Nellore, the southern most coastal district of Andhra Pradesh, covers an area of 20,620 sq.km. It is bounded by Prakasam in the north, Chittor in the south, Cuddapah in the west, Bay of Bengal in the east.
The district comprises older metamorphic of presumably Archaean age, Dharwar Supergroup of Archaean to lower Proterozoic age post – Dharwar intrusive, sedimentary rocks of Cuddapah Supergroup and Cuddalore Formation of middle Miocene age and laterite/alluvium of Quaternary age. The Archean rocks occupy major part of the district and are represented by older mentamorphics comprising migmatised garnetiferous quartz-mica schist with associated amphibolites, quartz-muscovite mica biotite schist, with kyanite/staurolite and the Peninsular Gneissic Complex comprising biotite-granite gneiss. The migmatised schist covers a large area in the central part of the district from west of Kavali in the north to Sulur in the south. Quartzite is exposed as several outliers, scattered over the migmatised schists. Kyanite and staurolite-bearing quartz-muscovite-biotite schist occurs as linear or circular shaped outcrops. These are exposed along the eastern boundary of the Dharwar suite of rocks to the west of Kaligiri peninsular gneiss, along the eastern margin of the Cuddapah Basin. It comprises pink to grey granite and gneiss. The rocks of Dharwar Supergroup form a prominent NW-SE trending belt from North of Udayagiri to south of Gudur attaining a width of 25 km in a broad synformal structure. It comprises an interbedded sequence of metavolcanic and metasedimentary rocks. The various lithotypes present in this group are chlorite schist, hornblende schist, actinolite schist, tuff/agglomerate, quartz-sericite schist, actinolite schist, phylite and quartzite. The post-Dharwar intrusive correspond to the Eparchaean interval and are represented by gabbro, anorthosite, carbonatite, granite and pegmatite. Pegmatite veins are seen mostly concentrated inthe area between Degapudi and Saidapuram. Mineralogically, two distinct types of pegmatites, namely “postash-feldspar pegmatite” devoid of commercial grade mica, and “Plagioclase pegmatite” containing mica of commercial value are identified in the district. Carbonatite in the district occurs as a narrow NW-SE trending band within the Dharwar metavolcanics, having a width of 50 to 60 m over a strike length of 8 km close to the margin of Dharwars with older schist in the northern part of the area. Anorthosite occurs as a circular body having a width of 1 to 1.5 km near Degapudi. Gabbro is exposed as small mounds within Dharwars in the western part of the district.
The rocks of Cuddapah Supergroup, occupying the western part of the district, are exposed as an outiler, west of Udayagiri. Only upper part of the Cuddapah Supergroup, viz, Nallamalai Group, consisting of quartzites is well exposed in the district. Rocks of Cuddalore Formation consisting of sandstone, gravel bed, grit and conglomerate are exposed as isolated patches to the north, south and SE of Nellore. Remnants of these, presumably show relicts of the eastern seabed of India during the Tertiary era. Laterite cappings are seento occur at the eastern end of the district. Deposition of beach sands by present day sedimentation, formation of gypsum, lime, in Pulicat lake, accumulation of alluvium along Penner and Swarnamukhi river tracks and formation of soils represent. Recent geological activity in the district.
Mica: Nellore district is a major producer of mica in the country and has enormous reserves of good quality mica in Gudur, Nellore and Rapur taluks. The mica pegmatities of Atmakur, Gudur, Kavali and Rapur Taluks have been mined for mica of commercial value for several decades. The muscovite mica occurs as books in the pegmatites traversing the schists and amphibolites of older metamorphic. The mica – bearing pegmatites occur in several isolated groups or clusters over a cumulative strike length of 25 km. Of this, a 15 km section between Saidapuram and Degapudi has very rich mica mineralization of green and ruby variety. Vermiculite is exploited from near Rachepalle and near Gudur in the district. It occurs in the form of lenses and veins of about 10 to 20 cm width in gneisses. It is also available in the mica dumps in the district, along with quartz and feldspar.
Barytes: Occurrence of barytes is reported from southwest of Vinjamur with BaO content varying from 32% to 50%.
Building material: A variety of granites, epidote – rich rocks, quartzites, dolerites and laterites are quarried in the district for building materials. Laterite, which occurs as thin capping over ferruginous sandstone, is quarried from Kadivedu-Chittendu area in Gudur taluk and from around Kavali. Granites and gneisses are extensively quarried near Kallur, Kaluvagu Bommararam in Atmakur taluk and near Tanamacherla in Rapur taluk.
Copper-ore: Old workings for Copper-ore occur at Garimenapeta, Gottigundla, Duttaluru and Udayagiri. The ore is associated with quartz or pegmatite veins intrusive into the schist.
Gypsum: Gypsum deposits occur in the islands of the Pulicat Lake near Suluru. It occurs in the form of colourless, irregular lumps in marine clays within a metre from the surface.
Kyanite: Kyanite is known to occur near Janaganapalle and Saidapuram within the older metamorphic rocks. It is generally of poor quality with about 37% to 55% A12 O3 content.
GEOMORPHOLOGY & GEOHYDROLOGY
Physiographically, the area forms a undulating uplands. The Veligonda range in the western part of the district rises upto 1105 m, above m.s.I while the low lying alluvial zone in the southern part of the district lies less than 10m above the m.s.I. The district is drained by Manneru, Penner, Kandleru and Swarnamukhi rivers. The ground water conditions in Archaean, Dharwar and Cuddapah rocks of the district is controlled by fractures and intergranular porosities. The ground water in the rocks is restricted to 60m depth and open wells tapping these formations yield 10-15 m3 day. The Cuddalore Sandstone, Quarternary formations and alluvium have ground water down to a depth of about 150 m b.g.I and the open wells in the rocks given about 100m3/hr. SOIL AND LANDUSE The district is mostly made of arable land with some prominent patches of grasslands and scrub seen west of Nellore and Gudur and east of Udayagiri with some Forest areas seen around Venkatagiri. Somasila and southwest of Udayagiri. A major water body in the form of Pulicat Lake is seen in the southeastern corner of the district.
The district is characterised by coastal alluvial soil all along the coast, mixed red and black soil around Somasila and lateritic soil to the north and south of Gudur. The deltaic alluvial soil is seen west of Udayagiri and red sandy soil is seen southwest of Kavali.
GEOTECHNICAL CHARACTERISTICS AND NATURAL HAZARDS
The area has been demarcated into five engineering provinces based on bearing capacity / compressive strength and foundation characteristics of the rocks units. Basement crystallines : With compressive strength of 1000-2000 kg/cm2 and very good foundation characteristics. Younger sedimentaries : With medium to very high compressive strength 600-2900 kg/cm2 and very good foundation characteristics. Laterite and lateritic soil: With low to medium compressive strength and fair foundation characteristics. Deltaic / costal sediment and alluvium : With low compressive strength (1-2 Kg/cm2) and poor foundation characteristics. One minor earthquake episode measuring 3.1 on Richter scale was recorded form Velikonda hills in the western part of the district on 28th March, 1975.
GEOLOGY AND MINERAL RESOURCES OF NELLORE DISTRICT
The district derivers its name Nellore from the home of its headquarters. It lies between the Lat. 13030 and 15006’ and Long. 70005’ and 800 15’and covers an area of 13.076 Sq.Km. lt is bounded on the north by Prakasam district. on the east by the Bay of Bengal. On the south by Chittoor district and Cengalpattu district of Tamilnadu and on the West by Veligonda hills, which separate it from Cuddapah district. It encompasses 46 Mandals.
The district is generally flat and of low elevation. It can be broadly divided into two divisions. The eastern half of the district is fairly flat and comprises of sandy coastal belt extending all along the district up to 7 km from the sea coast. There are numerous back water lakes, prominent among them is Pulicat lake. The western half of the district has a low elevation and covers large tracts of hills and plains. The Eastern ghats are the most important mountain ranges in the district. Locally known as Veligondas. The run in a north westerly direction from south of Venkatagiri to north of Kanigiri area in Prakasam district. Udaigiri Durg is an isolated hill with a height of 938 m.
The important rivers that drains the district are the Pennar and Suvarnamukhi. The Pennar flows for about 112 km in the district through Atmakur. Kovvur and Nellore mandals. Other important seasonal streams are Kanduluru and Boggem.
GEOLOGY OF THE DISTRICT:
The district forms a part of the lndian Peninsular sheild, of which the oldest rock formations encountered are the schists and gneisses of Pre- Cambrian age and the younger formation of alluvial sand and laterites of Pleistocene to recent age.
The various litho units occurring in the district are granite, gneiss, meta pelites, mafic and ultramafic complexes. Metavolcanics with psammites, acid, basic and ultramafic intrusives of Archean age sand stones quartzites and shales of Proterozoic age and alluvium and laterites of Pleistocene to recent times are also seen.
The Archean rocks occupy a major part of the district covering Seetharamapuram, Udaigiri, Varikuntepadu, Kondapuram, Jaladandi, Dagadarthi, Nellore, Thotapalli, Gudur, Pellakur, Balayapalli, Venkatagiri, Dukkili, Rapur, Koluvoya, Anantasagaram,, Narripadu, Ojili, Gudur, Sydapuram, Podakalur, Chejerla, Atmakur, Duttalur, Vinjamur, Kaligiri, Anumasamudrampeta & Sangam mandals.
The Archaeans are represented by granite gneisses, garnetiferous quartz & mica schists with staurolite and Kyanite, quartzites, Hornblende gneisses, gabbro with anothosite, Talc- anthophyllite- magnetite schists, Talc – Steatite / Chlorite anothophylite schists, Metavolcanics represented by hornblende schists, Amphibolites, Quartz Sericite schists, ultramafic intrusives represented by pyroxinites. Lamprophyres, acid intrusives such as pegmatites, quartz veins, granites and basic intrusives such as gabbro and dolerite.
The granite gneisses exposed in the south western & eastern part of Nellore mica belt at the contact with schist runs through Pilgrim, Balayapalli, Kodagunta, Akyam and Vemulachedu. The granite is homophanous and contains essentially quartz and feldspar with muscouvite as accessory mineral.
The metepelites are represented by quartz – muscouvite schist, quartz – biotite schist and biotite schist whereas psammites are represented by quartzites.
The mafic complex is represented by amphibolite schists, hornblende gneisses, associated with metapelites and psammites. Amphibolites are dark green to black, fine to medium grained and composed essentially of hornblende. Plagioclase, and quartz with magnetite and sphene as accessories. At place they are affected by profuse felspathisation and lit-injection of quartzo – felspathic material and alterated to biotite schist, which in turn altered to vermiculite at places as near Jogipalle, north of Kalichedu, west of Saidapuram and near Valasapalli.
Associated with the metapelites and hornblende gneiss are the sheets and lensoid bodies of meta ultramfices. They are represented by talc-steatite – chlorite/ actinolite schist, talc – anthophylite – magnetite schist and serpentine. They occur near Jogipalle, north and north east of Saidapuram, near Kandra, and Chilamanichenu.
Metavolcanies associated with quartzites are exposed near Kandra village. They are represented by massive, schistose and amygdular amphibolite with agglomerate and volcanic tuffs at places. The vesicles in amphibolite range in size from 0.05 to 1.0 cm and are filled with calcite, quartz and epidote.
Gabbros and dolerites occur as sills and dykes, near Kusumur Palicherla padu, and Jayampu etc.
Acid intrusives are represented by granites, pegmatites and quartz veins. Mineralogically they consists of quartz, microcline, plagioclase, perthite, biotite, muscovite, magnetite and sphene. At places hornblende and garnet are present.
The rocks of the Cuddapah Supergroup comprising Chitravati, Nallamalai and Krishna Groups occur on the west and north western parts of the district. They are spread over in the parts of Balayapalli, Venkatagiri, Dakkili, Rapur, Koluvoya, Anantasagaram, Marripadu and Seetharamapuram mandals. They consists of shales and quartzites and are considered to be the eastern margin of the Cuddapah basin.
PLEISTOCENE TO RECENT:
Laterite and alluvium are developed in the eastern parts of the coastal plains in the district.
MINERAL RESOURCES OF NELLORE DISTRICT
Nellore district is endowed with minerals like Mica, Barytes, Limeshell, Clays, Quartz,Silica Sand, Vermiculte, Iron Ore, Laterite, Garnet etc.
The Nellore Mica belt extends over a length of 80 Km from Vogil in the south, to Sangam in the north comprising an area of 1580 Sq.Km Mica occur as books in pegmatites Veins intruded into the Pre-Cambrian Schists in Rapur, Gudur, Saidapuram Atmakur mandals. The size of the Mica varies from few millimeters to few metres and are seen in White or Colourless ruby and green variety mostly, spooted, Ruby has the highest market value and spots in mica reduces the its value.
Barytes occur at Vinjamur, Bandakindapalle,sankavarm, R.F Gundamadakala in Vinjamur Mandal. The mineral is off-coloured and occurs in Schists in association with quartztites. G.S.I has proved 2.14 m.t of reserves in the area. The specific gravity varies between 3.8 and 4.2 with iron and silica on the higher side. Mining Leases cover an area of 100acres. The production of barites is around 400 metric tones per annum.
Silica Sand useful in the glass industry and as foundry sand occur at Ataknaithippa, in Sullurpet Mandal, Ballvelu, Chintavaram, Yerur of Chillakur Mandal. Mamidi of Muthukur Mandal, Pannamadugu of Tada Mandal, along the Coastal plains of the district. There are 32 mining leases granted for the mineral covering an extent of 1253 acres. The production of the mineral form the district is about 45,000 mt.t per anum.
Lime shell, useful for the manufacture of Calcium carbide and high grade lime, occurs near Atakantippa and Chengalanampalem in Sullurpet Mandal, godulapalle, Irrakam & Venadu Villages of Tada Mandal in Pulicat lake area. Lime Shell occurs intermixed with mud and slit in the back waters of Pulicatlake. The shells are enriched with 100% Caco3 and are useful in Chemical industry.
Quartz useful in glass and Ceramic industries occurs in association with pegmatites in Gudur Sydapuram Udaigir, Podakalur, Duttalur, Venkatagiri, Chejerla, Kaligiri, Vinjamur and Chillakur Mandals. There are 29 mining lease in the district covering an extent of 1586 acres. The Production mineral from the district is about 4200 mt per annum.
Laterite, useful in the manufacture of Cement, occurs in Kothapalli Koverugunta of Dagadarti Mandal, Rudrakota, Musunur of Kavali Mandals. There are 5 mining leases existing in the district covering an extent of 125 acres. The production of the mineral is 5400 m.t. per annum.
The Clays of Kaolinic nature are formed due to alternation of pegmatites and felspars. They are useful in stoneware and refractory industry, Clays occur at Oduru, Turnimerla, Perumallapadu, Pallicherla, Vadalapudi, Prabhagiripatnam, Kasumuru of Kavali & Nellore Mandals.
The Janakampet clay depot is estimated roughly to contain 1,00,000 tonnes of Clay. The Clay here is highly plastic & gritty. It is used in making stoneware, and refractory bricks. The Narasapuram clay is white, Plastic and grittiy and estimated at 4,15,000 tonnes. High Grade china clay occur at Prabhagiri palem. Gottapalem Vadlapudi. These clays are useful for making High grade whiteware, porcelain, high grade China ware or crockery.
MINERAL BASED INDUSTRIES
Mica, is one of the strategic minerals having applications several industries, the Prime Industry being electrical industry. The mica resources of the district of the district have paved way for the setting up 43 Mica powdering and punching units. It is the predominating industry in the district.
Cereamic Unit was set up at Gudur which manufactures LTinsulators, fues units and sanitary ware.
The other important mineral based industries existing in the district are 2 granite cutting and polishing units, 1 glass factory and graphite based powdering unit, 2 mineral powdering and processing units, 20 clay based small scale industries producing stone ware pipes, jars, refractory bricks, glazed tiles. Chalk crayon units 30 cement products and 88 units which include mangalore tiles. Granite metal and stone crushers, brick units etc. over all 181 small scale mineral based industries are existing in the district.
One medium scale unit for the manufacture of China Ware, Crockery and another medium scale unit for making chemical porcelain products (for scientific laboratories and industries) .
In view of the deposits dimensional stones available in the district and growing demand for the stone, it is suggested to set up one large scale cutting and polishing unit near Tada.
In the district Kyanite occur near Chundi. It is suggested that a small scale benefaction, calcination and pulversing unit may be established in the district. The product can be supplied to manufacture high alumina refractories.
In Pulicat lake, limeshell reserves are estimated at .04mt.t per squarekilometre. These can be used for industrial purpose, taking care not to upset the ecological and environmental balance. Based on these deposits large scale unit for manufacture of white cement, and 2 small scale units for manufacture of precipitated calcium carbonate, bleaching powder, calcium Chloride can be established near Tada.
Vermiculite, after exfoliation is highly useful in the manufacture of thermal and acoustic insulators, It can be mixed with gypsum plasters or concrete which imparts fire proof qualities. The fines can be used in heat resistant paints. Houses godowns, etc coated with exfoliated vermiculite, protects, them against fire. Hence it is suggested to set up a small scale unit for exfoliation near Gudur.
The myriad mica waste dumps can be brought into use, by setting up small scale industries around Gudur for recovering mica and using it for preparing oil well drilling cement from mica waste/Scrap.
Mica is one of the Strategic minerals having immense applications in several industries. The prime industry being electrical industry. Since the demand for mica is increasing. It is suggested to setup a small scale unit for utilizing mica scrap in mica powder industries for producing.
1)Micanite from Splitring 2) Glass bonded mica 3) Mica paper and tapers from scrap from scrap 4) Insulation bricks mica waste or 5) Mica based paints.
For Recovering mica from mica dumps or using it for oil well drilling.