Engineering Philosophies Associated With Subsea Diamond Sampling And Mining

Abstract

Abstract The offshore diamond mining industries of Namibia and South Africa have, since the late 1950's developed various techniques to sample for and mine gem quality stones in water depths up to 200 m. These techniques range from relatively simple airlift pumps to remotely operated vehicles. The paper describes the engineering philosophies which have been developed, tied and tested over the years to successfully establish a subsea diamond sampling or mining operation. The overall philosophy that emerges is of particular interest to international mining companies that are entering the marine mining industry for the first time. The philosophies developed involve firstly the consideration of the necessary engineering requirements associated with the establishment of the operation and secondly the order in which these requirements are considered. The requirements include the choice of the sampling or mining equipment, equipment positioning and control, launch and recovery of equipment, transportation of diamondiferous material from the seabed to the mother vessel, processing of the diamondiferous material, vessel station holding and selection of a suitable vessel Each of these requirements is, not only, evaluated in terms of the establishment of an operation, but in addition, an amount is given of current practices, actual experiences and developments that have been made. Future developments in the marine diamond industry will concentrate on the optimisation of current techniques and on water depths greater thm 200 m. Specific areas which require further development are therefore suggested and briefly discussed. Introduction The first step in establishing a sampling or mining operation is to determine and understand the level of technologies sophistication that the owner is prepared to fund and operate. The second step is to understand the geomorphology of the deposit and to after whether a sampling or mining operation is to be established. Sampling and Mining are two very different operations that require different techniques and approaches. Sampling is a bulk process which involves taking representative, predetermined portions of the seabed. Each individual sample is evaluated and an overall statistical picture of the deposit produced which culminates in the estimation of the ore reserve. Mining on the other hand is a continuous process which involves systematic and efficient cleaning of the seabed The level of technological sophistication, the geomorphology of the deposit and the type of operation to be established, determines the basis on which the engineering requirements are evaluated, Choice Of Sampling Equipment Sampling of the deposit follows a geophysical survey which is the important first stage of the prospecting programme. During the geophysical survey the geology of the deposit is determined utilising bathymetric, seismic, side wan sonar and vibrocore techniques. The specific information obtained during the geophysical survey largely controls the choice of sampling technology which is ultimately implemented.