This document summarizes a seminar on applications of vapor geochemistry. It discusses how gases emanate from geological phenomena like ore deposits, oil fields, and volcanoes. These gases can be studied in soils, waters, and the atmosphere. Specific applications discussed include exploration for sulfide deposits using CO2 anomalies, locating uranium deposits using radon anomalies, and forecasting earthquakes and volcanic eruptions by monitoring certain gases. The document also reviews techniques for vapor surveys and challenges in sampling and interpretation.

1. SEMINAR ON
APPLICATIONS OF VAPOR
GEOCHEMISTRY

2. CONTENTS INTRODUCTION
 SOURCE OF NATURALLY OCCURING GASES
 MOVEMENT OF GASES
 EXPLORATION FOR SULFIDE DEPOSITS
 EXPLORATION FOR URANIUM
 EXPLORATION FOR PETROLEUM
 LOCATION FOR BURIED FAULTS
 FORECASTING OF EARTHQUAKES
 FORECASTING OF VOLCANIC ERUPTIONS
 LOCATION OF GEOTHERMAL AREAS
 VAPOR SURVEY TECHNIQUES
 CONCLUSION
 REFERENCE

3. INTRODUCTION
• The gases emanating from ore deposits or oil fields
have recently attracted increased attention as
possible exploration guides.
• Very little development as indicators of various
geological phenomena.
• The gases which can be studied in three main
environments: open atmosphere, pore space of soil
and over burden, surface and ground waters with
dissolved gases.

4. SOURCE OF NATURALLY OCCURING GASES
a. ATMOSPHERIC GASES
•O2 is the dominant reactive constituent. Surface
water with dissolved O2 circulates to depths of tens or
hundreds of meters below surface to set up an
oxidizing environment.
•Atmospheric CO2 maintained at 0.035% by equilibrium
with CO2 dissolved in sea water.

5. b. DEEP-SEATED GASES
•Deep seated environment characterized by low
oxygen fugacity (effective concentration of
elemental oxygen) and relatively high fugacity of
reducing gases, such as H2 and CH4.
c. RADIOGENIC GASES
•Deep-seated or shallow origin
•Trapped in parent rock. Eg. He, Rn, K.

6. Cont…
d. BIOGENIC GASES
•Disintegration of organic matter
•eg. CH4, H2, H2S, CO and H20
e. GASES GENERATED IN SULFIDE DEPOSITS
•Abundance of free O2 in buried sulfide deposits
undergoing oxidation at grater depth.
•The sulfur in sulfides react with H20 and 02 to form
sulfuric acid.
f. Atmospheric Particulates
•Water droplets in the form of clouds and fog, are the
most common particulate materials in atmosphere.

7. MOVEMENT OF GASES
a. DIFFUSION
•Diffusion may be defined as the flow of a species
from a region of high concentration to low concen-
tration as a result of random thermal motion.
•Diffusion through a viscous liquid will be slower than
in open, unrestricted systems.
b. WATER TRANSPORT
•Mass movement of aqueous solutions of volatile
species through rocks and open fissures can be several
orders of magnitude faster than movements by
diffusion.

8. Cont…
c. TRANSFER BETWEEN WATER AND VAPOR PHASES
•Evaporation and condensation of gases are continually
taking place at any aqueous phase and a vapor phase.
•For gases generated at depth, a net upward movement of
gas from the water to the overlying vapor occur be-cause
the gas is continually replenished in water and leak away
towards the atmosphere.
d. VAPOR TRANSPORT
•Except in volcanic systems, mass movement of vapor is
restricted to the aerated zone above the water table.

9. Cont….
Only factors that can have a appreciable effect on the
flow of air in aeration zone are changes in pressure,
temperature and moisture, which are related either
directly or indirectly to changes in weather.
e. RELATIVE EFFECTS OF INFILTRATION VERSUS
DIFFUSION
•Diffusion is certainly the principal factor in the
movement of gases through impermeable rocks.
•Transport of volatile species by infiltration of aqueous
solution must dominate in aquifers both in permeable
rocks and in fractured igneous and metamorphic rocks.

10. EXPL0RATION FOR SULFIDE DEPOSITS
• Free or dissolved gas associated with oxidizing
sulfides ores report strong anomalies in CO2.
• Anomalies in soil air reported in these investigations
fall in the range 1.5-4% v/v, the normal contents
usually fall well below 1%.
• The CO2 content if gases dissolved in ground water
near oxidizing ore may be as high as 10% compared
to a background of 0.2%.
• Increases in CO2 are not uncommonly paralleled by
decreases in O2.

11. Exploration For Uranium
• The use of Rn in soil gas and in natural waters in
locating buried U deposits is becoming well
established as a prospecting method(smith et al.,
1976).
• In several areas, Rn anomalies have been detected
above ores covered by up to100 m of transported
overburden.
• In other circumstances , strong control of Rn
anomalies by faults or other permeable zones, or by U
dispersed away from its primary source, has been
demonstrated (Michie et al ., 1973).

12. EXPLORATION FOR PETROLEUM
• Light hydrocarbons and the radiogenic gases He and Rn.
• Methane, the dominant member of the hydrocarbon
group, tends to be most concentrated in the highest part of
the oil structure, where it may accumulate as a separate
vapor phase in the form of natural gas.
• The radiogenic gases are generated by U which tends to
be precipitated at the water-oil interface at the base of the
oil accumulation.
• In theory, He and CH4 can diffuse directly upward through
the impermeable cap rocks to form projected images near
the surface that reflect their distribution at depth.

13. LOCATION OF BURIED FAULTS
• Russian workers have carried out extensive studies of He
in soils and sedimentary cover as a guide to deep faults and
basement fractures(Bulashevich,1974; Eremeev et al .,
1974; Ivanov and Medovyi, 1975; Ovchinnikov et al .,1973).
• Mercury has also shown promise as a guide to deep
fracture zones. Carbon dioxide and other gases shown
anomalies along near surfaces faults and fracture zones
(Fridman and Petrov, 1976; Rosler et al ., 1977).

14. FORECASTING OF EARTH QUAKES
• Recent studies have suggested that immediately prior to
an earthquake, pervasive crackling and dilatancy occurs
throughout the rocks adjoining the potential fault surface,
resulting in the release of certain occluded vapor species.
• These gases are then free to move toward the surface
where they may be measured as components of the soil
air.
• The only vapor indicators of forthcoming earthquakes so
far reported are the radiogenic gases Rn, Ar, and He.

15. FORECASTING OF VOLCANIC ERUPTIONS
•Stoiber and Rose (1974) found that the fumarolic
condensates, leachates, and encrustations decreases before
a volcanic eruption, stays constant during the eruption, and
then returns to its normal value afterwards.
• Chirkov (1976) has reported that the Rn content of
volcanic fumaroles and hot springs in the U.S.S.R. increased
before and during the eruption of a volcano.

16. LOCATION OF GEOTHERMAL AREAS
Certain gases in soil air, particularly He, CO2, and
Hg, may under favorable conditions indicate the
presence of thermal water at depth (Koga and Noda,
1975; Reimer et al., 1976; Tikhomirov and Tikhomirova,
1971; Hinkle,(1978). These constituents are apparently
released by the heat and active water circulation of the
thermal zone.

17. VAPOR SURVEY TECHNIQUES
The particular advantage of vapor as an indicator of geological
phenomena that are hidden either in the ground or in the
future lies in its high mobility. This same quality also makes
vapors probably the most difficult of all geochemical indicators
to sample, analyze, and interpret.
If the geochemical signatures that are being carried upward by
vapors from the depths are to be deciphered at all, the
techniques of sampling and analysis must be perfected so that
even very low concentrations can be reproduced.
More research and trial surveys are also needed to understand the
natural processes whereby gases are transported and
destroyed, and the limitations of vapor surveys.

18. Cont….
Variations in pressure, temperature, and moisture
strongly affect the mobility and hence the relative
concentration of the various gas species in soil air.
Well defined anomalies in soil air have been known to
vanish entirely on resampling. Sampling soil air directly,
therefore, can be an extremely frustrating experience.
Fortunately, however, soil air is not the only medium
that will give us a measure of the gases escaping from
depth. The gases dissolved in ground water or sorbed to
natural traps or artificial traps, though less direct, may
give values that tend to level out the time variations that
are so dependent on the weather.

19. CONCLUSION
• Active oxidation of the sulphide mineralization
appears to be an essential condition for the
generation and dispersion of gases.
• Collection of three consecutive soil-gas sub samples
from boreholes 2 to 4 m deep provides sufficient
information for prospecting purposes.
• The nature and age of the overburden materials as
well as the supergene history of the deposits studied
are important in the interpretation of vapor
geochemical prospecting data.

20. REFERENCE
• Geochemistry in mineral exploration Rose,A.W
Hawkes. H.E & webb J.S 1979, pp-489-511.
• Rock geochemistry in mineral exploration.
G.J.S.Govett.Elsevier publication.1983, pp-123-135.
• www.Wikipedia.com
• www.google.com

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