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By Vynne J. F

Drill monitors for blasthole and exploration drills have been available to the mining industry since the 1970s. The early monitors were pen strip chart recorders which were developed for the oil drilling industry and adapted to mining. They recorded drilling parameters such as depth, pull-down pressure, torque, RPM, and bailing air pressure. While these recorders could generate a large volume of paper, the amount of useful data was minimal. The data was not summarised and required an engineer to interrupt the chart traces. Being a mechanical recorder, the devices were also susceptible to frequent failures.

Jan 1, 1993

By A B. Richards

Effective control of blast vibration and flyrock requires that significant factors be identified and quantified, that the blast be designed to ensure both blasting efficiency and compliance with applicable limits, and that the blast design be effectively implemented by field personnel. Significant factors contributing to ground vibration and airblast are: charge mass; distance and direction relative to the blast; drilling design: burden, spacing; stemming height and material type; hole diameter and depth; and initiation sequence and direction.In addition, airblast may be strongly influenced by shielding and meteorological conditions. Ground vibration is also influenced by the transmission characteristics of the ground and soil. Flyrock throw is determined by charge mass, burden, stemming height, blasthole diameter and depth. The contribution of each of the factors has been quantified and models developed to enable the environmental outcomes of blast design to be predicted. Environmental blast design is necessary to ensure compliance with regulatory limits and the implementation of æsafeÆ exclusion zones for flyrock clearance. This paper discusses the models used for environmental blast design and demonstrates the often significant effects that lapse during implementation of the design can have on predicted outcomes. In practice, drillers and shotfirers are sometimes confronted with situations that require modifications to the blast design to cope with the real site situation. Methods are presented that may be used by drillers and shotfirers to evaluate the effect of these modifications, the tolerances that must be reached during their work practice and checking procedures, and the consequences of their actions.

Jan 1, 2004

The effectiveness of three different types of longwall chock under the three different types of geological conditions worked recently is outlined. Some provisional analyses of the variation of chock load under the shale roof con- dition are briefly discussed and some problems and solutions of gateway and road- head support outlined.

Jan 1, 1974

By F J. van Zyl, C A. S Thomson

"Anglo American Thermal Coal conducted a high level study of all of its underground collieriesto determine if there were electrical power saving opportunities at the main fan stations.A systems approach to electrical power savings was used to identify potential savings in the various components of a primary ventilation system. Furthermore, only technological interventions were considered to obtain electrical power savings. From generic technological driven electrical power saving strategies four energy savings strategies were identifi ed, namely potential overall reduction in ventilation volume, improved underground air utilisation, optimisation of fan-set effi ciency and potential fan drift design optimisation. The study indicated the colliery (say Colliery D, Shaft A) that showed most potential in the four technology driven energy savings strategies. A detail study was undertaken at Colliery D, Shaft A to increase the confi dence level and the study confi rmed that up to 45 per cent of the main fan absorbed power can be saved (475 kW) with an estimated capital payback period of 18 months. The study clearly showed that an integrated approach to optimise the entire mine ventilation system has great potential for power saving, and that a clear, well -defi ned methodology will be applicable to similar underground collieries. This paper discusses the background to the study and the process followed to implement the energy savings initiative at Colliery D, Shaft A."

Jun 1, 2012

By McGhie R. R

The general structural features and the principal mineral relationships of the Black Star ore body, Mount Isa, Queensland, have been described in several previously published papers. But particular reference may be made to the work of Grondijs and Schouten, whose examination of over 200 polished sections revealed some remarkable features in the process of ore deposition. The observations by the present authors are based upon the study of a smaller ·set of specimens complementary to those examined by Grondijs and Schouten and are intended to elaborate certain aspects of the mineral relationships, more particularly those affecting the ore-dressing processes.The work described applies to the primary sulphide ore only, and to the present milling practice of fine-grinding and selective flotation.GEOLOGICAL FEATURESThe Black Star is one of several economic mineral concentrations in the Mount Isa series of thinly bedded carbonaceous shales, which are considered to be of preCambrian age. The nlineralization is apparently connected with pegmatite intrustions located within some miles of the ore bodies, and has been Gontrolled in the main by major folding of the shales and by a shear system which follows approximately the strike and dip of the beds. The detailed "The investigations described in this paper were made in the Metallurgy Department, University of Melbourne, where the senior author was formerly Senior Lecturer in Mining and Metallurgy. A report on a section of the work was submitted by the junior author as a thesis requIred by the University of Queensland.

Jan 1, 1939

By J P. Sykes, A Trench

Mineral commodity prices are subject to volatility over both the short and longer run – driving fluctuating operating margins for mining companies over time. Such market dynamics influence mine operating decisions depending on the interplay of company-specific and mineral market factors. The company factors include corporate financial strength and price-risk management strategy, as well as mining practices and methods at the operation level. The critical mineral market factor is the price of the ex-mine product. This results from underlying microeconomic and macroeconomic root-causes pertaining to mineral supply and demand, in addition to the activities of financial participants within commodity markets.Significant changes in commodity prices of an extended duration, either up or down, remain the principal influence upon mine economics – and therefore on mining practices too. Accurate and precise forecasting of commodity prices (and of relevant exchange rates) continues to prove elusive both to mineral economists and market analysts. Thus, at any given point in time, there are often widely differing price forecasts available for both the relevant commodity and currency. Companies as a result are unclear how to respond in practical operating terms to such price-side uncertainty – other than to manage incremental capital and operating expenditure. Typical company – and industry financier – responses to the difficulty in predicting future mineral commodity prices are to take measures to manage uncertainties in mining project revenues and costs. These operating practices are prudent – yet come at an economic cost: that is, lost revenue and margin opportunity is inevitable in any such system not easily capable of responding to price volatility in the market. The mine of the future will seek to capture this lost economic opportunity. This paper presents a three-stage framework for analysing commodity price forecasts to aide understanding of the commodity price cycle and the periods of high-margin opportunity.CITATION:Trench, A and Sykes, J P, 2014. Perspectives on mineral commodity price cycles and their relevance to underground mining, in Proceedings 12th AusIMM Underground Operators’ Conference 2014 , pp 19–32 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Mar 24, 2014

A new test coke oven of seven cubic foot capacity is described. The oven was designed to simulate conditions in a central section of a battery oven and a special feature is the achievement of unidirectional heating from the flues on either side of the charge. The method of charging permits close control of charge conditions'such as bulk density and moisture content. These conditions, as well as coking conditions (e.g. flue temper- atures., coking time) must be varied to simulate conditions in different batteries, The effects of several variables on coke quality are discussed. Using test oven conditions corresponding to those of Newcastle steelworks batteries, good agreement was obtained between strength indices of test oven and battery cokes; for 17 tests, the average A.S.T.M. stability and hardness indices for the test oven coke were 38,5% and 69.7%, while those for the battery coke were 37.1.% and 67.6%.

Jan 1, 1969

Physical model testing at Bergbauforschung is done in two rigs, a roadway rig and a longwall rig. The loading of such models, in scale relation to the con- ditions in the collieries provides valuable guidance to the probability and nature of failures, and thus to support requirements, in structural, roofbolts and self- auvancing supports. The success of such modelling when related to subsequent underground designs put to use suggests that such methods of investigation could be extended to pillar extraction problems also.

Jan 1, 1974

The underground mining of a narrow vein hard rock orebody is a capital and labour intensive method of extraction. Due to the nature of underground mining it is difficult for higher level managers to physically see the efficiencies and inefficiencies of a particular method. Extraction methods and sequencing often need to be altered from the original planned methods as a result of mine developent, providing more in depth information as it progresses. As a result of these issues contract mining of these orebodies is common practice. There are several types of contract structures for the purpose of underground contract mining with many complex permutations of them that reflect the different needs of each individual company and orebody. The different contracts are arranged dependent on the mining companyÆs desire to transfer or, alternatively, embrace risk. This presentation gives a brief overview on these different methods and their various advantages and limitations with regard to small scale and narrow vein underground mining. With respect to these different contracting methods, the presenter reviews the mutual growth benefits of emerging partnering opportunities, specifically with regard to smaller explorers exploring and developing prospective mining tenements. The specific advantages to small explorers include the resource flexibility and speed of project development that private mining contractors can provide. Given the contracting methods that are available, there is potential for small private mining companies to gain minor stakes in major projects and major stakes in medium sized projects by employing innovative contracting solutions to provide mutual benefits to the parties. Some potential scenarios to this effect are suggested in the presentation. This paper is available as a PowerPoint presentation only.

Jan 1, 2006

By C J. Moran

The Gladstone region, as one of the most industrially intense regions in Australia, uses significant quantities of fresh water. Awoonga Dam, situated on the Boyne River, is the only major source of water in the region. The current typical annual usage is 53 GL (Porteous, 2006) and approximately 80 per cent of the water is used by heavy industry (Gladstone Area Water Board, 2004). Until relatively recently, there has been ready and easy access to raw water for industrial use. The recent drought, which resulted in severe water restrictions in 2002 and 2003, emphasised the importance of water for a dominant industrial region like Gladstone. Although now in the process of changing, the typical contractual arrangements in the past have provided little financial incentive for efficient water use. From research undertaken on potential water reuse opportunities, several key questions have emerged related to water management in an industrial region such as Gladstone. This paper highlights these key questions, presents findings from recent regional strategies and assesses the potential for water reuse. Even though there is no clear-cut financial incentive for reusing water, there could be stronger regional and risk mitigation drivers for doing so. Initiatives to incorporate adaptive capacity through collaborative industrial synergies would allow for robustness and resilience in water security, leading to long-term sustainable water management across the Gladstone region.

Jan 1, 2006

By Voss Smith F, Matters C. W, Slee R. T, Coldham JC, Davies HW, Wallman H. H

The Committee desires to thank the managers of the various mines along the line of lode for their hearty co-operation in its labours. It would also extend thanks to Messrs. J. O. Moulden, Howchin, Twelvetrees, and the West Australian Geological Survey for various information; to Messrs. J. G. Dreyer, S. Pope, T. Read, P. Moncrieff, R. Williams, and W. J. Rose for analyses; and to a number of local gentlemen for advice and help. Professor Skeats, of the Melbourne University, gave much valued assistance in petrology, and Mr. Herbert Lavers kindly undertook the study of the garnets.INTRODUCTIONThe famous Broken Hill lode is situated in a low range of hills, the Barrier Ranges, near the western border of New South Wales. It has been worked since 1884-first for, silver, then for silver and lead, and at present for lead, silver, and zinc. No excuse seems necessary for placing before members even an imperfect report on the geological features of this notable ore deposit, since so little work has been done on the subject as to constitute almost a national reproach. This is the more deplorablesince the evidence laid open by mining operations is destroyed almost as soon as it is exposed, and there exists the real need of a continuous and connected record of geologieal developments.

Jan 1, 1911

To solve the mining safety and health needs of the future, access to, and sharing of, timely and relevant information will be crucial. The next generation of the Web will provide tools (RDF, OWL, SPARQL, etc) to define and link content for more effective discovery, integration, and reuse across applications and organisations. A recent Gartner Research Report (Finding and exploiting value in Semantic Web technologies on the web, May 2007) predicts these technologies will begin to coalesce in ten years. Implementing this Semantic Web requires structured web content described via metadata (information about information). If an industry or enterprise bases its metadata on a common vocabulary, it becomes possible to share and reuse information. The National Institute for Occupational Safety and HealthÆs (NIOSH) Mining web site provides access to more than 1500 NIOSH-developed publications, products, and topic pages on issues as diverse as ground control, respiratory diseases, and mine emergency management. As the site has grown, locating content has become increasingly difficult. To improve the searching process, a panel of internal experts representing all major research programs was established to develop a controlled vocabulary for indexing that content. The outcome is the NIOSH Mining Safety and Health Thesaurus, a faceted, hierarchical thesaurus containing hundreds of mining safety and health terms organised into 20 facets (eg diseases, injuries and disorders; hazardous events and exposures, equipment, engineering and administrative controls). One immediate goal of this project is to reduce the complexity of locating information on the NIOSH Mining web site by implementing metadata and faceted information retrieval techniques. Another goal is to stimulate discussion in the international mining community regarding developing metadata standards so the industry is ready to adopt future Semantic Web technologies to improve access to mining safety and health information.

Jan 1, 2008

By O N. Antzutkin, W Forsling, K J. Pike an

The adsorption mechanism of three different O,OÆ-di-alkyl-dithiophosphate (dtp) collectors, K[S2P(OR)2] with R = Et, i-Bu and i-Amyl, on the surface of synthetic chalcocite (Cu2S) was studied by means of solid-state 31P CP/MAS NMR spectroscopy. The morphology changes on the conditioned Cu2S surfaces, in the collector concentration range 0.1 - 10 mM, were also monitored with scanning electron microscope (SEM). In order to assign Cu(I)-dtp species on the surface of Cu2S, the corresponding bulk Cu(I)-dtp compounds, which are clusters of the monovalent copper containing either Cu6(antiprismatic) or Cu8(cubic) cores, were synthesised, and characterised by means of solid-state 31P CP/MAS and static 65Cu NMR. Further investigations on the crystal habits of the bulk systems were carried out by powder x-ray diffraction and SEM. A comparative analysis of the 31P chemical shift and chemical shift anisotropy (CSA) data estimated from the experimental NMR spectra of the polycrystalline bulk Cu(I) dialkyldithiophosphate complexes was used for assigning the 31P resonance lines in the NMR spectra of the collector treated Cu2S powder samples. The species formed on the synthetic Cu2S surfaces were assigned to polycrystalline phases of: Cu6L6 with L = Et2dtpû, Cu6L6 and Cu8L6(S) with L = i-Bu2dtpû, and Cu8L6(S) with L = i-Amyl2dtpû. A heterophase autocatalytic step process of both formation and growth of solid CuxLy (L = R2dtp, x = 6 or 8 and y = 6) complexes on the collector treated Cu2S surface is proposed. A possible role of the oxidised form of dithiophosphate collectors, bis[di-alkyl-thiophosphoryl]-disulfane (disulfide), is discussed in terms of a specific self-redox reaction. The second order quadrupolar lineshapes in 65Cu NMR spectra were simulated and the interaction parameters, CQ and hQ, for the bulk dialkyldithiophosphato-copper(I) complexes were obtained.

Jan 1, 2005

By E Nunes, R Mendes, D Jacobson, G Cota, T Machado, E Santos, J Almeida, E Pereira9, B Raso

Grinding circuits are known to be the highest consumer of energy used in the ore comminution process, with high operational costs and sensitivity to ore conditions. The mining industry is being encouraged to look for more energy efficient processes while increasing the mass and metallurgical recovery; a specific example is projects with lower iron ore grades, which demands a higher level of liberation and resulting higher energy consumption. This has led to increased usage of high-pressure grinding roll (HPGR) technology as an alternative design within the comminution circuit. A growing use of the HRC™ HPGR technology has been used to generate concentrate through a more sustainable process. In the Brazilian state of Minas Gerais, the readaptation of iron ore beneficiation circuits has been initiated, replacing the traditional crushing-to-grinding flow sheet with circuits using crushing-to-HPGR flow sheets, with the main driver being reduced energy consumption. Utilising results from sampling campaigns and analysis of experimental data collected in an industrial plant, the work herein presents a case study from the JMN Mineração operating plant, where the HRC™ HPGR was used as an alternative to traditional grinding using horizontal mills. The results show that the HRC™ HPGR performance in this iron ore processing plant showed benefits in terms of reduced energy consumption as compared to the projected performance with a traditional grinding circuit.

Sep 18, 2023

Mineral sands are different to almost any other commodity; however, it shares similarities with other commodity types, such as the importance of quality constraints of iron ore and coal or the importance of physical properties of diamonds. The mineral sands industry consists of two principal product streams; titanium dioxide minerals û in the form of rutile, ilmenite and leucoxene, and zircon. The principal valuable heavy minerals (VHM) include ilmenite, leucoxene, rutile and zircon. Variations of other titanium minerals occur between the end members of ilmenite and rutile, including pseudo rutile and anatase. Most mineral sands deposits are found in unconsolidated fossil shorelines several hundreds of metres to tens of kilometres and occasionally hundreds of kilometres inland from the present coastline. Mineral sands orebodies essentially fall into two categories based on the mode of deposition: alluvial or aeolian. Alluvial deposits are further split into marine beach placers (or strandlines) and lacustrine heavy mineral (HM) accumulations. Exploration for mineral sands involves the positive identification of key criteria leading to the focus of exploratory surface sampling, augering and drilling. Assaying is primarily focused around determining the percentage of HM contained within a given sample. Other results of interest include clay fines, sand and oversize. Metallurgical/mineralogical assessment is often undertaken via laboratory scale bench tests that replicate the wet concentration and dry mill processing routes. The most critical component in resource assessment for mineral sands is about quantifying HM grade, then mineralogical assemblage and then quality of those mineral species. This will determine whether a mineral sand final product is marketable or not. Mining of mineral sands is conducted either wet or dry. Wet methods are generally preferred for large tonnage, unconsolidated and low clay orebodies. Where ground conditions are hard and orebodies are small, high grade and discontinuous, dry mining techniques are generally employed. Concentration of mineral sands from the primary ore is carried out in two sections; wet, utilising sizing and gravity differentiation between HM, VHM, clay and quartz, and dry, exploiting the magnetic, electrostatic and to a lesser extent specific gravity (SG) properties of the minerals of interest. Mineral sands exploration, mining and processing faces the same operating challenges as the rest of the resource sector. Added to this are the issues that are unique to mineral sands and to which the industry devotes considerable resources to developing solutions.

Jan 1, 2009

The Douglas mineral sands deposit is located 75 km north of Hamilton in western Victoria, Australia. The deposit was discovered in the late 1990s by Basin Minerals Limited and purchased by Iluka Resources Ltd in 2002. Prestrip mining commenced in December 2004, with ore mining commencing in August 2005. Douglas is the first of several projects being implemented by Iluka Resources Ltd in the Murray Basin, with all heavy mineral concentrate planned to be treated at the companyÆs mineral separation plant in Hamilton. The mineralisation at Douglas lies along the south-eastern margin of the Murray Basin. It is hosted by marine Pliocene Loxton-Parilla Sands and consists of three discrete deposits; Bondi Main, Bondi West and Bondi East. The mineralised sediments dip at a low angle to the west and lie unconformably beneath a veneer of top soil (50 - 100 mm) and subsoil (up to 600 mm) and between three to 12 m of overburden. The barren overburden, characterised by high clay content (<53 ¦m material) generally provides a stark contrast to the sandy ore, which is between 1 m (parts of Bondi East) and 15 m (Bondi Main) thick. Both overburden and ore are removed utilising standard dry mining techniques using both scraper-bulldozer and truck-excavator combinations. All ore is delivered to run-of-mine (ROM) stockpiles before being reclaimed by front end loader into the processing plant. Grade control at Douglas is based around visual dig control aided by high precision survey, which enables accurate reference to the resource drilling and block model data. Vertical excavator faces, inclined scraper faces plus regular test pits and trenches provide opportunities for in pit mapping and sampling. This data is used to refine not only the resource estimate for Douglas but also the drilling, interpretation and resource modelling methods used for similar deposits across the basin. The foundations of the geological reconciliation process at Douglas are the in pit surveys undertaken each time the mining fleet has completed building a ROM stockpile. These surveys and the subsequent interrogation of resource models enable robust estimations of the heavy mineral content of the stockpiles, which are subsequently used to predict the daily input grades into the plant during their reclamation. Reconciliation of this daily data is then undertaken at the end of each month against metallurgical production data and plant balances. Learnings and results from the reconciliation process are used to further refine subsequent resource models and modelling methods.

Jan 1, 2009

The Mount Kasi gold deposit in Vanua Levu represents an epithermal, high sulphur, gold-enargite system occurring within a volcanic caldera of Middle to Upper Miocene age. High level breccia pipes flare upward and form flat lying, near surface, mushroom shaped sheets parallel and near to the present land surface. The upper portions of the pipes contain explosion breccias which are capped by sandy siliceous sinter-like beds and are cut by alunite veins. Outlying intercalated scoriasceous lavas and breccia sheets show evidence of subsidence within a shallow basin. Detailed mapping of breccia types, intensity of silicification and the presence of multiple quartz veining and enargite abundance outlined blocks of more consistent gold mineralization within the breccias. This work has provided a model for mineralization which will aid future exploration and ore reserve estimations. A significant eluvial concentration of gold occurs in soils overlying the breccia sheet.

Jan 1, 1987

By D J. Robinson, L L. Kuhar

In-situ recovery (ISR) is accepted and applied across many geographies, and approximately 50% of the world’s uranium is currently extracted by using an ISR method (World Nuclear Association, 2014). The low environmental impact, the elimination of risk for mine workers and the fact that all of the lowest-cost producers of uranium use an ISR approach should raise interest from traditional miners (IAEA, 2014). However, the broader application of ISR to other commodities and mineral systems remains limited. A number of demonstration (experimental) copper projects have been undertaken (Sinclair and Thompson, 2015) with a few copper projects in Arizona being close to demonstration (Florence, 2018 and Gunnison, 2018). Evidence of very few economically operating ISR copper projects can be found (for example, the Russian, Uralgidromed OAO, built by the Russian Copper Company in 2005 and operated as an ISR facility from the Gumeshevskoye deposit (Russia Mining, 2018). A number of gold deposits, particularly paleochannel deposits, have also been considered for ISR, but, to the best of our knowledge, only limited demonstration and no commercial operations have been established, yet (Kuhar et al, 2018 and references therein).CITATION:Robinson, D J and Kuhar, L L, 2018. Extending mine life through application of an in situ recovery approach, in Proceedings Life-of-Mine 2018, pp 56–57 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

In todayÆs evolving and globalised world, mining companies are being pressured to move beyond compliance towards long-term sustainability and sustainable development. Companies are expected to æengageÆ communities and measure the success of these engagements without a clear understanding of æhowÆ to do this. This move, away from compliance, develops more of a focus on sustainability and æcommunityÆ social responsibility rather than corporate social responsibility. This shift leads to the development of world-class projects that provide sustainable development for people, reduce the incidence of costly delays, and promote good global citizenship for companies. The process of æengagingÆ communities in mining project design and development leads to sustainable development, a stronger license to operate, and a reduction in social and political risk. To create this mutually beneficial relationship between communities and companies, communities must be æengagedÆ in the project development and risk assessment processes as early as possible, preferably during the exploration or the concept phases. How to create this æengagementÆ and manage this risk will be discussed.

Jan 1, 2007

By M, C A. RosiFre, R C. Figueiredo e Silva

Jaspilites and underlying basalt contacts of the Archaean volcano- sedimentary Grpo Parß Group, Carajßs, host giant iron mineralisation in the ~100-km long, E-W trending Carajßs fold. Preliminary, unpublished geochronological data point to a Palaeoproterozoic mineralisation event. Geochemically, jaspilites are typical volcanogenic banded iron formations. Basalts exhibit evidence of spilitic seawater interaction. Iron-associated hydrothermal alteration of mafic rocks was induced by fluid infiltration in amygdales, with development of chlorite- and hematite-dominated zones. In the case of jaspilites, iron mineralisation encompasses: partial replacement of jaspilitic microcrystalline hematite by blasts of martitic magnetite; jasper recrystallisation, producing fine-grained, hematite-free granoblastic quartz; martite recrystallisation, forming lobate¦subhedral hematite; pervasive porosity development by quartz-chert leaching; incipient cavity filling by microlamellar hematite; and advanced filling by coarser, euhedral and comb-textured, tabular- shaped hematite.Peak hydrothermal ore textures indicate typical epithermal-crust conditions, supported by preliminary fluid-inclusion calculations at 160 - 200¦C. Such temperatures and extreme fluid-to-rock ratios during alteration must have exceeded the ambient metamorphic conditions, with the infiltrating fluid relatively hot and capable of leaching SiO2. Therefore, mineralisation developed over exhumed, Archaean, brittly deformed rocks, with mineral associations representative of very low- to low-grade metamorphism. Considering that chlorite (¦talc) abounds in mafic rocks; hydrothermal albite is developed; dolomite fills veins and vugs; the typical rare-earth-element (REE) pattern of jaspilites is significantly modified in higher-grade hard hematite ores (higher LREE); pyrite, copper sulfide minerals and rare gold occur in association with carbonate-quartz-rich alteration zones, it is suggested that an alkaline, H2O-Fe-CO2 mineralising fluid dominated, also containing species like S¦Cu¦Au. Peak-mineralising conditions are likely to have resulted from a single, evolving fluid, via incipient- through advanced-stage alteration phases. The porous, high-grade soft hematite-type ore (SH), rich in microlamellar and anhedral hematite, must have derived from interaction with this relatively hot SiO2-leaching fluid, whereas the high-grade massive hard hematite-type ore (MH) developed due to closer fluid-rock temperature equilibrium conditions, attained by mineral reactions, with relative increase in the Fe/Σcations ratios allowing the precipitation of subhedral-tabular hematite that partially cements the soft-hematite ore. SH and MH hematite ore types must thus reflect intermediate and high fluid:rock ratios, respectively. Since the N5 deposit is to date understood to contain the largest amount of the MH ore, its units are interpreted as the loci of the highest fluid:rock ratios in the district. Preliminary mineralogical information regarding the S11 deposit of the Serra Sul (south range) implies higher-temperature conditions. The near-equant grain size and the granoblastic intergrain relationship, coupled with the presence of riebeckite, augitic pyroxene and garnet, suggest hornfels textures. The data collected, though still relatively sparse, permit the speculation that the immense driving force for the Carajßs world-class iron deposits was a relatively shallow, igneous-related hydrothermal system. If such a model is correct, then the Carajßs Palaeoproterozoic iron deposits could represent an end-member of the iron oxide-copper-gold hydrothermal system in the province.

Jan 1, 2005