HIGH SULFIDATION EPITHERMAL DEPOSITS: A CASE STUDY FROM NW TURKEY, BIGA PENINSULA

Kartaldağ gold mine, operated by ancient Troy is located to the southeast of Çanakkale city (Biga Peninsula, Turkey). A historic open pit with dimensions of about 200 m long, 10 m wide, 20 m deep, and several galleries with maximum depth of nearly 300 m are all controlled by regional ESE – WNW normal faults. The epithermal system and associated alterations are hosted by dacite porphyry with a hornblende Ar-Ar age of 42.19 ± 0.45 Ma. This age is likely to fall into the age interval during which post-collisional Eocene magmatism was pronounced in the Biga Peninsula. Wall rock alterations observed within the Kartaldağ epithermal system are propylitic, argillic, and silicic alterations. Propylitic alteration refers to assemblage of albite, chlorite-smectite mixed layer, epidote, illite, α-quartz ± calcite. The XRD and SEM/EDX analysis revealed that argillic alteration comprises two spatially distinct mineral paragenesis consisting predominantly of quartz-kaoline and pyrophyllite-alunite-quartz assemblages. The silicification occurs mainly as massive silicification of the dacite porphyry with vuggy quartz centered to the main argillic alteration of Kartaldağ epithermal system.

The assemblage of quartz-kaoline, that could also be referred to as a probable sub-zone in the argillic alteration is characterized by the kaoline (dominantly kaolinite), illite, pyrite, α-quartz ± chlorite. Pyrophyllite-alunite-quartz sub-zone is also termed as the advanced argillic alteration assemblage, and is accompanied by pyrite, covellite and sphalerite. Massive silicification is composed of fine to medium grained quartz crystals displaying mostly vuggy quartz textures typical for the high sulfidation epithermal systems. Euhedral pseudomorphs of the parental grains such as plagioclase and hornblende minerals appear to form the vugs during pervasive leaching of the dacite porphyry. Based on relative cross-cutting relationships of quartz textures, dacitic host rock is noticed to have experienced two phases of silicification as early and late silicification. The textural characteristics of the quartz crystals formed at each phase is different such that early silicification exhibits the vuggy quartz texture with fine grained quartz crystals, whereas late phase silicification is characterized by colloform, banded, zoned, and coarse-medium grained quartz crystals, and occurs as an overprint on the vuggy quartz. Oxygen isotope analysis performed for the early and late silicification phases separately yield δ ¹⁸O values of 7.93 and 8.33 per mil, and of 8.95 per mil, respectively. These successive silicification phases are likely to be formed by two boiling process throughout the hydrothermal evolution that formed the Kartaldağ deposit.

The advanced argillic alteration covers and/or envelopes the pervasively silicified zone (core of residual part of the system), and wall rock alteration can be traced from propylitic at the margins to massive silicification at the center of the mineralized system. This may be in lines of evidence that fluid (ore bearing) was channel through a single conduit close to or within the massive-vuggy quartz zone. The temporal and spatial association of alterations, zoning patterns, predominant clay mineral compositions being pyrophyllite, kaolinite and alunite, vuggy quartz texture, and covellite, pyrite, sphalerite ore minerals can be taken as the key parameters supportive of an argument that the Kartaldağ epithermal gold mineralization is formed by a low pH-oxidizing fluid and classified as high sulfidation type epithermal system.