Ore-forming fluid constraints on illite crystallinity (IC) at Dexing porphyry copper deposit, Jiangxi Province

Illite, a distinctive kind of clay minerals of potassium alteration within the hydrothermal alteration zone, frequently occurs at the Tongchang porphy ry copper deposit ore field. The illite crystallinity (IC) value and expand ability are mainly affected by water/rock ratio or fluid flux. It was forme d by illitization of plagioclase and micas during hydrothermal fluid-rock i nteraction within the porphyry body and near the contact zone with wall roc ks. Moreover, the negative correlation between illite index (IC) and copper grade indicates that within the alteration zone, the smaller the illite cr ystallinity value, the higher the alteration degree, and the higher the cop per grade due to higher water/rock ratio, At lower levels of the porphyry b ody, however, the illite crystallinity (IC) values are mainly controlled by temperature and time duration.