Origin of the Paleoproterozoic Giant Quartz Reef System in the Bundelkhand Craton, India: Constraints from Fluid Inclusion Microthermometry, Raman Spectroscopy, and Geochemical Modelling

The Bundelkhand giant quartz reef (BGQR) system comprises 20 major quartz reefs which run for tens of km in strike length of average width of 40m and occurs in spatial intervals of 12-19 km in the Bundelkhand craton, North Central India. The BGQR system is distinct from quartz vein systems originating from crustal scale shearing observed in ancient as well as modern convergent tectonic settings. Fluid inclusions studied in BGQR system are intriguingly diverse although dominated by aqueous fluid which exhibit a broad range of salinity from similar to 0 to 28.9 wt% NaCl equivalent and temperature of homogenization range of 58 to 385 degrees C. Primary and pseudosecondary aqueous inclusions in assemblages in grain interiors and growth zones vary randomly in their T-h-salinity characteristics that preclude identification of discrete fluid events. Aqueous fluid in the BGQR system evolved through mixing of two distinct sources of fluids-a meteoric fluid and a moderate temperature-moderate salinity fluid that was possibly derived from the Bundelkhand granodiorite based on an important clue provided by hydrous mineral bearing fluid inclusions detected by Raman microspectrometry. The results of modeling with PHREEQC indicate that mixing of fluids could be a suitable mechanism in formation of these giant reefs. The available 1-dimensional diffusive transport model for deposition of silica helps in putting constraints on the time span of deposition of silica in the context of the BGQR system. The BGQR system is a possible result of shallow-crustal sources of fluid and silica and could be visualized as a Paleoproterozoic geothermal system in a granitic terrane.

Automated summary

The Bundelkhand giant quartz reef (BGQR) system is a unique system of quartz veins in North Central India. The diverse fluid inclusions in the BGQR system suggest a mixing of two different fluid sources. Modeling results indicate that fluid mixing is a suitable mechanism for the formation of these giant reefs. The deposition time span for silica in the BGQR system can be constrained using a diffusive transport model.