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

Autor: Chinchilla, Darío, Arroyo, X., Merinero, R., Piña, Rubén, Nieto, F., Ortega, L., Lunar, Rosario
Rok vydání: 2017
Zdroj: Digital.CSIC. Repositorio Institucional del CSIC
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Popis: Trabajo presentado a la XVI International Clay Conference (ICC), celebrada en Granada (España) del 17 al 21 de julio de 2017
The Patricia Zn-Pb-Ag deposit represents an example of polymetallic epithermal mineralization, unusual in northern Chile. The sulfide mineralization occurs as W-E oriented veins hosted in volcanic rocks, mainly andesite of Upper Cretaceous to Middle Tertiary age. 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. The pre-ore and post-ore stage is characterized by quartz, pyrite and arsenopyrite whereas the second stage is characterized by sphalerite, galena and minor amounts of Ag-bearing minerals. Two textural types of chlorite are identified within the mineralised veins of Patricia deposit: massive and oscillatory-zoned radiated chlorites. 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.%). Temperature and pressure of mineralising fluids are essential parameters to characterise ore forming processes in hydrothermal systems. Changes in chemical and/or physical conditions during the sequence of mineralisation are reflected in banded veins and comb, crustiform and colloform textures as well as compositionally zoned minerals. Several methods are commonly used to trace thermal variations within hydrothermal systems, including fluid inclusions studies, stable isotopes and mineral geothermometry. However, careful paragenetic determinations on the mineralogical assemblage are essential for obtaining meaningful results from the geothermometric methods. The aim of this study is to calculate the temperature to both types of chlorites using four different chlorite geothermometers [1,2,3,4] based on the system SiO2 -Al2 O3 -FeO-MgO-H2 O, and contrasting the results with fluid inclusions data [5]. 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.
Databáze: OpenAIRE
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