Geological, mineralogical and geochemical properties of the Dagbast skarn ores (Arakh-Trabzon, NE Turkey)

Abstract

The Dagbasi skarns have developed as an exoskarn type along the nearest border of Upper Cretaceous Dagbasi Granitoid and block- and lens-shaped limestones of Berdiga formation located in the Liassic volcanics. the early garnets are predominantly grossular type (And(0-0.81)Grs(59).(69-78.65)Prs(21.35-38.11)), while pyroxenes have a composition between diopside and hedenbergite (Hed(24).(44-31.81)Diy(6.3-76.99)Joh(0.52-0.88)). the late garnets are characterized by high andradite (And(74.67-100)Grs(0.22.8)Prs(0.4.51)), and late pyroxenes by increasing johannsaiite content (Hed(22.17-62.63)Diy(0-36).(2)Joh(31.86-76.69)). High andradite content of late garnets is similar to Cu-Fe-type skarns, whereas the higher johannsenite and Mn/Fe ratios of pyroxenes are similar to Zn-type skarns. Higher andraditic garnets indicate an oxidized-type skarn and association with the shallow emplacement of intrusion. Increasing And/Grs ratios of garnets, from core to rim, also point out to increasing degree of oxidation. the retrograde skarn minerals are epidote, tremolite-actinolite, quartz, calcite, and chlorite. the ore minerals are composed of magnetite, hematite, pyrrhotite, pyrite, chalcopyrite, sphalerite, and galena. the Ag content of the galena (1.18-1.43wt%) suggests significant silver potential. Dagbasi Granitoid shows high-K (2.38-3.75wt.% K2O), calc-alkaline, metaluminous-peraluminous transitional (A/CNK=0.88-1.23) and volcanic arc type granitoid. the various main and trace element contents of the granodiorite observed along the skarn zones show similarities with Fe-Cu-Zn type skarn-related granitoids, whereas there is no clear relation between the skarn type and composition of outher granitoids. Therefore, the presence of sulfur phases, in addition to the oxide ore suggests that geochemical characteristics of granitoid had a large effect on the mineral composition.