Anion Composition of Apatite in the Au-Cu Epithermal Deposit of Palai-Islica (Almería, SE Spain) as an Indicator of Hydrothermal Alteration

Javier Carrillo-Rosúa,Salvador Morales-Ruano,Iñaki Esteban-Arispe

doi:10.3390/min11121358

Javier Carrillo-Rosúa, Salvador Morales-Ruano + Show 1 more

Open Access

https://doi.org/10.3390/min11121358

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Abstract

The Palai-Islica deposit (Almería, SE Spain) is an Au-Cu epithermal deposit hosted in Neogene calc-alkaline andesites and dacites from the Cabo de Gata-Cartagena volcanic belt in the Betic Cordillera. Major element compositions of apatite from Palai-Islica orebody and related hydrothermally altered and unaltered volcanic rock from the region hosting the deposit were obtained to clarify the processes involved in their formation. Apatite in the host volcanic rocks is rich in chlorapatite and hydroxylapatite components (50–57% and 24–36%) and poor in fluorapatite components (12–21%), indicating assimilation processes of cortical Cl-rich material in the magmatic evolution. Apatite in the orebody sometimes has corrosion textures and is mostly fluorapatite (94–100%). Apatite from the hydrothermally altered host rock of the orebody systematically bears signs of corrosion and has variable and intermediate fluorapatite (19–100%), chlorapatite (1–50%), and hydroxylapatite (0–47%) components. The style of zonation and the composition are related to the proximity to the orebody. These features can be interpreted as the result of hydrothermal modification of high Cl, OH-rich volcanic apatites into F-rich apatites. The enrichment of F is related to the intensity of hydrothermal alteration and could therefore constitute a geochemical index of alteration and of mineralization processes.

Highlights

Apatite [Ca5 (PO4 )3 (F,Cl,OH)] is the most abundant phosphate in the Earth’s crust and appears in very different geological environments
It should be noted that, whereas the composition of the apatite is well characterized in magmatic rocks (e.g., [1,3,4,5,6,7,8,9,10,11,12,13,14,15]), and to a lower degree in hydrothermal apatites (e.g., [16,17,18]), or even as a provenance indicator (e.g., [19]), there is very little information on epithermal deposits
It can be deduced that apatite grains in the zones of hydrothermal alteration are inherited and not neoformed

Summary

Introduction

Apatite [Ca5 (PO4 ) (F,Cl,OH)] is the most abundant phosphate in the Earth’s crust and appears in very different geological environments It is a very common accessory phase in igneous and metamorphic rocks. Apatite presents great chemical variability regarding its anion content, with a wide range of solid solutions among the different end members (e.g., [1,2]). SE of Spain) has been characterized texturally and chemically The aim of this lish the chemical variability of apatite a hydrothermal especially, environment to study is to establish the in chemical variabilityenvironment of apatite in aand, hydrothermal and, investigate the especially, use of major‐element content asofanmajor-element indicator of the intensity the miner‐.

Geological and Mineralogical

Diagrams

Origin of Apatite

Findings

Chemistry of Apatite Crystals and Their Evolution

Conclusions