The Biga Peninsula of NW Turkey is host to six major halloysite deposits in the G6nen, Yenice and Balya districts. Mineralization took place in areas of Permian limestone blocks where the Triassic Karakaya Complex is in contact with early Miocene cale-alkaline volcanic rocks. Hypogene halloysite mineralization was controlled by tile intersection of minor faults in the vicinity of clay deposits. During the Pleistocene, activity of the North Anatolian Fault (NAF) brought ascending geothermal solutions through the fault zones to the surface, which led to hydrotherrual alteration and halloysite formation. N-MORB normalized element values for each halloysite deposit and the volcanic rocks suggest genetic links. Alunite and halloysite were formed in the Turplu area where UpWelling hydrotherinal waters contained major H2S and S02 acids. Only halloysite 16 mineralization occurred in outflow areas of the same fossil geothermal field.