Fluorite Mineralization in Garampani Thermal Spring Area, Palamau District, Bihar

Fluorite mineralization in the form of salt (grains < 0.5mm diam, crystalline white) and veins (grains 1-6mm diam crystalline, in shades of blue and voilet) is a conspicuous associate of Garampani thermal spring, Palamau District, Bihar, that belongs to an ENE-WSW trending belt of thermal springs in the northeastern Peninsular India. The springs of the belt are chemivally similar, characteristicallt enriched in F^-, and are associated with Post-Gondwana faulting.

The Gararnpani spring (67.5°C) which emerges along a silicified shear zone in Barakar sandstone (L. Gondwana), is of Na-Cl-HCO₃ type with near neutral pH (7.52 at 25°C), moderate specific conductance (352 mmhos/cm at 25°C), and is relatively enriched in F^- (9.1 ppm) and SiO₂ (67.2 ppm). Shallow groundwaters of the region are Ca-Na-HCO₃ (within Gondwanas) to Na-HCO₃-Cl types (within Archaean crystallines) with near neutral pH (7.1-7.6 at 25°C), low specific conductance (132-207 mmhos/cm at 25°C) and have low F^- (0.5-1.2 ppm) and SiO₂(12.3-24.0 ppm) content. Minor variations in the physicochemical properties of the thermal spring water in different periods, indicate slight mixing of shallow water.

From the estimated activity products of [Ca⁺⁺] [F^-]², it is apparent that the spring water and shallow non-thermal groundwaters are respectively oversaturated and undersaturated with respect to AP_Fluorite values at respective on-site temperatures of the samples. Both are, however, undersaturated with respect to calcite solubility. Physically contrasted spring-salt fluorite and the adjoining vein fluorite are co-ceived as precipitates from spring water and mixed stream water respectively. In the latter case, however, precipitation appears as episodic in nature. It is further envisaged that near saturation values of the springs of the belt with respect to AP_Fluorite could be related to subsurface fluorite mineralization.