Search Documents

By P G. Rutherford, A W. McOnie

A volcanic sequence is described from the Golden Cross Mine, Waihi, New Zealand. The sequence includes seven lithostratigraphic units comprising flow and pyroclastic units of Coromandel Group andesite and dacite and overlying Whitianga Group dacite and rhyolite which is intruded by the Golden Cross dacite porphyry and rhyolite dykes. The sequence is mineralised and is unconformably overlain by two post-mineral units, the lacustrine Waitekauri beds and Omahine Subgroup andesite.   Detailed structural analysis of mine data has identified four deformational events (D 1-D4) and related these to the gold-silver mineralising events. Faulting was coeval with the mineralization and directly controlled the development, localisation, style and geometry of the ore shoots. Mineralization developed in competent lithologies where dilation occurred during faulting. The Empire Fault is the master shear which controlled fluid flow. Mineralised veining developed in response to tectonic pulses occurring at slightly different stages as represented by the underground Empire vein complex and the open pit vein array. The mineralising events culminated with the deposition of barren calcite veins. Post-mineral movement along the Western Boundary fault appears to have offset the orebody.

Jan 1, 1995

By K A. Bunker, A D. Campbell, E Ah Mu, A R. Penney

The Ernest Henry mine is a transverse sublevel cave (SLC), which is relatively unique due to the 45 degree inclination of the orebody. To economically recover ore, each sublevel is horizontally offset from the previous level by around 25 m, depending on the orebody geometry. Mine development, slotting and initial production within this zone occurs in a high stress abutment that increases in magnitude at depth. These areas are seismically active and close to the hanging wall where cave propagation is yet to initiate. High stress conditions and the close proximity to the cave seismogenic zone results in challenging geotechnical conditions in the step out zone of each level and requires management of hazards including stress driven rockfalls, rock bursts and pillar failure.This paper outlines how these hazards were forecast using numerical modelling and geotechnical monitoring. Risk management techniques included dynamic ground support design, development of a new mine layout and extraction sequence as well as delayed re-entry into seismically active areas. Ongoing monitoring, instrumentation measurements and field observations were used to track the effectiveness of the controls.Future production levels are forecast to experience increasing stress and seismicity, which will increase demand on excavations and installed ground support. Ensuring the techniques and controls for monitoring, measuring and mitigating stress and seismic hazards are enforced is essential for continued safe production.CITATION:Campbell, A D, Bunker, K A, Ah Mu, E and Penney, A R, 2016. Managing stress and seismicity in an inclined sublevel cave, in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 319–328 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

By D Thorburn

This paper reviews the history of environmental assessment in New Zealand with reference to mineral developments. Emphasis is given to larger more controversial projects particularly metal mines. The changing role and application of the Environmental Protection and Enhancement Procedures is examined in the context of changes in the government's environmental administration and the response of the Ministry of Energy's resource allocation group. Conclusions are drawn on the effectiveness of the present environmental assessment activities and on the allocation of administration of priorities in the Ministry. The Ministry of Energy has effectively ceased to exist.

Jan 1, 1990

By D N. B Skinner, R L. Brathwaite, M S. Rattenbury

The Institute of Geological and Nuclear Sciences Ltd has carried out a mineral resource assessment of the Coromandel region, one of the most mineral-rich regions of New Zealand. The assessment focussed on metallic minerals and clays, because these are the main commodities that have potential for increased production and export from the region (and from New Zealand).   Three steps were used in the assessment: 1) development of mineral deposit models, 2) comparison of the models with regional geology, structure, geochemistry and past mineral production to estimate the number of undiscovered mineral deposits, and 3) application of grade-tonnage models to determine the quantity and value of the known and undiscovered resources. In step 1, descriptive and grade-tonnage mineral deposit models were developed for 11 different types of mineral deposits: ò     Low-sulphidation andesite-hosted epithermal Au-Ag ò     Low-sulphidation rhyolite-hosted epithermal Au-Ag ò     High-sulphidation quartz-alunite epithermal Au ò     Porphyry Cu-Au-Mo ò     Andesite-hosted polymetallic veins adjacent to mineralised porphyry stocks ò     Zn-Pb-Ag skarn ò     Cu-Ag skarn ò     Hot spring Hg ò     Shoreline placer Ti ò     Rhyolite-hosted halloysite clay ò     Volcanic-related kaolinite clay   Step 2 was aided by a geographic information system (GIS) assembled from a number of digital spatial data sets including: a digital elevation model, an aeromagnetic map (from open file mining company data), a geological map (from the GNS QMAP project), location of areas of hydrothermal alteration, locations of mineral deposits (from the GERM database), stream sediment geochemical analyses (from the REGCHEM database), and a lineament map derived from satellite remote sensing data and the digital elevation model.   Based on May 2001 commodity prices, potential resources estimated for the 11 mineral deposit and grade-tonnage models total NZ$22 806 million for the metallic minerals, NZ$1000 million for halloysite clay deposits and NZ$57 million for kaolinite clay deposits.

Jan 1, 2001

By A Kitchen

For the past decade, demand for Australian resources has reached unprecedented levels, thanks mainly to the emerging superpowers of China and India. Meeting demand has meant miners and governments alike have ploughed billions into capital expenditure projects for logistics infrastructure such as roads, rail and ports, to support the ever expanding number of mines and mineral volumes. In more recent times, however, the effect of the global economic crisis has led to a decline in demand for Australian minerals. The downturn has seen companies lay off workers in droves, and delay or cancel expansion projects, in an attempt to preserve cash flow. Whilst the current economic cycle has hit the mining sector hard, it is an opportunity for companies to take stock of their existing operations and plan for the future. As mining companies grapple for scarce capital resources, it is inevitable that industry consolidation will ensue. This presents challenges and opportunities for both buyers and sellers alike, looking to expand operations, or sell off assets to raise cash.

Jan 1, 2009

By R B. Stewart

Where pasture production is the intended land use of the areas to be reclaimed, the creation of a suitable growing +medium is a major objective. To achieve this land reclaimers require a sound understanding of the proposed mining plan and a knowledge of the physical, biological and chemical properties of materials intended for resurfacing disturbed areas. Where the original soil is not being replaced in its natural state, research is usually required to determine an alternative growing medium. Results from field research conducted on waste material from the Waihi Gold mine are reported with emphasis on the significance of soil depth in relation to pasture production in this environment.  Problems in extrapolating field research to large scale operations are also considered.   Essentially the requirements for successful pasture production, on surrogate growing medium, are akin to conventional approaches used in New Zealand in the development of unimproved agricultural land. High inputs of fertiliser are initially needed, especially where volcanic soil is used, and careful management of pastures and soils is required to minimise soil erosion and create a sustainable system. In the first three to five years of pasture production, grazing use of the land requires to be dictated by pasture availability and soil conditions and not by animal feed requirements. The use of light stock (young dairy or sheep) is recommended.   Successful land restoration requires a team approach by a range of cooperative specialists including engineers, soil scientists, farm managers, agricultural contractors, landscape architects and environmental officers.

Jan 1, 1991

By D Craw, J Pope

The Greenland Group, Westland, can be characterised with respect to environmental issues by the application of a GIS database (DAME), and specific sampling campaigns. Waters draining gold mineralised areas have a distinctive chemistry characterised by neutral pH and arsenic as a trace element. The acid neutralising capacity (ANC) from carbonates usually exceeds the maximum potential acidity (MPA) from sulphides resulting in circum-neutral pH. These waters are readily distinguishable from waters draining coal mine related areas, which commonly have low pH (~4) and low As concentrations (~0.1 ppm). In contrast, dissolved arsenic mobilised from Greenland Group historic gold mining areas is up to 2.4 ppm. This As mobilisation is controlled by the secondary As mineral, scorodite (FeAsO2+2H2O). Maximum dissolved As concentrations increase with increasing pH, corresponding to the increasing solubility of scorodite with increasing pH. Dissolved As is attenuated by dilution, precipitation of scorodite, and/or adsorption to iron oxyhydroxide (HFO). Adsorption to HFO is an important attenuation mechanism in and adjacent to many mine sites. HFO is abundant at mine sites where pyrite was abundant in fresh rock, such as where the mineralised zone is dominated by disseminated pyrite. Pyrite, and resulting HFO, are relatively rare where mineralisation occurred as well-defined quartz veins. Localised HFO occurs also where ankerite oxidises in host rocks. Arsenic output flux (ca. 25 g/day) from historic gold mine sites is commonly less than the natural background flux from mineralised rocks (>5000 g/day).

Jan 1, 2006

By G J. Corbett, T M. Leach

Approximately 42 t of mercury were produced from Puhipuhi from the late nineteenth century until the end of World War II, with no significant gold or silver production. Sinter, eruption breccias and veins, mined for mercury at Puhipuhi and essentially barren of gold, are inferred in many geological models to represent the surficial levels of adularia-sericite style low sulfidation gold-silver systems. These systems may contain economic gold-silver mineralisation at depth. Conceptual geological models have been employed at Puhipuhi in the search for buried gold mineralisation. Homestake Mining utilised a McLaughlin model for exploration from 1982 to 1987, targeting mainly the vicinity of the sinter deposits. From 1987 to 1989 BHP sought deeper structurally controlled gold mineralisation within the basement greywackes, utilising models derived from studies of Round Mountain, USA and Hishikari, Japan. Macraes Mining Company Limited have accessed the previous work and applied a conceptual geological which invokes a north-south structural control for the emplacement of high-level felsic intrusions at depth. Dextral movement on these structures associated with oblique convergence facilitated the formation of a pull-apart basin in which lacustrine sediments overlie basement greywackes and are in tum overlain by Pliocene basalts. Continued activation of the NS structures created a series of inferred NE-trending dilational structures, which are targeted as fluid upflow centres for the surficial outflows. Upflows occur as eruption breccias (e.g., Plumduff) and outflow as silica sinters (eg Mt Mitchell, Williams) which are also partly obscured by the basalt cover. Argillic alteration and mercury mineralisation occur at elevated crustal levels (eg Puhipuhi mine). Modelling from structure and alteration zonations have targeted a fluid upflow in the vicinity of Bush Hill, which was not accessed by previous workers. This target was subsequently supported by surface geology and multi-element soil geochemistry.

Jan 1, 1997

To optimise the haulage of the large tonnages produced from stopes in this high production gold mine, an ore pass and feeder system was introduced. This ore pass was designed and developed in 2006 and the plate feeder installed and commissioned soon after. Cavity Monitoring Surveys (CMS) have been undertaken of the ore pass since it was commissioned. The original thickness that was surveyed of the pillar between the ore pass and decline in 2006 was approximated to be 19 m. Throughout its use large blocks of rock were reporting at the plate feeder. This was the first indication that the ore pass was failing somewhere between the tipping level of the 9410 level and the plate feeder at the 9330. Even so CMS surveys were not taken systematically to firstly identify the area of failure or for monitoring. In August 2008 after implementing management systems, large blocks were still reporting to the plate feeder. The decision was made to empty the pass enough to carry out a CMS survey of the area. Subsequently it was discovered that the area of failure was between the decline and ore pass and that since the first survey the pillar thickness had been reduced to approximately 9.7 m. Further management controls were put in place to slow movement of the material and to limit the use of the 9410 tipping level, but this did not alleviate the rate of failure entirely. The results of an initial inelastic numerical model indicated that most of the pillar was damaged and that failure into the decline likely if no changes were made. The numerical modelling predicted that even if material was no longer passing through the ore pass interaction between the voids was unavoidable and would most likely result in instability. The ore pass and plate feeder are an integral part of the haulage system for the remaining life-of-mnie. Two solutions were sought to firstly reinforce and stabilise the pillar between the ore pass and decline and secondly to rehabilitate the ore pass or find an alternate design that could still utilise the plate feeder. This paper summarises the analysis and resulting rehabilitation that was used to accomplish this.

Nov 25, 2010

OWING to two large falls of ground which resulted in serious accidents occurring towards the end of 1908, it became evident that the "open chamber" system then in use was unsuitable for the conditions existing in the Mount lVIorgan mine. It will be admitted that in all mining operation, the first consideration is the economy of the system adopted, combined with its safety and ability to give the desired output. A sectional system with square sets has been introduced into the mine, in which due attention has been paid to these factors. In this paper a brief description of this system will be given. An outline of those previously used will be ineluded, as it is necessary to understand the eonditions which existed in the mine at the initiation of the sectional system. Outside the actual mining methods employed, various points that might prove of interest will be touched on.The square set system of mining has been in use throughout the stopes in the gold ore in the upper levels of the mine since underground operations were started in Mount Morgan.

Jan 1, 1910

Conservation and environmental issues are raising their profile with respect to both demand restraint and electricity supply options. In New Zealand, conservation pressures and energy efficiency need to be seen in relation to the supply system currently in place which has capacity for economic supply of electricity in quantities substantially in excess of the current market. Consequently, energy efficiency and conservation need to be interpreted in relation to the supply system as well as in relation to end use. The relationship between the environment and conservation is strongest when new generation is required. New Zealand's electricity supply system consists of a large proportion of hydro production and this has significant environmental benefits when considered in relation to concerns of global wanning and the greenhouse effect. However, environmental trade-offs in supply options need to take account of both the efficiency of electricity end use, the trade-off between hydro and thermal generation and the inter-regional effects of shifting development options from one region to another. The Electricity Corporation has a high level of consciousness with respect to environmental and conservation issues and this paper demonstrates its own moves to maximise energy efficiency and illustrate the environmental trade-offs for supply.

Jan 1, 1990

The New Zealand microcontinent is relatively well endowed with gold deposits; its past gold production per unit area of 3.2 kg/km2 ranks high on a world scale. Total recorded production (1857 - 1986) is about 854 000 kg and most of this gold was mined between 1861 and 1920. There has been a strong revival in gold exploration and mining since 1979, with exploration expenditure of around $15 million per annum and a declared gold production in 1986 of 1265 kg (886 kg in 1985). In addition to numerous alluvial gold recovery plants working small to medium sized deposits (mainly in Westland and Otago), there are five medium to large projects that have started production (Martha Hill), or have reached advanced stages of construction (Grey River dredge), permitting (Golden Cross and Macraes) or exploration (Globe-Progress). This summary paper is taken from reviews by Brathwaite et al (1986) and Brathwaite (1988).

Jan 1, 1988

THIS paper proposes to give a general description of the pumping and other machinery in use at the Thames Hauraki Pumping Station, situated on the Thames goldfields of the North Island, New Zealand. An idea of the general arrangement of the pumping engines and pumps can be obtained, together with a certain amount of detail, by reference to the illustrations. The history of the pump is rather interesting, and is as follows: -In 1894 the Government decided that a subsidy of £1 for £1up to an amoUllt not exceeding £25,000 be granted towards the erection of suitable machinery to exploit the Thames low levels.With a guarantee of such assistance a company was floated in London, with a capital of £300,000, to develop several properties at Thames. As the old Queen of Beauty Company had produced bullion worth £400,000 prior to closing down on account ofa breakdown to its pumping gear, their shaft was chosen as the site of the principal work. As soon as the company was floated, operations were commenced at the Queen of Beauty shaft, situated at the entrance of the Waio-Karaka Creek, and not more than about half a mile distant from the principal mines on the field.

Jan 1, 1912

Ecological Fuel from High-Sulfur-Content Coal

Sep 13, 2010

By A B. Christie, R L. Brathwaite, A Swain

This study provides quantitative data on vein distributions within seven selected epithermal systems, four deposits hosted predominantly in rhyolitic rocks: Ohui, Wharekirauponga, Neavesville and Komata, and three major deposits mainly hosted in andesite: Martha Hill, Golden Cross and Karangahake. The technique of fractal analysis was used to help quantify vein distribution patterns. The fractal dimensions (D) obtained are related to the number of veins per metre, the degree of vein clustering, and vein thickness. An increase in any of these tends to increase the fractal dimension.   It is the relative relationship of these parameters that is important for the characterisation of vein distributions, and the comparison of different deposits. Within the same systems, the rhyolites are characterised by lower vein thickness and vein density, but have a higher degree of vein clustering compared to the andesites. Sections that are deeper and more centrally located within the epithermal system and/or close to major structures tend to have a greater degree of vein clustering, higher average vein thickness and density, and higher thickness to density ratios. This depth control is most pronounced in epithermal gold-silver systems because they have formed at shallow crustal levels where physico-chemical conditions change drastically both vertically and laterally. In addition to lithological and structural control at vein scale, deposit scale structure is of great importance in the deposition of economic mineralisation. Large open vein structures capable of sustaining high fluxes of hydrothermal fluid, favourable for the formation of large, high-grade gold deposits, are best developed in andesite sequences.

Jan 1, 1995

"An EXTENDED ABSTRACT is available for download. A full-length paper was not prepared for this presentation.Low-sulfidation epithermal gold mineralisation at Ridge Mountain occurs within the Oligocene to Miocene volcanic rocks comprising andesite, porphyritic dacite and diatreme breccia. A diatreme breccia complex with a NE–SW elongated orientation covers an area of 3.0 × 1.7 km. Four main stages of mineralisation were identified, comprising: E–W- to NW–SE-trending quartz-chalcedony veins with disseminated pyrite, chalcopyrite and gold. N–S- to NNE–SSW-trending breccia veins with quartz matrix and disseminated pyrite and accessory sphalerite, galena, chalcopyrite and gold. NE–SW-trending quartz and calcite veins with disseminated pyrite and accessory sphalerite, galena, chalcopyrite and gold. ESE–WNW- to ENE–WSW-trending quartz veins with disseminated pyrite. This stage is only mineralisation that is hosted by diatreme breccia and clearly postdates.Quartz veins of the first, third and fourth stage are less than 2 m wide. Only breccia veins of the second stage are up to 10 m wide. Gold is present in all stages as microscopic inclusions in quartz and sporadically in pyrite. Macroscopic gold can be seen in the first and second mineralisation stages. Gold commonly occurs in association with sphalerite, galena and chalcopyrite in the second and third mineralisation stages.CITATION:Kucera, J, 2015. Diatreme breccia-hosted epithermal gold deposit at Ridge Mountain, eastern Mindanao, Philippines, in Proceedings PACRIM 2015 Congress, pp 587–592 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Mar 18, 2015

Predicting the future is a task that should always be delegated. If that is not possible, then stating your views confidently, but retrospectively, is preferable. Hindsight encourages clarity of thought and sharpens perception. When all else fails one can look back into history and see the trends, evaluate the current situation and project it a little way into the future - in this case 10 years. In exploration the rate of change has been increasing over the past 20 years. With expected developments in technology, legislation, and their sociological impacts, we will see such rapid change over the next decade as to make us uncomfortable, unless we are prepared for it.   The social obligations of our industry also have changed enormously over the past 20 years and are still changing. This will lead to further changes in the way we conduct our business if we wish to stay in business. As exploration technology improves, a further dimension is added by the expectations of the communities in which we operate. This extra dimension needs to be quantified so that we not only keep up with current developments but also get ahead of the game. This paper is based on the New Zealand experience, some of which will be familiar to mineral explorers in other countries.

Jan 1, 1997

Peculiarities of Quartz Distribution in Zinc Flotation Products and their Influence to Mineral Processing

Sep 13, 2010

By K Lownie, R Sani, A Sianturi

Part of the PT Freeport Indonesia (PTFI) mine production is in the process of transitioning from the deep ore zone (DOZ) mine to the deep mill level zone (DMLZ) mine. The DMLZ mine is the next lift in the caving series and lies 500 m below the current DOZ footprint.In order to reduce the need for a very expensive additional ventilation system for the DMLZ mine, it was decided to reconfigure some infrastructure and upgrade the performance of the three existing DOZ mixed flow ventilation fans in situ, reducing the new fans required to two. This was far less costly than providing complete new installations.These fans are installed in individual underground chambers in DOZ mine exhaust drifts and connected to the DMLZ mine exhaust drifts system in 7 m × 7 m airways size, through sets of 6 m diameter by 500 m high raises.The upgrade process involved replacement of motors, fan shafts and bearings. The existing 1600 kW DOZ mixed flow fans are 3500 mm diameter and operate at a speed of 595 rev/min and were originally designed to deliver 390 m3/s at 3.3 kPa. Efficiency optimisation may be required at a later date.The upgraded DMLZ fans are required to deliver 425 m3/s at 3.7 kPa and it was necessary to increase in motor size and speed to 2200 kW at 710 rev/min. This paper will discuss the fan upgrade project and in particular the integration of an unusual ventilation system, which is based on the semi parallel operation of multiple large fans.CITATION:Sani, R, Sianturi, A and Lownie, K, 2017. Operation of deep mill level zone mixed flow fans after the first fan upgrade – a parallel fans case study, in Proceedings Australian Mine Vent Conference 2017, pp 285–292 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 28, 2017

The Geological Resource Map of New Zealand (GERM) is a computerised inventory of aggregate, mineral, coal, petroleum and thermal water occurrences, containing summary information on location, production, geology, and geochemistry. The types of occurrences include quarries, mines, gold dredges, wells, outcrops, seeps, springs, and fields. The file contains entries for about 10,300 sites and is used to produce tables of data and maps at any scale, for single or multiple commodities. The published format is the New Zealand 'Geological Survey map series Geological Resource Map of New Zealand 1:250 000'. Seventeen of the 27 map sheets covering New Zealand were published by August 1991, with three more close to publication.

Jan 1, 1991