Physicochemical conditions during the formation of Dalingkou Ag-Pb-Zn deposit, Zhejiang Province

Abstract

On the basis of mineral paragenesis and the chemistry and homogenization temperatures of fluid inclusions, the physicochemical parameters were calculated for the formation of the Dalingkou Ag-Pb-Zn deposit in Zhejiang. From the early to the late stage of mineralization the ore-forming temperature venation was found to be 298.5 °C → 267.0 °C → 217.6 °C → 167.3 °C, with a corresponding pH change of 3.0 ∼ 5.8 → 6.1 → 6.7→ 5.0 ∼ 7.3. The pressure changed from 403.8 to 128.5 atm, andlogf S₂-9.9 → -11.2 → < -15; logf o₂< -44→ -45.6 ∼ -42.6 → > -44.2; and logf co₂ around -1.55.

In conjunction with geological observations, the deposit is considered to be of meso-epithermal origin, i.e., it was formed after continental volcanic-subvolcanic activity. The major factors affecting ore precipitation are the decreasing temperature and the increasing pH of ore-forming solutions.