Laboratory experiments were conducted with cornstarch to study the effects of duet concentration, moisture, particle size, treatment with oil, and admixture of calcium carbonate on the dust-explosion hazard. One series of tests were made on five size fractions of starch and on samples with four different moisture contents, all prepared from a single batch. Within … Read more
The copper in many large low-grade and small high-grade deposits cannot be economically recovered by conventional methods because the value of the copper content of the large low-grade deposits is less than the cost of recovery, and the tonnage in the small deposits is not enough to amortize a recovery plant. These deposits are suitable … Read more
The extreme variability in gold mineralization in drill core is revealed through the detailed sampling experiment. This variability is that naturally present on the smallest scale that can be found by fire assay. With samples of substantially larger volumes, less variability would be found. Most of the variability is associated with among-feet rather than within-feet … Read more
Model studies, using rock, require carefully prepared specimens. Most preparation procedures use some form of grinding or polishing as the last of several steps. During these steps, particularly the final one, the surface formed acquires a configuration defined as texture. Texture is a composite term identifying the physical features called flaws, lay, waviness, and roughness. … Read more
Accidental firings of explosive initiators have occurred occasionally with some uncertain correlation to the pneumatic loading of ammonium nitrate-fuel oil (AN-FO) blasting agents. The exact association, if any, between these firings and static electricity is unknown. This report describes the role of pneumatic loaders in generation or transfer of static electricity and discusses the possible … Read more
The major conclusion to be drawn from the four series of tests is that reasonable care in preparing specimens and conducting compression tests on a hydraulic machine will provide an acceptable compressive strength value for most applications. For normal uniaxial compression tests, nonparallel ends, end surface texture, steel false end platens, and spherical head friction … Read more
Penetration rate is increased by an increase in applied thrust up to an optimum point after which penetration decreases until the drill eventually stalls. Higher operating pressures result in increased penetration rates with the only apparent limitations being the design characteristics of the drill and bit and the ability to remove the cuttings produced. Rock … Read more
In a room-and-pillar system of mining in which no artificial support is used (linings, sets, props, etc.), the weight of the overlying cover is sustained in part on the abutment and in part by the pillars. The pillars are usually the most important structural support element in a room-and-pillar system and their stability is responsible … Read more
For some time researchers have attempted to increase drilling efficiency by adding certain agents to the flushing medium. Much of this interest is the result of the observations of Rehbinder, Shreiner, and Zhigach. They postulated that in processes for the mechanical destruction of solids, a region of increased crack formation is created in the deformed … Read more
Mining companies have been confronted with a multitude of production problems in their endeavors to extract maximum quantities of ore at minimal costs. These problems are further compounded by the harsh mining conditions of deep vein operations, such as those found in the Coeur d’ Alene mining district of Idaho. One of the major obstacles … Read more