Parametric Analysis of Offshore Mining Systems
Authors: Richardson M.J. 
Published: October 2008

Offshore mineral resources have been exploited by dredges of various types, for such minerals as tin, sand and gravel, rutile, magnetite, ilmenite, gold and diamond. With expanded exploration and investment activity particularly in developing countries, new opportunities are being investigated for offshore mineral mining with dredges. The tradeoff between dredge mining systems can be analysed in a parametric analysis, comparing capabilities unique to each type of dredge with the nature of the prospective deposit to be mined..

Introduction

When considering plans for investing in mining, whether inland or offshore, there are basic fundamentals to be considered. They will include (1) the economics o f the target mineral(s) in today's and future markets, (2) the viability of the deposit itself from the standpoint of tenor or values of recoverable minerals, (3) the feasibility of the mining system and operation to result in profitable production, and (4) property rights for mining and sale of the minerals i.e., royalties, taxes, carried interest, that affect the bottom line.

The function of this paper will be to deal with the selection of mining systems with the assumption that reasonable terms for mining and taxes will have been secured. The methods of evaluation of deposits will be briefly discussed since it is n area too often minimized or glossed over in terms of its critical influence on the success of the mining venture. Ref I. includes illustrations and descriptions of placer mining systems and evaluation methods and is a complete text book on the subject.

Offshore Mineral Deposits

Deposits of minerals offshore fall into two general categories, (1) Precious Minerals, and (2) Industrial Minerals. This will deal only with unconsolidated deposits such as alluvials and eluvials. In the Precious Minerals category the primary targets are gold, platinum, and diamond. Industrial Minerals include tin, rutile, magnetite, ilmenite, zircon, sand and gravel, and phosphate. Other minerals may be considered but these represent the ones that appear to be the most promising targets at this time.

One of the Iargest activities of dredge mining offshore occurs with cassiterite (tin) in Indonesia, where there are over 21 bucket ladder mining dredges excavating ore to maximumdepths of 50m (164ft). Tin deposits offshore Malay Peninsula have been mined by dredges in Thailand, Burma (Myanmar), and Malaysia. Other offshore deposits include rutile, magnetite, ilmenite, zircon, diamond and gold.

Sand and gravel is another of the large applications of dredge mining offshore. Deposits are being exploited within the English Channel using trailing suction hopper (TH/M) dredges. One report stated there were over 120 such vessels in operation.

Deepwater manganese nodules have gained a great deal of publicity since the 1950's with large sums being devoted to research and experimentation by governments and mining companies. Faced with inordinate depths for mining combined with difficult problems to separate the minerals from the nodules, no commercial scale mining of manganese nodules is known to have occurred. Ref 2. includes an overview of offshore mining capabilities and potential within the perimeter of the U.S. coastline, termed the Exclusive Economic Zone (EEZ).