Biogeochemical anomalies

1. Biogeochemical
anomalies

2. ContentsContents
Introduction
Geochemical anomalies
Biogeochemical anomalies
Biogeochemical survey
Geobotanical Indicators
Geobotanical Survey Techniques
Conclusion
References

3. IntroductionIntroduction
 Geochemical exploration also known as geochemical prospecting and exploration
geochemistry, is the search for economic deposits of minerals or petroleum by
detection of abnormal concentrations of chemical elements or hydrocarbons in
surficial materials such as soils, waters and plants.
 Geochemical prospecting for buried ore deposits is an ancient technique. For
thousands of years prospectors have sought iron and copper stains on rocks as
possible indicators of mineralization below; the strains are geochemical
anomalies that arise as a result of the interaction of the atmosphere and
rainwater with a sulphide mineral deposit, and the dispersion of the oxidized
products so formed.
 The various methods of geochemical exploration may be classified according to
the type of sample in the search for ore deposits
 Litho geochemical method
 Pedo geochemical method
 Hydro geochemical method
 Biogeochemical method

4. Geochemical anomaliesGeochemical anomalies
Geochemical anomalies have been identified by setting threshold values,
which mark the upper and lower limits of normal variation for a
particular population of data. Values within the threshold values are
referred to as background values and those above or below as anomalies.
In mineral exploration interest is generally in positive anomalies, on the
assumption that ore deposits and their weathering have increased
element abundances above normal crustal levels. However, negative
anomalies can also be important, for example where they reflect
depletion in some elements during host rock alteration accompanying ore
formation.
At many locations within and on the earth concentrations of some
element or set of elements are found which are much higher than the
background concentrations normally encountered in the host material.
The host can be any naturally occurring substance such as rock, soil, a
stream or lake sediment, glacial debris, vegetation, or water, and the

5. Biogeochemical anomaliesBiogeochemical anomalies
Biogeochemical anomalies are areas where vegetation contains an
abnormally high concentration of metals.
Different species of plant take up different amounts of inorganic
material from the soil and the peculiar habit of each plant must be
understood.
Deep rooted plants that obtain their water from the zone of
saturation below the water table phreatophytes are in contrast to
shallow rooted xerophytes that can survive exclusively on vadose
water derived from rainfall.
The contrast between the background and anomalous values are
related to the mobility of element in soil solutions where the plant
is deep rooted directly over an ore deposit or in a superjacent soil
anomaly. In such cases, the biogeochemical anomaly will also be
superjacent.

6.  It has been observed that many species of
plants take up anomalous metals from an
ore body located at depth of 10-15mts.For
e.g., in Arizona live roots have been
reported at depths of 55 m in an
unconsolidated overburden overlying
porphyry copper deposits.
 The concentrations of trace elements
decreases in the order of leaves, twigs,
root and bark.
 In cases where the parent anomaly is
lateral groundwater or hydromorphic soil
anomaly the resulting biogeochemical
anomaly will also show the corresponding
displacement with respect to the ore.
 Controlling factors: the plant species
sampled, the plant organ sampled, age of
the plant or organ depth of the root
system, health of the plant amount and
direction of sunlight, soil, Eh & pH, soil
moisture and interferences due to other

7. Biogeochemical surveyBiogeochemical survey
Biogeochemical surveys are used in cases where vegetation can be used as a test medium.
The first stage is orientation survey during which the following aspects are determined.
 The optimum species based on distribution, contrast of anomalies, ease of recognition, ease
of sampling and depth of the root system.
 Part of the plant to be sampled: twigs, leaves, roots, bark, wood.
 Best indicator elements
 Effects of sunlight, drainage and interference of other elements
 Amount of vegetation required to give adequate ash.
 Contamination from dust or other sources
 Sampling pattern and intergrowth.
In biogeochemical survey deep rooted plants are generally preferred to shallow rooted
plants. In areas where densely populated vegetation are to be sampled the sampling points
can be plot as geometric grid of profile lines. In areas where vegetation is widely scattered,
sample points can be in places where they are available. During the chemical analysis
burning of plant organs should be carried out with a relatively low oxygen supply so that
the sample does not burst into flames but with sufficient oxygen supply to minimize
volatization of an oxidized organic matter.

8. Geobotanical IndicatorsGeobotanical Indicators
 Geobotanical studies have been used since ancient times as a prospecting tool.
It has long been known that specific plants or plant communities are
indicative of a high concentration of a given chemical element in the soil.
 All living plants respond to changes in physical, chemical and biological
environment which is reflected by their characteristic habit of growth.
Geobotany is the study of plant in relation to their geological environment
many factors other than geologic factor can have a major influence on the
health and major distribution like sunlight, length of season.
 Morphological changes in plants due to anomalous concentration of trace
elements include dwarfism, gigantism, mottling [dots on leaves] and chlorosis
[yellowing of leaves], abnormal fruits, changes of flower color and
disturbances in the rhythm of growth and flowering. These abnormal colors
and morphological changes of plants are caused by the presence of poisonous
element in the nutrient solution and referred to as toxicity.

9. There are two types of indicator plants:
 Universal indicators
 Local indicators
Universal indicators are found only on
mineralized soils and do not grows elsewhere.
Universal indicators are extremely useful
within limited areas of similar climate, geology
and topography.
e.g., Calamine violet which grows only on soils
rich with anomalous Zn content.
Local indicators are species that grow
preferentially on mineralized ground within
limited areas but grow over non-mineralized
areas in other regions.
e.g., a local indicator of copper in Arizona is the
California poppy, observed over outcrop of the
san manual copper porphyry deposit and at
other deposits.
Calamine
violet
California
poppy

10. Crotalaria cobalticola
[cobalt]
Astragalus
[selenium]
Deschampsia flexnousa
[lead]

11. Eriogonum ovalifolium [copper]
Oceum homblei
[copper]

12. Elements Effects
Aluminum Stubby roots, mottling.
Boron Dark foliage ,
deformed internodes .
Chromium Chlorosis of leaves .

13. Elements Effects
Cobalt White dead patches on leaves .
Copper Purple stem, stunted roots, chlorosis of leaves and dwarfism .
Iron Darkening of leaves, thickened roots.

14. Elements Effects
Manganese Curling of leaf margins,
distortion of laminae .
Molybdenum Stunting, yellow -orange coloration.
Uranium Abnormal number of chromosome in unusual shape of fruits.
Zinc Dead areas on leaf tips , stunted roots .

15. Geobotanical Survey TechniquesGeobotanical Survey Techniques
i. Population map of all species growing both in the vicinity of known but
undisturbed mineralization and in barren areas of other similar characters
to be made.
ii. Indicators plants are best found and mapped when they are in bloom,
mapping plants at other times of the year may be done but work progresses
at a slower rate and there is a chance of missing certain useful species as
indicators of ore deposits.
iii. Once a system of identifying geobotanical indicators has been established, a
geobotanical survey consists merely in plotting their occurrence on a map
and then sketching the outlines of areas where they occur.
iv. Remote sensing techniques can be developed for a rapid survey because the
IR radiations are very sensitive incase of plants it has been established
that vegetation with metal toxicity has a different reflection spectrum
than normal vegetation.

16.  Geobotanical surveys are useful in groundwater exploration because desert
plant respond spectacularly to the availability of water. Phreatophytes
indicate a water table within the reach of their root system ,in contrast
xerophytes have shallow roots which depends on occasional rains for their
survival ferns of considered to indicate water log soil or ground water
seepage areas. A high salinity is indicated by the presence of halophytes
plants with their roots in bituminous soil tend to have peculiar form
distinguished by their gigantism and deformed form of these plant show a
tendency for abnormal blooming.
 Geobotanical anomalies have the advantage of rapid scanning of large areas
at low cost however the problems in such method are related to identification
of species, plant spacing, depth and type of over burden etc.,
Phreatophyt
es
Xerophyte Halophyte

17. ConclusionConclusion
Biogeochemical exploration constitutes an
important component of mineral exploration.
It compliments other methods of mineral
exploration when effectively applied in the search
for ore deposits.

18. ReferencesReferences
Books:
 Geochemistry in mineral exploration by A W. Rose, H E.Hawkes &
J S Webb. Academic press. pp 657.
 Courseware of Geological survey of India 2005.
 Prospecting and Exploration of Mineral Deposits by M. Kuzvert &
M. Bohmer. Elsevier publication, 1986. pp 51-110.
Websites :
www.google.com
www.wikipedia.com
www.geology.com