isocon

Isocon is a term used in economic geology to describe a graphical mass-balance method for evaluating ore deposits. The concept centers on tracking how the concentration of a target metal relates to a reference immobile element across ore and gangue samples. An isocon diagram is constructed by plotting the concentration of the metal of interest against that immobile reference element for multiple samples. The resulting pattern typically forms a straight line, the isocon, whose slope represents the original ore-to-host-rock ratio and whose intercept helps estimate the initial metal content.

The isocon method is used to distinguish primary deposition from secondary processes such as enrichment, dilution, or alteration. If samples fall along the isocon line, it suggests that the observed variation in metal content can be explained by simple addition or removal of material without changing the source composition. Deviations from the line indicate post-depositional processes that have altered the metal concentration independently of the host rock, such as leaching, replacement, or mineralogical modification.

Applications include ore-reserve estimation, post-depositional alteration assessment, and exploration targeting. It is particularly useful in metal districts where a suitable immobile element can be identified to act as a reference.

Limitations include sensitivity to sample quality, the choice of a truly immobile reference element, and the assumption that a single dominant process governs the observed variation. When multiple processes are active, the interpretation of an isocon diagram becomes more complex.

See also: isocon diagram, mass balance, economic geology, ore deposit analysis.