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Turkish Journal of Earth Sciences

DOI

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Abstract

Most skarn deposits are directly related to magmatic activity, and there is a systematic correlation between the composition of causative plutons and the metal contents of the related skarns. This paper documents the composition of facies within the Evciler pluton and correlations between intrusion composition and the metal contents of associated skarns. There have been previous studies of mines (e.g., Cu mines) in the Evciler district, however, there have been no detailed geological investigations of such ore deposits or associated skarn mineralization. In the Evciler district both calcic exoskarn (garnet-pyroxene) and endoskarn (pyroxene-epidote) occur along the contacts between granitoid and marble. Calc-silicate mineral compositions in the Evciler skarns are similar to those in Au-Cu and Fe-Cu skarns. Based on mineralogy and geochemistry, three main facies have been recognized in the Evciler pluton: (1) the Çavuşlu monzodiorite, (2) the Karaköy granodiorite and (3) the Evciler quartz diorite-granodiorite, the mesocratic unit of the Evciler pluton. At the Evciler district, monzogranitic rocks, termed leucocratic Evciler, have a limited distribution compared to the mesocratic Evciler rocks. Field evidence for the relative timing of intrusions and trace- element geochemistry of the individual facies suggest that the Evciler pluton formed in a magmatic arc or post-collisional setting from a hybrid source, having crustal and mantle components contaminated by interaction with the upper crust. Whole rock d18O values of the Evciler granitoid decrease from 8.5 to 2.55 ^o/oo towards the intrusive contact, which is closest to the calcic skarn mineralization (Au-Cu), and the quartz d18O composition of the Evciler granitoid varies from 7.2 to 10.9 ^o/oo. These values are normal for I-type, primary unaltered values for this intrusive rock, but are too large to be accounted for by simple magmatic differentiation. Therefore, the Evciler granitoid must have been subjected to post-emplacement open-system hydrothermal alteration with introduction of external fluids (probably meteoric water) which changed the original magmatic d18O values. The present study shows that the geochemical characteristics of the Çavuşlu monzodiorite, Karaköy granodiorite and mesocratic Evciler rocks are similar to averages for Au-Cu and Fe-skarn granitoids, whereas the geochemical characteristics of the leucocratic Evciler rocks are similar to averages for Sn- and Mo-skarn granitoids. The Evciler granitoid is also characterized by relatively unevolved to moderately evolved and oxidized suites, as in most Au-Cu core metal associations globally.

Keywords

gold, copper, skarn, mineralization, Evciler granitoid, Kazdağ, NW Turkey

First Page

255

Last Page

280

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