Light Hydrocarbon Gases and Mineralization

Abstract

This chapter describes the results of an investigation into the possible use of light (C1-C5) hydrocarbons as geochemical pathfinders for mineral exploration, carried out by groups at Imperial College, London, and at Mercury Hydrocarbons Ltd., Limerick, Ireland.

The work involved two main areas of study:

• 1. A series of orientation surveys around known mineral deposits and over background areas, to demonstrate the existence of hydrocarbon gas anomalies associated with mineralization.

• 2. Experimental and theoretical studies to develop a better understanding of light hydrocarbon geochemistry and its relationships to mineralization.

The results of the orientation surveys have shown that there are major variations in the hydrocarbon gas contents of rocks which are closely related to the presence of mineralization. The origin of these changes is still not fully understood, but it seems likely that they reflect large-scale migration of hydrocarbons within the hydrothermal systems which produced the sulphide deposits. Thèse hydrocarbons could have been carried passively in the ore-forming solutions. Alternatively, they could have been generated at the site of mineralization by chemical reactions or by thermal decomposition of kerogens in the surrounding rocks.

Further research is needed, particularly to develop the analytical techniques and methods of processing the data, but the studies reported here have established an association between light hydrocarbons and mineralization, and suggest that there is considerable potential for using hydrocarbon gas geochemistry as an aid to mineral exploration.