Evaluating the Economic Significance of Polymetallic Sulfides Deposits
Authors: Broadus J.M. , Bowen R.E. 
Published: October 2008

The current economic significance of ocean ridge polymetallic sulfide deposits is evaluated. Present and future sources of demand and supply for the contained metals are considered along with the potential for and conditions likely to foster substitution away from their use and the implications of technical change for production costs over time. Estimates of future value are discounted into present terms. International legal and political parameters are examined. The deposits appear to have negligible present resource value, but knowledge about them is valuable in itself.

INTRODUCTION

This paper is a report of work in progress. The goal of our research is to define more carefully and systematically the current economic significance of marine polymetallic sulfide deposits at submarine crustal spreading centers (PMS). The purpose of the paper is to detail the major components of our analysis and to provide suggestive evidence for our tentative conclusions.

Table 1 presents some, general information describing the PMS deposits thus far discovered, including an indication of the percent weight of four major metals contained in assayed samples. Beyond zinc, copper, lead and silver samples have also been shown to contain iron, manganese, cadmium and trace amounts of other metals, however, these metals do not appear to exist in sufficient quantities to warrant particular economic consideration.

Although little is known about the processes that generate polymetallic sulfides, there are two factors that characterize general types of deposits. One involves the distinction between zinc-rich and copperrich areas. Most known deposits appear to align themselves along a copper-zinc continuum with silver being more directly associated with zinc-rich areas. The other involves a consideration of the size of a deposit. Most known deposits consist of relatively small chimneys (3-10 meters) of PMS sitting atop disaggregated mounds of sulfide material. However, the deposit discovered by Malahoff (1982) appears to be several times larger than any other yet found.

As Cooper (1977) has noted, "a potential resource takes on economic value only when it is in practice accessible and when it is not in infinite supply." By this quite proper standard, PMS currently have negligible economic resource value. They are not in infinite supply, claims of their renewability notwithstanding. But they are in practical economic terms inaccessible, and they will remain so until a great deal more time and other resources are spent on science, exploration, testing, and technological development and until society places greater value on the metals they contain. Zimmerman (1964) puts it: "Resources are not, they become."

ALTERNATIVE APPROACHES TO ECONOMIC SIGNIFICANCE

Three alternative conceptual approaches are considered here:addition to net surplus;in place value; andnet present value or rent.

Addition to net surplus is the, value we would ideally like to find, as it provides a direct measure of the improvement in everybody's welfare produced by PMS (assuming everybody gets equal marginal subjective benefits from income). "Consumer surplus" is just the area bounded by market price and the downwardly-sloping demand curve in a familiar supply-demand diagram.