Phlogopite Occurrences within Limestone-Ophiolite-Granitoid Triple Contact from Sivas-Divrigi Iron Deposit

Abstract

Alteration minerals determined in the ultramafic rocks of Gunes Ophiolite were divided into three main groups as pre-, syn-and post-serpentinization. Of these, phlogopite from pre-serpentinization minerals is one of the main components of mica-peridotites and is contemporaneous with the formation of the ophiolitic sequence. Listwaenitization and pyrometasomatism from later alterations caused an increase in grain size and accumulation of phlogopites in certain zones and also mixed-layer phlogopite-vermiculite (P-V) and vermiculite transformations in local. Syn-serpentinization alterations cover the conversions from felsic and mafic minerals to various clay and/or phyllosilicates. Post-serpentinization alteration covers the occurrences of ophicarbonate (commonly calcite and dolomite, rarely siderite and hydrotalcite), ophioxide-hydroxide (hematite, goethite, pyrite, marcasite and brucite) and locally ophisilicate (quartz) that refers to listwaenitization. Phlogopite, actinolite, epidote, johannsenite, scapolite, schorl and Fe-minerals (magnetite, hematite, pyrite, marcasite) form of the products of metasomatism in the pyrometasomatic rocks, and pyroxene and feldspar are residual primary magmatic phases. Divrigi phlogopites differ partly in respect to end-member of theoretical oxide compositions of phlogopite-biotite series. Biotite component of phlogopites is low (8-14 %) and they are called as Fe-Al phlogopite according to their average unit-cell composition. The main cation of P-V in the ultramafic-hosted rocks is Mg and this mineral is partially rich in Fe and poor in Al. Serpentines have tetrahedral and octahedral Fe substitutions which indicate Fe-lizardite. The concentrations of total trace element in the phyllosilicate minerals decrease from serpentine-phlogopite to P-V, whereas their rare earth element contents increase in the same direction in the Divrigi area. delta O-18 and dD values (SMOW) are determined as parts per thousand + 10.6-11.8 and parts per thousand -64 --102 for phlogopites,parts per thousand + 14.2 and parts per thousand -121 for P-V, and parts per thousand + 14.4 and parts per thousand-129 for serpentine. Phlogopites are plot hypogene and supergene fields, but P-V and serpentine are found under kaolinite weathering line on the basis of delta O-18 and dD values. Formation temperatures as similar to 130-150 degrees C for phlogopite and similar to 100 degrees C for P-V are obtained on the comparison of minimum isotopic value of granitic water. Additionally, stable isotopic values showed that serpentinization, phlogopitization and vermiculitization formed with different subsequent processes.