Investigation of petrograğhic and fluid inclusion characteristics of Karadag (Torul-Gümüşhane) Fe-Cu skarn mineralization

Karadağ Fe–Cu skarn mineralization is located about 57 km southwest of Gümüşhane city. The sdimentary and volcanic rocks in Karadag (Torul-Gümüşhane) is being late Cretaceous age, andesit containing limestone lenses is found at the base and basalt unit comes over it. These rocks are cut by Mid-Eocene age Karadag granitoid (quartz porphry and diorite) which provided Fe-Cu skarn mineralization in the area. Andesites have microlitic and glomero-porphyrytic textures, and comprises of plagioclas, horblende, pyroxene, epidote and opaque minerals. Limestones are recrystallized and partially turned into marble. It was observed that marbles were in lens form and have saccharoidal texture during field studies. Basalts have microlitic porphyritic texture and consist of plagioclase, hornblende, pyroxene and opaque minerals. The Karadag Granitoid is composed of quartz porphyry and diorite which both are mainly consist of plagioclase, quartz and orthoclase minerals. The skarn zone developed as a result of the contact metomorphism via intrusion of a diorite outcropping in a narrow area around the Fe-Cu skarn mineralization of Karadag and the intrusion of a quartz porphyry to the volcanics and limestone, which both covers a large area in the southeast of the Karadag mine. In the exoskarn zone developed between granitoid (quartz porphyry and diorite) and limestone the skarn minerals such as garnet, epidote, magnetite, calcite and quartz were formed. In skarn zone the pyroxene type is diopside and, garnet types are andradite and grossular-andradite. The ore minerals paragenesis of Fe-Cu skarn mineralization of Karadag are composed of magnesite, pyrite, hematite, chalcopyrite and gold. Also the acicular, spherulitic, tie and hair textures are seen in ore minerals of magnetite and hematite. As secondary ore minerals, goethite, limonite, digenite, malachite and azurite have been determined. The granitoids (quartz porhyry and diorite) in the Fe-Cu skarn mineralization of Karadag have high and medium-K-calc-alkaline characteristics; and quartz porhyry is peraluminum, while diorites are metaluminum in composition. The similarity of the trace element characteristics of granitoid rocks of Karadag Fe-Cu skarn mineralization with those of arc granites indicate that the granitoids associated with Fe-Cu skarn mineralization occurred after subduction. The fluid inclusions prepared from quartz and calcite minerals occurring within the exzoskarn zone of Karadag Fe-Cu skarn mineralization are classified as primary, secondary and necked inclusions. In fluid inclusion studies, for exzoskarn zone the homogenization temperatures and its NaCl equivalent salinity in quartz are determined as 175-405 °C and % 0.7-9 NaCl, in calcites 186-430 °C and 0.4-18 NaCl, respectively. These result support that they have epithermal and skarn genesis. In Karadag Fe-Cu skarn mineralization, the determined type of pyroxene (diopside) and garnet (andradite and grossular andradit), abundant magnetite, hematite and low pyrite in paragenesis, along with the data obtained from fluid inclusion studies shows and confirm that the mineralization occurred as a result of shallow intrusions under oxidized conditions.