The Yenipazar deposit of volcanogenic sulfide occurrence, situated approximately 9 km SW of Yenipazar, is hosted in quartz-muscovite schists and gneiss. Following the Late Cretaceous, the quartz-mica schists and gneiss have been altered to clay minerals, resulting in important kaolin deposits. The clay deposits consist mainly of halloysite, kaolinite, smectite, illite, muscovite, chlorite, and α-quartz. Biotite, alunite, jarosite, pyrite, hematite, calcite, low cristobalite, and feldspar are present in minor amounts. In places, some mixed-layer clays, such as kaolinite/smectite and smectite/illite, are also observed within the clay deposits. Barite is present in a few clay samples. α-Quartz is the dominant silica mineral in all parts of the clay bodies, though silicification becomes more intense in an upward direction. Kaolinite and halloysite are the dominant clay minerals in the upper section of the clay deposits containing up to 36.10% Al2O3. At the middle and lower parts of the clay deposits, smectite and illite/mica are predominant. The Yenipazar clays are characterized by 41.80%-66.10% SiO2, 16.80%-36.10% Al2O3, 2.10%-17.70% Fe2O3, 0.30%-6.20% MgO, 0.10%-5.70% CaO, 0.1%-0.70% Na2O, and 0.10%-3.80% K2O values. The silica gossan in the upper parts of the clay deposits and the mineral zonations reveal that hydrothermal alteration is the main cause for the development of the kaolin dominated clay deposits. Pb, Zn, Cu, Sr, Ba, and Zr enrichments and depletion of Cr, Nb, Ti, Ce, Y, and La within the clay deposits are supportive of the magmatic origin of the hydrothermal solution related to Late Cretaceous arc magmatism. Depletion of both total REEs and HREEs, as well as the enrichment of LREEs, in clay deposits refer to an altering acidic solution. The positive Eu and Ce anomalies indicate the presence of feldspar and Zr crystals in the clays, respectively. However, the data show that corrosive hot solutions, which might have arisen from magma, have played an important role in the kaolinization process together with hot meteoric waters. Scanning electron microscope investigations show that illite and smectite are the first minerals formed by the hydrothermal alteration of feldspar crystals.