CHEPTER III
Geophysical Techniques of mineral Exploration
By
G.P. Mathur, Geophysicist.
Geophysics as a science is more than three centuries old, but as an
exploration tool it is munch younger, although not as recent a development
as most people believe.
The word, geophysics' means the physics or nature of the earth. It embraces
the study of the earth, which evolves investigation of the materials and
transformation, and their changes in energy states ; it involves speculation
on the origin and age of the earth, as well as studies of its present appearance
and its reaction of forces, external and internal, acting upon it. some of the
knowledge thus gained, especially from these studies, when applied to the
search for mineral deposits become the art of geophysical exploration.
The exploration may be defined main as prospecting for mineral deposits
and geologic structure by surface measurement of physical quantities. The
methods used in geophysical quantities. The methods used in of physical
exploration are the techniques of geophysical exploration are the techniques
of exact science, but the interpretation, or translation of the observations thus
made into terms of geology and mineralogy is an art in which the
knowledge, the experience and the ability of the geophysicist are fully as
important as the physical properties he measure .
Application of geophysical methods:Though, the mineral resources are bountiful but they are always irregularly
distributed within the earth's crust. These mineral deposits and the host rocks
in which they occur have very often different physical properties.
This difference in physical property when detectable through instruments at
the surface forms the the basic of geophysical exploration techniques.
The main geophysical methods that are employed in the search of minerals
are listed in the following tables:S.No. Geophysical method
Physical property
1
Specific
Gravitational
geologic application
gravity Anticlinal structures,
contrast.
buried
ridges,
salt
domes,
faults,
intrusions.
major
structural trends
2
Magnetic
Magnetic
Anticlinal
susceptibility
burried
structure,
ridges,
instruction, faults iron
ore,
phyrrhotite,
associated
sulphide
ores, gold placers
3
Electrical
Natural
(a) Self potential
field
potential Sulphide ore bodies
flow of underground
water
b
Resistively
Conductivity or its sulphide ore bodies,
converse
bed
rock
resistively
ground water, Engg.
geology
depth,
problems,
etc.
c
Electromagnetic
Inductance
Conductive
ore
bodies sulphide ore
Disseminated
metallic ores
d
Induced polarization
Changeability
Disseminated
metallic
4(a)
Seismic (a) Refraction
Acrostic
Salt
Domes,
Impedance
anticlines, structures,
faults foundation and
highway
problems,
etc.
(b)
Refraction
Do
Low dip Structure,
buried rides faults.
5
Radioactive
Radioactive
Radioactive
ores,
well- logging
Metallic- minerals
The Metallic minerals are about 1000- fold more Conductive than the rock
of their environment. Also the metallic sulphides have 30% to 100% more
specific gravity and if these are associated with magnetic mineral like the
magnetite and pyrrhotite they have much higher magnetic susceptibility
compared to that host rocks. Thus, the metallic deposits are normally
distinguishable physically from the Precambrian rock topes in which they
occur by means of one or more of the following physical properties:1.
Electrical properties mainly conductivity contrast,
2.
Magnetic susceptibility, and
3.
Specific gravity
Non- Metallic Minerals
The Conventional geophysical methods comprising gravitation, magnetic,
seismic, electrical and radiometric have been already helpful; in discovering
important deposits of asbestos in Quebee & johns Manville in Canada the
phosphate deposits of Pennsylvania, and the coal seam in Australia to name
a few. However, the geophysical methods have been mostly useful as an
indirect in locating methods in locating the non- metallic minerals, since the
physical property contracts between these minerals and the host rocks is not
large. The following table shows the applicability of geophysical method for
non metallic minerals.
Table-2
S.No. Mineral
Geophysical parameter
Applicability
1
Electrical conductivity
Mica
Mica
Zones
in
pegmatite affected by
Post ore tectonics are
indicated by apparent
resistively zone due
to presence of ground
water.
2
Quartzand
felspar piezoelectric effect.
nepheline
Direct detection of
piezoelectric zones.
bearing rocks.
3
Asbestos
Magnetic
Chrysotile asbestos is
associate
magnetite
with
resulting
from
the
serpentinisation
of
ultra basic rocks.
4
Barite
and Mercury vapour
fluorite
High
mercury
anomalies over barite
and fluorite deposit
occurring
in
sedimentary
or
in
slightly
metamorphosed
rocks.
5
Barite
Gravitational
Direct application.
6
Rock Phosphate
Radioactive
Rock
Phosphate
deposits
associated
with uranium.
7
Coal
Gravity, electrical
Though
deciphering
suitable structure.
8
Graphite
Electrical S.P.
Direct application
The geophysical exploration techniques are if added use in the areas which
are covered by sand and solid. Over 7307% areas of Rajasthan is covered,
the remaining area being exposed by rock of pre-Cambrian age (19.6% area)
, Maspzoic (4%), Tertiary (1.3%), and by volcanic eruptives & batholiths
(1.3%). this means that the geophysical surveys have greater role to play in
the search for minerals in Rajasthan.
CHEPTER v
Nature of phosphate Mineralisation and Behaviour of Phosphorite ore
Bodies at Jhamarkota, Udaipur District, Rajasthan
By
-S.B.L. Srivastava, Director, Mines and Geology Deptt., Udaipur
Jamrkotara rock phosphate deposit is unique in its mode of occurrence of
phosphorite
which
is
confined
to
the
orange-sedimentary
called
stromatolites. The nature of mineralization is therefore controlled by the
density of stromatolites, deformation and leaching resulting in grade
variations. The algal phosphotic stromatolites are confined to the calcareous
deformation and farcies (diplomatic limestone) or rocks overlying basal
quantize and occurs in three distinct forms i.e. columnar and brecciated and
stratiform. of these columnar and braccaited forms are most common in this
area while startiform. of these columnar and brecciated forms are most
common in this area while start form type is confined to H and 1 block only.
The dolomitic limestone enclosing the phosphorite bed is generally fine
grained hard compact grey, massive or, cherty ferruginous and solidified
Towards the footwall side the dolomitic limestone is siliceous and
ferruginous while on siliceous or fine grained greyish .
The phosphatic stomatolites occur as layered branched or underbranced
columns in which laminae are well developed. The ore is in general bluish
grey to dark grey in colour which on account of its characteristic lithology,
appearance and continuity constitutes stratigraphic and structural market
bed. The ore body shows considerable variation in shape, size width and
depth persistence in different parts of the area. it is roughly horse-shoeshaped and extends for a strike length of about 16 km with an average with
of 15 mt. In the western sector comprising A,A (extension) I and J blocks
the general trend of ore body is N-S to NNE-SSW dipping due east with
moderate to dipp. The body show stratirfoms or laminated from in I block,
brecciated s. The ore body show stratirfom or laminated from in A block,
brecciated form in J, northern part of A,A (extn.) block and columnar in A
block. There is gradual increase in width from 4 mts. in J block to 15 Mts.
(average width) in the A block. But the grade on the whole falls as one
proceeds from north to south. In the central sector Comprising B,C,D,E and
F block the stormatolitic phosphate is columnar in most part of the central
part of block B,D,E and F mostly brecciated, deformed, fragmental and
friable ore has been found to occur. The grade of phosphorite is usually high
(+30%P2O5) in D,E, and F block and central part of B block, whereas it is of
medium grade (12-25% P2O5) in the west of B and C block. The ore body
shows decrease in width from west to east, the verge width of 30 meters in B
block decreases to 7-10 meters in E and F block. The trend of phosphorite in
this sector os E-W to NNW- SSE with low to moderate to dips (25-60) due
north.
In the eastern sector where G and H blocks are located the general nature of
phosphate ate body is patchy & discontinuous and exhibit number of bands
with considerable varrition in shape, size width and grade It is stratiform in
H block while columnar and brecciated in G blocks. The southern part of G
block contains high grade (+30%P2O5) from 15 to 22% P2O5 In block K
(near base camp) where is Considerable Varrition in attitude and width of
the ore body (Wirth Varying from 1 to 50 mt.) with an average grade of 23%
P2O5 the stromatolites are columnar thus it will be seen that phosphatic
stromatolites occur in various physical forms like massive, compact with
well developed stromatolites (as in block A,B,C,G & K) and brecciated
fragments, deformed, crushed and pulverized as in parts of A extn.
B,D,E,F&G block (Where stromatolitic columns are beyond the limit of
recognition ) and stratifoms in H and 1 block. The grade of the ore density of
their compaction by deformation usually massive, compaction by
deformation and leaching of their of non-phosphatic constituents usually
massive, compact, columnar, stromatolites, show low values of P2O5 while
brecciated loosed and powdery from contains high P2O5 content. The
microstructure of stromtotic columns show laminae of phoshatic and
carbonate material varying considerably in their relative properties
ultimately determining the grade. The intercolumnar space is practically free
of phosphate. A general P2O5 os associated with high silica and low
carbonates while low P2O5 is associated with low silica and high carbonates.
..
CHAPTER
.~ . XII
A preliminary Beneficiation Study on Kyanite From Khemli,
BY
B. C. Bhattacharya, Ceramic Technologist
Introduction:-Kyanite-Sillimanite are naturally occurring alumino silicate ahd owing
to their valuable properties asrefractorines's at high temperature i. e. above 1450"Cin
metaf-' lurgical and ceramic industry, th~ir"importat.te has rapidly increased with the
qrowtti'of indus;.try. The I chemical composition of' kyanitesillimanite equivalent to the
theoriticatformula of AI2O:i' Si02 ,is 62.93% AI20s (Alumina) and 37.07% Si02. the
higher percentage of AI20s in certain cases is due to presence of corundum.
The grade of rock containing kyanite, sillimanite is variable and a ,decision as to
whether a depositcah beworked'e'conomically wdu1d depend upon such other factors' as
the actual nature"'and quality of the mineral: the
natUre and amoUnt of the gangue.
I
Low grade kyanite sample from KhemliBisanV\ias area of tJdaipur lDistt. wasbeneficiated to obtain a 'high grade kyanite concentratefor the producl1on ,of high '
alumina're- , fractories. In tnis;im1estigation an exhaustive study on beneficiation 'Of low
grade kyanite mineral was' made.
Geological Investigation:-Starting from Kotri-Chandesra to Debari in the eastern
zone of. Udaipur Distt., the geological formation
encountered include migmatised granite, quartz sericite schist, sericite-pyrophyllite mica
schi-st, quartz-kyanite rock etc. These are
intruded by vein quartz, pegmatites, and amphibolites at places altered to chlorite..
biotite-quartz rock. Kyanite-quartz-pyrophyllite.!sericite 'rock occurs' as hard;massi.ve,
bluish"white, 1ightbrowrr in 'colour along hanging wall of pyrophyllite zones.. The
samples were drawn from kyanite bearing rock which
assayed '17%: to 49% At.2Os and 44% to 75% S~O 2' Best quality
kyahitemrneralizati'on oec'urs in ~the area lying about 1.5 'Kms. east
of eisanW8S1 ;!,
P",
I 0 ""
'1,,
,II ".,
Minerographic Characteristics :-Petrographie studies of various spot samples of
kyanite quartz. rock were carried out and it r~veaLedl . that quartz and pyrophyllite are
abundent mineral- in .the rock and it consists of white anhedral irregular grains
compressedly arranged. Kyanite occurs as broad elongated' plates with tabular
cleavages. The relief is very high. "f.he moderate. bire fringence and interfe{ence colour
range upto
first order red. Extinction angle varies from
1'8°.30". Pyrophyllite is associated with kvanite intricately. It occurs as thin tabular or
flaky crushed distorted crystals having straight extinction. The kyanite content in most of
the samples has been found to be
around 30..40%, pyrophyllite-sericite near
about, 40% and quartz 20%.
~;
.
("
I'
"I,
Reserves & Grade :- The investigations
carried out for kyanite sillimanite were primarily aimed to make preliminary
appraisal of
the deposit. The reserves have bee computed on the basis of preliminary study on
regional basis taking into consideration, the measured length of kyanite - sillimanite
bearing lenses and taking their average width as 2 metres. The Sp. gravity of kyanite
schist was deter. mined and found that it was around 3. A total reserve of about 0.54
million tonnes of kyanite has thus been computed under inferred
category, considering about 30% AI20a on
an average.
Specification of Kyanite :-Specifications for kyanite used for different industries are
different. It is used in metallurgical, glass, ceramics, chemical, electrical and cement
industries. Kyanite refractories are
particularly used in the furnaces for melting nonferrous metals such as copper, zinc,
nickle alloys and bronze. Presence of corundum, diaspore and pyrophyllite is sometimes
considered useful. The kyanite required for glass and electrical porcelain industries
should no tcontain more than 0.2% of Fe 20s' For use as refactory materials a hard,
tough grog of low porosity value as much as possible is required.
Experimental :-A representative sample was prepared after Cfushing to -10 mesh
size BSS i. e. 1680 microns by jaw crusher and roll crusher respectively. A
representative
.
sample was.. drawn and a part of it7was subject
ed to chemical cmalysis and the other to
petrological study. The sieve analysis was conducted on 1680 microns fraction of the
sample which is tabulated in table No.2. It is observed that the liberation of kyanite
from
gangue was between -22 to + 100 mesh i. e. -1680 microns to 150 microns. For all
experi
mental purpose the sample ground to pass 355
microns and retained
on 150 microns
was taken.
44
Scrubbing :-It was observed that by scrubbing with 0.1 % NaOH solution, about 2030% material could be removed as fines
which analysed Si02-61.9%, AI ~Os -31.30%, Fe20s-1.64%, Ti02-O.73% and LOI3.42%.
The remaining 70-75% material was mainly' kyanite and quartz, and scrubbed material
was 95% pyrophyllite and sericite, which were confirmed by petrological study.
Tabling :-Attempts were made to obtain a concentrate Qf kyanite by tabling of35+65 mesh ISS of kyanite. A concentrate of kyanite could be obtained ana lysing
47.58% Si02, 42.07% AI2Os. 0.48% Fe2Os' 0.31% Ti02, 0.56% CaO, 0.20% MgO with
41% weight
recovery and tailing analysed 60.60% Si02, 36.01 % AI::Os' li.48% Fe203, 0.32% Ti02, 0.58%
CaO and 0.20% MgO with weight
recovery of 59%. As the tabling did not give
satisfactory results flotation experiments were carried out to obtain a Kyanite
concentrate.
Floatation :--The entire-170 mesh ISS. i. e. 1680 microns sample was scrubbed
with 0.1 % NaOH solution and the remaining 7075% material was subjected to floatation.
Attempts were made to float pyrophyllite using
different reagents in different quantities and maintaining different conditions of
floatations. It was observ,ed that by using amino-acid
acetate (cataionic activator Armac-12D), almost entire quantity of the feed was floated.
Petroleum sulphonate (Aero-promoter 825) was not effective to float pyrophyllite.
Floatation characteristics of pyrophyllite as well
as kyanite were found to be more or less on same line and therefore, strict control of
con
ditions like quantity of collectors, pH, slurry density etc. was absolutely necessary to
have selective floatation. For this purpose combina
tion of Armac 12 D and aeropromoter 825 was used. Number of experiments to
determine
he .pf)tiID~m 'TSJPo- -of these two collectors Nere undertaken and it was observed that
f : 0.3 of Armac 12 D and- aeropromoter 825
3tio was most effective for pyrQphyHite fJoatation.
Tile sink maiJlly contained quartz and kyanite. .Attempts to float kyanite and depress quartz were made. Series of experiments for separating.kyanite from quartz in
different floatation conditions were undertaken. Th e
best results so far were obtained by hot conditioning the sink with quebrecho at 90°C and
using oleic acid to collect kyanite at pH-9. A very minor quantity of quartz and seric ite
was floated along with kyanite.
At least fifteen experiments were carried
out to obtain kyanite concentrate maint~ining
'differen~ fleatation conditions. The best resu It so far obtained in an experiment which is
described below. The reproducibility of this experiment was also examined:
Experiments:
1 A Floatation ( For pyrophyllite )
Floatation cell. Feed.
200 gms.
(350-350micron to 1'50 micron
mesh, 95% dry
ground sample200a gfT'l5-. 33%
8..5.to 9
Armac 12D' 0.80 KI T. Aero
promoter 8250.25 KIT.
Na2 COs-0.25 KIT.
6- Minutes.
5 minutes.
SJY!f'l gensity. B~I
Reagents added.
eondittonittg-timeFloatation time.
45
1. B Flotation ( For kyanite)
Floatatlon,ceU. Feed.
Slurry dtmsity. pH.
Reagents added
500 gms.
T~ilings of 1 A 31 %
9
oleic acid1. 5Kt T. Quebrch01.5K/T. Na2COS to main
tain pH..9 at-90~C for 5
Hot conditioning.
minutes.
Floatation time. 5 minutes.
Float of 1. B was cleaned twice.
RESULTS OF PRODUCT
Product. Assay. Distribution
-- -Wt-% Si03% AI20s % SiO~% AI_~O 3%
1. FloatPy. 59.557.52 35.03 58.04 59.37
2. Float Ky. 20
38.40 58.68
13.02 3'3".43'"
3. Tailings. 20.5 83.22 12.31 28.93
7.19
...... ""-'-"
.°. KIT-kg per tonee
Conclusion:
Kyanite concentrate obtained analysed from 52.84 to 58.68% AI20s wIt'" weight
recoveries varying from 10 to 20% and AI "Os recoveries from f8:3~ ro- 3~3-4.g%. The- best results were obtained in the experiment were tJie concentrate analysed Si02
38.40}v AI20s
58.68,%, TiG"2 0.98~"JFe 20S 0.71 , CaO 0.28% MgQ 020% and LOI 1.04% with 20%
weight and 33;439/(> AI2Oa' reo€>veries. This Proauet'
is'quite-suitable for high alumina refhlctbr;~s~ A composite sample-prepared by mixing
various
concentrate fractions obtained has been sen1 to CG&CRI Calcutta for determining its
proper
ties suitability for the production oft hiJ? alumina refractories' The pyrophyllite
reC0vere as by product is a'f50'of quite good and cal also be marketed