Anomolies in drainage sediments

ANOMOLIES IN DRAINAGEANOMOLIES IN DRAINAGE
SEDIMENTSSEDIMENTS

ContentsContents
Introduction
Spring and Seepage Areas
Active Stream Sediments
 Flood –Plain Sediments
Lake Sediments
Marine Sediments
Conclusion
Reference

IntroductionIntroduction
 Search for ore mineralization involves sampling of
various geological materials like rock, soil, water,
sediments occur in various environments.
 Systematic sampling of material followed by chemical
analyses of material and preparation of geochemical
anomaly maps are a pre requisite for exploration of
the mineral deposits.
 The presentation here pertains to nature of ore
anomalies in drainage sediments.

ANOMOLIES IN DRAINAGEANOMOLIES IN DRAINAGE
SEDIMENTSSEDIMENTS
 Drainage Sediments include spring and seepage
sediments, active string sediments, flood plain
sediments, and lake sediments which differ in character
of sediments, processes introducing metal and
application.
 Many drainage systems start in seepages and springs
where import and interchange b/w water and sediments
may occur.
 Sediments in seepage areas and near spring provide
strong anomalies and are useful in detailed surveys.

 Geochemical anomalies in drainage sediments include:
 SEDIMENTS IN SPRINGS & SEEPAGE AREAS
 ACTIVE STREAM SEDIMENTS
 FLOOD PLAIN SEDIMENTS
 LAKE SEDIMENTS

SPRING AND SEEPAGE AREASSPRING AND SEEPAGE AREAS
 The immediate source of the anomalous concentration of
the metal in the soil of seepage areas is the ground water
that comes to the surface at these points.
 The source of the metal may be somewhere along the
route traversed by the ground water.
 The route is determined by the pattern of the fissures,
and fractures, caverns and high- pressure artesian
channels in the bed rock.
 Location and form of seepages anomalies is controlled
by the local relationship b/w the relief and water table
and by the flow of the water within the seepage area.

 Edges of organic swamps are especially favorable sites for
the development of the seepage anomalies because organic
matter of the swamps tend to precipitate ore metals out of
the ground water solutions at the points where they first
encounter the swamp environment.
 As the ground water moves towards the center of the
swamp, it becomes progressively impoverished in the
metal.

ACTIVE STREAM SEDIMENTSACTIVE STREAM SEDIMENTS
Metal in anomalous stream sediments may have reached
its present position by one or more of more of a number of
routes:
 from the erosion and transport of metal-rich soils,
gossans, or other anomalous weathering products that
originate very near to the parent ore deposit
 from the erosion of clastic material from
hydromorphic anomalies in spring and seepage areas
or in the upper reaches of the streams
 locally precipitated from the stream waters directly on
to the clastic particles of the sediments
 Primary ore minerals like wolframite, columbite, pyrochlore,
cassiterite, or gold are resistant and dense and travel with the
heavy mineral fraction of the stream sediment.

 Secondary ore minerals( malachite, anglesite, or carnotite, and
fragments of anomalous gossan, limonite) are relative friable
and become finer in grain size downstream.
 Precipitates from stream water (trace minerals and Fe-Mn-
oxides or other precipitates containing anomalous elements)
coats the surface of clastic grains or occurs as very fine particles
that remain in suspension.
 Organic material containing ore elements includes plant,
degraded organic material from soils near the ore and organic
matter formed by biological activity.

 A major controlling the contrast of anomalies in stream
sediments is the primary contrast at the bedrock source
and the extent to which this is dilute with barren
material from the surroundings.
 The principal factors affecting the persistence of these
anomalies are:
– The contrast at the source
– The input of the metal along the stream course and
– Dilution by erosion of the bank material and by
confluence with barren tributaries.

Map of the Ganga river headwaters region showing locations of stream
sediment samples (open circles) .

Geochemical anomaly map showing the distribution of uranium. Sampling
points are shown as open circles and major rivers are shown in blue lines.

Geochemical map showing the distribution of
zirconium

FLOOD –PLAIN SEDIMENTSFLOOD –PLAIN SEDIMENTS
 The pattern of anomalous metals in flood-plain
sediments will reflect their distribution in the
abandoned channels previously followed by the
stream.
 Flood-plain sediments normally are characterized by
a higher proportion of the fine material.
 The lateral distribution of anomalous metal across
the flood plain varies somewhat depending on local
conditions.

LAKE SEDIMENTSLAKE SEDIMENTS
 Where lakes are abundant, the sediments trapped in them can
constitute a convenient sampling medium for the
reconnaissance and detailed stages of exploration.
 Metals may reach the lake sediment by a number of routes:
As clastic particles washed in by streams or eroded from the
margins of the lake.
As elements absorbed to or incorporated within colloidal
organic or inorganic materials entering through streams.
As dissolved material entering through streams or in ground
water and later precipitated, adsorbed to suspended particles
 As incorporated mateial in living matter finally settling to
from bottom sediment.
 The nature of the lake sediment and occurrence of elements in
it are complex function of the climate, vegetation, depth, area,
inflow and outflow of the lake, and geology.

 Thermal stratification of the lake water and oxidation-
reduction potential in the water in the lake sediment are
other factors determining the metal anomaly.
 In most lakes larger than about 0.5 Km2
, there is a difference
between near-shore sediments and center–lake sediments.
 The near-shore materials range in size from clay to boulders
and reflect the geology and characteristics of the shore and
streams, with only minimal sorting and reworking by the
lake water.
 In contrast, the center-lake sediments are predominantly
silt- and clay-size particles, and may contain a high
proportion of precipitated or flocculated organic matter. The
characteristics of these sediments depend strongly on the
nature of the lake and the chemistry of its water.

Anomalous elements in lakes occur in the
following forms :
As substitution for major constituent in minerals
of clastic particles
As element incorporated within colloidal and fine
particles of organic material formed by
flocculation in lake, tissues of plants and animals
growth in the lake.
As element adsorbed to surfaces of particles,
including flocculated organic material, Fe-Mn-
oxides, clay, and other small grains.
As inorganic precipitates formed in the lake.

Major differences in composition are usually
observed between near-shore lake sediment and
center-lake sediment.
Anomalies that are primarily clastic in origin
decay down-drainage mainly by dilution.
The length of anomaly depends on the size of the
tributary providing the anomalous sediment and
on the bottom topography of the lake.

Copper in lake sediments from lake section of the lgnace survey area

MARINE SEDIMENTSMARINE SEDIMENTS
 Recent years have seen an increasing interest in
exploration and exploration of mineral resources from
the continental shelf and ocean floor.
 These include Mn nodules on the deep sea floor, muds
and brines rich in Mn, Fe, Cu, Zn, Ag, and other
metals, phosphorites, heavy minerals (cassiterite, Au,
diamond, and other), and sand and gravel.
 However, the costs of exploration and production of
minerals covered by tens to thousands of meters of
depth of water is the limiting factor. Inexpensive
techniques for locating and outlining the deposits are
obviously needed.

• Sediments, waters and suspended particles have
been proven useful in detection of metalliferous
sediments of the type found in the red sea and
elsewhere near-ocean ridges.

ConclusionConclusion
 Drainage sediments are most useful in
geochemical reconnaissance surveys for
locating ore deposits.
 Very large areas can be scanned for mineral
potentials using drainage sediments because
of the great distances over which anomalies
containing sediments are carried by ground
and surface waters.

Books:
 M.Kuzvart and M.Bohmer (1986) Prospecting and
exploration of mineral deposits, Elsevier science
publishing company.Inc. Pp.160-168.
 Arthur W.Rose, Herbert E.Hawkes, John S.Webb- (1979)
Geochemistry in mineral exploration., Academic
press.Inc.Ltd. Pp. 384-428.
Web sites:
 www.google.com
 www.wikipedia.com
 http://earthscience.brookscole.com/ree4e
REFERENCEREFERENCE

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