24 CHAPTER – I INTRODUCTION “Kimberlites constitutes a rare, highly alkaline volatile rich rock type that has in many ways attracted more attention than its relative volume might suggest that it deserves. This is largely because it serves as a carrier of diamonds and garnet peridotites mantle xenoliths to the Earth‟s surface. Further more, its probable derivation from depths greater than any other igneous rock type and the extreme magma compositions that it reflects in terms of low SiO2 contents and high levels of incompatible trace element enrichment , make an understanding of kimberlite petrogenesis important ------ Le Roex et al ( 2003). Kimberlites along with the lamproites constitute, a fascinating group of mantle derived rocks and are products of intraplate alkaline magmatism. These ultramafic (and ultrabasic) rocks marked by mineralogical diversity and geochemical variability, assume significance because of their rarity in space and time. Though volumetrically insignificant and occur as small bodies in the continental cratonic interiors (with exceptions to lamproites of Argyle occur in mobile belts) they continue to garner utmost attention owing to their pre-eminent position as the primary source rocks for diamond on the surface of the earth. The present work relates to the identified kimberlite pipes from Kalyandurg and Timmasamudram areas in Anantapur district, Andhra Pradesh and assumes significance as it forms a part of the historically well known diamond belt in Southern India. I.1 Definition of Kimberlite: The term kimberlite was first used by Lewis (1887) to describe the host rock of diamond at the type locality, Kimberley in South Africa. Owing to the great diversity in terms of their textural, mineralogical, petrographic and geochemical characteristics, diverse definitions and classifications for Kimberlites were proposed, resulting in a great dispute on every front. Every term proposed for the kimberlites was greeted with hostility and contested with equal verve, and issue could not be resolved satisfactorily until proposed and subsequently modified by Mitchell (1979; 1986). Mitchel
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24
CHAPTER – I
INTRODUCTION
“Kimberlites constitutes a rare, highly alkaline volatile rich rock type that
has in many ways attracted more attention than its relative volume might
suggest that it deserves. This is largely because it serves as a carrier of
diamonds and garnet peridotites mantle xenoliths to the Earth‟s surface. Further
more, its probable derivation from depths greater than any other igneous rock
type and the extreme magma compositions that it reflects in terms of low SiO2
contents and high levels of incompatible trace element enrichment , make an
understanding of kimberlite petrogenesis important ------ Le Roex et al ( 2003).
Kimberlites along with the lamproites constitute, a fascinating group of
mantle derived rocks and are products of intraplate alkaline magmatism. These
ultramafic (and ultrabasic) rocks marked by mineralogical diversity and
geochemical variability, assume significance because of their rarity in space and
time. Though volumetrically insignificant and occur as small bodies in the
continental cratonic interiors (with exceptions to lamproites of Argyle occur in
mobile belts) they continue to garner utmost attention owing to their pre-eminent
position as the primary source rocks for diamond on the surface of the earth.
The present work relates to the identified kimberlite pipes from Kalyandurg
and Timmasamudram areas in Anantapur district, Andhra Pradesh and
assumes significance as it forms a part of the historically well known diamond
belt in Southern India.
I.1 Definition of Kimberlite:
The term kimberlite was first used by Lewis (1887) to describe the host
rock of diamond at the type locality, Kimberley in South Africa.
Owing to the great diversity in terms of their textural, mineralogical,
petrographic and geochemical characteristics, diverse definitions and
classifications for Kimberlites were proposed, resulting in a great dispute on
every front. Every term proposed for the kimberlites was greeted with hostility
and contested with equal verve, and issue could not be resolved satisfactorily
until proposed and subsequently modified by Mitchell (1979; 1986). Mitchel
25
attempted at introducing the concept of a kimberlite clan encompassing the
whole spectrum of the kimberlitic rocks including kimberlite-hosted macrocryst /
megacryst suites.
In simple terms, Kimberlites , constitute a hybrid group of rocks that
encompass a group of volatile rich (dominantly CO2) potassic, ultrabasic rocks
and that displays a pronounced inequigranular texture, resulting from the
presence of macrocrysts (and/or megacrysts) that are set in a fine grained
matrix.
It took nearly a century for gaining clarity as to what exactly should be the
definition of kimberlite - when Mitchel (1986) attemped to cover the whole
spectrum or related rocks. In general, the megacryst / macrocryst assemblage of
clinopyroxene (chrome diopside) and orthopyroxene (enstatite) set in a matrix
consisting of euhedral micro-phenocrysts of olivine, phlogopite together with
calcite, serpentine, clinopyroxene, monticellite, apatite, spinel, perovskite and
ilmenite. The macrocrysts may be xenocrysts (disaggregated constituents mantle
rocks like lherzolite, harzburgite or eclogite) and / or parts of megacrysts/cognate
xenoliths (disaggregated cumulates). They are distinctly encriched in CaO, H2O
and CO2 and poorer K2O and SiO2 in comparision to the other group.
The Group –II kimberlites (ca. Micaceous kimberlites of Wagner 1914),
although texturally similar to Group-I kimberlites, are characterised by the
presence of abundant phlogopite as macrocrysts, phenocrysts and in the
groundmass (showing composition range from phlogopite to tetraferriphlogopite),
31
rounded olivine megacrysts and highly magnesian olivine (Fo 91-93 mol%)
phenocrysts, groundmass diopside, spinels of magnesiochromite to
titanomagnetite composition, Sr- and REE rich perovskite Sr-rich apatite, Mn-rich
ilmenite, monticellite and magnesian ulvospinel and Ba-rich phlogopite are
conspicuously absent. Group-II or micaceous (phlogopite) kimberlites are richer
in K2O and isotopically similar to potassic volcanic rocks in continental settings.
While the Group-I kimberlites are found through out the world, the Group-II
kimberlites are found in found only in South Africa (Skinner, 1989).
In view of the petrological, geochemical characteristics of the Group-II kimberlites
are distinctly different from the Group-I. Mitchell (1994, 1995) proposed that the
Group-I kimberlites alone considered as kimberlites. He also revived the term
“Orangites” of Wagner (1928) to designate the Group-II kimberlites of Smith
(1983) and Smith et al (1985) and also suggested that the term Group-II
kimberlites be scrapped. The I.U.G.S. Sub-commission on the systematic of
Igneous Rocks, however, has not sanctioned the term “Orangite” and still retains
the two-fold classification of kimberlites into Group-I and Group-II (Woolley et al,
1996) and also endorsed the mineralogical – genetic classification of kimberlites
and lamproites (Wolley et al 1996).
Morphology and Facies Concept:
Kimberlites are the small volume igneous rocks of limited aerial extent. Based on
the studies of numerous diamondiferous deposits, 3 distinct units based on their
morphology and petrology. These units are:
1) Crater Facies Kimberlite
2) Diatreme Facies Kimberlite
3) Hypabyssal Facies Kimberlite
The Picture (Fig.I-2) shows the Model of idealized kimberlite magmatic system
illustrating the relationships between the Crater, diatreme and hypabyssal facies
rocks (After Mitchell 1986).
1) Crater Facies Kimberlites:
The surface morphology of un-weathered kimberlite is characterised by a crater,
up to 2 kilometers in diameter, whose floor may be several hundred meters
32
below ground level. The crater is generally deepest in the middle. Around the
crater is a tuff ring which is relatively small, generally less than 30 meters, when
compared to the diameter of the crater. Two main categories of rocks are found
in crater facies kimberlites; pyroclastic, those deposited by eruptive forces; and
epiclastic, which are rocks reworked by water.
A. Pyroclastic Rocks: These rocks are found preserved in tuff rings around the
crater and within the crater. Tuff rings have small height; crater diameter
ratios and are preserved in very few kimberlites. Igwissi Hills in Tanzania and
Kasami in Mali are the pipes with well preserved tuff rings (Dawson, 1995).
Heights range from 1-4 meters on one pipe, and 15-50 meters in one
kimberlite field. Deposits are commonly bedded, vesicular and carbonatised.
Tuff deposits preserved within the crater are also rare; however, the Igwissi
Hill pipes in Tanzania have been examined and revealed three distinct units.
From top to bottom, they are:
1. Well-stratified tuffs –layers defined by lapilli and ash size particles. Graded
bedding and depositional features appear absent. Believed to be products
of air fall and possibly settling through water.
2. Poorly stratified coarse pyroclastics – recognised by deposits of complex
folding and slumping.
3. Basal breccias.
33
NOTE:
DIKES & SILLS
EMPLACED AT
HIGHER LEVELS
THAN THE
ORIGIN OF
DIATREMES
CONCORDANT
TABULAR
PRE-DIATREME
DIKES & SILLS
DISCORDANT
TABULAR
CLASS 1 PIPE
Fig. I-2: Model of an idealized kimberlite system, illustrating the hypabyssal
dyke-sill complexleading to a diatreme and tuff ring explosive crater. From
Mitchell (1986) Kimberlites: Mineralogy, Geochemistry and Petrology. Plenum
Newyork, Winter (2001). An introduction to igneous and Metamorphic Petrology,
Prentice Hall.
B. Epiclastic Rocks – These sediments represent fluvial reworking of
pyroclastic material from the tuff ring in the Crater Lake formed on top of the
diatreme. They are complex and resemble a series of overlapping alluvial
fans mixed in with lacustrine deposits. They coarsen with distance from the
wall rock and become better sorted towards the centre. Fossils may be found
in these sediments. Some epiclastic deposits have been replaced with
chalcedony – evidence for late stage volcanic hot-spring activity.
C. Lavas – no concrete evidence for this.
Few kimberlites exist with well preserved crater facies. It is difficult to develop
a model with any certainty that all kimberlites will confirm to the observed
features above. Crater facies kimberlite is difficult to distinguish from diatreme
facies kimberlite. The most distinguishing feature is visible bedding.
34
2) Diatreme Facies Kimberlite:
Kimberlite diatremes are 1-2 kms deep, generally carrot-shaped bodies which
are circular to elliptical at surface and taper with depth. The dip contact with
the host rocks is usually 800-850. The zone is characterised by fragmented
volcanoclastic kimberlitic material and xenoliths plucked from various levels in
the earth‟s crust during the kimberlites journey to the surface.
Some textural features of Diatreme Facies Kimberlites:
i) Country rock fragments – angular
ii) Cognate fragments (juvenile) – rounded to angular
iii) Country rock xenoliths found 100 meters below depositional unit – it is
clear that sinking occurs in the pipe.
iv) Pelletal lapilli – appear to have formed by the rapid crystallisation of a
volatile poor magma containing phenocrysts. They are characterised by
a crystal nucleus surrounded by micro-phenocrysts which align
themselves tangentially to the central crystal.
v) Nucleated autoliths – similar to pelletal lapilli but lacking microphenocryst
orientation. Kernel grain usually country rock. Magmatic nucleation about
a nucleating center.
vi) Matrix composed almost entirely of fine grained diopside, serpentine and
phlogopite.
vii) Hardly and calcite found in matrix (wheras lots of calcite is found in
hypabyssal matrix). This suggests that the magma has already
degassed.
viii) Crystallisation in diatreme occurs at low temparatures based on the lack
of thermal effects seen in intruded limestones.
ix) Contact metasomatic/metamorphic effects with the country rock are few.
x) Up warping and fractures associated with the intrusive body are absent.
35
Fig. I-3: Photograph of diatreme facies kimberlite core (Mitchell (1986)
These fragments with halos of crystallised kimberlite magma are characteristic of diatreme facies rocks (Fig.I-3).
3) Hypabyssal Facies Kimberlite :
These rocks are formed by the crystallisation of hot, volatile –rich kimberlite
magma. Generally, they lack fragmentation features and appear igneous (Fig.
I-3a).
Fig. I-3a. Photograph of hypabyssal facies kimberlite from Anantapur area.
Some Textural features:
i. Calcite-serpentine segregations in matrix.
ii. Globular segregations of kimberlite in a carbonate –rich matrix.
iii. Rock fragmentation has been metamorphosed or exhibit concentric
zoning.
Inequigranular texture creates a pseudoporphyritic texture.
The general criteria for recognising kimberlite, lamproite and lamprophyre based
on their tectonic setting, texure,mineralogy and geochemical characteristics are
given at Table I.1 (Madhavan V.,2001).
36
Table I.1: General criteria for recognizing kimberlite, lamproite and lamprophyre( Madhavan, 2001 )
Kimberlite Lamproite Lamprophyre
Form Pipe, sill, dyke; diatremes tend to be carrot shaped
Pipe, sill, dyke, cinder cone; olivine lamproite diatremes are funnel or sherbet-glass shaped
Dyke, sill, plug, stock, sheet, diatremes or sub-volcanic vent.
Tectonic setting
Associated with intra plate magmatism (confined to craton interiors)
Associated with intra plate magmatism (confined to craton margins)
Associated with intraplate, divergent, convergent and passive-margin magmatism.
Texture Inequigranular with two generations of olivine and phlogopite (macrocrysts and micro-phenocrysts or groundmass). These rocks cannot be identified mainly on petrographic basis.
Inequigranular with two generations olivine and phlogopite. Like kimberlite, lamproite also cannot be identified on petrographic investigations alone.
Inequigranular with porphyritic-panidiomorphic with euhedral phenocrysts of mafic minerals. Felsic minerals are strictly confined to groundmass
Undersaturated ultrabasic rocks with low Al2O3 (<5%) and Na2O/K2O<0.5 Group-II kimberlites have many geochemical similarities with lamproite than with Group-I kimberlites. Kimberlites in general contaIn high Cr, Ni and LREE.
High K2O, TiO2, P2O5 and low Cao, FeO. Highest K2O/Na2O>3 (ultrapotassic), K2O/Al2O3 > 1 (perpotassic) and Na2O+K2O/Al2O3~1 (agpaitic-peralkaline), Highly enriched in Rb, Sr, Zr, Ba and REE.
Highly variable because of wide compositional variations. The order of LREE enrichment and slope of chondrite normalized pattern is less in lamprophyre than in lamproite.
(Source: V.Madhavan /Journal of Asian Earth Sciences 19 (2001) 321-332)
37
I.4 Kimberlites of world and India: a glance ii
For the first time, kimberlites were identified in their type locality in the Kimberley
region of South Africa by Lewis in 1887 and later in 1914, Wagner provided a
comprehensive petrographic description of kimberlites, in his monograph entitled
„ the diamond fields of South Africa” and around 1932 Williams gave an updated
imformation of the petrography of kimberlites. It can be stated that these earliest
reports are most invaluable and were the forerunners for the subsequent research
work carried out on kimberlites in the world. The identification of new kimberlite
occurrences in several areas has catapulted the significance of kimberlites around
1950‟s and resulted in a flood of information in the literature with reference to
their geology, petrography and geochemistry. Several aspects of kimberlites were
being looked into by pioneering workers who gave prominence to the distribution
of kimberlites of economic importance (Clifford 1966, Janse 1985), the structural
and tectonic controls of their emplacement (Arsenyev 1962, Marsh 1973, Bailey
1964, 1974, Pretorious 1973, Sharp 1974, Crough et al 1980, Haggerty 1982,
Taylor 1984, Helmstaedt and Gurney 1984) and their mineralogy, geochemistry
and Petrology (Mitchell 1986). For the first time an account of the different facies
(Crater, diatreme and hypabyssal or root zone) of kimberlite magmatism has been
provided by Hawthorne (1975). The publication of Nixon ( 1973 ) entitled “
Lesotho Kimberlites”, a compilation of the papers, the proceeding volumes of the
successive international kimberlite conferences starting from the first one held in
1973 in Cape Town, South Africa to the recent one held in India ( 2012) have
contributed a lot to the modern understanding toeh kimberlite geology.
The research work carried out on the kimberlites during 1970 – 1985
mainly focused on petrographic, mineralogical and geochemical characterisation
of kimberlites and their xenoliths (Mitchell 1979, Skinner & Clement 1979,
Clement et al 1984). Mitchell (1986) provided a detailed compilation of these
studies and Dawson (1980) and Nixon (1987) have given a detailed account of
the mantle xenoliths in kimberlites. During the 1980‟s and 1990‟s major thrust of
the research work on kimberlites was on petrogenetic aspects including the
nature of source, depth of magma, generation, contamination and ascent of the
magma based on mineralogical and petrochemical (including REE and Isotopic)
38
characterization of the kimberlites and related rocks . Most important conclusion
of these studies are:
1. Kimberlites are formed from high temperature magmas, which are products
of very low volume partial melting of metasomatised peridotitic mantle.
2. Existence of kimberlites in different facies viz; crater, diatreme and
hypabyssal.
3. Kimberlite bodies consist of multiple pulses of intrusions.
4. Diamonds in kimberlites are xenocrysts resulting from the disintegration of
their hosts (i.e., peridotite and eclogite) in the mantle (Meyer 1985).
5. The mantle xenoliths suites as denoted by the coexisting mineral phases
indicate the depth of generation of kimberlite magma.
Kuruman, S.Africa; Venezula Disko Bugt: W.Greenland
Lower
Proterozoic
Ca.2000 (Burkina Faso)
The word kimberlite is derived from the town of Kimberley in South Africa. The
African continent still remains the largest supplier of diamonds. The South African
block comprises three major components namely the Kaapvaal craton, the
Zimbabwe craton and the Limpopo mobile belt. The Kaapvaal and Zimbabwe
cratons are welded together by the Limpopo mobile belt to form the Kalhari
archon, which in turn is bordered by the Proterozoic mobile belts, such as the
Orange River belt, the Namaqualand Gneissic Complex, and the granite gneiss
complex of Namibia. The important pipes in south African block include
Bultfontein, Dutoitspan, Jagersfontein, Koffiefontein, De Beers, Kimberley,
Premier, Finsch, Venitia, Letseng La Tera, Kao in Lesotho, Dokolwayo in
Swaziland, Orapa and Jwaneng. The Central African block , which forms another
important kimberlite province, extends from Angola in the south to Cameroon in
the north and Tanzania in the east. Economically viable kimberlites are restricted
to Archaean parts of the Central African craton. The important kimberlites pipes
include Mbuji Maye, Kundulung in Zaire, Catoca in Angola, Mwadui in Tanzania.
The West African block constitutes another important Kimberlite province, which
includes Koidu limberlites in Sierra Leone and Soquinex in Guinea.
44
Russia is endowed with 20 kimberlite field and consists of more than 1000
kimberlite pipes and dykes representing another important kimberlite province.
The kimberlites are emplaced in to the Siberian craton, which comprises of two
Archons viz; the Anabar and the Aldan. The major diamond producing pipes in
this craton are Mir, Internatsionalnaya, 23rd Congress, Udachnaya, Aikhal,
Sytykanskaya, Zarnitsa and Yubileinaya.
Canada, arrival on the kimberlite scenario has been a little late. Though relatively
a latecomer on to the kimberlite map of the world since 1956, has turned out to
the most outstanding province in the world. This country has the largest extent of
cratonic blocks (or) Archons with intervening mobile belts (or) Protons. The most
important Canadian field are within the Slave craton of the Northwest Territories
(NWT) and the Superior craton, which came into prominence by the discovery of
diamondiferous kimberlite from Ponit Lake in the Lac De Gras area of Slave
craton in 1991. After these discoveries more than 600 kimberlites have been
discovered, some of which are of high economic potential. A newcomer (since
1998) as a supplier of gem quality rough diamonds to the world market, Canada is
presently ranking the third most important diamond producer (by value) in the
world.
Australia, with its large cratonic blocks like the Yilgarn and Pilbara
Archons(western Australia) and the Kimberley Archon (northwestern Australia),
contains kimberlites and lamproites. The first three kimberlite pipes were reported,
some of them with good diamond potential. However, the only diamond producing
mine of Australia is the Argyle olivine lamproite mine, which is a major global
contributor of diamonds. This lamproite is located in the Halls Creek Mobile Belt
bordering the eastern margin of the Kimberley Archon, northwestern Australia.
The other areas of kimberlite occurrence in the world include China with two
working mines, the USA with more than 25 kimberlite intrusions, and the
Arkhangelsk province, Ukraine, Belorus, Finland and Sweden with both
diamondiferous and barren kimberlites.
45
I.6 Indian Scenario:
As early as 300 BC , the grandeur of diamonds was introduced to the world by
India. Till the end of the 19th century India enjoyed the monopolous position by
being the exclusive supplier of diamonds to the entire world. Many well-known
diamonds like the Great Moghul (787 ct), the Koh-i-Noor (186 ct), the Pitt/Regent
(41ct), the Nizam (440 ct), the Hope (67 ct), the Orloff, the Darya-i-noor etc.. were
recognized and have been obtained from the mines along the courses of the
Krishna River, ( referred to as the diamond river by Ptolemy) in the state of
Andhra Pradesh, in southern Peninsular India. Since ages India is known its
wealth of most beautiful, famous and large sized diamonds, the existence of the
primary diamond source rocks were identified only in 1930 with the identification
of the Majhgawan pipe (where diamond production started a century back ) as
kimberlite (Sinor 1930) which was later termed as lamproite (Scot Smith 1989).
Subsequently a tuffaceous rock found near Wajrakarur in Andhra Pradesh,
(diamond mining was known since centuries), was recognised as kimberlite (Rao
and Phadtare 1966). These exciting works were the torch bearers that
provided an impetus to the geologists of the country to carry out the exploration
for diamonds in India. It is only with the ardous and sustained efforts by the
personnel of Geological Survey of India and other Government Agencies to locate
kimberlites and lamproites have have resulted in the identification of more than
sixty kimberlite bodies in the Dharwar Craton, five kimberlite bodies in the Bastar
Craton and three kimberlite bodies in the Southern part of the Bundelkhand craton
in recent years. In addition , around sixty lamproite bodies were also reported
from the region close to the eastern margin of the Dharwar Craton (Mitchell and
Bergman, 1991, Reddy et al 2003). The vast Archaean cratonic areas of
Peninsular India are ideal geological milieu for the emplacement of kimberlites. Of
the five ancient Cratons of India viz; Dharwar, Bastar, Singbhum, Bundelkhand
and Aravali, kimberlite emplacements are recorded from three (the Dharwar, the
Bastar and the Bundelkhand ) cratons only. (fig. I-5 & Fig.I- 5.1). It is only at the
Panna diamond belt (Madhya Pradesh) in Bundelkhand craton and the
Wajrakarur area (Andhra Pradesh) in Dharwar craton where diamond – mining
activity was known since a few centuries.
46
The Bundelkhand cratons has the distinction of hosting two kimberlite pipes –
Majhgawan and Hinota – in the Panna district of Madhya Pradesh. The
Majhgawan kimberlite has the distinction of being the sole working mine in India,
accounting for nearly 99% of the Indian diamond production. Sixty years prior to
the discovery of the kimberlites in south Africa, the Majhgawan pipe was
discovered in 1827 in the Bundhelkhand craton. The true identity of the
Majhgawan and the Hinota pipes as kimberlites was established only in the
1970s (Mathur and Singh 1971).
The Bastar craton hosts two kimberlite fields in the state of the Chattisgarh viz;
1. The Mainpur Kimberlite field (4 pipes) in the SE part of the Raipur district, rh
(Newlay, S.K. and Pashine, J.1993) and 2. The Tokapal kimberlite field, Bastar
district. In addition to these two pitpes, diamondiferous kimberlite diatremes are
reported from parts of Orissa adjoining the Mainpur Kimberlite Field and located
close to the contact of the Bastar craton with the Eastern Ghat mobile belt.
Apart from these identified bodies, a few alkaline intrusions occurring in the
Barakar formations in the Damodar Valley Coal fields of Eastern India that form a
part of the Singhbhum Craton. These rocks intrude into the fault bounded
Gondwana rift basin underlain by rocks of the Chotanagpur granite gneiss,
migmatite, granulite complex, These exotic rocks emplaced into Jharia, Raniganj
and Bokaro Coalfields were inititally classified as Lamprophyres/ Mica –
peridotites ( Ghosn, 1949) and later as calc alkaline lamprophyres ( minnettes)
and lamproites ( Middlemost et al., 1988 , Paul, 1991; Rocks et al.,1992 ).
Recently based on the detailed geological, geochemical and petrological studies(
Kent et al., 1998) classified them as Orangeites.
The emplacement of kimberlite / lamproite clusters in different diamond provinces
of India with their age given at Table I-3 & I-4.
47
Fig.I-5: Cratonic areas of India and distribution of kimberlites and lamproites (modified
after Radhakrishna, 1989).
48
Fig. I-5.1: Schematic distribution of Cratons (WDC= Western Dharwar Craton; EDC=Eastern Dharwar Craton), mobile belts (EGMB=Eastern Ghats Mobile Belt; CIMB= Central India Mobile Belt; DMB=Delhi Mobile Belt), rifts (GR=Godavari rift; MR=Mahanadi Rift), and kimberlite-clanintrusives (#) in the India sub-continent. The gravity lineament between Mumbai and Chennai seperates diamond-bearing KCRs to the south (Wajrakarur, B), from “non-diamond bearing” rocks in the north (Narayanpet,C). CB is the Cuddapah Basin, and SGT is the Southern Granulitic Terrane. (B) Distribution of diamond – bearing intrusive in the Wajrakarur Province. (C) Distribution of “non-diamond bearing” intrusive in the Narayanpet Province (Neelakantum,2000) (Source: Haggerty et.al, 2004).
I.7 Empalcement Ages of Kimberlites and Lamproites:
Kimberlites and Lamproites emplaced throughout geological timespan from
middle Proterozoic to Quaternary. The oldest kimberlites are in Venezuela (1700
Ma) and Kuruman-South Africa (1600 Ma) while the youngest emplacement
events recorded from Tanzania, Antarctica are of Quaternary age (50 – 55 Ma).
The ages of global kimberlites emplacement events indicate that not many
49
kimberlites erupted in the later Cenozoic period. However, many lamproites
eruptions like those of Leucite Hills, Smoky Butte in North America, Gaussberg in
Antarctica, Ellandale and Fitzroy Basin inWestern Australia, Murcia – Almeria of
Spain, Sisco in France took place around this time (Mitchell and Bergman, 1991).
Table: I-3: The summary of the emplacement of Kimberlite/Lamproite clusters in different Diamond Provinces of India and their age : S.NO Diamond