Alteration Mineralogy and Geochemistry of the Hydrothermally Altered Rocks of the Kutlular (Sürmene) Massive Sulfide Deposit, NE Turkey

Authors: EMEL ABDİOĞLU, MEHMET ARSLAN

Abstract: Volcanogenic massive sulfide deposits accompanying the Upper Cretaceous felsic rocks in the intra-arc rift zone of the Pontide palaeo-arc are common in the NE Turkey. One of them, the Kutlular (Sürmene, Trabzon) deposit, is an abandoned mine within the Upper Cretaceous mafic, felsic volcanics and subvolcanic rocks. Detailed mineralogical and geochemical studies indicate the presence of hydrothermal alteration zones around the Kutlular deposit; these alteration zones are represented by silicification-pyrite-illite zone, illite-silicification zone, illite/smectite-silicification zone, smectite zone accompanying kaolinite and halloysite in the dacitic pyroclastics, and additionally chlorite zone in the mafic volcanics. Lithogeochemical data indicate that the footwall dacitic rocks (Zr/Y= 1.39-16.39, La/Yb= 0.14-9.57) and hanging-wall basalts-basaltic andesites (Zr/Y= 2.13-5.65, La/Yb= 1.16-5.00) are transitional between tholeiitic and calc-alkaline in character. The trace element patterns of the rocks show considerable LILE enrichment (K, Rb and Ba) and depletion in Sr and Ti relative to N-type MORB. Chondrite-normalized REE patterns of the footwall show pronounced HREE enrichment. The Kutlular footwall and hanging wall alteration zones have several geochemical characteristics that show systematic changes with increasing proximity to ore body such as Na depletion as well as elevated alteration index (AI) and chlorite-carbonate-pyrite index (CCPI). Generally, hanging-wall mafic volcanics and footwall rocks have high CCPI (chlorite-carbonate-pyrite index) values, indicating the importance of chlorite and pyrite formation in these rocks. Calculated mass changes in the footwall dacites commonly are large, and result from major silica mass transfer (-9.11 to 99.68 g/100 g rock). Mass-change calculations indicate that CaO + Na_2O + MgO were leached from the rocks by hydrothermal solutions, whereas large amounts of hydrothermal iron were added. Hanging wall basalt and basaltic andesite shows mass changes that are generally much smaller than in the footwall.

Keywords: hydrothermal alteration, clay minerals, massive sulfide deposit, eastern Pontides, Turkey

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