Fluid-Related Characteristics of the Cakmakkaya and Damarkoy Copper Deposits, Northeast Turkey

摘要

The Cakmakkaya and Damarkoy copper deposits in the Murgul (Artvin) area are typical examples of Kuroko-type volcanogenic sulfide deposits that occur widely in the Eastern Pontide region of Turkey. These deposits are hosted by volcanic rocks in a sequence that consists upward of andesitic lavas, brecciated dacite tuff, covering tuff, and dacite porphyry. Mineralizations occur mainly in the form of stockwork ores that are hosted by brecciated dacite tuff. A thin stratiform ore zone and a gypsum lens occur above the stockwork in the Cakmakkaya deposit. The stockwork sulfide veinlets contain mainly pyrite and chalcopyrite, with minor sphalerite, galena, tetrahedtrite, and marcasite. Quartz is the only gangue mineral. The deposition of sulfides was largely controlled by microfracturing of the dacitic tuffs, with high concentrations especially at the intersections of fractures. The stratiform ore zone within the Cakmakkaya deposit contains ore clasts that indicate fragmentation and resedimentation of sulfides during or after discharge of the hydrothermal fluids onto the sea floor. The ore clasts contain the same minerals as the stockwork ores. Fluid-inclusion studies indicate that the ore-forming fluids contain NaCl, CaCl_2, and MgCl_2. Salinities and temperatures were high during the initial deposition of the ore minerals, and decreased during later episodes of mineralization from a maximum of approx 18 percent (NaCl equiv) and 254 deg C to 1 percent (NaCl equiv) and 110 deg C during mineralization. The delta~(18)O values of aqueous fluid inclusions were calculated from the measured delta~(18)O values of the host quartz and the temperatures derived by microthermometry. The calculated delta~(18)O (H_2O) values vary in a narrow range from -2.2 to +0.2 per thousand (SMOW). The delta D values of the inclusion waters were measured by direct isotope determination of the water hydrogen extracted from the fluid inclusions. The delta D values range from -61.6 to -35.5 per thousand (SMOW) and cluster around -60 per thousand (SMOW). These stable-isotope results of the Murgul deposits indicate that the hydrothermal solutions have a major meteoric component; however, there seems to be a small amount of sea water mixing. This study concludes that meteoric water, circulating through the continental crust underlying the volcano-sedimentary rocks, acted as mineralizing fluid, leached metals (Cu, Pb, Zn, Au and Ag) and sulfur from the surrounding volcanic rocks, and precipitated sulfides and sulfates along fractures within the brecciated dacitic host rocks and at the surface of the sea floor.