MARMOTA LIMITED Marmota is pleased to advise it has received the first pit wall parameters to be used in the design of an open pit at Aurora Tank.
The pit wall design was carried out by Rocktest, a specialised Geotechnical Engineering consultancy, based on analysis and testing of diamond core obtained from the company's recent diamond drilling program at Aurora Tank. The work determines the first realistic pit wall parameters for the design of an open pit at Aurora Tank.
Technical Details
The Aurora Tank deposit is hosted in Christie Gneiss, a metamorphic rock. Locally, this has undergone lower temperature metamorphism (referred to as retrograde metamorphism) that has caused the development of schistocity so that mineral grains have become orientated in such a way that the rock is easily split into thin flakes or plates. This layering in the rock (foliation) results in the gneiss being highly anisotropic i.e. the rock is significantly stronger perpendicular to the foliation than along the foliation. The engineering characteristics of the gneiss vary significantly with weathering grade, which varies with depth. Weathering in the upper part can result in these rocks displaying soil like characteristics, whereas in the less weathered and fresh rock zones, the areal extent and frequency of structural discontinuities (e.g. joints, foliations, shears, and faults) will have the greatest influence on rock mass stability. The groundwater level was assumed to be at approximately 70m Below Ground Level ('BGL') so the pit walls in domains D1 to D3 are expected to be dry, as will domains D4 and D5. In the latter two, local sumps in the floor of the pit are expected to be required. Rocktest recommended that access to the pit be developed by means of a clockwise spiral ramp from the NW corner of the pit.
ATV Logging
In addition, a number of holes were logged by a specialist geophysical wireline logging firm using an acoustic televiewer/scanner (ATV) which greatly increased the number of data points available for use in Rocktest's geotechnical analysis. Downhole geophysical measurements included acoustic and optical imaging, formation density and gyroscopic deviation. The analysis undertaken by Rocktest of the data collected identified five sets of structural features as identified through the ATV logging and confirmed by their logging of the core. The poles to these planes [i.e. a single point (pole) oriented at 90o to the plane] were plotted on a stereonet. The point is projected downwards to the position at which it would intersect the lower half of a sphere. Where points form tight clusters indicates where these discontinuities have a close common orientation. Poles clustered close to the centre of the stereonet indicate discontinuities that are shallow dipping to horizontal, whilst poles located closer to the perimeter of the circle indicate planes that are steeply dipping to vertical. This is one of the primary tools used in determining how pit wall orientation will intersect the various discontinuity sets, what that interaction may mean for wall stability and how design parameters may be established to mitigate any risk of instability.
Contact:
Tel: (08) 8294 0899
Web: www.marmota.com.au
About
(C) 2022 Electronic News Publishing, source
