A method for in situ undercut solution mining of a subterranean ore bed, said ore bed comprising a desired solute being selected from the group consisting of sodium sesquicarbonate, sodium carbonate, and sodium bicarbonate, said ore bed having a floor and a roof, the method comprising the following steps: ▪ injecting a solvent comprising water through an unlined borehole portion, said unlined borehole portion comprising a downhole end positioned within said ore bed and above said bed floor, said unlined borehole portion being horizontal or being slanted with one of its ends being at a higher elevation than the other end, in order to expose to the solvent an ore region within said unlined borehole portion or adjacent to said downhole end of said unlined borehole portion; ▪ dissolving at least a portion of the desired solute, from said solvent-exposed ore region in a manner effective to form a liquor comprising said dissolved desired solute, and to further form an undercut above the bed floor, said undercut comprising at least a section of said unlined borehole portion which has been eroded by dissolution; ▪ repeating the solvent injection to dissolve additional desired solute from the ore thereby enriching the liquor in desired solute, and further in a manner effective to widen the undercut and to trigger the fracture of unexposed ore located above said undercut and the downward movement of fractured ore rubble by gravity into the undercut, while allowing the ore roof to sag but not to break so as to minimize chloride contamination of the liquor by preventing exposure of said solvent to chloride-containing material located at or above the ore roof; and ▪ flowing the liquor towards a subterranean collection zone in order to pass said liquor to a terranean location. ▪ injecting a solvent comprising water through an unlined borehole portion, said unlined borehole portion comprising a downhole end positioned within said ore bed and above said bed floor, said unlined borehole portion being horizontal or being slanted with one of its ends being at a higher elevation than the other end, in order to expose to the solvent an ore region within said unlined borehole portion or adjacent to said downhole end of said unlined borehole portion; ▪ dissolving at least a portion of the desired solute, from said solvent-exposed ore region in a manner effective to form a liquor comprising said dissolved desired solute, and to further form an undercut above the bed floor, said undercut comprising at least a section of said unlined borehole portion which has been eroded by dissolution; ▪ repeating the solvent injection to dissolve additional desired solute from the ore thereby enriching the liquor in desired solute, and further in a manner effective to widen the undercut and to trigger the fracture of unexposed ore located above said undercut and the downward movement of fractured ore rubble by gravity into the undercut, while allowing the ore roof to sag but not to break so as to minimize chloride contamination of the liquor by preventing exposure of said solvent to chloride-containing material located at or above the ore roof; and ▪ flowing the liquor towards a subterranean collection zone in order to pass said liquor to a terranean location.