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Giant quartz veins (GQVs; earlier referred to as ‘quartz reefs’) occurring in the Archean
Bundelkhand Craton (29, 000 km 2 ) represent a gigantic Precambrian (∼ 2.15 Ga) silica-rich fluid
activity in the central Indian shield. These veins form a striking curvilinear feature with positive
relief having a preferred orientation NE–SW to NNE–SSW in the Bundelkhand Craton. Their out-
crop widths vary from ≤ 1 to 70 m and pervasively extend over tens of kilometers along the strike
over the entire craton. Numerous younger thin quartz veins with somewhat similar orientation cut
across the giant quartz veins. They show imprints of strong brittle to ductile–brittle deformation,
and in places are associated with base metal and gold incidences, and pyrophyllite-diaspore miner-
alization. The geochemistry of giant quartz veins were studied. Apart from presenting new data on
the geology and geochemistry of these veins, an attempt has been made to resolve the long stand-
ing debate on their origin, in favour of an emplacement due to tectonically controlled polyphase
hydrothermal fluid activity.
Figure 1. Location map showing Bundelkhand Craton in a generalized geological map of India (figure 1a), and the spatial
distribution of giant quartz veins modified after Basu (1986) (figure 1b). NW-trending younger mafic dykes have not been
shown for the sake of clarity. Thick dashed line in figure 1(b) marks the Bundelkhand Tectonic Zone, which is a crustal
scale brittle–ductile shear zone.
Geology and geochemistry of giant quartz veins 499
Figure 3. Field photographs. (a) Late generation thin quartz veins cut across the main vein suggesting multiple silica-rich
solution activity in time and space in parts of Bundelkhand Craton. (b) Large granitoid clasts within giant quartz vein.
Late generation thin quartz veins cut across the giant quartz vein as well as the granitoid clasts. (c) Giant quartz vein
intruding the host coarse-grained pink granitoid (∼ 2.5 Ga) with wavy contact. Some thin offshoot veins of quartz are
present. (d) Breccia texture in giant quartz vein resulting from brittle deformation. Angular fragments of quartz are set in
a fine-grained siliceous matrix.
The GQVs, in general, trend NNE–SSW with in the Mahoba district is an exception. In places,
sub-vertical dips (figures 1, 2). Lateral veering of some of the veins are found to coalesce with or
these veins is quite common and a few of them intersect each other, e.g., Jiraun Kasba of Jhansi
exhibit an EW orientation, some even showing district, Kandhari Kalan, Khariadhana, Bar and
NS to NNW–SSE trends. The prominent ones Patori of Lalitpur district and around Garhmau of
occur between Birdha and Bhuchera, to the NW Jhansi district. Interestingly, pyrophyllite-diaspore
of Bansi and north of Jamalpur, east of Ram- (Palar-Garhmau, Jhansi district; Larwari-Bar, Lal-
pur, and SE of Kotra (Lalitpur district). The EW itpur district) and sporadic Cu mineralization
trending GQVs occurring to the east of Bhainsai (Karesara Kalan, Lalitpur district) are largely
Geology and geochemistry of giant quartz veins 501
confined to intersecting GQVs. Using this cri- et al (1994) pointed out that these are “intru-
terion, a few pyrophyllite-diaspore occurrences sive quartz veins” possibly implying a magmatic
north and NNE of Pawagiri Jain Temple, Lalit- origin.
pur district have been located (Pati, unpublished
data).
The GQVs show wide variation in colour which 4. Microscopic study
is intriguing. There are four main types of GQVs
based on colour, namely, milky white, shades of Randomly oriented sections of GQVs reveal that
grey, hues of green, and shades of pink. The the samples are largely (> 90 volume %) composed
veins with local sigmoidal geometry are composed of quartz with minor-to-significant amounts of K-
of green-coloured quartz and have comparatively feldspar ± sericite, and trace-to-rare amounts of
higher associations with sulfides. The green colour ± sericite ± chlorite ± epidote ± zircon ± opaques.
is sometimes due to the presence of secondary epi- A total of 104 thin sections of GQVs have been
dote and chlorite. Very fine-grained green quartz studied but authigenic zircon grains, glauconite
similar to colloidal quartz is also observed in places. and tourmaline earlier reported by Mishra and
Quartz grains occurring within grey-coloured giant Sharma (1975) are not found. Small sericite clots
veins are highly strained in nature. are found enclosed within quartz grains and at
A number of thin (up to 10 cm; figure 3c) sub- places along grain boundaries. The grain size in
vertical, milky white quartz veins occur largely giant quartz veins is highly variable. Most of these
subparallel to the GQVs and locally cut across veins are crystalline and fine- to medium-grained,
them (figure 3a). In a number of places, thin off- but a few cherty varieties are also found. Brec-
shoot veins of quartz are found to intrude the host cia texture is abundant with large angular clasts
granitoid (figure 3c). Purple-coloured amethyst is set in a fine-grained quartz matrix. Micro-veins
noted in quartz druses occurring within granitoids of different generations are present and they are
near Hasar Khurd and Barora, Lalitpur district. observed to offset one another (figure 4a). Undula-
Colour in amethyst develops due to substitution of tory extinction and deformation lamellae in them
Fe3+ for Si followed by natural irradiation produc- are common in quartz (figure 4b). According to
ing Fe4+ (Gaines et al 1997). It is possible that the Passchier and Trouw (1996), ‘sweeping’ undulose
presence of transition elements, impurities, lattice extinction and deformation lamellae in quartz
defects and strain have contributed to the variation are the characteristic structures of low-grade con-
of colour in the vein quartz. Gaines et al (1997) ditions (300–400◦ C). Most quartz grains within
have noted that variable amounts of Al present in micro-veins show polygonization with some show-
quartz may contribute to its colour. ing serrated margins. Sutured and serrated grain
Since Pascoe (1950) noted the GQVs to occur boundaries are evidences of bulging recrystallisa-
as ridges similar to walls within host granitoids, tion (Stipp et al 2002). Earlier bands of quartz
various workers have suggested contrasting mod- are transected by bands of new grains formed
els to account for their origin, but a definitive by dynamic recrystallization. Some of the quartz
model is still lacking. On the basis of the “cata- grains show growth zoning (figures 4c, d), which
clastic and granulated nature and schistose struc- may reflect trace element compositional changes
ture” of these veins, Jhingran (1958) suggested across the grain profile and/or abundance of sub-
that the veins are long narrow zones of intense micron sized inclusions. The wide variability in
mylonitization. However, on account of the oppo- mesoscopic properties of quartz discussed earlier,
site trends of GQVs with respect to the basic and the zoning in quartz observed under micro-
intrusives, he felt the situation to be intriguing scope suggest that quartz precipitated from a poly-
and difficult to elucidate. Saxena (1961) consid- genic silica-rich hydrothermal fluid. It is notable
ered these veins as superficial features and older that in the case of hydrothermal quartz, compo-
than the granitoids. Mishra (1960) suggested that sitional zoning is more dominant than the self-
the GQVs are the result of recrystallization of ear- organized oscillatory zoning, resorption surfaces
lier quartzites. Mishra and Sharma (1975) assigned are absent and cross-cutting of growth zones is not
a sedimentary origin to these veins based on evi- observed (Müller 2000).
dences such as the presence of “cross beddings” and
the occurrence of various “heavy minerals (such
as authigenic zircon, glauconite, tourmaline and 5. Geochemistry of giant quartz
mica) within and along the primary surfaces”. Basu veins and its implications
(1986) suggested that these veins are of secreted
silica emplaced along shears that are basically Chemical analyses of 26 quartz vein bulk sam-
mylonites and further added that “mylonite forma- ples are given in table 1. Twenty three sam-
tion” pre-dated the emplacement of GQVs. Sarkar ples are from the GQVs, and three samples are
502 J K Pati et al
Figure 4. Photomicrographs under crossed nicols. (a) Thin cross-cutting veins of crystalline quartz within a sample of giant
quartz vein of fine-grained (‘cherty’) variety. (b) Giant quartz vein sample showing undulose extinction and well-developed
deformation lamellae suggesting crystal plastic deformation of quartz. (c) Zoned quartz grain (centre) with zones of variable
thickness which is cut across by a late quartz vein (left). (d) Close-up photomicrograph of a zoned quartz grain. Zoning
may be the result of trace element compositional changes across the grain profile and/or abundance of sub-micron sized
inclusions.
from relatively small quartz veins within granitoid. the help of Instrumental Neutron Activation Ana-
Out of the latter, one sample is medium-grained lytical method at the Chemical Laboratory, GSI
(BMQS286), and two samples are very coarse- (WR), Pune with a precision of 2 to 5%.
grained (BMQS281, BMQS290). The samples were The bulk chemical compositions of the quartz
broken into small chips and hand picked to avoid vein samples analysed are variable to a consid-
any surficial contamination or impurities. The erable extent. The SiO2 contents of the samples
quartz vein chips (± matrix) were translucent- are between 84 and 96 wt% which indicate the
to-opaque and were of varied colours as men- presence of phases other than quartz even after
tioned in table 1. Samples were ground in steps considering the analytical precision of 5–10 wt%
in an electrically-driven agate mortar to −200 and ignoring the volatile content that may not
mesh. The powdered samples were then processed exceed 1 wt%. The main accessory phases are K-
for chemical analysis. Elemental analyses except feldspar and sericite which together amount to a
REEs were made using an ICP-AES (JY-JOBIN total of up to 10 volume%. The SiO2 content of
YVON 70 model). For the sample BGM-34, ini- crystalline quartz veins is, in general, high com-
tial values of some elements were obtained by pared to cherty quartz veins. The Al2 O3 con-
XRF technique. Calibration of ICP-AES was car- tent lies between < 1 and 6.4 wt% and exhibits
ried out using the standards BRGM-51, 52, and a positive correlation with the K2 O content (fig-
53 (BRGM, France). The analytical precision is ure 5a) indicating the possible presence of potash
between 5 and 10%. The REEs were analyzed with feldspar and/or sericite. The total iron contents
Geology and geochemistry of giant quartz veins 503
Table 1. Chemical analyses of 23 representative samples of giant quartz veins, and 3 samples of small quartz veins in
granite from different parts of the Bundelkhand Craton. Oxide values are in wt%, and trace element concentrations are
in ppm. REE analyses of one sample each of migmatite leucosome, alkali feldspar granite and granodiorite from the
Bundelkhand Craton are given for comparison.
expressed as Fe2 O3 for fifteen quartz vein sam- tion with the colour of the samples although the
ples are less than 1 wt%, but the maximum is pinkish brown coloured quartz contains the maxi-
3.6 wt% and the minimum is as low as 0.34 wt%. mum total iron analyzed. The TiO2 concentrations
The total iron content does not have any correla- in the quartz vein samples are between < 0.01 and
504 J K Pati et al
Table 1. (Continued)
1.07 wt%. However, twenty samples have values of and MnO values do not vary with respect to the
< 0.05 wt% indicating a lower content of Ti, in SiO2 content, and therefore, may not be resid-
general. ing in quartz. In general, the incorporation of
The bivariate plots (figures 5b, c, d, e and f) trace elements in quartz of hydrothermal origin is
involving SiO2 and other major oxides do not dependent on the growth direction and velocity,
depict any marked correlation with the SiO2 con- solution chemistry and P–T condition of its equi-
tent, clearly an indication of the non-igneous ori- libration (Brown and Thomas 1960; Cohen 1960;
gin of the giant quartz veins. The CaO and MgO Siebers and Klapper 1984; Siebers 1986). The total
concentrations are less than 1 wt% each. The TiO2 iron content in quartz is known to be temperature
Geology and geochemistry of giant quartz veins 505
Table 1. (Continued)
dependent and its concentration increases with of mobility of various elements. While Ag, Sb, Cd,
temperature. Mo, As, Sn and Pb are invariably enriched in the
Most of the quartz vein samples containing mea- quartz vein samples, Co, Cu, Ni, B, Y, Cr and Zn
surable concentrations of Cu, Zn and Pb when plot- show enrichment in some and depletion in others.
ted in a triangular diagram (figure 6), cluster near One green-coloured quartz vein sample shows an
the Pb apex. Figure 7 shows the range of variation anomalous content of Cr (56 ppm) which may be
of trace elements in the quartz veins with respect due to the presence of accessory fuchsite. Ba and
to the average upper crust (Taylor and McLennan Sr both are greatly depleted. The Sr content varies
1985). The degree of variation is due not only to the between 6 and 80 ppm with a mean value of 14 ppm
dilution effect of quartz, but also to the wide range and is significantly less than the upper crustal
506 J K Pati et al
Table 1. (Continued)
average of 350 ppm. This mean value is even lower some of the quartz veins are auriferous (up to
than most sedimentary rocks, but is much higher 0.25 ppm Au). The obvious enrichment of the chal-
than in quartz reported from metamorphic and cophile elements Ag, Sb, Cd, Mo, As, Sn and Pb
some hydrothermal environments (Monecke et al along with the presence of sulfide minerals in the
2002). Such unusually high Sr content in the quartz quartz veins at places clearly indicates a hydrother-
veins can be attributed to Sr release during feldspar mal process responsible for their transport and
alteration in the wall rocks by hydrothermal fluid. precipitation. Chalcopyrite and malachite which
Be, Nb and V apparently are less variable because are locally associated with quartz veins occurring
of their concentration falling below the resolution within granitoids exhibit comb structure, suggest-
of the instrument. Pati et al (1997) reported that ing precipitation from a fluid (Dong et al 1995).
Geology and geochemistry of giant quartz veins 507
Figure 5. Bivariant major oxide plots (a–f) of GQVs. Only those samples with appreciable content of different oxides have
been plotted. Positive correlation is seen between Al2 O3 and K2 O (5a). SiO2 versus major oxides (5b–5f) depict a scatter
for elements such as Fe2 O3 (T), Al2 O3 , K2 O, MnO and TiO2 , respectively.
6. Discussion
Figure 8. Chondrite normalised (Sun and McDonough 1989) REE patterns of quartz veins. (a) Nearly flat pattern in four
samples of GQVs and one sample (BMQS290) of a small quartz vein within granite. Two samples of hydrothermal quartz
of Monecke et al (2002) are shown for reference. (b) Plot of four samples of GQVs showing LREEn enriched and HREEn
depleted or flat pattern. A third sample of hydrothermal quartz of Monecke et al (2002) is shown for reference. (c) Patterns
of two samples of GQVs, and one sample each from migmatite leucosome (BIGS-16C), alkali feldspar granite (BGM-16),
and granodiorite (BGM-8) from the Bundelkhand Craton.
for his great insight, help and tremendous encour- thanked for kindly sending all the required reprints
agement during his tenure as the Director, STM- and other necessary data. We thank Dr. Wanming
P, Op. U.P. (Lucknow). Dr. Thomas Monecke, Yuan, Dr. Tom Andersen, and Dr. Biswajit
Institute for Mineralogy, Technical University of Mishra for their thorough, critical and constructive
Bergakademie, Freiberg, Germany is sincerely reviews.
510 J K Pati et al