Application of lanthanides tetrad effect as a geochemical indicator to identify fluorite generations: A case study from the Laal-Kan fluorite deposit, NW Iran

Mansour Rezaei Azizi,Samad Alipour,Ali Abedini

doi:10.5802/crgeos.2

Abstract

The Laal-Kan fluorite deposit situated in north margin of the Sanandaj-Sirjan metamorphic belt and Urmia-Dokhtar magmatic arc, NW Iran. The fluorite mineralization in the form of open-space filling, veins and veinlets have been deposited in the contact zone between highly metamorphosed schist, gneiss, amphibolite of the Paleozoic age and the Jangutaran limestone of the Precambrian age. The occurrence of convex tetrad effect and the calculated tetrad values indicate that early and late stage fluorite mineralization display various geochemical behavior, which are supported by the bivariate diagrams including T1, T3 and T4 versus each other and some geochemical parameters such as La/Ho, Y/Ho and Zr/Hf ratios. It can, therefore, deduced that fluorite have been probably formed during two stages from hydrothermal fluids with a relatively constant composition. The fluid-rock interaction during deposition of fluorite and REE-F complex were likely the main mechanisms for the occurrence of tetrad effect.

Highlights

Lanthanides and Y known as Rare Earth Elements (REE) generally occur in the trivalent oxidation state (Ln3+) except Ce (Ce3+ and Ce4+) and Eu (Eu2+ and Eu3+), which display very similar behavior during geochemical processes in a wide range of geological environments [Bau and Dulski, 1995, Shannon, 1976]
In this paper we focused on the behavior of the REE and some trace elements with emphasizes on the occurrence of tetrad effect in fluorite samples to constrain the difference between early and late stage fluorite precipitation in the hydrothermal fluorite deposit of the Laal-Kan district
The mineralogy studies in the fluorite samples of this district showed that fluorite, quartz and Fe-oxides mostly hematite were the major mineral phases of the samples but, barite, calcite, hemimorphite and clays were distinguished as the minor mineral phases

Summary

Introduction

Lanthanides and Y known as Rare Earth Elements (REE) generally occur in the trivalent oxidation state (Ln3+) except Ce (Ce3+ and Ce4+) and Eu (Eu2+ and Eu3+), which display very similar behavior during geochemical processes in a wide range of geological environments [Bau and Dulski, 1995, Shannon, 1976]. The lanthanides are a coherent group of elements that their ionic radii gradually decrease with increasing the atomic number from La (1.03 Å) to Lu (0.86 Å), which is known as the lanthanide contraction [Shannon, 1976] These specifications cause them to display similar behaviors and graphically smooth distribution patterns in geochemical investigations indicating their charge and radius controlling characteristic [Bau, 1996]. The tetrad effect is another factor that controls the REE distribution beside other ones such as pH of fluids/solutions, scavenging, mineral phases and stability of REE-complex [McLennan, 1994, Sasmaz et al, 2005, Veksler et al, 2005]

Results

Discussion

Conclusion