The Proterozoic Aravalli-Delhi orogenic complex hosts a large number of economically important stratabound base metal sulphide deposits. In the present work, rock samples taken from Outcrop and Underground Mine of Sindeskar Kalan, Vedanta Group, Rajpura Dariba-Bethumni Belt which is located at a distance of 76 kms from Udaipur city, Rajasthan have been studied. The chief litho units of the group which contain sulfide-bearing calc-silicate and graphite mica schist, dolomite marble, calc-biotite schist and quartzite are identified. An attempt has also been made to study/or hydrothermal in origin in the different types of fluid inclusions, hosted predominately in Geothermometry viz. heating and freezing study of entrapped palaeo-fluids (such as sedimentary and quartz host grain and a few in sphalerites). The quartz hosts are identified with four types of fluid inclusions, such as 1) monophase (gas/vapour), 2) gas-rich biphase, 3) liquid-rich biphase and 4) polyphase types. The primary types of fluid inclusions show that melting temperature of ice or depression freezing point (DFP) (ranging from -2.5 °C to -7.2 °C)/(salinity ranging from 4.5 - 13.25 wt% NaCl eq.) and temperature of homogenization into liquid phase (ranging from +188 °C to +218 °C) have been measured. Data from the fluid inclusions and salinity calculation (low salinity) reveal that rate of cooling is the important mechanism of ore deposition in the study area.
The Aravalli province, which is located in the state of Rajasthan, India, constitutes the most important metallogenic province for base-metal deposits [
In general, Aravalli rocks in Udaipur-Zawar region show a low-grade metamorphism. The recrystallisation of the silicate minerals suggests the grade of metamorphism to be of greenschist facies [
The province is characterized by an Archaean basement overlain by thick successions of intensely deformed and metamorphosed volcanic and sedimentary rocks [
The geology of Rajasthan has been studied by many experts over decades and the different major geological units and prominent faults and lineaments of this region. The crust of the northwestern Indian Craton in Rajasthan comprises the Achaean Banded Gneissic Complex (BGC) forming the basement, overlain by the Proterozoic Delhi Aravalli Fold Belts of Delhi and Malani Igneous Suite, most of which are covered by the Tertiary and Quaternary sediments. Studies by [
The Aravalli mountain range in the northwest part of India extends over 700 km in length with a general NE-SW trend (
General stratigraphy of the study area [
A total of 50 samples were collected from the different Levels of underground mine as well as outcrop samples from the selected mine (both of ores and rocks) of the study area, out of which fresher and unweathered samples were selected for fluid inclusion petrography and its microthermometry. Petrographic studies of the polished section and doubly polished thin sections of quartz and sphalerite were carried out under transmitted and reflected light respectively.
The micro thermometric studies were performed by using a Chaixmeca stage fitted on a Leitz Laborlux microscope. The main purpose of micro thermometric study was to observe and record the different phase transitions within the fluid inclusions in response to temperature changes.
Quartz and sphalerite samples were initially examined but because the fluid inclusion population in sphalerite samples was far too low for any meaningful study, the work was restricted to samples of quartz.
1) Monophase Fluid Inclusions
The monophase fluid inclusions have only one phase at room temperature [
2) Biphase Fluid Inclusions
The biphase fluid inclusions have two phases at room temperature. The Primary biphase fluid inclusions appear to have a vapour phase ( Plate 1 ) (represented by a bubble inside the inclusion) and a liquid phase under the microscope and vice versa. The bubble phase generally observed to have a dark periphery. The biphase fluid inclusions are very wide in shapes and sizes (
3) Multiphase Fluid Inclusions
The multiphase fluid inclusions have more than two phases at room temperature. The Multiphase fluid inclusions have variable shape and size. Some of multiphase fluid inclusions have daughter crystal of halite, sylvite,
Plate 1. Photomicrographs showing―(a) and (b) Conoscopics and Orthoscopics view of the liquid rich polyphase fluid inclusion. (c) and (d) Conoscopics and Orthoscopics view of the liquid rich polyphase fluid inclusion. (e) and (f) Orthoscopics and Conoscopics view of the liquid rich biphase fluid inclusion. Rajpura-Dariba Belt, Uaipur (Rajasthan).
View | Type of fluid inclusion | L/V ratio | Size of inclusions | Shape of inclusion | Host mineral | |
---|---|---|---|---|---|---|
(a) | Conoscopic | Liquid rich polyphase | 80/15 | 10 μm | Polygonal | Quartz |
(b) | Orthoscopic | Liquid rich polyphase | 75/20 | 15 μm | Polygonal | Quartz |
(c) | Conoscopic | Liquid rich polyphase | 75/20 | 14 μm | Subrounded | Quartz |
(d) | Orthoscopic | Liquid rich polyphase | 70/25 | 14 μm | Subrounded | Quartz |
(e) | Conoscopic | Liquid rich biphase | 85/15 | 15 μm | Globular shape | Quartz |
(f) | Orthoscopic | Liquid rich biphase | 75/25 | 14 μm | Elongated | Quartz |
(g) | Conoscopic | Liquid rich polyphase | 85/15 | 20 μm | Polygonal | Quartz |
(h) | Orthoscopic | Liquid rich polyphase | 85/15 | 20 μm | Polygonal | Quartz |
(i) | Orthoscopic | Liquid rich biphase | 80/20 | 16 μm | Hexagonal | Quartz |
(j) | Orthoscopic | Liquid rich biphase | 80/20 | 18 μm | Hexagonal | Quartz |
(k) | Orthoscopic | Liquid rich biphase | 85/15 | 14 μm | Hexagonal | Quartz |
(l) | Orthoscopic | Liquid rich biphase | 75/25 | 14 μm | Oval | Quartz |
anhydrite [
4) Biphase and Polyphase Fluid inclusions
Biphase fluid inclusions have two phases at room temperature. The Primary biphase fluid inclusions appear to have a vapor phase (represented by a bubble inside the inclusion) and a liquid phase under the microscope ( Plate 2 ) and vice versa. The bubble phase generally observed to have a dark periphery. The biphase fluid inclusions are very wide in shapes and sizes (
Secondary fluid inclusions are those which are developed due to the filling by the later fluids along the fractures initiated during the mechanical and thermal stress on the early formed crystal. They give us information on the nature of fluids that have interacted with the minerals after their formation [
・ Planar groups, outlining healed fractures ( Plate 4 ).
・ Thin, flat nature and small in size ( Plate 4 ).
Touret [
Sang [
Plate 2. Photomicrographs showing―(g) and (h) Conoscopics view of the liquid rich polyphase fluid inclusion in different light focus. (i) and (j) Orthoscopics view of the liquid rich biphase fluid inclusion show negative crystal cavity. (k) and (l) Orthoscopics view of the liquid rich biphase fluid inclusion show negative crystal cavity. Rajpura-Dariba Belt, Uaipur (Rajasthan).
Plate 3. Photomicrographs showing―(a) and (c) Orthoscopics and conoscopic view of the liquid rich multiphase fluid inclusion. (b) and (e) Orthoscopic and Conoscopics view of the liquid rich multiphase fluid inclusion. (d) Multiphase inclusion, CO2 gas bubble may present (f) Trapped crystal along fracture plane. Rajpura-Dariba Belt, Uaipur (Rajasthan).
Plate 4. Photomicrographs showing secondary fluid inclusion. (a) and (b) Trails of secondary biphase fluid inclusion along the rehealed fracture zone. (c) and (d) Trails of secondary biphase fluid inclusions along the growth zone. (e) and (f) Trails of secondary biphase fluid inclusions which cross grain boundary.
Plate 5. Sets of parallel trails of biphase secondary fluid inclusions cutting by fractures.
Plate 6. Trails of biphase secondary fluid Inclusions cutting across the fracture within the grain.
appear to be variations in surface tension from temperature differences over the bubble surfaces, causing flow of the surface that drag fluid with it. The motions are useful in inclusions studies in various ways.
1) Motion of fluid depends on composition and viscosity of fluid, so viscosity of fluid may determined.
2) The phenomena determine the freezing temperature of those inclusions in which the last ice crystal sticks to the bubble liquid interfaces.
3) The thermal gradient may use to discriminate between glass and liquid inclusion.
Micro thermometry analysis is the most popular and widely used non-destructive analytical technique [
Salinity determinations of fluid inclusions are down by using the freezing point of the water in aqueous biphase inclusions and clathrate dissociation temperature in CO2 containing fluid inclusions. Bodnar [
where Ѳ = Freezing point depression (DFP) in ˚C.
Salinity of the CO2 containing fluid inclusions are not calculated by the above equation because in the H2O- CO2-NaCl system clathrate melting temperature is a function of salinity.
Micro thermometric studies carried on primary biphase fluid inclusions presents in the quartz. The primary biphase fluid inclusions freeze around −93.7˚C to −97.4˚C (
Plate 7. Microphotographs (a) to (d) showing false brownian motions of biphase fluid inclusions (smple no 1 of level 315, (e) to (h) showing false brownian motions of biphase fluid inclusions (smple no 2 of level 350. Host mineral quartz. Rajpura-Dariba Belt, Uaipur (Rajasthan).
S.N. | Sample and UG Level No. | Temperature of Freezing (Tf) in ˚C | Temperature of Melting of Ice (Tm) or DFP in ˚C | Temperature of Homogenization (Th) in ˚C | Salinity |
---|---|---|---|---|---|
1 | 315 Meter (1.0) | −93.7 | −3.7 | +188 | 6.67 |
2 | 1.2 | −94.1 | −3.2 | +218 | 5.76 |
3 | 1.3 | −94.3 | −3.2 | +200 | 5.76 |
4 | 1.4 | −94.1 | −3.2 | +218 | 5.76 |
5 | 1.5 | −94.1 | −7.2 | +200 | 13.26 |
6 | 1.6 | −94.1 | −7.2 | +200 | 13.26 |
7 | 1.7 | −97.1 | −3.2 | +201.1 | 5.76 |
8 | 1.8 | −97.1 | −3.3 | +202 | 5.76 |
9 | 1.9 | −96.8 | −3.4 | +201.9 | 6.15 |
10 | 1.10 | −96.8 | −3.7 | +201.2 | 6.68 |
11 | 1.11 | −97.1 | −3.3 | +201.1 | 5.95 |
S.N. | Sample and UG Level No. | Temperature of Freezing (Tf) in ˚C | Temperature of Melting of Ice (Tm) or DFP in ˚C | Temperature of Homogenization (Th) in ˚C | Salinity |
---|---|---|---|---|---|
1 | 350 Meter (2.0) | −97.1 | −3.3 | +201 | 5.95 |
2 | 2.1 | −97.5 | −3.2 | +202.1 | 5.76 |
3 | 2.3 | −96.8 | −3.2 | +201.1 | 5.76 |
4 | 2.4 | −97.1 | −2.4 | +210 | 4.30 |
5 | 2.5 | −97.1 | −2.4 | +198 | 4.30 |
6 | 2.6 | −97.4 | −2.5 | +188 | 4.48 |
7 | 2.7 | −96.8 | −2.5 | +201.1 | 4.48 |
8 | 2.8 | −96.8 | −2.5 | +209 | 4.48 |
9 | 2.9 | −93.7 | −2.5 | +201.1 | 4.48 |
10 | 2.10 | −102.1 | −3.2 | +188 | 5.76 |
S.N. | Sample and UG Level No. | Temperature of Freezing (Tf) in ˚C | Temperature of Melting of Ice (Tm) or DFP in ˚C | Temperature of Homogenization (Th) in ˚C | Salinity |
---|---|---|---|---|---|
1 | 375 Meter (3.0) | −98.1 | −3.7 | +201.1 | 6.68 |
2 | 3.1 | −96.1 | −4.5 | +188 | 8.15 |
3 | 3.2 | −98.2 | −3.4 | +188 | 6.14 |
4 | 3.3 | −97.1 | −3.2 | +201.1 | 5.76 |
Heating and cooling studies are performed on quartz samples of different underground levels using Chaixmeca stage (−196˚C to +600˚C) fitted on a Leitz Laborlux microscope. The accuracy of heating and freezing measurement is about ±0.5˚C. The phase transformations observed in inclusions during freezing and heating studies on the various types of inclusion observed in quartz associated with sphalerite and galena ores.
Salinity determination of fluid inclusions is done using values of freezing point depression in the equation of Bodnar [
Result is showing the low salinity ranges (4.5 - 13.23 wt% NaCl eq.) and also low temperature of homogenization which reveal that the rate of cooling was the important mechanism of ore deposition in the study area.
The present study of Rajpura-Dariba-Bethumni Belt, Udaipur (Rajasthan), is on fluid inclusions petrography of Proterozoic Carbonate hosted formation. The Underground samples collected from the level of 375 meter, 350 meter and 315 meter from the SK mines, Vedanta Group Udaipur. This work involved the study of ore-petro- graphy, thin section petrography, wafer thin section (0.3 mm) petrography for fluid inclusions. On the basis of above parameters the following discussion was made to bring out valuable conclusion at the end.
The fluid inclusions study of host mineral quartz samples show that the presences of primary inclusions which are mainly multiphase types ( Plate 2 ), biphase ( Plate 3 ) and very few of liquid-rich monophase types of fluid inclusions. The majority of the inclusions are liquid rich biphase types having small gas/vapour bubble. In multi phase fluid inclusions the presences of daughter crystals and trapped crystals are more prominent than liquid phase. The secondary fluid inclusions are mainly biphase and occur as trails. The Population study of fluid inclusions shows that primary biphase inclusions are more at 15 - 20 µm size ( Plate 3 ).
Fluid inclusions in different diagenetic environments show different features e.g. the post diagenetic fluid inclusions show occurrences along growth zone of the host quartz and in the cementing material of it. A few of them were of naturally decrepitated fluid inclusion cavities. These changes by occurrences of different generations of fluid inclusions may through some light on paleoclimatic conditions of the study area. The fluid inclusion stratigraphy (FIS) shows ( Plate 5 and Plate 6 ) the cross cuttings relationship between the trails of fluid inclusions and/or with the cleavages and micro-fractures, which gives the indication of younger and older sequences of generations of fluid inclusions within a particular quartz grain boundary.
The micro-thermometric analyses of primary biphase fluid inclusions (H2O-NaCl) system show that the salinity of trapped fluid is vary between 4.5 - 13.25 wt% NaCl which indicates that the paleo-fluids might have been moderate in salinity and were showing the temperature of homogenizations ranging from 188˚C to 218˚C.
The authors are thankful to Indian Institute Technology Bombay for field and laboratory support in carrying out the investigation, to Chairman of Department of Geology, AMU Aligarh for providing necessary facilities and to Mr. Partha Sarath Chaudhary and Mr. Mohd Shaif (Research scholars) for fruitful discussion and support.