Titles & Abstracts of Ph. D. Theses Guided

Geological Investigation of the Fluorspar Deposits of Rajasthan
Abstract of the Ph. D. thesis of Dr. P. S. Ranawat
Thesis submitted on 16.09.1972 to the University of Rajasthan.
Supervisor:Dr. M. K. Pandya

The thesis describes host rock petrology, mineralization structures & textures, and genesis of four fluorspar deposits / prospects of Rajasthan, viz., Mando-Ki-Pal, Chowkri-Chhapoli, Jhalara and Asind.

In the Mando-Ki-Pal area the country rocks are migmatites with occasional bands of muscovite-¬kyanite-schist. Lower Proterozoic Aravalli quartzite surrounds the migmatites of Precambrian Banded Gneissic Complex (BGC). This study has shown that the host rocks of fluorspar are not cherts and cherty limestone, as hither-to-considered, but are silicified cataclastic rocks. They include proto- to ultramylonite, blastomylonite, and gangmylonite. Consequently, the genetic model for the deposit will be different and its resource evaluation will have to be modified.

Green and purple fluorite, calcite ((mangeneferous at places, displaying red fluorescence) and quartz, are the main vein minerals, which display characteristic cavity: filling structures, viz., fissure filling, joint filling, fracture filling, symmetrical crustification, cockade structure, segmented veins, breccia filling and brecciated veins etc. Grains of pyrite, chalcopyrite, galena, and sphalerite are rarely present. Green fluorite and Mn-calcite display fluorescence. Epimorphs of calcite in gangmylonite is also common. Silicification and chloritization of the host rocks is observed. At Kaila persistent stratabound veins of brownish / grayish fluorite occur in quartzite. Jhalara is an extension of Mando-Ki-Pal area and the mineralization is very poor, occurring in migmatites, pegmatite and quartzite. This area was abandoned after prospecting.

At Chowkri the fluorspar occurs in tonalite boss intruding the Middle Proterozoic Ajabgarh garnet-biotite schist. While at the adjoining Chhapoli the fluorspar is confined to Ajabgarh feldspathic quartzite. Green & purple fluorite in both these areas occur as large, color-zoned octahedral crystals. Calcite and quartz are associated with fluorite. Secondary neodigenite and hydrous iron oxide are found in few sections. Mineral, zoning is noticed at Chowkri area. Fluorite, calcite, quartz occur in the central part while apatite, quartz form the outer zone. The hydrothermal mineralization has brought about kaolinization and hematitization of the host rocks. Ilmenite and magnetite is associated with hornblendite reefs in the area.

Near Asind the fluorspar veins occur in migmatites of Banded Gneissic Complex; amphibolite, pegmatite, aplite, epidosite, unakite are also present. Epidotization of vein wall in migmatite is characteristic features observed in the area. Associated minerals are quartz and rarely calcite. Here too the mineralization is poor and the area was discarded after prospecting.
The fluorspar mineralization in these areas is diplogenetic formed by low temperature hydrothermal solution related to migmatization at Mando-Ki-Pal, Jhalara, Asind and tonalite-granite at Chowkri-Chhapoli. Fluorine bearing solutions leached calcium front the country rocks and deposited fluorspar in the available cavities (fissures, fractures, joint planes, pore spaces, etc.). Since cavity filling in non-calcareous rocks is predominant and replacement poor, therefore, the deposits are of poor economic significance.

Abstract of the Ph. D. thesis of Dr. R. S. Dashora
Thesis submitted on 29.04.1981 to the University of Rajasthan.
Supervisor:Dr. P. S. Ranawat

The rocks around Karara (Rajasthan) belong to the late Proterozoic Malani suite of volcanic rocks and a range of pyroclastic rocks represented by: volcanic breccias, lapilli tuffs, and welded tuffs including ignimbrites and extrusive basalt, andesite, trachyte, dacite and rhyolite.  S-pole diagrams of joint planes show a peripheral spread of the sub-maxima, which is typical of central type of volcanic activity. Field and remote sensing studies in this desert region conclusively prove that the area represents a volcanic vent that had witnessed repeated volcanic-activity of violent nature.

Fluorspar mineralization at Karara is widely distributed in the pyroclastic rocks and is confined along fissures and joints.  Minor quantity of ore occurs in vesicles, shrinkage cracks and related vugs. The mineralization is essentially fluorspar-quartz-barite type.  Fluorites in the area are fine-grained, coarse grained and columnar. Barite occurs in coarse columnar form and the quartz in crystallized or granular.  Characteristic cavity filling structures and textures are crustification, cocked structure, banded, segmentation, breccia filling and brecciated ores.  Replacement is rarely seen but wall rock alteration as kaolinization is noted.

Mineralization structure and fluid inclusion study of fluorite and associated barite, quartz and calcite reveal three distinct stages of mineralization: Stage-I is represented by- crystallized (cubo-octahedron phantom crystal with in cubic crystal ) / coarse granular fluorite + acicular / crystallized barite + quartz + calcite; During the Stage-II – columnar fluorite + columnar barite + quartz + calcite / siderite formed.  Stage-III is represented by- fine-grained fluorite + fine grained quartz + pyrite (rare).  Two- phase primary aqueous fluid inclusions having a high degree-of-fill are present in fluorite, barite and quartz of Stage-I. T_h = 120°-240°C. Biphase fluid inclusions with more than 98% degree-of-fill or monophase (liquid only) inclusions occur in minerals of Stage-II, T = 80°-110°C, Fluorspar of Stage-III is fine grained and shows few monophase fluid inclusions. Leachate analysis shows that the fluid in inclusions is of very low salinity, being nearly pure water.

The mineralization is attributed to low temperature volcanogenic hydrothermal solutions. The veins were formed after volcanic activity had shattered the host rocks and provided channel ways for movement of mineralizing fluids.  During the first stage of mineralization slow nucleation of fluorite occurred from fluids having high oxidation potential and low fluorine concentration. Subsequently, fluorine concentration increased but crystallization was still slow (Stage-II). In final stage (stage-III) high concentration of fluorine and rapid nucleation is evident in reduced oxygen regime.

Abstract of the Ph. D. thesis of Dr. R. L. Somani
Thesis submitted on 12.01.1987 to the University of Rajasthan.
Supervisor:Dr. P. S. Ranawat

The thesis embodies a detailed fluid inclusion and rare earth element (REE) study of Chowkri -Chhapoli and Mando-Ki-Pal fluorspar deposits of Rajasthan.

At Chowkri the fluorspar mineralization occurs in the post-Delhi tonalite, reef quartz and hornblendite. At Chhapoli, on the other hand, the fluorspar mineralization is hosted in feldspathic quartzite (Ajabgarh Group of Delhi Supergroup).  At both the localities the fluorite occurs as large color-zoned octahedral crystals, a comparatively rare habit of fluorite crystallization.  Coarse granular fluorite is also present.  Associated minerals are quartz, calcite, apatite, galena, and pyrite.  Quartz occurs as granular (reef quartz, quartz-I) and twined crystallized (quartz-II).  Hornblendite contains magnetite and ilmenite. Wall rock alteration as hematitization of tonalite and kaolnization of feldspathic quartzite is conspicuous.

Fluorite contains primary aqueous fluid inclusions having faceted cavities usually of tetrahedral shape.  Another characteristic feature is rare occurrence of secondary inclusions in fluorite.  The phases present are – an aqueous phase, vapor bubble and occasionally a halite daughter mineral.  Two-phase (liquid + vapor) and three-phase (liquid + vapor + halite) fluid inclusions have been observed in the same polished plate.  Cryometric study has shown that the fluids in inclusions contain CaCl₂ and NaCl and the bulk fluid salinity in most of the fluorite crystals is nearly 26 ± 5 Eq.  Wt % NaCl. This just-saturated critical salinity is responsible for occurrence of two-phase and three-phase fluid inclusion in the same plate. In some of the two phase FIs the halite nucleates during freezing runs, which homogenizes ~10 ⁰ C! The general range of salinity of fluid in inclusions, taken as a whole for the entire area, however, ranges from 31 to 3.4 Eq. Wt. % NaCl.  The CaCl / NaCl ratio is fairly high (9: 1) based on the freezing study the fluid inclusion have been classified in to three types.  Temperature of homogenization ranges from 200° to 130°C. 

At Mando-Ki-Pal the fluorspar mineralization can broadly be classified into two types. 

1. One is that which occurs in mylonite and granitic gneisses of basement complex (Bhilwara Supergroup).  The mineralization displays fracture filling, joint filling, crustification, cockade structure etc.minerals present are-Green fluorite, purple fluorite, calcite, quartz with rare presence of galena, sphalerite, pyrite, pyrolusite. 

The minerals contain two-phase aqueous inclusions having high degree-of-fill.  They are of irregular shapes and have wider range of size.  Microthermometry data indicates presence of salts other than NaCl in the fluids, salinity of which range from 14 to 22 Eq. Wt. % NaCl in fluorite; in quartz and calcite it ranges from 10 – 19 Eq. Wt. % NaCl. The temperatures of homogenization range from 102° – 168°C for fluorite; 93° to 134°C for quartz; and 112° to 135°C for calcite.  All the minerals contain large number of pseudosecondary and secondary inclusions. 

2. Another type of fluorspar mineralization is the one that occurs as persistent stratabound veins in quartzite in Kaila and Nawagaon Blocks.  Fluorite is milky white or light brown in color and occurs as fine granular aggregate of fluorite and quartz. Both these minerals contain CO₂, CO₂-H₂O and rarely CH₄ inclusions. Cryometric data indicate that CH₄ density is about 0.24 g/cc.  Density for the CO₂ inclusions ranges from 1.10 to 0.6 g/cc although density of 0.8 to 0.7 g/cc is more common.  The aqueous FIs have salinity of 4 – 9 Eq.  Wt. % NaCl.  Rarely, a halite daughter crystal has also been observed in some of the fluid inclusions, indicating that the solutions were saturated with respect to NaCl. The temperature of homogenization for the H₂O – CO₂ type inclusions has a range of 185° to 360°C with maximum values lying between 220° to 270°C.

In Chowkri-Chhapoli, the mineralization fluids are possibly genetically related to Chhapoli Granite and Salwari Tonalite. In Mando-Ki-Pal region the quartzite-hosted mineralization appears to be metamorphosed while the mylonite and migmatite hosted mineralization is cavity filling hydrothermal type that deposited at fairly low temperatures and pressure.

The REE data for 20 samples of fluorite are plotted on Tb/Ca Vs. Tb/La diagram (Möller et al., 1976) and they fall in the “hydrothermal” field.

The thesis has seven chapters covering text in 144 pages and having 17 plates, 20 tables, 43 figures and bibliography of 127 references.

Abstract of the Ph. D. thesis of Dr. M. S. Shekhawat
Thesis submitted on 29.04.1987 to the University of Rajasthan.
Supervisor:Dr. P. S. Ranawat

India’s largest resources of anthophyllite occur within the ultramafic rocks exposed to the West of Udaipur, Rajasthan.  The ultramafic rocks constitute a linear belt designated as Jharol-West belt that extends for a strike length of about 25 km in NNE – SSW direction with maximum width of nearly 2 km.  The ultramafic bodies occur as intrusives within tile rocks of Jharol Group of Aravalli Supergroup and exhibits concordant relationship with them.  The original nature of the ultramafic rocks is difficult to ascertain since they have undergone high degree of steatitization and anthophyllitization. Quartz-mica schist, quartzite, few bands of impure marble along with isolated outcrops of amphibolite and pegmatite mainly represent the Aravalli metasediments of the area.

The anthophyllite deposits occur as lensoidal bodies of varying dimensions.  They show a characteristic set of lithological zoning where a zone of phlogopite separates the ore-bodies from enclosing quartz-mica schist.  Anthophyllite occur as parallel, triangular or radiating aggregates of acicles/fibers.  Minerals occurring in association with anthophyllite are talc + antigorite + chlorite + biotite + phlogopite + magnetite + ilmenite + olivine ± tremolite ± quartz ± calcite.

Based on geochemistry and field relationship it is concluded that the ultramafic rocks of the area are product of peridotitic magma (Orogenic “root-zone”), Iherzolite sub-type, which was emplaced in subsolidus state though of fractures developed in the crust during the Aravalli orogeny where the Aravalli sediments were suffering, folding.  Lensoidal shape of the ore-bodies was developed due to pinch-and-swell structure due to ductile deformation after their emplacement.  XRD & chemical study proved that the asbestos of the area is anthophyllite that is Mg-rich variety of ortho-amphibole.

Anthophyllite is product of metamorphism of the ultramafic rocks in amphibolite facies.  Based on minerals association and fluid inclusion study carried out on some of the co-genetic transparent minerals, it has been concluded that the rocks of the area were subjected to pressure of about 4.50 ± 0.20 kb. and temperature of about 670 ± 20°C.  It is also concluded that metamorphic fluids were H₂O + CO₂ type with variable CH₄ content from margin to core of the ore-bodies. Retrograde metamorphism in the form of’ steatitization of anthophyllite is observed specially in the northern part of the belt.

Anthophyllite deposits of the area are being developed by small-scale, manual, opencast methods of’ mining. The resource produced from tile area is being processed within the state for its industrial use. Anthophyllite of the area has much higher tensile strength (40,000 – 45,000 psi) compared to values reported for anthophyllite from other areas of world (< 4260 psi).  It also has good values of cement absorption capacity, resistance to acids and alkalis, wet volume (buoyancy), surface area.  Therefore, the resource is extensively utilized in a number of industries and hence, it has significant contribution in the development of economy of the nation.

Abstract of the Ph. D. thesis of Dr. B. S. Rathore
Thesis submitted on 20.02.1991 to the University of Rajasthan.
Supervisor:Dr. P. S. Ranawat

The scheelite skarn prospect of Kararavav (SW Rajasthan) belongs to Middle Proterozoic Kumbhalgarh Group of Delhi Supergroup. The principal rocks of the area are granite, skarn, calc-silicate, amphibolite and impure limestone.  The general strike direction of metasedimentary litho units is N20° W to N35° W and dips are moderately steep ranging from 60° to 75° towards NE.  The granite-limestone contact is marked by the development of skarn rocks where zonal pattern from limestone to intrusive is represented successively by limestone, calc-silicate, skarn, and granite.

Two types of granites are occurring in the area.  One is grayish to pink hornblende granite and other is gray biotite granite.  These scheelite skarn generating granitoids have been geo-chemically studied to decipher I, S, A or M-type characteristics.

The most important litho units of the area are skarn and calc-silicate that have been differentiated texturally and by the fact that skarn displays characteristic metasomatic zoning in terms of dominant mineral assemblages due to addition of material from the magma.

Based on field relation, petrography and mineral chemistry, it is inferred that impure limestone was subjected to high-grade regional metamorphism and subsequent metasomatism to generate calc-silicate and skarn rocks of the area under the influence of magmatic emplacement.

The activity of skarn forming fluids and chemical controls on scheelite deposition in metasomatized facies conditions are broadly reviewed and it is concluded that scheelite was precipitated between the zone where in-flowing W-rich boiling solutions became fairly Ca-rich for the solubility product of scheelite to be exceeded and the zone where W is being extracted from the out-flowing fluids due to scheelite deposition.  The concentration of Ca ion in the under-saturated solution was raised with the interaction of calcium rich rocks (e.g., limestone).

An estimate of P, T, X _C02 and F₀₂ conditions for the scheelite bearing host rocks (skarn and calc-silicate) has been made from coexisting stable phase equilibrium of mineral assemblages In the multi-component systems and from the fluid inclusion study of various calcio-silicate minerals.

Well-established mineral stability fields have been utilized to ascertain P-T conditions of skarn and calc-silicate rocks.  Various calcio-silicate viz., scheelite, vesuvianite, clinozoisite, garnet quartz and calcite, contain mostly H₂O + CO₂ type and multiphase fluid inclusions.  Microthermometric data indicates low X_CO2 content of boiling fluids that had temperature fluid activity occurred in the rocks as indicated by low temperature secondary fluid inclusions.

Abstract of the Ph. D. thesis of Dr. N. K. Sharma
Thesis submitted on 24.02.1994 to the University of Rajasthan.
Supervisor:Dr. P. S. Ranawat

The Precambrian formations of south-central Rajasthan host a unique lead-zinc deposit near Rampura-Agucha.  The deposit owes economic significance due to presence of 39.2 MT proved, 13.8 MT probable and 10.7 MT possible reserves of ore having an average grade of 13.6% Zn and 1.9% Pb.  This deposit has aggrandized the national resources by 16.6%. Its geological importance rests with the fact that the ore is hosted in highly metamorphosed Precambrian rocks having significant silicate, sulfide and oxide mineral assemblages.

The principal rocks in area are para-gneiss (Agucha Gneiss), calc-silicate, impure marble, amphibolite, mylonite and pegmatite. The general strike direction of metasedimentary lithounits and mineralization is NNE-SSW to NE – SW and the dips are moderately steep ranging from 60° to 75° towards SE.  The ore-body extends for a strike length of 1.6 kilometer in a long linear wedge-shaped depression.  The average width is 60 meters and it persists up to 380 meters below the surface.  The surface manifestation of ore-body is demarcated by multicolored, patchy oxidized exposures.

The mineralization in characterized by the diagnostic sulfide assemblage sphalerite (ferroan) + pyrrhotite + galena + graphite + marcasite with sporadic occurrence of chalcopyrite and arsenopyrite.  X-ray diffraction study has confirmed the existence of tetrahedrite, stephanite, smith­sonite, cerrusite, zincite and anglesite.  Microprobe study has revealed the presence of breithauptite (NiSb), gudumndite (FeSbS), ulmanite (NiSbS), tetrahedrite, pyrargyrite (Ag₃SbS₃), stephanite (Ag₅SbS₄). Miargyrite (Ag₂SbS₄), rutile, gahnite and karelianite-eskolite.

Based on field relations, petrography and petrochemistry, it is inferred that the Agucha Gneiss is the product of regional metamorphism of marine sediments of pelitic to graywacke composition.  Petrographic study under transmitted and incident light has proved that the silicates and sulfides have involved in high-grade regional metamorphism; cataclastic textures superimposed on the recrystallization textures are also prominently present.  The textural evidence is consistent with and reinforces interpretation of ore as stratiform metamorphosed type of mineralization.

Well-established mineral stability fields have been utilized to ascertain the P-T conditions of metamorphism of ore bearing rocks.  It has been observed that the ore bearing sediments were metamorphosed under P-T conditions of upper amphibolite facies (6.5 ± 0.8 Kb, 680° ± 30°C).  Common occurrence of migmatites and hydrous minerals and poor development of hypersthene in the rocks of the area indicates that during metamorphism P_H2O was equal to P_Total. The presence of sphalerite + pyrrhotite + pyrite assemblage has been used for the geobarometric study.

On the basis of field evidence, petrography, petrochemistry and nature of mineralization, it is concluded that the Rampura-Agucha lead-zinc deposit represents a synsedimentary-metamorphosed type of deposit.  Tectonic activities and major orogenic cycles (Aravalli and Delhi) brought about characteristic changes in the synsedimentary ore body into high grade metamorphosed (mobilized and remobilized) massive sulfide deposit, recrystallization and redistribution of chemical components were promoted by regional metamorphism under high P-T conditions, Dynamic metamorphism followed regional metamorphism which produced coherent finely granulated ore containing rounded porphyroclasts of host rock and those of pyrite (ball texture).

Preliminary lead-lead isotope data (²⁰⁷ Pb vs. ²⁰⁶ Pb / ²⁰⁴ Pb and ²⁰⁸ Pb / ²⁰⁴ Pb vs. ²⁰⁶ Pb / ²⁰⁴ Pb) indicates an age of recrystallized galena ca 1.8 Ga.  The metamorphism and remobilization of the massive lead-zinc deposit of Rampura-Agucha, has been eventuated near pre-Delhi geological cycle.  The sulfur isotope composition of ¹³ S (sphalerite) depicts the range +7 to + 10.3, indicates the source of sulfur for the present area was either seawater or leached tholeiitic basalt, carbon isotope reveals the range of – 24 to 29%₀.