Chlorite geothermometry applied to massive and oscillatory-zoned radiated Mn-rich chlorites in the Patricia Zn-Pb-Ag epithermal deposit (NE, Chile)

Abstract

Two textural types of chlorite are identified in the mineralised veins at the Patricia Zn-Pb-Ag epithermal ore deposit (NE, Chile): massive and oscillatory-zoned radiated chlorites. Three main stages of mineralisation have been defined in the Patricia deposit: (1) pre-ore stage, (2) base-metal stage which is divided into two substages: substage 2a and substage 2b and (3) post-ore stage. Both types of chlorite are classified as chamosite and occur coeval to the sphalerite precipitation during the substage 2a. Massive chlorite shows an average content of 33 wt.% FeO, 4.9 wt.% MnO, and 4 wt.% MgO. Oscillatory zoning in radiated chlorites consists of concentric bands with different contents on FeO (from 26.45 to 41.41 wt.%), MgO (from 1.7 to 5.44 wt.%) and MnO (from 1.7 to 9.32 wt.%). Four different chlorite geothermometers based on the system SiO2-Al2O3-FeO-MgO-H2O were applied to both types of chlorites. The temperature estimations are in agreement with temperatures data of fluid inclusions previously measured in sphalerite of the sub-stage 2a. Despite the high content in Mn of chlorites, the study confirms the applicability of the chlorite geothermometers without the knowledge of the Fe3 +/Fe ratio in low-pressure paragenesis and its usefulness as an important tool for characterising the thermal conditions in epithermal ore deposits.