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By D Connelly

There is now a new generation of mobile crushing and screening plant systems available which have been developed based on the motivation of reducing truck haulage. Newly designed mobile crushing and screening plant systems have the advantages of mobility, flexibility, economy and reliable performance, making this system very appealing for small- to medium-sized projects or projects where a number of resources are separated by distance.A brief review of the past history and experience with transportable crushing plants provides an insight into some of the issues with transportable plants in mineral processing. A closer look at a simple model based on exploiting small but high-grade orebodies suggests the concept has merit, however there are many more engineering, logistics, legal, technical and management aspects which have limited the application of such a concept in the resource sector. This paper explores the concept in detail and endeavours to analyse the preferred commodities and scenarios under which the concept could be used and the economic and logistical limitations for iron ore. The paper also looks at the risk assessment criteria to be applied in selecting the type of resource projects where the model could be applied successfully. Other aspects considered in this paper are the project planning requirements, technical and economic feasibility, bankability and operability. Reference is made to the operating experience of contractors at a number of sites and feedback from the resource companies as managers of the projects.CITATION:Connelly, D, 2013. Mobile crushing and screening plant applications for small- to medium-sized iron ore projects, in Proceedings Iron Ore 20 13, pp 349-354 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 12, 2013

Mining and metallurgical processing of gold and base metal ores often results in solid wastes and effluents containing high concentrations of arsenic. In addition, arsenic can be released to the atmosphere from gold roasters and base metal smelters. Speciation of arsenic in roaster products, in a stack sample from a copper smelter, in organic soils impacted by smelter emissions, and in an anaerobic effluent treatment system at a smelter site was determined in order to broaden our understanding of the nature and occurrence of arsenic in a wider range of metallurgical wastes. Micro-XANES spectra obtained from iron oxide particles forming in a gold roaster indicate preferential enrichment of As3+ species in maghemite-rich domains and microlayers. In comparison, haematite-rich iron oxide particles are dominated by As5+ species. It appears that maghemite is retarding oxidation of arsenic and its volatilisation during roasting. Arsenic occurs as both As3+ and As5+ species in a stack sample emitted from a Cu smelter, confined to fine-grained secondary product layers accumulated on the surfaces of spherical Cu particles. This is probably resulting from condensation of As species upon cooling following their volatilisation during the combustion process. Soil samples collected at various distances from the Cu smelter are dominated by As5+ species including monomethylarsonic acid and tetramethylarsonium iodide as the organic arsenic species. The presence of reduced As3+ species highlights the importance of organic material influencing the speciation of arsenic and mineralogical transformations taking place within the soil profile. The XANES spectra indicate that arsenic occurs predominantly as aqueous arsenite species in the anaerobic treatment system, contrary to the conventional thinking of As retention by the formation of secondary sulfides.

Jan 1, 2008

By D Craw, C E. Martin, C Smith, C Rufaut

Wangaloa Coal Mine opened in 1945, and by the time of its closure in 1989, had produced 750 000 tonnes of coal and disturbed an area of 75 ha. The original mining licence required land rehabilitation to exotic forestry, however the current owner, Solid Energy, has worked with Crown Minerals and local councils to write a new rehabilitation objective. The site is now being stabilised and replanted with native species, and may be available for public use before the coal mining licence expires in 2007. Site discharge permits expire in 2017, and by that time, it is anticipated that discharge water chemistry will be similar to background levels. MWH are currently contracted for management of the mine rehabilitation project. The Kaitangata coal unit mined at Wangaloa is sulfurous lignite with associated pyrite. Kaitangata coal contains 3.2 wt per cent sulfur, which is higher than most New Zealand coals. Initial analyses at Wangaloa indicate low pH (2.56.2) values in soil, groundwater and surface waters as a result of acid rock drainage (ARD) processes, leading to increased metal mobility and challenging conditions for vegetation. Pilot studies indicate pinus radiata needles contain up to 67 mg/kg boron, and elevated As, Cu and Zn concentrations in surface waters. The main lake at the site has a pH of approximately 4.9, despite lime dosage in 2002. There is a real need for a complete geochemical model of the Wangaloa coal mine. Such a model could be applied to similar restoration projects, and would assist by pinpointing geochemical processes and toxic metal relationships most harmful to the receiving environments. Using this model, rehabilitation in the future will be targeted and more efficient. This project is part of a larger scheme to characterise and model the Wangaloa mine site restoration, including waters, soil, vegetation, geology and invertebrates.

Jan 1, 2003

By P Rowe

New Zealand Steel's Taharoa titano-magnetite mine, south of Auckland, set two national load records when it transported around 2000 t of mining equipment three kilometres overland on time, under budget and without safety incident. It was the first time in New Zealand that four platform trailers were assembled end-to-end to transport a load. It was also the first time that a single load of 1000 t was transported on platform trailers. The need for the relocation of all equipment was realized five years ago. It took two years of planning and specialist advice to relocate the mine's 250 t dredge, 500 t surge bin, 1000 t concentrator plant and ancillary equipment from the Southern Mining Region across a specially designed haul road to the Central Mining Region. The project was carried out during a six-week shutdown in early 2001. Two dry docks were constructed, one at each end of the relocation route. The equipment was floated into a dismantling pond that was interconnected with the dry dock in the Southern Region. Through pumping, the water levels were controlled to allow transfer of the separated units from the dismantling pond into the dry dock. Once drained, sets of self-elevating platform trailers were used to transport the main units, one at a time, between the dry docks. Five prime movers were used to pull the loads. At the receiving end, the units were off-loaded in a dry dock interlinked with ,the first mining pond. The equipment was relocated because the reserves in the Southern Mining Region were mined out. A natural watercourse û the Wainui Stream û defines the northern boundary of the Southern Region and the objective became to relocate the mining plant to the other side of the stream and re-establish in the Central Region. The project team selected the trailers as the most effective means of transporting the equipment, particularly given the non-invasive means of crossing the Wainui Stream. Negotiations with prime contractor Tranzcarr Heavy Haulage Ltd commenced in mid-2000. The remainder of 2000 was spent in developing concepts with the contractor, detailed designing, preparing the dry docks, haul road and initial mine plan for the Central Region. These activities occurred with no conflict to the normal site production.

Jan 1, 2001

By J G. Webster-Brown, K L. Brown

The Waihi Region is host to many low sulphidation epithermal Au-Ag deposits. The Golden Cross mine located at the head of the Waitekauri River, eight kilometres NW of Waihi, was a gold mining operation that placed significant emphasis on environmental management. An assessment of the influence of this mining project on stream sediment geochemistry (Fe, Mn, As, Cu, Pb, Zn, Cr, Cd, Ni, Ag and Se) in the Waitekauri Catchment has been made. Effective waste management during the mine operation appears to have prevented contamination of stream sediment. Trace metal concentrations in the Waitekauri Catchment sediment have generally decreased since 1987, and are currently mainly below the ANZECC (2000) sediment quality guidelines. However, elevated As levels were recorded in the Upper Waitekauri River and Battery Stream, exceeding guideline values. Elevated levels of Cu, Pb, Zn and Cd were found in the Huanui Stream, a tributary of the lower Waitekauri River. This reflects the influence of past mining operations in the valley, as well as natural weathering of hydrothermally altered Coromandel Group andesite. At a number of sites, Mn concentrations also exceeded sediment quality guidelines, and this may be derived from the remediated Golden Cross mine site.

Jan 1, 2003

Background geochemistry of streams in mineralised terranes is affected by (a) natural sulphide oxidation and associated metallic discharges; and (b) previous mining history and associated discharges. Both of these processes elevate background metal concentrations by (i) directly adding dissolved metals to stream water; and (ii) adding sulphide-bearing sediments' to the stream system, to be trapped in old channels and bars for later chemical decomposition in situ or after flood reworking. Definition of downstream geochemical background, involving sediments and low-flow dissolved chemistry prior to mining is prudent, as this will provide a benchmark for any required estimation of new inputs from, for example, accidental tailings discharges. Two high-profile examples from western USA illustrate these points. Summitville mine in southern Colorado is an environmental disaster left when the operating company went bankrupt in 1991. Acid metal-rich discharges are leaving the site into a river system used for agricultural irrigation. However, nearby sub-catchments have substantial naturally occurring acid metal-rich discharges and locally discharge natural sulphide-rich debris flows into the same river. Distinction between natural and anthropogenic pollution in the downstream reaches is difficult. Early mining at Cooke City, Montana (New World District) released large volumes of sulphide-bearing tailings into the river system when a tailings impoundment dam failed. The event was equivalent to a 100-year flood, and tailings were deposited for 30 km downstream. These tailings are currently oxidising, and are being reworked into the modem stream during high flow events, thus perturbing background geochemistry.

Jan 1, 1999

Radioisotope x-ray and neutron techniques of analysis can be used for the determination of a wide range of elements in minerals. The most important applications of these techniques to the mineral industry are for onstream analysis of slurries and solids, and for geological assay.The radioisotope x-ray techniques are the more developed ones and two installations for on-stream analysis are in routine use in mineral processing plants in Australia. Neutron techniques are being developed, and should prove valuable for geological assay of large numbers of mineral samples, for borehole logging, and for specific on-stream analysis when the cost of the equipment is warranted.

Jan 1, 1970

The Phoenix mine on the Mararoa Reef at Norseman, Western Australia, provides an outstanding: AUstralian instance of the recurrence of payable ore beneath the bottom of an abandoned mine, and an interesting and instructive example of the development ofideas with regard to ore recurrence in a particular district. The Mararoa Reef is the most productive of several hypothermal goldquartz vains in pre-Cambrian basic volc81olics which strike northsouth and dip on the average, 45 degrees east. The Phoenix minewas abandoned at 500 ft. vertical depth after producing 342,000 tons of 9.9 dwt. recovery grade (equivalent to nearly half of the total production of the Norseman field) from a 2,500 ft.. long, horizontally disposed oreshoot, which is reported to have had an ore outcrop only 30 ft. in length.Interest in the field was revived in 1933, and by 1941 new ore mined and developed on the Mararoa Reef by Central Norseman Gold Corporation N.L. amounted to approximately 700,000 tons of 6.7 dwt. recovery grade. In the same period another oreshoot of similar size and grade was developed by Norseman Gold Mines N.L., south of the old Mararoa company's site. As shown by the plans, the ore occurs in discontinuous shoots. The intervening area of shear is poor in quartz as well as in gold. Geological work on behalf of Western Mining Corporation Ltd., and Central Norseman Gold Corporation N.L. has been in progress in the mine and in the field more or less continuously from 1913 to 1941 and again since 1946. This paper describes the successive advances in the understanding of the exploratory problem up to late 1941, to which several investigators have contributed. It is published by permission of the Board of Directors of Central Norseman Gold Corporation N.L., owners and operators of the Phoenix and other mines.Development of the Prospect.In 1933 Western Mining Corporation acquired an option over the Phoenix property and adjacent leases. H. E. McKinstryl visited the mine and recognised that the ore occurred primarily on the flatly dipping sections of the vein, as distinct from the steeply dippingsections, in a wide shear zone with reverse movement. Many of the flatly dipping fractures were seen to exhibit tension phenomena and to link one shear plane to the next below on the footwall side. The flat links carried much more quartz than the steeper shears.Later, H. J. C. Conolly, assisted by J. D. Campbell, examined the prospect and by contouring the vein with reference to an inclined...

Jan 1, 1950

By W C. Burton, J S. Kuszma, T O. Aspinall

The environmental impact of mining and evolving environmentallegislation has received increased attention worldwide in the last two decades (Bradfield, Shultz and Stone, 1996). The potential impacts associated with unstable spoil dumps from mine operations is the focus of concern both by the mining industry, environmental regulatory agencies and members of the public. Engineered slopes of mine spoils may be stable at the end of construction, but they can deteriorate over time. There is thus the need to increase the base of knowledge on the existing practices of spoil dump design and rehabilitation. Efficient engineering design and systematic economic evaluation of spoil dump reshaping techniques for mine rehabilitation assists in maintaining the expected standards of environmental compliance. As part of the overall approach for effective engineering design ofspoil dumps, a comprehensive, computational and efficient tool isrequired for assessing the economics and productivity of existing spoil dump reshaping practices for efficient mine rehabilitation. Such a design tool is useful in linking current spoil dump environmental management practices with engineering design planning and economic impact evaluation. This paper identifies the processes for the economic impact evaluation for existing spoil dump reshaping practices and proposed final site dump designs. Selection of an efficient spoil dump design at optimum costs will ensure operational efficiency. A case study is presented identifying economic impact evaluation in earthmoving equipment selection and the costs involved for the reshaping of spoil dumps to that of varying final site designs.

Jan 1, 2000

This article focuses on TurkeyÆs gold potential with respect to exploration, development and operation after 1985. Apart from TurkeyÆs geology, which offers a substantial number of volcanic-associated gold (Ag) and gold-copper (Au-Cu) projects, there are numerous other factors which make the country a favourable place for mining. Turkey has a mining history which goes back to pre-Roman times and an excellent mining code which ensures security for long-term production. In the country, the Government and local villagers are very positive and the country works extremely well logistically with excellent road and telecommunication links. The opportunities for new discoveries in Turkey are very high. Moreover, Turkey has its eyes turned west as it moves towards joining the European Community and it is no surprise that international companies believe it has got its timing as well as its partner relationship right. Newmont, Teck Cominco, BHP Billiton, Rio Tinto, Eldorado Gold, etc all have direct or indirect interests in Turkey, as do an increasing number of midtier and junior exploration companies. Turkish Koza Gold Mining is the first Au producing company of Turkey. The Eldorado Gold owned 245 t Kisladag Au deposit in Western Turkey is currently also producing Au. In the meantime Anatolia Minerals Development is advancing the 131 t resource at the C÷pler Au deposit in North Eastern Turkey. These are significant world-class deposits. Further encouragement for investment in the Au mining sector has been provided by the introduction of a new mining law in 1985. Foreign investments in the country were encouraged and have seen a rapid increase in the last two decades. Gross domestic product (GDP) growth is in excess of five per cent per annum, inflation is down from 70 per cent to single figures, the budget deficit has been cut by 40 per cent to 11 per cent and industrial output and productivity are increasing rapidly. Turkey is politically and economically stable, is a member of the European Customs Union, has a supportive mining legislation, is highly prospective and under-explored and hosts significant recent gold discoveries.

Jan 1, 2007

By A Kemp, I Taylor, S C. Lamoureux

Detailed landform designs were completed for six (integrated) iron ore waste rock dumps at a Western Australian iron ore mine site to meet closure objectives and to optimise material movements for closure. The designs were based on specific physical and geochemical properties of waste material and the design was undertaken to enhance long-term stability of the dumps and optimise material movements, and therefore minimise closure cost. Construction of the re-shaped waste rock dumps have been completed. Following construction, surface material characteristics were found to deviate from those used in the design assessment. Materials present at surface following re-shaping were generally finer textured than those sampled for modelling. It is anticipated that the embankment slopes may experience increased rates of surface erosion compared to the rates predicted from modelling and used in design. The finer textured material is thought to be generated from exposing finer material that has migrated into the coarser matrix over time or that was not present in the sampled top surface of the landforms. This is due to armouring processes over time and this phenomenon is likely to recur following further wet seasons. The majority of the waste materials present in the waste rock dumps were subgrade banded iron formations (BIF) and chert, which are generally competent and geochemically inert. Some waste material was known to have an elevated risk of erosion but present in relatively small quantities. The presence of a large number of dolerite dyke swarms indicates appreciable volumes of dolerite were produced as waste from the pits. This material has an elevated risk of being highly erodible/dispersive. Clays and shales are also likely to be present in the dumps and are considered to be less competent material (relative to the BIF/chert). This paper presents the process from upfront materials assessment through detailed design to construction of the rehabilitated waste rock dumps, and post-construction sampling and testing to validate model findings.CITATION:Kemp, A, Taylor, I and Lamoureux, S C, 2017. Design to closure – construction of detailed rehabilitation designed iron ore waste rock dumps based on upfront site specific assessment, in Proceedings Iron Ore 2017, pp 353–358 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 24, 2017

By A Watson

We tend to overestimate the volume of water used to process ore and the evaporation from tailings and heap leach stockpiles. During mine operation, a significant portion of the water collected from onsite water management systems is consumed and recycled by ore processing and lesser portion discharged to the environment. When mining and processing cease, however, the mine site water balance is altered and the real effort and cost associated with managing and disposing of excess mine-influenced water becomes evident. As these flows can no longer be recycled and may not be suitable for discharge to the environment, the cost of dealing with them can comprise a significant portion of the post-mining liability. The problem of dealing with large volumes of mine affected water has the potential to become worse in the future due to the established trend of lower grades which require more water per unit of mineral processing. As a result, future mines may be expected to have greater water needs and problems than we experience today.This paper discusses various aspects about how water usage changes when a mine transitions from operation to closure based on observations and numerical simulations of made with site-wide water balance models. The intention is to provide general considerations for mine operations in planning for end of mine life and post-mining care and maintenance.

Jan 1, 2009

By M J. Shearer

An investigation into the reliability of the data being collected at the Mount Isa Mines site operated by Glencore in Queensland allowed on-site ventilation personnel to scrutinise pressure and volume measurements collected from the primary surface fans. The investigation effectively identified discrepancies being reported to the on-site remote monitoring system. The difference between the real-time and static measurements on the P63 RAR shaft identified that the in situ differential pressure transducer and piezo annubar system was not operating correctly. This indicated a deficiency of approximately 30 per cent reporting back to the remote monitoring software versus the live readings measured with the Pitot tube bomb and ALNOR AXD610 pressure micro-manometer.Constant monitoring of an operations ventilation network is imperative to ensuring that the underground atmosphere provides a safe and healthy workplace. Further benefits to real-time monitoring allows for the early indication of network failures and promotes increased availability. An innovative approach to out engineer and improve the existing measuring equipment from the 1970s was sought.The use of ultrasonics in the mining industry is not new with ventilation management systems (VMS) equipment available within the marketplace. The introduction and implementation of a reliable product for real-time monitoring was a challenge to overcome due to limited access and suitable measuring points within the mine. The available equipment on the market through mainstream suppliers was not suitable for the unique application required due to the in situ installation of the surface fans. A solution was identified in the oil and gas industry through collaboration and innovative thinking. This paper describes the sustainable approach to implement a reliable air flow monitoring system on-site.CITATION:Shearer, M J, 2017. Case study – an analysis of reliability and efficiency: ultrasonic versus annubar technologies, in Proceedings Australian Mine Vent Conference 2017, pp 51–56 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 28, 2017

By D Craw

The Old Man Range, south of Alexandra, in central Otago consists of a package of highly folded greenschist facies schist of the Wanaka lithologic association. The range is crosscut by several east to ENE-striking high angle gold-bearing quartz veins, (eg Whites Reef and Grays Reef), which were extensively worked in the late 1800s. The range is bounded on its east side by the Old Man Fault, which separates these rocks from generally flat lying and planar Caples Terrane schist. To the west of the Old Man Fault, about halfway up the range, a large subparallel, 100 m wide fault zone strikes NNW and appears to cut off the historic veins. The fault zone consists of highly sheared and folded rocks and numerous high angle cataclasites and centimetre-scale clay gouge zones. Hydrothermal alteration is not apparent and the individual faults and shears are clay altered, possibly due to weathering, without visible quartz veins. Gold, limonite pseudomorphs after pyrite and rutile are concentrated in some of the narrow cataclasites and gouge zones. These mineralised structures are texturally similar to the gold-bearing reefs and may be structurally related. It is postulated that the NNW-striking shear zone and ENE-striking veins may be a conjugate array formed during a period of Cretaceous normal faulting.

Jan 1, 2004

Experiments in the bolting of a mine roof were commenced at Elrington Colliery on the South Maitland Coal Field early in 1949, following the appearance of an article in the American publication, "Coal Mine Modernisation Year Book" 1948. Prior to this, although bolting had not been used in the maintenance of satisfactory roof conditions, the principle of roof bolt anchorage had been illustrated in instances such as the hanging of a trolley locomotive power wire using an expanding shell type of bolt anchorage, or the insertion of an eye bolt with a split and wedge, as used to suspend a rope block over a winze being sunk in a metalliferous mine.The experiments at Elrington Colliery were the first efforts in this country to supplement the work of timber supports under a mine roof with systematic placement of roof bolts.Following the series of experiments at Elrington, full scale bolting was commenced at that Colliery in a trackless mobile section in April, 1950.The obvious success of the system at Elrington indicated that it might also be a success in the support of weak roof strata immediately overlying the workable section of the Victoria Tunnel Seam at John Darling Colliery.The system was commenced at John Darling Colliery in April, 1951, in one mechanical section on the Victoria Tunnel Seam, and the scope was gradually widened until by December, 1952, ail'six mechanical units then operating on this seam were working under bolted roofs.

Jan 1, 1954

Techniques Used and Problems Encountered in Normal and Reverse Circulation Drilling at the Mt Roseby Project, Cloncurry, North West Queensland

Sep 13, 2010

By Fogarty J. G H

Ausmelt Technology has a unique capability of removing the impurities, phosphorus and sulphur, from the feed materials to the process. Sulphur is removed to the gas phase almost completely because of the interactions of ore and coal in the reaction region at the top surface of the slag bath. Phosphorus is removed to the slag phase, with both basic and higher, controlled iron oxide levels in slag being achieved in the process. The significance of these features of the process relate to the production of pig iron with very low levels of these impurities for the further processing to steel, and to the treatment of high phosphorus and high sulphur raw materials. The marketability of pig iron and the raw materials are discussed in relation to this feature of Auslron.

Jan 1, 1999

By J Watt

The Hidden Valley Gold Project is located in a remote and mountainous area of the Morobe Province approximately 30 km south of the township of Bulolo and approximately 90 km south-southwest of the provincial capital, Lae. The Hidden Valley deposit was discovered in 1984 with the nearby Hamata and Kaveroi deposits discovered in 1987 and 1992 respectively. Reserves (Harmony, 2009) at these three deposits are 42.1 million tonnes of ore containing approximately 2.9 million ounces of gold and 45 million ounces of silver. A further 5.4 million ounces of gold and 84 million ounces of silver are in the resources category. The process plant is designed to treat 4.2 million tonnes per year of gold/silver ore extracted by open cut mining methods. Ore is classified into three ore types according to oxidation state: oxide, transition and primary. The silver to gold grade ratio is high for the Hidden Valley and Kaveroi ores, generally in the range 15 - 20:1, and much lower for Hamata, typically 1 - 2:1: Primary ore is the dominant ore type at Hidden Valley with sulfur grades up to about two per cent sulfur. Oxide and transition ores are more prevalent at the Hamata deposit, but its primary ore has up to five per cent sulfur grades. Variable ore types, particularly in the initial years of operation, high silver to gold ratios and limited plant site area, due to the challenging terrain, present the main processing challenges for this project. This paper describes the operating strategies and process development for the main areas of this circuit, highlighting selections of processes and equipment that achieve cost effective, yet flexible solutions to the treatment of ores from these deposits.

Jan 1, 2009

By Edwards A. B

The following note on the mineral association in the ores of the Tennant Creek Goldfield, Northern Territory, is largely based on Mineragraphic Reports Nos. 49, 89, 117 and 193 of the Council for Scientific and Industrial Research. These reports are the results of the examinations of auriferous specimens from a number of mines of the goldfield and are now supplemented by the examination of further specimens from Mt. Samuel forwarded by Mr. V. G. Martin.The Tennant Creek Goldfield lies in the central portion of the Northern Territory, about Lat. 190 35', Long. 1340 15', on the Overland Telegraph Line and about 369 miles north of Alice Springs. It comprise an area extending about 50 miles east and west, by 30 miles north and south.The geology of the goldfield has been described by Woolnough. (2)The rocks of the area are of pre-Cambrian age, and consist of talcose, chloritic, micaceous and siliceous schists of sedimentary origin, interbedded with flows or dykes of schistose quartz porphyry, and of granites which were intruded subsequent to the regional metarporphism of the area. The rocks are moderately folded, but the beclding tends to be obscured by a pronounced east-west cleavage. The most continuous orebodies run east and west, parallel with this cleavage.Numerous lenses of hematite occur in the schists, with their long axes, parallel to the cleavage, and the gold values of the field are frequently associated with such hematite bodies. The dimensions of these hematite bodies are variable but rarely exceed a length of 300 ft., with an average thickness between 10 and 30 ft.; the original vertical dimensions are thought to be comparable with their length. The lenses tend to occur in groups when they are arranged en echelon both horizontally and in depth; and erosion has exposed individual lenses to different degrees, ranging from incipient exposure to complete removal. The existence of unexposed hematite lenses at depth has been proved by geophysical surveys, coupled with drilling tests. (3)A few of the bodies are pipe-like. Many are surrounded by a casing of brecciated rock, composed of fragments of hematite and shattered country rock, and presumably caused by subsequent earth movements which crushed the country rock against the resistant hematite bodies. In the early days of the field most of the important gold occurences were found within these crushed zones, or, to a less extent, within the hematite bodies themselves.These occurrences appeared to be associated only with those hematite lenses which were intersected by quartz veins or other lines of weakness, of later origin than the crushing. This led Woolnough to think that the introduction of the gold and attendant bismuth was subsequent to the...

Jan 1, 1942

By D N. B Skinner

Changes in the configuration of late Cenozoic volcanic arcs related to Pacific-Australian plate convergence in northern New Zealand may have localised large-scale epithermal gold-silver mineralisation to a particular part of the volcanic arc system, the Coromandel Volcanic Zone (CVZ). The history of arc-type volcanism in northern New Zealand began with the development of the continental margin Northland Volcanic Arc from early-mid Miocene (26-15 Ma). From 18-15 Ma the Northland Volcanic Arc extended south into the northern and western part of the CVZ where it is dominantly composed of andesite with lesser dacite and very minor rhyodacite. In the south, centre and east of the CVZ, younger andesite-dacite volcanism overlapped in space and time (14-5 Ma) with voluminous rhyolitic volcanism associated with rift-hosted calderas and minor basaltic eruptions. This change to bimodal rhyolitic-basaltic volcanism and extensional tectonics was a result of southwest (SW)-directed propagation of the Colville-Lau oceanic island+ arc into the north-northwest (NNW) trending Northland Volcanic Arc and its underlying continental crust. The extensional tectonic regime created in the collision zone between the two arcs is also the site of the 14-6 Ma Coromandel epithermal gold-silver province, which contains some 50 separate deposits and has a production (1862-1996) of about 300 t Au and 1150 t Ag. Extensional tectonics facilitated the emplacement of silicic magma at shallow crustal level and led to reactivation of deep basement faults. The resulting enhanced heat flow and fault-focused fluid flow localised large hydrothermal systems and associated extensive low-sulphidation epithermal gold-silver deposits in the southern part of the province, as at Waihi, Golden Cross and Karangahake.

Jan 1, 1997