School of Earth Sciences

Drill bits having cutting edges formed of a matrix of sintered metal powder impregnated with diamond bort (the so called "impregnated" diamond bits) have the potential to greatly increase the economy of diamond drilling, due to low production costs and long bit life resulting from reconditioning of the cutting edges. However, little detailed research into the performance of impregnated bits has been conducted, and the capacity to predict their field behaviour is limited. As a contribution to the knowledge of impregnated bit performance, this project has studied basic relationships between thrust, rotational speed and the penetration of diamond bits into rock, with particular attention paid to the development of techniques suitable for laboratory testing using miniature impregnated bits. A conventional bench drill and a radial arm drill were modified and instrumented to enable operating conditions to be controlled and drilling parameters to be measured and monitored, for microscale and fullscale drilling using impregnated drill bits. Bit performance and drilling characteristics were studied for four rock types, and rock drillability studies were carried out on seven rock types. Statistical relationships between penetration rate, specific energy, torque and drilling distance that were determined enable projection of drilling data from a standard "sharp" condition. A wear measuring device was developed to assess matrix wear of the impregnated microbits. Reconditioning was done by drilling medium-strength, abrasive Stawell sandstone. Initial penetration rate increases linearly with increases in thrust and/or rotational speed, but only within a limited range, depending on rock type and the other operating parameters. Matrix contact with the rock surface, "clogging" of the diamonds, time-dependency, and strength of diamonds and the diamond-matrix bond play important roles in these phenomena. Comparison of rock drillability between that of microscale and fullscale bits shows a straight-line relationship indicating the possibility to predict drilling performance in the field. Uniaxial compressive strength, tensile strength, and Sklerograf hardness can be used as a preliminary, but not reliable guide, to predict drillability. Petrographic characteristics and the relative scale of diamond size to grain size of minerals affect rock drillability.

Oxide banded iron-formation-hosted gold deposits account for 12.8% of the gold production from greenstone belts in the Yilgarn Block of Western Australia, but rarely occur in the Kambalda-Kalgoorlie area. Western Mining Corporation initial observations indicated that gold mineralisation at the Victory Mine, Kambalda, Western Australia, although part of a much larger mineralised system, was in some way spatially related to an unusual magnetite - rich variant of the Kapai Slate Formation, but little was known on the nature of the Kapai Slate and its role in the genesis of gold mineralisation at the Victory Gold Mine. The Victory Gold Mine consists of an Archaean vein-associated system hosted in a complexly deformed, subvertical segment of the Кapai Slate Formation, intruded by quartz albite dykes. The veins cut all rock types, and wall-rock alteration is restricted to the siliceous magnetite argillite. The Kapai Slate Formation is a persistent, thin (≤ 10 m) regional marker horizon representing a major hiatus between two volcanic events; the Devon Consols Basalt Formation and the overlying Paringa Basalt Formation. These rocks form part of the mafic-ultramafic sequence of the Kalgoorlie Group which is overlain by felsic volcanic and sedimentary rocks of the Black Flag Group. Five sulphide and oxide bearing lithofacies are recognised within the Kapai Slate Formation; i) siliceous magnetite argillite, ii) siliceous pyrrhotite argillite, iii) carbonaceous pyrite argillite, iv) magnetite chert and v) sulphide chert. The argillites are typically thin-bedded (< 10 cm) and contain more than 15 wt% iron of sedimentary origin. The Victory Deposit is hosted by siliceous magnetite argillite but there is no correlation of lithofacies distribution with structural features. Oxygen isotopic composition of the Kapai Slate Formation lies between 9 o/oo to 12 o/oo indicating a strong depletion compared to Precambrian chert ( ≤ 20 o/oo) and recent marine chert (≤ 36 o/oo). These data together with other geologic data indicate that the magnetite facies is not the result of gold-related hydrothermal alteration but may be the result of both seafloor alteration and metamorphism. The Kapai Slate Formation is compositionally and mineralogically different from other Archaean Banded Iron Formations. The Kapai Slate has high Al, Ti, Na, V, Cr, Zr and Ga, low Ti/Zr ratios, and contains zircons derived from a pyroclastic air-fall tuff (Claoue-Long et al., 1988). The nature of the Kapai Slate lithofacies is interpreted to represent a primary facies variation formed in a deep water sedimentary basin during a hiatus in volcanic activity. It may initially have been composed of both air-fall and water-borne detritus derived from a felsic volcanic source as well as chemical precipitates (sulphide and oxide). This material was totally pseudomorphed and/or replaced by silica, sodium and iron minerals during prolonged exposure on the sea floor. The only elements unaffected by the replacement process were immobile elements such as Al, Ti, Zr, Cr and V. Potassium, Mg and Ca were mobile to a certain extent during the replacement process and the chalcophile elements Cu, Co, Zn, etc. were added to the argillite as chemical precipitants along with S. At the Victory Gold Mine three types of vein sets are recognised: i) ribbon veins, ii) subvertical veins and iii) flat lying quartz veins. However, only the flat lying quartz veins are related to gold mineralisation. The mineralised veins which formed during one episode of open/space filling cut all rock types. Pyritic alteration envelopes of the vein walls are restricted to the siliceous magnetite argillite. Magnetite layers are seen to be deformed by earlier deformations and cut by all vein sets. The development of the pyritic alteration envelopes began with the infiltration of hydrothermal fluid into open fractures resulting in the sulphide replacement of magnetite. Sulphide replacement of magnetite led to the mimicking of the primary layering of the siliceous magnetite argillite. Sulphidation of the vein walls ceased before filling of the veins. After the development of pyritic alteration envelopes, mineral coatings of actinolite and albite formed along the vein walls and later bulk quartz deposition filled the vein openings. The paragenetic sequence consists essentially of a concomittent deposition of pyrite, chalcopyrite, sphalerite, galena, tellurobismuthite and gold. Gold, chalcopyrite, sphalerite, galena, molybdenum and tellurobismuthite were subsequently remobilised into fractures and along grain boundaries of pyrite during a postfilling episode of deformation. The Kapai Slate Formation and the distribution of lithofacies had no influence on the localisation of gold mineralisation at the Victory Gold Mine on a regional scale. However the competent and the more iron-rich nature of the siliceous magnetite argillite probably acted as an efficient chemical and structural trap for the hydrothermally donated S and Au.

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