In this study, the boron isotopic composition of Paleoproterozoic seawater is reconstructed using 811B of tourmaline from the Paleoproterozoic Pb-Zn deposits of Rajpura-Dariba, Zawarmala, and Rampura-Agucha in the Aravalli-Delhi Fold Belt (ADFB) as well as non-mineralized tourmaline bearing metapelites from the Mangalwar Complex (MC) and Gangpur Schist Belt (GSB). This is then used to constrain the source of the mineralizing fluids in Sedimentary Exhalative (SEDEX)- and Mississippi Valley Type (MVT)-deposits. Based on textural relations and chemical variations, tourmaline in the Rajpura-Dariba and Zawarmala deposits can be grouped into two generations: syn-mineralization Tur-I and metamorphic Tur-II. In contrast, a single generation of metamorphic tourmaline is identified in the Rampura-Agucha deposit and in the MC. Tur-I from Rajpura-Dariba has XMg of 0.14-0.56, while Tur-II is more magnesian (XMg = 0.58-0.77). Similarly, Tur-I from Zawarmala has a wide compositional range (XMg = 0.22-0.67), whereas Tur-II is Mg-rich (XMg = 0.39-0.67). Tourmalines from Rampura-Agucha and MC are also magnesian (XMg = 0.66-0.70 and 0.59-0.69, respectively). The 811B values of syn-ore tourmaline from Rajpura-Dariba and Zawarmala vary between -18.8%o and -16.1%o, and between -6.6%o and -4.0%o, respectively. Metamorphic tourmalines from Rajpura-Dariba, Zawarmala, Rampura-Agucha and MC have 811B values between -19.1%o and - 7.7%o. The 811B of the pelitic sediments in Rajpura-Dariba, Rampura-Agucha, the MC and the GSB were estimated from the 811B of metamorphic tourmaline hosted in them using mass balance constraints and P-T pseudosection modelling. Applying the B-isotope fractionation factor between Miocene shale and modern clay (Delta 11Bmiocene shale - modern clay = -3.8%o to -2.2%o) to the modelled 811B of post-diagenetic protoliths of the metapelites, the 811B of marine sediments for these basins were constrained between -15.1%o and - 10.2%o. Subsequently, using the Bisotope fractionation factor between modern clay and seawater (Delta 11Bmodern clay - modern seawater = - 45.2%o to -40.8%o), the 811B of Paleoproterozoic seawater is estimated to have been between +27.3%o and +33.4%o. The isotopically light 811B of syn-mineralization tourmaline from Rajpura-Dariba and Zawarmala (-18.8%o to -16.1%o and -6.6%o to -4.0%o, respectively), and worldwide SEDEX/MVT-type deposits in general (a median value of -9.6%o; compilation of Trumbull et al., 2020), implies that the B was most likely sourced from continental evaporites and not evaporated seawater and/or connate brine. Dissolution of early rift-related continental evaporites most likely act as a major source of basinal brines for the formation of SEDEX/MVT deposits during the sag-phase of basin development.