Detecting hydrothermal alteration zones by alteration box plot and mass change calculations using immobile elements in the Gezildash massive sulfide copper deposit of Khoy

The Ghezildash massive sulphide copper deposit is located in the northwest of Iran. The area is a part of the ophiolotic colored mélange zone of NW Iran, also known as Khoy–Maku colored mélange. Copper mineralization occurred in part of basaltic meta-volcanic rocks, and extensive alteration zones such as chloritic–epidoitic along with minor carbonate and sericitic zones are consequently developed in the area. This paper aims at identifying hydrothermal alteration zones related to massive sulphide deposit particularly those associated with chloritic zones where the mineralization have been identified. Another aspect is to determine the elemental enrichment and depletion before and after alterations in the host rock. For this purpose, the alteration box plot was used, which approved Trend 4 of chlorite-carbonate zone in much of the samples and Trend 5 of sericite–carbonate in few samples. Furthermore, thin section studies showed similar results, confirming the method used. Maclean method as a useful reconnaissance tool for mineralized zones was then applied to identify the enriched and depleted alteration zones between unaltered host rock and altered chloritic and sericitic zones. Results of McLean method revealed in the chloritic alteration zone large enrichment of Fe and Mg and depletion of Na, K and Ca elements, which have occurred due to decomposition of feldspars in the rock during chloritic alteration. It was also observed that these rocks in the chloritic alteration zone were subjected to a moderate increase in Cu, Zn, Co, and V contents. Also, sericitic alteration zone showed a moderate enrichment in Fe and Mg. Therefore, alteration zone detection using box plot and mass change calculations by McLean method enabled us to identify mineralization zones in the Gezildash massive sulphide deposit of Khoy. Characteristic features of detected alterations and geochemical indices obtained by this study suggest the Cyprus type massive sulphide mineralization for the area associated with Cu-Zn enrichment and Ca and Na depletion. In some cases, very minor amount of K enrichment in sericitic zones was also observed. Overview of the deposit represents cluster form in a particular trend that emphasizes its structural control by faults. The presence of ophiolitic mafic volcanic rocks, Ocher horizons, exhalative cherts and regional pyrite horizons are considered as exploration signs for this deposit.