Epigenetic - Cavity Filling Process a Genetic Model of Barytess Deposits of Rajgarh, District Alwar (Rajasthan)

Barytess, or barite, (BaSO4) is a mineral consisting of barium sulfate. The barytes group consists of barytes, celestine, anglesite and anhydrite. Barytes itself is generally white or colorless, and is the main source of barium. Barytes and celestine form a solid solution (Ba,Sr)SO4. Barytes that is used as an aggregate in a "heavy"cement is crushed and screened to a uniform size. Most barytes is ground to a small, uniform size before it is used as a filler or extender, an addition to industrial products. Some 77% worldwide is used as a weighting agent for drilling fluids in oil and gas exploration to suppress high formation pressures and prevent blowouts. As a well is drilled, the bit passes through various formations, each with different characteristics. The deeper the hole, the more barite is needed as a percentage of the total mud mix. An additional benefit of barite is that it is non-magnetic and thus does not interfere with magnetic measurements taken in the borehole, either during logging-while-drilling or in separate drill hole logging.

Barytes occurs in a large number of depositional environments, and is deposited through a large number of processes including biogenic, hydrothermal, and evaporation, among others.[1] Barytes commonly occurs in lead-zinc veins in limestones, in hot spring deposits, and with hematite ore. It is often associated with the minerals anglesite and celestine. It has also been identified in meteorites. Sedimentary exhalative deposits are the most important source of lead, zinc and barites and that the ore minerals were deposited in a marine second-order basin environment, related to discharge of metal-bearing brines into the seawater. This is distinct from other Pb-Zn-Ag and other deposits which are more intimately associated with intrusive or metamorphic processes or which are trapped within a rock matrix and are not exhalative. The process of ore genesis of sedimentary exhalative mineralization is varied, depending on the type of ore which is deposited may be sourced from magmatic a magma chamber intruding into saturated sediments. This scenario is relevant to mid-ocean ridge environments and island arc volcanic chains where black smokers are formed by discharging hydrothermal fluids.

• Transport of these brines follows stratigraphic reservoir pathways toward faults, which isolate the buried stratigraphy into recognisable sedimentary basins. The brines percolate up the basin bounding faults and are released into the overlying oceanic water.

• Trap sites are lower or depressed areas of the ocean topography where the heavy, hot brines flow and mix with cooler sea water, causing the dissolved metal and sulfur in the brine to precipitate from solution as a solid metal sulfide ore, deposited as layers of sulfide sediment.

Upon mixing of the ore fluids with the seawater, dispersed across the seafloor, the ore constituents and gangue are precipitated onto the seafloor to form an orebody and mineralization halo which are congruent with the underlying stratigraphy and are generally fine grained, finely laminated and can be recognized as chemically deposited from solution. Arkose-hosted sedimentary exhalative deposits are known in some cases, associated with arkosic strata adjacent to faults which feed heavy brines into the porous sands, filling the matrix with sulfides, or deposited within a predominantly arkosic layer as a distinct chemical sediment layer usually associated with a shale interbed or at the lowermost levels of a shale formation directly overlying arkosic sands (for example, copper deposits near Maun, Botswana).

Barytess deposites of Alwar district, Rajasthan occur in two distinct belts i.e. Rajgarh and Alwar belt. The barytess producing mines are mainly located in Rajgarh belt. The deposits of Rajgarh area belong to the Proterozoic supra crustal of Delhi supergroup laying uncomformably over the Archaen granite of Aravali Supergroup. The stratigraphic sequence strats from Aravalli system overlain by Pre Delhi Formation. The sequence of Delhi Supergroup starts with basal conglomerates, which is arkosic at places. The entire sequence shows a facies change from arenaceous member in the lower portion to calcareous in the middle and argillaceous in the upper portion. Major structure in the area are NE-plunging syncline in Guarah Gujar mine area and N-plunging anticline in north of Rajgarh and Reni anticline. Beside the prominent faults are ; (1) The Rajgarh fault, (2) Sure fault and (3) Fault running to the S.E. of Guarah Gujar. quartz-sericite-schist intrbedded with quartzite. The different types of fissures veins of byrites viz: simple, chambered, dilation or lenticular, sheeted and linked and en’echelon veins, formed by the cavity filling process of hydrothermal solution is one of the most important feature.

In Rajgarh belt the barium is thought to be derived from magmatic and volcanic emanations. The metavolcanics present in the area, represented by massive amphibolites and amphibolites schist. Further more one of the source of barium was the meteoric water circulating downward which extracted barium from alkali felspars of granite of Aravalli system and felspathic and massive quartzite of Alwar series, which is similar to that of barites deposites of east Missouri(Leach 1981) and Iglesiente- Sulsis Italy (Cortecci et.al.1989).

The sulphur required for the precipitation of barites in the Rajgarh area thought to have been derived from the sulphides of the area. Besides, it might have been derived from Kho-Dariba Copper deposites area which is near to the barites deposites of the area, indicated by the following equation;- FeS₂+1½O₂ Normal temp. FeO + SO₂ + S ----------→ Oxidised Reduced The additional source of sulphure could be envisaged from chalcopyrite also, which is represented by the following equations 2CuFeS₂+ CO₂ + H₂O + 2O₂ ----------→ Cu₂(CO₃)(OH)₂ + 2FeO + 4S Malachite Reduced The presence of carbonaceous phyllite in the are suggested that the CO₂ was derived from the organic matter which is also responsible for the formation of malachite. Besides, the appreciable quantity of sulphure has been provided by leeching of granite of the Rajgarh belt, similar to that as suggested by Cortecci et.al.(1989) for lglesientesulsis barites of Italy.

The large amount of base metals can be transported and deposited by chemical solutions was similar to that which was required for the transport of large amount of barium and depositing as barites (Blount, 1977). Accordingly in Rajgarh area, the various gases

in anhydrous phase to form various brines like BaCL₂, BaF₂ and BaCO₃as barium has many affinities with highly electronegative elements like Cl, Br, CO₂ etc. accordingly barium is easily transported in the form of barium bearing brines.

The barites of Rajgarh area has been precipitated due to the non-equilibrium oxidation of reduced sulphure from sulphide ores in the country rocks. The oxidation of sulphur may also take place from H₂S or HS carried by brines and oxidation promoted by dissolved oxygen in meteoric water (Ohomoto and Rye, 1979) as shown in reaction:

HS + 2O₂ ----------→ SO₂²ˉ + H+

The precipitation of berytes of Rajgarh area can better be explained by chemical model in which a series of oxidation –reduction reactions are involved. Sulphides in country rocks and adjoining area is considered to be oxidation to form reduced sulphate. Pyrite and chalcopyrite get oxidized to form reduced sulphur at normal temp. and aereal conditions which further gets oxidized in to SO₂ and sulphite (SO₃)at some higher temperature, which are soluble in water and H₂SO₃ and H₂SO₄ respectively as shown in the following equation: FeS₂+1½O₂ Normal temp. FeO + SO₂ + S ----------→ Oxidised Reduced 2CuFeS₂+ CO₂ + H₂O + 2O₂ ----------→ Cu₂(CO₃)(OH)₂ + 2FeO + 4S Malachite Reduced SO₂ + ½O₂ ----------→ SO₃ (Oxidised Sulphur)

SO₂ + H₂O ----------→H₂SO₃ SO₃ + H₂O ----------→ H₂SO₄

H₂SO₄ further reacts with sulphides to form sulphate under some changed conditions of temperature at some greater depth. FeS₂ + H₂SO₄ ----------→ FeSO₄ + H₂S + S (Reduced) This sulphate percolates downward with meteoric water and combine with barium brine like BaCl2, BaF2 and Ba Co3 which formed due to interaction of barium emanations as shown in the following equation: Ba + 2HCl ----------→ BaCl₂ + H₂ Ba + 2HF ----------→ BaF₂ + H₂ Ba + CO₂ + H₂O ----------→ BaCO₂ + H₂ During the migration of ascending magnetic emanations and hydrothermal solutions the barium bearing brins combine with the sulphate to precipitate the barites as shown in the following reaction: BaCl₂ + FeSO₄ ----------→ BaSO₄ + FeCl₂ (Soluble in water) BaF₂ + FeSO₄ ----------→ BaSO₄ + FeF₂ (Soluble in water) BaCO₂ + FeSO₄ ----------→ BaSO₄ + FeCO₃ (Soluble in water) The precipitated mineralizing solution was travelled upward through the major NNE-SSW trending fault between Aravalli and Delhi’s and deposited along cross joints and at places along bedding foliation planes. It shows structural control of mineralization of Rajgarh area.

On the basis of mode of occurrence, texture and structure exhibited by the barites mineralization of the area, it is therefore concluded that the Rajgarh barites deposits formed at low temperature and pressure (telethermal) in which the mineralizating solution was controlled structurally and deposited at the open spaces as cavity filling during the last phase of hydrothermal activities

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