ABSTRACT

From a start-up in the late 1950's, the offshore diamond mining industry of Namibia and South Africa has eventually become a major productive force in the worldwide supply of gem quality stones. The paper briefly summarizes the development history and reviews the present status of the marine based industry which is now a target of interest for internationalmining companies.

The technologies used at various stages in the search for, and evaluation of, diamondiferous gravels in up to 200 mof water on the continental shelf are described. An account is given of the problems associated with estimating ore reserves and of quantifying expected production rates as part of any mining feasibility study.

All the different marine mining methods presently in use in a range of operating scales are reviewed, including diving, airlifting, remotely operated crawlers, and various forms of drilling techniques modified especially for the conditions. The critical advantages, limitations, and means of deployment of system are described.

The ever increasing diamond production levels of recent years are provided and consideration is given to the effect of factors such as environmental concerns and the future role of government.

Although centered on relatively shallow waters, the expanding, offshore, diamond operations of southern Africa have already inherited from the earlier attempts at deep ocean nodule recovery the role of "cutting edge" in a marine mining industry.

INTRODUCTION

The offshore mining of placer diamond deposits has recently developed into a significant multi-scale activity along the western coast of South Africa and Namibia. It is a successful offshoot from a land based mining industry operating along the coastline for over eighty years. On-shore diamond deposits have been worked by a variety of methods from the foreshore to some kilometers inland1 They are the foundation of a vast, on-going, onshore industry along the coastline of both South Africa and Namibia. Starting in the late 1950's, the offshore industry has now come of age. Production is achieved by several means along 800 km of coastline in water depths of almost 200 m. Half of that total coastline is in Namibia, north of the Orange River which defines the border, and half is in South Africa.

ORIGIN OF OFFSHORE DIAMONDS

The coastal diamonds are generally understood to have been eroded from the upper parts of diamond-bearing pipes, in the southern African hinterland2. Released stones were carried westward by the Orange River along its present and ancestral routes to the south Atlantic. They entered the sea at several points between Cape Town and the present Orange River mouth over a distance of about 400 km during a 60 million yearperiod.

Together with all the other river debris of silt, sand and gravels, the diamonds were swept northwards by the prevailing sea currents and winds. They were deposited in a large variety of geomorphological trap sites now up to many kilometers offshore. Larger stones were immediately trapped around, and to the north of, the river mouths, while the smallest ones were carried the furthest distance of many tens or more kilometers.

This content is only available via PDF.
You can access this article if you purchase or spend a download.