The design and implementation of a UHF radio system using distributed antennas, passive reflectors and two-way signal boosters in a room and pillar limestone mine
The Bureau of Mines (BOM) has established a project to demonstrate means for improving underground communications in metal/nonmetal room and pillar mines. The Black River Mine, a large limestone mine near Butler, Kentucky, was selected for conducting propagation tests on 466 and 812 MHz and to develop a practical operating system. Tests of communications between handheld 2 watt ultra high frequency (UHF) transceivers in the mine proved satisfactory for approximately 2,000 feet (610 m) through straight and level haulageways but the range of communication into intersecting crosscuts was quite limited. It was evident that radiation from the transceivers was not being efficiently reflected by limestone pillars into the intersecting crosscuts. Two passive aluminum reflectors, each four feet (1.22 m) square, were installed near the roof and positioned 45° with respect to the axis at an intersection of two haulageways and the range of communications down the intersecting haulageways was significantly extended. Two distributed antenna and base station systems, each feeding four antennas located at principal intersections of haulage and travel roads, were installed and signal or fade margins above 20 dB quieting were measured to determine where reflectors were needed. The reflectors were very effective when they were within direct line of sight and less than 1,000 feet (305 m) from an antenna. The two antenna systems provided satisfactory coverage along the principal travel and haulageways in approximately 70 percent of the central portion of the mine but coverage was unreliable in the active mining areas around the perimeter of the mine. The alternatives of either installing four additional base station and distributed antenna systems or extending the original distributed antenna systems by adding two-way multichannel signal boosters to compensate for cable attenuation were evaluated. The signal booster concept was selected because it is less expensive, simpler to control, avoids hetrodyne interference and communications can be readily extended as the mined area is expanded.
Mine-Wide Communication
The near impossibility of communicating by radio in mines, tunnels, and similar underground environments using conventional techniques has slowly become accepted with resignation since the first recorded attempts of the early 1920 s. It is true that frequencies in the very low frequency (VLF) and low-frequency (LF) bands may be used to communicate over limited ranges through the earth itself. With this realization of the problems, the need for effective radio communication in such underground conditions has also become more urgent (Chufo, 1978; Chiba et al., 1978; Isberg et al, 1982; Davis et al., 1984, 1989; Delogne, 1991; Chow, 1992; Saindon and Chow, 1993; Bandyopadhyay et al., 2002, 2009). The inductive-loop principle, using low frequencies and a laid conductor wire, has provided a partial solution in coal mines.
Igneous Rock Associations 23. The Bushveld Complex, South Africa: New Insights and Paradigms
SUMMARYThe Bushveld Complex has continued to serve as the basis for study into the fundamental nature of petrological processes for layered intrusion formation and for oxide and sulphide hosted Platinum Group Element (PGE)–Cu–Ni ore deposits. These studies have included discoveries in terms of the physical extent of Bushveld magmatism, both laterally and internally. Lateral variations in the mafic to ultramafic Rustenburg Layered Suite of the Northern Lobe of the complex have also revealed petrologically distinctive Upper Critical Zone equivalent rocks (the so-called Flatreef) with enhanced contamination and mineralization traits that reflect a transition between Eastern and Western Lobe equivalent stratigraphy and Platreef-style complexity. Traditional magma mixing models have been re-examined in light of radiogenic isotopic evidence for crustal involvement early in the chromite precipitation or formation process, combined with evidence for associated heterogeneous fluid contents, cryptic layering profiles, and textural evidence. A wide variety of alternative ore-genesis models have been proposed as a consequence. The fundamental mechanics of magma chamber processes and the existence of the magma chamber as an entity have been called into question through various lines of evidence which have promoted the concept of progressive emplacement of the complex as a stack of not-necessarily-quite-sequentially intruded sills (with or without significant quantities of transported phenocrysts), emplaced into variably crystallized and compacted crystal-liquid mush mixtures, modified by compaction-driven late magmatic fluid (silicate and aqueous) activity. Alternatively, petrological and geochemical observations have been used to discount these interpretations in favour of more conventional cooling and gravity-driven accumulation of silicate and ore minerals in a large, liquid-dominated system.RÉSUMÉLe complexe de Bushveld a demeuré à la base d’études sur la nature fondamentale des processus pétrologiques de formation d’intrusions litées et des gîtes des éléments du groupe platine (ÉGP)-Cu-Ni hébergés dans les oxydes et les sulfures. Ces études ont comporté des découvertes sur l’étendue physique, à la fois latérale et interne, du magmatisme de Bushveld. Les variations latérales de la suite stratifiée et mafique à ultramafique Rustenburg du lobe nord du complexe ont également révélé des roches équivalentes pétrologiquement distinctes de la zone critique supérieure (le communément désigné Flatreef) avec des traits de contamination et de minéralisation accrus qui reflètent une transition entre la stratigraphie équivalente des lobes est et ouest et la complexité de type Platreef. Les modèles traditionnels de mélanges magmatiques ont été réexaminés à la lumière de preuves isotopiques radiogéniques indiquant une implication de la croûte au début du processus de précipitation ou de formation de la chromite, combinées à des preuves de contenu fluide hétérogène associé, de profils de litage cryptique et de preuves texturales. Ainsi, une grande variété de modèles alternatifs de genèse de minerai a été proposée. La mécanique fondamentale des processus de la chambre magmatique et l'existence de la chambre magmatique en tant qu'entité ont été remises en question au moyen de divers éléments de preuve qui ont mis en avant le concept de mise en place progressive du complexe sous forme d'un empilement non-nécessairement séquentiel de sills injectés (avec ou sans quantités significatives de phénocristaux transportés) mis en place dans des mélanges de bouillie cristaux/liquide à cristallisation et compaction variable, modifiés par une activité tardive de fluide magmatique (silicaté et aqueux) induite par la compaction. Alternativement, des observations pétrologiques et géochimiques ont été utilisées pour écarter ces interprétations en faveur d'un processus plus conventionnel de refroidissement et d’accumulation de minérais silicatés et minéralisés induite par la gravité dans un vaste système à dominance liquide.