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Content archived on 2024-04-15

DEVELOPMENT OF LIGHT HYDROCARBON GAS LITHOGEOCHEMISTRY AND ITS RESPONSE TO DIFFERENT STYLES OF MINERALIZATION

Objective

THIS PROJECT SHOULD ESTABLISH THE ECONOMIC POTENTIAL OF THE USE OF LIGHT HYDROCARBONS LITHOGEOCHEMISTRY FOR A WIDE RANGE OF MINERAL DEPOSIT.
A new lithogeochemical exploration tool has been developed for use in the exploitation of hidden base metal deposits. The new method involves the uses chromatographic analysis of volatile organic compounds released by rocks.

The discovery of anomalously high amounts of methane in rocks adjacent to mineralization in the Northern Pennines Orefield led to the examination of a new lithogeochemical exploration tool for hidden based metal deposits. The method, based on the chromatographic analysis of the volatile organic compounds released by heating the rocks in sealed tubes was first tested on the site of the initial findings and later on deposits in Ireland and in other European countries.

Observations concerning the heat extraction process strongly supported the idea that volatile compounds can be strongly held in rocks, under the sorbed state. A comparison of the results provided by various techniques revealed that heating is the most appropriate way to release them effectively. Sorption is also the only process which permits the compounds to remain in the rocks for long periods of time, and also allows them sufficient mobility to migrate form concealed orebodies.

The analytical results were not as precise as expected, giving the conclusion that there is inherent variation in 1 to 4 mm rock fractions which cannot be easily reduced. This is consistent with the irregular distribution of organic matter, which is thought to provide the majority of hydrocarbon sorption sites.

Field studies demonstrated variations in gas signatures in response to mineralizing events, leading to the possibility of detecting corresponding variations in surface rocks. In Liassic sediments of low thermal maturity, higher trace metal levels tended to be associated with increasing proportions of methane. In addition, organic geochemical studies suggested new genetic hypotheses, supplementing or contradicting previous interpretations.
Studies in Carboniferous areas of very high thermal maturity, also pointed to a strong correlation between some hydrocabon species (propyne) and mineralization, be it with known mineral deposits, or with trace metal anomalies, or both. There was no obvious hydrocarbon response to the predominantly vein type mineralization in the Carboniferous rocks of Belgium and the United Kingdom. This difference in response is thought to be a function of deposit size, and could have considerable exploration significance.
SAMPLES WILL BE COLLECTED FROM THE LOWER CARBONIFEROUS LIMESTONES OF IRELAND AND THE UK, THE VESDRE BASIN IN BELGIUM, FROM THE MINE AREAS OF LES MALINES AND CHESSY IN FRANCE, MEGGEN IN GERMANY, ALMADEN AND CARTAGENA IN SPAIN. LABORATORY STUDIES WILL INCLUDE:

1) DEVELOPMENT OF THE HEAT EXTRACTION TECHNIQUE, TO IMPROVE ANALYTICAL PRECISION;
2) DETAILED TESTS TO OBTAIN INFORMATION ON THE ORIGINS OF ANOMALIES AND ON HOW THE GASES ARE HELD IN ROCKS. THESE WILL INCLUDE DETERMINATION OF ORGANIC CARBON CONTENT, ROCK-EVAL PYROLYSIS, CHROMATOGRAPHIC ANALYSIS OF BITUMENTS, STUDY OF BIOLOGICAL MARKERS, CARBON ISOTOPE ANALYSIS AND PETROGRAPHIC ANALYSIS OF KEROGEN;
3) TRACE ELEMENTS ANALYSIS TO RELATE TRACE METALS TO CONTENTS OF HYDROCARBON GAS AND OTHER ORGANIC CONSTITUENTS.

Topic(s)

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Call for proposal

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Coordinator

Mercury Hydrocarbons Ltd
EU contribution
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Address
Raheen Industrial Estate
61 Limerick
Ireland

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Total cost
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Participants (4)