Geochemical Drainage Surveys DEEPCHAND VDEPARTMENT OF GEOLOGYUNIVERSITY OF KERALA deepchandgeology@gamil.com

CONTENTS

• Introduction

• Orientation surveys

• Choice of material to be sampled

• Sample layout

• Collection and processing of samples

• Preparation of maps

• Interpretation of data

• Follow-up Techniques

• Conclusion

INTRODUCTION

Geochemical drainage survey is the most used exploration technique in residual areas of active weathering.

Applications

1.Primary Reconnaissance.

To locate geochemical provinces, mineralized districts and individual deposits.

2.Determine quality and quantity of ore deposits.

a. Location.

b. Areal extent.

c. Geophysical anomalies.

d. Mineral contained.

e. Favorable geological features.

ORIENTATION SURVEYS

• It is the preparation for GDS.

• For most favourable sample medium selection.

• Samples

Water

Stream Sediment

Seepage Sediment

• Collection and Analysis of samples.

WATER

SAMPLING

GROUND WATERMINES

BORE HOLES

WELLS

SURFACE WATERSPRINGS

STREAMS

LAKES

SAMPLING LOCATIONS• Up drainage source• At or near deposit• At every point in which a tributary stream starts or

changing environment in which composition of water changes

• Background locations in barren areas

ANALYSIS • PH• Salinity• Major constituents

Some test possible directly from the field

Some ionic metals may be concentrate at sample site

All determinations should be carried out with maximum precision and sensitivity

Should compare ratios of different constituents at extremely low concentration levels in natural water

Microscopic filters are used to filter fine suspended matter

DRAINAGE SEDIMENTS

should be collected at an interval of 50 m.

The interval may be increased with increasing distance from metal source

Sediments from all tributary streams and seepage areas should be collected

samples like sand, silt, clay and ooze should be sampled separately

Collection of samples from active channel should be taken away from the bank to avoid collapsed bank alluvium

The variation of metal content with depth in all kind of sediments should be checked by collecting samples from a number of experimental vertical profiles

Experimental samples flood plain

active channel

CONTAMINATIONSurface samples especially water samples than soil are more susceptible to contamination.

Careful attention should be given to this problem during orientation survey

Contaminations may come from

Zn and Cu Most common industrial and domestic contaminants

TrashMetal rich drainage from

factoriesMechanized farms

Metalliferous insecticidesAlgicides

Roads and railway beds with mine waste

Condensates from smog and industrial fumes

Wells with pumps most probability contaminated withy metals

Spring water is less contaminated expect that located near to a mine

Mining and smelting is more serious sources of contamination of surface water

Contaminated stream water also contaminates the stream sediments which have contact with it.

CHOICE OF MATERIALS TO BE SAMPLED

The sampling materials should be strongest, most reliable and readily detected by the techniques at hand.

Principle factors The mobility of the constituents of the ore Influence of local conditions on dispersion pattern Opportunities for sampling Availability of a suitable analytical method

A. Choice of WATER to be sampled

Elements sought are relatively mobile

Would not carried with detrital sediments

Choice of Lake, Ground and Surface water for sampling based on

• Availability of media in that area

• Humid region –Stream water

• Glaciated area- Lake water

• Arid area- Ground water

Water has more Physical homogeneity- more Dispersion

B. Choice of Seepage soil to be sampled Soils of swamps, seepages and spring areas

Elements sought are relatively semi mobile metals (Cu, Zn)

Area in which water is difficult to sampled

Composition of soil is not affected by the presence of water

C. Choice of Stream Sediments to be sampled Semi mobile and immobile elements are best suited

There is a possibility of having Hydro geochemical anomaly present in stream sediment due to the contact between water and sediment anomaly.

Data on the dispersion of semi-mobile and immobile elements in the sediment anomalies will also complement the data on the mobile elements from the water anomalies.

D. Choice of Heavy minerals to be sampled. Heavy mineral surveys are restricted to immobile elements.

Heavy mineral pattern often have the advantage of giving a longer dispersion train than that obtained by chemical analysis of sediment samples.

Heavy minerals may be analysed either by Chemical or Mineralogical examinations.

Based on ability to identify the diagnostic constituent.

E. Choice of Organic Sediment to be sampled Preferred sampling medium in drained area with sparse inorganic sediment and abundant

organic matter

Most applicable for Mobile and semi mobile Cu, Zn, Ni, Co, and Mo

These are adsorbed and incorporated into the partly decayed organic matter.

F. Choice of Lake sediment and Water These media is chosen in regions where abundant lakes and scares streams.

Sediments collected from centre part of the lake.

Lake water also very useful because anomalies are stronger and more easily detected

SAMPLE LAYOUT

Main objective of sample lay outing in GDS are

To maximize the probability of detecting any economic ore body in the surveyed area and to minimize the cost and time.

Main bases for deciding sample spacing are

Contrast and Down drainage decay pattern determined in orientation survey.

One ore body is indicated by two distinct anomalous samples.

Sample spacing determined in terms of Drainage area/Stream lengths which is determined in terms of orientation data.

Alternative methodIn this method Statistically determined variability used to estimate the best sample spacing Degeofffry et al.He uses spring water survey

Mean Zn content in spring water samples.

Sample layout in Ground water pattern

Drainage channel pattern

Ground water patternSample layout in ground water survey depend

1.Diamensions of pattern2.Distribution of wells, springs, seepages

If samples densely distributed survey run by systematic cross country traversing to collect samples at all wells

In some cases preferable to traverse along certain land forms which influenced by ground water

E.g.: Break water slopeImpermeable layeredge of swamp lake

Spring may also sought along geological features such as faults, contact between permeable and impermeable rocks etc.

Drainage Channel PatternsDepends upon The maximum area of drainage basin expected to show an anomaly

This areal considerations must be modified

Especially for water samples effects of drainage length, adsorption and precipitation, depositions

Limited catchment area is 10 km square to 50 km square

For large deposits (porphyry copper) anomalies detectable tens of kilometre.

For Mettallogenic provinces samples spacing may be of 25 km square

For lake water sediments a single sample from the centre of the lake considered sufficient

COLLECTION AND PROCESSING OF SAMPLES

The falsification of field observations are very important problem in GDS

There is a tendency for samplers to collect all samples from one single point

In order to overcome this problem the sampler’s leave a mark of some kind either at every site

These may then be spot checked b the supervisor at later date

A.WATERPolyethylene or other types of plastic bottles are used to collect water samples

They have high durability, Light weight, Less contaminated and less evaporating

Stream water samples should be collected from an active flow of water by rinsing the bottle in to the water several times.

The bottle should be cleaned by acid and distilled water.

Bottles used for storing chemical reagents are not allow to collect water samples

If the water contain particulate matter, Filtering of the sample is necessary.(Micro pore filters)

Pressure filtration also practices (a hand pump, a small tank of compressed nitrogen or argon)Filtration using filter paper removers all suspended particles but allows the colloidal particles and there is a chance of contamination during filtration.

Precipitation of Fe oxides, Organic materials and other materials by oxidation is an important problem in collection of water samples

Loss of CO2, growth of algae or bacteria, Other reactions to remove metal from the solution are also serious issues

Acidification of solution with a metal free acid to about pH 2 can prevent the precipitation of Fe-oxides

The addition of a few millilitres of Chloroform to water sample will inhibit the organic activity

Collection of deep water from lake or open well is not similar to collection of running water. It needs special equipment's. An empty polyethylene bottle fitted with friction stopper. Bottle weighed and lowered to the desired depth and sample collected by pulling the stopper.

Collection of water from a pumped well is difficult. There is a chance of contamination, precipitation, adsorption or any other reaction can take place at either pipe, pump or tank.

AnalysisElectrical conductivity, PH, Alkalinity and dissolved oxygen(Eh) are measured from the sampling site itself with using simple meters.

Analysis of water directly at the collection site is possible for number of elements.SO4, Mo, Zn and undifferentiated heavy metals.Cu, Pb when present at a concentration exceeding 10 ppb

Advantages of analysis of samples at the site itself 1.to avoid change of composition by contamination and precipitation 2.cost for shipping storing samples are avoid

Disadvantages are 1.only used for ionic compounds2.less precise 3.time consuming

B. Stream and seepage sedimentsStream and seepage sediments are not uniform everywhere

Size of sorting, composition, organic content and precipitation rate etc. are different

In order to obtain a sediment sample we need to collect small amounts of fine sediments at three to six times along a 10-15 meter stream bed and composite in a single container

At every point need care to avoid samples of collapsed bank materials along with the sample.Non contaminated scoops and towels are used to collect samples and no separate tools for stream and seepage sediments

If the sediment is fine about 10-50 g of sediment enough to collect because less than a gram of sediment is required for chemical procedure

If the sediment is coarse grained about 200 g of sediment should be collectedWet sieving is helpful to reducing fine samples from the large samples.

C. Lake sedimentsThree major types of sampling devices used in lake sampling are Augers, Cores and Dredges

In shallow water a conventional soil or peat auger may be used

For deeper water a simple type of coring sampler is suitable

Dredges scrape sample from the surface layer and thereby tend to accumulate Mn nodules and other surficial material that may not be the representative of the sediment

The corer sample is most satisfactory because it is more representative and homogeneousSamples were stored in paper envelopes in dried condition in the air or oven

D. Heavy MineralsHeavy minerals occur in greatest abundance near the base of a sequence of alluvial sediments usually just above the surface of bed rock

Samples are collected by simply digging pits or sinking holes with augers or post-hole diggers.

The heavy minerals may be separated from the filed by panning or shipped to the laboratory

PREPARATION OF MAPS

Complexity of information must be presented on a drainage map

Computer methods are used to recording data, producing maps and examine the characters of the subsets.

Drainage survey maps represents factual data's or interpretations.

During interpretation a set of maps showing only one element or one type of information are used.

At later stage of report preparation several type of data may be combined on a one map.

Different types of symbols and scales are used for water and sediment analysis

Direction of flow of water indicated by arrows.

Different symbols may be used to distinguish between different types of samples on a same sample

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

Geochemical map showing the distribution of Uranium and zircon.Source : Google.

INTERPRETATION OF DATA

The approach of Interpretation is common to all kind of geochemical anomalies.

To determine background fluctuation which is not only depend upon bedrock geology and sample type but also the changes in environment such as PH, Bulk composition, organic composition and Fe- Mn oxides in sediments.

Distinguishing between significant and non significant anomalies is difficult task in interpretation.

Every anomalies should be carefully examined.

After examination it may either selected as an indicator of ore or dismissed because of natural accumulation of metal unrelated to ore, or errors in techniques.

First reanalyse every critical samples against filed descriptions.

Available maps and Ariel photos should be examined with a view of possibility of contamination and of correlation of anomalies with recorded topographic and geologic features.

In many cases it may be necessary to revisit the sample site before decide weather an anomaly significant or not.

Intensity of drainage anomaly should be examined

It is the amount of material leached or eroded from the catchment area minus what has been precipitated from ground water below the surface.

A strong anomaly therefore1.A very large area of low grade mineralization.2.Swarms of very small deposits of high grade metalliferous materials3.Small deposits of weakly mineralized but highly fractured rock that asses to leaching 4.one or more large deposits of ore grade.

FOLLOW UP TECHNIQUES

Follow up techniques of GDS is mostly depends upon local conditions.

Detailed sampling is aimed to determine the essential quality of the water patterns by detailed geological and geophysical examinations along with detailed geochemical soil surveys.

The area of maximum interest may be find out by the careful study of the ground water pattern in relation with local topography and factors of subsurface drainage.

CONCLUSION

Geochemical drainage survey is the commonly used technique for Exploration of ore bodies.

There are some systematic methods and steps are available for practicing GDS

Orientation survey is the first step in GDS and it is the preparation take for GDS. Selection of sampling medium, Collection and its analysis are predetermined in this step. Also take care about the contamination of sampling.

There are lot of sampling mediums are available. But GDS practices step of Choice of medium which is strongest and most reliable to the aim of work.

To maximize the probability of getting ore body in the surveyed area and reduce the cost and time of survey GDS practices Sample Layout techniques.

The Collection and processing techniques for different types of samples are different.

In order to present a large collected data in simple way and make the workers more easier GDS practice to make maps of survey.

For understand the fluctuation, amount and intensities of the anomalies every anomalies should be reanalyzed in Interpretation part.

Detailed geological and geophysical sampling is carried out in Follow up techniques.

Thanks for your kind attention …