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By Spencer R. Titley

The subject of this lecture, a late century perspective on porphyry copper geology, is one of current interest and importance as the search for these ores remains intense. It is presented in the belief that an appreciation of our present understanding of the subject requires it to be viewed historically, thus providing a basis for evaluating appropriate directions for con¬tinued study. At the outset, it is important to note that the technology of mining and extractive metallurgy has developed ore from these low grade orebodies, starting with D. C. Jackling, and has continued to create them as copper grade and price have diminished. But the continued search for them is a geological problem that responds to growing expectations of people and societies; exploration based upon ever increasing knowledge of the habits of the ores has been very successful. This is the story of evolution of geological thought and practice in porphyry ore search across an interval of time beginning with the bulk mining of "low grade copper ores at Bingham and ending with late Century concepts. "How did we get here?" The lecture concerns the ideas of many different people. The ideas and events discussed reflect a bias on North American thought, where the great low grade orebodies were first recognized as such and where many of the basic geological ideas were developed. A very great number of geologists have contributed to this understanding. In no sense is it meant to minimize the contributions to the story that have evolved in the study and mining of ores of the Andes, whose development and expansion has been nearly synchronous with that in North America - nor to minimized comparable contributions made in the late century from studies of the newer discoveries of deposits in other regions, especially the southwestern Pacific regions. In expansion of this topic, I have found that many important concepts are marked by appropriate publication but some are not, or I have not been able to discover documentation. Many notions appear to have become conventional knowledge without publication, mostly being geological viewpoints developed synchronously from similar observation. Thus, apologies are extended in advance to those whose work I have might have missed and to those unknown to me whose unpublished ideas may have seeped into the pool of common knowledge without appropriate recognition. . The analysis here addresses events of two time segments, an older one extending from the developments at Bingham in the early 1900s through the Second World War, ending about 1950; the second period extends from that time to the present. This separation is seen in Figure 1, which traces numbers of publications through the period as extracted from some 700 publications, again with a North American bias, from an annotated bibliography of porphyry copper geology in preparation. During the early period, exploration was "immature" in North America, that is, geologists looked for new districts and sites of the deposits. Outcrops were sought that carried the signatures of former mineralization and regional controls related to structural geology were closely studied. In the later period, North American exploration had "matured" into a study of districts, rather than a search for them. As the studies of these ores intensified during the younger period concommitant with increasing demands for the metal, they did so with a broadened understanding of some habits of occurrence, of hydrothermal alteration, mineral zoning, petrology, and geochemical and geophysical signatures. Outside of North America, search remained "immature" but closely related to the

Jan 1, 1997

Technologies are receiving a lot of 'press' - and rightly so; as they are seen as the means for achieving quantum leaps in productivity and cost reductions. A point of concern for Caterpillar is that we do not believe there is enough understanding of the infrastructure needed to support some of the future technologies, as well there is not enough utilisation of the current systems.

Jan 1, 1997

By W. L. Hollinshead, Alwin Poltinger

GENERAL Tunneling by hand digging is as old as the history of humans. Mechanized tunneling did not begin to replace manual methods until around the beginning of the 19th century(Brunel patent, 1818). It brought with it a higher degree of safety for the workers and a much higher rate of boring. But for any kind of tunneling, an accurate and feasible method of survey must be accomplished during mining. That means, that for each tunnel project the most efficient survey method must be devised. The method to be defined depends on the spatial curve, diameter, speed of tunneling method, purpose of tunnel and contractual accuracy. The final accuracy of a finished tunnel is heavily dependent upon three critical elements: 1. Quality of the above ground survey 2. Tunnel traverse and directional transfer from above ground 3. Guidance for the mining job. Combining The Survey And The Guidance System Since the guidance system (GS) is one of the critical factors in the determination of the tunnel final accuracy, it is necessary to analyze how the directional control and tunnel traverse measurements can be effectively integrated into a GS. Any guidance system, whether manual or high technology, must continually detect and compensate for movement of its theodoliteor laser station standpoint. Movement beyond a preset allowable amount must generate a warning or error message to the user. Additionally, optical refraction can interfere with the results. Refraction will have an effect on any kind of optical GS. Therefore, careful selection of target and standpoint locations can minimize, but not completely eliminate, the influence of refraction. Some GS technologies, such as Gyro-based systems, are immune to the effects of refraction, but have other, methodical errors which will be described later in this paper. GUIDANCE Overview Why is a guidance system necessary? A GS, whether manual or automatic, compares the design direction and slope of a tunnel with the current position of the mining

Jan 1, 1997

By I. Iwasaki, H. Dho

Two aromatic-type chelating agents, 1,10 phenanthroline (phen) and 8-quinolinol (quip), were tested as specific depressants for magnetite in the cationic silica flotation of magnetic taconite concentrates. Micro and batch flotation tests, along with zeta potential and adsorption measurements, were used. In the presence of a cationic collector, dodecylammonium chloride (DAC), the Fe/phen surface chelate electrostatically repelled DAC, and the magnetite was depressed. The negatively charged Fe(quin)2(OH)2- on the magnetite surface attracted the cationic collector and made magnetite floatable.

Jan 1, 1997

In 1996, O&K Orenstein and Koppel Inc. announced big plans to increase its presence in the US mining market. Even though the company, a part of Ger- man-based O&K Mining GmbH, has been in the United States for about 100 years, it has lived in relative anonymity. That despite being one of the largest makers of hydraulic mining shovels and excavators in the world. The plan must be working. In the 14 months through December 1996,O&K increased its sales to surface mines and quarries in the United States by 250'70, according Rolf Weber, company president. "In the next five years, we anticipate total revenue from our US operations will grow from the current $50 million to $200 million," he said. "Toward that end, we have concentrated our efforts on the supply of reliable, high-output machinery and responsive service after the sale."

Jan 1, 1997

This paper describes some experiences in the design of flotation reagent schemes for the efficient flotation of complex gold ores containing free gold and/or gold associated with easily flotable sulphide minerals such as chalcopyrite and bornite. Historically, the design of gold flotation reagent schemes has been based primarily on experiences using high dosage levels of water soluble charged collectors such as xanthates and dithiophosphates and carefully controlled regions of pH. This approach has been effective with gold associated with complex sulphide minerals, in particular gold associated with iron sulphides such as pyrite. An alternative two-stage reagent approach is presented that is applicable to certain types of gold ores. This approach involves using very small dosages of uncharged water insoluble collectors at natural ore pH followed by a modified bulk flotation reagent approach for the second stage. The reasons for utilising this approach, when applicable, are discussed and illustrated with examples.

Jan 1, 1997

Commercially interesting deposits of zeolite rich tuffs and amorphous silica have been discovered recently in the Taupo Volcanic Zone (TVZ), North Island, New Zealand. This paper reviews them and comments on the potential for further discoveries. Potential markets for these unusual industrial minerals are discussed.

Jan 1, 1997

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

By S. J. Porter, M. T. McRae

The new tunnel at Genting Sempah is part of a privately funded infrastructure projectthat involves duplicating the existing highway extending from the Gombok Toll Plaza near Kuala Lumpur to Karak, in Malaysia. The 60 km long tollway includes an 800 m long, two-lane highway tunnel with excavated dimensions of 10.5 m wide by 8 m high. The majority of the tunnel extends through slightly to moderately weathered, moderately to highly jointed quartz porphyry. Excavation of the tunnel was performed using drill and blast methods and the primary tunnel support consists of rock dowels and shotcrete except for short sections adjacent to the portals where steel sets were utilized. A portion of the tunnel encountered sheared and altered material that was successfully supported using rock dowels and shotcrete. The final lining for the tunnel consists of mesh and fiber reinforced shotcrete. The flexible nature of the primary support and shotcrete final lining resulted in considerable cost savings and expedient construction methods.

Jan 1, 1997

By Charles R. Welch, Charles E. Joachim

Underwater blasting causes not only ground shock but water-shock. Underwater shock attenuates less with range from the explosive source than ground shock and has the potential for killing fish or marine mammals or for damaging marine structures. The collapse and subsequent oscillation of the gas cavity surrounding the detonation can sometimes produce a greater impulse than the initial shock wave from the detonation. The airblast from underwater detonations can range from nuisance levels to damaging levels.

Jan 1, 1997

By F. Essrich

A quantitative rockburst hazard assessment procedure was introduced on Elandsrand Gold Mine at the end of 1994. It is currently used to evaluate the seismicity-related risk in production areas on the mine. Six parameters related to seismicity, geology, mining layout, and production are rated and results are used as a planning tool on a regular basis. The applied assessment can be considered successful in that it promotes awareness of the seismic hazard and provides an opportunity to address seismicity-related mining problems. A comparison between high risk panels and those working areas with rockburst incidents showed that high hazard ratings reliably forecast the occurrence of larger events in the following month but they do not necessarily predict those working places with rockburst-related accidents. From this one may conclude that high levels of seismicity do not coincide with high rockburst rates.

Jan 1, 1997

By J. R. Rendón

Cylinders of commercial aluminium alloy 6063 were homogenized under different conditions. The experimental results indicated that the general mechanical behaviour as related to curves of 0.2% yield strength, ultimate tensile strength and Brunnell hardness versus homogeneizing process is the same in both cases. The mechanical properties as compared to those required by plant specifications, tend to be better with increasing values of % Mg2Si in the alloy, as expected. The electron microscopy investigations revealed that in both homogeneizing processes the resulting microstructure consist of significant spheroidizing of the alpha phase (AlFeSi) and fine-needle type structure of beta phase. The alpha phase was also present in a Chinese type scripture. Furthermore, the slow cooling within the furnace resulted in the nucleation and growth of Mg2Si precipitates generally along the grain boundaries.

Jan 1, 1997

By R. J. Sweigard

Fine coal refuse is often pumped, as slurry, into surface impoundments as a means of permanent disposal. As the available volume is filled, the height of the embankments are frequently increased. Many times the additional embankment material is placed upon consolidated fine coal refuse. There has been some concern about the long-term effect of consolidation of this material at or above the liquid limit upon its shear strength. A laboratory investigation was performed using three different types of fine coal slurry taken from Central Appalachian coal preparation plants. The refuse was consolidated in 10-foot plexiglass columns under incremental amounts of surcharge loading. The incremental loads were designed to simulate the effect of increasing the height of a refuse embankment on top of the consolidating coal slurry. After the refuse in the columns had consolidated for several months, the columns were cut apart and triaxial tests were performed on both the consolidated material and unconsolidated material for comparison of their shear strength parameters.

Jan 1, 1997

By Cooke D, Large R

The Cambrian structure in the Mt Read Volcanics was produced by four deformational events: obduction of forearc-derived mafic/ultramalic complexes in the early Middle Cambrian, a middle Middle Cambrian extensional phase related to the post-collisional Mt Read volcanism and VHMS mineralisation, Middle Cambrian E-W folding, and Late Cambrian N-S folding and basin inversion. The major phase of VHMS mineralisation in western Tasmania is restricted to the very brief period of extensional tectonics within the middle Middle Cambrian. Within this period a N-S graben was produced with a complex series of transfer zones, largely striking E-W. Most VHMS mineralisation is restricted to the top of massive volcanic successions, with several mines close to Cambrian transfer structures. Many of the transfer structures continued to be active until the Devonian. The later compressional Cambrian events are not significant in localising orc formation. Within the Rosebery mine a complex pattern of minor Cambrian normal faults has a second order control on the distribution of the mineralisation.

Jan 1, 1997

By Terry Owen

Business development process. Throughout Cyprus Amax's early months in Russia, the company stayed focused on what was needed from a deposit for economic success. Cyprus Amax's reason for success in Russia is that all involved - its Russian partners, the workforce and expatriates - provided a focused effort that served the project as it worked through the tender process and the Russian regulations. The company developed an understanding of the regulatory process by working with solid, ethical partners. Infused into the Kubaka management structure were Russians with the knowledge to facilitate the process and a professional group of expatriates. Developing credibility and a solid rapport with the Russian mining authority was critical to the success of this venture. Identifying and gaining the trust of key Russian individuals was also critical during the early stages. Gaining their trust and building credibility was part of the process. These key Russians were brought to the United States to visit existing Cyprus Amax mines. These efforts proved valuable in building an understanding with the Russians about the kind of company Cyprus Amax is and the kind of efficient operations that it can run. This was a learning process for all parties. Fortunately, the company was dealing with intelligent and educated people.

Jan 1, 1997

By Thomas M. Keevin, Gregory L. Hempen, David J. Schaeffer, John M. Jr Pitlo

Repelling charges are small explosive charges detonated to frighten and drive fish away from a blasting zone just prior to detonation of a major explosive charge. Use of repelling charges has been recommended by natural resource agencies to mitigate the effects of submerged explosives. Blasting companies have used this technique in a "good faith effort" to reduce potential damages to aquatic resources. It has been assumed that noise or pressure generated by the small charge will drive fish from the immediate area, thereby reducing impacts from the much larger and potentially more-damaging blast.

Jan 1, 1997

By H. Hinds

Plant testing of DuPont's Activator Technology in the vat leach circuit of the Homestake mine shows increased gold recoveries of 3-5%. Activators are catalysts of gold dissolution in cyanide solution. DuPont received the patent for this technology in January, 1996. The test was run in the west sand plant alternating control and activated vats to reduce the variability in head grade and cyanide consumption. Activated vats had gold in the preg solutions earlier, higher gold recovery, and lower gold residuals. Activator addition did not adversely affect mill operations or the environment. Optimization of the technology continues.

Jan 1, 1997

By Smele J. S, Dawes W. D

In recent years there has been a trend among mining companies to diversify exploration and development away from the countries that have dominated mining activity for the latter half of this century. With some exceptions, this trend is accelerating and is a function of the recognition that many parts of the world, with no previous exposure to modern exploration, are endowed with considerable mineral potential. In addition coincident with changing political and economic circumstances, many countries have recognised the benefits of attracting international mining investment and have radically changed policies, fiscal and legal regimes so as to encourage exploration and mining. Some countries, however, have not readily accepted mining for cultural or social reasons and have yet to make effective changes to mining legislation. For historical reasons, other countries may have little or no direct experience of western economics, nor may they fully recognise the need for stability and competitive fiscal and legal systems to attract foreign investment. Not all ventures in new countries have been commercial successes and there have been some lamentable and recent lapses from grace. Company strategies, company standards and management objectives can also vary widely from company to company. What may be an acceptable risk or rate of return for one may be completely

Jan 1, 1997

By John A. Herbst

At the last Comminution Symposium a challenge (Meloy and Williams, 1992) was issued to "predict the typical straight-line, self similar" tumbling mill product size distributions using a population balance model (PBM). Implicit in this challenge is the assumption that the PBM is inadequate for predicting real world grinding performance. This response is presented in three parts: I. Theoretical analysis of the general PBM and its appropriateness for comminution system modeling. II. Examination of the accuracy of prediction of real world milling behavior using linear and nonlinear PBMs. III. Evidence from recent microscale comminution research. This paper concludes with recommendations concerning future research which will: 1. further elucidate mechanisms of particle destruction and creation as well as attrition and 2. increase the accuracy of model predictions in highly nonlinear situations

Jan 1, 1997

By Marcel Haffen, Jean Janin

The purpose of grouting is to modify the permeability and strength characteristics of the subsoil in such a way that the planned structure can be efficiently constructed at a given location. This technique, which originally underwent considerable development in the field of dams construction is constantly evolving and it becomes more and more important in urban zones of intensive underground development for projects such as transport tunnels, stations, car parks, ect. Grouting becomes more and more indispensable whatever the natural characteristics of that subsoil ; such is the case particularly when the planned work runs through cohesionless granular soils, usually water-bearing such as alluvium, sands, disturbed ground, fill material, etc. The selection of the grouting method and the extent of treatment required at depends on two fundamental factors. 1º) nature and behaviour of subsoil to be treated. There is no need to stress the necessary of a good knowledge of geotechnical, hydrological and chemical characteristics of the ground to be treated. At the present time the specialists in these fields have available numerous methods of analysis, either laboratory or field tests, which enable to evolve a suitable treatment.

Jan 1, 1997