Ch. 2— Resource Assessments and Expectations • 63 



Table 2-5.— Estimates of Typical Grades of Contained Metals for Seafloor Massive 



Sulfide Deposits, Compared Witfi Typical Ore From Ophiolite Massive 



Sulfide Deposits and Deep-Sea Manganese Nodules 



Sulfides, lat 21° N. & Sulfides Sulfide ore, Deep-sea 



Juan de Fuca Ridge Galapagos rift Cyprus manganese nodules 



Typical grade. Typical grade. Typical grade, Typical grade, 

 Element in percent in percent in percent in percent 



Zinc 30 0.2 0.2 0.13 



Copper 0.5 5.0 2.5 0.99 



Nickel — — — 1.22 



Cobalt — 0.02 — 0.23 



Molybdenum — 0.017 — 0.018 



Silver 0.02 — — — 



Lead 0.30 — — — 



IVIanganese . . — — — 28.8 



Germanium. . 0.01 — — — 



SOURCE: Adapted from V. E. McKelvey, "Subsea Mineral Resources," U.S. Geological Survey, Bulletin, 1689-A, 1986, p. 82. 



Prospects for Future Development 



At the present time, too little is known about ma- 

 rine polymetallic sulfide deposits to project their 

 economic significance. Analysis of grab samples of 

 sulfides collected from several other spreading zones 

 indicate variable metal values, particularly from one 

 zone to another. In general, all of the deposits sam- 

 pled, except those on the Galapagos rift, have zinc 

 as their main metal in the form of sphalerite and 

 wurtzite. The Galapagos deposits differ in that they 

 contain less than 1 percent zinc but have copper 

 contents of 5 to 10 percent, mainly in the form of 

 chalcopyrite. Weight percentage ranges of some 

 metals found in the sulfide deposits are given in ta- 

 ble 2-5. Some of the higher analyses are from in- 

 dividual grab samples composed almost entirely of 

 one or two metal sulfide minerals and analyze much 

 higher in those metal values (e.g., a Juan de Fuca 

 Ridge sample which is 50 percent zinc is primar- 

 ily zinc sulfide). While this is impressive, it says 

 nothing about the extent of the deposit or its uni- 

 formity. In any event, it is certain that any future 

 mining of hydrothermal deposits would recover a 

 number of metal coproducts. 



Highly speculative figures assigning tonnages 

 and dollar values to ocean polymetallic sulfide oc- 

 currences have begun to appear. Observers should 

 be extremely cautious in evaluating data related to 

 these deposits. The deposits have only been exam- 

 ined from a scientific perspective related primar- 

 ily to the process of hydrothermal circulation and 

 its chemical and biological influence on the ocean. 



No detailed economic evaluations of these depos- 

 its or of potential recovery techniques have been 

 made. Thus, estimates of the extent and volume 

 of the deposits are based on geologic hypotheses and 

 limited observational information. Even estimates 

 of the frequency of occurrence of submarine sul- 

 fide deposits would be difficult to make at present. 

 Less than 1 percent of the oceanic ridge system has 

 been explored in any detail. 



A further note of caution is also in order. In 

 describing the potential for polymetallic sulfide de- 

 posits, several investigators have drawn parallels 

 or made comparisons to the costs of recovery and 

 environmental impacts of ferromanganese nodule 

 mining. There is also a parallel with regard to eco- 

 nomic speculation. Early speculative estimates of 

 the tonnages of ferromanganese nodules in the Pa- 

 cific Ocean were given by John Mero in 1965 as 

 1.5 trillion tons.*^ Even though this estimate was 

 subsequently expressed with caveats as to what 

 might be potentially mineable (10 to 500 billion 

 tons),*^ the estimate of 1.5 trillion tons was widely 

 quoted and popularized, thus engendering a com- 

 mon belief at the time that the deep seabed nod- 

 ules were a virtually limitless untapped resource — a 

 wealth that could be developed to preferential ben- 

 efit of less developed nations. The unlimited abun- 



■•^Mero, The Mineral Resources of the Sea, p. 175. 



"J.L. Mero, "PotentiaJ Economic Value of Ocean-Floor Manganese 

 Nodule Deposits," Ferromanganese Deposits on the Ocean Floor, 

 D.R. Horn (ed.). National Science Foundation, International Dec- 

 ade of Ocean Exploration, Washington, DC, 1972, p. 202. 



