Significance of Fluid Inclusion Studies of Barytes Deposits of Rajgarh Area, District Alwar (Rajasthan) India

Fluid inclusions are little droplets of fluids that were present when the enclosing minerals grew or recrystallised from the same fluids. These droplets may be of aqueous solution, carbon dioxide, oil or any other fluids (Sorby, 1958,; Kennedy,1950; Roedder, 1962, 1984). Gas bubbles that occasionally are trapped in minerals, growing from gas saturated or boiling liquids and the globules of immiscible fluids, such as oil, that are trapped along with water phase(Roedder, 1963). The gas bubbles present in fluid inclusions were result of differential shrinkage of the liquid and the enclosing mineral during cooling from the higher temperature of trapping to the temperature of observation (Sorby,1958). The temperature of trapping can be estimated by heating the sample to the temperature when the bubble disappears. The fluid inclusions are used as evidence of characteristics of ore forming fluid and environment of deposition of Barytes at the Rajgarh belt. The applications of fluid inclusion are based on certain major assumptions as pointed by Sorby (1858), Roedder (1967, 1976) and Edington and Wilkins (1980) are summarized as: 1. Trapping of some fluid medium takes place within the crystal during the process of growing and development of some irregularities in it. 2. The Trapped fluid is a sample of the mineralising fluid at the time of trapping. 3. The inclusions after trapping do not loose or gain any quantity of material. 4. The inclusions once formed remains always in the same position. 5. Due to the thermal expansion or precipitation on the walls during cooling, the inclusions may change in volume (1 to 2%) .

The observations and conclusions based on studies by Sorby (1958) and Zirkel (1870) regarding the significance of fluid inclusions are still valid and useful (Roedder 1972). The distinction was not made by various workers of nineteenth century on fluid inclusions (Humphrey, Davy, Brewater, Sorby, Zirkel etc.) (Smith, 1953). Consequently the range of homogenization temperatures commonly observed in single crystal eventually gave rise to the feeling that leaking must have been common place and that any fluid inclusion data was untrustworthy. However, single sample may have inclusions of different nature and chemical composition. In the first half of the century the fluid inclusion study is largely attributed to the lack of understanding of origin of inclusions. By 1923, it was clear that fluid could be trapped in minerals after their formation (Dale, 1923). This problem was solved by Laemmlein (1929) on the healing of fracture surfaces. Yermakov (1949) identified the important class of pseudosecondry inclusions, the only tools for satisfactory interpretation of fluid inclusion origins have been available. Perrin and Roubault (1952) thought of inclusions of secondary origin. Some other believed that data from fluid inclusions are unreliable as leakage of inclusions is invariably there. Later on, Roedder and Skinner (1968) has experimentally shown that leakage in fluid inclusions usually does not occur.

In the present course of the fluid inclusion study, the barytes samples from various deposits of Rajgarh area were selected. For the study , many polished plates as well as polished thin sections were prepared . The inclusions were studied by nondestructive methods. The identification and various petrographic characters were observed under the Jenapole C-Z microscope and Leitz Labour Lux microscope of COHU with video camera and Sony Videographic Printer. Microthermometry apparatuses and freezer were not used as the heating and freezing of the samples was not possible because most of the inclusions observed from the samples of Rajgarh barytes are of secondary monophase type having an aqueous phase (Plate 3,4 ). in rare cases a few small vapour bubbles are also visible (plate 6 ).

Transparent to translucent barytes samples were selected from five major deposits of Rajgarh area i. e. Khora-Makhrora, Bhagat ka Bas, Jamrauli, Guarah Gujar and Ramsinghpura. Only transparent barytes were found suitable for fluid inclusion study. Barytes which is not transparent is unsuitable for the study as it imparts opacity for microscopic work. In non transparent barytes, fluid inclusion occur as a network of interconnected cavities, some of which partially filled with fluid. From a few translucent barytes which have some transparent zones where fluid inclusions could be noticed, were also selected for the study. After the selection of suitable samples the polished plates of barytes were prepared by adopting the traditional method. The thick plates were found suitable for the study of large number of inclusions.

Guarah Gujar and Ramsinghpura deposits have been used for petrography study of the fluid inclusions. In the barytes of the area only primary and secondary type fluids inclusions could be traced. Most of the samples show secondary fluid inclusions except one or two samples from Bhagat ka Bas mine. Pseudo secondary inclusions have not been found in any of the samples.

Primary fluid inclusions are observed in one or two samples from Bhagat ka Bas mine which are of biphasic nature confined to growth planes of barytes crystal. The inclusions are roughly of triangular, oval or rounded shape (Plate 5) having rounded vapour inclusions at places. Some independent vapour bubbles are also observed out of which some occupy more than 90% space in fluid inclusions. No presence of carbon dioxide and methane is located in inclusions.

The detailed petrographic study of fluid inclusions of barytes deposits of Rajgarh area reveals that most of the inclusions are of secondary type and monophase (Liquid) where as some of them consisting of two phases (liquid+ vapour ). Cryometric study shows that the cavities contain low density gas owing to their small size. They are possibly occupied by low density aqueous phase. Trails of isolated gaseous inclusions are also observed. Some mineral inclusions such as quartz and amphiboles of irregular surface have also been observed (Plate 1). Fluid inclusion in the studied samples are variable in size & shape and some of them are typically related to healed fracture, crossing the cleavage plane and grain boundaries (Plate 2,4,6). Their morphology vary from tubular to subspherical with regular to irregular shapes. Most inclusions are monophase occure in trails of very small size (Plate 4). In a few samples more than two or three trails are running parallel which transgress the cleavage and mineral boundary. Furthermore, some isolated inclusions are distributed along cleavage planes. The monophase inclusions are quite irregular in shape (plate 3, 4) showing subspherical to subellipsoidal (Plate 6) shapes. Occasionally some flat, negative crystal shaped inclusions are also found.

As mentioned above the barytes samples from the area contained mostly the secondary monophase inclusions and display irregular to oval shape. Occasionally small vapour bubbles (plate 5) are also visible. Freezing study was not performed on these inclusions because they indicate false temperature , because of metastability (Roedder, 1984). Being

inclusions would form if the original fluid at the time of trapping has a temperature of more than 70⁰ C (Roedder , 1984). No carbon dioxide phase was identified in any of the inclusions. Thus the fluid inclusion study of the area reveals that they must have been trapped at a temperature of around 70⁰ C.

The fluid inclusion study of barytes of Rajgarh area reveals that most of the inclusions are of secondary type and monophase (Liquid) where as some of them consisting of two phases (liquid+ vapour ). These inclusions are possibly occupied by low density aqueous phase. Fluid inclusion study of the area reveals that the fluid inclusions are variable in size & shape and typically related to healed fracture, crossing the cleavage plane and grain boundaries. Most of the secondary inclusions are monophase, occurs in trails of very small size and quite irregular in shape. The fluid inclusion study further reveals that they have been trapped at a temperature of around 70⁰ C, which indicates that the barytes of the area was not formed at temp. more than 70⁰ C and also under the low pressure conditions. These results can also be compared with the results described by Boni (1986) for Iqlesiente-sulcis mining district (Italy) barytes vein deposits (Cortecci et.al. 1989). It may therefore be concluded that Rajgarh barytes deposits of magmatic affiliation form at a great distance from the magmatic source under low temperature, pressure conditions where cavity filling dominates (Bateman, 1959), termed as telethermal deposits. Thus the contribution of meteoric water is also easily supported under these conditions. Plate 1 Plate 2 Plate 3 Plate 4 Plate 5 Plate 6

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