundary for the Greta Coal Measures resulting from a northwest‐ward marine transgression. The Greta Coal Measures are interpreted to occupy a single sequence in which the lower fluvial and lacustrine Skeletar Formation makes up a transgressive systems tract, the Ayrdale Sandstone Member is an estuarine unit around the maximum flooding surface, and the upper fluvial to deltaic Rowan Formation occupies a highstand systems tract. The overlying Jasdec Park Sandstone Member of the Maitland Group infills incised valleys above a sequence boundary and then occurs as a transgressive shoreline system before passing into the glacial marine Branxton Formation. The Greta Coal Measures represent high accommodation where subsidence and sediment supply were approximately balanced over more than 100 m of accumulation, and the development of 14 recognisable coal seams occurred in a single sequence.     

Crustal and upper mantle seismic structure of the Australian Plate, South Island, New Zealand

Seismic reflection and refraction data were collected west of New Zealand's South Island parallel to the Pacific–Australian Plate boundary. The obliquely convergent plate boundary is marked at the surface by the Alpine Fault, which juxtaposes continental crust of each plate. The data are used to study the crustal and uppermost mantle structure and provide a link between other seismic transects which cross the plate boundary. Arrival times of wide-angle reflected and refracted events from 13 recording stations are used to construct a 380-km long crustal velocity model. The model shows that, beneath a 2–4-km thick sedimentary veneer, the crust consists of two layers. The upper layer velocities increase from 5.4–5.9 km/s at the top of the layer to 6.3 km/s at the base of the layer. The base of the layer is mainly about 20 km deep but deepens to 25 km at its southern end. The lower layer velocities range from 6.3 to 7.1 km/s, and are commonly around 6.5 km/s at the top of the layer and 6.7 km/s at the base. Beneath the lower layer, the model has velocities of 8.2–8.5 km/s, typical of mantle material. The Mohorovicic discontinuity (Moho) therefore lies at the base of the second layer. It is at a depth of around 30 km but shallows over the south–central third of the profile to about 26 km, possibly associated with a southwest dipping detachment fault. The high, variable sub-Moho velocities of 8.2 km/s to 8.5 km/s are inferred to result from strong upper mantle anisotropy. Multichannel seismic reflection data cover about 220 km of the southern part of the modelled section. Beneath the well-layered Oligocene to recent sedimentary section, the crustal section is broadly divided into two zones, which correspond to the two layers of the velocity model. The upper layer (down to about 7–9 s two-way travel time) has few reflections. The lower layer (down to about 11 s two-way time) contains many strong, subparallel reflections. The base of this reflective zone is the Moho. Bi-vergent dipping reflective zones within this lower crustal layer are interpreted as interwedging structures common in areas of crustal shortening. These structures and the strong northeast dipping reflections beneath the Moho towards the north end of the (MCS) line are interpreted to be caused by Paleozoic north-dipping subduction and terrane collision at the margin of Gondwana. Deeper mantle reflections with variable dip are observed on the wide-angle gathers. Travel-time modelling of these events by ray-tracing through the established velocity model indicates depths of 50–110 km for these events. They show little coherence in dip and may be caused side-swipe from the adjacent crustal root under the Southern Alps or from the upper mantle density anomalies inferred from teleseismic data under the crustal root.     

Geological controls on rock mass classification of coal from Huntly East Mine, New Zealand

Rock Mass Rating (RMR) measurements from 65 sites within Huntly East underground coal mine are presented. All measurements are in coal, for which the dominant discontinuities are vertical cleat. Basic RMR values using two discontinuity spacings are presented: overall RMR based on the average spacing of all individual discontinuities; and cleat zone RMR based on the average spacing between zones of cleat. Cleat orientations are highly variable, but on average approximately parallel horizontal stress axes (face cleat follows maximum horizontal stress axis, butt cleat follows minimum horizontal stress axis).Contours of RMR variations throughout the mine are used to compare rock mass conditions with geological structure. It is apparent that: (1) RMR is least within downthrown fault blocks, and particularly immediately on the downthrown sides of faults, and greatest in upthrown fault blocks; and (2) RMR contours parallel horizontal stress axes within fault-bounded blocks, and bend to parallel faults at block boundaries. From similar contours for parameters contributing to RMR, the Rock Quality Designation (RQD), groundwater rating, and discontinuity condition rating create most of the observed variations in RMR. RQD is determined from the measured discontinuity frequency and hence is a measure of the degree of fracturing of the rock mass. This is interpreted as influencing the groundwater and condition parameters directly by allowing greater water ingress. Discontinuity frequency is greatest (least spacing) in the immediate vicinity of faults, and in downthrown fault blocks, generating low RMR values. Within fault blocks RQD varies little, so RMR contours align with cleat orientations.As RMR contours, faults, stress field and cleat orientation are clearly interrelated, there is unequivocally a connection between RMR and structural geology; this allows some predictive capacity in terms of ground conditions. If geological features can be accurately defined through either drilling programs or seismic surveys, then ground conditions may be predicted before panels are driven.     

Geological controls on the sulphur content of coal seams in the Northumberland Coalfield, Northeast England

The sulphur content of coal is an important consideration when developing reserves for exploitation, driven by emission limits from power stations becoming more stringent. Variations in the sulphur content of Westphalian A and B coals from the predominantly freshwater Northumberland Coalfield, Northeast England, were studied according to their regional, stratigraphic and in-seam location. The observed variation in sulphur content spatially increases towards the source area away from more marine influenced areas, with increased sulphur content through time linked to changes in the general depositional environment as conditions became more marine-influenced. A model of basinal surface water and groundwater flow driven by post-depositional source area tectonism is thought to have played only a minor role in contributing secondary sulphur to the coal. However, the isotopic composition of coal pyrite shows a similar range in composition to that of pyrite and other sulphides from the North Pennine Orefield along the southern margin of the coalfield, suggesting an additional potential source of secondary sulphur, as sulphur-rich fluids were expelled northwards through the coal measures during early Permian Variscan transpression from the south. The Westphalian A and B are interpreted as third-order depositional sequences, defined by third-order maximum flooding surfaces. Each sequence is made up of several coal-bearing fourth-order parasequences, which tend to be more brackish to marine in character, on either side of the third-order maximum flooding surfaces when base level was relatively high. The lowest sulphur coals are confined to the lower to middle, relative low stand part of the Westphalian A third-order base level curve and the lowest part of the Westphalian B third-order base level curve. This difference is attributed to a more rapid rise of base level in the Westphalian B. The stratigraphic and spatial distribution of coal sulphur has been used as a guide to prediction of reserve identification for surface mining operations.     

淮南煤田丁集井田B组煤中硼元素与沉积环境演化分析

为了查清丁集矿区B组煤层的沉积环境及其赋存规律,对井田内3个补勘钻孔中142件煤样进行了测试分析,特别对硼元素的分布特征及其沉积环境进行了详细的探讨与分析,结果表明:从4-1煤至8煤硼元素呈现总体下降的趋势;B组煤层沉积在以咸水为主导的多变环境下,且大部分煤层沉积在半咸水—咸水的环境中;多变的沉积环境致使B组煤中部分煤层出现分叉与合并现象、其厚度较薄且间距较小。     

Seasonal controls on sediment transport and deposition in Lake Ohau,South Island,New Zealand: Implications for a high‐resolution Holocene palaeoclimate reconstruction

Laminated sediments in Lake Ohau, Mackenzie Basin, New Zealand, offer a potential high‐resolution climate record for the past 17 kyr. Such records are particularly important due to the relative paucity of detailed palaeoclimate data from the Southern Hemisphere mid‐latitudes. This paper presents outcomes of a study of the sedimentation processes of this temperate lake setting. Hydrometeorological, limnological and sedimentological data were collected over a 14 month period between 2011 and 2013. These data indicate that seasonality in the hydrometeorological system in combination with internal lake dynamics drives a distinct seasonal pattern of sediment dispersal and deposition on a basin‐wide scale. Sedimentary layers that accumulate proximal to the lake inflow at the northern end of the lake form in response to discrete inflow events throughout the year and display an event stratigraphy. In contrast, seasonal change in the lake system controls accumulation of light (winter) and dark (summer) laminations at the distal end of the lake, resulting in the preservation of varves. This study documents the key processes influencing sediment deposition throughout Lake Ohau and provides fundamental data for generating a high‐resolution palaeoclimate record from this temperate lake.     

Identification and significance of a late Pleistocene tephra in Canterbury district,South Island,New Zealand

A rhyolitic ash 4 to 8 cm thick is well preserved within a thick loess unit in a coastal section 2 km long near Teviotdale, Canterbury district, South Island, New Zealand. The ash (informally named Tiromoana ash) contains fresh glass shards which give a fission-track age of 20,300 ± 7100 yr B.P. The only possible source for such a tephra with this age range is from Taupo Volcanic Zone (TVZ), North Island, some 550 km north of Teviotdale. Within the time span ca. 15,000 to 42,000 yr B.P. five widespread and voluminous rhyolitic tephras (viz. Rerewhakaaitu Ash, Rotoehu Ash, Kawakawa Tephra, Omataroa Tephra, and Mangaone Tephra) were erupted from TVZ. On the basis of the fission-track age, ferromagnesian mineralogy, and electron-microprobe analyses of glass shards and titanomagnetites from Tiromoana ash and the five possible correlatives listed above, Tiromoana ash is correlated with Kawakawa Tephra (dated by ¹⁴C at ca. 20,000 yr B.P.). This is the only known occurrence to date of Kawakawa Tephra in the South Island. Its preservation is attributed to special site conditions (low precipitation and minimal sheet erosion) leeward of a prominent terrace. The identification of the ash at Teviotdale as Kawakawa Tephra supports recently revised age assignments for the upper loess sheet in Canterbury. Moreover, it implies that loess enclosing Kawakawa Tephra in nonglaciated districts of southern North Island and Taupo Volcanic Zone is a correlative.     

Late-glacial and Holocene vegetation and climatic history of the Cass Basin, central South Island, New Zealand

Lithology, pollen, macrofossils, and stable carbon isotopes from an intermontane basin bog site in southern New Zealand provide a detailed late-glacial and early Holocene vegetation and climate record. Glacial retreat occurred before 17,000 cal yr B.P., and tundra-like grassland–shrubland occupied the basin shortly after. Between 16,500 and 14,600 cal yr B.P., a minor regional expansion of forest patches occurred in response to warming, but the basin remained in shrubland. Forest retreated between 14,600 and 13,600 cal yr B.P., at about the time of the Antarctic Cold Reversal. At 13,600 cal yr B.P., a steady progression from shrubland to tall podocarp forest began as the climate ameliorated. Tall, temperate podocarp trees replaced stress-tolerant shrubs and trees between 12,800 and 11,300 cal yr B.P., indicating sustained warming during the Younger Dryas Chronozone (YDC). Stable isotopes suggest increasing atmospheric humidity from 11,800 to 9300 cal yr B.P. Mild (annual temperatures at least 1°C higher than present), and moist conditions prevailed from 11,000 to 10,350 cal yr B.P. Cooler, more variable conditions followed, and podocarp forest was completely replaced by montane Nothofagus forest at around 7500 cal yr B.P. with the onset of the modern climate regime. The Cass Basin late-glacial climate record closely matches the Antarctic ice core records and is in approximate antiphase with the North Atlantic.     

Hydrothermal alteration in metasedimentary rock-hosted orogenic gold deposits,Reefton goldfield,South Island,New Zealand

Orogenic or mesothermal quartz lodes in lower Palaeozoic Greenland Group metasedimentary rocks of the Reefton area have produced 67 tonnes (t) of gold prior to 1951, and recent exploration has identified new gold resources in several deposits, including the largest past producers, Blackwater and Globe-Progress. The metasedimentary rocks consist of alternating sandstone and mudstone beds that were metamorphosed to lower greenschist facies prior to being hydrothermally altered adjacent to the quartz lodes. The sandstones are feldspathic litharenites averaging Q₆₅-F₁₀-R₂₅, with detrital grains of quartz, rock fragments, muscovite, and plagioclase and biotite that were altered to albite and chlorite, respectively, during metamorphism. Accessory minerals are graphite, apatite, zircon, tourmaline and titanite. Hydrothermal alteration of the sandstones has developed a mineral assemblage of K-mica, carbonate (dolomite, ankerite, ferroan magnesite and magnesian siderite), chlorite, pyrite and arsenopyrite. The abundance of hydrothermal chlorite is greater at Blackwater than at the other prospects studied. Hydrothermal alteration associated with the quartz lodes is marked by bleaching, magnesian siderite spots, disseminated arsenopyrite and pyrite and thin carbonate, quartz and sulphide veins. These trends are accompanied by increasing concentrations of S, As and Sb and decreasing Na, and a decrease of Fe and Mg in K-mica. The alkali alteration indices 3K/Al (representing K-mica) and Na/Al (representing albite) generally show antipathetic trends, with 3K/Al increasing near the lodes and Na/Al decreasing. These trends reflect the replacement of albite by K-mica. Carbonate alteration indices CO₂/(Ca + Mg +Fe) and CO₂/[Ca + Mg + Fe -0.5(S + As)] quantify the abundance of hydrothermal carbonates, but they show variable correlation with the lodes. They increase the width of the alteration halo in the hanging wall of the lodes at the Globe-Progress and General Gordon prospects, but the peak values are as far as 150 m from the lodes. By contrast, peak values of the carbonate alteration indices are within 10 and 2 m of the lodes, respectively, at the Merrijigs and Blackwater deposits. Data show that for deposits with wide hydrothermal alteration halos, such as at the Globe-Progress and General Gordon prospects, the use of a suite of geochemical indicators can assist exploration by indicating trends in hydrothermal alteration that provide vectors to mineralisation. They also increase the size of the exploration target. By contrast, the alteration halo of the Blackwater deposit is restricted to within less than 5 m of the quartz lode and, therefore, the geochemical indicators are of more limited assistance to exploration.     

阳泉矿区含煤地层沉积环境及其对煤层厚度分布控制

阳泉矿区煤系地层形成于海陆交互相的过渡环境,其煤层的形成、赋存、厚度变化、分布均受沉积环境的控制和影响。根据分析成煤环境、预测煤层赋存变化情况,为煤炭资源补勘和开采生产提供指导。